Tool life

The domain of life planning and personal development includes the important techniques of values clarification, strengths identification, goal setting and action planning. In the past two decades practices such as life coaching have grown in popularity (Green, Oades & Grant, 2006). Moreover, in mental health contexts, the recovery movement has challenged the illness and deficit focus (Andresen, Caputi, Oades, 2006;

An optimum experimental design to determine the coefficients of the Extended Taylor's Equation in machining is proposed. The technique is based on the minimisation of the ratio between maximum and minimum singular values of the matrix of sensitivity of the tool life related to the machining parameter variations. This procedure generates the best set of cutting conditions to be used in tool life tests which results in a fast convergence of the coefficients and their confidence intervals. This technique was compared to the commonly used fractional factorial design when face milling AISI 1045 steel with cemented carbide cutting tools. The results showed a considerable reduction in the number of tests required to obtain a reliable equation when the optimum experimental procedure was used when compared to the factorial design.

This paper utilizes models for cumulative tool wear to study the effect of cutting fluid on the machinability of aluminum-based matrix composites reinforced with SiC or AI20~ particles. Pressurized cuttin~ fluid neither improves nor worsens the tool life because of either effective flushing of the chips or lack of a lubricating film. The surface finish and the cutting forces are insensitive to cutting fluid and cutting speed when machining with a new diamond tool, but deteriorate with greater tool wear. © 1997 Published by Elsevier Science S.A.

This paper presents a study for the development of first- and second-order tool-life models at 95% confidence level for turning high strength steel. The tool-life models are developed in terms of cutting speed, feed rate, and depth of cut, using response surface methodology and design of experiment. The effects of the main cutting variables (cutting speed, feed, and depth of cut) on tool life have been investigated by the application of the factorial design method. All of the cutting tests were performed using uncoated carbide tools under dry conditions. Tool-life contours have been generated from these model equations and are shown in different plots. Dual-response contours of metal removal rate and tool life are shown also. The results are presented in terms of mean values and confidence levels. © 1998 Elsevier Science S.A. All rights reserved.

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Tool condition monitoring (TCM) systems employed in industry are mostly used to detect tool fracture, although the prevention of it should be the principal aim. This would not only allow for the avoidance of any fracture-related damage to both the workpiece and machine tool, but also for recondition the tool for further use.

Industries and researchers are trying to reduce the use of coolant lubricant fluids in metal cutting to obtain safety, environmental and economical benefits. The aim of this research is to determine if the minimal quantity lubrication (MQL) technique in turning gives some advantages in terms of tool wear reduction. This paper reports the results obtained from turning tests and SEM analysis of tools, at two feed rates and two cutting lengths, using MQL on the rake and flank of the tool. The results obtained show that when MQL is applied to the tool rake, tool life is generally no different from dry conditions, but MQL applied to the tool flank can increase tool life.

Machining of titanium at high cutting speeds such as from 4 m/s to 8 m/s is very challenging. In this paper, a new generation of driven rotary lathe tool was developed for high-speed machining of a titanium alloy, Ti-6Al-4V. The rotary tool was designed and fabricated based on the requirements of compact structure, sufficient stiffness and minimal edge runout. Cylindrical turning experiments were conducted using the driven rotary tool (DRT) and a stationary cutting tool with the same insert, for comparison in the high-speed machining of Ti-6Al-4V. The results showed that the DRT can significantly increase tool life. Increase in tool life of more than 60 times was achieved under certain conditions. The effects of the rotational speed of the insert were also investigated experimentally. Cutting forces were found to decline slightly with increase of the rotational speed. Tool wear appears to increase with the rotational speed in a certain speed range. 

In cold forging of outer races for constant velocity joints tool loads during the backward extrusion operation lead to very high loading conditions in the tool inserts. Fatigue cracking is the common failure mode that ends the service life of the tooling.

