A cold drilling auxiliary device for thermoplastic materials and a working method thereof

Abstract

The present invention discloses a cold drilling auxiliary device for thermoplastic materials and its working method. In the present invention, the top cover is detachably fixed to an opening of the bin body, the cooling pipeline is fixed to the inner wall of the bin body, the outlet pipe of the temperature compensation bin is fixed to the bin body, the inlet pipe fixed to the cooling pipeline entrance passes through the outlet pipe, enters the temperature compensation bin, and passes through the inlet pipe of the temperature compensation bin, and the outlet pipe fixed to the cooling pipeline outlet passes through the hole of the bin body, and the outlet pipe and the inlet pipe are respectively connected to the inlet and outlet of the liquid nitrogen machine; a compensation thermal resistor is fixed in the temperature compensation bin, the workpiece clamping device and the workpiece translation device are both arranged in the inner circulation bin, the synchronous lifting mechanism of the workpiece clamping device drives the two U-shaped clamping plates to rise and fall synchronously, and the horizontal translation mechanism of the workpiece translation device drives the drilling base plate located below the U-shaped clamping plate to translate. The present invention can realize a low-temperature environment, and can also realize auxiliary drilling processing of thermoplastic materials in different low-temperature environments.

Description

Technical Field

[0001] The invention belongs to the technical field of automated processing of thermoplastic materials, and in particular relates to a cold drilling auxiliary device for thermoplastic materials and a working method thereof. Background Art

[0002] Thermoplastic materials have the characteristics of high specific strength, high specific modulus, easy molding, non-toxic and environmentally friendly, and have been widely used in the aviation field. Thermoplastic materials have the characteristics of softening when heated and hardening when cooled, and this characteristic can be repeated without chemical changes. Thermoplastic workpieces usually need to be fixed by riveting and screwing, and among the current methods of mechanical processing, drilling is the most widely used. Drilling research for various processing conditions is an important research method, but under the drilling conditions of thermoplastic materials, the drilling heat generated during the drilling process can easily cause deformation at the position of the processed hole, affecting the fixing effect of riveting or screwing. The existing research cost of drilling processing technology for thermoplastic workpieces in low temperature environments is high, the implementation steps are cumbersome, it is difficult to maintain a low temperature environment for drilling, and there are few auxiliary devices that can realize the drilling processing of thermoplastic workpieces in low temperature environments. Therefore, a simple operation method is continued, and an auxiliary device that can assist in the drilling processing of thermoplastic workpieces in low temperature environments is provided. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a cold drilling auxiliary device for thermoplastic materials and a working method thereof.

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

[0005] The invention discloses a cold drilling auxiliary device for thermoplastic materials, comprising a low-temperature control chamber, a workpiece clamping device and a workpiece translation device.

[0006] The low-temperature control chamber includes an internal circulation chamber, a temperature compensation chamber, and a cooling pipeline. The internal circulation chamber includes a chamber body and a top cover. An opening is provided at the upper end of the chamber body. The top cover is detachably fixed to the opening, and a circular hole is provided on the top cover. A temperature sensor is fixed on the inner wall of the chamber body. An outlet pipe integrally formed on the temperature compensation chamber is fixed and connected to the chamber body, and a compensating thermal resistor is fixed inside the temperature compensation chamber. The cooling pipeline is fixed on the inner wall of the chamber body, and the outlet of the cooling pipeline is fixed to the inlet of the outlet pipeline. The outlet of the outlet pipeline passes through the hole formed on the chamber body and is connected to the inlet of the liquid nitrogen machine. The inlet of the cooling pipeline is fixed to the outlet of the inlet pipeline. The inlet of the inlet pipeline passes through the outlet pipe, enters the temperature compensation chamber, and passes through the inlet pipe integrally formed on the temperature compensation chamber and is connected to the outlet of the liquid nitrogen machine. The outer walls of the internal circulation chamber and the temperature compensation chamber are coated with a thermal insulation coating. The workpiece clamping device and the workpiece translation device are both arranged in the inner circulation bin; the workpiece clamping device includes a synchronous lifting mechanism and a U-shaped clamping plate, the synchronous lifting mechanism drives two U-shaped clamping plates that are horizontally opposite and spaced apart to rise and fall synchronously, and the lower surfaces of the two U-shaped clamping plates are provided with stress plates; the workpiece translation device includes a drilling base plate and a horizontal translation mechanism, the horizontally arranged drilling base plate is arranged below the two U-shaped clamping plates, and is driven to move horizontally by the horizontal translation mechanism, and a second circular hole is opened in the middle of the drilling base plate.

[0007] Preferably, a second opening is provided on one side of the bin body, and a visual window is fixed on the second opening.

[0008] Preferably, the synchronous lifting mechanism includes a support frame, a transmission rod, a nut block and a screw. The horizontally arranged transmission rod and the bottom plate of the warehouse body form a rotating pair and are driven by a driving motor. Two integrally formed worm gears are provided at both ends of the transmission rod. Two symmetrically arranged support frames are fixed at both ends of the transmission rod in the warehouse body. Two vertically arranged screw gears and the two support frames respectively form a rotating pair, and a worm gear is fixed at the bottom end of each screw. The two worm gears are respectively engaged with the two worm gears. The two symmetrically arranged nut blocks respectively form a threaded pair with the two screws and form a sliding pair with the two support frames; two U-shaped clamping plates are respectively fixed to the two nut blocks.

[0009] More preferably, the housing of the driving motor 1 is fixed to the base plate, and the output shaft of the driving motor 1 is connected to the transmission rod 1 through the bevel gear pair 1.

