PIM sessions at EuroPM2008

as at 17 July 2008

Tuesday morning, 30 September

Session 9: Powder Injection Moulding - Materials

Fatigue Property of Ti-6Al-4V Components Fabricated by Metal Injection Moulding
Milagres Ferri, O (GKSS Research Centre GmbH)

High cycle four point bending fatigue tests were carried out with samples fabricated by metal injection moulding (MIM) and conventional processing. The conventionally manufactured samples demonstrated an almost twofold higher fatigue resistance of 890 MPa than those fabricated by MIM, whereas tensile strength and ductility were comparable. The possible reasons are related to the presence of pores and the relative coarse microstructure of MIM samples. The results are discussed in terms of mechanical properties, microstructure, composition and fracture surface.

Effects of Solvent Debinding Parameters on Oxygen and Residual Carbon in Injection Moulding of Titanium
Sidambe, A (University of Sheffield)

The solvent debinding properties of a water soluble binder have been investigated for the injection moulding of commercially pure Titanium powder. The investigation included analysis of the oxygen and residual carbon content, which affects the mechanical properties of the sintered part. The effect of several debinding parameters such as specimen thickness, powder loading, debinding time and debinding temperature were also studied.

Sintering and Heat-treatment of Injection Moulded 440K-type Martensitic Stainless Steel Compacts
Anwar, M Y (Univ. of Engineering & Technology)

Sintering and heat treatment of injection moulded hardenable stainless steel powder (440K-type) compacts has been studied. The binder system, known as the Sheffield Binder System, was used, which is comprised of two polymers, a major component of water soluble polyethylene glycols (PEGs) and a minor component of very finely dispersed polymethyl methacrylate (PMMA) derived from an emulsion. Mixing of a number of different feedstocks was carried out manually. Following the identification of the optimum binder composition (20 wt. % PMMA, 80 wt. % PEGs) and solid loading (68 Vol. %), several test specimens were injection moulded for further processing. The PEGs were removed by leaching with water. The PMMA was removed by pyrolysis, prior to the sintering stage. Samples were sintered to ~ 99 % of theoretical density. With careful control of the various processing parameters, including sintering temperature and time, cooling rate and heat treatment conditions, good mechanical properties including high hardness of HRC 60 were attained. In an attempt to reduce the process cycle time, the sintering ramp was modified to include solutionising and oil-quenching in a single sintering cycle. The hardened samples were tempered at temperatures from 150 to 350 °C for 2 hours. Scanning electron microscopy was used to reveal the micro-structural changes during various sintering and heat-treatment stages.

Towards Producing Magnesium Parts by Powder Metal Injection Moulding (MIM)
Wolff, M (GKSS Research Centre Geesthacht GmbH)

Aside from its well established use in lightweight construction, magnesium is highly suitable as a future material for medical applications such as biocompatible and biodegradable implants. Especially porous components enhancing the bone-implant interface offer new possibilities in medical treatment. Metal Injection Moulding (MIM) possesses a high potential for the economic production of such implants. However, sintering of magnesium powder is strongly inhibited by the stable oxide layer which is formed immediately after exposing to air. Contrary to e.g. titanium, no solubility of oxygen in magnesium exists; therefore, the oxide layer is not dissolved during sintering. In this study, different Mg-based powder blends were investigated to overcome this problem. For the sintering experiments at 605 °C, specimens with two different compositions were blended: MgCa1 and MgLi4. For this the pure Mg powder was blended with elemental calcium and lithium, respectively, their corresponding hydrides and, as a second route, master alloy powders to initiate solid phase sintering via a temporary liquid phase. In particular, the latter method yields a well sintered but porous material.

POSTERS

Fabrication the Nanostructure Sintered Carbon Steels of Nanocomposite Powders by Fe+3C Through Isostatic Pressing
Ciobanu, M (University of Craiova)

This paper presents characteristics some sintered carbon steels of composite nanopowders by Fe+Fe3C, obtain through mechanical alloy, for 40–60 hours, in a planetary mill with balls Pulverizette 6. The sample was obtained through injection in a machine by medium pressure type GOCERAM using the MEDPIMOULD technology. After feedstock’s with wax-based binders the three types by composite nanopowders, it was injection with pressure by 5-6 MPa, after that it was sintered at temperatures by 1100 – 11500C for 1 hour in medium by argon. Are presents correlations between composite nanopowders morphology, pressure injection, sintering temperatures and characteristics microstructures and resistance to wear the samples.

