Optimisation of shrinkage in the design of compaction tooling for WC-Co

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dc.contributor.authorBlaski, Krzysztof
dc.date.accessioned2008-02-29T07:58:51Z
dc.date.available2008-02-29T07:58:51Z
dc.date.issued2008-02-29T07:58:51Z
dc.description.abstractAbstract Tungsten carbide-cobalt powder is pressed before sintering into a compacted form using punches and a die cavity. After the powder has been pressed to a specific shape, it is sintered and shrinks a certain amount to a final size. To accommodate this shrinkage, the pressing tools are designed to a certain “shrinkage percentage” and thus the pressed component or compact is larger than the sintered component by that percentage amount. During the pressing process, there is a large amount of friction between the powder being compacted and the die cavity wall. To counter pressing friction, a lubricant is pre-mixed with the tungsten carbide powder. In the past at Powder Industries, the powder was mixed with wax and all of the tools were designed to a 20% shrinkage. In recent times, the wax in the powder has been replaced by PEG (polyethylene glycol) by most manufacturers as this increases the quality of the final product and is easier to remove in the furnaces. As a result of the new PEG lubricant, the tool wear rate at Powder Industries increased and because a higher pressure had been necessary to achieve powder pressing to the same shape and form, often the pressed components exhibited cracks or were not pressed ideally. On account of the problems introduced by PEG, correct tool design for the shrinkage was obtained by a ‘trial & error’ process. This project has been motivated by the need of establishing pressing and/or design ‘rules’ that would do away with trial and error when designing compaction tooling. The project has consisted of investigating the physical properties of 23 grades of WC-Co powder (with or without TiC and TaC) and of performing a series of pressing tests for each grade. A relationship between the apparent density of a powder and the ideal green density of the green compact pressed from the same powder has been found. Using this relationship, an equation has been derived between ideal shrinkage, powder apparent density, component sintered density and powder volatile content. Since the last three parameters are known to the tool designer, this equation can be used to calculate the ideal shrinkage when designing new compaction tooling. This method of calculating shrinkage is now in general use at Powder Industries and many successful sets of compaction tooling have already been manufactureden
dc.format.extent33861348 bytes
dc.format.mimetypeapplication/pdf
dc.identifier.urihttp://hdl.handle.net/10539/4499
dc.language.isoenen
dc.subjectWC-Co alloysen
dc.subjectshrinkageen
dc.subjectcompactionen
dc.titleOptimisation of shrinkage in the design of compaction tooling for WC-Coen
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