Using the acoustic sound pressure level for quality prediction of surfaces created by abrasive waterjet

The paper deals with an innovative way of cutting materials by abrasive waterjet with a view to increase its quality. In the research work, we were concerned with the search for a relationship between surface roughness and noise in the abrasive waterjet cutting process. Innovation lies in the use of negative characteristic of the technology—noise, which is a carrier of information about the quality of cutting process. In this way, the noise can be positively used in the on-line control of the technological process. The final result is a project for control of the process of abrasive waterjet cutting of materials by means of feedback according to the on-line measurement of acoustic pressure level L _aeq (dB). Instantaneous information about the state of cut according to the instantaneous value of L _aeq amplitude allows the automatic regulation of traverse speed of cutting head v _p (mm.min^?1), which is, together with the pressure p (MPa), one of the most important technological factors of control of production technology from the point of view of economic indicators and qualitative indicators of a semiproduct. The proposed model has been experimentally verified and was simulated in Matlab.     

Optimization of machining parameters in the abrasive waterjet turning of alumina ceramic based on the response surface methodology

A study on the radial-mode abrasive waterjet turning (AWJT) of 96 % alumina ceramic is presented and discussed. An experimental investigation is carried out to explore the influence of process parameters (including water pressure, jet feed speed, abrasive mass flow rate, surface speed, and nozzle tilted angle) on the material removal rate (MRR) when turning 96 % alumina ceramic. The experiments are conducted on the basis of response surface methodology (RSM) and sequential approach using face-centered central composite design. The quadratic model of RSM associated with the sequential approximation optimization (SAO) method is used to find optimum values of process parameters in terms of surface roughness and MRR. The results show that the MRR is influenced principally by the water pressure P and the next is abrasive mass flow rate m _a . The optimization results show that the MRR can be improved without increasing the surface roughness when machining 96 % alumina ceramic in the radial-mode abrasive waterjet turning process.     

Experimental investigations from conventional to high speed milling on a 304-L stainless steel

Last years analytical or finite element models of milling become more efficient and focus on more physical aspects, nevertheless the milling process is still experimentally unknown on a wide range of use. This paper propose to analyse with accuracy milling operations by investigating the cutting forces values, shape of cutting forces curves obtained for different cutting speeds, and related phenomena as tool wear or tool run-out. These detailed experimental data in milling constitute a suitable experimental basis available to develop predictive machining modelling. All the tests have been conducted on the 304-L stainless steel in many cutting configurations and for different tool geometries. The machinability of the 304-L stainless steel with different tools geometries and configurations in shoulder milling is defined by three working zones: a conventional zone permitting stable cutting (low cutting speed; under 200–250 m.min^?1), a dead zone (unfavourable for cutting forces level and cutting stability; between 250 and 450 m.min^?1), and a high speed machining zone (high cutting speed; up to 450–500 m.min^?1). All the used criteria (cutting forces, chips, wear) confirm the existence of these different zones and a correlation is proposed with cutting perturbations as tool run-out, cutting instability, ploughing, and abrasive wear.     

Topographical anomaly on surfaces created by abrasive waterjet

In the present study, real topographic function and maximal depth of neglected initial zone were analytically developed to predict surface roughness on the top region of surfaces created by abrasive waterjet. An upper area of workpieces was analysed in details. Experimentally created surfaces were measured by HOMMEL TESTER T8000 and non-contact profilometer Micro Prof FRT. As an experimental material, stainless steel AISI 304, AISI 309 and aluminium with a thickness of 10?mm have been used. On the basis of analysis and interpretation of data obtained from the surface, a topography function Ra _d , which is necessary to be known for the subsequent prediction and control of abrasive waterjet cutting technology, is derived. In the framework of interpretation of measured values, relations among these parameters are systematically analysed and physico-mechanical and distributional principles governing these parameter are formulated newly. Results are very important for further estimation of analytical expression of the real topographic function for any surface created by abrasive waterjet cutting.     

