Extend Tool Life Research Articles

A New Flank Face Design Leading to an Improved Process Performance when Drilling High-Temperature Nickel-Base Alloys

In previous investigations, the concept of a modified flank face design with a retraction behind the cutting edge was developed. Based on fundamental investigations regarding the mechanical and thermal loads, combined with simulation-based analyses, a new design of the flank face has been created with the largest possible free volume behind the cutting edge while maintaining the mechanical stability required for the challenging machining of nickel-base alloys. This flank face modification allows a greater amount of cutting fluid to flow along the back of the cutting edge at higher velocities while at the same time creating the potential of a friction reduction between the tool tip and bore hole ground. The described concept was implemented on solid carbide twist drills which were then used to machine Inconel 718. The results show that, while tools equipped with a flank face retraction perform up to four times longer compared to standard tools, they tend to reach the end of tool life rather suddenly due to cutting edge chipping. This typically occurred when the maximum width of flank wear land equalled the width of the remaining cutting edge. Since then, further investigations have been carried out in order to refine the concept of the flank face modification. A new design was implemented with regard to a more effective cooling of the flank face, presumably caused by an improved cutting fluid flow velocity particularly at the cutting edge corners. Simulation-based findings, combined with experimental tests of the new prototypes, could reveal that the improved cutting fluid flow in the area of the cutting edges leads to significantly extended tool life and machining performance when drilling Inconel 718.

Experimental Investigations on Tribological Characteristics of Ti–6Al–4V Under Wet Conditions

Titanium alloys are well known as difficult-to-machine materials due to their chemical affinity, low thermal conductivity, and low modulus of elasticity, causing premature wear of the tool, compromising the machining quality and increasing costs. Several solutions have been followed to improve the machinability of these alloys: development of new machining techniques, tool geometries, and protection of tools’ surface with coatings, to yield high productivity, good surface finish of the work piece, and extended tool life. In this paper, the contact phenomenon between tool and workwise used for machining operation in various machine tools is simulated to estimate the coefficient of friction (COF), friction force (FF), and wear rate of titanium alloy grade 5 (Ti–6Al–4V). In this work, the experiments are performed on a pin-on-disk apparatus to estimate tribological features of titanium alloy for different speeds and loading conditions. Pins were mounted in a pin holder and fed against a rotating disk at required speeds. The trials were performed on a titanium alloys for duration of 5, 7.5, and 10 min for load of 5 kg, 6 kg, 7 kg, 8 kg, 9 kg, and 10 kg with disk speeds of 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, and 900 rpm. The results show that the COF varies with duration of rubbing, normal load, and speeds. In general, COF decreases continuously for certain duration of rubbing and after that it remains constant for the rest of the experimental time. The wear of titanium alloys significantly increases initially as load varies from 7 to 10 kg due to more contents of Al and vanadium. Hence, it becomes imperative to analyze the wear characteristics of different types of titanium alloy.

An IoT Architecture for Automated Machining Process Control: A Case Study of Tool Life Enhancement in Turning Operations

Abstract With the advent of the Internet of Things (IoT) in manufacturing applications, current research is aimed at utilization of IoT data for process control. This article presents a novel approach to performing automated process feedback using a cloud-based IoT architecture. Specifically, a case study of automated spindle speed adjustment to enhance tool life in a machining operation is used to evaluate the proposed architecture. A data-driven model of tool flank wear evolution in a longitudinal turning operation is created on a cloud-based platform through measurements of a polyvinylidene fluoride thin film sensor voltage data and machine tool parameters monitored via MTConnect. The data are used to develop a Gaussian process regression (GPR) model to predict the average tool flank wear as a function of the measured quantities, which is then used to predict the remaining tool life. The performance of the GPR model is evaluated using 10-fold cross-validation and is shown to be sufficiently accurate for predicting the average flank wear with the coefficient of determination (R2) and the root mean square error values of 0.96 and 13.45 μm, respectively. A web application running the GPR model on the cloud platform is used to forecast the remaining tool life during a turning operation and when the predicted remaining tool life is less than desired, the web application commands a spindle speed override to automatically extend tool life. The architecture is demonstrated through longitudinal turning experiments on stainless steel 316L to extend tool life by 82 %. In addition, the latency of the architecture is evaluated and shown to be acceptable for the tool life enhancement application considered in this study.

