NUMISHEET 2005: Proceedings of the 6th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Process
778(2005); http://dx.doi.org/10.1063/1.2011187View Description Hide Description
After a brief review of the early development of sheet forming simulation, we discuss some of the more recent work. In particular, we consider how it has developed over the years since the NUMISHEET Conferences have been held. The aim here is to give a broad overview of the development of current capabilities in simulating sheet metal forming, not to explore any specific research topic. It is hoped that this short report will help set the stage for the more detailed lectures and papers to follow in this Conference.
778(2005); http://dx.doi.org/10.1063/1.2011188View Description Hide Description
The rapid change in customer needs and industrial environment has demanded innovations in the manufacturing sector. Metal forming industries have been confronted with new challenges of innovations in products, processes, machines, materials and production systems. From the viewpoints of competitiveness of products, new paradigms are required for innovation in manufacturing, especially in net shape manufacturing. Product innovations are increasingly put under emphasis beyond manufacturing innovations based on the holistic concurrent engineering approach. The presentation covers not only the innovation methodologies, but also the innovation directions in net shape manufacturing.
Experimentally‐ and Dislocation‐Based Multi‐scale Modeling of Metal Plasticity Including Temperature and Rate Effects778(2005); http://dx.doi.org/10.1063/1.2011189View Description Hide Description
Excluding high‐temperature creep, the plastic deformation of metals occurs by the motion of dislocations that produce slip on various slip planes in various slip directions. It is thus natural to seek to develop constitutive relations for metal plasticity, based on the concept of dislocations and their kinematics and kinetics. Such an approach has been successfully used by a number of investigators over the past several decades. More recently, however, the development of the recovery Hopkinson techniques by this writer and his coworkers at UCSD’s CEAM, has provided important experimental tools to obtain reliable data on stress‐strain response of variety of metals over broad ranges of strain rates and temperatures. A wealth of information has become available to guide and verify constitutive models that are proposed to describe metal plasticity. Using such data, I have been able to create a class of dislocation‐based models that involve a few material constants, and seem to accurately characterize the response of a large number of metals over 10−4 to 105/s strain rates, and 77 to 1,300K temperatures.
Advances of Plasticity Experiments on Metal Sheets and Tubes and Their Applications to Constitutive Modeling778(2005); http://dx.doi.org/10.1063/1.2011190View Description Hide Description
This paper provides a review of experimental techniques which are effective in observing and modeling the anisotropic plastic behavior of metal sheets and tubes under a variety of loading paths. These include biaxial compression tests, biaxial stress tests for metal sheets (cruciform specimens) and tubes using closed‐loop electrohydraulic testing machines, an abrupt strain path change method for detecting a yield vertex and subsequent yield loci without unloading, in‐plane compression or stress reversal tests for metal sheets and multistage tension tests. Comparison of observed material response with those predicted using phenomenological plasticity models are presented, where possible. Special attention is focus on the verification of the validity of conventional anisotropic yield criteria and its associated flow rule. The effects of the anisotropic yield criteria on the accuracy of forming simulations, such as springback and forming limit strains and stresses, are also discussed.
778(2005); http://dx.doi.org/10.1063/1.2011191View Description Hide Description
Conventional practices to predict preform shapes in hydroformimg and flanging processes are based on FEM analysis and/or experiment, which require many trials. In an effort to effectively improve the design procedure by overcoming the indirect nature of the conventional design tools, a direct design method based on the ideal forming theory has been previously developed as a newly added design tool in the design procedure. Here, the direct design method based on the ideal forming theory was applied to the preform design for hydroforming and flanging operations. In order to account for anisotropy, the anisotropic strain rate potential which simultaneously accounts for the anisotropy of yield stress as well as the anisotropy of plastic strain ratio was used as a part of the constitutive equation.
778(2005); http://dx.doi.org/10.1063/1.2011192View Description Hide Description
Over the last ten years, we have seen an explosion in the use of simulation‐based techniques to improve the engineering, construction, and operation of GM production tools. The impact has been as profound as the overall switch to CAD/CAM from the old manual design and construction methods. The changeover to N/C machining from duplicating milling machines brought advances in accuracy and speed to our construction activity. It also brought significant reductions in fitting sculptured surfaces. Changing over to CAD design brought similar advances in accuracy, and today’s use of solid modeling has enhanced that accuracy gain while finally leading to the reduction in lead time and cost through the development of parametric techniques. Elimination of paper drawings for die design, along with the process of blueprinting and distribution, provided the savings required to install high capacity computer servers, high‐speed data transmission lines and integrated networks.
