Rotomolding process PDF

p. 330.322.8707 e. [email protected]

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Gregory Stout Rotational Molding Design

Blue-Reed, LLC

Part Design and

Tooling for

Rotational Molding :

How to Achieve Success in Every Project

Gregory Stout

Blue-Reed, LLC

4191 Courtiff Circle

Stow, Ohio 44224

www.blue-reed.com


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Introduction

• Greg Stout - designer specializing in

hollow plastic parts.

• Over (17) years experience with

rotational molding process.

• SolidWorks

• This presentation will illustrate how part

design and tooling design influence and

affect each other.


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Tooling and Part Design

• All design has limitations to obey or

follow.

• Material limitations.

• Mold or Tooling limitations

• Machine or Oven limitations.

• To achieve success in your designs

you must understand and know your

options.


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Tooling Options

• Cast Aluminum molds.

• Fabricated Aluminum or Steel

molds.

• CNC molds.


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Tooling Advantages

• Cast Aluminum molds:

1. Can Mold Very Complex shapes

2. Can use Pattern or Model as a design check before pouring metal.

• Fabricated Aluminum or Steel molds:

1. Can Mold Nearly as Complex shapes

2. Can be lower cost.

3. Requires no Pattern or Model

4. Thinner mold wall makes for faster heat transfer.

5. Extremely large molds can be made

• CNC molds:

1. Very close dimensional tolerances can be held.

2. Requires no Pattern or Model

3. No Porosity


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Part Design

• The following are examples of how the mold

design was manipulated to help make the parts

be manufactured successfully.


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Dog Waste Receptacle & Bag Dispenser

• Two parts from two molds that

hinge together to form one part.

The top lid is a dispenser and the

bottom is a receptacle.


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• An inside look shows how diverse the parts are. The bottom

has no restrictions to shrink while the top has to shrink around

a large core.


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Features:

• Two large core pins.

• One small core pin.

• Large graphic area.

• Routered hole for bag insertion.

• Routered holes for bag dispensing.

• Pull pins for hinges.


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• Core is very deep in cavity to accommodate pull pins on

the side of the part and for the head of the router for the

hole to insert the boxes of bags.

• Notice the crown in the graphic area to fight warp.


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Features:

• Large graphic area

• Drilled holes for hinge to

match molded in holes

for lid.

• Recess in center for

mounting post

• Drilled drain holes in bottom.


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Problem:

The lid has restricted shrinkage and the bottom

has no restrictions on shrinkage. How will the

parts mate together if they don’t shrink the

same?

Solution:

Since the top will not shrink as much as the

bottom part, ¼” was taken out of the width of the

bottom and 1/8” was taken out of the depth of the

bottom part.


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Pontoon Bass Boat

• A Boat that was

originally vacuum

formed in two pieces

and then glued together.

Now molded as one

piece and foam filled.


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Pontoon Bass Boat

• Boat has to be strong and solid in feel when stood on.

• Walls have to withstand clamping force of motor mount and

forces when motor is running.


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Pontoon Bass Boat

• Foam filling has to happen in mold and no holes can be left

open.

• Areas in the mold have to be close enough to form a kiss-off

and yet open enough to let both materials flow.


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Pontoon Bass Boat

• Drop Boxes were used for foaming the part in mold.

• Study was done to find out the optimal kiss-off, foaming

distance.

• Holes from the Drop Boxes were filled with an additional

storage feature for the part.


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29 Gal. Gas Walker

• Many threaded features

• Had to pass DOT Packaging Certification tests

• Needed to have consumer appeal.


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29 Gal. Gas Walker

• Many molded in graphics as well as post molded

graphics

• Many ribs for strength also add problems with porosity

at P/L for mold maker.


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29 Gal. Gas Walker

• Large center core difficult for mold

maker to pour.

• Part had to be stackable for

shipment and for testing.

• DOT Testing spec.: Part had to

withstand 1100 lbs. stacking force

for 28 days with no deformation.

• DOT Testing spec.: Hydrostatic

Pressure of 17.5 PSI for 30 min.

with no deformation.

• Part had to have no more than

.200” wall thickness.


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29 Gal. Gas Walker

• Ribs to prevent

distortion from tests.

• Must hold at least the

amount on label.

• Limited room for

threaded caps and

bushings

• Be careful of narrow

walls for finishing and

texturing.


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29 Gal. Gas Walker

• Pull pins for axle

pins through two

walls on each side

for strength.

