High performance spiral flute tap for stainless steel

Abstract

This invention provides a high-performance spiral flute tap specifically for stainless steel. The tap has a coaxially arranged coarse shank, fine neck, and coarse thread section. The helix angle β of the chip removal groove in the coarse thread section is ≥48°. The chip removal groove has a three-groove structure, which is a straight-line three-arc structure. The three arcs are distributed in three equal parts relative to the tap's axis, and the three arcs are smoothly connected. The tap is made of high-speed steel material treated with vacuum heat treatment, passivation, and surface coating. This invention optimizes the tap's structural form and groove design, uses higher-performance materials, and combines heat treatment and surface coating processes to achieve high-efficiency tapping of stainless steel materials on CNC equipment, improving tap life and ensuring tap performance.

Description

Technical Field

[0001] This utility model belongs to the technical field of thread cutting taps for machine tools, specifically relating to a high-performance spiral groove tap for stainless steel, used for processing stainless steel materials. Background Technology

[0002] With the development of the manufacturing industry, the requirements for products are becoming increasingly stringent. More and more users are using taps for processing non-ferrous metal materials. Stainless steel, as an excellent corrosion-resistant material with superior strength and toughness, is seeing its applications continuously expand. Currently, stainless steel has become an indispensable material in people's production and daily life. Commonly used stainless steel materials (such as 304) have good corrosion resistance, heat resistance, low-temperature strength, and mechanical properties. They also have good hot workability such as stamping and bending, do not exhibit heat treatment hardening, and are non-magnetic. They are widely used in various fields such as automotive parts, medical devices, ship components, boilers, food industry, and industrial equipment manufacturing. The demand for taps for processing this material is very large, and the market prospects are broad.

[0003] Existing spiral flute taps are typically made of high-speed tool steel. The chip evacuation grooves in the working part of the tap are spiral-shaped, greatly enhancing chip flow control and guiding. Chips are continuously discharged in a spiral pattern, preventing clogging and improving working conditions. Furthermore, spiral flute taps do not require multiple tap withdrawals during tapping; they can be used to complete the tapping in one pass. Therefore, spiral flute taps have higher production efficiency than straight flute taps. In addition, spiral flute taps increase the actual rake angle and chip clearance, resulting in a sharper cutting edge, smoother operation, reduced cutting torque, and improved tap durability. Due to these advantages, spiral flute taps are particularly suitable for machining deep-hole threads in low-carbon steel, alloy steel, stainless steel, heat-resistant alloys, and non-ferrous metals. They are also suitable for machining fluted or discontinuous surface threads.

[0004] The selection of the helix angle is crucial for machining stainless steel using specialized spiral flute taps, as its value significantly impacts the tap's performance. A larger helix angle enhances chip guidance and removal, resulting in a larger rake angle and a smoother tapping process. However, an excessively large helix angle weakens the tap's cutting teeth and increases the difficulty of manufacturing the cutting cone. Therefore, the helix angle should be selected appropriately based on the machining conditions and the material being processed. Generally, a helix angle (β) greater than 40° is optimal for machining stainless steel.

[0005] Spiral flute taps are characterized by their closed-loop cutting mechanism. During tapping, multiple circumferentially distributed cutting edges work together, with the back of the edges cutting into the bottom hole wall. Only a semi-enclosed cutting space remains between the flute and the hole wall, making chip removal and cooling difficult. Furthermore, the excellent ductility of stainless steel causes the machined threaded hole to shrink and envelop the tool during cutting. Existing spiral flute taps on the market suffer from high tapping torque, difficult chip removal, easy damage to the cutting edges, and material-tool adhesion when machining stainless steel, resulting in poor durability and easy breakage. Therefore, resolving the contradiction between tap strength and chip space, as well as the adhesion problem between the tool and the workpiece, is a crucial aspect of tap optimization.

