A processing method for tapping a small threaded hole of a titanium alloy part

Abstract

The application relates to the field of machining methods, and particularly discloses a method for machining small screw hole tapping of a titanium alloy part. The method adopts an extrusion tap for numerical control machining, the thread pitch of the screw hole is P, the extrusion tap is a three-edge structure, and the length of a tap guide part is 4P; and the method specifically comprises the following steps: S1 parameter adjustment, S2 thread bottom hole machining, S3 hole expansion, and S4 extrusion tapping machining. The machining method of the small-diameter thread of the titanium alloy material applies the extrusion tap to the titanium alloy material, realizes the tapping work of the small screw hole of the titanium alloy part, improves the productivity and the product machining quality, and realizes the extremely significant improvement of automatic production.

Description

TECHNICAL FIELD

[0001] The application relates to the field of machining methods, and discloses a method for machining small threaded holes of titanium alloy parts. BACKGROUND

[0002] When a numerical control machine tool (a machining center) machines a small threaded hole, the tap is prone to breakage. The thread machining process of the extrusion tap does not generate cutting, the tap does not generate a broken blade phenomenon, tap breakage is avoided, and the service life of the extrusion tap is 2-40 times that of the ordinary tap.

[0003] The machining of small-diameter threads of titanium alloy materials usually adopts the method of using an ordinary jump tooth tap rigid tapping in cooperation with thread finishing by a bench worker and thread milling cutter machining on a machining center equipment. The method of using an ordinary jump tooth tap rigid tapping in cooperation with thread finishing by a bench worker on a machining center equipment is small cutting in a semi-closed state, and cutting fluid is difficult to reach the cutting area, so the heat dissipation and lubrication effect is poor. The titanium alloy has small elastic modulus, and has large springback during cutting, so that the friction torque is increased, and the tap is broken or broken.

[0004] The machining of small-diameter threads of titanium alloy materials can also use the method of thread milling cutter machining. For the thread machining of high-hardness materials and high-temperature materials, since the diameter of the cutter is smaller than the machined hole, the cutter is not easy to block the threaded hole after being broken. However, the disadvantage is that the cutting time is long and the machining efficiency is low due to the use of the machining center machine tool helical interpolation function for machining.

[0005] The extrusion tap is usually applied to the thread tapping of copper alloy and aluminum alloy parts with low strength and good plasticity, and can also be used for the thread tapping of stainless steel and low-carbon steel materials with low hardness and good plasticity. Titanium alloy has the characteristics of small thermal conductivity, low plasticity, large elastic deformation and high strength, but on the other hand, these characteristics make it unsuitable for extrusion taps.

[0006] How to apply the extrusion tap to the small thread tapping of titanium alloy materials is a difficulty in machining the threads of titanium alloy. SUMMARY

[0007] The idea of the application is that, according to the characteristics of the machining center, the structure of the extrusion tap is improved, the machining process is optimized, and the synchronous accuracy of the rigid tapping of the equipment is improved, so that the tapping machining of the small threaded holes of titanium alloy parts is realized.

[0008] The application discloses a tapping machining method for small threaded holes of titanium alloy parts, adopts extrusion taps for numerical control machining, the thread pitch of the threaded hole is P, the extrusion tap used is a three-edge structure, and the length of the tap guide part is 4P; and the method specifically comprises the following steps:

[0009] S1 parameter adjustment: Adjust the control parameters of the machining center's speed and position loops, as well as the time constants and loop gains of the spindle and feed axes, so that the spindle rotation and Z-axis feed are always synchronized, and the rigid tapping error is less than 1; adjust the clamping state of the extrusion tap, drill, and collet so that the radial runout of the extrusion tap and drill is no more than 0.01mm;

[0010] S2 thread bottom hole processing: calculate the thread bottom hole diameter S1, the S1 value is DP; perform thread bottom hole processing according to the S1 value; D is the nominal diameter of the thread, and P is the pitch;

[0011] S3 reaming: Use a drill to reame the processed threaded bottom hole to a diameter of S2. The S2 value is (D-0.5P+0.02mm) to (D-0.5P+0.05mm);

[0012] S4 extrusion tapping processing: evenly brush tapping coolant on the extrusion tap, and complete the processing of small threaded holes in titanium alloy parts in one extrusion tapping.

[0013] Preferably, the tapping coolant in step S4 is extreme pressure tapping oil.

[0014] Preferably, in the step S4, the extrusion speed during the processing is 3-5 m / min.

[0015] Preferably, through the processing of step S4, the threaded hole fit is detected, and the specific value of S2 in step S3 is further determined to be within the range of (D-0.5P+0.02mm) to (D-0.5P+0.05mm).

[0016] Furthermore, when processing the M2 thread, the diameter of the thread bottom hole is 1.84 mm.

[0017] The beneficial effects achieved by the present invention are as follows: the processing method of small-diameter threads of titanium alloy materials disclosed in the present invention applies an extrusion tap to titanium alloy materials, realizes the tapping of small threaded holes of titanium alloy parts, improves productivity and product processing quality, and realizes a very meaningful improvement in automated production. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clear and distinct, the present invention is further described in detail with reference to the following examples. It should be noted that the present invention is not limited to the following examples.

