Cutting force and hole quality analysis in micro-drilling of CFRP

Micro-drilling in carbon fiber reinforced plastic (CFRP) composite material is challenging because this material machining is difficult due to anisotropic, abrasive and non-homogeneous properties and also downscaling of cutting process parameters affect the cutting forces and micro-drilled hole quality extensively. In this work, experimental results based statistical analysis is applied to investigate feed and cutting speed effect on cutting force components and hole quality. Analysis of variance based regression equation is used to predict cutting forces and hole quality and their trend are described by response surface methodology. Results show that roundness error and delamination factor have similar trends to those of radial forces and thrust force, respectively. Non-linear trends of cutting forces and hole quality errors are observed during downscaling of the micro-drill feed value. Optimization results show that cutting forces and hole quality errors are minimum at a feed value which is almost equal to the tool edge radius rather than at the lowest feed value. Therefore, the presented results clearly show the influences of size effects on cutting forces and hole quality parameters in micro-drilling of CFRP composite material.     

Characteristic study of N07718 superalloy surface prepared by cold spray

For better performance in erosive–corrosive, wear and other extreme environmental conditions surface properties of metals and alloys are usually altered by different techniques. Amongst the various surface coating techniques cold spraying is a relatively new and less reported method. Coating formation at energy lower than the melting stage of materials brings novelty to this process. In this study surface of UNS No. - N07718 alloy is altered by cold spraying chromium-carbide (nickel-chromium) layer. The microstructure properties of this cold sprayed surface are observed by various characterization techniques and the results are used to study mechanism of coating layer formation by cold spray process. This newly developed cold sprayed surface is found to be eligible for further testing in wear and erosive-corrosive environmental conditions.     

Research on ultrasonic-assisted drilling in micro-hole machining of the DD6 superalloy

The DD6 nickel-based superalloy exhibits remarkably high temperature properties; therefore, it is employed as a crucial structural material in the aviation industry. Nevertheless, this material is difficult to process. Ultrasonic-assisted drilling (UAD) combines the characteristics of vibration processing technology and conventional drilling technology, significantly improving the machinability of difficult-to-machine materials. Thus, UAD experiments were performed on micro-hole machining of DD6 superalloy in this study. The effects of amplitude, frequency, spindle speed, and feed rate on thrust force, machining quality, and drill bit wear were studied; thereafter, a comparison was drawn between these effects and those of conventional drilling (CD). The experimental results reveal that the thrust force decreases with an increase in spindle speed or a decrease in feed rate for both UAD and CD. UAD can significantly reduce the thrust force. With the same processing parameters, the greater the amplitude, the greater the reduction of the thrust force. The surface roughness of the hole wall produced by UAD is lower than that of CD. Compared with CD, UAD reduces the burr height, improves machining accuracy, and reduces drill bit wear.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00301-6     

Sn含量对2011铝合金棒材显微组织、切削与力学性能的影响

以Sn、Bi替代Pb,制备无铅易切削2011铝合金棒材。利用光学显微镜、扫描电子显微镜、高速车床和拉伸试验机,研究了Sn含量对2011铝合金棒材显微组织、切削性能和拉伸力学性能的影响。结果表明：Sn含量为0.2%时,Sn以SnBi共晶相形式存在于铝合金棒材中。Sn含量超过0.2%时,Sn以单质Sn相和SnBi共晶相形式存在于铝合金棒材中。Sn含量越高,单质Sn相和SnBi共晶相的数量越多,铝合金棒材的切削性能越好,车屑长度越短,但拉伸力学性能略有下降。     

Mechanical and Wear Properties of Nanostructured Surface Layer in Iron Induced by Surface Mechanical Attrition Treatment

A porosity-free and contamination-free surface layer with grain sizes ranging from nanometer to micrometer in Fe samples was obtained by surface mechanical attrition treatment (SMAT) technique. Mechanical and wear properties of the surface layer in the SMATed and annealed Fe samples were measured by means of nanoindentation and nanoscratch tests, respectively. Experimental results showed that the hardness of the surface layer in the SMATed Fe sample increased evidently due to the grain refinement. The elastic moduli of the surface layers in the SMATed and annealed Fe samples were unchanged, independent of grain size in the present grain size regime. Compared with the original Fe sample, the wear resistance enhanced and the coefficient of friction decreased in the surface layer of the SMATed Fe sample.     

