Showing papers on "Tool wear published in 1988"

Diffusion wear in milling titanium alloys

Abstract: In this paper, diffusion wear during milling of titanium alloys is reported. In high speed milling, tool wear is mainly caused by diffusion. The wear pattern is characterised by the combined extension of crater wear on the rake face and glacier wear on the flank. Evidence of diffusion of cobalt and carbon at the interface between the milling cutter and the workpiece has been obtained. It was demonstrated for the first time that, as diffusion wear occurred, a carbon rich layer was formed at the tool/workpiece interface while the tool material below the flank wearland was depleted in carbon. Wear occurred as a result of embrittlement and weakening of the tool surface resulting from the diffusion process.MST/674

Modelling machining processes with a view to their optimization and to the adaptive control of metal cutting machine tools

Abstract: This paper describes an orthogonal machining theory which can be used to determine the stresses, temperatures etc involved in chip formation from a knowledge of the work material flow stress and thermal properties and cutting conditions It is shown how these can be used to predict machinability factors such as power consumption, built-up edge range, tool wear rates (tool life) and those cutting conditions which cause plastic deformation of the cutting edge An oblique machining theory which is more representative of practical machining processes than the orthogonal theory is then described, taking into account machining on more than one cutting edge as in bar turning Throughout the paper comparisons are made between predicted and experimental results

An SPC Approach to Compensating a Tool-Wear Process

Abstract: A fixed-interval compensator is proposed for a process where tool wear can be modeled over an interval of tool life by a regression model. The compensator consists of a batch mean adjustment plus the estimated wear since the last adjustment. The expecte..

Cutting tool wear detection apparatus and method

Abstract: Sharp tools have different cutting characteristics from dull or worn tools. Among these differences is that a wear land develops on the cutting tool so that more of the cutting tool comes into contact with the workpiece during the cutting process. The increased contact area between the tool and workpiece forces more energy to be consumed by the cutting machine in making a cut because more energy is expended in non-productive work. Indications of an increase in non-productive work are the increased power or force necessary to operate a spindle in lathes, milling machines, etc., and the increased energy in cutting vibrations in a low frequency range emitted during the cutting process. Another indication of decreased efficiency of the cutting process is the decreased energy in cutting vibrations in a high frequency range emitted during the cutting process. A method and apparatus are described for continuously monitoring a ratio of spindle force or power or low frequency vibration energy to high frequency vibration energy during the cutting process, and generating an output warning signal when the radio reaches a preselected level correlated with excessive tool wear.

EDM sinker cutting of a ceramic particulate composite, SiC-TiB sub 2

Abstract: An experimental investigation of the machinability of the ceramic particulate composite SiC-TiB{sub 2} was conducted using an electrical discharge machine sinker cutting process. Machinability was evaluated in terms of material removal rates, tool wear, wear ratio, and surface finish, using copper and brass electrodes under rapid, medium, and very slow cutting conditions. Copper was found to machine SiC-TiB{sub 2} material faster with less tool wear but with a poorer surface finish than brass. A comparison of the percent of electrode wear in machining of steel to that of SiC-TiB{sub 2} under very slow cutting conditions showed that machining of SiC-TiB{sub 2} is much more efficient than of mild steel.

Factors affecting surface roughness in finish turning of gray cast iron

Abstract: 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.

Tool break/wear detection using a tracking minimum of detected vibrational signal

Abstract: Gradual wear or breakage of a machine tool which occurs over a period of time is detected by sensing high frequency vibrations produced at the cutting tool/workpiece interface during a machining process The high frequency vibrations are converted to a unipolar vibration signal which is processed to produce a tracking signal which tracks the minimum value of the vibration signal The vibration signal is related to the effective cutting energy and it decreases due to gradual tool wear or breakage The tracking minimum signal is compared to a predetermined threshold level to detect excessive wear or breakage of the tool, and an alarm is provided

Acoustic emission monitoring of the cutting process negating the influence of varying conditions

Abstract: Earlier work has shown tool failure monitoring using frequency-based pattern recognition analysis of acoustic emission signals to be feasible while machining under fixed cutting conditions. However, cutting conditions change quite frequently in industrial production, and since AE signals are affected by varying conditions, a model is developed based on Taylor’s expansion using experimental data obtained for various process variables and their output AE spectra, and is used to filter the influence of varying conditions on signal classification. The experimental study involved a fractional factorial experimental design which delineated effects of variables on AE generation during machining. Normalized AE spectra within the 100 to 1000 kHz range were used as system output along with the AE power. While the normalized spectra were found unaffected by changes in the depth of cut, the total AE power was also little affected by the mixed flank and crater wear, and feed rate changes. Using the model and filter designed, performance of the tool wear, chip noise and tool breakage classifier improved to 83, 99, and 97 percent classification, respectively.

