PDA

View Full Version : Metal Warping?



hwingo
03-09-2015, 05:30 PM
Hi Guys,

I recently purchased a slotting saw and used it this morning. I secured a piece of 1/4" thick aluminum sheet-metal in the milling vise and cut a slot 7 inches in length. It was doing a fine job so I decided to continue and cut through the sheet producing a narrow strip of metal 0.500" wide X 1/4" thick X 7" long.

yThe strip bowed instead of remaining flat. I assume bowing is caused by internal stresses within the metal strip. The question is, how do I get the metal strip to go back to the original flat condition? I've tried several things but nothing has worked. Will heating remove stresses and *cause* the strip to "relax" and return to a flat position?

Harold

PixMan
03-09-2015, 08:21 PM
I would venture that you bought 5052 or wrought 6061, and not cold finished 6061-T651 that had been artificially aged and solution treated.

The aluminum needs to have the stress relieved BEFORE you machine it. Try heat, you got nothing to lose.

JoeLee
03-09-2015, 08:21 PM
Are you able to cut it on a table saw????? I know sometimes if you sheer narrow strips they will curl and / or twist depending on thickness but as to why that is happening when you cutting it on the mill is a good question. What size slotting cutter are you using?????? The only thing that I can think of is that your loading chips between the cutter and the two halves of alum. and that is forcing the strip to bend as you move along.

JL............

hwingo
03-09-2015, 09:04 PM
The metal is 6061 T6 aluminum. I suppose it can be cut on a table saw but greater accuracy is achieved using the mill. This piece was to have been used in a slot on a grinding table. My plan was to secure the piece to a 1/4" thick plate that's 6" wide X 7" long. The plate would slide front to back on the table top and be guided (held in register) by the piece (strip) that rides in the table slot.

I have been thinking of one last possibility. I might be able to add JB Weld between the strip and plate and clamp (compress the bow) the two pieces together thus eliminating the bow. Perhaps wait 24 hours then unclamp with hopes the cement will hold long enough for me to sink six to eight screws thus holding the guiding strip in juxtaposition to the plate.

Do you think that JB Weld might hold the strip flat when the clamps are removed?

Harold

Toolguy
03-09-2015, 09:51 PM
Drill and countersink the holes in the plate. Then put the bowed strip in the mill vise on parallels, seat it flat with a dead blow hammer and drill and tap it. With it still in the vise, screw the parts together. Done!

The part bows due to internal stresses that were released when the part was freed from the parent material. Usually the best way to straighten is overbend it the other way a little at a time in an arbor press. Check often with a straightedge and selectively work on the areas that need more.

JoeLee
03-09-2015, 09:56 PM
What I would do, since this is giving you trouble is cut it part way through on the table saw, just to score maybe .010 per pass half way through and then bend it back and forth until it breaks off, then mill it to finish width. Just allow yourself an extra 1/6" or so. 6061 shouldn't curl up. What is the width of your slotting cutter???

JL..............

hwingo
03-09-2015, 10:11 PM
The width of the slitting cutter is 3/32". Both ideas of either using the arbor press or making cuts in the metal are viable options of which I had not considered. I like both approaches.

The images shown below may help to visualize some of what I am wanting to do.

The bow is shown in the first image. The greatest amount of bow is 2.5mm. The second images shows the grinderís table and slot.
Harold

http://i234.photobucket.com/albums/ee38/hwingo_2007/Grinding%20Table%201_zpsuusjvusy.jpg (http://s234.photobucket.com/user/hwingo_2007/media/Grinding%20Table%201_zpsuusjvusy.jpg.html)



http://i234.photobucket.com/albums/ee38/hwingo_2007/Grinding%20Table%202_zpsbkfukzkf.jpg (http://s234.photobucket.com/user/hwingo_2007/media/Grinding%20Table%202_zpsbkfukzkf.jpg.html)

JoeLee
03-09-2015, 10:18 PM
Try slotting or cutting it with a thinner jewelers saw. I think what is happening is there is some stretching of the alum. due to the width of the cut and that is causing your cut strip to bow. You may be pushing through more than cutting through the material. Also I would wet it down with WD 40 as you cut. I don't know what your DOC is per pass.

JL................

Paul Alciatore
03-09-2015, 11:19 PM
Which edge is facing the camera in this photo, the 1/4" edge or the 1/2" edge?

http://i234.photobucket.com/albums/ee38/hwingo_2007/Grinding%20Table%201_zpsuusjvusy.jpg (http://s234.photobucket.com/user/hwingo_2007/media/Grinding%20Table%201_zpsuusjvusy.jpg.html)

hwingo
03-10-2015, 12:44 AM
Hi Paul,

The 1/4" edge is facing the camera. If I could push that down only 2.5mm and get it to stay then I would have it. That's not gonna easily happen. Will either have to slot the rail that's bowed or bend like suggested ...... or possibly a little of both. Once the bowed piece is closer to the plate, JB Weld will easily hold the track-rail in place allowing me the opportunity to drill and tap all the holes.

