Internal thread machining method suitable for TiA1 alloy

Abstract

The invention discloses an internal thread machining method for TiA1 alloy. The method comprises the specific steps of prefabricating a hole, determining grinding process parameters, determining the size of a grinding wheel, positioning a workpiece and machining an internal thread. Holes are formed in advance before grinding machining, cracks caused by stress concentration are avoided, the machining efficiency is improved while abrasion of the grinding wheel is reduced, in addition, when the threaded hole is machined, the grinding wheel is parallel to the axis of the threaded hole, a certain distance is kept between the grinding wheel and the axis of the threaded hole, and the situation that the grinding wheel is damaged when the deep threaded hole is machined can be avoided. The grinding wheel cutter bar collides with the upper surface of the threaded hole.

Description

Technical Field

[0001] The present invention relates to the field of mechanical processing technology, and in particular to a method for processing internal threads on TiΑ1 alloy intermetallic compound materials. Background Art

[0002] TiΑl intermetallic compound has both heat resistance and light weight, and its density is less than 1 / 2 of nickel-based high-temperature alloy (TiΑl density is 3.9~4.2, nickel-based high-temperature alloy is 7.8~9.2). It is internationally recognized as an ideal material for manufacturing hot end components such as aircraft engine rotor blades above 600°C.

[0003] However, as a typical intermetallic compound, TiAl alloy has high room temperature strength, low plasticity, high brittleness, poor processing performance, and the TiAl alloy lamellar structure has significant anisotropy, so its processing performance is more complicated. It has been found in practice that when using traditional turning and milling to process internal threads of TiAl alloy, broken teeth, cracks, chipping and tool edge breakage always occur, which seriously affect its processing quality and efficiency.

[0004] At present, there is no research on the relevant methods for internal thread processing of TiΑl alloy. Therefore, exploring a method for internal thread processing suitable for TiΑl alloy is of great significance for its wide application in engineering. Summary of the invention

[0005] The purpose of the present invention is to provide an internal thread processing method suitable for TiA1 alloy.

[0006] To achieve the above object, the technical solution of the present invention is: a method for processing internal threads of TiA1 alloy, comprising the following steps:

[0007] Step 1: pre-process a prefabricated hole where the thread needs to be processed, the diameter of the prefabricated hole is smaller than the minor diameter of the internal thread, and the depth is smaller than the depth of the internal thread;

[0008] Step 2: Determine the internal thread minor diameter, major diameter, pitch, number of teeth and machining accuracy;

[0009] Step 3: Determine the grinding wheel size;

[0010] Step 4: Make the axis of the grinding wheel parallel to the axis of the internal threaded hole and maintain a certain horizontal distance to process the internal thread. During the grinding process, the diameter of the grinding wheel changes due to the wear of the grinding wheel. According to the wear amount of the grinding wheel, readjust the horizontal distance between the axis of the grinding wheel and the axis of the threaded hole to the original position, or replace the grinding wheel.

[0011] Preferably, an electric spark punching machine is used to pre-process a small hole where the internal thread needs to be processed. The diameter of the pre-processed hole is 0.7-0.8 times the minor diameter of the internal thread, and the depth is 0.9 times the depth of the internal thread.

[0012] Preferably, the grinding wheel uses a diamond grinding wheel or a diamond wheel.

[0013] Preferably, the grinding wheel diameter is greater than twice the internal thread depth and smaller than the minor diameter of the internal thread.

[0014] Preferably, the axis of the grinding wheel is parallel to the axis of the internal thread hole and maintains a certain horizontal distance, which is half of the difference between the major diameter of the internal thread and the maximum diameter of the grinding wheel.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The present invention is not only applicable to TiAl alloy materials, but also applicable to the internal thread processing problems of other brittle and quasi-brittle metal materials.

[0017] 2. The present invention adopts a grinding processing method to avoid problems such as broken teeth and cracks during turning and milling.

[0018] 3. Before grinding, pre-holes are made to avoid cracks caused by stress concentration, which reduces grinding wheel wear and improves processing efficiency.

[0019] 4. When processing the threaded hole, the grinding wheel is parallel to the axis of the threaded hole and a certain distance is maintained, which can avoid the grinding wheel cutter bar from rubbing against the upper surface of the threaded hole when processing a deeper threaded hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of TiAl alloy internal thread hole processing.

[0021] Figure 2 This is a flow chart of the TiAl alloy internal thread hole processing method.

