Re: Popcorn RP

From: Delft Spline Systems (
Date: Tue Feb 01 2000 - 23:21:03 EET

At Monday 1/31/00 , you wrote:
>RP-ML readers are familiar with the additive and subtractive methods of
>RP: respectively, the mass of the part increases or decreases during the
>process. Logically there must be a third method where the mass stays the
>same. The process would then be one of internal reorganization. Call
>this internal RP.

Dear Jim,

The idea is fascinating, a great deal of which is caused by the visionary
subject line that you use: one day RP will be just as cheap, easy to use
and generally accepted as popcorn.

Still a remark:
This is indeed an example of the third basic method of fabrication (so next
to additive and surbtractive) which is formative. See the book and articles
of Marshall Burns for more information on fabrication theory
Perhaps one time we will even have a fourth method, based on some
biological growth principle.

The formative approach is not yet used in any commercial RP system
(though I am aware of two research projects: Univ of Southern California
end IPA in Stuttgart - Germany). The basic problem is that for most
formative fabrication technologies a mould is needed. For instance
metal casting, injection moulding, etc. This two-step procedure of
first making the mould (how ?) and then moulding the prototype is not
really rapid. It makes sense for small series production, not for 'singles'.

Still formative processes without a mould do exist as well, like for instance
traditional manual metal forging using a hammer. The idea of using this
type of fabrication for RP indeed intrigues me. I cannot yet imagine any
technology capable of doing so, however its application could have a
significant major advantage: the prototype could change !!!
While now all RP processes are in fact one-way processes: make a CAD
model, create a prototype, evaluate it, throw it away, change the CAD model,
create a new prototype, etc etc. This is in fact the basic design cycle.

A formative prototype (ideally) could be evaluated and then changed,
or even change (in real-time) with the CAD-model. This is in fact the same
idea as the virtual clay as proposed by Michael Rees (are you still there -
long time no rp-ml). The resulting RP system would be ideally suited
for REAL concept modelling: truly support the designer when generating
new concept designs. This in contrast with all current RP systems, that
do support him/her when evaluating the resulting geometries after having
generated them.

In short: some vague ideas still, but for me quite stimulating !

Best Regards from Holland,

Lex Lennings.

Delft Spline Systems, The Netherlands.
We offer DeskProto: affordable Rapid Prototyping using CNC milling Website:

For more information about the rp-ml, see

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