Harold

elf
03-10-2015, 12:57 AM
Why do you have to remove the clamps before drilling and tapping operations?

hwingo
03-10-2015, 01:52 AM
Why do you have to remove the clamps before drilling and tapping operations?

The clamps I have are too large to fit on my table and mill vise.

Harold

jhe.1973
03-10-2015, 03:28 AM
Hi Harold,

I would stay away from any heat to try and bend the aluminum. It would be WAAY too easy to end up taking all the 'heat treating' out of it and ending up with dead soft aluminum. Not very wear resistant if soft.

If you try the arbor press method (my first choice) I would use as hard a pieces of rubber at the ends & middle - something like auto tire hardness. The ram of the press and the supporting blocks might leave dents otherwise.

Another trick that will definitely work is to use a smooth, shiny ball end of a ball peen hammer and by supporting the side you show as the top on a flat piece of steel, tap the opposite side all along the center towards each end making sure the supporting steel is directly below the hammer.

The idea is to lengthen the bottom side by squeezing/stretching the metal a small bit on one side only w/each tap. You are not trying to bend the metal with the hammer. This will leave small dimples but that side can become the one in contact with your larger plate.

You may be surprised just how easy it is to move the metal with rather tiny dimples, not by blasting away on it.

By supporting the 'long' side on a flat surface, you are assured of distributing the forces and concentrating the stretching on the side where you want it.

I've straightened 2.5 inch diameter SS shafts this way w/o resorting to a massive press.

ptjw7uk
03-10-2015, 09:48 AM
Turn strip upside down, position and clamp at each end drill and tap in the middle - then work outwards until the clamps cannot be used!

Peter

hwingo
03-10-2015, 05:46 PM
Hey Guys,

I tried the "arbor press method" and it worked well enough to permit drilling and tapping. All went well and my project, though not complete, is on the way to completion. Once the rail was installed I squared all four sides of the plate with the rail and everything fits nicely. The next phase is to fabricate a protractor which will allow me to obtain various angles for grinding my lathe bits.

Many thanks to all for helping me to get to this point. ALL suggestions were very helpful and much appreciated. With further progress, I'll post my results.

Thanks,
Harold

boslab
03-10-2015, 07:04 PM
If you have the bit of sheet it came out of you might try cutting one at 90 degrees to the first.
Mark

hwingo
03-10-2015, 09:20 PM
If you have the bit of sheet it came out of you might try cutting one at 90 degrees to the first.
Mark

Hi Mark,

Should I expect a different result if cut at a 90 deg angle? Is it remotely possible that internal stresses run at a different angle? What should I be looking for or what different results should I expect or observe?

Harold

boslab
03-11-2015, 03:47 AM
You do get different properties depending on rolling direction, it looks like the peice is in the rolling direction, it's rolled, wound on a coil, then pulled from the coil and passed through a straightener, on thick stuff it can be just a pyramid set up, 2 rolls one side and a roll in the middle the other side and sheared into sheet size, the straightener puts just enough deformation to get the sheet flat, when you slit a straightened sheet it often reverts to the curve that was present before the straightener.
Cutting at 90, ie across the coil or 90 degrees to rolling often limits this, there is a tendency to bow but across a narrow strip it's not noticeable.
Cutting at 45 degrees to the rolling axis often leaves a twist.
Steel is the same, there are 3 axis, the steel industry call them R1, 2 and three but all the plants I went too call R1 rolling, R2 is 90 degree to rolling and R3 45 degree to rolling displaced in the rolling direction, we did come up with a R4 which was 45 degrees the other way or rolled, the steel is tested in all these directions with tensile test pieces being cut in these directions, the results are usually quite different so manufacturers can cut pits of car out of one sheet with different mechanical properties, same applied to Ali sheet, not saying that's universal but fairly in Europe. Eg land rover, jaguar and so on
Mark

Normanv
03-11-2015, 09:43 AM
Many years ago, when I was building a steam locomotive, I found that the BMS 1 1/4" x 1/4" that I was using for the connecting rods had lots of built in stress. I was horrified to see how it peeled open as I cut down the side of a 230mm piece. The cut opened out to 10mm as I proceeded down the edges. Fortunately this only happened as I roughed it out, it stayed straight during the subsequent machining.

hwingo
03-11-2015, 09:48 AM
You do get different properties depending on rolling direction, it looks like the peice is in the rolling direction, it's rolled, wound on a coil, then pulled from the coil and passed through a straightener, on thick stuff it can be just a pyramid set up, 2 rolls one side and a roll in the middle the other side and sheared into sheet size, the straightener puts just enough deformation to get the sheet flat, when you slit a straightened sheet it often reverts to the curve that was present before the straightener.
Cutting at 90, ie across the coil or 90 degrees to rolling often limits this, there is a tendency to bow but across a narrow strip it's not noticeable.
Cutting at 45 degrees to the rolling axis often leaves a twist...........................
Mark


Hi Mark,

I really didn't know the particulars but I suspected, when you suggested trying a different cut, that bowing may have something to do with the way the metal was finalized. That's interesting. Thanks for pointing that out.

Harold