Investigation on surface finish and metallic particle emission during machining of aluminum alloys using response surface methodology and desirability functions

The surface finish of a mechanical part plays an important role as it determines the part’s field performance. The machining parameters and conditions governing the part surface finish also impact on the other machining process performance indicators such as tool wear, tool life, cycle time, machining cost, and undesirable emissions of aerosols and metallic particles. In today’s metal cutting industry, a major concern is the occupational safety and health hazard associated with cutting fluids usage and metallic particle emission. It is therefore necessary to determine machining conditions that could improve the part surface finish while maintaining low the aerosol emission. In this research study, statistical methods are used to study the surface finish parameters and the metallic particle emissions during milling of aluminum alloys (6061-T6, 7075-T6, and 2024-T351) with two coated carbide tools (TiCN and a multilayer TiCN?+?Al₂O₃?+?TiN). Following an implementation of multilevel design of experiment, machining trials and determination of mains most influential factors, surface responses and desirability functions are used to determine the best process operational conditions and windows. The results of this research demonstrate that TiCN-coated tool generates fewer respirable airborne particles during machining than multilayers TiCN?+?Al₂O₃?+?TiN-coated tool. Overall, it is shown that the use of TiCN coating tool provides a better opportunity for an environmentally benign dry machining along with improvement on surface quality.     

<Emphasis Type="Bold">Prediction of Surface Topomorphy and Roughness in Ball-End Milling</Emphasis>

Milling is today the most effective, productive and flexible-manufacturing method for machining complicated or sculptured surfaces. Ball-end tools are used for machining 3D freeform surfaces for dies, moulds, and various parts, such as aerospace components, etc. Milling data, such as surface topomorphy, surface roughness, non-deformed chip dimensions, cutting force components and dynamic cutting behaviour, are very helpful, especially if they can be accurately produced by means of a simulation program. This paper presents a novel simulation model, the so-called MSN-Milling Software Needle program, which is able to determine the surface produced and the resulting surface roughness, for ball-end milling. The model simulates precisely the tool kinematics and considers the effect of the cutting geometry on the resulting roughness. The accuracy of the simulation model has been thoroughly verified, with the aid of a wide variety of cutting experiments. Many roughness measurements were carried out on workpieces, which were cut using a 5-axis machining centre. The calculated roughness levels were found to be in agreement with the experimental ones. The proposed model has proved to be suitable for determining optimal cutting conditions, when finishing complex surfaces. The software can be easily integrated into various CAD-CAM systems.     

Performance of coated, cemented carbide, mixed-ceramic and PCBN-H tools when turning W320 steel

TiN-coated cemented carbide, mixed ceramic and PCBN with a high percentage of CBN (PCBN-H) tools were used for reconditioned turning of hardened and tempered W320 steel hot working dies. The dies are usually scraped after their useful life because they are difficult to be reconditioned by machining. One alternative to scraping these dies is to convert them, increasing their internal diameters by internal turning. The machining experiments showed that coated carbide tools performed better at cutting speeds up to 120 m/min, while PCBN tools were superior at higher speeds up to 200 m/min. Mixed ceramic tools did not perform well under the conditions investigated. The tribological system showed abrasion, adhesion and plastic deformation as the dominant wear mechanisms. Chipping on the tool rake and flank faces, as well as catastrophic failure, was also observed in some experiments.     

高速铣削淬硬模具钢的工艺性与经济性研究

高速加工机床及其刀具技术的最新发展使得在模具和零件制造领域实现“以切代磨”成为可能 ,用超硬刀具高速切削淬硬模具钢等难加工材料已得到越来越广泛的应用。由于模具或零件的高速切削加工可免除磨削或抛光等后续工序 ,因此精加工时如何保证工件最终表面质量同时将加工成本控制在可接受范围之内是研究人员关注的重要问题。本文在调查的基础上分析了用于高速铣削淬硬模具钢的整体硬质合金涂层立铣刀的切削性能和经济性 ,并给出了部分应用实例     

Heat generation and heat transfer in cylindrical grinding process -a numerical study

