Influence of XHV-adequate atmosphere on surface integrity

In aerospace engineering, high temperature alloys such as titanium are the preferred choice. However, machining of such materials remains a major challenge due to high process forces and process temperatures. Currently, machining is performed almost entirely in the presence of oxygen. This results in a process-inherent oxidation of the metal surface, which leads to higher tool wear during machining. By means of an oxygen-free machining undesirable oxidation reactions will be avoided and thus results in an extension of tool life. In addition, oxygen-free machining in an extreme high vacuum (XHV) adequate environment can influence the resulting workpiece surface and subsurface properties due to change in process forces and chip formation. In the present work, the influence of machining under air and XHV-adequate atmosphere is examined with regard to chip formation, workpiece surface topography and residual stresses. Significant differences can be seen in resulting surface integrity depending on the machining atmosphere

Operational Planning of Maintenance Measures by Means of Event-driven Simulation

AbstractModern manufacturing systems are characterized by an increasing complexity and high dynamic. This leads to new challenges for the operational planning of maintenance and production. This paper introduces a novel approach to an online simulation which enables a cost-optimized integration of condition-based maintenance measures in the production plan. The dynamic approach is implemented by means of event-driven simulation. It enables to depict the actual state of a complex manufacturing system, to simulate the future development of the production and thereby to evaluate different planning alternatives of maintenance

Process design of the patterning process of profile grinding wheels

In production environment, grinding is often the last step along the process chain. At this step, the main share of the value chain is already manufactured. Correspondingly, the process result of this step directly influences the product quality. Thus, the avoidance of process induced damages is a major challenge in grinding. The major limiting factor in grinding is the thermal load on the workpiece, which leads to grinding burn and tensile residual stresses. This thermal load can be reduced, as previous fundamental studies have shown, by means of using microstructured grinding wheels. In this paper, the patterning process of profile grinding wheels is investigated with regard to the resulting geometry and the resulting grinding wheel topography. In detail, an analytical model is established and evaluated that enables a design of the patterning process of profile grinding wheels. The presented formulas describe the local depth and width of a pattern over its length of engagement. The influence of the inclination angle of the patterning tool and the profile angle of the grinding wheel on the resulting width and length of one pattern is investigated. Further influencing parameters on the size of a pattern that are investigated are e.g. the radius of the grinding wheel, the radius of the patterning tool, the corner radius of the patterning edge and the speed ratio between the grinding wheel and the patterning tool. In addition, grinding experiments were conducted to validate the process design. The results show a high correlation between the calculated and the resulting patterns on the grinding wheel as well as that a decrease in cutting forces can be achieved by this approach. When maintaining the workpiece and grinding wheel load, the productivity of the profile grinding process can be increased in this way

Increasing productivity in heavy machining using a simulation based optimization method for porcupine milling cutters with a modified geometry

Porcupine milling cutters offer a high potential for increasing the metal removal rate in heavy machining of steel and titanium. Here, the available machine power and the maximum radial force represent important process limits. According to the current state of the art, mainly rectangular indexable inserts are used. Investigations show that the use of round inserts can significantly reduce the resulting radial force and cutting torque similar to serrated endmills. However, the design of such tools is a major challenge due to the complicated shape of cross-section of the undeformed chip. Therefore, this paper presents a new method for optimizing the position of individual indexable inserts by means of geometric material removal simulations. With the new method, the radial force can be reduced by 14%

High performance peel grinding of steel shafts using coarse electroplated CBN grinding wheels

Grinding is widely known for its low material removal rates and high surface quality. However, recent developments in production processes for cubic boron nitride (CBN) abrasive grains have led to commercially available grain sizes larger than 300 µm. These superabrasive CBN-grains allow higher material removal rates during grinding of hardened steel components. Currently, these components are pre-machined with turning processes before hardening and finishing the work piece by grinding. However, the turning process can be eliminated by grinding with coarse CBN-grains since higher depths of cut are achievable when machining hardened components. This paper explores the limits of grinding wheels using grains with a size of B602 during soft and hard machining in comparison to conventional B252 grains. It is shown that the use of coarser grains leads to lower process forces, higher (tensile) residual stress and higher surface roughness. Residual stress and surface roughness are of less importance as these grains are to be used mainly in roughing operations with ensuing finishing operations for the required surface properties. Over all investigations, especially in hard machining, neither grain nor tool wear was observed for the B602 grains, whereas the B252 tool was severely clogged during the experiments. Additionally, the grinding force ratio indicates that the coarse grain tools have not yet reached their productivity limit as it increases over all investigated feeds. This indicates improving tool performance with lower amounts of rubbing for increasing feed rate during hard grinding and shows the potential for the industrial use of higher feed rates with larger grains

