1. Manufacturing Processes
Fastening
Manufacturing Processes

2. Outline Brazing Soldering Adhesive Bonding Threaded Fasteners Rivets
Filler Metals and Fluxes
Brazing Methods
Soldering
Adhesive Bonding
Adhesives
Design Consideration
Threaded Fasteners
Standard Screw Threads
Thread Classes
Rivets

3. Brazing
Brazing
A joining process in which filler metal is melted between the surfaces to be joined; the base metal is not melted

4. Brazing

5. Filler Metals and Fluxes
Melted between the surfaces to form the join
Brazing fluxes
Used to dissolve, combine with, or inhibit formation of oxides or other by-products; it is displaced by the filler metal and removed after the operation

6. Filler Metals

7. Brazing Methods Torch brazing
A flame is used to heat the joint, then filler is added
Furnace brazing
The parts and filler are heated in a furnace; flux may not be needed
Induction brazing
Uses heat from electrical resistance to an induced current in the work
Resistance brazing
A current is supplied directly to the part to cause resistance heating

8. Brazing Methods Dip brazing
Parts are immersed in a molten salt or metal bath to heat them
Infrared brazing
Uses heat from a high-intensity infrared lamp
Braze welding
Applies filler metal to a conventional weld joint; the base metal does not melt

9. Soldering
Soldering
A filler metal is melted and distributed between the surfaces to be joined; the base metal does not melt, but the filler metal combines with it to form a metallurgical bond

10. Soldering
Soldering a wire: soldering iron (heat source), left, solder rod, right

11. Examples of Soldered Parts

12. Examples of Soldered Parts

13. Soldering Materials

14. Soldering Fluxes Soldering fluxes should:
be molten at soldering temperatures
remove oxide films and tarnish
prevent oxidization
promote wetting of the surfaces
be displaced readily by the filler metal
leave residue that is not corrosive or conductive

15. Courtesy of Air Products and Chemicals, Inc
Adhesive Bonding
Courtesy of Air Products and Chemicals, Inc

16. Adhesive Bonding Types of Adhesives 1. Natural adhesives starch
animal products
2. Inorganic adhesives
sodium silicate
magnesium oxychloride
3. Synthetic organic adhesives
thermoplastics (soften when heated, harden when cooled)
thermosetting (harden permanently when heated)

17. Adhesive Bonding

18. Primers
Primers used as metal surface conditioners perform these functions:
protect corrosion sensitive surfaces
modify the properties of the bond
tacky resins help hold or position bonded parts

19. Theories of Adhesion Chemical bond theory
Adhesion between adhesive and adherend is related to the forces holding atoms and molecules together
The predicted strength of the attractive force is far higher than in reality; however, the theory is valid because chemically active primers improve adhesion

20. Theories of Adhesion Weak boundary layer theory
Poor adhesion or adhesive failure is caused by an inclusion of low-molecular weight liquid or an unpolymerized liquid; the liquid forms a weak boundary layer that prevents the proper bonding

21. Theories of Adhesion Surface energy theory
A liquid should have a lower surface tension than the critical surface tension of a solid in order to spread on the solid surface
Surface contamination of the solid could lower the critical surface tension below the surface tension of the liquid, causing the bond to be ineffective

22. Theories of Adhesion Inherent roughness theory
Once the adhesive has wet and spread over the adherend surface, the mechanical strength of the resin coupled to the rough surface is the basic reason for the strength of the bond
Roughness would increase the surface area in which electrostatic forces could operate

23. Theories of Adhesion Polar theory
Polar adhesives bond to polar adherends and nonpolar adhesives bond to nonpolar adherends
Liquids wet and spread more effectively on solid surfaces with similar properties

24. Common Adhesives 1. Epoxies thermosetting metal, glass, ceramic, wood
two-component epoxies
resin
curing agent
application time: 8-12 hours
2. Cyanoacrylates
liquid monomers
application time: 2 seconds

25. Common Adhesives 3. Anaerobics thermosetting polyester acrylics
almost any material
application time:6-24 hours; 5 min. with proper additives and heat
4. Acrylics
thermoplastic
plastics, metals, ceramics, composites, even with dirty surfaces

