Automated Machining Systems Research Articles

A Statistical Tool Replacement Procedure for the Design of a High-Reliability Machining System.

This study presents a statistical model for analyzing the reliability of a machining system considering a tool life distribution, as well as a statistical procedure for the design of a high-reliability machining system. Interruption of machining due to sudden tool failure or excessive tool wear is detrimental in automated machining systems. Not only does it disrupt production, but it also creates an obstacle in the construction of completely automated unmanned machining systems. High-reliability is a prerequisite for the design of an efficient and economical machining system. This study : ( 1 ) presents a new criterion (i. e., reliability criterion) for the design of a machining system, ( 2 ) defines the reliability of a machining system, ( 3 ) develops a statistical model to analyze the reliability of a machining system, and ( 4 ) presents a statistical procedure for the design of high-reliability machining systems.

The effects of progressive tool wear and tool restricted contact on chip breakability in machining

Chip breakability plays an essential role in automated machining systems. This paper presents an experimental investigation of the effects of progressive tool wear and the resulting formation of the tool restricted contact on chip breakability in a turning operation. Six parameters of tool wear, namely, major flank wear ( VB), crater wear depth ( KT), crater wear length ( KK), crater wear width ( KB), wear retract of cutting edge ( KS) and nose wear ( N), are shown to contribute to the variations of chip breakability with tool wear progression. The results show that the chip breakability varies significantly with tool wear progression, especially with the combined crater and flank wear progression, and contributes to the development of a restricted rake face land, making the tool behave like a restricted contact grooved tool. The chip curling and breaking action is largely influenced by the nature and magnitude of the restricted contact and the groove profile being developed on the tool face. The results presented in this paper are also intended to provide guidelines for designing effective chip grooves on the tool face.

Intelligent scheduling of automated machining systems

An automated machining system involves concurrent use of manufacturing resources, alternative process plans and flexible routings. High investment in the installation of automated facilities requires an efficient scheduling system that is able to allocate the resources specified for operations over a scheduling horizon. The primary emphasis of this paper is to generate schedules that accurately reflect details of the automated environment and the objectives stated for the system. In this paper, a rule for dispatching operations, named the Most Dissimilar Resources (MDR) dispatching rule, is introduced. A scheduling algorithm for automated machining is presented. Using the previous simulation research for this topic, a rule-based scheduling system is constructed. An architecture for an intelligent scheduling system is proposed, and the system has a high potential to provide efficient schedules based on the task-specific knowledge for the dynamic scheduling environment.

Regenerative Chatter Vibrations of Turning Workpiece. 5th Report, Detection of Regenerative Chatter by Fourier Transform.

It is important for fully automated machining systems or dynamic performance tests of a machine tool, to detect chatter and decide whether the cutting condition is stable or not. In this study, a method for judging the dynamic instability of cutting process is proposed. It is based on the ratio of inner to outer modulation amplitude estimated by the Fourier transform of regenerative chatter vibrations in every revolution of the workpiece. The validity of the present method is verified from numerical simulation data of regenerative chatter. Furthermore, we obtain the experimental limits of cutting process by this method, and compare them with the predicted limits which are calculated by the authors' criterion proposed in the previous paper. The predicted limits are almost in accord with the experimental ones at the cutting speed of 40-160 m/min and feed rate of 0.07-0.19 mm/rev.

Control of cutting tool replacement by durability distributions

For automated machining systems using cutting tools of indeterminate durability, a method for the determination of the most expedient (optimal) periods for tool replacement is considered. Statistical studies of tool reliability in field conditions are summarised, and analytical representation of durability as a random variable by means of the Weibull distribution is substantiated. Calculations of cutting tool replacement periods for transfer lines illustrate optimisation.

Control of cutting tool replacement by durability distributions

For automated machining systems using cutting tools of indeterminate durability, a method for determination of the most expedient periods of tool replacement is considered. Statistical studies of tool reliability in field conditions are summarized, and analytical representation of durability as random variable by means of the Weilbull distributions is substantiated. Calculations of cutting tool replacement periods for transfer lines illustrate optimization.

CUTTING FLUIDS

SYNOPSIS. A new type of cutting fluid is essential to achieving utilisation of the full potential of Automated Machining (AM). Coolant capabilities frequently determine the scope of multi‐tool machining applications. Identifying operational needs and overcoming AM system constraints has provided a unique opportunity to develop a new synthetic cutting fluid technology. A vision for the future is where the expansion of synthetic lubricant technology will continue to contribute significant benefits to an ever‐widening area of manufacturing industry's lubricant requirements.

Flexible automated machining in France: Results of a survey

Abstract This paper presents the findings of a survey concerning the flexible automation of machining processes in France. Three questions are dealt with. The first question concerns the extent to which flexible automated machining systems have been introduced in French industry. The second question concerns the reasons behind the introduction of these systems. To be more precise, the aims of the industrialists are examined in the light of the dual nature of the expression “flexible automation”. Has there been a strategic change in relation to the past trends and a real drive for greater flexibility (in what form?) or, on the contrary, has the aim been to develop automation processes? The third part describes the main technical characteristics of the equipment that has been surveyed. The beginnings of an approach to the measurement of the degree of flexibility of equipment is also proposed.

