Die Clearance Research Articles

Investigating the effect of Nylon 6.6 electrospun nanofiber mats and punch—Die clearance on the damaged area and residual strength of punched glass/epoxy composite laminates

Investigating the effect of Nylon 6.6 electrospun nanofiber mats and punch—Die clearance on the damaged area and residual strength of punched glass/epoxy composite laminates

Modeling and numerical analysis of the process of punching aluminum sheets taking into account punch wear

The paper presents the modeling and analysis algorithm as well as the results of simulation tests with the use of FEM of the process of punching aluminum sheets used for casings. The first part presents the results enabling the correct selection of the die clearance on production lines depending on the thickness of the sheet metal. The second shows how to prepare the punch geometry in the FEM environment, taking into account the typical defects that occur as the work cycles increase. Thanks to this, it was possible to determine their influence on the state of stresses and deformations as well as the quality of the cut edge. The developed numerical applications and the obtained test results can be used to design tools and optimize the punching process.

Effect of Die Clearance on Peak Punching Force During Cryogenic Micropunching of Polycaprolactone

Abstract Microscale holes were punched at cryogenic conditions in polycaprolactone (PCL) membranes to create synthetic three-dimensional (3D) tissue scaffolds through multilayer stacking of two-dimensional (2D) porous membranes. Punching forces were experimentally measured, and finite element modeling of the punching process was validated by comparing punching force results. Holes of nominal diameter of 200 μm were punched in PCL films of two different thicknesses: 40 μm and 70 μm. Die clearances used for holes in 40 μm thick films were 15.0%, 30.0%, and 45.0%. Die clearances used for holes in 70 μm films were 8.6%, 17.1%, and 25.7%. All holes were punched while the PCL film was in thermal equilibrium with a bath of boiling liquid nitrogen. Punching forces were analyzed to study the effect of die clearance and film thickness. A 3D finite element simulation of the punching process was done using deform 3d software. Cryogenic material properties of PCL used in the simulation were determined experimentally. It was concluded that finite element simulation for the cryogenic micropunching process can be used to predict peak punching forces with reasonable accuracy, which is a key factor to be considered while designing the punching dies. The finite element simulations did not predict an optimal die clearance to minimize peak punching force. However, the measured peak punching forces for 70 μm thick film seem to favor the smallest die clearance to minimize peak punching force.

Shearing and Shaving Process of Stainless Steel Wire at Micro Scale

This study investigated the effects of the die clearance on the shearing and shaving processes of the stainless steel (SUS316LVM) wire at micro scale. A die set was developed and installed on a precession press equipped with a load cell and a displacement sensor to conduct experiments. By using different punches in the same die set, the specimens prepared from 316LVM stainless steel wires with 0.5 mm diameter were first sheared and then shaved. Experimental results show that the burnished area of the sheared edge increases with the reduction of the clearance between the punch and die in the shearing process. The clearance also significantly affects the load curves. Moreover, the shaving process does increase the burnished area on the shaved edge of the specimen. By an appropriate feed in the shaving process, it is possible to trim the extra material from the sheared edge that results in a nearly complete burnished surface on the shaved edge of the stainless steel wire. This research provides a basis for understanding of the die clearance effect on the shearing and shaving processes at micro scale.

Optimal Design of Stamping Process for Fabrication of Titanium Bipolar Plates Using the Integration of Finite Element and Response Surface Methods

Due to the high importance of metallic bipolar plates (BPPs) in proton exchange membrane fuel cell (PEMFC) from mechanical properties and ease of production points of view, titanium is selected because of its excellent corrosion resistance and low density. The present study deals with the forming of titanium ultra-thin sheet (with a thickness of 0.1 mm) as an alternative for BPPs using the stamping process. A finite element (FE) model is developed to simulate the process, and the effect of forming parameters and their optimal level are found via response surface methodology (RSM). In this design, clearance of die, stamping speed, and die/sheet friction coefficient are assumed to be as input variables and the formability of the titanium sheet in terms of maximum filling depth of the microchannel is investigated as output. A strain-based damage model is considered to examine the failure of the sheet during the simulation. The FE results demonstrate that the friction coefficient and clearance are the most remarkable parameters on the maximum filling depth with 50 and 46% of contributions, respectively. Changing the stamping speed has no tangible influence on the stampability of the titanium sheet. In addition, a regression model for estimating the maximum filling depth is represented based on the input variables. Eventually, a stamping die setup is fabricated and some experiments are carried out to validate the accuracy of the FE simulations and RSM results.

