Tribological Performance of Textured Micro Forming Dies

Aim of this work is the tribological investigation of micro structured surfaces generated by micro milling and the performance testing of a micro structured micro deep drawing die. Three samples exhibiting different micro structured surfaces with arithmetical mean heights Sa in a range of 148 nm to 741 nm were manufactured by micro milling. The surface texture is determined by the process parameters of the micro milling operation. Tribological properties of the micro structured surfaces were investigated by means of a ball-on-plate micro tribometer and compared to those of a polished reference sample (Sa = 24 nm), a clear dependence of the frictional properties on the surface roughness was found. Lowest friction μ =0.26 was achieved for the sample with a roughness Sa = 148 nm. Surfaces with higher or lower roughness provoked increased friction in tribological testing being associated with an interlocking of surfaceâ s asperities or dominant adhesion, respectively. Subsequently, micro structures were machined into the surface of a micro deep drawing die for drawing of rectangular micro cups. The performance of this die was tested in deep drawing experiments against a polished reference die by means of achievable drawing ratio. At this stage the full advantage of the micro structuring of die surfaces was not achieved, yet. Still particular challenges within the micro regime, e.g. alignment of punch and die as well as blank positioning, have to be improved.Volume

Abrasive Particle Generation in Dry Rotary Swaging

Rotary swaging is an incremental bulk metal forming process for the manufacture of cylindrical lightweight components. Whilst conventional rotary swaging is still carried under the intense use of lubricants to provide desired work piece quality and to avoid forming die wear, recent scientific work focuses on the design of a dry process layout. Novel functionalized rotary swaging dies were introduced, exhibiting both diamond like carbon (DLC) hard coated and structured surfaces to encounter complex and opposing tribological requirements when dry machining. Such dies were successfully applied to infeed rotary swaging experiments machining steel 1.0038 and aluminum 3.3206 tubes. Although primary targets were achieved, the dry rotary swaging process is subject to an increased abrasive particle generation from the work piece material and accumulation of such particles in the forming zone. Abrasive particles provoke a loss of work piece quality and ultimately lead to a clogging of the swaging unit, associated with a significant earlier termination of the forming process. This work presents the investigation of the particle generation when dry rotary swaging with functionalized forming dies in dependence on the work piece material and the process parameter feed velocity. Subsequently, improvements of the die s design are discussed which are to reduce the generation of abrasive particles and conveying the particles from the swaging unit, indispensable for the robust layout of dry rotary swaging processes.16Volume

Methodology for Reliable Tribological Investigations Applying a Micro Tribometer in Ball-on-Plate Configuration

Aim of this work is the development of a methodology for reliable tribological investigations when applying a micro tribometer. Experiments were conducted in ball-on-plate configuration with linear reciprocating motion. Two different sphere materials were applied: Al99.9 aluminum alloy and 1.4301 austenitic stainless steel. A textured surface from 1.2379 hardened tool steel machined by micro milling exhibiting an areal arithmetic mean height of Sa = 295 nm was used as counterpart. The experiments comprised of the investigation of the coefficient of friction and the evolution of the facet area on the spheres in contact with the textured surface depending on the normal load applied and the number of reciprocating cycles. For the early stage of the experiments an ongoing increase of the area of the facet on the spheres was found; occurring friction was manly governed by abrasion of the sphere’s material and three-body deformation. This was considered as unstable state of the tribological investigation process, not producing meaningful results. For the later stage equilibrium facet areas on the spheres were found and an ongoing conduction of the tribological experiments did not provoke any increase of their sizes. Here, occurring friction was mainly governed by adhesion. The final facet area on a sphere was directly dependent on the sphere’s materials and the applied normal loads. For all subsequent investigations applying a micro tribometer, only spheres exhibiting an equilibrium facet area should be used to gain robust results of tribological investigations, required for the development of e.g. dry deep drawing processes

Reducing Abrasive Particle Generation in Dry Rotary Swaging by Utilizing DLC Hard Coated Dies

The emphasis of this paper is the investigation of the impact of the diamond like carbon (DLC) hard coating system on the amount of abrasive particles being generated during dry rotary swaging. Rotary swaging experiments applying coated and uncoated macro structured forming dies were carried out against aluminum and steel work pieces varying the process parameter feed velocity. It was found that DLC coatings effectively reduce the generation of abrasive particles from the work piece. For dry machining of aluminum the amount was reduced to a tenth of the original quantity achieved with uncoated dies. The results are discussed with regard to the mechanics of interfacing surfaces. Additionally, forming dies exhibiting macro structures surfaces of improved design were introduced and applied in dry rotary swaging experiments, which allowed minimizing the abrasive particle generation

Development of micro rotary swaging tools of graded tool steel via co-spray forming

In order to meet the requirements of micro rotary swaging, the local properties of the tools should be adjusted properly with respect to abrasive and adhesive wear, compressive strength, and toughness. These properties can be optimally combined by using different materials in specific regions of the tools, with a gradual transition in between to reduce critical stresses at the interface during heat treatment and in the rotary swaging process. In this study, a newly developed co-spray forming process was used to produce graded tool material in the form of a flat product. The graded deposit was subsequently hot rolled and heat treated to achieve an optimal microstructure and advanced properties. Micro plunge rotary swaging tools with fine geometrical structures were machined from the hot rolled material. The new forming tools were successfully applied in the micro plunge rotary swaging of wires of stainless steel