Failure and Control of PCBN Tools in the Process of Milling Hardened Steel

The polycrystalline cubic boron nitride (PCBN) milling tool can be used in the mold industry to replace cemented carbide tools to improve machining efficiency and quality. It is necessary to study the tool wear and failure mechanism to increase machining efficiency and extend tool life. Cr12MoV is used to analyze the failure form of PCBN tools in the interrupted cutting of hardened steels at low and high speed conditions in milling experiments. Experimental results show that the failure forms of PCBN tools include chipping and flank wear at low speed, and the failure modes at high speed are flank wear, the surface spalling of the rake face, and the fatigue failure on the flank face. The failure mechanism of different failure forms is analyzed by observing the surface morphology of the tool and using the theory of fracture mechanics. The results show that a high cutting speed should be selected to avoid the early damage of low speed and achieve better application of PCBN tools. At high cutting speed, tool failure is mainly caused by mechanical wear, diffusion wear, and oxidation wear. Moreover, a fatigue crack will occur at the cutting edge on the chamfered tool under thermal–mechanical coupling because of the intergranular fracture of the CBN grain and binder. A large area of accumulated fatigue damage may appear due to the influence of alternating mechanical stress and thermal stress. Finally, the control method to avoid tool failure is presented.

Effects of high-pressure cooling in the flank and rake faces of WC tool on the tool wear mechanism and process conditions in turning of alloy 718

The exceptional properties of Heat Resistant Super Alloys (HRSA) justify the search for advanced technologies that can improve the capability of machining these materials. One such advanced technology is the application of a coolant at high pressure while machining, a strategic solution known for at least six decades. The aim is to achieve extended tool life, better chip control and improved surface finish. Another aim is to control the temperature in the workpiece/tool interface targeting for optimum cutting conditions. In most of the existing applications with high-pressure coolant media, the nozzles are positioned on the rake face side of the insert and they are directed towards the cutting edge (the high-temperature area). The coolant is applied at high-pressure to improve the penetration of the cooling media along the cutting edge in the interface between the insert and workpiece material (chip) as well as to increase chip breakability. However, the corresponding infusion of coolant media in the interface between the flank face of the insert and the work material (tertiary shear zone) has been previously only scarcely addressed, as is the combined effect of coolant applications on rake and clearance sides of the insert. The present work addresses the influence of different pressure conditions in (flank: 0, 4 and 8 MPa; rake: 8 and 16 MPa) on maximum flank wear, flank wear area, tool wear mechanism, and overall process performance. Round uncoated inserts are used in a set of face turning experiments, conducted on the widely used HRSA “Alloy 718” and run in two condition tests with respect to cutting speed (45 (low) and 90 (high) m/min). The results show that an increase in rake pressure from 8 to 16 MPa has certainly a positive impact on tool life. Furthermore, at higher vc of 90 m/min, cutting edge deterioration: due to an extensive abrasion and crack in the wear zone were the dominant wear mechanism. Nevertheless, the increase in coolant pressure condition to 16 MPa reduced the amount of abrasion on the tool compared to 8 MPa. At the lower cutting speed, no crack or plastic deformation or extensive abrasion were found. When using 8 MPa pressure of coolant media on the flank, the wear was reduced by 20% compared to flood cooling conditions. Application of high-pressure cooling on the flank face has a positive effect on tool life and overall machining performance of Alloy 718.

Measurement and prediction of vibration displacement in micro-milling of nickel-based superalloy

The relative vibration between the micro-milling cutter and workpiece influences the processing quality and tool life. To solve the difficult problem of measurement of vibration displacement between cutting tool and workpiece during micro-milling process, we designed a laser displacement sensor holder, which realizes the adjustment on multi degrees of freedom. A set of vibration displacement measurement system is developed, which utilizes laser displacement sensor to collect vibration signal during micro-milling process. The frequency of micro-milling force is obtained by using varying cutting parameters method. The relationship between cutting force amplitude, frequency and vibration displacement is ascertained by using neural network method to realize vibration displacement prediction under given cutting parameters. The research lays the foundation for vibration suppression of micro-milling, which can help improve surface quality and extend tool life.