[0019] Example 1

[0020] An extrusion tap is used for CNC machining of an M2 thread. The thread pitch P of the screw hole is 0.4 mm. The extrusion tap used has a three-edge structure and the length of the tap guide portion is 1.6 mm.

[0021] During the threaded hole machining process, titanium alloy parts have poor cutting performance and are prone to tap breakage. To reduce tap consumption, taps must be selected scientifically. Common extrusion taps have 5 to 6 edges. The more edges a tap has, the greater the torque required when extruding a threaded hole. However, using a three-edge extrusion tap to machine titanium alloys can reduce the torque during extrusion and reduce tap wear. The tap guide length is also a key factor affecting the life of the tap. The longer the tap guide, the easier it is to introduce the tap when tapping. However, an excessively long guide increases the required torque and makes the tap more likely to break. Experiments have shown that when the tap guide length is 4P, the processed threaded hole can meet the process requirements for thread machining.

[0022] S1: Adjust the control parameters of the machining center's speed and position loops, as well as the time constants and loop gains of the spindle and feed axes, so that the spindle rotation and Z-axis feed are always synchronized, and the rigid tapping error is less than 1; adjust the clamping state of the extrusion tap, drill bit, and collet so that the radial runout of the extrusion tap and drill bit is no more than 0.01 mm;

[0023] When executing the rigid tapping cycle, in order to ensure that the Z-axis feed corresponding to one rotation of the spindle is equal to the tapping pitch, it is necessary to ensure that the rotation of the machine tool spindle and the Z-axis feed are always synchronized. In other words, the rotation of the spindle must not only be controlled by the speed loop, but also by the position loop. When machining the bottom of the threaded bottom hole, the start / pause, acceleration / deceleration of the spindle and feed axis must also meet the synchronization conditions. The time constant and loop gain of the spindle and feed axis are adjusted, and the rigid tapping error is adjusted to less than 1 to improve the rigid tapping accuracy. In terms of tool installation, high-precision tool holders and collets are used to improve the tool clamping accuracy and ensure that the radial runout of the tool is between 0 and 0.01mm. The tool runout value must be measured after each tool change. In order to unify the tool setting reference and clarify the reference surface position, the off-machine tool setting method is adopted.

[0024] S2: Calculate the thread bottom hole diameter S1. The nominal diameter D of the M2 thread is 2 mm, the pitch P is 0.4 mm, and the thread bottom hole diameter S1 is 1.6 mm.

[0025] S3 reaming: Use a drill to reame the processed threaded bottom hole to S2; after testing, the best processing effect is when S2 is 1.84mm.

[0026] The drilling-before-expansion processing method is used to reduce the work hardening of the thread bottom hole, thereby reducing the cutting torque of tapping.

[0027] S4 extrusion tapping processing: evenly brush tapping coolant on the extrusion tap, use an extrusion speed of 5m / min, and complete the processing of small threaded holes in titanium alloy parts in one extrusion tapping.

[0028] The extrusion tap is brushed with tapping coolant evenly to reduce the temperature in the machining process. The test shows that the tapping coolant is the extreme pressure tapping oil. According to the characteristics of the titanium alloy, the extrusion speed is 3-5 m / min, and the machining of the small screw hole of the titanium alloy part can be completed by one-time extrusion tapping.

Claims

1. A tapping method for small screw holes in titanium alloy parts, characterized in that: The CNC machining is performed using an extrusion tap, wherein the thread pitch of the screw hole is P, the extrusion tap used has a three-edge structure, and the length of the tap guide portion is 4P; the specific steps include: S1 parameter adjustment: Adjust the control parameters of the machining center's speed and position loops, as well as the time constants and loop gains of the spindle and feed axes, so that the spindle rotation and Z-axis feed are always synchronized, and the rigid tapping error is less than 1; adjust the clamping state of the extrusion tap, drill, and collet so that the radial runout of the extrusion tap and drill is no more than 0.01mm; S2 thread bottom hole processing: calculate the thread bottom hole diameter S1, the S1 value is DP; perform thread bottom hole processing according to the S1 value; D is the nominal diameter of the thread, and P is the pitch; S3 reaming: Use a drill to reame the processed threaded bottom hole to a diameter of S2, where S2 is (D-0.5P+0.02mm) to (D-0.5P+0.05mm); S4 extrusion tapping processing: evenly brush tapping coolant on the extrusion tap, and complete the processing of small threaded holes in titanium alloy parts in one extrusion tapping.

2. The tapping method according to claim 1, wherein: The tapping coolant in step S4 is extreme pressure tapping oil.

3. The tapping method according to claim 1, wherein: In the step S4, the extrusion speed during the processing is 3 to 5 m / min.

4. The tapping method according to claim 1, wherein: Through the processing in step S4, the threaded hole fit is detected, and the specific value of S2 in step S3 is further determined to be within the range of (D-0.5P+0.02mm) to (D-0.5P+0.05mm).

5. The tapping method according to claim 4, wherein: When processing the M2 thread, the S2 is 1.84 mm.