Rotary ultrasonic machining of CFRP: A comparison with grinding

Microstructure evolution of medium carbon steel during heat-assisted 3D ultrasonic vibration-assisted turning

Medium carbon steel is an excellent carbon structural steel, and is one of the most common materials for metal cutting. Little research has been done on the microstructural changes induced by thermal-force coupling. In this paper, a finite element simulation method based on the improved J-C model is used to predict the grain size, microstructure change depth and surface hardness of medium carbon steel surface induced by heat-assisted 3D-UVAT are studied. The numerical simulation results are compared with the experimental results, and the significant influence of turning conditions on them is analyzed. The results show that heat-assisted 3D-UVAT lowered the grain size of machined induced deformation zone. Numerical model foresees this case with a mean error of 9.4%. Microstructure and hardness measurements under different turning conditions show that the turning speed and feed rate contribute significantly to grain size and grain refinement layer depth in the area being machined.

Design of a High-Speed Rotary Ultrasonic Machining Machine Tool for Machining Microstructure of Brittle Materials

Aiming at the problems of low machining accuracy and more serious tool wear in the traditional diamond grinding machining (DGM) microstructure of hard and brittle materials, this paper proposes high-speed rotary ultrasonic machining (HRUM) technology and develops a HRUM machine tool. The hardware part of the machine tool mainly includes the spindle module, micro-motion system module, ultrasonic machining tank module, and data acquisition (DAQ) system module. The LabView-based controlled machining control system, including motion selection, initialization, coarse tool setting, constant force tool setting, control machining, and coordinate display module, is developed. Comparative experimental research of the HRUM and DGM of small holes in Al2O3 ceramics is carried out in the developed HRUM machine tool. The results demonstrate that HRUM effectively reduces axial cutting forces, reduces binder adhesion, and suppresses slippage while improving tool-cutting ability and extending tool life compared to DGM under the same machining parameters. This technology has essential research significance for the high-precision and efficient machining of microstructures in hard and brittle materials.

Development of Electrodeposited Wire Mesh Grinding Wheel for Cutoff and Grooving Carbon Fiber Reinforced Plastic

Carbon fiber reinforced plastic (CFRP) is used in various industries because of its high specific strength, but it is well known as a difficult material to cut. In this study, we developed a disc-shaped electrodeposited diamond wire mesh grinding wheel as a new method for cutoff and grooving with a large aspect ratio for CFRP. We confirmed that this tool could be used for machining at a feed rate of 1000 mm/min, equivalent to that of an abrasive waterjet. This tool discharges generated chips through the spaces in the wire mesh, preventing clogging and thereby enabling the suppression of machining temperature. No burrs or delamination were observed on the surface machined with the wire mesh grinding wheel, and the surface roughness was Ra = 2.76 µm. However, the groove width was larger than the wheel thickness due to the runout of the wheel. Additionally, the moderate elasticity and durability of the tool suggest that it might extend tool life by avoiding the crushing of abrasive grains.

High-frequency vibration effects on material removal mechanisms in ultrasonic transverse scratching of carbon fiber reinforced plastics

This paper represented some fundamental investigations on the potential effects of the high-frequency vibration on material removal mechanisms in ultrasonic transverse scratching of carbon fiber reinforced plastics (CFRPs). It was found that the ultrasonic superimposition brought about the evident reduction of the ductile-brittle transition depth of the unidirectional CFRPs. For the scratched groove generated without ultrasonic, the tensile stress and compressive stress caused by the indenter penetration were respectively responsible for the formations of the radial cracks at the leading edges and the central region. Under the combination of the inertia effects induced by the ultrasonic superposition and the skin-core structure of the carbon fibers, the micro-defects situated at the interior of the fibers were nucleated simultaneously, and their propagations caused the formations of the oblique cracks. Incorporated with the strain rate effects of the materials, a fresh theoretical model was proposed to describe the evolution of the mechanical stress during the scratching process. The fiber fragments induced by the oblique cracks were just concentrated on the top surface of the scratched groove, due to the coupling effects of the small penetration depth of the indenter and the express reduction of strain rate.

