Straightening 4140

[drolds]

Hi I am new to this forum and am seeking advice on the best way to strighten 4140 Ht. I have so parts that have been machined and have bowed .015" ove 24". Is there a way to straighten this without heat. The thinest part is 3/4" and the thickest is 1.5".


Thanks in advance.


Noel

 

[dbooker630]

Noel,

What condition is the steel in before machining, has it been quench-and-tempered or is it as-rolled?

At my company we straighten Q&T'd 4140 material with a at about the same size and length as your part at ambient temperatures using a Hydraulic Eitel machine.

My operators do prefer to work on them with heat, shortly after they come out of temper, or about 250F.

 

[swall]

It would help if you could be more precise about your part configuration. But from what you have stated so far, it might be preferable to clamp/fixture these parts to the desired configuration and then give them an 800F stress relief for several hours. What are your tolerances?

 

[drolds]

here is a pic of the part.I would be happy if I could get it flat within .002".The steel is 29Rc



Thanks Noel

 

[EdStainless]

booker and swall have given the two best options.

The only other pratical thing that I can think of is to use peening to straighten the parts.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[NickE]

Work wont let me see your photos.

But unless teh steel was ground it probably didn't have 0.002" flatness to begin with.

(or strip is high flatness requirement the best we can get teh mill to do is 2% of width. So for us thats a .100" wide to get 0.002" flatness. more like wire than strip.)

Heck can a milling machine cut a flat surface to 0.002"?

I know a surface grinder can.

 

[drolds]

I surface ground the parts flat within .001 bfore I machined them.I will probably talk to our heat treater on tuesday and see what he sugestes.



Noel

 

[tripleZ]

You're grinding and machining the parts before heat treatment? 4140 is oil quenched steel. If you're trying to hold tight dimensional tolerances prior to heat treating (unless using a vacuum furnace), you're fighting a losing battle. Judging from those side projections, you've also got some residual stresses in there from machining/grinding that will cause bowing/warping during a quench.

Are you roughing the form, then finishing it after heat treatment, or are you trying to finish machine the part PRIOR to heat treatment? And what medium are you using to quench the part? Finally, are you utilizing any stress relief cycles prior to heat treatment?

 

[drolds]

The material is pre hardened before machining. It is 28-32 Rc at delivery. It isn't a big deal if I can't straighten it as the parts will pull down straight at assembly.



Noel

 

[arunmrao]

How about leaving some stock for final grinding after heat treatment. This takes care of all your problems. I have always used this safe route.

 

[tripleZ]

So you're not heat treating it? If you can pull it straight, that's probably your best option. Otherwise, you can probably increase the number of setups and do it. Hog out a good portion of the stock on the top end where those projections are. I'm guessing it's bowing upwards after the large portions of material are removed. Flip it, and clean up the back end. Then flip and again and run your finish passes. Looks like there are a few other steps involved, but you get the idea. If you're only taking 0.020"-0.030" off (not in one cut) on your finish passes, you should keep your warping to a minimum.