Modeling of Workpiece Shape Deviations in face Milling of Parallel Workpiece Compounds

The mass reduction of components is one of the most effective ways to reduce fuel consumption and emissions in the automotive and aircraft industry. A lightweight strategy used for highly loaded components is the combination of different materials to workpiece compounds. In that way components can be designed depending on the local load using the most qualified material. For the production of high-performance workpiece compounds high quality requirements concerning the accuracy of dimension and shape as well as surface roughness must be fulfilled. However, machining of workpiece compounds leads to unfavorable changes of the workpiece quality in comparison to machining of the single materials. Significant shape deviations occur when different materials are machined alternately in one cutting operation. This is due to unequal material properties, cutting characteristics, chip formation mechanisms as well as characteristic interactions between the single components. This paper describes the causes of the three main criteria material height deviation, transition deviation and surface roughness deviation that significantly influence the surface quality in parallel machining. The focus is on the process understanding as well as modeling of the surface defects. The approaches and results show that the characteristic shape deviations can be predicted. With the knowledge of the causes that lead to the surface defects in parallel machining it is possible to optimize the process setup for a surface quality oriented machining process of a workpiece compound. Copyright © 2013 Elsevier B.V

Chip formation in machining hybrid components of SAE1020 and SAE5140

The requirements for massive high-performance components are constantly increasing. In addition to the reduction of component weight, requirements such as smaller design, more functionality and longer lifetime are increasing. By joining different materials in one component, these contradictory requirements can be met. In the process chain of manufacturing hybrid components, machining as the final step has a decisive influence on the application behavior and service life due to the surface and subsurface properties generated. Thereby thermomechanical loads during machining determine the final subsurface properties and the chip formation mechanisms determine the final surface properties of components. However, for the specific adjustment of required surface and subsurface properties, first of all an understanding of the generation of the addressed properties in the material transition zone is necessary. In the current work, the chip formation and the mechanical loads in the transition zone of hybrid components are presented. Within the scope of orthogonal cutting investigations, the influence of process parameters and tool microgeometry on mechanical loads and chip formation is analyzed. Chip forming has a significant influence on the surface properties of the hybrid component. The chip formation depends on the hardness of the machined material. During machining of hybrid components an abrupt change of the chip shape takes place in the material transition zone. The process variables influence the level in the surface topography of hybrid components. © 2020, The Author(s)

Parametric grinding wheel model for material removal simulation of tool grinding processes

Tool grinding is an essential process for the production of cemented carbide tools. In that context, the investigation of specific effects like the resulting surface profile and the fluid dynamic processes is of great interest, but requires microscopic modeling of the grinding wheel including its individual grains and bonding material. This paper introduces an approach for a parametric grinding wheel model, which provides a topography on microscopic scale depending on the grinding wheel specification and dressing conditions for subsequent use in material removal simulations. Scalable abrasive grains and variable distributions embedded in a shiftable bond layer are applied. Optical laser scans are used to derive surface parameters for an adaption and evaluation of the model. The prediction quality in terms of surface roughness is evaluated in surface grinding reference experiments

Analytic roughness prediction by deep rolling

Deep rolling is a widely applied mechanical surface and subsurface treatment method. It is typically used after conventional machining to improve the roughness, increase the surface hardness and to induce compressive residual stresses. The main influence parameters on the surface topography are the applied deep rolling pressure, the ball diameter and the feed. In general, low feeds, larger ball diameters and higher pressures result in an even surface finish. However, an exact prediction of the roughness is not possible. Therefore, it is the aim of the presented research to find a generally applicable method for surface roughness prediction after deep rolling for a variety of steel and aluminum materials. It is shown that the surface topography can be predicted by an analytical model with high accuracy

Process stability of a novel roughing-finishing end mill

In this paper, stability investigations of a novel roughing-finishing end mill are carried out. This tool possesses two sharp finishing teeth and two radially recessed, chamfered roughing teeth. By applying the same tool for roughing and finishing operations, tool changes and process time can be reduced. For the stability investigations, the semi-discretization method for calculating stability charts was extended and made applicable for the novel tool concept by taking into account the radial recession of the chamfered cutting teeth. This is necessary because the radial recession leads to varying time-delays during the tooth engagement. Stability charts were then calculated for roughing-finishing tools with different radial recession as well as for conventional finishing and roughing tools. Furthermore, experimental stability charts were created. The results show a good agreement between calculated and experimental stability charts for the finishing tool. However, the calculated stability limits of the roughing-finishing tool and the roughing tool do not met with the experimental stability limits, which is attributed to inaccuracies in the modelling of process damping. Nevertheless, calculated as well as experimental stability charts indicate a significant increase of the stability limit of the roughing-finishing tool compared to the finishing tool