CSME

Controllability of Surface Roughness by Adaptive Slicing in Rapid Prototyping Manufacturing

S. Sikder, A. Barari ,and H.A. Kishawy

Road Mapo Introduction

o Rapid prototyping processo Slicing Techniques and RPM o Researches on Slicing Techniques.

o Proposed Algorithm.o Results and Discussion. o Q &A.

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S. Sikder, A Barari and H. A. Kishawy

CSME-2012,MANITOBA, Canada

Introduction: Rapid Prototyping Manufacturing (RPM)o RPM is a layer based non-conventional

manufacturing technique. o Product is manufactured using layer by layer addition of material from a Computer Aided Design (CAD) model. o Compared to conventional machining , RPM can produce more complex part in a short time with higher accuracy. o This technology is widely used in automotive, aerospace, and medical industries.3 S. Sikder, A Barari and H. A. Kishawy CSME-2012,MANITOBA, Canada

Rapid prototyping ProcessSurface Representation

RP System

Creation of Solid CAD Model

Slicing

Scanning Paths

Deposition

Tessellated Representation

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Rapid prototyping Processo The slicing process is a highly critical stage in RPM. o RP machines generally have lower and upper layer

thickness limit. o Large thickness of slicing generally incorporates rough surface quality due to the stair-case effect and its corresponding cusp height. o Alternatively, utilizing very small thickness of layers makes the process too expensive and takes much longer time to finish a part. o These two contradictions have led to development of several slicing techniques.5 S. Sikder, A Barari and H. A. Kishawy CSME-2012,MANITOBA, Canada

Slicing Techniques and RPMo Depending on the CAD model is used in RPM, the slicing

process can be divided into 2 types: Slicing of direct CAD model. Slicing of tessellated CAD model.

o Tessellated CAD model slicing however has several o o o o6

disadvantages such as: STL file loses original topological and geometrical data due to approximation. It carries uncertainties and defects such as gaps, overlaps,etc. It sometime STL CAD files are bulky. It generally has higher slicing and Chordal error.S. Sikder, A Barari and H. A. Kishawy CSME-2012,MANITOBA, Canada

Slicing Techniques and RPMo Both direct and indirect slicing can be divided in to

two categories. They are: Slicing with uniform thickness. Slicing with adaptive layer thickness.

o In uniform slice thickness slicing slice thickness is

fixed. o In adaptive layer thickness layer thickness varies with slicing criteria and CAD geometry to reduce surface roughness and build time.S. Sikder, A Barari and H. A. Kishawy CSME-2012,MANITOBA, Canada

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Researches on RPM Slicing Techniqueso Starting from early 1990s several researchers worked on slicing

of slicing of tessellated CAD model. Most of the slicing model is based on: Allowable cusp height Limit. [1][2] Part and surface feature.[3]

Duel layer thickenss (For interior and exterior) [4] Allowable roughness limit.[5]

o However due to approximation in CAD model this type of

slicing is not appropriate.

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Researches on RPM Slicing Techniqueso Direct slicing algorithms come in existence during

1995. o In the early years most of the models are based on fixed slice thickness. [7][8] o Newer model are based on different adaptive slicing applied on various CAD file type. [9-15] o Hover no researcher have used IGES representation face for slicing using proper NURBS surface.9 S. Sikder, A Barari and H. A. Kishawy CSME-2012,MANITOBA, Canada

Proposed Algorithmo Central to the problem of slicing CAD model is the

determination of intersection points between the slicing plane and the model. o A computational platform is developed to implement the developed adaptive direct slicing algorithms. o The algorithm receives CAD model in IGES format as input instead of STL file. o First, a solid or surface or multi-feature CAD part is produced and converted to IGES format to be transferred to the developed computational platform.10 S. Sikder, A Barari and H. A. Kishawy CSME-2012,MANITOBA, Canada

Proposed Algorithmo Initial Graphics Exchange Specification(IGES) file is

plotted based on the geometric feature in IGES CAD file. If any feature entered our system can be represented by, G. Then G can be expressed as:G SN Sp SR

o Where, SN represents the NURBS surface, SP is Planer

surface and SR is revaluated and trimmed surface. o Maximum Z point (Zmax) and minimum Z point (Zmin) is computed for slicing algorithm from this data. o Then slicing algorithm is implimented.11 S. Sikder, A Barari and H. A. Kishawy CSME-2012,MANITOBA, Canada

Proposed Algorithm

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Start

Maximum and minimum slice thickness(tmax & tmin)

Minimum point of part in z axis Zj =Zmin+ti

ti =tmax

Zj cosmax Or ti

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