Cutting condition setting method, machining method, and cutting tool

Abstract

To provide a method for setting a cutting condition that prevents intense deposition between a tool and cutting chips to reduce frictional force, and to provide a method for processing.SOLUTION: A method for setting a cutting condition for a processing device to process a material to be cut using a cutting tool includes a step of setting a cutting condition including at least a cutting speed so as to sufficiently soften the material to be cut at a cutting point or cause a cutting point temperature to reach the vicinity of an upper limit temperature.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] This invention relates to a method for setting cutting conditions, a machining method, and a cutting tool. [Background technology]

[0002] Figure 1 schematically illustrates the cutting process. In the cutting of metallic materials such as aluminum alloys, copper alloys, and iron-based materials, a large frictional force acts between the tool and the chip, increasing the cutting force. This can lead to deterioration of machining accuracy due to deformation, tool wear, and chatter vibration problems. In addition, welding of the workpiece to the tool tip can also cause deterioration of the finished surface and tool wear.

[0003] Large frictional forces arise from high compressive stress between the tool rake face and the chip, and a high coefficient of friction between the tool rake face and the chip. As shown in Figure 1, cutting processes generate chips by causing plastic deformation (mainly in the primary plastic region) of the workpiece. Therefore, it is unavoidable that a large force is applied to a small area near the cutting edge, and it is fundamentally difficult to significantly reduce the compressive stress between the tool rake face and the chip.

[0004] On the other hand, a high coefficient of friction occurs because the rake face of the tool comes into contact with the newly formed and active surface of the workpiece, making it easy for chips to weld (adhere) to the rake face. In cutting operations such as drilling, where chip removal is often difficult, once chips begin to weld, they can easily clog the removal groove, potentially leading to tool breakage. Conventionally, to suppress welding and reduce the coefficient of friction between the tool rake face and the chips, cutting fluids are supplied or low-friction coated tools are used. Non-patent document 1 discloses a DLC (Diamond-Like Carbon) coated tool that achieves a low coefficient of friction. Cutting fluids and low-friction coated tools are often used together.

[0005] Non-patent document 2 is an academic paper in which one of the inventors is listed as a co-author, and it discloses the results of an evaluation of the relationship between the specific cutting energy ks required to remove a unit volume of workpiece and the thermal energy qc required to raise the temperature of a unit volume of chip to its melting point. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Yoshihiko Murakami, Current Status of Dry Processing in Aluminum Machining, Juntsu Net 21 (2006 / 12),<URL : https: / / www.juntsu.co.jp / mql / mql_kaisetsu1.php> [Non-Patent Document 2] Takashi Ueda, Seiichi Uto, Yuki Hirai, and Eiji Shamoto, "Study of Cutting Temperature by Dimensional Analysis (Part 2: Evaluation of the Influence of Thermophysical Properties of Workpieces and Tools)," Transactions of the Japan Society of Mechanical Engineers, Vol. 86(887), 2020, p. 20-00100. [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, in order to reduce the frictional force between the tool and the chip, it is important to reduce the coefficient of friction between the tool and the chip. The present invention has been made in view of this situation, and its objective is to provide a method for setting cutting conditions and a machining method that reduces the frictional force between the tool and the chip. [Means for solving the problem]

[0008] To solve the above problems, a method for setting cutting conditions according to one aspect of the present invention is a method for setting cutting conditions in a processing apparatus that processes a workpiece using a cutting tool, wherein the cutting conditions, including the cutting speed, are set so that the workpiece is sufficiently softened at the cutting point, or the temperature at the cutting point reaches near the upper limit temperature. Here, the cutting point refers to a plastic region or the vicinity of a plastic region where the workpiece contacts the tool at high pressure and shear slip occurs. Referring to Figure 1, the cutting point may be a secondary plastic region or the vicinity of it where chips contact the rake face of the tool at high pressure and shear slip occurs, and may further include a tertiary plastic region or the vicinity of it where the workpiece contacts the relief face of the tool at high pressure on the finishing surface side and shear slip occurs.

[0009] The cutting condition "the workpiece softens sufficiently at the cutting point" may be a cutting condition in which the degree of reduction in the coefficient of friction due to thermal softening of the workpiece when dry machining with a tool that is not coated to achieve a low coefficient of friction is substantially equal to the degree of reduction in the coefficient of friction when wet machining with a tool that is coated to achieve a low coefficient of friction. Furthermore, the cutting condition "the cutting point temperature reaches near the upper limit temperature" may be a cutting condition in which the cutting point temperature reaches a temperature in the range of 90% or more and 100% or less of the upper limit temperature. In this specification, temperature is expressed in Celsius temperature. Note that since the cutting point temperature reaches several hundred degrees Celsius or more, and room temperature is only about 20°C, which is orders of magnitude smaller, discussing in Celsius temperature is roughly the same as discussing in terms of temperature rise.

[0010] Another embodiment of the present invention is a machining method for machining a workpiece using a cutting tool, wherein the machined workpiece is processed by controlling a feed mechanism and a rotation mechanism according to cutting conditions including a cutting speed set such that the workpiece is sufficiently softened at the cutting point, or the temperature at the cutting point reaches near the upper limit temperature. As described above, the cutting point may be the secondary plastic region or its vicinity as shown in Figure 1, and may further include the tertiary plastic region or its vicinity.

