Lecture Five

MSE 257: INDIGENOUS METHODS OF MATERIALS PROCESSING

Course Code: MSE 257 Dr. Emmanuel Kwesi Arthur

Department of Materials Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

Email: [email protected] Phone #: +233541710532 Assembly

 The process of putting together all the components of a product before shipping.  Operation include handling, insertion, and/or attachment of parts.  Handling: grasping, moving, orienting, and placing parts, before insertion or attachment.  Attachment: either  - Permanent: welding, brazing, soldering, adhesive bonding, rivets, eyelets, staples, shrink fits, press fits, or  - Temporary: threaded fasteners such as screws, nuts and bolts, snap fits. Assembly processes – fastening / joining of 2 or more components

Manufacturing Processes

Sheet Polymer Deformation Casting Metal Processes Machining Finishing Assembly

Extrusion Centrifugal Bending Blow molding Boring Anodizing Automated Forging Die casting Blanking Casting Drilling Honing Bonding Rolling Investment Drawing Compression molding Facing Painting Brazing Bar drawing Permanent mold Punching Extrusion Grinding Plating Manual Wire drawing Sand casting Shearing Injection Molding Milling Polishing Riveting Spinning Thermoforming Planing Soldering Transfer molding Turning Welding Sawing ECM, EDM permanent? Assembly Operations

 Two or more separate parts are joined to form a new entity  Types of assembly operations:  Joining processes – create a permanent joint.  Examples: welding, brazing, soldering, and adhesive bonding  Mechanical assembly – fastening by mechanical methods  Examples: use of screws, bolts, nuts, other threaded fasteners; press fitting, expansion fits

4 Join Two or More Materials

1. Welding 2. Brazing 3. Soldering 4. Adhesive bonding 5. Fastening Brazing

 Brazing is a metal-joining process.  Brazing is when a filler metal or alloy is heated to its melting temperature above 450°C.  It is then distributed in liquid form between two or more close-fitting parts by capillary action.  The filler metal is then brought slightly above its melting temperature.  It then interacts with a thin layer of the base metal (known as wetting) and is then cooled quickly.  This forms a sealed joint.  Brazed joints are generally stronger than the individual filler metals that have been used to make them.  This is because of the geometry of the joint and the metallurgical bonding that occurs. Advantages of brazing

 It's easy to learn.  You can join virtually any dissimilar metals.  The bond line can be very neat in appearance.  Joint strength is strong enough for most non-heavy-duty use applications Disadvantages of brazing

 A badly brazed joint looks similar to a good joint, and can have a VERY low strength.  The metal used to bond the two parts may be different in color than the parts being bonded. This may or may not be a problem.  Long-term effects of dissimilar metals in constant contact may need to be examined for special applications.  Since the filler material (typically bronze) melts at a relatively low temperature, brazed parts may not be put in an environment which exceeds the melting point of the filler metal. Soldering  Soldering is a process in which two or more metals are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. Soft soldering is characterized by the melting point of the filler metal, which is below 400 °C.  The filler metal used in the process is called solder.  Soldering is distinguished from brazing as the filler metal used has a lower melting point.

Soldering is normally done by melting the solder with a soldering iron and applying it to the two metals that are going to be joined together. Advantages of soldering

 Low power is required;  Low process temperature;  No thermal distortions and residual stresses in the joint parts;  Microstructure is not affected by heat;  Easily automated process;  Dissimilar materials may be joined;  High variety of materials may be joined;  Thin wall parts may be joined;  Moderate skill of the operator is required. Disadvantages of soldering

 Careful removal of the flux residuals is required in order to prevent corrosion;  Large sections cannot be joined;  Fluxes may contain toxic components;  Soldering joints can not be used in high temperature applications;  Low strength of joints. Introduction

 Soldering and brazing are classified by the AWS as liquid- solid phase bonding processes Base material stays solid and filler material is liquid Hot Gluing  Phase is the temperature at which bonding takes place  Soldering and brazing differ Soldering takes place below 840° Fahrenheit FAA says its 800F?????????????????????  Capillary action is the force that pulls water up into a paper towel  Braze welding does not need capillary action Soldering/Brazing Applications

Steps in Sweat Soldering 1) Copper pipe is cleaned 2) Flux is applied 3) Heat is applied 4) Solder is added 5) Solder is drawn into fitting via heat (capillary Action) 6) Pipe is wiped cleaned 7) Brazing steps are the same except for Brazing filler metal s added instead of solder. Braze Welding

Steps in Braze Welding 1) Base material is cleaned 2) Flux is applied 3) Heat is applied 4) Braze is added 5) Braze material is added into a joint. Capillary Action is not used. 6) Post Braze weld is cleaned Capillary action

