We may need more than one definition to include every single idiosyncrasy.
Here is my contribution:
1. I agree that a broad RP definition should include CNC machining but the
words "arbitrary shape" cannot figure in any serious description. Semantic
(adverbial) consideration aside, Elaine's definition is broad enough to
include all sub-classes , i.e., subtractive, additive, formative,
2. Amongst the additive manufacturing community the terminology Solid
Freeform Fabrication has gained popularity in recent years. It avoids the
term "rapid", excludes machining, and could be defined along the lines of:
"a set of techniques capable to grow a physical object directly from
computer codes by the addition of material layer-by-layer, line-by-line or
voxel-by-voxel, and free from confining surfaces other than a base".
3. On the "rapid-being-quick-or-not" controversy I personally find useful
introducing another dimension to the discussion which is part complexity (in
terms of information content [bits]): SFF machines are indeed quicker above
a certain threshold. Moreover they can make things which have traditionally
been very difficult and in same cases impossible to obtain.
The difficulty lies on defining boundaries such as the above threshold:
Maybe we need to update the information of manufacturing processes selection
databases! I have exercised a bit on this and welcome an open discussion
with anyone interested.
From: email@example.com [mailto:firstname.lastname@example.org]On Behalf Of
Sent: Saturday, February 03, 2001 12:31 AM
To: Elaine Hunt; Jeff Katz; RP-ML; Terry T. Wohlers
Subject: RE: rp definition
The purpose of defining something will alter the definition you choose to
From a practical point of view, Jeff's broader definition is good. Rapid
should be that which is relatively more rapid than the alternatives, for the
given application. Prototyping should create a prototype that fits the
definition of a prototype for the end user, which much of what we consider
on the RP-ML to be prototyping is not.
From a market research point of view, Terry has to narrow the definition
down to something he can get his arms around. Furthermore, from a consulting
point of view, he must be able to point out what is new and what is changing
and what his clients should do about it. Which isn't to say that nothing new
is happening in CNC machining, but most people know what they can do with it
(sic). What is different is the appearance of new methods for realizing
arbitrary physical objects directly from virtual objects (CAD).
For many years, people in this forum have argued that neither rapid nor
prototyping are sufficient to describe the new machines (to Sheba's point),
but they agreed on a term for the sake of continuing discussion and sharing
of information. Perhaps that was a mistake. I am beginning to hear
complaints that corporate managers use the technology to shorten the time
for producing a model/prototype, but have failed to use it optimize the
design of their products by realizing, in the same amount of time, a larger
number of variations on the objects envisioned by creative people working in
CAD. They can see and measure whether they are getting more rapid
prototyping than they were previously, but they are not necessarily getting
better products, however you define >>better<<.
Perhaps the name and definition are partly to blame.
SRI Consulting Business Intelligence
Jeff Katz wrote:
>What's wrong with using CNC machining to do "Rapid Prototyping?" In some
>cases, depending on material and finish level, CNC machining is actually
>more "rapid" then RP. If the question is how do you rapidly produce parts
>directly from 3D CAD data, CNC should logically be included in the
>classification, otherwise it's an arbitrary distinction.
>We lump CNC and EDM in with all the others in our Rapid Manufacturing
>marketplace. If you really want to distinguish SLA, SLS, FDM, etc. from
>CNC, you really need to change the name from Rapid Prototyping to
>Prototyping or even Fabbing. Right, Marshall?
>Fast, Free, Secure
>Message text written by Elaine Hunt
>>The Rapid Prototyping Report in 1992 defined RP as
>The Fabrication of a physical, three dimensional part of arbitrary shape
>directly from a numerical description (typically a CAD model) by a quick,
>highly automated and totally flexible process.
>Does this definition define what you do with rapid prototyping? Should it
>be expanded and if so how would you change it?<
>I've been using the following to briefly define/describe RP:
>Rapid prototyping (RP) is a relatively new class of technology used for
>building physical models and prototype parts from 3D computer-aided
>(CAD) data. Unlike CNC machines tools, which are subtractive in nature,
>systems join together liquid, powder and sheet materials to form complex
>parts. Layer by layer, RP machines fabricate plastic, wood, ceramic, and
>metal objects based on thin horizontal cross sections taken from a
>Wohlers Associates, Inc.
>OakRidge Business Park
>1511 River Oak Drive
>Fort Collins, Colorado 80525 USA
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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