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The development of porous polymeric membranes is an important area of application in separation technology. This article summarizes the development of porous polymers from the perspectives of materials and methods for membrane production. Polymers such as polyethylene, polydimethylsiloxane, polypropylene, polyimide, and polytetrafluoroethylene are reviewed due to their outstanding thermal stability, chemical resistance, mechanical strength, and low cost. Six different methods for membrane fabrication are critically reviewed, including thermally induced phase separation, melt-spinning and cold-stretching, phase separation micromolding, imprinting/soft molding, manual punching, and three-dimensional printing. Each method is described in details related to the strategy used to produce the porous polymeric membranes with a specific morphology and separation performances. The key factors associated with each method are presented, including solvent/non-solvent system type and composition, polymer solution composition and concentration, processing parameters, and ambient conditions. Current challenges are also described, leading to future development and innovation to improve these membranes in terms of materials, fabrication equipment, and possible modifications.

This study presents a comprehensive numerical and experimental investigation into the influence of punch shaft geometry on punching force and tool durability in the cold forming of S500MC steel sheets using an AISI D2 punch. Finite element analyses were conducted to evaluate the effects of varying punch shaft diameters on stress distribution, deformation behavior, and resultant punching forces. Experimental validation was performed through controlled punching tests, measuring force responses and assessing tool wear. The results demonstrate that optimizing the punch shaft diameter reduces the maximum punching force and minimizes stress concentrations, thereby enhancing tool life. Specifically, larger punch shaft diameters contribute to more uniform stress distribution and decreased risk of premature tool failure. These findings provide valuable insights for tooling design in high-strength steel sheet forming processes, enabling improved efficiency and cost-effectiveness in manufacturing operations.

The present research investigates the optimization of the punching process in cold forming manufacturing, focusing on enhancing tool life, reducing damage, and improving product quality. Punching, a shearing process widely used in sheet metal forming, requires careful management of process parameters to prevent tool damage, especially to the punch and die. The research explores various design modifications to the punching tool, including conical, pointed, and stepped shafts, aimed at reducing punching force and minimizing wear, fatigue, and crack formation. Using numerical simulations (ABAQUS/Explicit), the study evaluates the impact of shear angle, punch geometry, and other key parameters on the maximum punching force and stress distribution. The results show that adjusting the punch shaft shape and optimizing the shear angle can significantly decrease stress concentrations, extend tool lifespan, and improve process efficiency. This work provides valuable insights for improving punching tool designs and ensuring longer, more efficient service lives in industrial applications.

In this study, experimental and numerical approaches are used to investigate the effect of pre-punches on the spring-back of U-channels made of St12 with 1-mm thickness. Three-channel section profiles were examined: a simple hole-less channel and two pre-punched channels with holes located in the bending zone and next to the bending zone. The rolls were designed using the constant bending radius method with an increment of 15° at three forming stations. Numerical solutions were obtained using Abaqus finite element software, with both isotropic von Mises and anisotropic conventional Hill’48 yield functions calibrated using R-values (Hill’48-R) and yield stresses (Hill’48-S). The results show that considering the anisotropic properties of the sheet by using the anisotropic Hill’48 yield criteria improves the accuracy of spring-back prediction in the range of 5 to 20%, depending on the calibration method of the yield criteria. The results also indicate that calibration of the Hill’48 criterion using R-values increases the accuracy of spring-back prediction by about 15% compared to stress-based calibration for hole-less and pre-punched channel with holes next to the bending zone, but decreases by about 5% for pre-punched channel with holes located in the bending zone.

A cold trimming technology reduces the process time and product cost compared to the common laser trimming method in hot stamping process. However, high stress concentration during the cold trimming can lead to quality defects such as premature cracking. Moreover, the defects may cause critical delayed fracture under hydrogen environment. In this study, experimental and numerical investigation are provided to understand the effect of cold trimming method on the surface quality and hydrogen induced delayed fracture of a hot stamped high strength steel. Specimens with different clearances, tool geometries, and process conditions are considered along with different trimming methods. The new trimming processes are the process division and double punching methods, which are suggested to overcome the drawback of the conventional single punching method. The experiments show that the sheared surface profile is mainly dependent on the trimming clearance, while the hydrogen embrittlement (or its resultant delayed fracture) is dominantly affected by the stress state of the trimmed surface. Especially, significant improvement in the hydrogen delayed fracture of hot stamped steel can be achieved by introducing the double punch method. This study suggests that the double punching can be a potential trimming method as an alternative to the laser trimming by reducing the cost and process time in producing the hot stamped automotive parts.

