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The surface and subsurface conditions of components are critical for their functional properties. Every manufacturing process modifies the surface condition as a consequence of its mechanical, chemical, and thermal impact or combinations of the three. The depth of the affected zone varies for different machining operations and is related to the process parameters and characteristics. Furthermore, the initial material state has a decisive influence on the modifications that lead to the final surface conditions. With this knowledge, the collaborative research center CRC/Transregio 136 “Process Signatures” started a first joint investigation to analyze the influence of several machining operations on the surface modifications of uniformly premanufactured samples in a broad study. The present paper focusses on four defined process chains which were analyzed in detail regarding the resulting surface conditions as a function of the initial state. Two different workpiece geometries of the same initial material (AISI 4140, 42CrMo4 (1.7225) classified according to DIN EN ISO 683-2) were treated in two different heat treating lines. Samples annealed to a ferritic-perlitic microstructure were additionally deep rolled as starting condition. Quenched and tempered samples were induction hardened before further process application. These two states were then submitted to six different manufacturing processes, i.e., grinding (with mainly mechanical or thermal impact), precision turning (mainly mechanical), laser processing (mainly thermal), electrical discharge machining (EDM, mainly thermal) and electrochemical machining (ECM, (mainly chemical impact). The resulting surface conditions were investigated after each step of the manufacturing chain by specialized analysis techniques regarding residual stresses, microstructure, and hardness distribution. Based on the process knowledge and on the systematic characterizations, the characteristics and depths of the material modifications, as well as their underlying mechanisms and causes, were investigated. Mechanisms occurring within AISI 4140 steel (42CrMo4) due to thermal, mechanical or mixed impacts were identified as work hardening, stress relief, recrystallization, re-hardening and melting, grain growth, and rearrangement of dislocations.
Florian Borchers; Brigitte Clausen; Lisa Ehle; Marco Eich; Jérémy Epp; Friedhelm Frerichs; Matthias Hettig; Andreas Klink; Ewald Kohls; Yang Lu; Heiner Meyer; Bob Rommes; Sebastian Schneider; Rebecca Strunk; Tjarden Zielinski. The Influence of Former Process Steps on Changes in Hardness, Lattice and Micro Structure of AISI 4140 Due to Manufacturing Processes. Metals 2021, 11, 1102 .
AMA StyleFlorian Borchers, Brigitte Clausen, Lisa Ehle, Marco Eich, Jérémy Epp, Friedhelm Frerichs, Matthias Hettig, Andreas Klink, Ewald Kohls, Yang Lu, Heiner Meyer, Bob Rommes, Sebastian Schneider, Rebecca Strunk, Tjarden Zielinski. The Influence of Former Process Steps on Changes in Hardness, Lattice and Micro Structure of AISI 4140 Due to Manufacturing Processes. Metals. 2021; 11 (7):1102.
Chicago/Turabian StyleFlorian Borchers; Brigitte Clausen; Lisa Ehle; Marco Eich; Jérémy Epp; Friedhelm Frerichs; Matthias Hettig; Andreas Klink; Ewald Kohls; Yang Lu; Heiner Meyer; Bob Rommes; Sebastian Schneider; Rebecca Strunk; Tjarden Zielinski. 2021. "The Influence of Former Process Steps on Changes in Hardness, Lattice and Micro Structure of AISI 4140 Due to Manufacturing Processes." Metals 11, no. 7: 1102.
