Grinding burn state evaluation system

Abstract

A grinding burn state evaluation system (1) evaluates a grinding burn state of a part (Wa) that is being machined in a workpiece (W) machined into a final target shape by grinding the surface of the workpiece (W) a plurality of times while supplying a cooling liquid (CL) by a grinding machine (2). The grinding burn state evaluation system (1) comprises: a grinding energy acquisition unit (31) that acquires grinding energy (Q') required for grinding the part (Wa) to be machined by means of a grinding machine (2); a film boiling boundary energy acquisition unit (50) that acquires a film boiling boundary energy (Q'w) required for a cooling liquid (CL) supplied to the part (Wa) that is being machined to assume a film boiling state when the part (Wa) is ground by the grinding machine (2); a cooling state ascertaining unit (102) that ascertains the cooling state by the cooling liquid (CL); a cooling state reflection unit (107) that reflects the cooling state in the film boiling boundary energy (Q'w) on the basis of the cooling state by the cooling liquid (CL); and an evaluation unit (60) that evaluates the grinding burn state of the part (Wa) that is being machined on the basis of the grinding energy (Q') and the film boiling boundary energy (Q'w) in which the cooling state has been reflected.

Description

Grinding burn condition evaluation system

[0001] The present invention relates to a grinding burn condition evaluation system.

[0002] Conventionally, when grinding a workpiece, the temperature of the workpiece's processed portion tends to become high, which can cause grinding burns on the workpiece's surface depending on the processing conditions. Grinding burns are undesirable because they can cause a decrease in the mechanical strength of the workpiece. One method for detecting such grinding burns is to evaluate the presence or absence of grinding burns and their depth by utilizing the fact that changes in the magnetic field caused by eddy currents generated in the workpiece by an excitation current differ depending on the presence or absence of grinding burns.

[0003] For example, in the configuration disclosed in Patent Document 1, the presence or absence of grinding burn is detected with high accuracy by comparing the output signals of eddy currents generated by two types of excitation currents with different frequencies using an eddy current sensor. Furthermore, in the configuration disclosed in Patent Document 2, the output signals of eddy currents generated by two types of excitation currents with different frequencies using an eddy current sensor are corrected to remove components of residual magnetic flux density remaining in the workpiece, thereby improving the accuracy of determining the presence or absence of grinding burn. In addition to these methods, the state of grinding burn on the surface of a workpiece is also evaluated by etching the workpiece after grinding with a corrosive solution such as nital and observing the surface condition.

[0004] JP 2011-106932 A JP 2018-189603 A

[0005] During grinding, a coolant is supplied to the workpiece during processing to prevent overheating of the workpiece. It is known that grinding burns occur when the coolant supplied to the workpiece transitions from nucleate boiling to film boiling due to heat generated in the workpiece, significantly reducing the cooling performance of the coolant. Therefore, if the film boiling state of the coolant in the workpiece could be detected, it would be possible to accurately evaluate the occurrence of grinding burns during processing. However, because it is difficult to detect the temperature of the workpiece and it is also difficult to detect the film boiling state of the coolant in the workpiece, no attempt has been made to evaluate the occurrence of grinding burns by detecting the film boiling state of the coolant in the workpiece. Furthermore, the configurations and etching-based evaluations disclosed in Patent Documents 1 and 2 do not take into account the film boiling state of the coolant in the workpiece, leaving room for improvement in accurately evaluating the occurrence of grinding burns.

[0006] The present invention provides a grinding burn condition evaluation device that can evaluate the grinding burn condition of a workpiece with high accuracy.

[0007] One aspect of the present invention is a grinding burn condition evaluation system that evaluates the grinding burn condition of a machined portion of a workpiece that is machined into a final target shape by grinding the surface of the workpiece multiple times while supplying a coolant with the grinding machine, the system comprising: a grinding energy acquisition unit that acquires grinding energy (Q'), which is the energy required to grind the machined portion with the grinding machine; a film boiling boundary energy acquisition unit that acquires film boiling boundary energy (Q'w), which is the energy required for the coolant supplied to the machined portion to reach a film boiling state when the machined portion is grinded with the grinding machine; a cooling state assessment unit that assesses the cooling state caused by the coolant and outputs information about the cooling state; a cooling state reflection unit that reflects the cooling state in the film boiling boundary energy (Q'w) based on information output by the cooling state assessment unit; and an assessment unit that evaluates the grinding burn condition of the machined portion based on the grinding energy (Q') and the film boiling boundary energy (Q'w) reflecting the cooling state.

[0008] According to the above aspect, the grinding burn state of the processed portion is evaluated based on the film boiling boundary energy (Q'w), which is the energy required for the coolant supplied to the processed portion to reach a film boiling state when the processed portion of a workpiece is ground by a grinding machine and reflects the cooling state of the coolant, and the grinding energy (Q').As a result, since it is not necessary to obtain the temperature of the processed portion, it is possible to achieve a highly accurate evaluation of the grinding burn state that takes into account the coolant reaching a film boiling state in the processed portion.Furthermore, because the film boiling boundary energy (Q'w) reflects the cooling state of the coolant, it is possible to evaluate the grinding burn state with even greater accuracy.

[0009] As described above, according to the above aspect, it is possible to provide a grinding burn state evaluation device that can evaluate the grinding burn state of a workpiece with high accuracy.

[0010] FIG. 1 is a conceptual diagram showing the configuration of a grinding burn state evaluation system according to a first embodiment. FIG. 2 is a functional block diagram showing the configuration of the grinding burn state evaluation system according to the first embodiment. FIG. 3 is a diagram of the vicinity of a sizing device equipped with an eddy current sensor according to the first embodiment. FIG. 4 is an enlarged cross-sectional view of the periphery of a machined portion according to the first embodiment. FIG. 5 is an enlarged cross-sectional view of a workpiece according to the first embodiment, showing (a) a cooling liquid in a nucleate boiling state according to the first embodiment. FIG. 6 is a conceptual diagram showing a first correspondence relationship according to the first embodiment. FIG. 7 is a conceptual diagram showing the configuration of a first correspondence relationship creation unit according to the first embodiment. FIG. 8 is a diagram showing an output signal of an eddy current sensor according to the first embodiment. FIG. 9 is a diagram showing the correspondence relationship between the actual cutting depth and grinding efficiency according to the first embodiment. FIG. 10 is a diagram showing (a) the output signal of an eddy current sensor, (b) the actual cutting depth, and (c) the power consumption of a tool spindle drive unit according to the first embodiment. FIG. 11 is a conceptual diagram explaining the amount of heat Jm passing through the film boiling region according to the first embodiment. FIG. 12 is a conceptual diagram showing a second correspondence relationship in the first embodiment. FIG. 13 is a conceptual diagram showing the configuration of a second correspondence relationship creation unit in the first embodiment. FIG. 14 is a diagram illustrating an overview of synchronous detection in an eddy current sensor in the first embodiment. FIG. 15 is (a) a diagram showing the relationship between time and an output signal of an eddy current sensor serving as a first inflection point determination criterion, and (b) a diagram showing, on a complex plane, the output signal of the eddy current sensor serving as the first inflection point determination criterion, in the first embodiment. FIG. 16 is (a) a diagram showing the relationship between time and an output signal of an eddy current sensor serving as a second inflection point determination criterion, and (b) a diagram showing, on a complex plane, the output signal of the eddy current sensor serving as the inflection point determination criterion, in the first embodiment. FIG. 17 is a diagram showing time changes in dimensional information of a workpiece and grinding burn depth in the first embodiment. FIG. 18 is a flowchart of grinding processing in the first embodiment. FIG. 19 is a flowchart of grinding burn state evaluation processing in the first embodiment. FIG. 20 is a flowchart of the grinding burn state evaluation process in the first embodiment.

[0011] (Embodiment 1) 1. Configuration of Grinding Burn State Evaluation System 1 The grinding burn state evaluation system 1 of embodiment 1 includes a grinding machine 2 as a processing device and a processing unit 3, and evaluates the grinding burn state of a workpiece W ground by the grinding machine 2.

[0012] In the first embodiment, as shown in FIG. 1 , the grinding machine 2 rotates the workpiece W about its center line C, rotates a grinding wheel 16 as a tool that is a rotating body, and moves the grinding wheel 16 relatively close to the workpiece W in a direction intersecting the axis of the workpiece W, thereby grinding the outer or inner peripheral surface of the workpiece W. The grinding machine 2 may be a table traverse type grinding machine, a wheelhead traverse type grinding machine, or the like. The grinding machine 2 may also be a cylindrical grinding machine, a cam grinding machine, or the like. The relationship between the rotation direction of the workpiece W and the rotation direction of the grinding wheel 16 may be either an up-cut or a down-cut.

[0013] In this embodiment, as shown in Fig. 1, the workpiece W is, for example, a member formed in a shaft shape, and the outer circumferential surface of the workpiece W is the part to be machined. However, the shape of the workpiece W is not limited to a shaft shape, and it can be any shape, such as a cylindrical shape having an inner circumferential surface. When the workpiece W is cylindrical, the inner circumferential surface of the workpiece W can be the part to be machined.

