Effect of P10 Cemented Carbide Cutting Tools Subjected to Electromagnetic Coupling Field Treatment on the Surface Roughness of Machined 45 Steel

Reducing the surface roughness of machined workpieces is of great interest owing to its potential for improving the quality of nished items and decreasing the cost of machining processes by reducing the need for post processing. This paper contributes to this research by analyzing the effect of P10 cemented carbide cutting tools subjected to pulsed electromagnetic coupling eld processing (EMCFP) treatment on the surface roughness of machined 45 steel workpieces. The effects of untreated and EMCFP-treated cutting tools on workpiece surface roughness, tool lifetime, friction coecient, electron paramagnetic resonance (EPR) spectra, dislocation density and residual stress are compared. The experimental results demonstrate that EMCFP treatment can reduce the average surface roughness of workpieces by 39.2%, enhance tool lifetime by a factor of 1.92, reduce the friction coecient by 11.4%, increase the intensities of peak EPR signals, increase the dislocation density by 38% and decrease the residual stress of the tool ank face by 51.4% . This research provides scientic data and technical support for EMCFP technology with important scientic signicance.


Introduction
The surface quality of machined metal workpieces has a signi cant in uence on the functional behavior and reliability of machine parts. In this regard, the surface roughness of workpieces is one of the most important features re ecting surface quality [1,2]. The surface roughness of workpieces has been demonstrated to be in uenced by the cutting tool material, tool geometry, the mechanical properties of the workpiece material, and cutting mode [3]. Among these, the tool material is the primary factor affecting the surface roughness [4]. This has led to the wide-scale development of cutting tools and various conditioning treatments for enhancing their mechanical properties.
Among the many proposed tool conditioning treatments, the application of magnetic elds, electric elds, and combined magnetic elds and electric currents, in what is herein denoted as electromagnetic coupling eld processing (EMCFP) treatment, has been demonstrated to enhance the mechanical properties of tool materials, improve tool cutting performance, and reduce residual stress. Moreover, the approach has numerous advantages, such as environmental friendliness, fast and economical tool treatment. For example, Dehghani et al. [5] applied a magnetic eld to both cutting tool and workpiece simultaneously, and thereby reduced the ank-face wear of the tool by 94%, reduced the cutting force by 66%, and modi ed the tribology of the tool/workpiece interface. Tharajak et al. [6] deposited poly(etherether-ketone) (PEEK) coatings on low-carbon steel by thermal spray coating in the presence of a magnetic eld. The results indicated that the optimum magnetic eld enhanced coating properties, resulting in a reduced friction coe cient and increased wear resistance. Zhang et al. [7] applied a magnetic eld during the processing of a titanium alloy, and the tensile stress was observed to be decreased by 24% owing to the homogenization of the residual stress via the excitation of dislocation relaxations by the magnetic eld. Xu et al. [8] investigated the in uence of pulsed magnetic eld treatment on the microstructure of TC4 titanium alloy. The dislocation density was observed to increase about by 10.9% owing to the excitation of the pulsed magnetic eld changing the energy state of electrons in the pinning area of dislocations, which led to enhanced dislocation movement and the transformation of the microstructure.
Ma et al. [9] investigated the effect of applying pulsed magnetic eld treatment to micro-tools on the tool wear, cutting force, and surface roughness of the machined workpiece. The results demonstrated that the surface roughness of the workpiece was reduced when machining ferromagnetic workpiece materials.
Song et al. [10] investigated the tribological properties of GCr15 steel under an alternating magnetic eld. Microstructural analyses of the magnetic eld treated material demonstrated that the substantially improved wear resistance of the treated material was due to increased dislocation density. Similarly, Xi et al. [11] observed substantially increased wear resistance and dislocation density for AISI 1045 steel after the application of a pulsed magnetic eld. Xiang et al. [12] investigated the effect of pulsed electric currents on the dislocation density and residual stress of quenched samples. Both drift electrons and Joule heating effects were found to promote the dynamic behavior of dislocations, which decreased the residual stress dramatically. Jung et al. [13] investigated the effect of pulsed electric currents on the growth of fatigue cracks in an aluminum alloy. The results demonstrated that the optimum pulsed electric current treatment increased the fatigue life of aluminum alloy by 55% owing to the repair of fatigue cracks by local melting on the crack surface. Zhang et al. [14] studied the effect of pulse current on the residual stress of quenched steel, and found that the electronic drift had a direct impact on the dislocation motion and contributed to the plastic strain. In addition, the dislocation caused by electronic wind was also found at the position of thermal activation. Under the in uence of electron drift, the motion of vacancy and dislocation accelerates the annihilation of dislocation. Liu et al. [15] applied EMCFP treatment to cemented carbide machining tools, and demonstrated that the proposed treatment promoted dislocation movement and decreased the wear loss of the tools by nearly 35%. Yuan et al. [16,17] researched the in uences of the electromagnetic coupling eld (TEMCP) on the carbide tool life and cutting performance. The experiments reveal that the optimally treated tools exhibit a fracture toughness increased by 18%, an average cutting temperature decreased by 10%, a friction coe cient for the rank face decreased by 7.9%, and that the magnetic intensity is a dominant factor.
The above-discussed results demonstrate that the application of magnetic elds, electric elds, and combined magnetic and electric elds increases cutting tool lifetime by improving wear resistance, and the indentation fracture toughness of the tools increased a lot. As such, the application of magnetic and electric elds can be expected to reduce the surface roughness of workpieces by reducing surface irregularities on the ank face of cutting tools and therefore reducing friction at the tool/workpiece interface. Moreover, the macro-residual stress of cutting tools has a close relationship with the quality of machined surfaces [18]. Therefore, the reduced residual stress provided by the application of magnetic and electric elds can be expected to yield further bene ts toward reducing the surface roughness of machined workpieces. However, no past studies have investigated the effect of EMCFP treatment on the surface roughness of workpieces.
Due to P10 cemented carbide cutting tools mainly used for rough machining and semi-ne addition, it's a huge consumption. There is great economic value on extended P10 cemented carbide cutting life. 45 steel has the characteristic of low hardness and easy cutting. Therefore, the cutting of 45 steel with P10 carbide tool is a classic combination to study the cutting performance. The present work addresses the effect of EMCFP treatment on the surface roughness of workpieces by analyzing the effect of P10 cemented carbide cutting tools subjected to EMCFP treatment on the surface roughness of machined 45 steel workpieces. The effects of untreated and EMCFP-treated cutting tools on workpiece surface roughness, tool lifetime, friction coe cient, electron paramagnetic resonance (EPR) spectra, dislocation density, and residual stress are compared. This research provides scienti c data and technical support for EMCFP technology with important scienti c signi cance.

