Sheet Metal Deep Drawing Research Articles

Multi-objective optimization of VBHF in sheet metal deep-drawing using Kriging, MOABC, and set pair analysis

The optimization of variable blank holder force (VBHF) in sheet metal deep-drawing has important significance in improving forming part quality. This paper proposed a new multi-objective VBHF optimization method to reduce the tearing, wrinkling, and springback in the drawing process. The influence mechanism of springback on forming precision is analyzed and a new evaluation criterion of springback is developed. Sidewall wrinkling is taken into account to quantify the wrinkling. Three quality evaluation criteria for ellipsoid forming part are established and a VBHF optimization model in deep-drawing is formulated by cooperated Kriging approximate model with three defects. Multi-objective artificial bee colony (MOABC) algorithm is employed to get VBHF Pareto-optimal set from the VBHF Kriging mode. Set pair analysis (SPA) is applied to select the best solution in Pareto set. An example of the head-type part deep-drawing is used to illustrate the method. The experimental results show that the VBHF multi-objective optimization problem can be solved well by proposed method.

Selective oxidation of tool steel surfaces under a protective gas atmosphere using inductive heat treatment

For the realization of liquid lubricant free forming processes different approaches are conceivable. The priority program 1676 “Dry forming - Sustainable production through dry machining in metal forming” addresses this issue in the context of metal forming processes. The present study reports results from one subproject of the priority program that employs selective oxidization of tool steel surfaces for the implementation of a dry sheet metal deep drawing process. Within the present study, specimen surfaces of the tool steel (1.2379) were heat-treated to optimize their tribological properties with respect to sliding wear behaviour in contact with drawn sheet metal (DP600+Z). The heat treatment was designed to result in the formation of selective oxide layers that can act as friction reducing separation layers. The heating setup employed an inductive heating under protective gas atmosphere. Selective oxidation was realized by controlling the residual oxygen content. Specifically, the specimens were heated in the near-surface region just above the annealing temperature, thus avoiding the degradation of mechanical properties in the bulk. Evaluation of hardness along cross-sections of each specimen revealed suitable initial temperatures for the inductive heat treatment. Oxide layer systems were analyzed regarding their tribological sliding wear behaviour after selective oxidation, as well as their morphology and chemical composition before and after the sliding wear tests.

Influence of process parameters on the formability of bead stamping part using advanced models

Beads are applied to deep drawn sheet metal parts to increase its stiffness. In order to form the bead, a two-stage manufacturing process including at least deep drawing and beading is performed. Thus, reductions of sheet metal thickness and consequently weight reduction can be effectively reached by numeric optimization. In order to apply the optimization algorithm to the production of non-virtual actual parts, the forming limits of the parts must be considered in both manufacturing steps. Bead formability is affected by process parameters such as blank holding force and lubrication. One way to investigate these influences is to use an accurate simulation model. In this study, the yield function named Yld2000-2D under non-associated flow rule is used to express anisotropic material behavior of blank and the Generalized Forming Limit Concept (GFLC) considering nonlinear strain paths is used to determine the formability. These models are validated by comparing the strain and bead forming limits measured in the Nakajima experiment. Then, the influences of mentioned process parameters are investigated by the validated model.

Virtual tryout planning in automotive industry based on simulation metamodels

Deep drawn sheet metal parts are increasingly designed to the feasibility limit, thus achieving a robust manufacturing is often challenging. The fluctuation of process and material properties often lead to robustness problems. Therefore, numerical simulations are used to detect the critical regions. To enhance the agreement with the real process conditions, the material data are acquired through a variety of experiments. Furthermore, the force distribution is taken into account. The simulation metamodel contains the virtual knowledge of a particular forming process, which is determined based on a series of finite element simulations with variable input parameters. Based on the metamodels, virtual process windows can be displayed for different configurations. This helps to improve the operating point as well as to adjust process settings in case the process becomes unstable. Furthermore, the time of tool tryout can be shortened due to transfer of the virtual knowledge contained in the metamodels on the optimisation of the drawbeads. This allows the tool manufacturer to focus on the essential, to save time and to recognize complex relationships.

