Residual stress distribution in PVD-coated carbide cutting tools - origin of cohesive damage

PVD-coatings for cutting tools mean a substantial progress for tool lifetime and cutting conditions. Such tools, however, hold the risk of cost intensive sudden process breaks as a result of cohesive damage. This damage mechanism does not consist of a coating adhesion problem, but it can be traced back to the residual stress distribution in coating and substrate. This paper shows how residual stresses develop during the process chain for the manufacturing of PVD-coated carbide cutting tools. By means of different methods for residual stress determination it is shown that the distribution of residual stresses within the tool finally is responsible for the risk of cohesive tool damage.DFG/DE 447-50-

Adaptive cutting force control on a milling machine with hybrid axis configuration

In the re-contouring process of aircraft engine components, the unknown geometry and inhomogeneous material properties of the workpiece are major challenges. For this reason a new repair process chain is supposed which consists of noncontact geometry identification, process simulation and NC-path planning, followed by a force controlled milling process. A new milling machine prototype is employed to ensure an effective force control loop. By use of a magnetic guided spindle slide, higher dynamics and precise tracking are enabled. Since variation of the process forces result in variable control plant characteristics, an indirect adaptive controller has been designed. Consequently, models of actuator and process are presented and the estimation of the present parameters by a recursive least square algorithm is outlined. Once the parameters are known, the control polynomials are calculated on the basis of a pole placement control approach. First experimental results of a force controlled milling process are put forward.DFG/SFB/87

Stock-market related price determination in consideration of time dynamic cost factors

Providing their customers with the most accurate pricing has become one of the key competitive factors ensuring commercial success for tool and mould manufacturers. However, time dynamic costs influence the pricing calculations significantly, indeed, they are rarely taken into consideration adequately. This paper presents an approach which allows to improve conventional tool performances by developing a novel forecasting method which combines mechanisms related to the stock market with techniques of stochastic prediction methods.DFG/DE 447/72-

Simulation-based planning of production capacity through integrative roadmapping in the wind turbine industry

The development and effective implementation of a production strategy requires an interdisciplinary planning of products, manufacturing technologies and factory concepts. The integrative roadmapping allows the merging of these planning areas and takes into account the occurring interactions. This article shows the concept and software implementation of the integrative roadmapping for a systematic creation of roadmaps using the example of rotor blade production in the wind turbine industry. To reduce planning time and cost the workflow in the rotor blade production has been transferred to a material flow simulation to estimate the mutual impact on the production capacity by product, technology and factory within the planning phase.DFG/DE 447/99-

Improving the Sensory Capabilities of an Electromagnetic Guided Rotary Table for the Use in Machine Tools

Difficult-to-machine materials are still challenging the production industry. Examples are highly complex components of aircraft engines. Alongside innovative processes, also improved machine tool components are helping to comply with the demands of this task. This paper presents a swivel rotary table with an active magnetic bearing (AMB). Opportunities in machining through employing a workpiece-sided AMB are presented. The inherent capabilities to work as a sensor and actor as well as its stiffness and damping depend on the precise knowledge of the magnets characteristics. Therefore, a methodology to automatically identify the characteristic curve is presented

Active tailstock for precise alignment of precision forged crankshafts during grinding

Within the Collaborative Research Centre 489 at the Leibniz Universitaet Hannover a new and innovative process chain for the manufacture of crankshafts is being investigated. By burr-free and near-net-shaped precision forging the process chain can be significantly shortened. However, this new production process requires a precise workpiece alignment before the grinding process due to the characteristics of the new process chain. In this paper a new machine-integrated positioning system consisting of an optical measurement system (sensor) and an active tailstock (actuator) is presented. For the detection of positioning errors, the geometric elements of the crankshaft are measured by the machine integrated optical measurement system. An algorithm evaluates the geometry data and calculates an adjustment vector. This vector contains the correction of the eccentric and tilt error. The degree of freedom (DOF) of the pendulum stroke of the grinding machine will be used to correct the eccentric error. The tilt error of the crankshaft is corrected by a new active tailstock. This tailstock produces a counter-tilt during the grinding process. For this purpose, a dynamic drive of the tailstock center in two DOF as a function of the angular position has been realized by two new developed piezo-hydraulic linear drives (stroke 4 mm). The dynamics and positioning accuracy of the active tailstock were verified. Up to 10 Hz a positioning accuracy in the range of ±1.5 μm can be achieved by using an iterative learning control. Furthermore, active alignment tests during grinding were performed

