Is it possible to achieve 0.02(mm) tolerance when cut thin tube with wire EDM ?

I need cut alot of tubes.
Its 1mm thickness,diameter from 25 to 51 mm.
The cut will be like this.



Angle of each side is about 7.5 degrees,so total 15 degrees/ 1 piecut.
Example short side is 18.2,long side is 25.6

But when cutting,the tolerance is too big.It is upto 1mm tolerence
The tube diameter tolerance is about 0.1mm
I dont care about tube diameter,just care about angle each side and length of short side and long side .


So please tell me what could be the problem.
I think the EDM guy (who makes the cuts) did not measure and having the approriate fixture for the tube.
Tube not parrallel with axis of the machine

Thank you

Yes its possible ( with the right machine and the right setup and right process). Too involved to explain the whole process here, but it won't be simple or fast. It will take multiple passes on each side which means multiple setups with fixtures. I'm thinking cut the first side (multiple passes) , then cut off (long) and cut the angle on the second side on a magnetic angle plate (holding the first side against the magnet).

With the right set-up 0.02mm should't be a problem.

Hold the tube down firmly and "zig zag" making several in succession.

Hi ronaldinho:
0.02 mm is easy to do on a wire EDM but you have a problem if your tubes are variable by +/- 0.1mm.
The difficulty is that you can make all the cuts very accurately but the small tubes will measure too big on the length of the short side and too small on the long side and the biggest tubes will all measure too big on the long side and too small on the short side if they are all cut so they're exactly the same at the axis of the tubes.
Also the fixture you make to hold the tubes will need to be able to accommodate the variable tube diameters and also accommodate out-of-round tubes.

The best way I can think of to fixture this is to make a long Vee block that sits on the front machine table and hangs into the worktank.
A separate clamp for each part is mounted to this vee and the tube is clamped horizontally with all the clamps spaced along the length; one for each part.
The clamps should not squash that part at one point like a setscrew would but should be like a hose clamp to distribute the clamping pressure.

Then the tube is sliced diagonally cutting right into the vee block and the cut sequence is rough toward the vee block, offset and skim one side of the cut on the way back out, offset the other way and skim the opposite side of the cut, back out of the cut, then move to the next cut and repeat until all tube segments are chopped to length but still clamped in the vee block.
Release all the clamps and take out your parts.
Load a new tube and begin again.
If you have very many of these to make, build your fixture so you can stack a bunch of tubes and cut several together.

Some things to watch out for:
Obviously if you are heavy handed with the clamping you'll distort the tubes.
Also your biggest tubes will sit in a different place in the vee than your smallest tubes.
If you care a great deal that the length of your segment is to size at the long end and the short end, you can compensate for the different tube diameters by doing a center-find routine before you start cutting and write the program so it can compensate for different tube diameters automatically.
So the routine is: touch the back of the tube, touch the front of the tube, split the difference to establish center, let the machine calculate the compensation factor and then let it cut.
You can write this touch routine once at the beginning of the program or, if you're very concerned about the lengths, you can do it before each cut so you compensate for clamping distortion at each station.

A bit of tuning of the offsets and you can get your tubes within microns totally automatically and without any effort at all once the program is working properly.

So this is not a difficult job: your original vendor was an incompetent hack.
Hitting your tolerance is really falling-off-a-log easy for any decent wire EDM shop, so I encourage you to find a new vendor who knows what they're doing!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

thank you guys for all useful advices
I am going to making a welding workcell (unmaned,fully automatic),for welding elbows for motorcycle exhaust pipe.So the biggest problem is accuracy of the pie cut.

Why do you need .02 mm accuracy on the length of a motorcycle exhaust that is going to be welded ?

ronaldinho_07 said:

thank you guys for all useful advices
I am going to making a welding workcell (unmaned,fully automatic),for welding elbows for motorcycle exhaust pipe.So the biggest problem is accuracy of the pie cut.

Click to expand...

Uhh... exhausts and .02mm tolerances???

RJT said:

Why do you need .02 mm accuracy on the length of a motorcycle exhaust that is going to be welded ?

Click to expand...

I have made myself a robot for welding pie cut,but the robot is taught without laser vision.It only run (line,arc)what it is taught
Each elbow included about from 4 to 8 pie cut,so example 0.02mm tolerance and i have to weld 8 pie cut
total is 7x0.02 = 0.14mm at final weld .My acceptable tolerance for the final weld is about 0.5mm for robot can be run well
Max tolerance for me is about 0.08 per pie cut
Thank you
Video will show you guys why i need a <0.07 tolerance for each pie cut

implmex said:

So this is not a difficult job: your original vendor was an incompetent hack.
Hitting your tolerance is really falling-off-a-log easy for any decent wire EDM shop, so I encourage you to find a new vendor who knows what they're doing!

Cheers

Marcus

Click to expand...

Not diplomatic but true

Now Gordon, I'm CRUSHED...DEVASTATED in fact .
And here I thought I was the absolute PARAGON of diplomacy.

Seriously though, if a wire EDM shop can't hold a dimension within a millimeter of the print, there's something seriously wrong.
That's breathtakingly terrible; I'm not sure a reasonably decent shop could screw it up that much on purpose.