[0014] In this embodiment, the workpiece W is generally rod-shaped and is supported at both ends by workpiece support members. However, the workpiece W shown in Fig. 1 is merely an example, and the grinding machine 2 can grind workpieces having various shapes.

[0015] The processing unit 3 includes a grinding burn state evaluation device 30 and a control device 33 that controls the grinding machine 2. As will be described later, the grinding burn state evaluation device 30 evaluates the grinding burn state caused by grinding on the workpiece W, and adjusts the processing conditions for the workpiece W based on the evaluation results. The control device 33 controls the grinding process by controlling the grinding machine 2.

[0016] The grinding burn state evaluation device 30 can function as a simulation device independent of the grinding machine 2 and the control device 33, or as a simulation device that operates in conjunction with the grinding machine 2 and the control device 33. In the former case, the grinding burn state evaluation device 30 can, for example, determine optimal grinding conditions without actually grinding the workpiece W. In the latter case, the grinding burn state evaluation device 30 can, for example, determine the presence or absence of grinding burn, adjust the grinding conditions, or operate to affect various controls by processing in parallel with the grinding process of the workpiece W by the grinding machine 2. The grinding burn state evaluation device 30 can also be an integrated system of the grinding machine 2 and the control device 33.

[0017] 2. Configuration of Grinding Machine 2 and Control Device 33 The configuration of the grinding machine 2 will be described with reference to Fig. 1. In this embodiment 1, the grinding machine 2 is a wheelhead traverse type cylindrical grinding machine as an example. However, a table traverse type can also be used for the grinding machine 2. The grinding machine 2 mainly includes a bed 11, a headstock 12, a tailstock 13, a traverse base 14, a grinding wheel 15, a grinding wheel 16, a sizing device 17, a grinding wheel dressing device 18, a coolant device 19, and an eddy current sensor 20.

[0018] The bed 11 is fixed on an installation surface. The headstock 12 is provided on the upper surface of the bed 11, on the near side in the X-axis direction (lower side in FIG. 1 ) and on one end side in the Z-axis direction (left side in FIG. 1 ). The headstock 12 supports the workpiece W rotatably around the Z-axis with the center line C of the workpiece W as the center. The workpiece W is rotated by driving a motor 12a provided on the headstock 12. The tailstock 13 is provided on the upper surface of the bed 11, in a position opposite the headstock 12 in the Z-axis direction, i.e., on the near side in the X-axis direction (lower side in FIG. 1 ) and on the other end side in the Z-axis direction (right side in FIG. 1 ). In other words, the headstock 12 and the tailstock 13 rotatably support both ends of the workpiece W.

[0019] The traverse base 14 is provided on the upper surface of the bed 11 so as to be movable in the Z-axis direction. The traverse base 14 is moved by driving a motor 14a provided on the bed 11. The wheel head 15 is provided on the upper surface of the traverse base 14 so as to be movable in the X-axis direction. A tool spindle 16b provided on the wheel head 15 is moved by driving a traverse base motor 15a provided on the traverse base 14. The grinding wheel 16 is connected to and rotatably supported via the tool spindle 16b, and rotates by driving a tool spindle motor 16a provided on the wheel head 15. The grinding wheel 16 is composed of a plurality of abrasive grains fixed with a bond material.

[0020] The sizing device 17 functions as a detector that measures the dimension (diameter) of the workpiece W. However, the detector is not limited to the sizing device 17, and may be a contact sensor having a single probe or a non-contact sensor such as a laser displacement meter. The sizing device 17 is provided so as to be movable in the Z-axis direction in synchronization with the traverse base 14 via a mechanism not shown.

[0021] 3( a), the sizing device 17 mainly includes a device main body 171, a pair of contactors 172a, 172b, a pair of fingers 173a, 173b, and a differential transformer 174. The contactors 172a, 172b are provided so as to be able to come into contact with the outer peripheral surface of the workpiece W. Specifically, of the pair of contactors 172a, 172b, one contactor 172a comes into contact with the outer peripheral surface of the workpiece W from above, and the other contactor 172b comes into contact with the outer peripheral surface of the workpiece W from below. The fingers 173a, 173b hold the contactors 172a, 172b and support the contactors 172a, 172b so as to be displaceable relative to the device main body 171. Specifically, one finger 173a of the pair of fingers 173a, 173b supports one contact 172a, and the other finger 173b supports the other contact 172b.

[0022] The differential transformer 174 is housed in the device main body 171. The differential transformer 174 detects the displacement of the pair of fingers 173a, 173b, which displaces in accordance with the displacement of the pair of contacts 172a, 172b, and outputs an electrical signal corresponding to the displacement of the fingers 173a, 173b to the control device 33. The control device 33 detects the positions of the fingers 173a, 173b when the pair of contacts 172a, 172b come into contact with the outer peripheral surface of the workpiece W based on the electrical signal output from the differential transformer 174, and can obtain the measurement result of the outer diameter of the workpiece W by the sizing device 17 based on the positions of the fingers 173a, 173b. Note that the sizing device 17 may be equipped with other detectors, such as an acceleration sensor, a microphone, or a temperature sensor.

[0023] The grinding wheel dressing device 18 shown in Figure 1 dresses the shape of the grinding wheel 16. The grinding wheel dressing device 18 is a device that performs truing of the grinding wheel 16. The grinding wheel dressing device 18 may be a device that dresses the grinding wheel 16 in addition to or instead of truing. Furthermore, the grinding wheel dressing device 18 also has a function of measuring the dimensions (diameter) of the grinding wheel 16.

[0024] Truing is a reshaping operation, such as shaping the grinding wheel 16 to fit the shape of the workpiece W when the grinding wheel 16 has worn down due to grinding, or removing runout of the grinding wheel 16 due to one-sided wear. Dressing is a dressing (sharpening) operation, such as adjusting the protrusion amount of the abrasive grains and creating cutting edges for the abrasive grains. Dressing is an operation to correct dullness, clogging, missing grains, etc., and is usually performed after truing.

[0025] The coolant device 19 supplies coolant (cooling liquid) from a coolant nozzle to the portion Wa of the workpiece W being machined by the grinding wheel 16. The coolant device 19 cools the collected coolant to a predetermined temperature and supplies it back to the grinding point. The coolant device 19 is capable of adjusting the coolant flow rate and supply timing. In FIG. 1, reference numeral 19 indicates the position of the coolant nozzle. As shown in FIG. 2, the coolant device 19 is equipped with a thermometer 191 that acquires the temperature of the collected coolant and a flowmeter 192 that detects the coolant flow rate as detectors. The type of coolant used is not limited, but the cooling capacity is specified for each coolant.

[0026] The control device 33 grinds the workpiece W by controlling the driving of the grinding wheel 16, the coolant device 19, etc. of the grinding machine 2 based on an NC program generated based on operation command data such as the shape of the workpiece W, grinding conditions, the shape of the grinding wheel 16, the cooling capacity of the coolant, and coolant flow rate or supply timing information. In particular, the control device 33 grinds the workpiece W until it reaches the finished shape (target shape) based on the machining conditions adjusted by the machining condition adjustment unit 63 (described later) and the diameter of the workpiece W measured by the sizing device 17. Furthermore, the control device 33 controls the grinding wheel dressing device 18, etc., at the timing to dress the grinding wheel 16, thereby performing truing and dressing.

[0027] 3. Grinding Burn Occurring on the Machined Portion Wa of the Workpiece W Next, the cause of grinding burn occurring on the machined portion Wa when the machined portion Wa of the workpiece W is ground by the grinding machine 2 will be explained from the perspective of changes in the state of the coolant CL supplied to the machined portion Wa during grinding, in a configuration in which the machined portion Wa of the workpiece W is ground while being supplied with the coolant CL, as shown in FIG.

[0028] When the temperature of the workpiece Wa rises due to heat generated in the workpiece Wa during grinding of the workpiece W and reaches the boiling point of the coolant, the coolant CL first boils near the surface of the workpiece Wa, producing bubbles Bo, as shown in Figure 5(a). In the initial stage of boiling, each bubble Bo is generally independent, and the coolant CL in liquid form is in contact with the surface of the workpiece Wa. This state is called the nucleate boiling state of the coolant CL. In the nucleate boiling state, the cooling performance of the coolant CL for the workpiece Wa is maintained, preventing the workpiece Wa from overheating and preventing grinding burns from occurring on the workpiece Wa.

[0029] On the other hand, if the temperature of the workpiece Wa further rises and exceeds the boiling point of the coolant CL, the boiling of the coolant CL near the surface of the workpiece Wa becomes more active, generating numerous bubbles B, which cause adjacent bubbles B to fuse together. As the bubbles B fuse together, a bubble layer Bm is formed, as shown in FIG. 5B. Because the surface of the workpiece Wa is covered by the bubble layer Bm, the liquid coolant CL no longer comes into contact with the surface of the workpiece Wa. This state is called film boiling of the coolant CL. In film boiling, the cooling performance of the coolant CL for the workpiece Wa is significantly reduced, causing the workpiece Wa to overheat, resulting in grinding burns on the workpiece Wa. Therefore, the timing at which the coolant CL transitions from nucleate boiling to film boiling is the timing at which grinding burns occur on the workpiece Wa.

