formed parts and removing the stretching

[vonhofs]

I made a "blank" for a part that we then form around a mandrel (a conical shape with ridges on it) but the formed part ends up being wider than the blank because of the stretching of the material. In real life, the "foil" we are using is not going to stretch in that direction as it is very thin and is simply not going to stretch (much).

Here are some images to help with the discussion.

Here is the blank information:

And the mandrel (it is round):

And the formed part drawing:

and a shaded view of the formed part:

Can you simply turn off the stretching of the material as it is formed?

To get the part the way it is now, I created a new part and did a merge with the blank part, converted it to sheetmetal and then did a form feature to get the new shape.

 

[srieger]

It will stretch. It may be thin enough that i may appear to be negligable as it is a function of thickness as well as material. If the blank is coming out that far off, most likely the numbers used in your stretch calculation are pretty far off.


You can adjust the values used in the calculation or you can measure the length difference of the part vs model and adjust the developed length value manually by that amount (found when you select the feature to edit).

 

[vonhofs]

Scott, can you edit the amount a feature stretches when using the form command? I can't see how to do it.

Yeah, the part will stretch some, but it is negligible because it's so thin. The metal we are forming around the blank is .038mm thick aluminum foil.

Using the blank information I have in the first image, the 9.65mm dimension, when formed, is coming out around 8mm instead of what Pro-E is figuring will be 9.71mm. That's WAY off as far as we are concerned, so we need to fix it, but the way it's set up now, if I increase the size on the blank to get the right number on the formed version, it will change the formed version as well, since they are linked.

 

[dross]

Change your K factor.

 

[vonhofs]

dross, does K factor do anything to parts that are created using the form tool? I have changed my K factor and it didn't do anything.

I am good enough at sheetmetal to be dangerous, but that's about it. I don't use it much.

 

[srieger]

Okay, reading back through the post it looks to me like you are actually using a form feature and not a bend feature. Bend allowance is not really applied to a form feature as it is not a straight forward linear or predictable stretch.


Normally with a form feature you have the blank and all the material is stretched to fit the form. The actual volume of material in the form is sort of ignored.


So, what I assume is happening is the edges of the material are essentially staying about the same size and the form feature is moving everything in between to match the die.


If you need to have both a correct finished part and a correct blank, (which I assume you do), you may actually be better off to draw the part as finished, then convert to sheetmetal and flatten.


Or, simply trim the formed part to what the actual part is and use this as the finished part model. I would assume this would only change based on how far around the die the form is. This would give you both the as cut blank and the as formed model.+


When you use a Flatten Form feature, no bend allowance is calculated and it simply puts the material back to the flat state by removing the merge data.

 

[vonhofs]

I am trying "Flatten form" and it isn't working. Possibly because there is not a flat surface or straight edge on the part.

FYI, this is on WF4.

 

[dross]

I don't know if the K factor affects forms.


Your formed part is going to be shorter in length than your blank. (9.8 dim)


If you created the model as a flat rather than conical, you can easily figure how much it will shrink.

 

[vonhofs]

dross, I wish I could have created a simpler part to start with, but that's what we needed for the geometry.

I agree that the formed part will be shorter than the blank, but that's not how Pro-E figured it using the form feature. I need to figure out how to correct that now. I do have an e-mail in to http://www.forming.com/ to see if their Pro-E plugin "Fast blank for Proe" will do what I hope. We shall see.

 

[dross]

I was not suggesting that you change your part design, only to make a flat model to determine how much shrinkage will occur since you are unable to flatten your formed model.

 

[vonhofs]

I got an e-mail back from Forming.com, they took my part and were able to make a blank of it, within the original model, here is what they sent back to me:

Image from the top and bottom, showing the geometry. Now we need to figure out how to work with this to get what we want the end result to be.

That is of course nobody else can figure out how to do this differently!

 

[vonhofs]

O.K., so going backwards now, it has been requested that I make a new blank for our part and then create a new model for the formed version.

Anyone know how to make a formed version of a blank that doesn't include stretching of the material and simply forming it? Maybe I should make a new thread about it.

 

[jdurston]

<h2>Perhaps you could try a "Torodial Bend"</h2>

It was originally created for tire manufacturers to take a flat strip with a geometrical pattern (like a tire flattened) and then bend in an arc to create the shape.

Beyond training, I don't have much experience with this beyond training (many moons ago), but it might be worth looking into.

Using Google, I found this reference. It's a "tweak" feature in solid mode.

http://www.frotime.com/tutorials/solid_modeling/tweak_featur es_2.aspx

Good luck.

 

[vonhofs]

Thanks, I will see if that will help.

I can't see the tutorial since I/We are not subscribers to that company, but I will still see what if anything can be done using this.