Heat Treatment before vs after Machining
Heat Treatment before vs after Machining
(OP)
Hi,
I would like to know if anyone has experience regarding heat treatment before and after machining process.
From my knowledge, if heat treatment were to be done before machining process, special tool bit must be required because the material will be hardened therefore, typically, heat treatment is to be done after machining.
However, I'm not sure what is the effect of heat treatment on the tolerance if it is done after machining. Does anyone has any knowledge in this?
Is there any way to keep the tolerance the same before and after heat treatment?
Thanks & Regards.
I would like to know if anyone has experience regarding heat treatment before and after machining process.
From my knowledge, if heat treatment were to be done before machining process, special tool bit must be required because the material will be hardened therefore, typically, heat treatment is to be done after machining.
However, I'm not sure what is the effect of heat treatment on the tolerance if it is done after machining. Does anyone has any knowledge in this?
Is there any way to keep the tolerance the same before and after heat treatment?
Thanks & Regards.





RE: Heat Treatment before vs after Machining
RE: Heat Treatment before vs after Machining
Barry1961
RE: Heat Treatment before vs after Machining
Manufacturing Freeware and Shareware
http://mrainey.freeservers.com
RE: Heat Treatment before vs after Machining
Perhaps I should provide more info on my parts so that I could get more advice.
The material I'm using is Stainless Steel 17-4 and heat treatment to H900 and H1075. The tolerance I'm looking for is H7g6 for cylindrical interface. Is that realistic? Furthermore, if the size of the part is around 300mm to 500mm, how will the overall dimension varies? Is an overall dimensional tolerance of 0.1mm possible without grinding after heat treatment?
Thanks & Regards.
RE: Heat Treatment before vs after Machining
RE: Heat Treatment before vs after Machining
RE: Heat Treatment before vs after Machining
Is there a formula to calculate for heat shrinkage? How about warpage? I thought it is difficult to determine the kind of warpage that will be encountered?
mrainey mentioned that "... to leave .100 on all surfaces prior to heat treat. Warpage varied, but there were times when we were really glad we left so much stock...".
.100 is inches or mm? Also, how do I overcome clamping problem if I were to do grinding after clamping?
Thanks & Regards.
RE: Heat Treatment before vs after Machining
The more common parts were 6"x8" to 12" x 16". First 1/2" countersunk holes are drilled/machined on the periphery then the part is Blanchard Ground to the required thickness. At this point hundreds of 2.9mm or 3.2mm holes with L/D’s of 12 to 17 are drilled. The bottom of the hole is then coined to a 60° included angle. The coining resulted in slight bulge on the face which is lapped off using conventional abrasives to the required thickness generally .012+" over the coined area. At this point a hole of .009" dia. is either drilled, punched or EDM to the apex of the 60° cone. The hole is then broached and then the part is lapped to the required .0120" depth of the hole and a square edge on the .0090" dia hole.
These parts along with numerous other PH parts of various sizes and descriptions are being made everyday. Unfortunately not in the quantity they once were.
RE: Heat Treatment before vs after Machining
The hardened material was turned off. Didn't do any grinding, because the size and finish requirements didn't make it necessary.
The key to working with our parts after heat treat was to first chuck the distorted part in a manual chuck, using the least amount of clamping force possible. Some parts would have to be indicated in. We would then turn a perfectly round tooling diameter, with corresponding perpendicular face (light, cleanup passes only). This gave us something we could work with on the CNC lathes, with their less-sensitive power chucks, to do the actual finish turning.
Chucking a piece that was significantly out-of-round, then finishing other features on the part in that same setup, never worked well for us.
Manufacturing Freeware and Shareware
http://mrainey.freeservers.com
RE: Heat Treatment before vs after Machining
They say "Normally, these grades are machined in the solution-treated condition (Condition A) to final dimensions because then, only the simple low temperature aging treatment is required to produce the desired combinations of mechanical properties."
They go on to give the following info on machinability
Condition H-900......20 ot 30 SFPM
Condition A..........70 to 80 SFPM
Condition H-1100.....80 to 90 SFPM
Condition H1150M.....100 to 130 SFPM
The booklet has lots of other good stuff. If you can get a copy, I'd recommend it.
Regards,
RebelBrill
RE: Heat Treatment before vs after Machining
RE: Heat Treatment before vs after Machining
Thanks for the info. May I know if the title of the guide book that you mentioned? Any idea whether I can get it online?
Thanks & Regards.
RE: Heat Treatment before vs after Machining
The copy I'm using was copyrighted in 1975 by Republic Steel corporation. The only other identifiers are on the outside bottom edge of the back cover. In the left hand corner of the cover it reads "ADV. 1958R3 10M 775E". In the right hand corner of the cover it reads "Printed in U.S.A.".
On the bottom left hand corner of page 32 is the following note
"For complete information on
these and other products,
contact Republic Steel Corporation
1441 Republic Building
P O Box 6778
Cleveland OH 44101"
The booklet was available free upon request when I got mine.
Good luck,
RebelBrill
RE: Heat Treatment before vs after Machining
Thread330-113147
the above thread is carried over to Thread1135-113274 in the S.S. for engineers forum.
RE: Heat Treatment before vs after Machining