Qualifying multi-technology machine tools for complex machining processes

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CIRPJ-343; No. of Pages 14 CIRP Journal of Manufacturing Science and Technology xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

CIRP Journal of Manufacturing Science and Technology journal homepage: www.elsevier.com/locate/cirpj

Review

Qualifying multi-technology machine tools for complex machining processes C. Brecher, F. du Bois-Reymond *, J. Nittinger, T. Breitbach, D. Do-Khac, M. Fey, S. Schmidt Chair for Machine Tools, Laboratory for Machine Tools and Production Engineering, RWTH Aachen University, Steinbachstraße 19, 52074 Aachen, Germany

A R T I C L E I N F O

A B S T R A C T

Article history: Available online xxx

Producing complex components requires a sequence of production steps which often includes machining and thermal treatment like hardening or deposition welding. Multiple processing technologies can be combined into a single machine to reduce logistic efforts in producing such components. This results in changing operating conditions and poses challenges to maintaining the machining accuracy. The presented research focuses on aspects which affect the accuracy of a machining center that operates in multiple workspaces. After a theoretical analysis of the potential precision loss, the major influences are examined experimentally on a multi-technology machine tool (MTMT) and an approach for a simulative analysis is developed. Motion synchronization between the machine tool and an integrated robot as well as the mechanical and thermal effects during processing are considered. ß 2015 CIRP.

Keywords: Multi-technology machine tool Accuracy

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multi-technology machine tool with multiple workspaces . . . . . . . Integrated technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Setup of the machine tool . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Setup of control and planning processes . . . . . . . . . . . . . . . . 2.3. Challenges of integrated machine tools with multiple workspaces Design phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Systems integration and commissioning . . . . . . . . . . . . . . . . 3.2. Use phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Concept requirements for production performance . . . . . . . . . . . . . Integration and performance of manipulators. . . . . . . . . . . . 4.1. 4.2. Optimization of structural components . . . . . . . . . . . . . . . . . Setup of the control system . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Programming process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Adjustment of accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical adjustment of components . . . . . . . . . . . . . . . . . 5.1. Setting of coordinates and software. . . . . . . . . . . . . . . . . . . . 5.2. Robot motion synchronization and calibration . . . . . . . . . . . 5.3. Qualification of interactions . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4. Thermal effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5. Proof of production ability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prototypic realization of an industrial use case. . . . . . . . . . . 6.1. Program generation and technology planning. . . . . . . . . . . . 6.2. Summary and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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* Corresponding author. Tel.: +49 241 80 28223; fax: +49 241 80 22293. E-mail address: [email protected] (F. du Bois-Reymond). http://dx.doi.org/10.1016/j.cirpj.2015.11.001 1755-5817/ß 2015 CIRP.

Please cite this article in press as: Brecher, C., et al., Qualifying multi-technology machine tools for complex machining processes. CIRP Journal of Manufacturing Science and Technology (2015), http://dx.doi.org/10.1016/j.cirpj.2015.11.001

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1. Introduction Within the two phases of the Cluster of Excellence ‘‘Integrative Production Technology for High-Wage Countries’’, research activity is grouped into four fields, each focusing on the reduction of the polylemma of production, which is being spanned between scale and scope as well as between plan and value orientation [1]. As one aims at reducing the dilemma between efficient scale production and flexible scope production, one of the objectives of the research field ‘‘Integrated Technologies’’ is to explore integrated production systems. Integrated production systems, as considered in this paper, may be subdivided into the following three categories.  Integrated applications or combinations of physical mechanisms of action [2–4]  Integrated machines that perform different processes in one place [5–7]  Integrated combination of production steps [8] All three categories have a combination of previously separated processes or entirely new processes in common to contribute to the field of integrated technologies. The motivation for the scientific discussion and industrial implementation of integrated production systems lies in advantageous characteristics for specific applications. Combining physical mechanisms may provide increased productivity when using new materials [9], while integrating production steps may enable entirely new products [8]. The integration of multiple manufacturing technologies into one machine, as discussed in this paper, is often motivated by potential for increased efficiency that originates from the ability to apply process chains in a single-clamping setup. The approach promises reduction of part transfers and a consolidation of several processing steps into one machine tool. Thus, this approach may contribute to reducing complexity in manufacturing, one of the biggest challenges manufacturing faces today [10]. Machines which use different technologies sequentially may actually suffer significant productivity losses by integrating added functionality [11]. Such an undesirable reduction of total productivity may often be traced back to the design decision to apply a process chain of several steps in a strictly sequential manner.

Existing multi-technology machine tool (MTMT) developments with integrated laser system technology contain the sequential combination of different laser processes and combined machining in lathes or milling machines [12–14]. These machines were restricted to a sequential application of different process steps. Nevertheless, these designs provided the merit of combining new laser machining processes with milling or turning processes and enabled products with specific advantages. Independent from machine tools, laser deposition welding may for example create forming tools with locally strengthened features [15] and give the opportunity to generate workpieces by additive manufacturing. These characteristics provided improved tools through the combination of milling and laser processes. The above-mentioned developments in integrating laser technology for material processing into machine tools did not focus on ways to use processing components in parallel, which would reduce total production times by increasing production throughput of the machine. As of yet, simultaneous mechanical and thermal processing, without mutual interference, cannot be achieved. The resulting low utilization of tools, including peripheral components such as the laser source, imposes an economic penalty on the design. It is currently unclear how and in which time frame the increased capital investment on such a platform can be economically recovered during production. The focus of the research presented here was to develop a scientific approach which enables the systematic design of MTMTs regarding the machining accuracy, Fig. 1. Other aspects such as the efficiency in throughput time and the utilization of MTMTs have already been discussed in some detail [7,19,32,33]. This paper presents the development of a MTMT, which offers parallelization of all processing steps through the integration of additional workspaces and tool guidance systems. This was implemented by fully integrating laser processing units and a robot into a milling center with two independent workspaces. This opens the possibility for using production processes in parallel, but also poses new requirements on the subsystems as well as their integration, mutual interferences, planning and application. Encapsulating the added complexity as much as possible and thereby improving the operability of the MTMT was a priority in the design process. The following chapters discuss the process of identifying and analyzing potential challenges regarding the machining accuracy as well as the development of methods to

Fig. 1. Outline of the Research Area C-2 on Multi-Technology Production Systems.

