plastic fantastic - solid solutions · plastic fantastic • plastic parts must be geometrically...

Wednesday, 14 November 2012

Andy Fulcher & Craig Hudson

Plastic Fantastic

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Agenda

Plastic Fantastic

• Plastic Fantastic?

• Challenges with Plastics

• Case Study – Plastic Razor

• Mechanical Performance of

Plastics

• Designing Plastic Parts for

Moulding

• Simulating the Injection

Moulding Process

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Fantastic?

Plastic Fantastic

Benefits of plastic moulded parts

• Complex shapes

• Net shape in one process

• Wide range of material properties

• Tight tolerances

• Economical for high volumes

• Little wastage / recyclable

Polyethylene usage predicted to increase by

100% from 2000 - 2020

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Challenges for Designers and Manufacturers

Plastic Fantastic

• Plastic parts must be geometrically capable of being

moulded easily – draft; parting lines etc.

• Injection moulding tooling is expensive

• Tools usually need development and often rework

• The ‘blame game’!

• Plastics behave differently from metals so need to be

designed and tested differently

• Many plastic parts snap fit together. Snap fits require

careful design so they work but do not break

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Case Study – Plastic Razor

Plastic Fantastic

• High volume part

• Complex shape

• Moulded body

• Over-moulded grip

• Cutter head snaps to body

• Moulded integral plastic spring for tension

• Plastic carrier

Will it fit together properly?

What will be the cycle time to mould it?

Can we mould it? Will it break?

Will there be

any surface

defects?

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Mechanical Performance

Plastic Fantastic

FEA is widely used to predict mechanical performance. But plastics have special

considerations…

• They are typically much softer than metals. So the restraints have to be carefully

selected to suitably model how it the part is fixed.

• The shapes they form are usually complex shapes – meshing is more demanding.

• Plastics experience much larger deformations than metals – so the FEA solution is

usually nonlinear because stiffness changes must be taken into account

• Nonlinear simulation is commonly needed to model sliding “snap-fits” and “push-fits”.

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Mechanical Performance - Static analysis

Plastic Fantastic

The razor handle has to be stiff enough not to bend when you

use it.

• Even on the thickest of moustaches!

• A 3-point bend test was performed to see how much it

would deform.

Fixtures

Load

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Mechanical Performance – Static analysis

Plastic Fantastic

• The curvature based mesh is ideal -

the element size adapts to fit into the

nooks and crannies!

• Results show that the

razor is very stiff!

• It takes around10 N to

give a 1mm deflection.

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Mechanical Performance – Nonlinear

Plastic Fantastic

The blade on the end of the razor is assembled

using a “push-fit” connection.

Due to this, the razor clip undergoes significant

large deformation and sliding contact.

To model this accurately, Nonlinear simulation will

be needed.

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Mechanical Performance – can it fit together?

Plastic Fantastic

When the component are assembled, we want to know..

• Is there physically enough space to fit the clip in-and-under the

blade groove?

• What force is required to push them together? – it should be

easy enough to push together by hand.

• More importantly, because it squashes when assembled, will this

cause the component to yield/fail?

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Plastic Fantastic

Using the Simulation tool we have been able to prove that..

• It is possible for the components to fit together.

• Even at the maximum inward angle, the clip of

the razor has enough room to fit under the

blade groove.

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Plastic Fantastic


• The force required to push the handle into the blade

would be reasonable for someone to do by hand.

• The push force

required is around 20N

for half of the model

(40 N total).

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Mechanical Performance – does it break when assembled?

Plastic Fantastic


• Some yielding does occur.

• Looking at an iso clipping, the yielded material penetrates

significantly into the depth.

• A redesign may be necessary!

• However since the mesh is very coarse, the stresses will

be more realistic after running a finer-high quality mesh.

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Mechanical Performance – tab spring stiff enough?

Plastic Fantastic

When in use, the blade oscillates back and forth within the

seat.

• Is the tab stiff enough to push the

blade back to the centre?

• If so, what force is required?

• Will it be long enough not to

unhook from the catch?

A central tab is needed to push it back after each stroke.

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Mechanical Performance – tab spring stiff enough?

Plastic Fantastic

The blade is rotated to it’s full travel, then allowed to recoil.

• Even at full tilt, results

confirm the razor remains seated.

It does not unhook!

