Investigation of iron powder friction on tungsten carbide tool wall

Abstract

In the powder shaping process, friction is often considered as one of the main limiting factors since it can be the cause of bad green density distributions as well as ejection defects. Therefore, knowledge of this is important for better controlling the compaction stage. This paper makes an attempt to bring out the different process parameters (density, normal stress, sliding velocity, temperature, and displacement) which influence the friction between a standard iron powder and a tool in tungsten carbide. With this view, a sliding piece device has been built and is described. Several tests have been performed; from the results emerge a decrease of the friction coefficient with increasing density or normal stress, conversely the velocity increases the friction while temperature has PM75554.10.1 no significant role. In this work, particular attention 1 Sliding piece device: 1=optical transducer, 2= is given to the amplitude of the displacement showing transducer, 3=disc, 4=parallelipipedic slab, 5=force that it can highly affect friction and wear of green transducer, 6=hydraulic press, 7=cylindrical die, 8= parts. An attempt is made at explaining the observed press phenomena and results are correlated with an analytical expression. PM/0952 the process parameters on friction. Using an iron powder, authors4,9 have observed that the friction coefficient Dr Doremus and Dr Toussaint are at Institut decreased when increasing normal stress while Mallender National Polytechnique de Grenoble, Laboratoire et al. are the only authors who have measured an increase Sols Solides Structures, Domaine Universitaire, of this coefficient with density. The second type of BP 53, 38041 Grenoble cedex 9, France and Dr Pavier equipment allows one to study the role of the different is with Ferroxdure, Aimants permanents, 41, rue parameters independently, such as the density of the Pierre Brossollette,

An Investigation For Optimal Tool Kinematics In Powder Compaction Cycle To Minimize Density Gradient In Green Powder Compacts

“…However, based on numerous studies it has been determined that upon powder compaction friction coefficient tends to vary and is a function of several process parameters, such as powder density, normal stress, sliding velocity, temperature, displacement, tool surface-roughness, and material hardness [10, 13, 19, 21, 31, 86, 88-90, 113, 114]. Most importantly, in the case of an instrumented-die, only a mean friction coefficient value may be derived; however, the local friction coefficient value varies over the height of the compact [3,10,13,19,21,31,85,89,90,111,113,114].…”

“…Using this shear-plate device, Pavier and Doremus have successfully measured variation of friction coefficient for iron-based powder with respect to a range of parameters. Their device consisted of a parallelepipedic slab (4), measuring 200 x 20 x 20 mm in size, to represent the tool surface, which was fixed on moving rolls (with friction coefficient of 0.001) [19,21,86]. The slab was connected through a force transducer (5) to a hydraulic press (6).…”

“…All tests were performed on a slab composed of tungsten carbide (91.5%WC and 8.5% Co), with a hardness of HV 1 = 1520 and a surface-roughness average, Ra, of 0.1 µm, which is the most common material composition for the die-wall [19,21,[84][85][86][87]. The powder used was an atomised iron-based powder, Distaloy AE, supplied by Ho gana s; same as the one used for determination of material properties.…”

“…Similar trends were observed in other studies [10,13,24,25,33,51,66,80,89,90,109,110,111,114,[124][125][126] Further, the influence of temperature on friction coefficient was studied. For this the slab was fitted with thermal resistors and several tests were conducted between 20 and 80°C to assimilate manufacturing conditions, where due friction and high production rate, temperature of the tools and the ejected green compact may reach close to 70°C [19,21,27,86]. The experimental data showed that friction coefficient is independent of the temperature under the specified test conditions; see Figure 28…”

“…Just for comparison, the hardness of a tungsten carbide composition (91.5%WC, 8.5%Co), typically used for construction of dies, is measured at HV 1 = 1520, whereas for iron-based powder, Distaloy AE, HV 0.025 = 105 [19,21,83,84,85,86], i.e., a difference of about 14 ½ times.…”