Equilateral triangular indexable micro-allowance oil pipe threading tool and machining method therefor

Abstract

The present invention relates to the technical field of tool machining. Disclosed are an equilateral triangular indexable micro-allowance oil pipe threading tool and a machining method therefor. The machining method comprises: performing blank design, using a high-precision die to press and form blanks in batches and directly forming three positioning surfaces, and the formed blanks being subjected to one tooth profile finishing process and one rake face finishing process to remove all allowances, so as to obtain an equilateral triangular indexable micro-allowance oil pipe threading tool. The step of blank design comprises: designing three positioning surfaces of an equilateral triangle, wherein the diameter accuracy of an inscribed circle is ±0.015-0.025 mm, the concentricity deviation between the center of the inscribed circle and the center of a blank hole is less than or equal to 0.1 mm, the absolute value of the difference between any two of the perpendicular distances from the center of the blank hole to the three positioning surfaces is less than or equal to 0.1 mm, and the tolerance of the included angle between any two positioning surfaces is ±7'; designing a thickness and a rake face, wherein the unilateral allowance of the thickness and the allowance of the rake face are both 0.1-0.15 mm; and designing a tooth profile, wherein the allowances in all directions of the tooth profile are 0.08-0.15 mm. The present solution integrates tool design, die technology, pressing technology and grinding technology, thereby significantly reducing batch production costs and greatly improving production efficiency.