Please cite this article in press as: Brecher, C., et al., Qualifying multi-technology machine tools for complex machining processes. CIRP Journal of Manufacturing Science and Technology (2015), http://dx.doi.org/10.1016/j.cirpj.2015.11.001

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minimize accuracy issues in the use phase using the example of laser-induced thermal loading. 2. Multi-technology machine tool with multiple workspaces Within the above-mentioned research cluster, the approach in the first phase was to combine several manufacturing technologies in one system. Resulting disadvantages in the utilization of specific technologies or processing resources should be counteracted by the use of multiple workspaces. Fig. 2 shows the structure of the MTMT that was built up. Key aspects in the second phase of the research cluster are the analysis and deeper understanding of occurring effects on the machining accuracy in addition to the development of methods which help to reduce the loss of accuracy. 2.1. Integrated technologies The technologies laser deposition welding, laser hardening and laser ablation were integrated into a milling machine platform. The design includes an industrial robot which operates the laser processing unit for laser deposition welding and laser hardening in order to enable parallel use of these technologies independently from the machine’s main spindle. Due to the accuracy requirements inherent to the processes, laser ablation is carried out by the machine’s main spindle using the second laser processing unit. To the left and right of the picture of the MTMT (Fig. 2) the integrated processes, both workspaces and the magazine for the laser processing units are shown. By integrating these technologies in combination with the additional workspace and the robot it is possible to manufacture two workpieces simultaneously using all processes within the bounds of the control system’s ability to operate both workspaces simultaneously. 2.2. Setup of the machine tool From a structural point of view it was essential to ensure the possibility of using both workspaces simultaneously, but still interchangeably. For this reason, the robot was integrated on an additional platform in the middle of the machine bed. With this symmetrical construction, two workpieces can be processed simultaneously without reclamping – each in its own workspace.

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Also, each workspace can be accessed equally by the spindle and the robot. This design offers an expanded range of processing tasks, a reduction in overall processing time as well as additional gains in accuracy. For the integration of additional technologies into a machine tool, different approaches may be taken. Application-specific manipulators for each process may be designed to optimally support each process, which enables innovative or specific kinematic systems [16]. With the introduction of many subsystems into one machine unexpected mutual effects may occur between the integrated systems, which consequently introduce some uncertainty about the behavior of the resulting machine (Sections 4 and 5). To reduce uncertainties from the separate specialized components themselves, the approach of modular integration was pursued. As was also stated in [10], ‘modularity generally has the purpose to make complexity manageable [. . .] and to accommodate uncertainty by using modules that have been proved successful in practice’. Hence, the choice of conventional and proven components (industrial robot, etc.) for the design relies on these advantages but must be made according to the intended use in the context of the MTMT. 2.3. Setup of control and planning processes Together with the machine structure (permitting access to both workspaces for the machine spindle as well as for the robot) a control architecture and programming workflow was designed to enable controlled and planned use of the integrated components. Combining a fairly large number of components in a single system (machine tool, robot, laser scanner systems, weld filler wire feeder, laser radiation source, safety PLC, gas supply) posed a significant challenge for the integration of the necessary control systems. In order to enable the use of both workspaces simultaneously, a dual channel NC setup was chosen. This provides the base to run two programs simultaneously, performing a process with the robot in one workspace while applying another process with the machine’s main spindle in the other workspace. In order to exploit modularity benefits of combining the machine tool NC and the robot control, a synchronization method was developed, allowing combined use of the machine’s turn

Fig. 2. Setup of the MTMT designed and built in the Cluster of Excellence.

Please cite this article in press as: Brecher, C., et al., Qualifying multi-technology machine tools for complex machining processes. CIRP Journal of Manufacturing Science and Technology (2015), http://dx.doi.org/10.1016/j.cirpj.2015.11.001

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swivel tables with the robot axes and referring to congruent workpiece coordinate systems. A programming workflow was devised which enables the application of robot-based laser hardening and deposition welding as well as milling operations directly at the human-machine interface (HMI). The feasibility of such a programming workflow depends on the automation of technology parameter programming, provided by NC cycles and technology databases.

the structure of this paper the individual challenges are referred to integrated machine tools with multiple workspaces and are assigned to the design phase, the commissioning and the use phase (Fig. 3). The following sections describe and discuss the main challenges of each phase with special focus on their impacts on machining precision and handling within the use phase of integrated machine tools with multiple workspaces.

3. Challenges of integrated machine tools with multiple workspaces

3.1. Design phase

Especially companies in high-wage countries need machine tools with high levels of technology integration and high degrees of technology utilization to produce economically. One possibility is the utilization of integrated machine tools [1]. Studies and surveys within the Cluster of Excellence have shown that the development and usage of hybrid system components has not been established, mainly for the following reasons [17]. Regarding the development of hybrid production systems the following shortcomings were identified: High investment requirements for machinery and equipment Difficult identification of effective technology combinations Inadequate prediction of the effects of process combinations High effort required to establish specific, application-oriented developments  Inadequate implementation of the necessary machine tools  Insufficient control systems for the integrated technologies  Questionable economic viability of the use of hybrid technologies    

According to the studies and surveys, potential users refrain from investing in MTMTs due to the following reasons:  High complexity of hybrid production systems  Difficult identification of technologically appropriate applications  Insufficient control systems and stability of the hybrid process These challenges of integrated machine tools can be associated with specific phases of machine tools. According to

Initially, the configuration of processes and machine layouts has to be defined in the design phase. On one hand for processes that are conducted sequentially, machine concepts with multiple workspaces, which can be used simultaneously, provide the opportunity to share existing machine components such as the bed and control unit and thus save investment. On the other hand, in contrast to existing MTMTs with a single workspace, idle time of manufacturing resources is avoided. Finding a compromise within this contrary behavior has been investigated by Brecher et al. [18] and Klocke et al. [7], concluding that the efficient utilization of multiple workspaces strongly depends on the task assignment conducted in the use phase. After the decision is made to integrate certain technologies into a machining center, it must be ensured that the required accuracy can be achieved during operation. In the design phase it has to be taken into account that the machine design must be able to execute the integrated processes in addition to the original processing tasks. Besides the integration of additional components, mechanical and thermal interactions should be reduced or avoided where possible. Especially with regard to the integration of additional workspaces, changes in the dynamic behavior must be considered and compared to the original design. These changing characteristics result from the extension or division of the working chambers, or the integration of additional manipulators that are required for the simultaneous operation of multiple processing units. The dynamic and thermal behavior of this new machine tool must be calculated carefully, taking into account the impact of the laser integration and the effects occurring during laser processes by using state of the art machine simulation tools [20].

