Cutting methods

Abstract

The aim is to improve machining quality even when the frame's position relative to the workpiece is displaced during machining. [Solution] A cutting method comprising: rotating the spindle 15 at the cutting rotation speed SL, cutting and feeding toward the workpiece 3 at the cutting feed speed FL, monitoring the thrust force T of the feed axis, and when the thrust force T exceeds the cutting threshold tL, returning the spindle 15 by a predetermined cutting return distance U0, rotating the spindle 15 at the cutting recutting rotation speed SU, cutting and feeding toward the workpiece 3 at the cutting recutting feed speed FU from the position where the thrust force T exceeds the cutting threshold tL to a position where it advances by the cutting recutting distance U1, rotating the spindle 15 at the first layer cutting rotation speed S1, and cutting and feeding the spindle 15 at the first layer cutting feed speed F1.

Description

Technical Field

[0004]

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

Background Art

[0002] Conventionally, an electric machining apparatus that performs machining on a workpiece with a tool that rotates and reciprocates by an electric motor is known (for example, Japanese Patent Application Laid-Open No. 2001-087918). This electric machining apparatus includes 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 as to be able to advance and retreat. The ram has a spindle to which a tool is attached and rotates at its tip. The ball screw is rotatably supported in the frame parallel to the ram. The linear bearing includes a guide rail and a slider. The guide rail is fixed in the frame parallel to the ram. The slider is supported so as to be movable on the guide rail. The screw supporter has a fixing portion, a locking portion, and a nut portion. The fixing portion is disposed in the frame so as to be able to advance and retreat and is fixed to the slider. The locking portion locks the base end portion of the ram. The nut portion is screwed onto the ball screw.

Summary of the Invention

Problems to be Solved by the Invention

[0003] When machining is performed by an electric machining apparatus, the position of the frame with respect to the workpiece may be displaced. When the position of the frame is displaced with respect to the workpiece, the machining quality deteriorates. An object of the present invention is to improve the machining quality even when the position of the frame with respect to the workpiece is displaced during machining.

Means for Solving the Problems

[0004] A first aspect of the present invention is rotating the spindle at a feed rotation speed, feeding the cutting at a feed cutting feed speed toward the workpiece, monitoring the thrust force of the feed shaft, When the thrust force exceeds the engagement threshold, the main spindle is returned by a predetermined engagement return distance. The spindle is rotated at the cutting and recutting rotational speed, and the cutting feed is performed toward the workpiece at the cutting and recutting feed rate from the position where the thrust force exceeds the cutting threshold to a position where the cutting and recutting distance is advanced. The spindle is rotated at the first layer cutting rotational speed, and the spindle is fed at the first layer cutting feed rate. This is a cutting process.

[0005] Machining quality refers to the degree of straightness, roundness, and flatness of a machined part, for example. Machining processes include, for example, drilling, reaming, tapping, and milling. Milling processes include, for example, face milling and end milling.

[0006] The machine has a spindle, a feed table, and a spindle feed mechanism. The machine may also be a machining center. The machine may have a frame and linear guides. The linear guides are mounted on the frame. The spindle is rotatably supported on the feed table. The feed table can reciprocate along the linear guides. The feed 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. The machining tool is mounted on the spindle. The machining tool is, for example, a drill, a reamer, a tap, an end mill, or a face mill. The tap may be mounted on the spindle via a tap holder.

[0007] The machining center may have a moving device. The moving device may be, for example, a robot or a moving column. The moving device supports the frame. The moving device moves the frame relative to the workpiece. During machining, the moving device may be subjected to machining reaction forces, causing the position of the frame relative to the workpiece to be displaced. The robot may be, for example, a vertical articulated robot, a Cartesian axis robot, or a parallel link robot. The moving device may support the workpiece instead of using a frame.

