Cutting coefficient recognition system in machine tool and cutting coefficient recognition method in machine tool

Abstract

The invention provides a cutting coefficient recognition system in a machine tool and a cutting coefficient recognition method in the machine tool, which can recognize a cutting coefficient with high precision by using a motor torque of the machine tool without using an additional sensor. A cutting coefficient identification system (21) acquires an average torque required for cutting a main shaft (4) and a feed shaft of a machine tool in a measured cutting force acquisition unit (22), and calculates a measured cutting force. Next, tool information is acquired by a tool information acquisition unit (23), cutting conditions are acquired by a cutting condition acquisition unit (24), and an estimated cutting force is calculated by an estimated cutting force calculation unit (25) on the basis of the information. Next, in a cutting coefficient identification unit (26), the measured cutting force and the estimated cutting force are compared to identify a cutting coefficient.

Description

Technical Field

[0001] The present disclosure relates to a cutting coefficient identification system in a machine tool and a cutting coefficient identification method in a machine tool, the cutting coefficient being used to predict a chatter stability limit, etc. Background Art

[0002] In the past, one of the parameters that determines the machining capability of a machine tool was the stability limit of self-excited chatter. When self-excited chatter is generated during cutting, the machining accuracy and quality of the machined surface of the product are reduced. Therefore, suppressing self-excited chatter has become a problem.

[0003] For example, Patent Document 1 discloses that a stable limit diagram for predicting the occurrence of self-excited chatter vibration is prepared using a transfer function measured by a hammer test and an estimated value of specific cutting resistance as a cutting coefficient, and that machining conditions with high energy efficiency and no self-excited chatter vibration are selected.

[0004] On the other hand, as a method for identifying the cutting coefficient, the following method is disclosed in non-patent document 1: the cutting coefficient is corrected in a manner that reduces the difference between the cutting force measured by a dynamometer as a sensor with a high response frequency and the cutting force estimated by a prediction model using a temporarily determined cutting coefficient, thereby identifying the cutting coefficient.

[0005] In addition, the following technology is disclosed in non-patent document 2: the cutting coefficient for each cutting force in the three vertical directions in the previous cutting force prediction model, which is composed of two cutting coefficients: a cutting coefficient representing the cutting force per unit cutting cross-sectional area and a cutting coefficient representing the cutting force per unit cutting edge length, is replaced with a cutting coefficient that takes the shear angle as a parameter, thereby identifying the cutting coefficient based on the torque of the spindle motor.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2022-21378

[0007] Non-patent document 1: Akagi Chihiro, Kaneko Junichi, Horio Kenichiro. Development of a high-speed automatic estimation system for specific cutting resistance in cutting resistance prediction. Proceedings of the Academic Lecture Meeting of the Society of Precision Engineering, 2014A, pp669-670, 2014.

[0008] Non-patent document 2: Kazuki Kaneko, Isamu Nishida, Ryuta Sato, Keiichi Shirase. Cutting force model of end mill machining based on inclined cutting theory. Proceedings of the Japan Society of Mechanical Engineers, Vol. 83, No. 856, 2017.

[0009] However, in Patent Document 1, since the measurement work is omitted, the cutting coefficient that varies depending on the machining conditions such as the combination of the tool and the workpiece material type and the presence or absence of a coolant is obtained by estimating the tool rake angle, friction coefficient, etc. Therefore, there is a problem that it is difficult to predict the occurrence of self-excited chatter with high accuracy.

[0010] In addition, in non-patent document 1, it is assumed that the cutting force is measured by a dynamometer with a high response frequency, but the dynamometer is very expensive. In addition, when it is installed in a machine tool as a production equipment, there is a possibility of interference between the dynamometer itself and the wiring. In addition, the rigidity of the circuit from the tool to the workpiece is reduced. Therefore, there is a problem that it is difficult to use at the production site.

[0011] In addition, the cutting coefficient using the shear angle as a parameter disclosed in Non-Patent Document 2 is nothing more than a replacement of the cutting coefficient indicating the cutting force per unit cutting cross-sectional area in the conventional cutting coefficient. Therefore, for materials such as titanium alloys and Ni-based heat-resistant alloys having a large cutting coefficient indicating the cutting force per unit cutting edge length, there is a problem of reduced recognition accuracy. Summary of the invention

[0012] Therefore, the present disclosure has been made in view of the above-mentioned problems, and an object thereof is to provide a cutting coefficient identification system and a cutting coefficient identification method in a machine tool, which can identify the cutting coefficient with high accuracy without using an additional sensor and regardless of the material of the workpiece.

[0013] In order to achieve the above-mentioned purpose, the first structure of the present disclosure is a cutting coefficient identification system in a machine tool, the machine tool comprising: at least one of a tool spindle and a workpiece spindle, the tool spindle being mounted with a tool and driven by a tool spindle motor, the workpiece spindle being mounted with a workpiece and driven by a workpiece spindle motor; and a feed axis, which uses a feed axis motor to move the tool and the workpiece relative to each other, characterized in that the cutting coefficient identification system in the machine tool comprises: a cutting force measurement acquisition unit, which acquires an average torque T of at least one of the tool spindle motor, the workpiece spindle motor and the feed axis motor in any period a during the process in which the tool cuts the workpiece a a tool information acquisition unit, which acquires tool information including the number of tool blades corresponding to the measured cutting force; a cutting condition acquisition unit, which acquires cutting conditions including the relative movement amount and the cutting amount between the tool and the workpiece during one rotation of the tool spindle or the workpiece spindle corresponding to the measured cutting force; an estimated cutting force calculation unit, which calculates the cutting force based on the cutting coefficient K including the cutting force per unit cutting cross-sectional area; c , cutting coefficient K, which represents the cutting force per unit cutting edge length e, the number of tool blades, the relative movement amount and the cutting depth calculation formula, calculates the estimated cutting force as the average cutting force during one rotation of the tool spindle or the workpiece spindle; and a cutting coefficient identification unit, which identifies the cutting coefficient K by comparing the measured cutting force with the estimated cutting force. c and cutting coefficient K e .

