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PART BUILDING ERRORS

IN RAPID PROTOTYPING

PROCESSES

Anup V K1MS09ME024

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PART BUILDING ERRORS IN

RAPID PROTOTYPING

Errors during part building are processspecific.

Material and shrinkage errors are majorfactors in case of thermal RP processes.Eg: SLS, FDM, LENS.

Curing and control errors are main factorsin SL & SGC.

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Part Building Errors in

Stereolithography process

Curing Errors- Caused due to Over Curingand Scanned Line Shape.

Control Errors- Caused due to LayerThickness and Scan Position Control.

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Curing Errors

Over CuringLaser over curing is necessary to adhere layers to

form solid parts. However, it causes dimensional andpositional errors to features.

(a) Thicker

bottom layer

(b) Deformed hole

boundary

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Scanned Line Shape

a) A scanned line is created when a laser

beam scans the resin surface The c/s of ascanned line is called a scanned line shape.

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b) As seen in the figure, the theoretical shape,a parabola, is not obtained. This is because the

process is not stacking of rectangles.c) The edges of the rectangles are jagged,

leading to a stair steps on the edge.

Control Errors

Theoretically, layer thickness should be atdefined value and border line should be at

specified positions.But in practice, layer thickness is variable andborder position varies.

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Figure shows uneven layer thicknessphenomenon. This occurs as the there is alimit to which the thickness can becontrolled, for a particular equipment.

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Part Building Errors in

SLS process

Main cause of part inaccuracy in SLS -shrinkage during sintering, which is not

uniform.Shrinkage can be constrained either by part

substrate or support powder.

Areas of high temperature tend to shrink more

relative to colder ones.Part geometries like thick walls tend to shrink

more.

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Best way to overcome shrinkage is tocalculate shrinkage using a test part and use

scaling factor for the actual model.But this is very time taking and expensive.

Hence the following relation is used-

C= a + b

c= new dimension; a= desired dimension;b= offset value

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A trial part is built and a and b values arecalculated in X and Y directions as shown inthe figures.

Scaling factor in Z axis is assumed constantand is specified by the manufacturer.

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THANK

YOU!