Experimental evaluation of blanking and piercing of PVC based composite and hybrid laminates

Blanking is one of the high speed processes to produce flat products from sheets economically. In order to expand this process to new materials, the blanking of polyvinyl chloride (PVC)/fiberglass thermoplastic composite laminates and composite/aluminum hybrid laminates was investigated. The laminates were produced by the film stacking procedure and then blanked by circular die and punches. The blanking process was done in two levels of clearance including 4% and 8% of the laminates thickness, two levels of punch speed including 40 mm/min and 200 mm/min and at two levels of temperature (room temperature and 80℃) for both composite and hybrid laminates. The effects of the parameters on the maximum blanking force, cutting energy, and quality and precision of sheared edges were studied. Cutting mechanism for blanking in different conditions was explained. It was concluded that at room temperature, blanked composite and hybrid laminates had a high quality of sheared edges but at elevated temperature, although the maximum blanking force was reduced, the quality of sheared edge was reduced significantly.     

Failure modes of liquid nitrocarburized and heat treated tool steel under monotonic loading conditions

The tensile properties and failure mode of heat treated and liquid nitrocarburized tool steels were studied. The tested steels are used as die and tool materials for plastic molds and punching/blanking dies, where wear resistance is required. In addition to intense friction, the main die block and other die components are subjected to tensile and repetitive stresses during operation (tension and fatigue loading). Therefore, hardness, tensile, and fatigue resistance are also critical quality parameters that contribute to material reliability and tool life. However, this study is an initial component of research and does not include fatigue data.     

Festwalzen und Schwingfestigkeit

Deep Rolling and Fatigue Strength The fatigue properties of specimens and components are largely increased by deep rolling. Depending on geometrical shape of components and material strength the compressive residual stresses and the increased surface hardness made by deep rolling have a different effect on the improvement of fatigue strength. The fatigue properties of smooth specimens and components with a sufficient toughness can be raised by increase of surface hardness, whereas in case of notched parts the influence of permanent compressive residual stresses is dominant. The application of deep rolling in case of crankshafts shows a clear superiority of mechanical strengthening procedure to thermal surface strengthening. If there are some reasons to improve the wear behaviour beside the fatigue strength it is commendable to combine thermal and mechanical surface strengthening.     

T2铜箔精密微冲孔工艺

随着微机电系统的飞速发展,微孔类零件广泛应用于生物医疗、微电子以及纺织印染等领域中,要求尺寸精度高、断面质量和重复性好,并且能够实现低成本批量制造.微冲孔技术具有传统塑性加工工艺的优点,生产效率高,工艺简单,成形件性能好和精度高,非常适合微型零件的低成本批量制造.针对箔板微孔类零件,设计了一套精密微冲孔模具,采用微冲孔技术研究了冲裁条件对微冲孔工艺的影响规律.结果表明,微冲孔过程与传统冲裁类似,经由弹性变形阶段和塑性剪切阶段,最后断裂分离.微孔断面分布仍然包括圆角、光亮带、断裂带和毛刺.随着相对冲裁间隙的增加,最大剪切强度先降低后逐渐增加;随着冲裁速度的增加,铜箔微冲孔过程最大冲裁力和最大剪切强度逐渐减小,微孔断面光亮带高度增加,断面质量提高.最后,在最佳的冲孔工艺即冲裁间隙为5%、冲裁速度为20mm/s的条件下冲出直径为0.4mm质量良好的微孔.     

The Influence of Fracture Toughness on the Fine Blanking Tools Life

One of the most important operations in the manufacturing of fine blanking tools from HSS AISI M2, is vacuum heat treatment with uniform high-pressure gas quenching. The importance of optimal heat treatment is the possibility of making the optimum combination of the basic characteristics of fine blanking tools made from HSS for the given working part/fine blanking tool combination. Four different austenitization temperatures and four different tempering temperatures were chosen to produce the correct hardness balance, toughness, cutting properties and wear resistance in the finished tool. The result of the present investigation is important for the optimization of vacuum heat treatments of different tools made from HSS which are under tensile impact stress during exploitation. For them the optimal combination of hardness and fracture toughness are decisive.     

