A method of making a reduced diameter external thread based on a standard metric external thread

Abstract

This invention discloses a method for manufacturing reduced pitch diameter external threads based on standard metric external threads. The method includes using a finished bolt conforming to the standard metric thread standard as a standard bolt to manufacture a reduced pitch diameter bolt; and calculating the thread rolling blank diameter d' of the reduced pitch diameter bolt based on the equivalent of the thread pitch diameter to the thread rolling blank diameter. P =d P -Δd2; The difference ΔV is calculated based on the difference between the thread rolling blank volume V1 of the standard bolt and the thread rolling blank volume V2 of the bolt with reduced pitch diameter. P ; through ΔV P =ΔV=F(Δd) to calculate the thread cutting depth Δd; using the thread cutting depth Δd as the turning depth, turn the outer diameter of the original thread of the standard bolt to obtain a semi-finished bolt; according to the original thread pattern on the semi-finished bolt, roll the threads, and after surface treatment, obtain a bolt with reduced pitch diameter. This invention can realize the production and processing of bolts with reduced pitch diameter using finished bolts, simplifying the production process and improving production efficiency.

Description

Technical Field

[0001] This invention relates to the field of fastener manufacturing technology, and in particular to a method for manufacturing reduced pitch diameter external threads based on standard metric external threads. Background Technology

[0002] Fasteners in standard parts mainly include bolts and nuts. Generally, bolts and nuts are connected by threaded connections. Thread profiles include triangular threads, rectangular threads, trapezoidal threads, and sawtooth threads. The most commonly used thread profile is the triangular thread, and the most common external thread tolerance is 6g. Bolts using standard metric threads usually have good interchangeability, are readily available in various sizes, and are easy to purchase. However, for some users' requests for bolts with reduced pitch diameters (reducing the pitch diameter of standard metric threads), these are considered non-standard bolts, and products on the market typically cannot meet the technical requirements.

[0003] In the existing technology, the production of bolts with reduced pitch diameter generally includes the following process: blanking → upsetting → machining → thread rolling / thread twisting → heat treatment → surface treatment. This production process is good for controlling costs for large-volume orders, but it is particularly complicated for small and medium-sized orders, resulting in low production efficiency and high costs. Summary of the Invention

[0004] In view of this, the present invention provides a method for manufacturing reduced pitch diameter external threads based on standard metric external threads with a tolerance of 6g and a tooth profile of 60° triangle. This method can realize the manufacturing of reduced pitch diameter bolts using finished bolts, simplifying the production process and improving production efficiency.

[0005] This invention is achieved through the following technical solution: a method for manufacturing reduced pitch diameter external threads based on standard metric external threads, comprising the following steps:

[0006] Step 1: Measure the pitch diameter and major diameter of the finished bolt thread and compare them with the standard. Finished bolts that conform to the standard metric thread standard are used as standard bolts to make bolts with reduced pitch diameter.

[0007] Step 2: Given the thread rolling blank diameter d of the standard bolt. P The reduction in pitch diameter is Δd2. Since the pitch diameter of the thread is equivalent to the diameter of the thread rolling blank, the reduction in the diameter of the thread rolling blank is Δd. P =Δd2, the thread rolling blank diameter d' of the reduced pitch diameter bolt is calculated. P =d P -Δd2;

[0008] Step 3: According to Calculate the difference ΔV between the thread rolling blank volume V1 of a standard bolt and the thread rolling blank volume V2 of a bolt with a reduced pitch diameter.P Where L is the known standard metric thread length;

[0009] Step 4: Difference ΔV P Similar to the thread cutting volume ΔV that needs to be removed from the outer diameter of the original thread of a standard bolt, the thread cutting volume ΔV is a univariate function F(Δd) of the thread cutting depth Δd, and is obtained through ΔV. P =ΔV=F(Δd) is used to calculate the thread cutting depth Δd;

[0010] Step 5: Using the thread cutting depth Δd as the turning depth, turn the outer diameter of the original thread of the standard bolt to obtain a semi-finished bolt;

[0011] Step 6: Roll the threads according to the original thread pattern on the semi-finished bolt, and after surface treatment, obtain a bolt with reduced pitch diameter.

[0012] Furthermore, in step 4, the univariate function F(Δd) is: Where D0 is the original major diameter of the thread, P is the standard metric thread pitch, and H is the original triangle height of the standard metric thread.

[0013] Furthermore, in step 2, the thread rolling blank diameter d of the standard bolt... p Using d P =D-0.695P is calculated, where D is the nominal diameter of the standard metric thread.