High performance drilling of T800 CFRP composites by combining ultrasonic vibration and optimized drill structure

Drilling of high-strength T800 carbon fiber reinforced plastic (CFRP) are widely employed in current aviation industry. Drilling-induced damages frequently occur and affect not only the load carrying capacity of components but also the reliability. As one of effective methods to reduce the drilling-induced damages, advanced tool structures have been widely used. Nevertheless, it is still difficult to realize high machining accuracy and efficiency by this method. This paper compared three different drill bits to evaluate the drilling performance of T800 CFRP composites and the results showed that the dagger drill was a good choice to drill T800 CFRP considering the lowest thrust force and damages. On this basis, ultrasonic vibration was successfully imposed on dagger drill to further improve the drilling performance. The experimental results showed that ultrasonic vibration reduced the thrust force and surface roughness with a maximum decrease of 14.1 % and 62.2 % respectively. Moreover, the maximum hole diameter errors were decreased from 30 μm in CD to 6 μm in UAD. Besides, the mechanisms of force reduction and hole quality improvement by ultrasonic vibration were also revealed. The results suggest that the combination of ultrasonic vibration and dagger drill is a promising strategy for high performance drilling CFRP.

Radial-torsional vibration conversion ultrasonic transducer based on radial chute disc

Using the stress wave generated by radial excitation, an ultrasonic transducer with pure torsional output based on a radial chute is developed. Based on the reflection principle of the stress wave from the radial chute, the mechanical model of the radial wave entering the chute disc then synthesizing the circumferential wave is established, and the stress state of the stress wave after the radial wave acts on the chute is deduced. On this basis, the influence of the chute angle on the circumferential wave is obtained. Theoretical analysis shows that there is an optimal chute angle for the synthesis of the circumferential wave. Then, the optimal inclined chute disc and ultrasonic transducer are selected for modal analysis. In the simulation, the radial wave generated by the excitation is evenly distributed at the disc and effectively converted into a circumferential wave. The converted circumferential wave is transmitted to the output end through the amplitude transformer of pure torsional mode, and the ultrasonic transducer realizes pure in-plane torsional output. When measured, the circumferential amplitude of the output rod is 5.22 times of the radial amplitude of the chute disc.

Numerical simulation and experimental study for ultrasonic vibration-assisted drilling of SiCp/AL6063

Thrust force and metal chips are essential focuses in SiCp/AL6063 drilling operations. Compared with conventional drilling (CD), the ultrasonic vibration-assisted drilling (UVAD) has attractive advantages: for instance, short chips, small cutting forces, etc. However, the mechanism of UVAD is still inadequate, especially in the thrust force prediction model and numerical simulation. In this study, a mathematical prediction model considering the ultrasonic vibration of the drill is established to calculate the thrust force of UVAD. A 3D finite element model (FEM) for the thrust force and chip morphology analysis is subsequently researched based on ABAQUS software. Finally, experiments of CD and UVAD of SiCp/Al6063 are performed. The results show that when the feed rate reaches 151.6 mm/min, the thrust force of UVAD decreases to 66.1 N, and width of the chip decreases to 228 um. As a result, the errors of the mathematical prediction and 3D FEM model of UVAD are about 12.1 and 17.4% for the thrust force, and the errors of the CD and UVAD of SiCp/Al6063 are 3.5 and 11.4% for the chip width, respectively. Compared with the CD, UVAD could reduce the thrust force and improve chip evacuation effectively.