[0014] Another aspect of the first structure of the present disclosure is characterized in that, in the above structure, a limiting cutting condition calculation unit is provided, and the limiting cutting condition calculation unit uses the cutting coefficient K c and cutting coefficient K e At least one of the above is used to calculate the limiting cutting condition that becomes the limit of the machining capacity of the machine tool, and the limiting cutting condition includes the rotation speed of the tool spindle or the workpiece spindle, the relative movement amount between the tool and the workpiece during one rotation of the tool spindle or the workpiece spindle, and at least one of the cutting amount.

[0015] Another aspect of the first structure of the present disclosure is characterized in that, in the above structure, the cutting force acquisition unit measures the average torque T in an arbitrary period b during cutting of the workpiece by the tool under cutting conditions different from those in the arbitrary period a. b The cutting forces are calculated and measured.

[0016] Another aspect of the first structure of the present disclosure is characterized in that, in the above structure, the measuring cutting force acquisition unit further uses an average torque T in any period c during non-cutting. c The cutting forces are calculated and measured.

[0017] Another mode of the first structure of the present disclosure is characterized in that, in the above structure, the parameters that determine the limit of processing capacity include the output upper limit of at least one of the tool spindle motor, the workpiece spindle motor and the feed axis motor, the bending stress and shear stress of the tool, the quality requirement value of the workpiece and at least one of the stability limit of self-excited vibration.

[0018] In order to achieve the above-mentioned purpose, the second structure of the present disclosure is a cutting coefficient identification method in a machine tool, the machine tool comprising: at least one of a tool spindle and a workpiece spindle, the tool spindle is equipped with a tool and is driven by a tool spindle motor, the workpiece spindle is equipped with a workpiece and is driven by a workpiece spindle motor; and a feed axis, which uses a feed axis motor to move the tool and the workpiece relative to each other, characterized in that the cutting coefficient identification method in the machine tool includes the following steps: a cutting force acquisition step, acquiring an average torque T of at least one of the tool spindle motor, the workpiece spindle motor and the feed axis motor in any period a during the process of the tool cutting the workpiece. aThe measured cutting force is calculated; a tool information acquisition step, obtaining tool information including the number of tool blades corresponding to the measured cutting force; a cutting condition acquisition step, obtaining cutting conditions including the relative movement amount and the cutting amount between the tool and the workpiece during one rotation of the tool spindle or the workpiece spindle corresponding to the measured cutting force; an estimated cutting force calculation step, based on the cutting coefficient K representing the cutting force per unit cutting cross-sectional area c , cutting coefficient K, which represents the cutting force per unit cutting edge length e , the number of tool blades, the relative movement amount and the cutting depth calculation formula, calculate the estimated cutting force as the average cutting force during one rotation of the tool spindle or the workpiece spindle; and the cutting coefficient identification step, by comparing the measured cutting force with the estimated cutting force to identify the cutting coefficient K c and cutting coefficient K e .

[0019] According to the present disclosure, the torque of the motor installed on the machine tool is used to identify the cutting coefficient representing the cutting force per unit cutting cross-sectional area and the cutting coefficient representing the cutting force per unit cutting edge length, respectively. Therefore, the cutting coefficient can be identified with high accuracy regardless of the material of the workpiece without using an additional sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a diagram schematically showing the structure of a cutting coefficient identification system in a machine tool.

[0021] Figure 2 : is a flowchart showing a method of predicting processing capability.

[0022] Figure 3 (a) is the motor torque history of the main shaft related to period a, period b and period c, Figure 3 (b) is the motor torque history of the feed axis related to period a, period b and period c.

[0023] Figure 4 (a) is a schematic diagram showing a situation where a milling process is performed in a machining center, and is a top view. Figure 4 (b) is a schematic diagram showing a situation where milling processing is performed in a machining center, and is a side view.

[0024] Figure 5 This is a diagram showing the relationship between the spindle speed, which is the upper limit of the output of the spindle motor in milling processing, and the radial cutting depth.

[0025] Figure 6 This is a diagram showing the relationship between the spindle speed, which is the upper limit of the output of the feed axis motor in milling processing, and the feed amount per spindle rotation.

[0026] Figure 7This is a diagram showing the relationship between the radial cutting depth, which becomes the bending stress of the tool in the milling process, and the feed rate per one rotation of the main spindle.

[0027] Figure 8 This is a diagram showing the relationship between the feed rate per spindle rotation and the axial cutting depth, which becomes the shear stress of the tool in the milling process.

[0028] Fig. 9 This is a diagram showing the relationship between the radial cutting depth and the axial cutting depth, which are required values ​​of the surface roughness of a workpiece in milling.

[0029] Fig.10 This is a diagram showing the relationship between the spindle speed and the axial depth of cut that is the stability limit of self-excited chatter in milling.

[0030] Description of symbols

[0031] 1: Bed; 2: Column; 3: Spindle housing; 4: Spindle (tool spindle); 5: Tool; 6: Worktable; 7: Workpiece; 11: NC device; 12: Mechanical action command unit; 13: Tool information storage unit; 21: Cutting coefficient identification system; 22: Cutting force measurement acquisition unit; 23: Tool information acquisition unit; 24: Cutting condition acquisition unit; 25: Estimated cutting force calculation unit; 26: Cutting coefficient identification unit; 27: Limit cutting condition calculation unit. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present disclosure will be described based on the drawings.

[0033] Figure 1 This is a schematic diagram of the structure of a machining center as an example of a machine tool.

