JP2014061568A - Chattering vibration suppression method and machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chattering vibration suppression method and a machine tool, which enable only harmful chattering vibration to be detected irrespective of a vibration amplitude, and which enable the rotational speed of a tool not bringing about chattering vibration to be determined.SOLUTION: When mounting a tool in a rotating main spindle and machining a workpiece, a machining load is detected. When vibration with a predetermined interval in the time axis of a machining load exists, the occurrence of the chattering vibration with the predetermined interval is determined. When it is determined that the chattering vibration has occurred, the rotational speed of the main spindle is changed into an optimal value according to the type of the chattering vibration.

Description

  The present invention relates to a chatter vibration suppressing method and a machine tool in machining using a rotating tool.

  When chatter vibration occurs when a workpiece is machined by rotating the tool, the machined surface accuracy may be reduced, or an excessive load may be applied to the tool. In order to prevent this, when chatter vibration is detected, the machining conditions are changed to suppress chatter vibration. Chatter vibration is detected by measuring vibration acceleration, vibration displacement, etc. of a machine tool or workpiece, and determining that chatter vibration has occurred when vibration exceeding a predetermined threshold is detected. (For example, refer to Patent Document 1).

JP 2008-290186 A

In the chatter vibration determination method using a conventional vibration detection sensor, in order to exclude vibration that does not grow and become chatter vibration, chatter vibration determination is performed by calculation processing only when the vibration amplitude exceeds a predetermined threshold. Do. For this reason, it is necessary to set the threshold value for each machining in accordance with the required machining accuracy. If the threshold value is excessively set, chatter vibration may be overlooked, and if it is too low, unnecessary machining condition changes may be repeated. There is.
The present invention has been made in view of the above circumstances, and provides a chatter vibration suppressing method and a machine tool capable of detecting only harmful chatter vibration regardless of vibration amplitude and determining the rotational speed of a tool that does not generate chatter vibration. The purpose is to provide.

A feature of the invention according to claim 1 for solving the above problem is that a tool held on a rotating spindle and a workpiece are moved relatively to each other to machine the workpiece. When processing the workpiece,
A load detection process for detecting a machining load;
A chatter determination step for determining that chatter vibration has occurred with the predetermined cycle when the value of the machining load vibrates at a predetermined cycle;
A spindle speed changing step of changing the rotational speed of the spindle when it is determined that the chatter vibration has occurred is performed.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, the chatter determination step is a determined machining load obtained by subtracting a reference machining load that is a machining load when chatter vibration is not generated from the machining load. Is determined to be regenerative chatter vibration when the amplitude of the vibration increases with time, and otherwise determined to be forced chatter vibration.

A feature of the invention according to claim 3 is that, in the invention according to claim 2, in the spindle shift step, the rotational speed of the spindle is
In the case of regenerative chatter vibration, change the frequency of the regenerative chatter vibration to a value divided by the product of the number of tool blades and a predetermined integer,
In the case of forced chatter vibration, the amount of change is proportional to the amplitude.

A feature of the invention according to claim 4 is that in a machine tool for processing the workpiece by relatively moving a rotating tool and the workpiece,
A spindle for rotating the tool;
Load detecting means for detecting a machining load acting on the spindle by machining;
Control means for controlling the spindle and the load detection means;
The control means is
Record a reference load that is a processing load when chatter vibration is not detected, detected by the load detection means,
A value of a determination load that is a load obtained by subtracting the reference load from the machining load torque vibrates at a predetermined cycle,
When the amplitude of the vibration increases with time, it is determined that the regenerative chatter vibration having the predetermined period has occurred, and the rotation speed of the spindle is determined based on the frequency of the regenerative chatter vibration and the number of tool blades. Change it to the value divided by the product of the integers,
When the amplitude of the vibration is constant, it is determined that forced chatter vibration has occurred, and the rotational speed of the spindle is changed by a change amount proportional to the amplitude.

