| 1. |
- Eggertsen, Per-Anders, 1981, et al.
(författare)
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A Phenomenological Model for the Hysteresis Behavior of Metal Sheets Subjected to Unloading/Reloading Cycles
- 2011
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Ingår i: Journal of Manufacturing Science and Engineering, Transactions of the ASME. - : ASME International. - 1087-1357 .- 1528-8935. ; 133:6
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Tidskriftsartikel (refereegranskat)abstract
- The springback phenomenon is defined as elastic recovery of the stresses produced during the forming of a material. An accurate prediction of the springback puts high demands on the material modeling during the forming simulation, as well as during the unloading simulation. In classic plasticity theory, the unloading of a material after plastic deformation is assumed to be linearly elastic with the stiffness equal to Young's modulus. However, several experimental investigations have revealed that this is an incorrect assumption. The unloading and reloading stress-strain curves are in fact not even linear, but slightly curved, and the secant modulus of this nonlinear curve deviates from the initial Young's modulus. More precisely, the secant modulus is degraded with increased plastic straining of the material. The main purpose of the present work has been to formulate a constitutive model that can accurately predict the unloading of a material. The new model is based on the classic elastic-plastic framework, and works together with any yield criterion and hardening evolution law. To determine the parameters of the new model, two different tests have been performed: unloading/reloading tests of uniaxially stretched specimens, and vibrometric tests of prestrained sheet strips. The performance of the model has been evaluated in simulations of the springback of simple U-bends and a drawbead example. Four different steel grades have been studied in the present investigation.
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| 2. |
- Eynian, Mahdi, 1980-, et al.
(författare)
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Analytical Chatter Stability of Milling With Rotating Cutter Dynamics at Process Damping Speeds
- 2010
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Ingår i: Journal of manufacturing science and engineering. - USA : ASME. - 1087-1357 .- 1528-8935. ; 132:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a chatter stability prediction method for milling flexible workpiece with end mills having asymmetric structural dynamics. The dynamic chip thickness regenerated by the vibrations of the rotating cutter and the fixed workpiece is transformed into the principle modal directions of the rotating tool. The process damping is modeled as a linear function of vibration velocity. The dynamics of the milling system is modeled by a time delay matrix differential equation with time varying directional factors and speed dependent elements. The periodic directional factors are averaged over a spindle period, and the stability of the resulting time invariant but speed dependent characteristic equation of the system is investigated using the Nyquist stability criterion. The stability model is verified with time domain numerical simulations and milling experiments.
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| 3. |
- Johansson, Joel, 1978-
(författare)
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How to Build Flexible Design Automation Systems for Manufacturability Analysis of the Draw Bending of Aluminum Profiles
- 2011
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Ingår i: Journal of manufacturing science and engineering. - : ASME Press. - 1087-1357 .- 1528-8935. ; 133:6
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Tidskriftsartikel (refereegranskat)abstract
- Manufacturingcompanies continually need to develop and produce products faster, cheaper,and of better quality to meet requirements from customers andinvestors. One key factor in meeting these requirements is theefficiency of the product development and the production preparation processes.Design automation is a powerful tool for increasing the efficiencyof these two processes. The benefits of automating manufacturability analyses,a part of the production preparation process, are shortened leadtime, improved product performance, and ultimately decreased cost. Further, theautomation is beneficial as it increases the ability to adaptproducts to new specifications since production preparations are done infew or in a single step. Extruded sections of aluminum(aluminum profiles) have many advantages, especially for light weight structuralmembers, and are used in many products. Many times asecondary forming process, such as bending, is required when thesematerials are used. The intention of the work presented inthis article has been to investigate how to automate theprocess of finding manufacturing limits of the rotary draw bendingof aluminum profiles with focus on the system architecture neededto make such systems flexible. Finding the forming limits ofan aluminum profile is not a trivial task. This isbecause the limits depend not only on the profile shapebut also on the layout of the tool. Hence, simulationshave to be done to evaluate different designs. A prototypesystem was developed to explore what was needed to automatesimulation of the rotary draw bending of aluminum profiles, andsubsequently, analyze the simulated production outcome with respect to wrinklingand developed length.
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| 4. |
- Segeborn, Johan, 1972, et al.
(författare)
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An Industrially Validated Method for Weld Load Balancing in Multi Station Sheet Metal Assembly Lines
- 2014
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Ingår i: Journal of Manufacturing Science and Engineering, Transactions of the ASME. - : ASME International. - 1087-1357 .- 1528-8935. ; 136:1, s. 7-
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Tidskriftsartikel (refereegranskat)abstract
- Sheet metal assembly is investment intense. Therefore, the equipment needs to be efficiently utilized. The balancing of welds has a significant influence on achievable production rate and equipment utilization. Robot line balancing is a complex problem, where each weld is to be assigned to a specific station and robot, such that line cycle time is minimized. Industrial robot line balancing has been manually conducted in computer aided engineering (CAE)-tools based on experience and trial and error rather than mathematical methods. However, recently an automatic method for robot line balancing was proposed by the authors. To reduce robot coordination cycle time losses, this method requires identical reach ability of all line stations. This limits applicability considerably since in most industrial lines, reach ability differs over the stations to further line reach ability and flexibility. Therefore, in this work we propose a novel generalized simulation-based method for automatic robot line balancing that allows any robot positioning. It reduces the need for robot coordination significantly by spatially separating the robot weld work loads. The proposed method is furthermore successfully demonstrated on automotive stud welding lines, with line cycle times lower than that of the corresponding running production programs. Moreover, algorithm central processing unit (CPU)-times are mere fractions of the lead times of existing CAE-tools.
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