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Hybrid thixoforming – A new process to produce hybrid components
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Procedia Manufacturing 00 (2018) 000–000 Available online atatwww.sciencedirect.com Available online www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000
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Procedia Manufacturing 15 (2018) 436–442 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
17th International Conference on Metal Forming, Metal Forming 2018, 16-19 September 2018, 17th International Conference on MetalToyohashi, Forming, Metal Japan Forming 2018, 16-19 September 2018, Toyohashi, Japan
Hybrid thixoforming – A new process to produce hybrid
HybridEngineering thixoforming – A new process produce hybrid Manufacturing Society International Conferenceto 2017, MESIC 2017, 28-30 June components 2017, Vigo (Pontevedra), Spain components Mathiasin Liewald Costing models forChristoph capacitySeyboldt*, optimization Industry 4.0: Trade-off Christoph Seyboldt*, Mathias Liewald Institute for Metal Forming Technology (IFU), University of Stuttgart, Holzgartenstraße 17, 70174 Stuttgart, Germany used capacity and operational efficiency Institutebetween for Metal Forming Technology (IFU), University of Stuttgart, Holzgartenstraße 17, 70174 Stuttgart, Germany Abstract A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb Abstract a optimized hybrid components can make an effective contribution to saving energy and The production of requirement and weight University of Minho, 4800-058 Guimarães, Portugal b The production of requirement and weight optimized components can make an effectiveatcontribution saving energy and conserving resources in production technology. For hybrid this89809-000 reason, current research activities the Institutetofor Metal Forming Unochapecó, Chapecó, SC, Brazil conserving resources in production technology. Forthethis reason, current research activities using at thesemi-solid Institute for Metalstrategies. Forming Technology, University of Stuttgart are focusing on manufacturing of hybrid components forming Technology, University Stuttgart focusing oninthe manufacturing of aluminium hybrid components semi-solid forming strategies. Thereby, a new formingof process wasare investigated which two different alloys areusing simultaneously heated up into the Thereby, new forming process was investigated in which two different alloys areansimultaneously heatedbetween up into the the semi-solida state and subsequently formed to a hybrid component. Duringaluminium the forming step, intermetallic phase Abstract semi-solid state and formed to a hybrid component. During properties the forming step,manufactured an intermetallic phase between the different materials is subsequently produced, which decisively determines the functional of the hybrid components. different materials produced, decisively thesemi-solid functionalforming properties of the manufactured components. In this context, thisispaper deals which with the inductivedetermines heating and of hybrid semi-finished hybrid materials consisting of Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, In this context, this paper deals with the inductive heating and semi-solid forming of hybrid semi-finished materials of two aluminium alloys having different melting points. By reason of the skin effect, which causes heating of materialconsisting solely near twoworkpiece´s aluminium alloys melting By reason of the effect, which causes heating of material solely near information based onhaving ainductive realdifferent time basis and,points. necessarily, much more efficient. In temperature this context, capacity optimization the surface, heated semi-finished materials show anskin inhomogeneous distribution in its volumes. the workpiece´s surface, inductive heated semi-finished materials show an inhomogeneous temperature distribution in its volumes. Therefore, thethe aluminium alloy having the higher melting pointcontributing was assembled at for the organization’s outer side and the alloy having the lower goes beyond traditional aim of capacity maximization, also profitability and value. Therefore, thewas aluminium alloy having the melting point was assembled the outer side andoptimization the alloy having the lower melting point assembled inand the core of higher the semi-finished material in order toat achieve the desired heat distribution within the Indeed, lean management continuous improvement approaches suggest capacity instead of melting was assembled the core ofoptimization the semi-finished material in order to the desired heat the differentpoint materials forstudy the subsequent semi-solid formingand process. After this graded distribution was distribution achieved in within the semimaximization. The ofin capacity costing models is achieve an heat important research topic that deserves different materials materialsby thedevelopment subsequent semi-solid forming process. After this trials heatperformed distribution wasa achieved in the semifinished the of and suitable heating strategies, forming were disc ashaped design to contributions fromforboth the practical theoretical perspectives. Thisgraded paper presents andusing discusses mathematical finished materials by theflow development of suitable heating strategies, forming trials were performed using a discby shaped design of to investigate the material of such graded materials. Furthermore, the transition zone built was investigated comparison model for capacity management based on different costing models (ABC and TDABC). A generic model has been investigatemodelling the material of such graded numerical andflow experimental results.materials. Furthermore, the transition zone built was investigated by comparison of developed and it was used to analyzeresults. idle capacity and to design strategies towards the maximization of organization’s numerical modelling and experimental value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity © 2018 The Authors. Published by Elsevier B.V. © 2018 The Authors. Published by Elsevier B.V. optimization might hide operational inefficiency. © 2018 The under Authors. Published by B.V. committee of the 17th International Conference on Metal Forming. Peer-review responsibility of Elsevier the scientific scientific Peer-review under responsibility of the of the 17th International Conference on Metal Forming. © 2017 The Authors. Published by B.V.committee Peer-review under responsibility ofElsevier the scientific committee of the 17th International Conference on Metal Forming. Peer-review under responsibility of the scientific committee ofHybrid the Manufacturing Engineering Society International Conference Keywords: Semi-solid forming; Thixoforming; Hybrid thixoforming; components; Intermetallic phase 2017. Keywords: Semi-solid forming; Thixoforming; Hybrid thixoforming; Hybrid components; Intermetallic phase Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