This paper presents an alternative hybrid approach, combining response surface methodology (RSM) and principal component analysis (PCA) to optimize multiple correlated responses in a turning process. Since a great number of manufacturing processes present sets of correlated responses, this approach could be extended to many applications. As a case study, the turning process of the AISI 52100 hardened steel is examined considering three input factors: cutting speed (V c ), feed rate (f) and depth of cut (d). The outputs considered were: the mixed ceramic tool life (T), processing cost per piece (K p ), cutting time (C t ), the total turning cycle time (T t ), surface roughness (R a ) and the material removing rate (MRR). The aggregation of these targets into a single objective function is conducted using the score of the first principal component (PC 1 ) of the responses' correlation matrix and the experimental region (Ω) is used as the main constraint of the problem. Considering that the first principal component cannot be enough to represent the original data set, a complementary constraint defined in terms of the second principal component score (PC 2 ) is added. The original responses have the same weights and the multivariate optimization lead to the maximization of MRR while minimize the other outputs. The kind of optimization assumed by the multivariate objective function can be established examining the eigenvectors of the correlation matrix formed with the original outputs. The results indicate that the multiresponse optimization is achieved at a cutting speed of 238 m/min, with a feed rate of 0.08 mm/rev and at a depth of cut of 0.32 mm.

Hardened steel turning has received special attention in recent years due to its many applications in modern industries. The characteristics that define its machinability-expressed in terms of multiple response problems-are usually represented by experimental model building strategies like response surface methodology (RSM). Such strategies, however, have a particular drawback when multiple correlated regression functions are present. The optimization of multiple process characteristics without considering the variance-covariance structure among the responses may lead to an inadequate optimum. To deal with this constraint, this paper presents a novel multiobjective optimization method; it correctly focuses the multiple correlated characteristics of the AISI 52100 hardened steel, based on the concept of multivariate mean square error. This novel approach combines principal component analysis with RSM focusing a multidimensional nominal-the-best problem. In this kind of optimization, all the characteristics (tool life, cutting time, cost, material removal rate, and surface roughness) have a specific target while maintaining a strong correlation structure. Transforming the original responses and respective targets to the plane of a multivariate principal component scores, an optimization routine is capable of finding out a compromise solution that attends all the established targets. The following AISI 52100 turning process variables were considered in this study: cutting speed, feed rate, and depth of cut. Theoretical and experimental results were convergent and confirmed in a case study. Keywords Hard turning . Multivariate mean square error (MMSE) . Response surface methodology (RSM) . Principal component analysis (PCA) Int

Tool performance of conventional tools is poor and a major constraint when used in milling titanium alloys at elevated cutting speeds. At these high cutting speeds, the chemical and mechanical properties of Ti6Al4V cause complex wear mechanisms. In this paper, a fine-grain polycrystalline diamond (PCD) end mill tool was tested, and its wear behavior was studied. The performance of the PCD tool has been investigated in terms of tool life, cutting forces, and surface roughness. The PCD tool yielded longer tool life than a coated carbide tool at cutting speeds above 100 m/min. A slower wear progression was found with an increase in cutting speeds, whereas the norm is an exponential increase in tool wear at elevated speeds. Observations based on scanning electron microscope (SEM) and energy dispersive spectroscopy (EDAX) analysis suggest that adhesion of the workpiece is the wear main type, after which degradation of the tools accelerates probable due to the combined effect of high temperature degradation coupled with abrasion.

The eternal goal achieving optimum gear manufacturing results in a quick and flexible way can be obtained by efficient machine tools and thorough processes know how. Gear manufacturing is associated with complicated generating kinematics, chip formation and tool wear mechanisms. To capture quantitatively the tool wear progress and the cutting loads, empirical, analytical, numerical as well as FEM-based methods describing the chip geometry and predicting the tool life and cutting forces have been developed. The application of innovative tool materials and coatings, optimized tool geometries and appropriate conduct of reconditioning procedures contribute to the significant reducing of the manufacturing cost.

In this study, tool life performance of multilayer hard coatings was evaluated for machining of nodular cast iron. With this regard, TiCN+TiC+TiCN+Al 2 O 3 +TiN and TiCN+TiC+TiCN+Al 2 O 3 +TiN multilayered coatings with different thicknesses were fabricated on WC substrates using high temperature chemical vapor deposition (HTCVD). These cutting tools with hard multilayered coating systems were used in longitudinal turning of nodular cast iron under cutting condition encountered in the shop floor. To investigate the tool life performance in cutting tools coated by HTCVD method, cutting experiments were performed in CNC turning bench by using three distinct cutting tools having multilayered hard coatings and WC insert with square edges, and two types of nodular cast irons. Cutting speed, depth of cutting, and feed rate were kept as constant values. Tool life based on flank wear was the parameters considered to compare the three cutting tools. It was found that TiCN+TiC+TiCN+Al 2 O 3 +TiN (T3) multilayer coating with 10.5 lm thick exhibited better performance according to all parameters.

