Engineering Process in the Mechanical Program at Cal Maritime: An Integrated Approach

Teaching and Learning in the Maritime Environment Conference The California Maritime Academy Vallejo, CA 94590

Mansur Rastani Cal Maritime Academy Mechanical Engineering Department Vallejo, CA 94590

Nader Bagheri Cal Maritime Academy Mechanical Engineering Department Vallejo, CA 94590

Garett Ogata Cal Maritime Academy Mechanical Engineering Department Vallejo, CA 94590

1 AbstractU The capstone design project has become an integral part of the mechanical engineering (ME) program at Cal Maritime. Students in the program take three courses in sequence starting in the spring semester of their junior year. The first course, Engineering Design Process, introduces the students to the ten tasks involved in the design process. These tasks are introduced and taught in five stages as follows: 1) Problem Definition, 2) , 3) Preliminary Design, 4) Detailed Design and prototyping, and 5) . The details of each task are introduced and discussed. Students implement the first three stages in their second course, Project Design I, and the last two stages in their third course, Project Design II. Successful completion and understanding of these courses are the key to completing the ME program requirements as well as on-time graduation at Cal Maritime.

IntroductionU Definition: Engineering design is an iteration process of devising a system to meet a set of desired needs. The design process begins with an identified need, which can be initiated based on any of the following sources: Observable deficiency (i.e., A car bumper that gets easily damaged in low speed collisions) Product improvement (i.e., A system for improving traction on ice without studs or chains) New products (i.e., A more effective alarm clock for reluctant students) Change in law (i.e., An average automobile gas mileage of 25 miles per gallon of gasoline)

When a new design problem is begun, very little is known about the solution, especially if the problem is a new one for the . As work on the project progresses, the designer’s knowledge about the technologies involved and the alternative solutions increase. Thus, the goal during the design process is to learn as much about the evolving product as early as possible in the design process because during the early phases changes are least expensive.

The systematic methodology of the evolutional engineering design process consists of five stages as follows:

1) Problem Definition In this stage the objectives, constraints, and the functional requirements of the designed objects are clarified through qualified terms by the customers, which in turn are converted into measurable engineering parameters.

2) Conceptual Design In this stage using method and morphological tool, from information compiled in prior phase, concepts are created, evaluated, and design alternatives are selected.

3) Preliminary Design In this stage the product (form and shape) is performed, materials are selected, and engineering analysis is carried out.

4) Detailed Design & Prototyping In this stage the preliminary design is refined through design for manufacturing, , and design for safety & reliability. Detailed drawings, bill of materials and final are executed.

5) Communication Design This is the last stage of the design process that includes the final written report and oral presentation.

Each stage has been itemized into instructional tasks as set of languages that we can use to describe how those designed objects came to be.

2 ProblemU Definition Stage This stage involves tasks 1A, 1B, 2, and 3. Each task is described below:

TaskU 1A: Identifying User Requirements / Clarifying Design Objectives This task presents a method for comprehensively identifying a set of customer needs. The goals of the method are to: 1 • Ensure that the product is focused on customerTPF F PT needs • Identify implicit needs as well as explicit needs • Provide a fact base for justifying the product specifications • Ensure that no critical customer need is missed or forgotten • Develop a common understanding of customer needs among members of the development team.

A team should be able to identify customer needs without knowing how it will eventually address those needs. Also note that we choose to use the word need to label any attribute of a potential product that is desired by the customer. Other terms used in industrial practice to refer to customerU needs U include customerU requirements, design attributes, and design objectives.U The latter is the terminology used in this course. Objectives are usually expressions of the desired attributes and behavior that the potential users would find attractive. They are normally expressed as "being" statements that say what the design will be, 2 as opposed to what the design must doTPF F.PT

Identifying customer needs is itself a process, for which we present a three-step method as follow:

1. Gather data on customer needs. 2. Organize the needs into a hierarchy of primary, secondary, and if necessary, tertiary needs (Objective Tree). 3. Establish the relative importance of the needs (Weighted Objective Tree).

StepU 1. Gathering data on customer needs Means for gathering data includes: 1. Literature Review on Similar Products 2. Market Research 3. Bench Marking 4. Interviews & Focus Groups 5. User Survey 6. Consulting Expertise 7. Questioning and Brainstorming 8. Reverse Engineering on Competitive products (Dissection) 9. Watching Customers Use an Existing Product 10. Web Sites for Similar Products

StepU 2. Organize the needs into a hierarchy of primary, secondary, ……. needs (Objective Tree). The results of step 1 may end up to a large number of need statements. Working with such a long list of detailed needs is difficult. The goal of this step is to organize these needs into a hierarchical list. Group the need statements according to the similarity of the needs they express. The list will typically consist of a set of primary needs, each one of which will be further characterized by a set of secondary needs. In some cases, the secondary needs may be broken down into tertiary needs as well. The primary needs are the most general needs, while the secondary and tertiary needs express needs in more detail. The groups of need statements are clustered according to the similarity of the needs they express, and then organized in hierarchical order by assigning a head-objective to a group of sub-objectives.

1 TP PT Word “customers” refers to: manufacturers, marketing staff, distributors, retailers, and the end users. 2 TP PT Functions are the things a design supposed to do, the actions that it must perform. Functions are usually expressed as "doing" terms. We will discuss functions in greater details later in task 2.

3 ObjectiveU Tree:U The above hierarchical list can then be put in an objective tree form, which is a graphical depiction of the objectives for the artifact. The top- goal in an objective tree, which we represent as a node at the peak of the tree, is decomposed or broken down into sub-goals that are at different levels of importance or that include progressively more detail, so the tree reflects a hierarchical structure as it expands downward. An objective tree also shows that related sub-goals or similar ideas can be clustered together, which gives the tree some organizational strength and utility.

StepU 3. Establish the relative importance of the needs (Weighted Objective Tree). So far we have assumed that all of the design objectives are equal, whereas it is almost certain that some objectives will be worth more than others. We use a fairly simple technique, pair-wise comparison, which can be used to rank a cluster of objectives that are at the same level in the objective tree. It is important to keep in mind that the pair-wise comparison method should be applied in a "top-down" , so that the higher-level objectives are compared and ranked before those at lower levels. Each design objective is listed and is compared to every other objective, two at a time. In making the comparison the objective that is considered the more important of the two is given a 1 and the less important objective is given a 0. A rating of 1/2 is given for objectives that are equally valued. The total number of possible comparisons is N= n(n-1)/2, where n is the number of objectives under consideration. The ratings are added and the total score for each one of the objectives are listed. In the resulting scores, if the smallest score for an objective is a zero, it is changed to one, which in turn moves up the scale for the other scores by one. The reason for doing this is simply due to the fact that an objective cannot have a zero value.

TaskU 1B: Identifying Constraints Constraints are restrictions or limitations on a behavior or a value or some other aspect of a designed object's performance. Constraints are important to the designer because they limit the size of design by forcing the exclusion of unacceptable alternatives. For example for a ladder design project, any design that fails to meet OSHA standards will be rejected. Objectives and constraints sometimes seem to be interchangeable, but they are not. On the other hand, objectives and constraints are closely related. Constraints limit the size of the design space, while objectives permit the exploration of the remainder of the design space (i.e. expand the design space).

Constraints are usually expressed in measurable, quantitative terms, such as dollars, pounds, cubic feet, Psi, etc, whenever possible.

Tools for identifying constraints, are listed below: 1. Identify sponsor-imposed constraints 2. Identify any compatibility constraints (with existing equipment, or mating parts) 3. Identify any restraints from codes/standards/regulations/law of physics

TaskU 2: Establishing Functions In this section we will look more deeply at what we mean when we talk about a design doing something. It is particularly important for a designer to be able to properly specify functions. There are consequences for the engineer who fails to understand and of the functions in a design. The literature of forensic engineering is rich with cases in which engineers failed to realize some additional function(s) that should have been met, often with tragic results.

What is Function? To , functions are simply the things that the designed object must do in order to be successful. As such, the statement of a function usually consists of a verb and a noun, and the verb will normally be an “ action” verb, rather than a “being” verb. For example, lift, raise, move, transfer, or light, are all action verbs.

