Prediction and optimisation models for turning operations

Selection of process parameters has very significant impact on product quality, production costs and production times. The quality and cost are much related to tool life, surface roughness and cutting forces which they are functions of process parameters (cutting speed, feed rate, depth of cut and tool nose radius). In this paper, empirical models for tool life, surface roughness and cutting force are developed for turning operations. The process parameters (cutting speed, feed rate, depth of cut and tool nose radius) are used as inputs to the developed machineability models. Two data mining techniques are used; response surface methodology and neural networks. The data of 28 experiments have been used to generate, compare and evaluate the proposed models of tool life, cutting force and surface roughness for the selected tool/material combination. The resulting models are utilized to formulate an optimisation model and solved to find optimal process parameters, when the objective is minimising production cost per workpiece, taking into account the related boundaries and limitation of this multi-pass turning operations. Numerical examples are given to demonstrate the suggested optimisation models.     

Formulation of Surface Roughness Models for Machining Nickel Super Alloy with Different Tools

This paper presents a study of the development of surface roughness models for turning supermet 718 nickel super alloy (300 BHN), using different tool materials namely; CBN (SANDVIK CB50), Carbide (SANDVIK HIP k10), and ceramic (SANDVIK CC680) under dry cutting conditions and a constant nose radius. The models are developed in terms of cutting speed, feed rate, and depth of cut. These variables were investigated using design of experiments and utilization of the response surface methodology (RSM). A separate surface roughness model corresponding to each tool material is established, tested and reported.     

Optimization of Tool Geometry and Cutting Parameters for Hard Turning

In the hard-turning process, tool geometry and cutting conditions determine the time and cost of production which ultimately affect the quality of the final product. So reliable models and methods are required for the prediction of the output performance of the process. In the present work, experimental investigation has been conducted to see the effect of the tool geometry (effective rake angle and nose radius) and cutting conditions (cutting speed and feed) on the surface finish during the hard turning of the bearing steel. First- and second-order mathematical models were developed in terms of machining parameters by using the response surface methodology on the basis of the experimental results. The surface roughness prediction model has been optimized to obtain the surface roughness values by using genetic algorithms. The genetic algorithm program gives minimum values of surface roughness and their respective optimal conditions.     

Nose radius and cutting speed effects during milling of AISI 304 material

Not only milling parameters, but also cutting tool properties affect the machining performance. Therefore, in the current work, the effect of nose radius and cutting speed on the wear, force, surface roughness and chip morphology in down and up milling of AISI 304 stainless steel was investigated. Machining experiments were conducted with cutting tools with radii of 0.4, 0.8 and 1.2?mm at various cutting speeds in both down and up milling. Experimental results showed that the main tool failure mechanisms and modes were adhesion, abrasion, chipping and fracture during milling with various nose radii. Cutting forces dropped with the increment in nose radius regardless of the cutting speed and milling direction, except for up milling at 100?m/min. From the experimental results, it was found that roughness diminished with increase in both nose radius and speed. Surface roughness and the resultant forces during up milling were found to be lower than that during down milling. It was observed that the increment in nose radius increased the edge serration in chip morphology.     

Correlation between edge radius of the cBN cutting tool and surface quality in hard turning

cBN cutting tools with superior mechanical properties are widely used in machining various hard materials. The microgeometry of cBN cutting tools, such as the edge radius, has great influence on the surface quality of components and tool life. For optimized tool geometry, it is crucial to understand the influence of the cBN cutting tool microgeometry on the machined surface quality. In this study, the attempt has been made to investigate the correlation between the cutting tool edge radius and surface quality in terms of the surface roughness and subsurface deformation through a FE simulation and experiment. Machining tests under different machining conditions were also conducted and the surface roughness and subsurface deformation were measured. Surface roughness and subsurface deformation were produced by the cutting tools with different edge radii under various cutting parameters. Both results from the FE simulation and machining tests confirmed that there was a significant influence on the surface quality in terms of both the surface roughness and subsurface quality from the edge radius. There is a critical edge radius ofcBN tools in hard turning in terms of surface quality generated.     

