Applied MethodologyDesign for Manufacturing

(Injection Molding)

Daniel Codd, Jason Liang,

Dan Tulayasathien, & Keith Ip

Background

• Project objective:– Reduce assembly time and cost.

• Design concept:– Replace existing honeycomb side-panels with

injection molded plastic panels.

Design Rationale

Why injection molding?– Reduce part count.– Less labor intensive.– Reduce assembly time.– Increase yield rate of the final product.– Reduce manufacturing cost.– “Unlimited” quantities.– Little or no finishing process.

Introduction to Injection Molding

Plastic hopperPlastic hopper

Die and pressDie and press

Injection ScrewInjection Screw

Common Problems withInjection Molding Process

• Part shrinkage

• Insufficient venting causing air bubbles

• Sink marks due to unequal thickness

• Poor surface finish

• Distortion from insufficient cooling

DFM: Injection Molding

Sharp corners restrict plastic flow.

DFM: Injection Molding

Radiused corners also add to the stiffness of the design.

DFM: Injection Molding

Webs around bosses reduce weightand prevent sinkage marks and voids.

Bad Good

DFM: Injection Molding

Keep in mind flow direction whenmaking changes in wall thickness

DFM: Injection Molding

Uniform wall thicknesses will minimize shrinkage and reduce void formation and sinkage.

Strategies to IncreaseStrength and Stiffness

• Ribs: rule of thumb for proportions.

• Rib thickness should be 2/3 of wall thickness.

Strategies to IncreaseStrength and Stiffness

• Ribs: rule of thumb for preventing sink marks.

Strategies to IncreaseStrength and Stiffness

• Ribs: Circular or diagonal ribbing reduces twisting; bidirectional ribbing reduces sagging and bending.

Strategies to IncreaseStrength and Stiffness

• Lip

The rounded lip (C) not only draws the eye away frommisalignment, but also acts as a decorative element andfunctions as a handle for taking the pieces apart.

Strategies to IncreaseStrength and Stiffness

• Webs around bosses

Strategies to IncreaseStrength and Stiffness

• Gussets

Strategies to IncreaseStrength and Stiffness

• Part contour and Metal reinforcement

Knowledge Captured

• Ribs = less weight, more stiffness.• Rib thickness = 2/3 wall thickness• Oriented to provide maximum bending stiffness.

(waffle pattern)

• Contoured shape helps increase stiffness.

• Use of lips and gussets stiffens the panel.

• Use of webs around bosses prevents sink marks.

Applied Methodology to Design

RibsRibsLipsLips

WebsWebs

Any Questions?