1. Introduction
* Corresponding author. Tel.: +49-711-685-83827; fax: +49-711-685-83839. * E-mail Corresponding Tel.: +49-711-685-83827; fax: +49-711-685-83839. address:author. [email protected] The cost of idle capacity is a fundamental information for companies and their management of extreme importance E-mail address: [email protected]
in modern©production systems. In general, it isB.V. defined as unused capacity or production potential and can be measured 2351-9789 2018 The Authors. Published by Elsevier 2351-9789 2018 Authors. Published Elsevier B.V.hours of the Peer-review underThe responsibility of theby scientific committee 17th International on Metal Forming. in several©ways: tons of production, available manufacturing, etc.Conference The management of the idle capacity Peer-review under responsibility thefax: scientific committee * Paulo Afonso. Tel.: +351 253 510of 761; +351 253 604 741 of the 17th International Conference on Metal Forming. E-mail address: [email protected]
2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 17th International Conference on Metal Forming. 10.1016/j.promfg.2018.07.240
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Christoph Seyboldt et al. / Procedia Manufacturing 15 (2018) 436–442 Author name / Procedia Manufacturing 00 (2018) 000–000
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1. Introduction In times of rising energy and resource costs, improvement of efficiency in production and application becomes an important technological driver for the development and optimization of manufacturing processes. Thereby, an effective input for saving energy and conserving natural resources is contributed by weight reductions through the production of locally optimized and on load cases adapted hybrid components. Those components can combine different material properties and lead to optimized parts in order to meet specified load cases. Within the framework of the research project "Hybrid interaction during and after thixoforging of multi-material systems" funded by the German Research Foundation (DFG), a thixoforming process for the production of cohesive metal-metal composites was developed and investigated. The general process flow considered in this context is shown in Fig. 1. Thereby, the semi-finished material consists of two different metallic materials that both have to be heated into the semi-solid state. By reason of the skin effect leading to inhomogeneous temperature distributions during inductive heating processes the material having the higher melting point is assembled at the outer side and the alloy having the lower melting point is assembled in the core of the semi-finished material. In the following, current investigations are described in which two different aluminium alloys (AlSi7Mg0.3 and AlMgSi1) were processed.
Fig. 1. Process flow for hybrid thixoforming of semi-finished materials.
In earlier research work, the inductive heating of such hybrid semi-finished materials into semi-solid material state has been investigated numerically and experimentally [1, 2]. The subsequent thixoforming process of those heated hybrid semi-finished materials is described in this paper. Thereby, the investigations also were carried out numerically using CFD simulation and experimentally in order to predict the material flow of hybrid semi-finished materials in the semi-solid state and to characterize the interaction mechanisms between both different materials during and after the thixoforming process. 2. State of the Art The production of requirement and weight optimized hybrid components can make an effective contribution to saving energy and conserving resources in production technology. For this reason, various research activities have been carried out on producing hybrid components. One field of research is the hybrid forming of steel and aluminium at elevated temperatures [3–5]. A second area deals with the simultaneous joining and forming of massive components with sheet metal parts [6]. The components produced in this way exhibit a non-detachable form-fit or force-locking connection between the joining partners. Composite casting is a common and already industrially used manufacturing process of hybrid components. In this process, a composite material is created by casting over inserts [7]. Further research projects are concerned with the reinforcement of sheet steel parts by cast light metal ribs. The components produced in this way feature a materiallocking connection as well as a form and force connection at the joining zone. The disadvantage is that the sheet metal formed parts tend to warp due to the large heat input during the casting process [8]. The joining of metallic inlays with steel alloys by thixoforming was investigated at various geometries [9, 10]. Joining on the basis of thixoforming allows form-, force- and material-locking connections as well as composite casting. Thereby, it must be ensured that the inlays can withstand the temperatures of the matrix material and that local melting does not occur [10].
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3. Experimental setup and results For the inductive heating of the hybrid semi-finished materials a pulse-width modulation heating system produced by KUKA was used. The forming experiments were carried out by using a specifically designed hydraulic high speed press and an open die for producing disc components (see Fig. 2). The press has a nitrogen piston accumulator which acts on a hydraulic column controlled by proportional valves. The maximum ram speed is 800 mm per second. The press enables its user to control the punch stroke and speed by adjusting it in correspondence to punch stroke. The maximum force applied is 5000 kN [11]. The high punch speed is necessary at the beginning to prevent the semi-solid material from premature solidification. While closing the die, the material has to flow laminar into the tool´s cavity in order to avoid entrapping air and embedding oxides. Compared to conventional forging, the required force during thixoforming is relatively low. During material´s solidification, immediately after the actual forming process, a high pressure of around 1000 bar must be applied to die cavity for avoiding shrinkage errors within the work piece´s volume like pores or voids [12].
