2.875 Mechanical Assembly and Its Role in Product Development

Team Members: Agus Sudjianto Jared Clark Milind Oak Eiichi Tanabe Gaurav Shukla

______Originators: Sudjianto/Clark/Oak/Shukla/Tanabe Page 1 of 78 Date Initiated: September 29, 1999 fInal_report.doc Date Revised: December 5, 1999 2.875 Mechanical Assembly and Its Role in Product Development

PROBLEM STATEMENT...... 4

3.6-VOLT SEARS/CRAFTSMAN CORDLESS SCREWDRIVER...... 4

1. REPORT #1: PRODUCT DESCRIPTION...... 5

1.1 PRODUCT ASSEMBLY DRAWING...... 6 1.2 TRANSMISSION ASSEMBLY...... 7 1.3 EXPLODED VIEW OF TRANSMISSION ASSEMBLY...... 8 1.4 CLEARANCE SPECIFICATION...... 9 1.5 SCREWDRIVER COMPONENT BREAKDOWN...... 11 1.6 BILL OF MATERIALS...... 12 1.7 ASSEMBLY TREE...... 14 1.8 FUNCTIONAL FLOW MODEL...... 15 1.9 SYSTEM HIERARCHY BREAKDOWN...... 16 1.9.1 Battery Module System Breakdown...... 16 1.9.2 Driver Mechanism System Breakdown...... 17 1.10 LIAISON DIAGRAMS OF PART MATING...... 18 1.10.1 Product Main Assembly...... 18 1.10.2 Battery and Housing Assembly...... 18 1.10.3 Torque Limiter...... 18 1.10.4 Transmission...... 19 1.10.5 Motor Assembly...... 19 2. REPORT #2: DATUM FLOW CHAIN...... 20

2.1 OVERALL TRANSMISSION KEY CHARACTERISTICS...... 20 2.2 FEATURE, MATE, AND CONTACT TABLE...... 24 2.3 COMPLETE BILL OF MATERIALS...... 25 2.4. EXPLODED VIEW...... 27 3. REPORT #3: ASSEMBLY SEQUENCE...... 28

3.1 REVISED LIAISON DIAGRAM...... 28 3.2 REVISED DATUM FLOW CHAIN...... 28 3.3 ALL POSSIBLE ASSEMBLY SEQUENCE...... 29 3.4 THE MOST CONVENIENCEE ASSEMBLY SEQUENCE...... 30 3.5 REQUIRED GROSS AND FINE MOTIONS...... 31 3.6 FUTURES, CHAMFERS AND LEAD INS...... 31 3.7 DIFFICULTIES & IDEAS IN ASSEMBLY...... 33 3.8 FEATURE PARTS AND ASSOCIATED ASSEMBLY TOOL AND FIXTURES...... 34 3.9. FIXTURES AND TOOLS FOR ASSEMBLY...... 35 3.10 GEAR SET ARCHITECTURE REDESIGN...... 36 3.11 IMPROVEMENT HIGHLIGHT...... 37 4. REPORT #4: ASSEMBLY FLOOR LAYOUT ANALYSIS...... 38

4.1. ASSEMBLY SEQUENCE...... 38 4.2 ASSEMBLY PROCESS TIME...... 39 4.3 ASSEMBLY LINE DESIGN AND ASSUMPTIONS...... 41 4.3.1 Design Parameters...... 42 4.3.2 Supplied Material...... 42 4.4 ASSEMBLY OPERATION STYLE...... 42 4.4.1 Assembly Line Design...... 42 5. REPORT #5: WORKSTATION DESIGN...... 46

5.1 REQUIRED CYCLE TIME TO COMPLETE THE PLANNED OPERATIONS...... 46 5.1.1 Assembly Flow Diagram...... 46 5.1.2 Final Assembly...... 47

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5.1.3 Testing and Packaging...... 47 5.1.4 Transmission Assembly...... 48 5.1.5 Grip Housing/Battery Assembly...... 48 5.2 STATION LAY OUT: IN AND OUT FLOWS OF ASSEMBLIES AND PARTS...... 50 5.3 REQUIRED MOTIONS OF EQUIPMENT AND PEOPLE...... 51 5.4 NECESSARY INSPECTIONS OR TESTS...... 52 5.5 GANTT CHART OF REQUIRED TIME OF ACTIVITIES AND A COMPLETE CYCLE...... 53 5.6 COST ESTIMATION OF WORKSTATIONS...... 56 5.7 ESTIMATION OF THE COST OF PERFORMING ONE ASSEMBLY CYCLE...... 57 6. REPORT #6: ECONOMIC ANALYSIS AND ASSEMBLY LINE SIMULATION...... 59

6.1 ECONOMIC ANALYSIS OF THIS ASSEMBLY LAYOUT...... 59 6.1.1 Estimated Manufacturing Cost...... 60 6.1.2 Inventory Cost and Distribution Cost...... 60 6.1.3 Development Cost...... 61 6.1.4 Unit Part Costs...... 62 6.1.5 Economic Analysis...... 63 6.2 DISCRETE EVENT SIMULATION OF ASSEMBLY LINE...... 64 6.2.1 Discrete Event Simulation: Configuration Study...... 64 6.2.2 Selection of Final Assembly Process...... 72

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Problem Statement 3.6-Volt Sears/Craftsman Cordless Screwdriver

September 29, 1999

Clients: Dr. Dan Whitney

Project Team: Name E-mail Agus Sudjianto [email protected] Jared Clark [email protected] Milind Oak [email protected] Gaurav Shukla [email protected] Eiichi Tanabe [email protected]

The team decided to analyze Sears/Craftsman 3.6-Volt Cordless Screwdriver. The product has dual-position handle design: in-grip position to work in confined areas which can be easily converted into pistol-grip for normal screw-driving tasks.

The followings are some notable features of the product: . Two-speed, 130 and 400 RPM, with 2-speed gear box to match the need for applications of high speed fast screw-driving and low-speed high-torque heavy duty screw-driving. . Planetary spur gears to provide the torque and power needed. . Adjustable torque clutch to match driving torque task . Trigger switch for reverse-off-forward control. . Impact resistant glass-filled nylon housing. . ¼-in. hex collet with automatic spindle lock. . 3.6-volt 3-cell rechargeable batteries. . Power supply to recharge the batteries. NOTE:  The battery charger sub-system is excluded from this study.  Sum of the sub-assembly such as motor may be treated as a module.

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1. Report #1: Product Description

In this report Sears/Craftsman 3.6-Volt Cordless Screwdriver is described as follows,

 Product Drawings  Product Assembly Drawing  Transmission Assembly  Exploded View of Transmission Assembly  Clearance Specification  Screwdriver Component Breakdown  Bill Of Material (Including Parts List, Function and Material)  Assembly Tree  Functional Flow Model  Functional System Breakdown  System Hierarchy Breakdown  Battery Module System Breakdown  Driver Mechanism System Breakdown  Liaison Diagrams of Part Mating  Product Main Assembly  Battery and Housing Assembly  Torque Limiter  Transmission  Motor Assembly

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1.1 Product Assembly Drawing

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1.2 Transmission Assembly

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1.3 Exploded View of Transmission Assembly

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1.4 Clearance Specification

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1.5 Screwdriver Component Breakdown

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1.6 Bill Of Materials

No Syst System Part Part Name Quantity Function Note Material # Name # 1 1 Battery 1.1 Battery Charger 1 Charge Battery 6V DC Power supply N/A Charger 2 2 Battery 2.1 Charger Contact 2 Contact Power Provide contact of battery SUS304 Closure Plates charger to battery 3 2.2 Battery Left 1 Enclose Battery Also function as hand grip Glass-filled Housing nylon 4 2.3 Bettery Right 1 Enclose Battery Also function as hand grip Glass-filled Housing nylon 5 2.4 Battery Cover 1 Enclose Battery Glass-filled nylon 6 2.5 Baterry Housing 2 Hold battery N/A Fasteners housing 7 3 Power 3.1 Rechargable 3 Store power Total of 3.6V battery N/A Storage Batteries 8 3.2 Battery Cables 2 Transmit power Provide connection from battery N/A to switch (+/-) 9 3.3 Battery Connectors 2 Connect cable Connecting cables to battery SUS304 10 3.4 Switch to Motor 2 Transmit power Provide connection from switch Polypropylene Cables to 11 3.5 Crim Connectors 2 Hold cable Holding cable to motor SUS304 12 3.6 Shrink wrap 1 Hold batteries Polypropylene 13 3.7 Tape 1 Hold cable cellophane 14 3.8 Cable connectors 2 Connect cables to battery SUS304 15 4 Torque 4.1 Torque Limiter 1 Accept hand Accept hand control to push Polypropylene Limiter Outer Cap needle bearing for torque limiter 16 4.2 Torque Limiter 1 Accept outer cap PS Inner Cap (Polystyrene) 17 4.3 Torque Limiter Cap 1 Hold inner and outer caps SUS304 Clip 18 4.4 Needle Bearings 4 Push PG1 To adjust torque limiter N/A internal gear 19 4.5 Ball Bearings 6 Allow internal gear PG1 slippage N/A 20 4.6 Bearing holder 1 Hold ball SUS304 plate bearings 21 4.7 Torque Limiter 4 Hold bearing 4 springs to privide uniform flex SUS304 Springs holder plate suport 22 4.8 Torque Limiter 1 Support springs Nylon Base Support 23 4.9 Torque Limiter 2 Hold base support to motor N/A Fasteners 24 5 Drive 5.1 Drive Left Housing 1 Provide Also to isolate noise Glass-filled Closure enclosure to nylon drive 25 5.2 Drive Right 1 Provide Also to isolate noise Glass-filled Housing enclosure to nylon drive 26 5.3 Grip Locking 1 Hold grip position Polypropylene Switch 27 5.4 Grip Locking 1 Support grip locking switch SUS304 Spring 28 5.5 Drive Housing 2 Hold housing N/A Long Fasteners 29 5.6 Drive Housing 2 hold drive N/A Medium Fasteners 30 5.7 Drive Housing 2 hold housing N/A Short Fasteners 31 6 Power 6.1 DC Motor 1 Convert EE to Kinetic Energy N/A generator 32 6.2 On/Off Button 1 Connect electric Polypropylene power 33 6.3 On/Off Spring 1 Support On/Off SUS304

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Button No Syst System Part Part Name Quantity Function Note Material # Name # 34 6.4 F/R/S Lever 1 Provide control for rotation direction Polypropylene 35 6.5 F/R/S Switch 1 Control polarity connection to battery PS Circuit (Polystyrene) 36 7 Bit Holder 7.1 Collet 1 Transmit torque Also to hold bit SUM 37 7.2 Bit Holder Housing 1 Provide housing to drive mechanism PS (Polystyrene) 38 7.3 Direction Stopper 2 Hold PG3 carrier To allow counter rotation SUS304 Clips 39 7.4 Direction Stoppper 4 Hold stopper PS Supports clips (Polystyrene) 40 7.5 Screwdriver bit 1 Act on screw SUM 41 8 Transmissi 8.1 Planetary Gear 1 1 Enclose pinion SUS304 on (PG1) Washer gears 42 8.2 PG1/PG3 Pinion 6 Increase torque SMF Gears 43 8.3 PG1 Internal Gears 1 Coordinate Allows all pinion gears to rotate SMF pinion gears along its internal gear 44 8.4 PG1 Carrier/PG2 1 Hold pinion gears Also transmit torque SUM Sun Gear 45 8.5 PG1 Sun Gear 1 Transmit torque SMF 46 8.6 PG2 Pinion Gears 3 Reduce speed SMF 47 8.7 PG2 Washer 1 Enclose pinion SUS304 gears 48 8.8 PG2 Coupling 1 Hold pinion gears PS Gear (Polystyrene) 49 8.9 PG2 Locking Gear 1 Hold PG2 system PS (Polystyrene) 50 8.10 Hi/Lo Lever 1 Transmit control By shifting coupling gear SUS304 51 8.11 Hi/Lo Button 1 Accept Hi/Lo Polypropylene control 52 8.12 Hi/Lo Fasteners 2 Hold Hi/Lo lever N? 53 8.13 PG2 Carrier/PG3 1 Hold pinion gears SUM Sun Gear 54 8.14 PG3 Washer 1 Enclose pinion SUS304 gears 55 8.15 PG3 Internal 1 Coordinate Allows all pinion gears to rotate SMF Gear/Direction pinion gears along its internal gear Openner 56 8.16 PG3 Carrier 1 Hold pinion gears SUM

