The Design Core

1. The Design Core Market Assessment Specification DETAIL DESIGN A vast subject. We will concentrate on: Materials Selection Process Selection Cost Breakdown Concept Design Detail Design Manufacture Sell

2. Screening: apply attribute limits (eliminate processes that cannot do the job) Ranking: order by relative cost (find processes that can do the job economically) All Processes Subset of Processes Prime Candidates Supporting Information: handbooks, suppliers data sheets, databases, WWW (Search “family history” of candidates) Local Conditions (does the choice match local needs, expertise etc.?) Final Process Choice Systematic Process Selection

3. SLENDERNESS Ratio of section thickness to the square root of section area: Similar to aspect ratio in 2-d COMPLEXITY Relates to the number of specified dimensions of the component and the precision required: But life is more complicated, e.g. spheres have low complexity, but are difficult to make compared with cylinders of higher complexity. We should also consider other attributes such as symmetry. Categories of Component Shape

4. Process for a Vacuum Cleaner Fan Fans for vacuum cleaners are designed to be cheap, quiet and efficient. Nylon and Al alloys have been identified as candidate materials. Net shape processing is preferred for low cost. Complexity is classified as 3-D solid.

5. Process choice is often limited by the capacity to make long, thin sections (slenderness S of a component), where Define a search region that has limits a factor of 2 on either side of the target values. The fan can be shaped in a large number of ways including die-casting for Al alloys and injection moulding for polymers. The hot working processes for metals cannot be chosen. Process for a Vacuum Cleaner Fan SLENDERNESS

6. The micro-electronic fabrication methods and sheet working processes for metals are eliminated. The search region falls in a regime in which many alternative processes are possible. Hence, in this case, we learn nothing new. Define a search region that has limits on either side of the target values. Process for a Vacuum Cleaner Fan COMPLEXITY

7. In this case almost all processes for polymers and metals are viable. Only electron beam casting is eliminated. Hence, in this case, we again learn nothing new. Define search regions that have limits on either side of the target values. Process for a Vacuum Cleaner Fan HARDNESS / MELTING POINT

8. The design constraints, R < 1 µm and T < 0.5 mm, define the search region on the tolerance/roughness process selection map. A significant number of processes are eliminated. A number of polymer moulding processes, including injection moulding are acceptable. Machining from solid meets the specifications, but is not net-shape. Many casting processes are eliminated, but pressure die-casting, squeeze casting and investment casting are acceptable. Process for a Vacuum Cleaner Fan SURFACE ROUGHNESS In the designer’s view, it is the surface finish is the discriminating requirement. It (and the geometry) determines the fan’s pumping efficiency of and influences the noise it makes.

9. Process for a Vacuum Cleaner Fan N.B. The charts can only narrow the choice. There are other considerations of course: capital investment, batch size and rate, supply, local skills etc. A cost analysis is now required to establish the best choice.

10. Forming Ceramic Tap Valves Vitreous alumina is commonly used in hot eater valves, but it may not be the best due to thermal shock. The materials selection procedure offered Zirconia as a possible alternative. How should the valve discs be shaped?

11. Process choice is often limited by the capacity to make long, thin sections (slenderness S of a component), where Define a search region that has limits a factor of 2 on either side of the target values. The ceramic discs are not particularly slender. Some metal forming and polymer moulding processes are eliminated, but we would not expect to use those processes for ceramics in any case. Hence, we do not learn much. Forming Ceramic Tap Valves SLENDERNESS

12. The micro-electronic fabrication methods and ceramic moulding processes are eliminated. Powder routes, machining and molecular methods are viable alternatives based on complexity. Define a search region that has limits on either side of the target values. Forming Ceramic Tap Valves COMPLEXITY

13. High melting point and hardness are restrictive. Machining is now eliminated. Electron beam casting, electroforming, and CVD and evaporation methods are possibilities. Powder routes emerge as the practical alternative, but can these methods adhere to the tolerance and surface finish required? Define search regions that have limits on either side of the target values. Forming Ceramic Tap Valves HARDNESS / MELTING POINT

14. SURFACE ROUGHNESS The surface of the discs must be flat and smooth to ensure a good seal between the mating faces. The design constraints, R < 0.1 µm and T < 0.02 mm, define the search region on the tolerance/roughness process selection map. Powder routes are now eliminated as they cannot give the required tolerance and surface finish. Mechanical polishing is possible. Forming Ceramic Tap Valves

15. Forming Ceramic Tap Valves No single process is ideal for producing the ceramic valve discs from zirconia. A combination of processes emerges. Powder methods can be used to form the discs. The mating faces could then be polished to the desired tolerance and surface finish.

16. Process Selection: Cost Three rules for minimizing cost • Keep things standard: It is cheaper to buy a standard part than make it in house. If nobody makes the part you want, then design it to be made from standard stock materials, and use as few of them as possible. • Keep things simple: If a part requires machining then it will need to be clamped. Keep it simple so that the number of times it has to be re-jigged is minimized. If a part requires casting the minimize re-entrant angles which require complicated and expensive dies. • Do not over-specify performance: Higher performance increases cost. Higher strength alloys are more heavily alloyed with expensive elements. Higher strength materials require more energy to form. Increased tolerance leads to higher machining or finishing costs.

17. Materials Costs

18. Process Selection: Cost Economic Criteria for Process Selection

19. Cost Modelling The producing a component consumes resources (see below). All processes consume these resources to some extent and thus a resource based approach is useful at the broad level we are dealing with.

20. Materials Tooling Time Capital Energy Space Cost: where m is the mass of material used, n is the batch size (no. units), is the batch rate (no. units per hour), tcis the capital write-off time, and L is the capital load factor (the fraction of time over which the equipment is used productively) Materials Dedicated cost/unit Gross overhead/unit This reduces to: Cost Modelling • So, Cost has 3 terms • Materials costs: independent of batch size and rate. • Dedicated capital investment (tooling, jigs, dies etc.): varies with the reciprocal of batch size. • Time dependent (operators, space, power etc.): varies with the reciprocal of batch rate.

21. Die Casting Sand Casting Labour (die) Labour (sand) Material Cost Cost Modelling: A Cast Connector Rod The materials and process selection processes have identified the sand casting and die casting processes for a connector rod. Which process is economical? . . All costs are normalized to the material cost The cost of both processes is dominated by capital and tooling costs for small batch sizes; and dominated by materials and labour costs for large batch sizes. For very large batch sizes the cost of die casting is dominated by material costs. For batch sizes < 4000, sand casting is most economical. For batch sizes > 4000, die casting is most economical.

22. 103 UNIT COST Vacuum forming Blow moulding Injection moulding 102 Contact moulding 10 1 1 10 102 103 104 105 106 107 ANNUAL PRODUCTION Process Selection: Cost

23. CASTINGS: Sand (top), Investment (bottom)

24. CNC MACHINING

25. ASSEMBLY *electronic/mechanical

26. Product Life Cycle SALES Maturity Decline Growth Introduction to market Development TIME

27. log UNIT COST log No. UNITS PRODUCED Cost Experience Curves UNIT COST No. CUMULATIVE UNITS PRODUCED

28. log £ log TIME Price pegged to manufacturing cost Pricing log £ log TIME Umbrella Pricing

29. The Design Core Market Assessment Specification MANUFACTURE Concept Design Detail Design Manufacture Sell

30. The Design Core Market Assessment Specification SELL Concept Design Detail Design Manufacture Sell