Cutting methods

Abstract

To improve machining quality even when the position of a frame relative to a workpiece is displaced during machining. [Solution] A cutting method in which the spindle 15 is rotated at a chamfering rotation speed SL and fed towards the workpiece 3 at a chamfering cutting feed rate FL, the thrust force T of the feed shaft is monitored, and when the thrust force T exceeds a chamfering threshold value tL, the spindle 15 is returned a predetermined chamfering return distance U0, the spindle 15 is rotated at a chamfering re-cutting rotation speed SU and fed towards the workpiece 3 at a chamfering re-cutting feed rate FU to a position that is chamfered a chamfering re-cutting distance U1 from the position where the thrust force T exceeds the chamfering threshold value tL, the spindle 15 is rotated at a first layer cutting rotation speed S1 and fed towards the workpiece 3 at a first layer cutting feed rate F1.

Description

[Technical Field]

[0001] The present invention relates to a cutting method. [Background technology]

[0002] Conventionally, there is known an electric machining device that performs machining on a workpiece using a tool that is rotated by an electric motor and moves back and forth (for example, JP 2001-087918 A). This electric machining device has a hollow frame, a ram, a ball screw, a linear bearing, and a screw supporter. The ram is held in a hole formed in the frame so that it can move back and forth. The ram has a spindle at its tip end, to which a tool is attached and which rotates. The ball screw is rotatably supported in the frame parallel to the ram. The linear bearing has a guide rail and a slider. The guide rail is fixed in the frame so that it is parallel to the ram. The slider is movably supported on the guide rail. The screw supporter has a fixed portion, a locking portion, and a nut portion. The fixed portion is arranged in the frame so that it can move back and forth and is fixed to the slider. The locking portion locks the base end of the ram. The nut portion is threaded onto the ball screw. Summary of the Invention [Problem to be solved by the invention]

[0003] When machining using an electric machining device, the position of the frame relative to the workpiece may be displaced, which reduces the machining quality. An object of the present invention is to improve machining quality even when the position of the frame relative to the workpiece is displaced during machining. [Means for solving the problem]

[0004] A first aspect of the present invention is The spindle is rotated at the cutting speed and fed toward the workpiece at the cutting feed rate. Monitors the thrust force of the feed axis, When the thrust force becomes equal to or greater than a bite threshold, the spindle is returned by a predetermined bite return distance; The spindle is rotated at a biting re-cutting rotation speed, and is fed toward the workpiece at a biting re-cutting feed rate to a position where the workpiece advances by a biting re-cutting distance from a position where the thrust force becomes equal to or greater than the biting threshold value; The spindle is rotated at a first layer cutting rotation speed, and the spindle is fed for cutting at a first layer cutting feed rate. This is a cutting method.

[0005] The machining quality indicates, for example, the degree of straightness, roundness, and flatness of the machined portion. The machining includes, for example, drilling, reaming, tapping, and milling. The milling includes, for example, face milling and end milling.

[0006] The processing machine has a spindle, a slide table, and a spindle feed device. The processing machine may be a machining center. The processing machine may have a frame and a linear guide. The linear guide is arranged on the frame. The spindle is rotatably supported on the slide table. The slide table can reciprocate along the linear guide. The slide table is, for example, a spindle head, a ram, or a quill. The axial direction of the spindle and the feed direction may be the same. The axial direction of the spindle and the feed direction may be perpendicular. A processing tool is attached to the spindle. The processing tool is, for example, a drill, a reamer, a tap, an end mill, or a face mill. The tap may be attached to the spindle via a tap holder.

[0007] The processing machine may have a moving device. The moving device is, for example, a robot or a moving column. The moving device supports a frame. The moving device moves the frame relative to the workpiece. During processing, the moving device may receive a processing reaction force, which may displace the position of the frame relative to the workpiece. The robot is, for example, a vertical articulated robot, a rectangular axis robot, or a parallel link robot. The moving device may support the workpiece instead of the frame.

