Contour finish turning operations with coated grooved tools: Optimization of machining performance

This paper presents a new methodology for optimization of machining performance in contour finish turning operations. Two machining performance measures, chip breakability and surface roughness, are considered as optimization criteria due to their importance in finishing operations. Chip breakability covers two major factors: chip shape and size. Comprehensive case studies are presented to demonstrate the determination and application of optimal cutting conditions through experimental validation.     

A hybrid predictive model and validation for chip flow in contour finish turning operations with coated grooved tools

Unlike straight turning, the effective cutting conditions and tool geometry in contour turning operations are continuously changing with changing workpiece profile. This causes a wide variation in chip flow during the operation. Unfavorable chip flow can cause scratch/damage the machined surface, and lead to tool failure due to chip build up at the cutting edge. This paper presents a new methodology to predict the chip side-flow angle for complex grooved tool inserts in contour turning operations as well as experimental validation. Computer program has been developed to apply the predictive model to any contour workpiece profile and the capability of the predictive program is also presented in this paper.     

Hard turning with variable micro-geometry PcBN tools

This paper presents investigations on hard turning with variable edge design PcBN inserts. Turning of hardened AISI 4340 steel with uniform and variable edge design PcBN inserts is conducted, forces and tool wear are measured. 3D finite element modelling is utilized to predict chip formation, forces, temperatures and tool wear on uniform and variable edge micro-geometry tools. Predicted forces and tool wear contours are compared with experiments. The temperature distributions and tool wear contours demonstrate the advantages of variable edge micro-geometry design.     

Automatic tool selection for rough turning operations

A method of automatically selecting cutting tools for rough turning operations on a CNC lathe is presented. While the selection procedure can deal with various economic objectives, only the minimum cost per component is considered in this paper. Selection is made from an appropriate tool library and in order to reduce the search time a heuristic method is employed.

The cost of machining with a given tool is estimated following the determination of the cutting conditions consistent with the constraints acting on the process. From a detailed examination of the constraints it is possible to ascertain whether the next tool in the library will give improved cutting conditions and the possibility of a lower cost. This procedure eliminates the need for an exhaustive search of the library and results in a very fast and efficient algorithm.

The results of ten tool selections are presented. In all cases the computation time for the heuristic approach was less than 5% of that for the exhaustive search. In eight out of ten cases the heuristic method selected the same tool as the exhaustive search; in the two cases where the tools selected were different, those selected by the heuristic method produced only a marginal increase in the operation cost.     

Effects of cutting geometry in turning with TiN-coated tools

The effects of cutting tool geometry on the performance of TiN-coated high-speed steel tools were studied. Turning tests were carried out with inserts made of conventional and powder metallurgical HSS. The workpiece material was a case hardening steel with a hardness of 170 HB. Two different cutting geometries were used. In addition to altering the cutting angles, the effect of honing the cutting edge before coating was studied. The results showed clearly that even small changes in the tool angles affect the performance of the TiN-coated tool. Honing the cutting edge significantly increased wear resistance by improving the edge strength and reducing microchipping. On the basis of the results the modification of cutting tool geometry for hard coatings is discussed.     

Chatter stability of a slender cutting tool in turning with tool wear effect

An analysis of the chatter behavior for a slender cutting tool in turning in the presence of wear flat on the tool flank is presented in this research. The mechanism of a self-excited vibration development process with tool wear effect is studied. The components contributing to the forcing function in the turning vibration dynamics are analyzed in the context of cutting force and contact force. A comparison of the chatter stability for a fresh cutting tool and a worn cutting tool is provided. Stability plots are presented to relate width of cut to cutting velocity in the determination of chatter stability. Machining experiments at various conditions were conducted to identify the characteristic parameters involved in the vibration system and to identify the analytical stability limits. The theoretical result of chatter stability agrees qualitatively with the experimental result concerning the development of chatter stability model with tool wear effect.     

