© 2011 Autodesk Complete Plastic Part Design in Autodesk Inventor MA3060 Ryan Bullock Mechanical...
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Transcript of © 2011 Autodesk Complete Plastic Part Design in Autodesk Inventor MA3060 Ryan Bullock Mechanical...
© 2011 Autodesk
Complete Plastic Part Design in Autodesk Inventor MA3060Ryan BullockMechanical Engineer
© 2011 Autodesk
Class Summary
Learn how to design plastic parts formed by injection molding. This is a beginner level class, assumes no / little experience designing plastic parts.
Inventor tools used in the process Material selection Surface finishes Design rules Injection molding vocabulary
*Inventor steps not specific to injection molding design will be used, but not explained in detail.
© 2011 Autodesk
What is Injection Molding?
Mother of all plastic processing techniques
Plastic pellets fed from a hopper Pushed by a screw through a heated
cylinder Injected at high pressure into a series
of gates and runners into a steel mold Plastic cools in the mold Mold opens and ejector pins release
the finished part from the mold
© 2011 Autodesk
Why Use Injection Molding?
High volume production Inexpensive unit price Very accurate – tolerances +-0.1mm Create complex shapes Variety of surface treatments Many options for materials, blended
materials, over-molding, co-injection, reaction injection, etc.
Relative long tool life
© 2011 Autodesk
Common Vocabulary Terms
Core - side of the tool where the plastic part will stick to and is ejected from Cavity - upper half of the injection mold usually the show surface of the
finished product Lifter - used to create undercuts that cannot be accessed from the outside Slide - Portion of Custom plastic injection molds that is used for creating
undercuts that can be accessed from outside the part Direction of Pull - the axis that the cavity and core separate on Shrinkage - how much the plastic material will shrink after cooled Undercut - feature that cannot be created by the cavity nor core because
other features are in the way Draft Angle – angle of the taper on the part / tooling
© 2011 Autodesk
Materials Used by Injection Molding
Virtually any type of Thermoplastic can be used for injection molding
Some common materials:
ABS Acetal Acrylic Cellulose Acetate Nylon Polyimide Polycarbonate Polyethylene Polypropylene
Polystyrene Polysulfone Polyurethane PVC Polyvinyl Acetate TFE
© 2011 Autodesk
Acrylonitrile Butadiene Styrene - ABS
Commodity Thermoplastic Low cost Rigid Can achieve hi gloss Scratch & flame resistant Good dimensional stability Strong & stiff Often blended with higher cost
plastics like PC for improved material characteristics
© 2011 Autodesk
Acrylic- PMMA
Hard and stiff Good weatherability Glass clear Glossy Scratch resistant Chemical resistant Used for aircraft cockpit covers in
WWII Can be fragile unless blended with
other plastics
© 2011 Autodesk
Polyamides (Nylon)- PA
Rigid, tough, hard-wearing Fatigue and creep resistant Resistant to fuels and solvents Can be sterilized by steam Slippery Good for gears Able to achieve high gloss Used on the Swiss Army Knife Can be drawn into fibers to make
clothing or rope
© 2011 Autodesk
Polycarbonate - PC
Rigid, stiff, tough Outstanding impact resistance Good weather and flame resistance Water-like transparency Can be made glossy UV stable Non-Toxic Excellent dimensional stability – even at
high temperatures Used on cellphone housings, helmets,
automotive headlamps, DVDs
© 2011 Autodesk
Ethylene Vinyl - EVA
Flexible (rubbery) Good Chemical resistance High friction coefficient Used for handle grips, beer tubing,
vacuum cleaner hose
© 2011 Autodesk
Polyvinyl Chloride – PVC
Cheap Easy to form Easy to color Water and Chemical resistant One of the first widely available plastics Considered environmentally unfriendly
Produces harmful dioxins Use of Chlorine Stabilizers and plasticizers that impede
degradation contain lead, barium and hormone disrupters
© 2011 Autodesk
Surface Texture
MoldTech / Yick Sang Hides surface imperfections Requires increased draft angle Cheaper than polishing mold for glossy
surface
© 2011 Autodesk
Glossy Surface
Levels of Gloss – Highest to lowest cost
SPI FINISH GUIDEA - 1 GRADE #3 DIAMOND BUFFA - 2 GRADE #6 DIAMOND BUFFA - 3 GRADE #15 DIAMOND BUFFB - 1 600 GRIT PAPERB - 2 400 GRIP PAPERB - 3 320 GRIP PAPERC - 1 600 STONEC - 2 400 STONEC - 3 320 STONED - 1 DRY BLAST GLASS BEAD #11D - 2 DRY BLAST #240 OXIDED - 3 DRY BLAST #24 OXIDE
© 2011 Autodesk
Design Rules – Wall thickness
Depending on the material type, there is a range for the wall thickness that will provide the best results. Here are some examples:
© 2011 Autodesk
Design Rules – Ribs & Bosses
Ribs and bosses should have a wall thickness of ~60% the thickness of the external walls and a maximum height of 5x the exterior wall thickness.
© 2011 Autodesk
Design Rules – Draft Angle
To allow the part to come out of the mold, a taper in the direction of pull is preferred, this is called the draft angle. Typically, 1.5 degree is the minimum required, but different finishes and materials can change this number
© 2011 Autodesk
Example 1 – Print Server
Learning objectives: Draft angles Ribs Bosses Shell tool Snap features Minimum wall thickness Multi-body & derived parts Slides & Lifters
© 2011 Autodesk
Example 2 – USB flash drive
Learning objectives: Small features Surface evaluation Closed loop loft Shell tool Snap features Minimum wall thickness Slides & Lifters
© 2011 Autodesk
More Information:
Recommended reading and websites:
Plastics 2 – Materials for Inspirational Design - by Chris Lefteri Industrial Design – Material and Manufacturing guide – by Jim Lesko www.matweb.com www.protomold.com/DesignTips.aspx
© 2011 Autodesk
Autodesk, AutoCAD* [*if/when mentioned in the pertinent material, followed by an alphabetical list of all other trademarks mentioned in the material] are registered trademarks or trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document. © 2011 Autodesk, Inc. All rights reserved.