Chip Breaking Research Articles

Modeling and Monitoring of the Tool Temperature During Continuous and Interrupted Turning with Cutting Fluid

In metal cutting, a large amount of mechanical energy converts into heat, leading to a rapid temperature rise. Excessive heat accelerates tool wear, shortens tool life, and hinders chip breakage. Most existing thermal studies have focused on dry machining, with limited research on the effects of cutting fluids. This study addresses that gap by investigating the thermal behavior of cutting tools during continuous and interrupted turning with cutting fluid. Tool temperatures were first measured experimentally by embedding a thermocouple in a defined position within the tool. These experimental results were then combined with simulations to evaluate temperature changes, heat partition, and cooling efficiency under various cutting conditions. This work presents novel analytical and numerical models. Both models accurately predicted the temperature distribution, with the analytical model offering a computationally more efficient solution for industrial use. Experimental results showed that tool temperature increased with cutting speed, feed, and cutting depth, but the heat partition into the tool decreased. In continuous cutting, cooling efficiency was mainly influenced by feed rate and cutting depth, while cutting speed had minimal impact. Interrupted cutting improved cooling efficiency, as the absence of chips and workpieces during non-cutting phases allowed the cutting fluid to flow over the tool surface at higher speeds. The convective cooling coefficient was determined through inverse calibration. A comparative analysis of the analytical and numerical simulations revealed that the analytical model can underestimate the temperature distribution for complex tool structures, particularly non-orthogonal hexahedral geometries. However, the relative error remained consistent across different cutting conditions, with less error observed in interrupted cutting compared to continuous cutting. These findings highlight the potential of analytical models for optimizing thermal management in metal turning processes.

Intercomparison of Indexable Cutting Inserts’ Wear Progress and Chip Formation During Machining Hardened Steel AISI 4337 and Austenitic Stainless Steel AISI 316 L

This article deals with a mutual comparison of indexable cutting inserts of the CNMG 120408 type from two different manufacturers during the machining of hardened steel AISI 4337 and austenitic stainless steel AISI 316 L. The main goal is to analyse the different wear processes depending on the difference in the manufacturer’s design and also depending on the properties of the different machined materials. The progress of the wear of the main spine of the tool, the types of wear and the service life of the cutting edge were monitored, with the achievement of the critical value VBmax = 300 µm being the standard. In addition to the wear of the inserts, the production of chips was monitored in terms of their shape, average size and number of chips per 100 g of chips produced. In order to understand the relationships arising from the obtained data, an SEM equipped with an elemental analyser was used to analyse the coating layers and the substrate of the unworn inserts and the types of wear and the intensity of the surface damage of the worn inserts. A several-fold difference in the lifetime of the cutting edge was found, both in terms of design and in terms of the selected machined material, while in both cases the cutting edge with Al2O3 and TiCN layers of half thickness achieved a better result in liveness. From the point of view of chip formation, very similar results in shape and average length were observed despite the different designs of chip breakers. Cutting inserts with half the thickness of the coating layers achieved longer cutting edge life in the non-primary material application compared to the target workpiece material. At the same time, it was observed that a thinner coating layer has a positive effect on chip formation in terms of its length and shape.

Wear behavior of novel CVD-coated wiper inserts’ with various chip-breakers and resulting surface integrity during dry drilling of Ti-6Al-4V

In this paper, a comprehensive investigation in terms of tool wear/life, chip morphology, surface roughness/damage, diametric error, burr height, and microstructure is conducted by using an innovative integration of peripheral wiper and central stepped inserts when drilling Ti-6Al-4V alloy in a dry-cutting environment. Two geometries of peripheral wiper inserts termed as LM (groove width-1000 mm, groove depth-65 mm) and GT (groove width-720 mm, groove depth-20 mm) are evaluated at two levels of cutting speeds (50 m/min and 60 m/min) and three levels of feed rates (0.10 mm/rev, 0.15 mm/rev, and 0.20 mm/rev) while keeping the geometry of central stepped insert constant. The GT wiper configuration is found to be more suitable in terms of tool life, drilling maximum number of holes (75) at a cutting speed of 50 m/min and feed rate of 0.10 mm/rev which is ∼3-fold higher than that of the LM geometry. With respect to majority of the drilled hole attributes, better performance of LM geometry is observed in comparison to its GT counterpart due to its improved chip breakability. In addition, all holes are oversized ranging from 30 µm to100 µm. Minor plastic deformation of grain boundaries in the machined sub-surface is noticed to a depth of 10–15 µm in the direction of cutting.