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1.7 Assembly Tree

3.6 V Dual Grip Craftmans Cordless Screwdriver

Battery Charger Module Driver Module Power Storage Module

Left Housing Fasteners Battery Cover Left Housing Assembly Label Batt. Housing Housing Fasteners Batt. Left Housing Driver Assembly Housing Charger Contact RH Fasteners F/R/S Lever Hi/Lo Button On/Off Switch Grip Locking Button Switch Spring Spring Batt. Right Housing Transmission Motor Housing Assembly Assembly Charger contact Torque Adj. Assy. RH Assembly Battery Assembly Outer Cap As. Label Out cap Housing Tape Clip Inner Cap Ball Bearing Switch Module Motor cables PG1 Int. Gear Assy Bearing Holder Batt. Cables Internal Gear Plate Connectors Washer Cables PG1 pinions Bearing Washer PG1 carrier Battery PG2 washer Torque Limiter Connectors PG2 pinions Springs Shrink Wrap PG2 locking gear Torque Limiter Batteries Hi/Lo Fasteners Torque Limiter Fasteners Hi/Lo Lever Base Support PG2 Coupling Gear Crim connectors PG2 Carrier Motor Assembly PG3 Washer Sun Gear PG3 pinions Motor PG3 internal gear Dir. Stop Support Dir Stop Clip Bit Holder Assy. Collet Housing

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1.8 Functional Flow Model

Tight/loose screw Hand Force Noise Electricity Turn Vibration Screw Heat Bit Screw Worn bit Control signal Damaged screw Torque slip signal Energy Material Information

Heat

Electric Energy 3. Store On/Off (EE) Energy Grip F/R/S EE Hand Force (HF) 1. HF 2. HF 4. Accept Position Switch Torque Limit Hand Grip Power Torque Slip Noise EE Vibration Torque/Speed 6. 5. (t,w) t,w 7. t,w Heat Control Convert Permit Torque/ EE to KE Slippage Speed Noise Noise Vibration Hi/Lo Speed Vibration Heat Heat

8. 9. 10. Tight/loose screw Prevent t,w t,w Transmit Act on Worn bit Reverse Bit Torque Object Damaged screw Direction Vibration Screw Noise Vibration Bit Heat

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1.9 System Hierarchy Breakdown

Cordless Screwdriver

Battery Module Drive Mechanism

1.9.1 Battery Module System Breakdown

Battery Module

2. Closure 3. Power Storage

2.1. 2 Contact Plates 3.1. 3 Rechargables

2.2. Left 3.2. 2 Batt. Cables

2.3. Right 3.3. 2 Connectors

2.4. Cover 3.4. 2 Motor Cables

2.5. 2 Fasteners 3.5. 2 Crim Connectors

3.6. Shrink Wrap

3.7. Tape

3.8. Cable Connectors

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1.9.2 Driver Mechanism System Breakdown

Drive Mechanism

8. Transmission 5. Drive Closure

4. Torque Limiter Planetary Gear (PG) 1 5.1. Left Housing

5.2. Right Housing 4.1. Outer Cap 8.1. Washer 1 5.3. Grip Locking 4.2. Inner Cap 8.2. 3 Pinion Gears 5.4. Spring 4.3. Clip 8.3. Internal Gear 5.5.-5.7. 6 Fasteners (3 Types) 4.4. 4 Needle Bearing Pins 8.4. Carrier + Sun Gear for PG 2

4.5. 6 Ball Bearings 8.5. Sun Gear 6. Power Generator

4.6. Bearing Holder Plate 6.1. DC Motor 4.7. 4 Springs Power Control 4.8. Base Support

4.9. 2 Fasteners On/Off Switch

Planetary Gear (PG) 2 Planetary Gear (PG) 3 6.2. Button

8.6. 3 Pinion Gears 8.2. 3 Pinion Gears 6.3. Spring

8.7. Washer 8.14. Washer Direction (F/R/S)

Hi/Lo Speed Control 8.15. Internal Gear + Direction Openner 6.4. Lever 8.16. Carrier 8.8. Coupling Gear 6.5. Switch Circuit

8.9. Locking Gear 7. Bit Holder

8.10. Lever 7.1. Collet 8.11. Interface Button 7.2. Housing 8.12. 2 Fasteners Direction Stopper 8.13. Carrier and Sun Gear for PG 3

7.3. 2 Clips

7.4. 4 Supports

Screwdriver Bit

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1.10 Liaison Diagrams of Part Mating

1.10.1 Product Main Assembly

1.10.2 Battery and Housing Assembly

1.10.3 Torque Limiter

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1.10.4 Transmission

1.10.5 Motor Assembly

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2. Report #2: DATUM FLOW CHAIN

Transmission/Motor sub-assembly is selected for a detailed Datum Flow Chain (DFC) analysis. The exploded view of this module is shown in Figure 7. Figure 1 shows the DFC of overall sub-assembly. Detailed analysis of Hi/Lo speed conversion is presented in Figures 2-6.

Datum Flow Chain for Transmission

4& 6: Torque Limiter & Power Generator

20 8.3: PG1 Internal Gears 18 KC#1 26 19 17 8.2: PG3 Pinion Gears KC#2 8.1: Planetary Gear 1 Washer 16 8.10:Hi/Lo Lever 25 24 21 8.4: PG1 Carrier/PG2 Sun Gear 8.8: PG2 Coupling Gear 14 13 15 12 8.7: PG2 Washer Alternative 8.6: PG2 Pinion Gears 23 8.9:PG2 Locking Gear 22 Alternative 9 8.13:PG2 Carrier/PG3 Sun Gear 11 10 8.14:PG3 Washer 8 4 7 8.15:PG3 Internal Gear 5 6 8.2: PG3 Pinion Gears 2 3 8.16 & 7.1:PG3 Carrier & Bit Holder 7.2: Bit Holder Housing 1

Figure 1. Datum Flow Chain (DFC) of Transmission/Motor Module

2.1 Overall Transmission Key Characteristics

KC#1: In order for screwdriver to function properly, Bit Holder rotation axis must be concentric with Power Generator axis. Thus concentricity is a key characteristic.

KC#2: The distance between PG3 Internal Gear & PG1 Internal Gear is important because this subassembly has to fit within the space provided by Transmission/Bit Holder housing. So Stack-up length is a key characteristic.

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KC#3-#5: Hi/Low Speed Configuration and Their Key Characteristics

The gear configurations for the high/low speeds and the transition are shown in the following figure.

High Speed Speed Transition Low Speed

8.9 8.9 8.9 8.8 8.8 8.8

8.6 8.6 8.6

8.13 7.2 8.13 7.2 8.13 7.2

Figure 2. Hi/Lo speed gear configurations.

There are distinct key characteristics for each configuration as follows.  High Speed: The Coupling Gear must successfully engage to lock PG2 Carrier and PG2 Pinion Gears together so that they become an integral unit. Therefore, the engagement of PG2 Carrier and Pinion Gears is the KC (KC#3).

8.10 Hi/Lo Lever 21 KC#3 8.8 PG2 Coupling Gear 22 8.13 PG2 Carrier 11 15 24 9

8.6 PG2 Pinion Gears 12 13

7.2 Bit housing

Figure 3. DFC for High Speed condition

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 Transition: The Coupling Gear must not engage with either PG2 Carrier or Locking Gear. Therefore, the KC is the gap between PG2 Carrier and Locking Gear (KC#4).

8.10 Hi/Lo Lever 21 8.8 PG2 Coupling Gear

8.13 PG2 Carrier 11 15 24 9 KC#4 8.6 PG2 Pinion Gears 13 12

8.9 Locking Gear 7.2 Bit housing

Figure 4. DFC for transition condition

 Low Speed: The Coupling Gear and the Locking Gear must be properly engaged to become an integral unit so that the Pinion Gear can rotate around the Coupling/Locking Gear unit. The situation of the KC is shown in the following figure.

h 8.9 8.8 g 2 g1

8.6

8.13 7.2

Figure 5. Low speed condition

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If (g1 – g2) < 2h then stress built up is occurring (over-constrained) and the mechanism will fail. On the other hand, if (g1 – g2) > 2h + , where  is the acceptable clearance, then wobbling problem is occurring. The former problem is more severe than the later problem. Therefore, the KC (KC#5) is defined by the Pinion Gears and the Locking Gear. The success of engagement between the Locking and Coupling gear is a key condition to this mechanism. The Datum Flow Chains for the above conditions are shown in the following figures.

8.10 Hi/Lo Lever 21

8.8 PG2 Coupling Gear 22 8.13 PG2 Carrier 11 15 24 9

8.6 PG2 Pinion Gears 12 13 KC#5

8.9 Locking Gear 7.2 Bit housing

Figure 6. DFC for low speed condition

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2.2 Feature, Mate, and Contact Table

Feature Part No. Part A Part No. Part B DOF MATE/ Comments Number CONTACT

1 7.2 Bit Holder Housing 8.16 & Carrier & Bit Five Mate Peg & Hole 7.1 Holder 2 7.2 Bit Holder Housing 8.15 Internal Gear Five Mate Peg & Hole 3 8.16 & 7.1 Carrier & Bit Holder 8.2 Pinion Gears Five Mate 3 Peg & Holes for 3 pinions 4 8.2 Pinion Gears 8.13 PG2 Carrier/PG3 Five Mate Overconstrained Dofs, Clearance Sun Gear 5 8.2 Pinion Gears 8.14 Washer Three Mate Overlap of 2 plates, OverCons. With #7

6 8.15 Internal Gear 8.2 Pinion Gears Four Mate Overconstrained Dofs, Clearance 7 8.15 Internal Gear 8.14 Washer Three Mate Overlap of 2 plates, OverCons. With #5

8 8.14 Washer 8.13 PG2 Carrier/PG3 Three Mate Overlap of two Plates Sun Gear 9 8.13 PG2 Carrier/PG3 Sun 8.6 PG2 Pinion Gears Five Mate 3 Peg & Holes for 3 pinions Gear 10 7.2 Bit Holder Housing 8.9 PG2 Locking Five Mate Peg & Hole Gear 11 7.2 Bit Holder Housing 8.1 Hi/Lo Lever Five Mate Peg & Hole 12 8.6 PG2 Pinion Gears 8.7 PG2 Washer Three Mate Overlap of 2 plates, OverCons. With #14

13 8.6 PG2 Pinion Gears 8.4 PG1 Carrier/PG2 Five Mate Overconstrained Dofs, Clearance Sun Gear 14 8.7 PG2 Washer 8.4 PG1 Carrier/PG2 Three Mate Overlap of 2 plates, OverCons. With #12 Sun Gear 15 8.6 PG2 Pinion Gears 8.8 PG2 Coupling Five Mate Overconstrained Dofs, Clearance Gear 16 8.4 PG1 Carrier/PG2 Sun 8.2 PG3 Pinion Gears Five Mate 3 Peg & Holes for 3 pinions Gear 17 8.2 PG3 Pinion Gears 8.1 Pinion Gears 1 Three Mate Overlap of 2 plates Washer 18 8.2 PG3 Pinion Gears 4 & 6 Torque Limiter & Five Mate Gear mate Power Generator 19 8.1 Pinion Gears 1 8.3 PG1 Internal Three Mate Overlap of 2 plates Washer Gear 20 8.3 PG1 Internal Gear 4 & 6 Torque Limiter & Three Mate Overlap of 2 plates Power Generator 21 8.1 Hi/Lo Lever 8.8 PG2 Coupling One Mate Gear 22 8.13 PG2 Carrier/PG3 Sun 8.8 PG2 Coupling Five Mate Gear mate Gear Gear 23 8.9 PG2 Locking Gear 8.8 PG2 Coupling Six Mate Properly constrained Gear 24 7.2 Bit Holder Housing 8.8 PG2 Coupling Three Mate Oversize hole Gear 25 7.2 Bit Holder Housing 8.3 PG1 Internal Three Mate Oversize hole Gear 26 7.2 Bit Holder Housing 4 & 6 Torque Limiter & Six Mate Properly constrained Power Generator 27 8.2 PG3 Pinion Gears 8.3 PG1 Internal Five Mate Gear mate Gear

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2.3 Complete Bill Of Materials

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Button No Syst System Part Part Name Quantity Function Note Material # Name # 34 6.4 F/R/S Lever 1 Provide control for rotation direction Polypropylene 35 6.5 F/R/S Switch 1 Control polarity connection to battery PS Circuit (Polystyrene) 36 7 Bit Holder 7.1 Collet 1 Transmit torque Also to hold bit SUM 37 7.2 Bit Holder Housing 1 Provide housing to drive mechanism PS (Polystyrene) 38 7.3 Direction Stopper 2 Hold PG3 carrier To allow counter rotation SUS304 Clips 39 7.4 Direction Stoppper 4 Hold stopper PS Supports clips (Polystyrene) 40 7.5 Screwdriver bit 1 Act on screw SUM 41 8 Transmissi 8.1 Planetary Gear 1 1 Enclose pinion SUS304 on (PG1) Washer gears 42 8.2 PG1/PG3 Pinion 6 Increase torque SMF Gears 43 8.3 PG1 Internal Gears 1 Coordinate Allows all pinion gears to rotate SMF pinion gears along its internal gear 44 8.4 PG1 Carrier/PG2 1 Hold pinion gears Also transmit torque SUM Sun Gear 46 8.5 PG2 Pinion Gears 3 Reduce speed SMF 47 8.6 PG2 Washer 1 Enclose pinion SUS304 gears 48 8.7 PG2 Coupling 1 Hold pinion gears PS Gear (Polystyrene) 49 8.8 PG2 Locking Gear 1 Hold PG2 system PS (Polystyrene) 50 8.9 Hi/Lo Lever 1 Transmit control By shifting coupling gear SUS304 51 8.10 Hi/Lo Button 1 Accept Hi/Lo Polypropylene control 52 8.11 Hi/Lo Fasteners 2 Hold Hi/Lo lever N? 53 8.12 PG2 Carrier/PG3 1 Hold pinion gears SUM Sun Gear 54 8.13 PG3 Washer 1 Enclose pinion SUS304 gears 55 8.14 PG3 Internal 1 Coordinate Allows all pinion gears to rotate SMF Gear/Direction pinion gears along its internal gear Openner 56 8.15 PG3 Carrier 1 Hold pinion gears SUM

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2.4. Exploded View

Figure 7. Exploded view of Transmission Sub-assembly.