An adaptive fuzzy control system for turning operations

In the paper, an adaptive fuzzy control system is developed and then applied to control turning processes with highly non-linear and time-varying cutting characteristics. The control system employs linguistic rules to obtain a constant turning force under varying cutting conditions. In order to improve the performance of the non-adaptive fuzzy logic controler, and adaptive algorithm using a turning process identifier to adapt the output scaling factor of the fuzzy logic controller is included. It is shown, by experimentation, that the adaptive fuzzy control system is capable of providing an effective solution to the control of the constant turning force under varying cutting conditions.     

A united model of diametral error in slender bar turning with a follower rest

Follower rest is an essential accessory for turning machines during the manufacture of slender bar. In order to analyze the effects of the follower rest and other machining conditions on diametral error, a united model is developed for predicting diametral error of slender bar. The proposed model consists of three components: geometric analysis of diametral error, finite element model of workpiece deflection and statistical model of cutting forces. Since there is a coupling between the actual depth of cut and the cutting force, a computer program is developed to determine the coupled depth of cut by using dichotomy. Then, a series of experiments are carried out to verify the prediction accuracy of the proposed model and a good agreement between the predicted and measured data is found. Finally, a series of numerical examples are calculated to analyze some important factors influencing diametral error of slender bar. The results show that the diametral error mainly depends on the location of follower rest, depth of cut and feed rate. But the cutting speed only has a slight effect on the diametral error.     

A self-organizing neural fuzzy logic controller for turning operations

This paper proposes a neural fuzzy logic controller to achieve self-organizing control for turning operations. A new learning method which is based on a performance index of sliding mode control is used for control rule modifications and some supervision rules are also given to secure rule modifications. One of the major advantages of the proposed model is that it can start from an empty control rule base. Simulation and experimental results of the control of a constant turning force under varying cutting conditions are given to illustrate the effectiveness of the proposed method.     

Development of a chip flow model for turning operations

A model is presented which predicts the chip flow direction in turning operations with nose radius tools under oblique cutting conditions. Only the tool cutting edge geometry and the cutting conditions (feed and depth of cut) are required to implement the model. An experimental study has verified the chip flow model and shown that the model's predictions are in good agreement with the experimental results.     

Modeling of turning process cutting forces for grooved tools

A mechanistic modeling approach to predicting cutting forces for grooved tools in turning has been developed. The model assumes the existence of an equivalent orthogonal cutting operation for any oblique operation. The effects of tool nose radius and chip flow have been incorporated by defining a set of equivalent groove parameters. Two calibration methods have been presented for the model. A variety of commercial grooved inserts were chosen to validate the model. The workpiece material used was AISI 1018 steel. The force predictions from the model were found in good agreement with the measured forces. The effects of cutting conditions and groove parameters on the cutting forces and their implication in designing grooved tools were also determined.     

Predictive machinability models for a selected hard material in turning operations

In this paper, empirical models for tool life, surface roughness and cutting force are developed for turning operations. Process parameters (cutting speed, feed rate, depth of cut and tool nose radius) are used as inputs to the developed machinability models. Two important data mining techniques are used; they are response surface methodology and neural networks. Data of 28 experiments when turning austenitic AISI 302 have been used to generate, compare and evaluate the proposed models of tool life, cutting force and surface roughness for the considered material.     

Surface finishes from turning and facing with round nosed tools

The range of surface roughnesses, and particularly the minimum roughnesses, achievable mainly with cemented carbide but also with single crystal diamond round nosed turning and facing inserts, has been experimentally studied, machining aluminium on engineering and precision lathes. Insert edge sharpness and roughness measurements and characteristic variations with feed rate of machined surface profile are presented. When machine tool limits are avoided, R_z values down to 0.02 times the insert edge radii have been obtained.     

PCBN刀具断续车削淬硬钢的试验研究

为了探索PCBN刀具在断续切削条件下刀具的破损规律,选用两种不同的PCBN刀具,在不同强度的断续方式及不同的切削速度下,对淬硬钢进行车削试验研究。根据试验条件,观察了刀具前、后刀面的磨损及破损情况,分析了刀具的失效机理,比较了刀具的切削寿命。结果表明：断续强度严重影响PCBN刀具的使用寿命,断续强度越高,刀具寿命越低;在相同强度的断续条件下,切削速度影响刀具的使用寿命,切削速度越高,刀具的寿命越低;本实验所用的断续条件下,刀具的失效判据为崩刃。     

关于虚拟车削加工中的粗糙度预测的研究

针对虚拟车削加工中振动问题的处理,对外圆车削加工的理论粗糙度模型进行了修正.通过预测工件与刀具的相对位移,实现了对加工工件的表面形貌的估算.通过对表面形貌的仿真,提高了虚拟车削软件的应用性.     

