JP2012196748A - Two-spindle opposed type nc lathe and vibration-proof machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce machining error or prevent bearings from generating heat due to deformation of a workpiece by preventing an unnecessary axial force from being applied to the workpiece in vibration-proof machining for the workpiece using a lathe with opposed two spindles.SOLUTION: This two-spindle opposed type NC lathe includes a load detection means for sequentially detecting a machining load, a calculation means for calculating an axial force or axial displacement applied to the workpiece being machined based on the detected machining load, and a spindle feeding means for sequentially driving a spindle feed motor so as to apply the calculated axial force or displacement to the workpiece. In machining the workpiece, both ends of the workpiece are held by the opposed spindles, and the spindle feed motor is controlled so that the axial force or displacement calculated based on the current machining load acts on the workpiece.

Description

  The present invention relates to a means for preventing desired machining from becoming impossible or difficult due to workpiece vibration when machining a workpiece with a lathe. In particular, the present invention relates to two pieces that are opposed to each other on the same axis. The present invention relates to the above means in an NC lathe provided with a main shaft.

  When machining a workpiece with a lathe, the workpiece may vibrate and the desired machining may not be performed. This phenomenon usually occurs when the workpiece is elongated, and it becomes impossible to give a desired cut to the blade due to the vibration of the workpiece, or a striped pattern caused by the vibration of the workpiece appears on the surface of the processed workpiece.

  Conventionally, as a means for preventing the vibration of the workpiece in such a case, a method of supporting the workpiece with a processing jig called a steady rest has been adopted. The processing method using a steady rest is extremely effective in preventing the vibration of the workpiece, but the part supported by the steady rest cannot be processed, and the manufacture / adjustment of the steady rest and the setup change during processing are complicated. There is a drawback of becoming.

  Therefore, the applicant of the present invention, in machining a workpiece on a two-spindle opposed lathe, grips both ends of the workpiece with the first spindle and the second spindle and retracts the second spindle by a predetermined amount, thereby causing the workpiece to have an axial force (axial direction). Proposed a vibration-proofing method for processing a workpiece with a high tension) (Patent Documents 1 and 2). By applying an axial force to the workpiece, the rigidity of the workpiece increases and vibration of the workpiece is suppressed, so that the range of workpieces that can be processed without using a steady rest can be expanded.

JP-A-3-287301 JP-A-5-245740

  The workpiece is machined in a plurality of steps by changing the cutting tool (tool) and the spindle rotation speed according to the machining location, the machining process, the difference in machining surface accuracy, and the like. Whether or not vibration occurs even in the same work varies depending on the process, and also changes sequentially depending on the positional relationship between the cutter and the work even during the same process.

  In the conventional vibration-proofing method, it is necessary to apply an axial force corresponding to a state in which vibration is most likely to occur to the workpiece. When an axial force is applied to the workpiece, an axial strain is generated, and an elongated workpiece, which is likely to be vibrated, also has a large axial strain of the workpiece due to the axial force, which adversely affects the machining accuracy of the axial dimension. Further, if the state where the axial force more than necessary is applied continues for a long time, the heat generation of the main shaft bearing also increases, the machine temperature rises, and the machining error due to the thermal deformation of the machine and the workpiece also increases.

  In order to avoid these problems, the axial force applied to the work must be reduced. Therefore, with the conventional technology, the axial force required for vibration isolation cannot be applied to the work and vibration can be prevented. There were often situations where it disappeared.

  The present invention improves the techniques proposed in Patent Documents 1 and 2 to prevent an excessive axial force from being applied to the workpiece during vibration isolation during machining of the workpiece using a two-spindle facing lathe. Thus, an object of the present invention is to obtain technical means capable of preventing vibration of the workpiece during processing while suppressing distortion of the workpiece and heat generation of the bearing.

  The two-spindle-facing NC lathe of the present invention is a spindle feed that moves and positions two spindles 1L, 1R facing each other on the same spindle axis and at least one moving-side spindle 1R of the two spindles in the spindle axis direction. A motor 3, a tool post 5, and tool feed motors 7 z and 7 x that send the tool post 5 are provided. The two-spindle-facing NC lathe according to the present invention further includes load detecting means for sequentially detecting a machining load during workpiece machining, and an axial force or axial displacement (hereinafter referred to as “working force”) applied to the workpiece being machined based on the detected machining load. , Simply referred to as “displacement”) and a spindle feed means 28 for sequentially driving the spindle feed motor 3 so as to apply the calculated axial force or displacement to the workpiece.