Experimental and FE analysis on spring-back of copper/aluminum layers sheet for a L-die bending process

This paper is a conduct of experimental tests to investigate different effective parameters of a UNS C10100 copper/aluminum 1100 spring-back on a two-layer L-die bending sheet through finite element simulations. The parameters are the radius and clearance of die, sheet length, thickness of each layer, different lay ups, and sheet annealing. The paper shows that the spring-back decreases with the reduction of the die clearance and radius, similar to the behavior of single-layer sheet and with the increase of the sheet length. The outcome displays a contradiction with ‘no significant effect’ in the single-layer sheets, previously published in other papers. Furthermore, the thicknesses of copper and aluminum are important roles to evaluate spring-back; however, there is no certain rule to decrease or increase the spring-back through changing the thickness of each layer. Moreover, this work shows the effects of stacking sequence of aluminum and copper layer on the spring-back, because of the different natural axis in each stacking sequence and also different ultimate strength of each layer. Finally, it is concluded that annealing heat treatment significantly reduces the spring-back, where the intermetallic bond hardness in the interface of Cu/Al layers and spring-back increases with the rise of annealing temperature.

Finite element simulation and experimental investigations of cold stamping forming defect of A588-A thick weathering steel bogie lower cover

In order to improve the stamping accuracy of the bogie cover plate of the rail vehicles. The cold stamping forming process of A588-A thick weathering steel plate with variable initial bending size (“H”) produced by the pre-straightening process was investigated by numerical simulation and experiment. The effects of “H”, curvature direction of the plate, and small curved fillets radius on the forming quality of the thick steel plate were analyzed. The results demonstrated that there are defects, such as serious springback, distortion of stamping fillet, and low profile accuracy. We propose some corresponding defect control methods. The larger initial bending size “H”, the higher springback value occurred. By applying 1.2–1.4 times springback compensation to the die geometry, the springback was reduced and the contour accuracy was enhanced exponentially. By replacing the original die fillet material with C12MoV and reducing the die clearance, the cross-section distortion of the stamping fillets due to bad die fittingness could be eliminated. The accuracy of the component can also be improved by controlling the curvature direction of the plate. The cold stamping test was carried out by using the best process parameters and defect control methods. The results show that the control methods are extremely effective.

Stretch bending defect control of L-section SUS301L stainless-steel components with variable contour curvatures

The stretch bending of L-section variable-curvature SUS301L stainless-steel roof bending beams for metro vehicles was numerically simulated. The causes of defects such as wrinkling, section distortion, and poor contour accuracy were analysed, and the corresponding control methods were proposed. The simulation results demonstrated that wrinkling in the small-arc segment could be eliminated by setting the die clearance and adjusting the elongation reasonably. Owing to the sidewall shrinkage of the profile in the process of stretch bending, the die groove depth was correspondingly reduced. Each section of the profile was effectively supported by the bottom of the die groove, and the section distortion could be controlled. Springback was the main reason for the poor contour accuracy, which could be compensated by modifying the die surface based on the springback value. Using the above defect control methods, forming experiments were performed on a new type of stretch bending die with variable die clearance and groove depth developed in this work. Finally, high-quality components were obtained, which verified the efficacy of the defect control methods.

