Punch Speed Research Articles

Lower Limb Maximal Power Predicts Punching Speed in Different Static and Dynamic Attacking Techniques in Karate.

Quinzi, F, Rosellini G, and Sbriccoli, P. Lower limb maximal power predicts punching speed in different static and dynamic attacking techniques in karate. J Strength Cond Res 36(5): 1353-1359, 2022-Punching performance of karate can be predicted from lower limb maximal power. However, this relationship was observed only in single actions starting from a static position, thus calling for an investigation on the applicability of this relationship to other conditions. This study aims at investigating whether the relationship between lower limb maximal power and punch speed holds true, not only for single actions, but also for a combination of upper limb techniques in static and dynamic conditions. Ten national-level karate athletes aged 22.3 ± 1.8 years were assessed for maximal power of upper and lower limbs during a bench press and a back squat, and for punching speed during 2 punching techniques (gyaku tsuki [GT]; kizami tsuki and gyaku tsuki [KG]) starting from a static (GTS; KGS) or a dynamic (GTD; KGD) condition. Pearson's correlations were obtained between upper and lower limb maximal relative power and punch speed across tasks and conditions. Significance level was set at p < 0.05. Significant correlations were observed between lower limb maximal relative power and punch speed for all tasks and conditions (r = 0.66-0.80; p = 0.005-0.037). The present results further our knowledge on the relationship between lower limb maximal power and punch speed showing that this relationship holds true also for combinations of punching techniques performed also in dynamic conditions. This information can be useful for karate trainers to predict the punching performance of their athletes using a simple test to assess maximal lower limb power.

Influence of lubrication on forming limit diagram for Inconel 625 alloy at elevated temperatures

Nickel-based Inconel 625 is engaged in many performance-critical applications in nuclear and aerospace industries because of its exceptional combination of mechanical properties at high-temperature conditions. One of the primary processes of producing high strength Inconel alloy components is sheet metal forming. The major challenge of forming of Inconel 625 alloy is very high strength and limited ductility at room temperature conditions. The main aim of this work is to enhance the forming limits of Inconel 625 alloy by using suitable lubricants. The stretch forming experiments are performed at room temperature (RT) and 400 °C using non-lubricated and lubricated conditions. Two different kinds of lubricants, mainly; molybdenum disulfide (MoS2) and hexagonal boron nitride (hBN) are used for the analysis. The experiments are performed at different kinds of specimens using a hydraulic press at 5 mm/min punch speed, and 2 MPa blank holding pressure. The formability of material is evaluated based on forming limit curve (FLC), surface strain distribution pattern, and Limiting Dome Height (LDH). It is perceived that forming behavior of material acquired from experimental stretch forming has a predominant effect by temperature and powdered solid lubricating conditions.

Numerical and Experimental Explorations for the Formability of Drawing Square Cups Through Deep Drawing Operation (January 2020)

This study aims to examine the formability of drawing cups having square shapes through direct deep drawing process on a single action press through one pass. This can be accomplished by conducting an FE simulation and performing an experimental investigation on steel substrate type AISI 1008 blank with diameter and thickness dimensions 80, 0.5 mm respectively. To explore and analyze the formability of such a drawing process, two process parameters have been included in this work which is the speed of punch (30 and 300 mm/min) and the lubrication state (with machine oil and dry drawing). Both direct and indirect measurements of thickness strain have been adopted as an indicator of the sheet formability. The results of both FE simulation and experimental work demonstrate that the square drawing of the AISI sheet has been accomplished for all the four cups produced since the highest thinning over the cup wall does not exceed 25% of the original thickness. Generally, there is a good match between the experimental values of the indirect method and the FEM results for all models such that the largest deviation is about 25%. The direct method of thickness measurement is determined to be non-confident as strain values are practically unacceptable. Additionally, higher formability of the sheet has been realized at lower punch speeds. Furthermore, no significant difference has been observed in the formability at both speeds of punch when using a lubricant compared to the dry drawing operation.