Fig. 3. Influences on design and utilization in the various phases of MTMTs.

Please cite this article in press as: Brecher, C., et al., Qualifying multi-technology machine tools for complex machining processes. CIRP Journal of Manufacturing Science and Technology (2015), http://dx.doi.org/10.1016/j.cirpj.2015.11.001

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During the design phase, the possible solution set, in which the control architecture and programming concepts can be implemented, is defined as well. Due to the selected control systems and components, the choice of options concerning for example communication networks is limited to the common denominators between all controllers that have to be combined (i.e. Profibus, Ethernet, Ethercat, DeviceNet, CC-Link, etc.). These considerations extend to the required performance levels of the control systems, for example their ability to receive and react to signals in real-time. Depending on the reaction time requirements of the integrated manufacturing processes, this also requires an approach to harmonize the interpolation cycle across the control systems sufficiently to enable the technological processes. While machine tool NC’s usually run interpolation cycles of a few milliseconds, laser scanner systems and laser radiation sources can react virtually instantaneously by comparison [21]. This limits the level of detail to which processing of a machine tool motion can be synchronized to a given laser scanner program. 3.2. Systems integration and commissioning Systems integration and commissioning of MTMTs faces more interconnected components and subsystems than traditional machining centers. This step in the development process decides on how the possible solution set, that was determined during the design phase, is exploited in order to provide an appropriate control system and programming workflow during the operational phase of the MTMT. In the design phase, a choice is made which control systems and communication technologies are available for the MTMT. During systems integration, the required number of real-time communications, and how a machine program will address different subsystems, are chosen. Additionally, the subsystems and their coordinate system orientations must initially be aligned to each other. In most cases, e.g. with the robot and the milling machine coordinate systems or the laser scanner and robot/machine coordinate systems, the mechanical disalignment has to be measured manually and is then configured within the machine controller for compensation. From a process ability point of view it must be investigated in how far multiple technologies and multiple workspaces can operate simultaneously without a significant loss in accuracy. 3.3. Use phase In the use phase it is essential to be able to produce with the machine as efficiently as possible. To achieve this, programming the machine and planning when to produce which part must be considered. For example, the presence of several workspaces should be made transparent to the NC programmer, i.e. the programmer should not need to know which workspace will actually be used for the NC program at the time the program is written. This is made possible by identically configuring both workspaces in the NC as symmetrical and equal. An enabling element is the control transfer mechanism that ensures equal conditions in the right and the left workspace for the robot detailed in Section 5.3. To best exploit both workspaces while processing two workpieces simultaneously is important. By having more than one workspace in the same machine, influences from one workspace to another are to be expected. To achieve maximum degrees of utilization without losing accuracy due to interactions, the mutual effects of different processes must be identified and qualified for all relevant process combinations. Effects of parallel processing regarding the efficient utilization of workspaces, manipulators and processing units have been presented in [11].

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4. Concept requirements for production performance In this section, the selection of machine tools, process units and additional manipulators are discussed. Boundary conditions regarding accuracy, productivity and handling are taken into account. 4.1. Integration and performance of manipulators Production of a workpiece requires a certain level of accuracy. All processes need a certain minimum precision, which may be compromised by the precision the guiding manipulators are capable of. In early stages of the design phase the manipulators need to be selected according to these boundary conditions as well. For laser deposition welding for example, the requirements are not as strict as for laser ablation processes like structuring or deburring. Especially deburring requires a high accuracy to hit the very small burr effectively. Consequently, manipulators with different levels of accuracy may be selected. In the presented machine platform, a comparatively cheap robot was selected to handle the processes laser welding and laser hardening. Milling and laser ablation are carried out by the main spindle, due to higher stiffness and precision requirements. 4.2. Optimization of structural components Within the design phase it is essential to ensure that the structural behavior of the machine tool is not negatively affected by the integration of additional manipulators or processing units or by the processes themselves. Nowadays it is common to predict the static and dynamic behavior of machine tools by simulation within the design phase. Thermal effects of processes as well as the prediction of interactions between process and machine are difficult and strongly depend on the chosen parameters such as power, speed, or the orientation of manipulator and workpiece in the workspace. For example potential spots where hot chips can transfer process heat for longer periods of time are important for the thermal behavior. These depend on the orientation of the machine components and the workpiece in the workspace. The same applies for the dynamic (pose-dependent stiffness) behavior and interdependency in a machine tool. In the presented case it was simulated how much the machine deforms due to the weight of the robot being integrated on the platform in the middle. The design and the dimensions of the platform were optimized in order to reduce the pose-dependent deflection of the robot as much as possible. Efforts for the integration of additional manipulators must be compared during the selection of a proper machine design. Due to a lack of appropriate simulation methods, thermal effects leading to a distortion of the tool center point have not been a subject of the design phase, but have been identified during the use phase [24]. The following necessary steps for predicting the thermal behavior in the design phase, such as understanding the occurring complex mechanisms of energy transfer, are being conducted in the second phase of the Cluster of Excellence. Up until now it was identified that the reflected laser beam, in contrast to conduction, radiation and convection effects, has the highest impact on the heating of machine components such as the turn swivel table and results in critical distortion. The focus will be on the simulation of the thermal elastic behavior of chosen machine components followed by an experimental verification. Hence, an experimental setup in a thermally controlled chamber will be developed to investigate the thermal behavior of the machine bed itself and in combination with the turn swivel table.