The surface and subsurface conditions of components are significant for their functional properties. Every manufacturing process step changes the surface condition due to its mechanical, chemical and/or thermal impact. The depth of the affected zone varies for different machining operations, and is predetermined by the process parameters and characteristics. Furthermore, the initial state has a decisive influence on the interactions that lead to the final surface conditions. The aim of the investigation presented here is to compare the influence of the load characteristics over the depth applied to manufactured components by several different machining operations and to determine the causing mechanisms. In order to ensure better comparability between the surface modifications caused by different machining operations, the same material was used (AISI 4140; German steel grade 42CrMo4 acc. to DIN EN 10083-3) and annealed to a ferritic-pearlitic microstructure. Based on interdisciplinary cooperation within the collaborative research center CRC/Transregio 136 “Process Signatures”, seven different manufacturing processes, i.e., grinding, turning, deep rolling, laser processing, inductive heat treatment, electrical discharge machining (EDM) and electrochemical machining (ECM), were used, and the resulting surface zones were investigated by highly specialized analysis techniques. This work presents the results of X-ray measurements, hardness measurements and electron microscopic investigations. As a result, the characteristics and depths of the material modifications, as well as their underlying mechanisms and causes, were studied. Mechanisms occurring within 42CrMo4 steel due to thermal, mechanical, chemical or mixed impacts were identified as phase transformation, solidification and strengthening due to dislocation generation and accumulation, continuum dynamic recrystallization and dynamic recovery, as well as chemical reactions.
Florian Borchers; Brigitte Clausen; Sandro Eckert; Lisa Ehle; Jeremy Epp; Simon Harst; Matthias Hettig; Andreas Klink; Ewald Kohls; Heiner Meyer; Markus Meurer; Bob Rommes; Sebastian Schneider; Rebecca Strunk. Comparison of Different Manufacturing Processes of AISI 4140 Steel with Regard to Surface Modification and Its Influencing Depth. Metals 2020, 10, 895 .
AMA StyleFlorian Borchers, Brigitte Clausen, Sandro Eckert, Lisa Ehle, Jeremy Epp, Simon Harst, Matthias Hettig, Andreas Klink, Ewald Kohls, Heiner Meyer, Markus Meurer, Bob Rommes, Sebastian Schneider, Rebecca Strunk. Comparison of Different Manufacturing Processes of AISI 4140 Steel with Regard to Surface Modification and Its Influencing Depth. Metals. 2020; 10 (7):895.
Chicago/Turabian StyleFlorian Borchers; Brigitte Clausen; Sandro Eckert; Lisa Ehle; Jeremy Epp; Simon Harst; Matthias Hettig; Andreas Klink; Ewald Kohls; Heiner Meyer; Markus Meurer; Bob Rommes; Sebastian Schneider; Rebecca Strunk. 2020. "Comparison of Different Manufacturing Processes of AISI 4140 Steel with Regard to Surface Modification and Its Influencing Depth." Metals 10, no. 7: 895.
Although high efforts were made to get a deeper understanding of grinding processes for many years, it is still not possible to clearly predict the alteration of the workpiece surface layer caused by grinding. To achieve this objective, the material loads occurring during grinding and the material modifications remaining in the material have to be considered. This knowledge enables the concept of Process Signatures describing correlations between internal material loads and induced modifications. For the prediction of residual stresses occurring in a single step grindin process, various theoretical approaches can be derived. In most of these approaches, grinding processes are investigated considering the same initial state of the workpieces in terms of material, heat treatment but also in terms of functional properties such as the residual stress state generated by the previous manufacturing processes. The influence of different initial states on the residual stress state after grinding is still not clear but of high interest, taking into account that grinding is usually performed as a process consisting of multiple steps (multistage grinding). In this context, this paper focusses on the effect of different initial states that are generated in the first grinding step on the grinding process in the subsequent grinding step e.g. regarding the residual stress state. Correlations are identified between internal material loads and the residual stress in multistage grinding. To gain a deeper knowledge of the interaction between thermally and mechanically induced internal loads, the combined laser and deep rolling process is introduced. In contrast to grinding, this process allows the variation of the thermal and mechanical load independently from each other, so that acting mechanisms regarding materials loads and resulting material modifications can be revealed which serve to optimize the multistage grinding processes in the future.
Ewald Kohls; Robert Zmich; Carsten Heinzel; Daniel Meyer. Residual stress change in multistage grinding. Procedia CIRP 2020, 87, 186 -191.
AMA StyleEwald Kohls, Robert Zmich, Carsten Heinzel, Daniel Meyer. Residual stress change in multistage grinding. Procedia CIRP. 2020; 87 ():186-191.