4 We can also categorize functions as being either basic or sub-functions. Here a basic function would be defined as “the specific work that a project, process, or procedure is designed to accomplish”. Sub- functions would be any other required functions needed to do the basic function.

FunctionalU Analysis Method Functional analysis is widely used to illustrate the interactions among the functions and sub-functions of the design object, which is part of formulating a design problem. It is a block diagram, which help us to identify which functions are connected, and where the interfacial connections might be. Functional analysis approach helps to define the design problem at the very early stages.

TaskU 3: Establishing Engineering Design Specifications (EDS) The goal of this task is to generate the information needed in the engineering design specifications development phase of the design process. There are many techniques used to generate engineering design specifications. One of the best and currently most popular methods is called quality function deployment (QFD). The QFD method was developed in Japan in the mid-1970s and introduced in the United States in the late 1980s. Using this method, Toyota was able to reduce the costs of bringing a new car model to market by over 60 percent and to decrease the time required for its development by one- third. It achieved these results while improving the quality of the product. A recent survey of 150 U.S. companies shows that 69 percent use the QFD method and that 71 percent of these have begun using the method since 1990.

The customers’ requirements (i.e. objectives, functions) must be translated into measurable design parameters. You cannot design a car door that is “easy to open” when you do not know the meaning of “easy”. Its easiness measured by force, time, or what? If force is a critical parameter, then is “easy” 20 N or 40 N? The answer has to be known before time and resources are invested in the design effort. Quality Function Deployment (QFD) is a technique for identifying customer requirements and matching them with engineering design parameters. Applying the QFD steps builds the house of quality shown in figure 1, which is a systematic graphic representation of information organized as a matrix of “rooms”, “roof”, and “basement”, each containing valuable data. Before we describe each step for filling in figure 1, a brief description of the figure is helpful. The numbers in the figure refer to the steps that are detailed in the sections below.

3. How (Engineering characteristics)

1. What 4. What vs. How 2. Now vs. What (Customer (matrix) (Competitive requirements) benchmark)

5. How vs. How Much (Target values for engineering spec.)

Figure 1. The house of quality, also known as the QFD chart

5 Developing information begins with identifying what the customers want (step 1). Then it is important to identify how the problem is solved now, in other words, what the competition (benchmark) is now for the product being designed (step 2). Next comes one of the more difficult steps in developing the house, determining how you are going to measure the product’s ability to satisfy the customers’ requirements (step 3). The how is the design specification (measurable parameter) and its correlation to the customers’ requirement is given by what vs. how (step 4).

Finally, target values (for measurable parameters) – how much are developed in the basement of the house and compared with the engineering specifications, how vs. how much (step 5). In other word, this last step in the QFD technique is used to determine a target value for each engineering design measure.

ConceptualU Design StageU This stage involves tasks 4, and 5. Each task is described below.

TaskU 4: Generating Design Alternatives Once the functions and sub-functions are listed, the next goal is to generate concepts that satisfy them. In other word, concepts are the means of providing functions. There is a great tendency for designers to take their first idea and start to refine it toward a product design. This is a very weak methodology, best expressed by the adage, if you generate one idea, it will probably be a poor idea; if you generate twenty ideas, you might have one good idea. This statement supports one of the key features of concurrent engineering; generate multiple concepts. The main goal of this task, then, is to present techniques for the generation of many concepts. Before continuing, note that the technique presented here is useful during the development of an entire system and also for each subsystem, component, and feature. This is not to say that the level of detail presented here needs to be undertaken for each flange, rib, or other detail; however, it is useful for difficult features. There are four steps to this technique.

StepU 1: List the functions/sub-functions that are essential to the product (task 2) Although not too long, the list must comprehensively cover the functions/sub-functions, at an appropriate level of generalization.

StepU 2: Develop concepts for each function For each function list the means by which it might be achieved. These lists might include new ideas as well as known existing components or sub-solutions. The goal of this step is to find as many concepts as possible that can provide each function or sub-function. In generating a new idea, an engineer can take great pride in his or her creativity. A characteristic of the creative process is that initially the idea is only imperfectly understood. Usually the creative individual senses the total structure of the idea but initially perceives only a limited number of the details. There ensues a slow process of clarification and exploration as the entire idea takes shape. The creative process can be viewed as moving from an amorphous idea to a well-structured idea, from the chaotic to the organized, from the implicit to the explicit. A considerable literature has been written on creativity, and some positive steps have been recommended to enhance the process, such as: develop an open mind, develop a creative attitude, unlock your imagination, be persistent, suspend your judgment, utilize lateral or divergent thinking, etc. Before looking at ways of enhancing creativity it is important to understand how mental blocks interfere with creative problem solving. A mental block is a mental wall that prevents the problem solver from correctly perceiving a problem or conceiving its solution. These mental bocks have to be overcome so that creative solutions to design problems can be sought. The most frequent occurring mental blocks are:

• Perceptual blocks (stereotyping), i.e. analytical & conventional thinking, • Judgmental blocks, i.e., problem solving with negative attitude, jump to conclusion, • Environmental blocks, i.e. frequent distraction in work environment, • Intellectual blocks, etc, i.e. lacking the necessary knowledge and information.

6 The exploration for ideas for concepts can take the path of employing as many as possible of the sources external to the design team. The more information that is gathered about the problem the better will be the ideas leading to design concepts. The following are some useful sources of design information:

• Using patents as an idea source, • Finding ideas in reference books and trade journals, • Using experts to help generate concepts, • Using existing products (benchmarking) and concepts as idea sources, • Exploring the Web, and • Brainstorming as source of ideas

The later source of ideas (Brainstorming technique) is discussed next.

BrainstormingU Brainstorming is a group approach for generating ideas in a non-threatening and non-inhibiting atmosphere. It is a group activity in which the collective creativity of the group is tapped and enhanced. The objective of brainstorming is to generate the greatest number of alternative ideas from the uninhibited responses of the group. Brainstorming is most effective when it is applied to specific rather than general problems. There are four fundamental principles to it. a. Generate as many solutions as possible__ quantity counts. b. Remove the constraints: be as creative as you can be, wild ideas are welcome. c. "Hitchhiking" is encouraged: build on the ideas of others. d. No criticism is allowed: defer judgment until later.

StepU 3: Construct a Morphological Matrix The third step is to combine these individual concepts into overall concepts that meet all the functional requirements. The word Morphology means the study of shape or form; so morphological analysis is a way of creating new forms, i.e. design concepts. The purpose of the method is to uncover combinations of ideas that comprise design concepts that might not ordinarily be generated. In fact, the morph matrix shows a view of the design space that allows us not only to identify potential , but also to get a sense of the size of the design space. The information in the resulting table of brainstorming session provides what we need to construct a morph matrix.

StepU 4: Identify feasible design concepts (alternatives)U A conceptual design or scheme can be constructed by linking one means, any means, for each of the identified functions, subject only to interface constraints that may prevent a particular combination. In other word, selecting one cell from each row and combining them can generate one alternative design. Using alphabets for columns and numerals in rows in the matrix can easily facilitate the identification of the concepts.

TaskU 5: Evaluation of Design Concept Alternatives If we have done the job of generating design alternatives properly, we almost certainly have several design concepts or alternatives from which to choose. We have reached the point where we must choose which concept or small set of concepts to develop into finished design(s). The selected design concept for further development should be the best one out of those design alternatives resulted in task 4, i.e. morph chart. The evaluation process consists of 5 steps as follows:

1) Design objectives are established by the objective tree and weighted through pair-wise comparison method, weighted objectives (αi). (This task has already been done, i.e., task 1)

2) Design alternatives are relatively rated (relativeU value βi)U in relation to the performance objectives using a method that employs a weighted decision matrix.

7 3) The true performance of each design alternatives with respect to each objective is measured

through multiplying each relativeU value U (βi) of that alternative design by the objective’s weighting value (αi), i.e., αiβ i 4) The overall performance of each design alternative is then calculated by adding up the measures established in step 3, i.e. Σαiβ i 5) The best alternative is the one with highest overall performance calculated in step 4.

The basic structure of a decision matrix is shown in table 1.

Table 1. The basic structure of a decision matrix

Criteria Importance Alt. 1 Alt.2 …. . (Objectives) (Weight)

Criterion 1 α1 β11 α1. β11 β12 α1.β12 .. ….