Detection of the onset of chatter vibration

In a flexible manufacturing system or a fully automated machining system, the computer control system of the machine tools must be able to recognize and control the cutting states, particularly the unwanted ones. Chatter vibration being one of them, its onset needs to be detected. Although a lot of research work has been carried out concerning the chatter of a machine-tool-work system, the exact definition of a chatter threshold has not yet been dealt with adequately. In addition, the need to establish a dynamic performance test procedure for machine tools is of increasing urgency, in which the determination of the chatter threshold is alsoof importance. A method to determine the chatter threshold very precisely is proposed in this paper. It has been found that the chatter onset can be easily detected through the in-process measurement of the horizontal deflection of the workpiece and a comparison of this method with other available ones has proved its superiority.

Mathematical model to predict the system reliability of tooling for automated machining systems

SUMMARY This paper outlines the development of a mathematical model for predicting the system reliability of the cutting tools for an automated machining system with various carbide inserts and spares subject to Weibull failures. A numerical method using Simpson's Rule was selected as a method to address the problem of multiple integration resulting from the Weibull distribution in the spares model. A recursive algorithm was developed for predicting the system reliability of the cutting tools. This paper demonstrates the application of the developed reliability prediction model with a realistic example in the interrupted cutting process.

Monitoring system for cutting tool failure using acoustic emission sensor.

Failure of a cutting tool is one of the largest troubles in the automated machining system. Therefore several methods have been proposed, so far to detect the cutting tool failure. However, most of them, have some problems from the viewpoint of the practical application. In this study, an acoustic emission sensor is used to detect the cutting tool failure, and a monitoring system which has high reliability is proposed. Failures of the single-point as well as multipoint cutting tool are successfully detected with the monitoring system developed in this study.

A tool-change scheduling model for machining centres

Robert P. Davis, Richard A. Wysk and Delbert L. Kimbler Department of lndustrial Enghzeering and Operations Research, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, 24061, USA (Received October 19 78; revised January 19 79) Introduction Because of the increased cost of direct labour, as well as the shortage of competent machinists, the metal cutting industry is looking toward automation as a means to improve its stagnating productivity. Since 1950, the metal machining industry has seen the advent of Numerical Control (NC), Direct Numerical Control (DNC), Computer Numerical Control (CNC), and Computer Integrated Manu- facturing Systems (CIMS). NC essentially eliminated the machinist from metal cutting. DNC and CNC facilitated part programming and increased control over NC machines. And finally, CIMS integrated material handling and machin- ing under the control of a common central computer. Today, CIMS exist where all of the machining and material handling is done under the control of a single computer (or under the control of a network of computers), and the system is virtually devoid of expensive direct labour. 1,2 The use of automation, however, has brought about some difficult analytical problems. Many problems formerly resolved by a machinist's experience and intuition, coupled with his adaptive interpretation of the system, must now be resolved by means of a static control strategy. A par- ticular example of this situation is that of the toot-changing cycle. In a Conventional machining system, the machine operator decided when a particular tool should be changed based on the accuracy of the last part produced, the sound produced by the metal cutting operation, and the number of parts which were left to be machined. The accuracy of the last part and the sound produced in the metal cutting operation are indicators of the extent of tool wear. The queue of parts waiting for a particular tool is viewed to determine the maximum wear rate which will allow tool replacement after the batch is completed. In today's more modern m~chining systems, an operator is seldom solely responsible for the monitoring of a single machine tool. This would be especially true for DNC, CNC and CIMS and may also be true of stand-alone NC. Because an operator is not present to monitor and 'adaptively control' the machine, a mathematical formulation of the problem is required in order to develop algorithms for the efficient operation of automated machining systems. Several models have been developed for the selection of the optimum machining parameters: feed, speed and depth of cut. 3-s All of these models employ a functional relationship between the machining parameters and 'expected tool life'. The most commonly used expression for tool life is one developed by F. Taylor 6 in 1907. Taylor's tool life equation has been expanded to include several variables, such as workpiece hardness, tool approach angle, slenderness ratio, etc. However, for a given tool and workpiece, tool life can most simply be expressed as: C T L = Vaf#d ~ where:

A Proposal of the Multilayered Control of Machine Tools for Fully Automated Machining Operations

To realize the fully automated machining system, a control system for turning operation has been built based on the concept of multilayered hierarchical system. On the first layer, the cutting torque, the vibration of tool and vrork-piece, and the power consumption are monitored in-process. The pattern of tool wear is also examined with a TV camera post-process. Cutting variables, such as feed rate and cutting speed are controlled for getting the minimum machining cost under predetermined constraints. On the second layer the parameters involved in the machining economy are modified with the results gathered in the turning operations. When any unfavorable cutting state is observed on the third layer, the tool material or tool geometry is changed according to the rules which are obtained by self-organizing process from the cutting data gathered in previous cutting.