- Email: [email protected]
Highly Rigid Assembled Composite Structures with Continuous Fiber-Reinforced Thermoplastics for Automotive Applications
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16th Global Conference on Sustainable Manufacturing - Sustainable Manufacturing for Global Circular Economy 16th Global Conference on Sustainable Manufacturing - Sustainable Manufacturing for Global Circular Economy
Highly Rigid Assembled Composite Structures with Continuous Highly Rigid Assembled Composite Structures with Continuous Fiber-Reinforced Thermoplastics for Automotive Applications Manufacturing EngineeringThermoplastics Society International Conference 2017, MESIC 2017, 28-30 June Fiber-Reinforced for Automotive Applications 2017, Vigo (Pontevedra), Spain Kroll, L.a,b, Meyer, M.a,c*, Nendel, W.a, Schormair, M.a Kroll, L.a,b, Meyer, M.a,c*, Nendel, W.a, Schormair, M.a
Chemnitz University of Technology, of Lightweight Structures and Polymer (SLK), Reichenhainer Str. 31-33, Costing models for Department capacity optimization in Technology Industry 4.0: Trade-off D-09126 Chemnitz, Germany Chemnitz University of Technology, Department of Lightweight Structures and Polymer Technology (SLK), Reichenhainer Str. 31-33, Opole University of Technology, Department of D-09126 Mechanics and Machine Design, ul. S. Mikolajczyka 5, 45-271 Opole, Poland Chemnitz, Germany between used capacity and operational efficiency Cetex Institut für Textil- und Verarbeitungsmaschinen gemeinnützige GmbH an der Technischen Universität Chemnitz, Altchemnitzer Str. 11, a a
b
c c
Opole University of Technology, Department of Mechanics and Machine Design, ul. S. Mikolajczyka 5, 45-271 Opole, Poland D-09120 Chemnitz, Cetex Institut für Textil- und Verarbeitungsmaschinen gemeinnützige GmbHGermany an der Technischen Universität Chemnitz, Altchemnitzer Str. 11, a a,* b b D-09120 Chemnitz, Germany b
A. Santana , P. Afonso , A. Zanin , R. Wernke
University of Minho, 4800-058 Guimarães, Portugal Abstract b Unochapecó, 89809-000 Chapecó, SC, Brazil Abstract Future technological and product developments will be measured by their improved resource and energy efficiency, as well as their competitiveness, while allowing effective climate environmental processes that areascurrently Future technological and product developments will beand measured by theirprotection. improved Manufacturing resource and energy efficiency, well as discrete for different while groupsallowing of materials such as metals, plastics or protection. textiles have to be merged to generate their competitiveness, effective climate and environmental Manufacturing processes that arelarge-scale currently Abstract technologies the sustainable production high-performance structures automotive applications. discrete for for different groups of materialsofsuch as metals, plastics or for textiles have to be merged to generate large-scale Fiber-reinforced plastics have production been established in manufacturing components of high strength, stiffness and lightweight technologies for the sustainable of high-performance structures for automotive applications. Under theWell-known concept ofexamples "Industry 4.0", production processes willof be pushed to fiber-reinforced be increasingly interconnected, structures. are sandwich composites: an assembly two continuous thermoplastic layers Fiber-reinforced plastics have been established in manufacturing components of high strength, stiffness and lightweight information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization and an intermediate injection molded core structure. The vision is to make the savings potential of technology fusion and structures. Well-known examples are sandwich composites: an assembly ofuse twoofcontinuous fiber-reinforced thermoplastic layers goes the traditional aim maximization, forsavings organization’s and value. lightweight structures pursuant to of thecapacity central idea ofThe resource-efficient technologies multi-material and anbeyond intermediate injection molded core structure. vision contributing is to makemanufacturing usealso of the potentialtoprofitability ofproduce technology fusion and Indeed, lean management continuous approaches suggest technologies capacity optimization instead of components. lightweight structures pursuantand to the central ideaimprovement of resource-efficient manufacturing to produce multi-material maximization. The study of capacity optimization and costing models is an important research topic that deserves components. © 2018 The Authors. Published by Elsevier contributions from both the practical andLtd. theoretical perspectives. This paper presents and discusses a mathematical © 2018 2019 The Authors. Published by Elsevier B.V. This is an open accessmanagement article under the CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) © The Authors. Published by Elsevier Ltd.differentlicense model for capacity based on costing models (ABC and TDABC). A generic model has been This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of design the 16thstrategies Global Conference the on Sustainable Manufacturing This is an open access article under CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) developed and it was used to analyze idle capacity and to maximization of organization’s Selection and peer-review under responsibility of the scientific committee oftowards the 16th Global Conference on Sustainable (GCSM) Peer-review responsibility the scientific committee of the 16th Global Conference on Sustainable Manufacturing value. The under trade-off capacity ofmaximization vs operational efficiency is highlighted and it is shown that capacity Manufacturing (GCSM). (GCSM) optimization might hide operational inefficiency. a
Keywords: Resource and Energy Efficiency, Lightweight Structures, Fiber-reinforced plastics, Multi-material components
© 2017 The Authors. Published by Elsevier B.V. Keywords: Resource and Energy Efficiency, Lightweight Structures, Fiber-reinforced plastics, Multi-material components Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
1. Introduction