[0034] The spindle housing 3 of the machining center M has a spindle 4 as a tool spindle that can be rotated by means of a spindle motor. In addition, a tool 5 is installed at the front end of the spindle 4. The spindle housing 3 as a movable body can move in the Z-axis direction relative to the column 2 installed on the bed 1 by means of a Z-axis ball screw as a feed axis. In addition, a workpiece 7 is fixed on a worktable 6 as a movable body of the machining center M. The worktable 6 can move on the bed 1 in the X-axis direction and the Y-axis direction perpendicular to each other. The movement of the worktable 6 in the X-axis direction is performed by the X-axis motor with the help of the X-axis ball screw as the feed axis. In addition, the movement of the worktable 6 in the Y-axis direction is performed by the Y-axis motor with the help of the Y-axis ball screw as the feed axis.

[0035] The machining center M includes an NC device 11 capable of controlling the machining center M. The NC device 11 includes a CPU and a memory connected to the CPU, and operates by utilizing these.

[0036] The NC device 11 has a mechanical motion command unit 12, which controls various parts such as a spindle motor and feed axis motors based on a program input by an operator through an input unit (not shown) such as a keyboard or a touch panel. The mechanical motion command unit 12 performs cutting processing by commanding the rotation of the tool 5 and the relative movement of the tool 5 and the workpiece 7.

[0037] The machining center M further includes a cutting coefficient identification system 21 . The cutting coefficient identification system 21 includes a measured cutting force acquisition unit 22 , a tool information acquisition unit 23 , a cutting condition acquisition unit 24 , an estimated cutting force calculation unit 25 , a cutting coefficient identification unit 26 , and a limit cutting condition calculation unit 27 .

[0038] In addition, the cutting coefficient identification system 21 is assumed to be included in the NC device 11, but may be included in a computer separate from the machining center M that is mechanically or electronically connected to the machining center M.

[0039] The measured cutting force acquisition unit 22 acquires the torque of each of the spindle motor and the feed axis motor from the machine operation command unit 12 to calculate the measured cutting force.

[0040] The tool information acquisition unit 23 acquires tool information including the number of tool blades Z and the tool diameter D from the tool information storage unit 13 included in the NC device 11 , which stores tool information.

[0041] The cutting condition acquisition unit 24 acquires cutting conditions according to a program, and the cutting conditions include a spindle speed S, a feed rate f per spindle rotation corresponding to a relative movement amount between the tool 5 and the workpiece 7 during one spindle rotation, and a feed rate f per spindle rotation corresponding to a relative movement amount between the tool 5 and the workpiece 7 during one spindle rotation. r , Tool axial penetration d a And the radial penetration of the tool d r .

[0042] The estimated cutting force calculation unit 25 calculates an estimated cutting force based on the tool information acquired by the tool information acquisition unit 23 and the cutting conditions acquired by the cutting condition acquisition unit 24 .

[0043] The cutting coefficient identification unit 26 compares the measured cutting force acquired by the measured cutting force acquisition unit 22 with the estimated cutting force calculated by the estimated cutting force calculation unit 25 to identify the cutting coefficient.

[0044] The limit cutting condition calculation unit 27 calculates the spindle speed S and the feed rate f per spindle rotation at which the machining capacity reaches the limit, based on the cutting coefficient identified by the cutting coefficient identification unit 26 and the tool information. r , Tool axial penetration d a And the radial penetration of the tool d r Each combination of .

[0045] Next, a method for predicting the machining capacity of the machining center M using the cutting coefficient identification system 21 will be described. Figure 2 The flowchart of will explain the method of identifying the cutting coefficient performed by the cutting coefficient identification system 21. Figure 2 2 is a flowchart showing a method for predicting machining capability. S1 to S7 are steps 1 to 7, respectively. S1 to S7 are realized by each of the parts 22 to 27 included in the cutting coefficient identification system 21 appropriately performing the above-mentioned operations.

[0046] As S1, after the cutting process of the workpiece 7 is actually performed using the tool 5, the following is obtained: Figure 3 (a) Figure 3 (b) shows the torque history of each axis motor.

[0047] Then, as S2, based on the torque T in any period a during cutting in the torque history obtained, a , the torque T in any period c when the motor of each axis is in motion and not in cutting c , calculate the axial cutting force of each axis motor. S1 and S2 are the cutting force acquisition steps in the present disclosure.

[0048] In order to accurately capture the high-speed cutting phenomenon, it is not accurate enough to use only the specific value in the control frequency band of each axis motor. Therefore, in the cutting force acquisition step, as the torque value used in the calculation of the cutting force, the average value in each arbitrary period that can be acquired with high accuracy is used. For example, the cutting force F applied to the workpiece 7 in the X-axis direction during period a is xm The mechanical information acquisition unit (not shown) of the cutting coefficient recognition system 21 obtains the ball screw specifications such as the lead L and the mechanical efficiency η obtained from the mechanical information storage unit (not shown) of the NC device 11, and the average torque T of the X-axis motor in the period a and the period c. ax 、T cx , calculated using Formula 1. For the Y-axis motor and the Z-axis motor, by using the same calculation formula as Formula 1, it is also possible to calculate the average torque T of the Y-axis motor and the Z-axis motor in period a and period c. ay 、T az 、T cy 、T cz Calculate the respective axial cutting forces F ym 、F zm .

[0049]

[0050] In addition, during the period a, the cutting force F applied to the cutting edge of the tool 5 in the tool tangential direction, that is, the rotation direction of the spindle 4 is tmAccording to the average torque T of the spindle motor in period a and period c as 、T cs , calculated using Formula 2.

[0051]

[0052] Next, tool information is acquired as S3, and cutting conditions are acquired as S4. S3 is a tool information acquisition step in the present disclosure, and S4 is a cutting condition acquisition step in the present disclosure.

[0053] Next, as S5, the cutting coefficient is temporarily determined, and the estimated cutting force is calculated based on the temporarily determined cutting coefficient, the tool information acquired in S3, and the cutting conditions acquired in S4.

[0054] Furthermore, as S6, the cutting coefficient is identified by comparing the measured cutting force with the estimated cutting force. When the difference between the measured cutting force and the estimated cutting force is large, the cutting coefficient is temporarily re-determined and the estimated cutting force is calculated again. On the other hand, when the difference between the measured cutting force and the estimated cutting force is small, the identification of the cutting coefficient is completed.