[0006] When machining stainless steel workpieces, ordinary spiral flute taps typically select a helix angle (β) of 40°–45°, a rake angle (γ) of 6°–10°, a cutting edge width of 0.38 times the nominal diameter (mm), and a cutting cone clearance angle (α cutting cone) of 4°–6°. For taps with a nominal thread diameter greater than or equal to 3mm, the thread profile should be honed, with a pitch diameter honing amount (α pitch diameter) of 0.01–0.02mm. These taps have a coarse straight shank structure without a neck. While this existing structure can machine a very small number of threaded holes with stable dimensions during manual tapping of stainless steel, it suffers from poor chip removal and short service life during high-efficiency tapping on CNC equipment such as machining centers and drilling and milling centers. In severe cases, it can even cause tap breakage, affecting thread machining, resulting in unstable performance and low work efficiency, often becoming a difficult problem to overcome in practical work. Therefore, the following improved technical solution is proposed. Utility Model Content

[0007] The technical problem solved by this utility model is to provide a high-performance spiral groove tap for stainless steel, thereby addressing the technical issue of how to improve the performance and lifespan of spiral groove taps for machining stainless steel materials.

[0008] The technical solution adopted in this utility model is as follows: a high-performance spiral groove tap for stainless steel, the tap having a coarse shank, a fine neck and a coarse threaded part arranged coaxially; the helix angle β of the chip removal groove of the coarse threaded part is ≥48°; the chip removal groove has a three-groove structure, which is a straight line three-circular arc structure, the straight line three-circular arc is distributed in three equal parts relative to the center line of the tap, and the straight line three-circular arc is smoothly connected; the tap is made of high-speed steel material treated by vacuum heat treatment, passivation process and surface coating process.

[0009] In the above technical solution, the preferred option is that the helix angle of the chip removal groove is a right-hand helix angle, and the right-hand helix angle of the chip removal groove is 48°.

[0010] In the above technical solution, preferably: the front angle γ of the chip discharge groove is selected as M4 specification 8°~10°; the front arc R1 is selected as M4 specification 0.3mm; the core diameter... The value of d is 1.65mm for M4 specifications; the value of the cutting edge width f is 0.8mm for M4 specifications.

[0011] In the above technical solution, the preferred option is that the high-speed steel for the tap is high-vanadium high-speed steel; the high-vanadium high-speed steel has a bending strength of 4200MPa and an impact resistance of 38J.

[0012] In the above technical solution, the preferred method is as follows: during tapping, the pitch diameter of the threaded section is offset, and the grinding amount α of the pitch diameter of the M4 specification threaded section is adjusted. 中径 The diameter is 0.02–0.035 mm; the back angle α of the cutting cone grinding is... 切削锥 The range is 6° to 8°.

[0013] In the above technical solution, the preferred embodiment is that the cutting cone length L is 2 to 3 times the pitch P, and the pitch P for M4 specification is 0.7; the cutting cone end diameter... The length dx is 3.18mm for M4 specification.

[0014] In the above technical solution, the preferred values ​​are: R1 of the three circular arcs in a straight line is 0.3mm; R2 is 1.44mm; and R3 is 3.50mm.

[0015] Advantages of this utility model compared to the prior art:

[0016] This invention optimizes the tap structure, groove design parameters, and machining processes, and uses higher-performance materials in conjunction with heat treatment and surface coating processes to achieve high-performance spiral groove taps for efficient tapping of stainless steel materials on CNC equipment, thereby improving tap life. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a spiral groove tap in the existing technology;

[0018] Figure 2 This is a schematic diagram of the structure of the spiral groove tap of this utility model;

[0019] Figure 3 This is a partially enlarged schematic diagram of the threaded portion S of this utility model;

[0020] Figure 4 This is a schematic diagram of the groove-shaped transverse section structure and a schematic diagram of the grinding back angle of this utility model;

[0021] Figure 5 This is a schematic diagram of the back angle of the thread pitch diameter after grinding in this utility model;

[0022] In the diagram: 1-shank, 2-neck, 3-threaded part, 4-cutting cone, 5-chip groove. Detailed Implementation

[0023] The following will refer to the appendix in the embodiments of this utility model. Figure 2-5 The technical solutions in the embodiments of this utility model are clearly and completely described herein. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0024] (like Figure 2 As shown, a high-performance spiral groove tap for stainless steel is provided, wherein the tap has a coarse shank 1, a fine neck 2 and a coarse threaded part 3 arranged coaxially.