* Corresponding author. Tel.: +49 371 531-36774; fax: +49 371 531-8 36774. E-mail address: [email protected] * The Corresponding author. Tel.: +49 531-36774; fax: +49 371 531-8 36774. cost of idle capacity is371 a fundamental information for companies and their management of extreme importance E-mail address: [email protected] in modern production systems. In general, it is defined as unused capacity or production potential and can be measured 2351-9789 © 2018 The Authors. Published by Elsevier Ltd. in several ways: tons ofunder production, available hours of manufacturing, etc. The management of the idle capacity This is an open access the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 2351-9789 © 2018 Thearticle Authors. Published by Elsevier Ltd. * Paulo Afonso. Tel.: +351 253 510 761; fax: +351 253 604 Peer-review under responsibility of the scientific committee of741 the 16th Global Conference on Sustainable Manufacturing (GCSM) This is an open access article under CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) E-mail address: [email protected] Peer-review under responsibility of the scientific committee of the 16th Global Conference on Sustainable Manufacturing (GCSM) 2351-9789 Published by Elsevier B.V. B.V. 2351-9789 ©©2017 2019The TheAuthors. Authors. Published by Elsevier Peer-review underaccess responsibility of the scientific committee oflicense the Manufacturing Engineering Society International Conference 2017. This is an open article under the CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 16th Global Conference on Sustainable Manufacturing (GCSM). 10.1016/j.promfg.2019.04.027
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1. Introduction One of the most important challenges facing the automotive industry lies in stringent environmental protection requirements and their associated emission laws, which are mainly focused on reducing CO 2 emissions. The design and integration of battery packages into the lightweight structure of automotive applications requires new approaches. An assembled new composite battery carrier was designed, and its manufacturing process developed to show lightweight and technological potentials of continuous fiber-reinforced thermoplastics (FRP) of woven fabrics in the form of so-called organo sheets [1]. For achieving the optimal economic lightweight potential, it is absolutely necessary to develop highly rigid sandwich parts with two continuous fiber-reinforced thermoplastics layers to replace relevant load-bearing parts in automotive applications [2, 3, 4]. In order to achieve these aims, it is possible to join the structure of one formed organo sheet bottom layer in combination with an injection molded or pressed rib structure to a second organo sheet top layer by a joining process (Fig. 1). In terms of reaching mass production and process reliability it is the advantage of thermoplastic FRP´s as opposed to thermoset FRPs which can only be joined by gluing. Therefore, the bonding strength of the joining process of the organo sheet and the injection molded rib structure plays a decisive role for the final part and the application conditions.
Fig. 1. Assembled thermoplastic battery carrier with continuous fiber reinforcement and its components.
2. Assembling of the organo sheets and the injection molded rib structure The assembled composite part, reinforced by continuous fibers (glass or carbon fibers), is subdivided into several functional areas for a better and more efficient manufacturing (Fig. 2). The assembly consists of a bottom and a top organo sheet. The connection between the bottom part and the top cover is mainly achieved using a short or long fiber-reinforced injection molded rib structure material, intended to stiffen and join the overall system. The force introduction points of the assembled component consist of two aluminum inserts integrated into the injection molded structure by form closure and additionally stabilizes the upper organo sheet to guarantee maximum strength and stiffness of the organo sheet layers and the force transmission into the overall component structure.
Fig. 2. Composite component made of organo sheets, injection molded rib structure and metal inserts with the critical bonding regions.
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For manufacturing the continuous fiber-reinforced sandwich structure with metallic inserts numerous properties of the complete process chain have to be evaluated, since the bonding strength between the organo sheet bottom layer and the injection molded rib structure can be selectively influenced by the design or extending the connecting surface of the injected rib foot geometry. For this reason, the limiting factor of the bonding strength is the connection between the upper surface of the rib top and the organo sheet top layer. Therefore, the investigation of the bonding strength in the critical area is one of the most important parameters for the highly rigid assembled composite structure [5]. 3. Investigation of the bonding strength as a function of process parameters: temperature, pressure and geometry A test piece was assembled to investigate the bonding strength of the critical region to obtain more information for the manufacturing of the assembled composite component. Fig. 3 shows the joining process of a test piece. In the first step the organo sheet and the molded rib are heated and melted by infrared emitters (a). By applying the top organo sheet the melted areas are reduced to a minimum (b). During the 3rd step of the joining process the force provides a consistent distributed pressure in the area between the organo sheet and the rib structure (c, red). In the melted areas of the organo sheet which are not in contact with the rib structure a consistent reconsolidation cannot be ensured (c, yellow).
Fig. 3. Joining process of a test piece for investigating the bonding strength.
In order to investigate the bonding strength between the organo sheet and the short fiber-reinforced rib structure, a special test specimen was developed. The test specimen was designed based on the actual application conditions and should serve to determine the maximum achievable bonding strength of the assembled composite. The test specimen consists of an injection molded rib structure reinforced with short glass fibers and a continuous fiberreinforced plastic with a matrix of PA6. The construction, the dimensions of the test specimen and the joining region are shown in Fig. 4. The investigation of the bonding strength was performed with a head pull test (marked in red). The organo sheet (top layer of the realized composite component) was fixed and the tensile force was applied on the rib structure.