[0008] The feed coordinate when the torque T exceeds the engagement threshold tL may be obtained as the cut start coordinate W1. When performing engagement return, the spindle may be moved back by the engagement return distance, using the cut start coordinate W1 as a reference. When performing engagement recutting, the spindle may be advanced by the engagement recutting distance U1, using the cut start coordinate W1 as a reference. The feed coordinate when the torque T falls below the penetration threshold tE may be obtained as the penetration start coordinate V0. When performing through cutting, the spindle 15 may be advanced by the penetration distance V, using the penetration start coordinate V0 as a reference. [Effects of the Invention]

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

[0010] [Figure 1] Schematic diagram showing the machining machine, workpiece, and machining feed method of this embodiment. [Figure 2] Configuration diagram of the control device for the processing machine of this embodiment [Figure 3] Flowchart showing the processing method of this embodiment [Modes for carrying out the invention]

[0011] The following describes the form of drilling. The present invention can also be applied to milling and other machining processes. In the case of milling, for example, the feed axis and the spindle are perpendicular to each other.

[0012] As shown in Figure 1, the machining center 10 of this embodiment includes a frame 11, a linear guide 12, a ram 13, a spindle 15, a connecting block 14, a feed screw 17, a spindle 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 positioned on the frame 11 and extends in the Z direction. The connecting block 14 is positioned on the linear guide 12. The connecting 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 connecting 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 mounted on the spindle 15. The spindle motor 18 is located on the frame 11 and connected to the spindle 15. The spindle motor 18 rotates the spindle 15. The lead screw 17 extends in the Z direction and is rotatably supported on the frame 11. The lead screw 17 moves the connecting block 14. The feed motor 19 is located on the frame 11 and connected to the lead screw 17. The feed motor 19 rotates the lead screw 17, feeding the spindle 15 in the Z direction. The processing machine 10 may also have a linear motor instead of the feed motor 19 and the feed screw 17.

[0015] Frame 11 is positioned at the tip of the arm of robot 30. Robot 30 moves frame 11 freely.

[0016] As shown in Figure 1, workpiece 3 in this embodiment is a laminated material in which multiple materials are stacked in the Z direction. Starting from the +Z end, the layers are stacked as follows: 1st layer, 2nd layer, ..., nth layer, ..., Eth layer. The Eth layer is the final layer. n is an index and is a natural number from 1 to E.

[0017] As shown in Figure 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 has a central arithmetic unit. The arithmetic unit 41 has 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 continuously acquires the Z coordinate (feed coordinate) of the main shaft 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 a sequence program, various parameters, and the coordinate Z. Here, the sequence processing unit 41c reads 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 coordinates from the coordinate acquisition unit 41a.

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

[0020] The relative coordinates 53b are the distances on the Z coordinate based on the surface of the workpiece 3 or the boundaries of each layer of the workpiece 3. The relative coordinates 43b store the retraction distance U0 for engagement, the re-cutting distance U1 for engagement, the minimum thickness dn of the nth layer, and the penetration distance V. The retraction distance U0 for engagement is the distance for retraction for engagement in the +Z direction from the surface of the workpiece 3. The re-cutting distance U1 for engagement is the distance for re-cutting for engagement in the -Z direction from the surface of the workpiece 3. The minimum thickness dn of the nth layer is the minimum thickness of the nth layer. The penetration distance V is the distance for performing through-cutting from the back surface of the workpiece 3.

[0021] Threshold 43c stores the engagement threshold tL and the nth layer switching threshold tn. The nth layer switching threshold is a threshold for torque T. The engagement threshold tL is the threshold at which torque T rises sharply when drill 1 first engages with workpiece 3. The nth layer switching threshold tn is the threshold at which the switch occurs from the nth layer to the (n+1)th layer. For example, if the (n+1)th layer is made of a harder material than the nth layer, torque T exceeds the nth layer switching threshold tn. Conversely, if the (n+1)th layer is made of a softer material than the nth layer, torque T falls below the nth layer switching threshold tn. In other words, the switch from the nth layer to the (n+1)th layer can be detected when torque T crosses the nth layer switching threshold tn. Threshold 43c stores the nth layer switching threshold tn for the number of layers in workpiece 3. The Eth layer switching threshold tE is the penetration threshold. The penetration threshold tE is the threshold at which the torque T decreases sharply when the drill 1 penetrates the workpiece 3. The nth layer switching threshold tn may include a comparison method with respect to the torque T.

