Comparison of Effectiveness of Primecast and

PMMA Additive Manufacturing Processes to produce

patterns for Investment Casting of Ti6Al4V and Al

206

N P Nkhasi, W B du Preez, J G van der Walt

Centre for Rapid Prototyping and Manufacturing

Central University of Technology, Free State

OVERVIEW

• Introduction

– Additive Manufacturing

– Investment Casting by AM

• Methodology

– Building of Patterns

– Metrology of Patterns

• Results and Discussion

• Conclusions

Introduction

Investment casting is an old process

AM patterns without tooling (Time and cost saving)

More complex patterns produced

Durability of the a pattern

In this study a comparison was done on patterns built by PrimeCast and

PolyMethyl Methyl Acrylate (PMMA) respectively, which were produced using

two types of AM technology. The focus of this study is a field in which little

work has been done.

This paper only deals with pattern production

This comparison of the two types of AM patterns is expected to assist the

foundry industry in achieving the most beneficial investment casting results

when using either of these AM technologies.

Introduction…Additive Manufacturing Process

Introduction…Investment casting by AM technology

Methodologyproject plan

Materials and Methodstandard test part with features

Materials and Method…building of PrimeCast

• Laser sintering process (CUT)

Materials and MethodHow a laser sintering work

Materials and Method…

building of PMMA

• Binder Jetting (VUT)

Materials and MethodHow a binder jetting work

Materials and Method…Metrology of Patterns

Two patterns, one each of PrimeCast and PMMA, were scanned at Stellenbosch

University (SU) using a General Electric Phoenix V|Tome|X L240 / NF180 Micro-

CT scanner.

Materials and Method…Metrology of Patterns

• Object attached to rotational

stage

• Object exposed to X-ray

source

• Absorbed radiation

measure with detector

• X-rays are taken from

different angles

• 3D reconstruction

Methodology

pattern to CAD comparisonReconstruction was done with system supplied Datos

reconstruction software

The results of the micro CT scanner were analyzed using Volume

Graphic VGStudio Max 2.1 software.

The best fit alignment was used for this study. Once the two

models were aligned, a simple 3D comparison option

automatically created a colored view showing all dimensional

difference between the two models.

Materials and Method…Mould making

• Mould making in three weeks

• Pattern assembly

Gating for

Titanium alloy

Materials and Method…Mould making and Casting

Gating for

Aluminium alloy

Materials and Method…Mould making..

• Successive stages of dipping and stuccoing

• Repeated until required shell thickness

Face coat secondary coat back-up coat

Materials and Method…Casting

On completion of the coating the pattern was removed by

melting in a steam autoclave, and the ceramic shell was fired

prior to casting.

Results and Discussion

pattern to CAD comparison

• Differences represented by colours

• Green (best fit)

• Yellow (Pattern larger)

• Blue (Pattern smaller)

Results and Discussion

pattern to CAD comparisonPrimeCast

Results and Discussion

pattern to CAD comparisonPMMA

Conclusions

Conclusions

Accuracy PrimeCast PMMA

Straightness (Cubes, square base) Very accurate accurate

Repeatability (Cubes, Free-form) Very accurate Very accurate

Perpendicularity ( Rectangular Protrusion, Rectangular hole) accurate accurate

Angularity ( Pyramid, wedges ) accurate accurate

Symmetry ( Half sphere, Free-Form ) Very accurate Not accurate

Non-constant sloping profile ( Free-form (Conical), Free-form (Sinkhole)) accurate accurate

Circularity ( hollow cylinder) accurate accurate

Flatness accurate Not accurate

Thank you

Contact details

Name of presenter : Nthateng Nkhasi

Cel.: 078 316 8881

E-mail: nthatengnp@gmail.com

www.cut.ac.za | Bloemfontein (051) 507 3911 | Welkom (057) 910 3500