Effect of abrasive jet process parameters on machining glass fibre reinforced polymer composite

An experimental and theoretical research work on abrasive jet machining of glass fiber reinforced polymer composite materials was conducted using abrasive jet machining setup fabricated in our workshop. The objective of this research work is to machine holes on the glass fiber reinforced polymer composite using an abrasive jet machine under various levels of process parameter. The material removal rate and hole geometry (kerf analysis) were observed as a part of the investigation. Four factors five levels central composite rotatable design matrix was used for optimizing the required number of experiments. The objective of the present investigation is to develop mathematical models using the response surface methodology. The adequacy of the models has been checked using the ANOVA technique. Use of the developed mathematical models, material removal rate and hole geometry of the machined glass fibre reinforced polymer composite helps prediction at 95% confidence level.     

Design of hybrid steel/composite circular plate cutting tool structures

Substituting composite structures for conventional metallic structures has many advantages because composite materials have both high specific stiffness and damping characteristics compared to conventional metallic materials. In this study, circular plate cutting tools which are used for rough machining of bearing sites in crankshafts or camshafts were designed with the fiber reinforced composite material to reduce tool mass and to improve the dynamic stiffness of circular plate cutting tools. The hybrid steel/composite circular plate cutting tool was analyzed by finite element method with respect to material types such as composite and foam, stacking angles of the composite, adhesive bonding thickness, and dimensions of the cutting tool. Also, the constrained damping characteristics of the tools were experimentally investigated with respect to the adhesive bonding thickness and material type such as composite and PVC foam. From the finite element analysis and experimental results, optimal design parameters for the hybrid steel/composite circular plate cutting tool were suggested.     

Assessment of factors influencing surface roughness on the machining of glass fiber-reinforced polymer composites

In recent years, the utilization of glass fiber-reinforced polymers (GFRP) composite materials in many different engineering fields has undergone a tremendous increase. Accordingly, the need for accurate machining of composites has increased enormously. In the present work, an attempt has been made to assess the influence of machining parameters on the machining of GFRP composites. Design of experiments (full factorial design) concept has been used for experimentation. The machining experiments were conducted on all geared lathe using coated cermet tool inserts with two level of factors. The factors considered were cutting speed, work piece fiber orientation angle, depth of cut and feed rate. A procedure has been developed to assess and optimize the chosen factors to attain minimum surface roughness by incorporating: (i) response table and response graph; (ii) normal probability plot; (iii) interaction graphs; (iv) analysis of variance (ANOVA) technique.     

MACHINABILITY OF SOME FIBER-REINFORCED THERMOSET AND THERMOPLASTICS IN DRILLING

Polymer-based composite materials are the major candidates for substitution for conventional materials in industry. Drilling is most frequently employed among machining processes for composite materials due to the need for structural integration. In this paper, some aspects of both experimental observation and machinability are presented for thermoset-based and thermoplastic-based composites with high and low fiber loading. The experimental observation discusses chip characteristics and specific cutting energy to reveal the mechanism of material removal. These materials fracture due to the brittle reinforcement, hence the sensitivity of defects in bulk volume is demonstrated. The level of fiber loading and the deformation behavior of matrix polymer determine the extent of plasticity in chip formation and the chip length. The discussions of machinability include drilling force, surface roughness and edge integrity affected by cutting conditions (feed rate and cutting speed), drill geometry and lay-up system. An optimal domain of cutting parameters is suggested for secured machinability.     

Application of new tool material for electrical discharge machining (EDM)

In EDM, Cu and graphite are commonly used as tool materials. The poor wear resistance is the drawback of these tools. In the current study, an attempt has been made to develop a ZrB₂-Cu composite as an EDM tool material to overcome this problem. Initially, the ZrB₂ powder is prepared by self-propagating high-temperature synthesis (SHS) technique and synthesized powder is mixed with different amounts of Cu powder. Dense composite is developed by a pressureless sintering at 1250°C. The composites are tested as tool material at different EDM process parameters during machining of mild steel. The ZrB₂-40 wt% Cu composite shows highest metal removal rate (MRR) with significant tool removal rate (TRR) than other composites. The performance of ZrB₂-40 wt% Cu composite is compared to conventional Cu tool. The composite shows higher MRR with less TRR than Cu tool but it shows more average surface roughness and diameteral overcut than Cu tool.     