Current Concepts for Cutting Metal-Based and Polymer-Based Composite Materials

Due to the variety of properties of the composites produced, determining the choice of the appropriate cutting technique is demanding. Therefore, it is necessary to know the problems associated with cutting operations, i.e., mechanical cutting (blanking), plasma cutting plasma, water jet cutting, abrasive water jet cutting, laser cutting and electrical discharge machining (EDM). The criterion for choosing the right cutting technique for a specific application depends not only on the expected cutting speed and material thickness, but it is also related to the physico-mechanical properties of the material being processed. In other words, the large variety of composite properties necessitates an individual approach determining the possibility of cutting a composite material with a specific method. This paper presents the achievements gained over the last ten years in the field of non-conventional cutting of metal-based and polymer-based composite materials. The greatest attention is paid to the methods of electrical discharge machining and ultrasonic cutting. The methods of high-energy cutting and water jet cutting are also considered and discussed. Although it is well-known that plasma cutting is not widely used in cutting composites, the authors also took into account this type of cutting treatment. The volume of each chapter depends on the dissemination of a given metal-based and polymer-based composite material cutting technique. For each cutting technique, the paper presents the phenomena that have a direct impact on the quality of the resulting surface and on the formation of the most important defects encountered. Finally, the identified current knowledge gaps are discussed.

Grindability of carbon fiber reinforced polymer using CNT biological lubricant

Carbon fiber-reinforced polymer (CFRP) easily realizes the integrated manufacturing of components with high specific strength and stiffness, and it has become the preferred material in the aerospace field. Grinding is the key approach to realize precision parts and matching the positioning surface for assembly and precision. Hygroscopicity limits the application of flood lubrication in CFRP grinding, and dry grinding leads to large force, surface deterioration, and wheel clogging. To solve the above technical bottleneck, this study explored the grindability and frictional behavior of CNT biological lubricant MQL through grinding experiments and friction-wear tests. Results showed that the CNT biological lubricant reduced the friction coefficient by 53.47% compared with dry condition, showing optimal and durable antifriction characteristics. The new lubrication was beneficial to suppressing the removal of multifiber block debris, tensile fracture, and tensile-shear fracture, with the advantages of tribological properties and material removal behavior, the tangential and normal grinding force, and the specific grinding energy were reduced by 40.41%, 31.46%, and 55.78%, respectively, compared with dry grinding. The proposed method reduced surface roughness and obtained the optimal surface morphology by preventing burrs, fiber pull-out, and resin smearing, and wheel clogging was prevented by temperature reduction and lubricating oil film formation. S_a and S_q of the CNT biological lubricant were reduced by 8.4% and 7.9%, respectively, compared with dry grinding. This study provides a practical basis for further application of CNT biological lubricant in CFRP grinding.

Lightweight Structural Materials in Open Access: Latest Trends

The aeronautical and automotive industries have, as an essential objective, the energy efficiency optimization of aircraft and cars, while maintaining stringent functional requirements. One working line focuses on the use of lightweight structural materials to replace conventional materials. For this reason, it is considered enlightening to carry out an analysis of the literature published over the last 20 years through Open Access literature. For this purpose, a systematic methodology is applied to minimize the possible risks of bias in literature selection and analysis. Web of Science is used as a search engine. The final selection comprises the 30 articles with the highest average numbers of citations per year published from 2015 to 2020 and the 7 articles published from the period of 2000–2014. Overall, the selection is composed of 37 Open Access articles with 2482 total citations and an average of 67.1 citations per article/year published, and includes Q1 (62%) and Q2 (8%) articles and proceeding papers (30%). The study seeks to inform about the current trends in materials and processes in lightweight structural materials for aeronautical and automotive applications with a sustainable perspective. All the information collected is summarized in tables to facilitate searches and interpretation by interested researchers.

High-frequency vibration effects on the hole integrity in rotary ultrasonic drilling of carbon fiber-reinforced plastic composites

This investigation represented a fundamental research on the potential effects of the high-frequency vibration on the hole integrity involved in rotary ultrasonic drilling (RUD) of carbon fiber-reinforced plastic (CFRP) composites. It was found the increased thickness of the CFRP plate shrunk the flowing velocity of the coolant, which brought about the residual chippings gradually accumulated at the radial clearance between the tool and the material. Furthermore, the chipping accumulation at the clearance seriously increased the friction effects and the resultant thermal load, thus leading to the chipping adhesions on the tool surface and machined cylinder jamming at the central hole of the tool. The mutual constrain between two vertical bundles brought the delamination around the holes generated in conventional drilling (CD) process to a termination at the bundle interface. The ultrasonic superimposition reduced the thrust force of the diamond tool which provided inadequate energy for the delaminated fibers reaching the bundle interface. Moreover, hole position on the two-dimensional orthogonal fabrics significantly influenced the propagation of the delaminated fibers, which weakened the effects of the drilling parameters on the delamination dimensions. Additionally, superimposing an ultrasonic vibration prolonged the abrasive trajectories and increased their overlapping probability, and the induced smoothing effects resulted in the obvious reduction of the surface roughness. The tensile stress exerted on the margin of the machined surface was responsible for the initiation of the CD delamination. After the delaminated fibers reached the bundle interface, the further extrusion of tool brought about the margin suffered from the shear stress, thus leading to the collapse of the machined cylinder. Considering the thrust force of the diamond tool and the undrilled thickness of the machined surface, the critical conditions of the delamination initiation were developed, which revealing that the decreasing of the thrust force caused the reduction of the critical undrilled thickness.