[0011] Another machining method according to an aspect of the present invention is a method of machining a workpiece using a cutting tool embedded with a heater, wherein the heater is controlled so that the cutting point temperature becomes equal to or higher than the temperature at which the workpiece is sufficiently softened, or reaches near the upper limit temperature, and the workpiece is machined. The "temperature at which the workpiece is sufficiently softened" may be a temperature of 80% or more of the upper limit temperature.

[0012] Another cutting tool according to an aspect of the present invention is a cutting tool for machining a workpiece, comprising a heater for heating a rake face, and during machining of the workpiece, the heater heats the rake face so that the cutting point temperature becomes equal to or higher than the temperature at which the workpiece is sufficiently softened, or reaches near the upper limit temperature. The "temperature at which the workpiece is sufficiently softened" may be a temperature of 80% or more of the upper limit temperature.

[0013] In addition, any combination of the above components, and those obtained by converting the expression of the present invention between methods, apparatuses, systems, etc. are also effective as aspects of the present invention.

Brief Description of Drawings

[0014] [Figure 1] It is a diagram schematically showing a cutting process. [Figure 2] It is a diagram showing a schematic configuration of a machining apparatus according to an embodiment. [Figure 3] It is a diagram showing the result of measuring the cutting point temperature during machining. [Figure 4] It is a diagram schematically showing the relationship of forces acting in a cutting process. [Figure 5] It is a diagram showing the measurement results of the cutting point temperature and the cutting force during coating wet machining. [Figure 6] It is a diagram showing the measurement results of the cutting point temperature and the cutting force during non - coating dry machining. [Figure 7] It is a diagram showing the result of measuring the influence of the temperature rise accompanying an increase in cutting speed on the specific cutting energy. [Figure 8]This figure shows the relationship between the specific cutting energy of multiple metal materials and the thermal energy required to raise the temperature of a unit volume of chip to its melting point. [Figure 9] This figure shows the results of the temperature rise analysis at the cutting point. [Figure 10] This figure shows an example of a cutting tool equipped with an internal heater. [Figure 11] This figure shows another example of a cutting tool with an internal heater. [Modes for carrying out the invention]

[0015] Figure 2 shows a schematic configuration of the machining apparatus 1 of the embodiment. The machining apparatus 1 is a cutting apparatus that processes a workpiece 6 using a cutting tool 10, and Figure 2 shows a cutting apparatus that performs turning by cutting the cutting edge of the cutting tool 10 into the workpiece 6. The machining apparatus 1 includes a headstock 2 and a tailstock 3 that rotatably support the workpiece 6 on a bed 5, and a tool post 4 that supports the cutting tool 10.

[0016] The rotating mechanism 8 is located inside the headstock 2 and rotates the spindle 2a to which the workpiece 6 is attached. The feed mechanism 7 is located on the bed 5 and moves the cutting tool 10 relative to the workpiece 6. In this machining apparatus 1, the feed mechanism 7 moves the tool post 4 in the X, Y, and Z directions, thereby moving the cutting tool 10 relative to the workpiece 6. Here, the X direction is the cutting direction, which is horizontal and perpendicular to the axial direction of the workpiece 6; the Y direction is the cutting direction, which is vertical; and the Z direction is the feed direction, which is parallel to the axial direction of the workpiece 6.

[0017] The control unit 20 includes a rotation control unit 21 that controls the rotation of the spindle 2a by the rotation mechanism 8, and a movement control unit 22 that causes the cutting edge of the cutting tool 10 to cut into the workpiece 6 by the feed mechanism 7 while the spindle 2a is rotating, thereby performing cutting. The processing device 1 may be an NC machine tool. The rotation mechanism 8 and the feed mechanism 7 are each configured with a drive unit such as a motor, and the rotation control unit 21 and the movement control unit 22 control the behavior of the rotation mechanism 8 and the feed mechanism 7 respectively by adjusting the power supplied to the drive unit. The control unit 20 also includes a heating control unit 23 and a temperature acquisition unit 24, the operation of which will be described later.

[0018] In the machining apparatus 1 of this embodiment, the workpiece 6 is attached to the spindle 2a and rotated by the rotation mechanism 8, but in another example, the cutting tool 10 may be attached to the spindle 2a and rotated by the rotation mechanism 8. The feed mechanism 7 only needs to move the cutting tool 10 relative to the workpiece 6, and only needs to have a mechanism to move at least one of the cutting tool 10 or the workpiece 6.

[0019] The cutting condition setting device 30 has the function of determining the cutting conditions to be used in the processing device 1 and setting them in the processing device 1. In this embodiment, the cutting condition setting device 30 sets cutting conditions including at least the cutting speed. The cutting condition setting device 30 may also generate NC data for use in the processing device 1 from the set cutting conditions and provide it to the control unit 20. The cutting condition setting device 30 may be configured as part of the processing device 1, or it may be configured as a separate device from the processing device 1.

