How do I make this thicken? Please help!

[howiep]

Hi everyone,


I'm working on a surfacethat I need to thicken to 2mm. The best I can get is 0.9mm currently. Whatever I try it just tells me the surface "becomes self-intersecting or inverted". It doesn'tshow me where the problem is either. I've tried manipulating/smoothing it slightlybut I can't getthe thicknesspast about 1.1mm without losing the original design intent. I've also tried the automatic fit function (which has saved me on many previousoccasions).I've attached a few pics below - I'm trying to thicken it outwards by the way.


I have done the usual "offset surface analysis" thing (see the pic on the left) but I can't see anything that looks even slightly dodgy. Through various experiments I've done bycutting bits off I've found the problem is at the top (skinny) end of the part, but other than that it's a mystery to me.


I've attached a few pics and the part file. Could someone PLEASE either tell me how I might resolve the problem, or even better - have a look at the part and tell me what I'm doing wrong?


Thanks in advance for any help you guys can give me. Hopefully one day I'll be good enough at proeto pay it forward.


Cheers,


Phil2009-06-12_111738_howiep_mcad_thicken_problem.prt.zip

 

[design-engine]

approximate offset in WF5.0 uses a new algorithm to offset impossible geometry such as this you posted.

In the past, cusp geometry like this has been difficult with any tool. Pro/ENGINEER just took it up a notch with WF5.0
Edited by: design-engine

 

[howiep]

HiDesign Engine,


On another point - I actually used your "toupee method" on another part of this model. Thanks, It worked really well.


I'll have to get WF5.0 soon, I am using WF4.0 currently.


I don't think I can get my hands on WF5.0 before I need this done though. What is it that makes this geometry impossible? I can't find any of thethings that normally cause meproblems when thickening.
Edited by: howiep

 

[jsantangelo]

I tried it in WF5 and it will only thicken in that direction upto 0.9mm also.

 

[design-engine]

Mathematically the surfaces will not offset normal from itself. The surface will cusp upon itself thus fail. The approximate offset will not cusp thus approximate.

The work around is to offset the part of the surface that will offset by cutting away the part that will not offset.

 

[mcgowanp]

Simply put you do not have the room to offset the geometry.
In your thicken feature if you change the ofset from nomal to approximate and try that you will see highlighted in red the intersection between the conflicting geometry, as in the image attached, you have to open out the surface to get your 2mm ofset.

WF5 may have a new algorithim, but if you use approximate ofset, you wont have 2mm ofset, so its pretty useless for you. You need to get your base geo right first, analysis and offset is a usefull tool to get a better understanding of whats happening.
Paddy

 

[design-engine]

you could veer from nominal wall if your product is specified as plastic...that would give you fill and potential venting issues...

 

[SW]

In situations like this why can't the software just create a sharp edge where the surface self-intersects? This would effectively remove the self-intersecting surface as the internal radius reduces to zero. I appreciate that there will probably be manufacturing issues with the sharp internal corner, but at least the model wouldn't keep failing as modifications are made.

Sam

 

[design-engine]

a 'just do it' button. I like that idea.I seldom use thicken in a production model. And then only on glass or porcelain. I don't even use Thicken for carbon fiber parts.
Edited by: design-engine

 

[howiep]

I've heard that Solidworks is more capable when it comes to "just do it" abilities. That said, there are drawbacks to such an approach.


As for my part, I have cut away the really curvy bit, and prettty much eliminated that crease that runs down the centreline (see picture)and it still won't thicken past 0.9mm. The automaticfeature on the thickenworks now, but it ends up really thick and with extremelyskewed edges.


I've thickened parts with waay more curves in the past. I'm only trying to do it outwards too, which is usually easy.Is there something fundamental that I still don't undersand about thickening?


By the way, the part is to be made from pressed and crimped steel, so it needs to be a uniform thickness.

 

[howiep]

Just thought I'd let you know I made it work by reducing a lot of the curves and creases and then extending the surface at the narrow end. It seems it was having a lot of difficulty with that edge.

 

[design-engine]

if you are creating a plastic part then to veer from nominal wall will require one to pack out the tool which increases cycle time. Thick sections cause sink marks... The list goes on.

First we should ask what is your part and what manufacturing process are you considering?

If it will be sand cast vs plastic injection those offer two very different scenario for tooling.

 

[howiep]

I got the thicken to happen eventually, but at the expense of some of the finer nuances of the shape. as a resultI'm now doing the offset surface by hand in another style feature, and I'll make it a solid later. I'm aware this will lead to a varying wall section.


The version I'm working on now is to be made from nylon.I mainly do kitchenware products, and their naturemeans Ioften have to do parts with varying wall thickneses (sometimesbetween 2 and 6mm). We just slow the cycle time a bit and if it's a real problem switch to glass reinforced nylon. This approach wouldn't work if we had to makeparts as cheaply as possible, but luckily we don't.


Thanks for your interest everyone, I might post the finished shape up here when I'm done.