Machinable Sintering Trays / Setters for MIM-Sintering
Springer, M (RATH AG)

Metal Injection Moulding (MIM) is recognized by many industrial branches as a cost-efficient and reliable production process for metallic parts. MIM is distinguished by total flexibility and freedom in the design and production of complex part geometries and an almost unlimited material variety.

The MIM market has grown considerably over the last 10 years. Due to the acceptance of the MIM process in automotive industry, many new applications and markets are now being developed.

One of the essential steps in MIM production is the sintering process that is the critical link between the green/brown part and the net-shaped end part.

To ensure a proper positioning during de-binding and/or sintering of the high complex MIM parts a new machinable material (ALTRAFORM KVR) for sintering trays/setters was developed and is successfully used.

Altraform KVR allows the end user to tailor unique setter designs to meet their specific process requirements and to position the MIM part on the contoured support during sintering process.

The excellent machinability of this material allows ultimate flexibility in setter design to fit customer needs with none of the hard tooling requirements or shape limitations of dense alumina materials. The sintering trays are CNC machined to customer drawings and according the MIM part geometry.

In turn this gives engineers more flexibility in setter design and this possibility of free design implicates an additional “degree of freedom” for an efficient and therefore economic MIM process from design to finished product.

Session 12: Powder Injection Moulding 2 - Binder/Debinder Process

Metal Injection Moulding Using a Water-Soluble Binder: Effect of Backbone Polymer in Process
Jorge, H (CTCV)

In the attempt to develop a water debinding feedstock, for powder injection moulding (PIM), based on AISI 316L steel, the formulation of the binder was designed and evaluated using polyethylene glycol as the base polymer. This paper reports a comparative study between two binders with different back-bone polymers: a widely used low density polyethylene (LDPE) and an elastomeric metallocene polyethylene (MPE).

Both feedstocks evidenced a similar and acceptable degree of homogeneity, yielding to stable moulding and debinding steps. Sintered parts had analogous characteristics - high density, low part weight variability and shrinkage and dimensional precision within the typical PIM ranges. However, the sintering process revealed some defects in LDPE-binder parts, attributed to phase separation during moulding, with a detrimental effect on the mechanical properties. Alternatively, MPE was found to provide mouldings with good quality.

High Strength Brown Parts Produced by Fast Microwave-Assisted Debinding
Veronesi, P (University of Modena & Reggio Emilia)

The binder removal from 430L-steel MIM parts was performed in a two-step procedure using chemical and thermal debinding. During the first step, almost 80% of the binder is removed and a porous structure is created, which then favours the subsequent step. The second step was performed in a multi-mode microwave applicator, at 2.45 GHz ISM frequency. Numerical simulation allowed to optimise the microwave applicator loading conditions, in terms of heating homogeneity and efficiency. Experimental validation confirmed that using microwaves it is possible to reduce conventional debinding times by a factor of 3, and that the resulting brown parts possess a 4 times higher compressive strength. This phenomenon can be ascribed to local over-heating of the regions surrounding neighbouring metal particles, triggered by the high frequency electric field. This promotes the formation of necks among the particles, leading to pre-sintering, despite the overall measured samples temperature, which never exceeded 600°C.

MIM using Supercritical CO2 Debinding Method and Its Improvement
Shimizu, T (AIST)

Commercial MIM processes use thermal debinding or an extraction method; the former requires an inordinate period of time, while the latter involves the use of toxic solvents. We have been investigating the application of supercritical CO2 extraction to this process, which promises to overcome these drawbacks. For this, we must first address the following: the prohibitive cost of the high-pressure vessels required and the low solubility of binders in supercritical CO2. In the process developed by Takishima and others, the latter problem is resolved by the use of activated carbon to adsorb the binder; this is efficient and fast but introduces the additional problem of having to deal with the waste activated carbon. Here we propose the use of a liquid solvent as an adsorbent; this allows easier control and better efficiency than activated carbon in adsorbing binders. Moreover, the dissolved binder can be re-extracted by distillation

New Furnace Uses Plasma and Laminar Gas Flow to Reduce Cycle Time for Powder Metal Injection Molded Parts
Joens, C (Elnik Systems)

A new furnace has been created for debinding the secondary binder and sintering parts made by Powder Metal Injection Molding. Debinding is achieved with the help of a plasma at 1 to 7 mbar pressures and sintering is done with laminar gas flow at 400 mbar pressure. The paper describes the furnace and results achieved by debinding and sintering in this furnace. The combination of these two technologies result in significant cycle time reduction compared to conventional debinding and sintering.

