Nanopowders for PIM

KE-31.5530 NanoparticlesArno Lehtonen

4. 5. 2011

For complex shaped components powder injection moulding (PIM) is the technology of choice since it is capable of producing near-net-shape parts in highly automated serial production. Four manufacturing steps have to be carried out: compounding of feedstock, injection moulding, debinding and sintering.

Why Injection Moulding?

Powder Injection Moulding Process

Why PIM and Nanopowders?

• PIM = P (powder properties) + IM (forming)• Rheology; thin details (MST-parts)• The general rule is that the minimum feature

that can be produced is ten times the particle size

• Mechanical properties (Drills, cutting tools)• Available powders: Copper, iron, tungsten,

cobalt, zirconia, alumina, tungsten carbide

General Powder Requirements

• Grain size and size distribution• Grain form• No agglomerates• No surface contamination• No closed pores

Formulating and Mixing Feedstock

• Most binder systems consist of waxes and polymers

• Surface active component• Requirements: Excellent flowability, high

solids loading, form retaining ability and easy debinding

Powder Loading

Binder System for Cemented Carbides

• Melting range C Evaporation C• 49 % Parafiin 43 - 66 230 • 39 % Polypropylen 170 350 • 10 % Carnauba-vax 83 - 86 280 • 2 % Stearinic accid 70 190

Vacuum Z-blade mixer

Injection Moulding

• Homogenous filling of the mould cavity• Low internal stress• Elimination of weld lines

Flow Patterns and Weld Lines

JSW 50 ton injection moulding unit

Debinding

• Vacuum assisted thermal treatment• As wax komponents evaporate, they create

chanels for escaping gasses• Rearrangement of particles• Forming of form sustaining sceleton

Debinding Defects

Sintering

• Vacuum and / or pressure assisted thermal treatment

• High density part; shrinkage• Porosity, chemical balance• Grain growth; inhibitors

Phase diagram of the W–C system

Problems with IM Nanopowders

• Pyrophoricity, working hazards• Large specific surface area and the associated

tendency to agglomerate• Effects of storage time to feedstock• Defects can be created in the bebinding stage;

capillary forces• Grain growth during sintering

Grain Growth

References (1/3)

• Influence of dispersant, storage time and temperature on the rheological properties of zirconia–paraffin feedstocks for LPIM

• Fatih A. Cetinel , Werner Bauer, Marcus Müller, Regina Knitter, Jürgen Haußelt• Journal of the European Ceramic Society 30 (2010) 1391–1400

• Micro powder injection moulding• Rudolf Zauner• Microelectronic Engineering 83 (2006) 1442–1444

• "The smaller they come, the harder they get"; metal-powder.net, December 2005

• Micro powder injection moulding of alumina micro-channel part• Junhu Menga, Ngiap Hiang Loha, Gang Fua, Bee Yen Tay, Shu Beng Tor• Journal of the European Ceramic Society 31 (2011), 1049 – 1056

• RM. Materials for microminiature powder injection molded medical and dental devices• German• Int. J. Powder Metall 2010;46:15–8.

References (2/3)

• Powder-binder separation in injection moulded green parts• Anne Mannschatz, Sören Höhn, Tassilo Moritz• Journal of the European Ceramic Society 30 (2010), 2827 – 2832

• Simulation of Micro Powder Injection Moulding: Powder Segregation and Yield Stress Effects during Form Filling• Andreas Greiner et al.• Journal of the European Ceramic Society (2011)

• Debinding behaviors of injection molded ceramic bodies with nano-sized pore channels during extraction using supercritical carbon dioxide and n-heptane solvent

• Sang Woo Kim• J. of Supercritical Fluids 51 (2010) 339–344

• An experimental study of the sintering of nanocrystalline WC–Co powders• Z. Fang, P. Maheshwari, X. Wang, H.Y. Sohn, A. Griffo, R. Riley• International Journal of Refractory Metals & Hard Materials 23 (2005) 249–257

• Grain growth during the early stage of sintering of nanosized WC–Co powder• Xu Wang, Zhigang Zak Fang , Hong Yong Sohn• International Journal of Refractory Metals & Hard Materials 26 (2008) 232–241

References (3/3)

• Sintering of nano-sized WC–Co powders produced by a gas reduction–carburization process• Gwan-Hyoung Lee, Shinhoo Kang• Journal of Alloys and Compounds 419 (2006) 281–289

• Other reading:

• Powder Injection Molding• Randall M. German• MPIF, Princeton, New Jersey; 1990, ISBN 0-918404-95-9

• Keraamien ruiskupuristus• Minna-Liisa Vesanen• DI-työ, TTKK:n Konetekniikan osasto, 1988