Grinding is the most common abrasive machining process and in many cases the last of the series of machining operations. Compared to other machining processes grinding requires very high-energy input per unit of volume of material removal. The chip removal process consists of rubbing, plowing and metal removal. The frictional resistance encountered between work material, the tool, and the chip tool interface and the resistance to deformation during shearing of chips contributes to a rise in temperature and the cutting zone. The temperature generated is not only quite high but the temperature gradients are also severe. Under abusive grinding conditions, the formation of the heat-affected zone was observed which damages the ground surfaces of the workpieces. The present work aims at optimizing the amount of heat generation and modeling the temperature rise between wheel and work contact zone in a cylindrical grinding process so as to achieve better surface integrity in AISI 3310, AISI 6150, and AISI 52100 steel materials. Taguchi’s methodology a powerful tool in design of experiments for quality is used for optimization process.     

Construction of a surface roughness prediction model for high speed machining

In manufacturing environment prediction of surface roughness is very important for product quality and production time. For this purpose, the finite element method and neural network is coupled to construct a surface roughness prediction model for high-speed machining. A finite element method based code is utilized to simulate the high-speed machining in which the cutting tool is incrementally advanced forward step by step during the cutting processes under various conditions of tool geometries (rake angle, edge radius) and cutting parameters (yielding strength, cutting speed, feed rate). The influences of the above cutting conditions on surface roughness variations are thus investigated. Moreover, the abductive neural networks are applied to synthesize the data sets obtained from the numerical calculations. Consequently, a quantitative prediction model is established for the relationship between the cutting variables and surface roughness in the process of high-speed machining. The surface roughness obtained from the calculations is compared with the experimental results conducted in the laboratory and with other research studies. Their agreements are quite well and the accuracy of the developed methodology may be verified accordingly. The simulation results also show that feed rate is the most important cutting variable dominating the surface roughness state.     

On the performance enhancement of self-tuning adaptive control for time-varying machining processes

This paper investigates efficient approaches to improve the performance of a self-tuning adaptive control system for time-varying machining processes. The milling process is a typical time-varying system because of variations of the cutting conditions, e.g., the change of cutting depths and variation of the cutting materials. On the other hand, the milling processes are considered as typically non-minimum phases since one or more zeros of discrete-time models of milling processes may be located outside the unit circle. In this paper, an efficient method, using the pole assignment method, is presented to design a self-tuning adaptive controller for time-varying and non-minimum phase milling processes, and an effective method to select appropriate design parameters in order to improve its performance has been proposed. Its effectiveness has been verified in experiments on controlling milling processes with varying cutting depth. The experimental results illustrate that improved control performances can be obtained using the appropriate design parameters selected according to the principles and criteria presented here.     

An experimental investigation on micro machining of fine-grained graphite

Industrial applications of the micro milling process require sufficient experimental data from various micro tools. Research has been carried out on micro milling of various engineering materials in the past two decades. However, there is no report in the literature on micro milling of graphite. This paper presents an experimental investigation on micro machinability of micro milling of moulded fine-grained graphite. Full immersion slot milling was conducted using diamond-coated, TiAlN-coated and uncoated tungsten carbide micro end mills with a uniform tool diameter of 0.5 mm. The experiments were carried out on a standard industrial precision machining centre with a high-speed micro machining spindle. Design of experiments (DoE) techniques were applied to design and analysis of the machining process. Surface roughness, surface topography and burrs formation under varying machining conditions were characterized using white light interferometry, SEM and a precision surface profiler. Influence of variation of cutting parameters including cutting speeds, feedrate and axial depth of cut on surface roughness and surface damage was analysed using ANOVA method. The experimental results show that feedrate has the most significant influence on surface roughness for all types of tools, and diamond tools are not sensitive to cutting speed and depth of cut. Surface damage and burrs analysis show that the primary material removal mode is still brittle fracture or partial ductile in the experimental cutting conditions. 3D intricate micro EDM electrodes were fabricated with good dimensional accuracy and surface finishes using optimized machining conditions to demonstrate that micro milling is an ideal process for graphite machining.     