Fig. 2. Semi-solid forming die for the production of disc shaped geometries.
3.1. Numerical modelling of forming of hybrid semi-finished materials in semi-solid state In order to model forming process of two fluids, the modified Carreau model deposited in the CFD program Flow3D [13] was used. Since the disc geometry used in these investigations is a rotationally symmetric component, only a section of 90° was simulated in order to minimize the calculation time. For the simulation objectives, an ideally heated raw material was used, whereby an initial temperature of 630 °C was assumed for the outer material and of 580 °C for the inner material as a first approach. In further investigations the temperature of the semi-finished material will be calculated by an inductive heating simulation. The ram speed was set constant to 100 mm/second. The forming die was set to a temperature of 300 °C and the heat transfer between die and the semi-finished material was set to 5 W/mK. Fig. 3 shows the calculated die filling of the selected disc geometry.
Fig. 3. Simulation of die filling by forming of hybrid semi-finished material in semi-solid state.
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The simulation results show, that the interface between the two fluids cannot be exactly identified after a relatively short flow path, since temperature compensation effects occurs between both materials. Therefore, the course of the interface was determined for the comparison with the experimental components at a temperature of 585 °C. 3.2. Heating of semi-finished materials Two different semi-finished material dimensions were investigated for manufacturing of the hybrid disc components. These dimensions and the positioning of thermocouples used for temperature measurement during inductive heating are shown in Fig. 4. The total volume of the semi-finished materials remained unchanged in all tests and was designed according to the disc geometry produced during the forming tests. Materials investigated were the aluminium alloys AlMgSi1 (outer material) and AlSi7Mg0.3 (core material).
Fig. 4. Positioning of thermocouples (TC) and dimensions of semi-finished materials for inductive heating.
Investigations performed have shown that a heating frequency of 1000 Hz is appropriate for the inductive heating of the hybrid semi-finished materials (consisting of AlMgSi1 and AlSi7Mg0.3) in order to achieve the desired temperature distribution. Furthermore, the investigations have shown that for the desired inhomogeneous temperature profile within the hybrid semi-finished materials´ volumes, heating should be carried out with constant power input. The system parameters determined and used during the heating tests are presented in Table 1. Table 1. Heating parameters for different hybrid semi-finished materials. Version A
Version B
Heating frequency (Hz)
1000
1000
Pulse width
137
125
Heating time (s)
54
66
In addition, the results of the heating tests have shown that if the proportion of higher-melting material in the semifinished materials increases, the heating power must be reduced in order to heat them more precisely heading a given temperature level. As expected, this reduction in performance was accompanied by a longer heating time. In order to take into account the transfer of the semi-finished material from the heating unit to the forming press, the effect of a transfer time of 5 seconds on the temperature distribution within the volume of the semi-finished materials was
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investigated. Having an ideal temperature distribution after heating stop (outside = 630 °C and inside = 580 °C), the transfer time caused the melting of the core material to such an extent that it slipped out of the compound partner and thus no longer allows a forming process. For this reason, the temperature profile during heating had to be set in such a way that the ideal temperature distribution within the semi-finished material´s volume is achieved during the transfer time. This was achieved by minimally "overheating" the higher-melting material (635 °C instead of 630 °C) and minimally “underheating” the lower-melting material (549°C instead of 580 °C). A corresponding heating process is shown in Fig. 5 for a hybrid semi-finished material with dimensions of version A. Thereby TC1 is the thermocouple indicating temperature in the outer material (AlMgSi1) and TC2 indicating temperature in the core material (AlSi7Mg0.3).
Fig. 5. Heating curve to the semi-solid state for a hybrid semi-finished material (version A).
3.3. Forming of semi-finished materials For the forming tests, the semi-finished materials were first heated using the system parameters determined during the heating tests. Afterwards, the ideal ram-speed profile of the press ram as well as the die temperature setting had to be determined, since these two process parameters, in addition to the heating of the semi-finished material, are the main influencing factors for the forming process. For this parameter identification, the disc components were initially manufactured from the alloy AlMgSi1 as a monolithic material. Thereby, a die temperature of 350 °C was the most successful setting. The ram-speed profile determined during the forming tests is shown in Fig. 6.
Fig. 6. Used ram-speed-profile for the production of disc geometries.
