Papers by Author: Fritz Klocke

Abstract: AISI H11 tool steel is a complex tool steel alloy used to manufacture hot forging dies. These dies however have a limited life, which depends upon the working conditions, the tool design, the heat treatment, and the quality of tool steels. In this paper, a novel wire-and powder-based laser metal deposition (WP-LMD) process was investigated to deposit H11 wire and niobium (Nb) powder simultaneously and develop a coating on existing forging dies for enhancing their life. The main aim was the development of a novel WP-LMD process, and consequently a new H11 tool steel with improved toughness and hardness. The developed WP-LMD process was later implemented to build a multilayer block made of the modified H11 tool steel. The overlap ratio was optimized in both, horizontal and vertical, directions, and were found to be 30% and 20% respectively in order to achieve a fully dense coating and avoid pores and unmelted Nb particles. The potential of the WP-LMD can be used to fabricate an outer layer of the modified H11 tool steel with improved toughness and hardness, which ultimately enhances the life of hot forging.

Abstract: Generally, hard finishing is the final step in manufacturing cylindrical gears. The most established processes for hard finishing are continuous generation grinding and discontinuous profile grinding [1]. Despite the wide industrial application of the continuous generation grinding process, only few scientific investigations exist. One possible reason for this are the complex contact conditions between tool and gear flank. Modelling the complex contact conditions between grinding worm and gear to calculate cutting forces, characteristic values as well as micro- and macroscopic gear geometry are the topics of this paper. The approaches are introduced and results for validation are presented and discussed.

Abstract: For the process design of a cutting process, the knowledge of the cutting force is of fundamental importance. The cutting force influences the dimensioning of machine components and process parameters [1]. A precise interpretation of those process elements enables for high manufacturing and component accuracy. Due to the complexity of the chip geometries, the cutting force in gear hobbing is calculated by using a penetration calculation. The applied cutting force models have been developed by BOUZAKIS [2] and GUTMANN [3] in the 1980s. These models are based on data from longitudinal turning processes. Advancements in machine tool technology of the past decades have led to more efficient processes. The use of new cutting materials allows for higher speeds and feeds. This led to larger chip thicknesses. The bases of the models by GUTMANN and BOUZAKIS covers today's usual hobbing parameters not extensive enough. The influence of tempered levels on the cutting force is not included in the models. Therefore, the aim is to create a cutting force model and adjust the calculation base after GUTMANN. A radial turning process with interrupted cutting is used as analogy process. The influence of the heat treatment at 42CrMo4 is to be examined for the cutting force. This will be compensated in three different tensile strengths. The investigated process parameters are extended beyond the current state of the art.

Abstract: In order to improve load carrying capacity and noise behaviour, case hardened gears are usually hard finished. One possible process for hard finishing of gears is generating gear grinding, which has replaced other grinding processes in batch production of small and middle sized gears due to high process efficiency. Especially generating gear grinding of large module gears with a module higher than mn > 8 mm can be challenging due to high process forces and the resulting excitation, which can influence gear quality negatively. TÜRICH suggested applying a pitch diameter shift during generating gear grinding to equal out the number of contact points between the left and right flanks of the gear with the grinding tool [1]. This qualitative approach is not sufficient to predict the process behaviour because it does not take the changing radii of the curvature of the involute into account and, therefore, the changing contact conditions along the gear profile. In this paper a methodology to quantify the influence of pitch diameter shift on the generating gear grinding process using a manufacturing simulation is introduced. Additionally this methodology is validated for one manufacturing test case.

Abstract: One research objective for generating gear grinding is to increase economic efficiency and productivity of the process. Furthermore, the gear quality must be equal or higher compared to the non optimised process. In addition to the grinding process and the grinding tools, the dressing process can be suitable to lead to an increase of efficiency of generating gear grinding. Due to the variety of dressing tool specifications process users have the problem of selecting the best fitting dressing tool for their demands. Therefore, it is necessary to know the interactions of dressing tool specification and dressing tool wear. But the influence of the dressing tool specification onto dressing tool wear has yet not been sufficiently investigated for generating gear grinding.