Description

Equilateral triangular indexable micro-threading tool for oil pipes and its machining method Technical Field This invention relates to the field of cutting tool technology, specifically to an equilateral triangular indexable micro-threading tool for oil pipes and its machining method. Background Technology The equilateral triangle structure is a common cutting tool structure (as shown in the forming tool 1 in Figure 1, with forming tooth profile 11 and forming positioning surface 12). It is characterized by reliable positioning, high cost performance and convenient use, and has a high application rate in the field of thread cutting tools. Because oil pipe threading tools have complex tooth profiles and require high precision, such as a linear accuracy of ±0.01mm and an angular accuracy of ±10′ (as shown in Figure 2), and are required to maintain consistent accuracy after indexing, this places high demands on the three positioning edges of the tool. The machining of the (surface) requires high precision (as shown in Figure 3), such as the tolerance of the included angle (60°) of the positioning edges (surface) being within ±7′, the tolerance of the diameter of the inscribed circle of the three positioning edges (surfaces) being ±0.015mm, and the concentricity deviation with the center of the blank hole being ≤0.1mm. The microscopic linearity of a surface can only be concave; a convex surface is unacceptable. In actual production, the aforementioned precision is mainly achieved using CNC peripheral grinding machines, with machine tool prices ranging from 1 million to 7 million yuan. Adding labor costs, the total cost remains high. If processing is done using ordinary equipment, neither the efficiency nor the precision required can be met. On the other hand, tool manufacturing is a process of blank—finished blank—finished product. Due to limitations in mold and pressing technologies, the blanks in the original technology had two defects: first, the allowance was large, usually exceeding 0.3mm in peripheral grinding, which was time-consuming and labor-intensive; second, they lacked morphological features (as shown in Figure 4, the existing blank 2 without morphological features). One blank could be adapted to multiple tools, resulting in a large amount of tooth grinding, usually requiring two rough grinding processes and one fine grinding process to complete the tooth machining. With the advancement of mold and pressing technologies, although blanks began to have morphological features (toothed blanks) to reduce grinding, there were still difficulties in precision control. To compensate for the uncertainty of interference factors in precision control, the tooth allowance was still set relatively large, exceeding 0.3mm. Summary of the Invention This invention aims to provide an indexable triangular micro-threading tool for oil pipes and its processing method. It deeply integrates tool design, mold technology, forming technology and grinding technology, and solves the problems of tooth profile and rake face grinding caused by mold and forming technology. More creatively, it directly presses the three positioning sides (faces) of the equilateral triangle into shape, saving peripheral processes, which greatly reduces the cost of the end product and greatly improves production efficiency, thus gaining a certain advantage in market competition, especially in overseas markets. The basic solution provided by this invention is: a method for machining micro-threading tools for equilateral triangular indexable oil pipes, the method comprising: S100, bare-bones design, including: S101, equilateral triangle three-positioning surface design, including an inscribed circle diameter accuracy of ±(0.015~0.025)mm, a concentricity deviation between the center of the inscribed circle and the center of the blank hole ≤0.1mm, an absolute value of the difference between any two perpendicular distances from the center of the blank hole to the three positioning surfaces ≤0.15mm, and an included angle tolerance of ±7′ between any two positioning surfaces; S102, thickness and rake face design, including thickness allowance on one side and rake face allowance of 0.1~0.15mm; S103, tooth profile design, including allowances of 0.08 to 0.15 mm in all directions of the tooth profile; S200 uses high-precision molds to batch press and form blanks. Each blank meets the blank design requirements of S100, and the three circumferential surfaces of the blank can be directly used as three positioning surfaces without grinding. S300, based on the allowance design in S100, the blank is subjected to one tooth profile finishing and one rake face finishing to remove all the allowance, thus obtaining the equilateral triangular indexable micro-oil pipe threading tool. The present invention also provides an equilateral triangular indexable micro-oil pipe threading tool, which is formed by the above-described equilateral triangular indexable micro-oil pipe threading tool processing method. The working principle and advantages of this invention are as follows: The key technical challenge in overcoming the aforementioned shortcomings lies in achieving high precision in the blank to reduce or completely eliminate excess material. Essentially, this involves using mold design and pressing processes to achieve finer blank forming, ultimately leading to efficient and low-cost manufacturing of the final product. By deeply integrating tool design, mold technology, pressing technology, and grinding technology, a new solution is provided for improving the production efficiency and product quality of indexable triangular micro-volume oil pipe threading tools, while reducing production costs. Analysis revealed that while equilateral triangular structures are common in oil pipe threading tools, micro-grinding technology has not yet been applied, and there is a lack of experience in mass production. In particular, there are no cases of direct pressing forming of three-position peripheral (surface) shapes. This presents multiple technical difficulties and practical challenges. Because oil pipe threading tools operate in extremely harsh environments, requiring high strength and wear resistance, higher demands are placed on material selection and processing. These specialized materials are often difficult to process efficiently with large allowances using traditional grinding processes, necessitating multiple grinding operations, which are time-consuming and labor-intensive. Furthermore, the technical difficulty of three-position peripheral direct pressing is immense. It requires not only complex mold design but also ensuring uniform and defect-free material distribution during pressing, posing significant challenges to mold manufacturing and forming processes. Under current technology, precisely controlling pressure, temperature, and material flow direction during pressing remains