Method for processing using machine tool

Abstract

According to one embodiment, a processing method includes a step for performing primary processing on a first workpiece that is held at a first workpiece spindle, a step for performing primary processing on a second workpiece that is held at a second workpiece spindle, a step for bringing the first workpiece spindle and the second workpiece spindle together to obtain a workpiece assembly, and a step for performing secondary processing on the workpiece assembly.

Description

Processing method by a machine tool

[0001] The present invention relates to a method for processing a workpiece by a machine tool having a plurality of workpiece spindles.

[0002] Machine tools include a turning center that moves a tool relative to a rotating workpiece, a machining center that moves a rotating tool relative to a workpiece, and a composite machining machine that combines these functions. There are also machine tools that have a plurality of workpiece spindles and can process a plurality of workpieces in parallel (see Patent Document 1). Due to recent advancements in functionality and performance, a single machine tool can perform various machining operations such as cutting, grinding, and threading.

[0003] Japanese Patent No. 6900564

[0004] As described above, by processing a plurality of workpieces in parallel, the processing efficiency of the workpieces themselves can be increased. However, generally, the assembly of the processed workpieces is performed by an operator (human) or a robot installed alongside the machine tool. In this regard, the inventor has come to the idea that further improvement can be achieved by making the most of the high functionality of the machine tool.

[0005] One aspect of the present invention is a processing method by a machine tool having a first workpiece spindle, a second workpiece spindle, and a tool holding portion that holds a tool for processing a workpiece held by each workpiece spindle. This processing method includes a step of performing primary processing on a first workpiece held by the first workpiece spindle, a step of performing primary processing on a second workpiece held by the second workpiece spindle, a step of obtaining a workpiece assembly by joining the first workpiece and the second workpiece by bringing the first workpiece spindle and the second workpiece spindle close to each other, and a step of performing secondary processing on the workpiece assembly.

[0006] According to the present invention, the processing efficiency of a plurality of workpieces can be increased in a machine tool.

[0007] This is a perspective view showing the external appearance of a machine tool according to an embodiment. This is a hardware configuration diagram of the machine tool. This is a perspective view showing the internal structure of the machine tool. This is a diagram showing the positional relationship between the first work spindle and the second work spindle. This is a diagram showing an example of a part that can be machined in this embodiment. This is a flowchart showing the machining procedure for a part. This is a diagram showing the machining process for a part. This is a diagram showing the machining process for a part. This is a diagram showing the machining process for a part. This is a diagram showing the main part of the machining method according to Modification 1. This is a diagram showing the main part of the machining method according to Modification 2. This is a schematic diagram showing the main part of the machine tool according to Modification 3. This is a diagram showing the main part of the machining method according to Modification 3. This is a diagram showing the main part of the machining method according to Modification 4. This is a flowchart showing the procedure for joining the first workpiece and the second workpiece.

[0008] An embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a perspective view showing the external appearance of the machine tool according to the embodiment. For convenience, the vertical, horizontal, and left-right directions of the machine tool 1, as viewed from the front, will be described below as the X, Y, and Z directions, respectively.

[0009] Machine tool 1 is a turning center that processes a workpiece into a desired shape by changing tools as needed. A processing chamber 4 is provided inside the housing 2 of machine tool 1. The processing chamber 4 is surrounded by splash guards that form the sides of the housing 2. A processing device for processing the workpiece is installed in the processing chamber 4. A door 7 is provided on the front of the housing 2 for accessing the processing chamber 4. An operation panel 6 for operating the processing device is provided to the side of the door 7.

[0010] A coolant tank 8 (see Figure 3) for storing coolant supplied to the machining chamber 4 is provided adjacent to the housing 2 of the machine tool 1. The coolant is used as a cutting fluid for heat removal and lubrication of the tool and workpiece during machining, but it is also used as a cleaning fluid to remove chips scattered in the machining chamber 4. Since the coolant becomes a mist in the machining chamber 4, if it is discharged outside the machine as is, it will cause contamination of the factory. For this reason, the machine tool 1 is provided with a mist collector 10 for recovering the misted coolant (also called "oil mist").

[0011] Figure 2 is a hardware configuration diagram of machine tool 1. Machine tool 1 includes an information processing device 100, a machining control device 102, and a machining device 104. The machining control device 102 functions as a numerical control unit and outputs control signals to the machining device 104 according to a machining program (NC program). The machining device 104 drives the workpiece spindle and moves the tool to machine the workpiece according to instructions from the machining control device 102.

[0012] The processing apparatus 104 includes a work spindle drive unit 110, a tool post drive unit 112, a coolant supply device 114, and a mist collector drive unit 116. In this embodiment, as described later, a first work spindle and a second work spindle are provided as work spindles capable of holding a workpiece. The work spindle drive unit 110 includes a first spindle drive unit 120 that drives the first work spindle and a second spindle drive unit 122 that drives the second work spindle. The tool post drive unit 112 drives a turret-type tool post, which will be described later.

[0013] The coolant supply device 114 supplies coolant to the machining chamber 4. The coolant supply device 114 is composed of the coolant tank 8 described above, as well as a coolant discharge unit (not shown), a pump, and a control valve arranged in the coolant circulation path. The coolant discharge unit includes a nozzle for discharging coolant and an actuator for driving the nozzle, and discharges coolant toward a set target position. The pump draws up the coolant stored in the coolant tank 8 and supplies it to the coolant discharge unit. The control valve includes multiple on-off valves and appropriately switches the flow path of the coolant in the coolant circulation path.

