georgemohr
Well Known Member
Hi all,
This is part T-1005B. The task is to dimple the #19 holes for a #8 screw. When I examined the part, the hole was already final sized (actually it was a bit larger than #19) so I didn't drill it. And it didn't have sharp edges so I didn't debur.
The dimples were created with a pneumatic squeezer using Cleveland's #8 dimple dies. The first dimple below shows the crack at 12 o'clock. Note that all of the cracks happened at the location of a dark spot on the metal. The picture of the undimpled hole shows this mark with more clarity. I believe this is some effect from laser cutting, perhaps?
Always, now that the part was toast I figured I'd experiment. I tried deburring and then also slightly overdrilling the next few holes, but both experiments cracked in exactly the same way.
Finally I decided to try drilling my own hole in the same material, deburr, and dimple. These dimples did not exhibit cracking. See the photo of the second dimple.
So my questions:
1) Is this part somehow flawed due to forming the holes?
2) What can I do to avoid this cracking?
3) Is it feasible to repair a crack like this by stop drilling a small hole in the radius of the dimple?
Thanks!
George
This is part T-1005B. The task is to dimple the #19 holes for a #8 screw. When I examined the part, the hole was already final sized (actually it was a bit larger than #19) so I didn't drill it. And it didn't have sharp edges so I didn't debur.
The dimples were created with a pneumatic squeezer using Cleveland's #8 dimple dies. The first dimple below shows the crack at 12 o'clock. Note that all of the cracks happened at the location of a dark spot on the metal. The picture of the undimpled hole shows this mark with more clarity. I believe this is some effect from laser cutting, perhaps?
Always, now that the part was toast I figured I'd experiment. I tried deburring and then also slightly overdrilling the next few holes, but both experiments cracked in exactly the same way.
Finally I decided to try drilling my own hole in the same material, deburr, and dimple. These dimples did not exhibit cracking. See the photo of the second dimple.
So my questions:
1) Is this part somehow flawed due to forming the holes?
2) What can I do to avoid this cracking?
3) Is it feasible to repair a crack like this by stop drilling a small hole in the radius of the dimple?
Thanks!
George
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