These process parameters were then used to produce completely formed disc components by forming of inductively heated hybrid semi-finished materials consisting of AlMgSi1 (outer material) and AlSi7Mg0.3 (core material). During
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the forming trials no difference in forming behaviour by varying the semi-finished materials geometry from version A to version B could be detected. For both versions completely formed disc components could be produced. Examples of manufactured disc components for version A is shown in Fig. 7(a) and for version B in Fig. 7(b). Subsequently, metallographic sections were made from these produced discs in order to examine the material flow and the structural properties of the components. It was found that there is no mixing between the two materials. However, a transition zone is formed (see Fig. 7(c)). The properties and characteristics of this interface are to be investigated in further investigations. (a)
(b)
(c)
Fig. 7. Produced disc geometry; (a) version A and (b) version B; (c) microsection of produced components showing an interface layer.
4. Comparison of simulation and real forming trials Step-shot experiments are commonly used to validate forming simulations in the semi-solid state. This means that the running forming process is interrupted at different points in time and emerging flow path can be compared with the simulation at particular time steps. In the forming process of hybrid semi-finished materials, such a procedure is impossible, as a complete melting of the low-melting compound partner occurs when the forming process is interrupted due to heat transition caused by the graded temperature distribution. Thus, the results become unusable. In order to be able to make a valuation with regard to the quality of the performed forming simulations, sections were taken from the produced components and compared with the last time step of the simulation. The numerically determined boundary layer pattern was determined along an isothermal temperature. Fig. 8 shows that simulation and reality differ only by a few millimeters (approx. 5 mm). On the one hand, this deviation can be explained by the estimated interfacial distribution and, on the other hand, by the estimated isotropic temperature distribution in the semi-finished material. Nevertheless, a general estimation of the position of the interface in the real hybrid component can be made on the basis of the forming simulation.
Fig. 8. Comparison of transition zone between numerical modelling and experiment.
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5. Summary and future perspective In this paper, a study for the production of hybrid components having intermetallic transition zones by semi-solid forming was presented. It was shown that completely shaped disc components can be manufactured by thixoforming of hybrid semi-finished materials. Furthermore, first investigations on modelling this thixoforming process using CFD simulation were shown. The results have been compared with the experimental results and showed a highly promising correlation that should be optimized in further investigations. In further investigations, a more detailed characterization of the transition zone between the compound partners will be carried out. For this purpose, the interface layers have to be examined in more detail by means of SEM investigations. Tensile and bending specimens are then taken from the components produced in order to characterize the strength of the intermetallic phase and thereby the mechanical properties of the hybrid components produced by thixoforming process. Acknowledgement The authors thank the German Research Foundation (DFG) for their financial support of the research project “Hybride Interaktionsmechanismen während und nach dem Thixo-Schmieden von Multimaterialsystemen” under grant LI 1556/51-1. References [1] C. Seyboldt, M. Liewald, Numerical simulation of the induction heating of hybrid semi-finished materials into the semi-solid state, AIP Conference Proceedings, 1896 (2017) 130001. [2] L. Schomer, C. Seyboldt, M. Liewald, Semi-solid metal forming - a process for manufacturing composite and hybrid materials, Defect and Diffusion Forum, 381 (2017) 47–51. [3] K.G. Kosch, B.A. Behrens, Herstellung lokal anforderungs - optimierter Hybridbauteile durch Verbundschmieden, SchmiedeJOURNAL, (2013) 60–63. [4] R. Leiber, Höher, schneller und weiter durch Hybridschmieden, Industrieanzeiger, (2011) 23–25. [5] K.G. Kosch, I. Pfeiffer, A. Foydl, B.A. Behrens, E. Tekkaya, Schmieden von partiell stahlverstärkten Aluminiumhalbzeugen, UTF-Science, 3 (2012) 1–9. [6] H. Kache, M. Stonis, B.A. Behrens, Hybridschmieden - monoprozessuales umformen und fügen metallischer blech- und massivelemente, wt Werkstattstech, online, 103 (2013) 257–262. [7] P. Fickel, Hohl- und verbundguss von druckgussbauteilen – numerische auslegungsmethoden und experimentelle verifikation, Dissertation, University of Stuttgart, (2017). [8] A.B. Polaczek, T. Röth, E. Baumeister, N. Nowack, T. Süssmann, Hybride leichtbaustrukturen in stahlblech-leichtmetall verbundguss, (2006). [9] R. Baadjou, H. Shimahara, G. Hirt, Automated semi-solid forging of steel components by means of thixojoining, Solid State Phenomena, 116– 117 (2006) 383–386. [10] R. Baadjou, Grundlagenuntersuchung zur herstellung thixogeformter stahlverbundbauteile, Dissertation, RWTH Aachen, (2013). [11] J. Baur, Anlagen für das thixo-schmieden, wt-online, 10 (2000) 441–445. [12] G. Meßmer, Gestaltung von werkzeugen für das thixo-schmieden von aluminium und messinglegierungen in automatisierten schmiedezellen, Dissertation, University of Stuttgart, (2006). [13] I. Flow Science, FLOW-3D User’s Manual 11.1. Flow Science Inc., (2015).
