Machining Of Ceramic Matrix Composites Research Articles

Review on Abrasive Machining Technology of SiC Ceramic Composites.

Ceramic matrix composites have the advantages of low density, high specific strength, high specific die, high-temperature resistance, wear resistance, chemical corrosion resistance, etc., which are widely used in aerospace, energy, transportation, and other fields. CMCs have become an important choice for engine components and other high-temperature component manufacturing. However, ceramic matrix composite is a kind of multi-phase structure, anisotropy, high hardness material, due to the brittleness of the ceramic matrix, the weak bonding force between fiber and matrix, and the anisotropy of composite material. Burr, delamination, tearing, chips, and other surface damage tend to generate in the machining, resulting in surface quality and strength decline. This paper reviewed the latest abrasive machining technology for SiC ceramic composites. The characteristics and research directions of the main abrasive machining technology, including grinding, laser-assisted grinding, ultrasonic-assisted grinding, and abrasive waterjet machining, are introduced first. Then, the commonly used numerical simulation research for modeling and simulating the machining of ceramic matrix composites is briefly summarized. Finally, the processing difficulties and research hotspots of ceramic matrix composites are summarized.

Machining of ceramic matrix composites: Challenges in surface integrity

Because ceramic matrix composites (CMCs) are often used to make high-value and safety–critical parts, it is essential to know how different machining methods affect them. Because CMCs have a complicated makeup, their mechanical and thermal behaviour is not uniform. One of their parts is usually very hard; machining them creates significant mechanical and thermal stresses. CMCs have a lot of orthotropic, brittle, and heterogeneous properties that affect how they are removed and how surface flaws are fixed. This work aims to do a literature review of research on conventional and non-conventional machining of CMCs so that the effects of different machining processes on the machined surfaces can be evaluated relatively. By comparing and contrasting different ways to describe materials, learn more about how mechanical and thermal surface and subsurface flaws can be fixed.

Coaxial helical gas assisted laser water jet machining of SiC/SiC ceramic matrix composites

• A novel coaxial helical gas atmosphere is firstly introduced to extend the stable length of water jet as well as expel the accumulated water layer during the machining of LWJ. • The influences of gas component and pressure on the stable length of water jet and accumulated water layer status on substrate surface are revealed. • Scribing and through cutting of CMCs substrates with thickness of 3 mm are realized by CGALWJ machining without the drawing of SiC fibers, formation of recast layer and delamination. SiC/SiC ceramic matrix composites (CMCs) offer an excellent combination of properties at high temperature such as high specific strength, chemical inertness and irradiation tolerance. Those superior properties make CMCs beneficial for use in high-temperature structural applications that are exposed to extreme environments such as aerospace and nuclear energy. However, well machining qualities can hardly be achieved by conventional machining techniques owing to these properties. Laser water jet (LWJ) machining is a promising solution, which is capable of ablating materials with less/no heat defects, well machining precision and consistency. Nevertheless, the machining capacity of LWJ is still limited by the stability of water jet to a great extent. A water layer may form on substrate surface during the impingement of LWJ, which also sets up obstacle for sufficient ablation. Therefore, a novel coaxial helical gas atmosphere is introduced to promote the machining capacity of LWJ in this paper. A theoretical model is established to describe the gas-water two-phase flow field during the ejection and impingement of coaxial gas assisted LWJ (CGALWJ). The influences of gas component and pressure on the stable length of water jet and surface water layer status are analyzed based on numerical simulations and experiments. Scribing experiments are further carried out on CMCs substrates with thickness of 3 mm. Groove with maximum depth-to-width ratio of 13.6 as well as through cutting are realized without the drawing of SiC fibers, formation of recast layer and delamination. The theoretical and experimental results provide solid foundation for the high-quality machining of ceramic matrix composites and other hard-to-process materials.

Unconventional Machining of ceramic matrix Composites – A review

With an increase in demand for materials that are lightweight, thermally stable, and can sustain higher temperatures, ceramic matrix composites or CMC’s turned out to be potential candidates however, the major challenge with these materials was the manufacturing aspect and so, there was a demand for machining methods which could easily machine these materials without having much tool wear, provide higher material removal rate (MRR), and produce low surface roughness. Conventional machining (CM) processes like milling, grinding, drilling, and so on were turning out to be disadvantageous as the hardness of these materials is high and it results in excessive tool wear, high surface roughness, and low MRR. Recent researches in unconventional machining processes such as laser machining, plasma machining, electric discharge machining, and abrasive water jet machining, etc. are showing positive results when compared with CM. The current work presents a review of the unconventional machining process of these difficult to machine materials. The unconventional machining processes considered here are the laser-assisted machining process, rotatory ultrasonic machining process, and abrasive water jet machining process. Furthermore, it also discusses how these machining processes are better than conventional machining processes and it compares their MRR, surface roughness (SR), change in the properties, and also discusses the effect of these machining processes on the same parameters.