[0014] The mist collector drive unit 116 drives the mist collector 10 when coolant is discharged in the processing chamber 4. The mist collector drive unit 116 includes a motor that drives the fan of the mist collector 10.

[0015] The information processing device 100 includes an operation panel 6 and outputs control commands to the processing control device 102 based on the operator's input. The information processing device 100 also controls the screen displayed on the monitor of the operation panel 6 in accordance with the operator's input.

[0016] Each component of the information processing device 100 is realized by hardware including arithmetic units such as a CPU (Central Processing Unit) and various coprocessors, storage devices such as memory and storage, and wired or wireless communication lines connecting them, and software stored in the storage devices that supplies processing instructions to the arithmetic units. The computer program may consist of device drivers, an operating system, various application programs located at a higher layer, and libraries that provide common functions to these programs.

[0017] Figure 3 is a perspective view showing the internal structure of the machine tool 1. For the sake of explanation, the front and left and right side covers (splash guards) of the housing 2 are shown removed. The machine tool 1 has a partition wall 12 that divides the space above the bed 3 (base) inside the housing 2 into a machining chamber 4 and a storage chamber 5.

[0018] The machining apparatus 104 is configured by mounting a first headstock 14, a second headstock 16, and a tool post 18, etc., on the bed 3. The first headstock 14 is housed in a storage chamber 5, and the second headstock 16 and tool post 18 are housed in a machining chamber 4. Since no moving parts are provided in the storage chamber 5, it is sized to be sufficient for housing the first headstock 14 and is considerably smaller than the machining chamber 4. The first headstock 14 rotatably supports the first workpiece spindle 20. The tip of the first workpiece spindle 20 penetrates the partition wall 12 and is exposed to the machining chamber 4. A chuck capable of holding a workpiece is attached to the tip of the first workpiece spindle 20. The first workpiece spindle 20 is rotationally driven by the first spindle drive unit 120 described above.

[0019] The second headstock 16 rotatably supports the second workpiece spindle 22. The second headstock 16 is covered with a dedicated cover 17 to prevent chips and coolant from entering. The second workpiece spindle 22 is exposed from the cover 17. A chuck capable of holding a workpiece is attached to the tip of the second workpiece spindle 22. The second workpiece spindle 22 is rotationally driven by the second spindle drive unit 122 described above. The second workpiece spindle 22 can be replaced with a tailstock (not shown) as needed.

[0020] The first work spindle 20 and the second work spindle 22 are arranged to face each other coaxially in the Z direction. The first headstock 14 and the second headstock 16 each have built-in spindle motors for rotating the work spindles. The second headstock 16 is movable in the Z direction by the drive of a moving mechanism (not shown). That is, the second headstock 16 can move the second work spindle 22 in a direction that brings it closer to or further away from the first work spindle 20, thereby adjusting the distance between the first work spindle 20 and the second work spindle 22. This moving mechanism is, for example, a screw feed mechanism using a ball screw.

[0021] The tool post 18 is located in the machining chamber 4, further back in the depth direction than the second spindle head 16, and functions as a "tool holder." The tool post 18 includes a turret base 24 and a turret 26. The turret base 24 has a rotation axis extending in the Z direction and rotatably supports the turret 26. The turret base 24 is equipped with a spindle motor for rotationally driving the turret 26. The turret 26 is provided with a plurality of clamping / unclamping mechanisms (not shown) along its periphery. These clamping / unclamping mechanisms allow for the attachment and detachment of multiple different types of tools (not shown).

[0022] The turret base 24 is movable in the X, Y, and Z directions by driving a moving mechanism (not shown), allowing adjustment of the positional relationship between the workpiece held by each workpiece spindle and the tool held by the turret 26. This moving mechanism is, for example, a screw feed mechanism using a ball screw.

[0023] With this configuration, the turret 26 is movable in the X, Y, and Z directions. Furthermore, the turret 26 is rotatable about an axis extending in the Z direction, thereby allowing the tool used for machining to be switched. In other words, the turret 26 moves relative to the workpiece supported by one or both of the first workpiece spindle 20 and the second workpiece spindle 22 in the three orthogonal axis directions, and the workpiece can be cut or turned using the tool.

[0024] A coolant discharge unit is provided at a predetermined location in the machining chamber 4 (not shown). The coolant discharge unit discharges coolant toward the tool when machining the workpiece, and also discharges coolant to wash away chips scattered in the machining chamber 4. Some or all of the tools supported by the turret 26 may also be equipped with the function of a so-called through-spindle coolant system. That is, an internal passage for circulating coolant may be provided in the tool, and this internal passage may be connected to a coolant circulation path. A discharge port is provided at the tip of the tool, forming one end of the internal passage and discharging coolant. By discharging coolant from the tip of the tool in this way during machining, it is possible to improve machining accuracy, shorten machining time, extend tool life, and improve chip evacuation performance.

[0025] The mist collector 10 is positioned in the space above the first headstock 14 in the containment chamber 5. The partition wall 12 is provided with a mist intake port 28 that opens toward the machining chamber 4. A pipe 30 is provided in the containment chamber 5 that connects the intake port 10a of the mist collector 10 to the mist intake port 28. A cover 32 is provided on the side of the partition wall 12 that covers the mist intake port 28 from above. The cover 32 opens toward the bottom and restricts the direct entry of coolant discharged from the coolant discharge port into the mist intake port 28. When the mist collector 10 is driven, oil mist in the machining chamber 4 is taken in by the mist intake port 28 and guided through the pipe 30 to the intake port 10a. The oil mist is collected inside the mist collector 10, and the purified air is discharged from the exhaust port 10b. The configuration of the mist collector 10 is publicly known, as described in, for example, Japanese Patent Publication No. 7144631, so a detailed explanation will be omitted.