A new model of grit cutting depth in wafer rotational grinding considering the effect of the grinding wheel,workpiece characteristics,and grinding parameters

Wafer rotational grinding is widely employed for back-thinning and flattening of semiconducting wafers during the manufacturing process of integrated circuits. Grit cutting depth is a comprehensive indicator that characterizes overall grinding conditions, such as the wheel structure, geometry, abrasive grit size, and grinding parameters. Furthermore, grit cutting depth directly affects wafer surface/subsurface quality, grinding force, and wheel performance. The existing grit cutting depth models for wafer rotational grinding cannot provide reasonable results due to the complex grinding process under extremely small grit cutting depth. In this paper, a new grit cutting depth model for wafer rotational grinding is proposed which considers machining parameters, wheel grit shape, wheel surface topography, effective grit number, and elastic deformation of the wheel grit and the workpiece during the grinding process. In addition, based on grit cutting depth and ground surface roughness relationship, a series of grinding experiments under various grit cutting depths are conducted to produce silicon wafers with various surface roughness values and compare the predictive accuracy of the proposed model and the existing models. The results indicate that predictions obtained by the proposed model are in better agreement with the experimental results, while accuracy is improved by 40%–60% compared to the previous models.     

Investigation and optimization of lubrication parameters in high speed turning of superalloy Inconel 718

Dry machining is sometimes less effective when higher machining efficiency, better surface finish quality, and severe cutting conditions are required. For these situations, semi-dry operations utilizing very small amount of cutting fluids called minimum quantity lubrication is expected to become a powerful tool and played a significant role in a number of practical applications. It has been observed from the literature survey that a systematic research work has to be carried out to determine the optimum quantity of lubricant with appropriate cutting conditions for achieving better machinability characteristics of a material. Hence, an attempt has been made in this paper to enhance the machinability characteristics in high speed turning of superalloy Inconel 718 using quantity of lubricant, delivery pressure at the nozzle, frequency of pulses, direction of application of cutting fluid, cutting speed, and feed rate as the process parameters. Results indicated that the use of optimized minimum quantity lubrication parameters under pulsed jet mode leads to lower cutting force, cutting temperature, and flank wear.     

A state-of-the-art review of ductile cutting of silicon wafers for semiconductor and microelectronics industries

Silicon is a typical functional material for semiconductor and optical industry. Many hi-tech products like lenses in thermal imaging, solar cells, and some key products of semiconductor industry are made of single crystal silicon. Silicon wafers are used as substrate to build vast majority of semiconductor and microelectronic devices. To meet high surge in demand for microelectronics based products in recent years, the development of rapid and cost efficient processes is inevitable to produce silicon wafers with high-quality surface finish. The current industry uses a sequence of processes such as slicing, edge grinding, finishing, lapping, polishing, back thinning, and dicing. Most of these processes use grinding grains or abrasives for material removal. The mechanism of material removal in these processes is fracture based which imparts subsurface damage when abrasive particles penetrate into the substrate surface. Most of these traditional processes are extremely slow and inefficient for machining wafers in bulk quantity. Moreover, the depth of subsurface damage caused by these processes can be up to few microns and it is too costly and time consuming to remove this damage by heavy chemical–mechanical polishing process. Therefore, semiconductor industry requires some alternative process that is rapid and cost effective for machining silicon wafers. Ductile cutting of silicon wafer has the potential to replace the tradition wafer machining processes efficiently. If implemented effectively in industry, ductile cutting of silicon wafers should reduce the time and cost of wafer machining and consequently improve the productivity of the process. This paper reviews and discusses machining characteristics associated with ductile cutting of silicon wafers. The limitations of traditional wafer fabrication, the driving factors for switching to ductile cutting technology, basic mechanism of ductile cutting, cutting mechanics, cutting forces, surface topography, thermal aspects, and important factors affecting these machining characteristics have been discussed to give a systematic insight into the technology.     

