A novel approach for simulating a sawing process with reduced simulation time

The numerical simulation of machining processes enables the analysis of thermo-mechanical effects and can be used to predict process-specific quantities such as cutting force and chip shape. This involves, however, a great amount of computational effort and time depending on the model design. Basically, a simulation can be carried out two- or three-dimensionally. Due to the lower computational effort, 2D simulations were often used in the past to analyse the machining properties. In orthogonal cutting, this leads to a good approximation to the real processes if a suitable ratio between cutting width and depth of cut is applied. Nevertheless, most industrially relevant machining processes cannot be completely simulated with a 2D simulation. For these purposes, 3D simulations must be created. This requires a much greater computational effort, which increases the simulation time. This paper shows an approach to determine the cutting force and the information about the chip shape during sawing (bound orthogonal cutting) with a shortened calculation time. This was achieved by dividing the entire cut into 2D and 3D areas. The ratio between the cutting width and the depth of cut defines the criterion for the division. When it was greater than 10, the cutting process between the corner radii was assumed to be a plane two-dimensional strain state. The results showed a good agreement of the cutting force calculated from the 2D–3D simulation approach with experimental investigations and a 3D simulation. The computing time could be reduced by more than 50%

Evaluation of methods for measuring tool-chip contact length in wet machining using different approaches (microtextured tool, in-situ visualization and restricted contact tool)

The contact length is one of the most important factors to evaluate the chip formation process and the mechanical loads in metal cutting. Over the years, several methods to identify the contact length were developed. However, especially for wet cutting processes the determination of the contact length is still challenging. In this paper, three methods to identify the contact length for dry and wet processes in cutting of Ti6Al4V and AISI4140 + QT are presented, discussed and analyzed. The first approach uses tools with a microtextured rake face. By evaluating the microstructures on the chip, a new method to identify the contact length is established. The second approach applies high speed recordings to identify the contact length. The challenge is thereby the application of high-speed recordings under wet conditions. In the third approach, tools with restricted contact length are used. It is shown that with all three methods the contact length is reduced using metal working fluid

Kalibrierverfahren für hybride Parallelkinematiken

Der Einsatz parallel- oder hybridkinematischer Maschinen in der Fertigung hat gegenüber dem Einsatz serieller Maschinen Vorteile. So können Roboter mit Parallelkinematik wegen ihre höheren Steifigkeit bei geringerer Gesamtmasse eine bessere Wiederholgenauigkeit erreichen und größere Kräfte aufbringen als konventionelle Knickarmroboter. Jedoch herrscht nach wie vor Zurückhaltung hinsichtlich ihres industriellen Einsatzes. Bisher mangelt es im Bereich der parallel- und hybridkinematischen Strukturen insbesondere an universell einsetzbaren, standardisierten Verfahren, mit denen eine Kalibrierung durchgeführt werden kann. In diesem Artikel werden Methoden zur parametrischen Kalibrierung hybrider Parallelkinematiken vorgestellt. Grundlage jeder parametrischen Kalibrierung solcher Kinematiken bildet ein kinematisches Modell der zu kalibrierenden Maschine, welches alle einwirkenden Fehlereinflüsse berücksichtigen soll. Diesbezüglich wird eine allgemeine Vorgehensweise zur kinematischen Modellbildung entwickelt. Das Verfahren stützt sich auf homogene Transformationen und die Denavit-Hartenberg-Konvention, die entsprechend den Anforderungen für die Modellbildung hybrider Parallelkinematiken erweitert wird. Basierend auf dem entwickelten kinematischen Modell wird das Identifikationsproblem der Fehlereinflüssse formuliert. Aufgrund der parallelen Strukturen sind einige Fehlereinflüsse redundant zueinander oder haben gar keinen Einfluss auf die Endeffektorpose und sind somit nicht identifizierbar. Mittels einer Sensitivitätsanalyse wird das entwickelte Modell reduziert wodurch gerade solche Fehlereinflüsse aus dem Modell eliminiert werden. Grundlage der Identifikation der Fehlereinflüsse sind Messungen der Endeffektorpose. In der vorliegenden Arbeit kommt ein Einfreiheitsgrad-Messgerät zum Einsatz. Der Aufwand der Trilateration zur Bestimmung der vollen Position ist jedoch sehr hoch, so dass in den vorliegenden Untersuchungen die Pose des Endeffektors nur teilweise bestimmt wird. Dabei ist die Wahl der optimalen Messorte hinsichtlich der Effizienz des Kalibrierungsprozesses von entscheidender Bedeutung. Aus diesem Grund werden Methoden zur Optimierung der Messstrategie entwickelt und diskutiert. Abschliessend werden die entwickelten Methoden und gewonnenen Erkenntnisse an Beispielen verschiedener Kinematiken angewandt und diskutiert

App-Based Coaching to Prevent Addictive Behaviors among Young Adults

Abstract: Background: Vocational students have an increased risk to engage in health-risk behaviors compared to same-aged peers. To date, evidence-based digital prevention approaches that address multiple health-risk behaviors are rare. Method: The randomized-controlled trial (RCT) “Prevention of at-risk substance and Internet use disorders among vocational students” (PARI) investigates the efficacy of an app-based prevention approach compared to a waitlist-control condition. The aim is to prevent substance-related and behavioral addictions and improve life skills. An existing app (ready4life) was adapted under consideration of focus groups with teachers, prevention experts, and students. A Delphi expert group rated the quality of the approach. The efficacy of the modified ready4life app is currently being tested in a RCT. The proactive recruitment takes place in German vocational schools. After participating in an app-based screening (T0), participants get individualized feedback and will be cluster-randomized per class to the intervention group (IG; n=1.250) or control group (CG; n=1.250). The IG chooses two out of six modules: Social competence, stress management, cannabis, tobacco, alcohol, social media/gaming. The CG receives information on how to improve health behaviors. Follow-ups are conducted after 6 months (T1) and 12 months (T2). Conclusion: This RCT provides data on a multibehavioral prevention approach for vocational students. Final results are expected in 2023

