machining aluminum without warping

[Bob W.]

I need to machine a piece about the size and shape of a laptop computer lid out of 6061 T6 aluminum and it needs to remain flat. What approach should I take to avoide warping due to internal stress?

 

Thanks,

Bob

[edmBosto]

I would start off with a flat piece.

I would wet grind it also before hand if it needed to be really flat. Then strap it down in its natural position when you machine it.

You may need to rough it out milling then finishing mill.

[Kevangel]

Assuming you bought it oversize, I would rough it out and then finish machine it, with stock having been takin off both sides, etc. I never have stress relieved alum.??? especially T6 which is heat treated grade. Have straightened some alum. parts in hyd. press...(I would use flood coolant and sharp cuttings tools also)

[Guest]

Bob,

 

Any chance we could get a look at the shape of that part. While I agree the vast majority of time you can do it without stress relieving it, I have had exceptions. Just finished machining one of them and I have a 3 piece order coming up that will require the same process. The customer is actually requiring it, they have provided a very specific stress relieving process.

 

What kind of flatness tolerances are you looking to hold?

[Bob W.]

Flat within a few thousandths would be fine, I just can't have it warping like a potato chip. The part is the size and shape of a laptop computer lid (~10.5" x 11" x ~.25" with much surfacing).

[Guest]

Must your part be inspected in free state or a restrained state?

 

That part, .25 thick, is going to want to warp, if you can machine one side to clean and flip it over to machine the rest. With thin parts like that it is critical to take stock off of both sides.

[Bob W.]

It will be inspected in the free state. I also do need to machine from both sides.

[Hardmill]

Rough, flip, rough, flip, finish, flip, finish.

You really need to be aware of how the part is being held.

 

 

PEACE

[Bob W.]

How much extra stock should I leave during roughing?

[Hardmill]

Id leave no more then .02-.03.

You just dont want to clamp the $hit out of it, or tighten

down too much in a vise.

 

 

PEACE

[medaq]

Also if you do have a little potatoe chip going on with your part. You can do a little hand tweaking. Setup some 3 point jacks. Inidcate right above the jacks, and set them all to 0 on the indicator. Now you can move and indicate around the part to see where surface is not flat. Apply a little force and check again. We had to do this back in the day making actuator heads. Not the most glamorous way to do it, but end results are good.

 

Also sharp tools are a must.

 

Dont use a vice imo, If you must use a vice to hold your part. Get a torque wrench so you can repeat the same amount of force from part to part. I would make a fixture and bolt it down wards though.

 

Jim

[Tim Johnson]

Does it have to be 6061-T6? If you can use cast alum jig plate.

[Bob W.]

For fixturing I was planning on using Invert-a-bolts at the corners which essentially clamps the part straight down. I also have the 6061 on hand and there isn't time to order alternative material, but it is something to think about in the future.

 

Thanks,

Bob

[Bruce Caulley]

Vacuum? We make some electronics box lids that are about 14"x14"x3/8" with 0.040" floor thickness. We suck down and skim, flip and suck down with the corners clamped, pocket out, flip onto male vac plate and finish. They stay flat as a tac. Mat=6061

 

HTH

 

Bruce

[Trevor Bailey]

rough one side and use bondo to fill, flip and final machine. bondo works great and you can cut wet with it.

 

1. rough inside

2. unclamp

3. rough back side

4. unclamp

5. finish inside

6. apply bondo....prespray with paint primer

7. face bondo flat

8. refixture and final machine

[Guest CNC Apps Guy 1]

Rough except for facing, release, face. ROugh the other Side except for facing, release then face.

 

Your part should be completely flat, then finish as normal. This worked for some NASTY 7050 Hand forged crap, should work for 6061 which is easy except for being so gummy.

[Guest]

Trevor,

 

While I find the idea if using bondo quite interesting and ingenius, the heat from the bondo curing doesn't cause any issues?

[Guest CNC Apps Guy 1]

Especially in Aluminum which has a very high expansion coefficient...

[Bob W.]

With the Bondo, how difficult is it to remove?

[bogusmill]

You mean the bondo from the part or the part thats bondoed from the machine? We machine small aluminum wings all the time and warpage is allways a problem. We use bondo to hold lots of hard to hold stuff and it takes a little work to remove but not bad. We've used Saran wrap between part and Bondo where we couldn't afford to have problems removing Bondo.

 

We've determined that 7075-T7 stays the most flat of any aluminum we've tried.

[mowens]

quote:

---

Rough, flip, rough, flip, finish, flip, finish.

You really need to be aware of how the part is being held

---

I agree; the only thing I would add is to shim when you flip to account for warpage.

[Trevor Bailey]

quote:

---

Trevor,

 

While I find the idea if using bondo quite interesting and ingenius, the heat from the bondo curing doesn't cause any issues?

---

If you spray the part with primer, the bondo comes right out. If you leave enough material on the 2nd(flip) side, there will be no warping from the "kicking" of the bondo. Depending on how big your part is also, you do not need to completely bondo the entire area. Apply a thin layer, add other blocks of aluminum to help take up space. Apply a little more bondo. By using filler "blocks", this will also cut down on heat by not having to use so much bondo over a large area.

[Roy Goncalves]

I don't take more than .020 per cut in this particular operation. 20230130_094915.heic20230130_094928.heic

[JoshC]

51 minutes ago, Roy Goncalves said:

I don't take more than .020 per cut in this particular operation. 20230130_094915.heic20230130_094928.heic

16 years later lol... you must have searched out this topic im guessing 

[Flycut]

On 10/28/2006 at 8:38 AM, Tim Johnson said:

Does it have to be 6061-T6? If you can use cast alum jig plate.

I would use Mic6 if possible.

WOW! Just noticed the date. :s