POSTERS

Case Studies Using New Binder System with Water Debinding
Auzene, D (CRITT MDTS)

With the support of the European community, French Government and Ardennes’ department, since end of 2006, CRITT-MDTS(1) has set up the MIM technology in order to transfer this manufacturing process to French companies. During the year 2007, injection press, debinding device and sintering furnace have been bought and installed. Together with the German’s company POLYMER-CHEMIE as a feedstock supplier, different industrials applications are developed. The binder system developed by POLYMER-CHEMIE uses tap water as a solvent with 0.5% inhibitor for corrosion prevention. Moreover the injection moulding process can use a low tool temperature and all in all permits to reduce significantly the debinding cost. Thence this binder removal in water is environment friendly and involves no hazards during MIM manufacturing.

Model and Method to Calculate Viscosity of Metal-Polymer Compositions (MIM feedstocks)
Dovydenkov, V (Metma JSC)

A model to calculate viscosity of metal and polymer composites where solid phase consists of one or two components is proposed. While elaborating the model we assumed that each of the solid phases consisted of spherical particles of similar diameter, packing of the particles on the sliding surface has simple cubic shape, and that on the surface perpendicular to sliding surface it is hexagonal. Analytical expressions for composite viscosity are obtained and examples of viscosity calculations depending on volume content of each of the solid phase components are given.

Properties of MIM Gas-Atomized 316L Stainless Steel using Locally Developed Palm Stearin Based Binder System
Ismail, M H (University of Sheffield)

IIn this present work, locally developed palm stearin based binder system has been investigated with one grade of gas atomized 316L stainless steel powder. Optimal powder loading of 65vol% was chosen based on critical powder volume percentage (CPVP) result obtained. Three different formulations of binder system comprised of palm stearin (PS) and poly-propylene (PP) at weight fraction of 50/50, 60/40 and 70/30 respectively were used in this study. Sintering process was performed at four different sintering temperatures; 1300oC, 1320oC, 1340oC and 1360oC in a controlled vacuum atmosphere. The properties of the sintered specimen such as density, hardness and tensile were studied and discussed.

Rapid Debinding of a Titanium Injection Moulded Component
Sidambe, A (University of Sheffield)

A two-step debinding process which uses a water soluble binder has been investigated. The binder consists of major fraction of water soluble polyethylene glycol (PEG), a minor fraction of polymethyl methacrylate (PMMA), and small amounts of Stearic Acid (SA) used as a lubricant. Debinding was carried out firstly by immersing parts produced via the metal injection moulding process (MIM) in distilled water at temperatures ranging from 40°C to 75°C to remove the PEG component of the binder and then, secondly, heating in an inert atmosphere to remove the remaining PMMA binder. The results show that no dilation or loss of shape was observed on the moulded specimens at the temperature of 60ºC during solvent debinding. The specimens had an adequate strength for handling even after PEG leaching. The pores formed after solvent extraction allowed for thermal debinding by pyrolysis. Lowering the temperature was shown to decrease the debinding time.

Tuesday afternoon, 30 September

Session 15: Powder Injection Moulding 3 - Moulding

Overmoulding of Cast Substrates
Haupt, U (Arburg GmbH & Co Kg)

The challenges and solutions of a new processing technology to manufacture two material metallic ceramic components manufactured in two different processing routes is described..

A ceramic substrate is produced in a non injection moulding process, for example casting or pressing. Then, depending of the demands of the final product, either directly overmoulded or shaped. This shaping can be done by deep-drawing. In the next processing step the substrate is overmoulded with a different material. In the examples shown it will be metal feedstock. One of the big challenges is to find suitable materials, which have the same shrink and require the same sintering schedule. The aim is to combine different material properties like conductivity and non conductivity in one sintered body.

