Thermoplastic infrared healing repair method and apparatus

Abstract

The application discloses a thermoplastic material infrared healing repair method and device, and belongs to the field of thermoplastic material repair. The method combines a mathematical model with a repair process to establish a mathematical model of an infrared heating repair process. The model is used to calculate the total radiation flux of the infrared device for heating the thermoplastic material under different working conditions, to match the feeding speed of the device with the crystallization speed of the material, and to finally predict the healing strength of the thermoplastic material. An infrared in-situ strengthening device is designed to match the mathematical model to optimize the healing repair. The method can adjust, control and distribute the healing energy of the thermoplastic material with high melting point and high viscosity, and has the advantages of firm healing repair, low cost, high efficiency, non-toxicity, harmlessness and non-pollution.

Description

Technical Field

[0001] This invention belongs to the field of thermoplastic material repair, specifically relating to an infrared healing repair method and apparatus for thermoplastic materials. Background Technology

[0002] Thermoplastic materials are lightweight and high-strength, with some specialized engineering thermoplastics achieving strength comparable to ordinary carbon steel while weighing only one-third as much. Similarly, thermoplastics exhibit excellent wear and corrosion resistance, boasting a longer service life than metals under the same corrosive conditions. Furthermore, unlike thermosetting materials, thermoplastics soften and melt upon heating, then harden and return to their original state upon cooling, maintaining essentially the same mechanical properties. Thanks to these advantages, thermoplastics are widely used in various fields, including machinery manufacturing, aerospace, medical, chemical, and agriculture.

[0003] However, traditional injection-molded thermoplastic materials are prone to cracking and failure under complex working conditions (such as alternating loads and thermal loads) over long periods of time; 3D-printed thermoplastic materials have poor interfilament and interlayer bonding, porosity, and some crystallizable thermoplastic materials do not crystallize sufficiently and uniformly. Therefore, it is necessary to propose an infrared healing repair method and device for thermoplastic materials to meet the performance requirements of the materials under actual working conditions. Summary of the Invention

[0004] This invention provides an infrared healing repair method and apparatus for thermoplastic materials. The healing energy for thermoplastic materials with high melting point and high viscosity is adjustable, controllable and distributable. It has the advantages of strong healing repair, low cost, high efficiency, and being non-toxic, harmless and pollution-free.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An infrared healing repair method for thermoplastic materials includes the following steps:

[0007] S1: Analyze the infrared heat transfer principle and actual working conditions to pre-establish several assumptions for mathematical modeling;

[0008] S2: Establish an infrared heat transfer model based on the structural characteristics of the infrared device;

[0009] S3: Establish a progressive convective heat transfer model with air under natural cooling;

[0010] S4: Establish a heat conduction model and boundary conditions within the thermoplastic material, and finally establish an infrared healing strength prediction model.

[0011] In the steps described above, the assumptions made in S1 are as follows:

[0012] ① Assume that both the infrared device and the thermoplastic material are diffuse radiation-gray bodies (diffuse gray bodies), that is, the emissivity ε is equal to the absorptivity α and the absorptivity is the same across the entire surface of the thermoplastic material;

[0013] ② Assume that the radiation intensity projected by the infrared device is uniform and equal in space;

[0014] ③ Assume that the space covered by the infrared device is approximately closed, and do not consider radiation leakage to the surrounding area;

[0015] ④ It is assumed that the radiation and absorption capacity of air gases (such as oxygen O2, nitrogen N2, and hydrogen H2) in the gap between the device and the thermoplastic material at high temperatures can be ignored, that is, it is assumed that they are transmissive.

[0016] ⑤ Assume that the higher-order reflection and absorption of infrared devices and thermoplastic materials can be ignored;

[0017] ⑥ It is assumed that heat transfer on the surface of thermoplastic materials mainly occurs through radiation from the infrared device to the surface of the thermoplastic material and natural convection between the air and the thermoplastic material.

[0018] ⑦ Assume that heat transfer within thermoplastic materials mainly occurs through thermal conduction;

[0019] ⑧ Assume that the thermoplastic material has been dried before printing, meaning there is no excess moisture inside.

