Showing papers in "Production Engineering in 2011"

Laser-assisted asymmetric incremental sheet forming of titanium sheet metal parts

Abstract: Asymmetric Incremental Sheet Forming (AISF) is a relatively new manufacturing process. In AISF, a CNC driven forming tool imposes a localized plastic deformation as it moves along the contour of the desired part. Thus, the final shape is obtained by a sequence of localized plastic deformations. AISF is suitable for small series production of sheet metal parts as needed in aeronautical and medical applications. Two main process limits restrict the range of application of AISF in these fields. These are the low geometrical accuracy of parts made from titanium alloys or high strength steels and, for titanium alloys, the limited formability at room temperature. In this paper a new concept for laser-assisted AISF is introduced including the required components. Furthermore, the CAX tools used for programming the NC path for the forming tool and the laser spot are illustrated. First experimental results show that the formability of the alloy Ti Grade 5 (TiAl6V4), which is usually used in aeronautic applications, can be increased.

Application of fuzzy logic for modeling surface roughness in turning CFRP composites using CBN tool

Abstract: In recent days, carbon fiber reinforced polymer (CFRP) composites play a vital role in various engineering and technological applications. They are replacing conventional materials due to their excellent properties. Tubes made of these materials are made up of either hand layup process or filament winding processes and are widely used in aircraft, automobile, sports industries, etc., The objective of this study is to examine the influence of machining parameters combination so as to obtain a good surface finish in turning of CFRP composite by cubic boron nitride (CBN) cutting tool and to predict the surface roughness values using fuzzy modeling. The results indicate that the fuzzy logic modeling technique can be effectively used for the prediction of surface roughness in machining of CFRP composites.

A discrete-event simulation approach to predict power consumption in machining processes

Abstract: Whereas in the past the sustainable use of resources and the reduction of waste have mainly been looked at from an ecological point of view, resource efficiency recently becomes more and more an issue of cost saving as well. In manufacturing engineering especially the reduction of power consumption of machine tools and production facilities is in the focus of industry, politics and research. Before power consumption in machining processes can be reduced it is necessary to quantify the amount of energy needed, to identify energy consumers and to determine the available degrees of freedom for an optimization. Simulation can be an adequate alternative to the measurement of power consumption during machining operation. However, many of the available simulation methods are not suitable for this task. This paper describes an approach based on the discrete-event simulation, which is known mainly from the simulation of logistical systems. It has been adapted to model machining operations and to generate workpiece-specific power consumption profiles and energy footprints. Two-axis turning in a CNC machining centre is shown exemplary. The aim is to provide a basis for further applications such as the simulation, comparison and optimization of power consumption in process chains and production systems in combination with logistical models.

Open production: scientific foundation for co-creative product realization

Abstract: Globalization and the use of technology call for an adaptation of value creation strategies. As the potential for rationalization and achieving flexibility within companies is to the greatest possible extent exhausted, approaches to the corporate reorganization of value creation are becoming increasingly important. In this process, the spread and further development of information and communication technology often provide the basis for a reorganization of cross-company value nets and lead to a redistribution of roles and tasks between the actors involved in value creation. While cooperative, decentralized and self-organizing value creation processes are in fact being promoted, the associated potential for development and production engineering is being underestimated and hence not implemented sufficiently. This contribution will introduce a value creation taxonomy and then, using its notion and structure, describe the emerging transformations in value creation on the basis of case studies. Finally an adequate framework for analysing and configuring value creation will be presented.

The preparation of cutting edges using a marking laser

Abstract: During the machining process, high mechanical and thermal loads occur at the cutting edge. Such loads can cause tool failure. Specifically non-uniform and sharp cutting edges that have a low cutting edge stability lead to such failures. In order to enhance the tool performance, the cutting edges are prepared by manufacturing both a pre-defined cutting edge geometry, and an appropriate cutting edge roughness. This paper describes the use of a low-cost marking laser for the preparation of cutting edges as an alternative to conventional preparation techniques, such as brushing or blasting. Cutting edge radii of 9–47 μm can be prepared with a machining accuracy of 1.5 μm. The maximum preparation time for an individual cutting edge is approximately 10 s. Uncoated indexable inserts manufactured in this way were tested in a face milling operation. The results of these investigations (using prepared cutting edges) show both an increase in tool life and an improved surface roughness of the machined workpieces compared to those using non-prepared cutting edges.

