Turning tool for heavy cutting of workpiece in radial direction

Abstract

The turning tool is applied to workpiece machining and comprises a tool bar and a tool, the tool is arranged at the end of the extension direction of the tool bar and comprises a first tool grain and a second tool grain, and the first tool grain and the second tool grain are arranged in the extension direction perpendicular to the tool bar. The tool nose of the first tool grain and the tool nose of the second tool grain have a height difference in the vertical direction, the tool nose of the second tool grain is higher than the tool nose of the first tool grain, and in the cutting process, the first tool grain firstly conducts rough machining on the outer circle of a workpiece, most materials are removed, and the workpiece is preliminarily formed; and then the second cutter blade carries out finish machining on the workpiece, and the surface smoothness and the size precision of the workpiece are ensured. Thus, rough machining and finish machining are conducted at the same time, time consumption in the cutting process is reduced, the step that a single cutter needs to be machined twice is avoided, the cutter does not need to be replaced or cutting parameters do not need to be adjusted again, and therefore the machining efficiency is greatly improved.

Description

Technical Field

[0001] The present application relates to the technical field of turning tools, and in particular to a turning tool for radial heavy cutting of a workpiece. Background Art

[0002] A turning tool is a cutting tool used on a lathe, mainly used for machining metal workpieces. The turning tool cuts away metal material layer by layer through the high-speed rotating workpiece in contact with the cutting edge fixed on the tool holder, so that the workpiece reaches the required size and surface finish. The main function of the turning tool is to perform rough machining and fine machining, and to achieve efficient and high-precision machining by adjusting the cutting parameters.

[0003] The turning tool in the prior art usually has only one blade, which is fixed on the tool holder through a tool handle. During the turning process, the blade moves along the axial direction of the workpiece to remove the circumferential outer part of the workpiece. However, the turning tool with a single blade has certain limitations in terms of processing efficiency, especially the conversion between rough machining and fine machining requires extra time. In order to improve the processing efficiency, it is usually necessary to replace the tool or readjust the cutting parameters, which not only increases the complexity of the operation, but also prolongs the processing cycle.

[0004] Therefore, it is necessary to propose a turning tool for radial heavy cutting of workpieces to solve the problems of long processing time, complex operation and low processing efficiency of existing turning tools. Utility Model Content

[0005] The purpose of this application is to overcome the deficiencies in the prior art and to propose a turning tool for radial heavy cutting of workpieces, thereby solving the problems of long processing time, complex operation and low processing efficiency of the prior turning tools.

[0006] This application is implemented through the following technical solutions:

[0007] The present application proposes a turning tool for radial heavy cutting of a workpiece, which is applied to workpiece processing and includes a tool bar and a tool. The tool is arranged at the end of the tool bar in the extension direction. The tool includes a first tool particle and a second tool particle. The first tool particle and the second tool particle are arranged along the extension direction perpendicular to the tool bar. There is a height difference between the tip of the first tool particle and the tip of the second tool particle in the vertical direction, and the tip position of the second tool particle is higher than the tip position of the first tool particle, so that during the cutting process, the first tool particle first rough-processes the outer circle of the workpiece, and the second tool particle then fine-processes the workpiece.

[0008] In one embodiment of the present application, the first knife grain and the second knife grain are both triangular in shape, and a first fixing groove adapted to the first knife grain and a second fixing groove adapted to the second knife grain are provided at the end of the knife rod in the extension direction. The first fixing groove and the second fixing groove are arranged along a direction perpendicular to the extension direction of the knife rod, and the first knife grain is fixed in the first fixing groove, and the second knife grain is fixed in the second fixing groove.

[0009] In one embodiment of the present application, the knife bar has a first side wall and a first bottom wall at the first fixing groove, and the first knife particle is simultaneously attached to the first side wall and the first bottom wall;

[0010] The knife rod has a second side wall and a second bottom wall at the second fixing groove, and the second knife particle is simultaneously in contact with the second side wall and the second bottom wall.

[0011] In one embodiment of the present application, the first blade particle and the second blade particle are both provided with a first edge, a second edge and a third edge, one end of the first edge is connected to the second edge, the other end is connected to the third edge, and the end of the second edge away from the first edge is connected to the third edge, forming an equilateral triangle;

[0012] The first edges of the first blade particle and the second blade particle are flush with the end of the blade rod in the extending direction;

[0013] The first fixing groove is extended out of the connecting part of the third edge and the first edge of the first blade particle, and the second fixing groove is extended out of the connecting part of the third edge and the first edge of the second blade particle.

[0014] In one embodiment of the present application, the third edge of the first knife particle extends out of the first fixing groove, and the third edge of the second knife particle extends out of the second fixing groove.

