Specialized Turning Blog

Solving Stainless Steel Machining Issues

Posted by Chip Holm on Feb 26, 2021 4:24:31 PM

Avoiding Timely and Expensive Problems

If you are in an industry that requires parts machined from stainless steel, you know that thin cross sections over singular and multiple diameters can become distorted and cause runout and concentricity problems. The materials, due to its fabrication and manufacturing at the steel mills, have inherent stresses built into them. While these stresses can be taken out through certain annealing operations, the fact remains that these stresses will remain in the body of the part and will be released when heat and pressure is applied through the machining process.

Stainless Steel Machining Properties

Being a nickel alloy, this family of steels can create machining problems for tooling and part geometry. In stainless steel machining, time-tested procedures are often upset by the thin wall geometries, even on repeat jobs. As an example, this can cause the aforementioned runout and concentricity issues, deformities and finishing inconsistencies, create calibration and tolerance issues, affect quality, and ultimately slow down production. To avoid this, each part requires careful process planning.

Stainless steel machining

Specialized Turning manufactures a thin-wall bearing seat for an aerospace engine that requires six different outside diameters and four internal diameters with a .0.059/.057” wall thickness across a 1-5/16” span. The diameter of the part is a little less than 3.5” and the smallest internal diameter is a little less than 2.5”. The part is manufactured from 17-4; heat treated to condition H900.

The trick is to hold the longest diameter to a .0004” tolerance while keeping the concentricity to .001” of the internal diameter, since the beefier section is where seven different diameters come together and taper or step down. The opposite end has five random and distinctly different slots cut around the flange portion. These attributes led to a release of stresses from both ends.

Even in the best of outcomes, the yield rate would be about 75%, with the customer rejecting a few more parts as the stresses relaxed over time in shipment to the customer. While the .0004” diameter could be held, the concentricity would collapse and be out of tolerance. Even a .0001” deviation was cause for rejection; no deviations were accepted. Finally, in desperation, Specialized Turning realized in order to keep the business and the customer, something had to change.

Solutions for Machining Stainless Steel

We set out to find solutions to avoid these complications. By making modifications and creating a proprietary process, Specialized Turning was able to remove this miniscule distortion and meet the requirements of the part, creating a more consistent and high-quality part for the customer. We put our years of expertise in machining thin-wall cross-sectioned parts on all alloys for your unique part and component applications. Our stainless-steel machining experts have years of experience working with different grades of this specific alloy.

While each type of material has its own intricacies, we match state-of-the-art tooling geometries and coatings along with our years of experience to ensure the most economical stock removal rates at the highest speeds possible for economical machining.

Let’s talk about your most demanding machining needs. We’d love to get the conversation started. Contact us today!

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