ME 330 Manufacturing Processes MECHANICAL ASSEMBLY: Joining Methods using Fasteners.
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Transcript of ME 330 Manufacturing Processes MECHANICAL ASSEMBLY: Joining Methods using Fasteners.
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ME 330Manufacturing Processes
MECHANICAL ASSEMBLY:Joining Methods using Fasteners
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Overview of processes
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Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
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Mechanical Assembly: Definition
Use of various methods to mechanically attach two or more parts together. This can be done by
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Two Major Types of Mechanical Assembly
1. allow for disassembly
2. create a permanent joint with no possibility of disassembly
Adhesion and bonding
Use of the third part component Use of the deformation between two components to
be assembled.
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Pros of Mechanical Assembly
1. Ease of assembly – can be accomplished with relative ease by unskilled workers Minimum of special tooling required Can be done in a relatively short time
2. Ease of disassembly – at least for the methods that permit disassembly Some disassembly is required for most products to
perform maintenance and repair
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Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
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Use of the third part component - fastener for the joining with a possibility of
disassembly
See for a good overview:
http://www.fastenal.com/web/search/products/_/N-gj4wao&
http://www.mcmaster.com/#fastening-joining
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Fastens: Screws, Bolts, and Nuts
1. Screw - externally threaded fastener generally assembled into a blind threaded hole. Some screws are self-tapping so there is no need to tap the hole.
2. Bolt - externally threaded fastener inserted into through holes and "screwed" into a nut on the opposite side.
3. Nut - internally threaded fastener having standard threads that match those on bolts of the same diameter, pitch, and thread form.
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Self-Tapping Screws
Designed to form or cut threads in a pre‑existing hole into which it is being turned.
For thicker materials, a hole needs to be drilled first, or cracking may result.
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Nut Types
Hex nut: plain type Wing nut: designed for hand tightening Nylon insert lock nut: has nylon insert to resist
loosening. Also called Nylock nut Castle nut: used with a cotter pin to prevent loosening
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Some Facts About Screws and Bolts
1. Screws and bolts come in a variety of sizes, threads, and shapes.
2. Much standardization in threaded fasteners, which promotes interchangeability.
3. Canada and US is converting to metric, further reducing variations.
4. Differences between threaded fasteners affect tooling
Example: different screw head styles and sizes require different screwdriver designs.
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Common head styles available on screws
Head Styles on Screws
Courtesy of www.mikesenese.com
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Common drive styles available on screws
Drive Styles on Screws
Courtesy of www.mikesenese.com
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Assembly functions such as fastening collars, gears, and pulleys to shafts
Setscrews
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Assembly enhancement: Screw Thread Inserts
Internally threaded plugs or wire coils designed to be inserted into an unthreaded hole and accept an externally threaded fastener
Assemble into weaker materials to provide strong threadsExpand when screwed into, in some cases
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(a) before insertion, and (b) after insertion into hole and screw is turned into insert
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Hardware component often used with threaded fasteners
to ensure tightness of a mechanical joint. Simplest form =
flat ring of thin sheet metal.
Functions:
1. Distribute stresses2. Provide support for large clearance holes3. Protect part surfaces and may help seal 4. Increases spring tension 5. Resists inadvertent unfastening
Assembly enhancement: Washer
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Washer Types
a) plain (flat) washers
b) spring washers: dampens vibration and resists loosing of bolt/screw
c) Lock washer: designed to resist loosening of bolt/screw
d) split lock washer: designed to resist loosening of bolt/screw
(d)
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Use of the third part component - fastener for the permeant joining
Rivets
Unthreaded, headed pins used to join two or more
parts by passing the pin through holes in parts and
forming a second head in the pin on the opposite
side
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Five Basic Types of Rivets
(a) Solid, (b) tubular, (c) sem itubular, (d) bifurcated, and (e) compression
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Applications and Advantages of Rivets
1. Used primarily for lap joints.
2. A primary fastening method in aircraft and aerospace industries.
3. Advantages:
High production rates Simplicity Dependability Low cost
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Tooling and Methods for Rivets
1. Impact - pneumatic hammer delivers a succession of blows to upset rivet.
2. Steady compression - riveting tool applies a continuous squeezing pressure to upset rivet.
3. Combination of impact and compression.
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Fastening with Eyelets
(a) Eyelet, (b) assembly sequence: (1) inserting eyelet through holes and (2) setting operation
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Summary
1. Mechanical assembly concept – providing force
constraints on two parts mechanically.
2. Assembly can be: permanent and disassemble.
3. Dissemble possibility: bolts-nuts, screw.
4. Permanent: rivets.
5. Rives: cheap, efficient used in aircraft, ship.