[0010] More preferably, the horizontal translation mechanism includes a transmission rod 2, a worm gear 2, a screw 2 and a nut block 2. The transmission rod 2 parallel to the transmission rod 1 forms a rotating pair with the bottom plate of the warehouse body and is driven by the drive motor 2. Two integrally formed worm gears 2 are provided at both ends of the transmission rod 2. Two screw gears 2 horizontally parallel and perpendicular to the transmission rod 2 are arranged between the two support frames and are located at both ends of the transmission rod 2, and both form a rotating pair with the bottom plate. A worm gear 2 is fixed to one end of the two screw gears close to the transmission rod 2, and the two worm gears 2 are respectively engaged with the two worm gears 2. The two symmetrically arranged nut blocks 2 respectively form a threaded pair with the two screw gears 2, and respectively form a sliding pair with the two guide rods horizontally fixed in the warehouse body; the drilling base plate is arranged between the two support frames, and the two ends of the drilling base plate are fixed to the two nut blocks 2.

[0011] More preferably, the housing of the second drive motor is fixed to the base plate, and the output shaft of the second drive motor is connected to the second transmission rod through a second bevel gear pair.

[0012] The present invention provides a working method of a cold drilling auxiliary device for thermoplastic materials, which is specifically as follows:

[0013] Step 1: Install the tank body on the workbench of the drilling machine.

[0014] Step 2: Remove the top cover, place the thermoplastic workpiece on the drilling base plate, make the position of the hole to be drilled on the thermoplastic workpiece be located at the second position of the circular hole, and install the top cover to its original position; then the horizontal translation mechanism drives the drilling base plate to drive the thermoplastic workpiece to translate, so that the thermoplastic workpiece is translated to directly below the two U-shaped clamping plates; then the synchronous lifting mechanism drives the two U-shaped clamping plates to move downward synchronously, so that the two U-shaped clamping plates contact the thermoplastic workpiece, clamp the thermoplastic workpiece with the drilling base plate, and each stress sheet detects that the positive pressure of the corresponding U-shaped clamping plate on the thermoplastic workpiece is within the preset pressure range, thereby completing the clamping of the thermoplastic workpiece.

[0015] Step 3. Open the inlet and outlet of the liquid nitrogen machine, and the hydraulic pump on the liquid nitrogen machine transports the liquid nitrogen from the liquid nitrogen machine through the inlet pipeline to the cooling pipeline, and from the cooling pipeline through the outlet pipeline and the heat exchanger back to the liquid nitrogen machine. At the same time, the thermal compensation resistor is heated to heat the liquid nitrogen in the inlet pipeline of the temperature compensation bin, so that the temperature of the liquid nitrogen entering the cooling pipeline changes to a preset temperature, and the liquid nitrogen in the cooling pipeline exchanges heat with the air in the bin body, thereby lowering the temperature inside the bin body to the preset temperature; then the drilling machine drives the drill bit to move, so that the drill bit enters the bin body from the circular hole 1, and drills the position to be drilled of the thermoplastic material workpiece.

[0016] Step 4. After the drilling work is completed, the drilling machine drives the drill bit to move to its original position, the hydraulic pump on the liquid nitrogen machine stops working, the thermal compensation resistor stops heating, and the top cover is removed. Then the synchronous lifting mechanism drives the two U-shaped clamping plates to move up to the initial position synchronously, and then the horizontal translation mechanism drives the drilling substrate to drive the thermoplastic workpiece to move horizontally, so that the drilling substrate moves horizontally to the initial position, the thermoplastic workpiece that has completed the drilling process is taken out, and the top cover is installed to its original position, thereby completing the drilling work of the thermoplastic workpiece.

[0017] Preferably, the preset pressure range is obtained through a drilling experiment, the process being:

[0018] S1. The U-shaped clamping plate exerts a positive pressure perpendicular to the surface of the thermoplastic workpiece on the thermoplastic workpiece. The positive pressure is the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece. The clamping stress failure equation of the thermoplastic workpiece during non-drilling processing is:

[0019]

[0020] Where σ is the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece during non-drilling processing, X 2t and X 2c It is the longitudinal tensile strength and longitudinal compressive strength of thermoplastic material workpiece;

[0021] The minimum value of σ obtained by formula (1) is min That is, the minimum clamping stress when the U-shaped clamping plate clamps the thermoplastic workpiece and causes the thermoplastic workpiece to fail during the non-drilling process. The clamping stress range of the U-shaped clamping plate on the thermoplastic workpiece when it does not damage the thermoplastic workpiece during the non-drilling process is (0, σ min ), and in order to make the U-shaped clamping plate clamp the thermoplastic workpiece, it is assumed that the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece during the non-drilling process is in the interval U1=[0.7σ min ,0.9σ min ] within the scope of;

[0022] S2. Conduct multiple drilling experiments using a thermoplastic workpiece sample under the same processing parameters. Before each drilling experiment, record the clamping stress σ1 of the U-shaped clamping plate on the thermoplastic workpiece sample, and σ1 is within the range of interval U1. During each drilling experiment, record the change in the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece sample during the drilling process in real time. After each drilling experiment, take the clamping stress peak value σ2 of the corresponding clamping stress change, and calculate the vibration stress coefficient β of the thermoplastic workpiece sample during the drilling process, where β = σ1 / σ2. After completing each drilling experiment, calculate the average value β0 of the vibration stress coefficient for each drilling experiment.