[0020] In S2, an infrared heat transfer model is established based on the structural characteristics of the infrared device. The effective radiation surface of the infrared device is equivalent to a planar or spherical region. The heat flux density of the infrared device intercepted by the micro-element on the surface of the thermoplastic material is as follows:

[0021]

[0022] In the formula, q 1→2 Let σ be the heat flux density projected by the infrared device onto the surface of the thermoplastic material micro-element, σ be the Stefan-Boltzmann constant, ε1 be the emissivity of the infrared device, T1 be the absolute temperature of the infrared device, dA2 be the surface area of ​​the thermoplastic material micro-element, A1 be the total area of ​​the equivalent annular region of the effective radiation of the infrared device, d be the inner diameter of the infrared device, θ1 be the vertical angle between the micro-element ring and the surface of the thermoplastic material micro-element, θ2 be the vertical angle between the surface of the thermoplastic material micro-element and the micro-element ring, and r be the distance from the micro-element ring to the surface of the thermoplastic material micro-element.

[0023] Assuming the thermoplastic material is a diffuse gray body, the emissivity J of the surface of the thermoplastic material micro-element is... A2 It is the total outward radiation density of the surface of the thermoplastic material micro-element, expressed as equation (ii):

[0024] J A2 =q A2→trans +q A2→refle (ii)

[0025] In the formula, q A2→trans The emitted heat flux density of thermoplastic materials is numerically equal to the heat flux density of the infrared absorption device on the micro-element surface of the thermoplastic material; q A2→refle For thermoplastic materials to reflect heat flux density;

[0026] The angular coefficient χ of thermoplastic micro-element faces of infrared devices 1,2 It can be calculated using the integral form, as shown in equation (iii):

[0027]

[0028] Where D is the outer diameter of the infrared device, and R is the vertical distance from the center of the annular region to the surface of the thermoplastic material micro-element;

[0029] A portion of the radiation emitted by the thermoplastic material is absorbed by the infrared device and then emitted back by the infrared device to the thermoplastic material's heat flux density q. re_ref As shown in equation (iv):

[0030] q re_ref =(J A2 ·α1)χ 2,1 ε1α2 (iv)

[0031] Where α1 is the reflectivity of the infrared device and α2 is the reflectivity of the thermoplastic material, the net emissivity of the thermoplastic material micro-element is given by equation (v):

[0032] J A2_net =J A2 +q re_ref (v)

[0033] The net heat flux density of the thermoplastic material micro-element surface receiving radiation from an infrared device and emitting and reflecting a portion of the radiation is given by equation (vi):

[0034] q A2_net =q 1→2 +J A2_net (vi)

[0035] Integrating equation (vi), we obtain the total radiative flux of the infrared interception device for thermoplastic materials as shown in equation (vii):

[0036]

[0037] In S3, a progressive convective heat transfer model between the thermoplastic material and air under natural cooling is established. The heat transfer between the thermoplastic material and air is natural convection. Therefore, the heat flux q of the thermoplastic material to air under natural convection heat transfer is established. 2→air For equation (viii):

[0038] q 2→air=h(T) s -T ∞ (viii)

[0039] In the formula, h is the convective heat transfer coefficient, and T s For thermoplastic materials, T ∞ The temperature of the air above the thermoplastic material;

[0040] In S4, a heat conduction model and boundary conditions are established inside the thermoplastic material. In a two-dimensional Cartesian coordinate system, the governing Fourier equation for general transient heat conduction inside the thermoplastic material is as shown in equation (ix):

[0041]

[0042] In the formula, ρ is the density of the thermoplastic material, and C p Here, Q represents the specific heat capacity of the thermoplastic material, T is the temperature of the thermoplastic material over time, x and y are the Cartesian coordinates, t is time, k is the thermal conductivity of the thermoplastic material, and Q is the temperature of the thermoplastic material. vol(x,y) It is the volumetric heat generation of thermoplastic materials;

[0043] The total heat flux consists of infrared thermal radiation and natural convection, and the model boundary conditions are as shown in equation (x):