Modeling modulated tool path turning using coupled smoothed particle hydrodynamics and finite element method

This paper describes a full-scale, three-dimensional coupled smoothed particle hydrodynamics (SPH) and finite element model for modulated tool path (MTP) turning. The chip breaking mechanism due to modulated motion of the tool is demonstrated by the developed machining model. In contrast, the simulation of conventional turning with the same machining conditions predicts long continuous chips. The cutting force predicted by the simulation is validated with a mechanistic force model based on the instantaneous chip thickness. This work expands the capabilities of machining simulations to predict complex machining phenomena such as MTP turning through a full-scale realistic simulation. The encouraging simulation results show the potential to study more complex phenomena, such as evaluating the parameters of tool path modulation, simulating ultrasonic machining, and studying machining stability.

Comparison of Modulation-Assisted Machining Strategies for Achieving Chip Breakage When Turning 17-4 PH Stainless Steel

Chip morphology is an intrinsic characteristic of the machining process that determines the quality of the process. When machining low machinability materials, the chips formed are usually long, continuous, and difficult to break. Due to the negative effect of the accumulation of the chip along the process, chip breakage and the correct extraction out of the machining area have become indispensable requirements. Although numerous chip-breaking methodologies have been proposed, modulation-assisted machining (MAM) is one of the most promising approaches, due to its independence from the workpiece material, tool geometry, and cutting conditions. In this work, a comparison of different modulation-assisted machining strategies, based on the modulation of the feed (F-MAM) or the depth of cut (D-MAM), were experimentally evaluated and compared to conventional turning in terms of chip morphology, surface roughness, and tool wear. Results showed that both MAM strategies enabled chip breakage and improved chip evacuation in comparison to conventional turning; however, D-MAM showed a better performance in terms of tool wear and surface roughness.

Chip breakage assisted by pulsed high-pressure jet during continuous cylindrical turning 42CrMo steel

Continuous high-pressure jet technology (CHPJ) is often used to break chips during turning. However, the chip-breaking effect is not satisfactory in turning high-strength and high-toughness materials with a small depth of cut. In this research, a pulsed high-pressure jet assisted chip breaking technology (PHPJ) is proposed based on the water hammer effect. Then, a set of PHPJ equipment with stable working performance and safety was developed. The chip length and chip curling radius were selected as the chip breakage indexes under various depths of cut (0.3, 0.4, 0.5 mm) and jet pressures (10, 20, 30 bar). The improvement of chip-breaking ability of PHPJ was firstly reflected in the reduction of chip entanglement degree and chip length. The chip length under PHPJ was decreased by at least 13 % compared to that under CHPJ. Secondly, the PHPJ could reduce the chip curling radius by 3.48–23.36 % compared to CHPJ. The compression effect of chip curling of PHPJ relative to CHPJ showed a trend of firstly increasing and then decreasing as the jet pressure increases, with a turning point of 20 bar. Moreover, the PHPJ technology exhibited a positive influence on tool wear and machined surface quality.

Cutting Performance of a Longitudinal and Torsional Ultrasonic Vibration Tool in Milling of Inconel 718

Inconel 718 has excellent thermal and chemical properties and is widely used in the manufacture of aerospace parts; however, there are some problems in the machining of Inconel 718, such as a large milling force, serious tool wear, and poor surface quality. In this research, a type of longitudinal–torsional ultrasonic milling (LTUM) tool is designed based on theoretical computations and FEM simulation analysis. To verify the design rationality of the developed LTUM tool, milling experiments are performed. It is verified that the LTUM tool can realize an elliptical vibration path at the tool tip. The resonance frequency of the tool is 21.32 kHz, the longitudinal amplitude is 6.8 µm, and the torsional amplitude is 1.4 µm. In the milling of Inconel 718, the experimental data of LTUM are compared with those of conventional milling (CM). The comparative experiments show that the LTUM tool can effectively lessen the milling force and tool wear in the milling of Inconel 718, improve the surface quality, inhibit the generation of burrs, and improve the chip breaking ability. The application potential of the LTUM tool in high-performance milling of Inconel 718 parts is proven.