[0023] S3. The failure equation of the clamping pressure of thermoplastic workpiece under drilling processing is:

[0024]

[0025] Wherein, σ0 is the clamping stress of the U-shaped clamping plate 302 on the thermoplastic material workpiece during drilling;

[0026] The minimum value σ0 obtained by formula (2) is 0min That is, the minimum clamping stress when the U-shaped clamping plate clamps the thermoplastic workpiece and causes the thermoplastic workpiece to fail during the drilling process. The clamping stress range of the U-shaped clamping plate on the thermoplastic workpiece when the thermoplastic workpiece is not damaged during the drilling process is (0, σ 0min ), and in order to make the U-shaped clamping plate clamp the thermoplastic material workpiece, it is assumed that the clamping stress of the U-shaped clamping plate on the thermoplastic material workpiece during the drilling process is in the interval U2=[0.7σ 0min ,0.9σ 0min ], the interval U2 is the preset pressure range of the U-shaped clamping plate on the thermoplastic material workpiece under the drilling processing state.

[0027] Preferably, the preset temperature in the chamber is controlled by changing the heating power of the compensation thermal resistor and the flow rate of the liquid nitrogen in the inlet pipe.

[0028]

[0029] Where T is the preset temperature inside the chamber, that is, the temperature when the liquid nitrogen flows into the cooling pipe, T0 is the temperature of the liquid nitrogen when it is in the liquid nitrogen machine, P is the heating power of the compensation thermal resistor, c is the specific heat capacity of liquid nitrogen, ρ is the density of liquid nitrogen, v is the flow rate of liquid nitrogen in the inlet pipe, and A is the cross-sectional area of ​​the inlet pipe;

[0030] Furthermore, considering the influence of the temperature difference between the liquid nitrogen in the liquid nitrogen machine and the cooling pipe and the heat exchange effect of the circular hole pair, as well as the influence of room temperature on the thermal insulation effect of the thermal insulation coating, the heat compensation coefficient λ and the heat exchange compensation heat power per unit time p are introduced, and

[0031] p=ε*d*ΔT

[0032] Where ε is the thermal conductivity of the thermal insulation coating, d is the thickness of the thermal insulation coating, and ΔT is the difference between the room temperature and the preset temperature inside the chamber;

[0033] but

[0034]

[0035] The value of λ is related to the temperature difference ΔT'=T-T0. When 0≤ΔT'≤30, λ=0.97; when 30<ΔT'≤70, λ=0.93; when 70<ΔT'≤100, λ=0.88; when ΔT'>100, λ=0.82.

[0036] The present invention has the following beneficial effects:

[0037] 1. The present invention can achieve the formation of a low-temperature environment required for drilling thermoplastic workpieces, and can realize auxiliary drilling of thermoplastic workpieces in a low-temperature environment, avoiding deformation of the processed holes caused by the drilling heat generated during the drilling process, which affects the fixing effect. The operation method of the present invention is simple and the production cost is low. Specifically, the present invention allows liquid nitrogen from the liquid nitrogen machine to flow through an inlet pipe into a cooling pipeline fixed on the inner wall of the silo, and then from the cooling pipeline back to the liquid nitrogen machine through an outlet pipe, so that the liquid nitrogen circulates in the liquid nitrogen machine, the inlet pipe, the cooling pipeline and the outlet pipe, and the liquid nitrogen in the cooling pipeline exchanges heat with the air in the silo, so that the temperature in the silo drops, thereby achieving the formation of a low-temperature environment, and the low-temperature environment is relatively easy to maintain. The drilling machine drives the drill bit to enter through the circular hole opened on the top cover, and drills a thermoplastic material workpiece in the silo that is pressed on the drilling base plate by two U-shaped clamping plates, thereby achieving auxiliary drilling processing of thermoplastic materials in a low-temperature environment. Furthermore, the present invention heats the liquid nitrogen in the inlet pipeline of the temperature compensation chamber through a compensating thermal resistor in the temperature compensation chamber, so that the temperature of the liquid nitrogen entering the cooling pipeline changes to a preset temperature. By changing the flow rate of the liquid nitrogen in the inlet pipeline and the heating power of the compensating thermal resistor, the temperature in the silo can be regulated, thereby achieving auxiliary drilling processing of thermoplastic materials under different low-temperature environments.

[0038] 2. Based on the thermal history principle of thermoplastic materials, the present invention utilizes the characteristic that the material strength of thermoplastic materials first decreases, then increases, and then decreases again after thermal cycling. The temperature in the bin is cycled between high and low temperatures within a preset temperature range. By controlling the cycle temperature difference, cycle period, and number of cycles, the strength of the thermoplastic workpiece can be controlled, thereby achieving strength control of the thermoplastic workpiece as needed.

[0039] 3. In the present invention, the two U-shaped clamping plates are driven to descend by a synchronous lifting mechanism provided in the bin body, so that the two U-shaped clamping plates press the thermoplastic workpiece onto the drilling base plate, thereby achieving the clamping of the thermoplastic workpiece, and the positive pressure of the U-shaped clamping plates on the thermoplastic workpiece is detected by the stress plate, so that the positive pressure of the U-shaped clamping plates on the thermoplastic workpiece is within a preset pressure range, thereby enabling the U-shaped clamping plates to clamp the thermoplastic workpiece without damaging the thermoplastic workpiece, thereby avoiding the failure of the thermoplastic workpiece under the vibration of the drilling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0041] Figure 2 This is a schematic diagram of the structure of the low-temperature control chamber in the present invention;

[0042] Figure 3 Schematic diagram of the internal structure of the temperature compensation chamber in the present invention;

[0043] Figure 4 Schematic diagram of the structure of the cooling pipeline in the present invention;

[0044] Figure 5 Schematic diagram of the structure of the workpiece clamping device of the present invention;

[0045] Figure 6 It is a structural schematic diagram of the workpiece translation device in the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to the accompanying drawings.

