14-01-2013, 04:24 PM
Injection Molding
Injection Molding.pdf (Size: 1.32 MB / Downloads: 284)
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
Compounding -extrusion
•An extruder is used to mix additives with a polymer base, to bestow the polymer with the required characteristics.
•Similar to an injection molding machine, but without a mold and continuous production.
•Thus it has a similar energy consumption profile.
Environmentally Unfriendly Additives:
•Fluorinated blowing agents (GHG’s)
•Phalates(some toxic to human liver, kidney and testicles)
•Organotinstabilizers (toxic and damage marine wildlife)