[0055] Then, as S7, the spindle speed S and the feed rate f per spindle rotation at which the machining capacity reaches the limit are calculated based on the identified cutting coefficient and tool information. r , Tool axial penetration d a And the radial penetration of the tool d r Then, the machining capacity of the machining center M is predicted based on the calculated results.

[0056] Below, with Figure 4 (a) Figure 4 The milling process shown in (b) is described as an example in which the rotating tool 5 and the workpiece 7 are relatively moved in the X-axis direction. In addition, the relative Y-axis direction position and Z-axis direction position of the tool 5 and the workpiece 7 are previously positioned so that machining can be performed.

[0057] The calculation of the estimated cutting force in S5 is performed by applying an instantaneous cutting force model to an end mill without a torsion angle.

[0058] When the tool is rotated at a certain angle θ, the cutting force acting from one cutting edge of the tool 5 on the workpiece 7 is calculated using the tool tangential direction cutting force F ts , Cutting force F in tool radius direction rs , and the tool axial cutting force F as The three perpendicular components are defined. Cutting force F in the tangential direction of the tool ts , Cutting force F in tool radius direction rs , and the tool axial cutting force Fas They can be calculated using Formula 3 to Formula 5, respectively.

[0059] F ts (θ)=(K tC A(θ)+K te l)g(θ) (Equation 3)

[0060] F rs (θ)=(K rc A(θ)+K re l)g(θ) (Equation 4)

[0061] F as (θ)=(K ac A(θ)+K ael )g(θ) (Equation 5)

[0062] Here, the cutting coefficient K in the tangential direction of the tool tc , Cutting coefficient K in tool radius direction rc , and the tool axial cutting coefficient K ac is the cutting force per unit cutting cross-sectional area. In addition, g is a unit step function that distinguishes whether the cutting edge of the tool 5 is involved in cutting. g is 1 during cutting and 0 during non-cutting.

[0063] On the other hand, the cutting coefficient K in the tangential direction of the tool te , Cutting coefficient K in tool radius direction re , and the tool axial cutting coefficient K ae It is the cutting force per unit cutting edge length. In addition, the cutting edge length l can be regarded as the axial cutting depth da. Therefore, the cutting cross-sectional area A can be calculated using formula 6.

[0064] A(θ)=h(θ)d a (Formula 6)

[0065] h(θ)≈f z sinθ

[0066] f z =f r / Z

[0067] Here, h is the cut thickness. z It is the feed rate of each edge of tool 5.

[0068] Cutting When the tool is cut radially into the amount d r When expressed as a ratio to the tool diameter of tool 5, in the case of upper cutting, it can be calculated using Formula 7 and On the other hand, in the case of down-cutting, it is possible to calculate using Equation 8 and

[0069] φ st =0,φ ex =cos -1 (1-d r ) (Formula 7)φ st =π-cos -1 (1-d r ), φ ex =π (Formula 8)

[0070] By using equations 9 to 11 respectively, the cutting force calculated by equations 3 to 5 can be converted into the cutting force component F in the X-axis direction: xs , Cutting force component F in the Y-axis direction ys , and the cutting force component F in the Z-axis direction zs .

[0071] F xs (θ) = F ts (θ)cosθ+F rs (θ)sinθ (Equation 9)

[0072] F ys (θ)=-F ts (θ)sinθ+F rs (θ)cosθ (Equation 10)

[0073] F zs (θ) = F as (θ) (Equation 11)

[0074] As described above, conventionally, a sensor with a high response frequency such as a dynamometer is used to obtain the cutting force change per rotation of the spindle 4, and the cutting force component F in the X-axis direction is reduced for each rotation angle of the tool 5. xs , Cutting force component F in the Y-axis direction ys , Cutting force component F in the Z-axis direction zs By optimizing the cutting coefficient K in the tangential direction of the tool per unit cutting cross-sectional area tc , Cutting coefficient K in tool radius direction rc and tool axial cutting coefficient K ac And the tool tangent direction cutting coefficient K per unit cutting edge length te , Cutting coefficient K in tool radius direction re and tool axial cutting coefficient K ae However, if the response frequency is low, for example, if the cutting force is calculated based on the torque obtained from the motors of each axis of the machining center M, the cutting coefficient cannot be identified with high accuracy.

[0075] Therefore, as described above, the applicant used the average value of the torque obtained from the motor of each axis during a predetermined period in calculating the cutting force in each axis direction. At the same time, the applicant discovered equations 12 to 15 in order to calculate the average value for the instantaneous cutting force model.

[0076]

[0077] P=φ ex -φ st

[0078] C=cosφ ex -cosφ st

[0079] S1=sinφ ex -sinφ st

[0080] S2=sin2φ ex -sin2φ st

[0081] S3=sin 2 φ ex -sin 2 φ st

[0082] Here, the torsion angle of the tool 5 does not affect the average cutting force component in the spindle rotation direction. (The upper horizontal line represents the average value, the same applies below), the average cutting force component in the X-axis direction Average cutting force component in the Y-axis direction And the average cutting force component in the Z-axis direction Therefore, even if the tool 5 is an end mill having a twist angle, by using equations 12 to 15, the average cutting force components in the spindle rotation direction and in each feed axis direction can be calculated for the instantaneous cutting force model. as well as In this embodiment, the average cutting force components in the spindle rotation direction and in each feed axis direction calculated in this way are as well as Treat it as an estimated cutting force.

[0083] The following shows Figure 3 (a) Figure 3 In the case shown in (b), an example of identifying the cutting coefficient using the obtained cutting force is shown. Here, when the cutting force is obtained using the feed axis, there is a tendency for the error of the stationary axis to increase, so the torque of the X-axis motor as the moving axis is used. In addition, Figure 3 (a) Figure 3In (b), the cutting force predicted by the instantaneous cutting force model is superimposed on the actual torque data during non-cutting.