challenging, easily leading to low yield and unstable quality. Moreover, the lack of experience in mass production means that related process parameter optimization and quality control systems are not yet mature, further limiting its large-scale application. In summary, these factors collectively constrain the application and development of micro-grinding and direct pressing technologies in oil pipe threading tools. This innovative solution addresses the micro-grinding of oil pipe threading tools. The challenge lies in three "micro" aspects: 1) no allowance around the perimeter, resulting in direct forming; 2) very small allowance on the tooth profile; and 3) very small allowance on the rake face (normal grinding allowance in the thickness direction). While micro-grinding with minimal allowance is achievable with existing mature technologies, the challenge of this solution lies in achieving these three micro-scales on the blank without affecting the tool's normal performance. This breakthrough was achieved through long-term exploration and analysis of actual production conditions, and through collaborative innovation and breakthroughs considering materials, molds, pressing processes, and control technologies. Compared to traditional machining, this innovative "micro" design for oil pipe threading tools offers significant advantages. Furthermore, this solution precisely controls key dimensions such as blank accuracy and allowance during the blank design stage, achieving the goal of high precision and low allowance. In particular, the design of the triangular three-positioning surface directly meets the forming requirements, and the tooth profile and rake face design adopt a minimal allowance approach, ensuring the blank achieves high precision and guaranteeing stability and reliability in subsequent processing. It is particularly noteworthy that, utilizing existing high-precision molds and pressing technology, the triangular three-positioning sides (faces) can be directly formed during blank forming, serving as the positioning reference for subsequent processing and application without additional grinding steps. The indexing accuracy is comparable to traditional grinding. After blank forming, only a minimal allowance fine grinding process is required on the tooth profile, rake face, and thickness to complete the entire manufacturing process, simplifying the production process, significantly improving production efficiency, and reducing costs. It also ensures the high quality and consistency of the final product without negatively impacting its lifespan. In addition, this solution can simultaneously cover both round threads and trapezoidal threads, meeting the needs of different application scenarios. Compared to existing technologies, this solution, through the deep integration of tool design, mold technology, forming technology, and grinding technology, not only solves many problems existing in traditional processes, such as complex grinding procedures, difficult-to-control precision, and high manufacturing costs, but also demonstrates superior performance in practical applications. This integrated solution makes the entire production process more efficient and precise, greatly improving yield and product quality. Furthermore, its low cost and high efficiency lay a solid foundation for subsequent market promotion. Overall, this solution not only breaks through the limitations of existing technologies, but its detailed key dimension design also demonstrates the rationality and feasibility of this innovative method. It also has significant implications for improving the overall technical level of the tool manufacturing industry, providing new ideas and directions. Attached Figure Description Figure 1 is a schematic diagram of the equilateral triangle structure of an existing oil pipe threading tool; Figure 2 is a schematic diagram of the tooth profile dimensions of existing oil pipe threading tools; Figure 3 is a schematic diagram of the positioning accuracy of an existing equilateral triangular indexable cutting tool. Figure 4 is a schematic diagram of the blank allowance without topographic features of an existing equilateral triangular indexable tool. Figure 5 is a partial accuracy diagram of the tooth profile of the equilateral triangular indexable micro-oil pipe threading tool blank provided in the embodiment of the present invention. Figure 6 is a schematic diagram of the toothed and rake-faced blank of the equilateral triangular indexable micro-oil pipe threading tool provided in the embodiment of the present invention. Figure 7 is a schematic diagram of the peripheral accuracy of the equilateral triangular indexable micro-oil pipe threading tool provided in the embodiment of the present invention; Figure 8 is a schematic diagram of the blank thickness and rake face allowance of the equilateral triangular indexable micro-oil pipe threading tool provided in the embodiment of the present invention. Figure 9 is a schematic diagram of the blank allowance distribution of the equilateral triangular indexable micro-oil pipe deflector trapezoidal thread cutting tool provided in the embodiment of the present invention. Figure 10 is a schematic diagram of the blank allowance distribution of the equilateral triangular indexable micro-oil pipe round thread cutting tool provided in the embodiment of the present invention. Figure 11 is a schematic diagram of the accuracy requirements for removing end face allowance from the blank of the equilateral triangular indexable micro-oil pipe threading tool provided in the embodiment of the present invention. Figure 12 is a schematic diagram of the removal of tooth profile allowance from the blank of the equilateral triangular indexable micro-oil pipe threading tool provided in the embodiment of the present invention. Figure 13 is a schematic diagram of the removal of the rake face allowance from the blank of the equilateral triangular indexable micro-oil pipe threading tool provided in the embodiment of the present invention. The markings in the accompanying drawings include: forming tool 1, forming tooth 11, forming positioning surface 12, existing blank without topographic features 2, blank 3, tooth 31, rake face 32, second fixture 4, forming grinding wheel one 41, third fixture 5, forming grinding wheel two 51. Detailed Implementation The following detailed explanation illustrates the specific implementation methods: The embodiment is basically shown in Figures 5, 6, 7 and 8: a method for machining an indexable micro-oil pipe threading tool with an equilateral triangle shape. The method includes the following steps, wherein the blank 3, the blank tooth profile 31 and the blank rake face 32 represent the blank of the indexable micro-oil pipe threading tool in this scheme. Figure 6(a) is a schematic diagram of the blank tooth profile and Figure 6(b) is a schematic diagram of the rake face.

