Feature article: PIM International, Vol.1 No. 3 September 2007, pages 17-24, 3151 words

Author: Dr Leo J. Prakash, WTP Materials Engineering, Germany

WTP Materials Engineering, Konrad Adenauerstr. 27, D-72108 Rottenburg, Germany

Introduction

Powder injection moulding (PIM) technology has been used for many years in the production of cemented carbide (hardmetal) products. Dr. Leo J. Prakash presents an introduction to cemented carbide technology and reviews how PIM technology is applied in this major sector of PM materials.

Cemented carbides, or hardmetals, are a mature class of powder metallurgical (PM) liquid phase sintered composite materials consisting of at least one hard and wear resistant phase (in the majority of cases this being tungsten carbide (WC)) and a ductile and softer metallic phase from the iron group of metals (mainly cobalt and its alloys). The invention of cemented carbides dates back to the beginning of the 20th century, and is generally attributed to Karl Schröter who disclosed his invention in 1923 in a patent application [1]. The first products were wire drawing dies and these were quickly followed by cutting tools for the machine tool industry. Cemented carbides today form the backbone of the tool manufacturing industry with such diverse applications as machining of metallic and non metallic materials, chipless forming (wire drawing, can tooling, forging, stamping, mill rolls, powder compacting punches and dies, high pressure dies and anvils), mining (oil well drill bits, rock drill bits), industrial nozzles (sand blasting, water jet cutting, painting, glue dispensers) industrial wear parts (dental and medical tools, paper, plastic and textile knives, guide rolls, seal rings, road planing knives, tire studs, forestry tools, earth moving and consolidation tools), and for functional applications (watch cases and bracelets). The smallest carbide part weighing a fraction of a gram is the tip of a ball point pen (produced in billions per year) and the largest parts like rolls and dies weighing up to a ton (produced in hundreds annually). The current annual production of cemented carbide worldwide is estimated to be in the range of...

Further sections of this article include:

- Production technology of cemented carbides
- History of PIM of cemented carbides
- The PIM process for cemented carbides
- Commercial success stories for PIM hard metal parts
- Low pressure injection moulding
- High pressure injection moulding
- Outlook

Figures and Tables:

Fig. 1 Hardness, wear resistance and fracture toughness of straight WC-Co cemented carbides as a function of WC grain size and cobalt content (Courtesy Sandvik Hardmaterials)

Fig. 2 Typical microstructure of a WC-Co Hardmetal (Courtesy Ceratizit)

Fig. 3 Application range of straight cemented carbide grades (Courtesy Sandvik Hardmaterials)

Fig. 4 PIM cemented carbide watch cases – left as sintered, middle after polishing, right coated (Courtesy Ceratizit)

Fig. 5 PIM cemented carbide milling heads with internal threads first produced in the early 1990’s by United Hardmetal, Horb, Germany in collaboration with Arburg [15]

Fig. 6 Clustering of PIM materials based on strength and the relative cost per unit volume [3]

Fig. 7 PIM process chart as also applied to cemented carbides

Fig. 8 Examples of PIM cemented carbide parts made by both technologies by Kennametal Widia [2]

Fig. 9 GOCERAM Medium Pressure Injection Moulding (MPIM) machines in various sizes are designed for moulding of ceramic, metal and cemented carbide feedstocks, primarily using wax-based binders [4]

Fig.10 An example of a moulding machine for HPIM of cemented carbide (Courtesy Arburg)

Fig. 11 Selection of parts made by low pressure injection moulding (Courtesy Retco Tool Co., Inc.) [6]

Fig. 12 Overview Safety lock with integrated drill through protection (Courtesy Ceratizit)

Fig. 13 Coated PIM metal cutting insert (Courtesy Ceratizit)

Fig. 14 Cylinder drill bit for blind hole drilling in wood based materials - right PIM carbide head, left assembled tool (Courtesy Tigra)

Fig. 15 Modular tool system showing a cutoff insert (Courtesy Horn)

Fig. 16 PIM coated cemented carbide bit for a drilling application (Courtesy Kennametal- Widia)

Fig. 17 Replaceable PIM coated cemented carbide drilling insert heads (Courtesy Seco)

Fig. 18 Tool cross section showing the replaceable PIM Carbide head and the steel tool holder (Courtesy Seco)

Fig. 19 optimised HPIM machine with the the RheoNoz feedstock viscosity measurement unit

Table 1 Comparison of the process of High and Low pressure PIM of cemented carbides [2]