Punch-die Clearance Research Articles

Optimisation of Springback Predicted by Experimental and Numerical Approach by Using Response Surface Methodology

Bending has significant importance in the sheet metal product industry. Moreover, the springback of sheet metal should be taken into consideration in order to produce bent sheet metal parts within acceptable tolerance limits and to solve geometrical variation for the control of manufacturing process. Nowadays, the importance of this problem increases because of the use of sheet-metal parts with high mechanical characteristics (High Strength Low Alloy steel). This work describes robust methods of predicting springback of parts in 3D modelling subjected to bending and unbending deformations. Also the effects of tool geometry in the final shape after springback are discussed. The first part of this paper presents the laboratory experiments in wiping die bending, in which the influence of process variables, such as die shoulder radius, punch-die clearance, punch nose radius and materials properties were discussed. The second part summarises the finite element analysis by using ABAQUS software and compares these results with some experimental data. It appeared that the final results of the FEM simulation are in good agreement with the experimental ones. An optimisation methodology based on the use of experimental design method and response surface technique is proposed in the third part of this paper. That makes it possible to obtain the optimum values of clearance between the punch and the die and the optimum die radius which can reduce the springback without cracking and damage of product.

Precision Small Angle Bending of Sheet Metals Using Shear Deformation

This paper deals with a new method to bend sheet metals at a small angle precisely, in which a sheet metal is slightly bent by shear deformation at negative punch-die clearance. Deformation behavior and key factors affecting on the bend angle were studied in detail with pure aluminum sheets. It was proved that the bend angle was changed in proportion to both punch penetration and negative punch-die clearance within a certain range. The same was true for high-strength steel and phosphor bronze, which are difficult to bend precisely by conventional methods due to large springback after unloading. By using this relationship as a control law, four kinds of sheet metals were precisely bent within a few degrees. This method was applied to correct the angular errors in U-bend products of high-strength steel and to bend leaf springs of phosphor bronze at an arbitrary small angle.

Cutting process influence on fatigue steel sheets properties

Accurate fatigue strengths of steel sheets are needed to assess the in-service fatigue life of automotive metallic components. Mechanical parts or structures made from steel sheets are generally obtained by stamping and cutting. In fact mechanical fatigue properties are strongly modified by the machining. Cutting generates a typical shape edge with tremendous geometrical defects that leads to a lowering in steel fatigue strength. The aim of the present paper is to investigate the fatigue properties modifications induced by the mechanical cutting. High cycle fatigue tests have been performed on nine steel grades specimens (with ultimate tensile strength from 300 MPa to 600 MPa) cut with punch-die clearance values ranging from 5% to 30% of the sheet thickness. The experiments allow us to define one critical value of the punch-die clearance as a function of the ultimate tensile strength of the steel. This value should not be exceeded for industrial applications in order to limit the detrimental cutting influence on fatigue properties. In fact, the punch-die clearance drives the location of the crack initiation site that can be clearly related to the fatigue strength reduction.

금속 소재의 미세 홀 펀칭 시 전단 파괴 거동 연구

In the micro hole punching, the size and shape of burr and burnish zone are very important factors to evaluate quality of micro holes which depend on punch-die clearance, strain rate, workpiece material and etc. To get micro holes with small burr and wide burnish zone for industrial demands, not only the parametric study but also a study on fracture behavior in shear band are necessary. In this study, 100 <TEX>$\mu$</TEX>m, 25 <TEX>$\mu$</TEX>m micro holes in diameter were fabricated on brass (Cu63/Zn37) and SUS 316 foils as aspect ratio 1:1, and the characteristics of micro holes was investigated comparing with those of macro holes over several mm by scanning electron microscopic views and section views. Like macro hole, micro hole is also composed of 4 portions, rollover. burnish zone, fracture zone and burr, and it shows similar fracture behavior in shear band. But by high strain rate (10<TEX>$^2$</TEX>∼10<TEX>$^3$</TEX>s<TEX>$^{-1}$</TEX> ) condition unlike that of macro hole fabrication and by the increment of relative grain size in the direction of the workpiece thickness, fracture zone is not observed.

Prediction of optimum clearance in sheet metal blanking processes

The blanking process and structure of the blanked surface are influenced by both the tooling (clearance and tool geometry) and properties of the workpiece material (blank thickness, mechanical properties, microstructure, etc.). Therefore, for a given material, the clearance and tool geometry are the most important parameters. The objective of the present work is to develop a methodology to obtain the optimum punch-die clearance for a given sheet material by simulation of the blanking process. A damage model of the Lemaitre type is used in order to describe crack initiation and propagation into the sheet. A comparative study between numerical and experimental results shows good agreement.