Mechanism of fracture in sheet metal cutting processes and its effect on sheared edge stretchability

In recent years, implementation of aluminum alloys, the advanced high strength steels and ultra high strength steels (UHSS) is quickly increasing in automotive industry. However, these materials are often sensitive to sheared edge cracking if stretching along the sheared edge occurs in such processes as drawing of panels with blanked windows, stretch flanging and stretch hemming of edges of the panel. This study is dedicated to development of experimental techniques necessary to account for sheared edge condition on material formability as well as reporting the experimental results and general trends. Analysis of the hole punching process indicated that uniformity of the cutting clearance is rather difficult to maintain, especially for UHSS material where cutting forces are substantially higher than for mild steels or aluminum alloys, and stiffness of the tool starts playing critical role. Therefore, the majority of experimental studies were performed as tensile tests of samples sheared along a straight line in a dedicated trim tool where special measures were taken to achieve consistency of the die clearance. Experimental results on sheared edge stretchability of aluminum alloys similar to 6111-T4 and UHSS steel DP980 are reported. The mechanism of fracture propagation in trimming and hole punching processes is discussed in conjunction with sheared edge stretchability. The rather unique mechanism of fracture observed for trimming of UHSS DP980 steel leads to burr breaking at the final stage of the shearing process.

Numerical Analysis On The Effect Of Various Parameters On Fracture Limit For Deep Drawn Cups

Deep drawing is the process of converting a blank into cup shaped articles like kitchen sinks, cooking pans, automobile panels, gas tanks, fountain pen caps etc. Wrinkles and fractures are the major defects in deep drawn products. Fracture is the separation or fragmentation of a solid body into two or more parts under the action of stress. In deep drawn cups tearing is usually an open crack in the vertical wall which occurs near the base due to high tensile stress that causes thinning and fracture of the metals at this location. During this process the punch force acting on the bottom of the cup is transferred to the side of the cup. The narrow ring of metal just above the bottom of the cup is subjected to plane strain condition. As a result, failure of the cup easily happens in this zone due to necking induced by the tensile stress, leading to tearing. This type of failure can also occur on the flange as the metal is pulled over the sharp die corner. In addition to this sharp corner on the punch could also cause fracture of the cup along the corner. The objective of this work is to predict the fracture limit of deep drawn cups. This would help in preventing rejections in deep drawing industry. This can be achieved by setting the blank holder force appropriately. Also it would save material and reduce the total cost. In this work numerical simulations are conducted by considering five different parameters namely punch radius, die radius, clearance, coefficient of friction and punch diameter using finite element explicit solver LSDYNA. Modeling of the set up is done using hyper mesh. In this work simulations are carried out as per L-27 orthogonal array suggested by Taguchi. A combination of finite element method and Taguchi analysis is used to determine the influence of process parameters on fracture limit in deep drawing process. During analysis the value of optimum BHF is arrived by performing a number of trial runs. Also Column effect method and plotting methods are used for finding out the most influencing parameters and their interactions respectively for analysis. The studies reveal that punch diameter is most significant parameter for deciding fracture limit followed by die corner radius and clearance. In addition to this regression analysis is carried out for developing an empirical model using Minitab 17 for predicting fracture limit.

An Experimental Work on Tool Wear Affected by Die Clearance and Punch Hardness

Die clearance is a widely known parameter affecting both tool life and edge quality of parts in blanking operations. Selecting the optimum punch–die clearance can give a longer tool life and better product quality by minimizing tool wear. In experimental studies, the effects of cutting die clearance and punch hardness on the punch edge and face wear were investigated. AISI D2 cold work steel with 50, 55 and 60 HRC-hardness punches was used as tool material. Three different cutting die clearances 3, 5 and 8% of sheet thickness were used. A modular punch–die set was prepared, and 2000, 4000, 6000 and 8000 samples are pressed. The results of the experiments showed that the punch edge and face wear decreased with increasing punch hardness and that smooth-sheared parts are strongly dependent on the clearance.