[0022] The spindle rotation speed 43d is the rotation speed of the spindle 15. The spindle rotation speed 43d stores the cut-in rotation speed SL, the cut-in recut rotation speed SU, the nth layer cutting rotation speed Sn, and the through-cut 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 for the number of layers of workpiece 3. The feed rate 43e is the feed rate of the spindle 15 in the Z direction. The feed rate 43e stores the rapid traverse rate F0, the feed rate at cut-off point FL, the feed rate at cut-off point recutting 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 workpiece 3.

[0023] The number of layers E may be stored in, for example, the memory device 43. Alternatively, for example, the sequence processing unit 41c may obtain E from the last digit of the number of stored values ​​n for the minimum thickness dn of the nth layer, the switching threshold tn of the nth layer, the cutting rotation speed Sn of the nth layer, and the cutting feed rate Fn of the nth layer. The sequence processing unit 41c may issue a warning if there are gaps or omissions in the stored minimum thickness dn of the nth layer, the switching threshold tn of the nth layer, the cutting rotation speed Sn of the nth layer, or the cutting feed rate Fn of the nth layer.

[0024] Note that workpiece 3 may be a single material. In that case, only one value each of the following will be stored: minimum thickness dn of the nth layer, switching threshold tn of the nth layer, cutting rotation speed Sn of the nth layer, and cutting feed rate Fn of the nth layer.

[0025] The data stored in the storage device 43 is input from an input device (not shown). The data stored in the storage device 43 may also be input via the I / O port 45. I / O port 45 communicates with the spindle motor 18, the feed motor 19, and the robot control device 49. Bus 47 connects the arithmetic unit 41, the storage device 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 the feed pattern 51 of the tip of the drill 1 relative to the workpiece 3. The feed pattern 51 is labeled with step numbers S1 to S10. 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 Figure 3, the processing method involves performing the following steps in order. First, the machine is rapidly traversed to the reference point (machining start point) R (step S1). Next, the spindle 15 is fed for cutting (step S2). When the drill 1 engages with the workpiece 3 (Y in S3), the process proceeds to step S4. Then, the drill 1 is moved back by the engagement return distance U0 (step S4). Next, under the engagement recutting conditions, the spindle 15 is fed for cutting slightly from the engagement position on the workpiece 3 (step S5).

[0028] From the first layer (n=1) to the final layer (n=E), the next steps S6 to S8 are repeated. Specifically, the spindle 15 is fed for cutting under the machining conditions of 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 less than or equal to E (N in step S8), the process returns to step S6. Next, through-hole machining is performed (S9). Then, the spindle 15 is rapidly moved back to the reference point R (S10).

[0029] The following describes each step in detail, referring to Figure 1. In step S1, the spindle 15 is rotated at the cutting speed SL and rapidly traversed to the reference point (machining start point) R. The feed rate during rapid traversal is the rapid traversal speed F0.

[0030] In step S2, the rotational speed of the spindle 15 is the cutting speed SL. The feed rate is the cutting feed rate FL. The spindle 15 is cut in the -Z direction. The torque monitoring unit 41b monitors the torque T. When the drill 1 makes contact with the workpiece 3, the torque T increases rapidly. When the torque T becomes greater than or equal to the cutting threshold tL (Y in step S3), the process proceeds to step S4. The coordinates at this time are defined as the cutting start coordinates W1. Furthermore, the torque monitoring unit 41b does not need to monitor the torque T until it has advanced by a distance dL from the reference point R. In this case, the distance dL of the torque detection ignore range 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 re-cutting rotation speed SU for biting. In the relative coordinate based on the cutting start coordinate W1, 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 based on 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. Based on the through-cutting start coordinate V0, 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 is holding the frame 11, the rigidity of the robot 30 may be insufficient to withstand the cutting reaction force that the drill 1 receives during machining. In this case, when the drill 1 cuts into the workpiece 3, the axes (not shown) of the robot 30's arms may bend, or the motors (not shown) of each axis may rotate. When the motors of the robot 30's axes rotate, the rotation axis of the motor will try to return to its original position. This may result in a decrease in machining quality. Furthermore, it can be difficult to accurately position the workpiece 3 relative to the robot 30. Also, when the robot 30 moves the frame 11, the positioning accuracy may decrease due to gravity and inertial forces acting on the frame 11.