[0015] In one embodiment of the present application, a connection between the second edge and the third edge of the second blade particle is disposed in the second fixing groove.

[0016] In one embodiment of the present application, a height difference between the tip of the first blade particle and the tip of the second blade particle in the vertical direction is h.

[0017] In one embodiment of the present application, the main rake angles of the tool tip of the first tool particle and the tool tip of the second tool particle are both 30°.

[0018] In one embodiment of the present application, the knife rod is provided with a first fixing hole connected to the first fixing groove, the first knife particle is provided with a first through hole, and the knife includes a first fixing column, which passes through the first through hole and is fixedly connected to the first fixing hole.

[0019] In one embodiment of the present application, the tool rod is provided with a first positioning groove and a first positioning hole connected to the first positioning groove, and the tool includes a first positioning member and a first fastener, the first positioning member is clamped in the first positioning groove and fits with the first tool particle, and the first fastener passes through the first positioning member and is threadedly connected to the first positioning hole.

[0020] Compared with the prior art, the beneficial effects of this application are:

[0021] The tool is arranged at the end of the extension direction of the tool bar, and the tool includes a first knife particle and a second knife particle, and the first knife particle and the second knife particle are arranged along the extension direction perpendicular to the tool bar, and the tip of the first knife particle and the tip of the second knife particle have a height difference in the vertical direction, and the tip position of the second knife particle is higher than the tip position of the first knife particle. During the cutting process, the first knife particle first performs rough machining on the outer circle of the workpiece to remove most of the material and make the workpiece initially formed; then, the second knife particle performs fine machining on the workpiece to ensure the surface finish and dimensional accuracy of the workpiece. In this way, rough machining and fine machining are carried out at the same time, which reduces the time consumption in the cutting process, avoids the step of two machining steps for a single knife particle, does not need to replace the tool or readjust the cutting parameters, reduces the complexity of the operation, and thus greatly improves the machining efficiency.

[0022] Other features and advantages of the present application will be described in the following description, and partly become apparent from the description, or be understood by practicing the present application. The purpose and other advantages of the present application can be realized and obtained by the structures indicated in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 A three-dimensional diagram of a turning tool for radial heavy cutting of a workpiece provided in one embodiment of the present application;

[0025] Figure 2 An exploded perspective view of a turning tool for radial heavy cutting of a workpiece provided in one embodiment of the present application;

[0026] Figure 3 A three-dimensional diagram of a first blade particle provided in an embodiment of the present application;

[0027] Figure 4 A top view of a turning tool for radial heavy cutting of a workpiece provided in one embodiment of the present application.

[0028] Description of reference numerals:

[0029] 10. A turning tool for heavy radial cutting of a workpiece; 100. A tool bar; 111. A first fixing groove; 1111. A first fixing hole; 112. A first side wall; 113. A first bottom wall; 114. A first positioning groove; 115. A first positioning hole; 121. A second fixing groove; 1211. A second fixing hole; 122. A second side wall; 123. A second bottom wall; 124. A second positioning groove; 125. A second positioning hole; 211. A first blade; 2111. A first through hole; a. A first edge; b. A second edge; c. A third edge; 212. A first fixing column; 213. A first positioning member; 214. A first fastener; 221. A second blade; 2211. A second through hole; 222. A second fixing column; 223. A second positioning member; 224. A second fastener. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of this application.

[0032] It should be noted that when an element is referred to as being "fixed on" or "set on" another component, it can be directly on the other component or indirectly set on the other component; when a component is referred to as being "connected to" another component, it can be directly connected to the other component or indirectly connected to the other component.

[0033] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "multiple" and "several" mean two or more, unless otherwise clearly and specifically defined.

[0035] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which this application can be implemented. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in this application without affecting the effects and purposes that can be achieved by this application.

[0036] Please refer to Figures 1 to 4 The present application proposes a turning tool 10 for radial heavy cutting of a workpiece, which is applied to workpiece processing, and includes a tool bar 100 and a tool (not marked in the figure). The tool is arranged at the end of the tool bar 100 in the extension direction, and the tool includes a first knife grain 211 and a second knife grain 221, and the first knife grain 211 and the second knife grain 221 are arranged along the extension direction perpendicular to the tool bar 100. The tip of the first knife grain 211 and the tip of the second knife grain 221 have a height difference in the vertical direction, and the tip position of the second knife grain 221 is higher than the tip position of the first knife grain 211, so that during the cutting process, the first knife grain 211 first rough-processes the outer circle of the workpiece, and the second knife grain 221 then fine-processes the workpiece.