Please cite this article in press as: Brecher, C., et al., Qualifying multi-technology machine tools for complex machining processes. CIRP Journal of Manufacturing Science and Technology (2015), http://dx.doi.org/10.1016/j.cirpj.2015.11.001

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4.3. Setup of the control system Combining several manufacturing systems requires consideration of the control systems for each individual processing step. Without MTMTs, a discrete approach is required that uses separate machines for each manufacturing process. As a consequence, the control systems are mostly orthogonal to each other, i.e. the individual control systems have no knowledge of – and cannot directly influence – each other. This approach relies on coordination through a coupling interface at the PLC level, possibly implemented using a Manufacturing Execution System (MES). This limits the integrated use of several control systems in terms of programming detail and control system response times of up to a few hundred milliseconds, which is usually acceptable in discretely coupled manufacturing on several machines. The possibilities are sufficient to coordinate the proper sequence of processing steps, since generally little more than program start and stop events are exchanged via the coordinating PLC. An interaction on the NC or process level however often requires significantly shorter system response times of a few milliseconds or less. The control integration approach taken in the presented MTMT prototype is based on a modular control architecture. The integrated robot is under direct control of the robot control system, which is modularly integrated into the central machine control [22]. Key to choosing this approach was the advantage of exploiting the specific compensation algorithms of the robot manufacturer which cannot be feasibly substituted by the machines NC controller. One robot-specific aspect is the significantly pose-dependent flexibility of the robot with respect to the current TCP, i.e. robots under a given constant load tend to deflect

by different amounts depending on their current pose as shown in Fig. 4 (source: [24,26]). As illustrated in Fig. 4, TCP deviations of up to 0.5 mm occur in the presented machine setup. As discussed in [24], deviations were analyzed by creating robot-guided circular laserpaths in the xyplane of the machine coordinate system. While pose- and weightspecific flexibility effects can be compensated by the robot control system, disturbance forces of the media supply chain (laser fiber, wire, air and protective gas supply) are not compensated. The pronounced variance of distortion across the workspace illustrates a significant reason for integrating separate control systems and combines their strengths for their respective applications. During the design phase of a MTMT it is essential to consider such precision characteristics and choose an appropriate integration strategy of manipulators. In the prototype presented here, integrating the control system of the used robot (Kuka KRC2) prevented excessive pose-dependent precision losses. One consequence of coupling several proven subsystems is the fact that each control system is designed to exploit the dynamic capabilities of the subsystem, i.e. the robot control is designed for less dynamic movements than the control system for the laser radiation source. Since the robot cannot move through every geometry at high speeds, it will decrease instantaneous feed rates in curves and tight corners. In any given laser process with a constant laser radiation power, the effective energy density along the path will rise whenever these deceleration phases occur. If the regions of decelerated motion are not known a priori, the only feasible approach is to provide real time compensation. Either the motion control must react to the process control system, or the process control must react to the lower current velocities. The

Fig. 4. Pose- and motion-dependent path accuracy of the robot [24].

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control system with the higher dynamic ability must be chosen to monitor a guide parameter (TCP velocity in the presented case) and then adapt the process’ set point values accordingly. In laser deposition welding laser power is one major process parameter that must be adapted to ensure constant energy input into the weld. An example of lowering instantaneous laser radiation power during robot slowdowns is shown in Fig. 5. The compensation accounts for a maximum laser output of 2.4 kW and a minimum necessary laser power to sustain the welding process. This requires functionality for real-time adaptation from the control systems and additional effort to appropriately set up these functions during commissioning. This effort during machine tool development is offset by the advantage of lower programming complexity, i.e. enable shop-floor programming of simple laser deposition welding tasks on the MTMT instead of requiring a full CAD/CAM process. If motion phases of the robot slowing down during a program are known, an alternative would be offline planning of locally reduced laser power levels. This may reduce the effort demands on the machine tool manufacturer in terms of systems integration, since a real-time adaptation of the laser radiation set points would not need to be implemented. This a priori offline approach would require an elaborate offline programming system, with according simulation facilities for program verification. As an inherent quality, such an approach cannot react to unforeseen slowdowns, e.g. when a machine operator dials down the override hand wheel.

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In discrete control coupling, which performs each manufacturing step on separate machines, one consequence is that several different programming languages may be needed to specify the manufacturing steps, i.e. laser welding might require a different programming language and approach than milling processes. This makes changing the different production steps more difficult, as a higher level and greater scope of programming competence is required in comparison to using a single machine tool. The implied cost of maintaining programming competence for several control systems is one reason for producing companies to strive for one single control system across their machines. Hence, qualifying a new machine type for industrial application must address the level of programming competence requirements. 4.4. Programming process The control concept [25] enables flexible and transparent programming of the robot. Due to the tight coupling of the control systems, a synchronization based on the NC interpolation cycle was implemented which allows programming of robot motions using the machine controllers g-code. Analogous closely-coupled integration of the other control systems resulted in the ability to program laser radiation and weld filler wire feed rates in a similar fashion. Making all these parameters programmable using the machines NC programming language significantly consolidated the programming workflows across the entire MTMT. The pursued

Fig. 5. Adaptation of laser power during velocity changes of the robot, NC set point value trace.

