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Rod bending and Pro/E best practices

Pearl

Rod bending and Pro/E best practices

Happy Friday, everybody!

Anybody out there willing to share some tips on bending rods and using Pro/E? We make lots of rods, and so know the basics, but it seems like our manufacturing engineers are having to go through 3 or more iterations before they get it dialed in. I am thinking this is because we are not compensating for bend back or the equivalent of a sheetmetal K-Factor.

(See attached screenshot for an example rod. Diameter is around 1/4 inch)

So my questions are these:
Do you bend rods? If so, what modeling techniques are you using?
Are you compensating for bend back through trial and error or do you have a way to calculate it?
If you are calculating bend back, how are you doing it?
What is the best practice?


-marc


1 REPLY 1

Rod bending and Pro/E best practices (Summary)

Here are all the responses that I have received to date.

*****Original Post*****

Happy Friday, everybody!

Anybody out there willing to share some tips on bending rods and using Pro/E? We make lots of rods, and so know the basics, but it seems like our manufacturing engineers are having to go through 3 or more iterations before they get it dialed in. I am thinking this is because we are not compensating for bend back or the equivalent of a sheetmetal K-Factor.

(See attached screenshot for an example rod. Diameter is around 1/4 inch)

So my questions are these:
Do you bend rods? If so, what modeling techniques are you using?
Are you compensating for bend back through trial and error or do you have a way to calculate it?
If you are calculating bend back, how are you doing it?
What is the best practice?



*****Reply 1*****
I've been using sheet metal because it has the bend allowance capabilities built in.
I start with a square section and add rounds at the end to get something round looking.
Hopefully there is a nicer way?!

Regarding bend allowances, I have had to make up my own bend tables for certain work we do because the stock tables 1,2,3 do not correspond to my manufacturing results.


Regards,

Walt Weiss


*****Reply 2*****
You could try using mechanica, but you would have to use the new Creo 1.0 version because of the non-linear requirements for your simulation.

However, surely there are some handbooks or something on this matter. Might try a google search first, then see if you can pick up a book on the cheap at either Amazon or ebay.

Steve


*****Reply 3*****
Hi Marc,
Am not doing this but can tell you that you are having the same issues that Sheetmetal does except that by fudging the K factor (based on in house info or general info you can glean for books or the web) you can get the flattened length correct in Sheetmetal. Sheetmetal does not allow for bend back nor does it locally distort the material in the bend area; all it does is set limits on that area and allow you to manually compensate.

As you say for rod, and particularly larger diameters such as 1/4", you will get really noticeable thinning on the outer surface and you will get bend-back. Nothing I know of in ProE will simulate this. You could use large deformations in Mechanica to work out the thinning and possibly the bend-back but really I think you need a more intensive package such as ANSYS to really give you these big deflection results.

However you could develop allowances in ProE yourself for the bend back based on empirical testing especially if you use a lot of the same size rod of the same specification. E.g. you could find that you need to bend +3.5degrees to get bend back to 90degrees (assumes constant bend form radius) and +5degrees for 120degrees of bend and so forth. If you see a mathematical relationship between your data points then you can calculate parameters for these bends that you call out in your model/drawing for machine set up. Complex but could be worth it to save setup time on an ongoing basis.

Hope this helps.

Regards, Brent Drysdale
Senior Mechanical Designer
Tait Radio Communications
New Zealand


*****Reply 4*****
Hi Marc,

If it is a lot, it's probably an error by the engineers. If it is a little, consider wire hardness and diameter. If those two characteristics vary, the results will vary. Small variations in angle are from the hardness - less of the rod will have plastic yield, so it springs back more. Small variations in bend-to-bend length that are not attributable to spring-back are due to the increased radius to the rod centerline as the rod diameter increases.

If you can measure the parts - record the rod diameter, the hardness, the desired bend angle, the actual angle, the desired distance between CL intersections, and the actual distance.

Some data and graphing should get you to the underlying problem. If not, write back.

Dave S.



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