Fig. 4. Specimen for testing bonding strength and material structure.
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In order to analyze the fiber displacement and the reconsolidation of the melted area of the organo sheet a specimen was cut and prepared. Fig. 5 presents the thickness profile and the fiber displacement in the joining region due to different bonding pressures. The raw material of the organo sheets measures an average thickness of 2.05 mm to 2.15 mm. With one-sided heating of the organo sheet the raw material lofted nearly 10 percent because of the fiber undulation of the fabric to its initial state. It is clearly recognizable that different joining pressures between the rib structure and the organo sheet lead to different depressions of the fibers at the organo sheets. Simultaneously, the areas without constant pressure around the rib structure stay at the lofted thickness and the thickness at the area of the rib structure with constant pressure is compressed. At the edge of the rib, the thickness achieved the initial state of the organo sheet. With a bonding pressure of 0.5 MPa, a fiber displacement of approx. 0.1 mm occurs in the top layer of the organo sheet. The following single fiber layers remain nearly in the initial state. In the area of the weld bead, increased voids formation is observed with air inclusions. At higher bonding pressures, a higher depression is formed in the transition region from the rib to the weld bead (Fig. 5).
Fig. 5. Thickness profiles of different bonding pressures and a cross section of the bonded the organo sheet (pressure 2.5 MPa).
In further sets of experiments, the tensile strength and bending strength were investigated for one side melted organo sheets with the result that an acceptable loss of strength (approx. 5 to 10 percent) was found in the tensile and bending strength. The conclusion is that organo sheets with continuous fiber reinforcement can be used after one-sided melting in specific areas without significant loss of properties. The tensile modulus decreased by 5 percent while the bending modulus increased even by 5 percent, which can be explained by the higher stiffness due the increase of the organo sheet thickness. The macroscopic view of the fracture surface is generated using a cut out of the joining sample from the tested specimen. The examined sample of the rib was joined at a bonding pressure of 1.5 MPa. At the fracture surface of the organo sheet a complete outbreak of the matrix material is recognized. Around the fracture surface a weld bead can be observed corresponding to the dimensions of the rib. At the base of the fracture the 0°/90° oriented fibers of the first single layer are clearly visible. Clear traces of free glass fiber filaments and matrix material of the organo sheet are shown around the fracture surface of the rib structure. This indicates a high bonding strength of the joining area than the cohesive fiber matrix connection of the organo sheet and is also an indicator for an optimal joining result of the assembled structure.
Fig. 6. Fracture surface of the rib and the deformed organo sheet.
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4. Results of the bonding strength 4.1. Influence of the heating power and the heating time In the first test series, the infrared heating power of the radiators and the heating time were varied to examine their influence on the bonding strength (Fig. 7). Two different power levels were selected for the joining process of the specimen. Heating times of 40 s and 50 s for a heating power of 180 W and heating times of 15 s and 20 s for a heating power of 360 W were used to investigate the influence of different joining temperatures and joining times. The initial value of 1.5 MPa for the joining pressure was selected based on preliminary tests for the joining pressures with heating elements. The temperatures for the joining process achieved 280 °C for the organo sheet and 250 °C for the rib structure. The influence of the heating power and the heating time to the bonding strength are shown in Fig. 7. The material combinations for the joining process were a fabric-reinforced organo sheet and a short fiber-reinforced injection molded material with a glass fiber content of 30 %, both with a PA6 matrix.
Fig. 7. Bonding strength as a function of heating power and heating time.
Test number 3 reached a maximum bonding strength of 28.3 MPa with a heating time of 20 s and a heating power of 360 W. With a higher heating power and a shorter heating time a primary heating of the organo-sheet surface takes place and the basic strength of the organo sheet remains largely intact. The usage of a longer heating time with the same or less heating power leads to material degradation or poorer bonding results [6]. The temperature measurements show that the lower heating power causes a change in the state of consolidation and the associated basic strength of the organo sheet. 4.2. Influence of the bonding pressure and the fiber orientation In the second test series, the bonding pressure and the fiber orientation are varied to evaluate the influence on the bonding strength between the rib structure and the organo sheet (Fig. 8). The constant parameters are the heating power (360 W), the heating time (20 s) and the heating distances. In this case, bonding pressures of 1.5 MPa ±1 MPa are set with the modification of additional weights. The aim is to record the right bonding pressure to achieve maximum bonding strength. Furthermore, the influence of the fiber orientation of the organo sheet is investigated with regard to the bonding strength. At a bonding pressure of 1.5 MPa, the organo sheets are compared with a fiber orientation of 0°/90° and ±45°. The maximum bonding strength is achieved in test number 5 at a bonding pressure of 0.5 MPa. The comparison of organo sheets with a fiber orientation of 0°/90° and ±45° takes place in tests number 6 and 7. The assumption that a fiber orientation of ±45° would lead to a higher bonding strength because of the increased fiber crossover points in the joining area cannot be confirmed. With a fiber orientation of 0°/90° there is the possibility that the rib structure is applied directly on a fiber bundle of the organo sheet, between two fiber
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bundles or a mixed form of both. If the bonding pressures are too high, a large value of the plasticized material will be forced into the weld beads. The reduced matrix value in the joining region can result in reduced adhesion of the rib material to the organo sheet.