[0038] S100, blank 3 design, determines the precision of the equilateral triangular blank 3 to ensure it can reach the level of CNC peripheral grinding, including: S101, as shown in Figure 7, features a three-positioning-surface design with an equilateral triangle. The accuracy requirement for the inscribed circle diameter is ± (0.015~0.025) mm. The deviation between the center of the inscribed circle and the center of the blank hole is ≤0.1 mm. In other words, the positional error of the inscribed circle's center must be controlled within a 0.1 mm diameter circle centered on the blank hole's center. The absolute value of the difference between any two perpendicular distances (e.g., K1, K2, K3) from the blank hole's center to the three positioning surfaces is ≤0.15 mm. In this embodiment, to further ensure accuracy, the absolute value of the difference between any two K values ​​is ≤0.1 mm. The tolerance for the included angle (60°) between any two positioning surfaces is ±... 7′, as shown in Figure 7. Equilateral triangular indexable thread cutters are generally available in three specifications with side lengths of 16mm, 22mm, and 27mm, corresponding to inscribed circle diameters of Φ 9.525mm, Φ 12.7mm, and Φ 15.875mm, respectively, all of which can be designed according to the above requirements. This solution comprehensively considers existing mold technology, pressing technology, and grinding technology, and directly presses and forms the three positioning sides (faces) of an equilateral triangle according to the actual positioning requirements of the tool. The indexing accuracy reaches the level of grinding, which also lays the foundation for the large-scale application of micro-grinding in equilateral triangle indexable oil pipe threading tools. S102, with a thickness and a 3+2 design for the rake face, including a thickness allowance of 0.1 to 0.15 mm on one side and a 3+2 allowance for the rake face. Similarly, taking three specifications with inscribed circle diameters of Φ 9.525mm, Φ 12.7mm, and Φ 15.875mm as examples, their finished product thicknesses are 3.18mm, 4.76mm, and 6.35mm, respectively. The remaining quantities in this embodiment are set as shown in Figure 8, and the corresponding values ​​are shown in Tables 1, 2, and 3. 3. The thickness allowance on one side is set to 0.1~0.15mm; the allowance on the front face is set to 0.1~0.15mm. The internal thread can be understood as the internal thread, and the external thread can be understood as the external thread. Table 1. Example of allowance design for tool blanks and finished products with an inscribed circle diameter of Φ 9.525mm. Table 2. Example of allowance design for tool blanks and finished products with an inscribed circle diameter of Φ12.7mm. Table 3. Example of allowance design for blank and finished tool with inscribed circle diameter Φ 15.875mm. S103, tooth profile 31 design, including a allowance of 0.08~0.15mm in each direction of tooth profile 31; This design primarily targets oil pipe thread cutting tools, covering both round and trapezoidal threads. Each angle of the triangle forms a cutting edge, and each cutting edge has one cutting tooth. Allowances are divided into tooth tip allowance, tooth root allowance, and tooth flank allowance, as shown in Figures 9 and 10. For tooth profile 31, allowances are added to the tooth tip, tooth root, and tooth flank according to their respective characteristics. The allowances in each direction are designed to be 0.08–0.15 mm, with a maximum not exceeding 0.15 mm. Allowance settings are shown in Table 4. Table 4 Examples of Allowance Design for Circular Threads and Offset Trapezoidal Cutting Tools