Titanium alloys have been widely used in the aerospace, biomedical and automotive industries because of their good strength-to-weight ratio and superior corrosion resistance. However, it is very difficult to machine them due to their poor machinability. When machining titanium alloys with conventional tools, the tool wear rate progresses rapidly, and it is generally difficult to achieve a cutting speed of over 60 m/min. Other types of tool materials, including ceramic, diamond, and cubic boron nitride (CBN), are highly reactive with titanium alloys at higher temperature. However, binder-less CBN (BCBN) tools, which do not have any binder, sintering agent or catalyst, have a remarkably longer tool life than conventional CBN inserts even at high cutting speeds. In order to get deeper understanding of high speed machining (HSM) of titanium alloys, the generation of mathematical models is essential. The models are also needed to predict the machining parameters for HSM. This paper aims to give an overview of recent developments in machining and HSM of titanium alloys, geometrical modeling of HSM, and cutting force models for HSM of titanium alloys.

In Southwest Asia, sickle blades first appear early in the sequence of the transition to agriculture. In the past, detailed qualitative research on silica bearing blade stone tools focus on the characterization of usewear traces such as polish types and accrual rates. In this paper we approach the study of sickle blades slightly different, choosing to examine tool life-history by developing a method to quantitatively estimate harvesting intensity. The method centers on an experiment of cutting cereal stalks and measuring stone blade edge thickness under a scanning electron microscope as a proxy for cutting time. We end with regressing the experimental results to provide an estimation of how intensively archaeological sickle blades recovered from the site of Dhra', Jordan were used for harvesting. The results, while preliminary, enable an initial interpretation of sickle blades as important tools with long use-life histories during the early Neolithic in the Southern Levant.

In the present investigation it is shown how the tool life of heavily loaded cold-forging dies can be predicted. Low-cycle fatigue and fatigue crack growth testing of the tool materials are used in combination with ®nite element modelling to obtain predictions of tool lives. In the models the number of forming cycles is calculated ®rst to crack initiation and then during crack growth to fatal failure. An investigation of a critical die insert in an industrial cold-forging tool as regards the in¯uence of notch radius, the amount and method of pre-stressing and the selected tool material is reported. # 1999 Elsevier Science S.A. All rights reserved. (P. Skov-Hansen) 0924-0136/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 4 -0 1 3 6 ( 9 9 ) 0 0 3 1 9 -2

The fatigue and wear behaviour of PVD coatings on cemented carbide inserts with various cutting edge radii are investigated experimentally and analytically in milling. The inserts with cutting edge radii from 8 up to 35 µm were manufactured by honing and micro-blasting. The tool wear progress was depicted through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) microspectral analysis. The Finite Elements Method (FEM) simulation of the contact between the tool and the workpiece highlights the effect of the cutting edge radius on the first coating fracture and the further wear development. The wear behaviour of the cutting edge radii manufactured by honing, in comparison to the corresponding ones by means of micro-blasting, is significantly enhanced, whereas the cutting edge radius increasing can lead to a higher tool life.

In Southwest Asia, sickle blades first appear early in the sequence of the transition to agriculture. In the past, detailed qualitative research on silica bearing blade stone tools focus on the characterization of use-wear traces such as polish types and accrual rates. In this paper we approach the study of sickle blades slightly different, choosing to examine tool life-history by developing a method to quantitatively estimate harvesting intensity. The method centers on an experiment of cutting cereal stalks and measuring stone blade edge thickness under a scanning electron microscope as a proxy for cutting time. We end with regressing the experimental results to provide an estimation of how intensively archaeological sickle blades recovered from the site of Dhra’, Jordan were used for harvesting. The results, while preliminary, enable an initial interpretation of sickle blades as important tools with long use-life histories during the early Neolithic in the Southern Levant.

The paper initially reviews prior work on the influence of operating parameters on tool life when milling Inconel 718. Following this review, experimental work is described which evaluates the effect of varying feed rate/chip thickness, immersion ratio (radial depth of cut), tool material and geometry on the tool life, tool wear and productivity obtained when end milling Inconel 718.

