Sheet Metal Drawing Research Articles

Numerical investigations of constitutive tensile behaviour of materials and wrinkling of cold-rolled aluminium sheet when deep drawn through a Tractrix die

Deep drawing is an important metal working process used for making cup shaped articles at a fast rate. The drawability of sheet metal can be quantitatively estimated by the Limiting Drawing Ratio (LDR). An inverse finite element procedure is developed and clubbed with ABAQUS computer code for the determination of constitutive tensile behavior of materials. The proposed inverse technique is based on the miniature specimen experimental load versus. elongation curve. In this paper miniature tension tests are conducted on dumb bell shaped specimen made from Aluminum. By using the output of experimental miniature tension test, constitutive stress strain curves are traced through inverse technique. The use of a Tractrix die enhances the limiting draw ratio as compared with that obtainable in a conventional drawing operation. Application of these dies, in most of the cases, eliminated the use of blank holder but it enhances the tendency of wrinkling in drawn products.

On the quantification of strain distribution in drawn sheet metal products

When a flat sheet is drawn into a product, ideally, a uniform strain distribution is desired. However, non-uniformity in strain distribution is generated by the product geometry, tool-sheet contact conditions and material properties. It is difficult to predict as to when and where the non-uniformity will develop. Non-uniformity in thickness reduces the usable ductility and leads to an early failure. Since the individual effects of the above mentioned factors and their combinations are not easily quantifiable and often not deterministic, the combined consequence of these on the strain distribution is quantified by newly defined variables, “constraint factor”, and the “strain non-uniformity index”. In this paper, the effect of geometric, material and process parameters on the variation of the constraint factor and the strain non-uniformity index over the punch stroke will be demonstrated. It is found that the effects of the processing variables on material formability as assessed using the ANOVA are confirmed by the behavior of the constraint factor and strain non-uniformity index as well.

Equal channel angular drawing of aluminium sheet

A method of equal channel angular drawing of sheet metals (ECADS) is presented and results of its application to a thin sheet of commercially pure aluminium are reported. The obtained mechanical properties, textures and microstructures are compared to those resulting from closely related processing techniques: (a) ECAD of rods, and (b) continuous shearing of sheets (CSS).

A new type of deep drawing die design and experimental results

Deep drawing is an important process used for producing cups from sheet metal in large quantities. The deep drawing is affected by many process variables, such as blank shapes, profile radius of punch and die, formability of materials and so on. Especially, in order to obtain the optimal products in deep drawing process, blank and die shapes are very important formability factor. In this study, we investigated the effects of blank holder and die shapes, using five kinds of blank holder and die shapes. We measured the distribution at blank holder force (BHF) according to the ratio of sheet metal drawing, under the constant conditions of profile radius of punch and die. Deriving from the experimental studies, it is clarified that angle of blank and die at deep drawing process influence blank holder force distribution and ratio of drawing.

An Elasto-Plastic Finite Element Analysis of the Hat-Type Drawing Process of Sheet Metal

This study aims to clarify the process conditions of the hat-type drawing of a sheet metal of steel. It provides a model that predicts not only the correct punch load for drawing, but also the precise final shape of products after unloading, based on the tensile properties of the material and the geometry of the tools used. An elasto-plastic incremental finite-element computer code, based on an updated Lagrangian formulation, was developed to simulate the hat-type drawing of sheet metal. In particular, selective reduced integration was adopted to formulate the stiffness matrix. The extended r-minimum technique was used to deal with the elasto-plastic state and contact problems at the tool-metal interface. A series of simulations were performed to validate the formulation in the theory, leading to the development of the computer codes. The whole deformation history and the distribution of stress and strain during the forming process were obtained by carefully considering the moving boundary condition in the finite-element method. Results in this study clearly demonstrated that the computer code for simulating the hat-type drawing process was efficient.

Parameter identification by neural network for intelligent deep drawing of axisymmetric workpieces

Intelligent deep drawing for axisymmetric workpieces is an important research field of intelligent sheet metal forming, and real-time identification of parameters is a key technology for intelligent deep drawing. This paper presents a feed-forward neural network model based on the LM algorithm (put forward by Levenberg and Marquardt), which is established to realize real-time identification of material properties and friction coefficient for deep drawing of an axisymmetric workpiece. Compared with the previous BP model (neural network based on back propagation algorithm) and GA-ENN (evolutionary neural network based on genetic algorithm) model, the error goal of parameter identification by the LM model is stepped downward to a new level. Therefore, accurate parameter identification, which provides preconditions as well as assurance for accurate prediction and control, lays the basis for intelligent deep drawing of sheet metal.