[0037] Specifically, the tool includes a first blade particle 211 and a second blade particle 221 arranged in parallel, and the tip of the first blade particle 211 and the tip of the second blade particle 221 have a height difference in the vertical direction, and the tip position of the second blade particle 221 is higher than the tip position of the first blade particle 211. During the cutting process, the first blade particle 211 first performs rough machining on the outer circle of the workpiece to remove most of the material and make the workpiece initially formed; then, the second blade particle 221 performs fine machining on the workpiece to ensure the surface finish and dimensional accuracy of the workpiece. In this way, rough machining and fine machining are carried out at the same time, which reduces the time consumption in the cutting process, avoids the step of requiring two machining steps for a single blade particle, does not require changing the tool or re-adjusting the cutting parameters, reduces the complexity of the operation, and thus greatly improves the machining efficiency.

[0038] It should be understood that the turning tool in the prior art usually has only one blade, which is fixed to the tool holder through a tool handle. During the turning process, the blade moves along the axial direction of the workpiece to remove the circumferential outer portion of the workpiece. However, the turning tool with a single blade has certain limitations in terms of processing efficiency, especially the conversion between roughing and finishing requires additional time. In order to improve the processing efficiency, it is usually necessary to replace the tool or readjust the cutting parameters, which not only increases the complexity of the operation, but also prolongs the processing cycle. In the present application, the first blade 211 first rough-processes the outer circle of the workpiece, and the second blade 221 then finishes the workpiece, so that the roughing and finishing are combined into one cutting process, reducing the conversion time of the workpiece between different processing steps. In addition, the tip of the first blade 211 and the tip of the second blade 221 have a height difference in the vertical direction, and the tip of the second blade 221 is higher than the tip of the first blade 211, which ensures the continuity and stability of the cutting process and improves the final quality of the workpiece.

[0039] In one embodiment, the first blade grain 211 and the second blade grain 221 are both triangular in shape, and a first fixing groove 111 adapted to the first blade grain 211 and a second fixing groove 121 adapted to the second blade grain 221 are provided at the end of the blade rod 100 in the extension direction. The first fixing groove 111 and the second fixing groove 121 are arranged along a direction perpendicular to the extension direction of the blade rod 100, the first blade grain 211 is fixed in the first fixing groove 111, and the second blade grain 221 is fixed in the second fixing groove 121.

[0040] Specifically, the first blade particle 211 is fixed in the first fixing groove 111, and the second blade particle 221 is fixed in the second fixing groove 121. This ensures that the first blade particle 211 and the second blade particle 221 remain stable during the cutting process, avoids machining errors caused by loosening or displacement of the first blade particle 211 and the second blade particle 221, and improves machining accuracy.

[0041] Please refer to Figure 1 and Figure 2In one embodiment, the knife rod 100 has a first side wall 112 and a first bottom wall 113 at the first fixing groove 111, and the first knife grain 211 is simultaneously attached to the first side wall 112 and the first bottom wall 113; the knife rod 100 has a second side wall 122 and a second bottom wall 123 at the second fixing groove 121, and the second knife grain 221 is simultaneously attached to the second side wall 122 and the second bottom wall 123.

[0042] Specifically, the first blade grain 211 is simultaneously attached to the first side wall 112 and the first bottom wall 113, and the second blade grain 221 is simultaneously attached to the second side wall 122 and the second bottom wall 123. In this way, multi-directional support can be provided for the first blade grain 211 and the second blade grain 221, thereby enhancing the stability of the first blade grain 211 and the second blade grain 221 during the cutting process.

[0043] In one embodiment, the first blade particle 211 and the second blade particle 221 are both provided with a first edge a, a second edge b and a third edge c, one end of the first edge a is connected to the second edge b, and the other end is connected to the third edge c, and the end of the second edge b away from the first edge a is connected to the third edge c, forming an equilateral triangle; the first edge a of the first blade particle 211 and the second blade particle 221 is flush with the end of the blade rod 100 in the extension direction; the first fixed groove 111 extends out from the place where the third edge c of the first blade particle 211 is connected to the first edge a, and the second fixed groove 121 extends out from the place where the third edge c of the second blade particle 221 is connected to the first edge a; the second edge b of the first blade particle 211 is in contact with the first side wall 112, and the second edge b of the second blade particle 221 is in contact with the second side wall 122.

[0044] Specifically, the first edge a of the first blade particle 211 and the second blade particle 221 is flush with the end of the blade rod 100 in the extending direction, the third edge c of the first blade particle 211 and the first edge a are connected to extend out of the first fixing groove 111, and the third edge c of the second blade particle 221 and the first edge a are connected to extend out of the second fixing groove 121. It is ensured that the first blade particle 211 and the second blade particle 221 contact the workpiece at the best angle during the cutting process, thereby optimizing the cutting effect and improving the surface finish and dimensional accuracy of the workpiece.