Interrupted hard turning performance of ceramic cutting tools possessing microscopic geometries established with the two-dimensional fluid-like characteristics of the chip considered

Interrupted hard turning performance of ceramic tools with varying microscopic geometries on the rake face was analyzed. A new performance index Gma was proposed for the ceramic tools. Both the external loads and the micromechanical properties of the tool material were incorporated in the proposed tool performance index. Quantitative analysis was conducted to reveal the two-dimensional fluid-like characteristics of the chip. Different kinds of microscopic textures such as MA, MB, MC, and MD were created on the rake face for ceramic tools considering the analysis results. Based on the tool performance index, performance of ceramic cutting tools which had varying microscopic textures were pre-evaluated for different groups of cutting speeds and cutting length ratios. Experimental tool lives were acquired to demonstrate the tool performance index and identify the optimum tool surface microscopic geometry. It was found that the tool performance index can be utilized to effectively pre-evaluate tool performance. Microscopic textures MB, MC, and MD were more efficient for tool life extension at relatively small cutting length ratio and relatively large cutting speed. Due to the consideration of the two-dimensional fluid-like characteristics of the chip in the design process, microscopic texture MD exhibited the highest efficiency in the tool performance enhancement.

Deposition of Trace Coolant Elements on Flank Face in Turning of mboxInconel 718 Under High Pressure Conditions

In this study, the coolant element deposition on the flank face of a coated tool in the turning of Inconel 718 when the coolant jet was supplied from the tool flank side at coolant pressures from 1 to 20 MPa was investigated. The flank wear-land was inspected after the cutting experiments using energy dispersive X-ray spectroscopy analysis to obtain the mappings of chemical elements contained in the workpiece, coating material, and coolant. It was found that coolant jet with pressures higher than 5 MPa extended the tool life dramatically compared to flood cooling. In contrast, increasing the coolant pressure beyond 5 MPa yielded only marginal improvements of the tool life, as has been reported previously for very high coolant pressures. Trace chemical elements contained in the coolant were mainly detected along the border of the tool-work contact area. The amounts of materials deposited had a complicated relationship with the pressure, and a large amount of sodium, silicon, calcium, and phosphorus deposited at very high coolant pressures of 10 and 20 MPa. It was concluded that the saturation of tool life extension at higher coolant pressures was ascribed to the thick deposited layer of a mixture of compounds, such as calcium phosphate and sodium silicide, along the border, which prevented the high-pressure coolant from penetrating into the tool/work contact area.

Influence of tool variables on wear when milling iron aluminide alloy Fe25Al1.5Ta [at.-%

Non-ferrous high-performance materials such as titanium- and nickel-base alloys are of great importance for the aerospace industry due to their advantageous properties. However, the high material prices of these alloys are a disadvantage. At the same time, iron aluminide alloys can feature similar mechanical and thermal properties combined with a significant economic advantage over other high-performance alloys. Thus, iron aluminides present a promising alternative to high priced non-ferrous alloys and have the potential to substitute established materials for components such as turbine blades.In aerospace part production, milling represents an important finishing process. Iron aluminides are considered difficult to cut materials. Therefore, occurring tool wear and its mechanisms are the primary issues in machining. These topics are not yet covered in depth by the prevailing knowledge base. In this paper, near-net-shape cast iron aluminide cross-samples were machined using ball end milling cutters to analyze the occurring tool wear and the performance of different milling tool systems. The results show a fundamental influence of the tungsten carbide substrate and the tool coating on tool wear when milling iron aluminide. The tools’ macro and micro geometry affect the active forces and stabilize the cutting edge. The present study provides insights about preferable tool variables that contribute to extending tool life in iron aluminide turbine blade production.

Development of a novel type of elliptical vibration cutting approaches with varying phase difference