[0008] The feed coordinate when the torque T becomes equal to or greater than the biting threshold value tL may be acquired as the cutting start coordinate W1. When performing a biting return, the spindle may be returned by the biting return distance, based on the cutting start coordinate W1. When performing biting re-cutting, the spindle may be fed by the biting re-cutting distance U1, based on the cutting start coordinate W1. The feed coordinate when the torque T becomes equal to or less than the penetration threshold value tE may be acquired as the penetration start coordinate V0. When performing through-cutting, the spindle 15 may be fed by the penetration distance V, based on the penetration start coordinate V0. [Effects of the Invention]

[0009] According to the present invention, even if the position of the frame relative to the workpiece is displaced during machining, the machining quality can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a processing machine, a workpiece, and a processing feed method according to an embodiment of the present invention; [Figure 2] 1 is a diagram illustrating the configuration of a control device for a processing machine according to an embodiment of the present invention; [Figure 3] 1 is a flowchart showing a processing method according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes a form in which drilling is performed. The present invention can also be applied to milling and other machining. In the case of milling, for example, the feed axis and the main axis are oriented perpendicular to each other.

[0012] As shown in FIG. 1, the processing machine 10 of this embodiment has a frame 11, a linear guide 12, a ram 13, a main shaft 15, a connection block 14, a feed screw 17, a main shaft motor 18, a feed motor 19, a robot (moving device) 30, and a control device 40.

[0013] The frame 11 is box-shaped. The frame 11 has a ram hole 11a. The linear guide 12 is disposed on the frame 11 and extends in the Z direction. The connection block 14 is disposed on the linear guide 12. The connection block 14 is guided by the linear guide 12 and reciprocates in the Z direction. The ram 13 passes through the ram hole 11a and is connected to the connection block 14. The ram 13 is guided by the ram hole 11a.

[0014] The spindle 15 is rotatably supported by the ram 13. A drill (tool) 1 is attached to the spindle 15. A spindle motor 18 is disposed on the frame 11 and connected to the spindle 15. The spindle motor 18 rotates the spindle 15. A feed screw 17 extends in the Z direction and is rotatably supported on the frame 11. The feed screw 17 moves the connection block 14. A feed motor 19 is disposed on the frame 11 and connected to the feed screw 17. The feed motor 19 rotates the feed screw 17 to feed the spindle 15 in the Z direction. The processing machine 10 may have a linear motor instead of the feed motor 19 and the feed screw 17.

[0015] The frame 11 is disposed at the tip of the arm of the robot 30. The robot 30 moves the frame 11 freely.

[0016] As shown in Fig. 1, the workpiece 3 of this embodiment is a laminated material in which multiple materials are stacked in the Z direction. Starting from the +Z end, the first layer, second layer, ..., nth layer, ..., Eth layer are stacked. The Eth layer is the final layer. n is a subscript and is a natural number from 1 to E.

[0017] As shown in FIG. 2, the control device 40 includes an arithmetic unit 41, a storage device 43, an I / O port 45, a bus 47, and a robot control device 49.

[0018] The arithmetic unit 41 includes a central processing unit, a coordinate acquisition unit 41a, a torque monitoring unit 41b, and a sequence processing unit 41c. The coordinate acquisition unit 41a monitors the rotation angle of the feed motor 19 and constantly acquires the Z coordinate (feed coordinate) of the spindle 15. The torque monitoring unit 41b constantly acquires the torque (thrust force) T of the feed motor 19. The sequence processing unit 41c controls the feed motor 19 and the spindle motor 18 based on the sequence program, each parameter, and the coordinate Z. Here, the sequence processing unit 41c reads the control parameters from the storage device 43. The sequence processing unit 41c receives the torque T from the torque monitoring unit 41b. The sequence processing unit 41c receives the coordinates from the coordinate acquisition unit 41a.

[0019] The storage device 43 includes a main storage device and an external storage device, and stores absolute coordinates 43a, relative coordinates 43b, a threshold value 43c, a spindle rotation speed (spindle rotation speed command value) 43d, and a feed speed (feed speed command value) 43e. The absolute coordinates 43a are machine coordinates, that is, Z coordinates from the origin. The absolute coordinates 43a store the reference point R.

[0020] The relative coordinate 53b is the distance on the Z coordinate based on the surface of the workpiece 3 or the boundary between each layer of the workpiece 3. The relative coordinate 43b stores the bit return distance U0, the bit re-cutting distance U1, the minimum thickness dn of the nth layer, and the penetration distance V. The bit return distance U0 is the distance from the surface of the workpiece 3 in the +Z direction at which the bit return is performed. The bit re-cutting distance U1 is the distance from the surface of the workpiece 3 in the -Z direction at which the bit re-cut is performed. The minimum thickness dn of the nth layer is the minimum thickness of the nth layer. The penetration distance V is the distance from the back surface of the workpiece 3 at which the penetration cut is performed.