[0053] Based on the existing high-precision molds and pressing technology that can directly press and form equilateral triangles with three positioning surfaces, the above-mentioned allowance design can be obtained simultaneously in the aforementioned technologies, greatly reducing the blank allowance. S200, using high-precision molds to batch press and form blanks 3, each blank 3 meets the blank design requirements in S100, and the three circumferential surfaces of the blank can be directly used as three positioning surfaces without grinding, that is, the equilateral triangular three positioning surfaces of the blank 3 meet the forming requirements of the equilateral triangular indexable micro-oil pipe threading tool when forming the equilateral triangular three positioning surfaces. Using 3R mold technology, high-precision molds are manufactured, with linear dimensional accuracy reaching ±0.03mm, angular accuracy reaching ±20′, and tooth profile linear accuracy reaching ±0.03mm when complex tooth profiles are added. The steps of batch pressing and forming blanks 3 include the preparation of cemented carbide mixture, blank pressing and blank sintering. In the preparation process of cemented carbide mixture, cemented carbide is mixed according to the formula and uniformly stirred by ball milling for 70 to 100 hours; spray granulation is carried out using a spray tower, with a batch of about 1 ton of material sprayed for 24 hours. In the blank forming process, an electric press is used with a pressure range of 4 to 4.5 t. With 10,000 pieces as the single furnace loading quantity, the pressing time is 70 to 100 hours. In the sintering process of the blank, a low-pressure sintering furnace is used for sintering at a temperature of 1400–1500 °C for a sintering time of 20 minutes. ~50 hours. Under the comprehensive application of this scheme in blank design, high-precision mold, and optimized pressing process, the accuracy of the batch-pressed blanks is no less than that of the peripheral grinding accuracy. This is mainly reflected in the accuracy of the inscribed circle diameter reaching ±(0.015—0.025) mm, and the concentricity deviation between the center of the inscribed circle and the center of the blank hole ≤0.1 mm. That is, the positional error of the inscribed circle center is controlled within a circumference of 0.1 mm in diameter centered on the blank hole center. The perpendicular distances from the blank hole center to the three positioning edges (surfaces) are K1, K2, and K3, and the absolute value of the difference between any two of these distances is ≤0.1 mm. The tolerance of the included angle (60°) between any two positioning edges is ±7′. As shown in Figure 5, the linear accuracy of the blank tooth profile obtained by this scheme can reach ±0.05 mm, and the angular accuracy can reach ±20′. S300, based on the allowance design in S100, the blank 3 undergoes one tooth profile finishing and one rake face finishing to remove the allowance and form the aforementioned equilateral triangular indexable micro-oil pipe threading tool. This includes the following steps: Remove the end face allowance. Based on the thickness allowance design on one side, use the first machine tool. The grinding allowance accuracy of each end face is ±0.01mm, the thickness accuracy is ±0.02mm, the parallelism of the two end faces is ≤0.01, and the flatness error is 0.005. To remove the tooth profile allowance, a second machine tool is used with a forming grinding wheel 41 for fine grinding. The feed rate is preset, and the tooth profile is removed in one pass. Remove the excess material from the front face using a third machine tool with a 251 forming grinding wheel for fine grinding. Set the feed rate and remove the excess material in one pass. As shown in Figure 11, taking an equilateral triangle structure as an example, assume the thickness allowance on one side is set to 0.1mm. Using the first fixture on the first machine tool, 0.1±0.01mm is ground off each side of the blank 3 to ensure a thickness of 4.76±0.02mm, parallelism of the two end faces ≤0.01, and flatness error 0.005. As shown in Figure 12, the second fixture 4 is used on the second machine tool. The second machine tool is a common form grinding machine MM7132. The form grinding wheel 41 is used to fine grind the blank 3. One pass is sufficient, and the feed speed is 12m / min. As shown in Figure 13, the third fixture 5 is used on the third machine tool. The third machine tool is a common form grinding machine MM7120. The second form grinding wheel 51 is used to fine grind the blank 3. One pass is sufficient, and the feed speed is 12m / min. Since the three positioning sides (faces) of the triangle already meet the forming requirements during blank forming, the machining surface of micro-grinding is greatly reduced. This reduces the technical difficulty of micro-grinding in the machining of equilateral triangular indexable micro-grinding oil pipe threads. Micro-grinding can be directly performed on the tooth profile, end face thickness, and rake face, while ensuring the tool accuracy under micro-grinding. This allows micro-grinding to be applied efficiently in the machining of equilateral triangular indexable micro-grinding oil pipe threads. This embodiment provides an equilateral triangular indexable micro-scale oil pipe threading tool and its machining method. This solution deeply integrates tool design, mold technology, forming technology, and grinding technology, offering a new solution to improve the production efficiency and product quality of equilateral triangular indexable micro-scale oil pipe threading tools. During the blank design stage, precise control of key dimensions such as blank accuracy and allowance achieves the goal of high precision and low allowance. In particular, the design of the three triangular locating surfaces directly meets the forming requirements, and the tooth profile and rake face design adopt a minimal allowance approach, ensuring the blank achieves high precision and guaranteeing stability and reliability in subsequent machining processes. It is especially worth mentioning that, utilizing existing high-precision molds and pressing technology, the three triangular locating sides (faces) can be directly formed during blank forming, serving as the positioning reference for subsequent machining and application without additional grinding steps. The indexing accuracy is comparable to traditional grinding. After blank forming, only a minimal allowance fine grinding process is needed on the tooth profile, rake face, and thickness to complete the entire manufacturing process, simplifying the production process, greatly improving production efficiency and reducing costs, while also ensuring the high quality and consistency of the final product without negatively impacting the product's lifespan. In addition, this solution can cover both round threads and trapezoidal threads, meeting the needs of different application scenarios. The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics of the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method of machining equilateral triangle indexable micro-petroleum pipe thread cutters, characterized in that, The method includes: S100, bare-bones design, including: S101, equilateral triangle three-positioning surface design, including an inscribed circle diameter accuracy of ±0.015~0.025mm, a concentricity deviation between the center of the inscribed circle and the center of the blank hole ≤0.1mm, an absolute value of the difference between any two perpendicular distances from the center of the blank hole to the three positioning surfaces ≤0.1mm, and an included angle tolerance of ±7′ between any two positioning surfaces; S102, thickness and rake face design, including thickness allowance on one side and rake face allowance of 0.1~0.15mm; S103, tooth profile design, including allowances of 0.08 to 0.15 mm in all directions of the tooth profile; S200 uses high-precision molds to batch press and form blanks. Each blank meets the blank design requirements of S100, and the three circumferential surfaces of the blank can be directly used as three positioning surfaces without grinding. S300, based on the allowance design in S100, the blank is subjected to one tooth profile finishing and one rake face finishing to remove all the allowance, thus obtaining the equilateral triangular indexable micro-oil pipe threading tool.