Abstract: One research objective for generating gear grinding is to increase economic efficiency and productivity of the process. At the same time gear quality must be equal or higher. In addition to machining parameters, tool specification has a significant influence on process productivity, workpiece quality and the wear of the tool itself. Due to the variety of tool specifications process users have the problem of selecting the best fitting tool for their demands. Therefore, it is necessary to know how interactions of tool specification and machining parameters influence tool wear and workpiece quality. But basic experimental studies, which take different tool specifications into account, are missing today.This paper focuses on the influence of different tool specifications and machining parameters on the tool wear for generating gear grinding. With analogy trials the influence of different specifications and machining parameters on tool wear and the process is mapped. The results are analyzed, discussed and summarized in a model. Furthermore, the applicability of the findings based on analogy trials to generating gear grinding is validated.

Abstract: Fibre reinforced plastics (FRP) are being increasingly used for advanced applications where an appropriate mechanical performance should be achieved at minimum weight. A substantial increase of the FRP usage is expected across various industries e.g. in automotive sector in the nearest future. This leads to the mass manufacturing of FRP components. Reduction of manufacturing costs of FRP components is regarded as the main enabler for the usage of this material in mass production. Although FRP components are manufactured near-net-shape, they often have to be pierced or trimmed in one of the last manufacturing steps. With rising production numbers blanking is a potentially more cost efficient technology for trimming and piercing of FRP components compared to the conventionally performed abrasive water jet cutting or machining. The mechanisms of FRP separation in blanking have not yet been researched. In particular, the influence of the fibre orientation relative to the cutting line on the cutting force is not known. In the scope of this work an experimental study of blanking of a unidirectional carbon fibre reinforced plastic with a thermoset resin at different fibre orientations to the cutting line was performed. It was shown that the cutting force decreases from the perpendicular to the parallel fibre orientation to the cutting line. A possible mechanical explanation of this dependency was formulated.

Abstract: Machine hammer peening is an incremental forming process for high frequency surface finishing of technical components. Recently, machine hammer peening has attracted automotive industry’s attention for the surface finishing and structuring of deep drawing tools. Deep drawing tools surface structured by machine hammer peening are characterized by beneficial friction and wear characteristics in lubricated sliding contacts. However, the physics of hydrodynamic effects in machine hammer peened structures is yet insufficiently researched. Therefore, this work investigates the hydrodynamic effects in surface structures generated by machine hammer peening using a two-dimensional computational fluid dynamic analysis. The effects of structure geometry, structure arrangement and selected sliding parameters on the hydrodynamic fluid pressure and velocity distribution within the structures are analysed. It was observed, that the sliding direction and the structure arrangement have a significant influence on the hydrodynamic fluid pressure maximum.

Abstract: Properties of workpieces, like residual stress in the rim zone, cannot be predicted for manufacturing technologies reproducible in advance. This lack of predictability shall be solved by a new approach, called Process Signatures. These Process Signatures will combine the material loadings forced by the manufacturing process with the change of state variables, e. g. the variation of residual stress in the surface layer. As the Process Signatures shall achieve comparability for different processes with same physical working principle, it is necessary to describe the transition from material loadings to the change of material properties in a uniform way. Consequently an energy based approach is chosen that considers these transitions by the dissipation of the several kinds of energy brought into the manufacturing process and especially in the respective working area.A first step for the development of such Process Signatures is the identification of all process specific material loadings. This paper presents several material loadings generated during the electrochemical sinking process. In a further step the contribution of the individual material loadings to the material removal process are estimated. Finally first approaches for the combination of the main material loadings and the change of material properties are presented.

Abstract: Increasing demands concerning the performance of tribological systems for metal forming due to ecological restrictions or technologically increased process loads require the development of innovative tribological systems, especially in forming of stainless steel. It could be shown in preliminary work that surface structures on deep drawing tools manufactured by the incremental forming process machine hammer peening have the potential to reduce friction in strip drawing test by about 58 % in comparison with a ground reference surface. This is explained by the effect of lubricant pockets and a reduced true contact area in the interacting zone. However, due to the effect of a reduced contact area, the wear resistance of these surface structures is of main concern for the effectiveness of their application in deep drawing. Therefore, in this work strip drawing tests are performed over a minimum of 500 repetitions for the evaluation of friction characteristics. Additionally, the coating of the surface structures is investigated to improve the wear resistance of the structures.