[0047] like Figure 1 As shown, the cold drilling auxiliary device for thermoplastic materials of the present invention includes a low temperature control chamber 101, a workpiece clamping device 102 and a workpiece translation device 103.

[0048] like Figure 2 、 Figure 3 and Figure 4As shown, the low-temperature control chamber 101 includes an internal circulation chamber 201, a temperature compensation chamber 202 and a cooling pipe 203. The internal circulation chamber 201 includes a chamber body and a top cover. An opening 1 is provided at the upper end of the chamber body. The top cover is detachably fixed to the opening 1 and a circular hole 1 205 is provided on the top cover. The circular hole 1 205 facilitates the drill bit to enter the interior of the chamber body for processing. A temperature sensor 206 is fixed on the inner wall of the chamber body. The temperature sensor 206 is used to detect the temperature inside the chamber body in real time. The outlet pipe integrally formed on the temperature compensation chamber 202 is fixed and connected to the chamber body, and a compensation thermal resistor 207 is fixed in the temperature compensation chamber 202. The cooling pipe 203 is fixed on the inner wall of the chamber body, and the outlet of the cooling pipe 203 is fixed to the inner wall of the chamber body. The inlet of the cooling pipe 203 is fixed to the inlet of the outlet pipe, and the outlet of the outlet pipe passes through the hole opened in the warehouse body and is connected to the inlet of the liquid nitrogen machine (which liquefies nitrogen into liquid nitrogen); the inlet of the cooling pipe 203 is fixed to the outlet of the inlet pipe; the inlet of the inlet pipe passes through the outlet pipe, passes into the temperature compensation warehouse 202, and passes through the inlet pipe integrally formed on the temperature compensation warehouse 202, and is connected to the outlet of the liquid nitrogen machine; the compensation thermal resistor 207 is used to heat the liquid nitrogen flowing from the inlet pipe into the cooling pipe 203, thereby controlling the temperature of the liquid nitrogen flowing into the cooling pipe 203, thereby controlling the temperature in the warehouse body. The outer walls of the internal circulation chamber 201 and the temperature compensation chamber 202 are coated with a thermal insulation coating 208. The thermal insulation coating 208 is used to isolate the internal circulation chamber 201 and the temperature compensation chamber 202, slow down the heat exchange between the internal circulation chamber 201 and the temperature compensation chamber 202 and the outside world, and ensure the effective cooling power of the cooling pipe 203 in the internal circulation chamber 201 or the effective heating power of the compensating thermal resistor 207 in the temperature compensation chamber 202.

[0049] The workpiece clamping device 102 and the workpiece translation device 103 are both arranged in the inner circulation bin 201. Figure 5 As shown, the workpiece clamping device 102 includes a synchronous lifting mechanism 301 and a U-shaped clamping plate 302. The synchronous lifting mechanism 301 includes a support frame, a transmission rod 305, a nut block 1 and a screw 307; the horizontally arranged transmission rod 305 and the bottom plate of the warehouse body form a rotating pair, and are driven by a driving motor 303, and two ends of the transmission rod 305 are provided with two worms 1 integrally formed and with the same rotation direction; two symmetrically arranged support frames are fixed at both ends of the transmission rod 305 in the warehouse body, and two vertically arranged screw rods 307 and the two support frames respectively form a rotating pair, and the bottom ends of the two screw rods 307 are fixed with worm gears 306, and the two worm gears 306 are respectively engaged with the two worm gears 1, and the two symmetrically arranged nut blocks 1 and the two screw rods 307 respectively form a threaded pair, and respectively form a sliding pair with the two support frames; the two relatively and symmetrically arranged U-shaped clamping plates 302 are fixed to the two nut blocks 1, and the lower surfaces of the two U-shaped clamping plates 302 are provided with stress plates.

[0050] like Figure 6As shown, the workpiece translation device 103 includes a drilling base plate 401 and a horizontal translation mechanism 402, and the horizontal translation mechanism 402 includes a transmission rod 405, a worm gear 406, a screw 407 and a nut block 407; the transmission rod 405 parallel to the transmission rod 1 305 forms a rotation pair with the bottom plate of the warehouse body and is driven by the drive motor 403, and both ends of the transmission rod 405 are provided with an integrally formed worm gear 407 with the same rotation direction; two screw gears 407 horizontally parallel to and perpendicular to the transmission rod 405 are provided between the two support frames and are located at both ends of the transmission rod 405, and are both connected to the transmission rod 405. The bottom plate constitutes a rotating pair, and a worm gear 2 406 is fixed to one end of the two screw rods 2 407 close to the transmission rod 2 405, and the two worm gears 2 406 are respectively engaged with the two worm rods 2; the two symmetrically arranged nut blocks 2 and the two screw rods 2 407 respectively constitute a threaded pair, and respectively constitute a sliding pair with the two guide rods 408 horizontally fixed in the bin body; the horizontally arranged drilling base plate 401 is arranged between the two support frames and is located below the two U-shaped clamping plates 302, and the two ends of the drilling base plate 401 are fixed to the two nut blocks 2, and a circular hole 2 is opened in the middle, and the circular hole 2 is used to avoid drilling interference.