With a significant progress achieved both in new cutting materials and in machine tool design, the weakest link in the machining system is, in many cases, the tooling structure serving as an interface between the cutting insert and the machine tool. lnadequacy of the tooling structure results in excessive static deflections limiting the achievable accuracy, and in forced and self-excited vibrations limiting the cutting regimes and surface finish of the machined surface. In order to advance the tooling structures' technology, it is important to assess the state of the art, keeping in mind that the majority of publications on the subject is not in English. This paper provides a worldwide analytical survey on six important subjects related to tooling structures: ?) Influence of machining system parameters on tool life and process stability; 2) Stiffness and damping of tools; 3) Tool/toolholder interfaces (tool clamping devices); 4) Modular tooling; 5) Tool-machine interfaces; 6) Tool balancing for high speed machine tools Keywords: tooling; stiffness; damping; t tHTRUWTtOH tool and the workpiece. it was suggested by W a l k , e t a/ (1991) to imptmt into the cutting surface atoms o f elements CI, Br, I, S, In, Ga, Sn. These elements are routinely used in lubricoo[ant fluids, especially for machining titanium alloys. tubricootants containing these etements sometimes cause corrosion, but their implantation to the depth of about 0.4 pm resutts M reduced friction and cutting forces and increased t o d life, without degrading the surface finish. A similar technique proposed by Pleshivtsev, et a1 (1994) results in 20 -30 % reduction in friction coefficient of HSS inserts while increasing their life by twotothree times. This implantation is performed by gas ion generators with or without magnetic field. The ion pulse length is 1 -7,500 ms, pulse energy 10 -80 Kev, and current t -60 A. 592 Keynote Papers tntroductton of uttra-high pressure (70 -280 MPa) wafer info the cuffing zone reduces the axial cuffing fmee by 5ooh while impwing 0 t h machining parameters, Mazclrkievfcz (7992). Even higher pressures, up to 380 MPa, were sumessftltty used by Cornier (1992).

The cooling applications in machining operations play a very important role and many operations cannot be carried out efficiently without cooling. Application of a coolant in a cutting process can increase tool life and dimensional accuracy, decrease cutting temperatures, surface roughness and the amount of power consumed in a metal cutting process and thus improve the productivity. In this review, liquid nitrogen, as a cryogenic coolant, was investigated in detail in terms of application methods in material removal operations and its effects on cutting tool and workpiece material properties, cutting temperature, tool wear/life, surface roughness and dimensional deviation, friction and cutting forces. As a result, cryogenic cooling has been determined as one of the most favourable method for material cutting operations due to being capable of considerable improvement in tool life and surface finish through reduction in tool wear through control of machining temperature desirably at the cutting zone. r

In the industry, only rotary dynamometers can be used for monitoring when multiple spindles are used in machining operations. The current commercial rotary dynamometers are bulky and expensive for most machining centers. The basic hardware and computational tools proposed are for a smaller, more cost effective Torque-based Machining Monitor (TbMM). The objective of the TbMM concept is to estimate the remaining tool life, detect chatter from the torque signal inside the proposed device, and communicate with the central computer only when problems arise. The remaining tool life estimation and chatter detection algorithms of the TbMM were developed by analyzing the experimental data collected by a commercial rotary dynamometer. The mechanical hardware of the TbMM was designed to generate voltage proportional to the cutting torque using a piezoelectric composite element. The remaining tool life was estimated from the standard deviation (or variance) of the torque signal. Teager-Kaiser algorithm (TKA) based procedure detected the chatter based on the frequency estimations only from four samples at a time. The accuracy and characteristics of the signal of the mechanical component of the TbMM were found satisfactory in the estimation of machining problems such as wear and chatter. The TbMM is a good choice particularly when multiple spindles work simultaneously on the same workpiece.

The production cost for cold forgings depends signi®cantly on the tool life. This paper summarizes an investigation of different alternatives to improve the life of a tungsten carbide insert used in a cold forming operation performed on an automatic cold header. These alternatives were as follows: (a) double tapered insert, (b) split insert design, and (c) change of insert material. Although, the techniques were applied to a speci®c case, they might he applicable to other cold forging tooling. To improve the life of the insert, the metal¯ow and stress analysis of the carbide insert was conducted using the commercial FEM software DEFORM. # 2000 Elsevier Science S.A. All rights reserved.

This paper presents a study of tool life, surface finish and vibration while machining nodular cast iron using ceramic tool. A series of cutting tests have been carried out to verify the change in surface finish of the workpiece due to increasing tool wear. The tests have been done under various combinations of speed, feed and depth of cut. The effects of vibration on the flank wear both in the direction of main cutting force and radial cutting force have been investigated. The vibration was measured using two accelerometers attached to the tool holder and the parameters used to make the correlation with surface roughness were the amplitude and acceleration of the signals.

