Here are  5 things that can unnecessarily add costs or delays to your Precision Machined Part:

  • Small  Order Quantities
  • Material Selection
  • Special Diameter Holes
  • Close Tolerances
  • Unnecessarily Fine Surface Finish
“Parts is parts.” But costs are influenced by decisions on manufacturability.

Small  Order Quantities are a two 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 set up 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 use must be paramount, but the material contribution to manufacturing costs need to be evaluated as well. The reduction in suppliers, suppliers’ inventories, and every one’s attention to ‘Lean’  along the supply chain means that the ‘perfect material’ for that part just might be a six month lead time 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 suopplier will need to purchase higher cost non-standard drills, reamers, and plug gages. Lead times for specials could also mean your parts are delayed while tools are made for your 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- are you asking for more precision (cost) than you need?

Unnecessarily Fine Surface Finish, like close tolerances can add higher costs when specified unnecessarily. 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 fit, sliding fit, and there is no movement on/of the surface, over-specifying surface finish can needlessly increase your part costs.

Practicing ‘Lean’ and minimizing waste is not just the responsibility of the producer. As the 5 items above point out, eliminating needless waste is also a responsibility of the customer.

As my grandparents- who came through the WWI, The Great Depression, WWII rationing, and a host of other economic and life challenges- used to say to me:

“Take what you need. No more, no less.”

I think it’s great advice.

The mechanical  properties of 17-4 PH  must be fully developed by age hardening from Condition A in order to reduce risk of failure and to take full advantage of the material’s capabilities.

Dodge Viper Throttles made by Bouchillon feature 17-4 PH shafts

17-4 PH  is a martensitic precipitation hardening (age hardening) stainless steel that can provide both high strength and excellent corrosion resistance.

In the annealed (solution treated condition- Condition A) the density of this material is 0.280 lb/in^3.

H 900 density is 0.282 lb/in^3.

H 1075 density is 0.283 lb/in^3.

H 1150 density is 0.284 lb/in^3.

These changes in density values show that this alloy undergoes a volume contraction when it is hardened. This volume contraction is predictable and must be taken into account if you are trying to hold close tolerances.

The contraction factor for the change from Condition A  to Condition H 900 ranges from 0.0004 to 0.0006 in/in or (mm/mm).

Hardening  from Condition A to Condition H 1150  contracts in the range of approximately 0.0009 to 0.0012 in/ in or (mm/mm).

Here are three reasons to NOT use 17-4 PH  in the Condition A  state:

  • The structure is untempered martensite. This means low fracture toughness.
  • The structure is untempered martensite. This means low ductility.
  • Without age hardening, this material is more susceptible to stress corrosion cracking.

17-4 PH  martensitic stainless steel can achieve high strength and superior corrosion resistance when precipitation hardened from Condition A to one of the Condition H tempers. It is used in many high performance applications made by our industry including valve parts for oilfield and chemical plant use; Fittings for aerospace and aircraft use; Jet engine componentry; Fasteners; Shafts for pumps; Dodge Viper carburetors! Many others.

In applications where high performance is mandatory, it is also mandatory to follow needed thermal treatment practices to assure the development of the full range of material properties that the material can provide.

For the savvy machinist, that also means understanding the pootential effect of that thermal treatment on final size due to dimensional contraction when hardened.

Thanks to Bouchillon for the throttle photo.

Material on Dimensional Contraction was taken from Schmolz + Bickenbach 17-4 Datasheet.

Density and European Equivalency data from  Rolled Alloys data sheet.

European designation note: Officially 17-4 PH is designated as UNS S17400. It is the US available nominal equivalent to DIN 1.4548, X5CrNiCuNb 17-4-4