Sheet Metal Design Research Articles

Evaluation of forming forces in ultrasonic incremental sheet metal forming

In this paper, a new type of sheet metal forming technology using ultrasonic vibration applied to SPIF (single point incremental forming) process is presented. Forming force during forming process can induce fracture and affect accuracy of the sheet metal. Design of ultrasonic sheet metal forming equipment can be based on this study, which takes into account magnitude and changing law of the forming force. ABAQUS finite element software was used to simulate and analyze influence of different frequencies and amplitudes of ultrasonic vibration on the forming force in single point incremental forming process. Results show that ultrasonic vibration can reduce forming force and improve surface quality of the forming process. In addition, an experimental system using ultrasonic single point incremental forming was designed. Effect of the amplitude on ultrasonic vibration was studied experimentally. Experimental results were consistent with the result from finite element simulation.

Design and analysis of aircraft sheet metal for spring back effect

Since sheet metal forming industry has become one of the major manufacturing centers for automobile, aerospace and defense industries, the popularity of sheet metal products is attributable to their light weight, great interchangeability, good surface finish and low cost. There has been a growing interest during the past decade in using finite element method for spring back prediction following formation of arbitrary shapes. While it is apparently simple in concept, the prediction of spring back has proven challenging for a variety of reasons, including numerical sensitivity, physical sensitivity and poorly characterized material behavior under reverse loading and unloading conditions. Spring back of sheet metal parts after forming causes deviation from the designed target shape and produces downstream quality problems as well as assembly difficulties. It’s economic impact in terms of delayed production, tooling revision costs and rejection of unqualified parts is estimated to $50million/year in the U.S. automotive industry alone. It is obvious that controlling spring back is a vital concern in manufacturing.

Automatic design of sheet metal forming processes by “un-forming”

Most sheet metal components are made by deep drawing, which requires expensive tooling. Although many new flexible forming processes have been invented, they have largely not had industrial application, so it would be valuable if intelligent means to design new processes existed. This has not previously been attempted, although there has been work to classify both products and processes and to define optimal forming processes. A body of work in garment production examines the optimal flattening of garments, starting from their final form on a human body, to deduce the best cutting pattern from flat fabric. This paper develops a related approach for the first time, “un-forming” sheet metal from its finished geometry to a flat blank without prior specification of a process. An algorithm is developed that allows specification of process constraints and great freedom in implementing un-forming strategies, leading to a prediction of the strain history of the un-forming process. Reversing the direction of this history, allows prediction of the stresses in the workpiece required to form the target part, by use of an appropriate material model. The external forces (boundary conditions) required to maintain equilibrium with this stress state can then be calculated, allowing an iterative refinement of the constraints on un-forming until a physically achievable process has been designed. The approach is validated against a known process, and used to demonstrate how several previously untried forming strategies could lead to specification of new process designs. In future work, the method could be extended to allow an iterative specification of tooling to create the required boundary conditions, and hence to complete automatic process designs.

Research on Computer Integrated Manufacturing of Sheet Metal Parts for Lithium Battery

Lithium battery has been widely used as the main driving force of the new energy vehicle in recent years. Sheet metal parts are formed by means of pressure forming techniques with the characteristics of light weight, small size and high structural strength. The sheet metal forming has higher productivity and material utilization than the mechanical cutting, therefore sheet metal parts are widely used in many fields, such as modern automotive industry, aviation, aerospace, machine tools, instruments and household appliances. In this paper, taking a complex lithium battery box as an example, the integrated manufacturing of sheet metal parts is studied, and the digital integrated design and manufacturing process system is proposed. The technology is studied such as sheet metal design, unfolding, sheet nesting and laser cutting, CNC turret punch stamping programming, CNC bending etc. The feasibility of the method is verified through the examples of products and the integrated manufacturing of sheet metal box is completed.

Numerical Investigation of Dry and Lubricated Sheet Metal Forming Processes

The current global development towards efficient and sustainable usage of resources as well as a stronger environmental awareness motivates lubrication abandonment in metal forming. Dry forming processes accomplish besides a green production technology also a shortage in production steps and time. However, the change of the tribological conditions influences the material flow during the forming operations and has therefore to be taken into account for the design of complex sheet metal forming operations. The aim of this study is a comparison of dry and lubricated processes by numerical as well as experimental investigations. To ensure reliable results a test setup is necessary which provides a discrete control of the process parameters. Furthermore, an analysis of the local material flow by an optical strain measurement system during the whole test procedure should be possible. These requirements are well fulfilled by the so called Nakajima test, which is typically used for the characterisation of the formability of sheet metals. The influence of varying friction coefficients on the material behaviour is discussed based on the numerical model built up in the Finite Element Software LS-Dyna. The numerical results show a good conformity with the experimental outcomes by identifying the strain localisation. Based on the gained knowledge of the investigations an increase of process understanding for dry forming operations will be derived.