Chip breakage in silk microfibre production using elliptical vibration turning

To overcome the precision limitation and environmental impact of current chemical-based production methods for manufacturing silk microfibres used for targeted drug delivery, this paper presents a high-precision, scalable, eco-friendly mechanical machining approach to produce such microfibres in the form of discontinuous chips obtained through elliptical vibration turning of silk fibroin film using a diamond tool. The length and waist width of fabricated microfibres can be precisely controlled. As each vibration cycle will produce one silk microfibre, complete and deterministic chip breakage becomes an essential and challenging task in this approach due to its unique two-phase structure. Thus, the hybrid FE-SPH numerical simulations and machining experiments were conducted to gain a pioneering and in-depth exploration of the chip-breaking mechanism in this process. It was found that applying a low depth ratio (ratio of the nominal depth of cut to the tool path vertical amplitude) and a high horizontal speed ratio (the nominal cutting speed versus the critical workpiece velocity) could effectively reduce the average tool velocity angle (the angle from the deepest cut to the tool exit point along the cutting direction). A smaller angle would enhance the diamond tool's shearing action and led to the reduction of hydrostatic pressure in the cutting zone and a consequent decrease in the ductility of silk fibroin due to its unique structure dominated by beta-sheet crystallites. The above adjustments collectively facilitated chip breakage. This paper, therefore, established a governing rule for the controlled and repeatable formation of microfibres based on the average tool velocity angle for the first time and revealed that the cutting chips would undergo complete and deterministic breakages once the angle approached below 22.6°. On this basis, the high-precision and scalable manufacturing of silk microfibres with precisely controllable length and waist width was ultimately achieved.

Effects of chip breaker groove and tool nose radius on progressive tool wear and behavior when turning GH3536 nickel-based superalloys

Nickel-based superalloys are typically challenging to machine and often exhibit severe tool wear during the turning process, thus attracting substantial research attention. This study not only explores the tool wear mechanisms when turning GH3536 nickel-based superalloys but also introduces a focus on the role of tool geometry configuration. Tools with different chip breaker groove structures and nose radii were investigated, with results indicating the tool wear mechanisms were predominantly abrasive and adhesive. For the 04HA chip breaker, which has a 9° rake angle and a "V"-shaped bottom, there is a single point of impact with the chip during cutting, while the 04VP3 chip breaker, with a 15° rake angle and a flat bottom, has two points of impact with the chip during cutting, increasing chip deformation and favoring chip breaking, thereby suppressing the formation of built-up edge. Additionally, changes in the nose radius influenced the degree of work hardening and consequently influence the severity of notch wear, with the nose radius also impacting the chip flow angle. Based on this finding, a theoretical mathematical model describing the initial chip flow angle was established and validated. Additionally, an examination of the effects of varying operating parameters on tool life was conducted, revealing that cutting speed was the most significant factor affecting tool life, followed by feed rate and depth of cut.

The effect of secondary cutting on the chip breaking in turning with (Ti,W)C cermet cutting tools

This study proposes a secondary cutting technique to address the chip breaking issue of cermet cutting tools. A cemented carbide blade is superimposed to cut off the chips while cutting with (Ti,W)C cermet tools, this approach allows for achieving chip breaking while maintaining excellent machining surface integrity. In this paper, the influence of the distance between the secondary cutting tool and the major cutting edge and the thickness of the tool on the chip breaking is studied, by using the combination of finite element simulation and experimental verification. The results indicate that the secondary cutting technique transforms the chips from long helical chips into dual-C-type chips. The distance between the secondary cutting tool and the major cutting edge is the primary factor affecting chip breaking. The reason is that the free end of the chip is subjected to the reaction force of the secondary cutting tool, which hinders the increase of the chip curl radius, increases the internal strain, and achieves the chip breaking condition. The thickness of the secondary cutting tool is also a significant factor influencing chip breaking, when the thickness reaches the critical value of 1.8 mm, the tool transitions from obstructive action to cutting action. When the cutting material is 45 steel, the cutting speed is 300 m/min, the feed rate is 0.142 mm/r, and the cutting depth is 0.2 mm, the distance between the secondary cutting tool and the major cutting edge is 1.5 mm, and the tool thickness is 1.3 mm, the chip breaking effect is the best, the main types of chips is dual-C type chips, with a chip length of 7.1 mm ± 0.3 mm and a chip fracture curl radius of 1.8 mm ± 0.1 mm. At this point, the surface roughness can be reduced to as low as 0.98 μm, good surface integrity is ensured while chip breaking.