A comparative study on the performance of boric acid with several conventional lubricants in metal forming processes

During metal forming, lubricants are necessary to prevent direct contact, adhesion, transfer, and scuffing of workpiece materials and tools. The lubricating action of boric acid is due to its layered crystalline structure, and is similar to the structure of MoS 2 and graphite. However, boric acid lubrication could offer distinct advantages in terms of its application prior to forming and removal after a forming operation since it can be dispensed using water and alcohol solutions, raising the possibility of being environmentally friendly. Its effectiveness under actual conditions of metal forming operations such as rolling, forging, and sheet metal drawing and stretching has been evaluated in this study with both ferrous and non-ferrous work materials. It was found that boric acid provided lowest friction in sheet drawing and stretching operations, which is attributed to its lattice layer structure that facilitates easy sliding between molecular layers. Under predominantly compressive conditions of forming, liquid or semi-solid lubricants have performed better as they could squeeze out along with forwarding workpiece surfaces. The findings presented in this paper increase the prospect for developing boric acid as an effective lubricant in the cold forming of materials under certain conditions.

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.

연속드로잉에서 아이어닝과 리드로잉의 복합공정

In deep drawing of sheet metal, there are many cases in which the uniform and thin wall thickness of the drawn products is more important than the bottom thickness. In this case, we can not easily get the deep drawn products with the uniform and precise wall thickness by only drawing process. Therefore in general the manufacturing processes which both the drawing and the ironing process are proceeded sequentially are used. But this method has the disadvantages of a cost-up, decrease of productivity and degradation of quality, because the ironing process is added after the drawing process. In this study, in order to improve those problems and to enhance the effect of deep drawing, the combined process of redrawing and ironing fur multistep drawing of cylindrical cups is used. In this experiment, we considered the characteristics of the combined process such as the relation between the drawing and ironing rates, the drawing limits and the forces needed for operations. The suggested force prediction shows that it can successfully represent experimental results.

マスレニコフ法による板材の絞り成形の数値シミュレーション(OS4 塑性加工のシミュレーション)

マスレニコフ法による板材の絞り成形の数値シミュレーション(OS4 塑性加工のシミュレーション)

Data fusion of distributed AE sensors for the detection of friction sources during press forming

The authors proposed a friction source detection system using multi-acoustic emission (AE) sensors and data fusion system in this study. In this work, three AE sensors are positioned at the metal forming tool for identification of the location of friction sources. The AE signals were processed by FFT and discrete wavelet transform (DWT), in order to reduce the noise and extract features of signals due to friction. The Fujimori method was employed to measure the arrival time from AE source to the distributed sensors. Furthermore, a database was constructed and employed to estimate the source location. The detection system was applied for measuring the friction during deep drawing of sheet metal. Several experiments were carried out by using the friction detection system and the results show that the location of friction source can be successfully detected by using the multi-AE sensors system even if location of friction resource on interface of the die and the workpiece is invisible.

Effect of variable friction coefficient on sheet metal drawing

A variable friction model that relates the parameters of sheet metal drawing to the local lubrication conditions taking place during the deformation, has been integrated to a finite element program. Variable friction coefficients for the contacting surfaces are determined from the friction model, which uses the related parameters obtained at each time step of the finite element program as inputs. A number of numerical runs have been performed and the strains are compared with the experimental results for circular blanks. A good agreement is obtained between the numerical and experimental results for the variable friction model used.

Friction aided deep drawing of sheet metals using polyurethane ring and auxiliary metal punch. Part 2: analysis of the drawing mechanism and process parameters

Friction aided deep drawing using a polyurethane ring as a pressure medium has been analyzed by the slab and the energy methods to understand the main features of the process and to find the optimum conditions to achieve successful drawing. The effect of an auxiliary metal punch on the stress distribution of the deformed blank and the increase in height of the drawn cup is also discussed. From these studies, the reason why the unusual circumferential crack occurs at the flange of the deformed blank has been clarified, based on the radial stress distribution of the deformed blank. A process parameter, which denotes the drawing characteristics of the friction aided deep drawing, has been proposed. In addition, the drawing region diagram has been presented to facilitate the drawing pressure control with the progress of the drawing process. It is shown that the successful drawing region is narrow at the early stage of drawing, although it becomes wide as the drawing proceeds. Therefore, in the early stage of drawing, special care should be paid to the drawing pressure control to avoid the flange crack.

Friction aided deep drawing of sheet metals using polyurethane ring and auxiliary metal punch. Part 1: experimental observations on the deep drawing of aluminium thin sheets and foils

Friction aided deep drawing based on the Maslennikov process is investigated as a method to facilitate the deep drawing of sheet metals with poor drawability. Aluminium foils and thin sheets of 0.1–0.4 mm in thickness are used as a model for the material with poor drawability. An auxiliary metal punch is used together with a polyurethane ring to increase the drawing efficiency and to improve the dimensional accuracy of the drawn cup. The effect of drawing conditions such as thickness, hole diameter and the hardness of the polyurethane ring on the cup height are mainly investigated. Also, the optimum number of drawing operations required to achieve a given drawing ratio is examined by repeating compression and unloading the polyurethane ring. The experimental results show that even for foil and thin sheets, deep cups with drawing ratios of 2.25 and with good shape and dimensional accuracy can be obtained by repeating the drawing operation about ten times. The achievable drawing ratio is appreciably larger when compared with that obtained by the conventional deep drawing process.