New Insights into Feedstock Behaviour and Injection Moulding Simulation for PIM
Kukla, C (Montanuniversitaet Leoben)

Nowadays PIM is an advanced technology for the production of complex shaped metal or ceramic parts. There is a high pressure on PIM to optimise the process. Two prerequisites for this optimisation are a better understanding of the feedstock, especially for quality control, and an improved simulation of the injection moulding process for PIM. For good and reliable simulations a high quality of material data is necessary. Extensive work has been done in investigating the feedstock behaviour, mainly viscosity, and in improving the simulation software with the findings of this investigation. The results of the mentioned investigations of the feedstock behaviour will be presented. They are showing the key points of the unique behaviour of feedstocks. The use of these results for improving the simulation software for PIM is highlighted by examples of injection moulding simulations.

Combining Materials by MIM
Hartwig, T (Fraunhofer IFAM)

Material combinations produced by MIM have been published for some years now and have received industrial interest. Although they can be produced by sinter joining more versatility may be obtained by combining the materials during moulding using two colour moulding machines. In this presentation we compare the mechanical properties of small and large tensile test specimens produced from feedstocks based on different binders and powders. The results show that a smaller interface can be produced with higher reliability than a large interface.

Sintering of Zirconia/430L Stainless Steel Bilayers for Co-Powder Injection Moulding
Dourandish, M (Sharif University of Technology)

To fabricate ceramic/metal complex-shaped part by co-powder injection moulding process (2K-PIM), it is essential to tailor the sintering parameters in order to gain a low mismatch shrinkage, i.e. high sintering compatibility. In the present work, nanocrystalline 3Y-TZP and commercial 430L MIM grade stainless steel powders were co-sintered at various sintering cycles. Isothermal and non-isothermal sintering behavior of the individual and composite layers in argon and vacuum atmospheres were examined. High resolution scanning electron microscopy (HRSEM) coupled with energy dispersive X-ray (EDX) analysis was used to study the bonding interface between the ceramic and metal joints. It is shown that the low difference in the coefficient of thermal expansion (CTE) and relatively low mismatch strain during sintering, a crack free joining is achievable. The analysis of the bonding zone indicated an interlayer diffusion of Zr, Fe and Cr, and a ternary Zr-Fe-Cr oxide interface during sintering.

Session 19: Powder Metal Injection 4 - Micro-PIM

Micro-MIM for Medical Applications
Imgrund, P (Fraunhofer IFAM)

In recent years the scope of Micro-MIM (µ-MIM) technology has expanded from iron-based materials to a considerable range of functional materials and materials for medical applications. In this paper, three examples of process development for biocompatible materials are discussed.

Pilot scale production of a replica of the smallest human bone (stapes) made by µ-MIM of Titanium is shown. Microstructure and properties of the material are investigated. As a second example, the development of µ-MIM technology for Nickel-Titanium parts with phase transformation temperatures in the range of body temperature for biomedical applications is shown. As a third example, micro-structuring of metallic surfaces for metal-based implants by µ-MIM is presented. Results on the development of moulding and sintering 316L stainless steel substrates using blends of micron and nano sized powders are shown. Repetitive micro surface patterns that were obtained in the form of positive hemispheres showed improved bioactivity compared to non-structured tissue control samples.

Role of Nanostructured Layers on Powders During Sintering of Low Carbon Austenitic Stainless Steel
Barreiros, F (Polytechnic Institute of Leiria)

The present study aims to optimize feedstocks for µMetal Injection Moulding (µMIM) of 316L stainless steel (SS) µpowders, using a thin film of similar chemical composition, mixed with a commercial organic binder. Coating SS powders with typical particle size for conventional powder technology can assume an important role [1]. Carbon enriched atmospheres during heat treatment contributes to an abnormal grain growth and to a depletion of chromium in the environs of grain boundaries, phenomena that can be blocked by coating the powders. The effect of nanosized grain thin films on SS powders concerning the final performance of the stainless steel used in µMIM is highlighted in present study. SS powders with d50 = 3 µm were treated in automatic sputtering equipment with a high-frequency vibrating powder holder and compared with d50 = 8 µm SS powders coated and uncoated. The debinding and sintering thermal treatments were similar. This study shows the importance of grain size/coating thickness in the performance of coated powders. The decrease of particle’s size and/or thin film thickness can improve the compactness but increase also the grain size of sinters. The last one is the main responsible for the hardness values. However, the hardness values are similar to the SS wrought. Finally, whatever the particle size used the coated powders contribute to avoid precipitation-free zones (PFZ) in sinters.