[0051] Among them, the compensating thermistor 207 is powered by a controller, and the controller can (in combination with the temperature signal of the temperature sensor 206) change the power supply voltage to the compensating thermistor 207, thereby changing the heating power and the heat generated by the compensating thermistor 207. The drive motor 1 303 and the drive motor 2 403 are both controlled by the controller, and the signal output ends of the temperature sensor 206 and each stress plate are connected to the controller.

[0052] As a preferred embodiment, a second opening is provided on one side of the chamber body, and a visual window 204 is fixed on the second opening to facilitate observation of the drilling process.

[0053] As a preferred embodiment, the housing of the driving motor 303 is fixed to the base plate, and the output shaft of the driving motor 303 is connected to the transmission rod 305 through the bevel gear pair 304.

[0054] As a preferred embodiment, the housing of the second driving motor 403 is fixed to the base plate, and the output shaft of the second driving motor 403 is connected to the second transmission rod 405 through the second bevel gear pair 404 .

[0055] A working method of a cold drilling auxiliary device for thermoplastic materials is as follows:

[0056] Step 1: Install the tank body on the workbench of the drilling machine.

[0057] Step 2: Remove the top cover, place the thermoplastic workpiece on the drilling substrate 401, make the position of the hole to be drilled on the thermoplastic workpiece be located at the position of the second circular hole, and install the top cover to its original position; then the controller controls the second drive motor 403 to drive the second transmission rod 405 to rotate forward, and the two worms 2 on the second transmission rod 405 are engaged with the two worm gears 2 406, and the two worm gears 2 406 drive the two screws 2 407 to rotate forward, and the two screws 2 407 drive the drilling substrate 401 and the thermoplastic workpiece to translate through the two nut blocks 2, so that the thermoplastic workpiece translates to the bottom of the two U-shaped clamping plates 302; then control The controller controls the drive motor 1 303 to drive the transmission rod 1 305 to rotate forward. The two worms 1 on the transmission rod 1 305 mesh with the two worm wheels 1 306. The two worm wheels 1 306 drive the two screws 1 307 to rotate forward. The two screws 1 307 drive the two U-shaped clamping plates 302 to move downward synchronously through the two nut blocks 1, so that the two U-shaped clamping plates 302 contact the thermoplastic workpiece and clamp the thermoplastic workpiece with the drilling base plate 401. The positive pressure of the corresponding U-shaped clamping plate 302 on the thermoplastic workpiece detected by each stress gauge is within a preset pressure range, thereby completing the clamping of the thermoplastic workpiece.

[0058] The preset pressure range is obtained through drilling experiments, and the process is as follows:

[0059] S1. The U-shaped clamping plate 302 exerts a positive pressure perpendicular to the surface of the thermoplastic workpiece on the thermoplastic workpiece. The positive pressure is the clamping stress of the U-shaped clamping plate 302 on the thermoplastic workpiece. However, when the clamping stress is too large, the thermoplastic workpiece will be damaged, causing the thermoplastic workpiece to fail. The clamping stress failure equation of the thermoplastic workpiece during non-drilling processing is:

[0060]

[0061] Where, σ is the clamping stress of the U-shaped clamping plate 302 on the thermoplastic workpiece during non-drilling processing, X 2t and X 2c It is the longitudinal tensile strength and longitudinal compressive strength of thermoplastic material workpiece, which is related to the workpiece material and can be obtained by looking up the table or tensile and compression tests.

[0062] Since σ>0, the minimum value of σ that causes the thermoplastic material workpiece to reach failure state is obtained according to formula (1): min , which is the minimum clamping stress when the U-shaped clamping plate 302 clamps the thermoplastic workpiece and causes the thermoplastic workpiece to fail during the non-drilling process. The clamping stress range of the U-shaped clamping plate 302 on the thermoplastic workpiece without damaging the thermoplastic workpiece during the non-drilling process is (0,σ min), and to ensure that the U-shaped clamping plate 302 can clamp the thermoplastic workpiece, the clamping stress of the U-shaped clamping plate 302 on the thermoplastic workpiece during the non-drilling process is controlled within the range of interval U1, and In this embodiment, it is assumed that U1 is [0.7σ min ,0.9σ min ].

[0063] S2. Perform multiple drilling experiments using a thermoplastic workpiece sample under the same processing parameters. Before each drilling experiment, record the clamping stress σ1 of the U-shaped clamping plate 302 on the thermoplastic workpiece sample, and ensure that σ1 is within the range U1. During each drilling experiment, record the change in the clamping stress of the U-shaped clamping plate 302 on the thermoplastic workpiece sample during the drilling process in real time. After each drilling experiment, measure the peak value σ2 of the corresponding clamping stress change, and calculate the vibration stress coefficient β of the thermoplastic workpiece sample during the drilling process, where β = σ1 / σ2. After each drilling experiment, calculate the average value β0 of the vibration stress coefficient for each drilling experiment.

[0064] S3. The failure equation of the clamping pressure of thermoplastic workpiece under drilling processing is:

[0065]

[0066] Wherein, σ0 is the clamping stress of the U-shaped clamping plate 302 on the thermoplastic material workpiece during drilling;

[0067] The minimum value σ0 obtained according to formula (2) is 0min , which is the minimum clamping stress when the U-shaped clamping plate 302 clamps the thermoplastic workpiece and causes the thermoplastic workpiece to fail during the drilling process. The clamping stress range of the U-shaped clamping plate 302 on the thermoplastic workpiece without damaging the thermoplastic workpiece during the drilling process is (0, σ 0min ), and at the same time, to ensure that the U-shaped clamping plate 302 can clamp the thermoplastic material workpiece, the clamping stress of the U-shaped clamping plate 302 on the thermoplastic material workpiece during the drilling process is controlled to be within the range of interval U2, and The interval U2 is the preset pressure range of the U-shaped clamping plate 302 on the thermoplastic material workpiece. In this embodiment, U2 is set to [0.7σ 0min ,0.9σ 0min ].

