Hole machining method for thermoplastic carbon fiber composite material

Abstract

The invention discloses a hole machining method for a thermoplastic carbon fiber composite material. According to the method, machining is sequentially conducted from the two sides of the laminated plate through the forward drilling holes and the reverse drilling holes, and the laminated plate is cooled before drilling; then, the cutter is vibrated through ultrasonic waves, and hole expanding machining is conducted on the hole; secondly, according to different included angles between the drilling direction of the drilling position of the drill bit and the extending direction of fibers in the drilling position towards the interior of the hole, the hole wall is divided into a forward fiber cutting type area and a reverse fiber cutting type area in the circumferential direction, and laser is adopted for treating the burr defect of the forward fiber cutting type area; and the tearing defect of the reverse fiber cutting type area is treated by adopting an ultrasonic-assisted surface plasticity repair technology. According to the method, the hole machining process of the thermoplastic carbon fiber composite material laminated plate is optimized, the layering phenomenon is avoided, and the problems of burrs and tearing defects on the hole wall are solved.

Description

Technical Field

[0001] The 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 and stratification at the hole exit position due to different interlayer bonding strengths during processing. 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 occur 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 prior art and to provide 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 material, which is specifically as follows:

[0006] Step 1, placing a laminate made of thermoplastic carbon fiber composite material into liquid nitrogen for cooling treatment, taking out the laminate after waiting for a preset time, using a drill bit to forward drill at a processing position on one side of the laminate to a depth of a remaining preset depth, and then placing the laminate into liquid nitrogen again for cooling treatment, waiting for a preset time 2, taking out the laminate, and using a drill bit to reverse drill 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.

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

[0008] Step three, according to the different angles θ between the drilling direction of the drill bit drilling position and the fiber extension direction 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 fiber cutting area against the fiber cutting area; and 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 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 to grind 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 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 type area and the direction of fiber extension into the hole 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: use a laser parallel to the hole axis to scan the laser along the hole wall multiple times in the fiber cutting area, and 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, and after each scan is completed, wait for a preset time of three before performing the next scan, so that the thermoplastic carbon fiber composite material melted on the hole wall can cool down.

[0014] Preferably, the tear defect processing process in step five is: use a spherical titanium alloy tool head to apply a preset pressure to the hole wall, rotate the spherical titanium alloy tool head under a preset feed speed condition, and perform 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 vibrations 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 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 "valleys" on the surface of the hole wall to be filled with "peaks", thereby eliminating the tear 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 from both sides of the laminate in sequence 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 to 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 a reverse 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 fiber cutting type area. In view of the fact that the burr defects mainly exist in the fiber cutting type area and the tearing defects mainly exist in the reverse fiber cutting type area, the burr defects in the fiber cutting type area are processed by laser to remove the burr defects. The ultrasonic-assisted surface plastic repair technology is used to process the tearing defects in the reverse fiber cutting type area using the processing technology of ultrasonic vibration superimposed static pressure to remove the tearing defects, 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 uses a combination of multiple processes to process the holes of the thermoplastic carbon fiber composite laminate, effectively improving the processing accuracy, surface quality and mechanical properties of the holes, and selecting a targeted surface smoothing process for processing different surface defects in different surface areas of the hole wall, while ensuring the surface quality of the hole wall, the processing efficiency is improved (not all surface smoothing processes are required 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. It 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 the 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 the tearing defect, 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 defect, 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 is further described below in conjunction with the accompanying drawings.

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

[0023] Step 1: Place the laminate made of thermoplastic carbon fiber composite material into liquid nitrogen for cooling treatment, wait for 40s to 45s before taking out the laminate, use a drill to forward drill at the processing position on one side of the laminate to a depth of 3.0 mm, then place the laminate into liquid nitrogen again for cooling treatment, wait for 35s to 40s before taking out the laminate, and use a drill to reverse drill 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 to other positions of the same layer is reduced. At the same time, through the cooling treatment of 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 a long time 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 of the laminate inside, and rapid cooling will also induce 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, and the temperature conduction to the inside of the material is insufficient. The temperature inside the material decreases relatively slowly, thereby avoiding the generation of residual stress and pores, thereby avoiding the occurrence of microcracks on the surface of the hole wall caused by residual stress and delamination or interface debonding of the laminate inside. In this embodiment, the laminate material is CF / PEEK composite material.

[0024] Step 2: Use ultrasound to vibrate the tool to 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 to grind 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, although the ultrasonic grinding in step 2 has been performed, 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 the fiber extending 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 fiber cutting type area, and according to the different angles between the drilling direction of the drill bit drilling position and the fiber direction, the intersection of the hole wall and the two areas is divided into a fiber shear separation type position and a fiber squeeze separation type position; 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 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 less, 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, 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. The carbon fiber material has a relatively strong absorption capacity for lasers in this wavelength range, 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 reverse 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: 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 wall along the hole axis in the reverse 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 vibrations along the normal direction of the hole wall through an ultrasonic generator. The spherical titanium alloy tool head exerts an extrusion effect on the hole wall through ultrasonic vibration superimposed static pressure, 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 hole processing method for thermoplastic carbon fiber composite material, characterized in that: Step 1, placing a laminate made of a thermoplastic carbon fiber composite material into liquid nitrogen for cooling treatment, taking out the laminate after waiting for a preset time, using a drill bit to forward drill a hole at a processing position on one side of the laminate to a depth of a remaining preset depth, and then placing the laminate into liquid nitrogen again for cooling treatment, taking out the laminate after waiting for a preset time 2, and using a drill bit to reversely 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: According to the difference in angle θ between the drilling direction of the drill bit drilling position and the fiber extension direction into the hole at the drilling position, the hole wall is divided into two areas along the circumferential direction: a fiber cutting type area and a fiber cutting type area against the fiber, and according to the difference in angle between the drilling direction of the drill bit drilling position and the fiber direction, the hole wall is divided into a fiber shear separation type area and a fiber squeeze separation type area at the junction of the two areas; Step 4: Use laser to process 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. A 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 to grind 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 processing method for thermoplastic carbon fiber composite material according to claim 1, characterized in that: The burr defect processing process in step 4 is as follows: 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 layer of thermoplastic carbon fiber composite material on the hole wall onto the hole wall. After each scan is completed, wait for a preset time of three before performing the next scan to allow the thermoplastic carbon fiber composite material melted onto the hole wall to cool.

5. The hole processing method for thermoplastic carbon fiber composite material according to claim 1, characterized in that: The tear defect processing process in step five is as follows: use a spherical titanium alloy tool head to apply a preset pressure to the hole wall, rotate the spherical titanium alloy tool head under a preset feed speed condition, and perform 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 vibrations 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 ultrasonic vibration and superimposed static pressure, causing plastic deformation of the thermoplastic carbon fiber composite material on the surface of the hole wall, thereby eliminating the tear defect.

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