This study aimed to investigate the influence of different constitutive models on the accuracy of predicting spring-back in cold roll forming for pre-punched profiles. Finite element analysis was conducted using Abaqus, employing eight distinct constitutive models that varied in terms of yield criteria, yield function calibration, and elastic modulus degradation. To evaluate the impact of holes and their positions on spring-back, three samples made of St12 with a 1 mm thickness were used: a sample without holes, a profile with holes in the bending zone (on the bend), and a profile with holes close to the bending zone (near the bend). The results show that ignoring variation in elastic modulus has less influence on the accuracy of spring-back prediction for “near the bend” than the two other profiles. This case is explained by less change in elastic modulus during roll forming of the “near the bend” profile. Additionally, calibrating yield criteria based on R -values, such as Hill48_R and Yld89_R, and yield stress values result in more precise spring-back estimations for the “on the bend” and “near the bend” profiles, respectively. This approach proves superior when contrasted with the alternative calibration methods. Moreover, neglecting the effect of Young’s modulus variation in Yld2000-2d and Hill48_S results in the lowest MAPE (mean absolute percentage error) of approximately 20% compared to other models. However, it is worth noting that Yld2000-2d underestimates the experimental values while Hill48_S tends to overestimate them. As a result, the most suitable constitutive model, considering elastic variation, is Yld2000-2d, with an average MAPE of 8% across all three samples.

A punching test for simply estimating the tensile strength and total elongation of steel sheets and formed parts was proposed. The tensile strength and total elongation were estimated from the shear stress at the maximum punching load and percentage of the burnished depth at the sheared edge of the slug measured without cutting, respectively. For a variety of steel sheets with a range of the tensile strength from 360 to 1500 MPa, linear functions for the estimation were experimentally obtained. The correlation of the estimated tensile strength of the steel sheets with the measured one from the uniaxial tensile test was considerably high, and the correlation of the estimated total elongation was high. The distributions of tensile strength and total elongation for hot- and cold-stamped parts were estimated. The proposed punching test is available under not only a laboratory environment but also a factory environment.

The working conditions of tools during plastic working operations are determined by, among other things, temperature, loads, loading method, and processing speed. In sheet metal forming processes, additionally, lubricant and tool surface roughness play a key role in changing the surface topography of the drawpieces. This article presents the results of friction analysis on the edge of the punch in a deep drawing process using the bending under tension test. A DC04 steel sheet was used as the test material. The influence of various types of titanium nitride and titanium coatings applied on the surface of countersamples made of 145Cr6 cold-work tool steel was tested by means of high-intensity plasma pulses, magnetron sputtering, and electron pulse irradiation. The influence of the type of tool coating on the evolution of the coefficient of friction, the change in the sheet surface topography, and the temperature in the contact zone is presented in this paper. An increase in the coefficient of friction with sample elongation was observed. Countersamples modified with protective coatings provided a more stable coefficient value during the entire friction test compared to dry friction conditions. The electron pulse irradiated countersample provided the highest stability of the coefficient of friction in the entire range of sample elongation until fracture. The skewness Ssk of the sheet metal tested against the coated countersamples was characterized by negative value, which indicates a plateau-like shape of their surface. The highest temperature in the contact zone during friction with all types of countersamples was observed for the uncoated countersample.

The life of industrial dies and punches can be effectively increased by timely repair of damaged surfaces. In the present investigation, a procedure was developed to recover VF800AT steel stamping punches by gas metal arc welding (GMAW) process, using Tube-Alloy 260-G metal-cored filler wire (MCFW) with a diameter of 1.2 mm, that deposits a martensitic steel alloy, and a gas-shielded mixture with 25 vol.% CO 2  + 75 vol.% Ar, and a flow rate of 12 l/min. The repair procedure included the following steps: surface preparation, pre-heating, manual welding, post-welding tempering, and final inspection. The samples were pre-heated at 450, 500, and 550 °C, repaired by gas metal arc welding, and post-welding tempering. Subsequently, were characterized before and after the weld repair concerning the macrostructure, microstructure, and microhardness. The correlation of the hardness in the weld metal (WM), heat-affected zone (HAZ), and base metal (BM) regions with the pre-heating temperature and post-welding tempering steps was statistically evaluated by the analysis of variance (ANOVA). Performance tests of the new and weld repaired punches were carried out to experimentally validate these conditions. Optical microscopy and scanning electron microscopy images, energy dispersive system analysis, and roughness measurements were carried out to evaluate the cutting-edge radius and the type of wear acting on the punches. Punches pre-heated to 450 °C and submitted to one post-welding tempering step presented the best results, being the most suitable to recovering VF800AT steel stamping punches by the GMAW process.

A seeding machine for planting potatoes in double rows on large ridges in the cold and arid regions of northwest China was designed and built at Gansu Agricultural University. The machine is capable to achieve the integrated operations of ridge formation, mulching, hole punching, and the precise covering of holes on the film. The key components were analyzed and designed, and the link lengths of the crank film-piercing and hole-punching mechanism were refined using MATLAB R2022a software. The structures and working parameters of the film-piercing and hole-punching mechanism, the dual-opening punching and seeding mechanism, the ridge-forming and soil-covering mechanism, and the seed-casting device were designed. The dynamics of the ridge-forming and soil-covering were simulated using the discrete element method to capture the effects of different machine parameters on the soil covering operation. Field tests showed that the full soil-covering rate of film holes, the qualified rate of hole spacing, the hole misalignment rate, the degree of damage to the light-receiving surface of the film, and the qualified rate of sowing depth under the film were 94.8%, 87.6%, 4.3%, 33.4%, and 95.6%, respectively. These indicators met the requirements of industry standards, and the test results met the design and actual operation requirements, enabling the integrated operations of ridge formation, mulching, hole punching, sowing on the film, and the accurate soil covering of the holes.