Fastening Flashcards
1
Q
Why have a joining process?
A
- Disadvantages of one piece: inconvenient, expensive, too big to make one piece, inefficient use of materials, complex design, limited customisation, limited repair options
- A product that required different properties in different places
- Transporting and replacement
2
Q
General Considerations
A
- Complexity
- Compatability
- Cost
- Flexibility
- What Ts are needed?
- What is the relative competitivenes of alternative processes?
3
Q
Material Issues
A
- Are materials similar or dissimilar? - determines selection of processes
- What is m. pt. of parts being joined? - upper limit on T
- Are the surfaces wettable? - essentail for adhesives, soldering etc.
- Are the materials machinable? - joining may have to subjectto machining (e.g. hole drilling)
- Do the materials degrade when heated? - limits usable T range
4
Q
Design Issues
A
- Is the joint to be permanent?
- Will there be any residual stresses?
- Heat treatment may be applied
- What surface finish will result from different types of joint?
- Will the joint be exposed to moisture?
- Corrosion problem s
- What is the area of the joint? - may affect strenght
- What geometry of joint is permitted?
- What loading will the joint see in service? - e.g. tension, compression, torsion
- What is the in-service stress status? - cracking - crack propagation
5
Q
Joining Process Types
A
- Mechanical fastening (e.g. riveting) - elastic and/or friction properties of a material are exploited to hold components together
- Permanent joining (e.g. welding)
- Adhesive bonding (e.g. gluing) - physically and chemically joining surfaces
6
Q
Why use mechanical assembly?
A
- Ease of assembly - can be accomplished with relative ease by unskilled workers (min. of special tooling required, relatively short time)
- Ease of disassembly - at least for the methods possible (some dissassembly is required ro perform maintenance and repairs)
6
Q
Two Major Classes of Mechanical Assessembly
A
- Disassembly - threaded fasteners
- Permanent - rivets
7
Q
Threaded Fasteners
A
- Discrete hardware components used to mechanically attach two or more parts together
- Permits disassembly
- Common fasteners are screws, bolts and nuts
8
Q
Riveting
A
- Unthreaded, headed pins used to join two or more parts by passing a pin through holes in the parts and then forming (upsetting) a second head in the pin on the opposite side
- Widely used fasteners for achieving a permanent joint
- Permanent or semi-permanent mechanical joining can be applied at room or elevated T
9
Q
Applications of Riveting
A
- (aircraft/aerospace) joining skins to channels and other structural members
- Used primarily for lap joints
10
Q
Advantages of Riveting
A
- High production rates
- Simplicity
- Dependability
- Low cost
11
Q
Tooling and Methods of Riveting
A
- Impact - pneumatic hammer delivers a succession of blows to upset rivet
- Steady compression - riveting tool applies a continuous squeezing pressure to upset rivet
- Combination of impact and compression
12
Q
Design for Assembly (DFA)
A
- Keys to successful DFA: few parts as possible in product, design remaining parts so they are easy to assemle
- Once these have been done, little can be done to reduce assembly costs
13
Q
Design Guidelines for Riveting
A
- Exposed shank is too long results in buckling instead of upsetting
- Placed sufficiently far from edges - avoids stress concentrations
- Ample clearance for riveting tools
- Section curvature should not interfere with riveting
14
Q
Fastening Advantages
A
- Easy assembly and transport
- Easy disassembly, maintenance or repair
- Versatility: easy in creating movable joints, hinges, sliding mechanisms etc. - can be used to join a wide range of materials, including metals, plastics and composites and dissimilar materials
- Cost-effective - low overall cost of manufacture and equipment/tooling
- Accessibility in a variety of settings
- Quality control - allows for easy injection and quality control during the assembly process