• Molded in insert for

hose valve is a tight

area for machining in

the mold


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Sharbade Scooter

• Game scooter for children, adults and for the

physically disabled.

• Has to support 250 lb. athlete.

• Has to approximate design of current foam

covered plywood scooter.


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Sharbade Scooter

• Part had to be deep enough to allow resin

powder movement and to charge it in one mold

half. 3:1 is standard but can go lower.

• Needed to run FEA to determine amount and

style of slots.


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Sharbade Scooter

• FEA results were very good in both stress and

deformation. Hint: Red – bad; Blue – good!

• The plastic part could actually hold 440 lbs. easily.

• Warning: FEA is a design guide. Actual behavior of product

could be different. Too many processing variables.


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Sharbade Scooter

• Slots or holes give you the most added strength.

• If the part were larger, wider slots would give more room for an

opening in the flange in the tool to help with air flow.


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Sharbade Scooter

• Mounting posts in the slots make for better shut-off, no flash.

• Don’t make slots so narrow that the tool will be solid resulting

in a cold spot which will make for a thin wall.


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Sharbade Scooter

• Registration in the slot bosses to keep mismatch of P/L to a

minimum.

• Vent hole will be covered up on the finished part by the caster

mounting plate.

• Quick-Sert pins to hold the molded in inserts for the casters.


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Tank/Skid

• Customer needs large tank in certain

sized footprint.

• Must be able to move with a hand

truck or a tow motor.

• Oh, no! Two sizes are needed!


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Tank/Skid

• Larger size- no problem. Use an

additional mold piece to enlarge the

tank portion of the mold.

• Whaddaya mean it’s got to fit in the

oven!??


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Tank/Skid Oven Fit

• Modeled the molders oven

• Expanded the part to include part shrink

• Modeled the P/L flange, mounting posts and spider tubing.

• Insert model assembly into the oven and look for conflicts with

oven limits and the part- remember mold wall thickness


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Tank/Skid Oven Fit

• Areas that had to be adjusted were the hose hanger

at the top right had to move in and the threaded cap

needed to move closer to the center- a clamp has to

hold it in.


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Tank/Skid

• Mold with insert for larger size

tank capacity.

• Fabricated aluminum mold.


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Typical Fab Mold

• Square mounting posts that are

welded on.

• Flat P/L with dowel pin registration.


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• Clamping Parting lines in different planes.

Multi-Piece Fab Mold


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• Another view

Multi-Piece Fab Mold


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• Round parts are best parted through the cross section rather than down the length to ensure roundness. The lengthwise parting line will make the part come out oval shaped instead of round.

Fab Mold


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• Large sheet metal mold.

Fab Mold


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• Some parts of a Fab mold may be machined.

Fab Mold


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• Fabricated mold with kiss-offs.

Fab Mold


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• Multiple piece Fabricated mold.

Fab Mold


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• Fab molds are repeatable.

Fab Mold


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Fab Mold

• Fabricated molds can be very large and of complex shapes.


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• Computer generated 3D models are used

by some fabricated mold makers to make

the sheet metal pieces.

Fab Mold


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• Large fabricated mold with complex

geometry.

Fab Mold


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• The backside of the same mold.

Fab Mold


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• Bending the sheet metal for the fab mold.

Fab Mold


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• A Sheet Metal tube mold.

Fab Mold


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• Sheet Metal tube mold spot welded.

Fab Mold


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• More complex shapes from a fab mold.

Fab Mold


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• Large pull pins to create holes in the part in

a fabricated mold.

Fab Mold


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• Clamping directly through the parting line

flange on a fabricated mold.

Fab Mold


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• Fine polish of a sheet metal mold.

Fab Mold


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• Complex parting line in a fabricated mold.

Fab Mold


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• Molded in arrow logo in a fabricated mold.

Fab Mold


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• Kiss-offs and other complex geometry.

Fab Mold


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• Duplicates of fabricated molds.

Fab Mold


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• Another very large fabricated mold. Too

large to be cast in one piece.

Fab Mold


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• Nice crisp lines.

Fab Mold


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• Spider tubing bent instead of pieced welded together. Very clean and strong.

Fab Mold


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• Clamping directly through a very complex

parting line.

Fab Mold


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Fab Mold

• Large cone shaped mold.


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6 Gal. Fuel Tank – Cast Mold

• A three piece cast mold with one male thread and two female threads molded in. Room must be left for the pins and bushings.