Trimming and Sheared Edge Stretchability of Light Weight Sheet Metal Blanks

Abstract In recent years, implementation of aluminum alloys, advanced high strength steels (AHSS) and ultra high strength steels (UHSS) is quickly increasing in automotive components due to their superior structural performance and vehicle weight reduction capabilities. However, these materials are often sensitive to sheared edge cracking if stretching along the sheared edge occurs in such processes as drawing of panels with blanked windows, stretch flanging and stretch hemming of edges of the panel. This study is dedicated to development of experimental techniques necessary to account for all these factors as well as reporting the experimental results and general trends. Analysis of hole punching process indicated that uniformity of the cutting clearance is rather difficult to keep consistent, especially for UHSS material where cutting forces are substantially higher than for mild steels or aluminum alloys, and stiffness of the tool starts playing critical role. Therefore, majority of experimental studies were performed as tensile tests of samples sheared along straight line in a dedicated trim tool where special measures were taken to achieve consistency of the die clearance. Experimental results on sheared edge stretchability of Aluminum alloy 6111-T4 and UHSS steel DP980 are reported. Mechanism of fracture propagation in trimming and hole punching processes is discussed in conjunction with sheared edge stretchability. Propagation of fracture from the upper cutting edge to the lower cutting edge of the trim die is the mechanism which enables higher stretchability of the sheared edge. Mechanism of fracture leading to crack propagation to the free surface of the blank usually results in formation of burrs and lower sheared edge stretchability. Rather unique mechanism of fracture observed for trimming of UHSS DP980 steel leads to burr breaking at the final stage of the shearing process.

Investigation of Die Clearance in Rubber Pad Forming of Metallic Bipolar Plates

In this research, rubber pad forming process of metallic bipolar plates made of stainlesssteel 316L with a thickness of 0.1 mm has been studied. In addition, a rubber pad made of polyurethanewith the hardness number of shore A 85 and a thickness of 25mm is used in order to apply pressure tothe plate to form the sheets. In order to study the effect of die clearance on depth filling, two die sets withdifferent clearances were made. The results showed that when clearance is applied between punch dieand matrix, the amount of uniformity becomes more in the depth of stuffed channel. But, the rubber padis destroyed after some forming operation and plastic deformation occurs in it. Also, in the die set withthe lower clearance, the amount of rubber pad life has been increased and the amount of flow channeldepth gets greater. In the research results, it was determined that when the channel depth is small and arubber pad is used with a higher hardness, the die set with a clearance has more favorable results due touniformity in the flow channels’ depth. However, by increasing the depth of bipolar plate channels, usingdie sets with lower clearance are better due to the increasing the rubber pad life.

Effect of Press Slide Speed and Stroke on Cup Forming Using a Plain-Woven Carbon Fiber Thermoplastic Composite Sheet

Carbon-fiber-reinforced thermoplastic (CFRTP) is viewed as a prospective material for high-cycle production of CFRP parts. This paper deals with a process whereby a preheated thermoplastic plain-woven carbon fiber fabric sheet is formed into a circular cup by a mechanical servo-press. The effects of press parameters, specifically the bottom dead center and slide speed in the forming of CFRTP cup, on the press load, pressure, internal temperature, shape accuracy, and internal structure have been investigated. A plain-woven carbon-fiber-reinforced PA6 thermoplastic sheet was used. The sheet consisted of four layers of woven 3K carbon and had a thickness of 1 mm. The sheet was heated to 320°C under a halogen heater so that it would be around the recommended temperature for forming 260°C after transfer to the mold. The sheet was pressed into a circular cup shape by a cold mold while the periphery was cramped by a heated holder so as not to cool the sheet before it was pulled into the mold cave. Die clearance was designed considering the thickness increase due to the fiber concentration during the forming. By increasing the slide stroke to the bottom dead center, the applied press load was increased and the internal structure was improved, showing no voids. By increasing the slide speed, the final press load was reduced and shape accuracy was improved through a good pressure distribution on the mold. Measurement of the surface temperature of the sheet during the forming revealed that it remained in the melting region of the resin in the case of fast slide speed, but dropped below the melting temperature in the case of low slide speed. This difference apparently led to spring-in or spring-back after the forming. The experimental results indicate that appropriate balance among press speed, bottom dead center, and sheet temperature is important in the high-cycle forming of CFRTP.

Optimization of Sheet Metal Thickness and Die Clearance of Progressive Press Tool Using Finite Element Analysis and Artificial Neural Network Technique

Optimization of Sheet Metal Thickness and Die Clearance of Progressive Press Tool Using Finite Element Analysis and Artificial Neural Network Technique

Influence of tool geometry variations on the limiting drawing ratio in micro deep drawing

In this study, the impact of different tool geometries on the limiting drawing ratio (LDR) in micro deep drawing was investigated. Experimental micro deep drawing tests to determine the limiting drawing ratios were carried out for a variation of the punch diameter, the die radius and the die clearance. In order to assess the impact of the material properties on the process limits the foil materials Al99.5 and E-Cu58, both with a thickness of 20 μm, and the stainless austenitic nickel-chromium steel 1.4301 (X5CrNi18-10) with a thickness of 25 μm were investigated. The results reveal an increase of the limiting drawing ratio with increasing die radius size for the foil materials E-Cu58 and austenitic steel. For a decrease of the die clearance to values smaller than 1.25 times the foil thickness an increase of the limiting drawing ratio was determined for all three materials.

