Tool Failure Modes Research Articles

Evaluation of wear mechanisms of coated carbide tools when face milling titanium alloy

In this paper, the performance and the wear mechanisms of coated carbide tools have been investigated when face milling titanium alloy, Ti–6Al–4V. The two tools used were PVD–TiN and CVD–TiCN + Al 2O 3 coated. Tool life, tool failure modes and wear mechanisms were examined for various cutting conditions. Both tools experienced long tool life at the low cutting speed of 55 m/min and feed of 0.1 mm per tooth. When considering the volume of material removed and tool lives, the CVD coated tools gave a better performance than the PVD coated tools. Excessive chipping at the cutting edge and chipping and/or flaking on the rake face were the dominant failure modes under most cutting conditions. Analysis carried out with the SEM suggests that coating delamination, adhesion of work material, attrition, diffusion, plastic deformation and thermal cracks were the operating wear mechanisms of the coated tools.

High-speed five-axis milling of hardened tool steel

This paper investigates critical issues related to high-speed five-axis milling of hardened D2 tool steel (hardness HRc 63). A forging die cavity was designed to represent the typical features in dies and molds and to simulate several effects resulting from complex tool path generation. Cutting tool materials used were coated carbide for the roughing and semi-finishing processes and polycrystalline cubic boron nitride (PCBN) for the finishing process. The effects of complex tool paths on several critical machining issues such as chip morphology, cutting forces, tool wear mechanisms, tool life and surface integrity were also investigated. The main tool failure mode was chipping due to the machine tool dynamics. A five-axis analytical force model that includes the cutter location (CL) data file for computing the chip load has been developed. The effect of instantaneous tilt angle variation on the forces was also included. Verification of the force model has been performed and adopted as a basis for explaining the difficulties involved with high-speed five-axis milling of D2 tool steel.

Wear of Coated Carbide Tools When Machining Nickel (Inconel 718) and Titanium Base (Ti-6A1-4V) Alloys

Nickel base, Inconel 718, and titanium base, IMI 318 (Ti-6A1-4V) alloys were machined with single (TiN) and multiple (TiN/TiCN/TiN) PVD coated carbide inserts at high cutting conditions in order to evaluate their performance and also to analyze their failure modes. The machining results show that coating material(s), tool geometry, machining parameters as well as material properties can singly or jointly affect tool performance and failure modes. Flank wear was the dominant failure mode at cutting speeds up to 42 m/min for the Inconel 718 alloy and up to 100 m/min for the IMI 318 alloy when machining at feed rates up to 0.25 mm/rev and depth of cut up to 2.00 mm. Excessive chipping/flaking off of tool particles and premature edge fracture also contributed to tool rejection, particularly when machining with the multi-coated inserts due to their sharp edges and instability of the machining system at higher speed conditions. The multi-layer coated tools generally produced lower flank wear rates, thus the best overall performance in terms of tool life, due to the higher resistance of the TiN/TiCN/TiN coatings to flank wear relative to the single TiN coating. Presented at the 53rd Annual Meeting In Detroit, Michigan May 17–21, 1998

High-Speed Milling of Dies and Molds in Their Hardened State

This paper presents an experimental investigation of high speed milling of dies and molds. Several critical issues involved with the high speed milling of H13 tool steel of hardness up to 55 HR C, have been studied and explained from a detailed analysis of experimental observations. The experiments were performed using several grades of PCBN ball-nose end mills with various edge preparations. The effect of different process parameters on the tool performance and the surface finish produced was also investigated. The cutting parameters involved were; cutting speeds in the range of 220 to 1320 m/min, feed variation from 0.0254 to 0.1 mm/tooth, axial depth of cut from 0.625 up to 2 mm, and radial width of cut of 0.254 mm. During the preliminary experimental investigation, the tilt angle was kept constant at 10 degrees. Several tests were conducted to study the effect of the different tool path directions on the cutting tool performance. Dry and wet cutting conditions were used and the effect of coolant on the tool life was also determined. The optimum cutting conditions have been specified based on the modes of tool failure, tool life and surface integrity produced.

