A hole processing method for thermoplastic carbon fiber composite materials

Abstract

The present invention discloses a hole processing method for thermoplastic carbon fiber composite materials. The present invention processes the laminate in sequence from both sides by forward drilling and reverse drilling, and cools the laminate before drilling; then uses ultrasound to vibrate the tool to expand the hole; then, according to the different angles between the drilling direction of the drill bit drilling position and the direction of fiber extension into the hole at the drilling position, the hole wall is divided into a fiber-cutting type and a fiber-cutting type area along the circumferential direction, and a laser is used to process the burr defects in the fiber-cutting type area, and an ultrasonic-assisted surface plastic repair technology is used to process the tearing defects in the fiber-cutting type area. The present invention optimizes the hole processing process of thermoplastic carbon fiber composite laminates, avoids the occurrence of delamination, and solves the problems of burrs and tearing defects on the hole wall.

Description

Technical Field

[0001] The present invention belongs to the technical field of hole processing, and in particular relates to a high-precision hole processing method for thermoplastic carbon fiber composite materials. Background Art

[0002] Thermoplastic carbon fiber composites are a type of high-performance engineering plastics that are widely used in aerospace, automotive, medical, and electronic fields due to their excellent mechanical properties, high temperature resistance, and chemical corrosion resistance. However, their hole processing process faces many challenges. First, the laminated structure of thermoplastic carbon fiber composites may cause interlayer separation at the hole exit position due to different interlayer bonding strengths during processing, resulting in delamination. Secondly, during the hole making process, due to the difference between the fiber direction of the carbon fiber and the drilling direction, different defects will be produced on the hole wall, and this situation is not taken into account in the existing hole making process. Therefore, a high-precision hole processing method for thermoplastic carbon fiber composites is needed to solve the above problems. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a high-precision hole machining method for thermoplastic carbon fiber composite materials.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention provides a hole processing method for thermoplastic carbon fiber composite materials, which is specifically as follows:

[0006] Step 1: Place a laminate made of thermoplastic carbon fiber composite material into liquid nitrogen for cooling treatment, wait for a preset time after taking out the laminate, use a drill bit to drill forward at the processing position on one side of the laminate to a depth remaining a preset depth, then place the laminate into liquid nitrogen again for cooling treatment, wait for a preset time after taking out the laminate, and use a drill bit to drill backward at the processing position on the other side of the laminate until it is drilled through; wherein, the direction of the drill bit is the same during forward drilling and reverse drilling.

[0007] Step 2: Use ultrasonic waves to vibrate the tool and expand the hole.

[0008] Step 3. According to the different angles θ between the drilling direction of the drill bit drilling position and the direction of fiber extension into the hole at the drilling position, the hole wall is divided into two areas along the circumferential direction: a fiber cutting area and a reverse fiber cutting area. According to the different angles θ between the drilling direction of the drill bit drilling position and the fiber direction, the hole wall at the junction of the two areas is divided into a fiber shear separation type position and a fiber squeezing and pushing separation type position.

[0009] Step 4: Use laser to process the burr defects in the fiber cutting area.

[0010] Step 5: Use ultrasonic vibration superimposed static pressure processing technology to treat the tearing defects in the reverse fiber cutting area.

[0011] Preferably, during the hole expansion process, the ultrasonic generator causes the tool to vibrate. As the tool vibrates and feeds, the abrasive particles on the tool produce a cutting action on the hole wall, grinding the hole wall. At the same time, grinding fluid is continuously supplied to the processing area to reduce cutting heat and remove particles generated by grinding.

[0012] Preferably, the angle between the drilling direction of the drill bit drilling position in the fiber cutting type area and the direction of the fiber extending into the hole at the drilling position is 0°<θ<90°, the angle between the drilling direction of the drill bit drilling position in the reverse fiber cutting type area and the direction of the fiber extending into the hole at the drilling position is 90°<θ<180°, the angle between the drilling direction of the drill bit drilling position at the fiber shearing separation type position and the fiber direction is 90°, and the angle between the drilling direction of the drill bit drilling position at the fiber squeezing and pushing separation type position and the fiber direction is 0° or 180°.

[0013] Preferably, the burr defect processing process in step four is: using a laser parallel to the hole axis, the laser is scanned multiple times along the hole wall in the fiber cutting area, and each time the laser scans, the burrs in the fiber cutting area and a layer of thermoplastic carbon fiber composite material on the hole wall are melted onto the hole wall, and after each scan is completed, the preset time is waited for three seconds before the next scan is performed to allow the thermoplastic carbon fiber composite material melted onto the hole wall to cool.

