Advanced Materials Research Vols. 966-967

Abstract: Off-line testing of new tribo-systems for sheet metal forming production is an important issue, when new, environmentally benign lubricants are to be introduced. To obtain useful results it is, however, vital to ensure similar conditions as in the production process regarding the main tribo-parameters, which are tool/workpiece normal pressure, sliding length, sliding speed and interface contact temperature. The paper describes a generic methodology for such tests exemplified on an industrial, multistage deep drawing example, where deep drawing is followed by two successive re-drawing operations leading to very high tool/workpiece interface pressure and temperature in the second re-draw. Under such conditions only the best lubricant systems work satisfactory, and the paper shows how the performance of different tribo-systems in production may be predicted by off-line testing combined with numerical modelling in order to ensure proper test conditions.

Abstract: Cold joining method using plastic flow has been useful for production of joint parts. The high torsional strength of the joint of a disk and a shaft was obtained by plastic flow serration joining, but the axial strength of the joint was not so high. To improve the axial strength, the serration joining was combined with additional upsetting joining. After upsetting joining high residual compressive stresses were induced between the shaft and the disk by a level with the yield stress of the disk material. The initial axial strength of joining of the disk and the shaft increases by 2.5 times by using the combination of upsetting joining and serration joining under a well-rinsed condition.

Abstract: As the scale and complexity of products such as aircraft and cars increase, demand for new functional processes to join mechanical parts grows. The use of plastic deformation for joining parts potentially offers improved accuracy, reliability and environmental safety as well as creating opportunities to design new products through joining dissimilar materials. This paper aims to provide an overview of the state of the art in such joining processes, including cold welding, friction stir welding, joining by forming, self-pierce riveting and mechanical clinching. The paper includes description of the mechanism of joint formation, joint strength and applicability.

Abstract: To help optimize cold rolling operations, mixed lubrication models have been developed and embedded in roll bite models. The resulting models combine micro-fluidics in a porous medium (the lubricant flow between the contacting rough surfaces), microplasticity (roughness flattening / scratching), macro-plasticity (strip reduction) and roll thermo-elasticity. They are therefore really complex and need a lot of physical data. Based on previous developments, a new, simpler version of our lubrication model has been coupled with a new roll bite model recently presented: slab method for the strip elastic-plastic deformation (Prandtl-Reuss equations), a complete influence functions set for the roll deformation with circumferential displacements, and an efficient, adaptive relaxation technique when iterating between roll and strip models. The lubrication model is elaborated on Wilson and Sheu’s mixed lubrication model. The paper describes the implementation and compares its results with our previous, more complex version; a reasonable agreement is found. Several test cases of increasing difficulty show the robustness of the model and of its implementation. As a conclusion, a brief perspective is provided on how this new type of roll bite model could be used in industry.

Abstract: With the growing demand of sustainability and rising requirements by law and politics, paper as a natural, renewable fiber material is in the focus of research and production technology again. With this, requests for the predictability of material behavior during the production process rise. Especially in forming, interactions between work piece and the tool surface can have a major influence on the forming behavior. This study discuss available friction measurement systems for paper in the context of forming processes. Based on this a new friction measurement device is presented. Effects of the measurement setup on the contact pressure distribution during tests is reviewed experimentally and via FEA. Finally, the friction coefficient between an industrial paperboard with different material orientations and steel, at different velocities and contact pressures is investigated. A dependency between the contact pressure and the friction coefficient can be seen.

Abstract: The objective of this work is to investigate the tribological behavior between WC-Co cemented carbide and austenitic stainless steel under repeated rotation sliding. Influences of cobalt content of commercial grade cemented tungsten carbide on friction coefficient and material transfer phenomena have been explored. Three grades of commercial WC-Co cemented carbide with similar medium WC grain size were employed; WC-12Co, WC-14Co and WC-19Co. The average grain size were ranges between 0.85-1.1 μm and the hardness of about 86-88 HRA have been given by the material maker. The composition analysis and the average grain size of tungsten carbide have been rechecked. Furthermore, the carbide grain size distribution was recorded and the fracture toughness was calculated for each WC-Co grade. The experiments were carried out using ball on disk test. The ball was made from SUS304 grade and the disk was fabricated by 3 grades of WC-Co cemented carbide. The friction coefficient was measured under dry sliding. The characteristics of contact surfaces were explored on the ball as well as on the disk after tests to reveal the presence of a metallic transfer on the WC-Co cemented carbide disk and the wear scar on the ball. The measurement results of wear volume on the stainless steel ball disclosed that maximum wear rate was found from the stainless steel ball rub against WC-19Co tool material.

Abstract: Tribometer measurements are used to simulate and investigate friction and wear mechanisms in sliding solid state systems. In metal forming and especially in deep drawing, tribometers are used to study the friction characteristics in the area of the stamp edge and draw edge rounding of a deep drawing tool. To replicate the reality of the deep drawing process a commercially available pin-on-disc tribometer is only useable to a certain extent because only a circular path can be traversed. At the Upper Austria University of Applied Sciences in Wels a spiral tribometer has been developed that can measure the friction coefficient along the desired friction distance. During the deep drawing process the temperature on the surface of a deep drawing tool rise due to the friction and wear conditions caused by the process. In order to investigate the influence of temperature the spiral tribometer is equipped with a heating system. To verify the results, comparison tests are performed with a commercially available pin-on-disc tribometer. Comparative tests confirm that the results obtained with the developed spiral tribometer match the values of the pin-on-disc tribometer.

Abstract: One way to improve the run-in period of the commutation system of an electrical motor is the modification of the commutator ́s roughness. The reduction of the run-in period affects the wear during the motor life time. Therefore, within this paper the influence of the initial commutator roughness on the run-in period and the electromechanical wear is investigated. The research is done with a special starter components test rig. During the tests the wear is analyzed while the applied electromechanical and mechanical load is varied in order to enforce different wear behaviors. It is expected that with an optimal initial surface roughness the amount of wear is reduced until the steady state has been reached. However, the results revealed that there is no significant influence of the initial surface roughness on the examined electromechanical tribological system. It was found, that the mechanical wear of the commutator and the brushes is similar to the electromechanical wear during the run-in period. The run-in period of the mechanical load tests is shorter compared to the other experiments.

Abstract: High temperature forging tools are highly damaged by wear shearing under cyclic loading which reduces the life of tools. In real conditions, depending upon the tool areas, the level of wear can change. The surfaces of tools can be treated by cobalt-based hardfacing using different welding processes. This study focuses on tribological damages of Stellite 21 deposited by MIG process. Wear tests are carried out at room and high temperature on a ring on disc tribometer under high normal load. Different testing conditions are examined. The surface plastic strain due to the friction shear stresses is demonstrated by different methods like SEM observations, micro-hardness measurements and XRD analyses. More particularly, it is shown that the initial (200) crystallographic preferred orientation due to the welding process is modified into (111) crystallographic preferred orientation due to shear stresses regardless the loading. Moreover, a relationship between the gradient of the plastic shear strain at the friction subsurface and the level of the micro-hardness measurement has been established. In regard of the results, when the shear strain exceeds a threshold, the micro-hardness measurement is stabilised. The ultimate value could be induced by the stacking fault energy that is considered as weak in Stellites.