[0068] Step 3: Open the inlet and outlet of the liquid nitrogen machine, and the hydraulic pump on the liquid nitrogen machine transports the liquid nitrogen from the liquid nitrogen machine through the inlet pipeline to the cooling pipeline 203, and returns to the liquid nitrogen machine from the cooling pipeline 203 through the outlet pipeline. At the same time, the thermal compensation resistor 207 is heated to heat the liquid nitrogen in the inlet pipeline of the temperature compensation chamber 202, so that the temperature of the liquid nitrogen entering the cooling pipeline 203 changes to a preset temperature. The liquid nitrogen in the cooling pipeline 203 exchanges heat with the air in the chamber, thereby lowering the temperature in the chamber to the preset temperature; then the drilling machine drives the drill bit to move, so that the drill bit enters the chamber from the circular hole 1 205, and performs tool setting to align the drill bit with the position to be drilled of the thermoplastic material workpiece, and then performs drilling.

[0069] The preset temperature in the chamber is controlled by changing the heating power of the compensation thermal resistor 207 and the flow rate of the liquid nitrogen in the inlet pipe, thereby making the preset temperature in the chamber adjustable, and realizing the drilling of thermoplastic materials under different low temperature environments. The preset temperature in the chamber is

[0070]

[0071] Wherein, T is the preset temperature in the silo, that is, the temperature when the liquid nitrogen flows into the cooling pipe 203, T0 is the temperature of the liquid nitrogen when it is in the liquid nitrogen machine, P is the heating power of the compensation thermal resistor 207, c is the specific heat capacity of liquid nitrogen, ρ is the density of liquid nitrogen, v is the flow rate of liquid nitrogen in the inlet pipe (which can be measured by setting a flow meter in the inlet pipe), and A is the cross-sectional area of ​​the inlet pipe.

[0072] Furthermore, considering the influence of the temperature difference between the liquid nitrogen in the liquid nitrogen machine and the cooling pipe 203 and the circular hole 205 on the heat exchange effect, as well as the influence of the room temperature on the heat insulation effect of the thermal insulation coating 208, the heat compensation coefficient λ and the heat exchange compensation heat power per unit time p are introduced, and

[0073] p=ε*d*ΔT

[0074] Wherein, ε is the thermal conductivity of the thermal insulation coating 208, which is determined by the material of the thermal insulation coating 208 and can be obtained through experiments at a preset temperature (for example, experiments according to standard GB / T10294-2008), d is the thickness of the thermal insulation coating 208, and ΔT is the difference between room temperature and the preset temperature in the chamber.

[0075] but

[0076]

[0077] The value of λ is related to the size of the temperature difference ΔT'=T-T0. The relationship between the value of λ and the size of ΔT' is shown in Table 1.

[0078] Table 1 Relationship between the value of λ and the size of ΔT'

[0079] Temperature difference ΔT' λ Temperature difference ΔT' λ 0≤ΔT'≤30 0.97 30<ΔT'≤70 0.93 70<ΔT'≤100 0.88 ΔT'>100 0.82

[0080] Step 4: After the drilling work is completed, the drilling machine drives the drill bit to move to the original position, the hydraulic pump on the liquid nitrogen machine stops working, the thermal compensation resistor 207 stops heating, and the top cover is removed. Then the controller controls the drive motor 303 to drive the transmission rod 305 to reverse, and the two worms on the transmission rod 305 engage with the two worm gears 306. The two worm gears 306 drive the two screws 307 to reverse, and the two screws 307 drive the two U-shaped clamping plates 302 to move upward synchronously through the two nut blocks, so that the two U-shaped clamping plates 302 and the thermoplastic material are in contact with each other. The workpiece is disengaged from the drilling substrate 401 and moves upward to the initial position. Then, the controller controls the driving motor 2 403 to drive the transmission rod 2 405 to reverse. The two worm gears 2 on the transmission rod 2 405 engage with the two worm wheels 2 406. The two worm wheels 2 406 drive the two screw rods 2 407 to reverse. The two screw rods 2 407 drive the drilling substrate 401 and the thermoplastic workpiece to translate through the two nut blocks 2, so that the drilling substrate 401 translates to the initial position. The thermoplastic workpiece is removed and the top cover is installed to its original position, thereby completing the drilling work of the thermoplastic workpiece.

[0081] Among them, based on the thermal history principle of thermoplastic materials, the characteristic that the material strength of thermoplastic materials first decreases, then increases, and then decreases after thermal cycling is utilized. The temperature in the warehouse is subjected to high and low temperature cycles within a preset temperature range, and the strength of the thermoplastic material workpiece can be controlled by controlling the cycle temperature difference, cycle period, and number of cycles. Therefore, the strength control of the thermoplastic material workpiece can be achieved as needed. The greater the cycle temperature difference, the smaller the workpiece strength. The longer the cycle period, the faster the temperature change, and the smaller the workpiece strength. As the number of cycles increases, the workpiece strength shows a trend of first decreasing, then increasing, and then decreasing.

