Investment casting - Parts bends during casting process 2

[fronse]

Hi

I have a problem with die-casted stainless steel(316) parts, that tends to bend during the casting process. It resolve in a lot of work on the parts afterwards to fit the tolerances. My idea is that the bending has something to do whit the cooling process. Hope someone can explain to me what might cause this problem.

I am new to investment casting, and the chinese suplier of cast parts my company use, seems to have a lack of knowledge about the process.

If any further informations is needed please ask.

Michael

 

[arunmrao]

Your question is not clear regarding the process used for manufacture. Diecast? Please check once more with your supplier,investment cast,then there are many reasons,in one short statement it is lack of process controls.

 

[EdStainless]

It could be solidification or cooling after the part is solid.
If these are investment castings then you may need to modify the pattern so that the part starts bent the other direction. If you try to stiffen it so that it does not bend it may crack or tear.

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Plymouth Tube

 

[swall]

The wax investments (i.e. patterns) could be bending before they are coated with the ceramic slurry. Or, the shells could be warping during firing. Or he shells are not supported properly during casting and they are sagging.

 

[JoeyV87]

It's unlikely to be the shell, you would see finning/runout if the shell bent during cast.

Depending on the part geometry, it is likely to be either wax deformation, which is easily solvable by putting in dimensional checks in wax; improper allowances for change of shape/size between wax and metal, which is much more of a trial and error process, contact an experienced die-make; or deformation on cooling. Since 316 is fully Austnintic, it is not as prone to bending during cooling as other steels, so if the parts are fairly small it is unlikely.

Finally, consider that if you are finishing/machining the surfaces of the part post cast, especially without a stress relief cycle, the parts will bend because of this.

What a surprise, a Chinese foundry with a lack of technical knowledge. First time I've ever heard that...

 

[MikeHalloran]

You do realize how the process works, right?
Basically, a wax form is coated with ceramic slurry, which is then baked and filled with molten metal.

After which, the ceramic must be removed from the finished part, by blasting or tumbling or, uh, beating the crap out of the part with a hammer, which may be an integral part of your vendor's process.

I.e., if the part is at all delicate, it may be distorted by the shell removal.



Mike Halloran
Pembroke Pines, FL, USA

 

[SaeidNorouzi]

Distortion in an investment casting part has several causes.
the most important of them are distortion in was pattern and distortion during solidification.
Preventing and repairing of distortion of was pattern is easy. Using specific fixtures and pre-inserted wax parts and also using ceramic parts as positioning parts can be useful.
however, the great amount of distortion takes place during solidification.
1- Increasing superheat or pouring temperature
2- Increasing ceramic mould preheat temperature
3- Having junction of long and thin sections to a thick section which causes non-uniform thermal gradient. (in this case using insulation cover or chill plate and even using different ceramic shell thickness in different areas can be useful)

 

[blacksmith37]

I vote with Mike H ; Look at the obvious. Shake-out or knock-out and rough cutting gates and risers must be evauated. Handling is likely to be very rough at this stage.

 

[ornerynorsk]

I concur with Joey regarding your (unfortunate)choice of a Chinese foundry. They are still recovering from the great leap forward and much of the "just do it and don't worry about silly details like metallurgy" attitude still pervades all sectors of manufacturing. Don't get me wrong, there are very modern and capable manufacturing plants in China, but you have no way of knowing unless you've visited in person.

 

[JoeyV87]

I'm more than aware how the process works, thank you.

Assuming that the method of knock off is not "crack the parts with a hammer" there is rarely any distortion during the process. Most people have the good sense to hit the runner instead, and certainly not to tumble off delicate parts.

Just thought I should comment that, since installing basic gauging in wax, the parts made in the foundry I work at have shown a 75% decrease in scrap for distortion.

And a friend of mine made similar progress using wax setting blocks (his place was making femoral implants)

 

[racookpe1978]

"Most people" isn't "all people" and isn't "every time the fixture is removed from the furnace by a new people" ...

What are your performance rules and who is monitoring them on all shifts over there by all people working with each mold over there every time? What training is being done when newbies come in very week from the rice field and the potato farm? So to speak, that is. 8<)