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3. Report #3: Assembly Sequence

3.1 Revised Liaison Diagram 6. Main Housing 1 6.1 Motor + PG1 Sun Gear

26 27 4 25 8.3 PG1 Ring Gear 8.9 Locking Gear 23 2 8.1 PG1 Washer 24 8.2 PG1 Pinion Gears

7 9 10 22

8.10 Hi/Lo Lever 8.7 PG2 Washer 21 8.4 PG1 Carrier 19 7.2 Gear Housing 29 30 20 6 11 8.6 PG2 Pinion Gears 8.8 Coupling Gear 5 12 18 8.15 PG3 Ring Gear 13 28 8.13 PG2 Carrier 8.14 PG3 Washer 17 14 8.2 PG3 Pinion Gears 3 16

8.16 PG3 Carrier

7.1 Shaft

3.2 Revised Datum Flow Chain 6. Main Housing 6 6.1 Motor + PG1 Sun Gear

3 4 6 5 8.3 PG1 Ring Gear 8.9 Locking Gear 4 6 8.1 PG1 Washer 3 8.2 PG1 Pinion Gears 6 5 6 3

8.10 Hi/Lo Lever 8.7 PG2 Washer 3 8.4 PG1 Carrier

1 4 7.2 Gear Housing 5 3 5 4 8.6 PG2 Pinion Gears 8.8 Coupling Gear 6 5 5 8.15 PG3 Ring Gear 3 3 8.13 PG2 Carrier 8.14 PG3 Washer 4 4 8.2 PG3 Pinion Gears 6 5

8.16 PG3 Carrier

7.1 Shaft

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3.3 All Possible Assembly Sequence

1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 11 12 7 8 9 10 11 12 7 8 9 10 11 12 7 8 9 10 11 12 13 14 15 16 17 18 13 14 15 16 17 18 13 14 15 16 17 18 13 14 15 16 17 18 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 25 26 27 28 29 30 25 26 27 28 29 30 25 26 27 28 29 30 25 26 27 28 29 30

1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 11 12 7 8 9 10 11 12 7 8 9 10 11 12 13 14 15 16 17 18 13 14 15 16 17 18 13 14 15 16 17 18 19 20 21 22 23 24 19 20 21 22 23 24 19 20 21 22 23 24 25 26 27 28 29 30 25 26 27 28 29 30 25 26 27 28 29 30

1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 11 12 7 8 9 10 11 12 13 14 15 16 17 18 13 14 15 16 17 18 19 20 21 22 23 24 19 20 21 22 23 24 25 26 27 28 29 30 25 26 27 28 29 30

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3.4 The Most Conveniencee Assembly Sequence

Transmission/Motor Sub-assembly R R R S F 6. Main Housing 8.12. Fastener for Hi/Lo Lever 8.10. Hi/Lo Lever 6.1. Motor Assembly 8.3. PG1 Ring Gear 8.1. PG1 Washer Grease 8.2. PG1 Pinion Gears 8.4. PG1 Carrier/PG2 Sun Gear 8.7. PG2 Washer Grease 8.9. PG2 Locking Gear F 8.8. PG2 Coupling Gear 8.6. PG2 Pinion Gears 8.13. PG2 Carrier/PG3 Sun Gear 8.14 PG3 Washer Grease 8.2 PG3 Pinion Gears F 8.15. PG3 Ring Gear

7.2. Bit Holder Housing (Including 7.1. Shaft and 8.16. PG3 Carrier)

F: Fixture R: Reorient S: Snap F: Remove Fixture : Downward insertion : Horizontal insertion

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3.5 Required Gross and Fine Motions The Gross and Fine motions are estimated using the Boothroyd & Dewhurst DFA table as follow.

1 2 3 4 5 6 7 9

e e e

) d l l f ) m m y h n e i i l t a a 6 i o r i t t

( e e e

f u u e .

s r e + v d d r n g o n n b n i ) e e a

i t o o o o n t a t a m 4 c i i f n i m r r ( c c m u m l t t m

( i s m m a o

a r u c s a t s * d

i t l i n g

) e t t p t n p e r n e f N n a i i

o n 2

No. r s a s a o r n r i i o a ( c t g g i l t D i u n i i n e p r e t o I h r i m t r i d

= i i g a d d a o p p t e t l l e i t r - - r n ) r c P a s a a . s b F

o e o o a r a t c n e u u e p e h i m w w P u e n n h p u O T T s t o a a ( o N M M 1 Bit Holder Housing (Including Shaft and PG3 Carrier) 7.2 1 03 1.95 03 2 3.95 1 2 PG3 Ring Gear 8.15 1 05 4 04 4.5 8.5 1 3 PG3 Pinion Gears 8.2 3 04 3.6 04 4.5 24.3 3 4 Grease 4 1 99 12 12 1 5 PG3 Washer 8.14 1 30 1.69 03 2 3.69 0 6 PG2 Carrier/PG3 Sun Gear 8.13 1 05 14 7.5 11.5 1 7 PG2 Pinion Gears 8.6 3 04 3.6 03 2 16.8 3 8 Fixture/Tool (for Hi/Lo lever) 1 00 1.13 03 2 3.13 0 9 PG2 Coupling Gear 8.8 1 05 4 03 2 6 1 10 PG2 Locking Gear 8.9 1 05 4 03 2 6 1 11 Grease 1 99 12 12 0 12 PG2 Washer 8.7 1 30 1.69 03 2 3.69 0 13 PG1 Carrier/PG2 Sun Gear 8.4 1 05 4 14 7.5 11.5 0 14 PG1 Pinion Gears 8.2 3 04 3.6 03 2 16.8 0 15 Grease 1 99 12 12 0 16 PG1 Washer 8.1 1 30 1.69 03 2 3.69 0 17 PG1 Ring Gear 8.3 1 05 4 13 5 9 0 18 Motor Assembly 6.1 1 00 1.13 14 7.5 8.63 0 19 Reorientation 2 80 9 18 0 20 Hi/Lo Lever 8.10 1 33 2.51 02 5.5 8.01 1 21 Snap fit 2 39 3.5 7 0 22 Fastners (for Hi/Lo lever) 8.12 2 24 4.35 83 6 20.7 0 Total 31 226.89 13

The Boothroyd and Dewhurst DFA suggest total assembly time of 226.89 seconds or 3 minutes and 46.89 seconds. The actual manual assembly experiments by us took about 4 minutes and 30 seconds without putting any grease.

3.6 Futures, Chamfers and Lead ins

Feature Part No. Part A Part No. Part B Chamfers and MATE/ Comments Number Lead-ins CONTACT

1 7.2 Bit Holder Housing 8.16 & Carrier & Bit Not Applicable Mate(5) Peg & Hole 7.1 Holder 2 7.2 Bit Holder Housing 8.15 PG3 Ring Gear N. A. Mate(5) Peg & Hole 3 8.16 & 7.1 Carrier & Bit Holder 8.2 Pinion Gears N. A. Mate(5) 3 Peg & Holes for 3 pinions 4 8.2 Pinion Gears 8.13 PG2 Carrier/PG3 Chamfer and Lead- Mate(5) Over-constrained Dofs, Clearance Sun Gear in on all 3 Pinion Gears and on Sun Gear 5 8.2 Pinion Gears 8.14 Washer N. A. Mate(3) Overlap of 2 plates, Over-Cons. With #7 6 8.15 PG3 Ring Gear 8.2 Pinion Gears Chamfer and Lead- Mate(4) Over-constrained Dofs, Clearance in on all 3 Pinion Gears and on Internal Gear

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7 8.15 PG3 Ring Gear 8.14 Washer N. A. Mate(3) Overlap of 2 plates, Over-Cons. With #5 8 8.14 Washer 8.13 PG2 Carrier/PG3 N. A. Mate(3) Overlap of two Plates Sun Gear 9 8.13 PG2 Carrier/PG3 Sun 8.6 PG2 Pinion Gears N. A. Mate(5) 3 Peg & Holes for 3 pinions Gear 10 7.2 Bit Holder Housing 8.9 PG2 Locking N. A. Mate(5) Peg & Hole Gear 11 7.2 Bit Holder Housing 8.1 Hi/Lo Lever N. A. Mate(5) Peg & Hole 12 8.6 PG2 Pinion Gears 8.7 PG2 Washer N. A. Mate(3) Overlap of 2 plates, Over-Cons. With #14 13 8.6 PG2 Pinion Gears 8.4 PG1 Carrier/PG2 Chamfer and Lead- Mate(5) Over-constrained Dofs, Clearance Sun Gear in on all 3 Pinion Gears and on Sun Gear 14 8.7 PG2 Washer 8.4 PG1 Carrier/PG2 N. A. Mate(3) Overlap of 2 plates, Over-Cons. Sun Gear With #12 15 8.6 PG2 Pinion Gears 8.8 PG2 Coupling Chamfer and Lead- Mate(5) Over-constrained Dofs, Clearance Gear in on all 3 Pinion Gears and on Coupling Gear 16 8.4 PG1 Carrier/PG2 Sun 8.2 PG3 Pinion Gears N. A. Mate(5) 3 Peg & Holes for 3 pinions Gear 17 8.2 PG3 Pinion Gears 8.1 Pinion Gears 1 N. A. Mate(3) Overlap of 2 plates Washer 18 8.2 PG3 Pinion Gears 4 & 6 Torque Limiter & Chamfer and Lead- Mate(5) Gear mate Power Generator in on all 3 Pinion Gears and on Sun Gear of Power Generator 19 8.1 Pinion Gears 1 8.3 PG1 Ring Gear N. A. Mate(3) Overlap of 2 plates Washer 20 8.3 PG1 Ring Gear 4 & 6 Torque Limiter & N. A. Mate(3) Overlap of 2 plates Power Generator 21 8.1 Hi/Lo Lever 8.8 PG2 Coupling N. A. Mate(1) Gear 22 8.13 PG2 Carrier/PG3 Sun 8.8 PG2 Coupling Chamfer and Lead- Mate(5) Gear mate Gear Gear in on Sun Gear and on Coupling Gear 23 8.9 PG2 Locking Gear 8.8 PG2 Coupling Chamfer and Lead- Mate(6) Properly constrained Gear in on Locking Gear and on Coupling Gear 24 7.2 Bit Holder Housing 8.8 PG2 Coupling N. A. Mate(3) Oversize hole Gear 25 7.2 Bit Holder Housing 8.3 PG1 Ring Gear N. A. Mate(3) Oversize hole 26 7.2 Bit Holder Housing 4 & 6 Torque Limiter & N. A. Mate(6) Properly constrained Power Generator 27 8.2 PG3 Pinion Gears 8.3 PG1 Ring Gear Chamfer and Lead- Mate(5) Gear mate in on all 3 Pinion Gears and on Internal Gear

Description of Chamfers and Lead-ins on Features: 1. Pinion Gears and Sun Gear (Feature #04, #13, #18): Chamfers and Lead-ins are provided on the Pinion Gears and Gun Gear in order to avoid jamming during assembly. Once the assembly operations are over, chamfer plays no role. 2. Pinion Gears and Internal Gear (Feature #06, #27): Chamfers and Lead-ins are provided on the Pinion Gears and Internal Gear to ensure the ease of assembly. Chamfer plays no role during the actual operation of mechanism.