Experiments
The cutting experiments were conducted using a 31303C P10 cemented carbide cutting tool on a G-CNC6135 lathe. The cylindrical workpieces were composed of 45 quenched and tempered steel with diameters of 90 mm and lengths of 300 mm. 45 tempered steel is a kind of medium carbon steel. After heat treatment process, it is quenched rst and then tempered at high temperature, which enhances its hardness and strength and maintains its good plasticity and toughness. 45 steel is widely processed into structural parts of various machines, and is the most commonly used type of steel in structured steel. Its chemical composition is shown in Table 1. In order to simulate the general rough machining and seminish machining state, all experiments employed equivalent cutting parameters, which included a spindle speed of 560 r/min, feed rate of 60 mm/min, and a cutting depth of 1 mm. The wear state of the tools was evaluated after each interval of cutting an equivalent linear length of 95 mm until experiencing tool failure. As illustrated in Fig. 1, the wear on the ank face surfaces of the tools was inspected using a VMS 3020 imaging instrument (DongGuan ZhongLi Instrument Technology Co., Ltd., China). The surface roughness of the workpieces was measured using a Bruker ContourGT optical pro ler. Then, the ank face wear (VB) and average surface roughness (Ra) values of the samples were input into a personal computer (PC). Friction tests were conducted using the ball-on-block reciprocating friction and wear tester presented in Fig. 2. The ball was composed of 45 steel and the block material was untreated and EMCFP-treated P10 cemented carbide. The load-carrying tests were performed with normal loads of 120 N, and a reciprocation frequency of 3 Hz was applied with a test duration of 3000 cycles.
The dislocation densities of the P10 cemented carbide inserts were evaluated before and after EMCFP by analyzing four different XRD peak pro les obtained using diffractometer (Empyrean) based on the Williamson-Hall method, which separates the length and strain stress effects of the various diffraction peaks. First, we estimate the crystallite size t of the P10 cemented carbide inserts as follows: Where B is the FWHM, θ is the diffraction angle, K is a constant with a value of about 1, λ is the wavelength of the X-ray source, and ε is the lattice microstrain which is a quarter tting slope of line graph ( ). Then, the dislocation density is given as: where b is the Burger vector (b = 2.61 m for P10 carbide).
The room-temperature ESR spectra of the P10 cemented carbide inserts were obtained before and after EMCFP using a JEOL JES-FA200 ESR spectrometer. The inserts were cut for testing by wire cutting to provide specimens with diameters d = 1 mm and lengths L = 5 mm. The microwave power employed was 1 mW, and the sweep width ranged from 0 mT to 800 mT.
The residual stress of the tool ank faces was measured before and after EMCFP by X-ray diffraction (XRD) in the (2 1 2) diffraction plane using a Proto LXRD residual stress measurement system with an Mn Kα X-ray source. Because the tool ank face directly contacts with the workpiece, the surface residual stress was measured at three points on the tool ank face region illustrated in Fig. 3.