[0030] As shown in Figure 4, in an example of up-cut grinding, coolant CL flows between the grinding wheel 16 and the workpiece Wa of the workpiece W along the rotational direction R of the grinding wheel 16. Of the contact arc LC between the grinding wheel 16 and the workpiece Wa, indicated by the symbol Lc, the region LW indicated by the symbol Lw, which is close to the inflow position of the coolant CL, is a nucleate boiling region, and the region LM indicated by the symbol Lm, which is far from the inflow position of the coolant CL, is a film boiling region. As the workpiece W is fed in the direction of arrow v during grinding, the workpiece Wa is removed as shown by the dashed line, and the film boiling region relatively advances in the opposite direction to the feed direction of the workpiece W. Even in the case of down-cut grinding, in which the rotational direction R of the grinding wheel 16 is the reverse, the region close to the inflow position of the coolant CL is a nucleate boiling region, and the region far from the inflow position of the coolant CL is a film boiling region.

[0031] 2, the grinding burn state evaluation device 30 includes a grinding power acquisition unit 31, a dimension information acquisition unit 41, a film boiling boundary power acquisition unit 50, a contact arc length acquisition unit 51, a contact arc heat flux calculation unit 52, a first correspondence relationship storage unit 53, a film boiling region length calculation unit 54, a heat transfer amount calculation unit 55, a feed rate acquisition unit 56, an evaluation unit 60, a display unit 61, a second correspondence relationship storage unit 62, a machining condition adjustment unit 63, a final state evaluation unit 64, a setting information acquisition unit 65, a margin evaluation unit 66, a first correspondence relationship creation unit 100, and a second correspondence relationship creation unit 200. These components are configured as storage devices or arithmetic units. Each component will be described in detail below.

[0032] 4-1. Grinding Power Acquisition Unit 31 The grinding power acquisition unit 31 constitutes a grinding energy acquisition unit that acquires grinding energy Q', which is the energy required to grind the workpiece Wa by the grinding machine 2. In this embodiment, the grinding power acquisition unit 31 acquires grinding power, which is the power required to rotate and drive the tool spindle motor 16a, as the grinding energy Q'. The grinding energy Q' is not limited to this grinding power, but can also be calculated as the product of the tangential resistance between the tool (grinding wheel 16) and the workpiece W and the relative speed V+v between the tool and the workpiece W. The grinding energy Q' is defined as the grinding power per unit width in the axial direction of the tool spindle 16b at the workpiece Wa.

[0033] 4-2. Dimensional Information Acquisition Unit 41 The dimensional information acquisition unit 41 acquires the output of the sizing device 17 and acquires dimensional information of the workpiece W. Note that if the actual cutting depth is obtained according to the command value, the dimensional information acquisition unit 41 may acquire dimensional information of the workpiece W based on the command value without using the sizing device 17.

[0034] 4-3. Film boiling boundary power acquiring unit 50 The film boiling boundary power acquiring unit 50 constitutes a film boiling boundary energy acquiring unit that acquires film boiling boundary energy Q'w, which is the energy required for the coolant supplied to the workpiece Wa to reach a film boiling state when the workpiece Wa is ground by the grinding machine 2. In this embodiment, the film boiling boundary power acquiring unit 50 acquires, as the film boiling boundary energy Q'w, film boiling boundary power that corresponds to the grinding power required for the coolant supplied to the workpiece Wa to reach a film boiling state.

[0035] 4-3. Contact Arc Length Acquisition Unit 51 The contact arc length acquisition unit 51 acquires the length Lc of the contact arc LC between the grinding wheel 16 and the workpiece Wa in a cross section (see FIG. 4) perpendicular to the main spindle 16b of the grinding wheel 16. The contact arc LC is a partial arc along the surface of the grinding wheel 16. Note that, since the length Lc of the contact arc LC between the grinding wheel 16 and the workpiece Wa is usually sufficiently small compared to the outer periphery of the grinding wheel 16, the contact arc LC may be approximated to a straight line, and the length Lc may be the length of a line segment. The length Lc can be geometrically calculated based on the dimensional information of the workpiece W acquired by the dimensional information acquisition unit 41, the outer diameter of the grinding wheel 16, and the cutting depth of the workpiece Wa.

[0036] The contact arc heat flux calculation unit 52 calculates the heat flux q per unit area in the contact arc LC between the grinding wheel 16 and the workpiece Wa. The heat flux q can be calculated from the following relational expression (1) based on the grinding power Q' acquired by the grinding power acquisition unit 31 and the length Lc of the contact arc LC acquired by the contact arc length acquisition unit 51.

[0037]

[0038] 4-5. First Correspondence Relationship Storage Unit 53 The first correspondence relationship storage unit 53 stores a first correspondence relationship which is the correspondence relationship between the length Lw of the non-film boiling region LW, which is the region that has not yet reached the film boiling state in the contact arc LC between the grinding wheel 16 and the workpiece Wa, the heat flux qw per unit area generated in the non-film boiling region LW by grinding, and the film boiling boundary power Q'w. Since qw and Lw are inversely proportional to each other, the following relational expression (2) holds. The first correspondence relationship indicates the boundary line for the occurrence of grinding burn on the graph of heat flux vs. contact arc length shown in FIG. 6.

[0039]

[0040] 4-6. First Correspondence Relationship Creation Unit 100 The first correspondence relationship creation unit 100 creates the above-mentioned first correspondence relationship. In this embodiment, as shown in Fig. 7, the first correspondence relationship creation unit 100 includes a structure change detection unit (eddy current sensor 20), an output signal acquisition unit 40, a dimension information acquisition unit 41, an actual cutting depth calculation unit 42, a grinding efficiency calculation unit 43, and a grinding burn occurrence estimation unit 44, which are configured by a storage device or a computing device. Note that, in the first correspondence relationship creation unit 100, the configurations provided in the grinding burn state evaluation device 30 can be used for the components that overlap with those provided in the grinding burn state evaluation device 30.

[0041] 4-6-1. Eddy current sensor 20 In this embodiment, an eddy current sensor 20 is used as a microstructural change detection unit that detects microstructural changes that occur in the workpiece Wa due to grinding by the grinding machine 2. In this embodiment 1, as shown in Fig. 3, the sensor head of the eddy current sensor 20 is attached to the device body 171 of the sizing device 17 and is located on the opposite side of the grinding wheel 16 with respect to the workpiece W. Note that in Fig. 3, the reference numeral 20 indicates the position of the sensor head, and the sensor body is not shown.

[0042] 7, the eddy current sensor 20 has a coil serving as an oscillator 21, and applies an output signal to a probe 22 provided at the tip of the sensor head of the eddy current sensor 20, thereby applying a magnetic field to the workpiece W and inducing eddy currents inside the workpiece W. The eddy current sensor 20 then amplifies the change in impedance acquired via the probe 22 in an amplifier 23 and inputs it to a detector 24, extracts only the frequency component of the oscillator 21, processes the signal in a signal processor 25, and outputs it. The magnitude of the eddy current, and therefore the magnitude of the output signal, changes depending on the condition of the processed portion of the workpiece W, etc.

[0043] The eddy current sensor 20 is configured to supply multiple excitation currents with different frequencies to the coil. The frequency of the excitation current can be set by a frequency setting unit (not shown). Since the penetration depth of the eddy current varies depending on the frequency of the excitation current, the frequency of the excitation current can be set according to the target penetration depth of the eddy current. The target penetration depth of the eddy current is set to match the surface layer where grinding burn may occur, and can be, for example, 1 to 100 μm from the machined surface, preferably 1 to 50 μm, and more preferably 10 to 30 μm. If the penetration depth is shallow, the sensitivity of the eddy current sensor becomes too high, resulting in a lower signal-to-noise ratio and reduced detection accuracy. On the other hand, if the penetration depth is deep, the detection level of magnetic property changes decreases in areas shallow from the machined surface, resulting in reduced detection accuracy.

[0044] The frequency of the excitation current according to the penetration depth can be set in a frequency band of 20 kHz to 200 MHz, preferably 20 kHz to 100 kHz, and more preferably 250 to 2500 kHz. In this embodiment, the frequency of the excitation current is set to 250 kHz so that the penetration depth of the eddy current is 30 μm.

[0045] 4-6-2. Output Signal Acquisition Unit 40 The output signal acquisition unit 40 acquires the output signal P output from the eddy current sensor 20. The output signal P is acquired as an eddy current voltage, as shown in FIG.

[0046] 4-6-3. Dimensional Information Acquisition Unit 41 The dimensional information acquisition unit 41 acquires dimensional information of the workpiece W. In this embodiment, as described above, the dimensional information of the workpiece W can be obtained by detecting the dimensions of the workpiece W during machining using the sizing device 17. Note that instead of using the sizing device 17, the dimensional information of the workpiece W may be indirectly calculated and acquired based on the coordinate position of the X-axis, which is the cutting axis of the workpiece W, output from the control device 33.