Investigation of cutting mechanisms in the machining of Ceramic Matrix Composites (CMCs)

Ceramic Matrix Composites (CMCs) are increasingly used in numerous engineering fields, e.g. the aerospace, automotive, energy & nuclear industry due to their higher permissible material temperature and their lower weight compared to metallic materials. Thanks to the quasi-ductile material behaviour, it is possible to carry out time- and cost-efficient finishing with a geometrically defined cutting edge.In this study the cutting mechanisms are analysed in fundamental cutting tests on an orthogonal cutting test bench by variance of the undeformed chip thickness. For the evaluation cutting force measurements, high-speed recordings, surface qualities measurements and chip analyses were conducted.

Machining of TiB<sub>2</sub>- SiC Ceramic Composites through WEDM Process

In the present study Spark Plasma Sintering (SPS) technique is used to synthesis of particulate Ceramic Matrix Composites (CMCs). SPS is a type of hot pressing method and in this method, the rate of heating is from 100C to 1000C per minute with high densification. TiB2 (average size of 14 μm) particles were chosen as matrix and SiC (average size of 1 μm) particles were used as reinforcement. In the first stage of the study, synthesis of CMCs with TiB2 matrix and SiC reinforcement with varying volume% (0, 5, 10 and 15 vol.%) was carried out using Spark Plasma Sintering furnace available at IIT Madras in 1100°C, 40MPa and 10 min hold of time. But machining of CMCs from conventional machining processes is difficult especially to make complex and precise parts from CMCs. Hence, in the second stage of the work, Wire Electric Discharge Machining (WEDM) studies were carried out on the processed four composites by varying current (2, 3 and 4 A), Pulse on (Ton-30, 60 and 90 μs) and Pulse off time (Toff-5, 10 and 15 μs) as per Taguchi L9 orthogonal array. WEDM studies revealed that at 4A current, 60μs Ton and 5μs Toff gave maximum material removal rate (MRR) of 2.93 mm3/s, 2.27 mm3/s, 2.71 mm3/s and 0.62 mm3/s for CMC with 0% SiC, 5% SiC, 10% SiC, 15% SiC vol.% reinforcement respectively. To reduce material wastage during machining, kerf width is considered and in which 3A current, 90μs Ton and 5μs Toff gave the least kerf of 0.35 mm, 0.32 mm, 0.33 mm and 0.28 mm for 0% SiC, 5% SiC, 10% SiC, 15% SiC vol.% reinforcement respectively.

An efficient strategy for grinding carbon fiber-reinforced silicon carbide composite using minimum quantity lubricant

Nowadays, in addition to technical efficiency, the demands for environmentally-friendly machining processes have increased. In this context, development of an efficient strategy for machining of ceramic matrix composites (CMCs) has found crucial importance. CMCs exhibit outstanding properties, especially under harsh and severe conditions. Machining of CMCs, however, suffers from several disadvantages such as substantial costs, high tool wear, poor surface quality and low material removal rate, highlighting the need for optimization and development of efficient machining strategies. Due to extreme hardness of the ceramic matrix, grinding with diamond abrasives is inevitable. The grinding variables and the coolant-lubricant medium play significant roles in reduction of the energy dissipation and improving the finishing quality. Among coolant-lubricant types, minimum quantity lubrication (MQL) technique, which is known as an inexpensive and environmentally-compatible grinding process, can give the best results. In comparison with dry grinding condition, 37.95% reduction in cutting force, 75.93% reduction in surface roughness, and 150% increase in grinding efficiency have been achieved by MQL method. Considering MQL as the optimum coolant-lubricant medium, four machining strategies were developed using desirability function method in which efficiency, quality, and productivity were studied. Moreover, microstructure analysis and also cutting mechanism of grinding process for different types of fiber orientation have been investigated.

Experimental study on vibration stability in rotary ultrasonic machining of ceramic matrix composites: Cutting force variation at hole entrance

Rotary ultrasonic machining (RUM) is a superior hole-manufacturing method for ceramic matrix composites (CMC) with reduced cutting force and improved hole quality. Among various processing parameters, sufficient and stable ultrasonic vibration is crucial to guaranteeing RUM effectiveness in terms of cutting force reduction. This study was devoted to investigating the effect of material characteristics on vibration stability in RUM of CMC. The variations of cutting force and ultrasonic power at hole entrance in RUM of C/SiC CMC, quartz glass and sapphire were evaluated. Experimental results on these three materials were all in good consistency with the predicted results of theoretical model, which describes the cutting force effect on ultrasonic power variation without considering whether the machined material was composite or not. Ultrasonic power variation was also used to help identify the effect of thermo-mechanical loading on resonant frequency during RUM of C/SiC CMC. It was revealed that the composite characteristic of CMC didn’t affect the effect mechanism of thermo-mechanical load on the stability of ultrasonic vibration. By pre-adjustment of tuning frequency, the indispensable effect of tool wear on cutting force increase in RUM of CMC can be weakened.