Approach for Increasing the Resource Efficiency for the Production Process of Titanium Structural Components

Titanium structural components for the aircraft industry are usually manufactured from ingots of primary material. The process chain for the fabrication of these components consists of the production of titanium sponge, the melting process, the forging process and the milling process. High chip removal rates from up to 95% due to the milling process and a high energy demand in producing the titanium sponge of about 85% of the overall energy consumption characterize the process chain. This obviously leads to a high optimization potential under monetary and energetic aspects. Recycling titanium chips for the ingot production could help to dramatically improve the overall production process in terms of ecological aspects. However, process-induced contaminations of the chips prevent the use of high amounts of these in the melting procedure. Macroscopic impurities like residues of cooling lubricant can be removed in a complex cleaning process. Yet, contaminations like oxidization cannot be eliminated, hence only a small amount of titanium chips is usable in the melting process to achieve the required purity of the titanium alloy. This paper describes a novel method to decrease the energy consumption in fabricating titanium products. By reducing process-induced contaminations, the amount of titanium chips usable in the melting process can be significantly increased and consequently the necessary quantity of titanium sponge reduced. The described method contains the investigation of relevant influencing factors like the impact of tool and cooling concept on chip quality or manufacturing costs. The research of cause-effect relationships identifies the trade-off between ecological and economic targets. A mathematical description of this relationship is implemented within a simulation environment to find an optimum between ecological and economic targets. The paper describes this approach with samples of the titanium alloy Ti6Al4 V.BMWi/03ET1174

Enabling an Industrial Robot for Metal Cutting Operations

AbstractThis paper focuses on a cost-effective manufacturing of large frame parts for aerospace industries with an industrial robot. The main challenge is the low stiffness of a serial kinematic, resulting in positioning errors due to gravity and cutting forces. Therefore, an approach is presented to optimize positioning of a robot by compensation of tool deflection. A static deflection model of the robot is built up to calculate the deflection caused by forces acting on the spindle. To detect these forces a suitable measurement device is presented. This sensing spindle holder is calibrated to detect cutting forces

Stock market related pricing mechanisms for the tool and mould manufacturing industry

Tool and mould manufacturers typically prepare their quotation provide an accurate price of, for example, a die casting mould is a key competitive factor for such companies. However, particularly in the customised production area, calculating the quotations and tenders has been proven as extremely challenging and subjective matter. One main cause is that time dynamic costs are rarely taken into consideration sufficiently even though they have a major impact on the final quotation due to the large time frame between the moment of the initial quotation and the actual production start. They neglect can lead to a significant discrepancy of up to 40 percent between pre- And post-calculation and thus to a loss of the corporate added value. A novel method developed at the Institute of Production Engineering and Machine Tools (IFW), Leibniz Universität Hannover, aims to provide a framework which allows tool and mould manufacturer to prepare a more precise and reliable quotation by taking time-dependent dynamic costs into consideration. The prediction of the time dynamic costs takes place by using stock market pricing mechanisms. Subsequently, based on enterprise related knowledge aggregation, this method also accounts for the probability of occurrence of each quotation thereby minimising the discrepancy between the pre- and post-calculation

Simulation based parameterization for process monitoring of machining operations

Process monitoring can prevent machine and tool failure in metal-cutting. A successful process monitoring of cutting processes depends on reliable monitoring limits for the process. In industrial applications these limits have to be generated in a learning phase during a ramp-up process. In order to enable process monitoring for single batch production without a learning phase, this paper describes a simulation based approach for generating reference data to set process limits. As a foundation for calculation of monitoring limits a position-based process simulation has to be established. In a first step an approach of modeling material removal is evaluated to check whether it fits the application for parameterizing the process monitoring. In this context the potentials of a process simulation for calculating process limits are clarified. Additionally the quality of data generated by this kind of simulation is discussed. In a second step a method is described to implement machine properties by a virtual machine tool within a simulation of material removal. For that purpose a method to use actual data of axis position and tool within the simulation of material removal is necessary. With these data a way-based simulation of material removal can generate reference parameters for monitoring limits instead of using data from a learning phase during the ramp-up process. By using position data of a virtual machine tool a reliable source for the actual position of all axes enables the position-based simulation to perform material removal in a more accurate way