[0047] 4-6-4. Actual Cut-in Amount Calculation Unit 42 The actual cut-in amount calculation unit 42 acquires the cut-in amount per rotation of the workpiece W based on the amount of change in the dimensional information of the workpiece W acquired by the dimensional information acquisition unit 41. Then, the grinding efficiency calculation unit 43 calculates the grinding efficiency Z' based on the cut-in amount per rotation acquired by the actual cut-in amount calculation unit 42. The grinding efficiency Z' can be calculated from the rotational speed of the workpiece spindle motor and the actual cut-in amount using the following formula (3):

[0048] Here, ta is the actual cutting depth, d is the diameter of the workpiece, and Nw is the spindle rotation speed.

[0049] Then, the rotational speeds (spindle rotation speeds) of the multiple tool spindles 16b are obtained from the tool spindle motor 16a, and calculation is performed for each spindle rotation speed. In the first embodiment, as shown in Fig. 9, the grinding efficiency Z' is calculated for three patterns of spindle rotation speeds R1, R2, and R3 (where the relationship R1 < R2 < R3 is satisfied).

[0050] The grinding burn occurrence estimation unit 44 detects a sudden change region Sc where the output signal P (eddy current voltage V) acquired by the output signal acquisition unit 40 suddenly changes as shown in FIG. 10( a) during a specific section Ts in which the grinding efficiency of the grinding machine 2 is continuously changed by the control device 33, and estimates that grinding burn has occurred in the processed portion Wa. The specific section Ts is a section included in the rough grinding step S11 in the grinding process. As shown in FIG. 10( b), the specific section Ts is a transient response period in which the actual cutting depth moves from an initial value A0 (a state in which the grinding wheel 16 and the workpiece W are not in contact) to a command value SA instructed by the control device 33 based on the grinding conditions. During this period, the actual cutting depth changes so as to continuously increase from the initial value A0 to the command value SA. As shown in FIG. 9, since the actual cutting depth is proportional to the grinding efficiency Z', in the specific section Ts, the grinding efficiency Z' also changes so as to increase continuously from the initial value corresponding to the initial value A0 to the target value corresponding to the command value SA.

[0051] The sudden change region Sc refers to a region in the specific section Ts where the output signal P suddenly changes from its initial value P0. For example, the sudden change region Sc can include a point where the value of the output signal P in the specific section Ts reaches a predetermined reference value Ps. In this embodiment, as shown in FIG. 10( a), the reference value Ps corresponds to half the maximum change amount Pm, which is the maximum change amount of the output signal P from its initial value P0 in the specific section Ts. When the output signal P reaches the reference value Ps, as shown in FIG. 10( b), the actual cutting depth is A, and as shown in FIG. 10( c), the drive power of the tool spindle motor 16a when the actual cutting depth is A is B. Alternatively, the reference value Ps can be a region in which the rate of change of the output signal P in the specific section Ts is greater than a predetermined reference rate of change.

[0052] In the sudden change region Sc, grinding burn occurs in the processed portion due to heat generated by grinding the processed portion of the workpiece W with the grinding wheel 16. Grinding burn occurs in a short period of time, and the output signal (eddy current voltage) of the eddy current sensor 20, which changes in response to the structural change (formation of a work-affected layer) caused in the workpiece W by grinding burn, also changes within a short period of time, so the output signal exhibits a steep change (sudden change).

[0053] Then, the driving power B (see FIG. 10(c)) of the tool spindle 16b acquired by the grinding burn occurrence estimation unit 44 is converted into a value per unit width and acquired as the film boiling boundary power Q'w in the above-mentioned first correspondence relationship. Further, the above-mentioned contact arc length acquisition unit 51 acquires the length of the contact arc in the abrupt change region Sc as Lw. Further, the above-mentioned contact arc heat flux calculation unit 52 calculates qw from the relational expression qw = Q'w / Lw. Then, these are stored as the first correspondence relationship in the first correspondence relationship storage unit 53.

[0054] 4-6-5. Cooling State Assessing Unit 102 The cooling state assessing unit 102 ascertains the cooling state by the coolant CL and outputs information relating to the cooling state. In this embodiment, the cooling state by the coolant CL includes at least the grinding wheel sharpness K and may further include the temperature Ta, flow rate Fa, and coolant power Qa as coolant energy. Here, the film boiling boundary power Q'w varies depending on the grinding wheel sharpness K, the temperature Ta, flow rate Fa, and coolant power Qa of the coolant CL, which are acquired by the cooling state assessing unit 102 shown in FIG. 7. Therefore, in order to reflect the influence of these changes on the film boiling boundary power Q'w, the cooling state reflecting unit 107 performs a regression analysis using the film boiling boundary power Q'w as the objective variable and at least one or all of the grinding wheel sharpness K, the temperature Ta, flow rate Fa, and coolant power Qa of the coolant CL as explanatory variables, and updates the film boiling boundary power Q'w stored in the first correspondence relationship storage unit 53 based on the results of the regression analysis. The explanatory variables preferably include the grindstone sharpness K, because it has a large effect on the film boiling boundary power Q'w.

[0055] The grinding wheel sharpness K is calculated by the grinding wheel sharpness calculation unit 103 in the cooling state grasping unit 102 based on the relational expression K=(Q / width) / Z' from the grinding power Q in the tool spindle motor 16a and the grinding efficiency Z' calculated by the grinding efficiency calculation unit 43.

[0056] The temperature Ta of the coolant CL is acquired by a coolant temperature acquisition unit 105 in the cooling state grasping unit 102. The flow rate Fa of the coolant CL is acquired by a coolant flow rate acquisition unit 106 in the cooling state grasping unit 102. The coolant power Qa is calculated by a coolant power calculation unit 104 as the difference between the spindle power Q0 when the tool 16 is idling without supplying the coolant CL in the grinding machine 2, and the spindle power Q1 when the coolant CL is supplied.

[0057] In this embodiment, the film boiling boundary power Q′w can be expressed as the following relational expression (4) using a multiple regression equation for the regression analysis. ０ ~b ４ are all coefficients. The regression analysis method is not limited to this, and known statistical methods or machine learning can also be applied.

[0058]

[0059] Then, the film boiling boundary power acquiring unit 50 acquires the film boiling boundary power Q'w from the heat flux q acquired by the contact arc heat flux calculating unit 52 and the length Lc of the contact arc LC acquired by the contact arc length acquiring unit 51, based on the first correspondence relationship (Q'w = q × Lw) that reflects the influence of each explanatory variable acquired by the cooling state grasping unit 102. That is, in the graph shown in Fig. 6, by specifying the coordinates (Lc, q), the film boiling boundary power Q'w on the curve that indicates the first correspondence relationship is acquired.

[0060] 4-7. Film boiling region length calculation unit 54 The film boiling region length calculation unit 54 calculates the length Lm of the film boiling region LM in the contact arc Lc based on the grinding power Q', the film boiling boundary power Q'w, and the length Lc of the contact arc LC. Lm can be calculated based on the following relational expressions (5) and (6).

[0061]

[0062]

[0063] Here, if the length Lm of the film boiling region LM is 0 or less, it can be determined that the film boiling region LM has not occurred and that grinding burn has not occurred, and if the length Lm of the film boiling region LM is greater than 0, it can be determined that grinding burn has occurred.

[0064] 4-8. Transmitted Heat Quantity Calculation Unit 55 The transmitted heat quantity calculation unit 55 calculates the film boiling region transmitted heat quantity Jm, which is the amount of heat generated in the film boiling region LM, which is the region where the coolant CL is in a film boiling state in the machined portion Wa, based on the grinding power Q' and the film boiling boundary power Q'w. In this embodiment, the film boiling region transmitted heat quantity Jm is calculated using the following relational expression (7) based on the length Lm of the film boiling region LM shown in FIG. 11, the heat flux q per unit area in the contact arc Lc, and the feed speed v of the workpiece W relative to the tool 16 provided on the grinding machine 2. The feed speed v of the workpiece W can be acquired by the feed speed acquisition unit 56 based on the rotational speed of the workpiece motor 12a.

[0065]

[0066] 4-8. Evaluation Unit 60 The evaluation unit 60 evaluates the grinding burn state of the workpiece Wa based on the grinding power Q' and the film boiling boundary power Q'w. In this embodiment, the evaluation unit 60 evaluates the grinding burn state of the workpiece Wa based on the film boiling region heat passing amount Jm. More specifically, the evaluation unit 60 evaluates the depth of grinding burn occurring in the workpiece Wa based on the film boiling region heat passing amount Jm and a second correspondence relationship described below.

[0067] Alternatively, the evaluation unit 60 can evaluate that the film boiling region LM has not occurred and that grinding burn has not occurred when the length Lm of the film boiling region LM is 0 or less, and can evaluate that the film boiling region LM has occurred and that grinding burn has occurred when the length Lm of the film boiling region LM is greater than 0. The evaluation unit 60 can also evaluate whether grinding burn has occurred or not based on the grinding power Q' and the film boiling boundary power Q'w. For example, when Q'w / Q'<1 is satisfied, it can evaluate that grinding burn has occurred. The evaluation result can be displayed on the display unit 61.

