Publications Search Results

Now showing 1 - 10 of 31
  • Publication
    Efficient Spot Welding Sequence Simulation in Compliant Variation Simulation
    ( 2021)
    Tabar, R.S.
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    Lorin, S.
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    Cromvik, C.
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    Lindkvist, L.
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    Wärmefjord, K.
    ;
    Söderberg, R.
    Geometrical variation is one of the sources of quality issues in a product. Spot welding is an operation that impacts the final geometrical variation of a sheet metal assembly considerably. Evaluating the outcome of the assembly, considering the existing geometrical variation between the components, can be achieved using the method of influence coefficients (MICs), based on the finite element method (FEM). The sequence with which the spot welding operation is performed influences the final geometrical deformations of the assembly. Finding the optimal sequence that results in the minimum geometrical deformation is a combinatorial problem that is experimentally and computationally expensive. Traditionally, spot welding sequence optimization strategies have been to simulate the geometrical variation of the spot-welded assembly after the assembly has been positioned in an inspection fixture. In this approach, the calculation of deformation after springback is one of the most time-consuming steps. In this paper, a method is proposed where the springback calculation in the inspection fixture is bypassed during the sequence evaluation. The results show a significant correlation between the proposed method of weld relative displacements evaluation in the assembly fixture and the assembly deformation in the inspection fixture. Evaluating the relative weld displacement makes each assembly simulation less time-consuming, and thereby, sequence optimization time can be reduced by up to 30%, compared to the traditional approach.
  • Publication
    Efficient spot welding sequence simulation in compliant variation simulation
    ( 2020)
    Tabar, R.S.
    ;
    Lorin, S.
    ;
    Cromvik, C.
    ;
    Lindkvist, L.
    ;
    Wärmefjord, K.
    ;
    Söderberg, R.
    Geometric variation is one of the sources of quality issues in a product. Spot welding is an operation that impacts the final geometric variation of a sheet metal assembly considerably. Evaluating the outcome of the assembly, considering the existing geometrical variation between the components can be achieved using the Method of Influence Coefficients (MIC), based on the Finite Element Method (FEM). The sequence, with which the spot welding operation is performed, influences the final geometric deformations of the assembly. Finding the optimal sequence that results in the minimum geometric deformation is a combinatorial problem that is experimentally and computationally expensive. For an assembly with N number of welds, there are N! possible sequences to perform the spot welding operation. Traditionally, spot welding optimization strategies have been to simulate the geometric variation of the spot-welded assembly after the assembly has been positioned in an inspection fixture, using an appropriate measure of variation. In this approach, the calculation of deformation after springback is one of the most time-consuming steps. In this paper, the cause of variation in the deformations after the springback, between different sequences is identified. The relative displacements of the weld points in the assembly fixture, when welded in a sequence, is the source of such behavior. Capturing these displacements leads to large time savings during sequence optimization. Moreover, this approach is independent of the inspection fixture. The relative weld displacements have been evaluated on two sheet metal assemblies. The sequence optimization problem has been solved for the two assemblies using this approach. The optimal sequence, the corresponding final assembly deformations, and the time-consumption have been compared to the traditional approach.
  • Publication
    Efficient Compliant Variation Simulation of Spot-Welded Assemblies
    ( 2019)
    Lorin, S.
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    Lindau, B.
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    Lindkvist, L.
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    Söderberg, R.
    During product development one important aspect is the geometric robustness of the design. This is due to the fact that all manufacturing processes lead to products with variation. Failing to properly account for the variability of the process in the design phase may lead to expensive redesign. One important tool during the design phase in many industries is variation simulation, which makes it possible to predict and optimize the geometric quality of the design. However, despite the increase in computer power, calculation time is still an obstacle for the wider use of variation simulation. In this article, we propose a new method for efficient compliant variation simulation of spot-welded sheet metal assemblies. The method is exact, and we show that the method leads to time savings in simulation of approximately 40-50% compared to current state-of-the-art variation simulation.
