Punch Penetration Research Articles

Tablet compression tooling – Impact of punch face edge modification

The influence of punch face edge geometry modification on tablet compression and the properties of the resultant tablets produced on a rotary press were investigated. The results revealed that tablets produced from the punches with radius edge face geometry consistently displayed better physical quality; higher tensile strength and lower capping tendency. Modification of the angled edge of the bevel face to the curved edge of the radius face, enabled deeper punch penetration in the die cavity during the compression cycle, bringing about greater compact densification. Improved die fill packing increased interparticulate bond formation and helped to dissipate destructive elasticity within the compact, consequently reduced tablet expansion during the decompression phase. The positive impact of punch face edge modification was also more noticeable at a higher turret speed. The application of the precompression force along with dwell time extension amplified the tableting performance of radius edge punch face design to a greater extent when compared to bevel edge punch face design. This could be attributed to the enhanced packing efficiency at both precompression and main compression stages.

Numeral simulation of double-layer plate deform process under punch impact

The numeral simulation of double-layer plate (metal and bio-tissue) deform process under steel punch impact is provided applying the method of finite elements. The solution of non-stationary thermos viscous elastic boundary value problem allowed to find out the parameters of the stress-strain deformed state within the layers of the plate. The analysis of the strain fields and stresses demonstrated that the deformation area of bio-tissue layers considerably exceeds the area of metallic local deformation during the incomplete punch penetration into a plate. The maximum displacement in the bio-tissue layer does not exceed the critical depth of the dent in the metal layer.

Function development for appraising brittleness of intact rocks using genetic programming and non-linear multiple regression models

Brittleness of rock is one of the most critical features for design of underground excavation project. Therefore, proper assessing of rock brittleness can be very useful for designers and evaluators of geotechnical applications. In this study, feasibility of genetic programming (GP) model and non-linear multiple regression (NLMR) in predicting brittleness of intact rocks is examined. For this purpose, a dataset developed by conducting various rock tests including uniaxial compressive strength, Brazilian tensile strength, unit weight and brittleness via punch penetration on rock samples gathered from 48 tunnels projects around the world is utilized herein. Considering multiple inputs, several GP models were constructed to estimate brittleness index of the rock and finally, the best GP model was selected. Note that, GP can make an equation for predicting output of the system using model inputs. To show applicability of the developed GP model, non-linear multiple regression (NLMR) was also applied and developed. Considering some model performance indices, performance prediction of the GP and NLMR models were evaluated and it was found that the GP model is superior to NLMR one. Based on coefficient of determination (R2) of testing datasets, by proposing GP model, it can be improved from 0.882 (obtained by NLMR model) to 0.904. It is worth mentioning that the proposed predictive models in this study should be planned and used for the similar types of rock and the established inputs ranges.

RETRACTED ARTICLE: Function finding for indirect determination of rock brittleness based on genetic programming and non-linear multiple regression models

Brittleness of the rock is one of the most critical features for design of underground excavation project. Therefore, proper estimating of rock brittleness can be very useful for designers and evaluators of geotechnical applications. In this study, feasibility of genetic programming (GP) model in predicting brittleness of the rock samples is examined. In this regard, several laboratory tests including uniaxial compressive strength, Brazilian, density and punch penetration were conducted on 48 rock samples collected from various locations of India. Considering multiple-inputs, several GP models were constructed to estimate brittleness index (BI) of the rock and finally, the best GP model was selected. Note that, GP can make an equation for predicting output of the system using model inputs. To show applicability of the developed GP model, non-linear multiple regression (NLMR) was also applied and developed. Considering some model performance indices, performance prediction of the GP and NLMR models were evaluated and it was found that the GP model is superior to NLMR one. Based on coefficient of determination (R2) of testing datasets, by proposing GP model, it can be improved from 0.882 (which was obtained by NLMR model) to 0.904. It is worth mentioning that the proposed predictive models in this study should be planned and used for the same conditions and the established inputs ranges.

