Punch Geometry Research Articles

Breakdown of continuum models for spherical probe adhesion tests on micropatterned surfaces

The adhesion of fibrillar dry adhesives, mimicking nature's principles of contact splitting, is commonly characterized by using axisymmetric probes having either a flat punch or spherical geometry. When using spherical probes, the adhesive pull-off force measured depends strongly on the compressive preload applied when making contact and on the geometry of the probe. Together, these effects complicate comparisons of the adhesive performance of micropatterned surfaces measured in different experiments. In this work we explore these issues, extending previous theoretical treatments of this problem by considering a fully compliant backing layer with an array of discrete elastic fibrils on its surface. We compare the results of the semi-analytical model presented to existing continuum theories, particularly with respect to determining a measurement system- and procedure-independent metric for the local adhesive strength of the fibrils from the global pull-off force. It is found that the discrete nature of the interface plays a dominant role across a broad range of relevant system parameters. Accordingly, a convenient tool for simulation of a discrete array is provided. An experimental procedure is recommended for use in conjunction with this tool in order to extract a value for the local adhesive strength of the fibrils, which is independent of the other system properties (probe radius, backing layer thickness, and preload) and thus is suitable for comparison across experimental studies.

Evaluation of Localized Necking Models for Fracture Prediction in Punch-Loaded Steel Panels

This study compared the experimental test results on punch-loaded unstiffened and stiffened panels with numerical predictions using different localized necking modeling approaches with shell elements. The analytical models that were derived by Bressan–Williams–Hill (BWH) were used in their original form and extended version, which considers non-proportional loading paths while using the forming-severity concept and bending-induced suppression of through-thickness necking. The results suggest that the mesh size sensitivity depends on the punch geometry. Moreover, the inclusion of bending effects and the use of the forming-severity concept in the BWH criterion yielded improved estimations of fracture initiation with shell elements.

Effects of Punch Geometry on Formability and Forming Load

Effects of Punch Geometry on Formability and Forming Load

An investigation on the effects of the process parameters of hydro-mechanical deep drawing on manufacturing high-quality bimetallic spherical-conical cups

This paper aims to analytically, experimentally, and numerically study the hydro-mechanical deep drawing (HMDD) process of bimetallic specimens. The blank included aluminum and steel sheets used to produce double-layer conical-spherical cups. The punch geometry, maximum fluid pressure, pre-bulge pressure, layer arrangement, and the drawing depth were the process parameters investigated in this article. Two criterions based on the thickness strain and thickness variation were used to assess the effects of these variables on the quality of the final product. The results of the analytical modeling and numerical simulations were verified by comparing with the related experimental data. Different outcomes were in acceptable agreement with each other. Based on the findings obtained, by increasing the fluid pressure up to 15 MPa, the quality of the final product was enhanced. Moreover, by applying the pre-bulge pressure in the HMDD process, the separation between the layers as well as the thickness variation decreased. The highest improvements in the values of the maximum thickness strain and thickness variation in the current investigation were gained to be 57% and 68%, respectively, in comparison with the traditional state of the deep drawing process.

Evaluation of the belt punching process efficiency based on the resistance force of the compressed material

Vacuum conveyor belt punching process by using the piercing punch which cooperates with the die has potential to be modified in aspects of lowering the perforation force, extending the tool life, and improving the hole quality in the perforated belts. All these parameters have an influence on the efficiency of the process and strictly depends on the punch geometry. This indicates that based on these criteria the optimization of the tool constructional features may be performed. In the presented research, authors have shown the linear correlation between the resistance force of the compressed material of the multilayer polymer composite belt in punching and the efficiency of the process. It was also proved that using the effective geometry of the piercing punch with spherical bowl can reduce the perforation force by 69%. Based on the obtained model, the simplified optimization as well as the evaluation of the punches with defined geometry can be performed, since all characteristics of the material compressive force obtained for the effective punches were almost consistent. For proper analysis, it is necessary to use the combination of the analytical and numerical modelling, computer simulations with using the finite element method (FEM) and the experimental tests. However, by performing simple compression tests for various tool geometry on the strength testing machine, it is possible to perform the comparison analysis of different piercing punches based on the derived models. This approach can be used to evaluate the properties of selected tools for the groups of materials with wide divergence of the mechanical properties without performing the complex research.