Fig. 8. Bonding strength as a function of bonding pressure and fiber orientation.
5. Investigation of the highly rigid composite structure with fiber-reinforced thermoplastics 5.1. Joining surface and transmittable forces The joining regions are represented in Fig. 9 (red areas). The surface area of the organo sheet which is in contact with the rib top is approx. 6200 mm². So, it is possible to create a sufficiently strong connection between the molded rib structure and the organo sheet top cover.
Fig. 9. Joining regions for the top cover and the molded rib structure of the assembled composite component.
Based on the test results in chapter 4 and a little safety factor a bonding strength of 20 MPa is suitable to generate highly rigid bonded composite components with continuous fiber-reinforced thermoplastics. Therefore, the bonding strength can resist a maximum force of 124 kN.
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5.2. Structural mechanical simulation The forces for generating the loading conditions are introduced into the component at the inserts (Fig. 10 P1, P2). The total deformation of the assembled composite component should not exceed 1 mm. The topology was optimized for the available design space and the boundary conditions. A thickness of 2 mm for the bottom and top organo sheet layer is sufficient to not exceed the required deformation. Based on the optimized topology, the alignment of the rib structure and geometry were derived and verified as a follow-up step. In the calculation, the maximum strength values for the bottom and top layers with continuous fiber reinforcement were not exceeded, so that partial breakdowns of the highly rigid assembled composite structure are not expected [2, 7].
Fig. 10. Component deformations for the loading conditions.
5.3. The bonding process of the assembled composite structure The new manufacturing technique is implemented to its best advantage on a rotating worktable with a press and an injection molding unit. The rotating worktable makes it possible to integrate four manufacturing stations into one unit. In addition to the rotating worktable, a preheating unit and a robot are used for joining and for removing the assembled composite structure (Fig. 11) [7].
Fig. 11. Complete process chain with rotating worktable for manufacturing of the highly rigid composite structure.
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The blank of the top layer is pre-formed in an external device and fed into the process by a robot handling system in the 4th station. Afterwards, both the surface of the top organo sheet layer and the fiber-reinforced rib structure are heated and joined together, see [1]. 6. Conclusion Within the scope of the described research project, the authors investigated the technological parameters and the bonding strength for joining short fiber-reinforced rib structures manufactured in an injection molding process and continuous fiber-reinforced thermoplastics of woven fabrics (organo sheets) to develop highly rigid assembled composite structures for industrial scale manufacturing. IR radiators were used for the joining process. The corresponding heating powers, heating times and joining pressures were determined in order to be able to produce corresponding composite components in a short time. The organo sheet was only melted on one side of the surface to ensure that its formed structure remains stable and to achieve a good bonding strength to the injection molded structure. In the case of a subsequent joining process the non-reconsolidated areas of the organo sheet lead to no significant loss of strength. The optimum bonding pressure should not be too high, otherwise the entire melted matrix material will be pressed out of the joining area and the bonding strength will be reduced. The resulting weld bead contributes to increasing the strength under shear loading. It is possible to install four bottom tool molds on the rotating worktable at the same time to further raise the productivity. With the investigations of the critical bonded region and the findings of optimized process parameters, the cycle time for the production of the assembled composite part could be reduced to less than one minute. Acknowledgements The work was performed within the Federal Cluster of Excellence EXC 1075 “MERGE Technologies for Multifunctional Lightweight Structures”, supported by the German Research Foundation (DFG). Financial support is gratefully acknowledged. References [1] Täger, O., Ehleben, M., Lohmann, J., Kharchi, K., Schweizer, K., Kroll, L., Meyer, M., Nendel, W., New Fibre-Reinforced Thermoplastic Metal Hybrids, ITHEC 2014, Bremen, 2104, ISBN 978-3-933339-25-6. [2] Meyer, M., Kroll, L., Täger, O., Ehleben, M., Kharchi, K., Lohmann, J., Schweizer, K., Carbon Fiber-Reinforced Thermoplastic Hybrid Composites – New Material Concepts and Process-Technologies for a Lightweight Battery Carrier; SEICO 14 – 35th International Conference and Forum, Paris 2014; Event ID 20544 AF. [3] Tröltzsch, J., Helbig, F., Kroll, L., Mechanical properties of polymer melt-impregnated fiber tape sandwiches using injection molding technology, Journal of Thermoplastic Composite Materials 2016, 29(8), pp. 1033-1046. [4] Schäfer, K., Anders, S., Valentin, S., Helbig, F., Tröltzsch, J., Roth-Panke, I., Nestler, D., Kroll, L., Investigation of the specific adhesion between polyurethane foams and thermoplastics to suited material selection in lightweight structures, Journal of Elastomers and Plastics 2018, article in press. [5] Nezhad, H., Zhao, Y., Liddel, P., Marchante, V., Roy, R., A Novel Process-linked Assembly Failure Model for Adhesively Bonded Composite Structures, CIRP, A, 66/1/2017, P.29. [6] Cetin, M., Herrmann, C., Schirl, S., Hochdynamisches und homogenes Aufheizen von Organoblechen, lightweight-design, 6/2017, pp. 54-60. [7] Kroll, L., Brands, D., Brymerski, W., Haanappel, S., Meyer, M., Nendel, W., FRP component design using forming simulations, JEC Composites Magazine 2017, 54 (115), pp. 61-65.
