Springback compensation

[lto]

I was wondering if anyone on this forum has a software solution to the problem of compensating the shape of a die or form to allow for springback in the material formed.

I understand that there are programs used by the auto industry in the engineering of dies for sheet metal forming http://www.dynaform.com/index.htm . I am looking for something less complex/expensive allowing compensation in a single plane only. Starting with a supplied dxf of a required finished part, and manually making adjustments in Parts Wizard has been inefficient at best. The last one I tried was basicaly a U shape although the bottom of the U was not a radius. I would ideally be able to break the shape into many small segments, adjusting the radius of each segment by a certain percentage based on the expected springback at that severity of bend.

I'm sure something like this is possible, I just haven't the time to "reinvent the wheel". Any ideas?

By the way, I'm sure someone will ask what these shapes are used for so I'll try and explain that too. I'm getting dxf's from manufacturers of high end solid wood furniture; they want us to bend a solid wood blank to a shape which will allow them to do secondary machining on CNC machines. this requires the bent parts to be considerably more accurate than those used by the hand craftsman. The shape of the form needs to allow for springback. When making these forms on with the bandsaw and sander method often it was best to adjust for minimal springback, run a test, and rmove more material where needed. This trial and error is time consuming and rarely produces a perfect shape outside of doing simple radiuses.

Thanks

[elcruisr]

Try contacting the US Forest Products Lab.

http://www.fpl.fs.fed.us/

If they don't have the answer, they usually know who does. Having dealt with a little of this before I can tell you it will vary between species and grain orientation within the same species. It will even require carefull control of moisture content from raw stock through finished product.

Eric

[ron brown]

LTO,

I would search "springback" in steam-bending of wood for boats. I seem to remember some formulas were found. The Forest Service also has "Wood as an engineering Material" in PDF form. I do not remember anything other than the most simple stuff in there.

Ron

[lto]

Thanks for the responses,

I just recovered from a hard drive problem keeping me from reading/replying here.

My problem is more in drawing springback allowances in Parts Wizard rather than dealing with the actual springback of the bent parts. Starting with properly conditioned wood and bending on a press greatly improves the shape consistency from piece to piece, that is after the molds have been perfected.

I was hoping there's a way of manipulating a shape on the screen similar to what happens when the bowstring is pulled back on a bow. Somehow CAD drawing is SO different from pencil tracing, bandsawing, disc sanding, etc. until things "look" right. When using that method I often thought there must be a better way, I just haven't found the solution yet.

I came across another thing I don't yet know how to accomplish. I need too establish a centerline of a tapered piece bent in a horseshoe shape. I thought possibly this could be done by toolpathing the shape as for a v-carving, and then converting the toolpath to a dxf. I would be grateful if someone would draw this for me or suggest how I could do it.The shape I need to centerline is enclosed in a rough blank drawing with a cross section of 2 1/4", the outer shape will be disregarded, with everthing else being included as a single piece.I will attempt to attach the drawing, I've never tried this here.


Thanks

[lto]

No luck with the dxf, I can't compress it enough to post.

[Brady Watson]

LTO,
Draw it in CAD or PW and post a screenshot of it.

-Brady

[hespj]

You could bend a blank and see what the springback is at various points and then draw a new curve in autocad with a spline which compensates the required amount:

4685

The bent wood would look like this:

4686

You would need to export from acad as dxf version 12 to turn the spline into a polyline.

......

As for the centreline on a tapered horshoe shape -
draw the shape in cad

4687

draw some random lines across

4688

trim the lines

4689

draw a spline centreline through the trimmed lines by "snapping to mid"

4690

I had to put in extra cross lines to get anywhere near centre, you'll have to put in more.

Is this what you're asking?

John

[hespj]

Upside down horshoes? Looks like my luck's run out.

[mikejohn]

Whats the snow like, John?
..........Mike

[hespj]

A few inches deep up on Exmoor, but none down here at sea level. The A30 on Bodmin Moor ground to a halt with those trapped in their cars retreating to the Jamaica Inn. We're just not used to it here.

What's the weather like out east?

John

[lto]

John H.

You've interpreted my need quite well. Now it looks like I need to check out autocad, as my only experiance is with Parts Wizard.

This is what I was trying to attach as a dxf.



4691

[hespj]

LTO, AutoCad is a bit overkill for doing this. Rhino will do it at considerably less cost. Look for simple cad software with a spline facility.