Drawn Sheet Metal Parts Research Articles

Sustainable tool technology: Wood-based forming tools for deep drawing of sheet metal

In order to improve adaptability to evolving manufacturing processes in an era marked by mass customization and individualization, while also meeting geopolitical climate objectives, it is necessary to employ more sustainable methods in sheet metal forming to enhance flexibility. Metal based rigid tooling systems require a lot of material and energy resources, when aiming for high flexibility and scalability with respect to small batch size production. To reduce the overall resource consumption and to meet climate restrictions, non-metallic tooling approaches can counteract these issues when aiming for individualization in sheet metal forming. Compared to conventional metal-based tooling approaches, wood-based forming tools may enable a potential resource reduction (e.g., carbon footprint) and offer an alternative tooling approach for sheet metal forming. Although the mechanical performance of wood is lower compared to conventional tooling steel, certain wood-based forming tools can potentially be implemented for sheet metal forming. In this work a feasibility study of wood-based tooling materials is executed to investigate the mechanical performance on drawn sheet metal parts in a deep drawing operation. Different composite structures are investigated for wooden forming tools of black locust (robinia pseudoacacia).

Sheet Metal Forming Using Additively Manufactured Polymer Tools

Due to various trends, such as e-mobility, a long-term change in the automotive value creation structure is foreseeable. Shorter development cycles demand early prototypes and cause more changes. Currently, there is no cost-effective production process for originally deep drawn sheet metal parts in series quality at small production volumes. In this paper, the application of additively manufactured functional elements in deep drawing tools is investigated. Besides the first concept of such tools, first experimental test series are described and analyzed.

Considering fluctuations of material properties, stainless steel 1.4301, on manufacturability of kitchen sinks

In production of deep drawn sheet metal parts, it is often challenging to achieve a robust process. Especially in the production of kitchen sinks made out of stainless steel, the fluctuation of the process and material properties often lead to robustness problems. Therefore, numerical simulations are used to detect critical regions. To keep a constant product quality, process control is realised based on metamodels, which are computed by means of a series of finite element simulations. In order to enhance the forecast capability of the simulation model and to increase the reliability of quality features, the yield curve, the yield locus and the forming limit curve (FLC) of different suppliers are measured with tensile, bulge and Nakazima experiments. Because of the large deformation capability of stainless steels, large drawing depths can be achieved. However, the classic Nakazima geometries are not distributed homogenously in the forming limit diagram (FLD). To overcome this shortcoming, a shape optimization of the Nakazima specimen has been performed. Furthermore the influence of alloying elements on the hardening behaviour and on the FLC are analysed. In addition, the measured FLC-T (temperature dependent FLC) conducted with heated Nakazima tests is compared with the computed FLC-T with the modified maximum force criterion (MMFC).

Metamodel-based methods to verify the feasibility of a process control in deep drawing

In production of deep drawn sheet metal parts it is often challenging to achieve a robust process. Especially in the production of kitchen sinks made out of stainless steel, the fluctuation of the process and material properties often lead to robustness problems. Therefore, numerical simulations are used to detect critical regions. By means of a series of finite element simulations with variable noise and design parameters, metamodels are computed for each quality criterion. Based on the metamodels, the influences of changing noise variables on the individual quality features are identified. To keep a constant product quality, the process settings (design parameters) should be adjusted. By means of new metamodel-based methods, the controllability of quality features is verified for user-defined production scenarios and visualised for each design and noise parameter. Thus it is possible to identify which design parameters are indispensable to control the desired quality feature and if it is controllable depending on the actual values of the noise variables. Furthermore the controllability of the entire part is analysed by using draw-in measurements for the feedback loop. Thereby it is possible to simulate, based on the metamodels, the effects of a series production, such as the heating of the tools during the first dozen of parts. Hence, the feasibility of a process control can be verified before realisation in order to optimize the concept of process control or even the process design.

