PMA OF SA ANNUAL CONFERENCE
DEBTECH AUDITORIUM CROWN MINES
27TH October 2010
Presenter: R German
Title: Machinability of PM titanium
Abstract: To reduce cost of manufacturing parts from titanium, powder metallurgy (PM) offers an attractive alternative processing technique. While PM is typically a netshape manufacturing process, the majority of PM parts require secondary machining operations for final part details. The machining of titanium alloys is difficult, time consuming and costly. In this investigation, titanium manufactured by PM at different sintered densities and is evaluated for its machinability by turning tests using an uncoated carbide cutting tool. The cutting speeds selection were 60 and 90 m min-1, depth of cut and feed rates were kept constant at 0.15 mm & 0.5 mm rev-1. Factors such as the final machined surface finish and tool wear are monitored in order to evaluate machining performance. The result of this study shows that the machinability of sintered titanium is however dependent on its hardness and thermal conductivity. The tool wear rate during machining of PM titanium is poor as compared to the wear of wrought titanium alloys which support literatures on the machinability of sintered PM product. The magnitude of the tool wear increases with increase in cutting speed but decreases with increase in the porosity of the material. The more dense part shows better surface texture and fewer defects during dry machining as compared to the porous material.
Presenter: R German
Title: Strength Evolution in Powder Metallurgy
Abstract: The mechanical properties of sintered materials are widely documented. Classic models exist to predict fracture properties versus the overt properties, such as density. However, the true controlling factor is probably the pore spacing since cracks link along weakest paths. Likewise, almost all property reports focus on showing the strength, ductility, hardness, toughness, or other property versus the sintering parameters - hold time, peak temperature, green density, particle size, or compaction pressure. All of this misses the underlying two important factors - how a component cracks in sintering and how a component cracks in use. During heating the green strength often decreases as the polymer phase softens. Thus, the component initially loses strength on heating; yet after sintering it is maybe 20 to 200 times stronger than it started. Damage to the component, such as cracking, blistering, or warpage occurs at low points of strength evolution during the heating cycle. Trials and data are shown for the in situ strength measured during heating using a combination of sinter bonding and thermal softening. Then, in service strength attention turns to any residual pore structure and determining the weak path, best treated using the mean free path concept. This in turn leads to some interesting implications on particle size distribution and other practical parameters.
Presenter: O. P Oladijo
Title: Abrasion of WC-4.88wt%Co thermal spray coatings on different substrates.
Abstract: Validation of measurement systems is a key step prior to making any process improvements or design changes. This talk discusses some of the techniques utilized in validating measurement systems by reducing measurement noise. The importance of quantifying repeatability and reproducibility errors is highlighted with the demonstration of some practical examples. The validation tools demonstrated are applicable in any discipline and are important in establishing the confidence to resolve differences prior to making process or design changes.
Thermally sprayed coatings of tungsten carbide–cobalt are used extensively in industry to protect the underlying substrate. They are mainly used in applications requiring good abrasion, sliding, fretting and erosion resistance. Although there have been many studies on abrasive wear of WC-Co coatings, the effect of the underlying substrate on the properties is not fully understood. This work is concerned with relating the abrasive wear of WC-Co thermal spray coatings on different substrates to their microstructures. The four substrates were: brass, super-invar, 304L stainless steel and commercial aluminum. They were coated with WC - 4.88 wt% Co using a High Velocity Oxygen Fuel System (HVOF). After characterization, three–body abrasive tests were carried out using rubber-wheel equipment as described in ASTM GC5-9ID, for 30 minutes.
Presenter: R M. Genga
Title: The properties of the WC-Co cemented carbides manufactured by Spark Plasma Sintering (SPS)
Abstract: Finer grain size optimizes the properties of cemented carbides, and can be achieved through the manipulation of the sintering time and alteration compositional chemistry. Spark plasma sintering (SPS) does not allow time for grain growth. Two approaches are taken in this study: partial substitution of cobalt with nickel, and complete substitution of cobalt by nickel, with TiC as a grain growth inhibitor.
Two compositions, WC-1wt% NbC- 10wt% Co (Ni) and WC- TiC 6.25wt%-Ni were produced by SPS method, and characterized.