Criterion 2 α2 β21 α2. β21 β22 α2. β22 .. ….

………. .. .. …. .. …. .. ….

Criterion n αn βn1 αn. βn1 βn2 αn. βn2 .. ….

Total Σαi. βi1 Σαi. βi2 ….

WeightedU Decision Matrix A decision matrix is a method of evaluating competing concepts by ranking the design criteria with weighting factors and scoring the degree to which each design concept meets the criterion (i.e., objectives). In doing this it is necessary to convert the values obtained for different design criteria into a consistent set of values. The simplest way of doing this is to first restate the objectives into assessable (measurable) parameters and then convert these parameters into a 5- point or 11-point scale values based on the weighted decision matrix, which are used to rate the design alternatives with respect to each of those objectives. A 5-point scale (0-4) is used when the knowledge about the objective is not very detailed and has five grades, representing performance that is, far below average, below average, average, above average, far above average. An 11-point scale (0-10) is used when the information is more complete, table 2.

8

Table 2. Evaluation scheme for design criteria

11-point-scale Description 5-point-scale Description ______0 Totally useless solution 0 Inadequate 1 Very inadequate solution ______2 Weak solution 1 Weak 3 Poor solution ______4 Tolerable solution 5 Satisfactory solution 2 Satisfactory 6 Good solution with a few drawbacks ______7 Good solution 3 Good 8 Very good solution ______9 Excellent solution 4 Excellent 10 Ideal solution ______

PreliminaryU Design Stage This stage involves tasks 6A, 6B, and 6C. Each task is described below.

TaskU 6A: Product Architecture & configuration In the discussion of conceptual design, emphasis was put on developing the means to perform the function of the product. In this task, product architecture & configuration, attention turns to the arrangement of the physical elements and developing producible forms that provide the desired means. The form of the product is roughly defined by the spatial constraints that provide the envelope in which the product operates. Within this envelope the product is defined as the configuration of connected components. In other words, form development is the evolution of components, how they are configured relative to each other and how they are connected to each other.

EstablishingU the Architecture The end result of this activity is an approximate geometric layout of the product, descriptions of the major chunks, and documentation of the key interactions among the chunks. A four-step method is used as follows: 1. Create a schematic of the product, 2. Cluster elements into chunks, 3. Make a rough geometric layout, and 4. Identify the incidental interactions among the chunks.

StepU 1: Create a schematic of the product The result of the concept generation task (i.e., task 4) was four potential design alternatives each with some general physical means, which satisfied the required functions. Task 5, evaluation of design alternatives, concluded an optimal design concept with an assemblage of optimal means.

9 A schematic diagram is the collection of the means (from the optimal design concept), each represented within a box, which we call physical elements. Each of these physical elements may be a simple component or a subassembly of components, which in latter case every effort must be made to decompose the assembly into individual components or at least smaller subassemblies.

The development of most components and subassemblies must begin with knowledge about spatial constraints resulting from interfaces with other objects. This is because for most parts, function occurs at the interfaces between components. These interfaces are in fact relationships that may be based on the flow of material, energy, or information as well as being physical such as features of mating parts. The team should identify the known interactions between the physical elements. For example, a sheet of paper flows from the paper tray to the print mechanism (i.e., pick-paper device). This interaction is planned, and it should be well understood, even from the very earliest schematic, since it is fundamental to the system's operation.

StepU 2. Cluster elements into chunks The above guidelines for defining the boundaries between components only help define part of the configuration. Equally important during configuration design are the location of the components relative to each other. The physical elements of a product are typically organized into several major physical building blocks, which we call chunks. Each chunk is then made up of a collection of components that implement the functions of the product. The challenge of step 2 is to assign each of the elements of the schematic to a chunk. The following factors are helpful in clustering the elements:

• Precision in geometry or location: Elements requiring precise location or close geometric integration can often be best designed if they are part of the same chunk. • Function sharing: When two physical elements can share function, these elements are best designed when they are clustered together.

• Similarity of design or production technology: When two or more physical and or functional elements are likely to be implemented using the same design and/or production technology, then incorporating these elements into the same chunk may allow for more economical design and/or production. A common strategy, for example, is to combine all functions that are likely to involve electronics in the same chunk • Change in component design: When a team anticipates a great deal of change in some element during its life cycle, it makes sense to isolate that element into its own modular chunk, so that required changes to the element can be carried out without disrupting any of the other chunk

StepU 3. Make a Rough Geometric Layout Geometric layout, which is the overall form and configuration of the product, may simply be determined by positioning (and or repositioning) the major chunks taking into consideration that the geometric interfaces among the chunks are feasible. Layout decision criteria are closely related to the clustering issues in step 2. In some cases, the team may discover that the clustering derived in step 2 is not geometrically feasible and thus some of the element should have to be reassigned to other chunks. The team may benefit from generating several alternative layouts and selecting the best one. A geometric layout is usually created in three-dimension, using 3-D drawings, computer solid modeling, or physical models (of cardboard or foam, for example). Creating a geometric layout also forces the team to work out the basic dimensional relationships among the chunks. Information generated here is further refined on the final detail drawings of the components (task 9A).

StepU 4: Identify the Incidental Interactions Examine the flow of matter, energy, and signal between chunks. Are the desired functions preserved? Some chunks, as result of their function, may have side effect on the neighboring

10 chunk. Identify additional interactions among the chunks, which are not desired such as unwanted vibration, or heat generation, or EMI, etc. These type interactions are referred to as incidental interactions and should be shown on the Incidental interaction diagram.

TaskU 6B: Materials Selection Process It has been reported that there are more than 40,000 currently useful metallic alloys and probably close to that number of nonmetallic engineering materials like plastics, ceramics and glasses, composite materials, and semiconductors. This large number of materials coupled with the complex relationships between the different selection parameters, often make the selection process a difficult task. If the selection process is carried out haphazardly, there will be the risk of overlooking a possible attractive alternative solution. Adopting a systematic selection procedure that includes Material Performance Requirements, Rigid & Soft requirements, and Performance Index Method can reduce this risk. These are introduced next.

MaterialU Performance Requirements The material performance requirements can be divided into five broad categories, namely functional requirements (i.e., material properties such as mechanical, electrical, etc.), operational requirements (i.e., resistance to service conditions such as high temp environment, corrosive environment, etc.), process-ability requirements (i.e., machine-ability, weld-ability, etc.), cost requirements, and reliability requirements.

RigidU & Soft Requirements An initial screening is used to eliminate the unsuitable groups of candidate materials. For this purpose two big material requirements are examined, Rigid and Soft. • Rigid requirements are those, which must be met by the material if it is to be considered at all. For example, metallic materials are eliminated when selecting materials for an electrical insulator. If the insulator is to be flexible (i.e., to have low stiffness) the field is narrowed further as all ceramic materials are eliminated. Examples of the material Rigid requirements include behavior under operating temperature, resistance to corrosive environment, ductility, electrical and thermal conductivity or insulation, and transparency to light, etc. • Soft requirements: After Rigid requirement screening, the remaining candidate materials are further screened and compared for their relative importance, which is referred to as Soft requirements. This is done in the performance index method as will be discussed next. Examples of soft requirements include mechanical properties, specific gravity, and cost.

PerformanceU Index method The Performance Index method can be used in optimizing materials selection when several properties should be taken into consideration. This is done in three steps,

I) Weighting Properties, the properties are compared against each other and weighted

(αιB )B in terms of their relative importance using a pair-wise comparison method.

II) Evaluation of Candidate Materials, the candidate materials are evaluated and scaled

(BiB )B against each of those properties (Scaled Values).

III) Calculation of Performance Index, a performance index (γ) is defined as

γ = Σ BiB B αiB ,B

The material with the highest performance index (γ) is considered as the optimum for the application.

11 StepU I. Weighting Properties (αιUB ):UB U The pair-wise comparison approach can be used as a systematic tool to determine the properties weighting factors (αιB )B . In this procedure evaluations are arranged such that only two properties are considered at a time. To determine the relative importance of each property a table is constructed, the properties are listed in the left-hand column, and comparisons are made in the columns to the right, as shown in table 3.

