Punching Operations Research Articles

Performance investigation of punching operation to optimize the over cut of circular hole using Design of Experiment Technique “Taguchi Method”

Current research investigates the optimization of over-cut in circular hole punching operations using a CNC turret punching machine. The study employs the Design of Experiment (DOE) technique, specifically the Taguchi method, to systematically analyze the influence of three critical factors: cutting load, hit rate, and material type. The factors were varied across three levels: cutting load (10, 12, and 14 kN), hit rate (100, 150, and 200 punches per minute), and materials (EN-8, EN-24, and EN-31). An L9 orthogonal array was used to design the experimental runs, resulting in nine unique combinations to explore the effects on over-cut (OC). Over-Cut (OC) was the key response parameter, measured using a microscopic testing machine to capture high-resolution images of the punched holes. ImageJ software was employed for image processing to accurately assess the deviations. The data were analyzed using Minitab software, focusing on signal-to-noise (S/N) ratio analysis with the criterion "smaller is better." The S/N ratio results indicated that the cutting load had the most significant impact on minimizing dimensional deviation, followed by material type and hit rate. The study revealed that the lowest dimensional deviation was achieved at a cutting load of 10 kN, hit rate of 200 punches per minute, and using EN-8 material. The mean effect and S/N ratio plots further confirmed that increasing the cutting load generally led to higher over-cut values, while higher hit rates improved precision. Interaction plots indicated that EN-31 material performed robustly across varying conditions, making it a suitable choice for diverse operational settings. ANOVA analysis supported these findings, with cutting load contributing the most to the variability in OC, followed by material type and hit rate. Current study provides valuable insights into the optimization of punching parameters to achieve minimal over-cut and enhance machining accuracy. The findings underscore the importance of selecting appropriate levels of cutting load, hit rate, and material type to optimize the performance of CNC punching operations.

Design and fabrication of circular sheet metal shearing machine

The growing use of sheet metal in various industries such as automotive, packaging, medical appliances, cylinder production, Apparatus construction, Tank construction, Aircraft bodies, Missile production, Satellite dishes, road building and road signs, and household appliances, is attributed to its ease of manufacturing, handling, and use. To meet customer demands, sheet metal product manufacturing industries are working towards producing circular feature products of good quality at a large scale and low cost. To this end, this research emphasis the design, analysis, and fabrication of an electric circular sheet metal shearing machine, this would replace the punching and blanking operations and reduce scrap value from the stock material. The research includes concept design, detail design and analysis, assembly, 3D modelling, and fabrication of the Machine.

A deep assessment of a pair of built-in winglets with similar disposition on a rectangular channel

Heat transfer enhancement is a constant objective in the design of heat exchangers. Several techniques have been implemented to achieve it. Passive techniques use the fluidˈs energy to improve the heat exchanger surface performance. As a passive technique, vortex generators produce a relatively low impact on drop pressure. They are a disruptive element of the boundary layers and when facing the flow, they create secondary flows responsible for the enhancement of heat transfer. Vortex generators can be implemented on surfaces using different methods, but a mechanical punching operation is probably the best option to create them. The operation produces a hole on the surface which plays a crucial role in the heat transfer process. There is a lack of studies where the influence of punched holes on the rectangular channelsˈ performance has been researched. Numerical methods allow to develop such analysis. As a novelty, this paper numerically analyzes the influence of two built-in punched vortex generators on a rectangular channel with a similar disposition and inside the laminar flow regime. Four dispositions with a variable transversal pitch are studied, for a total of 22 different models. The results are discussed using a modified non-dimensional parameter. The best overall performance was obtained using the arrangement with punched holes in front of the vortex generators. When compare to the others, that arrangement allowed to double the overall performance. A heat transfer enhancement ranging from 1 to 14% was obtained as a Reynolds number function. In contrast, the pressure drop increased from 3 to 17%.