Numerical Investigation on Key Process Parameters Affecting Blanking of Steel Sheet by Using Finite Element Method

The cutting surface obtained through the blanking process is often characterized by localized plastic deformations followed by crack propagation and ductile failure. The resulting blanked edge is essentially characterized by known areas such as shear zone, fracture zone and also sometimes burr. Their formation depends essentially on various process parameters and cutting material such as punch/die set, punch speed and temperature. The present study was carried out in order to investigate the possibilities for improving the quality of the cut-surface of high-alloy thick sheet steel. It was focused on modeling and analyzing blanking process of steel sheet using finite element method (FEM). The numerical results of the validation simulations were in agreement with the experimental results, thus validating the model parameters used. The model was developed in order to study the effects of process parameters on the blanking of mechanical steel parts, with particular attention to the study of punch-die gap influence.

Hot deformation behavior and optimization of processing parameters of a high-strength Mg-Gd-Nd-Zn-Sn-Zr alloy

Aiming at the forward extrusion forming and its parameter optimization of high-strength and heat-resistant Mg-9Gd-3Nd-1Zn-1Sn-0.5Zr alloy, the isothermal compression stress–strain behavior was investigated. The high-temperature plastic deformation constitutive equation and the microstructure evolution of the alloy were obtained. According to the results of variation of stress–strain with strain rates and processing temperatures, a thermal processing map of the alloy was constructed, to obtain a safe processing area where the material is not prone to be unstable. Based on the results of thermal processing map, the experiments were carried out with the punching speed of 2 mm/s, the temperatures of 400 °C, 425 °C and 450 °C and the extrusion ratio of 12. The results showed that the best comprehensive properties of the alloy were obtained at the extrusion temperature of 425 °C. In addition, our findings were in good agreement with the prediction of the thermal processing map.

The effect of punch speed on frictional contact mechanics of finite-thickness graded layer resting on the rigid foundation

The present article investigates frictional contact mechanics between a moving punch possessing sharp ends and a finite-thickness functionally graded layer resting on the rigid foundation. The rigid punch has either flat or semi-circular profiles, and it moves over the functionally graded layer at a steady subsonic speed. The tangential load developed by the moving punch is proportional to the normal applied load since Coulomb’s friction law is adopted. Variations of shear modulus and mass density through the thickness of the layer are expressed by exponential functions, whereas the variation of the Poisson’s ratio is neglected. Governing partial differential equations are derived considering two-dimensional theory of elastodynamics, and these equations are solved analytically utilizing Galilean and Fourier transformations. Equations are reduced to a singular integral equation of the second kind. Singular integral equation is solved, and results of analytical approach are compared with those obtained by means of the finite element method in elastostatic case. A very good agreement is achieved between analytical and computational results. Parametric analyses are performed to observe the influences of punch speed, material inhomogeneity and coefficient of friction upon contact stresses of a finite-thickness graded layer resting on the rigid foundation. Stresses observed for relatively thin softening layers are much sensitive to the variation in punch speed.

Experimental investigation on electromagnetic punching process of hybrid CFRP/Al stacks under different discharge energies

Abstract Machining holes on composites/metal stacks usually accompanied by burrs, chips and delamination damage. To solve those problems, this paper proposed a high speed punching technology for CFRP/Al stacks: electromagnetic punching (EMP). The machined hole qualities of CFRP/Al stacks (e.g. microscopic morphology, delamination damage and dimensional accuracy) for EMP process with various discharge energies were investigated. Besides, conventional quasi-static punching was performed as a comparing process. Note that the CFRP/Al stacks were fabricated with eight unidirectional CFRP plies and an aluminum alloy sheet, cured in an autoclave. The results showed that burrs of EMP were less than quasi-static punching, the heights of burnish zone under the discharge energies of 5 kJ, 6 kJ and 7 kJ (the corresponding maximum punching speed are 5.46 m/s, 7.63 m/s and 9.50 m/s) were respectively 32.5%, 40.0% and 55% higher than that of quasi-static punching process. Based on the results, the shear mechanism for the punching process was analyzed. The punching process could be divided into four stages, CFRP layers and Al sheet were sheared off sequentially. The dimension measurement results showed that diameter deviation between the hole entrance and exit became smaller under higher discharge energy. While the delamination was aggravated as the discharge energy exceeded 7 kJ, the discharge energy of 6 kJ was the most appropriate to machine holes on the CFRP/Al stacks.