As you know from your own experience; wire EDM's have one outstanding quality...they're ACCURATE.
'Nuff said.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

Do welding robots not adapt using a vision system?

Hi again Ronaldinho:
I had a good look at your processing method...very cool indeed!
However, there is a MUCH easier way to get to your goal, and that is to not cut the tube into segments but leave them attached to each other.
Make your pie-shaped cuts almost all the way through; in fact go one third into the wall at the pointy end of each cut.
Then nick one third of the way into the wall from the other side.
This will leave you with a flat hinge that is about a third of the wall thickness of the tube.
The back side nick is crucial to the success of this method; you want the hinge to be flat, thin and of constant cross section so it bends predictably.
The back side will open as the bend occurs, but the bend point is so close to that surface of the tube, the opening will be fractions of a millimeter and the TIG torch won't care at all.

now you can just bend a segment until it touches its neighbour, weld it. bend the next segment, weld it, and on and on until all segments are welded.
The great beauty of this is it solves your individual segment alignment problem without pain and allows you to keep using your robot without really changing anything.
It also gets rid of your accuracy problem because the cumulative errors will be the result of the machine precision, not the accuracy and alignment of the individual segments so the errors will no longer stack up in the same way.
Once you tune each segment length to allow for the bend radius at each hinge, all will be super consistent from that point forward and you will be able to predict the position of each weld relative to the tungsten on your TIG torch with complete confidence.
The curve radius of the overall pipe will be more consistent too.

Also, on a completely unrelated note, have you considered back purging those welds?
It'd be simple to do and a simple flow restrictor stuffed into the free end of the pipe would allow you to purge completely without using up much extra argon at all.
You'll get better (and better looking) welds that way at virtually no cost.

BTW, what material are these tubes made from?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

implmex said:

Now Gordon, I'm CRUSHED...DEVASTATED in fact .
And here I thought I was the absolute PARAGON of diplomacy.

Seriously though, if a wire EDM shop can't hold a dimension within a millimeter of the print, there's something seriously wrong.
That's breathtakingly terrible; I'm not sure a reasonably decent shop could screw it up that much on purpose.

As you know from your own experience; wire EDM's have one outstanding quality...they're ACCURATE.
'Nuff said.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

Click to expand...

I have cut other shapes ,solid steel,but workpieces is small.they cut seem ok,tolerance about <0.1mm
but when cutting this pie cut type,in first 500pcs.I have measure ,the tolerance is upto 1mm
i have classified them into 4 tolerances to use with different programs

snowluck2345 said:

Do welding robots not adapt using a vision system?

Click to expand...

No.it doesn't
that's beyond my ability.
Vision need some laser sensor
i can not afford for that

implmex said:

Hi again Ronaldinho:
I had a good look at your processing method...very cool indeed!
However, there is a MUCH easier way to get to your goal, and that is to not cut the tube into segments but leave them attached to each other.
Make your pie-shaped cuts almost all the way through; in fact go one third into the wall at the pointy end of each cut.
Then nick one third of the way into the wall from the other side.
This will leave you with a flat hinge that is about a third of the wall thickness of the tube.
The back side nick is crucial to the success of this method; you want the hinge to be flat, thin and of constant cross section so it bends predictably.
The back side will open as the bend occurs, but the bend point is so close to that surface of the tube, the opening will be fractions of a millimeter and the TIG torch won't care at all.

now you can just bend a segment until it touches its neighbour, weld it. bend the next segment, weld it, and on and on until all segments are welded.
The great beauty of this is it solves your individual segment alignment problem without pain and allows you to keep using your robot without really changing anything.
It also gets rid of your accuracy problem because the cumulative errors will be the result of the machine precision, not the accuracy and alignment of the individual segments so the errors will no longer stack up in the same way.
Once you tune each segment length to allow for the bend radius at each hinge, all will be super consistent from that point forward and you will be able to predict the position of each weld relative to the tungsten on your TIG torch with complete confidence.
The curve radius of the overall pipe will be more consistent too.

Also, on a completely unrelated note, have you considered back purging those welds?
It'd be simple to do and a simple flow restrictor stuffed into the free end of the pipe would allow you to purge completely without using up much extra argon at all.
You'll get better (and better looking) welds that way at virtually no cost.

BTW, what material are these tubes made from?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

Click to expand...

You mean this type of cut ?
Each cut through the tube (28mm tube) cost me about me about 0.26 usd (2000 cuts /order)
If i used this type of cut,i would be double ?

-Its a titanium tube ,grade 2.
There some reason that i have not purged the tube when welding.
This for small motorbike here,local selling .Under 150cc
The strength of the weld still be ok.
And the color of the weld,oh well,the customer here,they like weld with color blue,yellow...lol
I sell what my customer want

//all of these elbow,i can bend on a cnc tube bending
But the customer prefer pie cut welding than bending the tube,because pie cut welding has color lol

Sure, these could be wire edm'd to that tolerance but I don't think anyone would do it for 26 cents a piece........