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3. Pinion Gears and Coupling Gear (Feature #15): Chamfers and Lead-ins avoid the jamming of these two parts during assembly. They play no role after the product has been assembled. 4. Sun Gear and Coupling Gear (Feature #22): Here, Chamfers and Lead-ins have functional importance. The connection between Sun Gear and Coupling Gear is not permanent. It is established when the Coupling Gear is moved to achieve higher speed. So, the proper chamfer angle and lead-in are very important. They should be chosen in such a way that the connection between Sun Gear and Coupling gear is established irrespective of the angular position of Coupling Gear with respect to Sun Gear. 5. Coupling Gear and Locking Gear (Feature #00): Here again, Chamfers and Lead-ins have functional importance. The connection between Locking Gear and Coupling Gear is established when the Coupling Gear is moved to achieve lower speed. Coupling Gear and Locking Gear together form the Internal Gear and they act as one functional unit in this situation. So, the proper chamfer angle and lead-in are very important. They should be chosen in such a way that the connection between Locking Gear and Coupling gear is established irrespective of the angular position of Coupling Gear with respect to Locking Gear.

3.7 Difficulties & Ideas in Assembly In general, the following alternatives might be considered to eliminate difficult to assemble parts:  Modify assembly sequence or architecture to eliminate difficult to access assembly steps.  Modify assembly sequence or architecture to reduce lengthy assembly time.  Examples of the above approaches may lead to the following changes:  Modify the stacking of planetary gear sets. This step requires architectural changes as discuss in the next section.  Commonize and minimize fasteners.  Eliminate washers.  Avoid the use of fixtures/tools by finding assembly sequence alternatives.  Eliminate reorientation by choosing assembly sequence that requires less number of reorientations.  Eliminate multiple greasing steps.

The following are some of the possible problems and resolutions.

Liaiso Part Par Possible Problems/risks Possible solutions n # A t B 16 8.2 8.1  Insertion in deep and  Separate 7.2 Bit Holder Housing to two 6 narrow hole, blind cylinders operation  Develop gripper to improve operation (see fig #5) 18 8.6 8.1  Insertion in deep and  Separate 7.2 Bit Holder Housing to two 3 narrow hole, blind cylinders operation  Develop gripper to improve operation (see fig #5)

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27 6.1 8.2  Need to jiggle the motor  Change the assembly sequence by mating assembly to get proper gear pinion gears to motor assembly shaft. mating , blind operation 17 8.13 8.2  Need to jiggle the motor  Change the assembly sequence by mating assembly to get proper gear pinion gears to motor assembly shaft. mating 30 8.8 8.1  Mating 8.10 to 8.8, because  Use fixture to constrain 8.8, Coupling 0 8.8 is so free to be gear. positioned correctly, and obstructed view

3.8 Feature Parts and Associated Assembly Tool and Fixtures

The insertion tool, T-2, shown in Figure 5.a is used for loading multiple part into the transmission housing (7.2) during the transmission gear assembly build sequence. The gripper tool design can be used for loading all pinion carrier gears and ring gears. The parts in the following table will loaded using T-2.

Subsystem P/N Description Gripping feature Transmission 8.3 PG1 Ring Gears Inside diameter Transmission 8.4 PG1 Carrier 3 pinion shafts Transmission 8.8 PG2 Coupling Gear Inside diameter Transmission 8.9 PG2 Locking Gear Inside diameter Transmission 8.13 PG2 Carrier 3 pinion shafts Transmission 8.15 PG3 Ring Gear Inside diameter

The T-2 gripping tool is a spreader design. When tool is in a free (un-gripped) state, the tips of the tool, which contact the part, are in a closed position (see Figure 5.a). This position is maintained at free state by a spring above the tool pivot point.

When gripping pinion gear carriers, the tool is placed between the 3 pinion gear pins and loaded until the tool spreads to make sufficient contact (see Figure 5.a).

When gripping ring gears, the tool is placed anywhere on the inside diameter and loaded until tool spreads to make sufficient contact (see Figure 5.a).

The Pinion Gear Insertion Tool, T-1, shown in Figure 5.b, is used to insert pinion gears into the transmission housing (7.2). This tool is designed with magnetic inserts placed at two different depths to allow for diameters and lengths corresponding to both size pinion gears (8.2 and 8.6). Once the pinion gear has been loaded into the tool and onto a carrier pin, the button on the top of the tool is pressed by the operator to actuate the ejector pin. This motion extracts the pinion gear from the magnet, leaving it in final assembly position.

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The transmission housing holding fixture, F-1, shown in Figure 5.c holds and orients the transmission housing (7.2) during transmission assembly buildup. The fixture is hard mounted to the table in a work-cell in front of the operator. The operator mates the housing to the fixture by pushing the collet onto a pin at the base of the fixture. Fixturing the housing prior to gear assembly buildup allows the operator full use of both hands for loading parts into housing.

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3.9. Fixtures and Tools for Assembly

Figure 5.b. Tool T-1

Figure 5.a. Tool T-2

Figure 5.c. Fixture F-1

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3.10 Gear Set Architecture Redesign

Original Architecture Redesigned Architecture

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3.11 Improvement highlight

Planetary gear sets are rearranged by moving the Planetary Gear Set #1 next to the Planetary Gear Set #3. This new architecture results in significant part reduction and part integration (function sharing, see item #4 below). The redesign also requires some feature changes as described below. 1. Increasing the length of PG3 ring gear (8.15) to contains both planetary gear #1 and #3. Significant improvement is achieved by:  Eliminating PG3 washer (8.14)  Eliminating locking gear (8.9) by putting its functionality into PG2 Ring Gear (8.3) 2. Feature modification of PG1 carrier (8.4) to fit PG3 planetary gears and PG3 Ring gear. 3. Combining the function of locking gear (8.9) into (8.3) 4. Modification of sun gear at the motor shaft to fit PG2 planetary gears (8.6) 5. Shortening the length of bit holder housing (7.2) results the following benefits:  The assembly of the planetary gear sets #1 and #2 becomes much easier (eliminating deep insertions)  Eliminating multiple greasing steps.

The new architecture also provides significant assembly cost benefit by  Eliminating special tools required in the current design.  Reduction in the time required assembling the modified product.

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4. Report #4: Assembly Floor Layout Analysis

The following report steps through the analysis required to propose a feasible plant layout to effectively perform operations necessary to assembly package and ship the Sears Craftsman Screwdriver. The team broke the analysis into 3 primary tasks in order to provide the necessary information for a viable operations solution. These analysis activities are outlined in the report as follows:  Assembly Sequence  Assembly Process time  Assembly Line Design and Assumptions

4.1. Assembly Sequence The assembly sequence chosen for the Sears Craftsman Screwdriver are shown in Figures 1 and 2. This sequence was chosen because it was conducive to an efficient flow of assembly operations that were consistent with the overall operations strategy. The sequence allowed for easily "chunking" assembly task into workcells that allowed for optimal assembly line balance. This sequence also allowed the workcell subassemblies to be robust against damage or loss of parts during transition to downstream operation.

Packed Box Testing and Packaging

Manual

Testing

Screw Driver Bits Final Assembly Charger Base 1.1:Battery Charger Cardboard Bin Drive Housing Fasteners Box 5.2: Drive Right Housing

5.3: Grip Locking Switch 8.10: High/Lo Button

5.1: Drive Left Housing Wire Crimping

6: Motor Assembly

Grip Housing 4:Torque Limiter Battery Assembly

8:Transmission assembly

Figure 1 – Assembly Sequence Tree

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Transmission/Motor Sub-assembly

R R S F 8.12. Fastener for Hi/Lo Lever 8.10. Hi/Lo Lever

8.3. PG1 Ring Gear 8.1. PG1 Washer Grease 8.2. PG1 Pinion Gears 8.4. PG1 Carrier/PG2 Sun Gear 8.7. PG2 Washer Grease 8.9. PG2 Locking Gear F 8.8. PG2 Coupling Gear 8.6. PG2 Pinion Gears 8.13. PG2 Carrier/PG3 Sun Gear 8.14 PG3 Washer Grease 8.2 PG3 Pinion Gears F 8.15. PG3 Ring Gear

7.2. Bit Holder Housing (Including 7.1. Shaft and 8.16. PG3 Carrier)

F: Fixture R: Reorient S: Snap F: Remove Fixture : Downward insertion : Horizontal insertion

Figure 2 -Transmission Sub-Assembly Sequence Tree

4.2 Assembly Process time

Assembly times were determined using Boothroyd & Dewhurst DFA tables (see Figures 3,4,&5). These techniques used associated times correlated to previously determined manual insertion and handling codes. Once these times were determined, decisions were made as to what workstations needed to be developed for an optimal work flow and assembly line balancing. These decisions were also based on product architecture and interfaces between subsystems, which allow easy and robust transfer to the downstream workstation.

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2 3 4 5 6 7

e e e

) d l l ) m m y h n e i i l t a a 6 i i t t

( e e e

r u u s r e + v d d n g n n i ) e e a t o o o n t a t m a 4 c i i i r r ( c c m u

m l t t

( i m m a a r c s a t * d

i n g

) e t t p n p e

f N n i i

o n

No. 2 s s o r r n i i o a ( t g g i l t

n i i n e r e t o h r i r i d =

a d a d o p p t e l l e - - r n ) c P a s a a . b

e o o a r t c n u u p e h i m w w u e n n p O u T T s o a a ( o N M M 1 Box 1 00 1.13 30 31.13 2 Cardboard bin 1 03 1.95 00 1.5 3.45 3 Battery Charger 1 03 1.95 00 1.5 3.45 4 Charger Base 1 03 1.95 00 1.5 3.45 5 Bits 1 00 1.13 00 1.5 2.63 6 Screwdriver 1 03 1.95 00 1.5 3.45 7 Screwdriver testing 1 20 20 8 Manual 1 00 1.13 1.13 Total 8 68.69

Figure 3 - Testing and Packaging

2 3 4 5 6 7

e e e

) d l l ) m m y h n e i i l t a a 6 i i t t

( e e e

r u u s r e + v d d n g n n ) i e e a t o o o n t a t a m 4 c i i i r r ( c c m u

m l t t

( i m m a a r c s a t * d

i n g

) e t t p n p e

f N n i i

o n No. 2 s

s o r r n i i a o ( t g g i l t

n i i n e r e t o h i r r i d =

a d d a o p p

t e l l e - - r n ) c P a s a a . b

e o o a r t c n u u p e h i m w w u e n n p O u T T s o a a ( o N M M 1 Transmission Assembly 1 03 1.95 20 2.5 4.45 2 Torque Limiter 1 01 1.13 00 1.5 2.63 3 Grip Housing/Battery Assembly 1 03 1.95 03 2 3.95 4 Motor Assembly 1 00 1.13 1.13 5 Wire Crimping 2 39 3.5 7 6 Drive Left Housing 1 03 1.95 03 2 3.95 7 Hi/Low Button 1 13 2.25 03 2 4.25 8 Grip Locking Switch 1 13 2.25 03 2 4.25 9 Drive Right Housing 1 03 1.95 03 2 3.95 10 Drive Housing Fasteners 6 10 1.13 29 5 36.78 Total 16 72.34

Figure 4 - Final Assembly Process Time

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2 3 4 5 6 7

e e e

) d l l ) m m y h n e i i l t a a 6 i i t t

( e e e

r u u s r e + v d d n g n n i ) e e a t o o o n t a t a m 4 c i i i r r ( c c m u

m l t t

( i m m a

a r c s a t * d

i n g

) e t t p n p e

f N n i i

o n

No. 2 s

s o r r n i i o a ( t g g i l t

n i i n e r e t o r i h r i d =

d a d a o p p t e l l e - - r n ) c P a s a a . b

e o o a r t c n u u p e h i m w w u e n n p u O T T s o a a ( o N M M 1 Bit Holder Housing (Including Shaft and PG3 Carrier) 1 03 1.95 03 2 3.95 2 PG3 Ring Gear 1 05 4 04 4.5 8.5 3 PG3 Pinion Gears 3 04 3.6 04 4.5 24.3 4 Grease 1 99 12 12 5 PG3 Washer 1 30 1.69 03 2 3.69 6 PG2 Carrier/PG3 Sun Gear 1 05 14 7.5 11.5 7 PG2 Pinion Gears 3 04 3.6 03 2 16.8 8 Fixture/Tool (for Hi/Lo lever) 1 00 1.13 03 2 3.13 9 PG2 Coupling Gear 1 05 4 03 2 6 10 PG2 Locking Gear 1 05 4 03 2 6 11 Grease 1 99 12 12 12 PG2 Washer 1 30 1.69 03 2 3.69 13 PG1 Carrier/PG2 Sun Gear 1 05 4 14 7.5 11.5 14 PG1 Pinion Gears 3 04 3.6 03 2 16.8 15 Grease 1 99 12 12 16 PG1 Washer 1 30 1.69 03 2 3.69 17 PG1 Ring Gear 1 05 4 13 5 9 18 Reorientation 2 80 9 18 19 Hi/Lo Lever 1 33 2.51 02 5.5 8.01 20 Snap fit 2 39 3.5 7 21 Fastners (for Hi/Lo lever) 2 24 4.35 83 6 20.7 Total 30 218.26

Figure 5 - Transmission Assembly Process Time

It can be seen from the total assembly times found in the above tables that a total process cycle time of approximately 60-70 seconds should be targeted. The grip housing assembly process time, although not shown in this report, was calculated using the same method and found to be approximately 70 seconds. With this information the workstations were determined to be the following :

Grip Housing Assembly (1 workstation) Transmission Assembly (3 workstations) Final Assembly (1 workstation) Testing and Packaging (1 workstation)

4.3 Assembly Line Design and Assumptions

Production Volumes were estimated by gathering information about the product distribution network. This information was found from the Sears website. The table below summarizes all retail outlets where the products are sold in the 2 key markets of

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U.S and Canada. Phone surveys were then conducted to gain a reasonable estimate of the average number of units sold per month at these outlets.