[0014] Furthermore, in step 2, the thread rolling blank diameter d of the standard bolt... p Using d P =d2 is calculated, where d2 is the average value of the mean diameter of the finished bolt thread.

[0015] Furthermore, in step 4, D0 is taken as the nominal diameter D of the standard metric thread.

[0016] Furthermore, in step 4, D0 is taken as the average value d of the major diameter of the finished bolt thread.

[0017] Compared with existing technologies, the beneficial effects of this invention are:

[0018] 1. This invention is based on the equal volume method, i.e., ΔV P =ΔV, by modifying finished bolts to reduce the pitch diameter of bolts, the steps of blanking, pressing, and heat treatment are reduced, the production process is simplified and efficiency is improved; and the heat treatment performance of the original workpiece is not damaged, thus protecting the mechanical properties of the workpiece to the maximum extent.

[0019] 2. This invention is flexible and adjustable for different reduction amounts in pitch diameter, and the original thread cutting depth can be calculated for all cases, making it universally applicable.

[0020] 3. The method of this invention has high calculation accuracy and is low-cost and fast for small-batch customized bolts with reduced pitch diameter. Attached Figure Description

[0021] Figure 1 A flowchart for creating a method to reduce the pitch diameter of external threads.

[0022] Figure 2 This is a flowchart for calculating the cutting depth of the outer diameter of a thread.

[0023] Figure 3 This is a comparison diagram of standard bolts and bolts with reduced pitch diameter.

[0024] Figure 4 This is a schematic diagram of the cutting depth of the outer diameter of the thread. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] This invention provides a method for fabricating reduced pitch diameter external threads based on standard metric external threads. Specifically, it describes a method for fabricating a reduced pitch diameter external thread with a tolerance of 6g and a 60° triangular tooth profile, where the pitch diameter reduction is Δd2. The pitch of the reduced pitch diameter external thread is the same as the original standard metric external thread pitch. Figure 1 As shown in Figure 3, the method includes the following steps (all data are in mm, and all threads refer to external threads):

[0027] Step 1: Measure the pitch diameter and major diameter of the finished bolt thread. A pitch micrometer can be used to measure the pitch diameter and a vernier caliper to measure the major diameter. Compare the measured pitch diameter and major diameter of the finished bolt thread with standard GB / T15756-2008 (limit dimensions of ordinary threads) or standard GB / T197-2018 (tolerances of ordinary threads) to verify whether the pitch diameter and major diameter of the finished bolt thread conform to the standard metric thread standard. Only finished bolts that conform to the above standards can be used as standard bolts to make bolts with reduced pitch diameter.

[0028] Step 2: The required reduction in pitch diameter of the bolt thread compared to the standard metric thread is Δd2. The required pitch diameter of the bolt thread is... in This refers to the standard metric thread pitch diameter; since the thread pitch diameter approximates the thread rolling blank diameter, reducing the thread pitch diameter d'2 of the pitch diameter bolt is equivalent to reducing the thread rolling blank diameter d' of the pitch diameter bolt. PIt can be seen that the reduction in pitch diameter Δd2 is approximately equal to the reduction in diameter of the thread rolling blank Δd. P The required thread rolling blank diameter d' for reducing the pitch diameter of the bolt is calculated. P =d P -Δd P =d P -Δd2, d P This refers to the diameter of the thread rolling blank for a standard bolt.

[0029] The thread rolling blank diameter d of a standard bolt P The value is a known number, and its value is obtained according to the standard GB / T 18685-2017 (diameter of blank before thread rolling and thread forming). The thread rolling blank diameter is the diameter of the thread rolling blank processed before thread rolling of the bolt. The thread is formed by pressing the thread rolling blank with a thread rolling wheel.

[0030] Step 3: Calculate the difference ΔV between the thread rolling blank volume V1 of the standard bolt and the thread rolling blank volume V2 of the bolt with reduced pitch diameter according to formula (1). P :

[0031]

[0032] Where L is the known standard metric thread length.

[0033] Step 4: During the thread rolling process, no solid material is removed, meaning the volume of the bolt thread rolling blank is the same as the volume of the bolt produced. Therefore, the volume of the thread rolling blank for a reduced pitch diameter bolt is the same as the volume of the reduced pitch diameter bolt. In other words, the difference between the volume of the standard bolt and the volume of the reduced pitch diameter bolt is equal to the difference ΔV between the volume of the standard bolt thread rolling blank V1 and the volume of the reduced pitch diameter bolt thread rolling blank V2. P Make the difference ΔV P The volume of thread cutting ΔV removed from the outer diameter of the original thread of the standard bolt is the same as the volume of the bolt with reduced pitch diameter.