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Procedia Manufacturing 33 (2019) 224–231 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
16th Global Conference on Sustainable Manufacturing - Sustainable Manufacturing for Global Circular Economy 16th Global Conference on Sustainable Manufacturing - Sustainable Manufacturing for Global Circular Economy
Highly Rigid Assembled Composite Structures with Continuous Highly Rigid Assembled Composite Structures with Continuous Fiber-Reinforced Thermoplastics for Automotive Applications Manufacturing EngineeringThermoplastics Society International Conference 2017, MESIC 2017, 28-30 June Fiber-Reinforced for Automotive Applications 2017, Vigo (Pontevedra), Spain Kroll, L.a,b, Meyer, M.a,c*, Nendel, W.a, Schormair, M.a Kroll, L.a,b, Meyer, M.a,c*, Nendel, W.a, Schormair, M.a
Chemnitz University of Technology, of Lightweight Structures and Polymer (SLK), Reichenhainer Str. 31-33, Costing models for Department capacity optimization in Technology Industry 4.0: Trade-off D-09126 Chemnitz, Germany Chemnitz University of Technology, Department of Lightweight Structures and Polymer Technology (SLK), Reichenhainer Str. 31-33, Opole University of Technology, Department of D-09126 Mechanics and Machine Design, ul. S. Mikolajczyka 5, 45-271 Opole, Poland Chemnitz, Germany between used capacity and operational efficiency Cetex Institut für Textil- und Verarbeitungsmaschinen gemeinnützige GmbH an der Technischen Universität Chemnitz, Altchemnitzer Str. 11, a a
b
c c
Opole University of Technology, Department of Mechanics and Machine Design, ul. S. Mikolajczyka 5, 45-271 Opole, Poland D-09120 Chemnitz, Cetex Institut für Textil- und Verarbeitungsmaschinen gemeinnützige GmbHGermany an der Technischen Universität Chemnitz, Altchemnitzer Str. 11, a a,* b b D-09120 Chemnitz, Germany b
A. Santana , P. Afonso , A. Zanin , R. Wernke
University of Minho, 4800-058 Guimarães, Portugal Abstract b Unochapecó, 89809-000 Chapecó, SC, Brazil Abstract Future technological and product developments will be measured by their improved resource and energy efficiency, as well as their competitiveness, while allowing effective climate environmental processes that areascurrently Future technological and product developments will beand measured by theirprotection. improved Manufacturing resource and energy efficiency, well as discrete for different while groupsallowing of materials such as metals, plastics or protection. textiles have to be merged to generate their competitiveness, effective climate and environmental Manufacturing processes that arelarge-scale currently Abstract technologies the sustainable production high-performance structures automotive applications. discrete for for different groups of materialsofsuch as metals, plastics or for textiles have to be merged to generate large-scale Fiber-reinforced plastics have production been established in manufacturing components of high strength, stiffness and lightweight technologies for the sustainable of high-performance structures for automotive applications. Under theWell-known concept ofexamples "Industry 4.0", production processes willof be pushed to fiber-reinforced be increasingly interconnected, structures. are sandwich composites: an assembly two continuous thermoplastic layers Fiber-reinforced plastics have been established in manufacturing components of high strength, stiffness and lightweight information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization and an intermediate injection molded core structure. The vision is to make the savings potential of technology fusion and structures. Well-known examples are sandwich composites: an assembly ofuse twoofcontinuous fiber-reinforced thermoplastic layers goes the traditional aim maximization, forsavings organization’s and value. lightweight structures pursuant to of thecapacity central idea ofThe resource-efficient technologies multi-material and anbeyond intermediate injection molded core structure. vision contributing is to makemanufacturing usealso of the potentialtoprofitability ofproduce technology fusion and Indeed, lean management continuous approaches suggest technologies capacity optimization instead of components. lightweight structures pursuantand to the central ideaimprovement of resource-efficient manufacturing to produce multi-material maximization. The study of capacity optimization and costing models is an important research topic that deserves components. © 2018 The Authors. Published by Elsevier contributions from both the practical andLtd. theoretical perspectives. This paper presents and discusses a mathematical © 2018 2019 The Authors. Published by Elsevier B.V. This is an open accessmanagement article under the CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) © The Authors. Published by Elsevier Ltd.differentlicense model for capacity based on costing models (ABC and TDABC). A generic model has been This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of design the 16thstrategies Global Conference the on Sustainable Manufacturing This is an open access article under CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) developed and it was used to analyze idle capacity and to maximization of organization’s Selection and peer-review under responsibility of the scientific committee oftowards the 16th Global Conference on Sustainable (GCSM) Peer-review responsibility the scientific committee of the 16th Global Conference on Sustainable Manufacturing value. The under trade-off capacity ofmaximization vs operational efficiency is highlighted and it is shown that capacity Manufacturing (GCSM). (GCSM) optimization might hide operational inefficiency. a
Keywords: Resource and Energy Efficiency, Lightweight Structures, Fiber-reinforced plastics, Multi-material components
© 2017 The Authors. Published by Elsevier B.V. Keywords: Resource and Energy Efficiency, Lightweight Structures, Fiber-reinforced plastics, Multi-material components Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
1. Introduction