Experimental study on biological damage in bone in vibrational drilling

BACKGROUND

Drilling is a well-known mechanical operation performed for fixing fracture at required locations in bone. The process may produce mechanical and thermal alterations in the structure of the bone and surrounding tissues leading to irreversible damage known as osteonecrosis.

OBJECTIVE

The main purpose of this study was to measure the level of biological damage in bone when a drill assisted by low and high levels of vibrations is penetrated into bone tissue.

METHODS

Histopathology examination of sections of bones has been performed after drilling the bone using a range of vibrational frequency and rotational speed imposed on the drill with and without supply of saline for cooling.

RESULTS

Cell damage in bone was caused by the combined effect of drill speed and frequency of vibrations. Histopathology examination revealed more damage to bone cells when a frequency higher than 20 kHz was used in the absence of cooling. Cooling the drilling region helped minimize cell damage more at a shallow depth of drilling compared to deep drilling in the cortex of cortical bone. The contribution of cooling in minimizing cell damage was higher with a lower drill speed and frequency compared to a higher drill speed and frequency.

CONCLUSION

Vibrational drilling using a lower drill speed and frequency below 25 kHz in the presence of cooling was found to be favorable for safe and efficient drilling in bone.

The effects of thermo-mechanical load on the vibrational characteristics of ultrasonic vibration system

The vibrational characteristics of ultrasonic vibration system play an important role in the stability and processing effect in ultrasonic machining. In this study, a theoretical analysis and experimental verification were employed to investigate the effect of the thermo-mechanical load on the vibrational characteristics of ultrasonic vibration system. Initially, a dynamic model was designed to analyze the influence of the thermo-mechanical load on the vibration characteristics. Based on the model, the single variable method was adopted to explore the effect of different mechanical loading and the rigidity coefficient of the tool on the vibrational characteristics. Then the experiment was conducted by imposing variable loads on the tool end face, and the amplitude, current, frequency and temperature of ultrasonic system were measured. Finally, the ultrasonic vibration drilling test was conducted to verify the experimental results. It was observed that the ultrasonic amplitude initially increased and later decreased with the increase in static load. In addition, with the increase in static load, the thermal effect was significant and the ultrasonic frequency presented a similar tendency, as the ultrasonic amplitude. Meanwhile, the variation of ultrasonic frequency was not significant under the thermo-mechanical load. The results of this study could provide a favorable reference in the design of an ultrasonic vibration system and selection the different tools in ultrasonic machining.

Investigation on an Innovative Method for High-Speed Low-Damage Micro-Cutting of CFRP Composites with Diamond Dicing Blades