[0021] The threshold value 43c stores a biting threshold value tL and an n-th layer switching threshold value tn. The n-th layer switching threshold value is a threshold value for the torque T. The biting threshold value tL is a threshold value at which the torque T rises sharply when the drill 1 first bites into the workpiece 3. The n-th layer switching threshold value tn is a threshold value for switching from the n-th layer to the (n+1)-th layer. For example, if the (n+1)-th layer is made of a harder material than the n-th layer, the torque T exceeds the n-th layer switching threshold value tn. Conversely, if the (n+1)-th layer is made of a softer material than the n-th layer, the torque T falls below the n-th layer switching threshold value tn. In other words, the switching from the n-th layer to the (n+1)-th layer can be detected when the torque T crosses the n-th layer switching threshold value tn. The threshold value 43c stores the n-th layer switching threshold value tn for the number of layers of the workpiece 3. The E-th layer switching threshold value tE is a penetration threshold. The penetration threshold tE is a threshold at which the torque T drops sharply when the drill 1 penetrates the workpiece 3. The n-th layer switching threshold tn may include a comparison method for the torque T.

[0022] The spindle rotation speed 43d is the rotation speed of the spindle 15. The spindle rotation speed 43d stores the cutting rotation speed SL, the cutting re-cutting rotation speed SU, the nth layer cutting rotation speed Sn, and the through-cutting rotation speed ST. The nth layer cutting rotation speed Sn is the spindle rotation speed when cutting the nth layer. The spindle rotation speed 43d stores the nth layer cutting rotation speed Sn of the number of layers of the workpiece 3. The feed rate 43e is the feed rate in the Z direction of the spindle 15. The feed rate 43e stores the rapid feed rate F0, the chamfer feed rate FL, the chamfer re-cutting feed rate FU, the nth layer cutting feed rate Fn, and the through-cutting feed rate FT. The nth layer cutting feed rate Fn is the cutting feed rate for the nth layer. The feed rate 43e stores the nth layer cutting feed rate Fn for the number of layers of the workpiece 3.

[0023] The number of layers E may be stored in, for example, the storage device 43. Alternatively, for example, the sequence processing unit 41c may acquire the last number of the stored number n of the nth layer minimum thickness dn, nth layer switching threshold tn, nth layer cutting rotation speed Sn, or nth layer cutting feed rate Fn as E. The sequence processing unit 41c may issue a warning if there is a hole or an excess or deficiency in the stored nth layer minimum thickness dn, nth layer switching threshold tn, nth layer cutting rotation speed Sn, or nth layer cutting feed rate Fn.

[0024] The workpiece 3 may be a single material. In this case, only one of the nth layer minimum thickness dn, nth layer switching threshold tn, nth layer cutting rotation speed Sn, and nth layer cutting feed rate Fn is stored.

[0025] The data to be stored in the storage device 43 is input from an input device (not shown). The data to be stored in the storage device 43 may be input via an I / O port 45. The I / O port 45 communicates with the spindle motor 18 , the feed motor 19 , and the robot controller 49 . The bus 47 connects the arithmetic unit 41, the storage unit 43, and the I / O port 45. The robot control device 49 controls the robot 30 .

[0026] The machining method of this embodiment will be described with reference to Figures 1 and 3. Figure 1 shows a feed pattern 51 of the tip of a drill 1 relative to a workpiece 3. Step numbers S1 to S10 are assigned to the feed pattern 51. Each arrow in the feed pattern 51 indicates the movement of the tip position of the drill 1 in each step.

[0027] As shown in FIG. 3, the processing method involves the following steps in order: First, the drill is rapidly advanced to the reference point (machining start point) R (step S1). Next, the spindle 15 is fed for cutting (step S2). When the drill 1 bites into the workpiece 3 (Y in S3), the process proceeds to step S4. Then, the drill 1 is returned by the biting return distance U0 (step S4). Next, under the biting re-cutting conditions, the spindle 15 is fed for cutting slightly from the biting position on the workpiece 3 (step S5).

[0028] The following steps S6 to S8 are repeated from the first layer (n=1) to the final layer (n=E). Specifically, the spindle 15 is fed for cutting under the machining conditions for the nth layer (step S6). When the torque T crosses the nth layer switching threshold tn (Y in step S7), the process proceeds to step S8. Then, the layer number n is incremented to n+1. When the layer number n exceeds E (Y in step S8), the process proceeds to step S9. When the layer number n is equal to or less than E (N in step S8), the process returns to step S6. Next, the through-cutting is performed (S9), and the main spindle 15 is returned to the reference point R at a rapid traverse (S10).