[0037] In the machining method of this embodiment, first, the drill 1 is inserted into the workpiece 3 under cutting conditions (insertion rotation speed SL, insertion feed rate SF), and when the drill 1 has made slight contact with the workpiece 3, the drill 1 is temporarily withdrawn. At this time, the machining machine 10 performs re-insertion or cutting with the drill 1, using the cutting 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 machined accurately.

[0038] Substantive machining takes place from step S5. In step S5, drill 1 cuts until it bites into the workpiece 3 under cutting conditions suitable for the depth of cut (re-cutting rotation speed SU, re-cutting feed rate FU). Then, in step S6, after drill 1 has sufficiently bitten into the workpiece 3, the cutting conditions are changed to conditions suitable for cutting the first layer of workpiece 3. Because drill 1 cuts under re-cutting conditions (re-cutting rotation speed SU, re-cutting feed rate FU) when it bites into the workpiece 3, 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. Furthermore, the roundness and straightness of the drilled hole are improved.

[0039] The thickness of each layer constituting the laminated material may change depending on the position of workpiece 3. According to this embodiment, in step S7, the torque monitoring unit 41b monitors the torque T, and when the torque T changes beyond the nth layer switching threshold tn, it switches to the cutting conditions for the next layer ((n+1)th layer cutting rotation speed S(n+1), (n+1)th layer cutting feed rate F(n+1)). Therefore, even if the thickness of each layer changes depending on the position of the hole, as long as the stacking order of the materials for each layer is the same, processing can be performed successively without rewriting the program or parameters.

[0040] When drill 1 attempts to penetrate workpiece 3, a large burr may form on the back surface of workpiece 3. According to this embodiment, in step S9, the system switches to through-cutting conditions (through-cutting rotational speed ST, through-cutting feed rate FT). This suppresses the generation of burrs. In addition, in step S7, the exit point of the drill 1 can be detected. Therefore, the system can accurately switch to through-cutting conditions regardless of the position of the frame 11 and the back surface (not shown) of the workpiece 3. This suppresses the generation of burrs on the back surface. Furthermore, the cutting surface of the final layer (layer E) tends to be smoother.

[0041] Although this embodiment describes through-hole machining, it can also be applied to blind-hole machining. In that case, the machining depth (not shown) from the switching coordinate Wn to the final machining layer can be specified as the machining stop position.

[0042] The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. All technical matters included in the technical concept described in the claims are covered by the present invention. The embodiments described above are preferred examples, but those skilled in the art can realize various alternatives, modifications, variations, or improvements from the contents disclosed herein, 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 grip rotation speed SU cutting speed T thrust force tL feeding threshold U0 Return distance with bite U1 Cutting distance with engagement

Claims

1. The spindle is rotated at the cutting speed, and the cutting feed rate is applied to the workpiece at the cutting feed rate. Monitor the thrust force of the feed axis, When the thrust force exceeds the engagement threshold, the main spindle is returned by a predetermined engagement return distance. The spindle is rotated at the cutting and recutting rotational speed, and the cutting feed is performed toward the workpiece at the cutting and recutting feed rate from the position where the thrust force exceeds the cutting threshold to a position where the cutting and recutting distance is advanced. The spindle is rotated at the first layer cutting rotational speed, and the spindle is fed at the first layer cutting feed rate. Cutting method.

2. When the thrust force falls below the penetration threshold, the spindle is rotated at the penetration cutting rotational speed and the spindle is further advanced by the penetration distance. The cutting method according to claim 1.

3. The aforementioned cutting process is a drilling process, Return the spindle to the machining start position. The cutting method according to claim 2.

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

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

Images