Estimated Sales Amounts 8,358 /month Estimated Production 379.9 /day (22 working days/month)

units/month/ # of shops units/month SEARS Shops shop US Department stores 833 3 2499 Off-the-mall full-line stores 1,325 2 2650 Subr-lines in rural markets 1,384 1 1384 Canada Full-line stores 110 2.5 275 Catalog agent & dealers 1,550 1 1550 Total 8358

4.3.1 Design Parameters

Considering the estimated production size and the product packaging size, factory-out distribution of this product will be less than once a day and the batch size should be defined assembly process. Parts supply: Parts for one day production are brought to the working area by full-time worker, who is also responsible to other production Batch: 95 units (4 batches/ day) Set-up time 10 min./batch to carry parts from in-house inventory to each workstation Working time :7.5 hours/day (actual working time put off recesses)

Assumptive Cycle Time (temporary setting for designing) Cycle time/ unit (7.5 hours/day) / (379.9 units/day ) = 71.1 sec. Cycle time/ batch (Process time/ # of workers) * (95 units) + 10 min. < 71.1*95 sec. (1 hours and 53 min., 4 batches/ day)

4.3.2 Supplied Material It was estimated that supplied materials are all part level and all handicrafts are performed in house because of following observations:

. This product is made in China, in which labor cost is generally low.

. Since this product is an integrated product, possible outside sub-assembles are Battery Assembly and Grip Housing Assembly. However, if these are out-sourced, in comparison, Transmission Assembly operation requires too long time, even if separated to two workstation, and other assembly operations become too simple.

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4.4 Assembly operation style

Given that the annual production volumes were relatively low for a mass production product and that the assembly operations are in China where labor cost is very low, automated assembly operations were ruled out as a cost-effective means of assembly.

4.4.1 Assembly Line Design

Considering Assumptive Cycle Time, there is no need to organize highly sequential line, however, too much individual workstations increase overheads. To balance minimizing equipment cost and overhead cost, General Assembly Flow becomes as follows: The production workflow starts with an inventory stockpile that supplies approximately 1 shift of production (see Figure 7 - A). Inventory is transferred manually by laborers to supply all workcells during the shift. Enough inventory is transferred to workcells to supply a batch size of 95 units. This is because the space for stocking inventory is limited at the workcell tables. Also, this allows for the recirculation of the transmission housing fixtures, which are limited in number to approx. 100 to minimize investment cost (see line 1 dotted). The details of these fixtures, T-1, are shown in project report #3.

Workcell B assembles the grip housing assembly concurrently with wokcells C,D&E which assemble the transmissions. These 4 workcells are positioned around a common conveyor system that feeds into a "pool" for use by the final assembly workcell (F). This conveyor system consists of an inclined set of rollers or possibly a steel chute. It is approximately 6 meters in length, so an automated transfer system is not necessary. It is important to note that 3 workcells were used to assemble the transmissions to achieve proper assembly line balancing. This strategy was needed because cycle time for transmission assembly was 185 seconds (218 sec. without tool efficiency, see Figure 6). By having 3 workcells the combined cycle time becomes 62 seconds. This is less than the 72 seconds required for final assembly, which will prevent build up of inventory.

Note: Holding fixtures are used to hold the transmission gear assembly vertical. These fixture are placed on the conveyor along with assembled workpiece. After going through final assembly, these fixtures are recirculated to workcells C,D, and E by a manual labor head.

Workcell F is the place for final assembly. The transmission assembly is picked up and motor is assembled with it. The grip housing assembly is picked up next and it is assembled with it. Other part of the housing is snap fitted on to rest of the sub-assembly.

Workcell G stores the fixtures being used in the transmission assembly These fixtures are sent back to the workcells C,D and E.

Workcell H is for packaging and testing. The fully assembled screwdrivers are picked from workcell G and they are tested both in high speed and low speed operating conditions.

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Supplied Once a day In-house Material Inventory Set-up Time: 10 min./Batch Grip Housing Carried Once Assembly Testing & a day Final Assembly In-house Out-house Packaging Transmission Inventory Inventory Assembly

Cycle Time: about 62 sec. Cycle Time : about 72.34 sec. Cycle Time : about 68.69 sec. 1 worker for Grip Housing 1 worker 1 worker 3 workers for Transmission (Process Time:218.26--> 185 sec. by 15% tool efficiency)

Figure 6 –Assembly Flow Diagram Packaging & Testing H G Final Assembly Storage for Parts Shelf Trans. F Parts Pallet Housing Parts Shelf Fixture Tool Table Table Grip Housing P B Assembly

Pool Slider o o l

Once a day In-house Inventory by Forklift for Final Assembly (Pallet) J D Table

Transmission C

Assembly-2 o n

Parts Shelf v

e Parts Shelf

y Transmission o r Table C Assembly-1 A Once a day In-house Material by Forklift Inventory (Containers on Pallet) E Table

Parts Shelf Transmission Assembly-3 Closer position for heavier parts

1 m2 Assembly Sequence Material Supply

Figure 7 –Floor Layout

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Materials are ordered Right to Left along assembly sequence

Materials are supplied from rear side Tools & Grease-gun Hang Wall

Parts Shelf

Work Table

Small materials are automatically supplied on the table

Conveyer is located light-hand

Figure 8 –Workstation table Design

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5. Report #5: Workstation Design

5.1 Required cycle time to complete the planned operations

Following Assembly Flow Diagram shows cycle time for all the operations involved in screwdriver sub-assemblies, final assembly and testing/packing. For more details please refer to individual charts.

5.1.1 Assembly Flow Diagram

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5.1.2 Final Assembly

2 3 4 5 6 7

e e e

) d l l ) m m y h n e i i l t a a 6 i i t t

( e e e

r u u s r e + v d d n g n n ) i e e a t o o o n t a t a m 4 c i i i r r ( c c m u

m l t t

( i m m a a r c s a t * d

i n g

) e t t p n p e

f N n i i

o n No. 2 s

s o r r n i i a o ( t g g i l t

n i i n e r e t o h i r r i d =

a d d a o p p

t e l l e - - r n ) c P a s a a . b

5.1.3 Testing and Packaging

2 3 4 5 6 7

e e e

) d l l ) m m y h n e i i l t a a 6 i i t t

( e e e

r u u s r e + v d d n g n n i ) e e a t o o o n t a t m a 4 c i i i r r ( c c m u

m l t t

( i m m a a r c s a t * d

i n g

) e t t p n p e

f N n i i

o n

No. 2 s s o r r n i i o a ( t g g i l t

n i i n e r e t o h r i r i d =

a d a d o p p t e l l e - - r n ) c P a s a a . b

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5.1.4 Transmission Assembly

5.1.5 Grip Housing/Battery Assembly

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It can be seen from the total assembly times found in the above tables that a total process cycle time of approximately 60-70 seconds should be targeted. With this information the workstations were determined to be the following:

Grip Housing Assembly (1 workstation) Transmission Assembly (3 workstations) Final Assembly (1 workstation) Testing and Packaging (1 workstation)

= (Analyzed assembly time Tr1: Transmission Assembly Workstation #1: 218.26 sec.) Tr2: Transmission Assembly Workstation #2: 61.84 sec. Tr3: Transmission Assembly Workstation #3: * (1 - tool efficiency 15%) / Bat: Grip Housing/Battery Assembly Workstation: 69.69 sec. (3 workstations) Fin: Final Assembly Workstation: 72.34 sec. T&P: Testing and Packaging Workstation: 68.69 sec. Inp: Input Component Inventory, Out: Finished Good Inventory

 We have provided a small buffer (storage) between workstations to protect for process uncertainties, therefore the cycle time of assembly line is directly obtained as a longest cycle time among workstations.  Cycle Time of Assembly Line = 72.34 sec.  Critical Workstation is Final Assembly, which is located the second sequence

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5.2 Station lay out: in and out flows of assemblies and parts

In this report we are focusing on "Transmission assembly". The workstation layout and other details are shown in following diagrams.

Workstation table Design Materials are ordered Right to Left along assembly sequence

Materials are supplied from rear side

Parts Shelf

Work Table

Small materials are automatically supplied on the table

Conveyer is located light-hand

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7.2 Bit Holder Housing 8.1 Planetary Gear 1 Washer Transmission Workstation 8.2 PG1 Pinion Gears 8.3 PG1 Internal Gears 8.4 PG1 Carrier 8.6 PG2 Pinion Gears F-1 Stacked on spring loaded riser 8.7 PG2 Washer 8.8 PG2 Coupling Gear Fixtures enter onto Angled Chute 8.9 PG2 Locking Gear 8.8 8.13 PG2 Carrier 8.14 8.2 8.9 8.3 8.4 8.15 8.14 PG3 Washer 8.7 8.6 8.15 PG3 Internal Gear 8.1 8.13

Load stock here

Grease Gun Operator Grabs parts from here

Conveyor T-1, Insertion Tool

T-2, Insertion Tool

7.2

1 sq. ft.

Operator

5.3 Required motions of equipment and people

Evaluation of required motions according to various criteria is very important in manual assembly. The criteria can be summarized under following topics: Right and left hand should be operative for the same amount of time. Motions of right and left hand should be synchronized. I.e. the motions of right and left hand should be in succession. The arm movement should be minimized. The maximum movement of arm should be with in the reach of operator. The movement of the operator in the workstation area should be minimized. Parts should be placed in bins in such a way that they can be picked by the operator in correct orientation without any difficulty. I.e. parts should not entangle with themselves in the bins.

These are some of the rules of “motion and time study” which have been given attention while designing the “transmission workstation”. The slides show the configuration of the workstation. Following is the brief summary of the hand motions: The initial step for the operator is to place the transmission holding fixture (F-1) on the table in front of himself. These fixtures are supplied from the other side of the table where they are loaded onto a spring-loaded riser that feeds the fixtures down an angled

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chute. These fixtures are continuously being circulated from the final assembly workstation where the finished transmission assembly is removed from the fixture. Pick up the Bit Holder Housing (BH Housing 7.2) from right hand and shift it to the left hand. Pick up the T-1 Insertion Tool with right hand. Pick up PG1 Internal Gear (8.3) with the help of T-1 insertion tool with right hand while putting the BH Housing (7.2) in the Fixture with left hand. Insert the PG1 Internal Gear (8.3) in the BH Housing (7.2) with right hand. Put the T-1 Insertion Tool down and pick T-2 Insertion Tool in right hand. Pick up the PG1 Pinion Gears (8.2) with the help of T-2 Insertion tool and insert them one by one with right hand. Pick up the Grease Gun in the left hand and put grease in the sub-assembly. Pick up the PG1 Washer (8.1) with left hand and drop it in the BH Housing (7.2). Pick up the PG1 Carrier (8.4) with the help of T-2 Insertion tool with right hand and insert it. Pick up PG2 Pinion Gears (8.6) with the help of T-2 Insertion Tool and insert them one by one. Pick up PG2 Coupling Gear (8.8) with the left hand, grip it with T-2 Insertion Tool and insert it. Pick up PG2 Locking Gear (8.9) with the right hand, grip it with T-2 Insertion Tool and insert it. Pick up the Grease Gun in the left hand and put grease in the sub-assembly. Pick up the PG2 Washer (8.7) with left hand and drop it in the BH Housing (7.2). Pick up the PG2 Carrier (8.13) with the help of T-2 Insertion Tool with right hand and insert it. Pick up PG3 Pinion Gears (8.6) with the help of T-2 Insertion tool and insert them one by one. Pick up the PG3 Washer (8.14) with left hand and drop it in the BH Housing (7.2). Pick up the PG3 Internal Gear with left hand and drop it in the BH Housing (7.2).

