Additive manufacturing of metal components with the ARBURG plastic freeforming process

doi:10.1016/j.cirp.2018.04.104

CIRP Annals

Volume 67, Issue 1, 2018, Pages 225-228

https://doi.org/10.1016/j.cirp.2018.04.104 Get rights and content

Abstract

Using the ARBURG freeformer in the metal injection molding (MIM) process chain instead of an injection molding machine for molding the parts constitutes a new approach for the additive production of sintered metal components. Its main benefits are toolless manufacturing and using the conventional MIM feedstock. This paper presents this kind of approach with a carbonyl iron feedstock. The investigation includes the determination of the influences of the relevant printing process parameters on the mechanical properties of the sintered parts and the comparison with MIM. Experimental results are discussed, including an analysis of microsections, density, tensile strength R_m and shrinkage.

Introduction

The demand of high productivity, high precision and complex geometries initiated the development of metal injection molding, abbreviated MIM [1]. Fig. 1 on the left shows the conventional MIM process. In the first step, metal powder and binder are mixed to create a feedstock. In the second step, the feedstock is plasticized in an injection molding machine and injected into a mold with specific geometry. The resulting part is called green part. In the next step, the binder is removed from the green part by debinding, e.g. thermal debinding. In the following sintering step, the metal powder particles bond together which causes densification and shrinkage of the part [1], [2], [3].

The necessity of a mold for each geometry makes the process only economically usable for a large number of pieces (at least 10,000) [4].

In 2013, the company ARBURG launched the ARBURG freeformer, a 3D printer able to process commercially available standard plastic granulate which is normally used for plastic injection molding [5]. Compared to other additive manufacturing processes, usually requiring special and/or expensive materials, this represents an important advantage. However, the mechanical properties of plastic parts are limited. One opportunity for the production of high-strength components with the ARBURG freeformer is the usage of metal feedstock from MIM for printing green parts. Afterwards, the green parts must be debinded and sintered to obtain manufactured sintered metal parts. Fig. 1 on the right shows this ARBURG metal freeforming process. By replacing the injection molding machine with the ARBURG freeformer in the MIM process chain, a mold and the corresponding high number of pieces is no longer required. Furthermore the using of conventional MIM feedstock as raw material is also a main benefit in terms of material costs.

The processing of metal feedstock with the ARBURG freeformer has been subject of recent research. The aim of this publication is to determine the influences of the printing process parameters on the achievable mechanical properties of the sintered parts.

Section snippets

State of the art

Additive manufacturing processes offer a high degree of design freedom due to their layer-based production of three dimensional parts [7]. Additive manufacturing processes also do not require part-specific tooling [8]. There is a distinction between rapid prototyping concerning the production of prototypes and rapid manufacturing concerning the production of functional parts [9]. ARBURG plastic freeforming is a process capable of producing functional plastic parts. The functional principle of

Approach

The aim of this work is to determine the influences of the relevant printing process parameters on the production of metal parts with high mechanical properties comparable to MIM using the ARBURG freeformer. Therefore, a design of experiments (DoE) is created, which includes the selection of relevant independent variables (printing process parameters), their levels and the dependent variables (mechanical properties). Afterwards, the experiments are carried out, the mechanical properties are

Design of experiments

The aim of the investigation constitutes in determining the significant influence parameters of ARBRUG freeforming for the production of metal parts with high mechanical properties. The dependent variables which describe the mechanical properties are density, shrinkage and tensile strength R_m.

The mechanical properties of sintered parts mainly depend on porosity [1]. In the conventional MIM process, pores can occur during molding. High shear rates cause powder/binder separation, which leads to

Results

In the following, the results for the density, shrinkage and tensile strength R_m are presented and discussed.

Conclusion

This paper presents an experimental and statistical analysis of selected process parameters of the ARBURG metal freeforming process on the mechanical properties density, shrinkage and tensile strength R_m. In comparison to MIM, ARBURG metal freeforming reaches equal values: 98.3–100% of the density in the green state, compared to MIM, 99.0–100.4% of the density in the sintered state, compared to MIM, 16.05–16.26% shrinkage, compared to 16.08% shrinkage of MIM, 95.7–99.2% of the tensile strength R

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Additive manufacturing of metal components with the ARBURG plastic freeforming process

Abstract

Introduction

Section snippets

State of the art

Approach

Design of experiments

Results

Conclusion

CIRP Annals

CIRP Annals

CIRP Annals

CIRP Annals

Pulvermetallurgie: Technologien und Werkstoffe

Injection Molding of Metals and Ceramics