What do you do to keep parts from warping in heat treat?

[danielm]

I have relatively little H/T experience here....

 

The parts are roughly 12" X 6" X 4" and are roughed prior to heat treat. H/T is a double temper proccess. Parts are roughed prior to h/t to +.050" xs.

 

Can I make a brace or fixture that I could bolt the parts to that would keep them square during h/t? What kind of mat'l would it be?

[ablucra]

Is the heat treat done in house? Most distortion will come from the quenching.

From the thumbnail view in middle I would suspend part from both ends and lower

the part into quench tank as even and quickly as possibly. Keep the part suspended

once in quench moving part around as to keep even temp. HTH

[danielm]

Is the heat treat done in house? Most distortion will come from the quenching.

From the thumbnail view in middle I would suspend part from both ends and lower

the part into quench tank as even and quickly as possibly. Keep the part suspended

once in quench moving part around as to keep even temp. HTH

 

 

 

H/T is farmed out to a pretty reputable company. We're talking to the company about what they think can be done. It just seems to me that atleast the parts should repeat, but they're all over the place .010" here .030" there...

[K2csq7]

H/T is farmed out to a pretty reputable company. We're talking to the company about what they think can be done. It just seems to me that atleast the parts should repeat, but they're all over the place .010" here .030" there...

 

 

As my experience in this trade grows.... so does the stock I leave on parts going to HT.

 

How many are you talking about? Are they all roughed to +.05 already?

 

The more you try to restrain them during HT, the more they will move during finishing. (i.e. those bores would be tough to keep in-line in a free state...)

 

If you have to....

Get a big block of the same material (thicker cross sections will move much less) and bolt them down to that during HT.

The bolts will be a pain to remove after the HT process.... maybe some hi-temp screws...maybe a +.005 tap in the block...

[crazy^millman]

We always did min material removal for cross section requirements if Material needed it., Heat treated and finished after heat treat. Bringing within +.05 then heat treat is just asking for all kind of headaches.

[Newbeeee™]

I would leave around .15/.2 on all faces for this.

1st op after treat is key - do not twist or stress the part through clamping or you'll be chasing the job.

[Colin Gilchrist]

I would try leaving +.250 material all over the part, then semi-finish, re-clamp, then finish machine.

 

Since you know HT will warp the part, let it warp. Then machine into a finished state...

[Colin Gilchrist]

Dan,

 

If this is a Boeing part, they will sometimes publish specs on minimum/maximum material before heat treat. It really depends on the design group that produced the part.

 

What Newbee said is key: when the parts come back from HT, don't add any clamping stress when you machine the first op. You might have to get creative with the clamping.

[Müřlıń®]

Hog out.

 

Stress relieve.

 

Semi rough. Don't clamp a warp out. Machine it out.

 

Temper.

 

Finish machine. Don't clamp a warp out.

[crazy^millman]

Murlin my friend with all due respect that is not the best approach. I will give a case study and show what I help change at one place. Parts for 737 were being done with this approach. It was 14 set-ups per part. There was not real dedicated tooling and each set-up would take 2-6 hours average of 4. This was a family of parts and there was 8 dash numbers. They were run 3-5 times a year. The old approach took 22 weeks from start to finish. Time you got everything ready for heat treat so it all could be shipped out and got everything to the same place so it all could be shipped out for stress relieve it was just time consuming. Here you were looking at 1344-2240 hours a year just in set-ups for this one family of parts. There were several other parts that were using this same approach. Material has Roughing on slots machined leaving +.05. It got changed that the Material went out to heat treat 52rc. It was double disk ground after heat treat leaving +.05 on the thickness. 1st operation was finish machine 1st side. 2nd operation was put on 4th axis fixture then drill and countersink 100 deg holes. Put bolts in holes finish machine 2nd side. Then do last operation of drilling cross holes. It went from 14 internal operations to 4 internal operations. The setup times went from the average of 4 hours down to less that 1 hour. The reduction of time on this one family of parts paid my salary the whole time I worked there. That was only one of the parts we did there. The new apporach only took 4 weeks from start to finish.

[mkd]

what about heat treating before any machine work?

 

roughing +.05" is certainly does not leave enough material for a part that size.

[Müřlıń®]

Ron the reason I suggested stress relieving was because 4140, 4340, 4330, those types of steels that require double tempering are prone to cracking during quinching.

 

While the case cover might not need to go through that process, the other two parts that have the thru holes look like they might be critical and IMO require stress relieve process.

 

This would also help warping with the thin leg parts.

 

Stress relieving can be done in house and not require expensive and costly hteater expense.

 

You just have to get the parts up to 600 degrees and let it air cool and the process can get started as soon as they come off the machine after hogging it all out. The parts could be semi roughed the next day.

[danielm]

what about heat treating before any machine work?

 

roughing +.05" is certainly does not leave enough material for a part that size.

 

 

.050" XS is working fine...well within the amount of distortion that we're seeing. I learned today that a process called 'marquenching' can significantly cut down on warpage. Looking into that some more....

 

Further up this thread someone said that the majority of distortion happens during quenching. I wasn't aware of that,...but it makes sense considering that the material is being temperature shocked. Sort of like glass breaking under thermal stress.

[crazy^millman]

Murlin, I know the concerns and thanks for pointing them out. With today's coatings, tools and toolpath strategies you can do a lot to eliminate this from being an issue. I agree keeping it In-House is favorable but with Boeing you need to have the certificate it was done by an approved house. Unless a company goes through that process of getting approved they cannot do it in house.

[mkd]

.050" XS is working fine...well within the amount of distortion that we're seeing. I learned today that a process called 'marquenching' can significantly cut down on warpage. Looking into that some more....

 

Further up this thread someone said that the majority of distortion happens during quenching. I wasn't aware of that,...but it makes sense considering that the material is being temperature shocked. Sort of like glass breaking under thermal stress.

 

i should've known better than making blanket statements. since it is working, i would presume the material came in the hot-rolled condition?

i have had trouble with smaller parts (and similar stock before heat treat) have trouble cleaning-up due to simple linear shrinkage starting from cold rolled alloy.

[mkd]

Colin or any other heat treat Gurus,

how much hardness variation would you expect from the outside to inside core of the part. I'm thinking pre-hardend material here.

years ago i cut alot of FX-T2 which was of a similar hardness and alloy. seemed like it was thoroughly hard.

good method because what you machined is what the finished product you got. tough to cut, but with recent advance in toolpath technology it would be high on my list of things to try.

[Machineguy]

Marquenching' solves most of the distortation problem. Look at the specs for 4000 series steel. It has to be requested per spec because some dumb a.. took it out of the spec about 10 years ago. Not many houses can do this. Do you need a approved vendor?

Marquenching is uses a molten salt bath as the first quench. It stops a lot of the distortation and cracking for the 4000 series steels..

 

For the parts you are doing its the best way to go. Mag inspect should be required also.

 

Machine guy.

[Jeremy Herron@DBS Solutions™]

Heat treat and stess relieve before any machining and then Hardmill is usually my appproach on something this size, unless they specify otherwise. jm2c though.

[Müřlıń®]

I hear ya Ron.

 

I build 10-15 parts a year off old Boeing prints from the drafting table and sometimes I forget about their internial affairs....

 

It's funny how I have to make engineering design descisions on a dailey basis that affect the strength of a part it is not an issue, but you have to be on the certified Heat Treat Vendors list and own a digital discolor machine to tell ya what color gold is. They are pretty anal about heat treat...lol