2. The method for machining micro-threading tools with an equilateral triangular indexable shape according to claim 1, characterized in that, In S200, the linear dimensional accuracy of the mold is ±0.03mm, the angular accuracy is ±20′, and the linear accuracy of the tooth profile is ±0.03mm when complex tooth profiles are added.

3. The method for machining micro-threading tools with an equilateral triangular indexable shape according to claim 1, characterized in that, In S200, batch pressing of blanks includes preparation of cemented carbide mixture, blank pressing, and blank sintering. During the blank pressing process, an electric press is used with a pressure of 4–4.5 t. With 10,000 blanks per furnace charge, the pressing time is 70 minutes. 100 hours.

4. The method of machining equilateral triangle indexable micro-petroleum pipe thread cutters according to claim 3, characterized in that, In the preparation process of cemented carbide mixture, the pre-set cemented carbide is mixed and uniformly stirred by ball milling for 70 to 100 hours. Spray granulation is carried out using a spray tower, with a spraying time of 24 hours per ton of material.

5. The method of machining equilateral triangle indexable micro-petroleum pipe thread cutters according to claim 3, characterized in that, During the sintering process of the blank, a low-pressure sintering furnace is used for sintering at a temperature of 1400–1500 °C for a sintering time of 20–50 hours.

6. The method for machining micro-threading tools with an equilateral triangular indexable shape according to claim 1, characterized in that, In S300, the end face allowance is removed. Based on the thickness allowance design on one side, the first machine tool is used. The grinding allowance accuracy of each end face is ±0.01mm, the thickness accuracy is ±0.02mm, the parallelism of the two end faces is ≤0.01, and the flatness error is 0.

005.

7. The method for machining micro-threading tools with an equilateral triangular indexable shape according to claim 1, characterized in that, In the S300, the removal of tooth profile allowance is carried out using a second machine tool, a forming grinding wheel for fine grinding, a preset feed rate, and removal in one pass.

8. The method for machining micro-threading tools with an equilateral triangular indexable shape according to claim 1, characterized in that, In the S300, the removal of the rake face allowance is carried out using a third machine tool and a second forming grinding wheel for fine grinding. The feed rate is preset and the removal is done in one pass.

9. An equilateral triangle indexable micro-petroleum pipe thread cutter characterized in that, The cutting tool is formed using the machining method for the equilateral triangular indexable micro-oil pipe threading tool described in any one of claims 1-8.

10. A positive triangle indexable micro-petroleum tubing thread tool according to claim 9, characterized in that The cutting tool is either an equilateral triangular indexable micro-oil pipe deflector trapezoidal thread cutting tool or an equilateral triangular indexable micro-oil pipe round thread cutting tool.

Images