Prozessmodell zum Einbringen von Eigenspannungen durch Festwalzen

Defects in axles lead to a significant reduction of lifetime. Deep rolling provides a simple way to prevent crack growth emanating from defects or at least to slow down the crack growth rate, provided the flaw size does not exceed the size of the zone affected by the compressive residual stresses. In this work, a simple process model is presented for estimating the penetration depth of compressive residual stresses from deep rolling.     

Modified fine blanking of cam-shaped profile using a double-action hydraulic press

Blanking is a single stroke sheet metal cutting process that produces blanks with closed contour profiles. Fine blanking is a more precise version of this process that produces near-net products that require minimal post-forming finish machining operations. The process of fine blanking generally requires a triple action press. In the present work, fine blanking of a non-rotational symmetric profile using a double-action press while using rubber to apply counterforce has been investigated for four commonly used sheet metals viz. commercially pure aluminum, α-brass, extra deep drawing (EDD) steel and 304 grade stainless steel (SS304). Edge quality and product flatness while using rubber to apply counterforce were found to be meeting fine blanking quality standards. Percentage smooth shear and burr were found to be independent of material properties. Die roll, dishing and tearing behavior were found to be dependent on material properties. The effect of counterforce on the product quality was investigated by conducting experiments without counterforce. An empirical relation that relates the dishing tendency of a material (in the absence of counterforce) to its mechanical properties was developed.     

Relationships Between Blanking Force and Part Geometry vs. Clearance, Tool Wear, and Sheet Thickness

The blanking of metal parts for electronic components is subjected to a variety of process parameters. In this paper, an experimental investigation into the blanking process was carried out using tools with four different wear states and four different clearances. The aim was to study the effects of the interaction between the clearance, the wear state of the tool, and the sheet metal thickness on the evolution of the blanking force and the geometry of the sheared profile.

Designed experiments are an efficient and cost-effective way to model and analyze the relationships that describe process variations.

The results of the proposed experimental investigation show the strong dependence between the geometrical quality of the blanked part and the magnitude of the force applied on the tool as well as the variations in the process factors.     

Surface fatigue and wear of PVD coated punches during fine blanking operation

Performance of two different physical vapour deposited (PVD) TiCN and Alcrona® (AlCrN) coatings systems is under investigation. Coatings were deposited on the punches produced from the Böhler S390 Microclean steel. Two different surface preparation techniques were used – wet polishing (high surface roughness) and dry polishing (low surface roughness).Industrial trials of PVD coated punches in fine blanking operation were performed and studied. Wear of punches was analysed in regard to the punch geometry, position in the die and surface roughness, and measured after maximum 100,000 cycles at high loads.Punches with higher surface roughness seem to withstand numerous loading cycles with some traces of coating delamination and wear. On the other hand performance of PVD coatings with smaller surface roughness in a striking way was much worse.Comparative trials of the coatings surface fatigue wear and indentation surface fatigue testing were performed in the laboratory as well. In surface fatigue wear testing coatings were dynamically indented by ball (spherical) indenters made from conventional hardmetal (WC-6 wt.%). Testing parameters were identical to those of industrial trials. The Vickers diamond pyramid indenter was cyclically pressed with 500 N load at single point during indentation surface fatigue testing. Results are in agreement with surface fatigue wear tests results.Finally the microstructural investigations using SEM and XRD techniques were performed for better understanding of the surface fatigue and wear mechanisms during fine blanking process.Results of both trials are in good agreement and allow predicting performance of coatings.     

Residual stresses on flat specimens of different kinds of grey and nodular irons after laser surface remelting

Abstract

Laser surface remelting is one of the best procedures for surface modification of ferrite–pearlite nodular irons. Using this procedure on cast irons it is possible to achieve a very high wear resistance, which can be compared with the wear resistance of surface hardened heat treatable steels. The properties of the modified layer depend on the microstructure before heat treatment and on the amount of energy input transferred into the surface layer of the specimen. The research work has focused on the study of residual stresses after laser surface remelting of different kinds of grey and nodular irons. The identification of residual stresses was performed using the relaxation method, which involved measuring specimen strain. The results of the measured residual stresses confirm that the stresses strongly depend on laser surface remelting conditions. The measurement of residual stresses is very important in exacting dynamically loaded machine parts, which have been subjected to different kinds of heat treatment. In designing parts designers very frequently demand the presence of compressive residual stresses after heat treatment and finish grinding of the surface, since this increases the fatigue strength of the material and reduces the danger of fracture.     

