Chapter 2

Processes

The processes that are used to modify the shape of individual materials or combine them with others are discussed in this chapter. The large number of operations can be organised into five groups, as suggested by Carleton University Emeritus Professor of Industrial Design Wim Gilles:

1. Natural shape- Found materials require no shaping whatsoever

2. Subtraction- Cutting, shearing, grinding, sandblasting, lathing, etching, tumbling , crushing

3. Addition- Accreting (vapour forming) gluing, mortising, snapping, stitching, stapling, zipping

4. Forming- Casting, die casting, extruding , injection moulding

5. Transforming-Deforming drawing, rolling, stamping, explosion forming

6. Constructing-  combining materials using fasteners: pin joints, bonded joints, or form joints

Some of the common products produced by a number of the processes listed above:
 
 
 
extrusions in pvc and aluminum  Aluminum and zinc die-casts  injection moulded samples

The options open in the modern world of materials, and the competition that reigns can be felt in the following sample bulletin taken from the internet
 
 
Magnesium die casting vs Plastic injection molding 

A newly revised bulletin comparing material and part production costs of plastic injection molding vs magnesium die casting has been published by Hydro Magnesium, one of the world's leading suppliers of high purity magnesium die casting alloy.The bulletin, available from CWM, reflects today's materials market and the most recent processing economics, and demonstrates how magnesium die casting can offer parts at less cost than plastic, equally lightweight yet stronger and often easier to produce.Going beyond a comparison of average material price per lb., the analysis compares the cost of alternate materials to achieve equal performance properties. Achieving sufficient stiffness is essential to the performance of many products.Higher Performance, Lower Costs. One of several data charts in the bulletin illustrates the relative weights and costs of plastics to provide stiffness equal to that of magnesium. The analysis demonstrates how price can often be misleading if material performance is not considered.Similarly, the relative weight and price of materials shows that any of four enhanced plastic resins will result in higher material costs to provide equal tensile strength to that of die cast Mg. Stability of materials is one of many properties discussed: mag parts have significantly better dimensional stability, while thermoplastics have a greater tendency for creep--with many having significantly greater thermal xpansion.Environmentally, high-purity Mg alloy offers excellent corrosion resistance; plastics can suffer ultraviolet degradation and environmental stress cracking.

 

The six groups of processes listed above apply the basic material groups to different degrees, as outlined in the following lists.

natural state (found)

subtractive (formed by removing materials) additive (formed by adding materials) forming (casting, extruding) transforming-deforming (drawing, rolling, stamping, explosion forming) constructing (materials are combined using fasteners: pin joints, bonded joints, form joints) Constructing is the method with produces almost all our consumer products: artifacts are con-structed from sub-assemblies that may be manufactured from places around the world ( A modern computer for instance often has parts from dozen different countries)
Most of the collection of the Museum of Science consists of artifacts that have been assembled  or constructed. Just to give an example:

Sample Analysis of an manufactured artifact

This Bicycle, found at a WWW bicycle store  was listed under the following description:
1937 Cleveland Welding: REDUCED Men's ballooner with 26 x 2.125 tires. Everything has been repainted by an amateur. Everything is original except wrong kickstand. Rear facing dropouts, "dog leg" crank. Triple spring saddle. An art-deco bicycle waiting for restoration. $199 .
It is a typical example of a 20th century consumer product. It is constructed  mainly of metal elements, some alloyed, and the valves of the tubes are made of brass. Parts that needed to be flexible, like inner tubes and the saddle, are made of polymers: rubber and leather. The outer tube is a composite of tensile fabric and rubber. The bicycle's hundreds of parts are joined by three joint types: pin joints (reversible: nuts and bolts; non-reversible:rivets) form joints ( the spokes hooked to the hub and joined  to the rim with adjustable screws, the  tire held by the rim, the chain on the sprocket), and bonded joints ( the lugs are welded to the frame tubes). And, of course, the comfort of the ride depends on the pressure of the gas in the tires. If a bicycle was made with bearings as demanding as those of a watch, they would be made of 'jewels', ceramics.
In this one product we see almost all material groups represented, and all joints.
In terms of  production processes: the steel tubes and rims were rolled and welded, the spokes were drawn, the rubber inner tubes were extruded, the outer tubes were hot pressure moulded, the axles and cranks were pressure forged, the ball bearings were cast and tumbled to precision, the chain guard was stamped, as were the parts of the bell, the brass tire valves may have been cast.
Some of the parts may be chrome or nickel plated, while the rest of the exposed steel has been coated with a liquid polymer paint.

OVERVIEW OF SOME VARIABLES THAT HAVE A BEARING ON MATERIAL BEHAVIOUR; read down only
 
 
 
Basic Material Types Joints that
connect materials		 Forces that work upon

assemblies

 Energy Transfer Phase Changes
Polymers Pins
non-reversible:
nails , rivets
staples
reversible
bolts		 Normal forces
forces along the axis:
compression vs tension ; 
as in pushing and pulling.
Beware: Compression easily results in buckling		 Conduction
Movement of heat through solid matter		 Solid
Ceramics Bonded
soldering
welding
heat sealing		 Shear,
forces across the axis, as in scissors, shears,slicing		 Convection
hat transfer through movement of 
molecules, in gas, liquid		 Liquid
Metals

ferrous (steel, and alloys)

non-ferrous( gold silver, copper..

 Form,
zipper
tongue and groove
Velcro
zip lock		 Torsion
twisting action, tangential
axis:
corkscrew
propellor		 Radiation
sunlight
body heat
no medium required		 Gas
Composites
materials made up of at least two components, one reinforcing the other:
steel-reinforced-concrete
straw reinforced- mud
glassfibre- reinforced- resin		 Combinations
We often use a pin joint combined with glue.
Or a form joint
combined with a pin		 Bending
Bending is a combination of shear and normal forces		 Combinations
Heat transfer often occurs through a 
combination of the three mechanisms
outlined above		 Combinations

Different phases coexist

 
 
 
The story of materials and joints is dramatically told by the Geodisic Dome designed for Expo 67 in Montreal. Originally the design called for the thousands of struts to be linked by complicated but reversible clamp-screw joints. Cost prohibited this, and the joints were welded and thus became
non-reversable.		 The covering of the dome consisted of heat formed  curved plexiglass elements. During renovation work after |Expo 67 was over a welder dropped some hot sparks on one of the plexiglass elements- it caught fire and the whole cover of the dome was ablaze in a few minutes, visible from afar by the huge black plume of smoke rising straight up. Used in large continues areas, Plexiglas is clearly not a safe material for buildings. THE FLAMMABILITY OF POLYMERS IS ONE OF THEIR  INHERENT PROBLEMS.