Parameter design for cut surface characteristics in abrasive waterjet cutting of Al/SiC/Al2O3 composite using grey theory based RSM

The abrasive mixed waterjet was successfully employed to cut many materials including austenitic steel, inconel and glass for a variety of industrial applications. The present work focusses on studying the surface roughness, striation zone and striation angle in Abrasive waterjet cutting (AWJC) of Al/SiC/Al₂O₃ composite. The water pressure, traverse speed, abrasive flow rate and stand-off distance were included as the dominant parameters in the study. The features of striation zone (length and angle) and surface roughness were observed as the responses for each of the cutting trials planned as per Taguchi’s L₁₈ orthogonal array. Parameter design was performed using the grey theory based response surface methodology (g-RSM) by following the method of simultaneous optimization to forecast the optimal cutting condition. All the studied parameters and their interactions were found to have a substantial effect on the observed responses. Significant improvements were observed in the responses obtained with the optimal parameter setting predicted by the g-RSM approach. The Atomic force microscopy (AFM) images and P-profile plots were also studied to observe the texture of the cut surface.     

Parametric optimization of CNC turning process for hybrid metal matrix composite

Machining of hybrid metal matrix composite is difficult as the particulates are abrasive in nature and they behave like a cutting edge during machining resulting in quick tool wear and induces vibration. An attempt was made in this experimental study to evaluate the machining characteristics of hybrid metal matrix composite, and a mathematical model was developed to predict the responses, namely surface finish, intensity of vibration and work-tool interface temperature for known cutting condition while machining was performed in computer numerical control lathe. Design of experiments approach was used to conduct the trials; response surface methodology was employed to formulate a mathematical model. The experimental study inferred that the vibration in V _x, V _y, and V _z were 41.59, 45.17, and 26.45 m/s², respectively, and surface finish R _a, R _q, and R _z were 1.76, 3.01, and 11.94 μm, respectively, with work-tool interface temperature ‘T’ of 51.74 °C for optimal machining parameters, say, cutting speed at 175 m/min, depth of cut at 0.25 mm and feed rate at 0.1 mm/rev during machining. Experimental results were in close conformity with response surface method overlay plot for responses.     

Investigate on milling force of cryogenic cooling processing aluminum honeycomb treated by ice fixation

Aerospace metal honeycomb materials with low stiffness had often the deformation, burr, collapse, and other defects in the mechanical processing. They were attributed to poor fixation method and inapposite cutting force. This paper presented the improvement of fixation way. The hexagonal aluminum honeycomb core material was treated by ice fixation, and the NC milling machine was used for a series of cryogenic machining. Considering the similar structure of fiber-reinforced composite materials, the milling force prediction model of ice fixation aluminum honeycomb was established, considering tool geometry parameters and cutting parameters. Meanwhile, the influence rule on milling force was deduced. The results show that compared with the conventional fixation milling method, the honeycomb processing effect is improved greatly. The machining parameters affect order on milling forces: the cutting depth is the most important, followed by the cutting width, then the spindle speed and the feed. Moreover, too small cutting depth (a_p?=?0.5 mm) will cause insufficient cutting force, while a_p?>?2 mm with higher force will reduce the processing quality of honeycomb. Simultaneously, the honeycomb orientation (θ) has a great influence on processing quality. Using the model, the predicted and measured error values of the feed and main cutting force are all small in θ?<?90°. But, the rate is 33 and 26% for the main cutting force and feed force error in θ?>?90°, respectively, while they all exhibit the smallest error in θ?=?60°. This bigger error mainly is due to unstable cutting force with obtuse angle. In addition, the tool rake angle has little influence on cutting quality in θ?<?90°, but bigger on that in θ?>?90°. Furthermore, the calculation model successfully conforms to the main deformation mechanism and influences parameters of the cutting force in the milling process, and it can accurately predict the cutting force in θ?<?90° and guide the milling process.     

An integrated optimization of cutting parameters and tool path generation in ultraprecision raster milling

This paper provides a new methodology for the integrated optimization of cutting parameters and tool path generation (TPG) based on the development of prediction models for surface roughness and machining time in ultraprecision raster milling (UPRM). The proposed methodology simultaneously optimizes the cutting feed rate, the path interval, and the entry distance in the feed direction to achieve the best surface quality in a given machining time. Cutting tests are designed to verify the integrated optimization methodology. The experimental results show that, in the fabrication of plane surface, the changing of entry distance improves surface finish about 40 nm (R _a ) and 200 nm (R _t ) in vertical cutting and decreases about 8 nm (R _a ) and 35 nm (R _t ) in horizontal cutting with less than 2 s spending extra machining time. The optimal shift ratio decreases surface roughness about 7 nm (R _a ) and 26 nm (R _t ) in the fabrication of cylinder surfaces, while the total machining time only increases 2.5 s. This infers that the integrated optimization methodology contributes to improve surface quality without decreasing the machining efficiency in ultraprecision milling process.     