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Procedia Manufacturing 00 (2018) 000–000 Available online atatwww.sciencedirect.com Available online www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Manufacturing 15 (2018) 436–442 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
17th International Conference on Metal Forming, Metal Forming 2018, 16-19 September 2018, 17th International Conference on MetalToyohashi, Forming, Metal Japan Forming 2018, 16-19 September 2018, Toyohashi, Japan
Hybrid thixoforming – A new process to produce hybrid
HybridEngineering thixoforming – A new process produce hybrid Manufacturing Society International Conferenceto 2017, MESIC 2017, 28-30 June components 2017, Vigo (Pontevedra), Spain components Mathiasin Liewald Costing models forChristoph capacitySeyboldt*, optimization Industry 4.0: Trade-off Christoph Seyboldt*, Mathias Liewald Institute for Metal Forming Technology (IFU), University of Stuttgart, Holzgartenstraße 17, 70174 Stuttgart, Germany used capacity and operational efficiency Institutebetween for Metal Forming Technology (IFU), University of Stuttgart, Holzgartenstraße 17, 70174 Stuttgart, Germany Abstract A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb Abstract a optimized hybrid components can make an effective contribution to saving energy and The production of requirement and weight University of Minho, 4800-058 Guimarães, Portugal b The production of requirement and weight optimized components can make an effectiveatcontribution saving energy and conserving resources in production technology. For hybrid this89809-000 reason, current research activities the Institutetofor Metal Forming Unochapecó, Chapecó, SC, Brazil conserving resources in production technology. Forthethis reason, current research activities using at thesemi-solid Institute for Metalstrategies. Forming Technology, University of Stuttgart are focusing on manufacturing of hybrid components forming Technology, University Stuttgart focusing oninthe manufacturing of aluminium hybrid components semi-solid forming strategies. Thereby, a new formingof process wasare investigated which two different alloys areusing simultaneously heated up into the Thereby, new forming process was investigated in which two different alloys areansimultaneously heatedbetween up into the the semi-solida state and subsequently formed to a hybrid component. Duringaluminium the forming step, intermetallic phase Abstract semi-solid state and formed to a hybrid component. During properties the forming step,manufactured an intermetallic phase between the different materials is subsequently produced, which decisively determines the functional of the hybrid components. different materials produced, decisively thesemi-solid functionalforming properties of the manufactured components. In this context, thisispaper deals which with the inductivedetermines heating and of hybrid semi-finished hybrid materials consisting of Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, In this context, this paper deals with the inductive heating and semi-solid forming of hybrid semi-finished materials of two aluminium alloys having different melting points. By reason of the skin effect, which causes heating of materialconsisting solely near twoworkpiece´s aluminium alloys melting By reason of the effect, which causes heating of material solely near information based onhaving ainductive realdifferent time basis and,points. necessarily, much more efficient. In temperature this context, capacity optimization the surface, heated semi-finished materials show anskin inhomogeneous distribution in its volumes. the workpiece´s surface, inductive heated semi-finished materials show an inhomogeneous temperature distribution in its volumes. Therefore, thethe aluminium alloy having the higher melting pointcontributing was assembled at for the organization’s outer side and the alloy having the lower goes beyond traditional aim of capacity maximization, also profitability and value. Therefore, thewas aluminium alloy having the melting point was assembled the outer side andoptimization the alloy having the lower melting point assembled inand the core of higher the semi-finished material in order toat achieve the desired heat distribution within the Indeed, lean management continuous improvement approaches suggest capacity instead of melting was assembled the core ofoptimization the semi-finished material in order to the desired heat the differentpoint materials forstudy the subsequent semi-solid formingand process. After this graded distribution was distribution achieved in within the semimaximization. The ofin capacity costing models is achieve an heat important research topic that deserves different materials materialsby thedevelopment subsequent semi-solid forming process. After this trials heatperformed distribution wasa achieved in the semifinished the of and suitable heating strategies, forming were disc ashaped design to contributions fromforboth the practical theoretical perspectives. Thisgraded paper presents andusing discusses mathematical finished materials by theflow development of suitable heating strategies, forming trials were performed using a discby shaped design of to investigate the material of such graded materials. Furthermore, the transition zone built was investigated comparison model for capacity management based on different costing models (ABC and TDABC). A generic model has been investigatemodelling the material of such graded numerical andflow experimental results.materials. Furthermore, the transition zone built was investigated by comparison of developed and it was used to analyzeresults. idle capacity and to design strategies towards the maximization of organization’s numerical modelling and experimental value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity © 2018 The Authors. Published by Elsevier B.V. © 2018 The Authors. Published by Elsevier B.V. optimization might hide operational inefficiency. © 2018 The under Authors. Published by B.V. committee of the 17th International Conference on Metal Forming. Peer-review responsibility of Elsevier the scientific scientific Peer-review under responsibility of the of the 17th International Conference on Metal Forming. © 2017 The Authors. Published by B.V.committee Peer-review under responsibility ofElsevier the scientific committee of the 17th International Conference on Metal Forming. Peer-review under responsibility of the scientific committee ofHybrid the Manufacturing Engineering Society International Conference Keywords: Semi-solid forming; Thixoforming; Hybrid thixoforming; components; Intermetallic phase 2017. Keywords: Semi-solid forming; Thixoforming; Hybrid thixoforming; Hybrid components; Intermetallic phase Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
