Bernd Kuhfuss

In-process control of cutting depth during turning

During the turning process of a ring, the clamping force of the chuck causes circumferential deviations in the ring wall thickness and diameter. In order to minimise the wall thickness deviations, an experimental set-up for an in-process control of the cutting depth during turning is being developed. The set-up comprises a fast tool unit, an ultrasonic measurement system and a global control unit. In preliminary tests, the ultrasonic measurement proved suitable to acquire the changes in wall thickness. First turning experiments show that the developed fast tool unit and the applied control strategy fulfil the requirements for an in-process compensation of wall thickness deviations during standard turning conditions.

Dry Rotary Swaging - Tube Forming

Rotary swaging is an incremental cold forming process for tubes and rods. The established processes use lubricants based on mineral oil. The functions of the lubricant are the reduction of friction, wear and tool load, furthermore it cools the tools and flushes the working zone. But the use of lubricant increases the cost due to additional process steps and lubricant is diverted with the work piece during the process. Thus from economic and ecological points of view it is worthwhile to eliminate the use of lubricant. Therefore it is necessary to realize the functions of the lubricant in another way. For example by means of coating and micro-structuring of the tools the friction and wear can be influenced. In this study dry rotary swaging is tested with conventional tools and machine settings. The analysis of the recorded process parameters and the formed geometry of the workpiece reveal the potential of dry rotary swaging, but also the difficulties that arise. Dry rotary swaging needs a modification of the process and system parameters as well as an adjustment of the tools.

Process Chains in Microforming Technology Using Scaling Effects

Cold formed micro parts with dimensions <1 mm show in some aspects characteristics due to scaling effects that can be positively used in process chains. Whereas aspect ratios in upsetting processes are limited to l0/d0<2 in the macro scale, a laser induced free‐forming process generates droplet shaped pre‐forms for consecutive calibrating processes, i.e. micro rotary swaging. Scale effects on establishing and shortening of process chains like free‐form heading/rotary swaging/heat treatment are discussed. On the other hand a geometric scale‐up approach in the macro range is described to overcome the specific handling problems of miniature parts. This is achieved by leaving the parts in a physical linkage during the processing steps. An effective application of linked micro parts requires intensive modeling and simulation work.

Grain Size Modification by Micro Rotary Swaging

Rotary swaging is a well established cold forming process e.g. in the automotive industry. In order to modify the material properties by swaging systematically, a new process of swaging with asymmetrical strokes of the forming dies is investigated. The newly developed tools feature flat surfaces and do not represent the geometry of the formed part as in conventional swaging. Numerical simulation and physical tests are carried out with special regard to the resulting geometry, mechanical properties and the microstructure. During these tests copper wires with diameter d0=1 mm are formed. Regarding the microstructure in the longitudinal section of formed specimens, elongation of grains in the central part and grain size reduction in the boundary area are observed. Furthermore, this approach opens up new possibilities to configure the geometry of wires. 2D-simulation is applied and discussed in the paper to investigate change of the processed geometry (cross-section) and shear strain distribution during the rotary swaging process.

Simulation-based parameter identification of a reduced model using neural networks

Simulation models are used to study and design real systems in order to optimize their performance. However, the lack of complexity in models, as compared to systems, leads to differences between simulation and actual behavior. Identification of the effective system parameters in the simulation models would reduce the discrepancies between the model and the real system and results in better simulation of system behavior. In this paper, radial basis neural networks are proposed for the identification of the effective parameters of the machine tool feed drive system. Neural networks are first trained with an estimated set of model parameter values and corresponding step responses of the position control loop. After the training period, the response of the model with the identified parameters is compared to the system step position response at different axis positions for validation. An application of neural network to other trajectories is done on a ramp function. The obtained results reveal considerable potential of neural networks in identifying accurately the system parameters and in reducing the discrepancies between experimental test results and the model.

Plastic deformation history in infeed rotary swaging process

In bulk forming processes, the net shape of a final product is achieved by plastic deformation as the material flows from the initial shape to the final shape of the workpiece. The material flow during the process is an important issue for its relationship with forging force, heat generation, microstructure transformation and energy consumption. Hence, the final properties of the product are directly influenced. Former researches showed that the material flow in the rotary swaging process is affected by different processing parameters like die angle, feeding velocity and friction condition. Thus, a profound knowledge of detailed material flow during the process is essential for a better understanding of the process. By using FEM, the material flow was investigated by the history of the plastic strain (PEEQ) development. In this study a 2D-axisymmetric model was built by using ABAQUS explicit. Both aluminum alloy (3.3206) and steel (1.0308) are studied with different feeding velocities and coefficients of ...