  According to the invention of claim 1, it is determined that chatter vibration has occurred when the machining load vibrates, and chatter vibration can be suppressed by changing the rotational speed of the spindle. Since chatter vibration is detected from the vibration of the machining load regardless of the vibration amplitude, chatter vibration can be detected with high accuracy, and the chatter vibration can be suppressed by varying the rotation speed of the spindle before the chatter vibration grows greatly.

  According to the second aspect of the present invention, it is possible to determine in a short time whether regenerative chatter vibration or forced chatter vibration based on whether or not the amplitude changes with time. Since the determination time is short, chatter vibration suppression operation can be started early.

  According to the invention which concerns on Claim 3, according to the kind of chatter vibration, it can change to the rotational speed of the main shaft which can suppress chatter vibration in a short time. Before the adverse effect due to chatter vibration reaches an allowable value, the rotational speed of the main shaft changes, and chatter vibration can be suppressed.

  According to the invention which concerns on Claim 4, when chatter vibration generate | occur | produces, it can change rapidly to the optimal spindle speed according to the kind of chatter vibration. Since the rotational speed of the spindle changes before the adverse effect due to chatter vibration reaches an allowable value, it is possible to realize a machine tool in which the adverse effect due to chatter vibration does not occur.

1 is an overall view showing a machine tool according to an embodiment of the present invention. It is a figure showing processing by a tool provided with a plurality of cutting edges. It is a graph which shows the concept of the fluctuation | variation of the process load in the process shown in FIG. It is a schematic diagram of a process when the reproduction | regeneration type chatter vibration generate | occur | produces. It is a graph which shows the concept of the fluctuation | variation of the process load when regenerative chatter vibration generate | occur | produces. It is a schematic diagram of a process when a vibration frequency is an integral multiple of the value of the product of a tool rotational speed and the number of blades. It is a graph which shows the concept of the fluctuation | variation of the processing load when a frequency is an integral multiple of the value of the product of a tool rotational speed and the number of blades. It is a flowchart which shows the process of the chatter vibration suppression method. It is a graph which shows the time fluctuation of judgment load.

Embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a machine tool 1 includes a table 3 supported on a bed 2 so as to be movable in the X-axis direction, and a workpiece W is held on the table. Further, a column 4 is provided on the bed 2 so as to be movable in the Z-axis direction orthogonal to the X-axis. A column main body 5 is held in the column 4 so as to be movable in the Y-axis direction orthogonal to the X-axis and Z-axis directions. The main shaft body 5 rotatably supports the main shaft 6, and the main shaft 6 holds a tool 7 at the tip and is driven to rotate by a motor (not shown).

The control device 30 controls the feed of the recording unit 31 for recording various data therein, the X-axis control unit 32 for controlling the feed of the table 3, the Y-axis control unit 33 for controlling the feed of the main spindle body 5, and the column 4. A Z-axis control unit 34, a rotation speed control unit 351 and a torque detection unit 352, and a spindle control unit 35 that controls the rotation of the spindle 6, and a calculation unit 36 that executes various calculations.
The workpiece W is machined by the tool 7 by controlling the X axis, the Y axis, the Z axis, and the main axis based on the input NC data.

In the present embodiment, chatter vibration is detected from fluctuations in the machining load acting on the main shaft generated during machining, and a cutting process using the machine tool 1 and a chatter vibration detection method will be described.
First, the processing of a plane using an end mill having four tool blade numbers will be described with reference to FIG. Here, the tool 7 is cut by a depth D with respect to the workpiece W, and the workpiece W is processed by a downcut that rotates the tool 7 clockwise while feeding the workpiece W in the X direction. At this time, the work surface of the workpiece W cut by the blade 7a is Wa, the work surface cut by the next blade 7b is Wb, and the chips removed by the blade 7b are an area surrounded by Wa and Wb. Become. In this case, it is known that the cutting resistance acting on the blade 7b is proportional to the chip thickness t, and the machining load acting on the spindle is also proportional to this cutting resistance. Therefore, as shown in FIG. 3, the machining load is a graph that increases sharply at the beginning of cutting of the blade and then gradually decreases.