1. Introduction
* Corresponding author. Tel.: +49-711-685-83827; fax: +49-711-685-83839. * E-mail Corresponding Tel.: +49-711-685-83827; fax: +49-711-685-83839. address:author. [email protected] The cost of idle capacity is a fundamental information for companies and their management of extreme importance E-mail address: [email protected]
in modern©production systems. In general, it isB.V. defined as unused capacity or production potential and can be measured 2351-9789 2018 The Authors. Published by Elsevier 2351-9789 2018 Authors. Published Elsevier B.V.hours of the Peer-review underThe responsibility of theby scientific committee 17th International on Metal Forming. in several©ways: tons of production, available manufacturing, etc.Conference The management of the idle capacity Peer-review under responsibility thefax: scientific committee * Paulo Afonso. Tel.: +351 253 510of 761; +351 253 604 741 of the 17th International Conference on Metal Forming. E-mail address: [email protected]
2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 17th International Conference on Metal Forming. 10.1016/j.promfg.2018.07.240
2
Christoph Seyboldt et al. / Procedia Manufacturing 15 (2018) 436–442 Author name / Procedia Manufacturing 00 (2018) 000–000
437
1. Introduction In times of rising energy and resource costs, improvement of efficiency in production and application becomes an important technological driver for the development and optimization of manufacturing processes. Thereby, an effective input for saving energy and conserving natural resources is contributed by weight reductions through the production of locally optimized and on load cases adapted hybrid components. Those components can combine different material properties and lead to optimized parts in order to meet specified load cases. Within the framework of the research project "Hybrid interaction during and after thixoforging of multi-material systems" funded by the German Research Foundation (DFG), a thixoforming process for the production of cohesive metal-metal composites was developed and investigated. The general process flow considered in this context is shown in Fig. 1. Thereby, the semi-finished material consists of two different metallic materials that both have to be heated into the semi-solid state. By reason of the skin effect leading to inhomogeneous temperature distributions during inductive heating processes the material having the higher melting point is assembled at the outer side and the alloy having the lower melting point is assembled in the core of the semi-finished material. In the following, current investigations are described in which two different aluminium alloys (AlSi7Mg0.3 and AlMgSi1) were processed.
Fig. 1. Process flow for hybrid thixoforming of semi-finished materials.
In earlier research work, the inductive heating of such hybrid semi-finished materials into semi-solid material state has been investigated numerically and experimentally [1, 2]. The subsequent thixoforming process of those heated hybrid semi-finished materials is described in this paper. Thereby, the investigations also were carried out numerically using CFD simulation and experimentally in order to predict the material flow of hybrid semi-finished materials in the semi-solid state and to characterize the interaction mechanisms between both different materials during and after the thixoforming process. 2. State of the Art The production of requirement and weight optimized hybrid components can make an effective contribution to saving energy and conserving resources in production technology. For this reason, various research activities have been carried out on producing hybrid components. One field of research is the hybrid forming of steel and aluminium at elevated temperatures [3–5]. A second area deals with the simultaneous joining and forming of massive components with sheet metal parts [6]. The components produced in this way exhibit a non-detachable form-fit or force-locking connection between the joining partners. Composite casting is a common and already industrially used manufacturing process of hybrid components. In this process, a composite material is created by casting over inserts [7]. Further research projects are concerned with the reinforcement of sheet steel parts by cast light metal ribs. The components produced in this way feature a materiallocking connection as well as a form and force connection at the joining zone. The disadvantage is that the sheet metal formed parts tend to warp due to the large heat input during the casting process [8]. The joining of metallic inlays with steel alloys by thixoforming was investigated at various geometries [9, 10]. Joining on the basis of thixoforming allows form-, force- and material-locking connections as well as composite casting. Thereby, it must be ensured that the inlays can withstand the temperatures of the matrix material and that local melting does not occur [10].
Christoph Seyboldt et al. / Procedia Manufacturing 15 (2018) 436–442 Author name / Procedia Manufacturing 00 (2018) 000–000
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3. Experimental setup and results For the inductive heating of the hybrid semi-finished materials a pulse-width modulation heating system produced by KUKA was used. The forming experiments were carried out by using a specifically designed hydraulic high speed press and an open die for producing disc components (see Fig. 2). The press has a nitrogen piston accumulator which acts on a hydraulic column controlled by proportional valves. The maximum ram speed is 800 mm per second. The press enables its user to control the punch stroke and speed by adjusting it in correspondence to punch stroke. The maximum force applied is 5000 kN [11]. The high punch speed is necessary at the beginning to prevent the semi-solid material from premature solidification. While closing the die, the material has to flow laminar into the tool´s cavity in order to avoid entrapping air and embedding oxides. Compared to conventional forging, the required force during thixoforming is relatively low. During material´s solidification, immediately after the actual forming process, a high pressure of around 1000 bar must be applied to die cavity for avoiding shrinkage errors within the work piece´s volume like pores or voids [12].