[0020] The inventors have been conducting research on high-speed, high-efficiency cutting processes for various workpiece materials using high-speed machine tools and high-heat-resistant, high-toughness ceramic tools that are becoming increasingly practical in recent years. As a result, they discovered that under cutting conditions where the tool tip temperature becomes extremely high, the coefficient of friction between the tool rake face and the chip decreases significantly, suppressing welding. Furthermore, the inventors found that cutting speed has a particularly large influence on this phenomenon, and that, in addition to cutting speed, the cutting thickness and tool rake angle also have an influence.

[0021] Figure 3 shows the results of measuring the cutting point temperature during continuous turning of six different workpiece materials at varying cutting speeds. The measured cutting point temperature is the temperature in the secondary plastic region (see Figure 1) on the side in contact with the rake face of the tool. An alumina ceramic tool was used in this continuous turning process. In the graph shown in Figure 3, the horizontal axis represents the cutting speed, and the vertical axis represents the value obtained by dividing the cutting point temperature (cutting temperature) by the melting point of the workpiece material. As can be seen from these measurement results, the cutting point temperature increases power-law with respect to the cutting speed (each line shown in Figure 3 represents a function that fits the experimental values). The cutting point temperatures of Inconel 718 and titanium alloy, which have high strength and low thermal diffusivity, reach near the melting point at a cutting speed of about 500 m / min.

[0022] Figure 4 schematically illustrates the relationship between forces acting in a cutting process. The frictional force F is the value obtained by multiplying the force N perpendicular to the rake face by the coefficient of friction μ. A shear force Fs acts on the shear surface. The combined cutting force R consists of the main component force Fp and the back component force Ft. In Figure 4, the cutting speed v, the cutting thickness h, and the tool rake angle α constitute some of the cutting conditions.

[0023] Figures 5 and 6 show the results of measuring the cutting point temperature and cutting force when turning (more precisely, parting-off turning, which is an approximate two-dimensional cutting) an aluminum alloy (A7075) while varying the cutting speed. The horizontal axis represents the cutting speed, and the cutting conditions were a tool rake angle of 10 degrees and a cut thickness of 0.15 mm. Figures 5(a) and (b) show the measurement results of cutting point temperature and cutting force (main force component and back force component) when cutting with DLC-coated carbide tools while supplying cutting fluid (hereinafter also referred to as "coated wet machining"). Figures 6(a) and (b) show the measurement results of cutting point temperature and cutting force (main force component and back force component) when dry cutting with uncoated carbide tools (hereinafter also referred to as "uncoated dry machining"). Here, the cutting point temperature was measured by the tool-workpiece thermocouple method, and the cutting force was measured by a dynamometer.

[0024] Figures 5(a) and 6(a) show the relationship between cutting point temperature and cutting speed. The cutting point temperatures shown in Figures 5(a) and 6(a) are the average temperatures at the cutting point measured by the tool-workpiece thermocouple method. Figures 5(b) and 6(b) show the relationship between cutting force and cutting speed.

[0025] As described above, the relationship between cutting point temperature and cutting speed follows a power law. The cutting point temperature T is proportional to a power of the cutting speed v and can be expressed by the following relationship (temperature rise curve). T=Cv n If we determine the coefficient C and the exponent n in this relation to fit the experimental values ​​shown in Figures 5(a) and 6(a), we can derive the same relation (a) for both sets of experimental values. T = 60 × v 0.25 ...(a)

[0026] In Figures 5(a) and 6(a), the cutting point temperature saturates at approximately 420°C. If we call this saturated temperature the "upper limit temperature," then from the above relation (a), the cutting speed v at which the cutting point temperature reaches approximately 420°C is calculated to be approximately 2500 m / min. Referring to the experimental values ​​of the cutting point temperature in Figures 5(a) and 6(a), it can be seen that at cutting speeds lower than 2500 m / min, the cutting point temperature rises roughly power-law, and at cutting speeds higher than 2500 m / min, the cutting point temperature saturates and remains constant at the upper limit temperature.

[0027] Furthermore, it is known that in the high-temperature range, the strength of the workpiece decreases approximately linearly with increasing temperature. The back force is strongly affected by the decrease in the strength of the workpiece on the rake face, and under conditions where the strength decreases approximately linearly with increasing temperature, the back force Ft and the cutting point temperature T can be expressed by the following relationship. Ft = F0 - mT By determining F0 and the coefficient m in this relationship to fit the experimental values ​​of the back force shown in Figure 6(b), the following relationship can be derived. Ft = 420 - T ... (b) According to this relation (b), when the cutting point temperature is 420°C, the back force Ft is calculated to be 0. In other words, relation (b) shows that when the cutting point temperature reaches the upper limit temperature (approximately 420°C), the back force Ft becomes 0, and the accuracy of the cutting speed of 2500 m / min calculated by relation (a) is guaranteed.

[0028] Here, the melting point of aluminum alloy (A7075) is approximately 660°C, and the measured upper limit temperature (approximately 420°C) is lower than the melting point. However, the cutting point temperature plateaus in the cutting speed range of 2500 m / min and does not rise further. The reason why the cutting point temperature plateaus is discussed below.