26. Common Adhesives 5. Urethanes
one-part thermoplastic or two-part thermosetting
application time: solidifies in 2 min, cures fully in 24 hours
6. Silicones
silicone thermosets
metal, glass, paper, plastics, rubber
cures slowly

27. Common Adhesives 7. High-temperature adhesives
epoxy phenolics, modified silicones or phenolics, polyamides, ceramics
cures slowly
8. Hot melts
thermoplastic resins
not true structural adhesives; applied as heated liquids and bond as they solidify

28. Application Methods Brushing
Performed manually; coating is often uneven
Manual rollers
Similar to paint rollers
Silk screening
Brushing through open areas of a screen to coat selected areas
Flowing
Using manually operated flow guns; more consistent control than brushing

29. Application Methods Spraying
Using a spray gun for fast application over large areas
Automatic applicators
Automatic dispensers and nozzles for medium and high production rates
Roll coating
A roller is partially immersed in the adhesive and transfers it to the part
Pull-tab sheets
The adhesive sheet comes prepared covered by a protective layer which is removed before use

30. Design Consideration Material porosity, hardness, surface properties
thermal expansion
Assembly
bond area
stresses
Temperature
during use of parts
temperature extremes, rate of temperature change

31. Design Consideration Exposure
to solvents, water, fuels, light, ultraviolet, acid, weathering
Flexibility/stiffness
Stability
required length of time
load
Appearance
Adhesive application
Cost

32. Design Consideration

33. Limitations Proper selection is required
Most are unstable above 350°F (180°C)
High-strength adhesives are often brittle
Long term durability and life expectancy are difficult to predict
Surface condition, adhesive preparation, and curing can be critical

34. Limitations Assembly times may be greater than other methods
Joint quality is difficult to evaluate
Some adhesives contain or produce unfavorable chemicals
Many adhesives deteriorate under certain conditions
Joints cannot be easily disassembled

35. Threaded Fasteners Screw
An externally threaded fastener, generally assembled into a blind threaded hole
Bolt
An externally threaded fastener inserted through holes in parts and screwed into a nut on the opposite side

36. Types of Screw Heads

37. Types of Screws

38. Threaded Fastener Units
U.S. Standard
measured in inches and fractions of inches: ¼, 5/8,1-1/8 etc.
Metric (SI)
measured in millimeters
A fastener specified to one measurement system may have similar sizes to a fastener of the other system, but they will not fit together properly

39. Types of Screw Threads Coarse-thread series Fine-thread series
general use where not subjected to vibration
Fine-thread series
automotive and aircraft
Extra-fine thread series
thin-walled material
Eight-thread series
pipe flanges, cylinder-head studs
Twelve-thread series
not used extensively

40. Types of Screw Threads Sixteen-thread series American Acme thread
where fine threads are required
American Acme thread
transmitting power and motion
Buttress thread
Square thread
29° Worm thread
American standard pipe thread
pipe joints

41. Standard Screw Threads
60° d r p
Where p = thread pitch, d = thread depth, and r = fillet radius,
d = p
r = p
This applies to U.S. Standard and Metric bolts, but does not necessarily apply to screws

42. Standard Screw Threads

43. Standard Screw Threads

44. Standard Screw Threads

45. Thread Classes Unified system Class 1 – special applications
Class 2 – normal production grade
Class 3 – minimum tolerances, tight fit required
A – external thread
B – internal thread

46. Thread Classes ISO system e – large tolerance g – small tolerance
H – no allowance
3-9 – tolerance grade
Lower = fine quality; higher = coarse quality
Grade 6 is roughly equivalent to U.S. class 2A and B

47. Rivets

48. Rivets
Rivet
An unthreaded, headed pin used to join parts by passing the pin through holes in the parts and then forming a second head on the opposite side

49. Rivets

50. Summary Brazing and soldering melt only filler material to form a join
Adhesive bonding uses a viriety of chemicals that are applied as a liquid and solidify to form a bond
Screws, bolts, nuts, and rivets are applied and hold material together by physical means