Improving hole exit quality in rotary ultrasonic machining of ceramic matrix composites using a compound step-taper drill

Mechanical-machining-induced tearing defects at hole exits restrict the application of C/SiC composites. Rotary ultrasonic machining (RUM) is suitable for hole manufacture in brittle composites, providing reduced tearing size as compared with conventional grinding. Even so, substantial tearing defects at the hole exit remain with RUM. In this study, a novel compound step-taper diamond core drill for RUM of C/SiC was developed to further improve the hole exit quality. Contrastive machining tests were conducted to evaluate the effectiveness of the new type drill. Experimental results show that the compound drill can help reduce the tearing size by 30% on average. Results of variance analysis indicate that there is little dependency of tearing size on processing variables with the compound drill, whereas the common drill shows substantial dependence. Detailed observation of the thrust force reveals that the tearing size reduction using the compound drill is due to the reprocessing effects of its taper face. In the reprocessing process of the taper face, the thrust force gradually decreases at the hole exit. Increasing the ultrasonic amplitude can help further improve the hole exit quality when using our compound drill.

Innovative High-performance Ceramics – Challenge for the Life Cycle Engineering of Turbomachinery

Producers of turbomachines for the aviation and energy sectors have to meet the future challenges regarding environment protection, resource conservation and profitability. As part of the 2014 market and trend analysis on the subject of Life Cycle Engineering for turbomachinery, the market potential of the concept of Life Cycle Engineering for turbomachines as well as future trends and R&D issues have been identified. It has shown that the mechanical, chemical and thermodynamic characteristics of high-performance ceramics motivate new developments of Life Cycle Engineering in turbomachinery. However, particular material properties like high hardness and strength represent a challenge for the machining process of complex components made from high-performance ceramics. Since process and machining technologies are key components of the LCE concept, this paper will focus on the importance of a holistic hard machining of ceramic matrix composites with regard to technical and economic criteria.

Electrical discharge machining of ceramic matrix composites with ceramic fiber reinforcements

Ceramic matrix composites (CMC) are considered the next generation of advanced materials used in space and aviation due to their high-temperature strength, creep resistance, chemical resistance, low porosity, and low density. However, these materials are difficult to process owing to the large cutting force and high cost on tool consumption. electrical discharge machining (EDM), featured by the negligible machining force and acceptable tooling cost, is a potential nontraditional machining technique for CMC. In this paper, EDM was used to process a new class of advanced CMC, that is, those with continuous ceramic fiber reinforcements. The challenge is its low material removal rate (MRR) due to the low workpiece conductivity and debris evacuation efficiency. Electrode vibration and dielectric deep flushing were used to promote debris evacuation, and an increase of MRR and surface quality without sacrificing tool wear ratio was observed. Gap voltage, peak current, pulse duration, and duty ratio were studied using design of experiments for deeper understanding of the process. The effect of these parameters was investigated, and an analysis of variance was conducted. The optimal condition was also predicted and experimentally validated. It was found that a high gap voltage or low duty ratio leads to a high machining rate due to improved debris evacuation efficiency. The material removal mechanism was found to be cracking due to thermal expansion of the matrix and breakage of the nonconductive fibers.

Rotary ultrasonic machining of ceramic matrix composites: feasibility study and designed experiments

Ceramic matrix composites (CMC) are enabling materials for a number of high-temperature and demanding applications in aerospace, power generation, ground transportation, nuclear, environmental, and chemical industries. Tremendous progress has been made in technology development, manufacturing, commercialization, and applications of CMC over the last few years. However, significant challenges (such as the lack of specifications, databases, and in-service repair methodology, and high machining cost) still remain for their widespread applications. In this paper, rotary ultrasonic machining (RUM) is introduced into drilling holes on CMC panels for the first time. The feasibility to machine CMC using RUM is investigated. Cutting forces and material removal rates (MRR) are compared for machining of CMC with and without ultrasonic vibration and for two types of CMC materials and one typical advanced ceramic material (alumina). Chippings at the hole exit are also observed under a microscope. Furthermore, the paper presents the results of a designed experimental investigation into RUM of CMC. A three-variable two-level full factorial design is employed to reveal main effects as well as interaction effects of three RUM process parameters (spindle speed, feedrate, and ultrasonic power). The process outputs studied include cutting force, MRR, and hole quality (in terms of chipping dimensions).