Tapping problems - 3/8" hot roll pickled & oiled steel - seeking expertise

Ninja

Looking for Reality
Trusted
#11
Curiosity...what is your 'normal' tap life? 1 shift? 1 hour? 1 month?
Might be easy to set up an end of shift/month/week/whatever measurement of the tap to verify utility.
Certainly more data-centric than "it sqeals"...and might bypass/solve the issue entirely.
It would, however, require you to develop fail criteria on taps...
 

rstocum

Involved In Discussions
#12
Update for anyone interested. I did not have a good root cause for the customer so I called their quality engineer who agreed to let me get away with "reviewing all tap inventory for wear, discarding any worn taps found, training tapping personnel on tap wear issues, and raising awareness of the customers problem". No formal corrective action required.

I conducted the tap wear training the next day. I had pictures of wear on the lead cutting edge, buildup on cutting edges, chipping on cutting edges, cold welding, and bird nesting. Every operator recognized each of those conditions. Then I went over the various hole size and shape defects that can cause issues. That same afternoon one operator comes to me with a different part from the one that had the original issue. This part is also laser cut. The pierce point had a "blowout" which leaves the hole slightly oblong on the part face that was up when it was cut. He asked if that could be the problem. I had him tap it and check it. The nogo went in on that side about 4 turns. We sorted the whole job and found six parts with this condition, or worse. The laser chief told me that can happen if the surface of the sheet the parts are cut from has some irregularity. One area where the surface is bowed upward or downward a bit puts the focal point of the beam too deep or too shallow in the material and you don't get a good cut. His operators look for that, but don't catch them all. Now that the tap operators know what to look for, I expect to reduce this problem, but I don't see a good way to eliminate it, and I sure can't 100% inspect.
 
#13
Update for anyone interested. I did not have a good root cause for the customer so I called their quality engineer who agreed to let me get away with "reviewing all tap inventory for wear, discarding any worn taps found, training tapping personnel on tap wear issues, and raising awareness of the customers problem". No formal corrective action required.

I conducted the tap wear training the next day. I had pictures of wear on the lead cutting edge, buildup on cutting edges, chipping on cutting edges, cold welding, and bird nesting. Every operator recognized each of those conditions. Then I went over the various hole size and shape defects that can cause issues. That same afternoon one operator comes to me with a different part from the one that had the original issue. This part is also laser cut. The pierce point had a "blowout" which leaves the hole slightly oblong on the part face that was up when it was cut. He asked if that could be the problem. I had him tap it and check it. The nogo went in on that side about 4 turns. We sorted the whole job and found six parts with this condition, or worse. The laser chief told me that can happen if the surface of the sheet the parts are cut from has some irregularity. One area where the surface is bowed upward or downward a bit puts the focal point of the beam too deep or too shallow in the material and you don't get a good cut. His operators look for that, but don't catch them all. Now that the tap operators know what to look for, I expect to reduce this problem, but I don't see a good way to eliminate it, and I sure can't 100% inspect.
I am not sure how much you are able to experiment with the process, but you could drill the holes separately and then tap them, such as on a drill press or a CNC Mill. It would eliminate the variation from laser cutting and could better control the holes prior to tapping.
 

rstocum

Involved In Discussions
#14
I am not sure how much you are able to experiment with the process, but you could drill the holes separately and then tap them, such as on a drill press or a CNC Mill. It would eliminate the variation from laser cutting and could better control the holes prior to tapping.
Unfortunately, I am not able to change the basic process steps at all. The company is divided into two divisions. One for sheet/plate fabrication and one for machining. The machining division does not have tooling/fixturing for working on flat sheet material like these parts. The fabrication division does not have machining capability other than countersinking and tapping, and those are not done on rigid machines. I am stuck with the laser cut holes, and can only improve the process within those constraints. This is not the only problem that could be made better by being able to machine sheet parts. I can lobby for developing that capability, but there is tooling cost, and it probably won't fly.
 

Cari Spears

Super Moderator
Staff member
Super Moderator
#15
Update for anyone interested. I did not have a good root cause for the customer so I called their quality engineer who agreed to let me get away with "reviewing all tap inventory for wear, discarding any worn taps found, training tapping personnel on tap wear issues, and raising awareness of the customers problem". No formal corrective action required.

I conducted the tap wear training the next day. I had pictures of wear on the lead cutting edge, buildup on cutting edges, chipping on cutting edges, cold welding, and bird nesting. Every operator recognized each of those conditions. Then I went over the various hole size and shape defects that can cause issues. That same afternoon one operator comes to me with a different part from the one that had the original issue. This part is also laser cut. The pierce point had a "blowout" which leaves the hole slightly oblong on the part face that was up when it was cut. He asked if that could be the problem. I had him tap it and check it. The nogo went in on that side about 4 turns. We sorted the whole job and found six parts with this condition, or worse. The laser chief told me that can happen if the surface of the sheet the parts are cut from has some irregularity. One area where the surface is bowed upward or downward a bit puts the focal point of the beam too deep or too shallow in the material and you don't get a good cut. His operators look for that, but don't catch them all. Now that the tap operators know what to look for, I expect to reduce this problem, but I don't see a good way to eliminate it, and I sure can't 100% inspect.
Thanks for the follow up!!
 

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