• The blade is firmly pushed back to centre

with a force less than 1N.

• Results prove a re-design is not necessary.

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Mechanical Performance – will it come apart if dropped?

Plastic Fantastic

If the razor was dropped, ideally the blade

should stay on the handle.

• To simulate this, a drop test was conducted.

• One method that could be used is the drop test in Simulation

Professional.

• However in this case a nonlinear dynamic study was used. The

advantage is that it uses an implicit solver which gives a much

faster solve time.

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Mechanical Performance – will it come apart if dropped?

Plastic Fantastic

• As a possible worst case, the razor was dropped on a corner

point.

• Looking at the results, dropping the

razor from a height of 1m shows that

the blade does not come off.

• Practical test on my bathroom floor agreed with the simulation

results. Although it did eventually break after about the 20th drop!

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Mouldability

Plastic Fantastic

So we can predict how a plastic part will

perform under a variety of loading conditions

BUT ….

• Can we make it easily?

• Can we get the tool right first time?

• Can we minimise tool rework?

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Mouldability with Mould Tools

Plastic Fantastic

SolidWorks Mould Tools helps you …

• Predict draft requirements and

undercuts

• Create parting lines

• Build shut off and parting surfaces

• Build the die and cavity

SolidCAM enables you …

• To CNC the tools

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New for 2012 – SolidWorks Plastics

Plastic Fantastic

Enables you to ….

• Predict whether it will mould – even if you are

not an experienced mould designer

• See whether there will be surface defects

• Check where weld lines will occur

• Understand where the mould will be vented

• Predict cycle times and gate requirements

• Reduce tool development costs and lead time

2 Versions: Plastics Professional and Plastics Premium

Flow & Pack

Multi-Cavity Runner Balancing

Results vs. Time Shrinkage &

Sink Marks

Inserts &

Overmoulding Multishot & Co-

Injection

Gas-Injection & Valve Gates

Fibre Analysis &

Birefringence

Plastics Premium

Flow

Filling

Multiple Gates

Short Shots

Weld Lines

Air Traps

Plastics Professional

Plastic Fantastic

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Mouldability Case Study

Plastic Fantastic

We will predict the mouldability of 3 parts …

• The thin plastic razor carrier

• The main (bulky) body of the razor

• The over-moulded grip

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SolidWorks Plastics – Key Features

Plastic Fantastic

Sophisticated shell, solid and mixed meshing

Guided set-up making it easy to use

Extensive libraries of plastic materials and moulding machines

Flow and Pack simulation – filling and cooling of mould

Extensive results types and display methods

In formative results ‘Adviser’

Report generator – outputs to Word and MS PowerPoint

Video output tools

Plastic Fantastic Runner Design

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Short Shots

Plastic Fantastic

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Multiple Gates

Plastic Fantastic

Plastic Fantastic Weld Lines

Plastic Fantastic Air Traps

Multiple-Cavity

Plastic Fantastic

Runner Balancing (unbalanced)

Plastic Fantastic

Runner Balancing (balanced) Plastic Fantastic

Cooling Time

Plastic Fantastic

Shrinkage Plastic Fantastic

Sink Marks

Plastic Fantastic

Inserts & Overmolding

Plastic Fantastic

Inserts & Overmolding

Co-injection

Plastic Fantastic

Gas Injection Plastic Fantastic

Fibre Analysis

Plastic Fantastic

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Conclusions

Plastic Fantastic

Plastics are exceptional engineering materials

with many valuable properties

Manufacturing requirements must be designed

into the parts ‘up-front’

Strength and performance simulations needs

special care; often using non-linear tools

Designing the part so that it can be easily

moulded will save tooling development costs

and time

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How SolidWorks Can Help You …

Plastic Fantastic

SolidWorks has tools to help you design your

plastic parts …

• SolidWorks Mould Tools

• SolidWorks Simulation

• SolidWorks Simulation Premium

• SolidWorks Plastics Professional

• SolidWorks Plastics Premium

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Further Information and Contacts

Plastic Fantastic

www.solidsolutions.tv

[email protected]

[email protected]

• Simulating Rubbers and Plastics

• SolidWorks Plastics

• Sustainable Design and Plastic

Injection Analysis

[email protected]

plastic fantastic - solid solutions · plastic fantastic • plastic parts must be geometrically...

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