Condition based factory planning

Abstract: Consecutive planning approaches, common in the theory of factory design today, fail to support planning projects in practice. They neglect the interactions and dynamics in the planning task and project as well as the subjectivity introduced by the different stakeholders. Unconsidered interactions, conflicting motives and inflexible project structure lead to time-consuming, expensive and late adaptations. Local optimisation and deviations from the overall objectives are consequences of insufficient synchronisation and coordination. The approach proposed in this paper strives for a paradigm shift from consecutive processes to a modular, parallel approach, which can be reconfigured according to the specific conditions of the planning project and enterprise. This new approach integrates the modularisation and configuration of the planning process as well as aspects of management of instability and second order observation. It has been successfully employed in industry cases, which will be introduced in this paper.

High resolution supply chain management: optimized processes based on self-optimizing control loops and real time data

Abstract: The efficient dealing with the dynamic environment of production industries is one of the most challenging tasks of Supply Chain Management in high-wage countries. Relevant and current information are still not used sufficiently, to handle the influence of the dynamic environment on intra- and inter-company order processing adequately. Among other things, the problem is caused by missing or delayed feedback of relevant data. As a consequence of that, planning results differ from the actual situation of production. High Resolution Supply Chain Management describes an approach aiming on high information transparency in supply chains in combination with decentralized, self-optimizing control loops for Production Planning and Control. The final objective is to enable manufacturing companies to produce efficiently and to be able to react to order-variations at any time, requiring process structures to be most flexible.

Direct photonic production: towards high speed additive manufacturing of individualized goods

Abstract: World market competition currently boosts trends like mass customization and open innovation which result in a demand for highly individualized products at costs matching or beating those of mass production. This work focus on the resolution of the production related dilemma between scale and scope, e.g. either the low-cost production of high quantities or the high-end and thus cost-intensive low-volume production of individualized goods. One of the areas of greatest potential for the resolution of this dilemma are rapid manufacturing (RM) technologies due to their almost infinite geometrical variability and freedom of design without the need for part-specific tooling. Selective Laser Melting (SLM) is one of the RM technologies that additionally provides series identical mechanical properties without the need for downstream sintering processes, etc. However, the state-of-the-art process and cost efficiency is not yet suited for series production. In order to improve this efficiency and enable SLM to enter series production it is indispensable to increase the build rate significantly by means of increased laser power and larger beam diameters. To exploit this potential, a new generation production machine including a kW laser and an optical multi-beam system is developed and experimental results and real life components are shown.

Review on the development of a hybrid incremental sheet forming system for small batch sizes and individualized production

Abstract: Asymmetric Incremental Sheet Forming (AISF) has been developed as a flexible process for low-volume production of sheet metal parts. In AISF, a part is obtained as the sum of localized plastic deformations produced by a simple forming tool that moves under CNC control. In spite of about 20 years of research and development, AISF has not had much industrial take-up yet. The main reason for this is that attempts to improve, among other limitations, the accuracy, speed and range of feasible geometries of the process by adapted process strategies has not brought about general solutions. This paper presents an overview of the current state of development of hybrid asymmetric incremental sheet forming processes at RWTH Aachen University. The goal of the development of hybrid ISF processes is to allow for a quantum leap of the capabilities of AISF in order to enable a broader industrial use of AISF. Two hybrid process variations of AISF are presented: stretch forming combined with ISF and laser-assisted AISF. It is shown that the combination of stretch forming and AISF can improve the time per part, sheet thickness distribution and accuracy of the final part. Laser-assisted AISF is shown to enable the flexible forming of non cold-workable materials such as magnesium and titanium alloys when the forming conditions are adapted to the temperature and strain rate dependent formability of the sheet metal. In addition, first results of the forming of hybrid aluminum-steel sheet metal are shown.