[0026] Figure 4 shows the positional relationship between the first work spindle 20 and the second work spindle 22. The first work spindle 20 and the second work spindle 22 are arranged to face each other in the Z direction. The first workpiece W1 is attached to the first work spindle 20, and the second workpiece W2 is attached to the second work spindle 22. The axis L1 of the first work spindle 20 and the axis L2 of the second work spindle 22 coincide. The first work spindle 20 and the second work spindle 22 are rotationally driven around their axes. The second headstock 16 is movable in the Z direction, and the distance between the first work spindle 20 and the second work spindle 22 can be adjusted as appropriate.

[0027] A chuck cylinder (not shown) is provided on the first headstock 14. The chuck cylinder drives a chuck 21 attached to the tip of the first workpiece spindle 20. The chuck cylinder can be used to perform a gripping operation on the chuck 21. Similarly, a chuck cylinder is provided on the second headstock 16. The chuck cylinder can be used to perform a gripping operation on the chuck 23.

[0028] In this embodiment, these chuck cylinders are hydraulic cylinders, but air cylinders may also be used. The gripping operation of the chuck 23 can be performed by the operation of the chuck cylinders. The configuration and operation of such chuck cylinders are publicly known, as described in, for example, Japanese Patent Application Publication No. 2023-180634, so a detailed explanation is omitted.

[0029] In this embodiment, the worker manually attaches the workpieces to each workpiece spindle, but the workpieces may be automatically supplied by a bar feeder or robot (not shown). Note that the configuration and operation of the bar feeder are publicly known, as described in, for example, Japanese Patent Publication No. 7108148, so a detailed explanation is omitted.

[0030] The turret 26 moves relative to the first workpiece W1 and the second workpiece W2 in three orthogonal axial directions, and can cut or turn the workpieces using any of the clamped tools T (T1, T2…). When turning these workpieces, the workpiece spindle drive unit 110 drives the spindle motor to rotate one or both of the first workpiece spindle 20 and the second workpiece spindle 22. Subsequently, the servo motor is driven to feed the turret 26 and process the workpiece.

[0031] Next, a characteristic machining method using the machine tool of this embodiment will be described. As described above, the machine tool 1 is equipped with two work spindles (first work spindle 20, second work spindle 22), so that workpieces supported by each work spindle can be machined. In this embodiment, two workpieces are assembled by cooperating the two work spindles, and the resulting assembly (referred to as the "work assembly") is held on one of the work spindles and subjected to secondary machining (finishing). This makes it possible to perform a series of manufacturing processes, including primary machining, assembly, and secondary machining, automatically by the machine tool 1 alone, without substantially involving a human operator or robot.

[0032] Figure 5 shows an example of a part that can be processed in this embodiment. The left column of the figure shows the material before processing, and the right column shows the processed part. The first workpiece W1 (first material) and the second workpiece W2 (second material) are made of different materials. The first workpiece W1 is made of, for example, an aluminum alloy, and the second workpiece W2 is made of, for example, a copper alloy, but it may be stainless steel (SUS), brass, or other metal material. Alternatively, one or both of the workpieces may be made of a resin material. According to the processing method of this embodiment, primary processing, assembly, and secondary processing can be performed on the first workpiece W1 and the second workpiece W2 to obtain a finished part 50.

[0033] Figure 6 is a flowchart showing the processing procedure for part 50. Figures 7 to 10 are diagrams showing the processing steps for part 50. The processing method for part 50 will be explained below, based on Figure 6 and referring to Figures 7 to 10 as appropriate.

[0034] First, workpieces are set on the first workpiece spindle 20 and the second workpiece spindle 22, respectively (S10: workpiece setting process / Figure 7(A)). The first workpiece W1 is gripped by the chuck 21 of the first workpiece spindle 20, and the second workpiece W2 is gripped by the chuck 23 of the second workpiece spindle 22. This initial operation may be performed by an operator, or the workpieces may be automatically supplied by a bar feeder or robot.

[0035] Next, the first spindle drive unit 120 rotates the first workpiece spindle 20, and the tool post drive unit 112 controls the movement while appropriately changing the tool T, thereby performing primary machining of the first workpiece W1 (S12: Primary machining process of the first workpiece / Figure 7 (B)). Specifically, a pilot hole is drilled into the first workpiece W1 with a drill, and then a female thread 41 is machined (formed) using a boring tool.

[0036] Furthermore, the second spindle drive unit 122 rotates the second workpiece spindle 22, and the tool post drive unit 112 controls the movement of the tool T, thereby performing primary machining of the second workpiece W2 (S14: Second workpiece primary machining process / Figure 7(C)). Specifically, a male thread 42 is machined (formed) on one end of the second workpiece W2. Needless to say, either the formation of the female thread 41 or the formation of the male thread 42 may be performed first.