[0044] -n·(-kΔT) (x,y,t) =q A2_sum +q 2→air (x)

[0045] By using a two-dimensional transient heat transfer module to solve equations (i) to (x), a predictive formula for the healing strength of thermoplastic materials under infrared conditions can be obtained as a function of the specific heat capacity of the thermoplastic material, the feed rate, the crystallization rate (for semi-crystalline thermoplastic materials), and the total radiative flux, as shown in equation (xi):

[0046]

[0047] Where T c It refers to the healing strength of thermoplastic materials, V. c V is the feed rate of the infrared device. q It is the crystallization rate of thermoplastic materials, Q vol(x,y) It is the volumetric heat generation of thermoplastic materials in the (x,y) Cartesian coordinate system, where p, m, and n are constants.

[0048] The above assumptions are consistent with engineering conditions. In practical applications, they are corrected based on the infrared healing constants p, m, and n. In the above healing strength prediction formula, constant p is related to the properties of thermoplastic materials, constant m is related to the geometric relative position of thermoplastic materials and infrared devices, and constant n is related to the boundary conditions of thermoplastic materials.

[0049] The constant p is related to the properties of thermoplastic materials. It is adjusted according to the type and percentage of modifiers (such as plasticizers, coupling agents, etc.) and reinforcing fibers (such as glass fibers and carbon fibers) added to the thermoplastic material. Specifically, if no modifier or reinforcing fiber is added to the thermoplastic material, then p = 1. If a modifier is added, p increases with the increase of the modifier concentration. If reinforcing fiber is added, p decreases with the increase of the fiber content percentage.

[0050] The constant m is related to the vertical angle θ between the infrared device's radiating surface and the thermoplastic material, as well as the vertical distance R from the central region of the infrared device to the thermoplastic material. The structure and assembly position of the infrared device determine the vertical angle θ and the vertical distance R, which further determine the solid angle Ω and the angular coefficient χ subtended by the infrared device on the thermoplastic material, and further determine the constant m.

[0051] The constant n is related to the boundary conditions of the thermoplastic material, which are determined by external conditions such as the area of ​​the thermoplastic material heated by the infrared device, the natural convection heat flux, and the substrate temperature. The predictive formula (xi) can be understood as improving the healing strength T of the thermoplastic material. c The primary approach is to increase the total radiation flux, including increasing the power and density of infrared radiation elements. Secondly, different process parameters should be set to match the feed rate and crystallization rate. For example, when using a large feed rate, the vertical angle θ between the infrared device's radiation surface and the thermoplastic material and the vertical distance R should be reduced, and the heating area of ​​the infrared device should be increased to reduce the natural convection heat flux.

[0052] An infrared healing and repair device for thermoplastic materials includes an infrared heat source, terminals, a support plate, a multi-port retaining ring, an arc-shaped reflector, an outer ring, an inner ring, a top cover, a thermocouple, a temperature control PID controller, a high-temperature wire, a solid-state relay, an infrared camera, and a host computer. The circumferential spacing of the infrared heat sources is determined based on the heat flux density of the infrared device; the higher the heat flux density, the larger the spacing. Furthermore, the circumferential spacing of the infrared heat sources should preferably be controlled between 5mm and 10mm. The terminals are in contact with the lead wires at the ends of the infrared heat sources. The support plate has multiple holes and lugs, through which the infrared heat sources pass and are fixed. The multi-port retaining ring has multiple slots that engage with the lugs of the support plate. The system is as follows: The arc-shaped reflector is mounted on the infrared heat source; the outer ring has equally spaced threaded holes; the bottom of the inner ring is fixed with a multi-hole retaining ring; the top cover is positioned above the arc-shaped reflector and has holes for connecting terminals; the thermocouple temperature measuring terminals are positioned below the infrared heat source; the temperature control PID receives thermocouple signals and switches the circuit on / off to control temperature; one end of the high-temperature wire is connected to the terminal; the solid-state relay's AC contacts are connected to the high-temperature wire, and its DC contacts are connected to the temperature control PID to achieve contactless circuit switching; the infrared camera's thermal imaging field of view covers the infrared heat source and maintains a certain distance; the host computer samples the infrared camera's thermal image and outputs the feedback to the temperature control PID.