Technology roadmapping for the production in high-wage countries

Abstract: Manufacturing companies from high-wage countries must focus on future markets and products to remain competitive and to ensure long-term success. In a dynamic, global environment it is necessary to further improve the underlying production technologies and methodologies to achieve sustainable competitive advantages. Thus, a technology roadmap for advanced production technologies and approaches has been developed. The roadmap provides an overview of relevant technologies and their technological readiness. It points out challenges which manufacturing companies in high-wage countries have to face. Moreover, the applied roadmapping process is used to align the research activities within the Cluster of Excellence “Integrative Production Technology for High-Wage Countries” to the relevant topics concerning the cluster’s four main research areas, namely the individualized, virtual, hybrid and self-optimizing production. This paper describes the roadmapping process as well as its main results. Regarding each of the four research fields, a technology radar including exemplary technologies evaluated e.g., by their state of development is presented. Furthermore, relevant challenges, future trends and scientific tasks are discussed as main drivers influencing the cluster’s research activities.

Company-specific quantitative evaluation of lean production methods

Abstract: Small and medium-sized companies encounter enormous difficulties when trying to implement lean production methods according to the role model of the Toyota Production System. This is caused by the varying effects of lean methods on production figures depending on the production conditions concerning product variety and volumes, variation of process and set-up times, etc. This article presents approaches developed at the Institute of Production Science (wbk), Karlsruhe Institute of Technology, to evaluate and optimize the effects of lean methods in small series productions based on the quantified interdependencies with the relevant target figures. It enables the best combination of lean methods to be identified and recommendations for the efficient implementation of these lean methods.

Flexible gripping technology for the automated handling of limp technical textiles in composites industry

Abstract: A high level of cost-intensive manual tasks in the manufacturing process of composite parts impedes a further propagation of those innovative structures in important German industrial branches like the automotive sector or aviation. Especially the handling of semi-finished goods in several key process-chains could not be automated efficiently so far due to a great variety of materials and part contours as well as difficult handling properties of the limp, textile parts. Hence within the presented work a highly-flexible gripper system based on low-vacuum-suction is introduced, which is the result of a methodical investigation in the ideal gripping principle. Special actuators and an intelligent control strategy are combined into a selective gripping technology, which allows an automatic adaption of the pressure based holding force to different contours and materials, by closing certain apertures of a perforated plate. The experimental validation of a realized robotic end-effector shows that the challenging requirements of modern composite production could be fulfilled as the structural integrity of the technical textiles is preserved during the handling processes.

Advanced friction modeling for bulk metal forming processes

Abstract: The finite element method is a powerful tool for the design and optimization of hot forming processes. In order to obtain high accuracy in simulation results, exact knowledge of the process conditions is required. Due to the fact that friction in the contact area has a significant impact on the material flow during the forming process, a realistic description of this boundary condition in the FE simulation is important for the usability of the simulation results. The most important influencing factors are the contact pressure, the roughness of the contact surfaces, the sliding velocity and the flow behavior of the material. Currently, only constant friction coefficients are considered in commercial finite element systems for the simulation of bulk metal forming processes. However, this description does not represent the state of the art in tribology. A new friction model is developed, taking into account the sliding velocity between tools and workpiece. This is confirmed by experimental and numerical investigations on model experiments and industrial process.

Analysis of defect mechanisms in polishing of tool steels

Abstract: The polishing process in the mold and die making industries is nowadays still predominantly done manually. As a consequence of this the quality of the mold strongly depends on the worker’s skill, experience and also on his form on the day, patience and concentration. Furthermore, polishing is in most cases the last manufacturing step of the process chain and occurring surface defects are critical and often a “knock-out-criterion”. Until now there exists no systematical acquisition or explanation for the appearance of this polishing defects. This paper shows the results of experiments describing the polishing process and defect mechanisms in order to generate process strategies for manufacturing “defect-free” high-gloss polished tool steel surfaces. Ten different steel grades were analyzed in order to see how the final surface quality is influenced by e.g. the polishing system, the degree of purity or the microstructure. The surface quality is represented by roughness values and SEM-images. It could be concluded that the degree of purity and the homogeneity of the steel material are crucial to the final surface quality. The lower the amount of inclusions, the better the surface quality. Furthermore, a classification of the occurred defects during the polishing process is shown in this paper.