Chicago/Turabian StyleEwald Kohls; Robert Zmich; Carsten Heinzel; Daniel Meyer. 2020. "Residual stress change in multistage grinding." Procedia CIRP 87, no. : 186-191.
The knowledge of the loads occurring during a manufacturing process (e.g., grinding) and of the modifications remaining in the material is used in the concept of process signatures to optimize the manufacturing process and compare it with others (e.g., laser processing). The prerequisite for creating a process signature is that the loads can be characterized during the running process. Due to the rough process conditions, until now there is no in-process technique to measure the loads in the form of displacements and strains in the machined boundary zone. For this reason, the suitability of speckle photography is demonstrated for in-process measurements of material loads in a grinding process without cooling lubricant and the measurement results are compared with finite element method (FEM) simulations. As working hypothesis for the simulation it is assumed, that dry grinding is a purely thermally driven process. Despite the approximation by a purely thermal model with a constant heat source, the measured displacements differ only by a maximum of approximately 20% from the simulations. In particular, the strain measurements in feed speed direction are in good agreement with the simulation and support the thesis, that the dry grinding conditions used here lead to a primarily thermally affecting process.
Andreas Tausendfreund; Florian Borchers; Ewald Kohls; Sven Kuschel; Dirk Stöbener; Carsten Heinzel; Andreas Fischer. Investigations on Material Loads during Grinding by Speckle Photography. Journal of Manufacturing and Materials Processing 2018, 2, 71 .
AMA StyleAndreas Tausendfreund, Florian Borchers, Ewald Kohls, Sven Kuschel, Dirk Stöbener, Carsten Heinzel, Andreas Fischer. Investigations on Material Loads during Grinding by Speckle Photography. Journal of Manufacturing and Materials Processing. 2018; 2 (4):71.
Chicago/Turabian StyleAndreas Tausendfreund; Florian Borchers; Ewald Kohls; Sven Kuschel; Dirk Stöbener; Carsten Heinzel; Andreas Fischer. 2018. "Investigations on Material Loads during Grinding by Speckle Photography." Journal of Manufacturing and Materials Processing 2, no. 4: 71.
During the process of grind-hardening, the dissipated heat from the process is utilized for a surface layer hardening of machined components made of steel. A martensitic phase transformation occurs within the affected subsurface regions and compressive residual stresses are induced. However, the layout of a grind-hardening process for given hardness results (material modification) is very difficult. Thus, a series of extensive experimental tests is required. To reduce this experimental effort, the newly developed concept of Process Signatures is used to describe the material modifications based on the thermal load appearing during the grind-hardening process. Based on an analytical calculation of the temperature fields during the grind-hardening process (surface- and external-cylindrical-grind-hardening), the internal thermal load was characterized by the maximum contact zone temperature and the maximum temperature gradient at the surface and was correlated with the process quantities (heat flux to the workpiece and the contact time). Metallographic investigations were used to analyze the surface hardening depth and the hardness change at the surface, which were correlated with the quantities describing the internal material loads. The results show that the surface hardening depth was mainly governed by the maximum contact zone temperature and the maximum temperature gradient at the surface, whereas the hardness change at the surface was influenced additionally by the quenching time.
Benjamin Kolkwitz; Ewald Kohls; Carsten Heinzel; Ekkard Brinksmeier. Correlations between Thermal Loads during Grind-Hardening and Material Modifications Using the Concept of Process Signatures. Journal of Manufacturing and Materials Processing 2018, 2, 20 .
AMA StyleBenjamin Kolkwitz, Ewald Kohls, Carsten Heinzel, Ekkard Brinksmeier. Correlations between Thermal Loads during Grind-Hardening and Material Modifications Using the Concept of Process Signatures. Journal of Manufacturing and Materials Processing. 2018; 2 (1):20.
Chicago/Turabian StyleBenjamin Kolkwitz; Ewald Kohls; Carsten Heinzel; Ekkard Brinksmeier. 2018. "Correlations between Thermal Loads during Grind-Hardening and Material Modifications Using the Concept of Process Signatures." Journal of Manufacturing and Materials Processing 2, no. 1: 20.