The traditional elliptical vibration cutting (EVC) approaches have been widely employed in cost-effectively machining various complex optical surfaces on many difficult-to-cut materials, but the stiff usages of fixed phase difference and constant vibration frequency will have great limitations on improving performances and extending applications. Therefore, this paper will firstly concentrate on the innovations of a novel type of elliptical vibration cutting with a different frequency (DF-EVC) for several significant benefits, such as improving finish quality, extending tool life, and suppressing scattering effect. As modifications of DF-EVC, another novel type of elliptical vibration cutting with a varying phase difference (VPD-EVC) will be further developed, which can effectively enhance the machining capacities of DF-EVC processes by changing their unfixed phase differences within an available angle range. Beyond the conventional applications, like machining the microstructure and freeform surfaces, the improved VPD-EVC approaches can be elaborately adopted to fabricate two different microgrooves with U-shaped and V-shaped cross-sections, which integrate the high-frequency elliptical vibrations into the cross-feed motions instead of the up-feed motions of traditional EVC. In addition, the mechanism of how the VPD-EVC extends tool life will be discussed in detail, and the dependences of machining capacities to the phase difference amplitudes will be investigated by introducing a dimensionless relative cutting ratio (RCR). Subsequently, the toolpath generations and surface topography simulations of VPD-EVC will be performed and compared to traditional EVC; the suppressing capacity of the scattering effect will be further investigated based on the power spectral density (PSD). Finally, a series of cutting experiments will be practically conducted on the copper materials (T2) with poor machinability, the obtained results can well demonstrate the feasibility and effectiveness of the developed DF-EVC and VPD-EVC approaches for achieving various expected benefits, and several crucial conclusions on current research can be briefly summarized in the end.

Protocol for tool wear measurement in micro-milling

Micro-milling yields small accurate parts quickly for electromechanical, aerospace, and medical applications. Due to their small size, micro-tools wear quickly and unpredictably therefore tool wear is difficult to measure and is poorly understood, leading to excessive tool changes and reduced productivity. This paper, therefore, proposes a new protocol for micro-tool wear measurement to overcome these problems. A strict set of criteria as found in an ISO standard is impractical for micro-milling research. The method herein allows comparisons to be made across materials and situations and detailed are certain criteria that must be fulfilled to achieve this. To evaluate the protocol micro-tools were used to machine three materials: brass, titanium and Hastelloy; and wear curves produced. Using the described protocol, these wear curves can be analysed similarly to those for larger tools. Profile analysis of the slots machined provides valuable information about tool wear where direct measurement is impossible. This new protocol presents a novel method for analysing and reporting tool wear for micro-end-mills, allowing them to be compared under different machining conditions and/or milling different materials, something not afforded by existing machining standards. The information can then be transferred to industrial applications, extending tool life and improving process efficiency.

Coated cemented carbide tool life extension accompanied by comb cracks: The milling case of 316L stainless steel

Two typical commercial coatings were deposited on a cemented carbide substrate, including CVD multilayered TiN/MT-TiC0.7N0.3/TiCNO/α-Al2O3 (cm-Al2O3 based) and PVD nano-multilayered Al0.55Ti0.45N/TiN (pn-AlTiN based). Performance and mechanisms for tool failure and tool life extension were investigated for the face milling of 316L stainless steel under a tough milling condition. The results show that the pn-AlTiN based coating exhibits a strong ability against delamination, abrasion wear and comb crack widening. As a result, its tool life is 2.1 times as long as the one with the cm-Al2O3 based coating. Edge chipping resulted from comb crack evolution is still the dominated fatigue failure mechanism for both the coatings. Internal formation of longitudinal submicron to nano-scaled cracks, accompanied by clear lattice fringes with a coherent relation between AlTiN and TiN was observed in a FIB-cut specimen with a size of 6.5 × 6.5 µm with a transmission electron microscope. For the pn-AlTiN based coating, the strong ability against comb crack widening stems from its strong self-adaptive ability to plastic deformation through the internal formation of submicron to nano-scaled cracks and the associated strong stress dissipation ability. A design concept for improving the milling tool life is discussed.

Influence of shot peened surfaces on friction in hot forging

Dies in hot forging operations are subjected to a complex load combination consisting of thermal, mechanical and tribological loads. Therefore, hot forging dies exhibit short service life in comparison to other forming operations. An extension of tool life represents an effective way of increasing the efficiency of hot forging operations since the dies represent a large share of the process chain’s production costs. Since there is no prior knowledge of ideal die surface properties, a shot peening surface treatment was applied in order to create enhanced tribological properties in comparison to machined die surfaces.Peening is a surface treatment procedure which enables a repeatable and accurate adjustment of topographical parameters. In this scientific contribution, the technique is investigated as a method to enhance tribological properties of hot forging die surfaces resulting in less friction and wear. Hot forging dies of AISI H11 were peened using different peening media creating die surfaces with varying topography. Tribological properties of the peened die surfaces were analysed in ring compression tests in dry and lubricated conditions using water-based graphite lubricant. The lowest friction was detected under lubricated conditions for peened surfaces with slightly increased roughness compared to the initial smooth, unpeened die surfaces.