The Effects Of Cemented Carbide Binder Composition On Tool Wear Encountered In Surfacing Green Lumber

Abstract: This paper is a summary of work carried out over the past ten years on the wear of cemented carbides during cutting of green wood (Appalachian oak). Experimental evidence is presented showing that tool wear occurs through the preferential removal of the binder through chemical attack by extractives (tannic acid) in the wood followed by mechanical removal of tungsten carbide grains. This occurs when the remaining bond strength between the grains and the binder is no longer sufficient to withstand the action of the shear forces arising from relative motion between the cutting tool, work-piece, and chip. A theoretical model of the wear process based on this evidence is given. Experimental results are presented showing the wear of various cemented carbides under both laboratory (simulated) and actual (field) cutting conditions. The improvement in performance associated with the modification of the composition of the binder predicted from the analysis and measured through (simulated) wear tests agreed well with actual (field) test data. Specifically, a fivefold increase in tool life was obtained through substitution of a chromium/cobalt binder for a standard 6% cobalt binder.

A finite element analysis of temperature in accelerated cutting

Abstract: Temperature attained during machining has significant effects on the properties of tool, chip and workpiece. It governs the parameters like shear angle, cutting force, tool wear, surface finish etc. Review of literature reveals that hardly any information is available about the analytical determination of the tool-chip interface temperature and the temperature distribution during the accelerated cutting. This paper presents the temperature analysis of accelerated cutting (i.e. taper turning and facing) as well as longitudinal turning, using the finite element technique. It has been concluded that the temperature distribution within the tool-chip-work system and the average tool-chip interface temperature for the two classes of machining (viz longitudinal turning and accelerated cutting) are not the same, even though the conditions of machining are identical. Further, the average tool-chip interface temperature is lowest in case of facing and highest in case of longitudinal turning.

Tool wear monitoring and breakage detection based on intelligent filtering

Abstract: Several physical quantities can be used for indirect tool wear monitoring and breakage detection. Cutting forces are appropriate, since they determine the suitability of a tool for cutting. However, disturbances make the accurate and fast tool condition monitoring based upon force analysis difficult. To eliminate disturbances averaging or filtering within a predetermined bandwidth has often been applied. A new method of decomposing the force signal into components having close relationships with physical phenomena taking place during cutting is presented. The term “intelligent filtering” denotes decomposition based on on-line identification of model(s) of the cutting process. Application of “intelligent filtering” for the milling process with two cutting insert tools is discussed.

Tool wear prediction and economics in machining stepped parts

Abstract: For analysing economics of machining cylindrical stepped parts, tool life must be predicted. In this paper, tool life tests, to obtain tool life changing cutting speed before the tool reaches tool life criterion under a constant speed, are performed and the tool life is calculated. Using the results of the calculations machining economics of various forms of stepped parts for the constant spindle rpm method and the constant cutting speed method, are analysed.

Method of designing a turn broach

Abstract: An improved cutting tooth configuration in which, unlike the conventional, straight line tool pattern with its constant tool rise, each tooth is incrementally advanced relative to the prior tooth by an amount that progressively decreases. This accounts for the variations in reaction force on the cutting teeth caused by workpiece deflections, so that the net thickness of material removed by each cutting tooth remains relatively constant. Instability and variation in the cutting force is thereby avoided, and tool wear is decreased.

An Adaptive Observer for On-Line Tool Wear Estimation in Turning - Part I: Theory

Abstract: On-line sensing of tool wear has been a long-standing goal of the manufacturing engineering community. In the absence of any reliable on-line tool wear sensors, a new model-based approach for tool wear estimation has been proposed. This approach is an adaptive observer, based on force measurement, which us both parameter and state estimation techniques. The adaptive observer is based upon a dynamic state model of tool wear in turning. This paper (Part I) presents the model, and explains its use as the basis for the adaptive observer design. This model uses flank wear and crater wear as state variables, feed as the input, and the cutting force as the output. The suitability of the model as the basis for adaptive observation is also verified. The implementation of the adaptive observer requires the design of a state observer and a parameter estimator. To obtain the model parameters for tuning the adaptive observer procedures for linearisation of the nonlinear model are specified. The implementation of the adaptive observer in turning and experimental results are presented in a companion paper (Part II).

Cutting force characteristics in finish machining of hardened steel.

Abstract: The characteristics are investigated experimentally for the purpose of detecting tool wear and fracture by variations in cutting force. In this experiment, hardened steel (JIS SKD 11) is turned with a ceramic tool under finish machining condition. The main results obtained are as follows. (1) The influences of the shape of cutting edge and cutting condition on cutting force are clarified. (2) The ratio of radial force to feed force increases linearly with respect to tool flank wear width (VB). (3) When plastic deformation of cutting edge precedes fracture occurrence, the occurrence can be predicted by the increase in radial or feed force caused by the deformation.