Table 3. Determination of the relative weighting factor (α) Properties Number of possible decisions Positive Relative weighting factor N=n(n-1)/2 decisions

(αιB B) ______1 2 3 4 5 6 7 8 9 10

1 1 1 0 1 3

α1B =0.3B 2 0 1 0 1 2

α2B =0.2B 3 0 0 1 0 1

α3B =0.1B 4 1 1 0 0 2

α4B =0.2B

5U 0 0 1 1 2

α5UB =0.2UB Total number of positive decisions = 10 Σ α =1.0

In comparing two properties or performance goals, the more important goal is given numerical one (1) and the less important is given zero (0). The total number of possible decisions is given by N =n(n-1)/2, where n is the number of properties under consideration. A relative weighting factor, αιB ,B for each property is obtained by dividing the number of positive decisions for each property (m) into the total number of possible decisions (N, i.e. 10). In this case, Σ αιB B =1

StepU II. Evaluation of Candidate Materials (Scaled Value, Bi ):U All candidate materials are evaluated for each property by scaling them based on the highest numerical value (i.e., the highest scaled value does not exceed 100). When evaluating a list of candidate materials, one property is considered at a time. For a given property, when higher value of the property is desirable (i.e., strength), the highest value in the list is rated as 100 and the others are scaled proportionally, the scaled value B for a given candidate material is equal to:

B = (numerical value of property) x 100 / (maximum value in the list) (1)

For properties like cost, corrosion or wear loss, weight gain in oxidation, etc., a lower value is more desirable. In such cases, the lowest value is rated as 100 and B is calculated as:

B = (minimum value in the list) x 100 / (numerical value of property) (2)

StepU III. Calculation of Performance Index (γ): The combined material performance index is given by:

Material Performance Index, γ = Σ BiB B αiB B (for i= 1 to n) (3)

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The material with the highest comparative performance index (γ) is considered as the optimum for the application.

TaskU 6-C: Mathematical modeling & engineering analysis A distinguishing characteristic of a qualified engineer is the ability to solve technical problems. Mastery of problem solving involves a combination of art and science. By science we mean knowledge of the principles of mathematics, chemistry, physics, mechanics (static, dynamics, solid mechanics, mechanical design, fluid mechanics, heat transfer, etc.), and other technical subjects that must be learned so that they can be applied to the design problem at hand correctly. By art we mean the proper judgment, experience, common sense, and know-how that must be used to reduce a real life problem to such a form that science can be applied to its solution.

MethodsU of Analyses in Engineering Designs The main methods and software that are used for analyzing engineering designs are as follows:

Mathematical The mathematical methods for analyzing engineering designs are: • Functional calculations based upon the relationships involved (stress, strength and strains; electrical potential, resistance and current; thermodynamics; control laws; logic; fluid streamlines, etc.) • Mathematics software (such as MATLAB, Excel, etc. ), which can be used to create and solve complex equations and present graphical outputs. These methods can be used for analyzing simple to moderately complex designs, such as static of mechanical components, simple mechanisms and small systems.

Mechanical Mechanical components and system designs, which are more complex in nature, can be created and analyzed using computer aided design (CAD) and computer aided engineering (CAE) software. Most CAD software enables 3-D views to be created. CAD software is usually the starting point for many other CAE tasks such as Finite Element Analysis (FEA). Finite element analysis is a generic computer-based technique, which successively evaluates the effects of disturbances (mechanical stress, vibration, temperature, etc.). FEA programs interface directly with CAD software. The use of FEA for studies of fluid flow, including aerodynamics, is called computational fluid dynamics (CFD). CFD software can be used to analyze flow of liquids and gases, in streamlined, turbulent, viscous or supersonic flow, as well as heat flow and combustion. Some FEA and CFD software have the capability to analyze the effects of different physical phenomena, such as heat transfer, electromagnetic fields, etc.

Electrical/Electronic Electrical and electronic circuits can be analyzed using Electronic Design Automation (EDA) software that contains models of the behavior of components (Ohm’s law, transistor models, logic elements, etc.). The input data consists of the component details (types, values, etc.), the connections between the components, and the electrical input values (power, waveforms, etc.). The software creates the circuit diagram (schematic capture) and analyses its behavior.

Note. Some system simulation software (such as Monte Carlo) enables systems that include complex controls, logic, data, feedback, displays, and etc. to be designed and optimized. Some of the available software is suitable for a wide range of applications, while others are more specialized (signal processing, computer network, etc.).

13 DetailedU Design Stage This stage involves tasks 7A, 7B, 7C, 8, 9A, and 9B. Each task is described below.

TaskU 7A: Design for Reliability and Safety (DFR&S) Reliability is the probability of a product performing its intended functions over its specified period of usage, and under specified operating conditions, in a manner that meets or exceeds customer expectations. When one or more intended functions of a product are not fulfilled to the customer’s satisfaction, a failure is said to have occurred. The most serious failures are those caused by a deficiency in the product design that was not identified prior to the product’s release to the manufacturing environment. Failure Mode and Effect Analysis (FMEA) is used to assist in the identification of potentially critical failure modes up front in the design process. FMEA is a reliability-planning tool that consists of a systematized group of activities intended to: 1. Recognize and evaluate the potential failure of a product and its effects. 2. Identify the root causes of the potential failure mode at a very fundamental level that is related to the underlying failure mechanism or physics of failure. 3. Prioritize potential failures according to their risk. 4. Identify actions that could eliminate or reduce the chance of the potential failure occurring. 5. Provide a living document for future use and for continuous reliability improvement. It is complementary to the design process of positively defining what a design must do to satisfy the customer.

BenefitsU of FMEA The benefits of FMEA include the following: • Helps identify potential product failures in the product development phase • Helps identify and eliminate potential safety concerns • Documents the rationale for changes • Establishes a priority for design improvement actions • Provides information to help through product design verification and testing • Prioritizes testing and validation resources • Improves reliability, reduces warranty • Saves on prototype development • Helps to identify or ensure that defects do not “escape” to the field. • Improves customer satisfaction

ProcessU of FMEA FMEA is a stepwise procedure in which we first examine the mode or ways that each part in the product might fail to perform its intended function. A failure mode, which result in a number of effects, may arise from a variety of causes. Second, we analyze the severity of each effect. Then, we try to identify the potential defects in design that could cause each failure mode, along with the likelihood that the cause would occur. Next, we examine how we might have detected the defects by design review controls, testing, and/or inspection. Finally, we consider what corrective actions we should take, including eliminating the causes of the potential failure modes and/or reducing the severity of the failure mode.

14 FailureU modes A failure mode is the way in which a part could fail to perform its desired function. For example, a helical compression spring might fail in three modes: buckling, long-term set, or coil clash. Other examples are given in table 4, also a list of some common failure modes is given in table 5.

Table 4. Possible Failure Modes of Some Example Parts Table 5. Common Failure Modes

U U U U fracture bind Part or Component Failure Mode Fluid Valve Open, closed, partial open/close buckle delaminate Screw Loose, stripped, corroded bend erode Battery (dry cell) Discharged, partially discharged crush corrode Suspension cable Frayed, stretched, kinked seize leak Switch Open, closed deform open circuit Shaft Fractured, bent, seized vibrate short circuit

One way to identify the failure modes in particular for large system, which consists of many components, is to change the starting point of the analysis to the question: ‘how can the system fail? We then look at the outputs, and work downward through the system.

Effects/SeverityU The effects of a failure mode are the adverse consequences that the user might experience. An open switch (failure mode) might cause a commercial meat refrigeration unit to stop functioning, resulting in spoiled inventory (effect). A fractured automobile drive shaft (failure mode) might result in a car accident (effect). Also, the definition of the “customer” is herein broadened to include the end-user as well as others involved in the fabrication and assembly of the product. A cut hose may cause a waste of hydraulic fluid during assembly. The severity of an effect is an assessment of the extent of damage or injury to the product, the user, nearby people, or the environment. A small hydraulic leak on a portable log splitter, for example, might result in “very little degradation of function”, whereas a hydraulic leak in the rudder control of passenger aircraft might be “catastrophic”. A definition of the severity rating is depicted in table 6.