Microdeep drawability of very thin sheet steels

The purpose of the present study is to clarify the microdeep drawing characteristics of very thin sheet steels of below 0.2 mm thickness. An experimental study was conducted with specially developed experimental apparatus. In this study, a relative punch diameter D p/ t ( D p: punch diameter, t: thickness of sheet material) was chosen as an important experimental parameter and ranged from 10 to 100. Drawability was evaluated, and the similarity laws in deep drawing were examined with sheet steels of 0.05, 0.1, 0.2 and 1.0 mm thickness. For D p/ t from 10 to 100, ordinary drawability was obtained for very thin sheet steels without a large amount of blank holder pressure, and a decrease in value of limiting drawing ratio was observed with an increase in D p/ t. The similarity law of thin sheet metal drawing is adapted above D p/ t=40 because the drawing mechanism below D p/ t=20 should differ from the above D p/ t=40. The differences are also revealed in the shape of drawn cups. For D p/ t=10 and R d/ t=5.0, bending is the dominant forming mechanism since blank holder pressure has little effect on drawability and no effect on the working material during the latter half of the drawing process. Therefore, the drawing behavior seems similar to that in drawing thick sheet metals and is characterized as microdeep drawing of very thin sheet metals.

Development of rapid tooling for sheet metal drawing using nickel electroforming and stereolithography processes

Tooling is an important area in the manufacturing of various sheet metal products. This aspect can be extremely expensive as well as time consuming. The increase in the complexity of tooling for any operation results in a corresponding increase in the time and costs required in developing such tooling. The ideal candidate operations for rapid tooling (RT) have been those for which it is difficult to develop tooling by the usual methods. The quest is to produce complex tooling quickly and at low cost. This paper describes the development of RT techniques for the production of sheet metal drawing tooling by using a combination of stereolithograhy and nickel electroforming processes. Two types of prototype tools have been designed and manufactured. The first type is a stereolithography QuickCast pattern infiltrated with aluminium-filled epoxy designated as QuickTool, and the second type has been manufactured by combining stereolithography technique with the nickel electroforming process. While the QuickTool may be indeed rapidly manufactured it can be only a prototype tool, as the material it is made of does not render much durability. On the other hand, the nickel electroformed tool is far more durable and can withstand more extreme working conditions. By combining nickel electroforming and the stereolithography process, press tools for sheet metal forming have been successfully produced. Further, the developed tools have been evaluated in the press metal forming process by producing components with 0.8 mm aluminium sheets.

Strain field of deep drawn knitted fabric reinforced thermoplastic composite sheets

Deep drawing of sheet metals has been widely investigated and practiced for the past five decades. Previous investigations on the deep drawing of sheet metals centered around the strain distribution of a formed cup. Recently, deep drawing of textile composites has been receiving the attention of researchers. This paper explores the strain distribution of deep drawn knitted fabric reinforced thermoplastic composite sheets. The strain field gives an indication of the location of severe strains and their magnitude. The method of composite sheet production, experimental procedure and processing of data are also described. It has been found that strains are generally higher in the course direction than in the wale direction. The variation of the punch profile has also been shown to alter the strain field.

Process optimisation in deep drawing

ABSTRACT A numerical technique for process optimisation applied to the deep drawing of sheet metals is proposed in this paper. This technique is based on the combination of an optimisation algorithm and a finite element method. The optimisation algorithm is based on a gradient method containing a sensitivity analysis and allows to optimise process parameters in order to obtain a final product with the desired shape. Numerical examples are presented to illustrate the efficiency of the proposed approach.

A Study of the Optimization of Sheet Metal Drawing with Active Drawbeads

An experimental study is described in which active drawbead technology is used to attempt to optimize the sheet metal forming process. Oval AA 6111-T4 panels were drawn in a series of tests using various drawbead trajectories to establish the feasibility of the approach. The selection of drawbead trajectory was shown to have a dramatic effect on maximum attainable draw depth at fracture. Increasing drawbead penetration from zero to 5 mm in the early stages of the drawing process and retracting midway through the draw resulted in a 40% increase in draw depth compared to using a fixed 5 mm penetration. In the second part of the investigation, active drawbead technology was used to study its effect on highly nonsymmetric panel forming. Drawing limit curves in terms of drawbead depth versus blankholder forces (BHF) were plotted, and different drawbead trajectories were tested to determine an optimal drawbead trajectory scheme. A corresponding finite element model was also created. The results of strain path analysis successfully support the experiments.

Multiple Fault Detection and Isolation Using the Haar Transform, Part 2: Application to the Stamping Process

The sheet metal drawing operation is a complex manufacturing process involving more than forty process variables. The intricate interaction among these variables affect the forming tonnage which is measured by strain gages mounted on the press. A fault is said to occur when any of these process variables deviate beyond their specified limits. Current detection schemes based on thresholding do not fully exploit the information in the tonnage signals for the detection and isolation of multiple fault condition. It is thus an excellent case study for demonstrating the implementation of the detection methodology presented in Part 1. By partitioning the tonnage signature into disjoint segments, mutually exclusive sets of Haar coefficients can be used to isolate faults in each stage of the process.