[0037] Next, the second spindle drive unit 122 moves the second headstock 16 in the Z direction, bringing the second workpiece spindle 22 closer to the first workpiece spindle 20, and aligning the first workpiece W1 and the second workpiece W2 (S16: First moving step / Figure 8(A)). Then, the second spindle drive unit 122 rotates the second workpiece spindle 22, screwing the male screw 42 into the female screw 41, and fastening the first workpiece W1 and the second workpiece W2 together (S18: Assembly step / Figure 8(B)). In this way, the first workpiece W1 and the second workpiece W2 are assembled via the threaded portion 40, and a workpiece assembly 44 is obtained (Figure 8(C)).

[0038] In this embodiment, the first work spindle 20 is stopped while the second work spindle 22 is rotated, thereby rotating both work spindles relative to each other. However, both work spindles may be rotated while simultaneously rotating relative to each other. Specifically, the rotation of both work spindles may be in opposite directions. Alternatively, the rotation direction of both work spindles may be the same, but the rotation speed of one may be lower than that of the other. The tightening torque of the screw portion 40 can be adjusted by controlling the rotation of the work spindles in this way.

[0039] Multiple torque limiting modes are provided for screw fastening control in this assembly process. In this embodiment, two stages are set in this torque limiting mode: a low torque mode (weak mode) and a high torque mode (strong mode). In the low torque mode, the tightening torque of the screw portion 40 is smaller than in the high torque mode. In the first stage, the second workpiece spindle 22 is rotated in the low torque mode to temporarily fasten the second workpiece W2 to the first workpiece W1. Then, in the second stage, the second workpiece spindle 22 is rotated in the high torque mode to fully fasten the second workpiece W2 to the first workpiece W1. As a modification, when both workpiece spindles are rotated in the assembly process, multiple torque limiting modes are set not only for the second workpiece spindle 22 but also for the first workpiece spindle 20. The tightening torque due to the relative rotation of both workpiece spindles is adjusted in stages to perform temporary and final fastening. As a further modification, three or more torque limiting modes may be set, and temporary fastening prior to final fastening may be performed in stages.

[0040] Next, the first spindle drive unit 120 drives the chuck 21 to release the grip on the first workpiece W1, and detaches the first workpiece W1 from the first workpiece spindle 20 (S20: first workpiece detachment step). The second spindle drive unit 122 moves the second workpiece spindle 22 in a direction away from the first workpiece spindle 20 (S22: second movement step / Figure 9(A)), and detaches the workpiece assembly 44 from the first workpiece spindle 20. At this time, the workpiece assembly 44 is supported in a cantilevered state by the second workpiece spindle 22.

[0041] The tool post drive unit 112 controls the movement of the tool T from this state to perform secondary processing on the first workpiece W1 (S24: Secondary processing step of the first workpiece / Figure 9 (B)). In the illustrated example, the outer circumferential surface and end face of the first workpiece W1 are finished (cutting and chamfering).

[0042] Next, the second spindle drive unit 122 moves the second headstock 16 in the Z direction, bringing the second work spindle 22 closer to the first work spindle 20 again (S26: Third movement step / Figure 10(A)). Then, the first spindle drive unit 120 drives the chuck 21 to grip the first workpiece W1 (S28), while the second spindle drive unit 122 drives the chuck 23 to release the grip of the second workpiece W2 (S30: Workpiece change step). At this time, the workpiece assembly 44 is supported in a cantilevered state by the first work spindle 20. Then, the second spindle drive unit 122 moves the second headstock 16 in the Z direction, moving the second work spindle 22 away from the first work spindle 20 (S32: Retraction step / Figure 10(B)).

[0043] The tool post drive unit 112 controls the movement of the tool T from this state to perform secondary processing on the second workpiece W2 (S34: Secondary processing step of the first workpiece / Figure 10(C)). In the illustrated example, the outer circumferential surface and end face of the second workpiece W2 are finished (cutting and chamfering). In this way, part 50 is obtained (see Figure 5).

[0044] As described above, the machine tool has been explained based on the embodiment. In this embodiment, after performing primary machining on each of the first workpiece W1 held by the first workpiece spindle 20 and the second workpiece W2 held by the second workpiece spindle 22, the two workpieces can be assembled by coordinating the control of the two workpiece spindles. As a result, the obtained workpiece assembly 44 can be transferred between the two workpiece spindles, and secondary machining of each workpiece can be performed. In particular, by transferring the workpiece assembly 44 between the two workpiece spindles, the holding portions of each workpiece that could not be machined in the primary machining can be machined, so that the entire workpiece can be machined. Since a component (product) composed of a plurality of workpieces can be automatically completed without the intervention of an operator or a robot, the machining efficiency can be effectively increased.

[0045] When the component to be machined is made of different materials, it cannot be obtained by machining a single material, and a process of assembling a plurality of components is essential. The machining method of this embodiment is particularly effective in such a case.

[0046] [Modification Example] FIG. 11 is a diagram showing the main part of the machining method according to Modification Example 1. In this modification example, instead of the process of FIG. 8, the process of FIG. 11 is executed, and the first workpiece W1 and the second workpiece W2 are assembled by press-fitting. That is, while an insertion hole 60 is machined in the first workpiece W1 in the first workpiece primary machining process, a convex portion 62 having a complementary shape to the insertion hole 60 is machined in the second workpiece W2 in the second workpiece primary machining process (FIG. 11(A)). In this modification example, the insertion hole 60 is a circular hole and the convex portion 62 is a circular boss shape (circular cross-section), but a polygonal cross-section or other shapes may be adopted.