[0029] In the cutting process, almost all cutting energy is converted into cutting heat. The proportion of this cutting heat that flows into the chip side as the workpiece moves increases with increasing cutting speed and cutting thickness. In particular, in the high cutting speed range, almost all of the cutting heat flows into the chip side. One reason why the cutting point temperature saturated at the upper limit temperature in Figures 5(a) and 6(a) is that the cutting heat flowing into the chip side increases, causing the maximum temperature at the cutting point to reach the melting point of the workpiece. At this point, the heat of fusion prevents the maximum temperature from rising above the melting point, thus the cutting point temperature (average temperature at the cutting point) stops rising. It is known that the cutting point temperature is highest at a position slightly ahead of the cutting edge tip in the chip outflow direction on the rake face.

[0030] This analysis assumes that the highest temperature at the cutting point reaches the melting point of the workpiece. However, if the highest temperature does not reach the melting point of the workpiece, the temperature at the cutting point is thought to stop rising for the following reasons.

[0031] It is known that the specific cutting energy required to remove a unit volume of workpiece does not change significantly with respect to the cutting speed for any metal workpiece, and is close to the thermal energy required to raise the temperature of that workpiece to its melting point (see Non-Patent Literature 2). Figure 7 shows the results of measuring the influence of the temperature rise associated with an increase in cutting speed on the specific cutting energy ks in Non-Patent Document 2. These experimental results indicate that the specific cutting energy ks of S50C-N, 6 / 4 Brass, and AZ80 is approximately constant even when the cutting speed changes. Figure 8 shows the relationship between the specific cutting energy ks of a plurality of metal materials and the thermal energy qc required to raise the chips per unit volume to the melting point. On the dashed-dotted line in Figure 8, ks = qc, and as shown, the specific cutting energy ks and the thermal energy qc of each metal material are generally equal. Among these, the metal materials showing ks < qc are materials where the maximum temperature at the cutting point does not reach the melting point even when the cutting speed increases in the cutting process, and the cutting point temperature asymptotes (saturates) to the upper limit temperature determined by the material.

[0032] According to the experimental results disclosed in Non-Patent Document 2, when machining a metal material where the maximum temperature at the cutting point does not reach the melting point, if the cutting speed and the depth of cut are large, it is considered that almost all the cutting heat flows into the chip side, causing the maximum temperature at the cutting point to rise to a temperature relatively close to the melting point and then level off. In the examples, the leveled-off temperature (the temperature reached by the thermal energy qc corresponding to the melting point or the specific cutting energy ks) is referred to as the "upper limit temperature". The specific cutting energy ks depends on the rake angle as well, but in metal cutting, the practical rake angle is about ±15 degrees and has little significant effect. Therefore, as shown in Figure 8, since the specific cutting energy ks is more than about half of the thermal energy qc for reaching the melting point, the upper limit temperature becomes a value of about 1 / 2 or more of the melting point. The upper limit temperature can be determined by measurement.

[0033] In the practical cutting speed range of 600 m / min or less used in general cutting, since the chips adhere strongly to the tool rake face, in machining combinations that are prone to adhesion such as aluminum alloys and carbide tools, it is said that in practice, the use of low-friction coated tools and the supply of cutting oils are essential. Figure 6(b) shows the relationship between cutting force and cutting speed in non-coated dry machining. As shown in Figure 6(b), in the cutting speed range of 600 m / min or less, the back force is very large, and therefore it is shown that in the cutting speed range of 600 m / min or less, the coefficient of friction is high and a large frictional force is generated.

[0034] Figure 5(b) shows the relationship between cutting force and cutting speed under coating and wet machining. Compared with the measurement results shown in Figure 6(b), the measurement results in Figure 5(b) show that in the cutting speed range of 600 m / min or less, the back force is reduced, i.e., the coefficient of friction is reduced, due to the effects of the cutting fluid and DLC coating.

[0035] The inventors focused on high-speed regions beyond the conventional practical range and found that in high-speed regions with cutting speeds of approximately 1000 m / min or higher, there is no significant difference between the back force and main force in coated wet machining and in non-coated dry machining. In other words, in high-speed regions with cutting speeds of approximately 1000 m / min or higher, the effects of cutting fluids and low-friction coated tools in coated wet machining are no longer observed.

[0036] The inventors analyzed the factors behind this phenomenon as follows: Metallic materials tend to soften when heated. Generally, metals are said to begin softening at a temperature of about 0.4 to 0.5 times their melting point in absolute temperature. Therefore, this phenomenon is thought to have occurred because the cutting point temperature became high due to the high cutting speed, increasing the area and degree of softening at the contact surface, and thus reducing the frictional force. Generally, the frictional force in the dry state that occurs on a smooth surface is caused by the shearing of the material with lower strength (in this case, the workpiece) among the materials adhered to the true contact surface (Bowden's adhesion theory). In other words, it is presumed that the shear force, i.e., the frictional force in the secondary plastic region (see Figure 1) decreased because a part of the chip surface that rubs against the rake face of the tool was thermally softened. This can also be described as the occurrence of a lubricating effect.

