SheetMetal - Sample Model for Drawn Corners.

Howdy folks,

I have had this method of making a drawn part with "unfoldable" corners
in my back pocket for a while. This is a pretty clean work-around, so
don't be to quick to think that we have discovered some hidden modeling
technique.

While I have used this method many times, I though that due to the wave
of senseless spam and OT posts in this newsgroup lately, it might be
nice to share something that relates to . . . um . . . SolidWorks.

This is a pretty clean method that could be used for any of you folks
out there who might need to make a drawn corner or those of you in
tooling and fabrication who absolutely need some sort of unfolded draw.

http://www.sheetmetaldesign.com/Cad-SolidWorks/Example19-DrawnCorners.zip

I also have a How-To Tutorial in the works for this part and will post
it once it's done.

In any case, let's help ourselves get back on topic and leave all the
lame spammers and OT addicts in the dust.

Later,

SMA

 

Sean,

Pretty clever.

How close are the allowances for bends to the allowances for forming ?

Regards

Mark

 

Hi Mark -

The "Straight Aways" are as good as it gets, as the longer edges tend
to act like "regular" formed edges. The corners, while not accruate,
are a pretty good starting place and since the actual configuration of
any flat for a draw is a negotiable thing based on thickness, draw
height, curvature, inner vs outer shell and tooling factors, this is a
reasonable starting point.

Any draw tooling that I have been involved with generally needs a
couple iterations of the flat blank before anyone will commit to a
"hard tooled" development. Generally, the draw tool will be made and
the flat blank will be developed with laser blanks until the desired
shape is attained. It is not uncommon for this to take a couple (read
as a few, if hacks are involved) iterations for a drawn corner to be
developed. Generally, one can radially scribe out lines on a 15 degree
(or whatever is needed) radial grid and chart out the points on the
drawn piece - after that the next blank is developed with "reverse
compensation", charted, formed and compensated again. Eventually one
homes in on a smooth development. Essentially, when material is added
or taken away, the draw dynamics change and the part acts differently.

The model I posted has a "dreaded" internal draw which is near
impossible (as I drew it) to make it one hit. These are a problem as
all of the material is in tension, unlike an external draw where the
material bunches radially and elongates along the height. These two
forces work together to balance each other out, allowing a reasonable
chance at success. In any case, the part that one needs to make will
invariably involve some development. A large arc (based on thickness)
will form almost picture perfect as if it were linear, while a "sharp"
radius will have radical distortion. The height of the draw will also
influence its final state, a shallow draw will behave more like a
"standard" form while a deep draw will not.

I wonder if this is what prohibits SW from making a sheet metal feature
that addresses the drawn corner or curved flange. Fear of putting out
"bad" geometry, where no good solution is really possible a priori. I
think that there must be some element of FEA that could get one pretty
close and reduce the number of iterations in development (maybe there
is a perfect tool out there). People who develop this stuff usually
know better, not to say that some folks out there have a major ammount
of experience and can make a very strong estimation for the first hit
and be very close.

I know that round blanks for fully drawn shells have a bit of
mathematics behind them based on number of hits (reductions), shell
geometry and so on, but most of this stuff usually comes down to finer
& finer iterations until the part works. Some of this can be
translated to the corners here as imperfect 1/4 "shells", but we are no
where near "1st pass certainty".

Later,

SMA

 

hi Sean

take a look at

http://www.forming.com/blankworks.htm

steve

 

Hi Steve,

Have you used this one? How good of a job does it do? Do you like it?

I appreciate that they call this "predictive" - this shows that they
understand the problem and are helping people get closer in less time,
not giving them a perfect blank "magically".

Their quote: "Consistently reduces material costs and number of trials
in the blank die tryout stage". Leads me to believe that they know
that development of this type is iterative.

. . . "Legalistically speaking, I think that they probably mean _draw_
die tryout stage - if someone has a blank die already made, it's too
late in the process & someone got some 'splainin (and inserting) to
do", said Mr Adams, dressed in his finest Philadelphia Lawyers outfit
(grin).

Looks like cool stuff that could make life easier.

Testimonies anyone?

Later,

Sean