Table6. Severity Rating System for the Effects of a Failure Mode Severity of Effect Description Severity Rating (S) Catastrophic Causes injury to people, property, and/or environment 10 Extremely harmful Causes damage to product, people, or environment 9 Very harmful Causes damage to product 8 Harmful Major degradation of function 7 Significant Causes partial malfunction of product 6 Moderate Performance loss causes customer complaints 5 Annoying Loss of function is annoying, cannot be overcome 4 Minor Some loss of performance, but can be overcome 3 Insignificant Very little function degradation 2 None No noticeable effect in function or harm to others 1

Causes/OccurrenceU The cause of a potential failure mode is the reason why the part may fail owing to a defect in design. Every conceivable potential cause/mechanism should be listed for each failure mode. The shaft, for example, could facture because the engineering design team might have underestimated the applied static and/or dynamic loads, or selecting an inadequate material. It should be noted that not every cause has the same chance of occurring. Occurrence is the likelihood that a specific failure cause/mechanism will occur during the design lifetime of an item. The likelihood of occurrence of a specific failure cause/mechanism is estimated using the probability of failure of the item. Table 7 is designed to guide the design team to assign occurrence rating to a specific failure cause/mechanism.

15 Table 7. Occurrence Rating System for the Cause/Mechanism of a Failure Mode Likelihood of Cause Description Occurrence Rating (O) Expected >30% > One per day 10 Very likely 30% 9 Probable 5% One per week 8 Occasional 1% One per month 7 More plausible 0.3% One per three months 6 Plausible 5 Remote 0.006% One per year 4 Unlikely 0.00006% One per three years 3 Very unlikely 2 9 Improbable < 2 per 10P P events > 5 years per failure 1

DesignU Controls/Detection Design control is a test method or inspection procedure or a design review process, etc used to detect a cause of a potential failure mode and subsequently to prevent/reduce its occurrence. Usually the detection is lead to a list of corrective actions. Detection is the degree of confidence that the specific failure cause/mechanism will be caught using the existing design control methods. In other word, detection is a relative rating of the effectiveness of the design control to catch the specific failure cause/mechanism. In the design of a drive shaft, for example, we may be “certain” that the calculation checking procedure (control) would detect that the static and dynamic loads were estimated incorrectly (cause), which might result in fracture (failure mode). Detection can be estimated using table 8.

Table 8. Detection Rating System for the Design Control in identifying the Cause Likelihood of Detection of Cause by Design Control Detection Rating (D) Impossible, design control cannot detect a potential cause, or there is no design control 10 Very remote chance the design control will detect a potential cause 9 Remote chance the design control will detect a potential cause 8 Very low chance the design control will detect a potential cause 7 Low chance the design control will detect a potential cause 6 Moderate chance the design control will detect a potential cause 5 Moderately high chance the design control will detect a potential cause 4 High chance the design control will detect a potential cause 3 Very high chance the design control will detect a potential cause 2 Certain chance the design control will detect a potential cause 1

CalculatingU the Risk Priority Number (RPN) The risk priority number is a metric used to assess the risk of a failure mode. The RPN for a part failure mode is the product of three factors: a severity rating (S), an occurrence rating (O), and a detection rating (D), RPN = (S) . (O) . (D)

Each factor is a numerical rating that ranges between 1 and 10, as shown in tables 7 through 9. Note that lower rating numbers are better, consequently the smaller the RPN, the smaller the risk of failure mode. In other words, a part with almost no risk would have a severity rating of 1, an occurrence rating of 1, and a detection rating of 1, resulting in an RPN equal to 1. Similarly, a part having the most risk of failure would have a RPN = 10 . 10 . 10 = 1000. Even though there is no threshold value for RPN’s in terms of prioritizing failure modes for corrective actions, the following procedure can be adopted by the FMEA team to utilize the RPNs: • Under minor risk, no action is taken • Under moderate risk, some action may take place

16 • Under high risk, recommendations are made and definite actions will take place

StepsU of FMEA The 10-step FMEA method uses a tabular layout to organize the information and facilitate the calculations, as shown in table 9.

Table 9. Failure Modes & Effects Analysis Template Used to Calculate RPN

Failure U Severity (S) U U Occurrence (O) U U Detection (D) U RPN Recommended Mode Effects S Rating Causes O Rating Controls D Rating Action (step 1) (step 2) (step 3) (step 4) (step 5) (step 6) (step 7) (step 8) (step 9)

StepU 1: Determine the failure modes. Identify how the component might fail to perform its desired function(s). To do this, the design is reviewed to determine the interrelations of assemblies and the interrelations of the components of each subassembly. This can best be accomplished with block diagram like functional diagram or product architecture diagrams. A complete list of the components in each assembly and the function of each component are prepared. For each function ask: • What if the function fails to occur at the right time? • What if the function fails to occur in the proper sequence? • What if this function fails to occur completely? For each of the functions list the potential failure modes.

Note: In case of an existing similar product, obtain service and/or test records.

StepU 2: Determine potential effects of each failure mode. Establish the effects of each failure mode in terms of what the user might be subjected to.

StepU 3: Select a severity (S) rating for each effect. Delineate possible injury to users, damage to product, personal, or real property, and harm to the environment. Select an appropriate rating number from table 7.

StepU 4: Determine the possible causes for each effect Determine possible causes for each effect. Consider prevalent failure modes, effects, and causes for similar products. Brainstorm mechanical, electrical, chemical, and other physical mechanisms that could cause each effect.

StepU 5: Select an occurrence (O) rating for each effect. Estimate the probability each cause will occur and select an occurrence rating from table 7.

StepU 6: Determine design controls. Identify and list design control activities such as design checklist, a specific design calculation, engineering tests, etc., to detect the potential causes of failure mode. The implementation of these design controls will either prevent the cause/mechanism of failure modes or reduce their rate of occurrence.

StepU 7: Select a detection (D) rating for each design control. Estimate the likelihood that the controls will detect each cause and select an appropriate detection rating value from table 8.

StepU 8: Calculate the risk priority number for each failure mode. Compute the product of the severity, occurrence, and detection ratings, RPN =(S) . (O) . (D)

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StepU 9: Recommend and take action. Rank the failure modes and determine which failure mode has the greatest risk. Based on the RPN or criticality ratings, resources should be allocated for further design improvement or design verification. This might be reflected in the recommended actions column. The purpose of a recommended action is to eliminate/reduce potential failure modes. The design team should know that only a design revision could bring about a reduction in the severity ranking. Actions such as the following should be considered: Design revision, Revision of material specifications, Design of experiments, and Revision of test plans and inspection procedures.

StepU 10: Recalculate the risk priority numbers. After remedial action has been implemented, for the “corrected” failure mode revise the RPN,s by repeating the steps one through nine.

TaskU 7B. Design for Manufacturing Design for manufacturing (DFM) is the set of practices that aim to improve the fabrication of individual parts. As we plan the manufacturing of any product, we need to answer the following questions: • How do we choose the specific manufacturing processes? • How do the materials selected influence the choice of manufacturing processes? • What criteria should we use to select processes?