These are the steps required for the assembly process. Both of the hands have been used intermittently. This sequence has been developed by assuming that the operator is left- handed. If this is not the case, one needs to simply shift the bins on the right to the left and vice-versa. The jobs assigned to the right hand will then be done by left hand. The motion has been kept as synchronized as possible. More importantly, the location of feeder bins containing the Pinion Gears has been designed very close to the right hand of the operator because there are nine pinion gears in total in the part. Finally, the operator needs to put the finished sub-assembly along with the fixture on the conveyor.

5.4 Necessary inspections or tests

Screwdriver testing is done as a part of testing and packaging operation. We decided to test fully assembled screwdriver at "Packaging" station in order to balance times on the assembly line. The testing involves following steps: The fully assembled screwdrivers are picked from workcell Test high speed and low speed operating conditions

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Test Forward and Reverse feature Test Adjustable Torque feature (Torque Limiter) Test dual-position handle and pistol-grip lock feature After passing the test they are placed in cardboard bin (screwdrivers which fail are kept in a "rework" bin.

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5.5 Gantt chart of required time of activities and a complete cycle

The complete assembly process is shown in the following diagram where the sequence is bottom-up. The assembly sequence was then broken down in to specific assembly activity steps and a "Gantt" charts were created.

Packed Box Testing and Packaging

Manual

Testing

Screw Driver

Bits Final Assembly Charger Base 1.1:Battery Charger

Cardboard Bin Drive Housing Fasteners Box 5.2: Drive Right Housing

5.3: Grip Locking Switch

8.10: High/Lo Button

5.1: Drive Left Housing Wire Crimping

6: Motor Assembly

Grip Housing 4:Torque Limiter Battery Assembly

8:Transmission assembly

Assembly sequence

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Assembly process design mainly follows 1) required cycle time, which is obtained from planned production size, 2) modularity, the mass of assembly sequence which is difficult to be separated, 3) efficiency in assembly motions and equipment cost. In this case, we designed the assembly process from following observations:

Required Cycle Time As shown in the last report, planned production size is 8358 units/month, therefore; (7.5 hours/day) / (379.9 units/day) = 71.1 sec.

Modularity Transmission Assembly is toughly integrated and hard to separate to two or more workstations. Estimated assembly time for this module is 218 sec., which is approximately three times of Required Cycle Time.

Efficiency One thought to solve modularity problem in Transmission Assembly is organizing three parallel lines all of which perform full assemble sequence. In this case, estimated impact on the equipment cost is small since our assumption of line designing is full handcraft line. However, motional efficiency must be worse since small motions, for example, transmission assembly, and large motions, for example, packaging and carrying the packaged products to the storage, are combined in each workstation.

Finally, we used following logic to design the assembly process: Organize three transmission assembly workstations to meet Required Cycle Time. Organize packaging workstation to separate large motions from small assembly motions. Organize workstations gathering other activities to meet Required Cycle Time.

The designed assembly process logic is shown in the following figure. For cycle time calculations please refer to section 5.1.

Tr1

Tr2

Inp Tr2 Fin T&P Out

Bat

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The timing of the process is shown in the following Gantt chart.

Transmission Assembly 1 2 3 4 5 6 7 8 9 10 Station 1 T1 T4 T7 Station 2 T2 T5 T8 Station 3 T3 T6 T9 Grip Housing/Battery Assembly B1 B2 B3 B4 B5 B6 Final Assembly F1(T1,B1) F2(T2,B2) F3(T3,B3) F4(T4,B4) F5(T5,B5) F6(T6,B6) Testing and Packaging P1(F1) P2(F2) P3(F3) P4(F4) P5(F5) P6(F6)

Where T1: Transmission Assembly #1, T2: Transmission Assembly #2, … B1: Battery Housing Assembly #1, B2: Battery Assembly #2, … F1: Final Assembly #1, F2: Final Assembly #2, … P1: Testing and packaging #1, P2: Testing and packaging #2, …

Where the detailed subprocesses is shown in the following Gantt charts. The timing scale is shown in seconds.

Final Assembly Timing

ID Task Name 1 20 39 58 77 96 115 134 1 Build Final Assembly 2 Transmission Assembly 3 Torque Limiter 4 Grip Housing/Battery Assembly 5 Motor Assembly 6 Wire Crimping 7 Drive Left Housing 8 Hi/Low Button 9 Grip Locking Switch 10 Drive Right Housing 11 Drive Housing Fasteners

Testing and Packaging Timing

8:00 AM 9:00 AM 10:00 A ID Task Name 1 20 39 58 77 96 115 1 Test and Package 2 Box 3 Cardboard bin 4 Battery Charger 5 Charger Base 6 Bits 7 Screwdriver 8 Screwdriver testing 9 Manual

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Transmission Assembly Timing

ID Task Name -6 24 53 82 111 140 169 198 1 Build Transmission Assembly

2 Bit Holder Housing

3 PG3 Ring Gear

4 PG3 Pinion Gears

5 Grease

6 PG3 Washer

7 PG2 Carrier/PG3 Sun Gear

8 PG2 Pinion Gears

9 Fixture/Tool (for Hi/Lo lever)

10 PG2 Coupling Gear

11 PG2 Locking Gear

12 Grease

13 PG2 Washer

14 PG1 Carrier/PG2 Sun Gear

15 PG1 Pinion Gears

16 Grease

17 PG1 Washer

18 PG1 Ring Gear

19 Reorientation

20 Hi/Lo Lever

21 Snap fit

22 Fasteners (for Hi/Lo lever)

Grip Housing/Battery Assembly Timing

8:00 AM 9:00 AM ID Task Name Duration 1 20 39 58 77 96 1 Grip Housing/Battery Assembly 69.8 mins 2 Left Housing 4 mins

3 Battery Package 2.6 mins 4 Switch circuit 3.5 mins

5 Wiring 36.5 mins

6 Switch button 3.8 mins 7 Right Housing 4 mins

8 Closure 3.1 mins 9 Fasteners 12.3 mins

The timing represented in the above Gantt chart is acquired from motion and time study using Boothroyd & Dewhurst's DFA database as shown in the tables in section 5.1.

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5.6 Cost estimation of workstations

The screwdriver assembly line consists of standard equipment except small parts cases. The estimated purchase and installation costs are as follows: Purchase Making Cost Installing # Equipment units Sub Total ($) Cost ($) ($) Cost ($) Transmission Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 200 200 5 Parts Case 11 40 50 490 6 Insertion Tool (T-1) 1 80 80 7 Insertion Tool (T-2) 1 80 80 8 Grease Gun 1 15 15 9 Housing Fixture 100 15 1500 Workstation Total 3 2563 3 Workstations Total 7689 Grip Housing Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 200 200 5 Parts Case 12 40 50 530 6 Plier 1 3 3 7 Electoric Driver 1 40 40 Workstation Total 971 Final Assembly Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 200 200 5 Parts Case 8 40 50 370 6 Plier 1 3 3 7 Electoric Driver 1 40 40 Workstation Total 811 Final Assembly Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 600 600 Workstation Total 798 Common 1 Conveyor 1 2000 2000 2 Slider 1 500 500 3 Pooling Table 3 15 45 4 Fixture Storage Box 1 20 20 6 Parts Carrier 2 30 60 5 Spare Tools 1set 160 160 Ground Total 13054

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5.7 Estimation of the cost of performing one assembly cycle

Original assembly cycle time and cost to perform one assembly are obtained using following formula:

(Transmission AT+Grip Housing AT+Final AT+Packaging & Testing AT)*Labor Rate = (218.26*85% + 69.69 + 72.34 + 68.69)*(1/3600)*@1.3 = (396.24 sec.)*(1/3600)*@1.3 = $0.143 where; AT: Assembling Time 1/3600: Seconds to hours translation 85%: 15% tool efficiency @1.3: $1.3/hour Chinese labor rate

However, actual assembling cost follows Cycle Time of Assembly Line, and it’s obtained with following formula:

(Longest Cycle Time)*(# of Workers)*Labor Rate = (72.34)*6*(1/3600)*@1.3 = (434.04 sec.)*(1/3600)*@1.3 = $0.157

Where, the overhead of designed assembly line to the ideal assembly is 9.5%. = (434.04 – 396.24) / 396.24

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6. Report #6: Economic Analysis and Assembly Line Simulation

6.1 Economic analysis of this assembly layout As shown in following table this assembly line consists of standard equipment except small parts cases. The estimated purchase and installation costs are as follows:

Transmission Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 200 200 5 Parts Case 11 40 50 490 6 Insertion Tool (T-1) 1 80 80 7 Insertion Tool (T-2) 1 80 80 8 Grease Gun 1 15 15 9 Housing Fixture 100 15 1500 Workstation Total 3 2563 3 Workstations Total 7689 Grip Housing Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 200 200 5 Parts Case 12 40 50 530 6 Plier 1 3 3 7 Electoric Driver 1 40 40 Workstation Total 971 Final Assembly Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 200 200 5 Parts Case 8 40 50 370 6 Plier 1 3 3 7 Electoric Driver 1 40 40 Workstation Total 811 Final Assembly Workstation 1 Table 1 150 150 2 Side Desk 1 18 18 3 Chair 1 30 30 4 Parts Self 1 600 600 Workstation Total 798 Common 1 Conveyor 1 2000 2000 2 Slider 1 500 500 3 Pooling Table 3 15 45 4 Fixture Storage Box 1 20 20 6 Parts Carrier 2 30 60 5 Spare Tools 1set 160 160 Total 13054

(Equipment and Installation costs) / (Production amount: units/year)*(5 years)

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= $13,054/((6,490 units/month)*(12 months)*(5 years)) = $0.0202 per unit

*1: This 5 years is an assumptive lifecycle of this product, and means that this equipment is used only for this product, even though many of equipment are reusable to other products.

6.1.1 Estimated Manufacturing Cost

Assembling cost follows Cycle Time of Assembly Line and Set-up Time, which is needed for every batch to supply materials. This cost is calculated with following formula:

((Longest Cycle Time)*(# of Workers) + (Set-up Time)/(Batch size))*Labor Rate = (72.34)*6*(1/3600)*@1.3 = ((434.04 sec.)*(1/3600) +((15 min.)/(95 units))*(1/60))*@$1.3 = $0.1601 per unit

where; 1/3600: Seconds to hours translation 1/60: minutes to hours translation @$1.3:$1.3/hour Chinese labor rate

Adding on this, we assume success rate of assembly line to 95% including spec out assembly, equipment down time, and operational delay. Therefore, actual assembly cost is:

$0.1601/0.95 = $0.1685 per unit

Furthermore, managing costs are usually required to design the assembly line and handle the products. If we suppose that 0.1 manpower/day, whose labor rate is $3.5, is required in average for this product, the managing cost becomes as follows:

((Required managing manpower/day)*(Labor Rate)*(Working hours)) / (Daily production amounts) = ((0.1 man/day)*@$3.5*6.93)/((6490 units/month)/(22 working days/month) = $0.0157 per unit

where; working hours =(72.34sec/unit)*(295units/day)+(15min)*(4batchs) = 6.93

We don’t include other costs such as land space cost or indirect stuff cost to the manufacturing costs.

6.1.2 Inventory Cost and Distribution Cost

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As we mentioned in previous report, this manufacturing system includes in house inventories for materials and finished products. And, of course, distribution cost is also required to supply products to SEARS shops. However we directly assume these costs as follows since it’s quite difficult to estimate all numbers relating to these factors reasonably.