Assessment of ultrasonic drilling of C/SiC composite material

Ultrasonic drilling of two-dimensional carbon fiber-reinforced silicon carbide(C/SiC) composites was investigated in this study. The composites were made through a polymer pyrolysis route. X-ray diffraction was adopted to examine the formation of crystalline structure in the matrix of the fabricated composites. Density and porosity, and flexural strength were measured to study the densification efficiency and the mechanical properties, respectively, of the C/SiC composites fabricated under various conditions. The fracture morphologies were also examined by scanning electron microscopy to investigate the fracture behavior of the composites under flexural test. The effects of various parameters of ultrasonic drilling, including abrasives, volume ratio, electric current and down-force, on the material removal rate, hole clearance, edge quality and tool wear are presented and discussed. Optimal operating conditions are identified. In comparison with other feasible machining processes, ultrasonic drilling for this composite material possesses advantages concerning machinability and cost.     

复合材料薄壁管冲击断裂分析与吸能特性优化

为实现不同冲击载荷下的吸能管结构逆向设计, 应用复合材料强度和刚度理论, 计算得到树脂基纤维增强复合材料正交各向异性的力学参数, 同时应用非线性显式有限元算法模拟了轴向冲击载荷作用下管件的动态断裂过程。根据正交设计原理, 得到了管件比吸能与其几何参数之间的非线性映射关系, 并构造出了相应的响应表面。按照汽车正面碰撞对冲击加速度的要求, 应用序列二次规划算法对吸能管进行了优化设计, 得到了具有较优吸能效率和较小冲击力峰值的吸能管结构参数。结果显示: 方管的变形模式、吸能量、冲击载荷-位移曲线变化趋势、冲击载荷峰值等与试验结果吻合很好; 当管件的壁厚、截面长度、管长分别选取2.1、44、200 mm时, 可得到设计域内的最大比吸能29.23 J/g。      

高分子微粒吸声材料的声学特性

以聚氨酯泡沫组装不同高分子微粒制备出一种新型高分子微粒吸声材料。初步讨论了微粒种类、粒径、构造层次以及微粒本体性质等因素对材料吸声效果的影响。并尝试从材料的微观结构联系材料的声学性质(声阻抗等)，探索材料多层次结构与材料吸声性能的关系。     

Modelling of chip separation in machining unidirectional FRP composites by stiffness degradation concept

Progressive failure of unidirectional glass fiber-reinforced polymer composites (FRP) was studied using finite element analysis in orthogonal machining. Chip formation process and damage modes such as matrix cracking, fiber–matrix debonding and fiber breaking were modelled by degrading the material properties. Damage analysis was carried out using Hashin, Maximum stress and Hoffman failure criteria. After damage was detected, selective stiffness degradation was applied to the workpiece material. The objective of this study is to better understand the chip formation process and to analyse the cutting-induced damage from initiation stage until complete chip formation. The effect of the fiber orientation on cutting forces and sub-surface damage was investigated with different failure criteria. The results were addressed in terms of cutting forces evolution and damage progression in the composite structure during machining. It was demonstrated that the use of the stiffness degradation concept with the appropriate failure criterion responds potentially in a predictable fashion to changes in chip formation process for machining of FRPs.     

Optimization of delamination factor in drilling GFR–polypropylene composites

Glass fiber-reinforced polypropylene composites often replace the conventional materials due to their special or unique mechanical properties. As the applications of these composites increase for a number of industries, drilling of these composites is inevitable for subsequent composite product manufacturing stage. In the drilling of composites, the thrust force is induced during the drilling operation; as a result, it causes damage. This damage is characterized by the delamination factor, which depends on the machining parameters such as speed of the spindle, feed rate, and drill diameter. The study on the delamination in the drilling of glass fiber-reinforced polypropylene is limited and has been carried out comprehensively. The effect of machining parameters on delamination in the drilling of glass fiber-strengthened polypropylene (GFR-PP) composites is studied through the Box–Bhenken design. Response surface method, along with the desirability analysis, is used for modeling and optimization of delamination factor in the drilling. The result proves that the models are effectively used to forecast the delamination in the drilling of GFR-PP composites. Also, the result indicates that the foremost issue that influences the delamination is the feed rate.     

芳纶纤维增强树脂复合材料液氮冷却钻孔试验

芳纶纤维增强树脂（AFRP）复合材料是一种公认的难加工材料,加工中极易出现毛刺、烧蚀等缺陷,目前缺乏对其有效的加工工艺方法。为提高其加工质量,研究了液氮作为冷却介质的AFRP复合材料钻孔试验。在相同切削参数下进行了干式切削和超低温加工对比试验,测量了切削过程中的轴向切削力和孔临近区域的温度,并计算了孔的进出口毛刺面积和分层因子,分析了AFRP复合材料缺陷的成因,探讨了不同加工条件下缺陷的变化规律。结果表明:与干式切削相比,采用液氮超低温冷却加工的切削力升高了约15.2%,切削温度降低了约141.6℃,毛刺面积减少了约24.7%,因切削热产生的烧蚀现象得到抑制,明显改善了AFRP复合材料的加工质量。      