  As the load detection means, torque detection means for detecting the load torque of the spindle motors 11L and 11R and the tool feed motors 7z and 7x can be used.

  The calculation of the axial force or displacement applied to the workpiece 45 can be performed by describing an arithmetic expression in a machining program. However, with a general-purpose lathe for machining various workpieces, the creation of the program becomes very complicated. In addition, since vibration during machining is not related to the rigidity of the lathe itself or the rigidity of the blade, the error between the calculated value and the actually required axial force or displacement may increase, and the calculation takes time. There is also a possibility that it cannot follow the change of the processing load. Therefore, as the above calculation means, an arithmetic expression for calculating the axial force or displacement using the coefficient and constant determined in advance by test machining and the detected machining load value is registered in the NC device of each lathe. It is practical in that it can be used for calculation speed and other types of workpieces.

  At the time of machining, both ends of the workpiece 45 to be machined are gripped by the opposed spindles 1L, 1R, and the spindle is operated so that the axial force or displacement calculated based on the machining load at that time by the computing means acts on the workpiece 45. The feed motor 3 is controlled to process the workpiece 45 with a tensile stress applied.

  By applying an axial force in the tensile direction to the workpiece being processed, the apparent rigidity of the workpiece is increased. When the workpiece length is long, vibration may occur even when the machining load is not applied, and in order to prevent the workpiece from escaping when the cutter starts to cut the workpiece, It is preferable to use a calculation means for calculating the axial force or displacement as a non-zero value even when the signal is not detected.

  The axial force or displacement generated in the workpiece 45 during processing should be set higher as long as the workpiece does not undergo deformation that affects the processing accuracy, but it is necessary to consider the thermal expansion of the workpiece 45 due to processing. There must be a force within a range that does not cause the chuck claw to slide. Considering these points, it is preferable that the calculation means calculates the axial force or displacement as a value that does not exceed a preset maximum value. This can be easily realized by providing a maximum axial force setting means for setting the maximum value of the axial force together with an arithmetic expression for calculating the axial force for each workpiece.

  The machining load may be the detection of only the main component force Ft detected by the torque detection of the spindle motors 11L and 11R, or the axis with the main component force and the component forces Fz and Fx in the Z-axis direction and X-axis direction as variables. By registering calculation means for calculating force or displacement, the main component force Ft, the Z-axis direction component force Fz, and the X-axis direction component force Fx of the processing load are separately detected and calculated during machining, More advanced anti-vibration processing corresponding to the shape and cutting position can be realized. The Z-axis direction component force Fz and the X-axis direction component force Fx can be detected by detecting the torques of the tool feed motors 7z and 7x.

  As can be understood from the fact that the vibration of the workpiece during machining occurs when the cutting depth of the tool is increased and the vibration does not occur when the cutting depth is reduced, there is a large correlation between the generation of workpiece vibration during machining and the machining load. is there. By virtue of this invention, in the vibration isolation processing of a workpiece using a two-spindle opposed NC lathe, it is possible to prevent a situation in which an excessive axial force is applied to the workpiece, while reducing the machining accuracy and suppressing the heat generation of the machine, It is possible to effectively prevent vibrations generated therein. Further, when heavy cutting is temporarily performed, a large axial force necessary for vibration isolation is temporarily applied to perform vibration isolation processing, so that the machining efficiency can be improved.

  In addition, if an arithmetic expression with the detected machining load as a variable is registered for each workpiece type and process and the axial force or displacement applied to the workpiece being machined is calculated, it is possible to follow fluctuations in the machining load and Anti-vibration processing of different types of workpieces can be performed in an optimal state for each workpiece and lathe.

The block diagram which shows typically an example of the principal part of 2 spindle opposing NC lathe of this invention Illustration of processing load Flow chart showing the axial force application procedure

  FIG. 1 is a block diagram schematically showing an example of a main part of a two-spindle opposed NC lathe of the present invention. In the illustrated example, a two-spindle opposed NC lathe provided with a fixed-side left main spindle 1L and an axially movable right main spindle 1R is taken as an example. The fixed-side main shaft 1L is pivotally mounted on a fixed main shaft 2L that is substantially integrated with a lathe frame (bed) and is held in place. The moving-side main shaft 1R is attached to a moving main shaft 2R that can move in the axial direction (Z-axis direction) of the main shaft, and faces the fixed-side main shaft 1L. A feed screw 4 that is rotationally driven in the forward and reverse directions by a spindle feed motor (servo motor) 3 is screwed to the moving spindle stock 2R, and the moving-side spindle 1R is fixed to the fixed-side spindle 1L by the rotation of the spindle feed motor 3. Is closely spaced.