Extending the Mossakovskii method to contacts supporting a moment

In this article, we extend the Mossakovskii approach to half-plane contacts supporting a moment. Since the method relies on approximating the punch geometry by a series of flat punches, we choose the load path in (P, M)-space that fixes the body tilt, which allows us to reduce the standard Cauchy singular integral formulation to a non-symmetric Abel integral equation. We use the formulation to derive simple expressions for the applied normal force and necessary applied moment as functions of the contact extent and indenter tilt, while also deriving the coefficients of the square-root terms in the contact pressure expansion at the edges of the contact. These results are analysed in detail for two specific examples: the tilted wedge and the tilted flat-and-rounded punch. We conclude by briefly discussing the equivalent tangential problem when an applied shear force and differential bulk tensions are present.

Characterization and optimization of the hydroforming process of AISI 316L steel hydraulic tubes

Hydroforming is a metal forming technology that enables the fabrication of complex parts in a low cycle time. The process is based on the plastic deformation of a blank sheet using a pressurized fluid. This paper focuses on the design of a tube hydroforming (THF) process to replace the current cut-and-weld practice for components produced by a company. Specifically, the study focuses on the characterization and optimization of the THF process for stainless steel T-joint parts produced in two sizes: small and large. The new production must improve the final components’ quality and maintain the technical requirements of the previous one, especially in terms of the parts’ geometry (in particular, the third branch minimum height and thickness) and material (AISI 316L), with competitive production costs. Accordingly, the process optimization is performed in three sequential steps. Initially, the process is characterized by the material flow stress and the friction between a tube and die. Subsequently, this information is used to develop a finite element method (FEM) model, which is validated based on experimental data. The FEM is used to optimize the process parameters (pressure, stroke, and trust force of the counterpunch) to improve the final component quality and guarantee the specific dimensional requirements. Finally, further improvements of the process are implemented (initial precrash of the tube, optimal length of the blank tube, and calibration pressure to avoid wrinkles in the final component). After the THF process optimization, emphasis is placed on the punch geometry. A study is conducted to avoid stress concentrations that may cause punch breakage. The results of this study allow the minimization of tube thinning during the hydroforming process, and guarantee the target value for the third branch height with minimal material consumption. Moreover, the evaluation of different geometrical alternatives allows the stresses acting on the punches to be reduced by 45%.

THE EFFECT OF PUNCH GEOMETRY ON PUNCHING PROCESS IN TITANIUM SHEET

Reducing punch force, increasing the sheared surface, and improving the work hardening have been real challenges in developing a punching process, and the right selection of punch geometry can resolve these challenges. Selecting the appropriate geometry, however, has been difficult to do since the effect of punch geometry on the punching process is rarely studied, and therefore, this study aims to investigate the effect of punch force, sheared surface, and work hardening by using commercially pure titanium sheets. The punching process under the study employed three different punch geometries, namely flat (FLAT), single shear angle (SSA) and double shear angle (DSA) with a shear angle of 17°, while the Punch velocity used was 35mm/s and 70 mm/s. The results show that the punching process using SSA and DSA punch geometry with the punch velocity of 35 mm/s reduces the punch force by 18% and 13% consecutively compared to that of FLAT with the same velocity. However, the sheared surface quality seems to decline as the rollover height increases by about 48% and 32%. Moreover, the burnish height decreases by 34% and 7% and the resulted work hardening improves by 4.7% and 2.3% respectively. The study concludes that SSA and DSA punch geometry can be best used to reduce punch force and increase work hardening, but apparently fail in increasing the sheared surface quality.

Fabrication of clean cut surface on high strength steel using a new shaving die design

A shaving process is commonly applied to achieve a smooth cut surface thorough the workpiece thickness and a square cut-edge, also known as a finishing operation. However, this process is rarely successful for high-strength steel sheets, which is a major problem. In the present study, finite element method (FEM) simulation was used to clarify the main causes of this problem by comparing the shaving mechanisms between medium carbon steel grade SPCC (JIS) and high-strength steel grade SPFH 590 (JIS). Results show that in the case of SPFH 590 based on material flow, stress distribution, and strain distribution analyses, the shaved chip was difficult to form by sliding along the punch face. Moreover, the tensile stress generated in the shearing zone was increased and readily generated cracks. The shaving process was developed in the present study by generating the cutting-edge angle and rake radius on the punch. The cutting edge angle was designed to generate high compressive stress in the cutting-edge vicinity and shearing zone, and the rake radius was designed to tear a shaving allowance off and move it along the rake radius instead of moving downward along the punch movement direction, thereby decreasing the tensile stress in the shearing zone. Under these mechanisms, the increases in the generated tensile stress in the shearing zone could be delayed, and cracks could thus be prevented. The effect of the punch geometry on the cut surface characteristics and cutting forces were also investigated. Laboratory experiments were performed to validate the FEM simulation results. Experimental results agreed well with the FEM simulation results. Therefore, a smooth cut surface thorough the workpiece thickness of high-strength steel sheets could be successfully achieved by using the developed shaving process.

