Upload
dragon-innovation
View
3.611
Download
3
Tags:
Embed Size (px)
Citation preview
DRAGON INNOVATION, INC. !
DESIGN FOR MANUFACTURING !
COURSE 5: INJECTION MOLDING !!!!!!!
SCOTT N. MILLER | CEO | @DRAGONINNOVATE | WWW.DRAGONINNOVATION.COM
•Overview •Molding Process •Part Design •Materials •Techniques •Shot Nomenclature •Tooling Fabrication
AGENDA
Overview
Recommended References
www.matweb.com
Typical Engineering Molded Parts (Examples)
• Housings / Brackets
• Transmissions
• Joints
Injection Molding Advantages
• Supports highly integrated design - Complex geometry and fine details possible
• Low part cost • High volume production • Wide range of thermoplastic materials and fillers • Wide range of sizes • Low scrap rate • High reproducibility & Reasonable tolerances • Little post production required • Good surface finish • Can be fully automated • Reduces piece count • Simplifies assembly
Injection Molding Disadvantages
• High tooling costs and long lead-times
• Difficult to make changes
• Large undercuts are difficult
• Requires nearly uniform wall thickness
• Limited to Thermoplastic materials
• Cannot produce very large parts as a single piece.
Molding Process
Molding Cycle
1. Melt Shot
2. Clamp and Fill
3. Pack (Gate Freeze)
4. Cool
5. Eject
Molding Process
Three Plate Mold
Part Design
Temp and Pressure
12k psi @ 440F
Shrinkage
Design Guidelines
• Design for 2mm uniform wall thickness (0.5mm – 6mm).
• Ribs 80% wall thickness. • Draft depends on texture and resin. Assume 0.5 deg. • Use rounds and fillets. No sharp edges except parting
line. • Shoot for planar parting line if possible. • Tolerance is a function of the resin, part geometry and
mold construction. • ABS: +/- 0.1mm • ABS Hole: +/- 0.05mm up to 6mm diameter.
• Surface Finish: SPI A-1 Grade 3: 6000 Grit Diamond
Reference: Product Design for Manufacture and Assembly. Geoffrey Boothroyd,, Peter Dewhurst and Winston Knight.
Part Features
Use 2mm Uniform Wall Thickness
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Uniform Wall Thickness, con’t
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Gusset Bosses & Avoid Shrink Marks
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Draft Overview
Reference: http://www.diecastingdesign.org/design/basic/draft/
Use at 0.5 - 1.0 Degree Draft Angle (depends on texture)
Avoid Penetrations and Weld Lines
???
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Avoid Undercuts if Possible
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Avoid Undercuts if Possible
Lifter (Undercut)
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Screw Bosses
No Flatheads!
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Use Shut-Offs Instead of Slides
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Use Shut-Offs con’t
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Integrate Joint into Parts
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Living Hinge
Hide Rib Shrink Marks
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Materials
Materials
•Thermoplastic polymers (95%). Can go through molding cycle many times (i.e. similar to ice). No chemical bonds between strands.
•Thermosets (5%). Chemical react during process to form cross linked polymer chains. Irreversible. Excellent creep, dimensional stability, temperate and chemical resistance. Ex: phenolics and epoxies.
Materials, con’t
•Additives - Enhance a specific property (UV, stiffness, color,
flame retardants, etc). All have side effects. - Add chopped fiber (up to 30% volume). Strength
and stiffness, lose on impact, abrasion and tool live (cut down to 1/3). Properties approaching metal.
•Need to operate below 250C (400C max) •Low specific gravity (0.8 - 1.8) Steel = 7. Strength to weight ratio good. Automotive. •Some materials are transparent. •Very sensitive to changes in temperature (vs steel) •Good electrical insulation
Resin Comparison
Resin Use Yield (MN/m2)
Modulus (MN/m2)
Heat Deflect (1.8 MPa : C)
Cost ($/kg)
Shrink (cm/cm)
ABS Housings 39 1,800 86 $2.09 0.004
PC Lenses 65 2,400 128 $2.81 0.007
POM Gears 65 2,800 105 $1.48 0.02
Polyamide Strength 123 2,750 65 $3.63 0.013
PP Food 36 1,380 93* $1.76 0.015
Aluminum 276 68,900 $1.75
Steel 435 205,000 $0.39
http://www.matweb.com/ http://www.nhh.com.hk/eng/trading/price_trend.asp
Techniques
Use Moldflow Simulation
Use a clear shot to see mechanism (ABS -> PC)
Other Techniques
• Steel Safe Design
• Add additional ribs after first shots
• Use Inserts around change areas
• Review mold drawings carefully. Watch out for cooling lines.
Other Types of Molding
• Co-Injection / Overmolding (toothbrush)
• Gas Assist
• Low pressure (EE)
Calc Molding Size
• Assume holding 2 - 5 tons / sq. in
• Assume 50% cavity pressure lost due to friction
• Calc surface area of combined parts and runners
• Look up injection molding pressure (ABS = 1k bar)
• Calculate cavity pressure (Molding Pressure * 0.5)
• Calculate Tonnage: F = P * A
Shot Nomenclature
Shot
Shot Nomenclature
Shot Nomenclature
Reference: Plastic Part Design for Injection Molding. Robert A. Malloy.
Shot Nomenclature, con’t
Tooling Fabrication
Tool Shop
EDM
Open Tools
Polishing
Finished Tools
Questions?