Microstructure characterization of fine grains near hot-sheared surface formed during hot-stamping process

Submicron crystallization suppresses hydrogen-induced delayed cracking on hot-sheared surfaces, which are formed during a hot-stamping process. To gain insights into the mechanism of this suppression, in this study, detailed microstructural characterization in the vicinity of the hot-sheared surface was performed. A hot-halfway-cut test, which consists of punch penetration into an austenitized hot specimen followed by water quenching, was conducted for this characterization. This test provided information about the microstructural evolution with respect to equivalent plastic strain by controlling punch penetration. Furthermore, the microstructural analyses were straightforward because this test did not involve the difficult complication of accounting for material fracture during the hot shearing. For this test, a finite element simulation was used to evaluate the strain distribution in the hot-deformed zone. Optical observations and hardness measurements clarified that at 750°C, the microstructure that covers the hot-sheared surface starts to transform when the equivalent plastic strain is greater than approximately 1.0. In addition, scanning electron microscopy, electron backscatter diffraction analysis, electron probe microanalysis, and transmission electron microscopy revealed the following microstructural details: In the vicinity of the burnished part of the hot-sheared surface, the microstructure is composed mostly of ferrite that contains banded carbides and has grain sizes on the order of 0.4–0.6μm, rather than bainite or martensite. On the other hand, in the vicinity of the fractured part, the microstructure is composed of ferrite and banded bainite, and has grain sizes on the order of 0.6–2μm.

Performance Assessment of Hard Rock TBM and Rock Boreability Using Punch Penetration Test

Rock indentation tests are often called punch penetration tests and are known to be related to penetration rates of drilling equipment and hard rock tunnel boring machines (TBMs). Various indices determined from analysis of the force-penetration plot generated from indentation tests have been used to represent the drillability, boreability, and brittleness of rocks. However, no standard for the punch penetration test procedure or method for calculating the related indices has been suggested or adopted in the rock mechanics community. This paper introduces new indices based on the punch test to predict the performance of hard rock TBMs. A series of punch tests was performed on rock specimens representing six rock formations in Korea with different dimensions, i.e., the core specimens had different lengths and diameters. Of the indices obtained from the punch tests, the peak load index and mean load index showed good correlations with the cutting forces measured in full-scale linear cutting machine tests on the same rock types. The indices also showed good linear correlations with the ratio of uniaxial strength to Brazilian tensile strength, which indicates the brittleness of rock. The scale effect of using core specimens was investigated, and a preferred dimension for the punch test specimens is proposed. This paper also discusses the results of the punch test and full-scale rock cutting tests using LCM. The results of this study confirm that the proposed indices from the punch tests can be used to provide a reliable prediction of the cutting forces that act on a disc cutter. The estimated cutting forces can then be used for optimization of cutter-head design and performance prediction of hard rock TBMs.

Study of Formability of Sandwich Shells with Metal Foam Cores Based on Punch Penetration Test

The objective of this work is the study of the mechanical behaviour of a sandwich structure, composed by two out layers in aluminium sheets, separated by a core in metal foam also in aluminium, by penetration of a spherical punch. Considering a structure composed by these two different materials, each one presents a different mechanical behaviour separately [1, 2].The set up used in the present experimental work is composed by a punch, with a radius r, which imposes a displacement/force to a specimen fixed in its boundary.In these tests, specimens with four different length were considered; 25 mm, 50 mm, 75 mm and 150 mm. The values of force/displacement of the punch were registered.

Comparison of contact problem exact solutions for transversely isotropic half-space

Exact solutions to two contact problems with unknown contact domains on the elliptic punch penetration in the transversely isotropic elastic half-space are compared. In the first one - a “traditional problem” - the half-space boundary is parallel to the isotropy planes. There can be an axial symmetry case for a circular punch. In the second - a “nontraditional problem” - the half-space boundary is perpendicular to the isotropy planes. Here, the axial symmetry is impossible in principle: even for a circular punch, the contact domain will be elliptical. The contact domains and the forces required for the penetration of the punch at a given value are compared for both problems. The transversely isotropic body model is applicable for describing lots of materials which elastic parameters have been measured in recent decades: composites, ceramics, carbon fiber, graphite-epoxy, glass-epoxy, wood, aged concretes, some metals (titanium, cobalt, zinc), some semiconductors and rocks. They are widely used in the engineering and industry.

Study of Microstructure and Mechanical Properties Effects on Workpiece Quality in Sheet Metal Extrusion Process.