[0084] For machining, it is assumed that an end mill with a tool diameter D = 20 mm and a tool blade number Z = 4 is used as the tool 5. In addition, the following conditions are assumed: the tool axial penetration amount d a =5mm, as a ratio to the tool diameter, the tool radial penetration d r = 25%. In addition, as the workpiece 7, S45C carbon steel is assumed. And as the processing content, it is assumed that the upper cutting is performed. In addition, the radial cutting amount d of the tool is r Expressed as a ratio to the tool diameter.

[0085] When the cutting coefficient is identified based on the cutting force obtained from the spindle 4 and the X-axis motor, the unknown number is the tool tangent direction cutting coefficient K per unit cutting cross-sectional area. tc And the cutting coefficient K in the tool radius direction rc And the tool tangent direction cutting coefficient K per unit cutting edge length te And the cutting coefficient K in the tool radius direction re In this regard, the cutting force that can be obtained under one cutting condition is the cutting force F that the cutting edge of the tool 5 receives in the rotation direction of the spindle 4. tm And the cutting force F on the workpiece 7 in the X-axis direction xm Therefore, sometimes the identification of the cutting coefficient can be smoothly performed by studying the method of assigning the initial value of the cutting coefficient, but it is preferable to obtain the cutting force based on two or more cutting conditions.

[0086] Therefore, in this study example, in order to identify the cutting coefficient, the cutting force in an arbitrary period b where the cutting conditions are different from those in period a is also used. In period a, it is assumed that the feed rate per rotation is f r = 0.4mm / rev, in period b, it is assumed that the feed amount per spindle rotation is f r = 0.8 mm / rev. In addition, it is assumed that the X-axis ball screw lead L = 16 mm and the mechanical efficiency η = 95%. The cutting forces and cutting coefficients in period b are calculated based on the average torque T of the motors of each axis in period b. bs , T bx , T by and T bz The calculation is performed in the same manner as in the case of period a.

[0087] Under the above conditions, the average cutting force F received by the cutting edge of the tool 5 in the rotation direction of the spindle 4 during the period a obtained from the spindle motor is calculated using Formula 16: tmaand the average value F of the cutting force applied to the cutting edge of the tool 5 in the rotation direction of the spindle 4 during period b. tmb The average value F of the tool tangential direction component of the cutting force estimated from the cutting conditions during period a using the temporarily determined cutting coefficient tsa and the average value F of the tool tangential direction component of the cutting force estimated from the cutting conditions in period b using the temporarily determined cutting coefficient tsb The difference in evaluation value E t Based on the calculated evaluation value E t , identify the tool tangent direction cutting coefficient K per unit cutting cross-sectional area tc And the tool tangent direction cutting coefficient K per unit cutting edge length te .

[0088]

[0089] As the initial value of the cutting coefficient temporarily determined, the cutting coefficient K in the tangent direction of the tool per unit cutting cross-sectional area is tc = 1000MPa, cutting coefficient K in the tangential direction of the tool per unit cutting edge length te =0N / mm, each cutting force and evaluation value E t The results are shown in Table 1.

[0090] [Table 1]

[0091]

[0092] Repeat the temporary determination and evaluation of the cutting coefficient E t Calculate the evaluation value E t Cutting forces and evaluation values ​​E when sufficiently small t The results are shown in Table 2. Therefore, the cutting coefficient is identified as the cutting coefficient K in the tangential direction of the tool per unit cutting cross-sectional area. tc =1998MPa, cutting coefficient K in the tangential direction of the tool per unit cutting edge length te =10N / mm.

[0093] [Table 2]

[0094]

[0095] Next, the evaluation value E of the difference between the average value of the cutting force obtained from the X-axis motor and the average value of the X-axis direction component of the cutting force estimated using the temporarily determined cutting coefficient is calculated in the same manner as in Formula 16: x Based on the calculated evaluation value E x , identify the cutting coefficient K in the tool radius direction per unit cutting cross-sectional area rc, and the tool radius cutting coefficient K per unit cutting edge length re In addition, the tool tangent direction cutting coefficient K per unit cutting cross-sectional area tc And the tool tangent direction cutting coefficient K per unit cutting edge length te , using the values ​​identified above.

[0096] As the initial value of the cutting coefficient temporarily determined, the cutting coefficient K in the tool radius direction per unit cutting cross-sectional area is rc = 1000MPa, cutting coefficient K in the tool radius direction per unit cutting edge length re =0N / mm, each cutting force and evaluation value E x The results are shown in Table 3.

[0097] [Table 3]

[0098]

[0099] Repeat the temporary determination and evaluation of the cutting coefficient E x Calculate the evaluation value E x Cutting forces and evaluation values ​​E when sufficiently small x The results are shown in Table 4. Therefore, the cutting coefficient is identified as the cutting coefficient K in the tool radius direction per unit cutting cross-sectional area. rc =575MPa, cutting coefficient K in the tool radius direction per unit cutting edge length re =22N / mm.

[0100] [Table 4]

[0101]

[0102] In this way, the torque obtained from the motors of each axis installed on the machining center M is used to identify the tool tangential direction cutting coefficient K per unit cutting cross-sectional area. tc And the cutting coefficient K in the tool radius direction per unit cutting cross-sectional area rc And the tool tangent direction cutting coefficient K per unit cutting edge length te and the tool radius cutting coefficient K per unit cutting edge length re Therefore, there is no need to use an additional sensor, and the cutting coefficient can be identified with high accuracy regardless of the material of the workpiece 7.

[0103] Next, the cutting coefficient K in the tool radius direction per unit cutting cross-sectional area that has been identified is used. rc And the cutting coefficient K in the tool radius direction per unit cutting edge length re , calculate the cutting conditions that become the limit of the machining capacity of the machining center M.