Sent from my Nexus 5X using Tapatalk

Hi again Ronaldinho:
The cost should be less overall to do it the way I described.
The reason is that you no longer need exquisite precision to make your parts.
The first email I sent described 3 passes for one slice.
the first was a roughing pass.
The second and third cleaned up each side of the slot to give you one finished side on each slice of pie.
You cannot get 0.02mm precision on any wire I've ever used with a single pass especially with large diameter thinwall tubing.
The reason is that roughing passes are done with higher flushing pressures directed at both sides of the cut and with low wire tension to keep the wire from breaking.
So the wire flops around a bit and the thin tubing walls make the flow path complicated so the wire flops around a lot more when you cut tubes than when you cut solid blocks.
Now if you no longer need that level of precision, you can do everything in one vee shaped path for each weld joint rather than three separate cuts for each joint.

The cut path is longer, but it all goes quicker because it's just a roughing pass, not a rougher and two skims.
The nicks on the back take seconds each so they don't really count.

Davkult pointed out these cuts are going to take a LOT more than 26 cents if you had them cut in North America.
I can't buy the brass wire and the electricity for the machine at 26 cents per cut.
Obviously the prices are very different in Vietnam!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

davkult said:

Sure, these could be wire edm'd to that tolerance but I don't think anyone would do it for 26 cents a piece........

Sent from my Nexus 5X using Tapatalk

Click to expand...

implmex said:

Hi again Ronaldinho:
The cost should be less overall to do it the way I described.
The reason is that you no longer need exquisite precision to make your parts.
The first email I sent described 3 passes for one slice.
the first was a roughing pass.
The second and third cleaned up each side of the slot to give you one finished side on each slice of pie.
You cannot get 0.02mm precision on any wire I've ever used with a single pass especially with large diameter thinwall tubing.
The reason is that roughing passes are done with higher flushing pressures directed at both sides of the cut and with low wire tension to keep the wire from breaking.
So the wire flops around a bit and the thin tubing walls make the flow path complicated so the wire flops around a lot more when you cut tubes than when you cut solid blocks.
Now if you no longer need that level of precision, you can do everything in one vee shaped path for each weld joint rather than three separate cuts for each joint.

The cut path is longer, but it all goes quicker because it's just a roughing pass, not a rougher and two skims.
The nicks on the back take seconds each so they don't really count.

Davkult pointed out these cuts are going to take a LOT more than 26 cents if you had them cut in North America.
I can't buy the brass wire and the electricity for the machine at 26 cents per cut.
Obviously the prices are very different in Vietnam!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

Click to expand...

thank again Marcus !
I will buy an old wire EDM and trying your advices,old chinese made machine (with new electric cabinet) is about 3700usd.In vietnam,they usually use molybdenum wire instead of brass wire,because the wire is reusable.Each molybdenum coil (about 2000 meters) ~ 25-28usd

I love that you're wirecutting and welding just to give an exhaust pipe color.

That said, why not bend the pipe to the required form, then either do some surface-level welding to get the look, or, if you must have cuts for the weld to get the right look, make some partial wire cuts - not far enough through to make the whole thing really flexible, just enough to give you something to weld up? Either way it'd be a whole lot less cumbersome than making all those wedges and then having to line them up...

OffsetLeft said:

I love that you're wirecutting and welding just to give an exhaust pipe color.

That said, why not bend the pipe to the required form, then either do some surface-level welding to get the look, or, if you must have cuts for the weld to get the right look, make some partial wire cuts - not far enough through to make the whole thing really flexible, just enough to give you something to weld up? Either way it'd be a whole lot less cumbersome than making all those wedges and then having to line them up...

Click to expand...

the weld

because i want to make a workcell,fully automatic
there are 2 problem :
-bending thin wall titanium have big tolerance between the bends,so i can not weld on my robot
-when you bend you need to cut both side of tube after the bend,waste lot of titanium tube

Yes,i will try that way as soon as possible when i buy a wire edm.
Hope it works

OK, just my opinion here but, cutting these from tube (especially cutting them in a wire-edm) only to weld them into an exhaust tube is a ridiculous waste of time and money ... and a wire-edm that could be doing something more useful.

Cut them from flat sheet, roll them and weld them yourself.

You've already got the welder ...

Should be way cheaper, much faster, and you ought to be able to hit your numbers every time.

KilrB said:

OK, just my opinion here but, cutting these from tube (especially cutting them in a wire-edm) only to weld them into an exhaust tube is a ridiculous waste of time and money ... and a wire-edm that could be doing something more useful.

Cut them from flat sheet, roll them and weld them yourself.

You've already got the welder ...

Should be way cheaper, much faster, and you ought to be able to hit your numbers every time.

Click to expand...

This is what I initially thought of suggesting, however if he cuts, rolls and welds the pipes he should make one more longitudinal weld which will look really awkward on a bike exhaust. Compensating for this will be first making the longitudinal weld to the pipe and then grind the weld which first of all I can't think of a way that wouldn't suggest about the weld (maybe ask the customer if the longitudinal weld is not on the visible side but rather oriented towards the bike or the road? this would eliminate the need for grinding it) and second - it's titanium which adds a new level of complexity to the process. implmex made a really good suggestion on the process.