Sheet metal extrusion is a metal forming process in which the movement of a punch penetrates a sheet metal surface and it flows through a die orifice; the extruded parts can be deflected to have an extrusion cavity and protrusion on the opposite side. Therefore, this process results in a narrow region of highly localized plastic deformation due to the formation and microstructure effect on the work piece. This research investigated the characteristics of the material-flow behavior during the formation and its effect on the microstructure of the extruded sheet metal using the finite element method (FEM). The actual parts and FEM simulation model were developed using a blank material made from AISI-1045 steel with a thickness of 5 mm; the material's behavior was determined subject to the punch penetration depths of 20%, 40%, 60%, and 80% of the sheet thickness. The results indicated the formation and microstructure effects on the sheet metal extrusion parts and defects. Namely, when increasing penetration, narrowing the die orifice the material flows through, the material was formed by extruding, and defects were visibility, and the microstructure of the material's grains' size was flat and very fine. Extrusion defects were not found in the control material flow. The region of highly localized plastic deformation affected the material gain and mechanical properties. The FEM simulation results agreed with the experimental results. Moreover, FEM could be investigated as a tool to decrease the cost and time in trial and error procedures.

Deformation behavior in boss forming with small punch/die diameter ratio

Sheet metal parts with bosses or small pins can be manufactured by half blanking. This paper focuses on deformation in small boss forming on a sheet metal by half blanking at small punch/die diameter ratios of 1–1.8. In the case that the boss diameter is less than the sheet thickness, the boss height became lower than the depth of punch penetration at a punch/die diameter ratio of 1. The mechanism of decrease in the boss height and countermeasures to the problem were investigated through the FE analysis. The results showed that the boss height was improved up to the same level as the depth of punch penetration by both increasing punch/die diameter ratio and applying an appropriate blank holding force. The boss height was also affected by the material ductility and a higher boss was formed for the not-annealed sheet under the same forming conditions. The punch/die diameter ratio did not make a big difference in the mean punch pressure although a larger force was needed by using a larger diameter punch.

Influence of the Punch Penetration Depth in Half Punching on the Cut Edge after Shaving

Shaving is one of the precision shearing methods used to remove the rollover and fractured surface. The rollover and fractured surface formed in the punching stage are removed by shaving. It is expected that the rollover will be reduced when half punching with a negative clearance is carried out in the punching stage. In this study, the influence of the punch penetration depth in the punching stage on the cut edge after shaving was investigated. The results of this study clarified the followings: When the punch penetration depth in the punching stage with negative clearance is large, the sheared surface obtained by shaving after half punching with negative clearance is larger than that obtained by conventional punching. The sheared surface obtained by shaving after half punching with negative clearance increased with increasing the punch penetration depth in the punching stage with a negative clearance. The rollover produced by shaving after half punching with negative clearance is smaller than that produced by conventional shaving. In addition, the chip produced by shaving after half punching is connected to the sheet material under the punch. From the observed deformation of the chip produced in the shaving stage after half punching with negative clearance, the mechanism of shaving after half punching is considered to be cutting followed by shearing.

Experimental Investigation on Rotary Punching by the Compression of Polyurethane Pad

Rotary punching is a sheet metal blanking process which utilizes shearing tools fixed to a pair of rollers. The polyurethane pad is adopted as the die instead of rigid mold because it has the advantages of wide hardness range and high load-bear capacity. Due to the application of polyurethane pad, the surrounding region adjacent to the pierced hole will occur to plastically deform and deflect, which greatly differs from that in the conventional blanking. In this paper, the effects of blank material and thickness, polyurethane hardness, punch penetration depth on deformation behavior were mathematically analyzed and modeled, and then a series of experiments through varying process parameters were conducted to validate the relationship between process parameters and product quality. The degree of sample deflection was exactly measured by scanning electron microscope (SEM). The results show that the deformed area varies with different blank elongations and increases with increasing blank thickness for a given material. When polyurethane pad with low hardness level is employed, it results in large area deformation and quality degradation. Moreover, the deflection degree around the hole edge becomes more severe along with punch penetration, but the penetration depth along blank thickness is not in proportion to the amount of punch advancement.

かえりなしせん断加工の成功条件および切り口面品質に及ぼす材料延性の影響

In push-back blanking, burr-free products are produced by compressing a half-blanked sheet between platens, where success conditions are affected by the ductility of materials. In this study, the mechanism of success and the cut edge quality in the push-back blanking process using a ductile and a brittle steel sheet were discussed. Experiments were carried out, varying the punch penetration and clearance in the half-blanking step. Brittle steel showed a wider successful range and less shear droop on the cut edge than ductile steel. Corresponding simulations were conducted and the damage value based on a ductile fracture criterion was calculated around the shear zone. Negative clearance was effective in keeping the damage value low and allowed deep punch penetration without fracturing in the half-blanking step. In the following push-back step, a rapid increase in the damage was observed when the high mean stress zone prevailed over the half-blanked portion. The timing of increase in damage was earlier for brittle steel owing to the localization of deformation, resulting in a wider successful range than that of ductile steel.