[0034] The thread cutting volume ΔV is a univariate function F(Δd) of the thread cutting depth ΔΔd, which is calculated using formula (2) at the thread cutting depth ΔΔd:

[0035] ΔV P =ΔV=F(Δd) (2);

[0036] The univariate function F(Δd) is derived from the volume of the thread portion that needs to be cut away on the outer circle of the original thread. This portion is a helical structure. The volume of the thread portion that needs to be cut away can be obtained by calculating the volume of the helical structure. The width of the helical structure, i.e. the thread cutting depth Δd, is known. All other data are known. Formula (3) is derived from this:

[0037]

[0038] Where D0 is the original major diameter of the thread; P is the standard metric thread pitch; and H is the original triangle height of the standard metric thread. Both P and H can be obtained by referring to the table in GB / T192-2003 (Basic Tooth Profile of Ordinary Threads).

[0039] In practice, depending on the condition of the finished bolts, if the thread pitch diameter and thread major diameter of the finished bolts are almost identical to those of standard metric threads, D0 can be taken as the nominal diameter D of the standard metric thread; or D0 can be taken as the average value d of the major diameter of the standard bolt thread. This is because only finished bolts that meet the standard requirements can be used as standard bolts to manufacture bolts with reduced pitch diameters, and the major diameter of the standard bolt thread falls within the range required by the standard metric thread major diameter. The errors obtained from both methods are negligible.

[0040] Step 5: As Figure 4 As shown, the original thread outer circle of the standard bolt is machined with the thread cutting depth ΔΔd as the turning depth to obtain a semi-finished bolt. The volume of the semi-finished bolt is the same as the volume V2 of the thread rolling blank of the reduced pitch diameter bolt, that is, the same as the volume of the reduced pitch diameter bolt, and can be used to make reduced pitch diameter bolts.

[0041] Step 6: Following the original thread pattern on the semi-finished bolt, the thread rolling wheel automatically aligns with the original thread pattern and rolls the threads. After surface treatment, a bolt with reduced pitch diameter is obtained.

[0042] Example 1

[0043] This embodiment further explains steps 2 and 4. After sampling and confirming that the threads of the finished bolts conform to the standard metric thread, the thread rolling blank diameter d of the standard bolt can be calculated using the nominal diameter D and pitch P of the standard metric thread. p And reduce the thread rolling blank diameter d′ of the pitch diameter bolt p This significantly reduces the tedious steps of inspecting and measuring finished bolts and obtaining the blank diameter according to GB / T18685-2017. Step 2 involves obtaining the calculation formula for the standard metric thread rolling blank diameter through extensive experimental measurements. For finished bolts conforming to the standard metric thread standard, the thread rolling blank diameter d... p It can also be calculated using formula (4):

[0044] d P =D-0.695P (4)

[0045] Where D is the nominal diameter of the standard metric thread and P is the pitch of the standard metric thread;

[0046] Then reduce the thread rolling blank diameter d' of the pitch diameter bolt. p The following can be calculated using formula (5):

[0047] d' P =D-0.695P-Δd2 (5)

[0048] Where Δd2 is the decrease in median diameter;

[0049] In step 4, the standard metric thread nominal diameter D and standard metric thread pitch P are substituted into formula (3), with D0 being the standard metric thread nominal diameter D, to obtain:

[0050]

[0051] At this point, we can obtain the following from formulas (1)-(5):

[0052]

[0053] Simplified, we get:

[0054]

[0055] Where D, H, P, and Δd² are all constants, the thread cutting depth Δd is obtained by solving. The above calculation shows that the thread cutting depth Δd can be calculated without knowing the standard metric thread length L.

[0056] For example, after testing, the thread pitch diameter and thread major diameter of the finished bolt both conform to the standard metric thread of GB / T5783 M30*100 with a tolerance of 6g and a pitch of 3.5mm. Based on this, a bolt with a reduced pitch diameter of 0.3mm is manufactured. Then, where D = 30, H = 3.03, P = 3.5, and Δd2 = 0.3, the final result is:

[0057] -4Δd 3 +87.73Δd 2 +68.18Δd - 74.71 = 0

[0058] The thread cutting depth Δd = 0.618 mm is obtained, which means that the external thread of the finished bolt is cut off by a depth of 0.618 mm.

[0059] Example 2

[0060] This embodiment further explains steps 2 and 4. After confirming that the thread of the finished bolt conforms to the standard metric thread, the thread rolling blank diameter d of the standard bolt can be calculated using the average value of the pitch diameter of the standard bolt thread. p And reduce the thread rolling blank diameter d' of the pitch diameter bolt p .

