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Heat Treat and shrinkage

6ballchucks

Plastic
Joined
Feb 20, 2012
Location
Marion, IA U.S.A.
Hello Folks,

I am having a repeating issue come up with some of the products coming from our heat treat department to our grind and assembly department. I have a tough time believing even with my somewhat small but growing knowledge of heat treat that this perticular thing is happening but it seems to be the root of all that is scrap in our shop.

We are having parts come out of our lathe department and sometimes off the mill and after passing through heat treat and arriving at our grind and hone dept. they are then measured and found to be a few thousandths out of print. Most often its small but occasionally its big, the CNC guys are trying to convince everyone they are "shrinking" in heat treat (and growing when necessary) and that is why they are all small.

My question is does anyone out there have anything other than their past experience that can show me so I can show to those folks here what the average "shrinkage" or "growth" of a part is after being heat treated and hardened?

I have accepted distortion of the part as a reason before but have a hard time believing I can heat a part up to 1600 degrees+ and have it shrink.

I appreciate any feedback even if it is just examples of personal experience

Adam
 
i machined some parts out of O1 drill rod, and had them heated treated, the parts did not shrink after heat treat! not even 0.001" of shrinkage.

Hello Folks,

I am having a repeating issue come up with some of the products coming from our heat treat department to our grind and assembly department. I have a tough time believing even with my somewhat small but growing knowledge of heat treat that this perticular thing is happening but it seems to be the root of all that is scrap in our shop.

We are having parts come out of our lathe department and sometimes off the mill and after passing through heat treat and arriving at our grind and hone dept. they are then measured and found to be a few thousandths out of print. Most often its small but occasionally its big, the CNC guys are trying to convince everyone they are "shrinking" in heat treat (and growing when necessary) and that is why they are all small.

My question is does anyone out there have anything other than their past experience that can show me so I can show to those folks here what the average "shrinkage" or "growth" of a part is after being heat treated and hardened?

I have accepted distortion of the part as a reason before but have a hard time believing I can heat a part up to 1600 degrees+ and have it shrink.

I appreciate any feedback even if it is just examples of personal experience

Adam
 
Hello Folks,

I am having a repeating issue come up with some of the products coming from our heat treat department to our grind and assembly department. I have a tough time believing even with my somewhat small but growing knowledge of heat treat that this perticular thing is happening but it seems to be the root of all that is scrap in our shop.

We are having parts come out of our lathe department and sometimes off the mill and after passing through heat treat and arriving at our grind and hone dept. they are then measured and found to be a few thousandths out of print. Most often its small but occasionally its big, the CNC guys are trying to convince everyone they are "shrinking" in heat treat (and growing when necessary) and that is why they are all small.

My question is does anyone out there have anything other than their past experience that can show me so I can show to those folks here what the average "shrinkage" or "growth" of a part is after being heat treated and hardened?

I have accepted distortion of the part as a reason before but have a hard time believing I can heat a part up to 1600 degrees+ and have it shrink.

I appreciate any feedback even if it is just examples of personal experience

Adam

Quite common at one place I worked was to add .005 to each surface for grind after heat treat. We never had any parts of O1, D2, A2, or M42 (just to name a few) that did not clean up. The ID grinder guys screamed if you left more than a few .001 on the shoulder at the bottom of the hole.
 
Adam,

Personal experience:

We are a tool and die outfit that also does production machining. Heat treat can have a dramatic effect on part size, both growth and shrinkage can occur and it is highly dependent on the material type and the H/T process being used. A common tool steel for example is D2, I work with one of the best HT shops in the state and they can usually keep D2 to an expansion of .0005/inch. D2 is one of the more stable steels in H/T. I have turned medium carbon steels to fine tolerances and then had them case hardened, casing will cause dramatic dimensional changes.

H/T is a science all to itself, many factors including material type, shape, cross section, previous operations, and specific H/T parameters such as temp, time at temp, quench and temper can all play a major part in dimensional stability.

If it were me I would inspect parts prior to H/T and again after to determine what is really happening in H/T. As tool makers we always assume material growth in certain applications and shrinkage in others it is a normal and unavoidable part of H/T.
 
I can show to those folks here what the average "shrinkage" or "growth" of a part is after being heat treated and hardened?

I have accepted distortion of the part as a reason before but have a hard time believing I can heat a part up to 1600 degrees+ and have it shrink.

You're going to have to give us more information about material, quench, temper, part size, tolerances, and level of quality you are willing to buy.

As far as what you want to believe you need to look at the process anew. You expect to be able to heat a part so hot it changes its very crystalline structure, violently quench that part to lock the new crystalline structure in place, and then warm the part slightly to relax the internal stresses enough the part won't break itself. All this, and you are looking to four decimal places of stability? Its doable, but not for cheap.
 
We have a problem with shinkage after HT on parts with bores, always do final machining after HT if possible.
Co2 is right do your homework before and after measurement will identify the problem!!
 
You're going to have to give us more information about material, quench, temper, part size, tolerances, and level of quality you are willing to buy.

As far as what you want to believe you need to look at the process anew. You expect to be able to heat a part so hot it changes its very crystalline structure, violently quench that part to lock the new crystalline structure in place, and then warm the part slightly to relax the internal stresses enough the part won't break itself. All this, and you are looking to four decimal places of stability? Its doable, but not for cheap.