Effect of Plastic Deformation on Elastic and Plastic Recovery in CP-Titanium

The springback associated with cold deep drawing of sheet metals leads to undesired dimensional changes in the final products. This is often due to the heterogeneous plastic deformation in different areas of the intended geometry that creates various stress states throughout the part. The major objective of this study is to understand the interconnection between springback, level of plastic deformation, degradation of elastic modulus and strain recovery in a CP-Ti material. The mechanical properties of the sheet material and the dependency of mechanical properties on directionality are investigated by examining samples from three orientations of parallel to the rolling direction (RD), at 45° to RD and perpendicular to RD. The degradation of elastic modulus as a function of level of plastic deformation was explored for 0° and 45° samples by conducting multi-step uniaxial loading-unloading in tension.The experimental results showed that the mechanical properties vary for each direction, with the lowest elastic modulus along RD. A significant degradation was observed in elastic modulus (up to 50% reduction) with increased plastic deformation. This resulted in more strain relaxation compared to that associated with the initial elastic modulus. For stresses below 100MPa, a nonlinear (plastic) recovery was observed, resulting in additional relaxation in the total strain upon load removal in each step of the interrupted tests. This plastic recovery behaviour is observed to be dependent on sample orientation. It is concluded that accurate prediction of springback during sheet metal forming, requires a material model which takes into accounts the directional degradation of elastic modulus and the plastic recovery as a function of plastic deformation.

Determination of the bead geometry considering formability and stiffness effect using generalized forming limit concept (GFLC)

Beads are used in deep drawn sheet metal parts for increasing the part stiffness. Thus, reductions of sheet metal thickness and consequently weight reduction can be reached. Style guides for types and positions of beads exist, which are often applied. However, higher stiffness effects can be realized using numeric optimization. The optimization algorithm considers the two-stepped manufacturing process consisting of deep drawing and bead stamping. The formability in both manufacturing steps represents a limiting factor. Considering nonlinear strain paths using generalized forming limit concept (GFLC), acceptable geometries will be determined in simulation. Among them, the efficient geometry which has higher stiffness effects will be selected in numerical and experimental tests. These will be integrated in the optimization algorithm.

Process Windows for Sheet Metal Parts based on Metamodels

Achieving robust production of deep drawn sheet metal parts is challenging. The fluctuations of process and material properties often lead to robustness problems. Numerical simulations are used to validate the feasibility and to detect critical regions of a part. To enhance the consistency with the real process conditions, the measured material data and the force distribution are taken into account. The simulation metamodel contains the virtual knowledge of a particular forming process, which is determined based on a series of finite element simulations with variable input parameters. Based on the metamodels, process windows can be evaluated for different parameter configurations. This helps improving the operating point search, to adjust process settings if the process becomes unstable and to visualize the influence of arbitrary parameters on the process window.

Lubricants Based on Vegetable Oils as Effective Lubricating Agents in Sheet-Titanium Forming

Sheet metal forming processes allow for production of lightweight and durable goods. For this reason, drawing operations have been widely used across the automotive, aviation and construction industries and for production of various components of machines. Despite the popularity of deep-drawing steel sheet metal, non-ferrous materials, such as aluminium, magnesium and titanium are also used for such purposes. Titanium materials seem to be particularly attractive due to a beneficial ratio of strength to density and excellent corrosion resistance in the most of technological environments. However, titanium and its alloys belong to a group of materials with low tribological properties and tendencies for galling and build-up of layers of the deformed material on the tool surface. Therefore, this study will discuss the results of the investigations concerning selection of technological lubricants based on vegetable oils used for the operation of forming of sheet metal made of commercially pure titanium (Grade 2). The focus of the experiment is on lubricants based on vegetable oils i.e. rapeseed oil, sunflower oil and olive oil. The main lubricating additive was boric acid and stearic acid. The study presents the results of the determination of friction coefficient during a strip drawing test.

Optimisation of deep drawn paperboard structures by adaptation of the blank holder force trajectory

The deep drawing process of paperboard has proven to be comparable to deep drawing of sheet metal in only a few aspects due to the nature and completely different behaviour of the material. However the blank holder also plays a key role with regard to quality and rupture prevention at 3D-structures. The aim of this paper is to describe the capabilities of variable blank holder force trajectories to improve the distribution of wrinkles and the quality of 3D-structures. The results show that the blank holder force should be adapted to the punch position keeping the highest possible force level. The force can be increased during the drawing process and needs to be strongly reduced short before the blank is drawn out of the blank holder completely. The introduced force trajectories lead to a significantly improved visual quality increasing the initial height where wrinkles occur encouraging fibre to fibre movement at the beginning of the process. The results furthermore contribute to a better understanding of the rupture behaviour. The increase of the circumference towards the border of the blank can be used to generate a blank holder force design that does not lead to ruptures but is able to make more intensively use of the capability the material exhibits to avoid wrinkles or distribute them as uniform as possible over the wall.

