Our company has been processing a family of parts made from high strength, low alloy, 60 and 80ksi minimum yield steel plate. After laser cutting and Mig welding, we machine a series of holes using conventional drills, spade drills, boring bars and taps. The problem is we keep breaking taps of all different sizes, 5/16"-18, 3/8"-16 and even 3/4"-10. We have approached a number of industry representatives who keep moving the taps to successively more expensive versions intended for alloyed cutting, but they don’t solve the problem. Until this thing gets fixed, in order to produce a good part we need to destroy the tap that was in the hole, clean the hole out, weld it shut, and remachine the hole by hand. As you can imagine, this issue is killing delivery performance and profitability.
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Breaking taps making parts high strength, low alloy, 60 and 80ksi minimum yield
(6 posts) (6 voices)-
Posted 2 years ago #
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You've got to be getting localized hardening due to your mig and laser cutting operations. Can you draw the temper in the holes back a bit with a torch? Are you using two flute taps? If so, I'd stick with a 3 flute. I'd be inclined to open up the pilot hole slightly even if you didn't get a 75% thread.
Posted 2 years ago # -
I agree.
Reduce your drilling and tapping speeds and use a heavy sulphur-based coolant.
Use carbide tools if you can, but any tools need to be sharp, even if after only 5 cuts.
TomPosted 2 years ago # -
If this is being done on a CNC machine, another option is thread milling. There are manufacturers that make thread mills down to 2-56 threads. Also, some of the top tap manufacturers make coolant through taps. This could be another option.
Posted 2 years ago # -
Did your vendors recommend a steam oxide treatment? You didn't mention if the holes are blind or thru. Iv'e had success with gun taps on thru holes in tough, heat resistant high nickel alloy castings. The tap doesn't have to deal with stong chips in the flute. They are pushed ahead of the tap.
Posted 2 years ago # -
All of the suggestions are good. You did not say what machine you are using to tap with. The general rule is to make the minor dia as large as possible to meet the spec or print. The second is to slow the tap down, perhaps below 20 sfm. Next is a good steam oxide tap like osg or hypro. I would choose a 3 flute spiral point to start with.
Posted 2 years ago #
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