[0047] Subsequently, the second workpiece spindle 22 is displaced in the axial direction with respect to the first workpiece spindle 20, so that the convex portion 62 is press-fitted into the insertion hole 60 (the first movement process, the assembly process / FIG. 11(B)). That is, the second workpiece spindle 22 functions as a center rest. In this way, the first workpiece W1 and the second workpiece W2 are assembled, and a workpiece assembly 64 is obtained (FIG. 11(C)).

[0048] FIG. 12 is a diagram showing the main part of the processing method according to Modification 2. In this modification, instead of the steps in FIG. 8, the steps in FIG. 12 are executed, and the first workpiece W1 and the second workpiece W2 are assembled by friction welding. That is, in the first workpiece primary processing step, the tip surface of the first workpiece W1 is processed flat, and in the second workpiece primary processing step, the tip surface of the second workpiece W2 is processed flat (FIG. 12(A)). In these steps, the flatness of each tip surface (the accuracy of the tip surface perpendicular to the axis) is improved.

[0049] Subsequently, by displacing the second workpiece spindle 22 in the axial direction with respect to the first workpiece spindle 20, both tip surfaces of the first workpiece W1 and the second workpiece W2 are brought into contact, and friction welding is performed on the contact surface (the first movement step, the assembly step / FIG. 12(B)). In this way, the first workpiece W1 and the second workpiece W2 are assembled via the pressure contact portion 70, and the workpiece assembly 74 is obtained (FIG. 12(C)).

[0050] FIG. 13 is a diagram schematically showing the main part of the machine tool according to Modification 3. The machine tool of this modification is a composite machining center, and a tool spindle 80 is provided instead of a turret (tool post). The tool spindle 80 functions as a "tool holding portion" and is driven in the X, Y, and Z directions by a movement mechanism. Further, the tool spindle 80 is provided so as to be rotatable about a rotation axis L3 extending in the Y direction. This composite machining center further includes a tool storage portion and a tool exchange portion. The tool storage portion includes a magazine for storing tools. The tool exchange portion includes an ATC (Automatic Tool Changer), takes out a tool from the tool storage portion according to an exchange instruction from the machining control device 102, and exchanges it with the tool on the tool spindle.

[0051] As an exchangeable tool, a processing head 82 for additional processing is included. The additional processing is a technique (additive manufacturing) of processing an object while melting a material powder with a laser. As the material powder, for example, metal powders such as stainless steel, nickel-based alloys, and titanium can be used. The processing head 82 discharges the material powder toward the processing site and irradiates it with laser light. Note that the additional processing is known as described in, for example, Japanese Patent No. 7527483, and thus a detailed description thereof is omitted.

[0052] Figure 14 is a diagram showing the main part of the processing method according to Modification 3. In this modification, the process in Figure 14 is performed instead of the process in Figure 8, and the first workpiece W1 and the second workpiece W2 are assembled by additional processing. Similar to Modification 2, the tip surface of the first workpiece W1 is processed to be flat in the first workpiece primary processing process, and the tip surface of the second workpiece W2 is processed to be flat in the second workpiece primary processing process (Figure 14(A)).

[0053] Next, the second workpiece spindle 22 is displaced axially relative to the first workpiece spindle 20, bringing the two end faces of the first workpiece W1 and the second workpiece W2 into contact (first moving step / Figure 14(B)). Additional processing is performed along the boundary of the contact surface. This joins the two workpieces by sintering the material powder along the boundary (assembly step / Figure 14(C)). In this way, the first workpiece W1 and the second workpiece W2 are assembled, and a workpiece assembly 84 is obtained.

[0054] Figures 15 and 16 are diagrams showing the main parts of the machining method according to Modification 4. In this modification, the process in Figure 15 is performed instead of the process in Figure 8, and the first workpiece W1 and the second workpiece W2 are assembled by screw joining. Figures 15(A) to (F) show the assembly process of the first workpiece W1 and the second workpiece W2, and Figure 16 shows a part of the assembly method.

[0055] As shown in Figure 15, in this modified example, when assembling the first workpiece W1 and the second workpiece W2 after thread forming, the second workpiece spindle 22 is moved in the Z direction (-Z direction) to bring the second workpiece W2 coaxially close to the first workpiece W1 (Figure 15(A)). When the second workpiece W2 comes into contact with the first workpiece W1, the second workpiece W2 is pressed against the first workpiece W1 with a constant load (first step of the threading process: Figure 15(B)), and the first workpiece spindle 20 is rotated at a low speed in the threading direction (fastening direction) of the screw (second step of the threading process: Figure 15(C)).

[0056] As a result, when the phases of the female thread 41 of the first workpiece W1 and the male thread 42 of the second workpiece W2 align, the pressing load (load) from the second workpiece spindle 22 temporarily decreases, and the second workpiece spindle 22 moves in the axial direction. Here, "phase alignment" means that the female thread 41 and the male thread 42 mesh properly (their phases coincide for screwing).

[0057] At this time, the male screw 42 is pressed against the female screw 41 with a constant load in the axial direction, meaning that unnecessary load is placed on each screw. Therefore, the second workpiece spindle 22 is moved back by a predetermined amount (smaller than the screw pitch) in the Z direction (+Z direction) to bring the first workpiece W1 and the second workpiece W2 into a normal (proper) screwed state (Figure 15(D)). From this state, the first workpiece W1 and the second workpiece W2 are stably screwed together.