Next, when vibration occurs in the tool 7, different behavior is exhibited when the ratio of the vibration frequency and the product of the rotational speed of the tool 7 and the number of blades is an integer and when it is not.
When the ratio is not an integer (that is, in the case of regenerative chatter vibration), as shown in FIG. 4, the phase of vibration of the machining surface Wa ₁ cut by the blade 7a and the machining surface Wb ₁ cut by the blade 7b are different. Therefore, since the thickness t of the chips decreases while increasing or decreasing, the machining load becomes a curve that gradually decreases while vibrating as shown in FIG.

If the ratio is an integer, as shown in FIG. 6, the phase of the vibration of the processing surface Wb _2, which is cut by the working surface Wa ₂ and blade 7b which is cut by the blades 7a are the same. For this reason, when the vibration amplitudes of the machining surface Wa ₂ and the machining surface Wb ₂ are the same (the vibration amplitude does not grow and chatter vibration does not occur), the thickness of the chips decreases while gradually decreasing, so the machining load in FIG. a) As shown in the figure.
On the other hand, when the amplitude of the machining surface Wb ₂ is larger than the amplitude of the machining surface Wa ₂ (the vibration amplitude increases each time the blade acts, that is, in the case of forced chatter vibration), the thickness of the chip is the difference between the amplitudes of the two. The curve gradually decreases while oscillating with the amplitude of, and the machining load is as shown in FIG.

In other words, if chatter vibration that has an adverse effect due to an increase in amplitude occurs, it becomes a machining load that includes a vibration component of the chatter vibration cycle, and there is no vibration or vibration that does not increase in amplitude. Is a processing load that does not include vibration components. For this reason, the presence or absence of chatter vibration can be determined by determining whether or not the machining load vibrates.
In the chatter vibration determination method using a conventional vibration detection sensor, in order to exclude vibration that does not grow and become chatter vibration, the chatter vibration determination is performed by arithmetic processing when the vibration amplitude exceeds a predetermined threshold value. . For this reason, it is necessary to set the threshold value for each machining in accordance with the required machining accuracy. However, according to the present invention, the chatter vibration can be determined without setting the threshold.

Hereinafter, a chatter vibration suppressing method will be described based on a case where the machining torque of the spindle is detected as a machining load based on the flowchart of FIG.
The chip thickness t is calculated from the processing conditions input in advance to the recording unit 31, and the theoretical processing torque is calculated by the calculation unit 36 based on the chip thickness t, and recorded as the reference processing torque (reference processing load) Mk in the recording unit 31. (S1). Machining is started and a load detection step is performed. The torque detection unit measures the load torque Ms of the spindle being processed and records it in the recording unit 31 (S2).
Thereafter, the chatter determination process is performed from step S3 to step S5. In the calculation unit 36, a determination torque (determination processing load) Mh obtained by subtracting the reference processing torque Mk from the load torque Ms is calculated and recorded in the recording unit 31. The determination torque is divided into three types (S3) of FIG. 9 (a), (b), and (c). In the calculating part 36, the presence or absence of the extreme value of the determination torque Mh is determined. If there is no extreme value corresponding to FIG. 9A, it is determined that chatter vibration has not occurred, and the process ends. Otherwise, the process moves to S5 (S4). It is determined whether or not the maximum value increases with time. If it corresponds to (b) in FIG. 9 and increases, it is determined as regenerative chatter vibration, and the process moves to S6. If it is constant as shown in (c) in FIG. 9, it is determined as forced chatter vibration. Move to S8 (S5).