[0022] Figure 3 The figures are comparisons of internal thread holes processed by milling and by the method of the present invention, wherein (a) is processed by milling; (b) and (c) are the internal thread morphologies processed by the present invention. DETAILED DESCRIPTION

[0023] As a new type of high-temperature resistant material, TiΑ1 alloy has broad application prospects in aerospace due to its excellent mechanical properties. However, as a typical intermetallic compound, its processing performance is not ideal. When processing TiΑ1 alloy internal threads by traditional turning or milling, processing defects such as broken teeth, cracks, and collapse often occur, which seriously affect the processing quality and efficiency of the threads. In this regard, the present invention proposes to process TiΑ1 alloy internal threads by prefabricated holes and grinding.

[0024] The general idea of ​​the present invention is: first, a small hole of a certain depth and diameter is pre-processed by an electric spark puncher at the place where the workpiece needs to be tapped, so as to reduce the stress concentration in the place and avoid the occurrence of large cracks during the subsequent grinding process. In addition, a part of the material is reduced at the prefabricated hole, which reduces the friction contact area between the grinding head and the workpiece, while reducing the wear of the grinding tool and improving the processing efficiency. Afterwards, a diamond grinding wheel is used to process the internal thread, so that the axis of the grinding wheel is parallel to the axis of the threaded hole and a certain horizontal distance is maintained. By adjusting the rotation speed of the grinding wheel, the feed speed and the rotation speed of the workpiece, the pitch of the thread meets the requirements.

[0025] Example

[0026] Combination Figure 1 and Figure 2 For example, when machining an M4 internal thread with a depth of 6mm on TiAl alloy, the major diameter of the internal thread is 4mm, the pitch is 0.7mm, and the minor diameter is 3.55mm. First, a prefabricated hole is pre-machined by electric spark where the thread needs to be machined. The diameter of the prefabricated hole is 0.7 times the minor diameter of the internal thread, that is, 2.48mm, and the depth is 0.9 times the depth of the internal thread, that is, 5.4mm. Due to the high hardness of TiAl alloy, a diamond diamond grinding wheel with a grinding wheel diameter of 2mm is used. Then, clamp the workpiece on the chuck clamp on the grinder, install the grinding wheel, make the axis of the grinding wheel parallel to the axis of the internal threaded hole, and maintain a horizontal distance of 1mm, start processing the internal thread, the grinding wheel rotates around its own axis at high speed, and at the same time makes a linear feed along its own axis, the chuck and the workpiece rotate slowly, during the grinding process, the grinding wheel is worn and the diameter of the grinding wheel changes, but because the hole is small and shallow, when grinding to half the hole depth, adjust the horizontal distance between the grinding wheel axis and the threaded hole axis to restore to the original position.

[0027] Figure 3 The comparison diagram of the internal threaded hole processed by the milling method and the internal threaded hole processed by the present invention shows that the conventional milling method is not suitable for the internal thread processing of TiAl alloy, and obvious cracking will occur. However, by the method proposed by the present invention, the threaded hole has no cracks and the thread teeth are smooth.

Claims

1. A method for processing internal threads of TiA1 alloy, characterized in that: The steps include: Step 1: pre-process a prefabricated hole where the thread needs to be processed, the diameter of the prefabricated hole is smaller than the minor diameter of the internal thread, and the depth is smaller than the depth of the internal thread; Step 2: Determine the internal thread minor diameter, major diameter, pitch, number of teeth and machining accuracy; Step 3: Determine the grinding wheel size; Step 4: Make the axis of the grinding wheel parallel to the axis of the internal threaded hole and maintain a certain horizontal distance to process the internal thread. During the grinding process, the diameter of the grinding wheel changes due to the wear of the grinding wheel. According to the wear amount of the grinding wheel, readjust the horizontal distance between the axis of the grinding wheel and the axis of the threaded hole to the original position, or replace the grinding wheel.

2. The method according to claim 1, characterized in that Use an electric spark puncher to pre-process a small hole where the internal thread needs to be processed. The diameter of the pre-made hole is 0.7-0.8 times the minor diameter of the internal thread, and the depth is 0.9 times the depth of the internal thread.

3. The method according to claim 1, characterized in that The grinding wheel uses a diamond grinding wheel or a diamond wheel.

4. The method according to claim 1, characterized in that The grinding wheel diameter is greater than 2 times the internal thread depth and smaller than the minor diameter of the internal thread.

5. The method according to claim 1, characterized in that The axis of the grinding wheel is parallel to the axis of the internal thread hole and maintains a certain horizontal distance, which is half of the difference between the major diameter of the internal thread and the maximum diameter of the grinding wheel.

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