Study for Sheared Edge Quality of High Strength Steel Sheet

The empirical approach was adopted to investigate the process parameters that effect on the quality of high strength steel sheet sheared edge. As a result of study, the quality of sheared edge that can be represented as the ratio of the shiny burnished surface to the sheared surface was not under influence of die clearance, lubrication and cutting line direction but under influence of the material strength and the usage of lower pad. The roll-over and burr height is highly affected by the die clearance and the usage of lower pad. The lower pad underneath of blank is of help to reduce the amount of roll-over and burr even at large die clearance.

AN ADAPTIVE-NETWORK-BASED FUZZY INFERENCE SYSTEM FOR PREDICTING SPRINGBACK OF U-BENDING

Springback will occur when the external force is removed after bending process in sheet metal forming. This paper proposed an adaptive-network-based fuzzy inference system (ANFIS) model for prediction the springback angle of the SPCC material after U-bending. Three parameters were selected as the main factors of affecting the springback after bending, including the die clearance, the punch radius, and the die radius. The training data were obtained from results of U-bending experiment. The training data with four different membership functions – triangular, trapezoidal, bell, and Gaussian functions – were employed in the ANFIS to construct a predictive model for the springback of the U-bending. After the comparison of the predicted value with the checking data, the results show that the triangular membership function has the best accuracy, which make it the best function to predict the springback angle of sheet metals after U-bending.

Cold Piercing of Cylindrical Aluminum Billet with Counter Punch Pressure

To make a hole with a high aspect ratio (depth/diameter) for lightweight structural components, piercing of cylindrical billet of aluminum alloy was carried out against a counter pressure on a servo-controlled double axis press. To obtain smooth shear surface of pierced hole, the counter pressure was applied to the billet by a counter punch from the opposite side of a piercing punch during piercing. Irrespective of amount of clearance of die–piercing punch, ratio of the length of shear surface/depth of pierced hole in the pierced billet reached about 0.9 by applying a counter punch pressure of 0.2 GPa. The maximum aspect ratio of the hole in the proposed piercing method was estimated to be approximately of 15 for the aluminum billet from viewpoints of buckling and strength of the punch.

Dynamic Strength Behaviour of Punch Connections in Shear Cutting Processes

Two basic types of load for the tool active elements can be distinguished for the shear cutting process of sheet metal. For high strength, brittle materials, the stamping punch will be exposed to distinctive oscillating axial dynamic loads as a result of abrupt released potential energy, from the tool active elements, the blanking tool and the stamping press, caused by a sudden cracking of the sheet. In contrast, when shear cutting ductile materials, sheet metal will be drawn into the die clearance and the resulting friction between the punch and the cut surface can cause high forces when pulling the punch out of the hole. When using punches featuring a complex cutting peripheral form, - not available as a standard part - it is necessary to decide between head and shank of the punch manufactured out of one part or a shaft without head, which is usually cheaper and can be manufactured by electro-erosive wire-cutting. In the second case, a linking element must be accepted, transferring the load transmission between shaft and tool. This linking element, realized by a form lock or traction, can be the reason for premature failure of the punch. The two described cases of load, in combination with lacking knowledge of the real load on the link as well as eligibility of different punch linking types for each case of loading, cause unnecessary cost in tool manufacturing by oversizing or punch fracture. For this, solid punches as well as joined punches with dowelled or screwed heads have been compared in systematic tests. Brazed and bonded punch heads have been involved in the test series as cost-efficient alternatives to custom punches. Collaterally, characteristic values have been determined for each type of punch in static and dynamic measurements. Especially impact absorption and stiffness of the connection represent non-destructive measureable values allowing a comparison of stamping punches in terms of their dynamic fatigue limit.