  A tool post 5 having a turret 6 is arranged between the fixed side spindle 1L and the moving side spindle 1R. Usually, a two-spindle opposed lathe is usually provided with 2 to 4 tool rests, but only one of the tool rests is shown in the figure. The tool post 5 includes a tool feed motor 7z and a feed screw 8z in the lathe spindle direction (Z-axis direction) and a tool feed motor 7x and a feed screw 8x in the tool cutting direction (X-axis direction). It can be moved and positioned in the direction (X-axis direction).

  The tool feed motors 7z and 7x are servo motors, and a tool feed command of the machining program 21 is given to the tool feed motors 7z and 7x via the position counter 23 of the NC device 22 and the servo devices 9z and 9x. The tool feed motors 7z and 7x are provided with pulse encoders 10z and 10x, and a difference signal (position between position commands az and ax given from the NC device 22 and position feedback signals bz and bx detected by the pulse encoders 10z and 10x. Deviations cz and cx are given from the difference detector 25 to the compensation circuit 26. A difference signal between the speed command output from the compensation circuit 26 and the speed feedback signal from the differentiator 24 based on the position deviations cz and cx is given to the power amplifier 27. The power amplifier 27 is connected to the tool feed motor 7z. , A current having a value corresponding to the load torque of 7x is supplied to the tool feed motors 7z and 7x.

  Therefore, the NC device acts on the tool rest 5 from the load torque of these motors by comparing the position commands az, ax output by itself with the position feedback signals bz, bx of the tool feed motor. The Z-axis direction component force Fz and the X-axis direction component force Fx of the machining load can be detected.

  When machining is performed by moving the tool in the Z-axis direction, the X-axis direction component force Fx is the back component force of the machining load, and the Z-axis direction component force Fz is the feed component force. Further, when machining is performed by sending the tool in the X-axis direction, the Z-axis direction component force Fz is the back component force, and the X-axis direction component force Fx is the feed component force.

  In the drawing, the internal configuration of the servo device 9z for the tool feed motor in the Z-axis direction is not shown, but it is the same as the servo device 9x for the tool feed motor 7x in the X-axis direction.

  The spindle motors 11L and 11R are provided with pulse encoders 10L and 10R and spindle motor control devices 12L and 12R that control the speeds of the spindle motors 11L and 11R by the same control as the feed motors 7z and 7x. The main component force Ft (see FIG. 2) of the machining load can be sequentially detected based on the difference signals cr and cl between the command signal to the spindle motor control devices 12L and 12R and the feedback signal.

  The spindle feed motor 3 is controlled via a servo device 9a similar to that provided for the tool feed motors 7z and 7x. A position command a is given to the servo device 9a from the spindle feeding means 28 of the NC device 22. The spindle feed motor 3 includes a pulse encoder 10a, and a difference signal (position deviation) c between the position command a given from the NC device 22 and the position feedback signal b detected by the pulse encoder 10a is compensated from the difference detector 25. The circuit 26 is provided. A difference signal between the speed command output from the compensation circuit 26 and the speed feedback signal from the differentiator 24 based on the position deviation c is given to the power amplifier 27, and the power amplifier 27 loads the load torque of the spindle feed motor 3. Is supplied to the spindle motor 3.

  The maximum value of the current output from the power amplifier 27 is limited by the maximum current setting unit 29, and the limit value is commanded by the maximum axial force setting means 32 of the calculation means 31 registered in the NC device 22.

  Registered in the calculation means 31 of the NC device 22 is a calculation formula 41 for calculating the axial force applied to the workpiece during vibration isolation processing, and a table 42 for registering coefficients and constants used in this calculation for each type of workpiece. Yes. The coefficients and constants to be registered are determined on the workpiece to be machined based on machining results and test machining. When machining a new type of work, a set of coefficients and constants for the work is additionally registered in the table 42.