Al含量对Cu基Ni镀层表面渗Si层组织和力学性能的影响

采用料浆包渗法,以SiO2粉为Si源,纯Al粉为还原剂,NaF和NH4Cl作为复合活化剂,Al2O3为惰性添加剂,蛋白质(鸡蛋清)为黏结剂,在Cu表面预先镀Ni层随后900℃,12h表面渗Si,制备渗Ni-Si层。研究了Al粉含量对渗Si层组织和力学性能的影响。结果表明:随铝粉含量的增加,渗层组织出现以下转变:Ni3Si+Ni31Si12→Ni31Si12+Ni2Si→Ni3Si+NiAl,包渗过程由渗硅为主转变为渗铝为主;渗层硬度增加;摩擦系数由铝粉含量为10%(质量分数,下同)时的0.37降低到45%时的0.18,分别为纯铜的1/2,1/5。     

Preparation of silver coated nickel particles by thermal plasma with pre-treatment using ball milling

Recently, reducing noble metals in electric devices has been identified as a key factor to lower product cost. Among these, noble metal coated particles are considered an alternative with the potential to dramatically reduce the usage of noble metals. A dense coating of noble metals over all surfaces is desirable for maintaining the properties of noble metal. However, our previous research showed that coated surfaces onto which the nanoparticles were attached were non-uniform because of evaporation of the raw materials. Therefore, in this study, we improved the coverage ratio of silver coated nickel particles using thermal plasma processing followed by ball mill pre-treatment. Silver and nickel particles were mixed using a ball mill, then injected into the thermal plasma jet. The silver particles were subsequently attached onto the surface of the nickel particles through ball mill processing, after which the silver attached nickel particles were melted through thermal plasma processing to produce silver coated nickel spherical particles. The cross section of the as-prepared particles showed a dense silver shell and nickel core, while the sintered body of the as-prepared particles showed the net-like silver covering over the nickel cores. These findings suggest that attachment of silver on nickel could lead to complete silver coatings by limiting the formation of nanoparticles.     

Effect of Thickness on the Structure and Tribological Properties of MoSx Coating

MoSx coatings were prepared by bipolar-pulse DC unbalanced magnetron-sputtering system with the variation of coating thickness at different Ar pressures.The composition and surface morphology were determined by using energy dispersive X-ray and scanning electron microscopy;the structural characterization was analyzed by X-ray diffraction.The friction and wear properties were investigated by fretting tests in air with less than 10% and 50% relative humidity.At 0.40 Pa pressure,(002) basal plane orientation was formed throughout the coatings.At 0.88 Pa and 1.60 Pa pressures,(002) basal plane orientation was only noticed in the first stage of coating growth(around 0.20 μm in thickness), and then edge orientations with their basal planes perpendicular to the surface would be evolved in the coatings.Humidity has a minor influence on the coatings that have(002) basal plane orientation,whereas the tribological properties of MoSx coatings with edge orientations are greatly affected by humidity.The mechanisms of coating growth and friction and wear processes are discussed.     

Inconel718合金扩散连接接头的组织与性能研究

对细晶Incone1718高温合金无中间层和加Ni箔中间层两种情况下的扩散连接进行了研究,分析了不同的连接温度、连接压力、连接时间等工艺参数对接头剪切强度的影响;通过SEM、EPMA和金相技术对接头微观组织和力学性能进行了分析.确定了获得优质接头的最佳工艺参数区间,即扩散连接温度T=1 050℃,连接压力P=20 MPa,连接时间t=45 min,选用Ni箔作为中间层,厚度为25 μm.     