These historic changes in the application of CAE technology in manufacturing engineering paved the way for the implementation of simulation to all aspects of our business. The benefits are being realized now, and the future holds even greater promise as the simulation techniques mature and expand. Every new line of dies is verified prior to casting for interference free operation. Sheet metal forming simulation validates the material flow, eliminating the high costs of physical experimentation dependent on trial and error methods of the past. Integrated forming simulation and die structural analysis and optimization has led to a reduction in die size and weight on the order of 30% or more. The latest techniques in factory simulation enable analysis of automated press lines, including all stamping operations with corresponding automation. This leads to manufacturing lines capable of running at higher levels of throughput, with actual results providing the capability of two or more additional strokes per minute.
As we spread these simulation techniques to the balance of our business, from blank de‐stacking to the racking of parts, we anticipate continued reduction in lead‐time and engineering expense while improving quality and start‐up execution. The author will provide an overview of technology and business evolution of the math‐based process that brought an historical transition and revitalization to the die and stamping industry in the past decade. Finally, the author will give an outlook for future business needs and technology development directions.
CAE Based Die Face Engineering Development to Contribute to the Revitalization of the Tool & Die Industry778(2005); http://dx.doi.org/10.1063/1.2011193View Description Hide Description
Over the past two decades, the Computer Aided Engineering (CAE) tools have emerged as one of the most important engineering tools in various industries, due to its flexibility and accuracy in prediction. Nowadays, CAE tools are widely used in the sheet metal forming industry to predict the forming feasibility of a wide variety of complex components, ranging from aerospace and automotive components to household products. As the demand of CAE based formability accelerates, the need for a robust and streamlined die face engineering tool becomes more crucial, especially in the early stage when the tooling layout is not available, but a product design decision must be made. Ability to generate blank, binder and addendum surfaces with an appropriate layout of Drawbead, Punch Opening Line, Trim Line are the primary features and functions of a CAE based die face engineering tool. Once the die face layout is ready, a formability study should be followed to verify the die face layout is adequate to produce a formable part. If successful, the established die face surface should be exported back to the CAD/CAM environment to speed up the tooling and manufacturing design process with confidence that this particular part is formable with this given die face. With a CAE tool as described above, the tool & die industry will be greatly impacted as the processes will enable the bypass of hardware try‐out and shorten the overall vehicle production timing. The trend has shown that OEMs and first tiers will source to low cost producers in the world which will have a negative impact to the traditional tool & die makers in the developed countries. CAE based tool as described should be adopted, along with many other solutions, in order to maintain efficiency of producing high quality product and meeting time‐to‐market requirements. This paper will describe how a CAE based die face engineering (DFE) tool could be further developed to enable the traditional tool & die makers to meet the challenge ahead.
778(2005); http://dx.doi.org/10.1063/1.2011194View Description Hide Description
In the aerospace industry stretch forming is often used to produce skin parts. During stretch forming a sheet is clamped at two sides and stretched over a die, such that the sheet gets the shape of the die. However for complex shapes it is necessary to use expensive intermediate heat‐treatments in order to avoid Lüders lines and still achieve large deformations.
To optimize this process FEM simulations of this process are performed. A leading edge skin part, made of aluminium AA2024, has been chosen for a preliminary study. The material is modelled with the Vegter yield function, to account for the anisotropic behaviour of the aluminium sheet. Each annealing step is considered to reduce the work hardening completely. The strains in the part have been measured and are used for validation of the simulations. The used FEM model and the experimental results will be presented and conclusions and recommendations for future research will be given.