In the calculation formula 41 in the embodiment, the axial force P applied to the workpiece is expressed as P = A × Ft + B × Fz + C × Fx + D.
Calculated with here,
Ft: Main component force of cutting load Fz: Z-axis direction component force of cutting load Fx: X-axis direction component force of cutting load A: Coefficient (for main component force)
B: Coefficient (for Z axis direction component force)
C: Coefficient (for X-axis direction component)
D: Coefficient (intercept)
It is. The main component force Ft of the cutting load can be sequentially detected by the torques of the spindle motors 11L and 11R, and the Z-axis direction component force Fz and the X-axis direction component force Fx of the cutting load are the above-described tool feed motors 7z and 7x. Can be sequentially detected by command signals az, ax and feedback signals bz, bx. The coefficients A to D are the workpiece material, length, diameter, grasping force, grasping jig condition (claw and collet shape and grasping allowance), tool material used, tool mounting condition (tool shape and protrusion). Length), a cutting speed, a depth of cut, and the like. The value is determined by experimenting in advance for each workpiece, and is registered in the calculation unit 31 as a table 42 as shown in the table below.

  The NC device 22 includes a position deviation detecting means 33 for obtaining the position deviation c from the servo motor of the spindle feed motor, and the workpiece axial force detected from the obtained position deviation c and the axial force calculated by the calculating means 31. Comparing means 34 for comparison and spindle feeding means 28 for outputting a feed command for the moving headstock 2R based on the determination result of the comparing means 34 are provided. When the detected value of the axial force is larger than the calculated value, the main shaft feeding means 28 gives a movement command in the direction in which the moving main shaft 1R approaches the fixed main shaft 1L to the servo device 9a, and the detected value of the axial force is smaller than the calculated value. Sometimes, a movement command in a direction in which the moving-side main shaft 1R is separated from the fixed-side main shaft 1L is given to the servo device 9a.

  The two-spindle-facing NC lathe according to the present invention processes a workpiece including a vibration-proofing process by the procedure shown in FIG. A plurality of machining programs are registered in the NC device, and each machining program includes a number of machining processes (such as roughing turning, turning finishing machining, and drilling with a rotating tool) for each part of the workpiece to be machined with the program. Block) is described. The NC device 22 sequentially selects the designated machining program, reads the processes described in each program in order, and continuously machines the workpiece. Whether to perform anti-vibration processing is specified for each process of each processing program. If anti-vibration processing is specified for the read process, the NC unit sets the control to the anti-vibration processing mode (ON), If anti-vibration processing is not designated, the anti-vibration processing mode setting is canceled (OFF).

  The procedure shown in FIG. 3 is executed in parallel with the workpiece machining operation, and the procedure shown in FIG. 3 is executed simultaneously with the workpiece machining. The anti-vibration processing of the present invention is performed in a state where the workpiece is gripped at both ends. If the read process is not a double-sided process (including a standby time for loading or unloading a workpiece), the process branches at step 51, and the loop of step 56 and the process end determination step 56 is performed without doing anything. repeat. Further, even in the case of both-end processing, if the vibration-proof processing mode has not been switched, the process branches at step 52, and the loop from step 51, 52 to the end of processing step 56 is repeated.

  When double-sided machining is performed with the control set to the vibration-proof machining mode, in step 53, parameters corresponding to the type of workpiece specified by the workpiece number (coefficients A to D in the above embodiment) are tabled. 42 is read into the memory. Then, in step 54, the spindle force or displacement to be applied to the workpiece is calculated using the machining load detected at that time and the read parameter, and the spindle is applied to the calculated axial force or displacement to the workpiece. A feed command is given to the feed motor 3.

  That is, the main component force Ft, the Z-axis direction component force Fz, and the X-axis direction component force Fx of the machining load are obtained from the position deviation or output torque of the spindle motors 11L and 11R and the tool feed motors 7z and 7x, and these values and memory are obtained. The axial force P is calculated using the coefficients A, B, C, and D stored in FIG. This calculation result is compared with the axial force obtained from the position deviation c of the spindle feed motor 3 detected at that time by the comparison means 34, and if the calculated axial force P is larger, the spindle feed means 28 makes the spindle The feed motor 3 is given a movement command in a direction in which the moving-side main shaft 1R is separated from the fixed-side main shaft 1L. On the other hand, if the axial force detected from the position deviation c is greater than the calculated axial force P, the spindle feed means 28 gives the spindle feed motor 3 a movement command in the direction in which the moving spindle 1R approaches the fixed spindle 1L. . If the calculated axial force and the detected axial force are the same (the difference between them is equal to or less than a set threshold value), the position of the moving main spindle 1R at that time is held.

