Group 7

Assembly Techniques and Concerns

Rey JordanTim Goldmann

Phillip PinsonneaultCaleb Hanson

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Soldering and Brazing

• Soldering and brazing are used when you want to join materials that cannot withstand high temperatures, such as electric components.

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Soldering

• Soldering was first used as far back as 4000-3000 B.C.

• A soldering iron heats the solder to a molten state.

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Soldering

• Soldering comes from the Latin word solidare meaning to make solid.

• Solder is a type of metal with a low melting point.

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Soldering

• Part a: Not enough solder

• Part b: Right amount of solder

• Part c: Too much solder.

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Brazing

• Brazing and soldering are distinguished arbitrarily by temperature. Low temperature is for soldering, higher temperature is used brazing.

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Brazing

• Brazing was first used as far back as 3000- 2000 B.C.

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Brazing

• Surfaces that are to be brazed must be cleaned free of rust, oil and other contaminants in order to obtain proper wetting and spreading of the molten filler metal in the joint and develop max bond strength.

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Flux

• Flux is essential in brazing to prevent oxidation and to remove oxide films from workpieces. Generally made of Borax, boric acid, borates, florides and chlorides.

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Flux

• Because most fluxes are corrosive, they must be removed after brazing, usually by washing with hot distilled water.

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FillersMetals to be bonded

Filler metals Degrees C

Aluminum Alloys Alum-silicon 570-620

Magnesium alloys

Magnesium-aluminum

580-625

Copper Alloys Copper-phosphorous

700-925

Ferrous and non-ferrous

Silver, copper-alloy

620-1150

Iron-nickel and cobalt

Gold 900-1100

Stainless steel Nickel-silver 925-1200

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Mechanical Fasteners

• Ease of manufacturing

• Ease of assembly• Ease of disassembly,

maintenance, parts replacement, or repair

• Lower overall cost of manufacturing the product

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Threaded Fasteners

• Bolts and screws• Most commonly used

threaded fasteners• Can be secured with

a nut and lock washer

• Can be self-tapping

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Rivets and Staples

• The most common method of semi-permanent joining is by riveting

• Stapling is fast, and best suited for joining thin metallic and non-metallic materials

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Seaming and Crimping

• Seaming is similar to joining two pieces of paper by folding the corner

• Crimping can be done on both tubular and flat parts

• A good example of crimping use is attaching electrical connectors to wiring

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Snap-in Fasteners

• Several different types

• Fast and economical• Used widely in

automotive bodies and household appliances

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Shrink and Press Fits

• Shrink fitting is based on the thermal contractions of two components

• In press fitting, one component is forced over another

• A good example of shrink/press fit is a timing gear onto a crankshaft

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Design for Mechanical Fastening

• Less costly to use fewer (but larger) fasteners

• Fit between parts should be loose to reduce cost and facilitate assembly

• Standard size fasteners should be used when possible

• Holes should not be too close to edges or corners

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Joining Thermoplastics

• Ultrasonic welding is the most common used process to join thermoplastics

• Adhesive bonding as seen in household plumbing

• Mechanical fastening with self tapping screws

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Joining Thermosets

• Threaded or molded-in inserts

• Self-tapping screws and integrated snap fasteners

• Solvent or adhesive bonding

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Joining Ceramics and Glasses

• Ceramics can be joined during their primary shaping prior to firing

• Ceramics can be brazed after they have been coated with a metallic layer

• Glasses are joined by heating the surface to be joined and pressing the two pieces together

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Surface Structure

• Bulk metal or substrate

• Work hardened layer• Oxide layer (rust)• Adsorbed layer• Surface layer

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Surface Integrity

• Heat-affected zone is the portion of a metal that is heated without melting

• Inclusions are small, nonmetallic, elements in the material

• Residual stresses are caused by non-uniform deformations and temperature distributions

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Surface Texture and Roughness

• Regardless of the method of production, all surfaces have their own characteristics which are known as surface texture.

• Geometrical properties of surface texture are complex, however there have been simple guidelines defined to identify surface texture in measurable quantities.

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Surface Texture and Roughness• Lay- is the direction of the

predominant surface pattern and usually visible to the naked eye.

• Roughness- closely spaced, irregular deviations expressed in terms of height, width and distance along the surface.

• Waviness- reoccurring deviation from the flat surface. Measured between crests

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Measuring Surface Roughness

• Instruments called surface profilometers are used to measure and record surface roughness

• A diamond stylus travels in a straight line over the surface

• The path of the stylus in surface roughness measurements is used instead of the actual surface roughness profile.

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Friction• Friction- is the non

conservative resistance force that occurs when two surfaces travel along each other when forced together. It causes physical deformation and heat buildup.

• Two bodies in contact showing the real area of contact

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Reducing Friction• Friction can be

reduced by the careful selection of materials with low adhesion

• Lubricants interpose an adherent film which greatly minimizes friction between one surface and another

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Friction Measurement• Ring Compression Test

– a flat ring is pressed between two flat plates.

– As its height is reduced the ring expands radially outward.

– If the friction at the interfaces were zero, both the ID and OD would expand as if it were a solid disk.

– Increasing friction shrinks the ID

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Wear• Wear is significant

because it changes the shape of tools and dies also affecting tool life, size and the quantity of parts produced.

• The effects of wear are evident in the number of parts and components that have to continually be replaced.

(a)- wire brush(b)- ground surface

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Adhesive and Abrasive Wear• Adhesive wear occurs

when two surfaces sliding across each other and there is a constant breaking of the micro welds.

• Abrasive wear occurs when a hard rough surface slides across a softer surface causing chips and slivers

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Other Types of Wear

1. Erosion-loose particles abrading a surface

2. Pitting (lubricated dies only)

3. Thermal Fatigue4. Mechanical Fatigue5. Plastic Deformation

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Lubrication• Lubricants are used

widely for many rotary and linear moving components in metal work and machining

(a)Thick film- prevent accuracy

(b)Thin film- less friction with slight wear

(c) Mixed- load carried by metal contact

(d)Boundary- no metal to metal contact

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Metal Working Fluids

• Functions of metal working fluids include:– Reduce friction– Reduce wear– Improve material flow– Thermal barrier

between tool and work piece

– Act as a release or parting agent in dies and molds

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Metal Working Fluids

• Oils- effective in reducing friction and wear but do not prevent heat generation or plastic deformation

• Emulsions- water soluble oils which offer the cooling attributes of water with the lubrication properties of oils

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Metal Working Fluids

• Soaps- good boundary lubricants

• Greases- adhere well to metal surfaces

• Waxes• Additives- oxidation

and foam inhibitors, rust preventing, wetting and odor controlling agents

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References

• Wright, Thomas, Processes of Manufacturing, Goodheart-Wilcox Company, Inc., 1990

• Lindbeck, John R., Product Design and Manufacture, Prentice-Hall, 1995

• Kalpakjian & Schmid, Manufacturing Engineering and Technology, Prentice-Hall, Fifth Ed.