ME 330
Manufacturing Processes
MECHANICAL ASSEMBLY:
Joining Methods using Fasteners
Overview of processes
Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Mechanical Assembly: Definition
Use of various methods to mechanically attach two or more
parts together. This can be done by
Two Major Types of Mechanical Assembly
1. allow for disassembly


Use of the third part component
Use of the deformation between two components to
be assembled.
2. create a permanent joint with no possibility of disassembly

Adhesion and bonding
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
Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
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
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.
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.
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
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.
Head Styles on Screws
 Common head styles available on screws
Courtesy of www.mikesenese.com
Drive Styles on Screws
 Common drive styles available on screws
Courtesy of www.mikesenese.com
Setscrews
 Assembly functions such as fastening collars, gears, and
pulleys to shafts
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 threads
 Expand when screwed into, in some
cases
(a) before insertion, and (b) after insertion into hole and screw
is turned into insert
Assembly enhancement: Washer
 Hardware component often used with threaded fasteners
to ensure tightness of a mechanical joint. Simplest form =
flat ring of thin sheet metal.
 Functions:
1.
2.
3.
4.
5.
Distribute stresses
Provide support for large clearance holes
Protect part surfaces and may help seal
Increases spring tension
Resists inadvertent unfastening
Washer Types
a)
b)
c)
d)
plain (flat) washers
spring washers: dampens vibration and resists loosing of bolt/screw
Lock washer: designed to resist loosening of bolt/screw
split lock washer: designed to resist loosening of bolt/screw
(d)
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
Five Basic Types of Rivets
(a) Solid, (b) tubular, (c) sem itubular, (d) bifurcated, and (e)
compression
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
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.
Fastening with Eyelets
(a) Eyelet, (b) assembly sequence: (1) inserting eyelet
through holes and (2) setting operation
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.