冲头刃口形状对冲裁的影响研究

目的 研究不同冲头刃口形状对冲裁变形过程和冲头磨损情况的影响。方法 采用有限元方法和实验分析了相同工况下平冲头、台阶状冲头和屋顶状冲头对坯料冲断行为的影响,以及不同刃口形状的冲头在冲裁后的磨损情况。结果 冲头结构的改变使冲裁过程发生了变化,影响了冲裁时坯料内部的应力–应变分布、峰值冲裁力、裂纹扩展速度、弹性应变能和冲头单次磨损深度。屋顶状冲头在冲裁时峰值冲裁力最低,较平冲头与台阶状冲头的峰值冲裁力分别降低了15%、10%,坯料最早起裂,也最快完成断裂,坯料的高应力区域集中在凹模刃口,且该冲头冲裁时坯料内储存的弹性应变能最多,冲头工作区的单次磨损深度最小,较平冲头与台阶状冲头的单次磨损深度分别降低了84%、80%。结论 屋顶状冲头使坯料在断裂前发生了更大的拉伸变形,储存了更多的弹性应变能,坯料在拉伸状态下发生了剪切变形,冲裁力更小,高应力分布的改变降低了冲裁时坯料对冲头侧面的压力,冲断后的坯料发生弹性恢复,可防止冲头回程时坯料抱紧冲头造成的二次磨损。     

Modeling and experimental validation of the surface residual stresses induced by deep rolling and presetting of a torsion bar

During the production of torsion bars, two different mechanical processes of inducing the residual stresses into the torsion bar are used: the presetting of the torsion bar and the deep rolling of the torsion bar. The process of presetting the torsion bar is carried out by twisting the torsion bar to the desired angle and releasing it to the new residual angle position. With controlled overstraining, favorable residual shear stresses are induced into the torsion bar, so the material is strain hardened and the yield point of the material is shifted and increased in the stress and strain space. The objective of the deep rolling process is to introduce compressive residual stresses into near-surface regions in order to increase the fatigue strength of the torsion bar. These two processes influence each other. The final level of residual stresses depends on the production sequence of these two processes and the production parameters of each process. The correct production sequence of these two operations and distribution of beneficial residual stress was simulated using the finite element (FE) method. To validate this model, the predicted surface residual stresses were compared by the X-ray diffraction (XRD) measurements of residual stresses.     

Microstructure of cryogenic treated M2 tool steel

Cryogenic treatment has been claimed to improve wear resistance of certain steels and has been implemented in cutting tools, autos, barrels etc. Although it has been confirmed that cryogenic treatment can improve the service life of tools, the underling mechanism remains unclear. In this paper, we studied the microstructure changes of M2 tool steel before and after cryogenic treatment. We found that cryogenic treatment can facilitate the formation of carbon clustering and increase the carbide density in the subsequent heat treatment, thus improving the wear resistance of steels.     

An Investigation of Machining-Induced Residual Stresses and Microstructure of Induction-Hardened AISI 4340 Steel

Excessive induction hardening treatment may result in deep-hardened layers, combined with tensile or low compressive residual stresses. This can be detrimental to the performance of mechanical parts. However, a judicious selection of the finishing process that possibly follows the surface treatment may overcome this inconvenience. In this paper, hard machining tests were performed to investigate the residual stresses and microstructure alteration induced by the machining of induction heat-treated AISI 4340 steel (58–60 HRC). The authors demonstrate the capacity of the machining process to enhance the surface integrity of induction heat-treated parts. It is shown how cutting conditions can affect the residual stress distribution and surface microstructure. On the one hand, when the cutting speed increases, the residual stresses tend to become tensile at the surface; and on the other hand, more compressive stresses are induced when the feed rate is increased. A microstructural analysis shows the formation of a thin white layer less than 2 µm and severe plastic deformations beneath the machined surface.     

Thermal Oxidation Treatments in the Development of New Coated Biomaterials: Application to the MA 956 Superalloy

Reducing metal ion release and minimizing friction of orthopaedic implant bearing surfaces is of prime concern for long-term performance. Inert ceramic bearing surfaces eliminate these issues, and thus, various surface coating methods are being investigated. In-situ thermal oxidation treatment (1100°C) of MA 956 which produces a fine but tightly adherent cc-alumina scale is characterized. This layer enhances the in vitro corrosion resistance up to three orders of magnitude with respect to Ti-Al-V alloys. Additionally, compressive residual stresses are approximately 5000 MPa. The existence of elevated compressive residual stresses in the coating, without compromising the coating-substrate adhesion, guarantees its integrity during tensile deformation and should contribute to better wear and fatigue resistance.     