Improving the Performance of Stamping Systems

The wear of the working surfaces in stamping equipment is analyzed. Means of improving the surface layer of the working components so as to extend tool life are considered.

Energy centric selection of machining conditions for minimum cost

In the past, the cutting conditions that meet the economic and environmental objectives of the specified manufacturing process were selected based on minimum tooling cost and/or minimum electrical energy criterion. However, detailed modelling of electrical energy based on tool life and cost criterion has not been addressed. In this study, machining tests were conducted to develop a cost model which includes machining energy, and to assess the impact of the extended tool life model with regards to selection of cutting conditions, electricity cost and tool wear effect that satisfy these objectives. The model was validated with an industrial case study. Results show that cost savings at minimum energy were achieved. Hence, substantial cost savings could be achieved by selecting optimized machining parameters which could reduce machining costs by 47% compared to using tool supplier recommended feeds, depth of cut and cutting velocity. Thus, cost could be optimized fairly accurately without explicitly modelling energy demand due to the relative low contribution of energy costs compared to tooling costs. The optimized energy costs leads to minimum associated carbon footprint and reduces overall product cost. This creates an incentive for manufacturing companies to investigate the sustainability and energy efficiency of their manufacturing processes.

Application of nanoclay lubricants for lowering wear of tools for steel meshing - A case study

The tools that are employed for industrial woven steel wire mesh processing suffer significant wear, particularly those employed for bending the steel wire at the beginning of the process due to the high forces that are required. Lubricants are employed for the purpose of reducing friction between the tool and the steel wire in these types of processes, hence reducing tool wear. Nanoparticle additives have been investigated for improving the tribological performance of lubricants; due to their small size they may fill surface valleys reducing surface roughness, act as nanobearing limiting metal-metal contact, amongst others. Particularly, nanoclay nanoparticles, such as montmorillonite (MMT), have been proposed as nanoadditives for tribological applications due to being naturally occurring, environmentally friendly, and low-cost. In our work, MMT clay nanoparticles were dispersed by homogenization and ultrasonication in a water-based synthetic lubricant with varying concentrations (0.01, 0.05, and 0.10 wt.%). The wear preventive tribological properties of the prepared nanolubricants were characterized experimentally with a T-02 four-ball tribostester according to ASTM D4172. The wear scar diameters of the three lower steel balls of the four-ball tribopair were measured with an Alicona EdgeMaster optical measurement system. In our laboratory experiments wear scar diameter was reduced by 19% with a MMT clay nanoparticle concentration of only 0.01 wt.%. Higher concentrations (0.05 and 0.10 wt.%) resulted in lower improvements due to nanoparticle agglomeration in the lubricant. Finally, MMT clay nanolubricants were employed for the wire-bending process in a steel-meshing equipment with the nanoparticle concentration where the best tribological performance was found (0.01 wt.%). Tools were monitored for 120 h; tool wear was recorded by measuring the change in the wire-bending tool dimensions compared to the change obtained when the unfilled base lubricant was employed. For the first inch of the tool, where the highest force for bending the wire is required, tool wear in was lowered from 0.014 in to 0.006 in, representing an improvement of 57%. In average, the improvement on wear resistance for the tool was found to be 30%. The results found for this study demonstrate that MMT clay nanoparticle additives are able to improve wear resistance and extend tool life, resulting in considerable savings.

난삭재 절삭 가공공정 기술의 현황

Lightweight parts are necessary to improve fuel efficiency and reduce environmental impacts in transportation industry. As a result, there has been a shift away from using conventional metals toward using lighter materials with superior mechanical strength. These new materials typically include titanium alloys, nickel alloys, carbon fiber reinforced plastics (CFRPs), and CFRP-metal stacks, which are classified as advanced materials. However, due to the unique properties of these materials (e.g., high strength, low thermal conductivity, carbon fiber-induced hardness, etc.), the cutting process can be difficult. As a result, various manufacturing issues can occur during the cutting process, such as high tool wear, surface quality deterioration, delamination of the CFRP layer, fiber pull-out, and thermal deformation. In this paper, difficult-to-cut advanced materials were reviewed with regard to the influence of the physical properties of the materials and various defect issues that can occur during the mechanical cutting process. In addition, various approaches to improve the cutting process are introduced, including protecting tools with coatings, altering tool features, using high pressure or cryogenic cooling, extending tool life via ultrasonic vibration machining, and improving product quality and machinability.