Study on size-related product quality of multiscale central-punched cups fabricated by compound forming directly using brass sheet

Meso/microforming has gained much more attention in the last decades and is widely used as a reliable method to fabricate meso/micro-scaled metallic components. In this research, a compound meso/microforming system which combines deep drawing, punching, and blanking operations was developed to fabricate multiscale central-punched cups by using brass sheets. The parts with three scales were produced by using the brass sheets with various thicknesses and grain sizes to investigate geometrical and grain size effects on the deformation behaviors, dimensional accuracy, and material flow behaviors in the forming process. Through physical experiments and finite element simulations, it is revealed that the ultimate deformation load in the drawing-punching stage is smaller than that in the single deep drawing stage under microscale, but the results in the meso-scaled scenarios are opposite. In addition, the thickness variation is increased with grain size, but the variation of the normalized thickness variation does not show an obvious tendency with different size scales. In the bending area, the material flow is tangential to the thickness direction, leading to the formation of thinning area. In addition, the material flow is almost opposite to the punching direction in the punching area, avoiding the expanding deformation of the hole. Thus, the punching operation barely affects the dimensional accuracy including the thickness and hole diameter of the formed parts. Furthermore, the micro-scaled cups with finer grains have a better surface quality. These findings enhance the understanding of size effect in compound meso/microforming with the combined deep drawing and punching operations.

Modelling and Manufacturing of Progressive die for Mechanical Press Operations

A progressive die is a type of die in which multiple operations performed in a single stroke, which was mostly used in sheet metal operations. The working process of sheet metal is widely used in all manufacturing industries such as mechanical, defense and automotive etc. The key advantage of metal working process involves enhancement of production rate and cost reduction. This paper is aimed to develop a multi-functional die which can perform simultaneously both punching and blanking operations in one stroke. The present work is mainly focused on modeling and manufacturing of the die components, where PRO-E was used for modelling and FANUC controlled CNC machine was used to execute and prepared part program.

Application of fuzzy MOORA method in the design and fabrication of an automated hammering machine

PurposeIn most developing countries riveting, upset forging and punching operations among others are performed using manual hammering technique. The use of the manual method increases production time and reduces efficiency. The use of the manual approach is predominantly due to the high cost of imported automated hammering machines (AHM) which the majority of the end-users are incapable of acquiring. The purpose of this paper, therefore, is to produce an AHM that is affordable using an effective material selection methodology in the design and fabrication process.Design/methodology/approachThe material selection methodology proposed is the fuzzy multi-objective optimisation on the basis of the ratio analysis (MOORA) method. The tool was used to evaluate and determine the optimum material for the major of the components of the AHM from amongst alternative materials while considering several decision criteria. A case study of the shaft was applied to demonstrate the suitability of the proposed technique. The AHM components design is then carried out and machine fabricated and tested to ascertain performance effectiveness.FindingsThe result of the fuzzy MOORA evaluation showed that alloy steel is the optimal material for the shaft. The fuzzy MOORA approach was compared with the fuzzy Vlsekriterijumska Optimizacija Ikompromisno Resenje (VIKOR) and fuzzy grey relational analysis (GRA) methods to validate the proposed method. The fuzzy MOORA method produces completely the same result with the fuzzy VIKOR and fuzzy GRA methods. The machine was then designed, constructed and tested and found to be effective for the purpose of the design.Originality/valueThis is significant as no such study has been published by any other researcher to the best of our knowledge in this area.

Epitaxy Enhancement of Piezoelectric Properties in P(VDF‐TrFE) Copolymer Films and Applications in Sensing and Energy Harvesting

AbstractWith the rapid development of wearable and flexible electronics, energy harvesting from the environment has attracted much attention. As one representative piezoelectric polymer, poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] is an expected candidate for mechanical energy harvesting and self‐powered mechanical sensors due to its flexibility and moderate piezoelectricity. However, low crystallinity and electroactivity limit its electric performance. Controllable modulation of microstructure and crystallization is one feasible measure to enhance piezoelectric property. Here the piezoelectric properties of epitaxial P(VDF‐TrFE) films which are fabricated via removable polytetrafluoroethylene template method are reported. Piezoelectric measurement between 50 and 800 Hz presents an averaged d33 coefficient of −40.7 pC N−1 for epitaxial film, ≈61% enhancement to that of non‐epitaxial one. Transverse piezoelectric experiment indicated that epitaxy process enhanced open‐circuit voltage and short‐circuit current outputs. Simple piezoelectric energy harvesters are prepared by depositing both epitaxial and nonepitaxial films on flexible polyimide substrates. Epitaxial film shows a maximum generated power density of 0.118 µW cm−2 and energy conversion efficiency of 0.81%, both of which are much larger than those from nonepitaxial film (0.047 µW cm−2 and 0.30%). Piezoelectric films are used to monitor bending, punching, twisting and finger tapping operations, where epitaxial film exhibited larger open‐circuit voltage responses than nonepitaxial one.