[0068] 4-9. Second Correspondence Relationship Storage Unit 62 The second correspondence relationship storage unit 62 stores the correspondence relationship between the amount of heat passing through the film boiling region Jm and the depth tb of grinding burn that occurs on the processed portion Wa due to grinding by the grinding machine 2, as the second correspondence relationship described above. In this embodiment, the second correspondence relationship is a linear relationship between the amount of heat passing through the film boiling region Jm and the depth tb of grinding burn, as shown in Figure 12, and can be expressed by the relational equation tb = aJm (a is a coefficient). Note that Figure 12 shows the evaluation results when the processing conditions and grinding wheel sharpness shown in Figure 9 are changed.

[0069] 13 , the second correspondence relationship creating unit 200 includes an eddy current sensor 20, an output signal acquiring unit 40, a first characteristic information acquiring unit 71, a time memory unit 72, an inflection point determination criterion memory unit 73, an inflection point calculating unit 74, a dimension information acquiring unit 41, a second characteristic information acquiring unit 75, a rotation time acquiring unit 76, an inflection point time extracting unit 77, and a burn depth calculating unit 78, all of which are configured as a storage device or a computing device. Note that, in the second correspondence relationship creating unit 200, the components that overlap with those of the grinding burn condition evaluating device 30 or the first correspondence relationship creating unit 100 can use the components of the grinding burn condition evaluating device 30 or the first correspondence relationship creating unit 100.

[0070] 4-10-1. Eddy Current Sensor 20 The eddy current sensor 20 shown in FIG. 13 induces eddy currents inside the workpiece W using an excitation current and outputs an AC signal corresponding to the magnetic field generated by the eddy current. The eddy current sensor 20 may be configured to be able to change the phase of the output signal. In this embodiment, as shown in FIG. 13, the eddy current sensor 20 has a coil serving as an oscillator 21, and by supplying an excitation current to the coil, an output signal is applied to a probe 22 provided at the tip of the sensor head of the eddy current sensor 20, thereby applying a magnetic field to the workpiece W and inducing an eddy current inside the workpiece W. The eddy current sensor 20 then amplifies the change in impedance acquired via the probe 22 in an amplifier 23 and inputs it to a detector 24, extracts only the frequency component of the oscillator 21, and processes the signal in a signal processor 25.

[0071] The detection unit 24 detects the signal by synchronous detection. As shown in Fig. 14, the input signal v(t) to the detection unit 24 is a signal obtained by amplifying the output of the probe 22 by the amplifier 23, and v(t) is defined by the following equation (8): where t is time, A is amplitude, f is the frequency of the oscillator 21 inside the eddy current sensor 20, and θ is the phase difference with respect to the oscillator 21 inside the eddy current sensor 20.

[0072]

[0073] Then, in the detection unit 24, v(t) that has passed through the amplification unit 23 is multiplied by a sine wave sin2πft, which has the same frequency as the frequency f of the oscillation unit 21. This is defined as x(t). Similarly, the result of multiplying by cos2πft is defined as y(t). x(t) and y(t) can be expressed as the following equations (9) and (10).

[0074]

[0075]

[0076] Next, x(t) and y(t) are passed through a low-pass filter with a sufficiently low cutoff frequency fc. Note that generally, the relationship fc<<f holds. The first terms of equations (9) and (10) are AC because they include t, but the second terms are DC because they do not include t. Therefore, after passing through the low-pass filter, equations (9) and (10) become the real axis signal X and imaginary axis signal Y shown in the following equations (11) and (12), respectively.

[0077]

[0078]

[0079] Then, A and θ of v(t) can be obtained from equations (11) and (12) as shown in the following equations (13) and (14).

[0080]

[0081]

[0082] The signal processing unit 25 performs gain and phase manipulation on the real axis signal X and imaginary axis signal Y of the detection unit 24. Therefore, the output signal of the eddy current sensor 20 is output from the detection unit 24 through the signal processing unit 25, and the frequency characteristics of the eddy current sensor 20 are the product of the frequency characteristics of the detection unit 24 and the signal processing unit 25. In general, the frequency characteristics of the signal processing unit 25 are equal to or less than the frequency characteristics of the detection unit 24. In the output signal output from the signal processing unit 25, X represents the real axis signal and Y represents the imaginary axis signal. The real axis signal X represents the real axis value of the output signal P, and the imaginary axis signal Y represents the imaginary axis value of the output signal P.

[0083] The eddy current sensor 20 is configured to supply multiple excitation currents with different frequencies to the coil. In this embodiment, the frequency of the excitation current can be set by the frequency setting unit 26. Because the penetration depth of the eddy current varies depending on the frequency of the excitation current, the frequency of the excitation current can be set according to the target penetration depth of the eddy current. The target penetration depth of the eddy current is set to match the surface layer where grinding burn may occur, and can be, for example, 1 to 100 μm from the machined surface, preferably 1 to 50 μm, and more preferably 10 to 30 μm. If the penetration depth is shallow, the sensitivity of the eddy current sensor becomes too high, resulting in a lower signal-to-noise ratio and reduced detection accuracy. On the other hand, if the penetration depth is deep, the detection level of the magnetic property change characteristic decreases in areas shallower from the machined surface, resulting in reduced detection accuracy.

[0084] The frequency of the excitation current according to the penetration depth can be set in the frequency band of 20 kHz to 200 MHz, preferably 100 kHz to 200 MHz, and more preferably 250 to 2500 kHz. In this embodiment, the frequency of the excitation current is set to 250 kHz so that the penetration depth of the eddy current is 30 μm.

[0085] 4-10-1. Output signal acquisition unit 40 The output signal acquisition unit 40 acquires the output signal P output from the eddy current sensor 20. When expressed on a complex plane in Cartesian coordinate format, the output signal P has a value on the imaginary axis Y and a value on the real axis X, and can be expressed on the complex plane as shown in Figure 15(b) or Figure 16(b). The frequency of the excitation current output from the oscillator 21 in the eddy current sensor 20 can be adjusted by the frequency setting unit 26.

[0086] 4-10-2. First Feature Information Acquisition Unit 71 The first feature information acquisition unit 71 acquires first feature information. The first feature information is information that links at least one of the imaginary axis value and real axis value when the output signal P acquired by the output signal acquisition unit 40 is represented on a complex plane in the form of a Cartesian coordinate system with time information that is the time when the workpiece W is ground. In this embodiment, both the imaginary axis value and the real axis value of the output signal P represented on the complex plane shown in FIG. 15(b) are linked to the elapsed time from the start of grinding, which is measured by a time memory unit 72 described below.

[0087] 4-10-3. Time storage unit 72 The time storage unit 72 measures the elapsed time from the start time T0 of the grinding process. In this embodiment, the grinding process S1 of the workpiece W includes a rough grinding process S11, a fine grinding process S12, a fine grinding process S13, and a spark-out process S14, as shown in Fig. 17. Each process will be described later.

[0088] 4-10-4. Inflection Point Judgment Criterion Storage Unit 73 The inflection point judgment criterion storage unit 73 pre-stores inflection point judgment criteria for determining whether the output signal represented on the complex plane has reached an inflection point, described below, for each excitation current frequency. In this embodiment, the inflection point judgment criterion can be created based on the correspondence between the frequency of the excitation current, first characteristic information acquired by applying an excitation current having that frequency to a workpiece for creating an inflection point judgment criterion during machining, and the grinding burn state of the workpiece for creating an inflection point judgment criterion. The workpiece for creating an inflection point judgment criterion has the same shape and material as the workpiece W to be evaluated, as shown in FIG. 1.

[0089] Regarding the inflection point determination criteria, for example, the correspondence relationship between the first feature information and the grinding burn state when the excitation current frequency is 250 kHz is shown in Figures 15(a) and 15(b), and the correspondence relationship between the first feature information and the grinding burn state when the excitation current frequency is 1000 kHz is shown in Figures 16(a) and 16(b). Comparing the case where the excitation current frequency is 250 kHz with the case where the excitation current frequency is 1000 kHz, the correspondence relationship shown on the complex plane for the case where the excitation current frequency is 1000 kHz is expressed as a shape rotated -90 degrees from the case where the excitation current frequency is 250 kHz.

[0090] Next, the trajectory of the output signal P on the complex plane will be described with reference to Fig. 15(b). On the complex plane shown in Fig. 15(b), the output signal P output from the eddy current sensor 20 is plotted at the position indicated by the symbol A1 at the start of grinding. Thereafter, in the rough grinding step S11, grinding burn occurs on the workpiece W, and the magnetic characteristics change accordingly. As a result, the output signal P decreases in value on the real axis on the complex plane and slightly increases in value on the imaginary axis over time. Thereafter, the real axis value decreases and the imaginary axis value decreases, and then the real axis value increases and the imaginary axis value decreases, until the position indicated by the symbol A2 is reached, at which point the rough grinding step S11 is completed.