[0014] Preferably, the tearing defect processing process in step five is: using a spherical titanium alloy tool head to apply a preset pressure to the hole wall, rotating the spherical titanium alloy tool head under a preset feed speed condition, and performing a Z-shaped reciprocating motion along the hole wall along the hole axis direction in the reverse fiber cutting area, and at the same time, the spherical titanium alloy tool head generates vibration along the normal direction of the hole wall through an ultrasonic generator, wherein the spherical titanium alloy tool head produces an extrusion effect on the hole wall through ultrasonic vibration and static pressure, causing plastic deformation of the thermoplastic carbon fiber composite material on the surface of the hole wall, and the plastic flow generated during the processing causes the "valley" on the hole wall surface to be filled with "peaks", thereby eliminating the tearing defect.

[0015] The present invention has the following beneficial effects:

[0016] 1. The present invention optimizes the hole processing process of thermoplastic carbon fiber composite laminates, avoids the occurrence of delamination, and solves the problems of burrs and tearing defects on the hole wall; specifically, the present invention adopts a bidirectional drilling method, and processes the laminate in sequence from both sides through forward drilling and reverse drilling, so that the middle layer of the laminate is used as the exit layer of the processing hole during reverse drilling, and the adjacent layer below the middle layer supports the middle layer, so that the pulling ability of the drilling position on the middle layer on other positions of the same layer is reduced, and the laminate is cooled before drilling, so that the brittleness of the laminate is increased, the fracture is more crisp, and the occurrence of delamination defects is avoided. ; Further, the present invention divides the hole wall into a fiber-cutting type area and an anti-fiber-cutting type area according to the difference between the drilling direction of the drilling position and the angle between the fiber extension direction of the drilling position and the hole. In view of the fact that burr defects mainly exist in the fiber-cutting type area and tear defects mainly exist in the anti-fiber-cutting type area, laser is used to process the burr defects in the fiber-cutting type area to remove the burr defects. Ultrasonic-assisted surface plastic repair technology is used to process the tear defects in the anti-fiber-cutting type area using a processing technology of ultrasonic vibration superimposed static pressure, thereby improving the surface quality of the hole wall and reducing the degree of damage to the material. It can be seen that the present invention adopts a combination of multiple processes to process the thermoplastic carbon fiber composite laminate, effectively improving the processing accuracy, surface quality and mechanical properties of the hole, and selecting a targeted surface smoothing process for processing different surface defects in different surface areas of the hole wall, thereby improving the processing efficiency while ensuring the surface quality of the hole wall (not requiring all surface smoothing processes to process the entire hole wall).

[0017] 2. In the present invention, when cooling the laminate, the cooling time is controlled. The cooling time is short, the temperature conduction to the inside of the material is insufficient, and the temperature inside the material decreases slowly, thereby avoiding the generation of residual stress and pores inside the material caused by rapid cooling. This further avoids the occurrence of microcracks on the hole wall surface caused by residual stress during drilling, as well as delamination or interface debonding inside the laminate, thereby ensuring processing quality.

[0018] 3. When the present invention uses laser to process burr defects, the laser scans along the hole wall multiple times in the fiber cutting area without damaging the internal structure of the hole wall. During each scan, the laser melts a layer of thermoplastic carbon fiber composite material on the hole wall in the fiber cutting area onto the hole wall in the fiber cutting area to form a dense protective layer, thereby improving the quality of the hole wall in the fiber cutting area and enhancing the wear resistance and corrosion resistance of the hole wall in the fiber cutting area.

[0019] 4. When the present invention uses ultrasonic vibration superimposed on static pressure to treat tearing defects, the spherical titanium alloy tool head produces an extrusion effect on the hole wall in the inverse fiber cutting area through ultrasonic vibration superimposed on static pressure, causing plastic deformation of the hole wall surface material in the inverse fiber cutting area, and the plastic flow generated during the processing causes the "valleys" on the hole wall surface in the inverse fiber cutting area to be filled with "peaks", thereby eliminating the tearing defects, improving the surface roughness of the hole wall in the inverse fiber cutting area, and improving the smoothness and surface quality of the hole wall in the inverse fiber cutting area. At the same time, ultrasonic vibration helps to improve the residual stress state of the hole wall in the inverse fiber cutting area, and improve the fatigue strength, wear resistance and corrosion resistance of the hole wall in the inverse fiber cutting area. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the division of the area on the hole wall after drilling. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] The present invention provides a hole processing method for thermoplastic carbon fiber composite materials, which is specifically as follows:

[0023] Step 1: Place the laminate made of thermoplastic carbon fiber composite material in liquid nitrogen for cooling treatment, wait for 40s to 45s, take out the laminate, use a drill bit to drill forward at the processing position on one side of the laminate to a depth of 3.0mm, then place the laminate again in liquid nitrogen for cooling treatment, wait for 35s to 40s, take out the laminate, and use a drill bit to drill backward at the processing position on the other side of the laminate until it is drilled through. Among them, the direction of the drill bit is the same during forward drilling and reverse drilling. During reverse drilling, the middle layer of the laminate is used as the exit layer of the processing hole, and the adjacent layer below the middle layer supports the middle layer, so that the pulling ability of the drilling position on the middle layer on other positions of the same layer is reduced. At the same time, by cooling the laminate, the brittleness of the laminate is increased, and the fracture is more crisp, thereby avoiding the occurrence of delamination defects; in addition, if long-term and rapid cooling is adopted, residual stress will be generated inside, which will cause microcracks on the surface of the hole wall during drilling and delamination or interface debonding inside the laminate, and rapid cooling will also trigger pore generation during the thermal expansion and contraction of the material. The present invention uses a cooling time of 35s to 45s, which is short. The temperature conduction to the inside of the material is insufficient, and the temperature inside the material drops relatively slowly, thereby avoiding the generation of residual stress and pores, thereby avoiding the occurrence of microcracks on the surface of the hole wall and delamination or interface debonding inside the laminate due to residual stress during drilling. In this embodiment, the laminate material is CF / PEEK composite material.

[0024] Step 2: Use ultrasonic waves to vibrate the tool and expand the hole. During the expansion process, the ultrasonic generator causes the tool to vibrate. As the tool vibrates and feeds, the abrasive particles on the tool produce a cutting effect on the hole wall, grinding the hole wall. At the same time, grinding fluid is continuously supplied to the processing area to reduce cutting heat and remove particles generated by grinding.

[0025] Step 3: Figure 1 As shown in the figure, although the ultrasonic grinding in step 2 has been carried out, there are still surface defects on the hole wall, mainly burrs and tears, and the surface defects are closely related to the area where the hole wall is located. According to the different angles θ between the drilling direction of the drill bit drilling position and the direction of fiber extension into the hole at the drilling position, the hole wall is divided into two areas along the circumferential direction: the fiber cutting type area and the anti-fiber cutting type area. According to the different angles between the drilling direction of the drill bit drilling position and the fiber direction, the hole wall at the intersection of the two areas is divided into a fiber shear separation type area and a fiber squeeze separation type area. The angle between the drilling direction of the drill bit drilling position in the fiber cutting type area and the direction of fiber extension into the hole at the drilling position is 0°<θ<90°. The angle between the drilling direction of the drill bit drilling position in the reverse fiber cutting area and the direction of the fiber extending into the hole at the drilling position is 90°<θ<180°, the angle between the drilling direction of the drill bit drilling position at the fiber shear separation position and the fiber direction is 90°, and the angle between the drilling direction of the drill bit drilling position at the fiber squeezing and pushing separation position and the fiber direction is 0° or 180°; among them, for the fiber shear separation position and the fiber squeezing and pushing separation position, the range of these two positions is smaller and the defects are fewer, so these two positions are not processed.

[0026] Step 4. For the fiber cutting area, the main defect in this area is burrs. The burr defects in this area are processed by laser. The burr defect processing process is: use a laser parallel to the hole axis to scan the laser along the hole wall multiple times in the fiber cutting area. During each scan, the laser melts the burrs in the fiber cutting area and a thin layer of thermoplastic carbon fiber composite material on the hole wall onto the hole wall, forming a dense protective layer on the hole wall, improving the smoothness and surface quality of the hole wall, and improving the wear resistance and corrosion resistance of the hole wall. After each scan is completed, wait for 0.5 seconds before performing the next scan to allow the thermoplastic carbon fiber composite material melted on the hole wall to cool. In this embodiment, the laser pulse power is 70W, the pulse width is 15ns, the laser frequency is 15kHz, the spot diameter is 50μm, the laser scanning speed is 0.3mm / s, and the laser wavelength is 1060nm~1078nm. For lasers in this wavelength range, the carbon fiber material has a relatively strong absorption capacity, while the PEEK matrix material has a relatively weak absorption capacity. The laser only scans along the hole wall and does not affect the material inside the hole wall. Each fiber cutting area is scanned 3 to 5 times.