Application of 3D Imaging for Analyzing the Chip Groove Shapes of Cutting Inserts

An effective chip formation process is significant for an efficient metal-cutting process. Long continuous chips can lead to scratches on the machined surface, increasing the risk to operator safety and stability of the machining process. The use of chip grooves on cutting inserts allows for control of the chip formation and breaking process during machining. The shape of the rake surface and the design of the chip groove also affect the efficiency of the machining process. The article presents the use of 3D imaging to analyze changes in the selected chip groove shapes depending on the cutting depth ap = 0.10, 0.25, and 0.50 mm and the angular location of the cutting insert relative to the machined surface of the workpiece (i.e., major cutting-edge angle K = 60° and K = 90°). The analysis methodology was based on the use of 3D image registration and surface shape modeling. In the analysis based on the 3D imaging presented, the novelty was the adaptation of methods typically used to map and model the terrain surface, which have not been used previously in cutting processes. The evaluation of the shape of the chip groove surface was carried out using, e.g., watershed maps and 3D surface maps. The obtained results indicated a significant influence of the cutting depth and major cutting-edge angle on the surface shape, profile, and length of the chip former; chip groove volume; and the theoretical contact area of the formed chip with the cutting insert. It was observed that for small depths of cut, i.e., ap < 0.25 mm, the chip-curling process may be difficult due to the flattened shape of the rake surface. In addition, the influence of the convexity of the rake surface of the cutting insert on the chip formation process was demonstrated. The results of the experimental research that verified the conclusions are presented. The developed results may be useful in the process of selecting the parameters and conditions of the metal finishing through use of tools with a shaped rake surface.

THE EFFECT OF THE DESIGN OF A ROTARY PEAKLESS TURNING TOOL WITH CHIPBREAKER ON THE SURFACE ROUGHNESS

One of the methods of high-performance finishing turning is based on the use of peakless cutters, the cutting edge of which in the cutting plane is inclined to the axis of the workpiece, and the angle in the plan is most often zero. It is not the tip that is in contact with the workpiece, but a certain part of the cutting edge of the cutter, as a result of which turning is carried out in conditions close to the conditions of free cutting. The design of a rotary peakless rotary turning cutter with a chip breaker is devoid of one of the design disadvantages – the presence of a vertex, the weakest and most worn part of the cutting edge of conventional cutters. A constantly renewable cutting edge due to its rotation allows you to evenly distribute wear, temperature and specific loads, which significantly increases the service life of the cutting tool. Rotary peakless rotary turning cutter with a chip breaker for turning external surfaces, in the design of which a cup cutting plate is placed, mounted and rotating on an axis with bearings and due to its rotation allows the tool to provide high processing performance, increase the operating time and service life of the cutting tool due to the adjustable angle of inclination of the cutting edge – makes it possible to process various materials, and the presence of a chip breaker in the structure allows to improve the quality and reduce the roughness of the treated surface, as well as the chip formation process. Keywords: turning, self-rotating cutter, rotary cutter, peakless cutter, wear, roughness.

Experimental investigation of the effects of cooling-lubricating methods on the slot milling process of GTD-111 type nickel-based superalloy

Machining of nickel-based superalloys still poses several problems, especially slot milling, because the high work hardening, high metal carbide content and poor thermal conductivity cause the tool to wear quickly, with frequent breakages. This paper has dealt with the investigation of the effects of flood cooling, cryogenic cooling with Liquid Carbon Dioxide (LCO2), and the Minimum Quantity Lubrication and LCO2 combination on the cutting force, tool wear, chip morphology, surface roughness and the width of the milled slots. The authors have developed a new measurement method to measure the edge radius wear as a function of the depth of cut. The importance of this measurement method lies in the fact that at each measurement level, it is possible to determine the degree of wear of each edge radius and the homogeneity of the wear of the tool edges, which allows for determining how close the tool is to failure. Initially, the cooling had a positive effect on the cutting force for both LCO2 and LCO2 + MQL, but towards the end of the machining length, the cutting force was lower for flood cooling. The smallest tool wear resulted from the flood cooling, followed by LCO2 + MQL combination and LCO2. These results suggest that lubricating is more important than cooling for tool life. However, cooling plays a major role in chip breakage and surface quality, and in both cases, the best results were obtained by milling with the LCO2 + MQL combination.