Estimation of design parameters of TBM using punch penetration and Cerchar abrasiveness test

TBM의 사양을 설계하고 굴진성능을 예측할 때 실대형 선형절삭시험을 통하여 설계변수를 획득하는 것이 매우 효과적인 방법인 것으로 알려져 있다. 하지만 선형절삭시험을 위해서는 대형 시편을 획득하고 큰 하중용량의 시험을 수행하는 과정에서 상당한 비용과 노력이 소모된다는 단점이 있다. 따라서 선형절삭시험을 대체하는 경험적 예측 모델, 즉 CSM모델과 NTNU모델을 사용하여 몇 가지 지수를 산정하고 이로부터 설계변수를 추정하는 경우가 많다. 본 연구에서는 압입시험 및 세르샤 마모시험을 이용하여 TBM의 사양(추력, 토크)과 굴착에 따라 소요되는 디스크 커터의 개수를 추정하는 방법에 대하여 고찰하였다. 압입시험과 세르샤 마모시험은 TBM의 설계 변수를 추정하기 위한 유용한 시험법이나 그 활용법이 연구 되고 있지 못한 실정이다. 이 연구에서는 압입시험과 세르샤 마모시험결과를 간단한 형태의 지수형태로 도출하고 이를 선형절삭시험 및 실제 굴진자료와 비교하여 상관관계를 도출하고 이로 부터 디스크 커터의 작용력 및 수명을 예측하였다. 또한 이 일련의 계산 과정을 프로그램화 하였으며, 터널의 연장 정보, TBM의 기계정보, 구간별 암석의 물성을 입력변수로 하여 구간별 굴진율과 TBM 사양 및 운영조건, 디스크 커터의 소모개수를 예측할 수 있었다. Linear cutting test is known to be very effective to determine machine parameters (i.e. thrust force and torque) and to estimate penetration rate of TBM and other operation conditions. Although the linear cutting test has significant advantages, the test is expensive and time-consuming because it requires large size specimen and high load capacity of the testing machine. Therefore, a few empirical prediction models (e.g. CSM, NTNU and QTBM) alternatively adopt laboratory index tests to estimate design parameters of TBM. This study discusses the estimation method of TBM machine parameters and disc cutter consumption using punch penetration test and Cerchar abrasion test of which the researches are rare. The cutter forces and cutter consumption can be estimated by the empirical models derived from the relationship between laboratory test result with field data and linear cutting test data. In addition, the estimation process was programmed through which the design parameters of TBM (e.g. thrust, torque, penetration rate, and cutter consumption) are automatically estimated using laboratory test results.

A Study on the Nose Radius Influence in Press Brake Bending Operations by Finite Element Analysis

The sheet metal bending is one of the metal forming processes with the simplest geometric interpretation and usually a 2D analysis is considered. The bend over a sheet metal blank consists of a V shape forming by using a punch, with a certain nose radius, forcing the plate against an open die, with a V section. The forming result is a part with an angle obtained between the V legs, flanges, which is known as bending angle. The operation to get the required V angle is called air bending, or free bending. The most common used machines for this forming process are press brakes, special long presses, where the tools, punch and die, are attached to. With the spread use of CNC machines, and their computer control capabilities, most of them using graphical user interface (GUI), became important to get the required shape at first trial. Beyond the required bending angle obtained with just one hit, it is also important to position the gauge system in order to get the successive flange lengths to complete the programmed shape. The main variables controlled by the CNC are the punch penetration inside the die and the position of the back gauge, which is determined by the bend allowance. However this penetration is not the only responsible for the resulting bending angle and the gauging position is not the only responsible for the flange length. Additionally, the radius inside the V shape edge, known as bending radius, influences the geometry and correspondingly the bend allowance. Some authors believe that the punch nose radius has direct influence, both in the bending angle and bend allowance. In this paper, results are presented describing the use of finite element analysis as an aid in the prediction of the inside bending radius, that influences both punch penetration for the final bending angle and the bend allowance for the final flange length. From the air bending analysis, a natural inside bending radius is presented as an important variable in these kind of processes, as well as its minor dependence on the punch nose radius.