[0104] Regarding the machining, a cemented carbide end mill with a tool diameter D = 16 mm, a number of blades Z = 4, and a torsion angle of 0 degrees was assumed as the tool 5. t = 80 mm, the tool 5 held by the holder moves in the X-axis direction to perform upcutting on the S45C carbon steel as the workpiece 7. Here, the cutting coefficient is assumed to be the tool tangent direction cutting coefficient K per unit cutting cross-sectional area. tc =2000MPa, cutting coefficient K in the tangential direction of the tool per unit cutting edge length te = 10N / mm, cutting coefficient K in the tool radius direction per unit cutting cross-sectional area rc =600MPa, cutting coefficient K in the tool radius direction per unit cutting edge length re =20N / mm.

[0105] By using the cutting coefficient, the relationship between each cutting condition and the change in cutting force per spindle rotation is calculated according to Formulas 3 to 11, and the cutting condition that becomes the limit of the machining capacity is calculated.

[0106] For example, the spindle motor output P during processing s The average value F of the cutting force in the tangential direction of the tool can be used tave Calculated by formula 17.

[0107]

[0108] exist Figure 5 As a condition, the assumed tool axial penetration amount d is shown. a =20mm, feed rate per spindle rotation f r =0.8mm / rev, mechanical efficiency η = 95% when the spindle speed S and the tool radial penetration d r , the spindle motor output P during processing s Here, the radial penetration amount d r is the ratio to the diameter of tool 5. Figure 5 In the figure, dark colors indicate conditions where the output required by the spindle motor is large, and light colors indicate conditions where the output required is small. In addition, the upper limit of the output of the spindle motor is assumed to be 10 kW. In this case, the black solid line connecting the points where the output of the spindle motor is 10 kW indicates the cutting conditions that become the limit of the machining capacity.

[0109] In addition, for example, the feed axis motor output P during machining f The average cutting force F in the tool feed direction can be used xave Calculated by formula 18.

[0110]

[0111] Then, in Figure 6 As a condition, the assumed tool axial penetration amount d is shown. a =20mm, radial penetration of tool d r =70%, mechanical efficiency η = 95% when the spindle speed S, the feed rate per spindle rotation f r , and the feed axis motor output P during processing f The dark color indicates the condition where the output required by the feed axis motor is large, and the light color indicates the condition where the output required is small. In addition, the upper limit of the output of the feed axis motor is assumed to be 1kW. In this case, the black solid line connecting the points where the output of the feed axis motor is 1kW indicates the cutting condition that becomes the limit of the machining capacity.

[0112] In addition, the bending stress σ acting on the tool 5 during machining can be expressed as the cutting force F in the tool feed direction. x , cutting force F in the direction perpendicular to the tool feed direction and the tool axis y The maximum value of the resultant force R max (Equation 19) is calculated by equation 20.

[0113]

[0114] Here, I represents the cross-sectional moment of inertia of the tool 5 .

[0115] Furthermore, in Figure 7 As a condition, the axial penetration amount d of the tool is assumed to be a =20mm, spindle speed S = 3000min -1 In the case of r , the feed rate per spindle rotation f r , and the relationship between the bending stress σ acting on the tool 5 during machining. In addition, the cross-sectional inertia moment I of the tool 5 is calculated by assuming that the tool 5 is a solid round bar. The conditions where the bending stress σ acting on the tool 5 is large are represented by dark colors, and the conditions where the bending stress σ is small are represented by light colors. In addition, the allowable bending stress σ of the tool 5 is assumed to be 1000N / mm 2 In this case, the bending stress σ connecting the blade 5 is 1000 N / mm 2 The solid black line with dots indicates the cutting conditions that become the limit of the machining capability.

[0116] In addition, the shear stress τ acting on the tool 5 during machining can be calculated using the maximum value F of the cutting force in the tangential direction of the tool. tmax Calculated by formula 21.

[0117]

[0118] Here, I p It represents the second polar moment of the cross section of the tool 5.

[0119] Then, in Figure 8 In the figure, the radial penetration amount d of the tool is assumed as a condition. r =70%, spindle speed S=3000min -1 The feed rate f per spindle rotation is r , Tool axial penetration d a And the relationship between the shear stress τ acting on the tool 5 during processing. In addition, the cross-sectional secondary moment I of the tool 5 p The calculation is performed assuming that the tool 5 is a solid round bar. The conditions where the shear stress τ acting on the tool 5 is large are indicated by dark colors, and the conditions where the shear stress τ is small are indicated by light colors. In addition, the allowable shear stress τ of the tool 5 is assumed to be 300 N / mm 2 In this case, the shear stress τ of the connected blade 5 is 300 N / mm 2 The solid black line at the point indicates the cutting condition that becomes the limit of the machining capability.

[0120] The quality requirements of the workpiece 7 include dimensional accuracy, shape accuracy, surface roughness, etc. They are affected by the deformation of the system including the tool 5 and the workpiece 7 caused by the cutting force, so it is also necessary to consider the static stiffness and dynamic stiffness of the system including the tool 5 and the workpiece 7 to calculate the cutting conditions that become the limit of the processing capacity. For example, the processing of the end mill as the tool 5 is intermittent cutting, so relative displacement is generated between the tool 5 and the workpiece 7 by forced vibration. However, it is necessary to make it smaller than the required value of the surface roughness. Therefore, when the relative displacement is regarded as the surface roughness R z When the surface roughness R z The cutting force F in the direction perpendicular to the tool feed direction and the tool axis can be y Fourier transform is performed, and the product of the relative compliance between the tool 5 and the workpiece 7 is obtained for each frequency, and this is further calculated by inverse Fourier transform.

[0121] Here, regarding the tool 5, it is assumed that the equivalent mass m = 0.05 kg, the equivalent damping coefficient c = 47 N·s / m, and the equivalent stiffness k = 11 MN / m. In addition, it is assumed that the workpiece 7 is a rigid body, and as a cutting condition, the spindle speed S = 3000 min -1 , the feed rate per spindle rotation f r = The radial penetration of the tool when 0.8 mm / rev r , Tool axial penetration d a And the surface roughness R z The relationship is shown in Fig. 9The dark color indicates the surface roughness R z Large conditions, bright colors indicate surface roughness R z In addition, it is assumed that the surface roughness R z The required value is 25 μm. In this case, the connection surface roughness R z The black solid line at the point of 25 μm indicates the cutting condition that becomes the limit of the machining capability.