[0025] This utility model of a spiral groove tap adopts a coarse shank with a neck. The coarse shank 1 is conducive to clamping and transmitting large torque, while the tap's fine neck 2 structure is conducive to machining deep holes and sufficient flow of coolant during tapping. It is also conducive to CNC multi-wire grinding during the tap thread grinding process.

[0026] Specifically, this utility model adopts a three-section coaxial structure design of coarse shank-neck-coarse head. Through structural parameter optimization and machining process coordination (described later), it significantly improves the machining efficiency and tool life of stainless steel tapping. The shank 1, as the power input end, adopts a large-diameter cylindrical structure to ensure a rigid connection with the machine tool fixture. By increasing the clamping diameter of the shank 1 (15%-20% larger than traditional taps), it can withstand cutting torques of up to 500-800 N·m in stainless steel machining, avoiding slippage or shank breakage. The flexible transition area of ​​the neck 2, connecting the shank 1 and the threaded part 3, has a diameter 20%-30% smaller than that of the shank 1 and a length accounting for 15%-20% of the total length. The neck 2 structure reduces the contact area between the tap and the hole wall, reduces frictional resistance, and makes chip removal smoother, especially suitable for tapping deep holes in stainless steel with a hole depth ≥ 3 times the diameter. The narrow neck 2 forms an annular flow channel with the gap between itself and the hole wall, guiding the coolant directly to the cutting zone, enhancing lubrication and heat dissipation (improving cooling efficiency by more than 30%), and effectively suppressing the sticking phenomenon caused by high temperature in stainless steel machining.

[0027] The chip removal groove 5 of the coarse thread section 3 has a helix angle β ≥ 48°. This results in smoother chip removal and an increased actual rake angle, leading to sharper cutting. When the right-hand helix angle β > 48°, the chip removal groove 5 forms a large-angle spiral flow channel, and the chips are subjected to centrifugal force (Fc = mω). 2 Under the combined action of r and spiral thrust (Fs=μN, μ is the coefficient of friction), it is ejected in a spiral shape along the groove wall, avoiding accumulation and blockage.

[0028] In the above embodiments, preferably, the helix angle of the chip removal groove 5 is a right-hand helix angle, specifically 48°. When the helix angle β = 48°, the chip removal efficiency (chip volume discharged per unit time) of the chip removal groove 5 reaches the critical threshold for tapping stainless steel materials. Experimental data are shown in Table 1.

[0029] Table 1: Effect of helix angle β on stainless steel chip removal efficiency

[0030]

[0031] It is evident that increasing β from 45° to 48° increases the chip removal speed by 22%, while the rate of increase slows down after β > 48° (approximately 8% increase in the 48°-52° range). Therefore, 48° represents the optimal cost-effectiveness. Furthermore, combined with fluid dynamics verification, CFD simulations show that at β = 48°, the chip residence time in the groove is reduced by 37% compared to β = 40°, and the exit speed increases by 2.1 times (from 8.5 m / s to 17.8 m / s), significantly reducing the risk of secondary cutting. Simulations of cutting motion trajectories at different helix angles show that at β = 48°, chips can be ejected.

[0032] Furthermore, the right-hand spiral angle finger chip groove 5 is spirally ascending along the tap rotation direction (clockwise), which conforms to the international standard (ISO 3937-2) that "the positive Z-axis is the tool withdrawal direction", ensuring coordination with the machine tool spindle rotation direction (usually clockwise) to form a continuous chip removal flow.

[0033] Furthermore, the right-hand large-helix chip removal groove 5 and the coolant flow channel of the narrow neck 2 form a dual-channel lubrication system. The main channel, the narrow neck 2, guides the coolant to flow in axially; the secondary channel, the spiral structure of the chip removal groove 5, directs the coolant to the cutting edge, forming a spiral lubrication film. Simulations show that when β=48°, the cutting zone temperature is reduced by 42°C compared to β=40° (from 280°C to 238°C), effectively suppressing the "built-up edge" phenomenon in stainless steel machining.

[0034] The chip removal groove 5 has a three-groove structure, which is a straight line and three circular arcs. The straight line and three circular arcs are distributed in three equal parts relative to the tap axis, and the straight line and three circular arcs are smoothly connected.

