Your Customer's View of Cost
It costs your customers to operate your product. They will consider operating cost as part of the life-cycle cost when deciding whether or not to buy your product. A machine, which requires a skilled operator, costs more to operate than a machine, which requires only an unskilled operator. A machine which requires two operators costs more than a machine which requires one. A machine which requires frequent replacement of expensive components and supplies, such as special fuels and lubricants, costs more to operate than a machine which requires few replacements and supplies, both of which are inexpensive and readily obtainable. A machine which is more energy-efficient costs less to operate than one which is less energy-efficient.
To your customers the performance of the product can be measured as a cost. A fast machine is more cost-efficient than a slow machine. An accurate machine has cost benefits as compared with an inaccurate machine.
The cost of maintaining your product is of great importance to your customers and is part of their life-cycle cost. This cost includes both preventive (routine) maintenance and corrective maintenance (in case of a failure). Maintenance cost is affected by the skill required, the special tools required, the cost of replacement parts and supplies, and the time out of service required for maintenance.
Life-Cycle Cost
A valuable way for your customers to consider the cost of your product is its life-cycle cost. This is the original cost plus the operating cost plus the expected maintenance cost for the anticipated life of your product. From the customers' point of view it may be more desirable to spend more up front and have less operating and maintenance cost, or, if their available money is limited at present, they may prefer a lower initial cost at the expense of higher operating and maintenance cost. Furthermore, if they anticipate major modifications of the product as time goes on, they may well prefer a lower initial cost since there will be less cost thrown away when modifications are made. The importance of all this to you, the designer, is that you should get in the habit of thinking like your customers so that you will please them with your product to persuade them to buy it, endorse it to other prospective customers, and come back for more.
Some Ways to Reduce Costs
It is your responsibility to design for low cost; in almost every case your employers want you to do so and in their mind are paying you to do so. We sometimes hear of special market situations in which high cost is deliberately sought, but these are most unusual.
It's not easy. Anyone can make a product a little cheaper and a little worse. (Anyone can also make it a little better but a little more ex-pensive.) Your challenge is to make it just as good or better and a little cheaper too. This is an ongoing struggle for two-way winners. There is as much professional challenge in cost reduction as there is in making the product work in the first place.
Here are some techniques you can use:
Better tolerance
Study the dimensional combinations and tolerances of your parts. Can your assemblies be designed so that looser-tolerance parts will work? Are the tolerances stated on your drawings really the tolerances needed, or are they arbitrary "standard" tolerances which add cost without having real value?
There is a great tendency on the part of drafters and junior designers to use standard tolerances. Standard tolerances are usually either too tight or too loose. You may not want to spend the time to do a complete tolerance analysis for every detail drawing. However, you should scan all drawings looking for tolerances which may add unnecessary cost. When looking for tolerances, also look for dimension arrays (which point is dimensioned from which reference point) to permit a system of dimensions and tolerances having the least cost to manufacture. In making a tolerance study bear in mind the nature of the process to be used in making the part. Parts made in molds and dies have uniform dimensions, but those dimensions will all have tolerances.
Other processes, particularly those involving human operations in setting a dimension, are subject to human skill and must be tightly controlled by tolerances and inspection. Inspection itself is a cost, and reducing this cost and the cost of inspection errors is one of the motives for automation.
There is often a great deal of benefit to using match notes on the drawings of parts which go together instead of tight tolerances for the individual parts. You may want to line up two holes in part A with two holes in part B within 0.001 in, but you don't care whether the space between the holes varies from its nominal as much as 0.100 in. Attending to such considerations can save very substantial amounts of money in the cost of your product with no loss of quality.
Minimize part count
In electronic circuits minimizing the part count not only reduces cost but increases reliability. You can do it if you really try. In mechanical devices you can often combine parts into a single part.
There is a design doctrine which says that parts should be dimensioned for function without regard for manufacturing processes. This is a costly oversimplification. You should think of both and design for both.
Value engineering
Some years ago someone coined the term "value engineering" and built a career on it. Value engineering is simply second-guessing a design to make it better and cheaper. It is a good thing to do, although one should remember that it is itself an additional engineering cost. You should do it all the time while you are designing.
Design for easy assembly and automatic assembly
Have you designed for easy assembly? Have you visualized the assembly procedure as if you were an assembler on the bench? Have you designed for automated assembly if your quantities suggest the possibility of such manufacturing technology?