Claims

1. A cold drilling auxiliary device for thermoplastic materials, comprising a workpiece clamping device and a workpiece translation device, characterized in that: It also includes a low-temperature control chamber; the low-temperature control chamber includes an internal circulation chamber, a temperature compensation chamber and a cooling pipeline; the internal circulation chamber includes a chamber body and a top cover, an opening is provided at the upper end of the chamber body, the top cover is detachably fixed on the opening, and a round hole is provided on the top cover, and a temperature sensor is fixed on the inner wall of the chamber body; an outlet pipe integrally formed on the temperature compensation chamber is fixed and connected to the chamber body, and a compensating thermal resistor is fixed in the temperature compensation chamber; the cooling pipeline is fixed on the inner wall of the chamber body, and the outlet of the cooling pipeline is fixed to the inlet of the outlet pipeline, the outlet of the outlet pipeline passes through the hole provided on the chamber body and is connected to the inlet of the liquid nitrogen machine; the inlet of the cooling pipeline is fixed to the outlet of the inlet pipeline; the inlet of the inlet pipeline passes through The outlet pipe passes through the temperature compensation chamber and passes through the inlet pipe integrally formed on the temperature compensation chamber, and is connected to the outlet of the liquid nitrogen machine; the outer walls of the internal circulation chamber and the temperature compensation chamber are coated with a thermal insulation coating; the workpiece clamping device and the workpiece translation device are both arranged in the internal circulation chamber; the workpiece clamping device includes a synchronous lifting mechanism and a U-shaped clamping plate, and the synchronous lifting mechanism drives two horizontally opposed and spaced U-shaped clamping plates to rise and fall synchronously, and the lower surfaces of the two U-shaped clamping plates are provided with stress plates; the workpiece translation device includes a drilling base plate and a horizontal translation mechanism, and the horizontally arranged drilling base plate is arranged below the two U-shaped clamping plates and is driven to move horizontally by the horizontal translation mechanism, and a circular hole 2 is opened in the middle of the drilling base plate.

2. The cold drilling auxiliary device for thermoplastic materials according to claim 1, characterized in that: A second opening is provided on one side of the bin body, and a visual window is fixed on the second opening.

3. The cold drilling auxiliary device for thermoplastic materials according to claim 1, characterized in that: The synchronous lifting mechanism includes a support frame, a transmission rod, a nut block and a screw. The horizontally arranged transmission rod and the bottom plate of the warehouse body form a rotating pair and are driven by a driving motor. Two integrally formed worm gears are provided at both ends of the transmission rod. Two symmetrically arranged support frames are fixed at both ends of the transmission rod in the warehouse body. Two vertically arranged screw gears and the two support frames respectively form a rotating pair, and the bottom ends of the two screw gears are fixed with a worm gear. The two worm gears are respectively engaged with the two worm gears. The two symmetrically arranged nut blocks and the two screw gears respectively form a threaded pair, and respectively form a sliding pair with the two support frames; two U-shaped clamping plates are respectively fixed to the two nut blocks.

4. The cold drilling auxiliary device for thermoplastic materials according to claim 3, characterized in that: The housing of the driving motor 1 is fixed on the bottom plate, and the output shaft of the driving motor 1 is connected to the transmission rod 1 through the bevel gear pair 1.

5. The cold drilling auxiliary device for thermoplastic materials according to claim 3, characterized in that: The horizontal translation mechanism includes a transmission rod 2, a worm gear 2, a screw 2 and a nut block 2. The transmission rod 2 parallel to the transmission rod 1 forms a rotating pair with the bottom plate of the warehouse body and is driven by the drive motor 2. Two integrally formed worm gears 2 are provided at both ends of the transmission rod 2. Two screw gears 2 horizontally parallel and perpendicular to the transmission rod 2 are arranged between the two support frames and are located at the two ends of the transmission rod 2, and both form a rotating pair with the bottom plate. A worm gear 2 is fixed to one end of the two screw gears close to the transmission rod 2, and the two worm gears 2 are respectively engaged with the two worm gears 2. The two symmetrically arranged nut blocks 2 respectively form a threaded pair with the two screw gears, and respectively form a sliding pair with the two guide rods horizontally fixed in the warehouse body; the drilling base plate is arranged between the two support frames, and the two ends of the drilling base plate are fixed to the two nut blocks 2.

6. The cold drilling auxiliary device for thermoplastic materials according to claim 4, characterized in that: The housing of the second driving motor is fixed on the bottom plate, and the output shaft of the second driving motor is connected to the second transmission rod through the second bevel gear pair.