Comprehensive understanding of effective parameters on edge cracking sensitivity of hot-rolled complex phase steels

Good stretch-flangeability is an essential property for forming complex press-formed automotive parts such as chassis, suspension and control arm components. Continuous research is ongoing in developing materials that could improve the performance of Advanced High Strength Steels (AHSS) during industrial stretch-flangeable operations. Consequently, there is a great interest in investigating the sheared edge stretchability and determining the factors, critically influencing the product edge formability. The objective of the present research is to obtain a comprehensive understanding of effective parameters on the cut-edge behaviour of Hot-Rolled (HR) stretch-flangeable Complex Phase (CP) steels. The role of microstructural damage on the edge stretchability of CP steels was evaluated employing hole punching and Hole Expansion (HE) tests. The influence of product microstructure and inclusions were highlighted. A correlation between the Lankford coefficients (‘r’ value), strain hardening exponent (‘n’ value) and Hole Expansion Rate (HER) was investigated. Finally, a new specific testing procedure combining a shearing test followed by tensile test is proposed to correlate with hole punching and HE operations and to develop in-depth understanding.

Analysis of lubricant performance in punching and blanking

Abstract Punching and blanking processes are characterized by severe tribological conditions due to the creation of virgin surfaces, which are highly prone to develop pick-up of workpiece material on the punch surface. Hazardous forming lubricants are, therefore, commonly used in punching and blanking processes for avoidance of wear induced process deviations such as diminished surface quality, reduced dimensional accuracy and reduced tool life. The present study characterizes the function and performance of lubricants used for punching and blanking operations for assessment of the tribological lubricant properties necessary for adaption of environmentally friendly lubricant alternatives. Analysis of the tribochemical properties of the studied lubricants indicate that an applicable temperature range and a high load bearing capacity are central lubricant properties necessary for ensuring sufficient lubricating ability for punching and blanking operations.

Importance of hole punching conditions during Hole Expansion test

There is an increasing interest in the steelmaking and automotive industries to evaluate the edge cracking sensitivity of Advanced High Strength Steel sheets used in car body manufacturing. Currently, the Hole Expansion test is the only test procedure that is defined by norms (JFS and ISO). This test is increasingly used to assess the formability of cut-edges on punched sheets because it is relatively simple. However, it has been already shown that there can be large differences in Hole Expansion Ratio (HER) values generated by different testing facilities. Among the main sources of variability: punched hole quality and hole expansion termination point. Hole punching operation has a detrimental effect on cut-edge quality and HER values. However, current standards do not give any recommendation. No technical specification is given for the tooling, quality control system and punching speed. It has been stated that the press speed difference in the hole punching operation are significantly different from one laboratory to another one and some steel microstructures sensitive to it. However, very few papers and data are available. As a result, an experimental study was conducted to examine this important issue. A specific 4-post assembly tool was designed to guarantee the best punched hole quality. Different punching speeds, from 0.2mm/s to 367mm/s were tested on different steel sheets (mild steel, AHSS including TWIP and 3rd Gen steel) to emphasize or not the influence on final HER values.

High cycle fatigue strength assessment methodology considering punching effects

Since a decrease of the fatigue strength may result from punching operations, this study proposes a methodology for designing punched parts against high cycle fatigue crack initiation. To reach this goal, high cycle fatigue tests are performed on different specimens configurations with either punched or polished edges. Due to punching effects, the fatigue strength of punched specimens is significantly decreased. Fracture surfaces observations reveal that crack initiation occurs always on a punch defect. Additional investigations are combined to characterize how the edges are altered by the punching operations. High tensile residual stress levels along the loading direction are quantified using X-Ray diffraction techniques. Furthermore, micro-hardness measurements and X-Ray diffraction results reveals a strong hardness gradient due to punching operation. For a better understanding of crack initiation mechanisms, the edge geometries have been scanned with 3D optical microscopy, allowing us to identify the most critical defect (and its real geometry) by comparing the edges before and after fatigue failure. Finally, FEA are performed on identified defects. A non-local high cycle multiaxial fatigue strength criterion has been used as post-processing of FEA to take into account the effect on the HCF strength of defects and the strong stress-strain gradients around them.

