Product Design Specification

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  • Topic: Cost, Cost-of-production theory of value
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  • Published : December 15, 2012
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Points to cover in a PDS
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This section gives detailed advice on writing a PDS under the 29 headings listed below. It is therefore a good idea to write your PDS under these headings, leaving out only those that clearly do not apply. Some of the points overlap, but do not be tempted to skip any of them. Only by checking all of them can you be sure you will not overlook something important. One of the most important is the very last one. The advice for most of the points is illustrated by an example using the "Example" link. The complete example can also be read from beginning to end - see Section 6. 1 Performance

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Performance questions are usually the first to occur to engineers, so make these the first you answer. • What exactly is your product going to do?
• How fast will it run?
• Constantly or intermittently?
• Under what loads?
• For how long?

Remember, the more complex the product, the greater the likelihood of needing to specify ranges of values, rather than single, fixed values.

2 Economy
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Specifying a high performance product is one thing. Paying for it is another. Be realistic. Can the performance you desire be realised at a reasonable cost? Companies do not want to make products customers cannot afford. Also, beware of overspecifying. Whereas specialist items or one-offs are sometimes held up by belts as well as braces by over-cautious designers, mass-produced items are seldom overspecified. Companies cannot afford the unnecessary expense. 3 Target production cost

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This is an estimate of what it will cost to make your product. Set a figure early in the design process: • Be realistic. Beware of underestimating
• At the same time, bear in mind the prices of competing products; study cost patterns carefully • Estimate the cost of production in the factory. Too high a cost will price you out of the market If your company uses whole life costing, take account of maintenance trade-off and down-time.

4 Quantity
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How many units are to be produced? The numbers, too, affect production cost. One-offs usually need little tooling. Small product runs often just need cheap, temporary tooling. Large runs can mean permanent, expensive tooling.

5 Manufacturing facilities
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How much of your product is to be made in-house and how much bought elsewhere? If everything is to be made in-house, your design may be constrained by the company's existing machinery: • Check that your product can be produced on this

• Check whether there are any plans to replace existing machinery • Think ahead to later developments of your product. Will the machinery be able to cope with these too? 6 Product life span

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Estimate for how long the product is likely to stay on the market. This can affect important decisions: a long projected life span can make it worth investing in tools or plant which would not be justified for a short product life.

7 Customers
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Understanding customers' needs and preferences can greatly increase your product's chance of being successful. Find out as much about them as you can. If possible, talk to customers face to face. If not, use other methods, like postal surveys, to find out what they want.

8 Competition
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Analysing the competition your product will face is essential. A thorough analysis would cover: • all the relevant literature (possibly over a hundred papers) • any applicable patents (sometimes up to a hundred)

• competing products themselves (sometimes at least fifty). Consider not only products competing directly with yours but also similar or related ones, and not only existing products but also any others likely to be on the market when yours is released. Use parametric methods for these comparisons. This analysis can be laborious, but remember: for that very reason, not everybody does it. By analysing the competition, you could well give your product the edge.

9 Service life...
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