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Conference Papers School of Mechanical and Design Engineering

2010-01-01

A Study of Demoulding Force Prediction Applied to Periodic A Study of Demoulding Force Prediction Applied to Periodic Mould Surface Profiles Mould Surface Profiles

Kevin Delaney Technological University Dublin, kevin.delaney@tudublin.ie

Giuliano Bissacco University of Padua

David Kennedy Technological University Dublin, david.kennedy@tudublin.ie

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Recommended Citation Recommended Citation Delaney, K., Bissacco, G., Kennedy, D.: A Study of Demoulding Force Prediction Applied to Periodic Mould Surface Profiles. Society of Plastic Engineers' ANTEC 2010 conference. 2010.

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The following was presented at the Society of Plastic Engineers conference, ANTEC 2010,

held in Orlando, Florida from May 16-20 2010.

For further details and to access the full paper please refer to the conference proceedings.

-Kevin D. Delaney,26May2010

A STUDY OF DEMOULDING FORCE PREDICTION A STUDY OF DEMOULDING FORCE PREDICTION APPLIED TO PERIODIC MOULD SURFACE PROFILESAPPLIED TO PERIODIC MOULD SURFACE PROFILES

A STUDY OF DEMOULDING FORCE A STUDY OF DEMOULDING FORCE PREDICTION APPLIED TO PERIODIC PREDICTION APPLIED TO PERIODIC

MOULD SURFACE PROFILESMOULD SURFACE PROFILES

K. Delaney, Dublin Institute of Technology.Dr. G. Bissacco, University of Padova.Dr. D. Kennedy, Dublin Institute of Technology.

Aim of this researchAim of this research

Can we predict demoulding forces if we know: • Parameters used to fabricate the replication tool• Replication process parameters• Details of the mould and part materials

?

Presentation OutlinePresentation Outline

• The problem of demoulding force• Demoulding force modeling• Note regarding replication tool surfaces• Adapting Colton et al model to periodic profiles• Validation of the model

Examples ofExamples of the problemthe problem at micro scaleat micro scale

[Worgull et al]

Contributors to demoulding forceContributors to demoulding force

Representation of ejector pins

(x2) Volume where vacuum force

develops

Contact pressure and interface adhesion force acts on this boundary

Moulding core

Replicated part

Demoulding force modellingDemoulding force modelling

Release force(FR) prediction

Normal contact pressure (PA)

Demouldingforce model

FR=����x PA x AC

Coefficient of friction (����)

Area of contact (Ac)

Note regarding replication tool surfacesNote regarding replication tool surfaces• Replication tools are mainly

produced by mechanical processes with an inherent surface roughness.

• Even at the micro scale asperities and burrs cause interlocking which results in demoulding problems.

• During demoulding either the part or tool have to deform to slide over each other.

Micro replication tool and surface profile

The Colton et al modelThe Colton et al model -- 11

• Developed for stereo-lithographic tools• Stair-like surface profile

stairdefthermfricej FFF ,, +=

The Colton et al modelThe Colton et al model -- 22����

l

����

( )materialseTemperaturlfneq ,,,, θδµµ +=

The Colton et al modelThe Colton et al model -- 22����

l

����

( )materialseTemperaturlfneq ,,,, θδµµ +=

roughnesssurfacetodue

oncontributiAdditional µ

The Colton et al modelThe Colton et al model -- 33

• The Colton et al model has already been applied.

• It tries to explicitly capture how the coefficient of friction varies with surface roughness.

• We can benefit from adapting it for other periodic surfaces.

AdaptAdapting theing the Colton et al modelColton et al model1. Analogy between stereolithographic and periodic (turned) surface

2. Surface simulation and analysis for verification

3. Model Implementation

4. Model Validation using published data

5. Model Robustness study

Analogy between stereolithographic and periodic Analogy between stereolithographic and periodic (turned) surface (turned) surface -- 11

����

l

����

Stereolithographic, stair-step profile

Turned periodic mould surface profile

?

Analogy between stereolithographic and periodic Analogy between stereolithographic and periodic (turned) surface (turned) surface -- 11

Feed direction

Rate: f mm/rev Tool radius:R mm

l

����

����

l

����

Stereolithographic, stair-step profile

Turned periodic mould surface profile

Analogy between stereolithographic and periodic Analogy between stereolithographic and periodic (turned) surface (turned) surface -- 22

Rf

Ra×

=32

2

Rf×

=8

2

δFeed direction

Rate: f mm/rev Tool radius:R mm

l

����

Surface simulation and analysisSurface simulation and analysis for verificationfor verification

Sa 2.065 �m Sq 2.400 �mSy 8.152 �mSz 8.131 �m

Model implementationModel implementationDetails of Hopkinson and Dickens component used for validation

Moulding core

CollarSprue

Dimensional details:Diameter of the collar at base = 40mm, Diameter at opening of collar = 16mm,Length of the moulding = 40mm, All walls 2mm thick,Draft on male feature = 1.5 degrees.

Model validationModel validation

Robustness of the ColtonRobustness of the Colton et alet al ModelModel -- 11

0.25 ~ 0.4����Coefficient of friction160 ~ 173TpmPolymer melting temperature (����C)

40 ~ 60TpeComponent ejection temperature (����C)15 ~ 49TmiMould temperature at injection (����C)30 ~ 60TmeMould temperature at ejection (����C)0.2 ~1.0RCutting tool radius (mm)

ValueParameter

Robustness of the ColtonRobustness of the Colton et alet al ModelModel -- 11

0.25 ~ 0.4����Coefficient of friction160 ~ 173TpmPolymer melting temperature (����C)

40 ~ 60TpeComponent ejection temperature (����C)15 ~ 49TmiMould temperature at injection (����C)30 ~ 60TmeMould temperature at ejection (����C)0.2 ~1.0RCutting tool radius (mm)

ValueParameter

Robustness of the ColtonRobustness of the Colton et alet al ModelModel -- 22

Core surface roughness (Ra ����m)

Dem

ould

ing

Forc

e (N

)

ConclusionConclusion• Limitations of the Colton et al model applied to periodic

(non stereo-lithographic) surfaces highlighted. • Some issues related to micro machined surfaces listed.• More advanced model needed

– Should consider viscoelastic behaviour of replicating material together with any permanent deformation (instead of assuming elastic deformation).

• Model should be suitable for implementation in a Finite Element Modelling package.

• Efforts are ongoing towards the development of such a model.

Questions?Questions?

A Study of Demoulding Force Prediction Applied to Periodic Mould Surface ProfilesRecommended Citation

Microsoft PowerPoint - ANTEC2010_presentation_KDD26May2010.ppt