Hans-Christian Möhring

Case Study 1.1: Identification and Active Damping of Critical Workpiece Vibrations in Milling of Thin Walled Workpieces

In milling of impellers and blisks (blade integrated disks), critical workpiece vibrations of thin-walled blade structures occur due to the excitation by the process forces and the dynamic compliance of the sensitive elements of the parts. Workpiece vibrations lead to inacceptable effects on the blade surfaces and thus to the production of defective parts. Also, these vibrations provoke an increased tool wear progress. Within the INTEFIX project, fixture solutions were developed which enable the detection and compensation of chatter vibrations during machining of thin-walled workpiece elements. This contribution introduces the development of an intelligent chuck for the clamping of impellers. The chuck exploits CFRP embedded piezo patch transducers for the identification of critical workpiece vibrations during milling. By means of an integrated piezo actuator, counter vibrations can be applied which disturb the regenerative chatter effect and lead to a decreased waviness of the workpiece surface. The development of the mechatronic clamping system is supported by innovative process simulation approaches.

Case Study 2.1: Detection and Compensation of Workpiece Distortions During Machining of Slender and Thin-Walled Aerospace Parts

In machining of thin-walled large parts in aerospace industry, workpiece distortions occur during and after the processes due to residual stresses which are introduced or set free by the material removal process. These distortions lead to an inacceptable shape and geometric errors of the produced components and, thus, to deficient products. Considering that milling operations at large aerospace structural parts take several hours and that often expensive workpiece materials (such as titanium alloys) are used, these critical deformations cause high costs in the manufacturing companies. In some cases, post-treatments such as shot peening is applied in order to reduce the influence of residual stresses. This also means a significant increase of production costs of the parts. With the aim to overcome these challenges of part deformations, in this case study an intelligent fixture was developed which detects the tendency of workpiece distortions within sequenced processing steps and which allows an active adjustment of the clamping conditions in order to compensate for the influences of residual stresses on the final shape of the part.

Effects of grinding process parameters on the surface topography of PCBN cutting inserts

PCBN as a cutting tool material is a proper choice for machining difficult-to-cut materials. This is due to its hardness, chemical stability and toughness. The surface quality of PCBN tools, which are commonly ground with diamond wheels, strongly depends on the grinding parameters. The cutting forces, temperature, loading and wear of the grinding wheel influence the quality of the ground PCBN surface. The effects of cutting parameters on the cutting forces, roughness and loading of the grinding wheel during plunge face grinding of PCBN inserts are studied in this work. It was found that increasing the cutting speed from 20 to 40 m/s can decrease the cutting forces and surface roughness up to 20% and 30%, respectively. Additionally, the amount of oversize in roughing and the roughing parameters have a significant influence on the induced cutting forces in the finishing stage and the surface quality of the ground PCBN inserts.