Regardless of the type of material, even the simplest product involves many manufacturing processes. In the followings, we will: i. Examine the capability of some of the more widely used manufacturing processes and investigate their compatibility with alternative materials, ability to generate complex shapes, limitations as to the maximum or minimum part size, feasible production quantities, and overall economic viability, (Manufacturing Processes & their Capabilities) ii. Describe some general guidelines that will help select appropriate primary manufacturing processes, (Selection of Primary Processes) iii. Illustrate some general manufacturing recommendation, aimed to optimize part manufacture, which will help us to refine and improve our manufacturing process decisions such as determining secondary & tertiary processes. (General Manufacturing Guidelines)

i.U Manufacturing Processes & their Capabilities Manufacturing processes are used to transform raw materials into products. Processes are used to change materials’ forms (i.e., forging) alter their microstructure and properties (i.e., heat treatment), and also modify their chemical composition (i.e., chrome plating or galvanizing steel). Manufacturing processes can be categorized as bulk deformation, casting, sheet metalworking, polymer processing, machining, finishing, and assembly. They also are categorized as:

Primary processes: used to alter the material’s shape or form (sheet metalworking is used to form steel sheets into refrigerator housings), Secondary processes: used to add or remove geometric features from the basic forms (refrigerator housings are frequently drilled or hole-punched), Tertiary processes: relate to surface treatments such as polishing, painting, heat-treating, and joining (refrigerator housings are usually painted before they are assembled as final products)

ii.U Primary Processes Selection

18 Most parts undergo primary, secondary, and tertiary manufacturing processes. The cost to manufacture a product depends on the chosen materials and manufacturing processes. General guidelines to minimize the part cost are: a. Purchase less expensive materials b. Keep the finished part weight low c. Produce little manufactured waste d. Make many parts per production run (i.e., batch) e. Design simple parts that result in less expensive tooling f. Choose a manufacturing process that has a low cycle time

As was mentioned before some processes are not economically feasible unless significant quantities are produced. Some processes are incapable of producing large part sizes. Other processes cannot produce the desired geometric complexity, including notches, bosses, rotational symmetry, enclosed cavities, and undercuts. The feasible material classes that were selected based on the required properties and the nature of environmental conditions (i.e., result of task 6B) will be compatible with some manufacturing processes, to narrow the feasible processes further, we consider part information, including the geometric complexity of the part, the production volume, and part size. In brief, to select the feasible processes we take the following steps:

1. From the list of manufacturing processes, select the compatible processes for the selected material 2. Narrow the processes, considering part information such as: a. Production volume b. Size c. Shape Complexity, and 3. Select the feasible processes

iii.U General Manufacturing Guidelines We may have selected processes compatible with some materials, however, will the manufacturing processes produce the configured part features? (i.e., does the design include some impossible-to-machine feature?). In general we find that many design-for-manufacture recommendations focus on part features and how they are configured. For example, eliminate or reduce undercuts, add stiffening ribs, avoid narrow projections, reduce number of bend panes, and specify standard machining features. These recommendations aim to optimize part manufacture.

TaskU 7C: Design-for-Assembly (DFA) Evaluation Part of the labor cost in manufacturing a product is the cost of assembling it; for some products it is a significant part of the labor expense. Design for assembly, DFA, is the best practice used to measure the ease with which a product can be assembled. Since virtually all products are assembled out of many components and assembly takes time (that is, costs money), there is a strong incentive to make products as easily to assemble as possible. Assembling a product means that a person or a machine must (1) retrieve components from storage, (2) handle the components to orient them relative to each other, and (3) mate them. Then the ease of assembly is directly proportional to the number of components that must be retrieved, handled, and mated, and the ease with which they can be moved from their storage to their final, assembled position.

19 TaskU 8: Prototyping/testing The purpose of prototyping/testing is to identify any remaining design flaws and detecting any unanticipated detrimental phenomena, which may arise in the final product, before committing to production. Any resulting changes are feed backed into the loop of design process, toward the detailed design, to make sure that the product has achieved the desired level of functionality.

The report on this task should include:

1. Description of all the major processes involved in your prototyping 2. Problems encountered and remedies pursued 3. Description of testing and the results 4. Explain how well testing has verified the expected objectives

TaskU 9A: Detailed Drawings/BOM/Detailed Design

ProductionU Drawings/Specifications Production drawings and specifications include: detail drawings, assembly drawings, bill of materials, and a set of product design specification. The production drawings are the means for communicating the design to the manufacturer. Drawings are not only the preferred form of data communication for the designer; they are a necessary part of the design process. As the design of components and assemblies evolve through the iterative process of refining and patching, more formal drawings are used to keep the information organized and easily communicated to others. Drawings are used to:

1. Archive the geometric form of the design, 2. Support the analysis of a design as it evolves, 3. Simulate the behavior or performance of a design, 4. Check completeness. As sketches or other drawings are being made, the details left-to-be- designed become apparent to the designer. 5. Communicate ideas between designers and between designers and manufacturing personnel.

A General Electric survey showed 60 percent of all manufactured components are not made exactly as represented in the drawings. The reasons vary: 1) The drawings are incomplete, 2) The components cannot be made as specified, as some was discussed in DFM 3) The drawings are ambiguous, and 4) Components cannot be assembled if manufactured as drawn. Hence, in making drawings care must be taken not to create drawing, which makes it impossible to manufacture the part based on any of the above-mentioned reasons. Modern solid-modeling CAD tools help to overcome most of these problems.

DetailedU Drawings During the design process many types of drawings are generated. Sketches that were encouraged during conceptualization must evolve to final drawings that give enough detail to support production. The details of the components and assemblies are partially specified by the information developed on the layouts. As the product is refined, these information are transferred into detailed and assembly drawings. The development of the drawings is synergistic with the evolution of the product geometry and further refinement of its function. Detail drawings are orthographic projection views (front, side, or top) of a single component of a 2 product, showing its geometric features drawn to scale along with full dimensions, tolerancesTPF F,PT

2 TP PT Tolerance is the amount that a particular dimension is allowed to vary. In other word, to maintain control over dimensional variation, we specify upper and lower limits on part dimensions, that is, maximum and

20 manufacturing-process note and title block. Detail drawings do not have a bill of materials. Important characteristics of a detail drawing include the followings: • All dimensions must be toleranced. The upper and lower limits of the critical dimensions in figure 1 are given. • Materials and manufacturing detail must be in clear and specific language. Special processing must be spelled out clearly. • Drawing standards such as those given in DOD-STD-100, Engineering Drawing Practices and in ANSI14.5M-1994, Dimension and Tolerance, or company standards should be followed. • Since the detail drawings are a final representation of the design effort and will be used to communicate the product to manufacturing, each drawing must be approved by management. A title and a signature block is therefore a standard part of a detail drawing.

AssemblyU Drawings Assembly drawings focus on systems or subsystems. The goal in an assembly drawing is to show how the components of a product or subassembly fit together. They illustrate the location of each part in relation to the other parts and, in some cases, illustrate the operation of the product. The parts are shown to scale in orthographic and/or pictorial view. There are many types of drawing styles that can be used to show this; one type is an exploded view. Balloon notes are used to identify each part and cross-reference it to the bill of materials. A completed title block is added along with manufacturing and assembly notes. No dimensions are shown on assembly drawings.

An assembly drawing has the following specific characteristics:

• Each component is identified with a number or letter keyed to the bill of materials (BOM). • References can be made to other drawings and specific assembly instructions for additional needed information. • Necessary detailed views are included to convey information not clear in the major views. • As with detail drawings, assembly drawings require a title and a signature block.

BillU of Materials (BOM) The Bill of materials (BOM) is like an index to the product. It is a good practice to generate the bill of materials as the product evolves. This is commonly done on a spreadsheet, which is easy to update. To keep lists to a reasonable length, a separate list is usually kept for each assembly. There is a minimum of six pieces of information on a bill of materials:

• The item number or letter. This is a key to the components on the assembly drawing. • The part number. This is a number used throughout the purchasing, manufacturing, inventory control, and assembly systems to identify the component. • The quantity needed in the assembly. • The name or description of the component. This must be a brief, descriptive title for the component. • The material from which the component is made. If the item is a subassembly, then this does not appear in the BOM. • The source of the component. If the component is purchased, the name of the company is listed. If the component is made in-house, this line can be left blank.

minimum sizes. The specified difference between maximum and minimum size limits of a part feature is called a tolerance.

21 ProductU Design Specification (PDS) Product design specification (PDS) is a document that captures the specific details of the design problem. An example template, which lists some of the important information about a design, is given in table 10 below.

Table 10. Product Design Specification (PDS) Template Design problem description Repair Intended purpose or use Retirement Special features Pollution Functional performance Ease of use Operating environment Human factors Reliability & safety Appearance Geometric limitations EDS (i.e. QFD chart) Maintenance Other

DetailedU Design The choices that have been made during the tasks prior to engineering analysis were refined and articulated in much greater detail, during the mathematical modeling, down to specific part types and dimensions. Further refinement of preliminary design is achieved by a) Implementing any possible changes resulting from task DFR and DFM/DFA back into prior task(s) of design loop and repeating the process, and b) Physical prototyping and testing the design artifact and implementing any resulting changes back into any appropriate prior task(s) and repeating the process, and finally through c) Final design review described below, which result in the detailed design of the product.