FACTORS AFFECTING SURFACE ROUGHNESS IN FINISH TURNING OF GRAY CAST IRON

The objective of this study was to ascertain the effect of tool wear on surface roughness and develop a more thorough understanding of the process variables affecting surface roughness. Experimental data from a finish turning operation on gray cast iron with uncoated tungsten carbide tools was used to develop a model for surface roughness as a function of cutting speed, feed rate, nose radius of the tool and the amount of wear on the tool. The experiment was statistically designed to minimize the number of runs. Tool wear was treated as a variable notwithstanding the fact that it is one of the responses of the process. The results showed that surface roughness is significantly affected by tool wear and the interactions between tool wear and other variables like cutting speed, feed rate and nose radius. The results also provide better insight into the problem of “adaptive” process control for finish turning operations.     

Machinability Study of Laser Surface Treated 15-5 PH Stainless Steel

In this work, 15-5 PH stainless steel which is one of the hard to machine materials has been selected to investigate the machinability characteristics under dry cutting condition with the aid of laser surface treatment process. Turning experiments were performed on the laser surface treated 15-5 PH samples with TiAlN coated tungsten carbide inserts. Machinability of both as received and laser surface treated samples were evaluated in terms of microstructure, microhardness, tangential cutting force, surface roughness, chip morphology and tool wear. Experimental consequences revealed that laser surface treated sample exhibits a remarkable effect on microstructure and microhardness. From the parametric analysis, it is found that machining of laser surface treated samples are beneficial in terms of reducing cutting force and are effective in prolonging tool life when compared with that of as received samples.     

The Impact of Tool Material and Cutting Parameters on Surface Roughness of a Nickel-Base Superalloy

The objective of the present work, is to assess the effect of tool material and cutting parameters on surface roughness of the supermet 718 Nickel-base superalloy, under dry cutting conditions and a constant nose radius (0.5 mm). The parameters investigated are cutting speed, feed rate, depth of cut and tool material. The tool materials used were the ceramic (Sandvik CC 680) and the CBN (Sandvik CB 50) inserts. These variables were investigated using a 2^k factorial design.

The present work demonstrates a favorable effect for ceramic inserts on surface roughness, when compared with CBN inserts. The work also, showed that the feed rate has the dominant effect among the parameters studied on the surface roughness, irrespective of the tool material used.     

圆弧刃精密切削试验及其三维有限元分析

在商业化软件Marc的基础上建立了圆弧刃精密切削三维有限元模型,研究不同半径的圆弧刃精密切削条件下主切削力、切屑形状和切削温度场分布．该模型运用更新拉格朗日法的有限元方程、网格重划分准则,其刀一屑摩擦采用修正的库仑摩擦模型．模拟结果表明,圆弧刃的圆弧半径对主切削力、切屑形状和切屑的最高温度都有较大的影响．通过试验研究精密切削马氏体3J33在不同半径的圆弧刃条件下对主切削力的影响,结果表明模拟的主切削力与试验值在一定程度下是吻合的.     

High-feed turning of AISI D2 tool steel using multi-radii tool inserts: Tool life,material removed,and workpiece surface integrity evaluation

Multi-radii tool inserts offer novel configuration that comprises of multiple radii at tool nose. A review of the available literature indicates that there exists a need for experimental investigation on certain key machining characteristics of such tools. This paper reports on tool wear/life, material removed, and workpiece surface roughness when multi-radii mixed alumina TiN coated tool inserts are employed for turning D2 steel. Inserts of three different nose radii (0.40, 0.80, 1.20?mm) at six levels of feed rates (ranging from 0.157 to 0.562?mm/rev) are used. Results show that flank wear is the dominant wear mode with catastrophic tool failure occurring at highest nose radius (1.20?mm) and feed rate (0.562?mm/rev) combination. Also, there is ～59% reduction in tool life accompanied by ～62% increase in quantity of material removed as the feed rate increases from 0.157 to 0.562?mm/rev at maximum nose radius (1.20?mm). Feed rate is found to be statistically significant factor for all three responses considered herein at 95% confidence level. Surface integrity assessment at maximum feed rate reveals presence of a strain hardened layer extending to the depth of 150?µm below the machined surface without any observance of white layer for all the tool conditions and nose radius.     