[0029] Each step will be described in detail below with reference to FIG. In step S1, the main spindle 15 is rotated at the biting rotation speed SL and is rapidly traversed to the reference point (processing start point) R. The feed rate during rapid traversal is rapid traverse rate F0.

[0030] In step S2, the rotational speed of the spindle 15 is the biting rotational speed SL. The feed rate is the biting feed rate FL. The spindle 15 is fed for cutting in the -Z direction. The torque monitoring unit 41b monitors the torque T. When the drill 1 contacts the workpiece 3, the torque T rises sharply. When the torque T becomes equal to or greater than the biting threshold value tL (Y in step S3), the process proceeds to step S4. The coordinate at this time is defined as the cutting start coordinate W1. The torque monitoring unit 41b does not need to monitor the torque T until it advances by the biting torque detection neglect range dL from the reference point R. In this case, the biting torque detection neglect range dL is stored in the relative coordinates 43b.

[0031] In step S4, the relative coordinate Z of the cutting start coordinate is set as the origin (Z = 0). The main shaft 15 is rapidly fed from the relative coordinate Z = 0 to Z = U0 (U0 is a positive value). The main shaft rotation speed may be the biting rotation speed SL.

[0032] In step S5, the main shaft rotation speed is switched to the biting re-cutting rotation speed SU. In the relative coordinate with the cutting start coordinate W1 as the reference, the main shaft 15 is fed for cutting from Z = U0 to Z = U1 (U1 is a negative value).

[0033] In step S6, with the initial setting of n = 1, steps S6 to S8 are repeated until n = E. The main shaft 15 rotates at the nth layer cutting rotation speed Sn. The main shaft 15 is fed for cutting at the nth layer cutting feed speed Fn.

[0034] In step S7, the torque monitoring unit 41b monitors the torque T. The sequence processing unit 41c compares the torque T with the nth layer switching threshold value tn. When the torque T crosses the nth layer switching threshold value tn, it proceeds to step S8. Note that the coordinate acquisition unit 41a may acquire the switching coordinate Wn when switching to the cutting of the nth layer at 2 < n < E. Here, for the first layer, it is the cutting start coordinate W1. The torque monitoring unit 41b may not perform torque monitoring until the feed coordinate Z exceeds the nth layer minimum thickness dn with respect to the switching coordinate Wn.

[0035] In step S9, the rotation speed of the main shaft 15 is changed to the through-cutting rotation speed ST. The feed speed of the main shaft 15 is changed to the through-cutting feed speed FT. The coordinate when switching from the cutting conditions of the E-th layer (the E-th layer cutting rotation speed SE, the E-th layer cutting feed speed FE) to the through-cutting conditions (the through-cutting rotation speed ST, the through-cutting feed speed FT) is set as the through-cutting start coordinate V0. With the through-cutting start coordinate V0 as the reference, the main shaft 15 is machined by cutting from the feed coordinate Z = V0 to V (V is a negative value).

[0036] The operation and effect of this embodiment will be described. When the robot 30 holds the frame 11, the rigidity of the robot 30 may be insufficient to withstand the cutting reaction force that the drill 1 receives during cutting. In this case, when the drill 1 cuts into the workpiece 3, the axes (not shown) of the robot 30's arm may bend or the motors (not shown) of each axis may rotate. When the motors of each axis of the robot 30 rotate, the rotating shafts of the motors tend to return to their original positions. This may result in a decrease in processing quality. Also, it may be difficult to accurately place the workpiece 3 on the robot 30. Furthermore, when the robot 30 moves the frame 11, the positioning accuracy may be reduced due to gravity and inertial forces acting on the frame 11.

[0037] In the processing method of this embodiment, first, the drill 1 is driven into the workpiece 3 under cutting conditions (feeding rotation speed SL, feed rate SF), and when the drill 1 slightly engages the workpiece 3, the drill 1 is temporarily returned. At this time, the processing machine 10 performs re-feeding of the drill 1 and cutting processing using the feed start coordinate W1 as a reference. Therefore, even if the positions of the frame 11 and the workpiece 3 are slightly different, the workpiece 3 can be accurately processed.