Material inventory cost: $0.01 per unit Finished product inventory cost: $0.03 per unit Distribution cost: $0.60 per unit (primarily shipping cost from China to U.S)

6.1.3 Development Cost

We assume that this product was designed in the U.S. under the following conditions:

Engineers: 2 people Engineering labor rate: $10,000 /man-month Duration: 6 month (including from concept designing to drawing) Prototype modeling cost: $3,000

The development cost per unit is calculated as follows:

((2 engineers)*(6 month)*($10,000 /man-month) + $3,000) / ((6,490 units/month)*(12 months)*(5 years)) = $0.3546 per unit

We don’t consider other costs as follows: Designing equipment cost, including housing, energy, and devices such as CAD Managing cost Indirect stuff cost Designing supply chain cost, such as negotiating with suppliers and establishing delivery route

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6.1.4 Unit Part Costs No. System # System Name Part # Part Name unit cost Qty. Total Function 1 0 Packaging 0.1 Box 0.075 1 0.075 2 0.2 Cardboard bin 0.01 1 0.01 3 0.3 Manual 0.02 1 0.02 4 1 Battery Charger 1.1 Battery Charger 0.4 1 0.4 Charge Battery 5 2 Battery Closure 2.1 Charger Contact Plates 0.005 2 0.01 Contact Power 6 2.2 Battery Left Housing 0.15 1 0.15 Enclose Battery 7 2.3 Bettery Right Housing 0.15 1 0.15 Enclose Battery 8 2.4 Battery Cover 0.05 1 0.05 Enclose Battery 9 2.5 Baterry Housing Fasteners 0.0025 2 0.005 Hold battery housing 10 3 Power Storage 3.1 Rechargable Batteries 0.3 3 0.9 Store power 11 3.2 Battery Cables 0.004 2 0.008 Transmit power 12 3.3 Battery Connectors 0.01 2 0.02 Connect cable 13 3.4 Switch to Motor Cables 0.1 2 0.2 Transmit power 14 3.5 Crim Connectors 0.01 2 0.02 Hold cable 15 3.6 Shrink wrap 0.0015 1 0.0015 Hold batteries 16 3.7 Tape 0.0015 1 0.0015 Hold cable 17 3.8 Cable connectors 0.015 2 0.03 Connect cables to battery 18 4 Torque Limiter 4.1 Torque Limiter Outer Cap 0.175 1 0.175 Accept hand 19 4.2 Torque Limiter Inner Cap 0.175 1 0.175 Accept outer cap 20 4.3 Torque Limiter Cap Clip 0.025 1 0.025 Hold inner and outer caps 21 4.4 Needle Bearings 0.015 4 0.06 Push PG1 internal gear 22 4.5 Ball Bearings 0.015 6 0.09 Allow internal gear PG1 slippage 23 4.6 Bearing holder plate 0.05 1 0.05 Hold ball bearings 24 4.7 Torque Limiter Springs 0.01 4 0.04 Hold bearing holder plate 25 4.8 Torque Limiter Base Support 0.09 1 0.09 Support springs 26 4.9 Torque Limiter Fasteners 0.005 2 0.01 Hold base support to motor 27 5 Drive Closure 5.1 Drive Left Housing 0.375 1 0.375 Provide enclosure to drive 28 5.2 Drive Right Housing 0.375 1 0.375 Provide enclosure to drive 29 5.3 Grip Locking Switch 0.1 1 0.1 Hold grip position 30 5.4 Grip Locking Spring 0.01 1 0.01 Support grip locking switch 31 5.5 Drive Housing Long Fasteners 0.01 2 0.02 Hold housing 32 5.6 Drive Housing Medium Fasteners 0.01 2 0.02 hold drive 33 5.7 Drive Housing Short Fasteners 0.01 2 0.02 hold housing 34 6 Power generator 6.1 DC Motor 1.25 1 1.25 Convert EE to Kinetic Energy 35 6.2 On/Off Button 0.09 1 0.09 Connect electric power 36 6.3 On/Off Spring 0.01 1 0.01 Support On/Off Button 37 6.4 F/R/S Lever 0.04 1 0.04 Provide control for rotation direction 38 6.5 F/R/S Switch Circuit 0.4 1 0.4 Control polarity connection to battery 39 7 Bit Holder 7.1 Collet 0.325 1 0.325 Transmit torque 40 7.2 Bit Holder Housing 0.4 1 0.4 Provide housing to drive mechanism 41 7.3 Direction Stopper Clips 0.025 2 0.05 Hold PG3 carrier 42 7.4 Direction Stoppper Supports 0.02 4 0.08 Hold stopper clips 43 7.5 Screwdriver bit 0.04 2 0.08 Act on screw 44 8 Transmission 8.1 Planetary Gear 1 (PG1) Washer 0.02 1 0.02 Enclose pinion gears 45 8.2 PG1/PG3 Pinion Gears 0.05 6 0.3 Increase torque 46 8.3 PG1 Internal Gears 0.1 1 0.1 Coordinate pinion gears 47 8.4 PG1 Carrier/PG2 Sun Gear 0.11 1 0.11 Hold pinion gears 48 8.5 PG2 Pinion Gears 0.06 3 0.18 Reduce speed 49 8.6 PG2 Washer 0.015 1 0.015 Enclose pinion gears 50 8.7 PG2 Coupling Gear 0.14 1 0.14 Hold pinion gears 51 8.8 PG2 Locking Gear 0.115 1 0.115 Hold PG2 system 52 8.9 Hi/Lo Lever 0.04 1 0.04 Transmit control 53 8.10 Hi/Lo Button 0.06 1 0.06 Accept Hi/Lo control 54 8.11 Hi/Lo Fasteners 0.01 2 0.02 Hold Hi/Lo lever 55 8.12 PG2 Carrier/PG3 Sun Gear 0.125 1 0.125 Hold pinion gears 56 8.13 PG3 Washer 0.02 1 0.02 Enclose pinion gears 57 8.14 PG3 Internal Gear/Direction Openner 0.225 1 0.225 Coordinate pinion gears 58 8.15 PG3 Carrier 0.175 1 0.175 Hold pinion gears

TOTAL = 8.056 $

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6.1.5 Economic Analysis The engineering economic analysis for the payback period and Internal Rate of Return is shown in the following table. Since the process is a manual operation with minimum initial investment cost, the analysis indicates a very favorable result in terms of payback period (9 months) and IRR (21.5%). Production Volume = 6490 units/month Product Life Cycle= 5 yrs Discount Rate= 15.00% apr IRR = 21.5% Product Unit Price= 15 $ 1.2500% monthly rate Payback in 9 Months

NPV = 1,455,526 $ Fixed Cost Variable Discount Fixed Costs Month (investment) Cost Revenue Net Cost Factor PV month Cumulitive Tooling & Facilites 13054 1 -20000 -20000 0.9877 -19753.09 -19753.09 Prototype Modeling 3000 In 4th month 2 -20000 -20000 0.9755 -19509.22 -39262.31 3 -20000 -20000 0.9634 -19268.37 -58530.67 Development Costs (man-months, 6 mon PD cycle) 4 -23000 -23000 0.9515 -21885.06 -80415.73 Engineering Labor 20000 /month 5 -20000 -20000 0.9398 -18795.54 -99211.27 6 -33054 -57658.63 97350 6637 0.9282 6160.64 -93050.63 7 -57658.63 97350 39691 0.9167 36385.71 -56664.92 8 -57658.63 97350 39691 0.9054 35936.51 -20728.41 Variable Costs per unit 9 -57658.63 97350 39691 0.8942 35492.85 14764.43 Payback Manufacturing(Labor) 0.168526 10 -57658.63 97350 39691 0.8832 35054.66 49819.09 Management (Labor) 0.0157 11 -57658.63 97350 39691 0.8723 34621.89 84440.98 Purchased Parts 8.06 12 -57658.63 97350 39691 0.8615 34194.46 118635.44 Raw Mat'l Inv 0.01 13 -57658.63 97350 39691 0.8509 33772.30 152407.74 Finished Product Inv 0.03 14 -57658.63 97350 39691 0.8404 33355.36 185763.10 Distribution 0.6 15 -57658.63 97350 39691 0.8300 32943.57 218706.67 Total 8.884226 16 -57658.63 97350 39691 0.8197 32536.86 251243.53 17 -57658.63 97350 39691 0.8096 32135.17 283378.70 18 -57658.63 97350 39691 0.7996 31738.44 315117.13 19 -57658.63 97350 39691 0.7898 31346.60 346463.74 20 -57658.63 97350 39691 0.7800 30959.61 377423.34 21 -57658.63 97350 39691 0.7704 30577.39 408000.74 22 -57658.63 97350 39691 0.7609 30199.89 438200.63 23 -57658.63 97350 39691 0.7515 29827.05 468027.68 24 -57658.63 97350 39691 0.7422 29458.82 497486.50 25 -57658.63 97350 39691 0.7330 29095.13 526581.63 26 -57658.63 97350 39691 0.7240 28735.93 555317.56 27 -57658.63 97350 39691 0.7150 28381.17 583698.73 28 -57658.63 97350 39691 0.7062 28030.78 611729.51 29 -57658.63 97350 39691 0.6975 27684.72 639414.23 30 -57658.63 97350 39691 0.6889 27342.94 666757.17 31 -57658.63 97350 39691 0.6804 27005.37 693762.54 32 -57658.63 97350 39691 0.6720 26671.97 720434.51 33 -57658.63 97350 39691 0.6637 26342.69 746777.19 34 -57658.63 97350 39691 0.6555 26017.47 772794.66 35 -57658.63 97350 39691 0.6474 25696.26 798490.93 36 -57658.63 97350 39691 0.6394 25379.03 823869.95 37 -57658.63 97350 39691 0.6315 25065.70 848935.66 38 -57658.63 97350 39691 0.6237 24756.25 873691.91 39 -57658.63 97350 39691 0.6160 24450.62 898142.53 40 -57658.63 97350 39691 0.6084 24148.76 922291.29 41 -57658.63 97350 39691 0.6009 23850.63 946141.91 42 -57658.63 97350 39691 0.5935 23556.17 969698.09 43 -57658.63 97350 39691 0.5862 23265.36 992963.45 44 -57658.63 97350 39691 0.5789 22978.13 1015941.58 45 -57658.63 97350 39691 0.5718 22694.45 1038636.03 46 -57658.63 97350 39691 0.5647 22414.27 1061050.30 47 -57658.63 97350 39691 0.5577 22137.55 1083187.85 48 -57658.63 97350 39691 0.5509 21864.25 1105052.10 49 -57658.63 97350 39691 0.5441 21594.32 1126646.42 50 -57658.63 97350 39691 0.5373 21327.72 1147974.15 51 -57658.63 97350 39691 0.5307 21064.42 1169038.56 52 -57658.63 97350 39691 0.5242 20804.36 1189842.93 53 -57658.63 97350 39691 0.5177 20547.52 1210390.45 54 -57658.63 97350 39691 0.5113 20293.85 1230684.30 55 -57658.63 97350 39691 0.5050 20043.31 1250727.60 56 -57658.63 97350 39691 0.4987 19795.86 1270523.46 57 -57658.63 97350 39691 0.4926 19551.46 1290074.92 58 -57658.63 97350 39691 0.4865 19310.09 1309385.01 59 -57658.63 97350 39691 0.4805 19071.69 1328456.70 60 -57658.63 97350 39691 0.4746 18836.24 1347292.94

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6.2 Discrete event simulation of assembly line

6.2.1 Discrete Event Simulation: Configuration Study

The simulation layout for the complete screwdriver assembly is shown in the following figure.

Transmission Assembly 1

In 1 Transmission Buffer 1 Assembly 2 Buffer 3

Transmission Assembly 3

Final Test & Out Assembly Buffer 5 Packaging

In 2 Grip Housing Buffer 2 Assembly Buffer 4 Buffer 6

Repair

From previous report, it is estimated that the required assembly cycle is about 70 second per assembly. Bot of the assembly speeds of "Grip Housing Assembly" and the "Final Assembly" are about 70 seconds. To balance the assembly speed, the "Testing" and "Packaging" stations are combined to reach assembly speed of 70 seconds. Because the speed of assembling grip housing is three times the speed of assembling transmission module, three "Transmission Assembly" stations are employed to balance the total assembly speed. The final assembly testing is done at the end of the assembly considering that the sub-module testing impractical. That is, the transmission assembly and the grip housing assembly cannot be tested separately. If the assembly is failed upon the testing, the product is sent to the repair station. The repair station is going to "retest", "disassemble", and "reassemble" the product. The repair results are sent back to the "Buffer 5" to be packaged. It is assumed that 1 out of 100 final assembly will have to be repaired. The statistics and capabilities of each station in the assembly process are summarized in the following table. The capacity of the buffers were set according to the required size from some simulation runs (see the histograms below).

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No. Name Process (seconds) Failure (seconds)1 Repair (seconds)2 Remark 1 In 1 (Inou_1) Constant rate = - - Transmission 80/s components 2 In 2 (Inou_2) Constant rate = - - Grip Housing 80/s components 5 Transmission Normal ( = 218,  Normal ( = 7200, Log-Normal ( = Assembly 1 = 21.8)  = 900) 900,  = 200) (Mach_5) 6 Transmission Normal ( = 218,  Normal ( = 7200, Log-Normal ( = Assembly 2 = 21.8)  = 900) 900,  = 200) (Mach_6) 7 Transmission Normal ( = 218,  Normal ( = 7200, Log-Normal ( = Assembly 3 = 21.8)  = 900) 900,  = 200) (Mach_7) 8 Grip Housing Normal ( = 69.7, Normal ( = 7200, Log-Normal ( = Assembly  = 7)  = 900) 900,  = 200) (Mach_8) 11 Final Assembly Normal ( = 72.7, Normal ( = 7200, Log-Normal ( = (Mach_11)  = 7.3)  = 900) 900,  = 200) 13 Testing & Normal ( = 68.7, Normal ( = 7200, Log-Normal ( = Packaging  = 6.9)  = 900) 900,  = 200) (Mach_13) 15 Repair (Mach_15) Normal ( = 1200, Normal ( = 7200, Log-Normal ( =  = 300)  = 900) 900,  = 200) 3 Buffer 1 (Buff_3) Capacity = 24 Transmission component buffer 4 Buffer 2 (Buff_4) Capacity = 30 Grip housing component buffer 9 Buffer 3 (Buff_9) Capacity = 24 Finished transmission assembly buffer 10 Buffer 4 (Buff_10) Capacity = 30 Finished grip housing assembly buffer 12 Buffer 5 (Buff_12) Capacity = 30 Finished screwdriver assembly buffer 14 Buffer 6 (Buff_14) Capacity = 5 Repair buffer 1 Out (Inou_1) - - - Packaged screwdrivers

Because the limitation of the student version of Taylor II software to allow only up to 15 elements, the "Out" element after the successful "Testing and Packaging" is combined with the "Inp 1." The Taylor II layout model is shown in the following figure.

