IB Design and Technology Product Development Manufacturing Techniques

 Designers need to understand a wide range of manufacturing techniques to match their knowledge of materials. It is important to understand how the different techniques link together in the manufacture of a product. During manufacture material is usually first shaped crudely, then more precisely into finished parts or components and then assembled. Some products are made by a single technique although most require a mixture of techniques.

Manufacturing Techniques A finished product may be required in any one of an innumerable number of shapes and sizes, and there are many different techniques by which to produce the article. These techniques can be categorised into three major groups – shaping, joining and wasting.

Manufacturing Technique A manufacturing technique is a specific manufacturing term – sometimes relating to one material group only, eg Injection moulding The Manufacturing Processes (Techniques)/Materials Matrix details the techniques suitable for different materials.

Manufacturing Techniques – Materials Matrix TimberMetalCeramicsPlasticsTextilesFoodcompo sites Manufact uring processe s Common manufacturing techniques ShapingbendingBending, casting, moulding sintering, extruding casting, moulding sintering, casting, moulding extruding Weaving knotting knitting casting, Extruding fermenting JoiningUsing adhesives using fasteners jointing Using adhesives using fasteners fusing Using adhesives using fasteners fusing Using adhesives fusing stitching fusing WastingMachining Cutting by hand abrading Machining Cutting by hand abrading Machining Cutting by hand abrading Cutting by hand Machining Cutting by hand Straining heating

Shaping The process by which materials are formed into shape by particular techniques. There are 10 sub-groups within this manufacturing process. These are moulding, casting, weaving, fusing, stitching, cutting, machining, abrading, using adhesives and using fasteners.

Moulding Moulding (sometimes called forming) is similar to bending but is used when more complex shapes are required. Pressing sheet metal is one example of this process. Modern bending machines are able to produce very complex shapes out of sheet material but they need a lot of energy as large forces are required to press the metal into shape.

Metals can be moulded or formed by hand by beating using special hammers and mallets over leather sand filled bags or shaped formers.

There are several methods of moulding or forming plastics most of which we will examine later. One of the simplest methods is by vacuum forming.

Video clip – Plastic forming.mpg

A simpler method for less complex shapes is plug and yoke forming.

Once again woods are harder to mould than other materials. The most common methods of moulding woods is by lamination. This involves layering thin sheets, or veneers, of material over, or between, a forming mould and holding under pressure while the glue sets. The process can be eased by softening the veneer first by heating with steam but the bending forces must always be within the elastic limits of the material otherwise the veneers will crumple or split. If the veneers are inside a former, the force can be applied using cramps, clamps or a vice. If the veneers are over a former, however, this is not possible as the holding tool can mark and damage the woods. In this case, it is usual to use leather straps passing over the top of the mould with the force being applied by screwing them into the board onto which the mould is fixed.

Laminating is the process of building up a thick layer of material using thin layers of material joined with adhesives. Laminating produces products that need little or no specialist finishing. The process can be used to form complex shapes and surfaces and is very suitable for large surface areas. By careful material choice and preparation, combinations of material can be used to take advantage of specific aesthetic, physical or mechanical properties. The process is very labour intensive and requires the production of an accurate mould. The complexity of the shape can be limited by the glue, the clamping force available and elastic properties of the material which affect the angle of curvature attainable.

Casting Casting is a technique that can be applied to metals or plastics and involves heating the material until it liquifies and then pouring it into a hollow mould, allowing it to cool to the shape required. There are several methods of producing the mould into which the molten material is poured varying from plaster of paris to green sand through to wax. As a general rule, the harder a metal is, the higher the temperature required to melt it.

Video clip – casting.mpg

Some very soft metals (like silver or lead) can be melted by the heat from a normal cooker.

Some plastics come as a resin that can be mixed as a liquid and poured into latex moulds. As the chemical harder in the resin reacts, the material hardens and forms the shape required.

Sand Casting is a very common method of producing relatively small numbers of a component.

Casting is a process that is not only applied to resistant materials, it can be applied to foodstuffs as well!

Textiles cannot be shaped by the processes so far described. The most common method of shaping textile fibres is by weaving.

Knitting is just another form of weaving. The important feature of weaving is that fibres are cross threaded to build up a shape. It could perhaps be considered to be more like joining but is classified as a shaping technique.

Fusing Fusing is the process whereby two or more materials are joined by either: 1. Heating them until they melt and run together 2. Heating a third material until it melts and forms a join. Metals can be fused by the following processes – 1. Brazing 2. Soldering 3. Welding

You can join two metals by using a different metal with a lower melting point as the “adhesive”. When you heat the joint, the low melting point metal melts and flows into the gap. As the joint cools this metal turns solid, joining the other two pieces of metal together in a rigid, permanent joint. It is important to clean the pieces of metal to be joined. Use a flux to keep them clean when heating the joint. If they are dirty, the liquid metal will not stick to them properly so the joint will be weak or will not stick at all. Brazing and Soldering

Brazing

Soldering

Arc Welding Arc welding relies on the intense heat produced from an electrical arc. An arc forms when a current flows through two electrodes that are separated. The electricity arcs through the air, or another gas, between the electrodes and gives off light and heat. A protective viewing plate allows the welder to view the welding process without fear of damage to the eyes.

Welded Joints

`Plastics can also be joined using fusing techniques. Many plastics adhesives produce a welded joint as the solvent actually melts the plastic which runs together and fuses in a similar way to more traditional welds. In addition to solvent welding plastics can also be fused by: Frictional Welding Hot Gas Welding Fusing Plastics

Frictional Welding This technique is only suitable for similar thermoplastic material. The heat required for welding is produced by pressing the two pieces together and spinning or rotating one of them. This process is most suited to applications where the appearance of the joint is not critical and one of the parts is circular in section.

Hot Gas Welding This is a process that is very similar to gas welding for metals. In this case the plastic is heated using a stream of hot gas, usually air which is normally heated electrically. A filler rod is used to close the gap between the plastics.

Stitching  used for joining fabric together.  Can be complete by hand or using a sewing machine.  Main 2 stitches used are straight stitch and zig zag stitch.

Types of Seams and uses French Seam Double stitch seam Overlaid seam Look at your clothing, which seams have been used and where?

Cutting Task: Identify which piece of equipment is best for cutting which material from the materials matrix and why? Brainstorm additional methods suitable for cutting each material.

Machining CNC (Computer Numerical Control) CNC Milling Machine CNC Lathe

 Erosion by mechanical or particulate impact. Deburring machines for removing the burr from metal Polishing machines for metal Belt sander for timber Abrading Grinding for metal Lathe

Adhesives Data Sheet Adhesives

Fasteners for Metals and Plastics Metals and plastics can be fastened using Rivets, bolts or screws:

Wood products tend to be fastened together using nails or screws, although bolts can be used if necessary.

Wood Joints When wooden components are to be fastened using adhesive it is often good practice to use a joint to add mechanical strength to the joint.

Using fasteners in textiles  Zips  Hook and eye

Task  Using the materials matrix list the advantages and disadvantages of each manufacturing technique from the viewpoint of the manufacturer and the user.