A review of mechanical drilling for composite laminates

Composite laminates (CFRP, GFRP, and fiber metal composite laminates) are attractive for many applications (such as aerospace and aircraft structural components) due to their superior properties. Usually, mechanical drilling operation is an important final machining process for components made of composite laminates. However, composite laminates are regarded as hard-to-machine materials, which results in low drilling efficiency and undesirable drilling-induced delamination. Therefore, it is desirable to improve the cost-effectiveness of currently-available drilling processes and to develop more advanced drilling processes for composite laminates. Such improvement and development will benefit from a comprehensive literature review on drilling of composite laminates. This review paper summarizes an up-to-date progress in mechanical drilling of composite laminates reported in the literature. It covers drilling operations (including conventional drilling, grinding drilling, vibration-assisted twist drilling, and high speed drilling), drill bit geometry and materials, drilling-induced delamination and its suppressing approaches, thrust force, and tool wear. It is intended to help readers to obtain a comprehensive view on mechanical drilling of composite laminates.     

Carbon fiber-reinforced cyanate ester/nano-ZrW2O8 composites with tailored thermal expansion

Fiber-reinforced composites are widely used in the design and fabrication of a variety of high performance aerospace components. The mismatch in coefficient of thermal expansion (CTE) between the high CTE polymer matrix and low CTE fiber reinforcements in such composite systems can lead to dimensional instability and deterioration of material lifetimes due to development of residual thermal stresses. The magnitude of thermally induced residual stresses in fiber-reinforced composite systems can be minimized by replacement of conventional polymer matrices with a low CTE, polymer nanocomposite matrix. Zirconium tungstate (ZrW(2)O(8)) is a unique ceramic material that exhibits isotropic negative thermal expansion and has excellent potential as a filler for development of low CTE polymer nanocomposites. In this paper, we report the fabrication and thermal characterization of novel, multiscale, macro-nano hybrid composite laminates comprising bisphenol E cyanate ester (BECy)/ZrW(2)O(8) nanocomposite matrices reinforced with unidirectional carbon fibers. The results reveal that incorporation of nanoparticles facilitates a reduction in CTE of the composite systems, which in turn results in a reduction in panel warpage and curvature after the cure because of mitigation of thermally induced residual stresses.     

Exact elasticity solution for the vibration of functionally graded anisotropic cylindrical shells

An exact elasticity solution is presented for the free and forced vibration of functionally graded cylindrical shells. The functionally graded shells have simply supported edges and arbitrary material gradation in the radial direction. The three-dimensional linear elastodynamics equations, simplified to the case of generalized plane strain deformation in the axial direction, are solved using suitable displacement functions that identically satisfy the boundary conditions. The resulting system of coupled ordinary differential equations with variable coefficients are solved analytically using the power series method. The analytical solution is applicable to shallow as well as deep shells of arbitrary thickness. The formulation assumes that the shell is made of a cylindrically orthotropic material but it is equally applicable to the special case of isotropic materials. Results are presented for two-constituent isotropic and fiber-reinforced composite materials. The homogenized elastic stiffnesses of isotropic materials are estimated using the self-consistent scheme. In the case of fiber-reinforced materials, the effective properties are obtained using either the Mori–Tanaka or asymptotic expansion homogenization (AEH) methods. The fiber-reinforced composite material studied in the present work consists of silicon-carbide fibers embedded in titanium matrix with the fiber volume fraction and fiber orientation graded in the radial direction. The natural frequencies, mode shapes, displacements and stresses are presented for different material gradations and shell geometries.     

Material selection for the tool holder working under hard milling conditions using different multi criteria decision making methods

Nowadays machining of materials in their hardened state, also called hard machining, is a challenge in production of tools and molds. It has some advantages such as lower process time and lower manufacturing cost when compared to conventional machining. In machining of hard workpiece materials, however, very high stresses act on the tool holder through the cutting tool. These stresses necessitate the tool holder to have some specific properties. Especially in hard milling, the tool holder should have high stiffness and should be able to dissipate the energy generated during interrupted cutting. Material cost of the tool holder is also important since lower costs provide a competitive advantage for manufacturers. The material selection for the tool holder should be conducted considering aforementioned requirements. To tackle the difficulty of the material selection with specific properties from a large number of alternatives, multi-criteria decision-making (MCDM) methods have been used. In this paper a decision model including extended PROMETHEE II (EXPROM2) (preference ranking organization method for enrichment evaluation), TOPSIS (technique for order performance by similarity to ideal solution) and VIKOR (VIšekriterijumsko KOmpromisno Rangiranje) methods were used for the selection of the best material for the tool holder used in hard milling. The criteria weighting was performed by compromised weighting method composed of AHP (analytic hierarchy process) and Entropy methods. The candidate materials were ranked by using these methods and the results obtained by each method were compared. It was confirmed that MCDM methods can be used for the solution of real time material selection problems. Tungsten carbide–cobalt and Fe–5Cr–Mo–V aircraft steel were found as the best materials for the tool holder production. The obtained results are found to be rather satisfactory and can be used in design stage of hard machining operations.     