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closely-coupled approach caused significant development and testing effort during systems integration and machine commissioning. Alternately, a loosely-coupled approach would have faced the challenge of creating and synchronizing separate programs for each control system, since real-time adaptation of program execution is not given in such an approach. For a given workpiece process chain, a program for the laser radiation source, laser scanner and robot would be necessary. The ability to program each subsystem would be mandatory and the simultaneous starting and synchronous execution of the programs would need to be ensured. In cases where systems integration cannot afford to implement a closely-coupled system or when the participating control systems provide only insufficient communication methods and system openness, this may be a more feasible option. Planning the application of several different manufacturing technologies like laser deposition welding and milling requires process-specific knowledge about process parameters that need to be specified (speeds, feed rates, laser power and filler wire feed for example) as well as necessary preconditions and process side effects like melting of the workpiece during welding operations. Programming appropriate technology parameters for each process may be supported by integrated NC control cycles and support systems as well as CAM system modules. By providing the ability to program all crucial parameters inside the NC program, both approaches (support based on NC cycles or specific CAM modules) may be implemented for the presented MTMT. Depending on the process parameters that need to be specified in the program, different representations in the NC program may be appropriate. These were categorized into three classes: basic binary switching-command equivalents, discretely synchronized processes and continuously synchronized parameters. Parameters that closely resemble classical switched functions of machine tools, like activation of coolant or initiation of tool change, could be mapped to M-functions as extensions. Examples were activation of shielding gas for the welding process or the protective air cross-jet which protects the laser optics from welding sparks. Another set of functions which were fittingly represented by Mfunctions were discretely synchronized processes, i.e. subprograms which only rely on being synchronized at their start and stop times. One example is the process of the robot moving into the workspace. When the change into the workspace is initiated, all following commands of the program, which start a welding process for example, need a guarantee that the change has been completed. These commands need no further information or synchronization to the process of the robot changing into the workspace itself. Similarly, the robot picking up a tool is such a discretely synchronized process. In this case, the main program only requires a notification from the robot when the tool change has been completed so the program can proceed. The most involved synchronization implemented in the prototype are continuously synchronized parameters. For example the laser power level or the filler wire feed rate during laser deposition welding needed to be specified at different values for different materials or different desired weld seam geometries. Also, the ability to specify varying values along a given tool path was desirable. This was enabled by introducing proxy variables in the NC programs. Variables are a computational mechanism offered by most NC controllers (R parameters for Sinumerik, Q parameters for Heidenhain, etc.) which provide the advantage of being mutable during an NC program. A mechanism was created to configure fixed variables as representative proxies for process parameters which are synchronized to NC controlled motion in real time, providing a way to directly program these parameters as well.

The presented ability to program all required technological parameters can be directly utilized by custom CAM modules which would need to be developed with a specific post processor to handle new M-function definitions and process parameter proxy variables. For example, given combinations of process parameter settings for a deposition welding operation were implemented into a data table-based NC cycle, which facilitates programming of this process directly at the machine. By selecting a set of parameters which was previously verified in experiments, the programmer can select different hardening or welding operations from a process table, and the implemented NC cycles ensure appropriate settings for parameters such as laser radiation power and filler wire feed. While free-form geometries such as impellers will still require CAM system support, the application of laser processes alone does not require a CAM system as a necessary prerequisite in the approach presented here. 5. Adjustment of accuracy After discussing the design phase, it is essential to ensure that all components are adjusted properly and to investigate the remaining level of influences between the processes. In the following chapters, the most important sources for losses of accuracy are classified, discussed and options to avoid them are presented. 5.1. Mechanical adjustment of components Focusing on the arrangement of the machine tool axes, the robot and the laser processing units it is shown how to ensure that the real position fits the assumed position of the TCP in order to ensure process accuracy. Fig. 6 exemplarily shows a test for setting the coordinate systems and their origins. The axes of the turn swivel table are used as a reference for setting the coordinate system of the robot and of the laser processing unit. In order to get a reference of the rotary axis of the table a hole i, which has been milled by rotating the table instead of moving the axis of the tool, is used. In this way it can be ensured that the chamfer of the hole is concentric to the rotary axis of the table. 5.2. Setting of coordinates and software After setting this reference point, the robot was used to set some laser marks for being able to measure their location relative to the milled hole. Due to the fact that the laser scanner was deactivated, any additional displacements caused by the scanner software were absent in this test. Afterwards, a relative rotation of the coordinate system of the laser scanner can be investigated by comparing lines which are created by relative movement of the robot or by scanning with the laser without moving any other axes. Finally, after setting the physical axes, it is essential to ensure that the coordinate systems are transformed properly within the different control systems. 5.3. Robot motion synchronization and calibration The program execution concept for the presented MTMT prototype provides a mechanism to apply correction values obtained from a calibration test (Fig. 6) to the robot coordinate system. A calibration workflow provides a way to qualify the precision of all robot-based processes for a given requirement. The robot control operates the robot’s drives directly to maintain application of the compensation algorithms for the robot’s pose-dependent flexibility (Fig. 4). The motion program however is written for and interpreted by the machine NC in order to make robot-guided processes programmable in one common

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Fig. 6. Calibration process for the coordinate systems of the robot and the laser processing unit.

programming language. Executing the program with the robot kinematics is made possible by transferring control of the robot to the NC for the duration of these programs. Through a defined control transfer protocol, the source for all robot motion set point values can be switched over to the NC at reference positions defined during commissioning of the MTMT. In order to provide set point values according to the program, the machine NC operates on a set of virtual Cartesian axes and sends set point positions to the robot control in real-time. The robot control then performs transformation and compensation algorithms to eventually control the individual robot drives accordingly. It is important that at the time of the control switch between the two control systems, the reference position, which the robot control and the NC assume, are congruent. The precision of the robot motion w.r.t. the programmed motion depends on the difference Dp of the robot’s pose w.r.t. the reference position assumed by the NC at the time when control switches to the NC (Fig. 7). Without further calibration, there will be a position offset Dp between the virtual TCP of the NC and the current TCP of the robot. Since the reference position is stored in a data table inside the NC, these values can be updated with offsets from a calibration test. The concept of the synchronized motion approach and consequences from a deviation Dp in the reference point are illustrated in Fig. 7. Rotational deviations of the robot control axes and NC axes can be similarly calibrated and compensated for. The described approach has the advantage of permitting programs to treat the robot as a set of Cartesian axes controlled

by the NC, while maintaining the robot control’s use of compensation and transformation algorithms. This ensures that no robot-specific programming skills are required. As a limitation of this approach, the robot is used as a kinematic manipulator with only three degrees of freedom instead of the full six the robot could provide. This was chosen for several reasons. First, the NC approach to five-axis programming could be directly used as provided by the manufacturer. Second, this serves as a safety measure to ensure that the robot always points the laser toward the ground. Third, this evades challenges from singularity poses and redundancies that occur in kinematic systems with more degrees of freedom than required for a given process [27]. Combining the robot with the turn swivel table of a workspace would result in an eight-axis kinematic, which requires specific transformation algorithms and makes programming at the machine unfeasible using the available control systems [28,29]. The flexibility of the presented calibration mechanism also provides for tool length compensation in a similar manner. In applications of laser deposition welding and hardening, operating directly at the laser focal point is unsuitable, because the local energy intensity is generally too high for the desired technological results. To suitably lower the radiation intensity, a defocussed application of the laser radiation is commonly pursued. This can be achieved by redefining the TCP to be at a given defocussing length above or below the actual laser focus spot. For 2.5D part processing, using strictly three-axis programs, the desired effect can be achieved by adapting the z-coordinate for each programmed

Fig. 7. Calibration of the shared reference point.