Small Angle Bending Using Shear Deformation with Negative Punch-die Clearance

In sheet metal bending, bending die is designed in prospect of spring back after unloading. Although accuracy of spring back analysis has been improved, slight variation of thickness or material properties depending on production lot of sheet metal causes scatter of bend angle in mass production, which is a serious problem especially in bending high strength steels or low priced sheets. As a countermeasure, a new method for compensation of bend angle is proposed in this paper. When sheet metal is partially sheared with negative punch-die clearance, it is slightly bent by the gradient of plastic strain normal to bend axis developed in the sheared zone. By controlling this deformation, accurate and adjustable bending was studied. Change of bend angle depending on punch penetration, clearance, tool edge condition and lubrication was investigated experimentally for two kinds of pure aluminum sheets 0.8 mm in thickness. Among test parameters, punch penetration was found to be most influential one and to have linear relationship with bend angle, which suggests good angle-controllability of this method. Strength of bent portion was tested and sufficient strength was assured up to 20% punch penetration against sheet thickness under the optimum condition. Moreover, spring back was little observed since plastic strain is much higher than that by moment bending. These results were studied with strain distribution estimated by elastoplastic finite element analysis.

Prediction of burr height formation in blanking processes using neural network

Productivity and quality in sheet metal blanking processes part can be assessed by the burr height of the sheared edge after blanking. This paper combines predictive finite element approach with neural network modelling of the leading blanking parameters in order to predict the burr height of the parts for a variety of blanking conditions. Experiments on circular blanking operation has been performed to verify the validity of the proposed approach. The numerical results obtained by finite element computation including damage and fracture modelling and tool wear effects were utilized to train the developed simulation environment based on back propagation neural network modelling. A trained neural network system was used in predicting burr height of the blanked parts versus tool wear state and punch-die clearance. The comparative study between the results obtained by neural network computation and the experimental ones gives good results.

Prediction and elimination of springback in straight flanging using computer-aided design methods: Part 2: FEM predictions and tool design

Part 1 of this two-part paper presents the laboratory experiments on straight flanging, in which the influence of process variables, such as die shoulder radius, punch-die clearance, punch nose radius, pad force and material properties were discussed. This second part summarizes the FEM predictions for flanging and compares these results with some experimental data. Furthermore, flanging with coining to reduce springback has been investigated and evaluated by FEM for better dimensional control in flanging and hemming processes.

Finite element analysis of optimum clearance in the blanking process

Abstract We propose a methodology to obtain optimum punch-die clearance values for a given sheet material and thickness to be blanked, using the finite-element technique. In the present investigation, the shearing mechanism was studied by simulating the blanking operation of an AISI 304 sheet. Simulation used the FEM program ANSYS and also the Crockroft and Latham fracture criterion. The results of the present paper are in agreement with the results of experimental studies and reflect the results of previous theoretical work.

Process control in blanking

This paper summarizes the results of testing the performance of in-die sensors for controlling the stamping process. Piezo based as well as strain gage based in-die sensors were mounted at different locations within a progressive die. Furthermore, these signals were compared with load curves of press frame mounted sensors and the acoustic emission acquired from a triaxial acceleration sensor. The signals acquired from the different in-die sensors at the different mounting locations showed all the different phases of the process. It was shown that changing process variables such as punch-die clearance, material properties, stroke rate and punch-die alignment results in different load-stroke curves. Based on these results it could be concluded that in-die sensors provide the most detailed information about the process.

An investigation of process parameters in the dam-bar cutting of integrated circuit packages

The rapid evolution of micorelectronics is placing greater demands on the packaging technology of integrated circuits (IC), the trend being towards higher lead counts, smaller lead width, finer lead pitch and thinner leadframes. These demands impose stringent requirements on the quality of dam-bar cutting, the latter being a mechanical trimming process in which the dam bar btween the leads of an IC package after post-molding process is pierced out. The leadframe thickness and the area of cutting are in the order of one tenth of a millimeter and cutting is performed at a much higher speed than that found in conventional blanking and piercing processes. In this work, a purposely built single-punch dam-bar cutting press was constructed. The effects of percentage punch-die clearance, punch shear and the plastic anisotropy of the leadframe materials on the cutting force and energy, and the quality of the sheared edge of the dam-bar, were studied. The optimum punch-die clearance for minimum cutting energy was established. The cutting force, energy and burr height were found to be affected by the plastic anisotropy of the virgin leadframe materials. These findings can be applied in the design of trimming tools used in the dam-bar cutting of IC packages.

Material fracture and burr formation in blanking results of FEM simulations and comparison with experiments

This paper summarizes the results of simulating the blanking process by means of a modified DEFORM-2D FEM (Finite Element Method) code. Several modifications were made to this code in order to simulate the material fracture. Unlike most other approaches, it was possible to obtain each of the zones of a blanked part edge such as roll over, shear zone, rupture zone and burr. Several blanking simulations were performed and the results were compared with our experimental studies. It was shown that the influence of process variables such as punch-die clearance, material properties and punch and die wear could be simulated with a good correlation to experimental results. Furthermore, the simulated and experimentally obtained load stroke curves show the same changes of shape and absolute value due to variations in process conditions.