[0037] In high-speed cutting processes (see Figure 1), the primary and secondary plastic regions are the main heat sources. However, because the primary plastic region is roughly perpendicular to the direction of high-speed mass transfer of the workpiece, the heat generated in the primary plastic region is instantly carried away to the chip. In contrast, because the secondary plastic region is roughly parallel to the direction of high-speed mass transfer of the workpiece (in this case, the chip), the heat generated in the secondary plastic region tends to remain there. Furthermore, heat generated in the primary plastic region also moves into the secondary plastic region. Therefore, in high-speed cutting processes, the temperature in the secondary plastic region rises significantly.

[0038] Figure 9 shows an example of the analysis results of the temperature rise at the cutting point. The temperature analysis results shown in Figure 9 are from "Kensuke Yamamoto, Evaluation of Residual Stress of Surface-Processed Layers Due to Cutting Using Thermal-Structural Interaction Analysis, University of Tokyo Graduation Thesis, Submitted January 2016."<URL : https: / / www.fml.t.u-tokyo.ac.jp / img / graduation-thesis / 2015b_yamamoto.pdf> This is disclosed in [the document]. As shown in the analysis results in Figure 9, the temperature in the secondary plastic region (cutting point temperature) rises significantly compared to the temperature rise in the primary plastic region. Therefore, it is estimated that the secondary plastic region, especially the contact area with the rake face, softens due to heat, and the frictional force decreases, resulting in a significant decrease in stress in the frictional direction. The tertiary plastic region directly below the cutting edge is smaller than the primary and secondary plastic regions, but it becomes relatively hot due to the temperature rise caused by frictional heating, as well as heat conduction from the rake face side, which is the hottest.

[0039] In Figures 5(b) and 6(b), when comparing the high-speed region where the cutting speed is approximately 1000 m / min or higher, there is no difference in the main force component and back force component between coated wet machining and non-coated dry machining. Therefore, it can be inferred that when the cutting speed reaches approximately 1000 m / min, the cutting point temperature is at a temperature at which the workpiece material (aluminum alloy (A7075)) is sufficiently softened.

[0040] Furthermore, in the region where the cutting speed is approximately 2500 m / min or higher, there is no change in the main force component and the back force component, and the back force component is approximately zero. This zero back force component means that the friction angle is equal to the tool rake angle, which in this case is 10 degrees. Referring to Figure 4, when the friction angle β is equal to the tool rake angle α, the combined cutting force R and its reaction force R' are parallel to the cutting direction.

[0041] A friction angle of 10 degrees corresponds to a friction coefficient of 0.176 (=tan(10 degrees)). This value of friction coefficient is extremely small for solid friction between the tool rake face and the fresh surface of the workpiece. This friction coefficient is approximately equal to the friction coefficient between a wet DLC-coated tool and the workpiece in the region of near-zero cutting speed shown in Figure 5(b) (it is said that cutting fluids cannot penetrate the secondary plastic region where high pressure occurs, so the influence of cutting fluids on this friction coefficient is small, and it is mainly considered to be the effect of the DLC coating). In other words, in the region where the cutting point temperature saturates at the upper limit temperature, a lubrication effect comparable to that of the DLC coating can be obtained by the workpiece that partially reaches its melting point and melts, and / or by the sufficiently softened workpiece.

[0042] From the above experiments, it was found that in the conventional practical cutting speed range, non-coated dry machining is not practical due to severe welding and an excessively high coefficient of friction. However, in the cutting speed range where the cutting point temperature is above the temperature at which the workpiece softens sufficiently, non-coated dry machining can achieve a low coefficient of friction equivalent to that of coated wet machining.

[0043] Therefore, the cutting condition setting device 30 of the embodiment sets the cutting conditions, including at least the cutting speed, so that the workpiece softens sufficiently at the cutting point, or so that the temperature at the cutting point reaches near the upper limit temperature. This allows the processing device 1 to achieve cutting with reduced friction between the tool rake face and the chips. At this time, by performing dry machining using inexpensive non-coated tools (non-coated dry machining), cutting can be achieved with low environmental impact and low cost.

[0044] Here, the cutting conditions in which "the workpiece softens sufficiently at the cutting point" may be cutting conditions in which the degree of reduction in the coefficient of friction during coated wet machining is substantially equal to the degree of reduction in the coefficient of friction due to thermal softening of the workpiece during non-coated dry machining. In Figures 5(b) and 6(b), in the high-speed region where the cutting speed is approximately 1000 m / min or higher, the back force and main force in coated wet machining are substantially equal to the back force and main force in non-coated dry machining. Therefore, in the embodiment, the cutting conditions in which "the workpiece softens sufficiently at the cutting point" may be cutting conditions in which the back force and main force are substantially equal in coated wet machining and non-coated dry machining.

[0045] From another perspective, the cutting conditions in which the workpiece is sufficiently softened at the cutting point may be cutting conditions in which the cutting point temperature rises to 80% or more of the upper limit temperature. Referring to Figures 5(a) and 6(a), the temperature at which 80% of the upper limit temperature (420°C) is reached is 336°C. When the cutting speed v at a cutting point temperature of 336°C is calculated using relation (a), it is approximately 1000 m / min, which corresponds to the cutting conditions in which the back force and main force in coated wet machining are substantially equal to those in non-coated dry machining. Therefore, by setting the cutting conditions so that the cutting point temperature is 80% or more of the upper limit temperature, the machining apparatus 1 can perform dry machining using inexpensive non-coated tools (non-coated dry machining), achieving cutting with low environmental impact and low cost.