Manufacturing of dies from hardened tool steels by 3-axis micromilling

Abstract: In this paper the results of an experimental investigation to analyze the machinability of a hardened, carbide-rich cold-work tool steel 1.2379 (approx. 62 HRC) with coated micro end-milling cutters are discussed. Fundamental experiments were performed to determine a cutting-parameter set, which enables an economic manufacturing of dies by 3-axis micromilling with commercially available cemented-carbide tools. The evaluation of the applicability of different tool types is conducted by analyzing the process forces, the tool wear, the surface quality, the material removal rate, and the entire chip volume. Design of experiments was used to significantly reduce the number of experiments and to model the active and passive forces. Concerning the design of tools for the micromilling of such difficult-to-machine materials, it is shown that cemented-carbide tools with robust cutting edges are applicable for this kind of machining. Furthermore, test microstructures were manufactured with the intention of validating the determined cutting-parameter set in combination with the selected tool types. In addition, the dimension and shape accuracy of the microstructures are analyzed.

Tool flank wear prediction in CNC turning of 7075 AL alloy SiC composite

Abstract: Flank wear occurs on the relief face of the tool and the life of a tool used in a machining process depends upon the amount of flank wear; so predicting of flank wear is an important requirement for higher productivity and product quality. In the present work, the effects of feed, depth of cut and cutting speed on flank wear of tungsten carbide and polycrystalline diamond (PCD) inserts in CNC turning of 7075 AL alloy with 10 wt% SiC composite are studied; also artificial neural network (ANN) and co-active neuro fuzzy inference system (CANFIS) are used to predict the flank wear of tungsten carbide and PCD inserts. The feed, depth of cut and cutting speed are selected as the input variables and artificial neural network and co-active neuro fuzzy inference system model are designed with two output variables. The comparison between the results of the presented models shows that the artificial neural network with the average relative prediction error of 1.03% for flank wear values of tungsten carbide inserts and 1.7% for flank wear values of PCD inserts is more accurate and can be utilized effectively for the prediction of flank wear in CNC turning of 7075 AL alloy SiC composite. It is also found that the tungsten carbide insert flank wear can be predicted with less error than PCD flank wear insert using ANN. With Regard to the effect of the cutting parameters on the flank wear, it is found that the increase of the feed, depth of cut and cutting speed increases the flank wear. Also the feed and depth of cut are the most effective parameters on the flank wear and the cutting speed has lesser effect.

Application of an optimized SA-ANN hybrid model for parametric modeling and optimization of LASOX cutting of mild steel

Abstract: Laser assisted oxygen cutting (LASOX) process is an efficient method for cutting thick mild steel plates compared to conventional laser cutting process. However, scanty information is available as to modeling of the process. The paper presents an optimized SA-ANN model of artificial neural network (ANN) and simulated annealing (SA) to predict and optimize cutting quality of LASOX cutting process of mild steel plates. Optimization of SA-ANN parameters is carried out first where the ANN architecture and initial temperature for SA are optimized. The optimized ANN architecture is further trained using single hidden layer back propagation neural network (BPNN) with Bayesian regularization (BR). The trained ANN is then used to evaluate the objective function during optimization with SA. Experimental dataset employed for the purpose consists of input cutting parameters comprising laser power, cutting speed, gas pressure and stand-off distance while the resulting cutting quality is represented by heat affected zone (HAZ) width, kerf width and surface roughness. Results indicate that the SA-ANN model can predict the optimized output with reasonably good accuracy (around 3%). The proposed approach can be extended for prediction and optimization of operational parameters with reasonable accuracy for any experimental dataset.

