In a series of papers that we published back in 1993-1995 in the Proceedings
of the International Conference on Rapid Prototyping(The Dayton Conference)
and the SFF Conference (Univ. of Texas) we discussed the factors
contributing to warpage or curl as a result of resin cure shrinkage in SLA
part building. Three of the papers, in particular, summarize several
relevant guidelines for reducing the effects of shrinkage. These are in the
1993 SFF Proceedings (pages 245-252) and in the 1994 Dayton Conference
Proceedings (pages 109-125, and pages
181-189).
While the amount of shrinkage that contributes to warpage depends on the
resin reaction rate, resin shrinkage rate, and the overall degree of cure
achieved, it also depends on process parameters such as scan rate, when the
vectors are attached to each other(scan pattern), and whether the borders
are drawn first or last. We showed, for example, that reducing scan rates,
using short randomly drawn vectors, and drawing borders last, all improve
accuracy. We also showed that with the SLA epoxies(although shrinkage
initially appears to be lower than in the earlier acrylate resins) shrinkage
is, nevertheless, significant and the most important effects often do not
show up until post cure and even beyond post cure.
Richard P. Chartoff
Professor of Chemical and Materials Engineering
The University of Dayton
Center for Basic and Applied Polymer Research and
Ohio Rapid Prototype Process Development Consortium
Dayton, Ohio 45469-0130
tel 937-229-2517
FAX 937-229-2503
chartoff@udri.udayton.edu
http://www.udri.udayton.edu/PolymerCenter/
http://www.udri.udayton.edu/rpdl/
http://www.udri.udayton.edu/ebeam/
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 23:02:35 EEST