[0046] The following describes how the cutting condition setting device 30 sets the cutting conditions, including the cutting speed, the cutting thickness, and the tool rake angle, so that the workpiece is sufficiently softened at the cutting point, or the temperature at the cutting point reaches near the upper limit temperature.

[0047] The inventors, through various experiments on cutting conditions, confirmed that the cutting point temperature changes substantially power-function with respect to cutting speed, cutting thickness, and tool rake angle in the region before reaching the upper limit temperature. · Cutting speed v [m / min]: The cutting point temperature changes in proportion to v a (a is a constant). · Chip thickness h [mm]: The cutting point temperature changes in proportion to h b (b is a constant). · Tool rake angle α [deg]: The cutting point temperature changes in proportion to α c (c is a constant). From the above findings, the inventor of the present invention has derived that the cutting point temperature is in a proportional relationship with v a ×h b ×α c . Hereinafter, v a ×h b ×α c is called the "index value". In an experiment of cutting an aluminum alloy (A7075) with a carbide tool (continuous turning), a was approximately 0.25, b was approximately 0.08, and c was approximately -0.03.

[0048] The cutting condition setting device 30 utilizes the above relationship to set the cutting conditions including the cutting speed v, the chip thickness h, and the tool rake angle α so that the workpiece material is sufficiently softened at the cutting point or the cutting point temperature reaches near the upper limit temperature. Hereinafter, the cutting conditions when cutting an aluminum alloy with a carbide tool (continuous turning) will be described.

[0049] The cutting condition setting device 30 may set the cutting conditions so that the cutting point temperature is not less than the temperature at which the workpiece material is sufficiently softened. In FIG. 6(b), the cutting point temperature reached the temperature at which the workpiece material was sufficiently softened when the cutting speed reached 1000 m / min. Therefore, the index value when the cutting point temperature becomes the temperature causing sufficient softening of the workpiece material is obtained as follows. (Index value) = 1000 0.25 ×0.15 0.08 ×10 -0.03 = 4.51 The calculated 4.51 is used as the threshold value Th1 in the relational expression 1 for determining that the cutting point temperature is not less than the temperature at which the workpiece material is sufficiently softened. (Relational expression 1) v 0.25 ×h0.08 ×α -0.03 ≥Th1 Therefore, the cutting condition setting device 30 can set the cutting point temperature during cutting to a temperature above the temperature at which the workpiece softens sufficiently by determining the cutting speed v, cutting thickness h, and tool rake angle α to satisfy relational equation 1.

[0050] The cutting condition setting device 30 may set the cutting conditions so that the cutting point temperature reaches near the upper limit temperature. In Figure 6(b), the cutting point temperature reaches near the upper limit temperature when the cutting speed reaches 2500 m / min, so the index value when the cutting point temperature reaches near the upper limit temperature can be calculated as follows. (Index value) = 2500 0.25 ×0.15 0.08 ×10 -0.03 =5.67 The calculated value of 5.67 is used as the threshold Th2 in relational equation 2, which determines when the cutting point temperature reaches near the upper limit temperature. (Relationship 2) v 0.25 ×h 0.08 ×α -0.03 ≥Th2 Therefore, the cutting condition setting device 30 can set the cutting point temperature during cutting to near the upper limit temperature by determining the cutting speed v, cutting thickness h, and tool rake angle α to satisfy relational equation 2.

[0051] As described above, the cutting condition setting device 30 determines the cutting conditions, including the cutting speed v, cutting thickness h, and tool rake angle α, using a relational equation. (Relationship) v a ×h b ×α c ≧Th Here, a, b, c, and Th are constants determined experimentally or theoretically by the combination of the workpiece and tool set and an index value indicating the intermittency of the cutting process. Specifically, the index value of intermittency refers to the cutting time and non-cutting time, and the time ratio, within one cycle of intermittent cutting such as milling. The longer the cutting time per pass and the larger the cutting time ratio to one cycle, the higher the average and maximum values ​​of the cutting point temperature.

[0052] The cutting condition setting device 30 stores sets of a, b, c, and Th in memory for various combinations of workpiece and tool sets and intermittency index values. When an operator inputs a combination of workpiece and tool sets and intermittency index values ​​before starting machining, the cutting condition setting device 30 may read the corresponding sets of a, b, c, and Th from memory, determine cutting conditions including cutting speed v, cutting thickness h, and tool rake angle α that satisfy the relational expression, and set them in the control unit 20 of the machining device 1.

[0053] In the processing apparatus 1, the control unit 20 controls the feed mechanism 7 and the rotation mechanism 8 according to the set cutting conditions. Specifically, the rotation control unit 21 rotates the spindle 2a at a rotation speed corresponding to the set cutting speed v, the tool post 4 holds the cutting tool 10 so that the tool rake angle α is set, and the movement control unit 22 cuts the cutting edge of the cutting tool 10 into the workpiece 6 with a set cutting thickness h, thereby processing the workpiece 6.