Fig. 2. Semi-solid forming die for the production of disc shaped geometries.
3.1. Numerical modelling of forming of hybrid semi-finished materials in semi-solid state In order to model forming process of two fluids, the modified Carreau model deposited in the CFD program Flow3D [13] was used. Since the disc geometry used in these investigations is a rotationally symmetric component, only a section of 90° was simulated in order to minimize the calculation time. For the simulation objectives, an ideally heated raw material was used, whereby an initial temperature of 630 °C was assumed for the outer material and of 580 °C for the inner material as a first approach. In further investigations the temperature of the semi-finished material will be calculated by an inductive heating simulation. The ram speed was set constant to 100 mm/second. The forming die was set to a temperature of 300 °C and the heat transfer between die and the semi-finished material was set to 5 W/mK. Fig. 3 shows the calculated die filling of the selected disc geometry.
Fig. 3. Simulation of die filling by forming of hybrid semi-finished material in semi-solid state.
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The simulation results show, that the interface between the two fluids cannot be exactly identified after a relatively short flow path, since temperature compensation effects occurs between both materials. Therefore, the course of the interface was determined for the comparison with the experimental components at a temperature of 585 °C. 3.2. Heating of semi-finished materials Two different semi-finished material dimensions were investigated for manufacturing of the hybrid disc components. These dimensions and the positioning of thermocouples used for temperature measurement during inductive heating are shown in Fig. 4. The total volume of the semi-finished materials remained unchanged in all tests and was designed according to the disc geometry produced during the forming tests. Materials investigated were the aluminium alloys AlMgSi1 (outer material) and AlSi7Mg0.3 (core material).
Fig. 4. Positioning of thermocouples (TC) and dimensions of semi-finished materials for inductive heating.
Investigations performed have shown that a heating frequency of 1000 Hz is appropriate for the inductive heating of the hybrid semi-finished materials (consisting of AlMgSi1 and AlSi7Mg0.3) in order to achieve the desired temperature distribution. Furthermore, the investigations have shown that for the desired inhomogeneous temperature profile within the hybrid semi-finished materials´ volumes, heating should be carried out with constant power input. The system parameters determined and used during the heating tests are presented in Table 1. Table 1. Heating parameters for different hybrid semi-finished materials. Version A
Version B
Heating frequency (Hz)
1000
1000
Pulse width
137
125
Heating time (s)
54
66
In addition, the results of the heating tests have shown that if the proportion of higher-melting material in the semifinished materials increases, the heating power must be reduced in order to heat them more precisely heading a given temperature level. As expected, this reduction in performance was accompanied by a longer heating time. In order to take into account the transfer of the semi-finished material from the heating unit to the forming press, the effect of a transfer time of 5 seconds on the temperature distribution within the volume of the semi-finished materials was
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investigated. Having an ideal temperature distribution after heating stop (outside = 630 °C and inside = 580 °C), the transfer time caused the melting of the core material to such an extent that it slipped out of the compound partner and thus no longer allows a forming process. For this reason, the temperature profile during heating had to be set in such a way that the ideal temperature distribution within the semi-finished material´s volume is achieved during the transfer time. This was achieved by minimally "overheating" the higher-melting material (635 °C instead of 630 °C) and minimally “underheating” the lower-melting material (549°C instead of 580 °C). A corresponding heating process is shown in Fig. 5 for a hybrid semi-finished material with dimensions of version A. Thereby TC1 is the thermocouple indicating temperature in the outer material (AlMgSi1) and TC2 indicating temperature in the core material (AlSi7Mg0.3).
Fig. 5. Heating curve to the semi-solid state for a hybrid semi-finished material (version A).
3.3. Forming of semi-finished materials For the forming tests, the semi-finished materials were first heated using the system parameters determined during the heating tests. Afterwards, the ideal ram-speed profile of the press ram as well as the die temperature setting had to be determined, since these two process parameters, in addition to the heating of the semi-finished material, are the main influencing factors for the forming process. For this parameter identification, the disc components were initially manufactured from the alloy AlMgSi1 as a monolithic material. Thereby, a die temperature of 350 °C was the most successful setting. The ram-speed profile determined during the forming tests is shown in Fig. 6.
Fig. 6. Used ram-speed-profile for the production of disc geometries.