778(2005); http://dx.doi.org/10.1063/1.2011195View Description Hide Description
Sheet metal forming is a displacement or draw‐in controlled manufacturing process in which a flat blank is drawn into die cavity to form an automotive body panel. Draw‐in amount is the single most important stamping manufacturing index that controls all forming characteristics (strains, stresses, thinning, etc.), stamping failures (splits, wrinkles, surface distortion, etc.) and line die operations and automations. Draw‐in Map is engineered for math‐based die developments via advanced stamping simulation technology. Then the Draw‐in Map is provided to die makers in plants as a road map for math‐guided die tryout in which the die tryout workers follow the engineered tryout conditions and matches the engineered draw‐in amount so that the tryout time and cost are greatly reduced, and quality is ensured. The Map can also be used as a math‐based trouble‐shooting tool to identify the causes of formability problems in stamping production. The engineered Draw‐in Map has been applied to all draw die tryout for all GM vehicle programs since 1998. A minimum 50% reduction in both lead‐time and cost and significant improvement in panel quality in tryout have been reported. This paper presents the concept and process to apply the engineered Draw‐in Map in die tryout.
Integrated Stamping Simulation Using State Of The Art Techniques To Fulfill Quality Assessment Requirements778(2005); http://dx.doi.org/10.1063/1.2011196View Description Hide Description
The last few years have seen the use of stamping simulation evolve to the extent that it is now a mainstream activity; a core part of the press tool engineering process. Now, new requirements for the use of challenging materials like Dual phase / Complex phase steel, VHSS, and aluminum, together with more stringent quality expectations, and shorter development cycles, there is a need to assess the panel quality in a wider context, before committing to tool manufacture.
The integrated approach from ESI Group allows early up‐front feasibility assessment, geometry and process optimization, and detailed process validation all within one system. Rapid die design and quick forming simulation modules play an essential role in the early stages of the process. A seamless connection between simulation and geometry is a vital characteristic, with the accurate simulation being used to validate and fine tune the process in order to assess final component quality in unprecedented detail, utilizing some of the most accurate material models available today. The combination of the distributed memory processing (DMP) solver together with new cost effective cluster based compute servers provide a practical solution to the problems of ‘one million element’ model sizes, and more sophisticated modeling methodologies become realistic for the first time.
It is no longer sufficient to merely focus on the draw die, forming simulation must now consider the entire die line up. Typically, around half of forming issues arise from the draw die, so the time has now come to address the other half as well!
This paper will discuss how the PAM‐STAMP 2G™ integrated solution is successfully used to deliver a positive business impact, by providing virtual panel quality assessment, tolerance control, and springback compensation. The paper will also discuss how other forming processes can be accurately modeled using the new modules.
Evolutions of Advanced Stamping CAE — Technology Adventures and Business Impact on Automotive Dies and Stamping778(2005); http://dx.doi.org/10.1063/1.2011197View Description Hide Description
In the past decade, sheet metal forming and die development has been transformed to a science‐based and technology‐driven engineering and manufacturing enterprise from a tryout‐based craft. Stamping CAE, especially the sheet metal forming simulation, as one of the core components in digital die making and digital stamping, has played a key role in this historical transition. The stamping simulation technology and its industrial applications have greatly impacted automotive sheet metal product design, die developments, die construction and tryout, and production stamping. The stamping CAE community has successfully resolved the traditional formability problems such as splits and wrinkles. The evolution of the stamping CAE technology and business demands opens even greater opportunities and challenges to stamping CAE community in the areas of (1) continuously improving simulation accuracy, drastically reducing simulation time‐in‐system, and improving operationalability (friendliness), (2) resolving those historically difficult‐to‐resolve problems such as dimensional quality problems (springback and twist) and surface quality problems (distortion and skid/impact lines), (3) resolving total manufacturability problems in line die operations including blanking, draw/redraw, trim/piercing, and flanging, and (4) overcoming new problems in forming new sheet materials with new forming techniques. In this article, the author first provides an overview of the stamping CAE technology adventures and achievements, and industrial applications in the past decade. Then the author presents a summary of increasing manufacturability needs from the formability to total quality and total manufacturability of sheet metal stampings. Finally, the paper outlines the new needs and trends for continuous improvements and innovations to meet increasing challenges in line die formability and quality requirements in automotive stamping.
Development of JSTAMP‐Works/NV and HYSTAMP for Multipurpose Multistage Sheet Metal Forming Simulation778(2005); http://dx.doi.org/10.1063/1.2011198View Description Hide Description
Since 1996, Japan Research Institute Limited (JRI) has been providing a sheet metal forming simulation system called JSTAMP‐Works packaged the FEM solvers of LS‐DYNA and JOH/NIKE, which might be the first multistage system at that time and has been enjoying good reputation among users in Japan. To match the recent needs, “faster, more accurate and easier”, of process designers and CAE engineers, a new metal forming simulation system JSTAMP‐Works/NV is developed. The JSTAMP‐Works/NV packaged the automatic healing function of CAD and had much more new capabilities such as prediction of 3D trimming lines for flanging or hemming, remote control of solver execution for multi‐stage forming processes and shape evaluation between FEM and CAD.
