09-04-2011, 03:29 PM
Injection_Molding1.ppt (Size: 2.76 MB / Downloads: 674)
Short history of plastic
1862 first synthetic plastic
1866 Celluloid
1891 Rayon
1907 Bakelite
1913 Cellophane
1926 PVC
1933 Polyethylene
1938 Teflon
1939 Nylon stockings
1957 velcro
1967 “The Graduate”
Readings
Tadmore and Gogos
Molding and Casting pp584 -610
Boothroyd Dewhurst
Design for Injection Molding pp 319 - 359
Kalpakjian see Ch 18
Injection molding case study;Washing machine augers; see on web page
Process Operation
Temperature: barrel zones, tool, die zone
Pressures: injection max, hold
Times: injection, hold, tool opening
Shot size: screw travel
Part design rules
Simple shapes to reduce tooling cost
No undercuts, etc.
Draft angle to remove part
In some cases, small angles (1/4°) will do
Problem for gears
Even wall thickness
Minimum wall thickness ~ 0.025 in
Avoid sharp corners
Hide weld lines
Holes may be molded 2/3 of the way through the wall only, with final drilling to eliminate weld lines