[0054] The above explains parting turns. However, in normal turning operations, the thickness of the material cut is not constant along the cutting edge, so an average thickness of material cut may be used. Also, in hole machining, the cutting speed decreases significantly near the center of the hole, making it impossible to derive cutting conditions that satisfy the above relationship. Therefore, when machining holes, by using a hole machining tool that does not cut near the center (for example, a boring turning tool or a hole saw type tool), it becomes possible to derive cutting conditions that sufficiently soften the workpiece at the cutting point or bring the cutting point temperature close to the upper limit temperature.

[0055] Furthermore, when the maximum rotational speed of the processing device 1 is low, or when the diameter of the rotating tool or the diameter of the workpiece is small, when the cutting thickness is small, or when a tool with a large rake angle is used, it becomes difficult to derive cutting conditions that satisfy the above relationship. In such cases, non-coating dry machining may be performed by using a means to heat the vicinity of the tool cutting edge (especially the rake face).

[0056] Figure 10 shows an example of a cutting tool equipped with a heater 40. The cutting tool 10a shown in Figure 10 is a non-coated tool in which one or more heaters 40 for heating the rake face are embedded inside an insert fixed to the tool shank. An external power supply is connected to the heater 40, and the heating control unit 23 supplies power from the external power supply to the heater 40, causing the heater 40 to heat the rake face. Preferably, the heater 40 is embedded directly below the rake face near the cutting edge, and more preferably, to heat the chip contact surface in the secondary plastic region.

[0057] Figure 11 shows another example of a cutting tool equipped with an internal heater 40. The cutting tool 10b shown in Figure 11 is a non-coated tool in which one or more heaters 40 are embedded inside the tip to heat the rake face. The cutting tool 10b may be a drill for cutting a workpiece. An external power supply (not shown) is connected to the heater 40, and the heating control unit 23 supplies power from the external power supply to the heater 40, causing the heater 40 to heat the rake face. The heater 40 is preferably embedded directly below the rake face near the cutting edge, and more preferably to heat the chip contact surface in the secondary plastic region.

[0058] In the cutting tool 10a shown in Figure 10 and the cutting tool 10b shown in Figure 11, a temperature sensor (e.g., a thermocouple) may be embedded near the heater 40. Preferably, the temperature of the cutting point heated by the heater 40 is measured or estimated by the tool-workpiece thermocouple method or analysis. The heating control unit 23 controls the heating of the heater 40 embedded near the cutting edge (preferably on the rake face side), and the temperature acquisition unit 24 acquires the temperature near the cutting edge on the rake face side from the temperature sensor or analysis device. The heating control unit 23 monitors the temperature acquired by the temperature acquisition unit 24 and controls the heating of the heater 40 so that the cutting point temperature is above the temperature at which the workpiece softens sufficiently, or reaches a temperature near the upper limit temperature, thereby heating the rake face, and the workpiece is processed in this heated state. If the cutting condition setting device 30 cannot derive cutting conditions that satisfy the relational expression, the heating control unit 23 may auxiliaryly heat the heater 40 to control the cutting point temperature.

[0059] This heated cutting method is effective even in cutting operations using conventional drills or ball end mills that require cutting even near the rotation center where the cutting speed is zero, or in end face cutting operations that involve turning near the rotation center. In particular, for drills and ball end mills that have cutting edges near the rotation center where the cutting speed is zero, it is preferable for the heating control unit 23 to control heating by arranging the heaters so that the amount of heat generated increases the closer it is to the center.

[0060] The present invention has been described above based on embodiments. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their respective components and processing processes, and that such modifications also fall within the scope of the present invention.

[0061] The following is an overview of the embodiments of the present invention. A method for setting cutting conditions according to one aspect of the present invention is a method for setting cutting conditions in a processing apparatus that processes a workpiece using a cutting tool, wherein the cutting conditions, including the cutting speed, are set so that the workpiece is sufficiently softened at the cutting point, or the temperature at the cutting point reaches near the upper limit temperature.

[0062] By setting the cutting conditions in this way, severe welding between the tool and chips can be prevented, reducing the coefficient of friction and achieving machining with reduced frictional force. In this method, the cutting conditions, including the cutting speed, cutting thickness, and tool rake angle, may be set so that the workpiece is sufficiently softened at the cutting point, or so that the temperature at the cutting point reaches near the upper limit temperature.

[0063] The method may set the cutting conditions such that the cutting point temperature reaches a temperature that causes sufficient softening of the workpiece. The method may set the cutting conditions such that the cutting point temperature reaches near the upper limit temperature determined mainly by the workpiece. For example, the method may determine a cutting speed v, a cutting thickness h, and a tool rake angle α that satisfy a predetermined relationship. The method may determine the cutting speed v, the cutting thickness h, and the tool rake angle α, v a ×h b ×αc ≥Th (where a, b, c, and Th are constants) It is acceptable to decide such that the relationship satisfies the given equation.

[0064] Another embodiment of the present invention is a machining method for machining a workpiece using a cutting tool, wherein the machine is performed by controlling a feed mechanism and a rotation mechanism according to cutting conditions including a cutting speed set so that the workpiece is sufficiently softened at the cutting point, or so that the temperature at the cutting point reaches near the upper limit temperature.