It's doable? How? Austempering? (I think that's the right term? Heat treating in liquid salt bath, going directly to draw temperature salt bath)
 
The man needs an authoritative source he can point at, since he may not have access to the parts before heat treat... fiefdoms, you know. There was a thread about dimensional change in O-1 about a week ago, and someone posted a scan of a chart with hardness AND DIMENSIONAL CHANGE plotted for varying tempering temperatures. I don't have the book, but it was
Heat Treatment, Selection, and Application of Tool Steels

$32 at amazon.com:

Heat Treatment, Selection, and Application of Tool Steels 2E: William E. Bryson: 9781569903766: Amazon.com: Books

Dennis
 
Allow extra material before grinding. Not only does this solve any potential shrinking issues, but it also covers any issues with warping. That's how we deal with that type of work.
 
It is the responsibility of Engineers to design practical/possible parts without extraneous/superflous features or tolerances.

Its the responsibility of the lathe hand/dept to provide the part to HT is a size that will allow for full cleanup of the part post HT in the grind dept. Also, it is the responsibility of the grinder hand/dept to make sure the lathe hand/dept is told that they dont have enough stock left to clean up the parts.

It is the responsibility of both depts to take concerns to the appropriate higher ups, if either side is uncooperative. It is the responsibility of management to make sure that both sides communicate, problem solve and work together to get correct parts out the door.

It is the responsibility of machine operators and management to report to Engineers when things are problematic/unrealistic.

Ultimately, the real blame goes to management. they need to see the problem and fix it. If the problem persists, management is at fault. Additionally, it is managements responsibility to determine the cause and dictate corrective action.

(speaking as a grinderhand who has experience with running out of "grind stock" for complete cleanup)

Note: possibly, someone has taken "lean" manufacturing too seriously...

Note also: engineers should have to work in a machine shop for 1 year before being certified.
 
Tom (TDegenhart),

The chart that you posted - what size and shape does that refer to? Those can't be constants. (or can they?!!?) I would think that a 1 inch cube would change size differently than a 1 foot cube, or 1 meter cube, etc. and what shape is it? Flat bar, rod, block, sheet, etc. should change size differently from each other as well...

Think I'll go buy the book...
Cheers,
Chris
 
ha! Only 1 year? I say at least 5. Those five years of hands on experience will save more than that much time in effed up drawings and overly complicated designs.

The best engineers I ever had the privilege to work with did at least that much time on the floor before continuing their formal education and moving into engineering.
 
Adam,

By your description, it makes me wonder if the machinists are using enough coolant when cutting, or letting the part cool off before mic-ing it. At least with Stainless (304 & 316) I have seen a few thousandths change between hot in the machine and room temp parts.

Just a thought,
Rich C.
 
We were surprised by this before as well, though I know next to eff all about the science of heat threat, some 17-4 round pieces about 9" long 1" od were ending up .020-.030" shorter, going from annealed to HH1150.
 
ha! Only 1 year? I say at least 5. Those five years of hands on experience will save more than that much time in effed up drawings and overly complicated designs.

The best engineers I ever had the privilege to work with did at least that much time on the floor before continuing their formal education and moving into engineering.

No, not really. Some engineers who were on the floor for that much time before getting the BSME are incapable of thinking outside the box and are constrained in their thinking. Yeah, they can make a clear print, but so can half the other engineers with twice the imagination, half the superiority complex, and a two years working in a professional environment. That said, the ones who can make a clear print tend to have a mill or lathe in thier garage at home... but one year in a shop before being certified? get real.

to the topic at hand... I've had parts of one alloy shrink after an anneal->age cycle, and parts of another allow grow after a similar cycle. These were in high nickle superalloy castings, so I can't say how I'd expect yours to behave.

collect before and after data, on different sectional thicknesses, OD's, IDs before and after HT to truely characterize any dimensional change through the process. It's the only way to know.

-Nick
 
Having worked as a moldmaker for most of my life, material shrinkage is ALWAYS expressed as thousands per inch. Whatever material you're working in will grow or shrink as a function of it's dimensions.
I worked in S7 for the most part and heat treat was critical in the way it was done. Vacuum furnace was the best method, although more expensive. The parts were cleaner and more dimensionally stable. We had to always leave grind stock on any surface for fit, usually .010" on large parts and .005" on smaller ones. Finish hardness was between 55 to 58 Rc. Our parts usually had o-ring grooves for cooling and we never had problems holding tolerances; finish, yes.

D2 is nasty stuff to grind. It will surface burn and crystalize if you're not careful. Guys who work in D2 swear by it, we swore at it!

Richard Leed of Leed Steel once told us at a seminar "Never, ever, ever heat treat anything with a torch!"
 
Seems funny to me but some thirty years ago that's one of the first things we learned. If your going to heat treat tap the holes +.005 and leave grind stock. It don't matter who you are or what you do the part will change size when heat treated and in some cases warp. Different steels act differently O-1, A-2, D-2, and 1018 are just a few I used. Bottom line leave stock to clean up after heat treat!!!

Dave1123 I don't think I've ever heat treated O-1 without a torch you just need to learn the right way to treat then anneal it's very simple and works well.
 








 
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