Technology perspective on CVD and PVD coated metal-cutting tools

This review gives an account of the technological developments in hard coatings that have been commercially implemented in modern metal-cutting tools. Both CVD and PVD coatings have been successfully applied to cemented carbide metal-cutting inserts, in spite of the apparent competition between the two technologies. CVD coatings have evolved over the past 20 years with multilayer configurations that are still predominant today. PVD single-layer coatings have found niche applications, where conventional CVD coatings have not been particularly successful, and are expected to challenge standard CVD coatings with further advancements. Recently, a CVD/PVD layer combination has been commercially introduced. Scenarios for the development of newer coatings such as diamond and CBN are discussed. A failure mode diagram is proposed as a conceptual framework for metal-cutting tool design which takes into account the total system: the wear environment imposed by workpiece and machining parameters, corresponding tool failure modes and the synergy between hard coating and substrate.

Monitoring of turning operation via force signals Part 1: Recognition of different tool failure forms by spectral analysis

During machining, the cutting edge is subjected to various forms of tool failure such as: progressive wear leading to plastic deformation; chipping; fracture or breakage. Force signals are highly valid carriers of information about the machining process and they are, hence, among the best alternatives for tool monitoring and diagnostic techniques if a proper manipulation technique is devised. A cumulative power approach using the cumulative distribution function (CDF), is introduced in this study to investigate the possible correlation between the force signals variations and the different forms of tool failure in turning operations. The CDF, in association with the proposed failure index, has added some advantages over the simple computation of average forces. It is more accurate and sensitive (better signal-to-noise ratio) approach for detecting small disturbances resulting from any of the various modes of tool failure. Also, the technique has the ability to distinguish between various forms of tool failure and this allows for better judgement of the actual tool state. Additionally, the approach is proven to be less sensitive to cutting conditions and therefore produces a more universal solution to the problem of tool wear monitoring and control.

An investigation of the effects of chip flow on tool-wear in machining with complex grooved tools

This paper presents a systematic approach towards understanding of the tool-wear mechanisms in grooved tool inserts based on chip-flow patterns. It has been observed through high-speed filming experiments and scanning electron microscopy that improper design of chip-groove geometry and/or inappropriate application of the cutting conditions result in “undesirable” chip-flow patterns and consequent rapid tool-wear and tool failure, especially in cases, where the flank wear ( VB) or the crater wear ( KT) are not severe. Thus, the different forms of tool-wear in grooved tools can be seen as more due to the mechanical action of the flow of the chip than due to the adhesion or diffusion process. The present work is expected to lead to a better understanding of the influence of individual chip-groove and machining parameters on tool failure modes, and consequently, would contribute to a more effective tool-life prediction.

Tool-wear prediction using artificial neural networks

A mixed-oxide ceramic cutting tool (type K090) has been used to machine grey cast iron (grade G-14) in a turning process. Different values of feed rate and cutting speed have been used for machining at a constant depth of cut. Tool life and failure mode have been recorded for each experiment and the associated data have been used to train an artificial neural network (multi-layer perceptron) using the back-propagation algorithm. The trained network has been used to predict tool lives and failure modes for experiments not used in training. The best results are 58.3% correct tool-life prediction (within 20% of the actual tool life) and 87.5% correct failure-mode prediction, but it was felt that these could be improved significantly if more real data was generated for the training of the neural network.

Effects of nickel and chromium additions on properties of cemented carbides: B. Jiashgen et al (Shanghai Research Inst. of Materials, Shanghai, China), PM Technology, Vol 11, No 1, 1993, 43–46. (In Chinese)

High strength steel 30Cr3SiNiMoVA (30Cr3) is usually used to manufacture the key parts in aviation industry owing to its outstanding mechanical properties. However, 30Cr3 has poor machinability due to its high strength and high hardness. Hard milling is an efficient way in machining high strength steels. This paper investigated hard milling of 30Cr3 using a PVD-AlTiN coated cemented carbide tool with regard to cutting forces, surface roughness, chip formation and tool wear, respectively. The experimental results indicated that the increase of cutting speed from 70 to 110 m/min leads to direct reduction of cutting forces and improvement of surface finish, while both feed rate and depth of cut have negative effect on surface finish. The occurrence of oxidation on chip surfaces under high cutting temperature makes the chips show different colors which are strongly influenced by cutting speed. Saw-toothed chips were observed with the occurrence of the thermo-plastic instability within the primary shear zone. Micro-chipping and coating peeling were confirmed to be the primary tool failure modes. Serious abrasion wear and adhesive wear with some oxidative wear were confimed to be the main wear mode in hard milling of 30Cr3.