[0058] Specifically, the first workpiece spindle 20 is rotated in the fastening direction, and the second workpiece spindle 22 is moved in the assembly direction (-Z direction) (third step of the screwing process: Figure 15(E)). The rotation of the first workpiece spindle 20 by one pitch corresponds to the movement of the second workpiece spindle 22 by one pitch. By linking (coordinating) the rotation of the first workpiece W1 and the movement of the second workpiece W2 in this way, stable screwing of both can be achieved. Then, screw fastening control using the torque limiting mode described above is executed (Figure 15(F)).

[0059] Furthermore, in order to adjust the phase of the threads as described above, as shown in Figure 16, a position A1 in the Z direction of the second workpiece spindle 22 is set in advance for the position A of the second workpiece spindle 22, which is the position where the phase matches in design (the appropriate position where no load is applied between the threads), and a position A2 in the phase-matched state where the male thread 42 of the second workpiece W2 is pressed axially against the female thread 41 of the first workpiece W1 (the pressing position where a load is applied between the threads). In this embodiment, since the workpieces were machined, the phase of the threads of the female thread 41 of the first workpiece W1 and the male thread 42 of the second workpiece W2 is known. That is, A1 and A2 are known values.

[0060] Furthermore, a predetermined distance R away from position A2 in the direction of A1 (+Z direction) is set as position Aset (Aset < A1). When position A of the second workpiece spindle 22 is within the range between A2 and Aset (A2 ≤ A ≤ Aset), it is determined that even if the second workpiece W2 is in phase alignment with the first workpiece W1, it is within the range where load due to pressing between screws should be avoided (the range where the second workpiece spindle 22 should be returned in the +Z direction: also called the "return range"). When the second workpiece W2 is located within the return range, the second workpiece spindle 22 is returned by a predetermined amount in the +Z direction as described above.

[0061] Figure 17 is a flowchart showing the procedure for screw joining the first workpiece W1 and the second workpiece W2. The following operations are performed under the control of the machining control device 102. First, the tailstock function is turned on and the second workpiece spindle 22 is moved in the -Z direction to bring the second workpiece W2 into coaxial contact with the first workpiece W1 (S110). The second workpiece spindle 22 performs a pressing operation to press the second workpiece W2 against the first workpiece W1 with a constant load (S112).

[0062] Once the pressing is complete (S114), the process based on the position A of the second workpiece spindle 22 described above is executed. When position A is greater than A2 + R (Y in S116), it can be determined that the phases of the female thread 41 and the male thread 42 may not be aligned. For this reason, while maintaining the load on the second workpiece spindle 22 (i.e., while allowing the second workpiece spindle 22 to move in the -Z direction), the first workpiece spindle 20 is rotated at a low speed in the threading direction (fastening direction) of the screw (S118).

[0063] At the moment the phases of the threads align, the load on the second workpiece spindle 22 temporarily decreases (S120). Subsequently, as the first workpiece spindle 20 rotates, the second workpiece spindle 22 moves in the -Z direction with a constant load (S122). As a result, with the phases of the threads aligned, the male thread 42 of the second workpiece W2 is pressed axially against the female thread 41 of the first workpiece W1 (S114).

[0064] At this time, if position A is within the return range (A2 ≤ A ≤ Aset) (N in S116, Y in S124), the tailstock function is turned off and the second workpiece spindle 22 is moved to position A1 in the +Z direction (S128). This ensures that the female thread 41 and the male thread 42 are properly engaged. From this state, interpolation feed is performed to coordinate the rotation of the first workpiece spindle 20 and the movement of the second workpiece spindle 22 in the Z direction (S130). That is, the assembly of the first workpiece W1 and the second workpiece W2 proceeds while properly screwing the female thread 41 and the male thread 42 together.

[0065] Then, when fastening the first workpiece W1 and the second workpiece W2 in the final stage of assembly, screw fastening control similar to that of the above embodiment is performed (S132). That is, preliminary tightening and final tightening are performed in torque limiting mode.

[0066] When position A becomes smaller than A2 (A < A2), or when an abnormal value is indicated (N in S124), an abnormality is detected (S134), and the operator is notified accordingly (S136). For example, notification information is displayed on the monitor of the control panel 6.

[0067] In this modified example, an example is shown in which a female thread 41 is formed on the first workpiece W1 held by the first workpiece spindle 20, and a male thread 42 is formed on the second workpiece W2 held by the second workpiece spindle 22. In other modified examples, a male thread may be formed on the first workpiece held by the first workpiece spindle, and a female thread may be formed on the second workpiece held by the second workpiece spindle.

[0068] Furthermore, in this modified configuration, the first workpiece spindle 20 is rotated around its axis, and the second workpiece spindle 22 is moved in the axial direction. In other modified configurations, the second workpiece spindle may be rotated around its axis, and the first workpiece spindle may be moved in the axial direction.

[0069] The above technical concepts can be expressed, for example, as in the following "Note." (Note 1) A machining method using a machine tool having a first work spindle, a second work spindle, and a tool holder for holding tools for machining workpieces held on each work spindle, comprising: a step of primary machining a first workpiece held on the first work spindle; a step of primary machining a second workpiece held on the second work spindle; a step of obtaining a workpiece assembly by bringing the first work spindle and the second work spindle closer together and joining the first workpiece and the second workpiece; and a step of secondary machining the workpiece assembly, wherein the step of primary machining the first workpiece involves machining an internal thread in the first workpiece; the step of primary machining the second workpiece involves machining an internal thread in the second workpiece that can be screwed into the internal thread; and the step of obtaining the workpiece assembly involves rotating the second work spindle relative to the first work spindle to screw the internal thread into the internal thread and fasten the first workpiece and the second workpiece together. The process for obtaining the workpiece assembly is a machining method using a machine tool, which has a plurality of torque limiting modes with different tightening torques as a screw fastening control for fastening the first workpiece and the second workpiece together.