This paper describes hard machining which offers many potential benefits over traditional manufacturing techniques. In this work, investigations were carried out on end milling of hardened tool steel DIEVAR (hardness 50 HRC), a newly developed tool steel material used by tool- and die-making industries. The objective of the present investigation was to study the performance characteristics of machining parameters such as cutting speed, feed, depth of cut and width of cut with due consideration to multiple responses, i.e. volume of material removed, tool wear, tool life and surface finish. Performance evaluation of physical vapour deposition-coated carbide inserts, ball end mill cutter and polycrystalline cubic boron nitride inserts (PCBN) was done for rough and finish machining on the basis of flank wear, tool life, volume of material removed, surface roughness and chip formation. It has been observed from investigations that chipping, diffusion and adhesion were active tool wear mechanisms and saw-toothed chips were formed whilst machining DIEVAR hard steel. PCBN inserts give an excellent performance in terms of tool life and surface finish in comparison with carbide-coated inserts. End milling technique using PCBN inserts could be a viable alternative to grinding in comparison to ball end mill cutter in terms of surface finish and tool life.

In machining processes, a major quality related output is integrity of the machined part surface. In machining of difficult-to-cut materials, a drastic decrease in tool-life makes the machining process even more difficult. By considering the broader perspective of the machining system tailored towards sustainable operations, in this work an alternative-cryogenic machining is evaluated for machining performance. The surface integrity characteristics of machined surface as a function of depth have been analyzed for different combinations of cooling/lubrication machining conditions. The residual stresses on the machined surface and sub-surface, surface hardness, and surface roughness are among the significant characteristics studied in this work. The results show that cryogenic machining processes can be implemented to improve all major surface integrity characteristics, thus improving the final product quality level.

One of the main goals of the metal-mechanical industries is the reduction of the production costs through the productivity increase. In the attempt to reach this goals, many researchers have been used the hot machining method. This method consists, basically, in the heating of the work piece hundreds of degrees Celsius above room temperature with aid of an external source of heat. Thus, the reduction of the shear stress of the material of the piece is gotten and, hence, is possible to obtain a smaller wear of cutting tool in relation to the conventional machining. This paper presents a review of hot machining, where the different techniques are presented together their results. This review paper presents a survey on variation in process parameter i.e. temperature, cutting speed, feed etc. and their effect on surface roughness, hardness, material removal rate, tool wear, tool life.

Gear hobbing remains a cutting technology where high speed steels continue to find wide applications in modern manufacturing practice. The improvements in hobbing tool design are problematic due to the very long duration of wear tests. The application of an analogy process called 'fly hobbing' has been developed on a five-axes milling machine so as to improve the productivity of the investigations. This process has been used to investigate the influence of the cutting edge preparation on the wear resistance of gear hobs made of PM-HSS in the context of dry high-speed manufacturing. An original edge preparation procedure, based on the abrasive flow machining technology, has revealed a great improvement of the tool life.

Machining processes such as milling, which are characterized by interrupted cutting, are often susceptible to problems involving vibration of the machine-tool-workpiece fixation device system because of the proximity between their natural frequency harmonics and the frequency of tool entry on the workpiece. This phenomenon is particularly important in the milling of titanium alloys, because these materials show a low Young modulus, and hence, an extended elastic behavior, which means tremendous variations in chip thickness and fluctuating cutting forces. Moreover, very low heat conductivity causes the formation of serrated chips, which further increase the fluctuation in cutting forces. The purpose of this work is to study the influence of the tool entering angle on the stability of the process and on tool life based on a time and frequency domain analysis of the cutting forces. The results show that lower entering angles may provide stabler cutting, as indicated by the regular tool wear instead of the microchipping resulting from the use of a higher value of this angle. Although cutting forces are larger at lower entering angles, the tool life is much longer, since most of this load is associated with low frequencies, at which the tool behaves like a rigid body.