Thereafter, the main shaft shifting step is performed from step S6 to step S12. After calculating the maximum value (or minimum value) period T of the determination torque Mh shown in FIG. 9B, the calculation unit 36 calculates the vibration frequency n of the chatter vibration by the equation n = 1 / T. (S6). In the calculation unit 36, the recommended spindle rotational speed Ns is calculated by the formula Ns = n / (4 × K) and recorded in the recording unit 31. Here, K is an integer, and is selected such that the value of Ns is close to the spindle rotational speed N that was initially set (S7). The calculator 36 calculates the amplitude A shown in FIG. 9C (S8). Amplitude A is determined whether larger than the threshold value A _0, moves to S10 is larger, moves to step S11 otherwise. In the case of forced chatter vibration, the amplitude grows rapidly when the ratio between the frequency and the product of the rotational speed of the tool 7 and the number of blades is an integer, and when the ratio is slightly different from the integer, the growth is slow. If the decimal part is between 0.3 and 0.7, forced chatter vibration does not normally occur. For this reason, when the amount of increase in the amplitude is large, the main shaft rotational speed is greatly changed, and when the amplitude is small, the main shaft rotational speed can be set earlier by changing the main shaft rotational speed small (S9). Since the amplitude A is larger than the threshold A ₀ and the spindle rotational speed needs to be changed greatly, the recommended spindle rotational speed Ns is calculated by Ns = N × 0.8 and recorded in the recording unit 31. (S10). Since the amplitude A is smaller than the threshold A ₀ and the spindle rotational speed needs to be changed small, the recommended spindle rotational speed Ns is calculated by Ns = N × 0.9 and recorded in the recording unit 31. (S11). The recommended spindle rotation speed Ns is called from the recording unit 31, and the spindle rotation speed is changed to Ns (S12).

  In the conventional chatter vibration detection method, there is a possibility that vibration other than chatter vibration that has an adverse effect may be determined as chatter vibration. In addition, it is possible to determine whether the chatter vibration is regenerative chatter vibration or forced chatter vibration, and it is possible to set a spindle rotation speed that can suppress chatter vibration suitable for each.

In the above embodiment, the torque of the main shaft is used as the machining load. However, the amount of bending of the main shaft in the radial direction may be used. Moreover, you may use the processing load which acts on a workpiece.
Although the reference machining load is obtained by theoretical calculation, a load due to actual cutting in low-speed rotation where chatter vibration does not occur may be used as the reference machining load.

1: Machine tool 2: Bed 3: Table 4: Column 5: Spindle body 6: Spindle 7: Tool 30: Control device 31: Storage unit 35: Spindle control unit 36: Calculation unit 351: Rotational speed control unit 352: Torque detection Part

Claims (4)

When processing the workpiece using a machine tool that processes the workpiece by relatively moving the tool held on the rotating spindle and the workpiece,
A load detection process for detecting a machining load;
A chatter determination step for determining that chatter vibration has occurred with the predetermined cycle when the value of the machining load vibrates at a predetermined cycle;
A chatter vibration suppressing method for performing a spindle shift step of changing a rotation speed of the spindle when it is determined that the chatter vibration has occurred.   The chatter determination step is performed using a determination processing load obtained by subtracting a reference processing load that is a processing load when chatter vibration is not generated from the processing load, and a reproduction type when the amplitude of the vibration increases with time. The chatter vibration suppressing method according to claim 1, wherein the chatter vibration is determined as chatter vibration, and otherwise determined as forced chatter vibration. In the main shaft shifting step, the rotational speed of the main shaft is
In the case of regenerative chatter vibration, change the frequency of the regenerative chatter vibration to a value divided by the product of the number of tool blades and a predetermined integer,
3. The chatter vibration suppressing method according to claim 2, wherein in the case of forced chatter vibration, the vibration is changed by a change amount proportional to the amplitude. In a machine tool for processing the workpiece by relatively moving the rotating tool and the workpiece,
A spindle for rotating the tool;
Load detecting means for detecting a machining load acting on the spindle by machining;
Control means for controlling the spindle and the load detection means;
The control means is
Record a reference load that is a processing load when chatter vibration is not detected, detected by the load detection means,
A value of a determination load that is a load obtained by subtracting the reference load from the processing load vibrates at a predetermined period,
When the amplitude of the vibration increases with time, it is determined that the regenerative chatter vibration having the predetermined period has occurred, and the rotation speed of the spindle is determined based on the frequency of the regenerative chatter vibration and the number of tool blades. Change it to the value divided by the product of the integers,
A machine tool that determines that forced chatter vibration has occurred when the amplitude of the vibration is constant, and changes the rotational speed of the spindle by a change proportional to the amplitude.

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