[0091] Thereafter, when the fine grinding process S12 begins, as grinding burns (process-affected layer, softened layer) that had occurred on the workpiece W are gradually removed, the output signal P in the complex plane decreases in value on the real axis and gradually increases in value on the imaginary axis. That is, near the start point B1 of the fine grinding process S12, the vector direction in the imaginary axis direction in the locus of the output signal P in the complex plane is pointing upward. Thereafter, as grinding progresses further and the position indicated by reference symbol B2 is reached, the value on the real axis increases but the value on the imaginary axis continues to gradually increase. Then, at the position indicated by reference symbol B3, the value on the real axis continues to increase but the value on the imaginary axis decreases. That is, at reference symbol B3, the output signal P reaches its maximum value in the fine grinding process S12, and thereafter the vector direction in the imaginary axis direction in the locus of the output signal P in the complex plane changes to a downward direction. Thereafter, the value on the real axis increases while the value on the imaginary axis decreases until the position indicated by reference symbol B4 is reached and the rough grinding process S11 is completed.

[0092] 4-10-5. Inflection Point Calculation Unit 74 The inflection point calculation unit 74 calculates an inflection point based on an inflection point determination criterion. An inflection point indicates a point at which the vector direction of the output signal P changes in the complex plane in the imaginary axis direction or the real axis direction. Therefore, when the frequency of the excitation current shown in FIG. 15(b) is 250 kHz, the inflection point is represented by point B3 where the vector direction of the output signal P changes from upward to downward in the imaginary axis direction. Note that when the frequency of the excitation current shown in FIG. 16(b) is 1000 kHz, the inflection point is also represented by point B3 where the vector direction of the output signal P changes from downward to upward in the imaginary axis direction.

[0093] Since the locus of the output signal P in the complex plane changes depending on the frequency of the excitation current, the inflection point determination criterion for the inflection point also changes. In this embodiment, the inflection point determination criterion storage unit 73 stores the locus of the output signal P in the complex plane for each excitation current frequency for the workpiece used to create the inflection point determination criterion (master), and based on this, the inflection point determination criterion is stored for each excitation current frequency. For example, as described above, the inflection point determination criterion for a 250 kHz excitation current frequency is such that the inflection point is determined to be the point at which the direction of the vector of the locus of the output signal P stored in the inflection point determination criterion storage unit 73 shown in Figure 15(b) changes from upward to downward in the imaginary axis direction in the fine grinding process S12. Furthermore, the inflection point determination criterion when the frequency of the excitation current is 1000 kHz is that the inflection point is the point at which the direction of the vector of the trajectory of the output signal P stored in the inflection point determination criterion memory unit 73 shown in Figure 16 (b) changes from downward to upward in the imaginary axis direction in the fine grinding process S12.

[0094] Furthermore, the inflection point judgment criterion storage unit 73 also stores the correspondence between the first characteristic information and the grinding burn state for the workpiece used to create the inflection point judgment criterion. When the excitation current frequency is 250 kHz as shown in FIG. 15( b), in the precision grinding process S12, the region from the precision grinding process start point B1 to the inflection point B3 indicates a state in which a softened layer that will cause grinding burn is present on the workpiece W. The region from the inflection point B3 to the vicinity of the processing end point B4 indicates a state in which no softened layer is present on the workpiece W, but a retained austenite-reduced layer that had formed deeper on the softened layer remains on the workpiece W. Note that the retained austenite-reduced layer has mechanical properties closer to the base material than the softened layer, and is therefore not included in the grinding burn. Furthermore, at the processing end point B4, no retained austenite-reduced layer is present. This is also true when the excitation current frequency is 1000 kHz as shown in FIG. 16( b).

[0095] 13 acquires dimensional information of the workpiece W as described above, and in this embodiment, the sizing device 17 can detect the dimensions of the workpiece W during machining. Note that instead of using the sizing device 17, the dimensional information of the workpiece W may be indirectly calculated and acquired based on the coordinate position of the Z axis, which is the cutting axis of the workpiece W, output from the control device 33.

[0096] Second characteristic information acquisition unit 75 The second characteristic information acquisition unit 75 acquires second characteristic information. The second characteristic information is information that links the dimension information acquired by the dimension information acquisition unit 41 with time information.

[0097] 4-10-7. Rotation Time Acquisition Unit 76 The rotation time acquisition unit 76 shown in FIG. 13 stores, as rotation times, the times acquired for each rotation or a predetermined number of rotations of the workpiece W from the end of the rough grinding step S11. In this embodiment, the times acquired for each rotation of the workpiece W from the end of the rough grinding step S11 are stored as rotation times. In the grinding process S1, grinding burn occurs in the rough grinding step S11, which has high grinding efficiency. Therefore, the workpiece ground by the grinding wheel 16 at the end of the rough grinding step S11 has the greatest burn depth, which is the depth of grinding burn. This rotation time corresponds to the time of the bottom of the valley shape repeatedly appearing in the real axis signal in FIG. 15(a). The lower envelope is drawn by connecting the bottoms of each valley shape.

[0098] 13 extracts, from the first feature information, times at which inflection points appear in the trajectory of the output signal represented on the complex plane as inflection point times. In this embodiment, the inflection point times are extracted from the multiple rotation times acquired by the rotation time acquisition unit 76. For example, in FIGS. 15(a) and 16(a), the inflection point time extraction unit 77 extracts the time at which inflection point B3 appears as inflection point time T2.

[0099] 13 calculates the grinding burn depth of the processed portion of the workpiece W based on the inflection point time extracted by the inflection point time extraction unit 77. As shown in Fig. 17, in the dimensional information of the workpiece W from the grinding start time T0 to the grinding end time Te, the grinding burn depth tb at the rough grinding step end time T1 is calculated as the difference D1 between the dimensional information at the rough grinding step end time T1 and the dimensional information at the inflection point time T2.

[0100] In parallel with the calculation of the grinding burn depth tb in the second correspondence relationship creation unit 200, the heat quantity Jm passing through the film boiling region is calculated as described above by the heat quantity calculation unit 55 shown in Fig. 2. Then, by changing the grinding conditions and obtaining a plurality of relationships between the grinding burn depth tb and the heat quantity Jm passing through the film boiling region, a second correspondence relationship approximated by a straight line as shown in Fig. 12 is created, and this is stored in the above-mentioned second correspondence relationship storage unit 62 shown in Fig. 13.

[0101] 4-11. Evaluation of grinding burn depth by evaluation unit 60 As described above, in this embodiment, the evaluation unit 60 shown in Fig. 2 evaluates the depth of grinding burn occurring in the processed portion Wa based on the amount of heat Jm passing through the film boiling region and the second correspondence relationship created as described above. That is, by acquiring the amount of heat Jm passing through the film boiling region for the workpiece W to be evaluated, the depth tb of grinding burn at the end of the rough grinding step S11 can be evaluated using the second correspondence relationship shown in Fig. 12.

[0102] In addition, instead of using the second correspondence relationship, the evaluation unit 60 may evaluate the grinding burn depth in stages, such as "large," "medium," or "small," based on the magnitude of the heat quantity Jm passing through the film boiling region.

[0103] 2 adjusts the machining conditions for grinding the workpiece Wa by the grinding machine 2 based on the evaluation results of the evaluation unit 60. The machining condition adjustment unit 63 can adjust the machining conditions during grinding by the grinding machine 2 (for example, the fine grinding step S12 and the fine grinding step S13). Alternatively, the machining condition adjustment unit 63 may adjust the machining conditions for the next workpiece W to be ground.

[0104] The adjustment of the machining conditions in the machining condition adjustment unit 63 is based on the current film boiling boundary power Q'w, the grinding wheel sharpness K described later, and the margin setting value Jm ０ Based on the above, the grinding efficiency Z' and the grinding feed rate Vf can be determined from the following relational expressions (15) and (16).

[0105]

[0106] where v is the peripheral speed of the workpiece, and d is the diameter of the workpiece.

[0107] 2 compares the setting information of the planned final finish surface of the workpiece W by the grinding machine 2 with the grinding burn depth tb at the end of the rough grinding step S11 as the evaluation result of the evaluation unit 60, and evaluates the grinding burn state of the workpiece Wa at the end of processing by the grinding machine 2. The setting information of the planned final finish surface of the workpiece W by the grinding machine 2 can be acquired from the control device 33 by the setting information acquisition unit 65.

[0108] The setting information acquired by the setting information acquisition unit 65 includes the finishing allowance tf of the workpiece W in the precise grinding step S12 and / or the fine grinding step S13. The final state evaluation unit 64 then calculates the difference tf-tb between the grinding burn depth tb at the end of the rough grinding step S11 and the finishing allowance tf. If tf-tb<0, it is evaluated that grinding burn remains on the machined portion Wa at the end of machining by the grinding machine 2. On the other hand, if tf-tb≧0, it is evaluated that no grinding burn remains on the machined portion Wa at the end of machining by the grinding machine 2.