[0070] (Note 2) The process of obtaining the workpiece assembly includes, as the torque limiting mode, a high torque mode and a low torque mode having a tightening torque smaller than that of the high torque mode, wherein the first workpiece and the second workpiece are temporarily tightened in the low torque mode, and then the first workpiece and the second workpiece are fully tightened in the high torque mode, the processing method using the machine tool described in Note 1.

[0071] (Note 3) The process of obtaining the workpiece assembly is a machining method using a machine tool as described in Note 2, wherein in the screw fastening control, both the first workpiece spindle and the second workpiece spindle are rotated, a plurality of torque limiting modes are set in stages for both the first workpiece spindle and the second workpiece spindle, and preliminary and final fastening of the first workpiece and the second workpiece are performed in stages.

[0072] (Note 4) A machining method using a machine tool having a first work spindle, a second work spindle, and a tool holder for holding tools for machining workpieces held on each work spindle, comprising: a step of primary machining a first workpiece held on the first work spindle; a step of primary machining a second workpiece held on the second work spindle; a step of joining the first workpiece and the second workpiece by bringing the first work spindle and the second work spindle close together to obtain a workpiece assembly; and a step of secondary machining the workpiece assembly, wherein the step of primary machining the first workpiece involves machining one of the male threads and the female threads on the first workpiece; the step of primary machining the second workpiece involves machining the other of the male threads and the female threads on the second workpiece; and the step of obtaining the workpiece assembly involves a screwing step of screwing the male threads into the female threads by rotating the second work spindle relative to the first work spindle. A machining method using a machine tool, comprising: a fastening step of performing screw fastening control for fastening a first workpiece and a second workpiece, wherein the screwing step includes: a first step of pressing the first workpiece and the second workpiece together in the axial direction by moving the first workpiece spindle and the second workpiece spindle relative to each other in the axial direction; a second step of matching the phases of the male screw and the female screw by rotating the second workpiece spindle relative to the first workpiece spindle while maintaining the load caused by pressing the first workpiece and the second workpiece together; and a third step of advancing screwing in the screw fastening direction by coordinating the relative rotation of the first workpiece spindle and the second workpiece spindle about the axis and the relative movement of the first workpiece spindle and the second workpiece spindle in the axial direction, wherein the fastening step has a plurality of torque limiting modes with different tightening torques as the screw fastening control.

[0073] (Note 5) The machining method using a machine tool as described in Note 4, wherein, in the second step, a pressing position is set in which the male screw and the female screw are pressed against each other in the axial direction in a phase-matched state, and a return range is set which is a predetermined distance from the pressing position, and the second step is to optimize the phase-matched state by moving the first work spindle and the second work spindle a predetermined distance in a direction that separates them when the positional relationship between the first work spindle and the second work spindle reaches the return range.

[0074] [Other Modifications] Although examples of machining methods have been shown in the above embodiments and modifications, other machining methods can also be realized by coordinating the control of the first workpiece spindle, the second workpiece spindle, and the tool holder. For example, a screw hole may be machined in the first workpiece while a screw insertion hole is machined in the second workpiece, and the two workpieces may be held together with the screw hole and screw insertion hole aligned by coordinating the control of the first workpiece spindle and the second workpiece spindle. In this state, the screw is held and moved by the tool holder and inserted into the screw insertion hole. By rotating the tool holder around its axis and screwing the screw into the screw hole, the first workpiece and the second workpiece can be fastened together.

[0075] Alternatively, the first and second workpieces may be assembled by using rivets instead of screws. Furthermore, instead of the additional processing described in Modification 3 above, an adhesive treatment may be performed. Specifically, a processing head that dispenses adhesive may be provided. The processing head is held by a tool holder. By controlling the movement of the processing head, adhesive can be applied to the contact surfaces of the first and second workpieces, thereby bonding the two workpieces together.

[0076] In the above embodiment, a first work spindle 20 and a second work spindle 22 are provided as work spindles, and the second work spindle 22 is configured to be movable in the Z direction. An example is shown in which both work spindles are arranged coaxially opposite each other in the Z direction. In a modified example, both the first work spindle 20 and the second work spindle 22 may be configured to be movable in the Z direction. Regardless of which work spindle is moved, both work spindles may be positioned closer together or further apart.

[0077] Furthermore, at least one of the first headstock 14 and the second headstock 16 can be moved in the Y direction, allowing both workpiece spindles to be positioned on the same axis, as well as being positioned with offset axes. This makes it possible to assemble the first workpiece W1 and the second workpiece W2 with offset axes.

[0078] In the above embodiment, an example is shown in which, after obtaining a workpiece assembly by joining a first workpiece and a second workpiece, the grip of the first workpiece spindle is released and the first workpiece spindle and the second workpiece spindle are separated to separate the workpiece assembly from the first workpiece spindle; secondary processing is performed on the first workpiece held on the second workpiece spindle; the first workpiece spindle and the second workpiece spindle are brought closer together again and the first workpiece is gripped by the first workpiece spindle; the grip of the second workpiece spindle is released and the first workpiece spindle and the second workpiece spindle are separated to separate the workpiece assembly from the second workpiece spindle; and secondary processing is performed on the second workpiece held on the first workpiece spindle.