Integral sheet metal design via severe plastic deformation – state of the art and future challenges

The innovative forming processes Linear Flow Splitting (LFS) and Linear Bend Splitting (LBS) were developed to facilitate the continuous production of branched profiles with tailored sheet thickness by inducing severe plastic strain. In contrast to most SPD processes the stress state in LFS and LBS is very complex and plastic deformation is confined to limited volumes which results in steep strain gradients and consequently ultrafine grained (UFG) gradient microstructures. Even though the processes have been commercialized, the increased lightweight potential that originates from the local grain refinement remains mostly idle since it is neither fully understood nor easily assessable yet.The present work shows the state of the art for the LFS and LBS processes and compares the microstructures and distribution of mechanical properties for different steels processed with different LFS parameters. The data is used to identify characteristic manufacturing induced properties that are insensitive to processing parameters. Based on the experimental results a material flow model for the processing zone is proposed which is discussed with respect to the current understanding of plasticity at severe strains.

Unfolding Method of Non-Developable Surface for Sheet-Metal Design

The organized vertex coordination of the triangular surfaces is obtained by the meshing method in the 3D kernel based developing environment. To optimize the flattened form, the energy method is used to find the reasonable unfolding scheme, which seeks the solution to minimize the deforming energy generated when flattening the triangular surfaces. This algorithm is not the fastest one, but the versatile one especially for the non-developable surface with a large bending degree. With the unfolding method and the 3D kernel environment, the 3D unfolding system for the arbitrary surface satisfying the requirements is constructed.

Manufacturability of Sheet Metal Design with the Help of Product Data Management (PDM)

In the today’s industry the sheet metal design plays a huge role, it has been said that almost the half of the designing is concentrating to sheet metals. But the lack of knowledge of the typical sheet metal aspects and basic rules of sheet metal designing, has led in to situation where more and more products are poor designed. This automatically leads to situation that the products are not manufacturing friendly. Designing time is shortening year after year, so the pressure to design the part as fast as possible is huge. Unfortunately all the design information and the design intent is processed and filtered to be fit for the Product Data Management (PDM) system. As the PDM was firstly designed to be used only for the storage base for the design drawings and other data; the feature-information and design intent is lost. This paper deals with two distinct yet interlinked themes. The first theme is the new requirements set for the new Product (Life-time) Information systems that can save the product information and design intent. And the second theme is the modern, light-weight and updatable product-services that allow the manufacturability to be ensured before product realization. With the help of novel product-service such as Design Manufacturing and Assembly (DFMA) for sheet metal industry designers will able to design in shorter time manufacture friendly sheet metal products.

Warm forming die design, part I: Experimental validation of a novel thermal finite element modeling code

Finite element analysis (FEA) has become an invaluable tool in the design of sheet metal stamping dies and processes. FEA has gained widespread acceptance as the best method of optimizing dies for conventional stamping processes. More recently, FEA has been shown to be an effective method of designing tooling for sheet forming processes. In this work, an FEA based approach is applied to the warm stamping (warm forming) process. This work introduces a new thermal finite element analysis software called PASSAGE®/Forming (PASSAGE) that enables the up-front design of the thermal management of warm forming dies. This thermal finite element analysis software is designed to specifically handle the forming and optimization scenarios related to the heating of a stamping die while minimizing user interface time. In this work, PASSAGE has been applied to a simple block of steel embedded with cartridge heaters to validate the prediction capability of this software under two different heating conditions. The results show that PASSAGE is capable of predicting the actual steady-state temperature distribution within the block with an acceptable level of accuracy while yielding notable information to the user with respect to specifying power requirements. A finite element software package like PASSAGE is a valuable tool that will aid greatly in the implementation of warm forming as a manufacturing process beyond the scope of the laboratory and into production.

Experimental and numerical analysis of springback prediction in U-bendings of anisotropic sheet metals

Springback is one of the most important problems that should be taken into consideration during design of sheet metal forming process with the increasing application of advanced high strength steels and light-weight alloys. The degree of springback experienced with the latest generation materials is so high, and the materials so strong, that it is not possible to eliminate the springback in the prototyping. It becomes mandatory to compensate for springback as part of the draw die design, which is usually carried out through numerical simulation. The springback behavior of three categories of sheet steels (TRIP, HSLA and mild steel) with thicknesses ranging from 0.75 to 0.85 mm was investigated by means of the cyclic U-bending test. This phenomenon can be defined as an elastically-driven change of shape of the deformed part upon removal of external loads. Steel sheets were bent on the two different die radii and after first cycle were bent reverse. The influence of die radius on amount of springback of the steels was considered. Value of the springback angle change after the first and second cycle was measured. The change of values of angles between cycles is caused by the Bauschinger effect. This process was investigated experimentally and numerically. Numerical investigation was performed in static implicit finite element code Autoform.