[0109] If the final state evaluation unit 64 evaluates that grinding burns will remain on the workpiece Wa when processing by the grinding machine 2 is completed, the processing condition adjustment unit 63 can adjust the processing conditions so that grinding burns will not remain on the workpiece Wa when processing by the grinding machine 2 is completed.

[0110] 2 evaluates the grinding margin of the workpiece W based on the dimensional information of the workpiece W at the end of machining acquired by the dimensional information acquisition unit 41 and the evaluation result of the final state evaluation unit 64. For example, the margin can be set to a value of tf-tb (>0). The machining condition adjustment unit 63 can adjust the machining conditions based on the margin evaluated by the margin evaluation unit 66. The evaluation result of the margin evaluation unit 66 can be displayed on the display unit 61. Note that if it is determined in the rough grinding step S11 that the grinding burn depth tb exceeds the finish machining allowance tf, it may be determined that a machining abnormality has occurred and the machining by the grinding machine 2 may be interrupted.

[0111] The margin can also be expressed based on the amount of heat Jm passing through the film boiling region of the processed portion Wa at the end of processing by the grinding machine 2, instead of the difference between the grinding burn depth tb of the processed portion Wa and the finishing allowance tf. For example, the margin for grinding burn can be expressed based on the amount of heat Jm passing through the film boiling region of the processed portion Wa at the end of processing by the grinding machine 2. ０ The difference between the heat quantity passing through the film boiling region Jm and the heat quantity passing through the film boiling region Jm is set as Jm-Jm ０ The machining conditions can be adjusted by the machining condition adjustment unit 63 so that the quantity of heat Jm passing through the film boiling region becomes 0. The adjustment of the machining conditions may be performed when grinding the next workpiece W, or may be performed while grinding the current workpiece W. For example, the grinding feed rate may be adjusted so that the quantity of heat Jm passing through the film boiling region becomes 0 in the rough grinding step S11.

[0112] 5. Description of Grinding Process S1 The grinding process S1 will be described with reference to Fig. 18. As described above, the grinding process S1 performed by the grinding machine 2 includes a rough grinding step S11, a fine grinding step S12, a fine grinding step S13, and a spark-out step S14.

[0113] In the rough grinding step S11, the control device 33 rotates the grinding wheel 16 at a predetermined speed based on operation command data such as the shape of the workpiece W, grinding conditions, the shape of the grinding wheel 16, and coolant flow rate or supply timing information, to grind the workpiece W with a first depth of cut. In the fine grinding step S12, the control device 33 grinds the workpiece W with a second depth of cut that is smaller than the first depth of cut. In the fine grinding step S13, the control device 33 grinds the workpiece W with a third depth of cut that is smaller than the second depth of cut. In the spark-out step S14, the workpiece W is rotated at a preset rotation speed to grind away the portion left unground in the fine grinding step S13, thereby forming a perfectly circular cross-sectional shape. The depth of cut in the spark-out step S14 can be set to zero.

[0114] The cutting depth can be adjusted by controlling the cutting position of the grinding wheel 16 with the control device 33. The first to third cutting depths in each of steps S11 to S13 are appropriately set within a range that satisfies the above-mentioned relationship, and the actual cutting depth in the spark-out step S14 is substantially zero. The first cutting depth in the rough grinding step S11 is the largest, and the rough grinding step S11 has the highest grinding efficiency among steps S11 to S14. Therefore, grinding burn occurs substantially only in the rough grinding step S11.

[0115] 6. Grinding Burn State Evaluation Process S2 Next, the grinding burn state evaluation process S2 by the grinding burn state evaluation system 1 will be described with reference to the flowcharts of Figures 19 and 20. The grinding burn state evaluation process S2 is performed in parallel with the grinding processing process S1.

[0116] In the grinding burn state evaluation process S2, first, in step S21, the coolant power Qa is acquired by the coolant power calculation unit 104. Next, in step S22, the coolant temperature acquisition unit 105 and the coolant flow rate acquisition unit 106 acquire the coolant temperature Ta and the coolant flow rate Fa.

[0117] In step S23, the dimension information acquiring unit 41 acquires the dimensions of the workpiece W, and in step S24, the grinding power acquiring unit 31 acquires the grinding power Q'. Then, in step S25, the grinding wheel sharpness calculating unit 103 acquires the grinding wheel sharpness K.

[0118] Thereafter, in step S25, the contact arc length acquisition unit 51 acquires the contact arc length Lc at the machined portion Wa of the workpiece W. Thereafter, in step S26, the contact arc heat flux calculation unit 52 calculates the contact arc heat flux q.

[0119] Then, in step S27, the film boiling boundary power acquisition unit 50 calculates the film boiling boundary power Q'w based on the grinding power Q', the contact arc heat flux q, the contact arc length Lc, and the first correspondence relationship. Note that the film boiling boundary power Q'w is calculated by reflecting Ta, Fa, Qa, and K by the cooling state reflection unit 107.

[0120] Next, in step S28, the film boiling region length calculation unit 54 calculates the length Lm of the film boiling region LM using the film boiling region power Q'w, the grinding power Q', and the contact arc length Lc. Then, in step S29, the evaluation unit 60 determines whether Lm > 0 is satisfied. If Lm > 0 is not satisfied, the process proceeds to No in step S29, and in step S30, the evaluation unit 60 evaluates that grinding burn has not occurred in the processed portion Wa and displays this on the display unit 61. On the other hand, if Lm > 0 is satisfied, the process proceeds to Yes in step S29. Then, in step S31 shown in FIG. 20, the evaluation unit 60 evaluates that grinding burn has occurred in the processed portion Wa and displays this on the display unit 61.

[0121] Thereafter, in step S32, the feed rate acquisition unit 56 acquires the feed rate v of the workpiece W. Then, in step S33, the heat transfer calculation unit 55 calculates the film boiling heat transfer amount Jm based on the contact arc heat flux q, the length Lm of the film boiling region LM, and the feed rate v of the workpiece W. Next, in step S34, the evaluation unit 60 estimates the burn depth tb based on the film boiling heat transfer amount Jm and the second correspondence relationship.

[0122] Next, in step S35, the final state evaluation unit 64 uses the finish grinding allowance tf and the grinding burn depth tb to determine whether or not tf - tb > 0 is satisfied. If tf - tb > 0 is satisfied, the process proceeds to Yes in step S35, and in step S36 it is evaluated that there is no grinding burn on the final machined surface, and this fact is displayed on the display unit 61. Then, in step S38, the margin evaluation unit 66 evaluates the margin as a tf - tb value.

[0123] On the other hand, if tf-tb>0 is not satisfied in step S35, the process proceeds to No in step S35, and in step S37 it is evaluated that grinding burn has occurred on the final machined surface of the machined portion Wa of the workpiece W, and this is displayed on the display unit 61. Then, in step S38, the margin evaluation unit 66 evaluates the margin as 0. Note that even if it is evaluated that no grinding burn has occurred in step S30 shown in FIG. 19, a predetermined margin can be set in step S38 shown in FIG.

[0124] Next, in step S39, the machining condition adjusting unit 63 adjusts the machining conditions in accordance with the margin, and the process ends.

[0125] 7. Effects According to the grinding burn condition evaluation system 1 of this embodiment, the grinding burn condition of the processed portion Wa is evaluated based on the film boiling boundary energy Q'w, which is the energy required for the coolant CL supplied to the processed portion Wa to reach a film boiling state when the processed portion Wa of the workpiece W is ground by the grinding machine 2 and reflects the cooling state caused by the coolant CL, and the grinding energy Q'. This eliminates the need to obtain the temperature of the processed portion Wa, making it possible to achieve a highly accurate evaluation of the grinding burn condition that takes into account the fact that the coolant CL reaches a film boiling state in the processed portion Wa. Furthermore, because the film boiling boundary energy Q'w reflects the cooling state caused by the coolant CL, the grinding burn condition can be evaluated with even greater accuracy.

[0126] In this embodiment, the grinding energy Q' is grinding power that indicates the power required to rotate the tool spindle 16b of the grinding machine 2. This makes it possible to easily obtain the grinding energy.

[0127] In this embodiment, the film boiling boundary energy Q'w is a film boiling boundary power equivalent to the grinding power required for the coolant CL supplied to the workpiece Wa to reach a film boiling state, thereby making it possible to easily obtain the film boiling boundary energy.

[0128] The present embodiment also includes a contact arc length acquisition unit 51 that acquires the length Lc of a contact arc LC between the tool 16 and the workpiece Wa in a cross section perpendicular to the spindle of the tool 16 provided on the grinding machine 2, a contact arc heat flux calculation unit 52 that calculates the heat flux q at the contact arc LC, and a first correspondence relationship storage unit 53 that stores a first correspondence relationship between the length Lw of a non-film boiling region LW, which is a region at the contact arc LC that has not yet reached film boiling, the heat flux qw generated in the non-film boiling region LW by grinding, and a film boiling boundary energy Q'w that reflects the cooling state by the coolant CL. A film boiling boundary power acquisition unit 50, which is a film boiling boundary energy acquisition unit, acquires the film boiling boundary energy Q'w that reflects the cooling state by the coolant CL based on the first correspondence relationship and the heat flux q at the contact arc LC. Thus, by creating the first correspondence relationship in advance, the film boiling boundary energy Q'w can be acquired with a simple configuration.