The fatigue and wear behavior of PVD coatings on cemented carbide substrates in milling are investigated experimentally and Ž . analytically through Finite Elements Method FEM simulation of the cutting process. Cutting inserts with different cutting edge radii and at various feedrates were examined. The initiation and progress of the tool failure is depicted through Scanning Ž . Electron Microscopy SEM and Energy Dispersive X-ray microspectral investigations of the used cutting edges. The FEM simulation of the contact between the tool and the workpiece enables a quantitative description of the influence of mechanical stress components on the coating fatigue failure. Hereby critical coating fatigue stresses determined by means of the impact test were considered. The experimental and computational results exhibit quantitatively the effect of tool radius and feed rate on the coating fatigue failure as well as on the overall cutting performance for various substrates and film structures. In order to utilize the superior characteristics of coatings towards improving the cutting performance, it is highly recommended to optimize the cutting insert wedge radius, as well as the cutting conditions. Herewith a premature coating failure and a consequent rapid wear development can be prevented. ᮊ

The cooling applications in machining operations play a very important role and many operations cannot be carried out efficiently without cooling. Application of a coolant in a cutting process can increase tool life and dimensional accuracy, decrease cutting temperatures, surface roughness and the amount of power consumed in a metal cutting process and thus improve the productivity. In this review, liquid nitrogen, as a cryogenic coolant, was investigated in detail in terms of application methods in material removal operations and its effects on cutting tool and workpiece material properties, cutting temperature, tool wear/life, surface roughness and dimensional deviation, friction and cutting forces. As a result, cryogenic cooling has been determined as one of the most favourable method for material cutting operations due to being capable of considerable improvement in tool life and surface finish through reduction in tool wear through control of machining temperature desirably at the cutting zone. r

Coating technology is one means of achieving a crucial enhancement in tool performance, especially in hobs that were among the first tools to be coated on a large scale. Nevertheless only few detailed analysis of wear mechanism have been done on field machines. The bifunctional coatings (combination of a tough, hard and refractory coating and of a self lubricating coating possessing a good thermochemical and abrasion resistance but a lower hardness) are very interesting since it is difficult to get a simple coating showing all these characteristics. The use of bilayer coatings raises several problems especially for dry and high speed cutting. Therefore, in order to investigate the behaviour of these bifunctional coatings, hobs have been coated by physical vapour deposition (PVD) methods. After the elaboration of a procedure for hobs testing, field tests have been performed. Results of tool life tests and investigations on tool wear mechanisms for different coated hobs are presented and discussed. The interesting performance in high speed gear hobbing of sintered high speed steel (HSS) hobs (ASP2052) combined with a (Ti,Al)N + MoS 2 coating is particularly underlined.

Woven carbon fibre composites are extensively used in aerospace, automotive and civil applications. Optimization of high speed drilling of composites is an issue of great economical impact. Tool wear and part quality are central to the definition of the objective function and constraints of the optimization scheme. This paper presents an experimental investigation of the wear mechanisms of tungsten carbide (WC) drills during dry high speed drilling of quasi-isotropic woven graphite fibre epoxy composites. Tool wear was evaluated at spindle speeds of up to 15,000 rpm using a standard two flute drill. The paper examines the nonlinear behavior of this tribo-system and the interdependence of the wear process and cutting forces in relation to surface damage of the system components. It was found that chipping and abrasion were the main mechanisms controlling the deterioration of WC drill. The two friction regimes, the lightly and heavily loaded, were found to dictate the increase in forces, delamination of composite and surface roughness. The aggressive rubbing by fractured graphite fibres and WC grains against the soft epoxy matrix caused high temperature rise and consequently enhanced flank wear. During the primary and secondary wear stages, wear on the flank face of main cutting edges was found to be dominant, while adhesion of carbon was found to occur along with abrasion in the tertiary zone. Tool life results revealed the increase in the delamination and surface roughness with transition from the primary to tertiary wear regime. The correlation between tool wear, delamination damage and surface roughness was established. Finally it was concluded that a tool replacement strategy could be devised by monitoring the cutting forces.