[0045] The second edge b of the first blade particle 211 is in contact with the first side wall 112, and the second edge b of the second blade particle 221 is in contact with the second side wall 122. The position of the blade particles in the fixing groove can be ensured to be accurate, thereby improving the processing accuracy. This design reduces the processing error caused by the position error of the blade particles and improves the dimensional accuracy and surface quality of the workpiece.

[0046] It is worth noting that there is a knife tip at the connection between the first edge a and the second edge b, or at the connection between the first edge a and the third edge c, or at the connection between the third edge c and the second edge b.

[0047] In one embodiment, the third edge c of the first blade particle 211 extends out of the first fixing groove 111 , and the third edge c of the second blade particle 221 extends out of the second fixing groove 121 .

[0048] Specifically, the third edge c of the first blade particle 211 extends out of the first fixing groove 111, and the third edge c of the second blade particle 221 extends out of the second fixing groove 121. In this way, it is ensured that the cutting edges of the first blade particle 211 and the second blade particle 221 are completely exposed to the outside and can fully contact the workpiece during the cutting process, thereby improving the cutting effect.

[0049] In one embodiment, the connection between the second edge b and the third edge c of the second blade particle 221 is disposed in the second fixing groove 121 .

[0050] Specifically, the connection between the second edge b and the third edge c of the second blade particle 221 is arranged in the second fixing groove 121, so that the second blade particle 221 is more stable during the cutting process, and the second blade particle 221 is prevented from loosening or shifting during the cutting process.

[0051] Please refer to Figure 4 In one embodiment, the height difference between the tip of the first blade particle 211 and the tip of the second blade particle 221 in the vertical direction is h.

[0052] Specifically, h=0.1-1 mm, the tip of the first blade 211 is lower than the tip of the second blade 221, so that during the cutting process, the first blade 211 first contacts and cuts the outer surface of the workpiece for rough machining; then the second blade 221 contacts and cuts the outer surface of the workpiece for fine machining. This ensures that rough machining and fine machining can be performed continuously without changing the tool or adjusting the cutting parameters.

[0053] Please refer to Figure 4 In one embodiment, the main rake angles of the tool tips of the first tool grain 211 and the second tool grain 221 are both 30°.

[0054] Specifically, the main deflection angle refers to the angle between the main cutting edge at the front end of the blade tip and the cutting direction of the workpiece surface. The blade tips of the first blade grain 211 and the second blade grain 221 are both processed with a main deflection angle of 30°, which can provide better cutting effect and surface finish. In addition, a smaller main deflection angle helps reduce cutting resistance, making the cutting process smoother and more efficient.

[0055] It should be noted that the turning tool 10 used for radial heavy cutting of a workpiece of the present application, since the tool has a first blade grain 211 and a second blade grain 221, and the first blade grain 211 and the second blade grain 221 are arranged side by side, can only perform double cutting on the outer circle of the workpiece, that is, radial cutting of the workpiece, and cannot perform double cutting on the end face of the workpiece.

[0056] Please refer to Figure 1 and Figure 2 In one embodiment, the knife rod 100 is provided with a first fixing hole 1111 connected to the first fixing groove 111, the first knife grain 211 is provided with a first through hole 2111, and the knife includes a first fixing column 212, and the first fixing column 212 passes through the first through hole 2111 and is fixedly connected to the first fixing hole 1111; the knife rod 100 is provided with a second fixing hole 1211 connected to the second fixing groove 121, the second knife grain 221 is provided with a second through hole 2211, and the knife includes a second fixing column 222, and the second fixing column 222 passes through the second through hole 2211 and is fixedly connected to the second fixing hole 1211.

[0057] Specifically, the first fixing column 212 passes through the first through hole 2111 and is fixedly connected to the first fixing hole 1111, and the second fixing column 222 passes through the second through hole 2211 and is fixedly connected to the second fixing hole 1211, which is used to prevent the first knife particle 211 and the second knife particle 221 from loosening or shifting during the cutting process, thereby improving the stability and safety of the processing.