[0079] In the modified example, after obtaining the workpiece assembly, the workpiece assembly may be gripped by both the first workpiece spindle and the second workpiece spindle. Then, the first workpiece or the second workpiece may be subjected to secondary processing. Alternatively, both the first workpiece and the second workpiece may be subjected to secondary processing.

[0080] Alternatively, after obtaining the workpiece assembly, the workpiece assembly may be gripped by the first workpiece spindle and the first or second workpiece may be subjected to secondary processing. Or, both the first and second workpieces may be subjected to secondary processing.

[0081] Alternatively, after obtaining the workpiece assembly, the workpiece assembly may be gripped by the second workpiece spindle and the first or second workpiece may be subjected to secondary processing. Or, both the first and second workpieces may be subjected to secondary processing.

[0082] Furthermore, after obtaining the workpiece assembly, the workpiece assembly may be gripped by the lower tool post (a gripping device mounted on the tool post) or the third workpiece spindle, and the first or second workpiece may be subjected to secondary processing. Alternatively, both the first and second workpieces may be subjected to secondary processing.

[0083] In the above embodiment, the machine tool 1 was described as a turning center, but it may also be a combined machining center that combines the functions of both a turning center and a machining center. It may also be a turning center-based combined machining center capable of milling and turning.

[0084] It should be noted that the present invention is not limited to the embodiments and modifications described above, and the components can be modified and implemented without departing from the spirit of the invention. Various inventions may be formed by appropriately combining the multiple components disclosed in the embodiments and modifications described above. In addition, some components may be deleted from all the components shown in the embodiments and modifications described above.

[0085] This patent application claims priority to Japanese Patent Application No. 2024-184079 (filed October 18, 2024), which is incorporated herein by reference in its entirety.

Claims

1. A machining method using a machine tool having a first work spindle, a second work spindle, and a tool holder for holding tools for machining workpieces held on each work spindle, comprising: a step of primary machining a first workpiece held on the first work spindle; a step of primary machining a second workpiece held on the second work spindle; a step of obtaining a workpiece assembly by bringing the first work spindle and the second work spindle close together and joining the first workpiece and the second workpiece; and a step of secondary machining the workpiece assembly, wherein the step of primary machining the first workpiece involves machining an internal thread in the first workpiece; the step of primary machining the second workpiece involves machining an internal thread in the second workpiece that can be screwed into the internal thread; and the step of obtaining the workpiece assembly involves rotating the second work spindle relative to the first work spindle to screw the internal thread into the internal thread and fasten the first workpiece and the second workpiece together. The process for obtaining the workpiece assembly is a machining method using a machine tool, which has a plurality of torque limiting modes with different tightening torques as a screw fastening control for fastening the first workpiece and the second workpiece together.

2. The machining method using a machine tool according to claim 1, wherein the step of obtaining the workpiece assembly includes, as the torque limiting mode, a high torque mode and a low torque mode having a tightening torque smaller than that of the high torque mode, and after pre-tightening the first workpiece and the second workpiece in the low torque mode, the first workpiece and the second workpiece are final-tightened in the high torque mode.

3. The machining method using a machine tool according to claim 2, wherein the step of obtaining the workpiece assembly is to rotate both the first workpiece spindle and the second workpiece spindle in the screw fastening control, set a plurality of torque limiting modes in stages for both the first workpiece spindle and the second workpiece spindle, and perform preliminary fastening and final fastening of the first workpiece and the second workpiece in stages.

4. A machining method using a machine tool having a first work spindle, a second work spindle, and a tool holder for holding tools for machining workpieces held on each work spindle, comprising: a step of primary machining a first workpiece held on the first work spindle; a step of primary machining a second workpiece held on the second work spindle; a step of joining the first workpiece and the second workpiece by bringing the first work spindle and the second work spindle close together to obtain a workpiece assembly; and a step of secondary machining the workpiece assembly, wherein the primary machining step of the first workpiece involves machining one of the male threads and the female threads on the first workpiece; the primary machining step of the second workpiece involves machining the other of the male threads and the female threads on the second workpiece; and the step of obtaining the workpiece assembly involves a screwing step of screwing the male threads into the female threads by rotating the second work spindle relative to the first work spindle; and a fastening step of executing screw fastening control to fasten the first workpiece and the second workpiece together. A machining method using a machine tool, wherein the screwing step includes: a first step of pressing the first workpiece and the second workpiece together in the axial direction by moving the first workpiece spindle and the second workpiece spindle relative to each other in the axial direction; a second step of aligning the phases of the male screw and the female screw by rotating the second workpiece spindle relative to the first workpiece spindle while maintaining the load caused by pressing the first workpiece and the second workpiece together; and a third step of advancing screwing in the screw fastening direction by coordinating the relative rotation of the first workpiece spindle and the second workpiece spindle about the axis and the relative movement of the first workpiece spindle and the second workpiece spindle in the axial direction, wherein the fastening step has a plurality of torque limiting modes with different tightening torques as the screw fastening control.

5. The machining method using a machine tool according to claim 4, wherein, in the second step, a pressing position is set in which the male screw and the female screw are pressed against each other in the axial direction in a phase-matched state, and a return range is set which is a predetermined distance from the pressing position, and in the second step, when the positional relationship between the first work spindle and the second work spindle reaches the return range, the first work spindle and the second work spindle are moved relative to each other by a predetermined distance in a direction that separates them, thereby optimizing the phase-matched state.

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