“Parts is parts.” But costs are influenced by decisions on manufacturability.
These five factors can unnecessarily add costs or delays to a precision machined part: small order quantities, material selection, special diameter holes, close tolerances, unnecessarily fine surface finish.
Small order quantities are a 2-edged sword. Minimizing inventory on hand is an important lean concept, but often the cost of separate setups for small runs is more expensive than holding a modest inventory. If your parts are standard to you, getting the economic order quantity correct can save you money by minimizing what you have to pay for setup costs. (And by the way, we’re working like crazy to reduce those setup costs!)
Material selection can increase costs of production and can mean missed deliveries if the grade is “just not commercially available.” Engineering requirements for the end user must be paramount, but the material contribution to manufacturing costs needs to be evaluated as well. The reduction in suppliers and suppliers’ inventories, and everyone’s attention to “lean” along the supply chain, means that the “perfect material” for that part just might be a 6-month leadtime rolling lot accumulation with no assurances of delivery.
Special diameter holes are often overlooked as a cost driver. But with every non-standard hole diameter specified, the supplier will need to purchase higher cost non-standard drills, reamers, and plug gages. Leadtimes for specials could also mean that parts are delayed while tools are made for the job. Are you certain that a standard hole size won’t do the job needed?
Close tolerances are a source of pride to the craftsmen of the precision machining industry. Our people, processes, and engineering can assure that the hole delivered is as specified. But if you specify tolerances that are “closer than needed,” the extra attention, more frequent tool adjustments and changes, and loss of productivity to make those adjustments can add incrementally to the cost. We can make what you need, but are you asking for more precision (cost) than you need?
Unnecessarily fine surface finish, like close tolerances, can add higher costs. What is the reason for the finish specified? While today’s modern tooling and machines are able to provide better surface finish than machining technology of the distant past, for some requirements a separate grinding, shaving, burnishing or other treatment may be required. If there is not really a close or sliding fit, and there is no movement on/of the surface, the surface finish may be over-specified, needlessly increasing part costs.
Lean practices and waste minimization are not only the responsibility of the producer. As the 5 items above point out, eliminating needless waste is also a responsibility of the customer.
Blog post originally from PMPA Speaking of Precision.
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