Feedstock Development of Micro Metal Injection Molding (µ–MIM)
Tai, C K (Advanced Materials Technologies Pte Ltd)

Micro metal injection molding (µ–MIM) is a promising process for low cost mass production of three-dimensional microstructures. The fabrication of micro-structured parts with high aspect ratios requires considerations on the powder and binder composition for successful injection molding. For complete molding of small and complex detailed microstructures, powder with a small particle size has to be used. In addition, the binders of the feedstock have to allow pressure free and complete debinding and sintering without deformation. In this paper, initial study on the processing of 316L stainless steel micro-gear is investigated. 316L powder with different particle sizes and different multi-component binder systems are used for the preparation of feedstock. The green and final parts characteristics will be examined for suitability of the feedstock in MIM processing of microstructures

Accuracy Evaluation of Ultra-Compact Gears Manufactured by Micro-MIM Process
Nishiyabu, K (Osaka Prefectural College of Technology)

The production of micro-size and micro-structured parts by metal powder injection moulding (MIM) process require more sophisticated techniques than conventional MIM. New techniques for the quality evaluation of those tiny parts are also necessary to be developed. A micro-planetary gear made of 17-4PH stainless steel has been developed by micro metal powder injection moulding (µ-MIM) process. This study describes the method of fabrication and quality evaluation of the ultra-compact plain gears (module: m=0.07, number of teeth: z=24) manufactured by µ-MIM. Cross-sections of the gear teeth were observed with a digital microscope and dimensions of the teeth were measured by image analysis. The variation in dimensions of teeth was evaluated for mold, green compacts, sintered parts and age-hardened ones. It was shown that those experiments contributed useful information on the quality of the ultra-compact gears.

POSTERS

Micro Powder Injection Moulding - New Developments and Results
Piotter, V (Forschungszentrum Karlsruhe)

With the use of polymer materials, micro injection moulding nowadays represents an established variant of micro manufacturing. The development was furthered by the trend towards miniaturization, i.e. the growing market for micro products. On the other hand, industrially viable processes for stronger materials are still lacking. Therefore, development of so-called MicroPIM for the fabrication of metal and ceramic micro components was taken up. To increase process performance, the interdependencies between tool and parameters on one side and the resulting dimensions of the products on the other side have been investigated comprehensively. Replication of more complex nearly free-formed parts by special solutions for e.g. the demoulding procedure is a further trend to be identified. Mainly to reduce mounting costs Micro-Two-Component Injection Moulding is under development. Here, the main technical challenge is the process configuration to obtain either mobile or immobile combinations. As an interesting example 2-component shaft-gear wheel prototypes consisting of different ceramic or metal materials are described.

Special Thematic Workshop on the Quality of MIM Products

Wed Oct 1, 2008

09.00 – 12.30 hrs

Chairmen: Dr. Bruno Vicenzi (MIMItalia srl, Italy) and Dr Frank Petzoldt (Fraunhofer – IFAM, Germany)

Objectives : Quality of MIM products

Metal Injection Moulding (MIM) is a steadily growing PM production process that is nowadays already acknowledged among common production routes for mass products with intricate shapes and excellent properties in several materials, from plain carbon steel to stainless steel, non ferrous alloys and even superalloys and titanium. MIM customers are still looking at MIM as a great occasion to innovate shapes and capabilities of their products with good economy, but they also require a growing attention on quality of delivered parts, especially when more requiring applications are involved.

This workshop is aimed to dig into the subject of the quality of MIM products, analysing it 'bottom-up' (starting from the properties that the customers can feel and measure) instead of the usual 'top-down' approach (analysing process steps to see the influence on part quality). The invited speakers will give the audience their look on four different aspects of product quality, and a general discussion will enable information exchange between MIM suppliers, producers and customers.

(More informaiton and papers will be added shortly)