Application of the local strain approach on a rolling point contact model

A newly developed cold forming process, the linear flow splitting process, allows the bifurcation of thin metal sheets by severe plastic deformation (SPD). This process produces flanges with an ultra-fine grained (UFG) microstructure, which is characterized by an increased hardness and lower surface roughness in comparison to the material in as-received state. The technology is researched within the Collaborative Research Centre 666 (CRC 666) “Integral Sheet Metal Design with Higher Order Bifurcations”. The increased hardness and reduced surface roughness of the flanges make this technology suitable for manufacturing linear guide rails. In order to achieve the required reliability and fatigue strength, the assessment of the performance of the linear flow-split profiles with gradient microstructure is of great importance. When considering rolling contact fatigue, the examination of the mechanical behavior of the side of the flange with higher hardness due to the UFG microstructure is required. In order to reduce time and costs, a numerical method to determine the rolling contact fatigue behavior would be useful minimizing the normally applied experimental effort. The present work aims to check the applicability of the local strain approach for the evaluation of the rolling contact fatigue behavior of linear flow split components by a Finite Element (FE) analysis. The Hertzian theory is only valid for homogeneous materials and cannot be directly applied to the flanges with gradient microstructure. Therefore an accurate modeling of the material in order to take into account the gradient in the mechanical properties is required. In this paper the characterization of the material behavior under axial cyclic loading will be presented. These results will be used for the Bergmann damage parameter to analyze the rolling contact fatigue behavior. Some parameters required for the application of the Bergmann approach are determined by a numerical simulation of the rolling contact. Results are compared to rolling contact fatigue tests performed on a recently developed test rig under the assumption of rolling without sliding and neglecting the effect of surface roughness and residual stresses.

Variable fidelity design based surrogate and artificial bee colony algorithm for sheet metal forming process

Optimization integrated with either one step solver (low fidelity model) or incremental nonlinear finite element solver (high fidelity model) has respectively gained increasing popularity in the design of sheet metal forming process to improve product quality and shorten lead time. However, the one step solver directly incorporated with optimization may result in inadequate design precision, while the incremental method often leads to a prohibitively low computing efficiency. In order to take the full advantages of both the one step solver and incremental solver, we present a variable fidelity algorithm which integrates the one step solver with incremental solver for optimizing sheet metal forming process in this study. In the variable fidelity method established, we need to determine the difference between the two solvers at some predefined experimental points firstly, and then constructing a corrected function using surrogate models for compensating the responses of the one step solver at other points. Different surrogate models, such as response surface methodology (RSM), Kriging (KRG), radial basis function (RBF) and support vector regression (SVR), are considered and compared for best modeling accuracy in this paper. The compensated low fidelity model can be used as a high fidelity model in the optimization process. In this study, we adopt the artificial bee colony (ABC) algorithm to obtain the global optimum. To demonstrate the capability of the variable fidelity method combined with the ABC algorithm, the optimal design of draw-bead restraining forces for an automobile inner panel is exemplified herein. The results show that the optimization with variable fidelity method presented significantly improves the computational efficiency and formability of the workpiece.

A knowledge-based manufacturing advisor for pressworked sheet metal parts

This paper describes an expert system for die design and process planning of sheet metal forming operations functioning on a part representation by custom-defined features input incrementally. Knowledge acquired from industrial experts pertains mainly to operations sequencing towards a complete process plan and to die and tool configuration, whilst knowledge acquired from handbooks pertains to calculations required to determine basic characteristics of individual manufacturing operations. The expert system is composed of seven modules: initial calculations, cutting-piercing, drawing-stamping, process planning, finishing, die and press selection, and tools selection. Part shape is converted from CAD environment to appropriate constructs in the expert system through a suitable interface to a library of customisable features. The expert system exports manufacturing advice in the form of a report. This can be used mainly by the product designer obtaining feedback on the production feasibility issue, or by the inexperienced die designer. In both cases design and manufacturing efficiency are greatly improved.

Fuzzy Multi-Objective Optimization for Die Structures Design in Sheet Metal Forming

Abstract: Finite element analysis and fuzzy multi-objective optimization technique have been integrated to solve the die structure design of sheet metal forming by transforming fuzzy multi-objective problem into a normal optimization problem. A mathematical model of fuzzy optimization for bending die was established. A fuzzy goal set was constructed. The fuzziness of multi-objective functions and constraints were defined. The optimal solution and optimal constraint value of individual objective function in the feasible field were found using the genetic algorithms. An electronic part bending case shows that this approach is more effective and accurate than traditional finite element analysis method and the ‘trial and error’ procedure.