PENGARUH LATIHAN PUSH UP DAN LATIHAN BENCH PRESS TERHADAP KECEPATAN PUKULAN PADA PENCAKSILAT

This research is a field experimental study that aims to find out the different effects of push up and bench press exercises on punch speed on pencaksilat. The population was all students of the FOK UNG Sport Coaching Education Study Program and the sample involved were 60 people. But in accordance with the research design, two research groups were formed consisting of group A for push up exercises and group B for bench press exercises. Data analysis techniques used t-test at a significant level of 95%. Based on the results of data analysis, it can be concluded that: There is a significant effect of push up exercises on the speed of the punch on pencaksilat (to = 9,151&gt; tt = 2,045). There is a significant effect of bench press training on punch speed on pencaksilat (to = 7,620&gt; tt = 2,045). There is a significant difference in effect between push up and bench press exercises on punch speed on pencaksilat (to = 12,828&gt; tt = 2,000).

A Study of Improving the Formability of the Commercial Pure Titanium Foils

Abstract In order to obtain the optimum forming process for commercial pure titanium grade 2 foils, a series of tensile tests and micro scale limited dome height (µ-LDH) tests at four temperatures, and meso scale limited dome height tests (meso-LDH) with three punch speeds were conducted on the as-received foils with a thickness of 75 µm. The effects of temperature, geometry, and high-velocity impact were investigated to understand their influences on the formability of the foils. It has been found in the tensile tests that the formability can be improved by elevating temperatures; this has been validated by the µ-LDH tests. Based on forming limit diagrams (FLDs) of the meso-LDH specimens, the high-velocity impact forming process results in not only much better formability but also more uniform thickness distributions than the quasi-static. By analyzing the fractographical scanning electron microscope (SEM) pictures of the meso-LDH specimens, it has been proven that the formability of the foils by using high-velocity impact process is superior to the conventional process. Furthermore, high-velocity impact causes forming limit curve (FLC) to shift in the upper right direction on the right-hand side of FLD. Therefore, it is suggested forming the foils by using high-velocity impact forming process at the elevated temperature for obtaining a better formability and more uniform thickness distribution. It is also recommended to make the radius of the LDH hemisphere punch close to the smallest feature of the designed products for obtaining more accurate FLCs.

Influence of material modeling on warm forming behavior of nickel based super alloy

The present study helps in providing a systematic approach towards the investigation of deep drawing and stretch forming processes for Inconel 625 alloy. Firstly, the flow stress nature and material properties of Inconel 625 super-alloy have been investigated and it has been found that temperature and deformation rate significantly affects the flow stress behavior. By using experimental flow stress data, four different constitutive models namely; modified Jhonson-Cook (m-JC), modified Zerilli-Armstrong (m-ZA), modified Arrhenius (m-A), Khan–Huang–Liang (KHL) model have been formulated of which m-A has been found to have the best predictability for flow stress. Hill 1948 and Barlat 1989 anisotropic yield criterion have also been applied and it has been found that Barlat 1989 criteria more accurately capture the yielding behavior of Inconel 625 alloy. The deep drawing analysis has been carried out using target and noise performance measures for different process parameters viz., temperature, punch speed and blank holding pressure. Uniformity in thickness has been major cause of concern, hence experiment at 473 K, 5 mm/min speed and 20 Bar pressure was found to have least variation in thickness. Furthermore, the forming limit diagram (FLD) and fracture curve (FC) obtained from stretch forming analysis along five different strain paths was found to be significantly affected by temperature. Further, user defined material (UMAT) subroutine have been incorporated in ABAQUS 6.13 software to have effect of m-A model and Barlat 1989 yield criteria in finite element analysis (FEA) of deep drawing and stretch forming processes.

