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ptc-7261111-Visitor
1-Visitor
April 30, 2012
Question

Question: Why would someone design sheetmetal parts using surfacing techniques with thicken?

  • April 30, 2012
  • 10 replies
  • 3304 views
Hello,

I have some sheetmetal parts design by another engineer (I do not know who), and I noticed that several of these sheet metal parts use surfacing features that are thickened after all the surfaces are merged together. There is nothing wrong with the sheetmetal parts are far as the design is concerned. However, I am puzzled why this person did not design the parts using sheetmetal features when surfacing was not needed to produce the geometry. Any ideas why someone would do this?

I have no problem with using surfacing techniques, and use it myself when designing molded parts. It is just that I cannot thick of a logical reason to model a sheetmetal part using surfaces when it could have been as easily modeled using sheetmetal features. One clue is that I did notice some component features dimension that reference other features in the assembly, so it appears to be related to a top-down design method.

I guess the main reason this annoys me is that the flat pattern is not as simple to create as it is from a true sheetmetal part, and the bend radius are not automatically linked to the material thickness if the gauge is changed.

Chris
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10 replies

S
sshannon1-Visitor
1-Visitor
April 30, 2012
I think the obvious answer to your question here is the original designer did not know about or how to use the Sheet Metal application.
There's a million ways to "skin a cat" using Pro-E. Being annoyed because someone else did it differently or was not required to supply a flat pattern sounds like a personal problem to me. 😉

Regards, SMS

P
ptc-7261111-VisitorAuthor
1-Visitor
May 1, 2012

From the responses I received, I should probably clarify a few things:




  • The sheetmetal models were done by an outside source and not internally (I am also an outside contractor with this company)

  • These sheetmetal parts should have been beyond the concept stage and ready from production

  • Several of the models cannot be converted to a sheet metal part by selecting a driving surface, and they needed to be remodeled in order to obtain a flat pattern

  • These parts are not stamping (where surfacing would be appropriate), but formed using a break press after laser cutting.

  • I was temporarily pulled from my project to work on another project for someone else, hence delaying both projects by several days. It was not just a few minutes or even hours of inconvience as dozens of these sheetmetal parts were modeled using surfaces and cannot be easily converted to a flat pattern.

So I am just suggesting before sending parts out for fabricationthat people model them within reason so they can be modified without waisting another engineer's time torecreate them. Earilier this year, I previously inherited some SolidWorks parts from an engineer who leftto take a job with another company. Unlike Pro/E which uses "weak" dimensions in sketches, SolidWorks permits more sloppy practices in sketches where sketches can be created without any dimensions. In the entire part with hundreds of sketches, very few sketches had any type of dimension and they were not even splines. I spend hours redefining the sketchs so I could modify a part that should have only taken minutes to update. This cost the company in both time & money as several parts were like this in the assembly. So is it really a personal problem if I am annoyed by sloppy modeling practices where someone should have known better, or at least asked for help?


So the point isthat engineers / designersshould use good modeling practices for the benefit of yourfuture predecessor or clients. If you are designing lots of sheetmetal parts formed on a break press and do not know how to use the sheetmetal module, then ask for training.


BTW, my boss was let go a few weeks ago, and mytemporary boss is in agreement with me as he feels it wastes him time as well.


Chris

In Reply:



R
Rev2_Steve6-Contributor
6-Contributor
May 1, 2012

These are valid points. It's a good reminder that our work will often be continued by someone else. The models should be robust enough to support efficient and accurate modifications. For that reason, it's prefferable to have standards and best practices in place but this isn't easy to enforce when you are sharing design responsibilities with othercompanies or contractors.

T
TimKnier1-Visitor
1-Visitor
May 1, 2012
To quote a great line from the Ghostbusters movie, "I have seen sh*t that will turn you white". Obviously whoever did this either didn't know, didn't care or was just lazy about what they were doing. We all have expectations that the people around us are competent in their jobs, but that just doesn't happen all of the time and we're left scratching our heads. Training, mentoring and best practices (standards) all help reduce incompetency but will never eliminate it. Chalk it up as a "what not to do" example for others.

Tim Knier
QG Product & Support Engineering
QuadTech
A Subsidiary of Quad/Graphics
Sussex, Wisconsin
414-566-7439 phone
-<">mailto:->
www.quadtechworld.com<">http://www.quadtechworld.com>
S
sshannon1-Visitor
1-Visitor
May 1, 2012
There's a knee-jerk part of me that just wants to say;

So what you're telling us (and your boss) is that you're incapable of coming up w/ a flat layout w/o using pro-e sheet metal. That grabbing a pencil, scratch pad, straight edge and calculator is beyond you. That your solution is to spend hours remodeling rather than 10 minutes doing it the "old fashioned way"? Then complain that it's the responsibility of other people that don't even know you or work w/ you to make your job easier?

Then there's the experienced side of me that would say;

Tell your boss to suggest to his boss that - based on the project requirements - the company recruit outside contractors that are proficient in sheet metal design. That some type of written instructions regarding CAD methodology and expectations be created and distributed. This would go long way towards eliminating unnecessary rework such as you describe.

After 30+ year career in engineering that started on the drawing board, I've learned the experienced side of me usually wins out over the knee-jerk part of me.

Regards, SMS





M
merrill.rosenow1-Visitor
1-Visitor
May 2, 2012

I've seen people do similar things becuase they were much more comfortable with one Pro/E module than another.

M
mpeterson1-Visitor
1-Visitor
May 2, 2012
Chris,

I hate to admit that many years ago I created sheet metal parts in general pro/e
solid modeling because I was new to Pro/E and well before WF the sheet metal
module was very different than the general part mode and harder to use. That
said I did make sure my part would flatten for creating a flat pattern and I
learned the ways to model to make sure it would convert to sheet metal. Years
later I worked for another company that specified that ALL sheet metal parts HAD
to be created in the sheet metal module, but that was around WF2 and sheet metal
module was much easier to use.

Related to this issue is just bad modeling practices that people get away with
not thinking about how them or someone else might need to use their model down
the road. If there are no people or software options to help police this than we
are left with what each person will do on their own and thus you have robust
models from people who care or who are thinking about work down the road and
then there are others who just do the minimal amount of work to get done what
the boss wants imediately.

Sincerely,
Mark A. Peterson
Sr Design Engineer
Igloo Products Corp
-


K
kimndave91-Visitor
1-Visitor
May 3, 2012
Hi Chris,

I got to see the work of a contractor who created a model of a complex
casting. The original 2D drawing was spread across a few sheets and had
a few hundred dimensions. When I went to review the model for accuracy,
I found random selections for dimension origins. Moving a single boss
that had two dimensions originally would require changing dozens of
dimensions. I figured he thought we'd keep him around because no one
else could fix it.

As to sheet metal - is it possible to convert it to sheet metal? Uniform
thickness and lack of most edge quirks? It doesn't have to be perfect
like it used to be. If necessary, create a relation to control the
values of the thickness and bend radii.

On the bright side - anyone remember when sheet metal features didn't
work if you picked the green side, but it let you pick it anyway?

Dave S.

P
pfadams1-Visitor
1-Visitor
May 3, 2012
Does anyone still remember when we drew with paper and pencil or ink and still were able to design and build the computer without a green side to the line. I appreciate what a computer can do for us but we still need to use our heads for the final draft. Software is only as good as the minds that developed it
THINK TWICE CUT ONCE.....
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