On the machining characteristics of H13 tool steel in different hardness states in ball end milling

This paper investigates and compares the machining characteristics of AISI H13 tool steel in hardness states of 41 and 20 HRC in the ball end milling process. The machining characteristics are illustrated through three types of process outputs from the milling experiments: the milling force, the chip form, and the surface roughness. Characteristic differences in these process outputs are shown to reflect the hardness effect of the tool steel on the ball end milling process. The mechanistic phenomena of the milling process are revealed by the six shearing and ploughing cutting constants extracted from the milling forces. The experimental results show that all the cutting constants of the softer tool steel are greater than those of the hard steel, indicating that higher cutting and frictional energies are required in the chip shearing as well as in the nose ploughing processes of the softer tool steel. The higher cutting energy is also attested by the more severely deformed, shorter, and thicker chips of the softer steel. Surface roughness of the hard steel is shown to be considerably better than that of the soft steel at all cutting speeds and feed rates and is independent of cutting speed, whereas the surface roughness of the softer steel is significantly improved with increasing cutting speed.     

Enhancement and verification of a machined surface quality for glass milling operation using CBN grinding tool—Taguchi approach

Nowadays, the demand for high product quality focuses extensive attention to the quality of machined surface. The (CNC) milling machine facilities provides a wide variety of parameters set-up, making the machining process on the glass excellent in manufacturing complicated special products compared with other machining processes. However, the application of grinding process on the CNC milling machine could be an ideal solution to improve the product quality, but adopting the right machining parameters is required. Taguchi optimization method was used to estimate optimum machining parameters with standard orthogonal array L₁₆ (4⁴) to replace the conventional trial and error method as it is time-consuming. Moreover, analyses on surface roughness and cutting force are applied which are partial determinant of the quality of surface and cutting process. These analyses are conducted using signal to noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) to determine which process parameters are statistically significant. In glass milling operation, several machining parameters are considered to be significant in affecting surface roughness and cutting forces. These parameters include the lubrication pressure, spindle speed, feed rate, and depth of cut as control factors. While, the lubrication direction is considered as a noise factor in the experiments. Finally, verification tests are carried out to investigate the improvement of the optimization. The results showed an improvement of 49.02% and 26.28% in the surface roughness and cutting force performance, respectively.     

超精密车削切屑形成过程的试验研究

超精密车削中的各种物理现象，如切削力、刀具磨损以及加工表面质量等问题，都是以切屑形成为基础的。而生产实践中出现的许多问题，如振动、卷屑和断屑等，又都与超精密切削过程密切相关。选用的材料种类和切削条件不同，可生成不同形态的切屑。文章提出了一种研究切屑形成过程新的试验方法，利用该方法能够得到金刚石车削时高清晰的金属材料塑性流动图像。     

Investigating the cutting phenomena in free-form milling using a ball-end cutting tool for die and mold manufacturing

This paper presents an investigation of nonplanar tool-workpiece interactions in free-form milling using a ball-end cutting tool, a technique that is widely applied in the manufacturing of dies and molds. The influence of the cutting speed on the cutting forces, surface quality of the workpiece, and chip formation was evaluated by considering the specific alterations of the contact between tool-surface along the cutting time. A trigonometric equation was developed for identifying the tool-workpiece contact along the toolpath and the point where the tool tip leaves the contact with the workpiece. The experimental validation was carried out in a machining center using a carbide ball-end cutting tool and a workpiece of AISI P20 steel. The experimental results demonstrated the negative effect of the engagement of the tool tip into the cut on machining performance. The length of this engagement depends on the tool and workpiece curvature radii and stock material. When the tool tip center is in the cut region, the material is removed by shearing together with plastic deformation. Such conditions increase the cutting force and surface roughness and lead to an unstable machining process, what was also confirmed by the chips collected.     