  • Publication
    Efficient Variation Simulation of Spot-Welded Assemblies
    ( 2019)
    Lorin, S.
    ;
    Lindau, B.
    ;
    Tabar, R.S.
    ;
    Lindkvist, L.
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    Warmefjord, K.
    ;
    Soderberg, R.
    Variation simulation for assembled products is one important activity during product development. Variation simulation enables the designer to understand not only the features of the nominal product but also how uncertainty will affect production, functions and the aesthetic properties of the final product. For parts that are able to deform during assembly, compliant variation simulation is needed for accurate prediction. For this the Finite Element Method (FEM) is used. Despite many effective efforts to decrease simulation times for compliant variation simulation, simulation time is still considered an obstacle for full scale industrial use. In this paper, a new formulation for compliant variation simulation of assemblies that are joined in sequential spot-welding will be presented. In this formulation the deformation in the intermediate springback steps during the simulation of a spot-weld sequence do not have to be calculated. This is one of the most time consuming steps in sequential spot-welding simulation. Furthermore, avoiding the intermediate springback calculation will reduce the size of memory of the computer models since the number of sensitivity matrices is reduced. The formulation is implemented using the latest developments in compliant variation simulation, that is the Method of Influence Coefficients (MIC) where the Sherman-Morrison-Woodbury-formula is used to update the resulting sensitivity matrices and the contact and weld forces are solved using a Quadratic Programme (QP). Industrial cases are used to demonstrate the reduced simulation time. It is believed that the reduction in simulation times will have future implications on sequence optimization for spotwelded assemblies.
  • Publication
    An information and simulation framework for increased quality in welded components
    ( 2018)
    Söderberg, R.
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    Wärmefjord, K.
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    Madrid, J.
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    Lorin, S.
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    Forslund, A.
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    Lindkvist, L.
    The recent trend toward using simulation models with real-time data as digital twins is rapidly increasing in industry. In this paper, a digital framework supporting real-time geometrical quality control of welded components, is presented. The concept is based on a structured process model for all operations included in typical welding, strategies for selective assembly, automatic adjustment of fixtures and optimization of weld sequence. The concept utilizes recently developed algorithms for fast welding simulation and in-line scanning to be used in the optimization loop of an automated welding station - a digital twin for a welding cell.
  • Publication
    Minimizing weld variation effects using permutation genetic algorithms and virtual locator trimming
    ( 2018)
    Forslund, A.
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    Lorin, S.
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    Lindkvist, L.
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    Wärmefjord, K.
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    Söderberg, R.
    The mass production paradigm strives for uniformity, and for assembly operations to be identical for each individual product. To accommodate geometric variation between individual parts, tolerances are introduced into the design. However, this method can yield suboptimal quality. In welded assemblies, geometric variation in ingoing parts can significantly impair quality. When parts misalign in interfaces, excessive clamping force must be applied, resulting in additional residual stresses in the welded assemblies. This problem may not always be cost-effective to address simply by tightening tolerances. Therefore, under new paradigm of mass customization, the manufacturing approach can be adapted on an individual level. This paper focuses on two specific mass customization techniques: permutation genetic algorithms (GA) and virtual locator trimming. Based on these techniques, a six-step method is proposed, aimed at minimizing the effects of geometric variation. The six steps are nominal reference point optimization, permutation GA configuration optimization, virtual locator trimming, clamping, welding simulation, and fatigue life evaluation. A case study is presented, which focuses on the selective assembly process of a turbine rear structure of a commercial turbofan engine, where 11 nominally identical parts are welded into a ring. Using this simulation approach, the effects of using permutation GAs and virtual locator trimming to reduce variation are evaluated. The results show that both methods significantly reduce seam variation. However, virtual locator trimming is far more effective in the test case presented, since it virtually eliminates seam variation. These results underscore the potential of virtual trimming and GAs in manufacturing, as a means both to reduce cost and increase functional quality.
