My two cents
Regards,
Sean O'Reilly
-----Original Message-----
From: O'Reilly, Sean (S.B.)
Sent: Friday, August 06, 1999 10:18 AM
To: 'pdickens@dmu.ac.uk'
Subject: RE: RP Paper
Phil:
Several years ago we did a study on the relative costs of producing plastic
(as opposed to metal) parts. To do the study we had to make several
assumptions:
1.) Materials - we ignored the difference between materials (for example,
many automotive components are made with glass-filled nylon or talc-filled
polypropelyne - both VERY abrasive. Most of the processes we looked at could
NOT produce parts made of these materials - at least at that time.)
2.) Geometry - we assumed a fairly simple geometry - no undercuts, etc. -
something that could be made in a simple core/cavity mold.
Based on these assumptions, we looked at a number of processes:
- Free From Fabrication ( I still refuse to call it "Rapid Prototyping").
Materials limited to the particular process used (SLA, FDM, etc.)
- RTV molding (from an FFF master)Materials limited to 2-component urethanes
and some castable epoxies.
- Kirksite spray tooling (sprayed on to an FFF master). Materials included
"benign" plastics - No Glass-filled nylon, for example.
- Traditional machined steel tooling - Any material
We were interested in cost as measured by per-piece cost. The costs
included "tooling" cost amortized over the expected life of the tool, labor
costs measured at a constant hourly cost, material costs (much higher for
SLA for example)and so forth.
It is no surprise that the higher the number of parts required, the
more cost effective traditional methods became.The most significant factor
turned out to be the tooling costs. We estimated about 40 pieces per
silicone rubber mold, about 200 - 300 pieces from spray metal tooling, etc.
While interesting, the study really didn't help much because of the
REAL material requirements for REAL parts, together with other attributes
such as surface finish, weight, etc. I have tried to find the study, but
have been unable to do so. I'm on my third new computer since we did the
study ( around 1994) and it appears to be long gone.
Two additional OPINIONS:
1.) Rapid Fabrication or Free Form Fabrication will never compete
with traditional production processes unless there is a vast increase in the
kinds of materials available and a dramatic increase in process
speed/throughput. This statement in made in the context of HIGH VOLUME ( say
50,000 units per year or higher)
2.) The true strength of FFF lies in its ability to produce geometry
of ANY complexity (have you ever played with the Cubital "Brain Gear").
Fundamentally, it can produce ANYTHING that can be modelled in solid CAD.
Virtually all of the "Design Rule Knowledge" that is implicitly at work in
the design world today imposes subconscious constraints on designs based on
the capabilities and limitations of existing manufacturing processes. The
consequence of this is that until we can break the creative barriers in
peoples' brains, the true advantages of FFF will never be realized. For the
most part, we have compared FFF to traditional processes, measured it by the
traditional measures and tried to force it into traditional engineering and
manufacturing processes. We really need an entirely new paradigm.
Regards,
Sean O'Reilly
-----Original Message-----
From: Prof. P. M. Dickens [mailto:pdickens@dmu.ac.uk]
Sent: Thursday, August 05, 1999 8:33 PM
To: Sean M. Gladieux
Cc: rp-ml@bart.lpt.fi
Subject: RE: RP Paper
Sean,
I saw your message to the rp mailing list earlier and the comments that you
got.
This is a subject that is dear to my heart.
You have started a very important thread here. The original work we did was
with a company called Flymo (part of the Electrolux group), they make garden
care equipment. We wanted to see if it was economically feasible to
manufacture end use parts by RP instead of injection moulding. We found that
RP cost about 100 times more and injection moulding was about 100 times
faster. With the development of newer machines such as the SLA 5000 and then
the SLA 7000 these numbers will have changed. However, what we also showed
was that it was economic to make even small simple parts in numbers up to
6,000 before injection moulding became cheaper!
We have just installed an SLA 7000 so it would be interesting to redo the
numbers.
I am 100% convinced that RP will move into direct manufacture of end use
parts with numbers into the thousands. This raises lots of other issues.
1. If we use RP then assuming the material properties are okay how would you
change the design to make it better. Remember an RP machine (of some sort)
can make any geometry.
2. How often would you change the design if you are not limited by tooling.
3. Do other factors limit you e.g. physics of the process in the product or
other parts e.g. filters in your case.
4. How will manufacturing change. Is everything Just in Time. Why make to
stock?
5. Can you eliminate parts e.g. if you sinter the part could you also make
the filter as well at the same time.
6. How will this freedom affect part variation. Is greater variety a good
thing? We have spent a long time reducing part counts. What are the pros and
cons?
7. If you use RP instead of die-casting which process would you use? Would
you try and make a sintered metal part to get near to what you have now? Why
do you have a die cast part now? Would a plastic RP part be okay? Would you
need to change the design to make it okay in plastic?
These are the issues that spring to mind now. I am sure there are lots of
other issues. You could do your project in any one of these. Choose the one
that is of most interest to you. If you would like us to make you some parts
for this project let me know. We have a Thermojet, SLA 7000, FDM 2000 and a
new EOSint M extended (metal sintering) will be installed in September.
I am in Atlanta at the moment visiting Georgia Tech and then onto Texas for
the SFF Symposium and then onto University of Arizona and so I will not be
able to email the paper until I get back to the UK on the 19th. Please email
me then to remind me.
COMMENT TO EVERYONE ELSE
There must be lots of other ideas on this. Lets start sharing. Have I missed
some important points? Is this all rubbish? Don't just sit there. Get
contributing.
Prof. P. M. Dickens
Dept. of Mech. & Manuf. Eng.
De Montfort University
The Gateway
Leicester
England LE1 9BH
Tel: +44 (0)116 257 7689
Fax: +44 (0)116 257 7025
Mobile: +44 (0)468 827039
Email: pdickens@dmu.ac.uk
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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