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Straightening Flat Washers that Became Bowed After Tumbling

GreekQC

Plastic
Joined
Sep 21, 2023
I am currently having issues with flat washers that became bowed after we tumbled them. the OD is 1.500, The thickness is .014, the material is 301 Stainless 1/4 Hard. I have to be flat within .010. Any suggestions on making the parts flat? I cannot use Heat to straighten them because it will mess up the material.
 
These are stamped shims, I guess. You do the stamping? and they are flat prior to tumbling? You tumble them to debur them or to texture them? The ID is? You are making ten, 100, ten thousand? lf they are so thin, how does flatness matter? Won’t they simply conform under pressure?

Denis
 
It sounds like the tumbling is relieving some stress that was in the stock before they were stamped from it.

Perhaps running the stock several trips through some rollers before stamping can relieve those stresses. Bend it one way then back another, but to a lesser degree. Then back the first way but less still. Four or six trips, with the final one bringing it back to flat may do the trick.
 
Does it have to be 301? Stainless steel grade 301 and low carbon variants of this grade are predominantly used as high-strength stainless steel. The work hardening rates of these grades are very high, in the range of a 14MPa increase per 1% reduction in the area of cold work. As a result of this characteristic, high strength can be achieved from cold rolling and roll forming operations. Through such forming methods, strain-hardened austenite may be partially transformed into martensite. In spite of achieving such high strengths, the residual ductility in the alloy is capable of causing severe cold deformation. Tumbling will increase the surface hardness, and it probably does it unevenly. Are you tumbling for deburring or for surface finish? Can you try an alternate method for the same purpose?
 
These are stamped shims, I guess. You do the stamping? and they are flat prior to tumbling? You tumble them to debur them or to texture them? The ID is? You are making ten, 100, ten thousand? lf they are so thin, how does flatness matter? Won’t they simply conform under pressure?

Denis
Yes these are Stamped. The parts are flat prior to tumbling. We tumble for deburring and this part has a call out for surface finish. We made 10,000pcs. Flatness w/in .010 is required per the spec we are making it to.
 
Does it have to be 301? Stainless steel grade 301 and low carbon variants of this grade are predominantly used as high-strength stainless steel. The work hardening rates of these grades are very high, in the range of a 14MPa increase per 1% reduction in the area of cold work. As a result of this characteristic, high strength can be achieved from cold rolling and roll forming operations. Through such forming methods, strain-hardened austenite may be partially transformed into martensite. In spite of achieving such high strengths, the residual ductility in the alloy is capable of causing severe cold deformation. Tumbling will increase the surface hardness, and it probably does it unevenly. Are you tumbling for deburring or for surface finish? Can you try an alternate method for the same purpose?
It has to be 301 Stainless 1/4 hard per the spec requirements. We tumble after we stamp. We are tumbling to deburr and for surface finish.
 
What is your media? Perhaps a different type / size might help. How many are you tumbling at a time? Maybe slow down the vibrations? Just thinking out loud
 
I'll offer an attempt at advice with no assurance that it is good advice. I wonder if the shape of your media would help. We do parts exactly as you describe with triangle shaped media. I could imagine that our media would hit a lot on the faces of the washers just as much as it would on the edges, but it is really the edges/corners that you want to be hit. Maybe media that is pin/cylindrical shaped would not do as much to the faces and do more to the corners?

Maybe put 100 of them loose on all thread and tumble cylinders of them loosely held together so the outside edges get hit and not so much the face.
 








 
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