FinalU Design Review The final design review should be conducted when the production drawings are complete and ready for release to manufacturing. In most cases qualification prototype testing will have been completed. The purpose of the final design review is to compare the design against the most updated version of the engineering design specification (EDS) and a design review checklist, and to decide whether the design is ready for production. An effective design review consists of three elements:

3 1) Input Document: the input for the review consists of documents such as the EDS, the QFDTPF F PT analysis, key technical analysis like FEA, the results of the qualification tests, the detail and assembly drawings, and cost projections.

2) Review Meeting Process: The final design review is more of an audit in contrast to earlier reviews, which are more multifunctional problem-solving sessions. The meeting is structured so it results in a documented assessment of the design. The review uses a checklist of items that need to be considered. Each item is discussed and it is decided whether it passes the review. The documents in part (1) are used to support the evaluation. Sometimes a 1-5 scale is used to rate each requirement, but in a final review an “up” or “down” decision needs to be made. Any items that do not pass the review are tagged as action items. Table 11 shows an abbreviated checklist for a final design review. While the checklist in table below is not exhaustive, it is illustrative of the many details that need to be considered in the final design review.

3) Output from Review: The output from the design review is a decision as to whether the product is ready to be released to the manufacturing department. The design review builds a paper trail of the decisions or ratings for each design requirement, and a clear action plan of

3 TP PT The QFD chart is the most updated used in the PDS (i.e., ready for submission to manufacturing plant)

22 what will be done to fix any deficiencies in the design for those action items before the product is submitted to manufacturing Department.

1

TaskU 9B: Product Cost Evaluation

ManufacturingU Cost of a Part It is the responsibility of the to know the manufacturing cost of components designed. The total cost of a piece component (or subassembly) of a product and its constituent elements are shown in figure 1. All costs can be lumped into two broad categories, direct costs and indirect costs. Direct costs are those that can be traced directly to a specific component or subassembly of a product. All other costs are called indirect costs.

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DirectU Cost:U Direct cost is the sum of the material, processing, and tooling costs.

Material/Purchased-partU cost U (CBm)B A major part of the direct cost is the material costs. These include the expenses of all the materials that are purchased for a product, including the expense of the waste caused by scrap and spoilage. Components that are purchased from vendors and not fabricated in-house are also considered direct costs. At a minimum, this purchased-parts cost includes fasteners and packaging materials used to ship the product. At a maximum, all components may be made outside the company with only the assembly performed in-house. In this case there are no material, processing, and tooling costs, and direct cost of a part will only include the cost of the purchased part. It should be mentioned however, that assembly cost is also considered direct cost since it can be traced directly to the product, however since the cost of this process will tie into the cost of assemblage of all parts in the product rather than just the component cost, it will be discussed separately.

ProcessingU cost (CU pB )B Is the labor cost and the charges for machine time. Labor cost is the cost of wages and benefits to the workforce needed to manufacture the products. This includes the employees’ salaries as well as all fringe benefits, including medical insurance, retirement funds, and vacation times. Both labor cost and charges for machine time vary with the type of manufacturing equipment. The type of machine - lathe, horizontal mill, vertical mill, etc. – used in manufacturing affects the cost of the machine time. Also the tighter the tolerance and surface finish requirements, the more time and equipment are needed in manufacturing the part

Tooling/setupU cost U (CtB ),B The last element of direct costs is the tooling/setup cost. This cost includes all jigs, fixtures, molds, and other parts specifically manufactured or purchased for the production of the part (tooling cost). It also includes the cost for the work required to prepare the equipment for a production run (setup cost).

IndirectU Cost U This cost Is the overhead cost. 4 OverheadTPF FPT cost includes all cost for engineering, administration, secretarial work, utilities, leases of buildings, and other costs that occur day to day, even if no product rolls out the door. An approximate estimate of overhead cost accounts for about 30% of the manufacturing costs.

ManufacturingU Cost U The manufacturing cost is the direct cost plus the overhead. The manufacturing cost can be broken down in another important way, variable cost and fixed cost.

Variable cost, The material/purchased-parts cost plus processing costs are variable costs, as they vary directly with the number of units produced.

Fixed cost Other manufacturing costs such as tooling/setup plus the overhead are fixed costs, because they remain the same regardless of the number of units made. Even if production fell to zero, funds spent on tooling and the associated expenses would still remain the same.

Assuming a mass production run of quantity, n, in general the manufacturing cost of a part, CpartB B , is given by:

C C p t (1) C part = Cm + + • n n Where,

CmB B is the material cost per part, and may be calculated from

CBm B = CwB B . WpB B (1 + α),

4 TP PT Overhead costs are usually considered as part of the tooling costs, however, sometime processing costs included overhead charges.

24 Where CBw B is material cost per unit weight, WpB B is weight of finished part, and α is the ratio of wasted material weight / finished weight

CtB isB the total cost of tooling/setup; hence, CtB /nB is the tooling cost per part. Note that in mass production of a part setup cost may be considered negligible. • 5 CpB B is the processing cost per unit time (cost of machine and laborTPF F),PT and n is the number of components produced per unit time. 1 Note that cycle time (i.e., processing time needed to make a part) is equal to , and hence t = • n

CpB .tB is the processing cost per part. Note. Cost for machine time depends on the initial cost of the machine and its age, in other word machine cost rate ($/hr) = Initial equipment cost / machine life

AssemblyU Cost (CU AssemblyB )B ,U U One method of estimating the cost of assembly is based on the assembly advisor shown in figure 2, in which the parts are rated as poor designs, good designs, costly designs, most costly designs from an ease-of assembly point of view only. This qualitative evaluation depends upon whether or not the part is easy to grasp and manipulate, and on the ease or difficulty of alignment and insertion. The numerical values shown in figure 2 are simply the approximation of the amount of time (taB )B in seconds required to handle and insert a part that exhibits the characteristics indicated. The total assembly time (tassemblyB )B is then calculated by the summation of the assembly times for all the parts in the product, tassemblyB B = Σ tBaB .

Hence, the Assembly cost would be, CAssemblyB B = (tassemblyB )B . (ClB )B

Where, ClB B is the cost of labor per unit time. Information on labor cost for assembly can be found in Statistical Abstract Handbook or in Bureau of Labor Statistics.

DesignU Communication Stage This stage involves tasks 10A and 10B. Each task is described below.

TaskU 10-A: Final (Written) Report A good final design report is built from a well thought-out proposal, solid research, complete laboratory record binders or portfolios, and detailed progress reports on tasks. The point now is to put them together into a complete and comprehensive document that summarizes what you have done, how you have done, and what the outcomes are. To be useful, the report must clearly and concisely communicate the results of your work. The technical report should not contain superfluous or unsupportable material. Each word should be essential and used in a clear and understandable manner. Quality, not quantity, is the key to a successful report. The report should be carefully organized to strike a balance between technical accuracy and completeness on one hand, and readability and conciseness on the other.

SpecificsU a. Technical reports will be submitted in a (loose-leaf) manila folder. b. The report will be prepared using a commercial word processing system and printed on standard 8.5" x 11" paper. c. Writing will be on one side only and will be double-spaced, using a 12-size font, and indent five spaces for paragraphs. d. Sequentially number all pages. Start the abstract page with page i (roman numerals) and start the introduction with page 1 (standard numerals). e. A minimum left margin of 1.5" must be observed on all pages, all other margins will be at least one inch. This includes figures, tables, and computer printouts.

5 TP PT Statistical Abstract Handbook is a database of hourly labor cost for manufacturing and production workers such as machine operators, assemblers, fabricators, etc. It also lists the capital costs on manufacturing machines and equipments. These data can also be found in Bureau of Labor Statistics or on the web site www.bls.gov/cps/home.htm

25 f. Equations found in the main report will be numbered sequentially for easy reference. g. Supporting mathematical derivations/sample calculations are normally located in appendices. h. Use figures and tables to communicate information more clearly. Whenever a figure or table is used in the report it must be referenced in the report's body. All figures and tables will have complete descriptive titles. i. Figures consist of drawings and/or graphs supporting the body of the report. Descriptive titles for figures appear at the bottom of the figure. Figures will be numbered sequentially, independently of table numbering. j. Tables, Descriptive titles for tables appear at the top of the table. Tables will be numbered sequentially, independently of figure numbering. k. Any combination of the following options may be used for different level headings: st 1P -levelP headings: centered, boldface or underlined, in all capital letters, nd 2P -levelP headings: left aligned, boldface or underlined &/or italic, capitalizing first letter of each word, rd 3P -levelP headings: indented, boldface or underlined &/or italic, capitalizing first letter of each word.