On the other way, a multi‐stage multi‐purpose inverse FEM solver HYSTAMP is developed and will be soon put into market, which is approved to be very fast, quite accurate and robust.
Lastly, authors will give some application examples of user defined ductile damage subroutine in LS‐DYNA for the estimation of material failure and springback in metal forming simulation.
778(2005); http://dx.doi.org/10.1063/1.2011199View Description Hide Description
In order to see the effect of die deformation on the forming of sheet metals, the draw‐ins, strains, and spring‐backs of an automotive fender panels are numerically simulated considering the die deformation, which is found by the simultaneous structural analysis of press and dies. By coupling the forming analysis and the structural analysis, the die deformation is simultaneously taken into account in the forming process. Furthermore, for the consideration of load difference transferred among the upper die, punch, and blank holder due to the changes in sheet thickness, the gap elements are employed instead of the blank sheet in the structural analysis. The numerical simulation results of an automotive fender draw panel are compared with the measurements. The comparison of the forming and spring‐back analysis results between the rigid die and the deformed die shows that the deformed tool provides more accurate forming and spring‐back prediction.
778(2005); http://dx.doi.org/10.1063/1.2011200View Description Hide Description
After gaining a huge success in applying stamping simulations and formability analysis to validate die face developments, GM moves forward to winning total manufacturability in stamping process. Of which, ensuring die structure integrity and minimizing weight is one of the important initiatives. Stamping die design (or solid modeling of stamping dies) was traditionally conducted by following the die design manuals and standards. For any design changes beyond the standards, however, there are no math‐based tools available to die designers to verify the outcome of the changes. Die structural analysis (DSA) provides a math‐tool to validate the design changes and quantify the safety factors. Several years ago, GM Manufacturing Engineering — Die Center started die structural analysis to meet the increasing demands of customer needs in various areas: (1) to validate design changes; (2) to identify root cause of die breakage during the tryout and stamping operations and propose repair schemes; (3) to optimize the die design for weight reduction; (4) to improve press throughput via optimizing the scrap chute openings, and (5) to provide a math‐based tool to validate revisions to the current die design standards. In the integrated forming and die structural analysis, after successful line die surface developments, the forming loads (binder force, pad force, and forming tonnages) are extracted from forming simulations and applied to solid die members for structural analyses of stress, strains, and deflections. In the past few years, Die Center conducted static, dynamic and fatigue analysis for many dies that covers the die design changes requested by die design, die construction and stamping plants. This paper presents some fundamentals and issues of integrated forming and die structural analysis and illustrates the significant impact of die structural analysis on die design, die construction and production stamping.
Modelling and simulation of the influence of forming processes on the structural behavior of high strength steels778(2005); http://dx.doi.org/10.1063/1.2011201View Description Hide Description
The paper first describes experiments and modeling concerning the identification of material behavior for high strength steels with phase transformations associated to plastic deformation. The experiments consist of tensile and bulging tests carried out on 316L stainless steels and TRIP 700 steels used in automotive industry. These experiments have permitted to determine the hardening curves of such materials vs. the martensite volume fraction associated to plastic deformation. It has been demonstrated that the stress triaxiality has a major role in the martenstic transformation and a model is proposed to define the flow stress vs. effective strain accounting planar anisotropy and variation of martenstic volume fraction. Then a plasticity model has been proposed in an anisotropic form and the related flow rules have been defined. The resulting model has been implemented in different finite elements software, and applied in numerical simulations of stamping and hydroforming of typical components to prove the effects of forming processes on the resulting properties of the components. Finally, the structural behavior of the resulting components is investigated and the effects of forming processes on the resulting structural behaviour are analyzed. Two cases are presented, one concerns the deep drawing of a cylindrical cup and the other concerns the stamping of a closed U channel used as a structural part for crash frames. Is has been clearly proved that the variation of martensite volume fraction arising during processing has a strong influence on the resulting behaviour of the parts considering springback and crash resistance.