Tool path correction algorithm for single-point incremental forming of sheet metal

There exists some error between the manufactured part shape and the designed target shape due to springback of this part after forming. To reduce the error, an iterative algorithm of closed-loop control for correcting tool path of the single-point incremental forming, based on Fast Fourier and wavelet transforms, has been developed. Moreover, the data of the springback shapes, after unloading, of the sheet metal parts formed with the trial and corrected tool paths, used for iterative correction of tool path in the algorithm, are obtained with finite element model (FEM) simulation. Then, a truncated pyramid-shaped workpiece, whose average errors are +0.183/−0.175 mm, was made with the corrected tool path after three iterations solved by the above algorithm and simulation data. The results show that the tool path correction algorithm with Fourier and wavelet transforms is reasonable and the means with FEM simulation are effective. It can be taken as a new approach for single-point incremental forming of sheet metal and tool path design.

Sheet Metal Design with Modeling Kernels Technology

Current sheet metal designing systems calculate the unfolding result automatically without the foundational information interaction with the designers, which limits the special material designing process. This paper concentrates on constructing the 3D environment for the sheet metal design, which is developed by modeling kernels technology and is favorable to construct the relationship between characteristic of material and unfolding parameters. Firstly, the developing mode is presented, by which the data structure is established. Then, the main procedure to realize the system is illustrated. The model construction is the key point. Finally, the oblique cut cylinder is unfolded as an instance to illustrate the approach. In addition, this work is the geometric foundation of the further study of sheet metal designing library.

Sheet Metal Design with Modeling Kernels Technology

Current sheet metal designing systems calculate the unfolding result automatically without the foundational information interaction with the designers, which limits the special material designing process. This paper concentrates on constructing the 3D environment for the sheet metal design, which is developed by modeling kernels technology and is favorable to construct the relationship between characteristic of material and unfolding parameters. Firstly, the developing mode is presented, by which the data structure is established. Then, the main procedure to realize the system is illustrated. The model construction is the key point. Finally, the oblique cut cylinder is unfolded as an instance to illustrate the approach. In addition, this work is the geometric foundation of the further study of sheet metal designing library.

Intelligent Multi-Objective Optimization for High Strength Sheet Metal Forming Process of Body Part

In high strength sheet metal forming process of body part, crack, wrinkle and severe thinning are the main faults usually. The degree of the faults varies with the change of input process parameters. Optimization for sheet metal forming process of body part is often considered as a multi-objective problem. Design of experiment method and genetic algorithm are often combined together to cope with this multi-objective optimization problem. High strength steel sheet metal forming process is relatively complex and difficult. An intelligent multi-objective optimization strategy for high strength sheet metal forming process was suggested based on genetic algorithm. Latin Hypercube Sampling method was introduced to design the rational experimental samples; the objective function was defined based on crack factor, wrinkle factor and severe thinning factor; the accurate response surface model for sheet metal forming problem was built; Multi-objective genetic algorithm was adopted in optimization and Pareto solution was selected. The strategy was applied to analyze a rocher. The result has proved this strategy suitable for optimization design of sheet metal forming process .

Intelligent Multi-Objective Optimization for High Strength Sheet Metal Forming Process of Body Part

In high strength sheet metal forming process of body part, crack, wrinkle and severe thinning are the main faults usually. The degree of the faults varies with the change of input process parameters. Optimization for sheet metal forming process of body part is often considered as a multi-objective problem. Design of experiment method and genetic algorithm are often combined together to cope with this multi-objective optimization problem. High strength steel sheet metal forming process is relatively complex and difficult. An intelligent multi-objective optimization strategy for high strength sheet metal forming process was suggested based on genetic algorithm. Latin Hypercube Sampling method was introduced to design the rational experimental samples; the objective function was defined based on crack factor, wrinkle factor and severe thinning factor; the accurate response surface model for sheet metal forming problem was built; Multi-objective genetic algorithm was adopted in optimization and Pareto solution was selected. The strategy was applied to analyze a rocher. The result has proved this strategy suitable for optimization design of sheet metal forming process .

The optimal design of sheet metal forming processes: application to the clinching of thin sheets

The production of high-strength clinched joints is the ultimate goal of the manufacturing industry. The determination of optimum tool shapes in the clinch forming process is needed to achieve the required high strength of clinched joints. The design of the tools (punch and die) is crucial since the strength of the clinched joints is closely related to the tools geometry. To increase the strength of clinched joints, an optimisation procedure using the response surface methodology, based on an adaptive moving target zone, is presented. The cost function studied here is defined in terms of the maximum value of the tensile force computed during the simulation of the sheets separation. Limitations on the geometrical parameters due to feasibility issues are also taken into account. The kriging interpolation is used to provide an approximation to the optimisation problem and to build the response surfaces.