Comparison of Electronic Speckle Laser Interferometry Hole-Drilling and X-ray Diffraction Techniques for Determination of Residual Stresses in the Heat Treated Steels

Carburizing is widely used to improve wear resistance and fatigue life of high duty machine parts. Fatigue performance of the carburized components is greatly dependent on the residual stress state in the surface layer. The aim of this paper is to measure the depth profiles of residual stresses in the carburized steels by electronic speckle laser interferometry (ESPI) assisted hole-drilling, and to compare the results with those measured by X-ray diffraction technique. To comprehend the differences in the residual stress state, the low-C steel components were carburized, and then, tempered in the range of 180–600 \(^{\circ }\)C. Microstructural investigations and hardness measurements were also conducted. The results obtained from both techniques gave identical results, and showed that the beneficial compressive residual stresses exist at the surface after carburizing, and their magnitudes decrease with increasing tempering temperature. It was concluded that ESPI assisted hole-drilling, with optimized drilling and stress calculation parameters, is suitable for determining the residual stress state of the carburized and tempered steels.     

A comprehensive review on residual stresses in turning

Residual stresses induced during turning processes can affect the quality and performance of machined products, depending on its direction and magnitude. Residual stresses can be highly detrimental as they can lead to creeping, fatigue, and stress corrosion cracking. The final state of residual stresses in a workpiece depends on its material as well as the cutting-tool configuration such as tool geometry/coating, cooling and wear conditions, and process parameters including the cutting speed, depth-of-cut and feed-rate. However, there have been disagreements in some literatures regarding influences of the above-mentioned factors on residual stresses due to different cutting conditions, tool parameters and workpiece materials used in the specific investigations. This review paper categorizes different methods in experimental, numerical and analytical approaches employed for determining induced residual stresses and their relationships with cutting conditions in a turning process. Discussion is presented for the effects of different cutting conditions and parameters on the final residual stresses state.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00371-0     

Effect of electric contact surface treatment on microstructure and wear behaviour of ductile iron

Abstract

A study of electric contact surface treatment to ductile iron has been carried out. This technology was based on the application of the contact resistance heating between the electrode and workpiece. For comparison, the experiments of induction hardening to ductile iron were studied. The microstructure, microhardness, surface residual stress and wear properties were investigated using optical microscope, scanning electron microscope, X-ray diffraction, Vickers microhardness and rolling contact wear tests. Electric contact surface treatment resulted in the formation of fine ledeburite (white bright layer) and martensite in the ductile iron surface, in which the hardness in these areas was higher than that of induction hardened surface. The wear test results showed that the ductile iron surface after electric contact surface treatment had better wear resistance owing to the fine microstructure, high hardness and residual compressive stress.     

金刚石刀具刃口的动态微观机械强度各向异性评价方法

为了评价金刚石刀具刃口动态微观机械强度的各向异性,对金刚石晶体的动态微观机械强度进行了理论建模,包括抗拉、剪切和抗压强度.通过比较分析动态微观机械强度的各向异性分布特征,提出了基于金刚石晶体动态微观抗拉强度的刀具刃口微观机械强度各向异性评价新方法,即刀具刃口强度评价因子.刀具刃口强度评价因子越高,其对应的刀具刃磨质量或刀具耐用度就越好.最后,分别采用刃磨工艺实验和刀具耐用度实验对刃口强度评价因子的评价适用性进行了验证,实验数据和理论分析结果具有很好的一致性.     

Characteristics of the wear process in the cutting of free-cutting steels

The paper brings some interesting results of the investigation of the cutting edge wear at cutting of free cutting steels by cemented carbide plates. These steels are characterized by the additions of sulphur and lead to increase machinability. The experimental results have shown that the additives of sulphur and lead can strongly affect not only chip generation but also the form and rate of wear. Previous investigations have indicated clearly that the criterion of wear on the clearance faces provides too little information on tool life. The experimental results have also shown that at equal wear on the clearance face the form and rate of wear on the rake face differ essentially.