[0027] Step 5. For the inverse fiber cutting area, the main defect in this area is tearing. Ultrasonic-assisted surface plastic repair technology is used, and the tearing defect is treated by using ultrasonic vibration superimposed static pressure processing technology. The tearing defect treatment process is as follows: a spherical titanium alloy tool head with a diameter of 3 mm is used to apply a pressure of 20 N to the hole wall, so that the spherical titanium alloy tool head rotates and performs a Z-shaped reciprocating motion along the hole axis along the hole wall in the inverse fiber cutting area. The feed speed of the spherical titanium alloy tool head is 0.2 mm / s. At the same time, the spherical titanium alloy tool head generates vibration along the normal direction of the hole wall through an ultrasonic generator. The spherical titanium alloy tool head uses ultrasonic vibration superimposed static pressure to squeeze the hole wall, causing plastic deformation of the hole wall surface material, and the plastic flow generated during the processing causes the "valley" on the hole wall surface to be filled with "peaks", thereby eliminating the tearing defect, achieving the treatment of the tearing defect, and improving the smoothness and surface quality of the hole wall. At the same time, ultrasonic vibration helps to improve the residual stress state of the hole wall, and improve the fatigue strength, wear resistance and corrosion resistance of the hole wall. In this embodiment, the ultrasonic frequency is 20 kHz and the amplitude is 5 μm.

Claims

1. A method for machining holes in thermoplastic carbon fiber composite materials, characterized by: Step 1: Place a laminate made of thermoplastic carbon fiber composite material in liquid nitrogen for cooling treatment, wait for a preset time after taking out the laminate, use a drill bit to forward drill a hole at a processing position on one side of the laminate to a depth remaining a preset depth, then place the laminate in liquid nitrogen again for cooling treatment, wait for a preset time after taking out the laminate, and use a drill bit to reverse drill a hole at a processing position on the other side of the laminate until it is drilled through; wherein, the direction of the drill bit is the same during forward drilling and reverse drilling; Step 2: Use ultrasonic waves to vibrate the tool and expand the hole; Step 3: Divide the hole wall into two regions along the circumferential direction: a fiber cutting region and a fiber cutting region, based on the difference in angle θ between the drilling direction of the drill bit and the direction of fiber extension into the hole. Furthermore, based on the difference in angle θ between the drilling direction of the drill bit and the fiber direction, the hole wall is divided at the junction of the two regions into a fiber shear separation region and a fiber squeeze and push separation region. Step 4: Use laser to treat the burr defects in the fiber cutting area; Step 5: Use ultrasonic vibration superimposed static pressure processing technology to treat the tearing defects in the reverse fiber cutting area.

2. The hole processing method for thermoplastic carbon fiber composite material according to claim 1, characterized in that: During the hole expansion process, the ultrasonic generator causes the tool to vibrate. As the tool vibrates and feeds, the abrasive particles on the tool produce a cutting effect on the hole wall, grinding the hole wall. At the same time, grinding fluid is continuously supplied to the processing area to reduce cutting heat and remove particles generated by grinding.

3. The hole processing method for thermoplastic carbon fiber composite material according to claim 1, characterized in that: The angle between the drilling direction of the drill bit drilling position in the fiber cutting type area and the direction of the fiber extending into the hole at the drilling position is 0°<θ<90°, the angle between the drilling direction of the drill bit drilling position in the reverse fiber cutting type area and the direction of the fiber extending into the hole at the drilling position is 90°<θ<180°, the angle between the drilling direction of the drill bit drilling position at the fiber shearing separation type position and the fiber direction is 90°, and the angle between the drilling direction of the drill bit drilling position at the fiber squeezing and pushing separation type position and the fiber direction is 0° or 180°.

4. The hole machining method for thermoplastic carbon fiber composite material according to claim 1, characterized in that: The burr defect processing process in step four is as follows: using a laser parallel to the hole axis, the laser is scanned multiple times along the hole wall in the fiber cutting area. During each scan, the laser melts the burrs in the fiber cutting area and a layer of thermoplastic carbon fiber composite material on the hole wall onto the hole wall. After each scan is completed, the laser waits for a preset time of three before performing the next scan to allow the thermoplastic carbon fiber composite material melted on the hole wall to cool.

5. The hole machining method for thermoplastic carbon fiber composite material according to claim 1, characterized in that: The tearing defect treatment process in step five is as follows: a spherical titanium alloy tool head is used to apply a preset pressure to the hole wall, and under a preset feed speed condition, the spherical titanium alloy tool head is rotated and performs a Z-shaped reciprocating motion along the hole wall in the direction of the hole axis in the reverse fiber cutting area. At the same time, the spherical titanium alloy tool head generates vibration along the normal direction of the hole wall through an ultrasonic generator, wherein the spherical titanium alloy tool head exerts an extrusion effect on the hole wall through the superimposed static pressure of ultrasonic vibration, causing the thermoplastic carbon fiber composite material on the surface of the hole wall to produce plastic deformation, thereby eliminating the tearing defect.

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