Study on deformation characteristics of tailored blanks having thickness distribution by successive forging process

Tailored blanks are used in car body-in-white parts for the purpose of reducing weight and improving safety. The reduction of weight in a car decreases the fuel consumption and global emissions. In this study, the deformation characteristics of tailored blanks having thicknesses distribution produced by successive forging were analysed using finite element method. The successive forging produced tailored blanks without joining similar to tailor rolling by means of presses. The blank was locally and repeatedly compressed using upper and lower punches hence compression load is small. The punch geometry was varied to understand the deformation behaviour of the blanks for feeding interval of 10 mm. Waving was observed on the sides of the tailored blanks. The width of the blanks after successive forging increases as the punch width increases and when using an inclined punch.

Residual stress and elastic recovery of imprinted Cu-Zr metallic glass films using molecular dynamic simulation

Molecular dynamics simulations are employed to study mechanistic characteristics of Cu-Zr metallic glasses films during the imprinting process. The influences of punch geometry, loading velocity, temperature, and alloy composition are exhaustively analyzed in terms of imprinting force, deformation characteristic, residual stress, displacement vector, radial distribution function, and elastic recovery ratio. The results show that the imprinting force and the shear transformation zones (STZs) of the Cu50Zr50 MGs films increase, while the residual stress has slightly changed with increasing angle of the punch. In the case of different imprinting velocities, the imprinting force increases. The residual stress also increases in the loading stage; however, it decreases in the unloading stage. The imprinting force, residual stress, highest peak of the radial distribution function (RDF) decrease and movement of atoms become irregular as increasing of temperature. As increasing Cu proportion, the imprinting force increases, the density of atom movement and residual stress increases, while the highest peak of the RDF decreases. The formality of the Cu-Zr MGs films can be improved by increasing Cu proportion and loading velocity, decreasing temperature due to lower average elastic recovery ratio. The imprinting force values are in the range of 100–185 nN, the residual stress values of the loading stage are from 0.44 to 0.82 GPa and the residual stress values of the unloading stage are from 0.4 to 0.9 GPa, the elastic recovery ratio are in the range of 0.17–20.26%.

Investigation on wear-induced edge passivation of fine-blanking punch

Edge passivation of the punch is a common phenomenon that is induced by wear and which would affect tool life and part quality. To investigate the edge passivation of fine-blanking punch, a wear tester based on sheet metal extrusion was designed. The relevance of the designed tester in terms of the stress state to the fine-blanking process was analyzed via finite element methods. Meanwhile, material flow at the punch edge was studied with pad printing technology, and the effects of the punch geometry and extrusion stroke on the worn profile have been discussed. The results shows that reducing the length of straight lines and radius of arcs results in a large relative sliding distance of material at the punch edge, and for a punch with circular and linear edges, wear on the circular segment is more severe than that on the linear segment. In addition, from the viewpoint of simulation, adaption of the wear coefficient in different periods could lead to a more precise worn profile of the punch.

An Investigation of the Shearing Forces Using Blanked Carbon Steel Sheets

An important challenge confronted when using blanking to machine sheet metal is the treatment of the shearing force in demand for great strength and heavy stock. One of the methods used to decrease the force wanted is the increase of a punch shear angle. In this work, experiments were conducted to study the effect of shear angle for blank has a diameter (50 mm) on shear force of a low carbon steel sheet (AISI 1008). Low carbon steel is a very common material used in fabrication of sheet metal components, with thickness of (0.5 mm). Tools used in the blanking tests were one traditional flat end punch and four different bevel sheared rooftop punches, which rooftop punches were compared to. and it (0°, 5°, 10°, 15°, 20°) a punches diameter (49.95 mm) by clearance (0.025mm) for each side , with a blanking speed (500mm/min). A special blanking die set is designed and manufactured and was a blank cut by a hydraulic press whose capacity (20 ton). The results showed that the blanking forces of (AISI 1008) low carbon steel metal could be decreased radically with best bevel punch geometry. Using (10°) shear angle at the punch end, the cutting forces decreased up to (90%) compared to the ones of the traditional flat end tool