Tool wear condition monitoring using a sensor fusion model based on fuzzy inference system

One of the biggest problems in manufacturing is the failure of machine tools due to loss of surface material in cutting operations like drilling and milling. Carrying on the process with a dull tool may damage the workpiece material fabricated. On the other hand, it is unnecessary to change the cutting tool if it is still able to continue cutting operation. Therefore, an effective diagnosis mechanism is necessary for the automation of machining processes so that production loss and downtime can be avoided. This study concerns with the development of a tool wear condition-monitoring technique based on a two-stage fuzzy logic scheme. For this, signals acquired from various sensors were processed to make a decision about the status of the tool. In the first stage of the proposed scheme, statistical parameters derived from thrust force, machine sound (acquired via a very sensitive microphone) and vibration signals were used as inputs to fuzzy process; and the crisp output values of this process were then taken as the input parameters of the second stage. Conclusively, outputs of this stage were taken into a threshold function, the output of which is used to assess the condition of the tool.     

复合喷雾加工法在切削加工过程中的冷却和润滑效果

对喷雾加工法应用于连续切削的可能性进行了探讨。复合喷雾加工法是将冷却性能很好的水形成小颗粒的水雾,并将其同微量植物油油雾同时供给切削区,以降低切削区温度,保证微量切削油的润滑性的加工方法。试验结果证明,复合喷雾加工法对于被认为对切削区供给切削油困难的连续切削,也是十分有效的加工方法。应用这种加工方法可提高加工表面的精度,改善刀具的磨损,并由此实现清洁生产方式。     

Machining of complex-shaped parts with guidance curves

Nowadays, high-speed machining is usually used for production of hardened material parts with complex shapes such as dies and molds. In such parts, tool paths generated for bottom machining feature with the conventional parallel plane strategy induced many feed rate reductions, especially when boundaries of the feature have a lot of curvatures and are not parallel. Several machining experiments on hardened material lead to the conclusion that a tool path implying stable cutting conditions might guarantee a better part surface integrity. To ensure this stability, the shape machined must be decomposed when conventional strategies are not suitable. In this paper, an experimental approach based on high-speed performance simulation is conducted on a master bottom machining feature in order to highlight the influence of the curvatures towards a suitable decomposition of machining area. The decomposition is achieved through the construction of intermediate curves between the closed boundaries of the feature. These intermediate curves are used as guidance curve for the tool paths generation with an alternative machining strategy called “guidance curve strategy”. For the construction of intermediate curves, key parameters reflecting the influence of their proximity with each closed boundary and the influence of the curvatures of this latter are introduced. Based on the results, a method for defining guidance curves in four steps is proposed.     

Machining and simulation studies of bimetallic pistons

Light aluminium alloy piston is suitably reinforced at high load-bearing region with cast iron insert, and machining of such bimetallic material is more difficult with a single cutting tool material. Present study focuses on the orthogonal cutting of bimetallic material machining using cubic boron nitride as a cutting tool through finite element analysis. The effects of cutting parameters such as cutting velocity, feed rate and depth of cut on resultant cutting forces and the surface roughness were analysed. Those parameters yielding minimum cutting forces were identified as minimal cutting force parameters, so numerical simulation and experiments were carried out on these parameters. After machining, the intermediate bonding between metallic regions was studied using ultrasonic testing. Bimetallic machining is successfully simulated, and its potential is readily applied to an industrially important component.     

An experimental study on machining techniques of cutting composite armors

The machining of laminated composite components or armors consisting of engineering ceramics, fiber-reinforced plastic, and even aluminum or titanium alloy is a great challenge to manufacturing engineers. So far, quite limited literatures can be found concerning the machining of laminated composite components, and the quite limited studies are mainly focused on the stacks consisting of metal plates and composite materials. Also, there is hardly any report concerning the cutting techniques of laminated composite components or armors. In this work, the cutting techniques of three types of composite armors such as the Kevlar fiber-reinforced plastic (KFRP) protection inner lineplate, the ceramic composite armor (ceramics/glass fiber-reinforced plastics/aluminum alloy laminate), and the double-plate composite armor (ceramics/KFRP laminate) were studied experimentally on a desktop cutting machine, using a sintering diamond saw. Two types of machining processes such as cocurrent cutting and reverse cutting were discussed, and finally, reverse cutting is recommended for better cutting quality. Cutting tests indicated that under proper processing conditions, high-quality cutting of composite armors can be carried out by using a sintering diamond saw.