Numerical simulation of non-circular spinning: a rotationally non-symmetric spinning process

Abstract: This paper describes the peculiarities encountered in the numerical modeling of non-circular spinning processes using motion-controlled roller tools and applying the Finite Element Method (FEM). This process is suitable for producing non-circular, hollow components in small to medium-sized production lots. Numerical simulation can be used to optimize the process. Therefore, it is necessary to make a realistic sheet thinning and wrinkling calculation by using the FEM. This can be achieved through the definition of the real kinematics, a suitable flow curve and an optimal sheet meshing strategy using solid elements. An optimal sheet meshing strategy is particularly necessary in order to realistically calculate the process within an acceptable computing time. Reference experiments with the rotationally non-symmetric mandrel types, the “Tripode” and “Pagoda”, were carried out to compare simulations and experiments. A comparison of the reference experiments with the “Tripode” mandrel demonstrated that it is possible to simulate non-circular spinning with a deviation of less than 5% with respect to minimum sheet thickness. It is also possible to predict wrinkling in critical, non-circular spinning processes. This has been confirmed by comparing the “Pagoda” reference experiment with the FEM simulation.

Closed-form inverse kinematics of 6R milling robot with singularity avoidance

Abstract: For a 6R milling robot, it is necessary to convert the postprocessing cutter locations (CL) into the robot’s revolute joint variables. This paper introduces an algorithm for calculating the forward and inverse kinematics of a 6R robot according to the CL data generated by conventional CAD/CAM systems. A redundant mechanism is analyzed to avoid the singular configurations and joint limits. The Denavit–Hartenberg (D–H) convention is referred to for developing the forward kinematics, and a closed-form solution of the inverse kinematics is presented by means of kinematic decoupling. A fundamental approach with modifying factor for avoiding singularity are developed with regard to three-axis and five-axis CL data. A gap bridging strategy is applied to reduce the jerk motion caused by tool retraction and cut paths connection. Finally, the result is conducted to simulation and machining test to verify the algorithms.

Hardware in the loop simulation of production systems dynamics

Abstract: Constantly growing competitive pressure forces machine and plant manufacturers to find new innovative ways to reduce the development costs as well as to increase the quality. In order to achieve these goals, simulation tools are used in many phases of the development process. An integrated simulation of the system “production plant” requires not only the dynamic behavior of the production system but also the consideration of the applied control technology. For this purpose, especially the coupled simulation between real control system and virtual machine became widely accepted in recent years. This paper will give an overview of the current state of the art of hardware-in-the-loop simulation of production systems dynamics at the ISW.

Experimental studies for verification of thermal effects in cutting

Abstract: Investigations on metal-cutting machining processes that were conducted since the second half of the twentieth century have considerably contributed to disclosing the principles underlying the cutting process. Although numerous studies have been carried out on this subject, a generally valid model of the cutting process and the interactions in the separating processes does not exist yet. Such a model could guarantee the disclosure of the principles of thermodynamic interactions between the cutting process and the involved machine structure. This contribution is twofold and presents an experimental setup used to determine cutting forces and temperatures in orthogonal cutting processes. The results are then used as a reference for simulations made with the Discrete Element Method (DEM). The DEM is due to its meshless nature well suited to capture large deformations and rupture of material which is included very naturally. It is examined to which extent the measured results can be captured with the DEM model.

Reduction of wear at hot forging dies by using coating systems containing boron

Abstract: The near surface area of forging dies is exposed to high mechanical loads. Additionally thermal and chemical stresses appear during the hot forging process. Depending on the number of forged parts, several kinds of stresses occur in the near surface area, which lead to the initial failures of forging dies. Wear is the main reason for production downtimes with a ratio of 70%. Furthermore, thermal and mechanical cracks are typical causes for failures causes as well as plastic deformation. In order to reduce wear, the abrasion resistance of the forging die surface has to be increased. Hence, different methods like plasma nitriding and optional additional thin hard coatings (TiN, TiCN, TiC, TiBN and TiB2) were successfully examined. Recently developed Ti–B–N coatings in specific multilayer designs are thermally stable, wear-resistant and anti-adhesive regarding the sticking of work piece material. This paper presents the wear reduction possibilities of boron-containing multilayer coating systems applied to forging dies by using the plasma enhanced chemical vapor deposition treatment. A basic mechanical and analytical characterization of different coating systems is realized in the first stage of the project. Best qualified multilayer coating variants were applied to forging dies for experimental investigations. As a result of the tests, wear can be reduced significantly by using thermally stable boron multilayer coatings. To receive realistic wear values under production conditions, an automated forging process was used for testing. After 3,000 forged parts, the coatings were examined by tactile measurement, SEM and EDX analyses to characterize the occurring wear.