  By repeating the loop of step 51 and step 56 at short time intervals, the machining load during machining is sequentially detected, the axial force in the tension direction corresponding to the machining load is applied to the workpiece, and the workpiece vibration is appropriately adjusted. Processing of the workpiece is continued in the prevented state.

  When the limit value of the maximum axial force to be applied to the workpiece is described in the machining program, the maximum axial force setting unit 32 of the calculation unit 31 uses the current corresponding to the axial force as a limit value to set the maximum current setter 29. Thereby, even if it is going to move the main spindle 1R so that the axial force more than the maximum axial force restricted from the spindle feeding means 28 may be applied, the torque of the spindle feeding motor 3 is restricted and cannot be moved. It is possible to prevent an excessive axial force from acting on the workpiece.

  When a process for which anti-vibration processing is not specified is read, the anti-vibration processing mode is switched off, and in step 55, the loop is exited, machining without applying axial force or displacement to the workpiece, or load unloading of the workpiece, etc. Is executed. This procedure is repeated up to step 56 where the end signal of a series of machining operations is received.

  In the above description, the example in which the spindle motor is controlled so as to apply the calculated axial force to the workpiece has been described, but the axial force applied to the workpiece and the displacement of the workpiece (axial strain) caused by the axial force. Therefore, even if the spindle feed motor 3 is controlled so as to generate the displacement by calculating the displacement instead of the axial force, the same vibration proofing as in the above embodiment can be realized. Can do. Further, the arithmetic expression of the above embodiment is an expression for calculating the axial force as a temporary function of the machining load, but is not limited to such an arithmetic expression, and is an arithmetic expression including a square, a square root, a fraction, and the like. In short, the calculation formula that can calculate the relationship between the change in the machining reaction force and the axial force or displacement necessary for vibration isolation according to the change in the machining reaction force in an appropriate and simple relationship. Register. The simple arithmetic expression referred to here is an arithmetic expression that can determine a coefficient to be used by a small number of experiments and that can be repeatedly calculated in a short time.

1L, 1R Spindle 3 Spindle feed motor
11L, 11R spindle motor
28 Spindle feed means
31 Calculation means Ft Main component force Fz Z-axis direction component force Fx X-axis direction component force

Claims (5)

Two spindles (1L, 1R) that face each other on the same axis so as to be freely separated from each other, spindle motors (11L, 11R) that drive these, turret (5), and tool feed motor (7z, 7x) that sends them And a two-spindle opposed NC lathe equipped with a spindle feed motor (3) for moving and positioning the moving-side spindle (1R) in the axial direction,
Load detecting means for detecting the machining load of the workpiece, calculation means (31) for calculating the axial force or axial displacement applied to the workpiece being machined based on the detected machining load, and the calculated axial force or shaft A two-spindle opposed NC lathe, comprising: a spindle feed means (28) for driving the spindle feed motor (3) so as to impart a directional displacement to the workpiece.   The two-spindle opposed NC lathe according to claim 1, wherein the calculation means calculates an axial force or axial displacement when a machining load is not detected as a non-zero value.   The two-spindle opposed NC lathe according to claim 1, wherein the calculating means calculates an axial force or axial displacement as a value not exceeding a preset maximum value.   The computing means computes the axial force or axial displacement using the detected main component force (Ft), Z-axis direction component force (Fz) and X-axis direction component force (Fx) as variables. The two-spindle opposed NC lathe according to claim 1. Using the two-spindle opposed NC lathe according to claim 1,
When one end of the workpiece to be machined is gripped by one of the opposing spindles (1) and the workpiece is machined, the other spindle (3) grips the other end of the workpiece to reduce the machining load on the workpiece being machined. Sequentially detecting, calculating the axial force or axial displacement with the detected machining load and the calculation means corresponding to the type of the workpiece, and feeding the spindle so that the calculated axial force or axial displacement is applied to the workpiece An anti-vibration machining method for a two-spindle opposed NC lathe, wherein a workpiece is machined while sequentially controlling a motor.

Images