Dressing of filigree fine-grained metal bonded grinding wheels

Metal bonded grinding tools offer a remarkable potential for micro grinding because of their favorable wear behavior. However, metal bonded grinding tools, especially dicing blades, are hard to dress by conventional dressing methods. Electro contact discharge dressing, which is presented in this paper, is a numerically controlled dressing process offering the possibility to create the geometry and topography of the grinding wheel simultaneously at negligible dressing forces. The power of an electric circuit thermally removes the metal bond of the grinding wheel during the dressing process. The quality of the created profiles and the influence of the dressing parameters on the specific material removal rate of the grinding tool as well as the wear of the electrode are investigated at fine-grained grinding wheels.     

Computability by finite automata and pisot bases

We prove that the function of normalization in base , which maps any -representation of a real number onto its -development, obtained by a greedy algorithm, is a function computable by a finite automaton over any alphabet if and only if is a Pisot number.Christiane Frougny was supported in part by the PRC Mathématiques et Informatique of the Ministère de la Recherche et de l'Espace.     

Repairing parts from nickel base material alloy by laser cladding and ball end milling

Due to rising costs of raw material, companies of the aerospace industry increasingly seek to repair components of aircraft engines instead of replacing them. Particularly the clad repair of turbine blades made of high strength nickel-base alloys with directionally solidified or single crystalline structure is a difficult issue, especially due to high requirements regarding the conditions of the final part surface. The present work deals with the question whether the prediction of surface and subsurface conditions, e.g. surface topography and residual stresses, is possible after repairing the inhomogeneous nickel-base alloy Rene 80. For this purpose, laser deposition cladding is applied for the polycrystalline Rene 80, using the filler material Rene 142. In the following re-contouring process, the claddings are milled with a ball end mill cutter. The influence of the inhomogeneous base material and the shape of the clad on the cutting forces as well as the final part surface are experimentally investigated. Superficial residual stresses are measured and evaluated. The cutting forces and the final surface reveal characteristic variations in the area of the material deposition and the dendrites. A geometric process simulation shows that the prediction of cutting forces and surface conditions for the polycrystalline material is only possible to some extent.     

Holistic process planning chain for robot machining

Today, machining of large, integral constructed structural parts requires expensive machining centers. In contrast, modern industrial robots are suitable for a wide field of applications and are characterized large working spaces and low capital investment. Therefore, they provide high economical potential for machining applications in aerospace industry, especially for the machining of near to shape pre-products like extruded profiles. However, their constructive characteristics like low stiffness and high sensitivity to vibrations lead to disadvantages compared with conventional machining centers and have to be considered during process planning. Therefore, several methods for offline and online optimization of robot machining processes were developed and integrated in a new process chain for manufacturing of structural fuselage parts. Thereby, the conventional CAD–CAM process planning chain was extended with simulation based analysis and optimization methods and a load-depending trajectory planning. These methods for offline process optimization within this novel process chain are presented in this paper.     

Chip formation in grinding: an experimental study

Due to high cutting speeds and low single grain chip thicknesses no reliable approach to interrupt the cut in grinding was realized so far. This paper presents a new method to experimentally obtain and analyze chip roots during up-grinding. By means of high resolution SEM-micrographs several chip roots are analyzed, classified and discussed with regard to the fundamental chip formation and material removal mechanisms. Furthermore, there are conclusions drawn about the distribution and number of the active grains, which are in a good correlation with the Abbott-curve of the grinding wheel layer and the process parameters.     

Dynamic analysis of a motor-integrated method for a higher milling stability

The productivity in High Speed Cutting is often limited by undesirable vibration effects in the main spindle (chatter). In many cases these limits are far below the technically possible cutting parameters provided by the machine technology. This paper presents a new approach to a motor-integrated milling spindle with an embedded electromagnetic actuator to actively reduce chatter vibrations and increase productivity. It is based on the non-contact application of highly-dynamic damping forces on the spindle shaft. That way the process stability can be increased significantly. By measurement and simulation-based analysis of spindle dynamics and transient and analytical approaches to process stability, the efficiency of the damping method is demonstrated in theory. Finally, a new, soft magnetic composite based motor-integrated electromagnetic actuator is introduced in this article.     

Prediction of plastic surface defects for 5-axis ball end milling of Ti-6Al-4 V with rounded cutting edges using a material removal simulation

The resulting surface quality after 5-axis ball end milling is of superior importance because finish milling is often the last process step determining the functional performance of a component. However, the prediction of surface topography is still a challenging task. Especially in ball end milling with the characteristic sickle shaped chip cross section, ploughing effects in the area of low chip thickness result in plastic deformation and surface defects (also known as burr). This paper provides a new approach to predict those surface defects by considering the minimum chip thickness for complex milling engagement conditions within a virtual process design. This allows the choice of suitable process parameters without extensive experimental efforts.     

Influence of the residual stress state of coatings on the wear behavior in external turning of AISI 4140 and Ti–6Al–4V

The residual stress state of coatings influences tool life and performance in machining significantly. Due to thermo-mechanical loads during the cutting process the coatings require tailored properties. Beside the coating structure the two most important properties are the residual stress state and the chemical composition of the coating. Therefore, the influence of these two properties is investigated in this study, comparing the cutting performance in continuous and interrupted cutting of 42CrMo4 (AISI 4140) and Ti–6Al–4V. It is shown that the residual stress states of the coating close to the surface and close to the substrate are important for the wear behavior. High compressive residual stresses near the substrate combined with a material-optimized composition increase the resistance against chipping. Flank wear resistance increases with high compressive residual stresses near the surface and decreasing stresses towards the substrate.     

Multicriteria dimensioning of hard-finishing operations regarding cross-process interdependencies

The production of high performance metal parts requires a well balanced sequence of operations and can usually technologically not be achieved in a single process. This issue leads to complex process chains on the shop floor and the requirement to split single processes into multistage processes in hard-finishing operations. In both cases, the objective for the process planning is to achieve not only a local optimum for the individual processes but rather an overall optimum for the complete sequence. In order to reach the overall optimum, the process planner needs to integrate the effects between the processes into consideration. These effects which are referred to as cross-process interdependencies lead to balanced settings of process parameters and results in a much more effective operation of the sequence. In this paper, a novel approach dealing with the integration of cross-process interdependencies in the hard-finishing process of multistage grinding is introduced. It is based on an a-priori multicriteria dimensioning procedure which allows the integration of cross-process interdependencies and is implemented in software programmed in JAVA. A multistage plunge grinding process for crankshaft journals is used for evaluation of the results predicted by a developed software prototype.