  • Publication
    Non-Rigid Variation Simulation Using the Sherman-Morrison-Woodbury Formulas
    ( 2017)
    Lorin, S.
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    Lindau, B.
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    Lindkvist, L.
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    Söderberg, R.
    Variation simulation is one important activity during early product development. It is used to simulate the statistical distribution of assemblies or sub assemblies in intended manufacturing process to assure that assembly, function and aesthetical properties comply with the requirements set. In non-rigid variation simulation, components or sub assemblies can deform during assembly. To simulate non-rigid variation the Method of Influence Coefficient (MIC) is typically used. Solving the necessary sensitivity matrices used by MIC is time consuming. In this article we will apply the Sherman-Morrison and Woodbury formula (SMW) for updating the sensitivity response in the different assembly steps. It is shown that SMW can lead to substantial saving in computation time, when compared to the standard MIC.
  • Publication
    Inspection Data to Support a Digital Twin for Geometry Assurance
    ( 2017)
    Wärmefjord, K.
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    Söderberg, R.
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    Lindkvist, L.
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    Lindau, B.
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    Carlson, J.S.
    Geometrical variation is a problem in all complex, assembled products. Recently, the Digital Twin concept was launched as a tool for improving geometrical quality and reduce costs by using real time control and optimization of products and production systems. The Digital Twin for geometry assurance is created together with the product and the production systems in early design phases. When full production starts, the purpose of the Digital Twin turns towards optimization of the geometrical quality by small changes in the assembly process. To reach its full potential, the Digital Twin concept is depending on high quality input data. In line with Internet of Things and Big Data, the problem is rather to extract appropriate data than to find data. In this paper, an inspection strategy serving the Digital Twin is given. Necessary input data describing form and shape of individual parts, and how this data should be collected, stored and utilized is described.
  • Publication
    Toward a digital twin for real-time geometry assurance in individualized production
    ( 2017)
    Söderberg, R.
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    Wärmefjord, K.
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    Carlson, J.S.
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    Lindkvist, L.
    Simulations of products and production processes are extensively used in the engineering phase. To secure good geometrical quality in the final product, tolerances, locator positions, clamping strategies, welding sequence, etc. are optimized during design and pre-production. Faster optimization algorithms, increased computer power and amount of available data, can leverage the area of simulation toward real-time control and optimization of products and production systems - a concept often referred to as a Digital Twin. This paper specifies and highlights functionality and data models necessary for real-time geometry assurance and how this concept allows moving from mass production to more individualized production.
  • Publication
    Data flow and communication framework supporting digital twin for geometry assurance
    ( 2017)
    Bohlin, R.
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    Hagmar, J.
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    Bengtsson, K.
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    Lindkvist, L.
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    Carlson, J.S.
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    Söderberg, R.
    Faster optimization algorithms, increased computer power and amount of available data, can leverage the area of simulation towards real-time control and optimization of products and production systems. This concept - often referred to as Digital Twin - enables real-time geometry assurance and allows moving from mass production to more individualized production. To master the challenges of a Digital Twin for Geometry Assurance the project Smart Assembly 4.0 gathers Swedish researchers within product development, automation, virtual manufacturing, control theory, data analysis and machine learning. The vision of Smart Assembly 4.0 is the autonomous, self-optimizing robotized assembly factory, which maximizes quality and throughput, while keeping flexibility and reducing cost, by a sensing, thinking and acting strategy. The concept is based on active part matching and self-adjusting equipment which improves geometric quality without tightening the tolerances of incoming pa rts. The goal is to assemble products with higher quality than the incoming parts. The concept utilizes information about individual parts to be joined (sensing), selects the best combination of parts (thinking) and adjust locator positions, clamps, weld/rivet positions and sequences (acting). The project is ongoing, and this paper specifies and highlights the infrastructure, components and data flows necessary in the Digital Twin in order to realize Smart Assembly 4.0. The framework is generic, but the paper focuses on a spot weld station where two robots join two sheet metal parts in an adjustable fixture.