Surface finish prediction models for fine turning

Surface finish data were generated for aluminium alloy 390, ductile cast iron, medium carbon leaded steel 10L45, medium carbon alloy steel 4130, and inconel 718 for a wide range of machining conditions defined by cutting speed, feed and tool nose radius. These data were used to develop surface finish prediction models, as a function of cutting speed, feed, and tool nose radius, for each individual metal. A general purpose surface finish prediction model is also proposed for ductile cast iron, medium carbon leaded steel, and alloy steel. Statistical analysis of experimental data indicated that surface finish is strongly influenced by the type of metal, speed and feed of cut, and tool nose radius. While the effects of feed and tool nose radius on surface finish were generally consistent for all materials, the effect of cutting speed was not. The surface finish improved with speed for ductile cast iron, medium carbon leaded steel, medium carbon alloy steel, and aluminium alloy, but it deteriorated with speed for inconel. Apparently, speed effect on surface finish is not always positive. For all metals, the surface finish improved with the tool nose radius while it deteriorated with speed.     

A comparative evaluation method of machinability for mica-based glass-ceramics

The machinability of mica glass-ceramics is evaluated using a tool dynamometer. Several samples with different chemical compositions and microstructures were tested in turning operations using TiCN cermet tools. The cutting rate dependence of specific cutting energy has been studied to find a simple method for the evaluation of machinability. The mechanical strength, the surface roughness of the machined surface and the fracture toughness were measured to support the machining behaviour. For the determination of machinability, the specific cutting energy at low cutting rate conditions, neglecting an elastic impact effect, and the slope of the log-log plot of the specific cutting energy versus cutting rate were considered as the reasonable parameters. These results are correlated with the microstructure and the hardness of the workpiece. In particular, the microhardness of the sample is shown to control the cutting characteristic.     

Effect of machining parameters on surface roughness and material removal rate in finish turning of ±30° glass fibre reinforced polymer pipes

This paper studies the effect of varying machining parameters in turning on surface roughness and material removal rate (m.r.r.) for ±30° filament wound glass fibre reinforced polymers (GFRP) in turning operations using coated tungsten carbide inserts under dry cutting conditions. The paper describes the development of an empirical model for turning GFRP utilising factorial experiments. Second order predictive model covering speed, feed, depth of cut and tool nose radius has been developed at 95% confidence interval for surface roughness and material removal rate. Contour plots of the surface roughness and m.r.r. for different machining conditions have been generated from the empirical equations. Overlaid contour graph help in obtaining iso-value of roughness for different values of m.r.r.     

Design,evaluation and optimisation of cutter path strategies when high speed machining hardened mould and die materials

The use of high speed milling (HSM) for the production of moulds and dies is becoming more widespread. Critical aspects of the technology include cutting tools, machinability data, cutter path generation and technology. Much published information exists on cutting tools and related data (cutting speeds, feed rates, depths of cut, etc.). However, relatively little information has been published on the optimisation of cutter paths for this application. Most of the research work is mainly focused on cutter path generation with the main aim on reducing production time. Work with regards to cutter path evaluation and optimisation on tool wear, tool life, surface integrity and relevant workpiece machinability characteristics are scant. Therefore, a detailed knowledge on the evaluation of cutter path when high speed rough and finish milling is essential in order to improve productivity and surface quality. The paper details techniques used to reduce machining times and improve workpiece surface roughness/accuracy when HSM hardened mould and die materials. Optimisation routines are considered for the roughing and finishing of cavities. The effects of machining parameters notably feed rate adaptation techniques and cutting tools are presented.     

Effect of Cold Deformation on the Machinability of a Free Cutting Steel

The effect of cold deformation on the machinability of a free cutting steel has been investigated through characterization of the variation in size and morphology of the sulfide inclusions. The machinability has been indexed in terms of cutting force, surface roughness, and chip characteristics. The possible interrelations between inclusion characterizing parameters and machinability indices have been examined. Increased cold deformation was found to increase interinclusion spacing as well as aspect ratio of the inclusions. These variations in inclusion characteristics, in turn, were found to reduce the cutting forces and the chip length up to a critical amount of deformation. The results highlight the influence of inclusion characterizing parameters on machinability characteristics of free cutting steels.     