Equipment and analysis of EMCFP
The custom-designed equipment employed for applying EMCFP treatment to P10 cemented carbide cutting tools is illustrated in Fig. 4(a), and consisted mainly of a pulsed magnetic eld generator, a pulsed electric eld generator, and a water-cooled working chamber within which the carbide inserts are placed at atmospheric pressure for treatment. The pulsed magnetic eld generator shown in Fig. 4(a) is composed of a capacitor discharge system and the magnetic induction coil shown in Fig. 4(b). The capacitor discharge system produces a square wave with a frequency of 1-10 Hz that passes through the magnetic induction coil to generate a magnetic eld with an intensity ranging from 0-3.5 T. The magnetic ux density of the generated magnetic eld is measured by a gaussmeter placed at the center of the magnetic induction coil (Fig. 4(b)). The pulsed electric current generator shown in Fig. 4(a) is composed of a power supply system and a computer numerical controlled (CNC) pulse system. The EMCFP treatment is a process in which electric and magnetic elds act on the tool simultaneously. In this process, electric and magnetic elds are coupled. The direction of the electric eld is the same as that of the magnetic eld.

Results And Discussion
3.1 In uence of EMCFP on tool lifetime The VB values obtained for three untreated and three EMCFP-treated P10 cemented carbide tools are presented in Fig. 6. We note that all tool lifetime curves obtained conform to a standard tool wear mechanism, where the value of VB increased rapidly in the initial worn stage, increased at a lower rate in an approximately linear fashion during the normal worn stage, and nally increased rapidly again in the acutely worn stage as the tool approached failure. The results indicate that EMCFP treatment increased the average tool lifetime signi cantly by a factor of 1.92.