Automation of robotic assembly processes on the basis of an architecture of human cognition

Abstract: A novel concept to cognitive automation of robotic assembly processes is introduced. An experimental assembly cell with two robots was designed to verify and validate the concept. The cell’s numerical control—termed a cognitive control unit (CCU)—is able to simulate human information processing at a rule-based level of cognitive control. To enable the CCU to work on a large range of assembly tasks expected of a human operator, the cognitive architecture SOAR is used. On the basis of a self-developed set of production rules within the knowledge base, the CCU can plan assembly processes autonomously and react to ad-hoc changes in assembly sequences effectively. Extensive simulation studies have shown that cognitive automation based on SOAR is especially suitable for random parts supply, which reduces planning effort in logistics. Conversely, a disproportional increase in processing time was observed for deterministic parts supply, especially for assemblies containing large numbers of identical parts.

Condition-based preventive maintenance of main spindles

Abstract: Machine tools need to be highly reliable with minimal down time. Unintended failure incurs high costs due to repairs and production losses. Maintenance is a major cost factor and is still handled reactively to a great extent. Maintenance plans by manufacturers that recommend preventive maintenance based on operating hours are often not consistently implemented. Ideally condition-dependent preventive maintenance of the most critical and cost-intensive assemblies of a machine tool would be performed. This would enable a shift of planned maintenance times to non-productive periods and would also enable procuring any spare parts at the right time. Eventually, this would lead to cost savings. This article describes the design of a condition monitoring system for machine tools and shows examples of main spindle monitoring.

Collaboration platforms to enable global service provision in the tooling industry

Abstract: The European tooling industry is strongly as ever confronted with the turbulent global economic environment. As a sole focus on price and technical feasibility does not lead to sustainable competitive advantages, toolmakers need to find new ways for differentiation. A promising approach are industrial product service systems but the lack of local presence and the small company sizes complicate the delivery of such services to global customers. Web-based collaboration platforms can link toolmakers to build up a stable network of partners around the globe and help to maintain competitive advantages. These platforms include toolmaker, tool user, tool owner and service provider for global service provision in the tooling industry. The concept of this platform and their features are presented in this paper.

Optimizing the order processing of customized products using product configuration

Abstract: For the better part of the 20th century many large companies have been focussed on optimizing their mass production process as a way of maximizing their profits. Nowadays, in the existing environment of global competitiveness, enhancing the production process remains a significant issue as well. Product configuration based on integrated modular product structure and product family architecture has been recognized as an effective means for implementing mass customization. In order to evaluate the effects of product configuration on order processing, a study has been conducted by the Department of Management Engineering and Operations Management of the Technical University of Denmark in cooperation with the Institute of Production Engineering and Machine Tools of the Leibniz Universitat Hannover. Thereby, a product configuration system has been modelled for a manufacturer of mass customized products and its benefits for the order processing have been evaluated.

Reconfigurable handling system

Abstract: The demand for more versatile assembly and handling systems to facilitate customized production is gaining in importance, especially with regard to the constantly-increasing cost pressure, to expansion of the range of product versions and the shortening of innovation cycles. As a cost-effective approach for frequently changing assembly tasks, a novel manipulation concept has been developed by combining given robot technologies. This new handling system has a modular and adaptable layout, which consists of several mobile arms to manipulate the object in six-dimensional Cartesian space. After grasping, when the arms are attached to the object, the mechanical architecture is similar to parallel manipulators or cooperating robots. As the mounting and gripping points of the arms can easily be changed, the manipulator can be reconfigured so as to match the user’s preferences and needs. In addition to the kinematic adaption the regarding task, the hardware and new functions can be reconfigured as well. Contact elements, measurement and assembly devices as well as testing modules can easily be in integrated in the concept. A modular automatic control concept combined with a self-optimizing planning tool helps the user to find the optimal configuration and realize it in an economic way.