Handling in the Production of Wire-Based Linked Micro Parts

For simplified processing and the enhancement of output rate in multi-stage production, micro parts are handled as linked parts. This contribution discusses handling specific challenges in production based on an exemplary process chain. The examined linked parts consist of spherical elements linked by wire material. Hence, the diameter varies between the wire and part. Nevertheless, the linked parts must be handled accurately. The feed system is an important component too, but special focus is given to the guides in this present study. They must adapt to the diameters of both the parts and the linking wires. Two alternative variants of adaptive guides are presented and investigated under the aspects of precise radial guiding, vibration isolation, damping behavior and friction force.

Coupling System for Ultra Precision Machining

The mass production of plastic parts containing micro structures in optical quality requires molds with corresponding surface quality. These micro structured molds can be produced by UPC (ultra precision cutting). To produce a high surface quality the ultra precision machine spindles must be well balanced. It is not sufficient to balance the tools and the spindle separately. They have to be balanced while assembled to ensure the required balance quality grade better than G0.4. One possibility to decrease setup times and increase the quality of the spindle balancing is to enhance the unbalance induced vibrations and thus allowing better unbalance detection. In this paper a coupling system between the spindle and machine frame based on flexure joints is presented. The experimental setup provides two states: operational and setup. The operational state provides a high stiffness, whereas the setup state allows the spindle to vibrate along one degree of freedom, enhancing the vibrations created by the unbalance. The system is analyzed concerning its ability to restore the defined conditions in the operational state as well as its capability to enhance the detection of unbalances in the setup state.

Investigation of Deformation Induced Martensitic Transformation during Incremental Forming of 304 Stainless Steel Wires

Wires with 1 mm initial diameter have been reduced between 10 and 64 percent at different temperatures and strain rates by infeed rotary swaging, which is an incremental cold forming process mainly used for rods and pipes. The volume fraction of martensite in the deformed wires has been determined by X-Ray diffraction and by magnetic induction for different processing parameters. Measurements show that for already small percentage of reduction, martensite is present in the wires and its amount changes with the strain rate and temperature. While for smaller strain rates at room temperature the formation of martensite is promoted, it is restrained for higher strain rates and higher temperatures. Results also reveal that the martensite distribution in the sample is inhomogeneous. Further investigations have been made to analyze the microstructure by optical microscopy and to determine mechanical properties by tensile testing.

Dry rotary swaging with structured and coated tools

Rotary swaging is a cold bulk forming process for manufacturing of complex bar and tube profiles like axles and gear shafts in the automotive industry. Conventional rotary swaging is carried out under intense use of lubricant usually based on mineral oil. Besides lubrication the lubricant fulfills necessary functions like lubrication, flushing and cooling, but generates costs for recycling, replacement and cleaning of the workpieces. Hence, the development of a dry process design is highly desirable, both under economic and ecological points of view. Therefore, it is necessary to substitute the functions of the lubricant. This was realized by the combination of newly developed a-C:H:W coating systems on the tools to minimize the friction and to avoid adhesion effects. With the application of a deterministic structure in the forging zone of the tools the friction conditions are modified to control the axial process forces.In this study infeed rotary swaging with functionalized tools was experimentally investigated. Therefore, steel and aluminum tubes were formed with and without lubricant. Different structures which were coated and uncoated were implemented in the reduction zone of the tools. The antagonistic effects of coating and structuring were characterized by measuring the axial process force and the produced workpiece quality in terms of roundness and surface roughness. Thus, the presented results allow for further developments towards a dry rotary swaging process.Rotary swaging is a cold bulk forming process for manufacturing of complex bar and tube profiles like axles and gear shafts in the automotive industry. Conventional rotary swaging is carried out under intense use of lubricant usually based on mineral oil. Besides lubrication the lubricant fulfills necessary functions like lubrication, flushing and cooling, but generates costs for recycling, replacement and cleaning of the workpieces. Hence, the development of a dry process design is highly desirable, both under economic and ecological points of view. Therefore, it is necessary to substitute the functions of the lubricant. This was realized by the combination of newly developed a-C:H:W coating systems on the tools to minimize the friction and to avoid adhesion effects. With the application of a deterministic structure in the forging zone of the tools the friction conditions are modified to control the axial process forces.In this study infeed rotary swaging with functionalized tools was experimentally inve...