Optically Transparent Multiscale Composite Films for Flexible and Wearable Electronics

One of the key breakthroughs enabling flexible electronics with novel form factors is the deployment of flexible polymer films in place of brittle glass, which is one of the major structural materials for conventional electronic devices. Flexible electronics requires polymer films with the core properties of glass (i.e., dimensional stability and transparency) while retaining the pliability of the polymer, which, however, is fundamentally intractable due to the mutually exclusive nature of these characteristics. An overview of a transparent fiber-reinforced polymer, which is suggested as a potentially viable structural material for emerging flexible/wearable electronics, is provided. This includes material concept and fabrication and a brief review of recent research progress on its applications over the past decade.     

Residual surface stress: comparing traditional and modulated tool path machining processes

Traditional machining processes, where material is removed by a cutting tool from a workpiece, can introduce residual stresses at the surface of machined pieces. This paper provides an examination of an alternative machining methodology called modulated tool path machining. The ultimate objective of this research is to determine the effects of modulated tooling path machining processes, as applied to control chip geometry, on the surface stress of selected materials. Residual stresses in machined samples were characterised through the use of X-ray diffraction by comparing the modulated path method with a more traditional material removal technique (i.e. constant surface speed and constant contact).

This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.     

Endbearbeitung von Aluminiummatrix‐Verbundwerkstoffen durch Drehen

Final Machining of Aluminium Matrix Composites by means of Turning Aluminium matrix composites usually consist of a relatively soft as well as ductile matrix alloy and a hard ceramic reinforcing component in the form of fibers, particles or whiskers, which are embedded in it. The very different characteristics of the composite elements on the one hand facilitate the specific aiming of appropriate combinations of material properties by selection of the components as well as their quantitative ratio. But on the other hand, during machining they cause permanently changing loads on the cutting edge of the tool. Apart from the rapid tool wear, damages of the workpiece surface due to ripped out or destroyed particles proves to be a problem during final machining of such components. The reliable generation of an extensively flawless surface with a small roughness sets high demands on the cutting material, tool geometry and cutting parameters. In order to achieve a long tool life super‐hard CVD diamond tippings (chemical vapour deposition = CVD) are used for the research. On the basis of turning tests with aluminium matrix composites the potential of chip breakers as well as an especial tool nose geometry to improve the workpiece surface is described under consideration of the feed.     

Cutting tool material selection using grey complex proportional assessment method

In today’s metalworking industry, many types of materials, ranging from high carbon steel to ceramics and diamonds, are used as cutting tools. Because of the wide range of conditions and requirements, no single cutting tool material meets all the needs of machining applications. Each tool material has its own properties and characteristics that make it best for a specific machining application. While evaluating a cutting tool material for a machining operation, the applicability is dependant on having the correct combination of its physical properties. Thus, it is extensively important to select the most appropriate cutting tool material with the desired properties for enhanced machining performance. This paper considers an exhaustive list of 19 cutting tool materials whose performance are evaluated based on ten selection criteria. The grey complex proportional assessment (COPRAS-G) method is then applied to solve this cutting tool material selection problem considering grey data in the decision matrix. Synthetic single crystal and polycrystal diamonds emerge out as the best two choices. Oil quenched tool steel (AISI O2) and powder metal tool steel (AISI A11) may also be used as the suitable cutting tool materials. Sialon and sintered reaction bonded silicon nitride are the worst chosen cutting tool materials.     

Development of ANFIS model and machinability study on dry turning of cryo-treated PH stainless steel with various inserts

This present investigation deals about the machinability comparison of cryogenically treated 15-5 PH stainless steel with various cutting tools such as uncoated tungsten carbide, cryogenic-treated tungsten carbide and wiper geometry inserts. Cryo-treated PH stainless steel is considered as the work material in this investigation and experimental trials were performed under dry turning condition. The machinability aspects considered for evaluation are cutting force (F_z), surface roughness (R_a) and tool wear. The outcomes of experimentation reveal that the tungsten carbide inserts which are cryogenically treated provide improved performance in machining while comparing with conventional and wiper geometry inserts at all machining conditions. The measured cutting force and the observed flank wear were less for the cryo-treated inserts. However, wiper tool produces a better surface finish during machining. An artificial intelligence decision-making tool named Adaptive Neuro Fuzzy Inference System has been evolved to determine the relation among the considered input machining variables and output measures, namely cutting force and surface roughness of the machined surface. An analysis has been performed to compare the results obtained from developed models and experimental results.