A benchmark study for different numerical parameters and their impact on the calculated strain levels for a model part door outer778(2005); http://dx.doi.org/10.1063/1.2011202View Description Hide Description
To increase the accuracy of finite element simulations in daily practice the local German and Austrian Deep Drawing Research Groups of IDDRG founded a special Working Group in year 2000. The main objective of this group was the continuously ongoing study and discussion of numerical / material effects in simulation jobs and to work out possible solutions. As a first theme of this group the intensive study of small die radii and the possibility of detecting material failure in these critical forming positions was selected. The part itself is a fictional body panel outside in which the original door handle of the VW Golf A4 has been constructed, a typical position of possible material necking or rupture in the press shop. All conditions to do a successful simulation have been taken care of in advance, material data, boundary conditions, friction, FLC and others where determined for the two materials in investigation — a mild steel and a dual phase steel HXT500X. The results of the experiments have been used to design the descriptions of two different benchmark runs for the simulation. The simulations with different programs as well as with different parameters showed on one hand negligible and on the other hand parameters with strong impact on the result — thereby having a different impact on a possible material failure prediction.
Evaluation and Visualization of Surface Defects — a Numerical and Experimental Study on Sheet‐Metal Parts778(2005); http://dx.doi.org/10.1063/1.2011203View Description Hide Description
The ability to predict surface defects in outer panels is of vital importance in the automotive industry, especially for brands in the premium car segment. Today, measures to prevent these defects can not be taken until a test part has been manufactured, which requires a great deal of time and expense. The decision as to whether a certain surface is of acceptable quality or not is based on subjective evaluation. It is quite possible to detect a defect by measurement, but it is not possible to correlate measured defects and the subjective evaluation. If all results could be based on the same criteria, it would be possible to compare a surface by both FE simulations, experiments and subjective evaluation with the same result.
In order to find a solution concerning the prediction of surface defects, a laboratory tool was manufactured and analysed both experimentally and numerically. The tool represents the area around a fuel filler lid and the aim was to recreate surface defects, so‐called “teddy bear ears”. A major problem with the evaluation of such defects is that the panels are evaluated manually and to a great extent subjectivity is involved in the classification and judgement of the defects. In this study the same computer software was used for the evaluation of both the experimental and the numerical results. In this software the surface defects were indicated by a change in the curvature of the panel. The results showed good agreement between numerical and experimental results. Furthermore, the evaluation software gave a good indication of the appearance of the surface defects compared to an analysis done in existing tools for surface quality measurements. Since the agreement between numerical and experimental results was good, this indicates that these tools can be used for an early verification of surface defects in outer panels.
778(2005); http://dx.doi.org/10.1063/1.2011204View Description Hide Description
Sheet metal forming processes, especially deep drawing processes give diverse results by various materials. Extreme differences occur between steel sheets and aluminum sheets. The main causes of these differences are variances in micro‐ and macroscopic material properties, such as anisotropy. In this study, the behavior of two distinct materials, steel and aluminum alloy, during an axisymmetrical cup drawing operation has been studied numerically. For this purpose, finite element (FE) simulations of a simple cup drawing process, which was studied in the benchmarks of the NUMISHEET 2002 have been conducted using a commercial dynamic‐explicit FE‐analysis package. The materials analyzed have been 6111‐T4 aluminum alloy and mild steel graded as deep drawing quality. Basic process parameters, which are the blank holding force and the lubrication condition, have been varied to obtain a “successful” product and the process windows for these two materials have been compared and investigated. Thickness distributions in the blank, force requirements for the process and product quality have been used for the basis of comparison. The results are also compared with an analytical model developed by Ramaekers.
778(2005); http://dx.doi.org/10.1063/1.2011205View Description Hide Description
A new scheme for blank holding force (BHF) is introduced in order to apply more realistic BHF in simulation. The present study has been carried out for deep drawing processes of a washing‐trough. Different blankholder gaps and separation forces simulate the blank holding process. The optimum blankholder gap and separation force are determined through a systematic approach. It is found that the wrinkling in the flange region of the blank increases with the augmentation of the blank holder gap. And the BHF increases owing to the elevation of the rigidity of the sheet metal. The simulated thickness with separation force is lower than that with the blankholder gap because the BHF is variable in the flange region. A comparison of the thickness and flange contour between the simulation results and experiment shows that the blankholder gap is better in the simulation of the BHF in sheet metal forming process.