In uence of EMCFP on workpiece surface roughness
The workpiece topographies obtained at cutting lengths of 900 mm and 1800 mm when machining with untreated and EMCFP-treated P10 cemented carbide tools are presented in Figs. 7(a) and (b), respectively. The results indicate that the surface roughness of the workpieces was signi cantly reduced when machined by the EMCFP-treated cutting tool owing to the enhanced surface smoothness of the tool.
The workpiece topographies obtained at cutting lengths of 2700 mm and 3600 mm when machining with untreated and EMCFP-treated P10 cemented carbide tools are presented in Figs. 8(a) and (b), respectively. These results obtained at greater cutting lengths very clearly demonstrate the bene ts of employing the proposed EMCFP treatment, where the cutting furrows of the workpiece surface machined by the untreated tool are particularly deep and jagged because the VB value of the tool is greater than 0.2 mm, which is indicative of an acutely worn tool with a very rough surface.
Sections of the actual machined workpiece surfaces subjected to cutting lengths of 3600 mm were removed for three-dimensional (3D) imaging using a VHX-2000 optical microscope (Kenyence Corp. of America). The 3D images and corresponding topologies obtained are presented in Figs. 9(a) and (b), respectively. The results clearly reveal that the surface roughness of the machined workpiece was greatly reduced after subjecting the cutting tool to EMCFP treatment, and the pro le height decreased by 22.81% to 22 μm relative to the conditions obtained with the untreated tool.
The Ra values (μm) of the machined workpieces and the corresponding VB values (mm) of the untreated and EMCFP-treated tools are listed in Table 2 for different cutting lengths. The results indicate that the Ra values of the workpiece machined by the EMCFP-treated tool decreased signi cantly, particularly at cutting lengths of 1800 mm and 2700 mm. In addition, while the changes in the corresponding VB values of the tools are much less than those of the Ra values of the workpiece at cutting lengths of 1800 mm and 2700 mm, these changes are much greater than those of the Ra values at cutting lengths of 900 mm and 3600 mm. Accordingly, we can conclude that the decreased tool wear leading to an enhanced tool lifetime contributes strongly to the reduced surface roughness of the machined workpieces. The surface waviness observed over a lateral distance perpendicular to the cutting direction is another important index re ecting the surface roughness of a machined surface. This condition is illustrated schematically in Fig. 10. The waveform in Fig. 10 (b) was obtained from Fig. 10 (a). The extracted wave pro les indicative of wave width W and wave height R for workpieces subjected to machined by untreated and EMCFP-treated P10 cemented carbide tools are presented in Fig. 11. Comparing the wave width W and wave height R in Fig. 11, the wave width W obtained with the untreated tool and the treated tool were the same. However, wave height R is different, especially in Fig. 11 (b) and Fig. 11 (c).
Additional surface waviness features, including the root mean square deviation (Rq), maximum pro le peak height (Rp), and the maximum pro le valley depth (Rv) along the lateral x direction are illustrated in Fig. 12, and their corresponding calculation formulas based on the average position of the surface Z(x) over the lateral space considered are presented as well. The calculated values of Rq, Rp, and Rv obtained for workpieces machined by untreated and EMCFP-treated tools are listed in Table 3. The results indicate that the values of all features decreased after subjecting the cutting tool to EMCFP treatment, particularly Rv. Accordingly, we can conclude that the waviness of the microstructure of the machined surface was decreased to a large extent after EMCFP, and the cutting process became more stable.

In uence of EMCFP on the friction coe cient
The results of ball-on-block reciprocating friction testing obtained for untreated and EMCFP-treated P10 cemented carbide materials are presented in Fig. 13 according to the mean friction coe cient calculated at each reciprocating cycle of testing. The average friction coe cient obtained over the full 1800 cycles for the untreated sample was 0.583, while this value decreased by 11.4% to 0.516 after EMCFP treatment. Moreover, we note from the results that the mean friction coe cient values obtained at each testing cycle for the treated sample were more uniform over the full number of cycles compared with those of the untreated sample.