Development of micro rotary swaging tools of graded tool steel via co-spray forming

In order to meet the requirements of micro rotary swaging, the local properties of the tools should be adjusted properly with respect to abrasive and adhesive wear, compressive strength, and toughness. These properties can be optimally combined by using different materials in specific regions of the tools, with a gradual transition in between to reduce critical stresses at the interface during heat treatment and in the rotary swaging process. In this study, a newly developed co-spray forming process was used to produce graded tool materials in the form of a flat product. The graded deposits were subsequently hot rolled and heat treated to achieve an optimal microstructure and advanced properties. Micro plunge rotary swaging tools with fine geometrical structures were machined from the hot rolled materials. The new forming tools were successfully applied in the micro plunge rotary swaging of wires of stainless steel

Development of micro rotary swaging tools of graded tool steel via co-spray forming

In order to meet the requirements of micro rotary swaging, the local properties of the tools should be adjusted properly with respect to abrasive and adhesive wear, compressive strength, and toughness. These properties can be optimally combined by using different materials in specific regions of the tools, with a gradual transition in between to reduce critical stresses at the interface during heat treatment and in the rotary swaging process. In this study, a newly developed co-spray forming process was used to produce graded tool materials in the form of a flat product. The graded deposits were subsequently hot rolled and heat treated to achieve an optimal microstructure and advanced properties. Micro plunge rotary swaging tools with fine geometrical structures were machined from the hot rolled materials. The new forming tools were successfully applied in the micro plunge rotary swaging of wires of stainless steel

Chances and Limitations in the Application of Laser Chemical Machining for the Manufacture of Micro Forming Dies

Laser chemical machining, a non-conventional processing method based on thermally activated electrochemical material dissolution, represents a promising technology for manufacturing metallic dies for micro forming applications. Prior to widespread industrial acceptance the machining quality of laser chemical machining should be characterized. For this purpose, laser chemical machining is compared with micro milling regarding both the dimensional accuracy and the surface quality. Therefore, square micro cavities exhibiting side walls between 100 μm and 400 μm in length and 60 μm in depth are machined with both manufacturing processes into the cobalt-chrome alloy Stellite 21. The geometrical features are investigated using laser-scanning confocal microscopy and scanning electron microscopy. On the one hand, laser chemical machining is more suitable for manufacturing cavities with dimensions < 200 μm due to higher shape accuracy with stable mean edge radii of (11.2 ± 1.3) μm as a result of roughing and finishing steps. On the other hand, the finish quality of micro milling with mean surface roughness Sa of 0.2 μm could not be achieved with laser chemical machining due to in-process induced waviness. Finally, the metallographic analysis of the surface-near layers reveals that both manufacturing processes ensure gentle machining without any noticeable micro structural impact

Potentials of Dry Rotary Swaging

AbschlussberichtInfeed rotary swaging is an appropriate cold massive forging technology for the manufacture of cylindrical shaped components made of iron or aluminum base alloys. The process is focused on reducing the cross-section of full profiles or tubes and is e.g. widely used in automotive industry. The design of swaged hollow components can easily be adapted to the external load in such a way, that the wall thickness is partially reduced and the material cross-section is increased where needed. The above-mentioned advantages result in a high potential for light-weight production while the produced components exhibit high geometric accuracy and surface quality. However, an excellent CO2 balance is yet limited due to high demands for lubricants significantly increasing the number of process steps for further component refinement. In order to increase the overall process efficiency, a changeover to a dry process design becomes necessary. A dry processing will cause high die wear and deterioration of workpiece quality. The most important functions of the lubricant have to be substituted by other approaches and strategies. Development and removal of heat, generation and discharge of wear debris and, above all, die wear and the resulting workpiece quality have to be considered. The effective tribological friction conditions have to be adjusted by means of geometric adaptations of the active die surfaces to realize good workpiece qualities at comparable cycle times. This paper gives a review of the state-of-the-art in dry rotary swaging. Extensive experiments in laboratory scale as well as application tests were performed with various die setups. The most important findings regarding wear, wear minimization, process kinematics, workpiece quality, FEM simulation are presented. The overarching goal is to achieve a longterm stability for the successful dry processing.19222

Development of micro rotary swaging tools of graded tool steel via co-spray forming

In order to meet the requirements of micro rotary swaging, the local properties of the tools should be adjusted properly with respect to abrasive and adhesive wear, compressive strength, and toughness. These properties can be optimally combined by using different materials in specific regions of the tools, with a gradual transition in between to reduce critical stresses at the interface during heat treatment and in the rotary swaging process. In this study, a newly developed co-spray forming process was used to produce graded tool materials in the form of a flat product. The graded deposits were subsequently hot rolled and heat treated to achieve an optimal microstructure and advanced properties. Micro plunge rotary swaging tools with fine geometrical structures were machined from the hot rolled materials. The new forming tools were successfully applied in the micro plunge rotary swaging of wires of stainless steel