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.     

Machinability investigation in hard turning of AISI D3 cold work steel with ceramic tool using response surface methodology

The hard turning process has been attracting interest in different industrial sectors for finishing operations of hard materials. In this paper, the effects of cutting speed, feed rate, and depth of cut on surface roughness, cutting force, specific cutting force, and power in the hard turning were experimentally investigated. An experimental investigation was carried out using ceramic cutting tools, composed approximately with (70 %) of Al₂O₃ and (30 %) of TiC, in surface finish operations on cold work tool steel AISI D3 heat-treated to a hardness of 60 HRC. Based on 3³ full factorial designs, a total of 27 tests were carried out. The range of each parameter is set at three different levels, namely, low, medium, and high. Analysis of variance is used to check the validity of the model. Experimental observations show that higher cutting forces are required for machining harder work material. This cutting force gets affected mostly by feed rate followed by depth of cut. Feed rate is the most influencing factor on surface roughness. Feed rate followed by depth of cut become the most influencing factors on power; especially in case of harder workpiece. Optimum cutting conditions are determined using response surface methodology (RSM) and the desirability function approach. It was found that, the use of lower depth of cut value, higher cutting speed, and by limiting the feed rate to 0.12 and 0.13 mm/rev, while hard turning of AISI D3 hardened steel, respectively, ensures minimum cutting forces and better surface roughness. Higher values of depth of cut are necessary to minimize the specific cutting force.     

Study on the effect of frequency tracing in ultrasonic-assisted drilling of titanium alloy

Drilling titanium alloys are difficult because of the inherent material properties, particularly the low thermal conductivity and high chemical reactivity. This paper presents the design of a frequency tracing system and the experimental investigation in ultrasonic-assisted drilling (UAD) of titanium alloy. In order to realize the degree of influence between developed frequency tracing system and cutting parameters (frequency tracing, operating voltage, drill diameter, feed rate, and spindle speed) in UAD of titanium alloy, a L₁₈ (2?×?3⁷) orthogonal array was employed. Based on the experimental results, the importance of drill diameter, feed rate, and spindle speed in assessing thrust force is highlighted. On the other hand, average thrust force reduction of 3.2% was realized with frequency tracing compared to without the frequency tracing counterpart in UAD of titanium alloy. Moreover, the best combination to get lower thrust force in UAD of titanium alloy is A₂B₂C₃D₁E₃ (i.e., frequency tracing = YES, operating voltage?=?500 V, drill diameter?=?3 mm, feed rate?=?10 mm/min, and spindle speed?=?1,000 rpm) within the selected test range.     

Effects of process parameters on surface roughness in abrasive waterjet cutting of aluminium

Abrasive waterjet cutting is a novel machining process capable of processing wide range of hard-to-cut materials. Surface roughness of machined parts is one of the major machining characteristics that play an important role in determining the quality of engineering components. This paper shows the influence of process parameters on surface roughness (R_a) which is an important cutting performance measure in abrasive waterjet cutting of aluminium. Taguchi’s design of experiments was carried out in order to collect surface roughness values. Experiments were conducted in varying water pressure, nozzle traverse speed, abrasive mass flow rate and standoff distance for cutting aluminium using abrasive waterjet cutting process. The effects of these parameters on surface roughness have been studied based on the experimental results.     