In situ strain measurement in the chip formation zone during orthogonal cutting

Abstract: The strain and stress state in the chip formation zone determines the chip formation. However, it is difficult to obtain experimental data about the strain/stress fields during machining. For this reason, present chip formation models highly simplify the chip formation process. In order to extend the knowledge regarding the chip formation mechanisms, an experimental method for the in situ measurement of the elastic deformations within the chip formation zone during the cutting process has been developed. Using these deformations, the stress state can subsequently be calculated. The method is based on X-ray diffraction using high-energy synchrotron X-radiation during machining the workpiece in an orthogonal cutting process under quasistatic experimental conditions. The diffraction patterns are captured with a 2D detector. A comparison of the experimentally determined stresses at different measuring positions within the chip formation zone with results from a FEM cutting simulation shows a good qualitative and partially also quantitative consistency. Possibilities for the further performance increase of the method are identified so that the method can be used for the verification and extension of existing chip formation models in future.

Compensation of thermo-dependent machine tool deformations due to spindle load: investigation of the optimal transfer function in consideration of rough machining

Abstract: The thermal behavior of a machine tool is an important indicator for the grade of production accuracy and indirectly for the market success. The load-dependent temperature distribution and the resulting deformation of the machine tool are influenced by a variety of design and thermo-technical parameters. The main spindle of a machine tool is, without any doubt, the major heat source within the machine structure. The object of the scientific investigation presented in this article is the development of an approach to robust compensation of thermo-dependent machine tool deformations due to spindle load in consideration of rough machining. The focus of the work concentrates on the identification of the model with the highest compensation performance. The underlying concept for the compensation of thermo-dependent machine tool deformations is the indirect approach by using the speed and the effective power of the main spindle for the calculation of the Tool Center Point (TCP) displacement. The presented modeling approach requires the knowledge of the TCP displacement in X-, Y- and Z-direction depending on the speed and the effective power of the main spindle. As a tool for modeling the thermo-dependent behavior of a milling machine, a load test rig for repeatable, defined long-term loading of the main spindle has been developed. It simulates the cutting force depending on the spindle speed and the torque and applies load to the main spindle. The spindle speed and the spindle effective power can be taken directly from the numerical control of the machine tool. An important advantage of the presented compensation method is the fact that it does not require any external sensors. The displacement of the TCP has to be measured, but only during modeling. The relationship between the speed/power of the main spindle as a cause and the displacement of the TCP in X-, Y- and Z-direction as an effect can be determined by a transfer function. This paper compares the compensation results depending on the transfer function and identifies the model with the best compensation performance. The validation of the compensation method is executed by using the example of two different speed and power spectra of the main spindle.

Injection molding of products with functional surfaces by micro-structured, PVD coated injection molds

Abstract: Molding of micro structures by injection molding leads to special requirements for the molds e.g. regarding wear resistance and low release forces of the molded components. At the same time it is not allowed to affect the replication precision. Physical vapor deposition (PVD) is one of the promising technologies for applying coatings with adapted properties like high hardness, low roughness, low Young’s modulus and less adhesion to the melt of polymers. Physical vapor deposition technology allows the deposition of thin films on micro structures. Therefore, the influence of these PVD layers on the contour accuracy of the replicated micro structures has to be investigated. For this purpose injection mold inserts were laser structured with micro structures of different sizes and afterwards coated with two different coatings, which were deposited by a magnetron sputter ion plating PVD technology. After deposition, the coatings were analyzed by techniques regarding hardness, Young’s modulus and morphology. The geometries of the micro structures were analyzed by scanning electron microscopy before and after coating. Afterwards, the coated mold inserts were used for injection molding experiments. During the injection molding process, a conventional and a variothermal temperature control of the molds were used. The molded parts were analyzed regarding roughness, structure height and structure width by means of laser microscopy.