Investigation of the Titanium Alloy Turning Process with Prime A Tools under High-Pressure Cooling Conditions

When turning titanium alloys, it is difficult to ensure the required quality with maximum machining efficiency. A typical problem in the turning process of titanium alloys is to achieve effective breaking and removal of chips from the machining zone. The combination of the new construction of cutting tools and machining methods in the machining of titanium alloys increases the efficiency of the machining. For this reason, the use of tools typical for the Prime Turning method in combination with the high-pressure cooling (HPC) method was analysed. The longitudinal turning of the Ti6Al4V ELI titanium alloy was performed using Sandvik Coromant grade 1115 carbide tools. An increase in the pressure of the cutting fluid to p = 70 bar was used. Measurements of the components of the total cutting force for finishing machining with variable cutting parameters in the range of: feed rates f = <0.1;0.4> mm/rev, cutting depth ap = <0.25;1.0> mm and cutting speed vc = <40;80> m/min were performed. It has been shown that the values of cutting force are mainly dependent on the feed and the depth of cut. An analysis of the forms of chips obtained is presented. The dependence of the applied cutting parameters on the value of the chip breakage coefficient Cch was determined. The method of searching for the maximum efficiency of the turning process was determined, taking into account the desired value of the chip breakage coefficient.

The design of chip breaking grooves for spade drill inserts

A chip breaking groove was designed on a spade drill insert to break chips. The effects of the anti-chip angle, width and height of chip breaking groove on the chip curl radius were investigated with simulations and drilling experiments. The forces acting on the chip were analyzed to clarify the chip breaking processes. The chip breaking process of a spade drill insert with chip breaking groove was simulated with the finite element technique to study the chip breaking mechanism. The calculation formulas for calculating the width, height and radius of the chip breaking groove were established. The research results show that the chip curl radius is affected by the chip breaking groove parameters. The chip curl radius increases with the anti-chip angle but decreases as width decreases or height increases. When the values of anti-chip angle, width and height of chip breaking groove reach thresholds, the chip wind or piling phenomenon will occur during the drilling experiments. The formulas for calculating chip breaking grooves are feasible. A design method of chip breaking grooves for spade drill inserts is proposed. Spade drill inserts whose chip breaking groove parameters are calculated according to formulas of the width, height and radius can effectively break chips at different drilling parameters.

Tool-integrated thin-film sensor systems for measurement of cutting forces and temperatures during machining

Effective in-process control mechanisms are vital for the future development of production processes and ask for reliable monitoring of process variables. For this, new tool-integrated sensor systems for measuring cutting forces and temperature for machining of hardened steel are proposed. Thin-film technology is used to apply a thermoresistive temperature sensor in the chip-workpiece contact area for the first time on industrial cutting inserts with chip breaker geometry. Complementary piezoresistive thin-film sensors based on diamond-like carbon (DLC) and manganin layers were developed and deposited on a washer. It was placed beneath the indexable insert to measure the cutting forces. Turning experiments were conducted to study sensor life and accuracy. All sensors showed an adequate lifetime for laboratory purposes. Temperature compensation methods were investigated for force measurement and results compared to forces recorded by a dynamometric platform. While temperature compensation for the DLC-based sensor needs further optimization, results of the manganin-based sensor compared well with the expected cutting forces. The manganin thin-film sensor exhibited rapid responsiveness and great reproducibility, underscoring its prospective utility for real-time monitoring of cutting forces in machining operations.

Investigations on chip breakability in lead-free brass alloy CW511L using different chip breaking geometries

Brass is an alloy of copper and zinc, commonly alloyed with lead. Due to legal restrictions, the lead-content is decreasing nowadays. This leads to higher cutting forces and worse chip breakability. To face these challenges, adapted tool geometries were investigated. To decrease cutting forces, positive rake angles can be utilized. On the other hand, this will lead to worse chip breakability in single phase lead-free brass alloys. Therefore, chip breaking geometries are necessary. This paper investigates and compares different forms of chip breaking geometries to improve chip breakability when using highly positive rake angles in lead free brass alloy CW511L.

Investigation of ultrasonic vibration assisted orthogonal turning under dry and minimum quantity lubrication conditions and performing sustainability analyses