[0065] By using these cutting conditions, it is possible to prevent severe welding between the tool and the chips, reduce the coefficient of friction, and achieve machining with reduced frictional force.

[0066] A further embodiment of the present invention is a method of machining a workpiece using a cutting tool with an embedded heater, wherein the heater is controlled so that the cutting point temperature is above the temperature at which the workpiece softens sufficiently, or reaches near the upper limit temperature, while machining the workpiece.

[0067] By using such cutting tools, it is possible to prevent severe welding between the tool and the chips, reduce the coefficient of friction, and achieve machining with reduced frictional force.

[0068] A cutting tool according to yet another aspect of the present invention is a cutting tool for processing a workpiece, comprising a heater for heating the rake face, wherein during processing of the workpiece, the heater heats the rake face such that the cutting point temperature is above the temperature at which the workpiece is sufficiently softened, or reaches near the upper limit temperature.

[0069] By using such cutting tools, it is possible to prevent severe welding between the tool and the chips, reduce the coefficient of friction, and achieve machining with reduced frictional force. [Explanation of Symbols]

[0070] 1... Processing device, 6... Workpiece, 10, 10a, 10b... Cutting tool, 20... Control unit, 21... Rotation control unit, 22... Movement control unit, 23... Heating control unit, 24... Temperature acquisition unit, 30... Cutting condition setting device, 40... Heater.

Claims

1. A method for setting cutting conditions in a machining apparatus that processes a workpiece using a cutting tool, The cutting point temperature changes power-law with respect to the cutting speed, cutting thickness, and tool rake angle before reaching an upper limit temperature at which the cutting point temperature does not rise even when the cutting speed is increased. The cutting conditions, including the cutting speed v, the cutting thickness h, and the tool rake angle α, are set so that the cutting point temperature reaches 80% or more of the upper limit temperature. The set cutting speed v, cutting thickness h, and tool rake angle α are: v ａ ×h ｂ ×α ｃ ≧Th Satisfying the conditions, a, b, and c are indices that represent the power-law function change of the cutting point temperature with respect to the cutting speed, cutting thickness, and tool rake angle, respectively. Th is an index value representing the point at which the cutting point temperature reaches 80% of the upper limit temperature. a, b, c, and Th are constants determined by the combination of the workpiece and the cutting tool. A method for setting cutting conditions characterized by the following:

2. A machining method for processing a workpiece using a cutting tool, wherein the feed mechanism and rotation mechanism are controlled according to cutting conditions including a cutting speed v set such that the cutting point temperature reaches 80% or more of the upper limit temperature at which the cutting point temperature does not rise even when the cutting speed is increased, a cutting thickness h, and a tool rake angle α, and the cutting tool is used to process the workpiece. The cutting point temperature changes power-function with respect to the cutting speed, cutting thickness, and tool rake angle before reaching the upper limit temperature. The set cutting speed v, cutting thickness h, and tool rake angle α are: v ａ ×h ｂ ×α ｃ ≧Th Satisfying the conditions, a, b, and c are indices that represent the power-law function change of the cutting point temperature with respect to the cutting speed, cutting thickness, and tool rake angle, respectively. Th is an index value representing the point at which the cutting point temperature reaches 80% of the upper limit temperature. a, b, c, and Th are constants determined by the combination of the workpiece and the cutting tool. A processing method characterized by the following.

3. A machining method for processing a workpiece using a cutting tool with an embedded heater, Before the cutting point temperature reaches the upper limit temperature where it remains constant without increasing even when the cutting speed is increased, for each of the cutting speed, the depth of cut, and the tool rake angle, it changes in a power function. Here, a, b, and c are the exponents representing the power function change of the cutting point temperature with respect to the cutting speed, the depth of cut, and the tool rake angle respectively. Th is an index value when the cutting point temperature becomes 80% of the upper limit temperature, and it is a constant determined for the combination of the workpiece and the cutting tool. When the cutting speed v, the depth of cut h, and the tool rake angle α that satisfy the relational expression v ａ ×h ｂ ×α ｃ ≧ Th cannot be set, the heater is controlled so that the cutting point temperature reaches a temperature of 80% or more of the upper limit temperature, and the workpiece is machined. A machining method characterized by this.

4. A cutting tool for machining a workpiece, comprising a heater for heating the rake face, The cutting point temperature changes power-function with respect to cutting speed, cut thickness, and tool rake angle, respectively, before reaching an upper limit temperature at which the cutting point temperature does not rise even when the cutting speed is increased. a, b, and c are indices representing the power-function change of the cutting point temperature with respect to cutting speed, cut thickness, and tool rake angle, respectively, and Th is an index value at which the cutting point temperature reaches 80% of the upper limit temperature. The relationship v using a, b, c, and Th is a constant determined for the combination of workpiece material and cutting tool. ａ ×h ｂ ×α ｃ When it is not possible to set a cutting speed v, cutting thickness h, and tool rake angle α that satisfy ≥ Th, the heater heats the rake face during machining of the workpiece so that the cutting point temperature reaches 80% or more of the upper limit temperature. A cutting tool characterized by the following features.

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