Capillary action pulls water into a thin tube. Advantages of Soldering and Brazing  Some advantages of soldering and brazing: Low temperature Permanently or temporarily joined Dissimilar materials can be joined Speed of joining Less chance of damaging parts Slow rate of heating and cooling Parts of varying thicknesses can be joined Easy realignment  Disadvantage Service Temp!!!!!!!!!!!!!!!!! Fluxes

 Fluxes used in soldering and brazing have three major functions: Remove oxides that result from heating parts Promote wetting Aid in capillary action (if soldering or brazing)  Flux must be thin, when heated to its reacting temperature  Fluxes are available in many forms  Paste  Liquid  Powder Soldering and Brazing Methods

 Grouped according to method of applying heat: Torch (TB) Furnace Induction Dip Dip Soldering and Brazing

 The parts to be joined are fixtured and the brazing compound applied to the mating surfaces, typically in slurry form. Then the assemblies are dipped into a bath of molten salt (typically NaCl, KCl and other compounds) which functions both as heat transfer medium and flux.  Advantages of dip processing:  Mass production  Corrosion protection  Distortion minimized  Disadvantages of dip processing:  Steam explosions  Corrosion  Size  Quantity Filler Metals  Should be selected by considering as many of the criteria as possible  Welders decide most important criteria  Soldering and brazing metals are alloys Solder being shaped as it cools to its paste range. Soldering Alloys

Usually identified by their major alloying elements Base metal can be joined by more than one solder alloy Tin-lead

 Most popular solder  Least expensive  Most commonly used on electrical connections  Never used for water piping Brazing Alloys

 The AWS 's classification system for brazing alloys uses the letter B  Next series of letters indicate the atomic symbol of metals used  Not all available brazing alloys have an AWS classification  Some special alloys are known by their trade names Copper-zinc

 Most popular brazing alloys  Available as regular and low-fuming alloys  Tendency to burn out when overheated  If breathed in, it can cause zinc poisoning  If you think you have zinc poisoning, get medical treatment immediately Copper-zinc and Copper-phosphorus A5.8

 Known as brazing rods  Referred to as phos-copper  Vast differences among the five classifications  Five classifications of copper-zinc filler rods: BRCuZn BRCuZn-A BRCuZn-B BRCuZn-C BRCuZn-D  If overheated will cause zinc fumes Building up Surfaces and Filling Holes

 Surfaces on worn parts are built up again with braze metal  Ideal for parts that receive limited abrasive wear  Braze buildup has no hard spots Good for flat and round stock  Holes in light-gauge metal can be filled using braze metal Silver Brazing

 Melting temperature for alloys is around 1400° Fahrenheit  Copper pipe glows a dull red  Best types of flame to use: Air acetylene Air MAPP Air propane Any air fuel-gas mixture Soldering

 Practices use tin-lead or tin-antimony solders  Both have low melting temperature  Best type of flame: Air acetylene Air MAPP Air propane Any fuel-gas mixture Material Removal Processes

 Excess material removed from the starting workpiece so what remains is the desired geometry  Examples: machining such as turning, drilling, and milling; also grinding and nontraditional processes

 Turning Drilling Milling 30 Property-Enhancing Processes

 Performed to improve mechanical or physical properties of the work material  Part shape is not altered, except unintentionally  Examples: Heat treatment of metals and glasses Sintering of powdered metals and ceramics

31 Surface Processing

1. Cleaning - chemical and mechanical processes to remove dirt, oil, and other contaminants from the surface 2. Surface treatments - mechanical working such as sand blasting, and physical processes like diffusion 3. Coating and thin film deposition - coating exterior surface of the workpart

 Several surface processing operations used to fabricate integrated circuits

32 Waste in Shaping Processes

 It is desirable to minimize waste and scrap in part shaping i.e. have high material utilization  Material removal processes tend to be wasteful in the unit operation, simply by the way they work  Casting and molding waste less material

 Terminology:  Net shape processes - when most of the starting material is used and no subsequent machining is required to achieve final part geometry  Near net shape processes - when minimum amount of machining is required MSE 257:33 Indigenous Processes You should have learned today:

 The key design responsibility of a manufacturing engineer  Key categories of manufacturing materials  Key categories of manufacturing processes  How to compare them  materials-processes-geometry  IE 337: Got to work hard  tons of information, regular study habits

34  QUESTIONS  CONCERNS  COMMENTS How would we manufacture a mountain bike ?

36 (Courtesy of Trek Bicycle, 2002)