DRAGON INNOVATION, INC. !

DESIGN  FOR  MANUFACTURING  !

COURSE 7: PART 1 - ROTOMOLDING !!!!!!!

SCOTT N. MILLER | CEO | @DRAGONINNOVATE | WWW.DRAGONINNOVATION.COM

•Overview •Process •Part Design •Materials

AGENDA

Rotomolding Overview

Typical Rotomolded Parts

• Hollow Parts

• Storage Containers and Vessels

• Doll Heads and Limbs

• Kayaks and Outhouses

Rotomolding Advantages

• Hollow parts in one piece with no weld lines • Suitable for large parts • No internal stresses due to flow • Undercuts are OK • Suitable for short and high volume. • Can use multiple colors. • Shorter and cheaper tooling times (non pressurized). No

purging required between shots. • Minimal scrap (no “plumbing”) • Outside corners are stronger than blow molding • Can use rigid or flexible materials

Rotomolding Disadvantages

• Larger parts have a slow cycle times due to cooling time constants.

• Some geometrical features (such as ribs) can difficult to mold.

• Can’t control wall thickness precisely • Material cost will be higher due to additional processing

required

Rotomolding Process

Rotomolding Process

1. Fill Mold with metered shot. 2. Heat & Spin. Resin adheres

to inside surface of mold. Spinning results in relatively even wall thickness.

3. Cool 4. Extract

http://en.wikipedia.org/wiki/Rotational_molding

Rotomolding Machines

Example: Kayak Fabrication

Example: Baby Doll

Rotomolding Part Design

Design Guidelines

• Hollow part with ~ uniform wall thickness • Can include inserts and undercuts • Tune wall thickness by varying shot weight (0.8mm -

25mm) • Avoid nooks and crannies / ribs • Typically uniform wall, but can use stop process to thicken

one side

Materials

Common Materials - Polys

Material Young’s  (MN/m2)

Yield  (MN/m2)

Spc  Gravity  (g/cm3)

Cost  ($/kg)

Melting  Temp  (C)

PE  (85%) 70,000 250 6.6 1.80 420

PP 80,000 330 5.8 1.90 430

PC 28,000 70 1.13 4.00 130

PVC 45,000 150 1.8 2.93 650

Nylon 100,000 215 8.4 6.60 950

dragon@dragoninnovation.com