* Corresponding author. Tel.: +49 371 531-36774; fax: +49 371 531-8 36774. E-mail address: [email protected] * The Corresponding author. Tel.: +49 531-36774; fax: +49 371 531-8 36774. cost of idle capacity is371 a fundamental information for companies and their management of extreme importance E-mail address: [email protected] in modern production systems. In general, it is defined as unused capacity or production potential and can be measured 2351-9789 © 2018 The Authors. Published by Elsevier Ltd. in several ways: tons ofunder production, available hours of manufacturing, etc. The management of the idle capacity This is an open access the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 2351-9789 © 2018 Thearticle Authors. Published by Elsevier Ltd. * Paulo Afonso. Tel.: +351 253 510 761; fax: +351 253 604 Peer-review under responsibility of the scientific committee of741 the 16th Global Conference on Sustainable Manufacturing (GCSM) This is an open access article under CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) E-mail address: [email protected] Peer-review under responsibility of the scientific committee of the 16th Global Conference on Sustainable Manufacturing (GCSM) 2351-9789 Published by Elsevier B.V. B.V. 2351-9789 ©©2017 2019The TheAuthors. Authors. Published by Elsevier Peer-review underaccess responsibility of the scientific committee oflicense the Manufacturing Engineering Society International Conference 2017. This is an open article under the CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 16th Global Conference on Sustainable Manufacturing (GCSM). 10.1016/j.promfg.2019.04.027
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1. Introduction One of the most important challenges facing the automotive industry lies in stringent environmental protection requirements and their associated emission laws, which are mainly focused on reducing CO 2 emissions. The design and integration of battery packages into the lightweight structure of automotive applications requires new approaches. An assembled new composite battery carrier was designed, and its manufacturing process developed to show lightweight and technological potentials of continuous fiber-reinforced thermoplastics (FRP) of woven fabrics in the form of so-called organo sheets [1]. For achieving the optimal economic lightweight potential, it is absolutely necessary to develop highly rigid sandwich parts with two continuous fiber-reinforced thermoplastics layers to replace relevant load-bearing parts in automotive applications [2, 3, 4]. In order to achieve these aims, it is possible to join the structure of one formed organo sheet bottom layer in combination with an injection molded or pressed rib structure to a second organo sheet top layer by a joining process (Fig. 1). In terms of reaching mass production and process reliability it is the advantage of thermoplastic FRP´s as opposed to thermoset FRPs which can only be joined by gluing. Therefore, the bonding strength of the joining process of the organo sheet and the injection molded rib structure plays a decisive role for the final part and the application conditions.
Fig. 1. Assembled thermoplastic battery carrier with continuous fiber reinforcement and its components.
2. Assembling of the organo sheets and the injection molded rib structure The assembled composite part, reinforced by continuous fibers (glass or carbon fibers), is subdivided into several functional areas for a better and more efficient manufacturing (Fig. 2). The assembly consists of a bottom and a top organo sheet. The connection between the bottom part and the top cover is mainly achieved using a short or long fiber-reinforced injection molded rib structure material, intended to stiffen and join the overall system. The force introduction points of the assembled component consist of two aluminum inserts integrated into the injection molded structure by form closure and additionally stabilizes the upper organo sheet to guarantee maximum strength and stiffness of the organo sheet layers and the force transmission into the overall component structure.
Fig. 2. Composite component made of organo sheets, injection molded rib structure and metal inserts with the critical bonding regions.
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For manufacturing the continuous fiber-reinforced sandwich structure with metallic inserts numerous properties of the complete process chain have to be evaluated, since the bonding strength between the organo sheet bottom layer and the injection molded rib structure can be selectively influenced by the design or extending the connecting surface of the injected rib foot geometry. For this reason, the limiting factor of the bonding strength is the connection between the upper surface of the rib top and the organo sheet top layer. Therefore, the investigation of the bonding strength in the critical area is one of the most important parameters for the highly rigid assembled composite structure [5]. 3. Investigation of the bonding strength as a function of process parameters: temperature, pressure and geometry A test piece was assembled to investigate the bonding strength of the critical region to obtain more information for the manufacturing of the assembled composite component. Fig. 3 shows the joining process of a test piece. In the first step the organo sheet and the molded rib are heated and melted by infrared emitters (a). By applying the top organo sheet the melted areas are reduced to a minimum (b). During the 3rd step of the joining process the force provides a consistent distributed pressure in the area between the organo sheet and the rib structure (c, red). In the melted areas of the organo sheet which are not in contact with the rib structure a consistent reconsolidation cannot be ensured (c, yellow).
Fig. 3. Joining process of a test piece for investigating the bonding strength.
In order to investigate the bonding strength between the organo sheet and the short fiber-reinforced rib structure, a special test specimen was developed. The test specimen was designed based on the actual application conditions and should serve to determine the maximum achievable bonding strength of the assembled composite. The test specimen consists of an injection molded rib structure reinforced with short glass fibers and a continuous fiberreinforced plastic with a matrix of PA6. The construction, the dimensions of the test specimen and the joining region are shown in Fig. 4. The investigation of the bonding strength was performed with a head pull test (marked in red). The organo sheet (top layer of the realized composite component) was fixed and the tensile force was applied on the rib structure.
Fig. 4. Specimen for testing bonding strength and material structure.