Effect of punch geometry on hole expansion ratio

Stretch-flangeability of sheet metal is normally quantified by hole expansion ratio. Researchers have determined hole expansion ratio with various punch geometries such as conical, flat-bottom and hemispherical, and reported different hole expansion ratio values for identical test condition. Finite element investigation confirms that alteration of deformation path with punch geometries consequence different hole expansion ratio values. Necking and failure take place slightly away from the central hole edge for flat-bottom and hemispherical punches, while at the central hole edge for conical punch. Approximately plane strain tensile deformation prevails at the failure location for flat-bottom and hemispherical punches, while pure uniaxial tensile deformation prevails for conical punch.

Shear-induced contact area anisotropy explained by a fracture mechanics model.

This paper gives a theoretical analysis for the fundamental problem of anisotropy induced by shear forces on an adhesive contact, discussing the experimental data of the companion Letter. We present a fracture mechanics model where two phenomenological mode-mixity functions are introduced to describe the weak coupling between modes I and II or I and III, which changes the effective toughness of the interface. The mode-mixity functions have been interpolated using the data of a single experiment and then used to predict the behavior of the whole set of experimental observations. The model extends an idea by Johnson and Greenwood, to solve purely mode I problems of adhesion in the presence of a nonaxisymmetric Hertzian geometry, to the case of elliptical contacts sheared along their major or minor axis. Equality between the stress intensity factors and their critical values is imposed solely at the major and minor axes. We successfully validate our model against experimental data. The model predicts that the punch geometry will affect both the shape and the overall decay of the sheared contact area.

Determination of the Hole-flangeability for thin Sheets

Sheet metal stretching is one of the most frequently applied sheets forming operation in the industry. Hole flanging is a common sheet forming operation to produce structural sheet metal components. Flanges are used for appearance, rigidity, hidden joints, and strengthening of the edge of sheet metal parts. Trial-end-error is the most common approach for tooling and process design in flanging operations. This paper presents some experimental results of hole-flanging process performed on flat deep drawing steel sheets with circular hole drilled or punched in the centre of blank. Three punches of different geometry i.e. cylindrical, hemispherical and conical were used in this experiment. The effect of both the punch geometry and material mechanical parameters (especially strain hardening and plastic anisotropy) on the limit expansion of the hole, limit strain dependence on hole performing technology as well as sheet thickness distribution along collar formed was determined.

Warm and cold blanking of manganese-boron steel 22MnB5 with different tool geometries

Abstract Two main processes for shaping press hardened ultra-high strength steels (UHSS) are laser cutting and cold blanking, which are either cost-intensive and time-consuming or require high blanking force. Therefore, the integration of warm blanking and hot forming in one process represents a possible alternative for shaping UHSS. Due to the integration of various process steps such as forming, blanking and quenching, a reduction of process steps is possible. This leads to a decrease of time and operating costs. Tool load can be reduced as well because of the lower tensile strength of heated steel. However, there are several disadvantages to integrating these process steps. High process temperatures encourage warpage of tool and sheet and therefore an increase in tool and maintenance costs. To investigate the influence of process integration on the blanking and retraction forces and the quality of the cutting surface, several surveys were conducted by one-hole-blanking. One possibility to deal with the disadvantages could be the use of different punch geometries (plane, conical, truncated conical) in combination with different clearances during warm blanking of typical quenched 22MnB5. Characteristic cutting and retraction forces and temperatures as well as parameters of cutting surfaces were measured and analyzed. A variation of the punch geometry and clearance does not give a significant improvement in the forces and quality of the cutting surface. However, for a high part quality with less burr, a plane punch is recommended and a conical or a truncated conical punch may reduce friction induced wear in industrial applications by producing less burnish.

