Wear reduction at double face grinding with planetary kinematics

To machine high performance materials efficient and process safe, innovative tool concepts are required. Double face grinding with planetary kinematics is a process, which can be used to machine workpieces with high demands on flatness. Especially the kinematic of this process leads to an unequal wear shaping, which has a negative effect on the quality of the workpieces. Fulfilling the sophisticated task of ceramic machining, it is necessary to consider the chip formation and the associated wear of grinding tool based on existing approaches under consideration of the radius dependent speed gradient and significantly increased grinding wheel speeds as well. The research is the basis for the development of a tool, which allows predicting wear on the tool for double face grinding with planetary kinematics. Based on the knowledge about the wear, it is possible to design tools with requirements and customized for special processing task.     

Thermal modelling of an HSC machining centre to predict thermal error of the feed system

Machine tools equipped with linear motors can achieve high feed speed as well as high accuracy. However, the direct feed drive system generates heat through power loss and friction. In combination with environmental influences such as machine shop climate, this can lead to a local deformation of the machine tool structure and induce a direct positioning error. This paper presents a thermal model, using the finite element method, to simulate the thermal behaviour of a high-speed cutting machining centre equipped with linear motors. This model considers the complex boundary conditions such as heat sources, contact and convective heat transfer. Transient changes in temperatures and deformations are allowed in the solution. The comparison of the experiments show that this model can predict the temperature distribution and positioning error under specified operating conditions very well.     

Influence of Irradiation Temperature on Grafting of Styrene into Poly(tetrafluoroethylene‐co‐hexafluoropropylene) Films

This study concerns with the investigation of the effect of irradiation conditions on grafting of styrene into FEP films by the pre‐irradiation method. EPR spectroscopy was used to characterize the base polymer material regarding the trapped radical species and their concentration. Radiation‐induced changes in the chemical structure were studied by IR spectroscopy. Tensile strength and elongation at break as well as yield of grafting were found to be strongly influenced by irradiation temperature. Main‐chain scissions were identified to be the reason for the deterioration of the mechanical properties after radiation treatment at temperatures below glass transition temperature.

     

Influence of tilt and lead angles on 5-axis grinding with spherical mounted points

Through the kinematics involved on the grinding process, part of the grinding wheel topography is imprinted on the machined component in the form of grain scratches. During 5-axis grinding using spherical mounted points, the tilt \(\beta _{fN}\) and lead \(\beta _{f}\) angles can be used to locate the tool and align these scratches to achieve a desired angle in relation to the feed direction, creating a defined structure and decreasing the roughness on the ground surface. Moreover, different tool orientations change the force distribution over the tool, affecting the geometric deviation of the workpiece. The current work reveals a reduction of 50% of the roughness and geometric deviation for grinding of hot isostatically pressed silicon nitride HIPSN through optimization of the tilt \(\beta _{fN}\) and lead \(\beta _{f}\) angles.     

An extended shear angle model derived from in situ strain measurements during orthogonal cutting

There are numerous cutting models which describe the chip formation process. However, they are based on a number of simplifying assumptions. In order to verify these assumptions and to get a better understanding of the cutting process, the different stress states in the chip formation zone were determined by means of diffraction experiments with monochromatic high-energy synchrotron X-radiation during orthogonal, quasistatic cutting of the material C45E. The results from the experiments are compared with simulated stresses. The experimental data indicate that the assumption of a free chip flow according to the shear angle model of Opitz and Hucks is not valid. The model was therefore extended considering the normal stresses in direction of the chip flow.     

Quasi-static chip formation of intermetallic titanium aluminides

As a result of the development of new materials for high temperature applications the potential for mass reduction and increased process temperatures is constantly being expanded. Intermetallic γ-TiAl alloys can meet these demands to a large extent. The properties necessary for these applications have an adverse effect on the machinability however and render intermetallic titanium aluminides as difficult to machine materials. Cutting operations tend to produce damaged surfaces which are unsuitable for the intended applications. As the basis for a reliable and economic cutting technology, the chip formation of the intermetallic TiAl alloy TNBV5 has been examined in quasi-static cutting experiments. Observations showed that increased workpiece temperatures lead to a transition of the chip formation from segmented to continuous chips. By decreasing the undeformed chip thickness crack-free surfaces could be produced at low workpiece temperatures. In this case other mechanisms than the thermal activation of slip systems must be the reason for the observed large plastic deformations. The theory that hydrostatic pressure leads to this behavior is substantiated by the results of finite element simulations. This offers the possibility for damage free machining at lower cutting speeds, thus enabling the use of conventional tool materials at an acceptable tool life.     

Investigation of micromilled tool steel H13 using tungsten carbide micro-end mills

Micromilling allows for the high precision machining of different types of materials and thus promotes the manufacturing of micro-components for various te     

Structure of adrenodoxin and function in mitochondrial steroid hydroxylation

The three-dimensional structure of a truncated mutant of bovine adrenodoxin has been resolved at 1.85 A resolution by MAD. The protein consists of a large core region and a more flexible hairpin loop bearing residues which have been previously described as being involved in redox partner recognition. To study the role of distinct protein domains and amino acids of adrenodoxin in interaction with adrenodoxin reductase (AdR), CYP11A1 and CYP11B1, as well as in electron transfer, mutants of adrenodoxin have been prepared by site-directed mutagenesis and produced in Escherichia coli, and their structural and functional properties have been characterized in detail. It could be demonstrated that Tyr82 is located at the edge of the flexible interaction loop of adrenodoxin participating in interactions with AdR and P450s. His56, being close to Tyr82, forms a bridge between the core region of adrenodoxin and the interaction loop. Its role in transmitting changes of the cluster region to the interaction site has also been supported by functional studies. Pro108 of adrenodoxin, the only proline residue contained in the protein and being conserved in this position among several other vertebrate-type ferredoxins, has been demonstrated to be of importance for the correct folding of this protein.