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In order to analyze the fiber displacement and the reconsolidation of the melted area of the organo sheet a specimen was cut and prepared. Fig. 5 presents the thickness profile and the fiber displacement in the joining region due to different bonding pressures. The raw material of the organo sheets measures an average thickness of 2.05 mm to 2.15 mm. With one-sided heating of the organo sheet the raw material lofted nearly 10 percent because of the fiber undulation of the fabric to its initial state. It is clearly recognizable that different joining pressures between the rib structure and the organo sheet lead to different depressions of the fibers at the organo sheets. Simultaneously, the areas without constant pressure around the rib structure stay at the lofted thickness and the thickness at the area of the rib structure with constant pressure is compressed. At the edge of the rib, the thickness achieved the initial state of the organo sheet. With a bonding pressure of 0.5 MPa, a fiber displacement of approx. 0.1 mm occurs in the top layer of the organo sheet. The following single fiber layers remain nearly in the initial state. In the area of the weld bead, increased voids formation is observed with air inclusions. At higher bonding pressures, a higher depression is formed in the transition region from the rib to the weld bead (Fig. 5).
Fig. 5. Thickness profiles of different bonding pressures and a cross section of the bonded the organo sheet (pressure 2.5 MPa).
In further sets of experiments, the tensile strength and bending strength were investigated for one side melted organo sheets with the result that an acceptable loss of strength (approx. 5 to 10 percent) was found in the tensile and bending strength. The conclusion is that organo sheets with continuous fiber reinforcement can be used after one-sided melting in specific areas without significant loss of properties. The tensile modulus decreased by 5 percent while the bending modulus increased even by 5 percent, which can be explained by the higher stiffness due the increase of the organo sheet thickness. The macroscopic view of the fracture surface is generated using a cut out of the joining sample from the tested specimen. The examined sample of the rib was joined at a bonding pressure of 1.5 MPa. At the fracture surface of the organo sheet a complete outbreak of the matrix material is recognized. Around the fracture surface a weld bead can be observed corresponding to the dimensions of the rib. At the base of the fracture the 0°/90° oriented fibers of the first single layer are clearly visible. Clear traces of free glass fiber filaments and matrix material of the organo sheet are shown around the fracture surface of the rib structure. This indicates a high bonding strength of the joining area than the cohesive fiber matrix connection of the organo sheet and is also an indicator for an optimal joining result of the assembled structure.
Fig. 6. Fracture surface of the rib and the deformed organo sheet.
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4. Results of the bonding strength 4.1. Influence of the heating power and the heating time In the first test series, the infrared heating power of the radiators and the heating time were varied to examine their influence on the bonding strength (Fig. 7). Two different power levels were selected for the joining process of the specimen. Heating times of 40 s and 50 s for a heating power of 180 W and heating times of 15 s and 20 s for a heating power of 360 W were used to investigate the influence of different joining temperatures and joining times. The initial value of 1.5 MPa for the joining pressure was selected based on preliminary tests for the joining pressures with heating elements. The temperatures for the joining process achieved 280 °C for the organo sheet and 250 °C for the rib structure. The influence of the heating power and the heating time to the bonding strength are shown in Fig. 7. The material combinations for the joining process were a fabric-reinforced organo sheet and a short fiber-reinforced injection molded material with a glass fiber content of 30 %, both with a PA6 matrix.
Fig. 7. Bonding strength as a function of heating power and heating time.
Test number 3 reached a maximum bonding strength of 28.3 MPa with a heating time of 20 s and a heating power of 360 W. With a higher heating power and a shorter heating time a primary heating of the organo-sheet surface takes place and the basic strength of the organo sheet remains largely intact. The usage of a longer heating time with the same or less heating power leads to material degradation or poorer bonding results [6]. The temperature measurements show that the lower heating power causes a change in the state of consolidation and the associated basic strength of the organo sheet. 4.2. Influence of the bonding pressure and the fiber orientation In the second test series, the bonding pressure and the fiber orientation are varied to evaluate the influence on the bonding strength between the rib structure and the organo sheet (Fig. 8). The constant parameters are the heating power (360 W), the heating time (20 s) and the heating distances. In this case, bonding pressures of 1.5 MPa ±1 MPa are set with the modification of additional weights. The aim is to record the right bonding pressure to achieve maximum bonding strength. Furthermore, the influence of the fiber orientation of the organo sheet is investigated with regard to the bonding strength. At a bonding pressure of 1.5 MPa, the organo sheets are compared with a fiber orientation of 0°/90° and ±45°. The maximum bonding strength is achieved in test number 5 at a bonding pressure of 0.5 MPa. The comparison of organo sheets with a fiber orientation of 0°/90° and ±45° takes place in tests number 6 and 7. The assumption that a fiber orientation of ±45° would lead to a higher bonding strength because of the increased fiber crossover points in the joining area cannot be confirmed. With a fiber orientation of 0°/90° there is the possibility that the rib structure is applied directly on a fiber bundle of the organo sheet, between two fiber
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bundles or a mixed form of both. If the bonding pressures are too high, a large value of the plasticized material will be forced into the weld beads. The reduced matrix value in the joining region can result in reduced adhesion of the rib material to the organo sheet.
Fig. 8. Bonding strength as a function of bonding pressure and fiber orientation.