Approximately two-thirds of all the superalloys produced are consumed by the aerospace industry for the manufacture of jet engines and associated components, mainly in the hot end of aircraft engines and land-based turbines. The remaining third of superalloy consumption is used by the chemical, medical and structural industries in applications requiring high temperature properties and/or exceptional corrosion resistance. Ability to retain high mechanical and chemical properties at elevated temperatures make superalloys ideal materials for use in both rotating and stationary components in the hot end of jet engines. These materials as well as structural ceramic and hardened steels pose formidable challenges for cutting tool materials during machining, hence they are referred to as difficult-to-cut. The basic difference between rotary cutting and conventional cutting is the movement of the cutting edge in addition to the main cutting and feed motions. Self-propelled rotary tools (SPRT) employs round inserts rotating continuously about its axis as a result of the driving motion impacted by the cutting force, thus minimising the effect of thermal energy along the entire edge and preventing excessive heating of a particular portion of the insert edge. Major benefits provided by SPRT include several hundred-fold increase in tool life, lower cutting temperature, higher metal removal rate, generation of fine surface finishes due to the circular cutting edge and improved machinability of difficult-to-cut materials such as nickel and titanium base alloys. Extremely low rate of flank wear can be obtained when machining aerospace superalloys, particularly titanium alloys, even at higher speed conditions with very negligible or no effect on the machined surfaces. This paper will provide an overview of developments in rotary tools, the principles of rotary cutting, structure and design of SPRT, factors influencing rotary tool life and detail information of practical machining data as well as analysis of tool failure modes and tool wear mechanisms in comparison to conventional (fixed tool) machining technique.

Traditional tool life models do not take into account the variation inherent in metal cutting processes. As a consequence, the real tool life rarely matches the predicted values. To compensate for this uncertainty, tools are usually replaced prematurely, which leads to unnecessarily high tool costs. In some cases, however, wear-out occurs earlier than predicted, which imposes a risk of workpiece damage or rework and can lead to other extra charges. To balance these costs, this paper proposes an age replacement model. It is assumed that penalty costs are incurred each time a tool fails before the planned replacement. The probability of such an event is determined from the tool reliability function, which models the wear-out by a mixture of Weibull distributions, while failures due to external stresses are accounted for by a homogeneous Poisson process. The optimal replacement time is then determined from a total time on test (TTT) plot. The adequacy of the proposed approach for practical application is tested and confirmed in a case study on turning of Inconel 718 with cubic boron nitride (CBN) N) tools.

Surface engineering approaches are being increasingly employed for enhancing the effective life of twist drills with a view to reduce machining costs. The electro-spark coating (ESC) technique provides a promising means of depositing wear resistant coatings that can potentially enhance the performance of these tools. However, it is often necessary to also optimize the machining conditions for coated tools to achieve an enhanced tool life. In the present investigation, varying spindle speeds were employed at a fixed vertical feed to evaluate the performance of WC–8Co ESC coated HSS drills in comparison to bare HSS drills. The number of holes drilled before reaching a preset average flank wear (0.5 mm), or catastrophic failure of the drill, was taken as the measure of tool life. The drill flank wear, monitored at regular intervals, as well as the cutting torque and thrust measured for all holes, were considered to be the key criteria for optimizing the cutting conditions. Results indicate that the WC–8Co coated drill tool life can be increased by a factor of more than 5, depending on the machining conditions selected. Furthermore, flank wear of the drill was found to increase rapidly at the end of drill life. Cutting torque data was also found to provide a useful indicator for predicting the end of tool life.

Tool life a b s t r a c t Drilling is one of the most important processes in aerospace manufacture and is often the last operation performed. When combined with the fact that holes amplify any in service stresses a significant demand for high surface integrity and production process security is created. In contrast to other machining processes there are relatively few publications regarding the drilling of nickel-based superalloys.

A comprehensive study and FEM simulation of ball nose end milling on tool wear behavior and chip formation had been performed on Inconel 718 (nickle-based superalloy) under minimum quantity lubricant (MQL) condition. In this paper, the investigation was focusing on the comparison of up-milling and down-milling operations using a multi-layer TiAlN/AlCrN-coated carbide inserts. A various cutting parameters; depth of cut, feed rate and cutting speed were considered during the evaluation. The experimental results showed that down-milling operation has better results in terms of tool wear compared to up-milling operation. Chipping on cutting tool edge responsible to notch wear with prolong machining. It was observed that the chips formed in up-milling operation were segmented and continuous, meanwhile down-milling operation produced discontinuous type of chips.

The application of Computer Aided Engineering and physical modeling techniques in forging R & D continues to increase. In using tools such as Finite Element Modeling and experiments with model materials, the forging tool designer can decrease costs by improving achievable tolerances, increasing tool life, predicting and preventing¯ow defects, and predicting part properties. At the Engineering Research Center for Net Shape Manufacturing, Design Environment for Forming (DEFORM) and DEFORM 3D, and a multiple action press for physical modeling are tools available for forging research and for educational purposes.