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Fig. 8. Classification of mutual influences on sequential processing.

position. When using five-axis motions however, the tool axis may not be parallel to the z-axis and hence requires more complicated program changes, depending on the tool lead and tilt angles. By adding the tool length to the reference point, where control of the robot motions passes to the NC, this tool length compensation can be easily implemented. The implemented mechanism hence permits a calibration of the robot at commissioning time of the MTMT, while also permitting changes to the tool length compensation for which each program might require different values. The presented approach provides the additional advantage of being fully independent of the actual tool manipulator used. In the implemented prototype, a 6R robot was used for workspace reachability reasons, but the synchronization mechanisms can be applied to SCARA or parallel kinematics as well. The approach does however incur some requirements, such as an increased cost during systems integration as well as minimum requirements on communication system responsiveness, synchronization and control system openness. 5.4. Qualification of interactions Besides the adjustment of coordinate systems and the arrangement of synchronized movements between the manipulators, the process ability of the integrated machine tool was

investigated. Within the design phase it was tried to configure a design that is inherently robust against mechanical and thermal interactions of the subsystems using conventional methods such as the simulation of static and dynamic machine behavior as well as ensuring appropriate machine cooling. Nevertheless, some interactions always occur and must be investigated a priori in order to be able to avoid them during the use phase. Figs. 1 and 8 show the interactions that might occur within one workspace, assuming that the spindle carries out mechanical operations and the robot is used for thermal processing. Especially the impacts resulting from the heat input differ from a non-integrated machine design. Due to the high temperature inertia and therefore long cool down periods, information about the process history is much more crucial. Expanding the machine tool to multiple workspaces also increases the number of mechanisms of interaction. Fig. 9 shows this additional increase exemplarily for a machine tool with two workspaces and two manipulators for parallel processing. On one hand, the mechanical interactions increase. On the other hand, the thermal deformation of all components is much more complex, due to the fact that the components are not necessarily exposed to thermal loading at the same time. For example, during a laser process in the left workspace the robot and the turn swivel table are heated up and deform. Afterwards, the cold spindle switches

Fig. 9. Classification of mutual influences in simultaneous processing.

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Fig. 10. Experimental setup to investigate thermally caused deviations.

over from the right workspace and the deformed robot switches over into the cold right workspace. Avoiding losses of accuracy caused by thermal deformation and constantly changing initial conditions is an as of yet unsolved challenge. Depending on the design of the machine tool and the possibilities for interactions and changes between workspaces, a set of tests must be carried out to be able to predict the effects on the accuracy during processing. For example, it is important to know how much the robot deforms during laser processing and how long it takes until the deformation receds during cooldown and can be neglected.

Fig. 11. Thermally caused displacements.

Focussing on mechanical interactions between workspaces, it is essential to know which kind of processing affects which process to what extent. Investigations into the sensitivity of the processes themselves, but especially investigations into the transmission behavior of the machine structure, are much more important than for common machine tools.

Fig. 12. Locally generated part geometry and metallographic analysis, bulk hardness at 200 HV0.1.

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5.5. Thermal effects

6.1. Prototypic realization of an industrial use case

Even though the integration of multiple technologies in common machine tools is a chance to optimize process chains, it also poses a challenge concerning the handling of occurring interactions. Nowadays the industry increasingly accepts and develops niche technologies like additive manufacturing. Also technologies such as deposition welding or selective laser sintering (SLS) are combined with common manufacturing processes like milling and turning [30,31]. One goal is to shorten non-productive times by minimizing handling, alignment and clamping operations and to benefit from the obtained accuracy of single clamping. Additionally, besides mechanical effects, thermal effects caused by the integration of laser manufacturing processes have to be taken into account. Previous experiments investigating the relative thermal deviation between spindle and workpiece show significant displacement of the machine structure. The experimental setup is shown in Fig. 10 and the experiment follows the economical use of the developed MTMT, performing milling- and laser machining sequentially in the same workspace for the same amount of time. 16 sets of two periods, a heating and an idle period, were performed representing laser and milling machining. The laser processing unit for deposition welding and hardening introduces a lot of heat energy by emitting a laser beam during a circular rotation (defocused by 5 mm) above a workpiece. After the first 16 sets, the heating was ceased and another series of measurement sets during the idle period (110 min) were conducted. The results of the relative displacement between the turn swivel table (Point A), the clamping device (Point B) and the spindle are shown in Fig. 11. Relative deviations in z-direction of up to 10 mm at the turn swivel table and of up to 50 mm at the clamping device were detected during the experiments. Deviations of up to 260 mm in ydirection at the clamping device and of up to 400 mm in z-direction at the workpiece itself occurred. The thermal effects due to laser integration differ from the thermal effects resulting from chipremoving manufacturing processes where only heat conduction, radiation and natural as well as forced convection affect the accuracy of the manufacturing process. The thermal effect with the highest impact on the structural deviation is heat conduction. Radiation and convection have less influence on the deviation. They can still be relevant for the thermal behavior of the machine tool. In addition to the chip-removing process, the complex reflection of the individual laser beam fractions affect the machining accuracy of integrated machine tools by reaching parts of the machine structure which are nonrelevant for the observation of common thermal effects. The degree of beam absorption and thus the degree of reflection depends on numerous factors like material, surface quality, angle of dip and the wavelength of the beam. In order to predict displacements in an early stage of machine design, as well as for the active compensation in the use phase it is important to completely understand the occurring effects and interactions caused by the laser beam. In the presented research all effects are taken into account, which significantly increases the complexity of the deviation prediction and compensation.