Integrated strain gauge printing in a CFRP structure

Our approach is to integrate printed strain gauges into a structure of laminated carbon fibre reinforced plastics (CFRP). This can provide minimizing disturbances caused by an additional sensor weight. Another point is to reduce the occurrence of pre-damage, as a printed structure is integrated directly into the CFRP. Due to the printing, no additional masses are applied to the CFRP by cables. To this end, the boundary conditions for the print are first explained. Subsequently, the strain gages were printed. For this purpose, studies were carried out regarding the orientation of the strain gage printing direction, the influence of repeated printing, the overlapping during printing and the subsequent lamination in CFRP plates. The sensors are to be used in the structure of the CFRP plate in a machine tool

Influence of LPBF parameters and strategies on fine machining of pre-built bores

Additive manufacturing changes the classical possibilities of production. However, post-processing is usually unavoidable for these components to achieve functional performance. To obtain an optimum product, knowledge of the characteristics of the additive manufactured part and the machining mechanisms depending on these characteristics is required. In this paper, the influence and the interaction of the laser powder bed fusion process parameters on the subtractive post-processing are shown. The effects of the parameters on the geometry of bores are examined and subsequently the precision machinability is analysed using reaming. In addition, a process simulation is carried out to correlate the simulated deformation to the required machining allowance for subsequent reaming. The aim of this investigation is to examine the capabilities of the laser powder bed fusion process to produce bores at angles of 90° (vertical), 60° and 45° that can be machined directly with a reaming tool without the need for drilling

Numerical Modeling of Cutting Characteristics during Short Hole Drilling: Part 2—Modeling of Thermal Characteristics

The modeling of machining process characteristics and, in particular, of various cutting processes occupies a significant part of modern research. Determining the thermal characteristics in short hole drilling processes by numerical simulation is the object of the present study. For different contact conditions of the workpiece with the drill cutting inserts, the thermal properties of the machined material were determined. The above-mentioned properties and parameters of the model components were established using a three-dimensional finite element model of orthogonal cutting. Determination of the generalized values of the machined material thermal properties was performed by finding the set intersection of individual properties values using a previously developed software algorithm. A comparison of experimental and simulated values of cutting temperature in the workpiece points located at different distances from the drilled hole surface and on the lateral clearance face of the drill outer cutting insert shows the validity of the developed numerical model for drilling short holes. The difference between simulated and measured temperature values did not exceed 22.4% in the whole range of the studied cutting modes

Development of an adaptronic spindle for a faultless machining of homogeneous and inhomogeneous materials

One of the latest topics in construction concerns the difficulty of producing faultless drill holes in parts made of composite and sandwich materials. At the Institute for Machine Tools of the University of Stuttgart, a prototype of an adaptronic drilling spindle for a machining of components made of homogeneous and inhomogeneous materials was developed within the framework of a research project, funded by the Federal Ministry for Economic Affairs and Energy. The spindle made it possible to limit the axial force and the torque acting on the tool, thus protecting the tools and the workpieces from any possible damage. The tests carried out with the spindle prototype proved that the axial feed force acting from the spindle can be reliably controlled by means of the developed spindle. It might be possible to restrict critical machining situations arising due to the removal of drill chips or the reduction of process temperatures

Determination of the Shear Angle in the Orthogonal Cutting Process

Determination of the shear angle by experimental and analytical methods, as well as by numerical simulation, is presented. Experimental determination of the shear angle was performed by analyzing the chip roots obtained by the method of cutting process quick stop through purposeful fracture of the workpiece in the area surrounding the primary cutting zone. The analytical determination of the shear angle was carried out using the chip compression ratio and was based on the principle of a potential energy minimum. Measurement of the shear angle in the numerical simulation of orthogonal cutting was performed using the strain rate pattern of the machined material at the selected simulation moment. It was analyzed how the parameters of the Johnson–Cook constitutive equation and the friction model affect the shear angle value. The parameters with a predominant effect on the shear angle were determined. Then the generalized values of these parameters were established with a software algorithm based on identifying the intersection of the constitutive equation parameter sets. The use of generalized parameters provided the largest deviation between experimental and simulated shear angle values from 9% to 18% and between simulated and analytically calculated shear angle values from 7% to 12%

A study of low-frequency vibration-assisted bandsawing of metallic parts

Sawing is often the first work step in the metal cutting production chain. Especially for larger workpieces, bandsawing is used for this purpose. Nevertheless, studies on sawing have led a niche existence in the research landscape for a long time. However, as a result of the optimization of manufacturing processes in terms of economic efficiency, bandsawing is increasingly becoming the focus of research, since there are still saving potentials here. The aim of this paper is to investigate the extent to which the bandsawing process can be influenced by active, low-frequency vibration superimposition in the feed direction. First, analogue tests were carried out and parameter combinations were determined which have a positive influence on the process. Subsequently, these parameter combinations were investigated on a real sawing machine with an excitation unit, analysing the extent to which the results from the analogue tests could be transferred to the real process