On the modelling of abrasive waterjet cutting

Abrasive waterjet cutting operates by the impingement of a high-velocity abrasive-laden waterjet against the workpiece. The jet is formed by mixing abrasive particles with high-velocity water in mixing tubes and is forced through a tiny sapphire orifice. The accelerated jet exiting the nozzle travels at more than twice the speed of sound and cuts as it passes through the workpiece.This cutting process is being developed as a net-shape and near-net-shape machining process for cutting many metals and hard-to-machine materials. The narrow kerf produced by the stream results in neither delimitation nor stresses along the cutting path. This new technology offers significant advantages over traditional processes for its ability to cut through most sections of dense or hard materials without the need for secondary machining, to produce contours, and to be integrated into computer-controlled systems.The abrasive waterjet cutting process involves a large number of process and material parameters which are related to the waterjet, the abrasive particles, and workpiece material. Those parameters are expected to effect the material removal rates and the depth of cut. The purpose of the present work is to propose a model which is capable of predicting the maximum depth of cut for different types of materials using different process parameters. A comparison of the results of the proposed model and the models reported in the literature is introduced along with a discussion of the limitations of those models.On leave from: Mechanical Engineering Department, Suez Canal University, Egypt.On leave from: Industrial Production Engineering Department, Mansoura University, Egypt.On leave from: Mechanical Power Engineering Department, Alexandria University, Egypt.     

碳纤维复合材料超声辅助钻削加工孔质量研究

碳纤维增强复合材料(carbon fiber reinforced plastics,CFRP)因其是编织材料,具有各向异性、强度高等特点,其加工难度大,加工质量较差.针对这一现状,采用电镀金刚石套料钻,对CFRP开展了超声辅助钻削与普通钻削对比实验,通过出入口质量、内壁形貌分析,研究了超声振动作用对孔出入口、内壁质量...     

A study on the use of single mesh size abrasives in abrasive waterjet machining

This paper details the studies on the use of single mesh size garnet abrasives in abrasive waterjet machining for cutting aluminum. The influence of three different single mesh size abrasives, pressure, traverse rate, and abrasive flow rate; on depth of cut, top kerf width, bottom kerf width, kerf taper, and surface roughness are investigated. Experiments designed using standard L9 orthogonal array and the analysis of variance helped in the determination of highly significant, significant and weakly significant cutting parameters. Single mesh size abrasives are found to yield decreased surface roughness than multi mesh size abrasives. Based on these studies, response equations are developed to predict the target parameters. Using single mesh abrasives, a practitioner not only can cut faster but also achieve reduced surface roughness.     

Comparison of drilled hole quality evaluation in CFRP/CFRP stacks using optical and ultrasonic non-destructive inspection

In aeronautical industry, stringent requirements relate to the quality of drilled holes in carbon fiber reinforced plastic (CFRP) composite laminates as low hole quality determines poor assembly tolerance, structural properties reduction, and risk for long-term part performance. Non-destructive quality control techniques were applied to drilled CFRP laminate stacks for aeronautical applications to characterize the material damage induced by drilling in order to assess the hole quality for product acceptability. Experimental metrology procedures, including optical measurements and ultrasonic non-destructive evaluation, were employed to appraise both external and internal induced material damage in holes machined under diverse drilling conditions. The optical inspection procedure, comparable to the visual inspection method regularly utilized in industry, provided delaminated area evaluations that are underestimated in the case of severe drilling conditions by up to 7% for hole exit and up to 5% for hole entry. In the case of less severe drilling conditions, the underestimation was limited to <2.5% for both hole exit and hole entry, which can be considered a practically negligible disparity.     

磨料水射流加工工程陶瓷工艺参数对加工效率的影响

研究用磨料水射流加工工程陶瓷，通过分析各工艺参数对加工效率的影响，提出了一种优选工艺参数的方法。     

An investigation into the aspheric ultraprecision machining using the response surface methodology

Aspheric ultraprecision machining is increasingly important to the manufacturing industry. The performance of aspheric optical components manufactured by mass-production is largely dependent on the form error of molds and dies. It is believed that productivity of a machining process could be improved if the form error is predictable. In this study, the response surface methodology (RSM) was employed to derive predictive models of rough and compensation cuttings for an aspheric convex mold, with an outer aperture of ϕ12 mm and curve height of 0.6 mm. Two control factors, the depth of cut and spindle speed, were selected for study. The 2K factorial design with four center points was adopted. Two linear models for both rough and compensation cuttings were derived experimentally based on the form errors obtained. The models adequacy was examined through ANOVA (analysis of variance) results for the surface responses. It was found that the linear model of rough cutting is adequate, reflected by the significant regress coefficients and the high R² value. However, the model of compensation cutting was found to be inadequacy.     

