Rotational Molding Design

Gregory StoutRotational Molding Design p. 330.688.1324 e. gstout@blue-reed.com

Blue-Reed, LLC

Part Design and Tooling for Rotational Molding :How to Achieve Success in Every Project

Gregory StoutBlue-Reed, LLC4191 Courtiff CircleStow, Ohio 44224www.blue-reed.com

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.

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.

Tooling Options

• Cast Aluminum molds.

• Fabricated Aluminum or Steel molds.

• CNC molds.

Tooling Advantages

• Cast Aluminum molds:1. Can Mold Very Complex shapes2. Can use Pattern or Model as a design check

before pouring metal.

• Fabricated Aluminum or Steel molds:1. Can Mold Nearly as Complex shapes2. Can be lower cost.3. Requires no Pattern or Model4. 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 Model3. No Porosity

Part Design

• The following are examples of how the mold design was manipulated to help make the parts be manufactured successfully.

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.

• An inside look shows how diverse the parts are. The bottom has no restrictions to shrink while the top has to shrink arounda large core.

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.

• 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.

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.

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.

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.

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.

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.

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.

29 Gal. Gas Walker

• Many threaded features

• Had to pass DOT Packaging Certification tests

• Needed to have consumer appeal.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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!

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!??

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

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.

Tank/Skid

• Mold with insert for larger size tank capacity.

• Fabricated aluminum mold.

Typical Fab Mold

• Square mounting posts that are welded on.

• Flat P/L with dowel pin registration.

• Clamping Parting lines in different planes.

Multi-Piece Fab Mold

• Another view

Multi-Piece Fab Mold

• 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

• Large sheet metal mold.

Fab Mold

• Some parts of a Fab mold may be machined.

Fab Mold

• Fabricated mold with kiss-offs.

Fab Mold

• Multiple piece Fabricated mold.

Fab Mold

• Fab molds are repeatable.

Fab Mold

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

• Computer generated 3D models are used by some fabricated mold makers to make the sheet metal pieces.

Fab Mold

• Large fabricated mold with complex geometry.

Fab Mold

• The backside of the same mold.

Fab Mold

• Bending the sheet metal for the fab mold.

Fab Mold

• A Sheet Metal tube mold.

Fab Mold

• Sheet Metal tube mold spot welded.

Fab Mold

• More complex shapes from a fab mold.

Fab Mold

• Large pull pins to create holes in the part in a fabricated mold.

Fab Mold

• Clamping directly through the parting line flange on a fabricated mold.

Fab Mold

• Fine polish of a sheet metal mold.

Fab Mold

• Complex parting line in a fabricated mold.

Fab Mold

• Molded in arrow logo in a fabricated mold.

Fab Mold

• Kiss-offs and other complex geometry.

Fab Mold

• Duplicates of fabricated molds.

Fab Mold

• Another very large fabricated mold. Too large to be cast in one piece.

Fab Mold

• Nice crisp lines.

Fab Mold

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

Fab Mold

• Clamping directly through a very complex parting line.

Fab Mold

• Large cone shaped mold.

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.

Cabinet – Cast Mold

• Cast mold with multiple pieces on slides and hinges, with pull pins and molded in inserts.

Spider Height Issues

• Die spring within mounting post. A way to reduce the overall spider height.

Spot Teflon Coating

• Spot Teflon coating allows areas with deep cores to be pulled easier.

Cast Mold

• Multiple piece cast mold.

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

Cast Mold

• Completely removable mold piece.

Cast Mold

• The other side.

Cast Mold

• Close up of slide for large mold piece.

Cast Mold

• Mold opened on slide.

Cast Mold

• Another view of the slide.

Cast Mold

• The inside of the cast mold with Brown Teflon coating.

Cast Mold

• Another view.

Cast Mold

• Kiss-Offs for strength.• Difficult for the foundry.

Cast Mold

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

Cast Mold

• A precision slide for a molded undercut.

Cast Mold

• Close up of slide.

Cast Mold

Various Clamps

Pneumatic Clamp

• Normally used on multiple cavity spiders to clamp and unclamp quickly.

• Heat pins or fins attracts more heat to a particular mold area which will thicken the part wall in that area.

Cast Mold

• Heat pins can be put all over.

Cast Mold

• More heat pins! To help reduce cycle time.

Cast Mold

• Heat pins used to help heat a deep core that would be difficult to get hot oven air to.

Cast Mold

• 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.

• Foundry tooling to make the sands that the metal is poured into.

Cast Mold

• Pouring molten aluminum into the sand castings.

Cast Mold

• Mold polishing. Necessary in all mold making.

Cast Mold

• Another multiple piece mold.

Cast Mold

• 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

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

Cast Mold

Mounting Plate

• A mounting plate.

• This is a grate for mounting numerous dissimilar molds.

Grate Mount

• Two molds mounted on a grate.

Multiple Mold Spider

• Multiple molds on a spider to make more parts in the same amount of time.

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.

Pull Pins

• Pull pins are used to create molded in holes in parts.

European Mold Making

• The following are examples of how the European mold makers are making strides in our industry.

Cast Molds

• A large complex cast mold with a lot of different mold pieces to produce a lot of different configurations.

CNC Molds

• CNC molds make up approximately 40% of the molds sold there.

CNC Molds

• Nice multiple piece CNC mold.

CNC Molds

• Another good example.

CNC Molds

• A CNC mold for a liquid nylon part.

CNC Molds

• Another complex mold!

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.

Machines

• The next slides will talk about advancement in automation for the rotomolding machines.

Leonardo Machine

• A fully automated rotomolding machine – no operator!

• When will we see them in the US –Very soon!

• See the presentation later today!

•• Human resource reduced to machine setHuman resource reduced to machine set--up, 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

• 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

Summary

Thank-youAny Questions?

www.blue-reed.com

Rotational Molding Design

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