Experimental and numerical investigation of ironing in deep drawn parts

Majority of the industrially relevant deep drawn sheet metal parts undergoes an additional process after the drawing operations. Operations like flanging or hole extrusion are widely used especially in the automotive industry. In such industrial applications it is seen that process planers design the tools by using a clearance less than the sheet thickness. Due to this smaller gap between the forming steels and the post, sheet material is compressed in the thickness direction. This additional compression is definitely needed for collar forming and it is beneficial in flanging operations in terms of springback. Addition of compressive deformation state on flange regions reduces the bending effects on those parts. Ironing in sheet thickness direction is a challenging deformation state for numerical simulations. This effect can be modelled by 3D continuum elements. However, due to high computation times this solution is not feasible for industrial applications. On the other hand, shell elements are widely used in sheet metal forming problems due to their efficiency but the conventional shell elements cannot predict ironing effects since the formulation does not consider through-thickness deformation. In order to analyze the effect of ironing, cup drawing experiments were performed. Ironing level is controlled by changing the die diameter while keeping the punch diameter constant. DC04-SUPERMOD with 1.75 mm thickness was used in the experiments. The thickness distribution along the cup wall and height of the cups were measured after each operation. Same experimental procedure was modeled using new thick shell elements which accounts for the through-thickness deformation. Comparison with the experimental measurements show that the enhanced formulation of the shell elements can be used to simulate the ironing effects in deep drawn parts.

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.

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.

Effect of Mesh Size on Calculation of Strain Non-uniformity Index in Drawn Sheet Metal Parts

The spatial variation of the true major, minor and thickness strains is the combined outcome of a number of material, tool, geometric and deformation variables (many of which cannot be measured) and their complex interactions over various levels.When one calculates the strain nonuniformity index from an FEM simulation, the mesh size can be expected to influence the value of the strain nonuniformity index leading to a wrong prediction of failure. This is similar to the effect of grid circle size and circle spacing in experimentally measured strain distribution. The present paper attempts to bring out a minimum mesh size for the critical strain nonuniformity index to remain unaffected by the meshing effects. This will enable the user to set an adequate level of mesh refinement during adaptive meshing without an excessive increase in the computational cost. Comparatively, the ‘constraint factor’, which denotes the ratio of the difference between the minor strains at the peak and the pole to that between the major strains at these two locations, is likely to be much less affected by the mesh size. strain nonuniformity index reaching a critical value is accompanied by the constraint factor moving towards zero.

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.

A Knowledge Based System for Process Planning of Axisymmetric Deep Drawn Parts

This paper describes a knowledge based system (KBS) developed for process planning of axisymmetric deep drawn sheet metal parts. The proposed system is structured into three modules. For the development of proposed system technical knowledge is acquired from different sources of knowledge acquisition and it is represented by using IF-THEN rules. Rules are coded using AutoLISP language and user interface is created using Visual Basic 6. The proposed system automatically models the part geometry in the drawing editor of AutoCAD, calculates blank size, selects the necessary process parameters required for production of deep drawn parts and generates process sequence. The system is flexible because its knowledge base can be extended and modified as old manufacturing facilities are discarded or newer ones are acquired in a particular enterprise. The suitability of proposed system is demonstrated by taking an example of industrial deep drawn sheet metal part. As the system can be implemented on a PC having AutoCAD software and therefore its low cost of implementation makes it affordable for small and medium scale sheet metal industries.

A Knowledge-Based System for Manufacturability Assessment of Deep Drawn Sheet Metal Parts

In this paper a knowledge based system (KBS) for checking manufacturability of deep drawn sheet metal parts is described. For the development of proposed system technical knowledge acquired from different sources of knowledge acquisition is framed in the form of production rules of ‘IF-THEN’ variety and then coded using AutoLISP language. For consultation, the user loads the system into the prompt area of AutoCAD. The proposed system generates friendly prompt eliciting from the user for data pertaining to the job at hand. The system output includes recommendations on suitability of geometrical features of the part for required manufacturing operations. The system is flexible and its knowledge base can be extended and modified as old manufacturing facilities are discarded or newer ones are acquired in a particular enterprise. Effectiveness of the proposed system is demonstrated by taking an example of an industrial sheet metal part. The low cost of implementation of proposed system makes it affordable for small and medium scale sheet metal industries.

A study on the bi-directional springback of sheet metal stamping

The U-draw bending process is traditionally adopted to evaluate the springback of drawn sheet metals because of its large amount and uni-directional characteristic of springback. The results of springback of the U-draw bending process are, however, more or less limited to apply to general stamping processes. In this work, the bi-directional springback of drawn sheet metal parts is studied using the modified U-draw bending process. In the process, a strip with the fixed width is drawn by the elliptical tool and laid freely. Therefore, the primary springback along the longitudinal direction and the secondary springback along the transverse direction of the strip occur at the same time. In the numerical analysis, the explicit time integration method is used in the simulation of drawing stage, whereas the implicit time integration method is applied to the springback stage in order to get readily the static solution. To verify the results of numerical analysis, the experiment is also carried out. Both results are shown to be generally coincident with each other. The study is considered to be helpful to understand multi-directional springback phenomena which take place generally in industrial sheet metal stamping processes.