[0061] Step 2: Based on the approximate bolt pitch diameter to the bolt thread rolling blank diameter, the standard bolt thread rolling blank diameter d... p The value can be taken as the average value d2 of the thread pitch diameter of this batch of standard bolts, and the thread rolling blank diameter d of the standard bolt. p The following can be calculated using formula (6):

[0062] d P =d2(6)

[0063] Then reduce the thread rolling blank diameter d' of the pitch diameter bolt. p The following can be calculated using formula (7):

[0064] d' P =d2-Δd2 (7)

[0065] Where Δd2 represents the decrease in median diameter.

[0066] In step 4, the average value d of the major diameter of the standard bolt thread is substituted into formula (3), that is, D0 is taken as the average value d of the major diameter of the standard bolt thread, and the following is obtained:

[0067]

[0068] At this point, we can obtain the following from formulas (1)-(3) and (6)-(7):

[0069]

[0070] Simplified, we get:

[0071]

[0072] Where d2, d, H, P, and Δd2 are all constants, the thread cutting depth Δd is obtained by solving.

[0073] For example, after testing, the thread pitch diameter and thread major diameter of the finished bolts both conform to the standard of GB / T 5783 M30*100 with a tolerance of 6g and a pitch of 3.5mm for standard metric threads. They can be used as standard bolts for further manufacturing. The average thread pitch diameter d2 of this batch of standard bolts is 27.55mm, and the average thread major diameter d2 is 29.78mm. Taking d2 = 27.55 and d = 29.78, based on this batch of standard bolts, bolts with a reduced pitch diameter of 0.3mm are manufactured, where H = 3.03, P = 3.5, and Δd2 = 0.3. The final result is:

[0074] -4Δd 3 +87.07Δd 2 +67.68Δd - 74.66 = 0

[0075] The thread cutting depth Δd = 0.621 mm is obtained, which means that the external thread of the finished bolt is cut off by a depth of 0.621 mm.

[0076] The thread cutting depth Δd obtained in Embodiment 1 and Embodiment 2 of this invention differs by 0.003 mm. Based on the nominal diameter D of the standard metric thread = 30 mm, the error is 0.1‰, which can be ignored. Whether it is calculated using the nominal diameter D and pitch P of the standard metric thread in Embodiment 1, or using the average value d2 of the mean diameter of the standard bolt thread and the average value d of the major diameter of the thread in Embodiment 2, the cutting depth Δd can be obtained. Moreover, the error of the results obtained by the two calculations is extremely small, and the accuracy of the results is high.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating reduced pitch diameter external threads based on standard metric external threads, characterized in that, Includes the following steps: Step 1: Measure the pitch diameter and major diameter of the finished bolt thread and compare them with the standard. Finished bolts that conform to the standard metric thread standard are used as standard bolts to make bolts with reduced pitch diameter. Step 2: Given the thread rolling blank diameter of the standard bolt The decrease in median diameter is Based on the fact that the thread pitch diameter is equivalent to the thread rolling blank diameter, the reduction in the thread rolling blank diameter can be determined. The diameter of the thread rolling blank for reducing the pitch diameter of the bolt was calculated. ; Step 3: Calculate the volume of the thread rolling blank for the standard bolt using the following formula. With reducing the volume of thread rolling blanks for pitch diameter bolts The difference : in, This refers to the standard metric thread length. Step 4: Difference The thread cutting volume that needs to be removed from the outer diameter of the original thread of the standard bolt. Same, thread cutting volume For thread cutting depth Univariate function The thread cutting depth can be calculated using the following formula. : in, For the original thread major diameter, H represents the standard metric thread pitch, and H represents the original triangle height of the standard metric thread. Step 5: Using the thread cutting depth As the turning depth, the original thread outer diameter of the standard bolt is turned to obtain a semi-finished bolt; Step 6: Roll the threads according to the original thread pattern on the semi-finished bolt, and after surface treatment, obtain a bolt with reduced pitch diameter.

2. The method as described in claim 1, characterized in that, In step 2, the thread rolling blank diameter of the standard bolt The following formula is used to calculate: in, This refers to the nominal diameter of the standard metric thread.

3. The method as described in claim 1, characterized in that, In step 2, the thread rolling blank diameter of the standard bolt The following formula is used to calculate: in, This represents the average value of the pitch diameter of the finished bolt thread.

4. The method as described in claim 2 or 3, characterized in that, In step 4, The value is the standard metric nominal diameter of the thread. .

5. The method as described in claim 2 or 3, characterized in that, In step 4, The value is the average value of the major diameter of the finished bolt thread. .

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