Implementation of a process and structure model for turning operations

The consideration of the dynamic interaction between the machine tool structure and the cutting process is a prerequisite for the simulative prediction and optimization of machining tasks. However, existing cutting force models are either dedicated to already examined manufacturing operations or require extensive measurements for the determination of cutting coefficients. In this context this paper outlines a modular, analytical cutting force model applicable to common turning processes. It takes into account the dynamic material behavior, nonlinear friction ratios on the rake face as well as heat transfer phenomena in the deformation zones. On the part of the machine tool structure a parametric model based on the Finite Element Method (FEM) is implemented. Both models are coupled for the simulation of process and structure interactions, whereas the influence of the control system is considered as well. The simulation results were verified experimentally on a turning center.     

Properties and performances of innovative coated tools for turning inconel

Three innovative nanostructured coatings have been developed to be applied on cutting tools for continuous cutting of nickel-based super-alloys, in Minimum Quantity Lubrication (MQL) or dry conditions.The coatings, TiN+AlTiN, TiN+AlTiN+MoS₂ and CrN+CrN:C+C, were applied by PVD techniques on WC-Co inserts, developing nanostructured layers, characterised by superior performances, as confirmed both by laboratory tests and machining experiments.Coatings surface qualification included SEM observations with EDS analysis, ball erosion test, nanoindentation and scratch tests, classic tribological evaluation by ball-on-disc set-up, surface texture analysis.Results were analysed in light of the outcome of machining experiments performed mainly in dry and MQL turning of Inconel 718. Ball-on-disc and scratch tests, as well as machining experiments, agreed in classifying the coatings in the following decreasing performance order: TiN+AlTiN+MoS₂, followed by TiN+AlTiN, and by CrN+CrN:C+C.     

Analytical model for tool wear monitoring in turning operations using ultrasound waves

This paper presents an analytical model to monitor the gradual wear of cutting tools, on-line, during turning operations using ultrasound waves. Ultrasound waves at a frequency of 10 MHz were pulsed continuously inside several cutting tools, towards their cutting edge. The change in tool geometry, due to gradual wear, has been related, in a mathematical form, to the change in the acoustic behavior of ultrasound waves inside the body of the cutting tools. Physical laws governing the propagation and reflection of ultrasound waves along with geometrical analysis of the wear area were used in deriving the mathematical model. The experimental setup and model evaluation is based on a previously published research work by the author, which presented an empirical model showing a corresponding change in the ultrasound behavior with tool gradual wear. The current work emphasizes the previous findings and presents the relation between the acoustic behavior of ultrasound waves and the progressive tool gradual wear in a mathematical form that can be easily used in machine control operations.     

Optimizing the use of dry cutting in rough turning steel operations

The main objective of using cutting fluids in machining operations is the reduction of temperature in the cutting region to increase tool life. However, the advantages offered by cutting fluids have been strongly debated because of their negative effects on the economic aspect, the environment and the health of workers using them. A trend to solve these problems is cutting without fluid, a method named dry cutting, which has been made possible due to technological innovations. This work aims to seek conditions in which dry cutting is satisfactory compared with the flood of fluid (called here wet cutting) usually used. Aiming at this goal, several experiments were carried out varying parameters such as cutting speed, feed, depth of cut and tool material in rough turning of ABNT 1045 steel in dry and wet cutting. The analysis of the results showed that wet turning is, as expected, better for tool life. The second conclusion is that dry cutting cannot be used with large depth of cut. But the main conclusion is that, if the tool material is changed to a more wear resistant one, dry cutting can be used with results very similar to those obtained with a flood of fluid.