The experimentally manufactured part is shown in Fig. 10. It was milled from common steel and enhanced at three functional edges which were locally generated using laser deposition welding. The added material consists of a different alloy that is provided through welding filler wire and can thus be chosen according to specific needs. A metallographic analysis of the completed workpiece proved that the requirement of increased hardness at the functional edges was achieved without any defects being visible in the analyzed section of generated material. 6.2. Program generation and technology planning To manufacture the bending nipper with reinforced edges by local laser deposition welding, an intermediate geometry was defined which allowed for the three edges to be generated. This intermediate geometry was chamfered at the edges, so that 1 mm of material could be added to form each of the edges. This intermediate geometry was programmed for milling using a traditional CAD/CAM/NC chain with an appropriate post processor. Programming the welding operations to locally add the three strengthened edges was done manually at the machine including several test runs to ensure accessibility of all areas with the laser welding tool (Fig. 13). Since the milling operation already provided clamping and a defined workpiece coordinate system, programming and executing the welding operations could seamlessly follow the milling of the intermediate part.

6. Proof of production ability The design phase and commissioning of MTMTs have been discussed. To gain experimental results concerning the use phase of a prototypic MTMT, an actual workpiece from industry was manufactured using a new process chain. The produced bending nipper is conventionally wire cut from hardened steels to maintain precision and withstand abrasive wear. It is used as a component in a blanking and bending application for electrical contacts.

Fig. 13. NC program for welding one of the reinforced edges of the bending nipper (A3 B3 and C3 designate the desired tool axis relative to work part coordinates).

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While the laser welding tool shape required five-axis programming, the chamfered geometry of the intermediate part limited programming complexity sufficiently to enable manufacturing of the prototype part in less than two days, including drafting of intermediate geometry and CAM milling programming. Finishing the part geometry was conventionally planned with a CAD/CAM/ NC chain and ensured that the surplus material from the welding operations is milled into the final part contour (Fig. 12). 7. Summary and outlook The integrated execution of a process chain with several different processes on an integrated MTMT provided unique advantages. Logistic and operative synergies were exploited by applying milling and laser deposition welding to a raw part in a single clamping. Prototypic manufacturing of the bending nippers demonstrated the possibilities of an alternative, hybrid process chain. The integrated MTMT poses greater requirements on process know-how and the systems integration phase of machine tool development, in order to provide a homogenous programming and control environment. By process-specific NC cycle support, manual programming of complex laser processes was enabled. The final metallographic analysis of the work piece showed that specific requirements to locally different wear resistance could be achieved in a five-axis single-clamping process chain. The design provided parallel processing potential which enables a more economical operation of the MTMT as a whole. The need for a systematic approach to evaluate mutual interference between processes and workspaces was discussed and an industrial application was demonstrated. While the experiments showed that the application of laser processes can be supported to an extent where they become manually programmable directly at the machine tool, in cases of free-form surfaces the typical requirement of a CAD/CAM/NC which supports the process cannot be evaded. As in milling applications, the complex geometries of metal sheet forming tools for example cannot be processed without CAD/CAM support. The implementation of appropriate CAM extensions may be designed in several ways, assuming NC support as used in this paper for example, or assuming the need to plan all process parameters (laser power, filler wire, feeds and speeds) in detail in the CAM system. Efficient ways to provide such extensions require further inquiry, as does the question how such an approach can be generalized, considering the growing spectrum of manufacturing processes that may be integrated into a machine tool. Going forward, theories on the characteristics of different design choices in technology integration need to be developed and verified experimentally with the established prototype. It was proven that the integration of a wide spectrum of technologies can be realized and applied to industrial applications. Consequences for the design, commissioning and operational phases of MTMTs with respect to changing the scope of technologies, different levels of NC programming support, interference between simultaneous processes and a different number of workspaces are not sufficiently analyzed yet. Such knowledge may prove critical in providing design guidelines and a more complete understanding of MTMTs, which will help machine manufacturers and the production community to harness the potential of Integrated Technologies at manageable complexity. Acknowledgements The authors would like to thank the German Research Foundation (DFG) for the support of the presented research within the Cluster of Excellence ‘‘Integrative Production Technology for High-Wage Countries’’.