[0122] The cutting conditions that become the stability limit of self-excited chatter that reduces the processing accuracy and surface quality of the product can be calculated using the cutting coefficient Kc that represents the cutting force per unit cutting cross-sectional area, using a method for obtaining a chatter stability critical line diagram such as that shown in "Technical Explanation > Generation mechanism and suppression of chatter in cutting (Technical Explanation > Generation mechanism and suppression of chatter in cutting)" by Eiji Shamoto, Electric Steelmaking (Electric Steelmaking), Vol. 82, No. 2, 2011, pp143-155.

[0123] Here, regarding the tool 5, it is assumed that the equivalent mass m = 0.05 kg, the equivalent damping coefficient c = 47 N·s / m, and the equivalent stiffness k = 11 MN / m. In addition, it is assumed that the workpiece 7 is a rigid body, and as a cutting condition, the assumed radial penetration amount d of the tool is r =70%, feed rate per spindle rotation f r = 0.8 mm / rev, spindle speed S and tool axial penetration d under the stable limit cutting condition of self-excited chatter a The relationship is shown in Fig.10 .Right now, Fig.10 The diagram shown is a flutter stability critical line diagram assuming the above-mentioned conditions.

[0124] In this way, the torque T obtained from the motors of each axis installed on the machining center M can be used. a 、T b 、T c The cutting coefficients identified are used to calculate the cutting conditions that will limit the machining capability in various aspects.

[0125] The cutting coefficient recognition system 21 in the machine tool of the above structure is provided in a machining center M having a spindle 4 on which a tool 5 is mounted and driven by a tool spindle motor, and a feed axis ball screw for relatively moving the tool 5 and the workpiece 7 by a feed axis motor, and comprises: a cutting force measurement acquisition unit 22 for acquiring an average torque T of the spindle motor and the feed axis motor in any period a during the process in which the tool 5 cuts the workpiece 7. a The cutting force F is calculated and measured. m Tool information acquisition unit 23, which obtains and measures the cutting force F mcorresponding tool information, the tool information includes the number of tool edges Z; a cutting condition acquisition unit 24, which acquires and measures the cutting force F m The corresponding cutting conditions include a feed rate f per spindle rotation corresponding to the relative movement of the tool 5 and the workpiece 7 during one spindle rotation. r , Tool axial penetration d a And the radial penetration of the tool d r Estimated cutting force calculation unit 25, which includes a cutting coefficient K representing the cutting force per unit cutting cross-sectional area c , cutting coefficient K, which represents the cutting force per unit cutting edge length e , the number of tool edges Z, the feed rate per spindle rotation f r , Tool axial penetration d a And the radial penetration of the tool d r The average cutting force during one rotation of the spindle 4 is calculated by the calculation formula

[0126] ˉˉ

[0127] Force F s And the cutting coefficient identification unit 26, which is measured by the cutting force F m and estimated cutting force F s Identify the cutting coefficient K by comparison c And cutting coefficient K e .

[0128] In addition, a limiting cutting condition calculation unit 27 is provided. The limiting cutting condition calculation unit 27 uses the cutting coefficient K c and cutting coefficient K e At least one of the following is calculated: the rotation speed S of the spindle 4, the feed rate per rotation corresponding to the relative movement amount between the tool 5 and the workpiece 7 during one rotation of the spindle 4, which is the limit of the machining capacity of the machine tool. r , Tool axial penetration d a And the radial penetration of the tool d r At least one of the limiting cutting conditions.

[0129] In addition, the cutting force acquisition unit 22 measures the average torque T in an arbitrary period b during which the tool 5 cuts the workpiece 7 under cutting conditions different from those in the arbitrary period a. b To calculate and measure cutting forces.

[0130] In addition, the measured cutting force acquisition unit 22 also uses the average torque T in any period c during non-cutting. c To calculate and measure cutting forces.

[0131] The parameters that determine the limit of the machining capability include the output upper limit of at least one of the tool spindle motor, the workpiece spindle motor, and the feed axis motor, the bending stress σ of the tool 5, the shear stress τ, and the surface roughness R as the quality requirement value of the workpiece. z and at least one of the stability limits of the self-excited flutter.

[0132] Therefore, the torque T obtained from the motors of each axis installed on the machining center M is used. a 、T b 、T c , respectively identify the cutting coefficient K per unit cutting cross-sectional area c And the cutting coefficient K per unit cutting edge length e Therefore, without using an additional sensor, the cutting coefficient K can be identified with high accuracy regardless of the material of the workpiece 7. c And cutting coefficient K e .

[0133] In addition, the torque T obtained from the motors of each axis installed on the machining center M can be used. a 、T b 、T c The identified cutting coefficients are used to calculate the cutting conditions that will limit the machining capability in various aspects.

[0134] The configurations of the cutting coefficient identification system and the cutting coefficient identification method in a machine tool disclosed herein are not limited to those described in the above-mentioned embodiments, and can be appropriately modified as needed without departing from the gist of the invention.

[0135] For example, in the present embodiment, the cutting force is measured based on the torque history of the actual machining after the cutting machining is completed. However, the cutting force may be measured during the cutting machining.

[0136] In the present embodiment, the mechanical information acquisition unit acquires the specifications of the ball screw through the NC device, but the specifications may be acquired from a source other than the NC device, or may be directly input by separately providing an input unit or the like.

[0137] In the present embodiment, the tool information acquisition unit acquires the tool information from the NC device, but the tool information may be acquired from a source other than the NC device, or an input unit or the like may be separately provided to directly input the tool information.

[0138] In the present embodiment, the cutting condition acquisition unit acquires the cutting conditions according to the program, but an input device or the like may be separately provided to directly input the cutting conditions.