Crack separation mechanism in CO2 laser machining of thick polycrystalline cubic boron nitride tool blanks

An improved method for cutting thick polycrystalline cubic boron nitride (PCBN) tool blanks is explored because current methods of pulsed Nd:YAG laser cutting and wire electrical discharge machining (EDM) are constrained by low speed and low precision. We present a CO₂ laser/waterjet (LWJ) process to cut 4.8-mm-thick PCBN tool inserts by a crack separation mechanism. In LWJ, the PCBN blank is locally heated using a high-power continuous wave CO₂ laser to cause phase transition from cubic to hexagonal followed by water quenching to generate thermal stresses and form boron oxide leading to increased brittleness, subsequent cracking, and material separation. A 2³ fractional design of experiment (DOE) approach was employed to determine the factors of laser power, cutting speed, and waterjet pressure on the responses of phase transformation depth, taper, and surface roughness. A numerical heat flow model, based on Green’s function, was used to calculate the temperature distributions along the depth. Surface profilometer, scanning electron microscopy, and Raman spectroscopy were utilized to analyze the phase transformation and crack zones. Results from LWJ compared with pulsed Nd:YAG laser and laser microjet? methods indicate LWJ cuts 30 times faster; this was attributed to a nonconventional material removal (crack separation) mechanism. When LWJ was compared against nitrogen-assisted CO₂ laser cutting, improved cut quality (less taper and smaller heat-affected zone) was observed due to a greater control on phase transformation and crack propagation. DOE analysis revealed laser power and waterjet pressure, and the interactions among them are more significant factors than others.     

Performance and wear mechanisms of whisker-reinforced alumina, coated and uncoated PCBN tools when high-speed turning aged Inconel 718

Inconel 718, an efficient superalloy for energy and aerospace applications, is currently machined with cemented carbide tools at low speed (v _c?≈?60 m/min) due to its unfavorable mechanical and thermal properties. The article presents results of a study of superalloy machinability with whisker-reinforced alumina, uncoated and coated polycrystalline cubic boron nitride (PCBN) tools. Turning of age-hardened Inconel 718 (45 HRC) was done under high-speed machining conditions (v _c?=?250…350 m/min). Aspects of tool life, tool wear, and generated surface quality were studied. Application of uncoated PCBN tools resulted in surface quality and force level superior to other tool materials. Considerable sideflow of workpiece material was found to affect surface quality, especially for coated PCBN and ceramic tools. It was found that protective function of the coating, which increases the tool life up to 20 %, is limited only to low cutting speed range. EDX and AFM analyses suggested dominance of chemical and abrasive wear mechanisms. EDX mapping of worn tools pointed absence of diffusional wear for PCBN tools and intensive degradation of whisker reinforcement in ceramic tools due to diffusion of Ni, Fe, and Cr.     

Abrasive flow machining applied to plastic gear matrix polishing

The topic of this paper is the application of abrasive flow machining (AFM) to gear tool inserts polishing. Polished surface on plastic gear teeth improves surface geometry stability, and it increases the lifespan, which was proved on the gear testing rig. Experiments have shown that it is an efficient alternative to the hand polishing procedure. Besides significant cost and processing time savings, AFM generates constant surface quality. The achieved roughness is homogeneous on the entire machined surface; it is reduced from R _a?=?0.68 μm to R _a?=?0.08 μm in 120 s. At the same time, the tooth geometry profile is not damaged. The first time, surface polishing should be done at request because of individually manufactured tool inserts. Processing parameters depend on the type of the abrasive machine, the polishing paste and part geometry. Computer-aided abrasive flow analyses and practical experiments assist in setting optimum AFM process parameters. The paper presents a working set of parameters and a detailed report on machined surface measurement data. On the base of better understanding of AFM process, the surface roughness prediction model and thickness of removed material model was setup. It has high accuracy and reliability for specific applications. The use of plastic gears for various applications is widespread; the presented process improvement is an important innovation for injection molding tools manufacturers.     

Combined rough and finish machining of Ti–6Al–4V alloy by electrochemical mill-grinding

Abstract

This study proposes a combined method for the electrochemical mill-grinding of Ti–6Al–4V alloy to achieve a high material removal rate, high machining accuracy and good surface quality based on rough and finish machining. In the rough machining stage, a maximum feed rate of 2.7?mm min^?1 and a material removal rate of 248.3?mm³ min^?1 were achieved experimentally at a 10?mm cut depth using an abrasive tool with five rows of tool-sidewall outlet holes. In the finish machining stage, there were almost no overcuts or stray corrosions produced. The sidewall surface roughness and sidewall flatness were Ra = 1.06 and 76.8?μm after the finishing stage, which represent a 68% and 79.2% improvement compared with the rough machining stage, respectively. Finally, we fabricated a 1-mm-thick thin-walled structure using the combined machining operations, in which approximately 96% of the total material removal volume was performed at the rough machining stage.     