Tool Monitoring by Acoustic Emission during Machining

Abstract: Tool breakage has been successfully detected by Acoustic Emission in turning, milling, drilling. A new adaptive system has been developed and validated in industrial conditions. Tool wear is a slow evolving phenomenon. Acoustic Emission includes information on cutting conditions and tool wear is one parameter of cutting conditions. Presently, no general relationship between Acoustic Emission parameters and tool wear has been derived. However, experimental results show that Acoustic Emission could be used to monitor the type of chips (continuous or discontinuous) and to study the cutting processes.

Aluminum alloy reduced in tool wear loss and excellent in resistance to wear and corrosion

Abstract: PURPOSE:To provide an Al alloy having superior wear resistance and corrosion resistance and reduced in tool wear loss, by incorporating specific amounts of Ni, Si, Fe, etc., to an Al-Mg-base alloy. CONSTITUTION:The alloy has a composition consisting of, by weight, 3.0-5.0% Mg, 0.6-3.0% Ni, 0.1-0.5% Si, 0.1-0.7% Fe, and the balance Al with impurities, and further, 0.05-1.0% Mn and 0.05-0.5% Cr are incorporated to the above composition, is necessary. In this composition, Ni, Si, and Fe form fine and hard compounds of Al-Ni, Al-Ni-Fe, Al-Si-Fe, etc., in the alloy. Due to its excellent resistance to wear and corrosion, this Al alloy is suitable for use in rotary sliding members for video tape recorder, VTR cylinder, etc., brake disks, piston members, etc.

In-process Detection of Tool Wear and Breakage by Autocorrelation Coefficient of Dynamic Cutting Force in Turning

Abstract: Automatic in-process detection of cutting tool wear and breakage is an important capability required in unmanned machining. This paper presents an indirect method of in-process detecting tool wear and breakage using autocorrelation coefficient p(r) of dynamic cutting force in turning. A new cutting force measuring system, used to measure 3-component static and dynamic cutting forces in the experiment, is introduced in this paper. Composed of a new kind of strain gauge machinetool dynamomter and a new amplifier, etc, this new cutting force measuring system possesses very good dynamic performance. With this system and autocorrelation coefficient calculation, the relationships between autocorrelation coefficient and wear, or breakage are found. A strategy for in-process detection of tool wear and breakage is proposed.

Adaptive Observer for Optimal Control of Lathe Tool Wear

Abstract: Lathe turning is a single point cutting process, thus the cutting edge of the tool is not accessible for direct tool wear measurement. A variety of indirect in-process measurements have been proposed and/or tested in laboratories, but none have found practical application. A new approach to in-process tool wear sensing is described in this paper. It employs an observable, control-oriented state space model having a six-variable state vector. Four state variables are measureable by practical means, but the other two are tool wear characteristics that cannot be directly measured. In past work, the operation of a linear observer for tool wear was verified by simulation. This paper describes an adaptive observer that reduces the dependence on knowledge of plant parameters. Its operation is being verified by simulation. The results of the simulation will permit the development of requirements for practical application in the adaptive control of lathes.

Modeling and measurement of wear of coated and uncoated high speed steel end mills

Abstract: A research program was conducted to study tool wear on uncoated and coated (with TiN) high speed steel (HSS) for fluted end mill cutters. These cutters were used to machine AISI 4340 steel at axial and radial engagements of 12.7 mm (0.5 in.). All the machining was carried out using production conditions with the process periodically interrupted to carefully measure the wear condition of the cutting tool. Cutting conditions were carefully chosen so that a linear wear model for the useful life of the cutting tool could be statistically tested. One phase of testing used uncoated tools from 30 different suppliers and the nonstationary linear wear model provided a stochastic representation to determine tool quality using reliability and economic measures. Another phase used the coated tools and a stationary linear wear model to relate force, power, specific cutting energy, and mechanistic model parameters to service life measures. The cutters from each of these phases were carefully examined using optical and scanning electron microscopes so that the dominant wear mechanisms could be identified.

A New Rapid Wear Test for Cutting Tools

Abstract: The paper discribes a new rapid wear test for use in the assessment of cutting tool performance. Tool wear readings at each of the several cutting speeds are taken from different periods of tool life using the same cutting edge until the wear criterion is reached. The differences between the previously presented rapid vear tests and the new one are that (1) the calculation of the tool life in the new test takes the whole wearing process into account and (2) whether the Taylor’s equation is valid or not the new method is applicable.