7. A method for operating a cold drilling aid device for thermoplastic materials according to any one of claims 1 to 6, characterized in that: The details are as follows: Step 1: Install the tank body on the workbench of the drilling machine; Step 2: Remove the top cover, place the thermoplastic workpiece on the drilling base plate, so that the position of the hole to be drilled on the thermoplastic workpiece is located at the second circular hole position, and install the top cover to its original position; then the horizontal translation mechanism drives the drilling base plate to drive the thermoplastic workpiece to translate, so that the thermoplastic workpiece is translated to directly below the two U-shaped clamping plates; then the synchronous lifting mechanism drives the two U-shaped clamping plates to move downward synchronously, so that the two U-shaped clamping plates contact the thermoplastic workpiece, clamping the thermoplastic workpiece with the drilling base plate, and each stress plate detects that the positive pressure of the corresponding U-shaped clamping plate on the thermoplastic workpiece is within a preset pressure range; Step 3: Open the inlet and outlet of the liquid nitrogen machine, and the hydraulic pump on the liquid nitrogen machine transports the liquid nitrogen from the liquid nitrogen machine through the inlet pipeline to the cooling pipeline, and then from the cooling pipeline through the outlet pipeline and the heat exchanger back to the liquid nitrogen machine. At the same time, the thermal compensation resistor is heated to heat the liquid nitrogen in the inlet pipeline of the temperature compensation chamber, so that the temperature of the liquid nitrogen entering the cooling pipeline changes to a preset temperature. The liquid nitrogen in the cooling pipeline exchanges heat with the air in the chamber, thereby lowering the temperature in the chamber to the preset temperature. Then, the drilling machine drives the drill bit to move, so that the drill bit enters the chamber from the circular hole 1, and drills the position to be drilled of the thermoplastic material workpiece; Step 4: The drilling machine drives the drill bit to move to its original position, the hydraulic pump on the liquid nitrogen machine stops working, the thermal compensation resistor stops heating, and the top cover is removed. Then the synchronous lifting mechanism drives the two U-shaped clamping plates to move up to the initial position synchronously, and then the horizontal translation mechanism drives the drilling substrate to move the thermoplastic workpiece horizontally, so that the drilling substrate moves horizontally to the initial position, takes out the thermoplastic workpiece that has completed the drilling process, and installs the top cover to its original position.

8. The method for operating a cold drilling auxiliary device for thermoplastic materials according to claim 7, characterized in that: The preset pressure range is obtained through drilling experiments, and the process is as follows: S1. The U-shaped clamping plate exerts a positive pressure perpendicular to the surface of the thermoplastic workpiece on the thermoplastic workpiece. The positive pressure is the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece. The clamping stress failure equation of the thermoplastic workpiece during non-drilling processing is: Where σ is the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece during non-drilling processing, X 2t and X 2c It is the longitudinal tensile strength and longitudinal compressive strength of thermoplastic material workpiece; The minimum value of σ obtained by formula (1) is min That is, the minimum clamping stress when the U-shaped clamping plate clamps the thermoplastic workpiece and causes the thermoplastic workpiece to fail during the non-drilling process. The clamping stress range of the U-shaped clamping plate on the thermoplastic workpiece when it does not damage the thermoplastic workpiece during the non-drilling process is (0, σ min ), and in order to make the U-shaped clamping plate clamp the thermoplastic workpiece, it is assumed that the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece during the non-drilling process is in the interval U1=[0.7σ min ,0.9σ min ] within the scope of; S2. Conduct multiple drilling experiments using a thermoplastic workpiece sample under the same processing parameters. Before each drilling experiment, record the clamping stress σ1 of the U-shaped clamping plate on the thermoplastic workpiece sample, and σ1 is within the range of interval U1. During each drilling experiment, record the change in the clamping stress of the U-shaped clamping plate on the thermoplastic workpiece sample during the drilling process in real time. After each drilling experiment, take the clamping stress peak value σ2 of the corresponding clamping stress change, and calculate the vibration stress coefficient β of the thermoplastic workpiece sample during the drilling process, where β = σ1 / σ2. After completing each drilling experiment, calculate the average value β0 of the vibration stress coefficient for each drilling experiment. S3. The failure equation of the clamping pressure of thermoplastic workpiece under drilling processing is: Wherein, σ0 is the clamping stress of the U-shaped clamping plate 302 on the thermoplastic material workpiece during drilling; The minimum value σ0 obtained by formula (2) is 0min That is, the minimum clamping stress when the U-shaped clamping plate clamps the thermoplastic workpiece and causes the thermoplastic workpiece to fail during the drilling process. The clamping stress range of the U-shaped clamping plate on the thermoplastic workpiece when the thermoplastic workpiece is not damaged during the drilling process is (0, σ 0min ), and in order to make the U-shaped clamping plate clamp the thermoplastic material workpiece, it is assumed that the clamping stress of the U-shaped clamping plate on the thermoplastic material workpiece during the drilling process is in the interval U2=[0.7σ 0min ,0.9σ 0min ], the interval U2 is the preset pressure range of the U-shaped clamping plate on the thermoplastic material workpiece under the drilling processing state.

9. The method for operating a cold drilling auxiliary device for thermoplastic materials according to claim 7, characterized in that: The preset temperature in the chamber is controlled by changing the heating power of the compensation thermal resistor and the flow rate of the liquid nitrogen in the inlet pipe. The preset temperature in the chamber is Where T is the preset temperature inside the chamber, T0 is the temperature of the liquid nitrogen when it is in the liquid nitrogen machine, P is the heating power of the compensation thermal resistor, c is the specific heat capacity of liquid nitrogen, ρ is the density of liquid nitrogen, v is the flow rate of liquid nitrogen in the inlet pipeline, and A is the cross-sectional area of ​​the inlet pipeline; Furthermore, considering the influence of the temperature difference between the liquid nitrogen in the liquid nitrogen machine and the cooling pipe and the heat exchange effect of the circular hole pair, as well as the influence of room temperature on the thermal insulation effect of the thermal insulation coating, the heat compensation coefficient λ and the heat exchange compensation heat power per unit time p are introduced, and p=ε*d*ΔT Where ε is the thermal conductivity of the thermal insulation coating, d is the thickness of the thermal insulation coating, and ΔT is the difference between the room temperature and the preset temperature inside the chamber; but The value of λ is related to the temperature difference ΔT'=T-T0. When 0≤ΔT'≤30, λ=0.97; when 30<ΔT'≤70, λ=0.93; when 70<ΔT'≤100, λ=0.88; when ΔT'>100, λ=0.82.

Images