In uence of EMCFP on the ERP spectra of cutting tools
The effect of EMCFP treatment on the ERP spectra of P10 cemented carbide samples is shown in Fig. 15.
Here, an increased EPR signal intensity represents a larger number of unpaired electrons in the sample. We note that the peak values of the EPR spectra increased by 7.28% at the signal crest and 29% at the signal trough after EMCFP treatment. Magnetic eld can increase the number of unpaired electrons which can change the state of free radical form (Singlet) S to (Triplet) T [7,19]. The combine energy of electron pair is strong in S state, but weak in T state. In T state, the force of dislocation and pinning centers is weak, even depinning and move. The dislocation multiply lead the plasticity improvement angles after EMCFP treatment, which is indicative of reduced residual stress [20]. The dislocation densities were calculated using Eqs. (1) and (2), and the results are listed in Table 4. We note that the dislocation density increased by 38% after EMCFP treatment. Under the combined impacts of the electro-plastic effect [21,22] and the magnetostriction effect [23], the EMCFP treatment increased dislocation mobility by decreasing the activation energy of dislocation movement, which promoted internal stress release. In addition, the EMCFP process provides the necessary energy for dislocation motions to occur, resulting in the homogenization of the dislocation distribution in the material [7]. Simultaneously, applied electric elds reduce entanglement between dislocations, which removes obstacles toward dislocation slippage, so that the material exhibits higher plasticity [24].  Table 5. The results indicate that residual stress values at all three points of the ank face surfaces decreased signi cantly after EMCFP treatment, and the average residual stress value of the three points was reduced by 51.4% compared with that of the untreated tool. The decreased residual stress can improve the mechanical properties of tool [25] and improve the tool wear resistance, thus decrease the workpiece surface roughness. Accordingly, we can conclude that EMCFP treatment can reduce the workpiece surface roughness signi cantly due to reduced residual stress of the ank face surface. Dislocation, as a crystal defect, produces a special stress eld. EMCFP can effectively increase the dislocation density and make the dislocation more uniform. Dislocation homogenization can affect the tool friction coe cient and residual stress. Dislocation homogenization can reduce the lattice distortion and thus reduce the tool friction coe cient. The friction coe cient of tools directly affects the workpiece surface roughness. When the friction coe cient of the tool is reduced, the ank face wear can be directly reduced, thus improving the life of the tool. Dislocation homogenization can also reduce tool residual stress and improve tool life [26]. Fig. 16 showed the relationship between tool lifetime, workpiece surface roughness, the friction coe cient, the dislocation density, and residual stress.

Conclusions
This work investigated the effect of pulsed EMCFP treatment applied to P10 cemented carbide tools on the surface roughness of machined workpieces for the rst time. The effects of untreated and EMCFPtreated cutting tools on the surface roughness of 45 steel workpieces, tool lifetime, friction coe cient, EPR spectra, dislocation density, and residual stress were compared. The extensive experimental results support the following conclusions.
i. The average surface roughness of workpieces machined using the EMCFP-treated cutting tool decreased by 39.2%, and the values of four surface waviness indexes were signi cantly decreased as well.
ii. The EMCFP treatment increased tool lifetime by a factor of 1.92. Accordingly, EMCFP increased the wear resistance of the tools and reduced surface irregularities on the tool cutting surface.
iii. The average friction coe cient at the cutting tool/workpiece interface decreased by 11.4% after applying EMCFP treatment. Accordingly, the tribological properties of P10 cemented carbide were improved.
iv. The intensity of EPR signal peaks was enhanced due to the increased dislocation density obtained after the EMCFP treatment.
v. The dislocation density of the tool material increased by 38% after EMCFP treatment. Accordingly, EMCFP can increase dislocation mobility by decreasing the activation energy, while providing the necessary energy for dislocation motions to occur, resulting in the homogenization of the dislocation distribution in the material.
vi. The residual stress on the ank face surfaces of cutting tools deceased by 51.4% after EMCFP treatment. Accordingly, EMCFP is a potential method for enhancing the mechanical properties of metals.
These results collectively demonstrate that the proposed EMCFP treatment is a fast, economical, environmentally friendly, and effective metal-enhancement technology that can reduce the surface roughness of workpiece materials signi cantly, reduce the residual stress of cutting tools, and extend cutting tool lifetimes. Accordingly, EMCFP represents a highly bene cial means of supporting the sustainable manufacturing of machined parts.
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Declarations
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Declaration of interest statement
The author(s) declared no potential con icts of interest with respect to the research, authorship, and/or publication of this article.