Parameter Optimization in the Thermo-mechanical V-Bending Process to Minimize Springback of Inconel 625 Alloy

The present research deals with experimental and finite element analysis for minimization of springback in the V-bending process for Inconel 625 alloy. Different material properties were determined at three distinct temperatures (303 K, 473 K and 673 K) and deformation speeds (1 mm/min, 5 mm/min and 10 mm/min). Temperature was found to have significant effect on the flow stress of the material. Taguchi analysis was applied to find springback of Inconel 625 by considering four process parameters (temperature, punch speed, holding time and orientation of the sheet) and at the three predetermined levels of settings. Based upon signal-to-noise ratio analysis, temperature (46.93%) was found to be the most influential parameter affecting the springback followed by holding time (26.29%), sheet orientation (24.07%) and punch speed (2.69%). The optimized setting for the minimum springback of Inconel 625 alloy obtained after the conformation test was 673 K temperature, 1 mm/min punch speed, 90 s holding time and 90° to the rolling direction of a sheet. The springback was significantly reduced by 69.63% with the optimized setting of process parameters. The springback factor was also evaluated, and it was found to be directly proportional to the temperature and holding time and inversely proportional to the punch speed, but no particular trend was followed for the sheet orientation as a process parameter. The Arrhenius constitutive model with both Barlat and Hill yield criteria was implemented by adopting user-defined material (UMAT) subroutine for finite element analysis. Numerically computed springback from Barlat criterion was found to be in good relation with the experimental results.

Parameter optimisation in V-bending process at elevated temperatures to minimise spring back in Ti-6Al-4V alloy

ABSTRACT In the forming of Ti-6Al-4V alloy, during assembly high spring back is one of the main problem that causes changes in the dimensions of the component. This work focuses on obtaining the minimum spring back by optimising the process parameters, namely, temperature, punch speed and holding time. Using Taguchi (L9) orthogonal array, V-bending finite element simulations have been performed and validated with experiments. Simultaneously, full factorial simulations (L27) are carried out and the response surface method has been applied in order to study the impact of process parameters and then optimised by using genetic algorithm. Based on the experimental results, the Analysis of variance is applied to determine the influence of individual process parameter in minimising the spring back. In addition, the finite element simulation results are found to be in good agreement with the experimental results. Finally, using the genetic algorithm, the optimal process parameters have been obtained for minimum spring back, which has been validated through experiments as well as finite element simulations.

Moving contact problems involving a rigid punch and a functionally graded coating

Frictional contact mechanics analysis for a rigid moving punch of an arbitrary profile and a functionally graded coating/homogeneous substrate system is carried out. The rigid punch slides over the coating at a constant subsonic speed. Smooth variation of the shear modulus of the graded coating is defined by an exponential function and the variation of the Poisson's ratio is assumed negligible. Coulomb's friction law is adopted. Hence, tangential force is proportional to the normal applied force through the coefficient of friction. An analytical method is developed utilizing the singular integral equation approach. Governing partial differential equations are derived in accordance with the theory of elastodynamics. The mixed boundary value problem is reduced to a singular integral equation of the second kind, which is solved numerically by an expansion-collocation technique. Presented results illustrate the effects of punch speed, coefficient of friction, material inhomogeneity and coating thickness on contact stress distributions and stress intensity factors. Comparisons indicate that the difference between elastodynamic and elastostatic solutions tends to be quite larger especially at higher punch speeds. It is shown that use of the elastodynamic theory provides more realistic results in contact problems involving a moving punch.

Effect of Stamping Clearance in Rapid CNC Punching of WPC Sheets

Wood Plastic Composites are gaining momentum due to their ability to contain recycled materials. The material usage is mostly limited to extruded deck profiles. This paper investigated if punching tools typically used in sheet metal stamping could be directly utilized in feasible post-processing of WPC sheets to enable a wider array of WPC products. A set of punches and dies with variable clearances and various punching speeds were tested and the results were investigated using 3D measurement macroscope. The results indicated that typical sheet metal punch clearances and speeds are suitable for WPC materials with some material specific considerations.

Spring back in air bending of CRCS

This study attempts to investigate the effect of process variables like punch travel and punch speed in air bending of cold reduced low carbon steel (CRCS), by varying one parameter at a time approach. Experiments were conducted using different combinations of sheet orientations, punch travel and punch speed. Tooling parameters and specimen size were kept constant. Universal testing machine was used at different speeds. Effect of various parameters on spring back has been analysed graphically. The increase of spring back was observed due to an increase of punch travel and punch speed as well. By changing the orientation of steel sheet from longitudinal to transverse, spring back was increasing. It was observed that the spring back follows power equation by curve fitting method. The results will be useful for tool design engineers and press shop engineers in the sheet metal forming industry.