玻璃纤维增强树脂复合材料的直角切削技术研究

以单向玻璃纤维增强复合材料为研究对象,通过改变切削参数对在不同纤维方向角情况下的切削力和已加工表面的粗糙度进行了测试,并结合已加工表面的SEM观察,对复合材料的直角切削技术进行了试验研究。结果表明,纤维方向角对切削力和粗糙度以及切削区损伤程度的影响较大,是影响单向复合材料切削性能的重要因素;切削速度越快,粗糙度变化趋势越大。     

Development of ANFIS model and machinability study on dry turning of cryo-treated PH stainless steel with various inserts

This present investigation deals about the machinability comparison of cryogenically treated 15-5 PH stainless steel with various cutting tools such as uncoated tungsten carbide, cryogenic-treated tungsten carbide and wiper geometry inserts. Cryo-treated PH stainless steel is considered as the work material in this investigation and experimental trials were performed under dry turning condition. The machinability aspects considered for evaluation are cutting force (F_z), surface roughness (R_a) and tool wear. The outcomes of experimentation reveal that the tungsten carbide inserts which are cryogenically treated provide improved performance in machining while comparing with conventional and wiper geometry inserts at all machining conditions. The measured cutting force and the observed flank wear were less for the cryo-treated inserts. However, wiper tool produces a better surface finish during machining. An artificial intelligence decision-making tool named Adaptive Neuro Fuzzy Inference System has been evolved to determine the relation among the considered input machining variables and output measures, namely cutting force and surface roughness of the machined surface. An analysis has been performed to compare the results obtained from developed models and experimental results.     

Surface Roughness Analysis in Machining of Titanium Alloy

The use of response surface methodology for minimizing the surface roughness in machining titanium alloy, a topic of current interest, has been discussed in this article. The surface roughness model has been developed in terms of cutting parameters such as cutting speed, feed, and depth of cut. Machining tests have been carried out using CVD (TiN-TiCN-Al₂O₃-TiN) coated carbide insert under different cutting conditions using Taguchi's orthogonal array. The experimental results have been investigated using analysis of variance (ANOVA). The results indicated that the feed rate is the main influencing factor on surface roughness. Surface roughness increased with increasing feed rate, but decreased with increasing cutting speed and depth of cut. The predicted results are fairly close to experimental values and hence, the developed models can be used for prediction satisfactorily.     

Performance Improvement of End Milling Using Graphite as a Solid Lubricant

In any machining operation, the use of coolants is essential to dissipate heat generated during machining and hence to improve productivity, machinability, etc. However, the use of cutting fluids in machining operations may seriously degrade the quality of environment. New cutting techniques are to be investigated to alleviate the problems associated with wet machining. To overcome some of the problems, an attempt has been made to use graphite as a solid lubricant. This paper deals with an investigation on using graphite as a solid lubricant to reduce the heat generated at the milling zone. An experimental setup has been developed to direct graphite powder continuously onto the workpiece and tool interface at the required flow rate. Experimental studies have been conducted to see the effect of tool geometry (radial rake angle and nose radius) and cutting conditions (cutting speed and feed rate) on the machining responses such as cutting forces, specific energy, and surface finish in solid lubricant assisted machining using four fluted solid coated carbide end mill cutters. Results indicate that there is a considerable improvement in the performance of milling AISI 1045 steel using graphite as a solid lubricant when compared with machining using cutting fluids in terms of specific energy requirements, cutting force, and surface finish.     

Experimental study on the meso-scale milling of tungsten carbide WC-17.5Co with PCD end mills

Tungsten carbide is a material that is very difficult to cut, mainly owing to its extreme wear resistance. Its high value of yield strength, accompanied by extreme brittleness, renders its machinability extremely poor, with most tools failing. Even when cutting with tool materials of the highest quality, its mode of cutting is mainly brittle and marred by material cracking. The ductile mode of cutting is possible only at micro levels of depth of cut and feed rate. This study aims to investigate the possibility of milling the carbide material at a meso-scale using polycrystalline diamond (PCD) end mills. A series of end milling experiments were performed to study the effects of cutting speed, feed per tooth, and axial depth of cut on performance measures such as cutting forces, surface roughness, and tool wear. To characterize the wear of PCD tools, a new approach to measuring the level of damage sustained by the faces of the cutter's teeth is presented. Analyses of the experimental data show that the effects of all the cutting parameters on the three performance measures are significant. The major damage mode of the PCD end mills is found to be the intermittent micro-chipping. The progress of tool damage saw a long, stable, and steady period sandwiched between two short, abrupt, and intermittent periods. Cutting forces and surface roughness are found to rise with increments in the three cutting parameters, although the latter shows signs of reduction during the initial increase in cutting speed only. The results of this study find that an acceptable surface quality (average roughness R_a<0.2 μm) and tool life (cutting length L>600 mm) can be obtained under the conditions of the given cutting parameters. It indicates that milling with PCD tools at a meso-scale is a suitable machining method for tungsten carbides.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00298-y