1 For all these manual operations, failure is the scheduled (allowed) break at about every 2 hours. 2 Repair means the length of allowable break for about 15 minutes. Log-normal distribution is assumed because people tend to take a longer than a shorter break than allowed.

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An example of simulation run result is shown below. screwd4 Taylor II Element report Date: 27-11-1999 Time: 22:30 ======Cluster Elnr Elname Produced AvgQueue Util Down ------0 1 Inou_1 360 1.00 100.00 0 2 Inou_2 360 1.00 100.00 0 3 Buff_3 349 5.54 0 4 Buff_4 356 4.13 0 5 Mach_5 116 0.99 89.59 9.13 0 6 Mach_6 117 0.97 89.29 8.21 0 7 Mach_7 113 0.97 85.46 11.27 0 8 Mach_8 355 0.96 86.73 9.40 0 9 Buff_9 334 9.41 0 10 Buff_10 12.78 0 11 Mach_11 333 0.94 83.88 10.08 0 12 Buff_12 332 3.31 0 13 Mach_13 331 0.90 79.06 11.31 0 14 Buff_14 6 0.05 0 15 Mach_15 5 0.26 23.42 9.61

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The queue utilization in each buffer is shown in the following histograms.

No. 3 - Buffer 1 No. 4 – Buffer 2 No. 9 – Buffer 3

No. 10 – Buffer 4 No. 12 – Buffer 5 No. 14 – Buffer 6

At the beginning of operation when there is nobody taking a break, the buffers are almost empty. The condition of high number of items in the buffers happened when the assembly operators start taking breaks. The large size of buffers are the main concern for the efficiency because in addition to taking space, buffers also mean a tight up capital because the work-in-process inventory is sitting idle in the factory. The length of time that a work in process inventory is sitting in a buffer is shown in the following waiting time histograms.

No. 3 - Buffer 1 No. 4 – Buffer 2 No. 9 – Buffer 3

No. 10 – Buffer 4 No. 12 – Buffer 5 No. 14 – Buffer 6

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Therefore, it is preferable to minimize the amount of inventory and keeping the throughput as high as possible. This can be done by some alternatives as follows:  To use the underutilized "Repair" person to do various tasks to substitute a person that is taking a break. This simulation model of this situation is too complicated for the student version to handle. Another alternative is described next.  Schedule the break at the same time. Therefore, during the break, the whole assembly line is shut down so that nobody is accumulating work in progress inventory for the next station. The duration of breaks are kept the same as the previous simulation setting. That is, they are following Log-Normal distribution with mean of 15 minutes and standard deviation of 200 seconds. screwd5 Taylor II Element report Date: 28-11-1999 Time: 12:34 ======Cluster Elnr Elname Produced AvgQueue Util Down ------0 1 Inou_1 360 1.00 100.00 0 2 Inou_2 360 1.00 100.00 0 3 Buff_3 350 5.83 0 4 Buff_4 355 5.45 0 5 Mach_5 115 0.98 87.65 9.86 0 6 Mach_6 118 0.97 88.34 8.30 0 7 Mach_7 114 0.98 87.72 9.87 0 8 Mach_8 354 0.97 86.32 10.43 0 9 Buff_9 346 1.97 0 10 Buff_10 4.31 0 11 Mach_11 345 0.97 88.15 8.90 0 12 Buff_12 347 1.04 0 13 Mach_13 346 0.93 83.03 10.41 0 14 Buff_14 6 0 15 Mach_15 6 0.24 23.61 11.14

The queue size of each buffer is shown in the following histogram.

No. 3 - Buffer 1 No. 4 – Buffer 2 No. 9 – Buffer 3

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No. 10 – Buffer 4 No. 12 – Buffer 5 No. 14 – Buffer 6

The corresponding waiting time in queue is shown in the following histogram.

No. 3 - Buffer 1 No. 4 – Buffer 2 No. 9 – Buffer 3

No. 10 – Buffer 4 No. 12 – Buffer 5 No. 14 – Buffer 6

Notice now that the required size of buffers 3, 4, 5, and 6 become much smaller than before. The size of buffers 1 and 2 are still the same because we assume that a constant stream of components are coming to these two buffers.

A more realistic situation can be simulated by assuming that the stream of components from "In 1" and "In 2" also follow random pattern with "breaks" represented by MTBF and MTTR. Negative exponential distributions are used for both the inputs to represent a constant supply with random fluctuation. The following are the results of the simulation with simulation parameters shown in the following table.

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No. Name Process (seconds) Failure (seconds)3 Repair (seconds)4 Remark 1 In 1 (Inou_1) Neg. exponential, Constant every Log-Normal ( = Transmission  = 80/s 7200 s 900,  = 200) components 2 In 2 (Inou_2) Neg. exponential, Constant every Log-Normal ( = Grip Housing  = 80/s 7200 s 900,  = 200) components 5 Transmission Normal ( = 218,  Constant every Log-Normal ( = Assembly 1 = 21.8) 7200 s 900,  = 200) (Mach_5) 6 Transmission Normal ( = 218,  Constant every Log-Normal ( = Assembly 2 = 21.8) 7200 s 900,  = 200) (Mach_6) 7 Transmission Normal ( = 218,  Constant every Log-Normal ( = Assembly 3 = 21.8) 7200 s 900,  = 200) (Mach_7) 8 Grip Housing Normal ( = 69.7, Constant every Log-Normal ( = Assembly  = 7) 7200 s 900,  = 200) (Mach_8) 11 Final Assembly Normal ( = 72.7, Constant every Log-Normal ( = (Mach_11)  = 7.3) 7200 s 900,  = 200) 13 Testing & Normal ( = 68.7, Constant every Log-Normal ( = Packaging  = 6.9) 7200 s 900,  = 200) (Mach_13) 15 Repair (Mach_15) Normal ( = 1200, Constant every Log-Normal ( =  = 300) 7200 s 900,  = 200) 3 Buffer 1 (Buff_3) Capacity = 20 Transmission component buffer 4 Buffer 2 (Buff_4) Capacity = 15 Grip housing component buffer 9 Buffer 3 (Buff_9) Capacity = 25 Finished transmission assembly buffer 10 Buffer 4 (Buff_10) Capacity = 10 Finished grip housing assembly buffer 12 Buffer 5 (Buff_12) Capacity = 15 Finished screwdriver assembly buffer 14 Buffer 6 (Buff_14) Capacity = 3 Repair buffer 1 Out (Inou_1) - - - Packaged screwdrivers screwd6 Taylor II Element report Date: 28-11-1999 Time: 12:55 ======Cluster Elnr Elname Produced AvgQueue Util Down ------0 1 Inou_1 317 1.00 92.64 7.36 0 2 Inou_2 304 1.00 90.34 9.66 0 3 Buff_3 317 2.65 0 4 Buff_4 304 1.95 0 5 Mach_5 110 0.92 84.24 8.09 0 6 Mach_6 105 0.84 78.18 9.14

3 For all these manual operations, failure is the scheduled (allowed) break at every 2 hours. 4 Repair means the length of allowable break for about 15 minutes. Log-normal distribution is assumed because people tend to take a longer than a shorter break than allowed.

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0 7 Mach_7 99 0.79 74.12 9.14 0 8 Mach_8 304 0.83 73.06 9.81 0 9 Buff_9 304 7.46 0 10 Buff_10 1.05 0 11 Mach_11 304 0.85 76.92 8.03 0 12 Buff_12 309 1.21 0 13 Mach_13 308 0.82 73.25 10.38 0 14 Buff_14 5 0.03 0 15 Mach_15 5 0.27 23.04 11.40

The corresponding Queue size and waiting time histogram are shown in the following figure.

Queue size hitogram

No. 3 - Buffer 1 No. 4 – Buffer 2 No. 9 – Buffer 3

No. 10 – Buffer 4 No. 12 – Buffer 5 No. 14 – Buffer 6

Waiting time histogram

No. 3 - Buffer 1 No. 4 – Buffer 2 No. 9 – Buffer 3

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No. 10 – Buffer 4 No. 12 – Buffer 5 No. 14 – Buffer 6

6.2.2 Selection of Final Assembly Process To make more realistic condition, the "Input" elements "In 1" and "In 2" are assumed to supply buffers 1 and 2 in batch sizes of 20 according to an exponential distribution with rate of 900 seconds (15 minutes). This is the estimated time to move the components to the buffers of "Transmission Assembly" and "Grip Housing Assembly" stations. Using this assumption, an investigation was conducted to determine the proper size of the rest of the buffers. The important buffers will be the buffers before the bottleneck station: "Final Assembly" with the longest cycle time (72.7 seconds). The results of the investigation are summarized in the following table.

No. Station Buffer size = Buffer size = Buffer size = Buffer size = 1 5 10 20 1 In 1 (Inou_1) 53.7 66.25 53.33 48.88 2 In 2 (Inou_2) 29.24 31.71 29.57 32.09 3 Buffer 1 (Buff_3) 4 Buffer 2 (Buff_4) 5 Transmission 59.9 73.98 76.62 77.24 Assembly 1 (Mach_5) 6 Transmission 61.72 70.22 77.94 77.16 Assembly 2 (Mach_6) 7 Transmission 62.14 71.77 75.54 77.75 Assembly 3 (Mach_7) 8 Grip Housing 58.25 69.74 75.12 74.83 Assembly (Mach_8) 9 Buffer 3 (Buff_9) 10 Buffer 4 (Buff_10) 11 Final Assembly 60.7 71.63 74.94 73.67 (Mach_11) 12 Buffer 5 (Buff_12) 13 Testing & Packaging 57.88 69.98 72.85 70.82 (Mach_13) 14 Buffer 6 (Buff_14) 15 Repair (Mach_15) 21.92 44.68 20 21.55 Finish Output 244 295 304 294 Buffer size = 10 for the bottleneck station is selected because it is not as much different from buffer size = 5 in terms of size requirement, but it provides higher utilization as well

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as higher throughput. Buffer #5 and #6 are set equal to 1 (no buffer) because these are not bottleneck stations. The queue and waiting time histograms for this selected setting are shown below.

Queue Histograms

No. 3 – Buffer 1 No. 4 – Buffer 2

No.9 – Buffer 3 No. 10 – Buffer 4

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Waiting Time Histograms

No. 3 – Buffer 1 No. 4 – Buffer 2

No.9 – Buffer 3 No. 10 – Buffer 4

The statistics of this assembly operation is as follow. screwd7 Taylor II Element report Date: 29-11-1999 Time: 19:55 ======Cluster Elnr Elname Produced AvgQueue Util Down ------0 1 Inou_1 320 1.00 53.33 10.02 0 2 Inou_2 320 1.00 29.57 9.82 0 3 Buff_3 307 8.77 0 4 Buff_4 313 10.84 0 5 Mach_5 102 0.86 76.62 9.11 0 6 Mach_6 102 0.84 77.94 6.48 0 7 Mach_7 100 0.85 75.54 9.37 0 8 Mach_8 312 0.98 75.12 9.06 0 9 Buff_9 302 1.55 0 10 Buff_10 9.37 0 11 Mach_11 301 0.85 74.94 9.33 0 12 Buff_12 305 0.21 0 13 Mach_13 304 0.82 72.85 9.01 0 14 Buff_14 5 0.08 0 15 Mach_15 4 0.28 20.00 10.17

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In general, the utilization of the stations (around 75%) are considered appropriate for the assembly workers. The Input stations (Inou_1 and Inou_2) and the repair station (Mach_15) total utilization is about 100% (53.33% + 29.57% + 20%). These three tasks are performed by 2 people instead of 3 people. That is, Inou_2 and repair are done by the same person. A low utilization value of 50% is considered appropriate for these tasks as these people need to walk around in between jobs to transfer the raw materials.

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