Analysis on Micro Complex Shape Via Hole Punching on Low Temperature Co-Fired Ceramics

The quality of a via hole on a multilayer stack of Low Temperature Co-fired Ceramic (LTCC) tape is of utmost importance to its functionality. This paper investigates a substitute for the commonly used circular shape hole to a more complex one and its implications when different parameters such as sheet thickness, punch speed, travel distance and tool clearance are changed. Fabrication of the punch tools and the punching process is carried out at the same machine, ensuring alignment. Two types of non-circular shape are chosen to carry out the experiment. Pre-sintered complex shape hole measurements show that while punch conditions such as speed and tool gap have little effect on the size, sheet thickness and travel depth play a vital role in the overall dimension. Albeit having only a slight effect on the size, those parameters are significant in other aspects of hole quality. Post-sintering investigation is also observed and discussed.<

High-Speed Deformation of Pinless FSWed Thin Sheets in AA6082 Alloy

The high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition.

Real-Time Contingent Feedback to Enhance Punching Performance

Reinforcement has been shown to change exercise behavior, often in contingency management programs. In this study, boxers received conjugate reinforcement-like performance feedback through both visual cues and changes to music. A device made music speed contingent on punching speed, and the music volume contingent on punching force. Participants could see green or red cues for being above or below a goal. Multiple baseline design and reversal designs were used to evaluate the effectiveness of our audio-visual intervention in increasing the speed and force of punches for eight participants. Punching force and speed appeared to increase for five of the eight participants compared to punching performance when using unaltered music alone in baseline.

V-shaped bending of Ti-6Al-4V titanium alloy sheet with elliptical hole

The internal elliptical hole defect in the Ti-6Al-4V titanium alloy sheet strongly affects the material mechanical properties during the bending process. In this study, the finite element method (FEM) is used to study the effect of internal hole on mechanical properties of the sheet subjected to the V-shaped bending. The fracture damage, the equivalent strain and the principal stress in the sheet with elliptical hole (the defect sheet) and the hole-free sheet (the perfect sheet) are analyzed contrastively under different punch speeds and radii. The results show that the load in the defect sheet and the perfect sheet has different trends during the bending process. Compared to the perfect sheet, both the damage and the equivalent strain in the defect sheet obviously increase, and the distribution of the principal stress in the bending zone of the defect sheet has a significant change. The hole causes the different evolution of the maximum damage, the equivalent strain, and the maximum tensile and compressive stresses with the increase of punch speed and radius for the defect and perfect sheets. The current results serve a feasible approach to predicting the fracture of the sheet with internal hole during the V-shaped bending process, and provide a guidance for the V-bending experiments of the defect and perfect sheets in the subsequent work.

Warm Forming Simulation of a ZEK100 Magnesium Door Panel

The warm forming of a door panel made of commercial grade ZEK100 magnesium alloy sheet was modelled using finite element techniques (Autoform). The operation consisted of a heating step, a forming step and a cooling/springback step. The material properties of the ZEK100 blank were modelled using a set of temperature- and strain rate-dependent stress-strain curves, which were derived based on a Zerilli-Armstrong constitutive model. In order to simplify the material model to enable its complex response to be represented within a commercial finite element code, the anisotropy of the magnesium sheet was approximated using a Banabic-2005 yield surface and yield asymmetry was neglected, a reasonable approach for warm forming. Necking was predicted using a set of forming limit curves obtained at different isothermal temperatures. The entire forming model was run at a punch speed of 160 mm/s, and two initial blank temperatures: 215 and 230 °C. The tooling was initially at room temperature. The model predicted that the blank cracked when its initial temperature was 215 °C due to excessive cooling. The best formability (lack of wrinkling and necking) was predicted when the blank was heated to 230 °C. These predictions agree well with the forming trial outcomes.