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Cabinet – Cast Mold

• Cast mold with

multiple pieces on

slides and hinges,

with pull pins and

molded in inserts.


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Spider Height Issues

• Die spring within mounting post. A way

to reduce the overall spider height.


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Spot Teflon Coating

• Spot Teflon coating allows

areas with deep cores to be

pulled easier.


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Cast Mold

• Multiple piece cast mold.


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• Multiple piece cast mold. Notice the heavy duty slide for the mold piece on the right.

Cast Mold


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• Completely removable mold piece.

Cast Mold


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• The other side.

Cast Mold


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• Close up of slide for large mold piece.

Cast Mold


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• Mold opened on slide.

Cast Mold


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• Another view of the slide.

Cast Mold


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• The inside of the cast mold with Brown

Teflon coating.

Cast Mold


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• Another view.

Cast Mold


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• Kiss-Offs for strength.

• Difficult for the foundry.

Cast Mold


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• Multiple piece mold on slides and hinges enable molding of what would have been undercut. Nice mold detail to the right.

Cast Mold


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• A precision slide for a molded undercut.

Cast Mold


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• Close up of slide.

Cast Mold


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Various Clamps


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Pneumatic Clamp

• Normally used on multiple cavity spiders

to clamp and unclamp quickly.


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• Heat pins or fins attracts more heat

to a particular mold area which will

thicken the part wall in that area.

Cast Mold


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• Heat pins can be put all over.

Cast Mold


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• More heat pins! To help reduce cycle time.

Cast Mold


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• Heat pins used to help heat a deep core

that would be difficult to get hot oven air to.

Cast Mold


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• This is a wooden pattern or model - critical to making the cast mold. The model has both plastic material shrink and aluminum shrink factored in so it is actually larger than what the part will be.

Cast Mold

• The model is often used to communicate parting line and other info.


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• Foundry tooling to make the sands

that the metal is poured into.

Cast Mold


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• Pouring molten aluminum into the sand

castings.

Cast Mold


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• Mold polishing. Necessary in all mold

making.

Cast Mold


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• Another multiple piece mold.

Cast Mold


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• Close up of a kiss-off in a

cast mold.

• Usually a good idea to

leave metal safe in the

mold to allow the molder

to adjust.

Cast Mold


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• A cast mold with an insulated area on top. This will make the insulated area mold a large open area.

Cast Mold


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Mounting Plate

• A mounting plate.


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Grate

• This is a grate for mounting numerous dissimilar molds.


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Grate Mount

• Two molds mounted on a grate.


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Multiple Mold Spider

• Multiple molds on a spider to make more

parts in the same amount of time.


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Air Amplifiers

• Air Amplifiers direct the heated air to a

particular area that may be difficult to heat

or to make a particular area’s wall thickness

thicker.


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Pull Pins

• Pull pins are used to create molded in

holes in parts.


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European Mold Making

• The following are examples of how the European

mold makers are making strides in our industry.


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Cast Molds

• A large complex cast mold with a lot of different mold

pieces to produce a lot of different configurations.


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CNC Molds

• CNC molds

make up

approximately

40% of the

molds sold

there.


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CNC Molds

• Nice multiple piece CNC mold.


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CNC Molds

• Another good example.


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CNC Molds

• A CNC mold for a liquid nylon

part.


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CNC Molds

• Another complex mold!


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Model, Mold, and Part Inspection

Complete Moulds

CTR Dimensional

control, to ensure

Tolerances,

Shrinkage and

correct Shape.

• Available with

some mold

makers in the

USA.


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Machines

• The next slides will talk about advancement in

automation for the rotomolding machines.


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Leonardo Machine

• A fully automated

rotomolding

machine – no

operator!

• When will we see

them in the US –

Very soon!

• See the

presentation later

today!


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• Human resource reduced to machine set-

up, human influence eliminated from the

product quality.

• Improved product quality thanks by the

uniform wall thickness distribution.

• Increased productivity.

• Absence of mould refurbishment needed.

• Clean and fresh working area.

Leonardo Machine


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• Automatic mould opening/closing.

• Automatic moulds control: product demolding, inserts loading, material loading, mould temperature control.

• Alarm signals in case of danger or Dysfunctions.

• Automatic product demolding.

• Accurate Material dosing system.

Leonardo Machine


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Summary

Thank-you

Any Questions?

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Engineering

Rotomolding process PDF