[0035] In the above embodiments, preferably, the rake angle γ of the chip removal groove 5 is selected as 8° to 10° according to the M4 specification; to balance sharpness and strength, the cutting force increases by 15% when γ < 8°, and the strength of the groove bottom decreases by 22% when γ > 10°.

[0036] In the above embodiments, preferably, the front arc R1 is M4 with a specification of 0.3mm; matching the thickness of stainless steel chips (0.2-0.4mm), to achieve the optimal chip curling condition of "initial curling radius ≈ chip thickness".

[0037] In the above embodiments, the preferred core diameter is... The value of d is M4, which is 1.65mm; to ensure tap rigidity: When d < 1.65 mm, the torsional stiffness is insufficient. When d > 1.65 mm, the chip removal space is reduced by 30%.

[0038] In the above embodiments, preferably, the cutting edge width f is 0.8mm for M4 specification, and the cutting load is controlled so that the cutting force per unit edge length is evenly distributed when f=0.8mm, thus avoiding local overload.

[0039] Furthermore, the three-groove structure increases the chip-holding space by 1.8 times compared to the traditional double-groove design. The optimized groove shape further increases the chip-holding space, facilitating tight chip curling. The cross-sectional area of ​​the straight-line-circular arc composite groove gradually increases, starting from 2.1mm at the cutting edge. 2 Increased to 4.5mm at the chip discharge port. 2 To prevent chip clogging, CFD simulations show that the chip filling rate in the groove is reduced from 85% in the traditional groove shape to 62%, and the chip removal resistance is reduced by 33%. The increased chip space increases the coolant contact area by 50%, the cutting zone temperature is reduced by 35°C compared to the traditional groove shape, and the tool life is extended by 70%.

[0040] The tap is made of high-speed steel that has undergone vacuum heat treatment, passivation, and surface coating. The vacuum heat treatment process is preferred to provide excellent surface protection, preventing oxidation and decarburization, improving mechanical properties, minimizing deformation, increasing machining accuracy, reducing the volatility of alloying elements, and ensuring quality. A new passivation process is added to resist physical wear of the cutting tool, maintain workpiece surface finish, and facilitate chip removal from the groove. A new surface coating process is added to reduce the coefficient of friction, prevent adhesion, remove grinding stress remaining on the surface during grinding, and improve surface hardness, wear resistance, and heat resistance.

[0041] In the above embodiments, preferably, the high-speed steel used for the tap is high-vanadium high-speed steel; the high-vanadium high-speed steel has a bending strength of 4200 MPa and an impact energy of 38 J. Through analysis of various raw material compositions, bending tests, and cutting tests, it was concluded that high-vanadium high-speed steel, with a bending strength of 4200 MPa and an impact energy of 38 J, possesses high hardness and wear resistance, sufficient strength and toughness, high heat resistance, and high thermal conductivity, which can significantly improve the life of CNC tools, doubling the original tool life.

[0042] (combined) Figure 4 , Figure 5 (As shown) During the research and trial production process, a reasonable machining process was selected. In the above embodiment, the preferred process is: when machining the tap, the pitch diameter of the threaded part 3 is scraped, and the grinding amount α of the pitch diameter of the threaded part 3 (M4 specification) is...中径 The diameter is 0.02–0.035 mm; the back angle α of the cutting cone after grinding is 4 mm. 切削锥 The range is 6° to 8°.

[0043] Specifically: For the threaded portion, a spade is applied to the pitch diameter using a CNC multi-thread thread grinder. The spade position is accurately calculated based on the helix angle, resulting in precise and reliable spade backing and positioning. The spade backing amount α is used for M4 specification pitch diameter grinding. 中径 When the angle is 0.02–0.035 mm, it effectively achieves the purpose of scraping, reduces cutting resistance, and improves product life. Secondly, a reasonable scraping relief angle is selected. Machining a cutting cone with a large helix angle spiral groove tap is quite difficult. It is necessary to ensure the reasonable distribution of the cutting amount, as well as its sharpness and wear resistance. Through multiple life verifications, the scraping relief angle α was finally determined. 切削锥 When the temperature is between 6° and 8°, the product lifespan is more stable.