OrganizationU The outline of a typical formal report, in order, includes: a. Title Page, consisting of the title of the design project, course name and number, names of the team members, names of the instructor, technical advisor, and the department head, and the date. This page should comply with the enclosed sample title-page handout. Do not number this page. b. Abstract Page, usually a half-page long (not more than a page) summary of the project and its findings, and is placed right after the title page. It should briefly describe what has been studied, how it has been done and what are the results? This is usually the very last section of the report to be written. Start this page with page i. The abstract must be written as a stand-alone document and must convey to the reader the essence of the report. It allows the reader the choice whether to read the remainder of the report for details. c. Table of Contents, a complete listing of all the material in your final design report by page number for ready reference. d. List of Tables, this is a list of all tables in the report, their descriptive titles and page numbers. e. List of figures, this is a list of all figures in the report, to include drawings and graphs, their descriptive titles and page numbers. f. List of Symbols, this is a list of any abbreviation or symbol used in the report along with its definition and units. It is arranged alphabetically with English letters first, then Greek symbols, and then other symbols. g. Body of the Report, Refer to specific guidance under “BodyU of Report” U given below. h. Project Management, The design team will explain how they plan, organize and monitor their activities by responding to the following steps: 1. Generate a WBS (work breakdown structure) chart, which lists all the required tasks and subtasks from beginning of the project to the end. 2. Establish the scheduling of the project activities using Gantt chart for the period covering the two semesters. 3. The team will generate a linear responsibility chart (LRC) or similar to show how these tasks and subtasks are assigned to team members, (i.e., who does what), for both semesters. 4. Explain how often the team meets and what resources are used. Give an analysis of how well your design team functioned in meetings and joint work sessions and remedial efforts like conflict resolution, mediation, and intervention. i. Works Cited, the works cited portion of the technical report (often called a "Bibliography") lists all outside sources (library, Internet, Vendors, etc) used to complete the project. The sources are listed alphabetically by the author's last name followed by the title in quotation marks, name of the journal, publisher, and date. The main body of the report must reference all the

26 cited works. (i.e., Gage, W. G., “Procurement Quality Planning & Control”, Proceedings of the Annual American Society for Quality Control Conference, ASQC, 1978, pp. 158-161) j. Acknowledgements, make acknowledgement to all those who assisted you with your project. k. Appendices, a place to supplement discussion with material that is illustrative or informative, such as pertinent technical data, correspondence, research studies, and other supporting material which may be essential to the completeness of the report, but which would be distracting if placed in the main body. The effective use of appendices enhances the readability and coherence of the main body of the report. The main body of the report must reference all appendices.

Body of Report 1. Introduction This is a maximum of two-page background on the subject to tell the reader why the design was performed. The background is extended to demonstrate the history of the similar existing products, and how your project artifact is going to be advantageous over the benchmark product. The scope of your project (i.e., from conceptual design to prototyping and testing) is described. Any assumption or condition (realistic and kept to the minimum required), which in addition to the known facts, are considered essential to the completeness and validity of the project, should be listed.

2. Methodology The report in this section should start with the general definition of the engineering design process. Then, it should demonstrate the evolutional process of your project, in the five stages described.

3. Conclusion & Recommendation This section should be thought of as a summary of findings and results. Discuss the lessons learned from success as well as failures. Summarize you conclusion concisely, preferably in itemized form. The conclusion should state the final choice for the design, with complete engineering specifications. Make any recommendation concerning further study of the topic.

Task 10B: Oral Presentation Your design project will be presented to a panel of faculty members and professionals from industries. You can look at this as a threat or as a challenge; the better choice is to view it as an opportunity to demonstrate your skills and knowledge. Focus not on yourself but on the design project; better yet, focus on your audience - their needs, interests, and desires. Do they want to hear excuses or lessons learned? Do they want glitz or substance? Do they want to experience the pain and frustration you may have felt, or would they prefer sound logic and clear thinking? Are they more interested in the design problems you encountered or in the solutions you created? The answers should be obvious.

Realize now that your presentation team might not function like an accomplished symphony orchestra or a well-rehearsed stage play production. Invariably, one team member may lose heart or interest and another might get mad and walk away. Just look back on the collaboration, communication, and conflict management skills you may have mastered by now, and use them. The skills discussed below will help you make a polished and professional presentation of your engineering design.

Project Management

Design projects are characterized by the fact that they have a clear-cut start and finish and they usually have limited resources. Hence a positive and effective management is required over various phases and sequences of the project to complete the activities successfully. The

27 processes of project management are implemented as follows: 1) Planning, 2) Directing, 3) Controlling, 4) Communicating through Information Resources, and 5) Administrating.

1. Planning Planning includes the following steps: Work Breakdown Structure, Scheduling tasks (Gantt chart)

Work Breakdown Structure (WBS): A work breakdown structure (WBS) is a block diagram that illustrates the major work tasks to be completed during a project. The primary work task categories are shown at the top level, with subordinate tasks underneath each major task. A WBS is similar to System breakdown structure with the difference that a task is substituted for a component.

Scheduling: Once subtasks are identified, develop a realistic estimate of how long it will take to perform each subtask, and establish a timetable within the project completion date.

Gantt Chart The simplest bar chart (or Gantt Chart) shown in figure is probably the most widely used project- scheduling technique. Gantt chart is a horizontal time scale to show and compare the planned with actual progress of project tasks. In addition to its simplicity the advantage of this method include the following: a. Direct correlation with time, b. Relatively straightforward task relationship and integration of subtasks. c. Time schedule is flexible and can be expanded to show daily activities or compressed for longer term tasks, and d. Progress against the plan is easily reflected by partially or fully filling in the bars.

Time (day, week, month,…) TASKS present time

(Gantt Chart)

Jan Feb March April Activities 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Task 1 Task 1-a Task 1-b Task 2 Task 2-a Task 2-b Task 3 ……………… ………………

In planning the schedule you may consider whether subtasks might be done concurrently rather than sequentially.

2. Directing Directing includes: Reviewing project objectives with tasks, and assigning tasks

28 This step is simply making assignments for each team member. Be fair about allocating subtasks, so every one has some enjoyable tasks. Write down WHO will make sure what SUBTASK is completed by what Date? This is done by Linear Responsibility Chart (LRC), figure below. Be sure that everyone knows that the team is collectively responsible for each subtask. Even if one person is responsible for a particular subtask, others must be willing to work together to see that the task is completed. Similarly, each member should be ready to ask for help when they need it, don’t wait till the deadline to tell your team members that a job is too big for you. A sample of LRC is shown below.

Tasks Team Team Team Team Member # 1 Member # 2 Member # 3 Member # 4

Conduct Research 1 2 2 2 Develop Obj Tree 2 1 3 Develop wght’d 2 1 3 Obj Tree Identifying 2 3 3 1 Constraints …………………. ……………..….. ………………… 1 = Primary responsibility 2 = Support/work 3 = Review

Fig. 2 Sample of linear Responsibility Chart (LRC)

3. Controlling Controlling includes the following steps: Review the progress, Comparing with the planned, Make necessary corrections, and resolve issues.

4. Information & Communication The team members list all the primary resources their team needs to acquire to perform its task, and consider how they should be acquired. Team communicating through these resources is critical to the project’s success. These resources include libraries, professional-engineering societies, federal governments, private sectors & industries, colleges & universities, web sites, standards, codes, and regulations. For detail information on these resources refer to your handouts.

5. Administrating Administrating includes: Communicating Design internally (among the team members) and externally (Oral Presentations & Written Reports).

Conclusions This paper discussed in details the engineering design process that the Cal Maritime mechanical engineering students go through in order to successfully finish, complete, construct, test and evaluate, manage, and present their capstone design. The various tasks discussed offer a systematic way to initiate and complete a design project.

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