This paper presents an innovative method for high-speed micro-cutting of carbon fiber reinforced plastics (CFRP). It employs a diamond dicing blade for micromachining applications, with a thickness of about 200 μm and rotational speeds up to 30,000 rpm so as to meet the low-damage surface integrity requirements. The process parameters, cutting damage, surface roughness, and the spindle vibration were thoroughly investigated to evaluate and validate the method. The results indicate that a high cutting speed up to 76 m/s not only remarkably increases the rigidity of an ultra-thin dicing blade, but also decreases the cutting depth per diamond grit to below 10 nm, both of which are very conducive to obtaining a very fine machined surface of about Ra 0.025 μm, with no obvious damage, such as delamination, burrs, and fiber pull out. The serious spindle vibration limits the rotational speed to increase further, and the rotational speed of 25,000 rpm achieves the best fine machined surface. Furthermore, unlike most research results of the drilling and milling method, the proposed micro-cutting method obtains the maximum cutting current and surface roughness when cutting at 0° fiber orientation, while obtaining a minimum cutting current and surface roughness when cutting at 90° fiber orientation. The metal-bonded dicing blade achieves smaller surface roughness than the resin-bonded dicing blade. This paper also discusses the cutting mechanism by investigating the morphology of the machined surface and concludes that the micro breakage and plastic-flow in local regions of fibers and resin are the main material removal mechanisms for dicing CFRP composites with a diamond abrasive blade.

A mechanistic ultrasonic vibration amplitude model during rotary ultrasonic machining of CFRP composites

Rotary ultrasonic machining (RUM) has been investigated in machining of brittle, ductile, as well as composite materials. Ultrasonic vibration amplitude, as one of the most important input variables, affects almost all the output variables in RUM. Numerous investigations on measuring ultrasonic vibration amplitude without RUM machining have been reported. In recent years, ultrasonic vibration amplitude measurement with RUM of ductile materials has been investigated. It is found that the ultrasonic vibration amplitude with RUM was different from that without RUM under the same input variables. RUM is primarily used in machining of brittle materials through brittle fracture removal. With this reason, the method for measuring ultrasonic vibration amplitude in RUM of ductile materials is not feasible for measuring that in RUM of brittle materials. However, there are no reported methods for measuring ultrasonic vibration amplitude in RUM of brittle materials. In this study, ultrasonic vibration amplitude in RUM of brittle materials is investigated by establishing a mechanistic amplitude model through cutting force. Pilot experiments are conducted to validate the calculation model. The results show that there are no significant differences between amplitude values calculated by model and those obtained from experimental investigations. The model can provide a relationship between ultrasonic vibration amplitude and input variables, which is a foundation for building models to predict other output variables in RUM.

Feasibility study of ultrasonic elliptical vibration-assisted reaming of carbon fiber reinforced plastics/titanium alloy stacks

The production of high quality bolt holes, especially on the carbon fiber reinforced plastics/titanium alloy (CFRP/Ti) stacks, is essential to the manufacturing process in order to facilitate part assembly and improve the component mechanical integrity in aerospace industry. Reaming is widely used as a mandatory operation for bolt holes to meet the strict industry requirements. In this paper, the ultrasonic elliptical vibration-assisted reaming (UEVR) which is considered as a new method for finish machining of CFRP/Ti stacked holes is studied. The paper outlines an analysis of tool performance and hole quality in UEVR compared with that in conventional reaming (CR). Experimental results show that the quality of holes was significantly improved in UEVR. This is substantiated by monitoring cutting force, hole geometric precision and surface finish. The average thrust forces and torque in UEVR were decreased over 30% and 60% respectively. It is found that, during first 45 holes, better diameter tolerance (IT7 vs. IT8), smaller diameter difference of CFRP and Ti holes (around 3μm vs. 12μm), better geometrical errors were achieved in UEVR as compared to CR. As for surface finish, both of the average roughness and hole surface topography in UEVR were obviously improved.

Investigations on the critical feed rate guaranteeing the effectiveness of rotary ultrasonic machining

Rotary ultrasonic machining (RUM) is a well-known and efficient method for manufacturing holes in brittle materials. RUM is characterized by improved material removal rates, reduced cutting forces and reduced edge chipping sizes at the hole exit. The aim of this study is to investigate the critical feed rate to guarantee the effectiveness of RUM. Experimental results on quartz glass and sapphire specimens show that when the feed rate exceeds a critical value, the cutting force increases abruptly, accompanied by a significant decrease of ultrasonic amplitude. An analytical model for the prediction of critical feed rates is presented, based on indentation fracture mechanic and the theory of impact of vibrating systems. This model establishes the theoretical relationships between the critical feed rate, idling resonant ultrasonic amplitude and spindle speed. The results predicted by the analytical model were in good agreement with the experimental results.