Presenter: D O. Kumi
Title: A phase diagram of W-C systems for potential binders for WC
Abstract: For many years, the cemented carbides industry has been interested in substituting cobalt as the binder metal. The reasons include price fluctuation of cobalt, and especially the health implications of the powdered cobalt used for manufacturing, since the powder can be carcinogenic. This work is trying to identify new binders using a phase diagram approach.
Potential binders were identified from a phase diagram study searching for solid solution formation, a similar melting point to cobalt, and a small solubility for WC as key requirements. The first samples were: W25:C25:Ni47.5:V2.5 (at. %), W25:C25:Ni43:V7 (at.%) and W25:C25:Ni45:Zn5 (at.%). The samples were designed to be 50 at. % WC and 50 at.% binder for easy analysis, to ascertain the degree of solubilities.
Presenter: R Nilen
Title: A Brief Introduction to Element Six and Some Aspects of PCD Sintering
Abstract: Element Six is a global leader and innovator in superhard materials. With a history spanning more than 50 years, our diamond, cubic boron nitride and carbide products are used across a wide range of industries. The talk will give a very brief overview of the company, its history and various businesses. A closer look at some aspects of polycrystalline diamond (PCD) sintering will then be presented, together with a quick look at some of our hardmetals research.
Presenter: D Markoulides
Title: Techniques to Validate Measurement Systems: A fundamental basis for making process improvements.
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Abstract: Validation of measurement systems is a key step prior to making any process improvements or design changes. This talk discusses some of the techniques utilized in validating measurement systems by reducing measurement noise. The importance of quantifying repeatability and reproducibility errors is highlighted with the demonstration of some practical examples. The validation tools demonstrated are applicable in any discipline and are important in establishing the confidence to resolve differences prior to making process or design changes.
Presenter: M Dollman
Title: Energy consumption in the mass production of PM components
Abstract: Powder metallurgy (PM) offers the possibility to manufacture high volumes of relatively complex components. Continuous improvement of material properties have allowed PM to easily compete with more traditional processes. In comparing processing alternatives, the focus is often now on the price/ performance ratio, which is largely determined by personnel, materials and energy costs. Despite the perception that PM is energy efficient relative to other processes, this advantage is not always obvious. The present investigation seeks to understand the breakdown of energy consumption for the PM process and draw comparisons with competing processes such as die-casting, forging and machining (or combinations of these). The general rise of energy prices and the need to lower CO2 emissions makes such an analysis of particular interest. Energy consumption figures from 27 of GKN Sinter Metals production plants were analysed and compared with consumption data for other processes. It was determined that PM does indeed offer an advantage in terms of energy efficiency with and average consumption of approximately 7 kWh per kilogram of finished components. Competing processes varied from approximately 8 kWh/kg to over 15 kWh/kg. In all cases, the energy consumption required for the production of feedstock materials was considered. For PM, it was determined that nearly one third of energy is consumed during sintering, with compaction and other processes (such as compressed air generation) together accounting for another third. In order to retain and improve on this competitive advantage, there should be a continual drive towards optimisation of all production steps with respect to energy consumption. Particular attention should be given to the further development and implementation of innovative sintering practices.
Presenter: K Sobiyi.
Title: Machinability of PM titanium
Abstract: To reduce cost of manufacturing parts from titanium, powder metallurgy (PM) offers an attractive alternative processing technique. While PM is typically a netshape manufacturing process, the majority of PM parts require secondary machining operations for final part details. The machining of titanium alloys is difficult, time consuming and costly. In this investigation, titanium manufactured by PM at different sintered densities and is evaluated for its machinability by turning tests using an uncoated carbide cutting tool. The cutting speeds selection were 60 and 90 m min-1, depth of cut and feed rates were kept constant at 0.15 mm & 0.5 mm rev-1. Factors such as the final machined surface finish and tool wear are monitored in order to evaluate machining performance. The result of this study shows that the machinability of sintered titanium is however dependent on its hardness and thermal conductivity. The tool wear rate during machining of PM titanium is poor as compared to the wear of wrought titanium alloys which support literatures on the machinability of sintered PM product. The magnitude of the tool wear increases with increase in cutting speed but decreases with increase in the porosity of the material. The more dense part shows better surface texture and fewer defects during dry machining as compared to the porous material.
Presenter: A Smith
Title: An Inconvenient Lie