[0139] In addition, in the present embodiment, the cutting coefficient is identified by using the torque required for cutting obtained by taking the difference between the motor torque during non-cutting and the motor torque during cutting. However, the cutting coefficient can also be identified by using interference observation technology to obtain the torque required for cutting without using the motor torque during non-cutting.

[0140] In addition, in the present embodiment, the cutting force is obtained under two conditions with different feed rates per spindle rotation, but the cutting force can also be obtained under different parameters such as tool axial cutting and tool axial cutting, and the feed rate of the spindle per rotation can also be the same.

[0141] In addition, in this embodiment, the tool tangent direction cutting coefficient K per unit cutting cross-sectional area is sequentially identified. tc and the tool tangent cutting coefficient K per unit cutting edge length te And the cutting coefficient K in the tool radius direction per unit cutting cross-sectional area rc and the tool radius cutting coefficient K per unit cutting edge length re , but the evaluation value E can also be t and E x Summarize and identify all at the same time.

[0142] In addition, in this embodiment, the identification of the cutting coefficient and the prediction of the machining capacity are performed continuously, but the identified cutting coefficient may be associated with the tool information and stored in the database, and the machining capacity may be predicted by calling the stored cutting coefficient from the database at another time.

[0143] In addition, in the present embodiment, the cutting coefficient is identified and the machining capacity is predicted based on the information related to the tool spindle. However, the cutting coefficient can be identified and the machining capacity can be predicted based on the information related to the workpiece spindle that can be rotated by the workpiece spindle motor instead of the tool spindle. The cutting coefficient can also be identified and the machining capacity can be predicted based on the information related to both the tool spindle and the workpiece spindle.

Claims

1. A cutting coefficient identification system in a machine tool, The machine has: at least one of a tool spindle and a workpiece spindle, the tool spindle being mounted with a tool and driven by a tool spindle motor, and the workpiece spindle being mounted with a workpiece and driven by a workpiece spindle motor; and A feed shaft, which uses a feed shaft motor to move the tool and the workpiece relative to each other, It is characterized in that The cutting coefficient identification system in the machine tool has: A measuring cutting force acquisition unit is configured to acquire an average torque T of at least one of the tool spindle motor, the workpiece spindle motor, and the feed axis motor in any period a during the process in which the tool cuts the workpiece. a And calculate and measure the cutting force; a tool information acquisition unit that acquires tool information including the number of tool edges corresponding to the measured cutting force; a cutting condition acquisition unit for acquiring a cutting condition corresponding to the measured cutting force, including a relative movement amount and a cutting depth amount between the tool and the workpiece during one rotation of the tool spindle or the workpiece spindle; The estimated cutting force calculation unit includes a cutting coefficient K representing the cutting force per unit cutting cross-sectional area. c , cutting coefficient K, which represents the cutting force per unit cutting edge length e , a calculation formula for the number of tool blades, the relative movement amount, and the cutting depth, to calculate an estimated cutting force as an average cutting force during one rotation of the tool spindle or the workpiece spindle; as well as A cutting coefficient identification unit that identifies the cutting coefficient K by comparing the measured cutting force with the estimated cutting force. c and the cutting coefficient K e .

2. The cutting coefficient identification system in a machine tool according to claim 1, characterized in that: The cutting coefficient identification system in the machine tool includes a limiting cutting condition calculation unit, which uses the cutting coefficient K c and the cutting coefficient K e At least one of the above is used to calculate a limiting cutting condition that becomes the limit of the machining capacity of the machine tool, and the limiting cutting condition includes at least one of the rotation speed of the tool spindle or the workpiece spindle, the relative movement amount between the tool and the workpiece during one rotation of the tool spindle or the workpiece spindle, and the cutting amount.

3. The cutting coefficient identification system in a machine tool according to claim 1 or 2, characterized in that: The measured cutting force acquisition unit further uses an average torque T in an arbitrary period b during which the tool cuts the workpiece under a cutting condition different from that in the arbitrary period a. b The measured cutting forces are calculated.

4. The cutting coefficient identification system in a machine tool according to claim 1 or 2, characterized in that: The measured cutting force acquisition unit also uses the average torque T in any period c during non-cutting. c The measured cutting forces are calculated.

5. The cutting coefficient identification system in a machine tool according to claim 2, characterized in that: The parameters that determine the limit of the processing capability include the output upper limit of at least one of the tool spindle motor, the workpiece spindle motor and the feed axis motor, the bending stress and shear stress of the tool, the quality requirement value of the workpiece and at least one of the stability limit of self-excited vibration.

6. A method for identifying cutting coefficients in machine tools, The machine has: at least one of a tool spindle and a workpiece spindle, the tool spindle being mounted with a tool and driven by a tool spindle motor, and the workpiece spindle being mounted with a workpiece and driven by a workpiece spindle motor; and A feed shaft, which uses a feed shaft motor to move the tool and the workpiece relative to each other, It is characterized in that The cutting coefficient identification method in the machine tool comprises the following steps: A cutting force obtaining step of obtaining an average torque T of at least one of the tool spindle motor, the workpiece spindle motor and the feed axis motor in any period a during the process in which the tool cuts the workpiece a And calculate and measure the cutting force; A tool information acquisition step of acquiring tool information including the number of tool edges corresponding to the measured cutting force; A cutting condition acquisition step of acquiring a cutting condition corresponding to the measured cutting force, including a relative movement amount and a cutting depth amount between the tool and the workpiece during one rotation of the tool spindle or the workpiece spindle; The estimated cutting force calculation step is based on the cutting coefficient K representing the cutting force per unit cutting cross-sectional area. c , cutting coefficient K, which represents the cutting force per unit cutting edge length e , a calculation formula for the number of tool blades, the relative movement amount, and the cutting depth, to calculate an estimated cutting force as an average cutting force during one rotation of the tool spindle or the workpiece spindle; as well as A cutting coefficient identification step of identifying the cutting coefficient K by comparing the measured cutting force with the estimated cutting force c and the cutting coefficient K e .

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