辉光等离子渗氮对纯钛铸件表面性能的影响

使用NH3在氮化炉中对纯钛铸件进行辉光等离子渗氮。分别应用X线衍射仪XRD、显微硬度计、扫描电镜、摩擦磨损实验及电化学实验研究等离子渗氮对纯钛铸件机械性能、摩擦学性能、耐腐蚀性的影响。铸造纯钛表面氮化处理后,颜色呈暗金黄色,表面由TiN、Ti2N相及氮在钛中的固溶体α-Ti(N)组成,显微硬度、耐磨性显著提高,在人工唾液中的耐腐蚀性亦明显提高。     

Hardness,wear resistance and bonding strength of nano structured functionally graded Ni-Al2O3 composite coatings fabricated by ball milling method

Using initial powder mixtures with different Ni:Al₂O₃ weight ratios ranging from 1:1 to 16:1, nano structured Ni-Al₂O₃ composite coatings were deposited onto an aluminum plate by means of a planetary ball mill. It was shown that initial charges with Ni:Al₂O₃ weight ratios of 4:1 and greater, yielded well-compact coatings. Coating deposited from the powder charge with Ni:Al₂O₃ weight ratio of 4:1, contained 20?vol% of alumina particles in the Ni matrix and submitted the highest hardness value (657?±?28?Hv) and wear resistance. Nevertheless, composite coating containing smallest amount of alumina particles showed the highest cohesive strength of 9.8?±?0.3?MPa. In the next step, nano structured functionally graded composite coatings were produced by the deposition of two separate layers containing different amounts of alumina particles. Although the graded coating showed superior hardness and wear resistance compared with the non-graded coatings, it suffers from low cohesive strength attributed to the presence of alumina particles at the interface region between the two layers. To overcome the poor adhesion between two layers, a thin intermediate plain Ni one was deposited between two layers leading to 80% and 30% improvement in the adhesion strength and wear resistance, respectively.     

汽车发动机用ZL114合金表面涂层制备与性能研究

以Cr作为中间过渡层, 采用磁控溅射的方法在ZL114合金表面制备了类金刚石 (DLC) 硬质涂层, 对比分析了母材与涂层的硬度、耐蚀性能和干/湿摩擦学性能。结果表明:在ZL114合金表面制备了Cr过渡层厚度约为2μm、表面DLC涂层约为10μm的Cr-DLC涂层;Cr-DLC涂层具有DLC薄膜的特性, 显微硬度和纳米硬度分别为母材的3.73倍和3.96倍;Cr-DLC涂层的腐蚀倾向和腐蚀速率都要小于ZL114合金母材, ZL114合金表面沉积Cr-DLC涂层后耐腐蚀性能得到提高;母材和Cr-DLC涂层在湿摩擦条件下的摩擦系数和磨损率低于干摩擦条件下, 且干/湿摩擦条件下Cr-DLC涂层的磨损率都要低于ZL114合金母材;Cr-DLC涂层在湿摩擦 (3.5%NaCl溶液) 条件下仍然具有较好的耐磨性。     

天然生漆膜的化学镀及其表征

以天然生漆膜为基材,利用化学镀技术在其表面化学沉积一层光亮的金属铜、镍、银等而获得生漆/金属复合膜材料,并用SEM(扫描电镜)、DMTA(动态热分析)、DSC-TG(热分析)及其他试验方法对镀层及其复合膜材料的性能进行了研究.结果表明,化学镀技术易在生漆膜表面实现金属化,镀层结合力强,金属粒径匀称、排布规整且致密;生漆/金属复合膜具有优良的动态力学性能,在25～360℃范围内,模量均在1×107～1×109Pa之间,具有优良的耐热性.     

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.     

Folding ratio and erection of folding boxes under production conditions

The bending ratio describes the technical quality of creased cartons. In comparison with the fold-ratio of Grebe and Grohmann it has practical advantages, moreover it is physically clearly defined. The applicability of the bending ratio under production conditions has been tested by erecting experiments in a Rovema cartoning machine. The frequency of failure during the machine erecting tests and the bowing of the side walls of the boxes were compared with the bending ratio for different creased cartons. An optimum condition during the tests could be realized for a ratio of 0.6. It could be proved that the bending ratio is useful to describe the technical quality of crease of folding boxes.     

Investigation of small fatigue crack initiation and growth behaviour of nickel base superalloy GH4169

Surface replication method was utilized to monitor the small fatigue crack initiation and growth process of single‐edge‐notch tension specimens fabricated by nickel base superalloy GH4169. Three different stress levels were selected. Results showed that small fatigue cracks of nickel base superalloy GH4169 initiated from grain boundaries or surface inclusions. The small fatigue crack initiation and growth stages took up about 80–90% of the total fatigue life. Multiple major cracks were observed in the notch root, and specimen with more major cracks seemed to have smaller fatigue life under the same test conditions. At the early growth stage, small crack behaviour might be strongly influenced by microstructures; thus, the crack growth rates had high fluctuations. However, the stress level effect on the small fatigue crack growth rates was not distinguishable for the three different stress levels. And no clear differences were found among the crack initiation lives by using replication technique.     

