During turning of quenched and tempered AISI4140 surface layer states can be generated, which degrade the lifetime of manufactured parts. Such states may be brittle rehardened layers or tensile residual stresses. A soft sensor concept is presented in this work, in order to identify relevant surface modifications during machining. A crucial part of this concept is the measurement of magnetic characteristics by means of the 3MA-testing (Micromagnetic Multiparameter Microstructure and Stress Analysis). Those measurements correlate with the microstructure of the material, only take a few seconds and can be processed on the machine. This enables a continuous workpiece quality control during machining. However specific problems come with the distant measurement of thin surface layers, which are analyzed here. Furthermore the scope of this work is the in-process-measurement of the tool wear, which is an important input parameter of the thermomechanical surface load. The availability of the current tool wear is to be used for the adaption of the process parameters in order to avoid detrimental surface states. This enables new approaches for a workpiece focused process control, which is of high importance considering the goals of Industry 4.0.

Open Access October 1, 2020

Temperature monitoring in the subsurface during single lip deep hole drilling

Measuring of the thermomechanical load at different cutting parameters, including wear and simulative validation

Robert Wegert, Vinzenz Guski, Hans-Christian Möhring, Siegfried Schmauder

Page range: 757-767

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Abstract

The surface quality and the subsurface properties such as hardness, residual stresses and grain size of a drill hole are dependent on the cutting parameters of the single lip deep hole drilling process and therefore on the thermomechanical as-is state in the cutting zone and in the contact zone between the guide pads and the drill hole surface. In this contribution, the main objectives are the in-process measurement of the thermal as-is state in the subsurface of a drilling hole by means of thermocouples as well as the feed force and drilling torque evaluation. FE simulation results to verify the investigations and to predict the thermomechanical conditions in the cutting zone are presented as well. The work is part of an interdisciplinary research project in the framework of the priority program “Surface Conditioning in Machining Processes” (SPP 2086) of the German Research Foundation (DFG). This contribution provides an overview of the effects of cutting parameters, cooling lubrication and including wear on the thermal conditions in the subsurface and mechanical loads during this machining process. At first, a test set up for the in-process temperature measurement will be presented with the execution as well as the analysis of the resulting temperature, feed force and drilling torque during drilling a 42CrMo4 steel. Furthermore, the results of process simulations and the validation of this applied FE approach with measured quantities are presented.

Open Access October 1, 2020

Development of thin-film based sensors for temperature and tool wear monitoring during machining

Marcel Plogmeyer, Germán González, Volker Schulze, Günter Bräuer

Page range: 768-776

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Abstract

The development of thin-film sensors for temperature and wear measurement in machining operations is presented in this work. A functional thin-film system, consisting of an Al 2 O 3 insulation layer, a chromium sensor layer structured by photolithography and an Al 2 O 3 wear-protection and insulation layer, is deposited by physical vapor deposition (PVD) processes onto the surface of cemented carbide cutting inserts. First specimen of the sensors are successfully fabricated and tested in laboratory experiments as well as in machining operations to demonstrate their functionality. These tool-integrated sensors can be used as an in-process monitoring device to determine the temperatures on the rake face at or close to the tool-chip contact area and to measure the progress of the flank-wear land width. The knowledge of these important process parameters opens up the possibility to develop new in-process control mechanisms in order to modify and improve the surface integrity of manufactured components. Thereby, their performance and lifetime can be enhanced.

September 23, 2020

Metrological characterization of the thermomechanical influence of the cross-section of the undeformed chip on the surface properties in turning of the aluminum alloy EN AW-2017

Thomas Junge, Thomas Mehner, Andreas Nestler, Andreas Schubert, Thomas Lampke

Page range: 777-786

Abstract

The surface integrity strongly affects the performance properties of parts. Therefore, it is of great importance to be able to measure and adjust the surface-layer properties during the manufacturing process. In particular, cutting operations are characterized by high mechanical loads and temperature gradients in the area of chip formation. To enable a targeted control of the surface-layer properties, a fundamental comprehension of the interrelationships between the thermomechanical impact and the thereby induced material modification is required. Hence, the subject of this study is to measure the thermomechanical changes during turning of the aluminium alloy EN AW-2017 and find correlations thereof to the surface integrity. In order to achieve a large variation of the thermal and mechanical loads, the feed f (0.04 mm to 0.2 mm) and the depth of cut ap{a_{\mathrm{p}}} (0.4 mm to 2 mm) are varied over a wide range. The cutting speed vc{v_{\mathrm{c}}} is kept constant (300 m/min). For the in-process measurement of the temperatures and contact conditions at the interface of the tool and the specimen, a tool-workpiece thermocouple is used. Additionally, the components of the resultant force are measured by a dynamometer. The characterization of the surface layer is performed by the measurement of the residual stresses using X-ray diffraction and supplemented by the determination of the geometrical properties of the machined surface using a stylus measurement instrument. The results show an increase in temperature and the components of the resultant force with the enlargement of the cross-section of the undeformed chip. Due to the temperature gradient, tensile residual stresses are introduced in the tangential direction of the surface layer. Compressive residual stresses occur only in the axial direction and can be correlated with the in-process measurement data by introducing the C -value. Consequently, the calculation of the presence of compressive residual stresses allows for a targeted control of the surface-layer properties during machining.

Open Access November 26, 2020

Potential of magnetic Barkhausen noise analysis for in-process monitoring of surface layer properties of steel components in grinding

Rahel Jedamski, Jonas Heinzel, Maximilian Rößler, Jérémy Epp, Jochen Eckebrecht, Jens Gentzen, Matthias Putz, Bernhard Karpuschewski

Page range: 787-798

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Abstract

Grinding processes are often the last step in the value-added chain of high-performance hardened steel components. However, thermo-mechanical loads which can take place during the process can have a detrimental effect on the surface integrity of ground parts, which are generally tested by post-process measurements. In the present study, two different approaches for an in-process inspection of the workpiece surface integrity were assessed using magnetic Barkhausen noise analysis during cylindrical grinding of hardened workpieces. The results showed that both measuring systems are able to detect changes in the surface state of workpieces in-process or directly after grinding in the grinding machine. After preparations to protect the sensors from influences during the grinding process, changes in the residual stress state and a decrease of hardness could be reliably detected. Due to constant contact conditions between sensor and workpiece a high reproducibility of the measurements was achieved.

About this journal

Objective

The journal promotes dialogue between the developers of application-oriented sensors, measurement systems, and measurement methods and the manufacturers and measurement technologists who use them.

Topics

The manufacture and characteristics of new sensors for measurement technology in the industrial sector
New measurement methods
Hardware and software based processing and analysis of measurement signals to obtain measurement values
The outcomes of employing new measurement systems and methods