Control of tribofilm formation in dry machining of hardened AISI D2 steel by tuning the cutting speed

This study is focused on the investigation of nano-scale tribological effects formed during the machining of hardened material. Tribofilm formation was associated with the transfer of workpiece material to the cutting tool surface with further tribo-oxidation occurring through interaction with the environment. In addition to wear evaluation studies, a number of advanced surface analytical techniques were used to characterize surface phenomena, including X-ray photoelectron spectroscopy (XPS) and Auger Electron Spectroscopy (AES) (including AES imaging). This was combined with Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDX) studies. Wear performance of uncoated ceramic (mixed alumina and TiCN) tools was studied in detail at different constant cutting speeds (50; 80; 100 and 120 m/min) and tuned through two-step and three-step cutting speed adjustments (120–100 and 120–100–80 m/min) during hard dry turning of AISI D2 tool steel. The tuning of the cutting speed was performed in order to enhance the generation of favourable tribofilms and obtain an extended tool life. As a result of these tuned cutting approaches, tool life was increased by 36% at 120–100 m/min and improved 99% at 120–100–80 m/min when tested separately. Both the two-step and three step speed adjustment involved enhanced formation of beneficial tribofilms on the tool surface under a higher cutting speed, with a subsequent lower speed preventing the wearing out of these films and thus sustaining the improved tribological conditions. This research provides a novel strategy to enhancing the efficiency of machining processes which operate under extreme tribological conditions of dry machining of hardened tool steels.

Wet vs dry CFRP drilling: Influence of cutting fluid on tool performance

Carbon fibre reinforced polymer (CFRP) cutting operations have core features which include; i) chip types consisting of sub 50 micron particles and ii) aggressive abrasion-dominated tool wear. The workpieces used in this investigation were manufactured in a single batch from aerospace-grade, out-of-autoclave, quasi-isotropic, thermoset prepreg materials. Initially, a number of conventional tests were performed to assess the performance of isolated cutting fluid chemicals. The fluid-to-fluid variance was shown to be less significant in these tests when compared against dry conditions. A 6 percent basic micro-emulsion concentrate produced the best results with dry setup produced lower torque results than any cutting fluid tested. Production-style drilling trials were undertaken to investigate the tool life under varying fluid conditions from basic to commercially available. These trials indicated that dry, tip-extracted conditions enabled an extended tool life prior to coating failure against the best cutting fluid with identical parameters, machine tool, cutting tool and workpiece material manufacture conditions. The hypothesis for this reduction in tool performance under general wet conditions is that heat introduced by the drilling process changes the CFRP polymer’s visco-elastic properties thus reducing the abrasive interaction between tool and workpiece during material removal processes. The best cutting fluid, a 5 percent semi-synthetic, commercially available chemistry, produced approximately 60 holes more than the poorest performing chemistry.

Kinematics and tool-workpiece separation analysis of vibration assisted milling

High precision components made of hard and brittle materials are increasingly in demand in many applications owing to the superior physical, mechanical, optical, or electronic properties offered by these materials. Mechanical machining, primarily milling, is the main shaping method used to achieve tight tolerances and high quality surface finishes on those hard materials, but excessive tool wear and poor surface integrity is a pressing challenge. Vibration assisted machining can significantly reduce cutting forces, enhance surface integrity and extend tool life, but the application of vibration assistance to milling has received little attention due to the complexity of kinematics and dynamics of this process. This paper investigates the kinematics of vibration assisted milling. Generic kinematic equations of vibration assisted milling are firstly formulated, and then three types of tool-workpiece separation mechanism is proposed and the requirements to realize each type of separation are discussed through kinematic analysis and simulation. Finally, an ABAQUS finite element model of vibration assisted milling is used to verify the proposed kinematic models and tool-workpiece separation types.