Mechanical and wear behaviours of nano and microfilled polymeric composite: Effect of filler fraction and size

The addition of ceramic reinforced material, SiC particles, to resin matrices, results in the improvement of the overall performance of the composite, allowing the application of these materials as tribo-materials in industries such as: automotive, aeronautical and medical. Particle-reinforced polymeric composites are widely used as biomaterials, for example as dental filler materials and bone cements. These reinforced composites have improved mechanical and tribological performance and have higher values of elastic modulus and hardness, and also reduce the shrinkage during the polymerisation compared with resin matrices. However, the effect of the filler level in mechanical and tribological behaviour is not quite understood.The aim of this work is to determine the influence of the particle volume fraction and particle size in the wear loss of the composites and their antagonists. Reciprocating wear tests were conducted using a glass sphere against resin polyester silica reinforced composite in a controlled medium, with an abrasive slurry or distilled water. For 6 μm average particle dimension, seven particles contents were studied ranging from 0% to 46% of filler volume fraction (FVF). Afterwards, filler volume fractions of 10% and 30% were selected; and, for these percentages, 7 and 4 average particle dimensions were tested and were evaluated regarding their wear behaviour, respectively. The reinforcement particle dimensions used ranged from 0.1 μm to 22 μm with the 10% filler fraction, and for 30% of filler content the range extended from 3 μm to 22 μm. The results allow us to conclude that in an abrasive slurry medium the composite abrasion resistance decreases with the increase of the particle volume fraction, in spite of the accompanying rise in hardness and elastic modulus. With constant FVF, and abrasive slurry, the composite wear resistance increases with increasing average particle dimension. In a distilled water medium and with several FVF values, the minimum wear was registered for a median particle content of 24%. In this medium and with constant FVF the highest wear resistance occurred for average reinforcement particles of 6 μm. The removal mechanisms involved in the wear process are discussed, taking into account the systematic SEM observations to evaluate the wear mechanisms.     

Enhancement of oxidation and wear resistance of Fe-based amorphous coatings by surface modification of feedstock powders

Surface oxidation of the in-flight powders during the preparation of amorphous coatings in high velocity oxygen fuel process causes the formation of oxygen-rich intersplat regions. These regions are brittle in nature and can dramatically deteriorate the mechanical performance of the coatings. To solve this problem, the starting FeCrMoCBY amorphous feedstock powders were modified by electroless plating a thin layer of Ni–W–P amorphous phase. It was found that the covering of the Ni–W–P layer can significantly reduce the oxygen content in the resultant Fe-based amorphous coatings. The wear resistance of the coatings with and without the modification of Ni–W–P thin layer was comparatively studied by ball-on-disk wear tests against Si₃N₄ counterpart in air. It revealed that the wear of two types of coatings follows the same oxidation wear mechanism but the modified coating exhibits much better wear resistance due to the improved oxidation resistance.     

Microstructure and wear resistance of electrodeposited RE-Ni-Mo-P-B4C-PTFE composite coating

Abstract

The structure, hardness and wear resistance of RE-Ni-Mo-P-B₄C-PTFE composite coating have been studied by means of X-ray diffraction, scanning electron microscopy, abrasion testing and microhardness testing. The results show that the structure of RE-Ni-Mo-P-B₄C-PTFE composite coating experiences a transformation from amorphous via a mixture to crystalline as the heat treatment temperature is increased. Crystalline particles in the coating become gradually finer with the addition of B₄C, B₄C plus polytetrafluoroethylene (PTFE) and B₄C plus PTFE plus rare earths (RE), in that order. The hardness and wear resistance of the RE-Ni-Mo-P-B₄C-PTFE composite increase with increasing temperature, reaching peak values at 400°C and 300°C, respectively. The wear resistance of the composite coating is greatly superior to that of other traditional coatings.