Computer aided system for parametric design of combination die

In this paper, a computer aided system for parametric design of combination dies is presented. The system is developed using knowledge based system technique of artificial intelligence. The system is capable to design combination dies for production of sheet metal parts having punching and cupping operations. The system is coded in Visual Basic and interfaced with AutoCAD software. The low cost of the proposed system will help die designers of small and medium scale sheet metal industries for design of combination dies for similar type of products. The proposed system is capable to reduce design time and efforts of die designers for design of combination dies.

Increase of Lifetime for Fine Blanking Tools

To improve the lifetime of blanking tools, the application of high quality steel, heat treatment and coatings has become an interesting issue for many European companies dealing with stamping, punching and blanking operations. Important trends such as longer lifetime, higher accuracy and higher complexity of the products are challenging and require more special materials and techniques.The technological solutions to improve the existing processes are not obvious because of the enormous amount of possibilities in available materials, heat and surface treatments such as PVD coatings for the envisaged industrial processes and applications. An in-depth research to understand the manufacturing processes with the consequence of an increased performance and lifetime of the tools as well as the opportunity of further optimization was the main goal of this project.In many blanking processes where heavy duty conditions are applied, the use of hard metals, durable coatings and wear resistant tool steel is already established to extend the lifetime. The tools studied in this project were applied without coatings. The increasing production rate and the use of high strength steel sheet induce wear, crack formation and flaking of blanking tools with consequent low lifetimes. This project studied the tribological synergy of the substrate-heat treatment-surface preparation relationship and their influence on lifetime in heavy load conditions. A preliminary study was performed on the cutting edges of special designed triangular punches made of several high alloyed steels which were heat treated in a conventional way and by deep cryogenic treatment after quenching.After this research some demonstration tools were tested in industrial conditions to show the feasibility of certain selected combinations.

High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets

Abstract Some parts of electrical machines are built from stacks of thin steel sheets, for which the coarse grain microstructure allows for minimizing magnetic losses. The fabrication process of these parts usually involves punching operations that generate important defects on the edges. Since these alterations may result in a degradation of the fatigue strength, this study aims at elaborating on a fatigue design strategy for such punched parts. To reach this objective, high cycle fatigue tests are performed on different specimens with either punched or polished edges. The results show a significant decrease of the fatigue strength for punched specimens. Scanning electron microscope observations of specimen facture surfaces reveal that defects on punched edges are at the origin of the fatigue cracks. The influence of temperature is also investigated. Fatigue tests are performed at ambient temperature (20°C) and at 180°C. According to the experimental results, no significant influence on the median fatigue strength is observed. Since crack initiation always occur on the edges, additional investigations are performed to characterize how edges are altered by punching operations. Residual stresses are determined on punched edges using x-ray diffraction techniques. As a consequence of punching, important tensile residual stresses exist along the loading direction. In association with the stress concentration caused by geometrical defects, residual stresses promote crack initiation and fast crack propagation. For a better understanding of crack initiation, edge geometries are scanned with a 3D optical profilometer, allowing us to identify the critical defect. It is found that the typical defect size is comparable to the grain size.

Edge crack sensitivity of lightweight materials under different load conditions

This study addresses the analysis of edge crack sensitivity of DP800 steel and AA5182 aluminum alloy in dependency of punching and machining operation as well as load case of subsequent forming. The inserting of a round hole by punching with defined punch-to- die-clearance, milling and drilling is compared. Subsequent forming is performed by standardized hole expansion test and by Nakajima-tests with three different specimen geometries. Local strain distribution at the surface for Nakajima-tests is measured by optical strain measurement technique and investigated in order to evaluate local deformation before failure. Additionally, resulting hole expansion ratio λ is determined. Significant higher X as well as local strain values εmax are achieved by machined holes. This is directly coupled to higher local formability and stretchability for both materials. Furthermore, the load condition has a strong impact on the edge crack sensitivity of the material. Prior failure is observed with changing stress conditions using different specimen geometries also influencing the reachable maximum failure strain. Higher edge crack sensitivity is observed for DP800, which is in good accordance to the material properties in terms of ductility and strength. These data in dependency of the process parameter can be used for the design of automotive components.