4829237 Circuit device having a self-testing function and a testing method thereof

The improvement in the productivity of the leadframe blanking industry of is a key for its competitiveness. Consequently the challenge for researchers covers a wide range of scientific areas (materials, lubrication, process, etc.). Among others the improvement of the punch wear resistance is one of the most important parameters in the blanking process. Consequently punch wear understanding is the topic of this paper.Because of the strong influence of the centering of the punch-die clearance upon the burr amount, it is crucial to directly measure punch wear in the blanking press without disassembling the tool. In this paper a new method for a direct measurement of the punch wear, selective activation technique, which has never been applied in the field of blanking is described. With the help of this technique, a precise relation between the loss of activity and the worn volume on the punch has been established. In addition this method allows the influence of the blanking process parameters, like lubrication or nature of the blanked material, to be quantified in real time.The measured wear volumes by this method have been confirmed by means of measurements of the profile of the worn punch carried out after completion of a large amount of blanked parts. These geometrical results exhibit a good agreement with the selective activation technique.

Theoretical investigation of optimum clearance in blanking

In this work a method is described to investigate theoretically the optimum punch-die clearance in the blanking operation for given parameters, using the finite-element technique. The effect of the ductility on the value of the optimum clearance and of the optimum penetration is established. The results obtained through the finite-element analysis are compared with available theoretical and experimental results. It is found that the results of the present work are in close agreement with the results of experiment and the trends match well with the results of the theoretical work.

Effect of punch clearance in the high-speed blanking of thick metals using an accelerator designed for a mechanical press

This paper examines the effects of varying (a) the punch-die clearance and (b) the hardness of the specimen, on the surface finish and quality of blanked specimens for a variety of metals. The blanking speeds used were both low (0.13 m/s) and high (10 m/s). To achieve the high speed required, an accelerator has been developed to convert the low speed of a mechanical press into the fast movement of a piston, using the compression of air through a differential piston system. Features of the sheared surfaces of both low- and high-speed blanks were observed using an optical and a Scanning Electron Microscope, details of which are also reported in the paper.

An Experimental Investigation into the Redrawing of Cylindrical Shells

Cups having a height/diameter ratio greater than unity cannot as a rule be produced from flat circular blanks in a single stage, and redrawing in one or more operations has to be carried out until the desired shape of the shell is attained. In this paper an account is given of an experimental investigation into the forces, work, and strains involved in the first redrawing process. The work was carried out in an experimental crank press (Seed and Swift 1950)‡ of 50 tons nominal capacity, and was based on a first-stage cup diameter of 4 inches. Brass, mild steel and aluminium (in two tempers) were used. The conditions examined include the direct and reverse methods of redrawing, first-stage drawing ratio, inter-stage heat-treatment, punch profile radius, first-stage punch-die clearance, redrawing ratio, blank thickness, material, and temper. It is thought that the results are sufficiently accurate and detailed to give a reasonably complete insight into the redrawing process, and conclusions have been drawn to assist press-tool engineers in the design of drawing tools.

An Experimental Investigation into the Redrawing of Cylindrical Shells

Cups having a height/diameter ratio greater than unity cannot as a rule be produced from flat circular blanks in a single stage, and redrawing in one or more operations has to be carried out until the desired shape of the shell is attained. In this paper an account is given of an experimental investigation into the forces, work, and strains involved in the first redrawing process.The work was carried out in an experimental crank press (Seed and Swift 1950)‡ of 50 tons nominal capacity, and was based on a first-stage cup diameter of 4 inches. Brass, mild steel and aluminium (in two tempers) were used.The conditions examined include the direct and reverse methods of redrawing, first-stage drawing ratio, inter-stage heat-treatment, punch profile radius, first-stage punch-die clearance, redrawing ratio, blank thickness, material, and temper.It is thought that the results are sufficiently accurate and detailed to give a reasonably complete insight into the redrawing process, and conclusions have been drawn to ...

Cup-drawing from a Flat Blank: Part I. Experimental Investigation

Part I gives an account of an experimental investigation of the forces, work and strains involved, and the conditions for successful drawing of a cylindrical shell from a flat circular blank. It is claimed that the results are sufficiently accurate to provide a basis of reference for theoretical treatments of cup-drawing, as well as an empirical basis of comparison between different drawing conditions. The work was carried out in an experimental crank-press of 50 tons nominal capacity, and was based on a cup diameter of 4 inches. Blank thicknesses from 0·025 to 0·060 inch were used, and although most of the work was carried out on a low-carbon rimming steel, comparative tests were made with aluminium, brass, and copper, of different tempers. The conditions examined included methods of blank-holding, drawing ratio, punch and die profile radii, punch-die clearance, and blank thickness. Although this part has no theoretical pretensions, it includes a descriptive account of stresses and strains in the deep-drawing process, based on plastic theory.