Recently, increasing pressure on industries to innovate and adopt sustainable techniques has sparked investigations into machining strategies that have minimal carbon emissions, minimal energy consumption by machine tools, and low machining costs. The primary aim of this paper is to identify the machining conditions that can fulfill the criteria of clean production and sustainable chip forming for low-alloy steel which is extensively used in the many industrial field. To achieve this goal, experiments were done under both dry and Minimum Quantity Lubrication (MQL) conditions, aided by ultrasonic vibration assisted hybrid machining conditions at various cutting speeds (100 and 140 m/min) and uncut chip thicknesses (0.1, 0.14, and 0.18 mm). The study was conducted in two stages. In the first part, machining experiments were performed afterward, cutting forces, cutting temperature, chip morphology, surface roughness, and texture were examined. The second part of this study evaluates the sustainability of various machining parameters and cutting environments. The analysis of economic feasibility or rather the total machining costs were estimated by evaluating the costs incurred due to investment of machine tools, lubricant/coolant delivery systems and ultrasonic vibration system costs, waste processing and management costs, cutting tool and labor costs, cost of cutting fluid and energy consumed. On the other hand, environmental viability was evaluated by estimating the carbon emissions (CE) due to the power consumed, material utilization (i.e., the cutting tool and cutting fluid), and the waste processing and management (i.e., disposal of cutting tool, cutting fluid and chip recycling). Results indicate that both dry and MQL ultrasonic-assisted machining processes resulted in improved chip breakability, and produced short-comma chips. Additionally, it reduced cutting force by 28% and the cutting temperature was lowered by 30 %. Besides, Minimum Quantity Lubrication + Ultrasonic Vibration Assisted Machining (MQL + UVAM) hybrid method prevented surface defects and reduced average surface roughness by 24%–35% compared to dry conditions. While utilizing the MQL + UVAM method, the overall machining cost decreased in the range of about 20–30 % as compared to dry and dry + UVAM conditions. From an environmental standpoint, the MQL + UVAM hybrid machining process was found to be a significant contribution to the overall CE due to use of cutting fluids and increased machine tool utilization. This paper contributed to the understanding of sustainability and cleaner production to mitigate CO2 emissions by using the MQL + UVAM hybrid method.

Influence of particle parameters on micro-machining performance of CoCrFeNiAlX/Al composite materials

This study delves into the influence of particle size on the micro-machining performance of CoCrFeNiAlXp/Al composite materials. It employs a combination of experimental and simulation methods to investigate the effect of different particle sizes on the surface integrity of the composite material. The research also scrutinizes the impact of tool particle size on cutting forces, cutting temperatures, and chip morphology across a range of cutting parameters. Additionally, it establishes a clear link between the quality of the machined surface and the relative position of the tool particles. The findings reveal that an increase in particle diameter leads to a reduction in cutting forces. Furthermore, at a constant particle size, an initial rise in cutting speed results in an increased cutting force, which subsequently decreases. Specifically, the maximum cutting force is observed at a particle size of 10 μm, reaching its peak at a cutting speed of 60 m/min, approximately 1.6 times that of the 40 μm particle size. The primary cutting force displays a positive correlation with cutting depth but a negative correlation with particle diameter. For particles of uniform size, an increment in the Al element content initially reduces the cutting force, which subsequently increases, with the minimum force occurring at an Al element molar ratio of 13 %, roughly 60 % of the Al0 particle. Cutting temperature rises with higher cutting speed and depth but inversely correlates with particle diameter and Al content. A particle size of 10 μm generates the highest cutting temperature, approximately 1.4 times that of a 40 μm particle with identical Al content. The completeness of the chip positively correlates with cutting speed, but at a speed of 70 m/min, chip breakage experiences a significant upsurge. The bending radius of the chip increases with cutting depth, ultimately leading to fracture at a depth of 60 μm. A higher Al content in the particles results in more pronounced chip breakage. The optimal surface quality is achieved when the tool is positioned above the particles, while positioning it below or at a 1/2 distance from the particles is more likely to cause damage to the machined surface.

A novel dealloying assisted machining method to improve the machinability of NiTi alloy as a typical high toughness difficult-to-machine material

High quality and high efficiency cutting process is of great significance to the components manufacturing related to machinability of workpiece materials. As a typical difficult-to-machine material induced mainly by high toughness, NiTi alloy faces challenges such as high cutting force and difficult chip breaking during the cutting process. To solve these problems, this paper presents a novel surface dealloying assisted machining method, i.e., the preparation of nanoporous structures on the workpiece surface with dealloying treatment, to improve the machinability of NiTi alloy. Based on high speed in-situ imaging of material removal process, the presence of dealloyed layer leads to a segmented flow mode instead of homogeneous severe plastic deformation without dealloying treatment. The change in material removal mode is beneficial to decrease the cutting force and energy and improve the machined surface quality. The embrittlement effect of dealloyed layer inhibits material plastic flow and promotes periodic crack nucleation and propagation. An analytical model is developed to characterize the brittle crack propagation, which provides theoretical basis for explaining embrittlement effect of dealloyed layer. This work verifies the feasibility and effectiveness of the proposed method to modify the machinability of NiTi alloy and provides new ideas for the development of manufacturing processes.