Investigation of machining parameters for the multiple-response optimization of micro electrodischarge milling

This paper investigated the influence of three micro electrodischarge milling process parameters, which were feed rate, capacitance, and voltage. The response variables were average surface roughness (R _a ), maximum peak-to-valley roughness height (R _y ), tool wear ratio (TWR), and material removal rate (MRR). Statistical models of these output responses were developed using three-level full factorial design of experiment. The developed models were used for multiple-response optimization by desirability function approach to obtain minimum R _a , R _y , TWR, and maximum MRR. Maximum desirability was found to be 88%. The optimized values of R _a , R _y , TWR, and MRR were 0.04, 0.34 μm, 0.044, and 0.08 mg min^?1, respectively for 4.79 μm s^?1 feed rate, 0.1 nF capacitance, and 80 V voltage. Optimized machining parameters were used in verification experiments, where the responses were found very close to the predicted values.     

Abrasives for water-jet cutting of high-strength and thick hard materials

The paper discusses abrasive water-jet cutting of hard-to-cut materials represented by high carbon steel DIN norm No.1.2436 (CSN EN 19437) plate 61–mm-thick and high-strength concrete cube sized 150 mm. Four relatively hard minerals with different densities not commonly used in water-jet technology were tested and their cutting results compared to those of three types of almandine garnets: Ukraine, Australian, and sorted Australian. Cutting efficiency was evaluated utilizing declination angle. Dependence of cutting efficiency on abrasive density and hardness was investigated. High density of abrasive appeared to be disadvantageous in our experiment. Cutting efficiency dependence on hardness exhibited nearly linear course, the increase was much more significant for concrete than for steel. Evaluation of experimental results led to the conclusion that cutting mechanism in case of very thick samples is different from common abrasive waterjet cutting. The limit declination angle for thick samples is significantly smaller, it was found to be approximately 22°. This result represents entirely new finding. The most promising finding from the economical point of view appears to be behavior of corundum, when cutting concrete. Our experimental results promise 20 % increase in cutting speed for brittle materials.     

Predictive depth of jet penetration models for abrasive waterjet cutting of alumina ceramics

A study of the depth of jet penetration (or depth of cut) in abrasive waterjet (AWJ) cutting of alumina ceramics with controlled nozzle oscillation is presented and discussed. An experimental investigation is carried out first to study the effects of nozzle oscillation at small angles on the depth of cut under different combinations of process parameters. Based on the test conditions, it is found that nozzle oscillation at small angles can improve the depth of cut by as much as 82% if the cutting parameters are correctly selected. Depending on the other cutting parameters in this study, it is found that a high oscillation frequency (10–14 Hz) with a low oscillation angle (4–6°) can maximize the depth of cut. Using a dimensional analysis technique, predictive models for jet penetration when cutting alumina ceramics with and without nozzle oscillation are finally developed and verified. It is found that the model predictions are in good agreement with the experimental results with the average percentage errors of less than 2.5%.     

基于淹没环境的超高压后混合磨料水射流切割试验研究

利用超高压水射流切割试验系统,在80～280MPa压力范围内进行淹没磨料水射流切割试验研究,通过试验及数据分析,验证了后混合淹没磨料射流切割的可行性,得出了磨料粒径和质量流量、射流压力、靶距、切割横移速度等参数对射流切割性能的影响规律,对于脆性和塑性材料,试验中各参数对切割深度的影响基本一致.结果表明:在试验给出的工况条件下,磨料流量存在最佳值,在一定范围内切割深度随磨料流量增加而增加,当磨料流量达到一定值后,切割深度随流量增加反而下降;切割深度与射流压力基本呈线性增长关系;随着靶距的增大,切割深度逐渐减小;切割深度随切割速度的增加呈指数衰减趋势,并且相同试验工况下淹没射流切割深度要大于非淹没状态.试验结果为超高压淹没磨料水射流的实际应用和研究提供了参考.