Utilising of linear and non-linear prediction tools for evaluation of penetration rate of Tunnel Boring Machine in hard rock condition

Predicting Tunnel Boring Machine (TBM) penetration rate is a crucial issue for the successful fulfilment of a mechanical tunnel project. Penetration rate depends on many factors such as intact rock properties, rock mass conditions and machine specifications. In this paper, linear and non-linear multiple regression as well as Artificial Neural Network (ANN) techniques were applied to predict the penetration rate of TBM. In developing of the proposed models, five parameters, which include Uniaxial Compressive Strength (UCS), Brazilian Tensile Strength (BTS), peak slope index (punch penetration), spacing of discontinuities (of weakness planes) and orientation of discontinuities with respect to the tunnel axis (β angle), were incorporated. For this study, 46 datasets were collected. Performance of these models was assessed through the R2, RMSE and MAPE. As a result, these indices revealed that the prediction performance of the ANN model is higher than that of the non-linear and linear multiple regression models.

Plane contact problem for a prestressed incompressible elastic layer clamped along the base

The problem of a rigid punch penetration into the upper face of a layer is considered in the case of a homogeneous field of initial stresses. The model of isotropic incompressible nonlinearly elastic material determined by the Mooney potential is used. The case of rigid clamping of the layer along its lower face is considered under the assumption that the additional stresses caused by the penetrating punch are small compared with the initial ones. This assumption allows one to linearize the problem of determining the additional stresses. This problem is then reduced to solving an integral equations of the first kind with a difference kernel which allows one to determine the pressure in the contact region. An asymptotic solution is constructed for large values of the parameter characterizing the relative thickness of the layer. Amodified Multhopp-Kalandiyamethod is also used to obtain a solution for a wider range of the parameter.

TBM의 굴진성능 예측을 위한 압입시험에 대한 연구

This paper discusses the methods of estimating the punch penetration indices and data analysis punch penetration test to estimate the TBM normal force and penetration rate. In punch penetration test is known as a useful test to estimate penetration rates and normal force of TBMs directly with several slope indices indicated drill-ability and brittleness of rocks. However, the standard methods and indices for punch penetration test are not suggested yet. The main purpose of punch penetration test which is prediction of normal force of TBM disc cutter when cutters excavate rock mass. In this study, the punch penetration tests were performed for 6 representative Korean rock types and variety length and diameter of rock core specimens. Among slope indices were obtained from punch penetration test, PLI and MLI which is suggested in this study show high correlation with cutter force measured by full-scale cutting test. The results show that the predicted normal force of a single disc cutter and the experimental error was 10%. Based on these results, it is concluded that punch penetration test is reliable laboratory test for estimating thrust and penetration rates of TBM.

A novel punch design approach with progressive clearance variation for the punching–broaching process

Thick sheet punching is a process used in the automobile industry, especially in the heavy vehicles segment. Aimed at generating holes of good cylindricity and surface quality, the definition of the process parameter values and the tool design are critical to the process. For this purpose, the finite element method is useful to decrease the trial-and-error procedures and also the tool development costs. The main aim of the present study was to analyse the influence of the punch design on the final quality of punched/broached holes produced on thick steel sheets (8 mm, NBR 6656). Several geometries of punch with combined broaching teeth as well as punches with traditional geometries have been analysed. The results of the simulations led to a detailed understanding of the influence of punch geometry during the punching–broaching process. In addition, a novel punch design approach was proposed which allowed the production of holes of good cylindricity due to the progressive variation of the clearance between the punch and the die during the punch penetration progress.

Contact with stick zone between an indenter and a thin incompressible layer

Abstract The dominant asymptotic term for the indentation of a thin elastic incompressible layer by an axisymmetric rigid indenter is considered. Complete adhesion is supposed everywhere in the contact area or else in a given inner region surrounded by an annular frictionless zone. Both the problems are formulated in the form of systems of coupled dual integral equations. Using operators transforming kernels of the Hankel transform into kernels of the Weber–Orr transform, the dual integral equations are reduced to systems of Fredholm integral equations of the second kind whose structures permit deriving asymptotic solutions. Simple expressions for the contact stresses, the penetration depth, and the contact radius in the case of an unknown contact area are obtained. Explicit formulae, derived for the flat and power law indenter profiles, allow us to analyze how stick and frictionless zones affect mechanical characteristics. Results manifest that the punch penetration exhibits strong sensitivity to contact conditions inspite of the fact that the radial traction is small. A conical indenter is less sensitive than flat-ended and spherical indenters.