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References [1] Brecher, C., et al, 2012, Integrative Production Technology for High-Wage Countries, Springer, Berlin, ISBN: 978-3-642-21066-2. [2] Attia, H., Tavakoli, S., Vargas, R., Thomson, V., 2010, Laser-Assisted High-Speed Finish Turning of Superalloy Inconel 718 Under Dry Conditions, CIRP Annals, 59/1: 83–88. [3] Bejjania, R., Shi, B., Attia, H., Balazinskia, M., 2011, Laser Assisted Turning of Titanium Metal Matrix Composite, CIRP Annals, 60/1: 61–64. [4] Zieris, R., 2005, Laserunterstu¨tztes atmospha¨risches Plasmaspritzen, Dissertation Fraunhofer IWS Dresden978-3-816-76795-4. [5] Eßmann, J., 2007, Entwicklung eines Bearbeitungs-zentrums zur Mikrofertigung durch Fra¨sen und Laserabtrag, Neue Konzepte fu¨r Werkzeug-maschinen: Begleitband zur 2, Berliner Runde, Berlin, ISBN: : 978-3-981-14581-6121– 132. [6] Moriwaki, T., 2008, Multi-Functional Machine Tool, CIRP Annals, 57/2: 736–749. [7] Klocke, F., To¨nissen, S., Wegner, H., Roderburg, A., 2011, Modeling Economic Efficiency of Multi-Technology Platforms, Production Engineering, 5/3: 293– 300. Springer Berlin. [8] Jakob, M., Queudeville, Y., Vroomen, U., Bu¨hrig-Polaczek, A., 2009, Processing of High Pressure Die Casting Alloys and Engineering Polymers to New Hybrid Metal/Plastic Products in a Combined Process, in: Proceedings of the 4th International Light Metals Technology Conference (LMT) (Broadbeach Gold Coast, Queensland, Australia), pp.419–422. [9] Rosen, C.-J., 2012, Laserunterstu¨tze Fra¨sbearbeitung hochfester Werkstoffe, Dissertation Fraunhofer IPT, Apprimus Verlag, Aachen, ISBN: 978-3-86359051-2. [10] ElMaraghy, W., ElMaraghy, H., Tomiyama, T., Monostori, L., 2012, Complexity in Engineering Design and Manufacturing, CIRP Annals, 61/2: 793–814. [11] Brecher, C., Breitbach, T., Do-Khac, D., 2012, Strategies and Boundaries for Cost Efficient Multi Technology Machine Tools, The 15th International Conference on Machine Design and Production (Pamukkale, Denizli, Turkey), 978-975429-304-3pp.251–266. [12] Brecher, C., Klocke, F., Wenzel, C., Emonts, M., Frank, J., 2008, KombiMasch – hybride Werkzeugmaschine zur Verku¨rzung der Prozesskette, wtOnline, 98/7/ 8: 525–532. [13] Bichmann, S., Emonts, M., Glasmacher, L., Groll, K., Kordt, M., 2005, Automatisierte Reparaturzelle ‘‘OptoRep’’, wtOnline, 95/11/12: 831–838. [14] Heinen, D., 2011, Signifikante Erho¨hung der Verschleißbesta¨ndigkeit von Bauteilen mittels kombinierter Oberfla¨chenbehandlung (CURARE), Werkzeubau Akademie – Forschungsbericht 2010/2011 (Aachen), pp.142–146. [15] Schmidt, M., Kolleck, R., Grimm, A., Veit, R., Bartkowiak, K., 2010, Direct Laser Deposition of Cu Alloy on Forming Tool Surfaces – Process Window and Mechanical Properties, CIRP Annals, 59/1: 211–214. [16] Riedel, M., Nefzi, M., Corves, B., 2010, Performance Analysis and Dimensional Synthesis of a Six DOF Reconfigurable Parallel Manipulator, in: Proceedings of the IF-ToMM Symposium on Mechanism Design for Robotics (Mexico City, Mexico), . [17] Schuh, G., Kreysa, J., Orilski, S., 2009, Roadmap ‘‘Hybride Produktion’’ Wie 1+1=3-Effekte in der Produktion maximiert werden ko¨nnen, ZWF – Zeitschrift fu¨r wirtschaftlichen Fabrikbetrieb. ISSN: 0947-0085. [18] Brecher, C., Schuh, G., Breitbach, T., Bohl, A., du Bois-Reymond, F., 2013, Nutzwertanalyse integrierter Bearbeitungszentren Integrierte Fertigung in mehreren Arbeitsra¨umen – Gewichtung und Bewertung von Aufwand und Nutzen, wt Werkstattstechnik online 103, VDI Du¨sseldorf: 813–818. ISSN: 1436-4980, S.. [19] To¨nissen, S., Klocke, F., Feldhaus, B., Buchholz, S., 2012, A Study on Throughput Time of Multi-Technology Platforms, Procedia CIRP, 2:60–63. [20] Altintas, Y., Brecher, C., Weck, M., Witt, S., 2005, Virtual Machine Tool, CIRP Annals, 54/2: 115–138. [21] Brecher, C., Do-Khac, D., Herfs, W., Lohse, W., 2012, Produktives Laserschneiden durch Achsredundanz, wt Werkstatttechnik online, VDI Du¨sseldorf : 354–362. [22] Perovic, B., 2008, Spanende Werkzeugmaschinen: Ausfu¨hrungsformen und Vergleichstabellen, Springer, Berlin, ISBN: 978-3-54089-951-8. [24] Brecher, C., Breitbach, T., du Bois-Reymond, F., 2013, Qualifying Laser integrated Machine Tools With Multiple Workspaces For Machining Precision, Proceedings in Manufacturing Systems, 8/1. Bucharest. ISSN: 20679238. [25] Brecher, C., Karlberger, A., 2010, Control Concept for a Hybrid Machining Center, in: Proceedings of 2010 International Symposium on Flexible Automation (ISFA 2010) (Tokyo, Japan), 978-4-915740-48-0. [26] Fleischer, J., Krauße, M., 2013, Physically Consistent Parameter Optimization for the Generation of Pose Independent Simulation Models Using the Example of a 6-Axis Articulated Robot, 8th CIRP Conference on Intelligent Computation in Manufacturing Engineering, Procedia CIRP, pp.217–221. [27] Wenlei, X., Ji, H., 2012, Redundancy and Optimization of a 6R Robot for FiveAxis Milling Applications: Singularity, Joint Limits and Collision, Production Engineering, 6/3: 287–296. Springer Berlin. [28] Paul, R.P., 1981, Robot Manipulators: Mathematics, Programming and Control, The Massachusetts Institute of Technology, Cambridge, ISBN: 0-26216082-X. [29] Rieseler, H., 1992, Roboterkinematik – Grundlagen, Invertierung und symbolische Berechnung, Dissertation Braunschweig University .. ISBN: 3-52806515-X.

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CIRPJ-343; No. of Pages 14 14

C. Brecher et al. / CIRP Journal of Manufacturing Science and Technology xxx (2015) xxx–xxx

[30] DMG MORI SEIKI Deutschland GmbH. 2013, Generative Fertigung in, Fertigteilqualita¨t, Company Publication, Leonberg. [31] Matsuura Machinery Corporation. 2013, Metal Laser Sintering Hybrid Milling Machine, LUMEX Avance-25, Company Publication, Urushihara-cho Fukui City .

[32] To¨nissen, S., Klocke, F., Mattfeld, P., Shirobokov, A., 2013, Productivity Boundaries of Multi-technology Platforms with Two Workspaces, Procedia CIRP, 9:13–17. [33] Brecher, C., Schuh, G., Breitbach, T., Bohl, A., du Bois-Reymond, F., 2013, Nutzwertanalyse integrierter Bearbeitungszentren wt Werkstatttechnik online, VDI Du¨sseldorf.

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