Finite Element Analysis for Deep Drawing Process and Part Shape Optimization

The paper presents some aspects regarding the sheet metal deep drawing process and shape optimzation for such parts using Finite Element Analysis. Simulation based design approaches have been used for forming processes. Using similar approach, a full process simulation and optimisation was undertaken in the present work. The work done here involved computer simulations of the forming processes to evaluate the amount of strain and stress each forming process contributed to the final product. Based on the simulation results, recommendation to change the product shape were presented. Not all the virtual products should be manufactured and the Finite Element Analysis eliminate all the possible errors and let the designers to optimize the geometry before designing the Molds and Dies for Deep Drawing process.

Structural integration of piezoceramic fibers in deep drawn sheet metal for material-integrated health monitoring

The integration of active piezoceramic sensors and actuators into passive sheet metal assemblies produces smart structures. Smart structures are capable of sensing the condition of parts and systems as well as interacting with the environment. Today, smart sheet metal parts are manufactured by surface bonding of sensors and actuators on shaped structural parts. This paper presents a technology for the direct structural integration of lead-zirconate-titanate (PZT) fibers. The fibers are integrated in flat sheet metal, which is subsequently shaped by forming. Microcavities are formed into the surface of the flat metal sheet in which the piezoceramic fibers are inserted and joined. After that, the composite is shaped into a complex 3D surface by deep drawing. The production technology is discussed in detail with regard to the limits of each process step.Functional prototypes with ten interconnected parallel piezoceramic fibers were fabricated. The function as actuator and sensor for ultrasonic elastic waves is demonstrated and the degradation due to the shaping is compared for different parameters of the deep drawing process. The composite shapes are cups with a double curvature radius of 100mm and 250mm respectively.As a result, degradation of the piezoelectric function varies with the process parameters. In the case of a double curvature of 250mm, a degradation of the transducer function of 20% was shown in the experiments. The cause of the decreased performance after shaping is discussed and explained by debonding mechanisms. Results of numerical simulations show a good agreement with the experimental findings of the optimum process parameters.Furthermore, a setup of a wing assembly segment is used to demonstrate the potential of integrated PZT fibers in shaped metal structures. The integrated fibers are used for health monitoring of a multiple bolted joint. It is shown that loosening of a single screw can accurately be detected by the directly integrated PZT fibers.

Radial Lorentz force augmented deep drawing for large drawing ratio using a novel dual-coil electromagnetic forming system

In order to overcome the limitations of the existing electromagnetic forming systems for deep drawing, a dual-coil system has been developed for deep drawing of sheet metal with large drawing ratio. In addition to the conventional driving coil that generates the axial Lorentz force on the workpiece, a radial inward force in the flange region is generated by a second coil that is energized by an individual power supply. The axial force pushes the sheet into the die in axial direction, while the radial Lorentz force enhances the material flow of the flange. The effectiveness of the novel system is validated by a series of experiments for deep drawing a cup of AA1060-H24 with drawing ratio of 3.25. It is demonstrated that with the dual-coil system the material flow of the flange can be significantly enhanced, and the maximum forming depth without failure is greatly increased from 8.44mm to 20.28mm. The new electromagnetic forming method is expected to break through the bottleneck of deep drawing and enable major advances in forming metallic parts and components that are difficult to form, by developing driving coils with advanced design.

Analysis of Earring in Circular-shell Deep-drawing of bcc and hcp Sheet Metals

The occurrences of earrings in circular-shell deep-drawing tests for two different types of crystal materials were investigated. The simulation was conducted with whole 360̊circumference analysis. As the first result, the earring height is proportional not only to ΔR/Rave but also to ΔTLave ((R90-R00)/Rave). Secondly, the optimum m-value in yield function for the pure titanium and the low-carbon aluminum-killed steel, which led to the fairly good reproduction of experimental results, is 8 and 2 respectively. Furthermore, the blank mesh pattern is assumed to clarify the influence of R-values of three directions.

A Knowledge Based System for Cost Estimation of Deep Drawn Parts

Cost estimation of deep drawn sheet metal parts requires substantial knowledge and experience. It is a time consuming task and dependent on the expert personnel available. This paper presents the research work involved in the development of a knowledge based system for cost-estimation of deep drawn sheet metal parts. The proposed system is structured in form of two modules viz., module COMPC for estimation of total manufacturing cost of deep drawn parts and module TOOLC for estimation of total tooling cost of deep drawing tool. The system modules are coded in VB.6.0 in windows operating environment. The system has been tested for various types of axisymmetric deep drawn sheet metals parts taken from industries. System is flexible enough as its knowledge base can be extended or modified easily.