[0038] Actual machining begins in step S5. In step S5, the drill 1 continues cutting under cutting conditions (start-to-cut re-cutting rotation speed SU, start-to-cut re-cutting feed rate FU) suitable for the depth of cut until it bites into the workpiece 3. Then, in step S6, after the drill 1 has sufficiently bitten into the workpiece 3, the cutting conditions are changed to conditions suitable for cutting the first layer of the workpiece 3. When the drill 1 bites into the workpiece 3, cutting is performed under the start-to-cut re-cutting conditions (start-to-cut re-cutting rotation speed SU, start-to-cut re-cutting feed rate FU), so fluctuations in the force acting on the robot 30 can be suppressed. As a result, deflection and vibration of the robot 30 can be suppressed. This improves the roundness and straightness of the drilled hole.

[0039] The thickness of each layer constituting the laminated material may vary depending on the position of the workpiece 3 . According to this embodiment, in step S7, the torque monitoring unit 41b monitors the torque T, and when the torque T changes and exceeds the n-th layer switching threshold tn, the cutting conditions for the next layer (the (n+1)th layer cutting rotational speed S(n+1), the (n+1)th layer cutting feedrate F(n+1)) are switched to those for the (n+1)th layer. Therefore, even if the thickness of each layer changes depending on the hole position, as long as the layering order of the materials for each layer is the same, machining can be performed one after the other without rewriting the program or parameters.

[0040] When the drill 1 tries to penetrate the workpiece 3, a large burr may be generated on the back surface of the workpiece 3. According to this embodiment, in step S9, the through-cutting conditions are switched to (through-cutting rotation speed ST, through-cutting feed rate FT). This makes it possible to suppress the occurrence of burrs. Also, in step S7, the edge of the drill 1 coming out can be detected. Therefore, the through-cutting conditions can be accurately switched to regardless of the positions of the frame 11 and the back surface (not shown) of the workpiece 3. This makes it possible to suppress the occurrence of back burrs. Also, the cutting surface of the final layer (layer E) tends to be smooth.

[0041] Although the present embodiment has been described with respect to through-hole machining, it can also be applied to blind hole machining. In this case, the machining depth (not shown) from the switch coordinate Wn to the final machining layer can be specified as the machining stop position.

[0042] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention, and all technical matters included in the technical ideas described in the claims are subject to the present invention. The above-described embodiments are preferred examples, but a person skilled in the art can realize various alternatives, modifications, variations, or improvements from the contents disclosed in this specification, and these are included in the technical scope described in the appended claims. [Explanation of symbols]

[0043] 3 Work 15 Spindle Fn nth layer cutting feed rate Sn nth layer cutting rotation speed SL Engagement rotation speed SU Re-cutting rotation speed T thrust force tL Engagement threshold U0 Chasing return distance U1 Re-cutting distance before chamfering

Claims

1. A method of cutting a workpiece by rotating a spindle to which a tool is attached at a cutting feed rate and cutting the workpiece at a cutting feed rate. Monitors the thrust force of the feed axis, When the thrust force becomes equal to or greater than a biting threshold, which is a threshold value when the thrust force increases rapidly when the tool first bites into the workpiece, the spindle is returned by a predetermined biting return distance; The spindle is rotated at a biting re-cutting rotation speed, and is fed toward the workpiece at a biting re-cutting feed rate to a position where the workpiece advances by a biting re-cutting distance from a position where the thrust force becomes equal to or greater than the biting threshold value; The spindle is rotated at a first layer cutting rotation speed, and the spindle is fed for cutting at a first layer cutting feed rate. Cutting method.

2. When the thrust force becomes equal to or less than the penetration threshold value, the spindle is rotated at a penetration cutting rotation speed, and the spindle is further fed by a penetration distance. The cutting method according to claim 1 .

3. The cutting process is a drilling process, After the spindle is fed by the penetration distance, the spindle is returned to the processing start position. The cutting method according to claim 2.

4. the workpiece is a laminated material, The processing feed direction is the stacking direction of the workpiece, When machining the nth layer along the machining feed direction, the spindle is rotated at an nth layer cutting rotation speed and fed at an nth layer cutting feed rate; When the thrust force crosses the n-th layer switching torque, the spindle is rotated at a (n+1)-th layer cutting rotational speed and fed at a (n+1)-th layer cutting feed rate. The cutting method according to any one of claims 1 to 3.

5. After switching to the machining conditions for the nth layer, the monitoring of the thrust force is interrupted, and when the feed coordinate advances by the minimum thickness of the nth layer, the monitoring of the thrust force is started. The cutting method according to claim 4.

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