Effect of puncher profile on the precision of punched holes on composite panels

As structural materials, assembly for a composites panel cannot be avoided. Typically, composite panels are assembled using a fastener through a drilled hole. The main problem of drilling is delamination, which affects the strength of the assembly. In addition, the cost of drilling is high because of severe wear on drill bits. The main goal of this research is to develop a new punching operation method as an alternative to drilling during hole preparation. In this study, we investigated the effect of different puncher profiles on the quality of punched holes on composite panels. Six types of puncher profiles with minimum die clearance (1 %) were fabricated. Three quality aspects, namely, precise hole diameter, incomplete shearing, and delamination factor were measured. The conical shape puncher produced the lowest defect in terms of delamination and yielded an acceptable amount of incomplete shearing compared with the other punchers.

Experimental study of the impact of punching operations on the high cycle fatigue strength of Fe–Si thin sheets

In this paper, the impact of punching operations on the high cycle fatigue strength of Fe–Si thin sheets is investigated. High cycle fatigue tests are performed on both punched and polished edge specimens. Results show a significant decrease of the fatigue strength in the case of punched specimens. Different factors are found to be responsible for this degradation. First, according to SEM observations of fracture surfaces and to 3D surface topography, fatigue crack initiation is strongly governed by the geometrical defects resulting from punching operations. Second, important tensile residual stresses, which are analyzed using X-ray diffraction techniques, are observed on punched edges. Depending on the loading conditions, it is possible for the residual stress field to be redistributed as a result of cyclic plasticity. Third, punching operations are responsible for the introduction of a plastically hardened zone which, according to both micro-hardness measurements and diffraction data, is about 200μm deep. Based upon this experimental dataset, the parameters of the Murakami criterion are identified. This criterion is found to provide a reasonable description of the experimental results when the residual stresses around punched edges are accounted for.

Characterization and Simulation of the Effect of Punching on the High Cycle Fatigue Strength of Thin Electric Steel Sheets

Rotors of electric machines are built from stacks of thin steel sheets. The fabrication process of these components usually involves punching operations that generate defects on the steel sheet edges. In this study, high cycle fatigue tests are performed on punched and polished edges specimens to investigate the effect of the punching process on the fatigue behaviour of these thin sheets. Results show a significant decrease of the fatigue strength for punched specimens. SEM observations of fracture surfaces reveal that crack initiation always occurs on a punching defect. Residual stresses on punched edges are analysed using X-Ray diffraction techniques. High tensile residual stresses along the loading direction are found. Some specimens edges were scanned using 3D topography prior to the fatigue tests. This allows for identifying the real geometry of the most critical defect. Murakami criterion was then evaluated in order to take into account the effect of defects. The best trend of the experimental results is given when residual stresses are taken into account. Local elastic stresses for 3 defects geometries have been calculated using FEA. Crossland fatigue criterion has been evaluated to try accounting for the local stress state around defects. Results show that the assessed fatigue strength is overestimated using this criterion.

Effects of Acoustic Softening and Hardening in High-Frequency Vibration-Assisted Punching of Aluminum

Punching operations contain high shear stress gradients which can exhibit adiabatic strain rate effects in certain materials at higher speeds due to a localized reduction of thermal lattice vibrations. Ultrasonic forming is known to soften material undergoing plastic deformation by direct application of lattice vibrations. Punching speed and ultrasonic vibration amplitude effects are investigated in sheets of 1100-O aluminum. Ultrasonic vibration more than negated adiabatic strain rate effects at high speeds with reductions in punching force of up to 30%. At lower speeds, a competing effect from acoustoplastic hardening resulted in a smaller effect on punching force, but increased ductility.

COMPUTER ASSISTED COMPOUND DIE DESIGN: A CASE STUDY

A compound die set for a blanking, drawing and punching operations are in many cases is very complex and expensive device. It is time consuming design die set by combining these three operations manually. This paper presents a Computer assisted design method to design compound die set for downlight housing. The design calculations take account of the quality of the workpiece material and they determine the optimal size for the die punch sets. The proposed method can be used for any configuration of the parts which need to be processed. The design calculations are verified by using manual die design process.