碳复合材料钻孔加工性研究

从刀具材料,几何角度,切削用量等几个方面分析了碳复合材料钻孔工艺性和表面质量,给出了改善复合材料钻孔质量的工艺参数。     

碳纤维复合材料-钛合金层板钻孔质量研究

对比钻削碳纤维复合材料(CFRP),碳纤维复合材料-钛合金层板(CFRP-Ti),得出钻削CFRP-Ti时的CFRP入口分层、孔径误差、形状误差以及孔的表面粗糙度均比单独钻削CFRP时的要差.其原因是CFRP在上层,当钻削钛合金层时,一方面轴向钻削力大,钻削过程不平稳;另一方面钛合金的钻屑为螺旋长条状,这些都会影响已形成的孔壁.尤其在高转速下,此影响更为严重.     

An investigation on use of colemanite powder as abrasive in abrasive waterjet cutting (AWJC)

In the present study, the cutting performance outputs (surface roughness, surface waviness and kerf taper angle) of colemanite powder as abrasive in abrasive waterjet cutting (AWJC) with varying traverse rate and abrasive flow rate were investigated experimentally. The performance outputs were compared to that of garnet which is in common use in industry as abrasive in AWJC industry. Al7075, marble, glass, Ti6Al4V and a composite material were selected as sample materials in the experiments. Furthermore, colemanite powder was mixed with garnet powder at certain proportions and the obtained surface characteristics were compared with those cut with pure garnet powder. It is found experimentally that in spite of higher amount of colemanite powder consumption with respect to garnet to perform the same cutting action, the colemanite powder could be an alternative powder for AWJC process.     

Effect of tool vibration on chip formation and cutting forces in the machining of fiber-reinforced polymer composites

This article investigates the chip formation mechanism and its influence on cutting forces during the elliptic vibration-assisted (EVA) cutting of fiber-reinforced polymer composites. To clarify the effect of the vibration, systematic finite element and experimental studies were performed on both the EVA and the traditional cutting of unidirectional fiber-reinforced polymers with various fiber orientations. The key factors that govern the cutting forces have been taken into account, such as the depth of cut, feed rate, tool vibration frequency and amplitude. The study found that fiber orientation significantly affects the chip formation and cutting forces. Fiber fracture can happen either above or below the trimming path, but that above the path dominates chip formation. When a fiber orientation is less than 90°, chipping is mainly through bending-induced fracture of fibers; when it is beyond 90°, however, chipping is mostly by crushing the fracture of fibers. Compared with a traditional cutting process, the EVA cutting can minimize the fiber orientation effect through localized fiber fracture. A dimensional analysis was then performed to provide a quantitative prediction of the cutting forces.     

An investigation on machinability assessment of Al-6XN and AISI 316 alloys: an assessment study of machining

This work presents machinability assessment of AL-6XN super austenitic stainless steel alloy. Cutting forces, surface roughness, work hardening tendency and tool wear were analyzed. The assessment was conducted based on a comparison between the AL-6XN alloy and the well-known alloy in the machining field AISI 316. Finite element analysis (FEA) study was also conducted and used in this assessment. Experimental results showed maximum increase of 70% and 57% in the feed and normal forces of the AL-6XN alloy, respectively. Maximum increase in the work hardening tendency of 59% was recorded for the AL-6XN alloy while only 29% was recorded for the 316 alloy. The roughness analysis recorded an increase of 186% for the AL-6XN alloy compared to the 316 alloy. Tool wear analysis revealed the build-up edge formation, severe chipping, flank and crater wear (CW) during cutting AL-6XN alloy whereas small chipping, flank and CW were noticed during cutting 316 alloy. FEA study showed when the AL-6XN alloy machined using 65 and 94?m/min cutting speeds, the increases (compared to the 316 alloy) were: 12% and 8% in plastic strain; 20% and 20% in stresses; 48% and 100% in residual tensile stresses; 22% and 92% in residual compressive stresses, respectively.     

Experimental investigation on the effects of thermomechanical loading on the vibrational stability during rotary ultrasonic machining

Ultrasonic vibration is assumed to be stable or unchangeable during the process of rotary ultrasonic machining (RUM) on brittle materials, neglecting the effects of different processing parameters. However, no experimental evidence has been reported to validate this assumption. In this study, the effect of thermomechanical load on the stability of ultrasonic amplitude during RUM was investigated by theoretical analysis and experimental procedures on quartz glass and sapphire. It was shown that the instability of ultrasonic amplitude during the machining process is mainly attributed to variation of resonant frequency under the implementation of thermomechanical load. The thermal effects of ultrasonic vibration decrease the resonant frequency of the ultrasonic machine, while mechanical loading during the machining process increases the resonant frequency. Furthermore, a higher feed rate or a harder material leads to a higher resonant frequency change. The variation of ultrasonic power can be used to review the validity of difference-neglected assumption when different values of processing variables, materials, or even machine tools are used during modeling. The results of this study should be well considered for future references when designing an ultrasonic machine.     

Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites

In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100 N at a constant sliding distance of 6000 m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined.The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10 wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking.     

Effect of reinforcement size and volume fraction on the abrasive wear behaviour of AA7075 Al/SiCp P/M composites—A statistical analysis

In the present study, a new mathematical model was developed to predict the abrasive wear rate of AA7075 aluminum alloy matrix composites reinforced with SiC particles. Five factors, five levels, central composite, rotable design matrix was used to optimise the required number of experiments. The model was developed by response surface method. Analysis of variance technique was applied to check the validity of the model. Student's t-test was utilised to find out the significant factors. The effect of volume percentage of reinforcement, reinforcement size, applied load, sliding speed and abrasive size on abrasive wear behaviour was analysed in detail.     

Thermal influence on surface layer of carbon fiber reinforced plastic (CFRP) in grinding

In this study, we investigated thermal influence on surface layer of CFRP in grinding with heat conduction analysis using grinding temperature at wheel contact area on dry and wet condition. Moreover, the thermal affected layer was analyzed through an experiment to examine the temperature of glass transition and thermal decomposition of the matrix resin that composes the CFRP used in this study. The influence of thermal effect on grinding of CFRP was verified based on observation of ground surface finish after grinding using SEM and the measurement of surface roughness. From the measurement result of DSC (Differential Scanning Calorimetry),TG-DTA (Thermogravimetry-Differential Thermal Analysis), It was found that the thermal affected layer of CFRP includes a layer in which the matrix resin is changed in quality by exceeding the glass transition temperature and a layer in which the matrix resin is thermally decomposed by exceeding the thermal decomposition temperature. In addition, it was found that the surface roughness was significantly reduced if the thermal affected layer with thermal decomposition was generated. In each grinding atmosphere, it tended to increase of grinding temperature at wheel contact area with increasing in the setting depth of cut. In the case of dry grinding, grinding temperature at wheel contact area increased up to t thermal decomposition temperature of the matrix resin. However, in the case of the wet grinding, grinding temperature at wheel contact area did not increase until thermally decomposition temperature. From the result of simulation about thermal affected layer, influence of grinding heat increased with increasing in the setting depth of cut. Ultimately, the thermal affected layer with thermal decomposition was generated in dry grinding. Moreover, from the results of SEM observation, it was confirmed that the surface finish properties deteriorated significantly due to thermal decomposition of the matrix resin in the case of Δ = 400 μm in the setting depth of cut at fiber angle θ = 0°. On the other hand, it was confirmed that the micro damage of carbon fiber was occurred in wet grinding at each setting depth of cut.     

Effect of machining parameters on the milling process of 2.5D C/SiC ceramic matrix composites

Abstract

The C/SiC ceramic matrix composites are widely used for high-value components in the nuclear, aerospace and aircraft industries. The cutting mechanism of machining C/SiC ceramic matrix composites is one of the most challenging problems in composites application. Therefore, the effects of machining parameters on the machinability of milling 2.5D C/SiC ceramic matrix composites is are investigated in this article. The related milling experiments has been carried out based on the C/SiC ceramic matrix composites fixed in two different machining directions. For two different machining directions, the influences of spindle speed, feed rate and depth of cut on cutting forces and surface roughness are studied, and the chip formation mechanism is discussed further. It can be seen from the experiment results that the measured cutting forces of the machining direction B are greater than those of the in machining direction A under the same machining conditions. The machining parameters, which include spindle speed, feed rate, depth of cut and machining direction, have an important influence on the cutting force and surface roughness. This research provides an important guidance for improving the machining efficiency, controlling and optimizing the machined surface quality of C/SiC ceramic matrix composites in the milling process.     

An autonomous low-Cost infrared system for the on-line monitoring of manufacturing processes using novelty detection

This paper describes the implementation of a process monitoring system using a low-cost autonomous infrared imager combined with a novelty detection algorithm. The infrared imager is used to monitor the health of several manufacturing processes namely: drilling, grinding, welding and soldering. The main aim is to evaluate the use of low-cost infrared sensor technology combined with novelty detection to distinguish between normal and faulty conditions of manufacturing processes. The ultimate aim is to improve the reliability of the manufacturing operations so as to ensure high part quality and reduce inspection costs. The paper describes several case studies, which have shown that the new low-cost technology could provide an inexpensive and autonomous methodology for monitoring manufacturing processes. Novelty detection is used to compare normal and faulty conditions in order to provide an automated system for fault detection.     

SiC颗粒增强铝基复合材料高速铣削实验研究

对SiC颗粒增强铝基复合材料的高速切削加工性能进行了试验分析，研究了铣削速度对铣削力、切削温度、加工表面粗糙度、表面形貌和刀具磨损的影响，从而获得了能够保证对其进行高效率、高精度加工的合理工艺参数。