[0129] In this embodiment, the evaluation unit 60 evaluates whether or not grinding burn occurs on the workpiece Wa as the grinding burn state. This makes it possible to evaluate with high accuracy whether or not grinding burn occurs on the workpiece Wa.

[0130] Furthermore, this embodiment includes a heat transfer calculation unit 55 that calculates the film boiling region heat transfer amount Jm, which is the amount of heat generated in the film boiling region LM, where the coolant CL is in a film boiling state, based on the grinding energy Q' and the film boiling boundary energy Q'w, which reflects the cooling state by the coolant CL, and the evaluation unit 60 evaluates the grinding burn state of the workpiece Wa based on the film boiling region heat transfer amount Jm. This improves the accuracy of evaluating the grinding burn state of the workpiece Wa based on the film boiling state of the coolant CL.

[0131] Furthermore, in this embodiment, the information relating to the cooling state output by the cooling state grasping unit 102 includes at least the tool sharpness K of the tool 16 provided on the grinding machine 2. As a result, the film boiling boundary energy Q'w takes into account the tool sharpness K, which is likely to change with use, and therefore the grinding burn state of the workpiece Wa can be evaluated with even greater accuracy.

[0132] Furthermore, in this embodiment, the information relating to the cooling state output by the cooling state grasping unit 102 further includes the temperature Ta of the coolant CL, the flow rate Fa of the coolant CL, and a coolant energy Qa based on the difference between the grinding energy Q1 when the tool 16 provided on the grinding machine 2 is rotated with the coolant CL supplied and the grinding energy Q0 when the tool 16 is idly rotated with no coolant CL supplied. This allows the cooling state by the coolant CL to be more accurately reflected in the film boiling boundary energy Q'w, making it possible to evaluate the grinding burn state of the workpiece Wa with even greater precision.

[0133] In this embodiment, the cooling state reflecting unit 107 performs a regression analysis using the film boiling boundary energy Q'w as the objective variable and at least one of the tool sharpness K, the coolant temperature Ta, the coolant flow rate Fa, and the coolant energy Qa as the explanatory variables, and updates the film boiling boundary energy Q'w based on the results of the regression analysis. This allows the cooling state by the coolant CL to be more accurately reflected in the film boiling boundary energy Q'w, making it possible to evaluate the grinding burn state of the workpiece Wa with even greater precision.

[0134] Furthermore, this embodiment includes a film boiling region length calculation unit 54 that calculates the length Lm of the film boiling region LM in the contact arc LC based on the film boiling boundary energy Q'w that reflects the grinding energy Q' and the cooling state by the coolant CL, and the length Lc of the contact arc LC, and a passed heat quantity calculation unit 55 calculates the film boiling region passed heat quantity Jm based on the length Lm of the film boiling region LM, the heat flux q in the contact arc LC, and the feed speed v of the workpiece W relative to the tool 16 provided on the grinding machine 2. This makes it possible to calculate the film boiling region passed heat quantity Jm with higher accuracy, thereby improving the accuracy of evaluation of the grinding burn state of the workpiece Wa.

[0135] Furthermore, this embodiment includes a second correspondence relationship storage unit 62 that stores a second correspondence relationship between the heat quantity Jm passing through the film boiling region and the depth tb of grinding burn that occurs in the processed portion Wa due to grinding by the grinding machine 2, and the evaluation unit 60 evaluates the depth tb of grinding burn that occurs in the processed portion Wa as the grinding burn state based on the heat quantity Jm passing through the film boiling region and the second correspondence relationship. This makes it possible to evaluate the depth tb of grinding burn in the processed portion Wa with a simple configuration and with high accuracy.

[0136] In this embodiment, the processing condition adjustment unit 63 adjusts the processing conditions during grinding by the grinding machine 2. This allows the processing conditions to be adjusted in real time, thereby improving yield and shortening the processing preparation period.

[0137] As described above, according to the above-described embodiment, it is possible to provide a grinding burn state evaluation system 1 that can evaluate the grinding burn state of a workpiece W during grinding with high accuracy.

[0138] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention.

Claims

1. A grinding burn condition evaluation system for evaluating the grinding burn condition of a machined portion of a workpiece which is machined into a final target shape by grinding the surface of the workpiece multiple times while supplying a cooling liquid with the grinding machine, comprising: a grinding energy acquisition unit which acquires grinding energy (Q'), which is the energy required to grind the machined portion with the grinding machine; a film boiling boundary energy acquisition unit which acquires film boiling boundary energy (Q'w), which is the energy required for the coolant supplied to the machined portion to reach a film boiling state when the machined portion is grinded with the grinding machine; a cooling state grasping unit which grasps the cooling state of the coolant and outputs information about the cooling state; a cooling state reflection unit which reflects the cooling state in the film boiling boundary energy (Q'w) based on information output by the cooling state grasping unit; and an evaluation unit which evaluates the grinding burn condition of the machined portion based on the grinding energy (Q') and the film boiling boundary energy (Q'w) with the cooling state reflected.

2. The grinding burn condition evaluation system according to claim 1, wherein the grinding energy (Q') is grinding power indicating the power required to rotate a tool spindle of the grinding machine.

3. The grinding burn state evaluation system described in claim 2, wherein the film boiling boundary energy (Q'w) is a film boiling boundary power equivalent to the grinding power required for the cooling liquid supplied to the workpiece to reach a film boiling state.

4. A grinding burn condition evaluation system as described in claim 3, comprising: a contact arc length acquisition unit that acquires the length (Lc) of a contact arc between the tool and the workpiece in a cross section perpendicular to a main axis of the tool provided on the grinding machine; a contact arc heat flux calculation unit that calculates a heat flux (q) in the contact arc; and a first correspondence relationship storage unit that stores a first correspondence relationship which is a correspondence relationship between the length (Lw) of a non-film boiling region that is a region in the contact arc that has not reached a film boiling state, the heat flux (qw) generated in the non-film boiling region by the grinding, and the film boiling boundary energy (Q'w) reflecting the cooling state, wherein the film boiling boundary energy acquisition unit acquires the film boiling boundary energy (Q'w) based on the first correspondence relationship and the heat flux (q) in the contact arc.

5. A grinding burn condition evaluation system as claimed in any one of claims 1 to 4, wherein the evaluation unit evaluates whether or not grinding burn occurs on the processed part as the grinding burn condition.

6. A grinding burn condition evaluation system as described in any one of claims 1 to 4, further comprising a heat passing calculation unit that calculates a film boiling region heat passing amount (Jm), which is the amount of heat generated in a film boiling region, which is a region in which the cooling liquid in the processed part is in a film boiling state, based on the grinding energy (Q') and the film boiling boundary energy (Q'w) reflecting the cooling state, and the evaluation unit evaluates the grinding burn condition of the processed part based on the heat passing amount in the film boiling region.

7. A grinding burn condition evaluation system as described in any one of claims 1 to 4, wherein the information regarding the cooling condition output by the cooling condition grasping unit includes at least the tool sharpness (K) of a tool provided on the grinding machine.

8. A grinding burn condition evaluation system as described in claim 7, wherein the information relating to the cooling condition output by the cooling condition grasping unit further includes the temperature of the coolant, the flow rate of the coolant, and coolant energy based on the difference between the grinding energy when a tool provided on the grinding machine is rotated with the coolant supplied and the grinding energy when the tool is idling with no coolant supplied.

9. The grinding burn state evaluation system described in claim 8, wherein the cooling state reflection unit performs a regression analysis using the film boiling boundary energy (Q'w) as a response variable and at least one of the tool sharpness, the temperature of the coolant, the flow rate of the coolant, and the coolant energy as an explanatory variable, and updates the film boiling boundary energy (Q'w) based on the results of the regression analysis.

10. A grinding burn condition evaluation system as described in claim 6, further comprising a film boiling region length calculation unit that calculates the length (Lm) of the film boiling region in the contact arc based on the grinding energy (Q'), the film boiling boundary energy (Q'w) reflecting the cooling state, and the length (Lc) of the contact arc between the tool and the workpiece in a cross section perpendicular to the main axis of the tool provided on the grinding machine, and the transmitted heat calculation unit calculates the transmitted heat (Jm) in the film boiling region based on the length (Lm) of the film boiling region, the heat flux (q) in the contact arc, and the feed speed (v) of the workpiece relative to the tool provided on the grinding machine.

11. A grinding burn condition evaluation system as described in claim 10, further comprising a second correspondence relationship memory unit in which a second correspondence relationship is stored, which is a correspondence relationship between the amount of heat passing through the film boiling region (Jm) and the depth (tb) of grinding burn generated in the processed portion due to grinding by the grinding machine, and the evaluation unit evaluates the depth (tb) of grinding burn generated in the processed portion as the grinding burn condition based on the amount of heat passing through the film boiling region (Jm) and the second correspondence relationship.

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