[0053] In the device described above, the infrared heat source includes one or more composite infrared heating units. For most thermoplastic materials, the peak distribution of the infrared absorption band is in the medium or medium-long wave. Especially for thermoplastic composite materials with added short carbon fibers or continuous fibers, the infrared heat source has two types of infrared heating units. The two types of infrared units are arranged concentrically in the inner ring on the outer side. The number of rings is calculated by the heat flux density predicted by the healing strength. Each type of infrared unit is controlled independently by the host computer and the temperature control PID without interference.

[0054] The support plate is made of insulating and high-temperature resistant material. It has holes to accommodate and support the infrared heat source. The lower end of the support plate is provided with a lug to insert into a multi-hole retaining ring and is vertically arranged at equal intervals around the outer side of the inner ring. The holes in the support plate are connected to the multi-hole retaining ring, and the inner and outer rings are spaced a certain distance apart to prevent the infrared heat source from directly contacting the infrared heat source.

[0055] The arc-shaped reflector is a bright parabolic surface and is positioned above the infrared heat source. The parabolic surface reflects surrounding infrared rays and the focal point is located below the geometric center of the device.

[0056] The multi-port retaining ring has retaining holes with equal central angles arranged circumferentially. The retaining holes are connected to the support plate lugs. The multi-port retaining ring has a circular hole in the center to insert the inner ring. The diameter of the retaining ring is equal to the inner diameter of the outer ring.

[0057] The thermocouples are arranged in sections, with section one measuring the temperature of the first type of infrared heating unit and section two measuring the temperature of the second type of infrared heating unit.

[0058] The infrared camera is set up to cover an infrared high-temperature zone and a low-temperature zone. The infrared camera calibration steps include: heating the thermoplastic material from room temperature to its melting point and setting multiple temperature nodes. The thermoplastic material is heated to each temperature node and held for 5 minutes. The infrared camera measures the surface temperature of the material. The measured temperature is compared with the actual value of the temperature node to calibrate the error of measuring the thermoplastic material at different temperatures and ensure the matching of the measured temperature and the actual temperature.

[0059] The host computer receives infrared thermal image field signals from the infrared camera and outputs the infrared temperature monitored by machine vision as a feedback signal to the lower computer temperature control PID. The lower computer temperature control PID input signal includes at least one of a thermocouple or the host computer. The initial temperature of the infrared heat source is measured by the thermocouple, and the temperature of the thermoplastic material during the repair process is measured by the infrared camera. The temperature signal determines the control deviation and the rate of change of deviation, realizing real-time adjustment of the three parameters P, I, and D.

[0060] The infrared device is equipped with an external leakage current protection switch, an overload protection switch, and a grounding wire, among other safety protection measures.

[0061] Beneficial Effects: This invention provides an infrared healing repair method and apparatus for thermoplastic materials. It establishes a mathematical model for key process parameters of infrared healing repair, quantitatively calculates the total infrared heat flux required per unit area of ​​the thermoplastic material, and designs an infrared healing repair device based on this calculation. Furthermore, it can predict the healing strength. The infrared device uses multiple infrared units to specifically heat the thermoplastic material body and reinforcing materials such as short or continuous carbon fibers. A thermal imaging camera and host computer sample the infrared heat signal in real time for feedback adjustment and precise temperature control. The infrared device has a wide heating area and deep penetration, making it suitable for the healing repair of large composite components. Simultaneously, for the additive manufacturing field, it helps improve inter-filament / inter-layer bonding, releases residual stress, reduces warpage, and improves crystallization and the overall mechanical properties of the specimen. Attached Figure Description

[0062] Figure 1 This is a flowchart of the infrared healing and repair method in an embodiment of the present invention;

[0063] Figure 2 This is a schematic diagram of the overall layout of the infrared healing and repair device in an embodiment of the present invention;

[0064] Figure 3 This is a schematic diagram of the main structure of the infrared healing and repair device in an embodiment of the present invention;

[0065] Figure 4 This is an exploded view of the main structure of the infrared healing and repair device in an embodiment of the present invention;

[0066] Figure 5 This is a diagram of the support sheet in the infrared healing and repair device in an embodiment of the present invention;

[0067] Figure 6 This is a diagram of the multi-port retaining ring in the infrared healing and repair device of this invention.

