(no subject)

From: Junghoon Hur (Seoul National  University), Amit Bagchi (Clemson  University)
To: Junghoon Hur (Seoul National  University), RP-ML
Cc: RP-ML
Date: Friday, February 10, 1995
> This is a message from Seoul National University, Seoul, Korea. 
> I am Junghoon hur, MD student in CAD Laboratory, SNU. My professor is Kunwoo Lee. I am doing MD in the area of Stereolithography(SLA), especially for "determination of optimal orientation in SLA". M
>  main interest is minimization of the Support Structur
> s and Stable Equilibrium in the SLA process. 
> 
> By the way,I have two questions.
>  ONE> when you determine the orientaion of object, WHAT THE IMPORTANT FACTOR 
IN SLA IS ?  

	The fundamental factor in the SLA or any other RP system is to 
be able to produce a part that is  ACCEPTABLE and ACCURATE to 
you and to your client -- dimensionally, functionally and from a form 
and fit consideration.  Everything else comes in as secondary 
factors.  Some of the factors that my graduate student and I 
have considered are: (1) volume of the support structure, 
(2) trapped volume, (3) form error, (4) surface texture, 
(5) stability of the part during building and post-processing; and 
(6) tessellation error.  While we have not addressed all of these in 
our present work, and there are several other factors that can 
be added to this list, these are definitely some factors to start with.

> 
>  THE OTHER> Once orientation of the object is determined, 
>HOW CAN YOU DETERMINE THE AREA WHERE SUPPORT 
>STRUCTURES IS NEEDED?

	This relates to the issue of support structure design and 
incoporation into the appropriate part for the process (not only 
SLA but others as well) used.  We have done some work (and we 
believe that we were among the first) to automatically generate 
the support structure for any orientation of the part 
orientation.  I refer you to papers co-authored by Charles 
Kirschman and other from Clemson in rapid prototyping 
conferences as far back as 1990/1991. I am aware of other 
packages such as Bridgeworks which are commercially available 
for the same purpose.  I cannot suggest the contact for 
Bridgeworks offhand, but someone else in this group will 
definitely be able to give you that information.

>IS THERE ANY SLOPE THRESHOLD OF THE SURFACE WHERE 
>SUPPORT STRUCTURES IS NEEDED ?  

	Again, this is dependent upon the process used.  Typically, 
most software packages, such as the one developed in Clemson by 
Kirschman, and Bridgeworks use some type of simple rules that 
depend on the build material used, geometry of the component, 
and the local slope of the facet or geometry.  A simple rule is 
if the section is "reasonably vertical" it is unlikely to need any 
support structure; if it is "almost horizontal" it is definitely 
going to require a support structure; anything in between will 
depend on the ability of the process and the material to provide 
sufficient strength to hold the structure in place.  For details 
I would refer you to the MS thesis from Clemson by Kirschman.

>If you have any informations or References, you  can let me know. 
>I will wait for your reply. It would be thankful for you to answer my 
>questions. You can get in touch with me by this address. 

	Furthermore, you may want to refer to the paper by my 
colleague, Dr. Fadel and his graduate student, Mr. Dietmar 
Frank, in the Dayton Conference Proceedings, 1994,  and a paper 
that has just now been accepted for the Transactions of the 
North American Manufacturing Research Institute for its 1995 
volume co-authored by my graduate student, Mr. Minoo Bablani and 
myself.  I will be happy to send you an advance copy of our 
paper if you are interested.  You may also want to contact Dr. 
Deba Datta at the University of Michigan, who has been working 
on optimal orientation of the build for the RP processes.  He 
and his colleague presented a paper at the 1994 SFF Sympsium in 
Austin, TX.

>Thank you in advance.
> Junghoon Hur
> Kwanakgu Shilimdong San 56-1
> Seoul National University
> Dept. Mechanical Design and Production Engineering 
> CAD Laboratory
> Seoul, Korea.
> 
> e-mail: hur@cadal1.snu.ac.kr
> FAX) 82-2-887-2283
> TEL) 82-2-880-7447
> // written by Hur Jung Hoon

							Amit Bagchi