[0044] (like Figure 3 (As shown) In the above embodiment, preferably: the cutting cone length L of the cutting cone 4 is 2 to 3 times the pitch P, and the pitch P of the M4 specification is 0.7; the end diameter of the cutting cone 4 The length dx is 3.18mm for M4 specification.

[0045] It should be noted that the cutting cone length L of the cutting cone 4 is 2 to 3 times the pitch P, which provides good low-cutting guidance. During tapping, the cutting cone first contacts the workpiece and begins cutting. When the cutting cone length is 2 to 3 times the pitch P, it can guide the threading tool (such as a tap) into the workpiece material more smoothly. Taking an M4 specification with a pitch P = 0.7 mm as an example, the cutting cone length is in the range of 1.4-2.1 mm. This length allows the tool to gradually apply cutting force during the initial entry stage, avoiding vibration or impact caused by excessive entry, thus ensuring the stability of the cutting process and improving the machining accuracy of the thread. In addition, it can effectively form and remove chips. A suitable cutting cone length helps to form continuous and uniform chips. During the cutting process, the geometry and length of the cutting cone determine the curling and breakage mode of the chips. A length range of 2 to 3 times the pitch allows sufficient space for the chips to curl during formation and be smoothly discharged from the cutting area. If the cutting cone is too short, the chips may not curl properly, easily clogging the cutting area, leading to increased cutting force and accelerated tool wear. Conversely, if the cutting cone is too long, the chips may become too thin and elongated, which is also detrimental to chip removal and machining efficiency. From the perspective of cutting force, a cutting cone length of 2 to 3 times the thread pitch achieves a good balance between cutting force and tool strength. During tapping, the cutting cone bears significant cutting force and torque. While a shorter cutting cone provides higher tool strength, the uneven distribution of cutting force can easily lead to tool misalignment, affecting thread accuracy. A longer cutting cone, while providing a more even distribution of cutting force, reduces the overall strength of the tool and increases the risk of breakage. A length of 2 to 3 times the thread pitch ensures a reasonable distribution of cutting force while maintaining sufficient tool strength, extending tool life, and balancing cutting force and tool strength.

[0046] Cutting cone 4 end diameter The length dx is 3.18mm for M4 specification, which conforms to thread standards and fit requirements. M4 thread specification has its specific standard dimensions and tolerance range. Cutting taper diameter. The 3.18mm dx design is based on precise calculations and long-term practical verification, ensuring a good fit between the machined threads and the corresponding nuts or bolts. This size guarantees the integrity of the thread profile and dimensional accuracy, providing sufficient strength and reliability for the threaded connection to meet the requirements of mechanical assembly and use. The size of the cutting taper directly affects the cutting area and cutting force during the cutting process. For M4 thread machining, a 3.18mm cutting taper ensures cutting efficiency while reasonably controlling the cutting force. If the cutting taper is too large, the cutting area increases, and the cutting force will rise significantly, potentially leading to accelerated tool wear and workpiece deformation; conversely, if the cutting taper is too small, cutting efficiency decreases and machining time increases. The 3.18mm size is the optimal value determined after comprehensively considering material properties, tool performance, and machining efficiency. A suitable cutting taper helps reduce tool wear during the cutting process. The 3.18mm cutting taper ensures that the cutting force is evenly distributed on the cutting edge of the tool, avoiding localized stress concentration and thus reducing the tool wear rate. At the same time, this size also facilitates the dissipation of cutting heat, preventing the tool from failing rapidly due to overheating, further improving the tool's durability and service life, and reducing production costs.

[0047] (like Figure 4 As shown in the above embodiment, preferably: the arc R1 of the straight line with three arcs is 0.3mm; R2 is 1.44mm; and R3 is 3.50mm.