An expert system for selection of process parameters and strip-layout design for production of deep drawn sheet metal parts

The selection of process parameters and strip-layout design are important activities in sheet metal industries for production of deep drawn sheet metal parts. Traditionally, these are manual, tedious, time consuming and highly experience-based tasks. In the present work, an expert system (ES) is developed for automation of these activities for production of sheet metal parts on progressive deep drawing die. Production rule-based approach is used for constructing system modules. The proposed system automates the selection of appropriate values of process parameters and design of strip-layout for production of deep drawn parts on progressive deep drawing die. The system is also capable to model blank layout and strip-layout automatically in the drawing editor of AutoCAD. The system has been tested successfully for wide variety of industrial deep drawn parts. The system can be easily implemented on a PC having AutoCAD software; therefore it has low cost of implementation.

Thinning and residual stresses of sheet metal in the deep drawing process

This paper presents a Finite Element (FE) model developed for the 3-D numerical simulation of sheet metal deep drawing process (Parametric Analysis) by using ABAQUS/EXPLICIT Finite Element Analysis (FEA) program with anisotropic material properties and simplified boundary conditions. The FE results are compared with experimental results for validation. The developed model can predict the thickness distribution, thinning, and the maximum residual stresses of the blank at different die design parameters, including both geometrical and physical parameters. Furthermore, it is used for predicting reliable, working parameters without expensive shop trials. Predictions of the thickness distribution, thinning and the maximum residual stresses of the sheet metal blank with different design parameters are reported. Frictional limitations and requirements at the different interfaces are also investigated.

The Numerical Simulation Analysis of the Rectangular Box Straight Springback Law

Abstract. Springback is one of the main factors that affects the quality of sheet metal deep drawing. Due to the springback is inevitable, so to explore the springback law becomes an important content in the process of sheet metal forming. In this paper, the ETA/DYNAFORM finite element software was applied to simulate four different length-width radio model of rectangular box. The simulating data shows that the rectangular box with short straight edge rebounded inward when the central of the long straight edge rebounded outward and near the corner part rebounded inward. The study had a very important guiding significance to the stamping process of rectangular box part and mold design.

Thinning and spring back prediction of sheet metal in the deep drawing process

The spring back simulation helps to get the required tolerance of the punch travel distance. This tolerance is needed in getting the required height of the final drawn part. Prediction of the forming results as spring back, determination of the thickness distribution and of the thinning of the sheet metal blank reduces the production cost of the material and time. In this paper, A Finite Element (FE) model is developed for the 3-D numerical simulation of sheet metal deep drawing process (Parametric Analysis) by using ABAQUS/EXPLICIT FEA program with the proper material properties (anisotropic material) and simplified boundary conditions. The FE results are compared with experimental results for validation. The developed model predicts the spring back, the thickness distribution and thinning of the blank as affected by the die design parameters (geometrical parameters and physical parameters). Furthermore, with numerical simulation, working parameters such as punch force, the blank holder force, and the lubrication requirements can be determined without expensive shop trials.

Formability Analysis with Precise Surface Building for the Automobile Outer Clutch Shell

Majority of automobile and appliance components are made by deep drawing sheet metal process. So these growing needs demand a new design methodology based on metal forming simulation. With the help of metal forming simulation we can identify the problem areas and solutions can be validated. The aim of this research is to develop techniques that would reduce the amount of time spent during the tool qualifying stage. In this paper the draw tools on Automobile outer clutch shell surface are designed by the precise die surface at different dimensions and draw processes is analyzed with appropriate simulation parameters. From this we got the most reliable results. The compression with the tryout part shows that the simulation process can accurately predict the formability problems.

Development of Intelligent Control of Optimum Parameters in Deep Drawing of Sheet Metal Using Genetic Algorithm and Finite Element Methods

The main purpose of this work is to develop an intellectualized control technique on the deep drawing of rectangular pan made of AISI 304 DDQ stainless steel using genetic algorithm and finite element methods. These control methods are employed in order to investigate the most significant parameters in sheet metal forming process such as drawing force, with a view of optimizing these parameters. The genetic algorithm is used for the optimization purpose to minimize the force of the deep drawing process and to investigate the roles of other parameters. Experimental results show that these combinations of control system can cover a wide range of both materials and influential forming parameters automatically. The results further confirm that the developed system is effective and valid alternative for quick responsible control system with high flexibility.