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Thread insert tolerance

Thread insert tolerance

Thread insert tolerance

We are having great difficulties getting the tolerance right of M10 holes in cast aluminium plates with M10 thread inserts (make helicoil).
Aluminium type "EN 1706 AC-AlSi7Mg-F" and EN 1706 AC-AlSi7Mg-T6" (F = as cast and T6 = solution treated and artificially aged).
Quality of the threaded hole before and after insertion of the insert does not comply with thread caliber 6H. The no-go end will go in 1 or more threads, in random cases more than 3 threads.
Does anyone have experience with the practical tolerance that can be reached.
Threads were manufactured at a machining company with a lot of experience.

RE: Thread insert tolerance

Aluminium castings, with and without thread inserts, are capable of tight tolerances.  6H is not a tight tolerance, so there are definite problems with your products.  I don't have any specific advice other than the usual - check material properties, tooling geometry, etc.

RE: Thread insert tolerance

A comment on CoryPad's statement on aluminum castings and tolerances.

Cast features are closely controlled usually only in die castings.  Other casting methods such as plaster cast, investment cast, V-process, etc. don't provide tolerances as tight as die casting.  Be careful, CoryPad, about making such sweepingly general statements.

RE: Thread insert tolerance


Your statement about care with sweeping statements is missplaced.  

Since the insert in question is a Heli-coil, the hole is threaded before insertion.  Threaded holes are not as-cast features.  Cored holes may be used, or a hole can be drilled into solid metal.  Then the hole would be threaded using a cutting or rolling tap.  The combination of these processes can produce tight tolerances for threads, regardless of the casting process.

RE: Thread insert tolerance

The 6H is recommended by the heli-coil
manufacturer which means it is not impractical
to call out that specification.  We do it
all of the the time in T6 treated aluminum.
It sounds like you are having taper at the start
of the holes.  What is producing this phenomenom?
Are you holes too close to the edges?  

RE: Thread insert tolerance

There could be an effect of the holes being close to the edge of the material. I also spoke with a helicoil representative and he thought that the tensile of the AlSi7Mg-F material of 140 N/mm2 was very low, he suggested to take at least the T6 with tensile 220.

RE: Thread insert tolerance

HeliCoil is a good product. Ask the Rep. for bulletin 1000
Also a copy of Mil Spec. MS33537E

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