Investigation of the Mechanical Punch Loads during Fine Blanking of High-Strength Steels with Cemented Carbide

Abstract The increasing ecological demands require emissions reduction of automotive vehicles. This challenges the automotive industry for the increased application of light-weight components made of high-strength steels. The processing of high-strength steels brings many manufacturing processes to its mechanical limitations. In fine blanking, conventional tool materials lack on compressive strength in order to separate high-strength sheet metal. Nowadays, high-speed steels used for tool applications must be substituted with materials having a higher compressive strength, such as cemented carbides. However, with the increased compressive strength the carbides show a significantly lower ductility. During a repeated stripping off process, the low ductility of cemented carbides leads to a premature punch fracture and with this reduced economic feasibility of the process. The stripping off force required for the final punch ejection is generated by the clamping force applied by elastic deformation of the scrap material. Currently, phenomenological models exist allowing only approximate prediction of the clamping force. The precise prediction is not possible, since the clamping force depends on plenty parameters, such as sheet material strength and thickness, as well as punch geometry, ambient temperature, nest positioning, etc. A comprehensive investigation of the influence of these parameters on the punch load is strictly required. In order to enhance the applicability of cemented carbides as an alternative punch material in fine blanking of high-strength steels, a tool for process forces quantification, such as clamping and stripping off forces during one cutting-ejection cycle, must be provided. To achieve this goal, a comprehensive numerical study on the influence of process parameters such as sheet metal strength, sheet thickness and cemented carbide grade on the cutting, clamping and stripping off forces is performed. The developed three-dimensional numerical model of a fine blanking process with an elastic punch is validated by means of the experimentally measured punch force during an industrial fine blanking process of spacer discs. Based on the obtained numerical results, a basic correlation between the clamping force during the cutting step and the stripping off force during the ejection step are analyzed. The identified tendencies are used to create an analytical model of the clamping force and a regression model of the stripping off forces. The developed models allow for improved prediction of the expected process forces during fine blanking of high-strength steels and with this for the selection of the appropriate grade of cemented carbide as a punch material.

Effect of Pressing Parameters on the Quality of Joint Formation of Heat Exchanger Fins with the Base Plate

In this paper, the results of experimental and numerical studies on joining the thin fins to the thick base plate of a heat exchanger are presented. The elements of the heat exchanger were joined by using developed method of press forming. The joining technology consists in clamping the sheet metal into the channel of the base plate using a punch with specific geometry. The effect of different configurations of the punch geometry (shape, radius and distance between fin and punch) and the indentation depth on the depth of the interface between the fin and base plate is analysed. Furthermore, the effect of different combinations of fin-base plate materials has been numerically studied. The plate material was the AA2219 -T851 aluminium alloy, while the fins were made of the AA5251 aluminium alloy. The elastic-plastic numerical computations of the joining process have been carried out using the finite element-based MSC.Marc program. It was found that the area of the contact of the fin with the base plate can be optimised by choosing the right parameters of the tool geometry and technological parameters. Experimental research has shown that increasing the punch indentation causes the material to flow in the transverse direction to the punch and the indirect extrusion in the region between the punches.

Influence of punch geometry (head-flat diameter) and tooling type (‘B’ or ‘D’) on the physical–mechanical properties of formulation tablets

The presented study assessed the influence of punch geometry (head-flat [HF] diameter) and tooling type (‘B’ or ‘D’) on the physical–mechanical properties of tablets prepared by direct-compression of two guaifenesin (25% or 40% w/w) formulations. Tablets of both formulations were prepared on instrumented, single-layer, rotary tablet press using 10 mm, flat-faced, ‘B’ or ‘D’-type tooling with different HF diameters, and compression forces (CF) ranging from 5 to 25 kN with 5 kN increments. The tablets were evaluated for dimensions, weight variation, tensile strength (TS), friability, and capping index. In general, tablets prepared using ‘D’ tooling showed a significantly (p < 0.05) higher TS compared to those prepared using ‘B’ tooling, likely due to higher dwell-times associated with ‘D’ tooling. Formulations containing 25% w/w guaifenesin showed a significantly (p < 0.05) higher TS compared to those containing 40% w/w guaifenesin, at given compression CF, punch geometry, or tooling type. This could be due to the higher ratio of Prosolv® SMCC contributing to the compressibility. For both formulations compressed using ‘B’ tooling, differences in TS profiles were observed between different HF tooling. The TS of these tablets increased significantly with increasing HF diameter. For formulations compressed using ‘D’ tooling, this trend was observed only up to a CF of 15 kN, beyond which the TS plateaued, possibly due to work-hardening of the formulation at higher CF. These formulations also exhibited capping at CF above 15 kN and with higher HF diameters. The study showed a significant influence of punch geometry and tooling type on the physical properties of tablets.