5. Investigation of the highly rigid composite structure with fiber-reinforced thermoplastics 5.1. Joining surface and transmittable forces The joining regions are represented in Fig. 9 (red areas). The surface area of the organo sheet which is in contact with the rib top is approx. 6200 mm². So, it is possible to create a sufficiently strong connection between the molded rib structure and the organo sheet top cover.
Fig. 9. Joining regions for the top cover and the molded rib structure of the assembled composite component.
Based on the test results in chapter 4 and a little safety factor a bonding strength of 20 MPa is suitable to generate highly rigid bonded composite components with continuous fiber-reinforced thermoplastics. Therefore, the bonding strength can resist a maximum force of 124 kN.
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5.2. Structural mechanical simulation The forces for generating the loading conditions are introduced into the component at the inserts (Fig. 10 P1, P2). The total deformation of the assembled composite component should not exceed 1 mm. The topology was optimized for the available design space and the boundary conditions. A thickness of 2 mm for the bottom and top organo sheet layer is sufficient to not exceed the required deformation. Based on the optimized topology, the alignment of the rib structure and geometry were derived and verified as a follow-up step. In the calculation, the maximum strength values for the bottom and top layers with continuous fiber reinforcement were not exceeded, so that partial breakdowns of the highly rigid assembled composite structure are not expected [2, 7].
Fig. 10. Component deformations for the loading conditions.
5.3. The bonding process of the assembled composite structure The new manufacturing technique is implemented to its best advantage on a rotating worktable with a press and an injection molding unit. The rotating worktable makes it possible to integrate four manufacturing stations into one unit. In addition to the rotating worktable, a preheating unit and a robot are used for joining and for removing the assembled composite structure (Fig. 11) [7].
Fig. 11. Complete process chain with rotating worktable for manufacturing of the highly rigid composite structure.
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The blank of the top layer is pre-formed in an external device and fed into the process by a robot handling system in the 4th station. Afterwards, both the surface of the top organo sheet layer and the fiber-reinforced rib structure are heated and joined together, see [1]. 6. Conclusion Within the scope of the described research project, the authors investigated the technological parameters and the bonding strength for joining short fiber-reinforced rib structures manufactured in an injection molding process and continuous fiber-reinforced thermoplastics of woven fabrics (organo sheets) to develop highly rigid assembled composite structures for industrial scale manufacturing. IR radiators were used for the joining process. The corresponding heating powers, heating times and joining pressures were determined in order to be able to produce corresponding composite components in a short time. The organo sheet was only melted on one side of the surface to ensure that its formed structure remains stable and to achieve a good bonding strength to the injection molded structure. In the case of a subsequent joining process the non-reconsolidated areas of the organo sheet lead to no significant loss of strength. The optimum bonding pressure should not be too high, otherwise the entire melted matrix material will be pressed out of the joining area and the bonding strength will be reduced. The resulting weld bead contributes to increasing the strength under shear loading. It is possible to install four bottom tool molds on the rotating worktable at the same time to further raise the productivity. With the investigations of the critical bonded region and the findings of optimized process parameters, the cycle time for the production of the assembled composite part could be reduced to less than one minute. Acknowledgements The work was performed within the Federal Cluster of Excellence EXC 1075 “MERGE Technologies for Multifunctional Lightweight Structures”, supported by the German Research Foundation (DFG). Financial support is gratefully acknowledged. References [1] Täger, O., Ehleben, M., Lohmann, J., Kharchi, K., Schweizer, K., Kroll, L., Meyer, M., Nendel, W., New Fibre-Reinforced Thermoplastic Metal Hybrids, ITHEC 2014, Bremen, 2104, ISBN 978-3-933339-25-6. [2] Meyer, M., Kroll, L., Täger, O., Ehleben, M., Kharchi, K., Lohmann, J., Schweizer, K., Carbon Fiber-Reinforced Thermoplastic Hybrid Composites – New Material Concepts and Process-Technologies for a Lightweight Battery Carrier; SEICO 14 – 35th International Conference and Forum, Paris 2014; Event ID 20544 AF. [3] Tröltzsch, J., Helbig, F., Kroll, L., Mechanical properties of polymer melt-impregnated fiber tape sandwiches using injection molding technology, Journal of Thermoplastic Composite Materials 2016, 29(8), pp. 1033-1046. [4] Schäfer, K., Anders, S., Valentin, S., Helbig, F., Tröltzsch, J., Roth-Panke, I., Nestler, D., Kroll, L., Investigation of the specific adhesion between polyurethane foams and thermoplastics to suited material selection in lightweight structures, Journal of Elastomers and Plastics 2018, article in press. [5] Nezhad, H., Zhao, Y., Liddel, P., Marchante, V., Roy, R., A Novel Process-linked Assembly Failure Model for Adhesively Bonded Composite Structures, CIRP, A, 66/1/2017, P.29. [6] Cetin, M., Herrmann, C., Schirl, S., Hochdynamisches und homogenes Aufheizen von Organoblechen, lightweight-design, 6/2017, pp. 54-60. [7] Kroll, L., Brands, D., Brymerski, W., Haanappel, S., Meyer, M., Nendel, W., FRP component design using forming simulations, JEC Composites Magazine 2017, 54 (115), pp. 61-65.