[0048] It should be noted that: the small arc R1 (0.3mm) precisely guides fine chips in the initial stage of chip formation, preventing chip accumulation in certain areas; the medium arc R2 (1.44mm) further widens the chip removal channel, allowing chips to pass through more smoothly; and the large arc R3 (3.50mm) ensures that chips are not obstructed during discharge, smoothly exiting the tap along the chip removal groove, effectively preventing chip blockage and reducing increased cutting force and tool wear caused by chip accumulation. During tapping, different chip shapes are generated due to variations in material properties and cutting parameters, such as spiral and ribbon shapes. The small arc R1 can handle fine chip fragments, while the medium arcs R2 and R3 can accommodate and guide longer spiral or ribbon-shaped chips, allowing all types of chips to exit smoothly, improving the versatility and reliability of chip removal. The reasonable setting of R1, R2, and R3 ensures that the chip removal groove provides sufficient chip removal space without excessively weakening the tap's strength. For example, a smaller R1 provides better local strength support, while a larger R3 maintains the overall structural stability of the tap while ensuring smooth chip removal, making the tap less prone to breakage or deformation when subjected to large cutting torque and axial force.

[0049] The design principle of this utility model is as follows: Stainless steel chips are continuous ribbons that easily entangle the tap. A right-hand helix angle (β > 48°) forces chip breaking (increasing the collision frequency between the chip and the groove wall by 3 times) and directional discharge, breaking long chips into short C-shaped chips (length < 5mm), thus preventing tool entanglement. When tapping stainless steel, the actual diameter of the threaded hole shrinks by 0.02–0.05mm due to elastic recovery. The large helix angle chip removal groove 5 increases the contact length of the cutting edge (40% longer than a straight groove tap), dispersing the cutting force, reducing single-point overload, and ensuring the thread tolerance remains stable at 6H grade. The right-hand helix angle is highly compatible with CNC multi-line grinding technology (five-axis linkage), allowing precise control of groove parameters (helix angle error ≤ 0.3°, groove width tolerance ± 0.01mm), avoiding poor chip removal or cutting vibration caused by groove shape deviations.

[0050] This invention, through the above optimizations, enables high-performance spiral flute taps to overcome unfavorable factors in the machining process, nearly doubling their lifespan in high-efficiency CNC thread machining of stainless steel. This invention's taps offer high cost-effectiveness, reliable performance, and longer lifespan, making them suitable for widespread adoption.

[0051] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0052] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the scope of protection of the present utility model. Any modifications and equivalent substitutions made within the spirit and principles of the present utility model are included within the scope of protection of the present utility model.

Claims

1. A high-performance spiral groove tap for stainless steel, characterized in that: The tap has a coaxially arranged coarse shank (1), fine neck (2), and coarse thread (3); the chip removal groove (5) of the coarse thread (3) has a helix angle β ≥ 48°; the chip removal groove (5) has a three-groove structure and a straight line three-circular arc structure, the straight line three-circular arc is distributed in three equal parts relative to the tap axis, and the straight line three-circular arc is smoothly connected; the tap is made of high-speed steel material treated by vacuum heat treatment, passivation process and surface coating process.

2. The tap according to claim 1, characterized in that: The chip removal groove (5) has a right-hand helix angle, and the right-hand helix angle M4 of the chip removal groove (5) is 48°.

3. The tap according to claim 2, characterized in that: The chip removal groove (5) has a groove front angle γ of 8° to 10° (M4 specification); a front arc R1 of 0.3mm (M4 specification); a core diameter φd of 1.65mm (M4 specification); and a cutting edge width f of 0.8mm (M4 specification).

4. The tap according to claim 3, characterized in that: The tap is made of high-vanadium high-speed steel; the high-vanadium high-speed steel has a bending strength of 4200MPa and an impact resistance of 38J.

5. The tap according to claim 4, characterized in that: During tapping, the threaded part (3) is scraped at the pitch diameter, and the M4 specification pitch diameter scraping amount α of the threaded part (3) is used. 中径 The diameter is 0.02 to 0.035 mm; the back angle α of the cutting cone (4) is shoveled. 切削锥 It ranges from 6° to 8°.

6. The tap according to claim 5, characterized in that: The cutting cone length L of the cutting cone (4) is 2 to 3 times the pitch P, and the pitch P of the M4 specification is 0.7; the end diameter φdx of the cutting cone (4) is 3.18mm for the M4 specification.

7. The tap according to claim 6, characterized in that: For a straight line with three circular arcs, the arc radius R1 is 0.3mm; R2 is 1.44mm; and R3 is 3.50mm.

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