[0068] Figure 7 This is a schematic diagram of the assembly of the support piece and the multi-hole retaining ring in an embodiment of the present invention;

[0069] Figure 8 This is a schematic diagram of the internal assembly of the infrared healing and repair device in an embodiment of the present invention;

[0070] Figure 9 This is a bottom view of the infrared healing and repair device body in an embodiment of the present invention;

[0071] Figure 10 This is a feature diagram of the infrared device in an embodiment of the present invention;

[0072] In the diagram, 1-infrared heat source, 2-terminal block, 3-support plate, 4-multi-port retaining ring, 5-arc reflector, 6-outer ring, 7-inner ring, 8-top cover, 9-thermocouple, 10-temperature control PID, 11-high temperature wire, 12-solid-state relay, 13-bolt, 14-angle code. Detailed Implementation

[0073] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0074] like Figures 2-5 As shown, an infrared healing and repair device for thermoplastic materials includes: an infrared heat source 1, a terminal block 2, a support plate 3, a multi-port retaining ring 4, an arc-shaped reflector 5, an outer ring 6, an inner ring 7, an upper cover 8, a thermocouple 9, a temperature control PID 10, a high-temperature wire 11, a solid-state relay 12, a bolt 13, and a corner bracket 14.

[0075] The infrared heat source 1 includes at least one infrared heating unit, which includes halogen heating wire, carbon fiber heating wire, quartz heating wire, etc. Preferably, the infrared heating unit is a combination of halogen heating wire and carbon fiber heating wire, wherein the halogen heating wire emits medium-wave and medium-long-wave infrared rays, and the carbon fiber heating wire emits long-wave infrared rays. The medium-wave infrared rays mainly cover the absorption band of thermoplastic materials, and the long-wave infrared rays cover the absorption band of short-fiber or continuous-fiber carbon fibers. The infrared heating unit can be combined with one carbon fiber heating wire and multiple halogen heating wires, or it can be an alternating combination of carbon fiber heating wires and halogen heating wires, or it can be a combination of only one type of heating wire. Preferably, the infrared heating units are arranged circumferentially on the outer side of the inner ring 7 and on the upper side of the hole of the support plate 3. The spacing and number of rings are quantitatively calculated based on the healing strength to ensure the total radiation flux requirement. Each infrared heating unit of the infrared heat source 1 is connected to the terminal 2.

[0076] The lower end of the terminal block 2 is connected to the infrared heat source 1, and the upper end is fixed with the high-temperature wire 11. Preferably, the terminal block 2 is made of a high-temperature resistant insulating material.

[0077] The support plate 3 is provided with holes and lugs. The holes support and fix the infrared heat source 1. Furthermore, the holes are provided at a certain distance from the bottom of the support plate 3 to prevent the installed infrared heat source 1 from touching the multi-port retaining ring 4. The lugs are inserted into the slots of the multi-port retaining ring 4 to fix the support plate 3 vertically to the multi-port retaining ring 4. Preferably, the material of the support plate 3 is a high-temperature resistant insulating material, including but not limited to mica, ceramic and composite material laminate.

[0078] The multi-hole retaining ring 4 is provided with multiple concentric rings. The outer and inner rings of the concentric rings are provided with multiple retaining holes. The retaining holes are arranged at equal intervals around the circumference and the width of the retaining holes is equal to the thickness of the support plate 3. The support plate 3 is inserted and fastened. The inner ring diameter of the multi-hole retaining ring 4 is equal to the inner ring diameter 7 and is fixed outside the inner ring 7. The bottom surface of the multi-hole retaining ring 4 and the bottom surface of the inner ring 7 are kept at the same level.

[0079] The arc-shaped reflector 5 has a bright parabolic surface and is set above the infrared heat source 1 and supported and fixed by the support plate 3. The parabolic surface reflects the surrounding infrared rays and the focal point is located below the geometric center of the device.

