Joining Processes A2

Question one Products can be manufactured by either redistribution, wasting or fabrication processes. Discuss the merits and disadvantages of each type of process, making reference to specific products that you are familiar with. [24]

(Making products or components by moulding, casting or pressing). Redistribution (Making products or components by moulding, casting or pressing). Example product: - Bosch hammer drill casing manufactured from injection-moulded ABS. Benefits of making by redistribution: - Speed of production. Much faster than trying to fabricate a case. Essential for high- volume manufacture. - Complexity of design. Ergonomic grips and aesthetic styling features can be moulded into the design. - Integrated fastening methods. Holes for self-tapping screws and plastic ‘click’ fastenings can be moulded into the design. - Standardised product, exactly the same each time. - Impossible to achieve the same design features with fabrication. - Tough construction. With very few joints, the casing is resistant to impacts. Any join is a potential area for failure. Disadvantages: - High set-up costs for injection-moulding dies. - Dedicated equipment. Dies can only make one type of case and this is vulnerable to changes in market demand.

Wasting (Making products by removing material, E.g. Turning, milling, grinding, spark erosion). Example product: - Parker stainless steel biro, manufactured by CNC turning. Benefits of manufacturing through wasting: - High-quality surface finish. This would be difficult to achieve through casting, which tends to leave a pitted or rough surface. - Precision-engineered product requiring manufacture to fine tolerances. - Interchangeable parts for pens require machining of screw threads, and so forth. - High-speed, high-volume production when linked to CNC. - Wasting processes are not dedicated. CNC lathes and milling machines can be reprogrammed and retooled quickly to make alternative products, responding to market forces. Disadvantages: - Waste is produced, for example swarf, which has to be recovered and recycled, adding cost to the manufacture. - Materials such as stainless steel or titanium are very hard. They require expensive cutting tools to turn them and tools will wear quickly.

Fabrication (The manufacture of products by joining parts together with permanent joints such as welding, gluing or riveting,or with temporary methods such as screws or nuts and bolts). Example product: - Aluminium bicycle frames manufactured by MIG (Metal Inert Gas) welding. Benefits of fabrication: - Products can be made to individual customer specifications, for example custom- made bike frame to suit body size of client. - Relatively simple equipment required with less investment. - Flexible manufacture. The same equipment can be used to fabricate many different types of product. - Job satisfaction from ‘building’ a product from raw material. Disadvantages: - Highly skilled job. Demands fairly high wages. - Can be unpleasant to work in welding area – fumes, heat, welding flash, and so forth. - Requires good management of health and safety. - Relatively slow production compared to other methods of manufacture. - Some inaccuracy. Extremely difficult to fabricate identical products.

Question two Explain the joining methods used to manufacture two of the following products: car body panels; domestic appliances such as washing machines; flat-pack furniture. You should describe the type of joining method used and the reasons why each method is used. [2 x 12]

Spot welding

WELDING

Self-tapping screw

KD fittings

BONDING PLASTICS = METALS = WOODS =