These process parameters were then used to produce completely formed disc components by forming of inductively heated hybrid semi-finished materials consisting of AlMgSi1 (outer material) and AlSi7Mg0.3 (core material). During
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the forming trials no difference in forming behaviour by varying the semi-finished materials geometry from version A to version B could be detected. For both versions completely formed disc components could be produced. Examples of manufactured disc components for version A is shown in Fig. 7(a) and for version B in Fig. 7(b). Subsequently, metallographic sections were made from these produced discs in order to examine the material flow and the structural properties of the components. It was found that there is no mixing between the two materials. However, a transition zone is formed (see Fig. 7(c)). The properties and characteristics of this interface are to be investigated in further investigations. (a)
(b)
(c)
Fig. 7. Produced disc geometry; (a) version A and (b) version B; (c) microsection of produced components showing an interface layer.
4. Comparison of simulation and real forming trials Step-shot experiments are commonly used to validate forming simulations in the semi-solid state. This means that the running forming process is interrupted at different points in time and emerging flow path can be compared with the simulation at particular time steps. In the forming process of hybrid semi-finished materials, such a procedure is impossible, as a complete melting of the low-melting compound partner occurs when the forming process is interrupted due to heat transition caused by the graded temperature distribution. Thus, the results become unusable. In order to be able to make a valuation with regard to the quality of the performed forming simulations, sections were taken from the produced components and compared with the last time step of the simulation. The numerically determined boundary layer pattern was determined along an isothermal temperature. Fig. 8 shows that simulation and reality differ only by a few millimeters (approx. 5 mm). On the one hand, this deviation can be explained by the estimated interfacial distribution and, on the other hand, by the estimated isotropic temperature distribution in the semi-finished material. Nevertheless, a general estimation of the position of the interface in the real hybrid component can be made on the basis of the forming simulation.
Fig. 8. Comparison of transition zone between numerical modelling and experiment.
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5. Summary and future perspective In this paper, a study for the production of hybrid components having intermetallic transition zones by semi-solid forming was presented. It was shown that completely shaped disc components can be manufactured by thixoforming of hybrid semi-finished materials. Furthermore, first investigations on modelling this thixoforming process using CFD simulation were shown. The results have been compared with the experimental results and showed a highly promising correlation that should be optimized in further investigations. In further investigations, a more detailed characterization of the transition zone between the compound partners will be carried out. For this purpose, the interface layers have to be examined in more detail by means of SEM investigations. Tensile and bending specimens are then taken from the components produced in order to characterize the strength of the intermetallic phase and thereby the mechanical properties of the hybrid components produced by thixoforming process. Acknowledgement The authors thank the German Research Foundation (DFG) for their financial support of the research project “Hybride Interaktionsmechanismen während und nach dem Thixo-Schmieden von Multimaterialsystemen” under grant LI 1556/51-1. References [1] C. Seyboldt, M. Liewald, Numerical simulation of the induction heating of hybrid semi-finished materials into the semi-solid state, AIP Conference Proceedings, 1896 (2017) 130001. [2] L. Schomer, C. Seyboldt, M. Liewald, Semi-solid metal forming - a process for manufacturing composite and hybrid materials, Defect and Diffusion Forum, 381 (2017) 47–51. [3] K.G. Kosch, B.A. Behrens, Herstellung lokal anforderungs - optimierter Hybridbauteile durch Verbundschmieden, SchmiedeJOURNAL, (2013) 60–63. [4] R. Leiber, Höher, schneller und weiter durch Hybridschmieden, Industrieanzeiger, (2011) 23–25. [5] K.G. Kosch, I. Pfeiffer, A. Foydl, B.A. Behrens, E. Tekkaya, Schmieden von partiell stahlverstärkten Aluminiumhalbzeugen, UTF-Science, 3 (2012) 1–9. [6] H. Kache, M. Stonis, B.A. Behrens, Hybridschmieden - monoprozessuales umformen und fügen metallischer blech- und massivelemente, wt Werkstattstech, online, 103 (2013) 257–262. [7] P. Fickel, Hohl- und verbundguss von druckgussbauteilen – numerische auslegungsmethoden und experimentelle verifikation, Dissertation, University of Stuttgart, (2017). [8] A.B. Polaczek, T. Röth, E. Baumeister, N. Nowack, T. Süssmann, Hybride leichtbaustrukturen in stahlblech-leichtmetall verbundguss, (2006). [9] R. Baadjou, H. Shimahara, G. Hirt, Automated semi-solid forging of steel components by means of thixojoining, Solid State Phenomena, 116– 117 (2006) 383–386. [10] R. Baadjou, Grundlagenuntersuchung zur herstellung thixogeformter stahlverbundbauteile, Dissertation, RWTH Aachen, (2013). [11] J. Baur, Anlagen für das thixo-schmieden, wt-online, 10 (2000) 441–445. [12] G. Meßmer, Gestaltung von werkzeugen für das thixo-schmieden von aluminium und messinglegierungen in automatisierten schmiedezellen, Dissertation, University of Stuttgart, (2006). [13] I. Flow Science, FLOW-3D User’s Manual 11.1. Flow Science Inc., (2015).