[0058] Please refer to Figure 1 and Figure 2 In one embodiment, the tool rod 100 is provided with a first positioning groove 114 and a first positioning hole 115 connected to the first positioning groove 114, and the tool includes a first positioning member 213 and a first fastener 214. The first positioning member 213 is clamped in the first positioning groove 114 and fits with the first knife grain 211, and the first fastener 214 passes through the first positioning member 213 and is threadedly connected to the first positioning hole 115; the tool rod 100 is provided with a second positioning groove 124 and a second positioning hole 125 connected to the second positioning groove 124, and the tool includes a second positioning member 223 and a second fastener 224. The second positioning member 223 is clamped in the second positioning groove 124 and fits with the second knife grain 221, and the second fastener 224 passes through the second positioning member 223 and is threadedly connected to the second positioning hole 125.

[0059] Specifically, the first fastener 214 and the second fastener 224 are both bolts, the first positioning member 213 is clamped in the first positioning groove 114 and fits with the first blade 211, the first fastener 214 passes through the first positioning member 213 and is threadedly connected to the first positioning hole 115, ensuring the stability of the first blade 211 during the cutting process and preventing the first blade 211 from shifting or loosening. Similarly, the second positioning member 223 is clamped in the second positioning groove 124 and fits with the second blade 221, the second fastener 224 passes through the second positioning member 223 and is threadedly connected to the second positioning hole 125, ensuring the stability of the second blade 221 during the cutting process and preventing the second blade 221 from shifting or loosening.

[0060] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A turning tool for heavy radial cutting of a workpiece, applied to workpiece processing, comprising a tool bar and a tool, wherein the tool is arranged at the end of the tool bar in the extending direction, characterized in that: The tool includes a first blade particle and a second blade particle, and the first blade particle and the second blade particle are arranged along an extension direction perpendicular to the tool rod. There is a height difference between the tip of the first blade particle and the tip of the second blade particle in the vertical direction, and the tip position of the second blade particle is higher than the tip position of the first blade particle, so that during the cutting process, the first blade particle first rough-processes the outer circle of the workpiece, and the second blade particle then fine-processes the workpiece.

2. The turning tool for radial heavy cutting of a workpiece according to claim 1, characterized in that: The first blade particle and the second blade particle are both triangular in shape, and a first fixing groove adapted to the first blade particle and a second fixing groove adapted to the second blade particle are provided at the end of the blade rod in the extension direction, and the first fixing groove and the second fixing groove are arranged along a direction perpendicular to the extension direction of the blade rod, the first blade particle is fixed in the first fixing groove, and the second blade particle is fixed in the second fixing groove.

3. The turning tool for radial heavy cutting of a workpiece according to claim 1, characterized in that: The knife bar has a first side wall and a first bottom wall at the first fixing groove, and the first knife particle is simultaneously attached to the first side wall and the first bottom wall; The knife rod has a second side wall and a second bottom wall at the second fixing groove, and the second knife particle is simultaneously in contact with the second side wall and the second bottom wall.

4. The turning tool for radial heavy cutting of a workpiece according to claim 3, characterized in that: The first blade particle and the second blade particle are both provided with a first edge, a second edge and a third edge, one end of the first edge is connected to the second edge, the other end is connected to the third edge, and the end of the second edge away from the first edge is connected to the third edge to form an equilateral triangle; The first edges of the first blade particle and the second blade particle are flush with the end of the blade rod in the extending direction; The first fixing groove is extended out of the connecting part of the third edge and the first edge of the first blade particle, and the second fixing groove is extended out of the connecting part of the third edge and the first edge of the second blade particle.

5. The turning tool for radial heavy cutting of a workpiece according to claim 4, characterized in that: The third edge of the first knife particle extends out of the first fixing groove, and the third edge of the second knife particle extends out of the second fixing groove.

6. The turning tool for heavy radial cutting of a workpiece according to claim 4, characterized in that: The connection between the second edge and the third edge of the second blade particle is arranged in the second fixing groove.

7. The turning tool for radial heavy cutting of a workpiece according to claim 1, characterized in that: The height difference between the tip of the first blade particle and the tip of the second blade particle in the vertical direction is h.

8. The turning tool for radial heavy cutting of a workpiece according to claim 1, characterized in that: The main deflection angles of the tool tips of the first tool grain and the second tool grain are both 30°.

9. The turning tool for radial heavy cutting of a workpiece according to claim 2, characterized in that: The knife rod is provided with a first fixing hole connected with the first fixing groove, the first knife particle is provided with a first through hole, and the knife comprises a first fixing column, which passes through the first through hole and is fixedly connected with the first fixing hole.

10. The turning tool for radial heavy cutting of a workpiece according to claim 1, characterized in that: The tool rod is provided with a first positioning groove and a first positioning hole connected with the first positioning groove. The tool includes a first positioning piece and a first fastener. The first positioning piece is clamped in the first positioning groove and fits with the first tool particle. The first fastener passes through the first positioning piece and is threadedly connected with the first positioning hole.

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