Performance of Whisker-Reinforced Ceramic Tools in Milling Nickel-Based Superalloy

This paper investigates failure characteristics and cutting performance of silicon carbide whisker-reinforced ceramic tools during milling of Inconel 718. Cutting tests were performed using round and square inserts, at cutting speeds ranging from 200 to 700 m/min. and feeds from .05 to .15 mm/tooth. Various immersion ratios were also considered. Tool wear was examined under the various cutting conditions. The behaviour of the cutting forces and temperatures during machining were then examined. The results show that an improved performance was obtained using the round inserts in comparison with the square ones. Modes of tool failure were found to be depth of cut notch wear and trailing edge wear. The former wear was dominant at cutting speeds from 200 to 400 m/min, while the later wear was dominant at speeds from 400 to 700 m/min. Flank wear was mainly due to adhesion of workpiece material on the tool surface. The best performance was achieved at a speed of 700 m/min, feed of 0.15 mm/tooth and 1.25 mm depth of cut.

The performance of ceramic tool materials for the machining of cast iron

Ceramic tools produced by Kennametal Inc. have been used for the machining of three grades of cast iron. The results show that tools based on mixed ceramics give better performance than those based on oxide and nitride ceramics. Study of the tool life and failure modes shows that tool life was determined by the flank face wear, fracture and surface roughness generated on the workpiece. Detailed microstudy of the used tools showed attrition and diffusion to be the dominant wear mechanisms. Attrition was dominant at slower speeds. A diffusion wear mechanism controlled the tool life at higher speeds where spinel formation was observed.

Adaptive Control in Machining—A New Approach Based on the Physical Constraints of Tool Wear Mechanisms

An optimization procedure for adaptive control based on the physical constraints of the machining process is proposed. Three different modes of tool failure have been examined and constraints for each mode of failure identified accordingly. A mapping procedure has then been used to transform these constraints into a control variable space and obtain a “safe working range.” The optimum working conditions are determined in terms of the control variables (cutting speed and feed rate) based on a chosen performance index (metal removal rate, in this case). Also, further consideration of time-varying situations such as tool wear and engage-exit conditions can be included in this formulation. Several numerical examples are presented for the identification of the dominant modes of failure, in particular, experimental cases. The results are in good agreement with the experimental data available.

The performance-envelope concept in the economics of machining

The performance-envelope concept, representing the permissible and desirable operating regions of machining, is developed for a particular combination of workpiece and tool. Analysis of cost and time provides an economic envelope bounded by the maximum and minimum production rates, and within which a choice of near-optimal operation is available. One objective is to utilize the flexibility which is a basic characteristic of machining. The effect of various constraints in limiting the operating range is examined, and include the machine tool in terms of range and power, and the tool-workpiece combination in terms of various tool failure modes, workpiece rigidity and surface roughness produced. Finally, experimental data is used to demonstrate the undesirable effects of operating near the built-up edge region, and also some aspects of the effect of the operating point on the nature and quality of the machine surface.

Zur spanabhebenden bearbeitung von kupfer und kupferlegierungen mit hartmetallwerkzeugen

This paper presents a systematic approach towards understanding of the tool-wear mechanisms in grooved tool inserts based on chip-flow patterns. It has been observed through high-speed filming experiments and scanning electron microscopy that improper design of chip-groove geometry and/or inappropriate application of the cutting conditions result in “undesirable” chip-flow patterns and consequent rapid tool-wear and tool failure, especially in cases, where the flank wear (VB) or the crater wear (KT) are not severe. Thus, the different forms of tool-wear in grooved tools can be seen as more due to the mechanical action of the flow of the chip than due to the adhesion or diffusion process. The present work is expected to lead to a better understanding of the influence of individual chip-groove and machining parameters on tool failure modes, and consequently, would contribute to a more effective tool-life prediction.