[0080] The outer ring 6 is cylindrical and has a circular hole and is fixedly connected to the bolt 13. Preferably, the outer ring 6 is a steel ring with a thickness of 1 mm to 2 mm to control the weight while maintaining a certain rigidity. The inner diameter of the outer ring 6 is equal to the outer ring diameter of the multi-hole retaining ring 4, and the outer ring 6 and the inner ring 7 are arranged concentrically. The multi-hole retaining ring 4 is set in the middle of the two rings and fixed.

[0081] The inner ring 7 is cylindrical and concentrically arranged with the outer ring 6. The bottom surface of the inner ring 7 is installed on the same horizontal plane as the bottom surface of the multi-hole retaining ring 4 and the bottom surface of the outer ring 6. Preferably, high-temperature resistant insulating materials such as sandalwood paper or glass fiber cotton are provided in the assembly gaps between the outer ring 6 and the multi-hole retaining ring 4, and between the multi-hole retaining ring 4 and the inner ring 7.

[0082] The top cover 8 is provided with holes, the number, angle and diameter of which are the same as the holes in the outer ring 6. The top cover 8 is connected to the outer ring 6 by angle brackets 14 and the connection method is bolts 13.

[0083] like Figure 1 As shown, an infrared healing repair method for thermoplastic materials includes the following steps:

[0084] S1: Analyze the infrared heat transfer principle and actual working conditions to pre-establish several assumptions for mathematical modeling;

[0085] S2: Establish an infrared heat transfer model based on the structural characteristics of the infrared device;

[0086] S3: Establish a progressive convective heat transfer model with air under natural cooling;

[0087] S4: Establish a heat conduction model and boundary conditions within the thermoplastic material, and finally establish an infrared healing strength prediction model.

[0088] The aforementioned assumptions are as follows:

[0089] ① Assume that both the infrared device and the thermoplastic material are diffuse radiation-gray bodies (diffuse gray bodies), that is, the emissivity ε is equal to the absorptivity α and the absorptivity is the same across the entire surface of the thermoplastic material;

[0090] ② Assume that the radiation intensity projected by the infrared device is uniform and equal in space;

[0091] ③ Assume that the space covered by the infrared device is approximately closed, and do not consider radiation leakage to the surrounding area;

[0092] ④ It is assumed that the radiation and absorption capacity of air gases (such as oxygen O2, nitrogen N2, and hydrogen H2) in the gap between the device and the thermoplastic material at high temperatures can be ignored, that is, it is assumed that they are transmissive.

[0093] ⑤ Assume that the higher-order reflection and absorption of infrared devices and thermoplastic materials can be ignored;

[0094] ⑥ It is assumed that heat transfer on the surface of thermoplastic materials mainly occurs through radiation from the infrared device to the surface of the thermoplastic material and natural convection between the air and the thermoplastic material.

[0095] ⑦ Assume that heat transfer within thermoplastic materials mainly occurs through thermal conduction;

[0096] ⑧ Assume that the thermoplastic material has been dried before printing, meaning there is no excess moisture inside.

[0097] Furthermore, an infrared heat transfer model is established based on the structural characteristics of the infrared device, where the effective radiating surface of the infrared device is equivalent to a plane or spherical region, such as... Figure 6 As shown:

[0098] Where D is the outer diameter of the infrared device; d is the inner diameter of the infrared device; A1 is the total area of ​​the equivalent annular region of the effective radiation of the infrared device; dA2 is the surface of the thermoplastic material micro-element; R is the vertical distance from the center of the annular region to the surface of the thermoplastic material micro-element; x is the distance from a certain micro-element ring on the annular region to the center of the annular region; r is the distance from the micro-element ring to the surface of the thermoplastic material micro-element; dx is the width of the micro-element ring; θ1 is the vertical angle between the micro-element ring and the surface of the thermoplastic material micro-element; θ2 is the vertical angle between the surface of the thermoplastic material micro-element ring and the micro-element ring.

[0099] The heat flux density of the infrared device intercepted by the surface micro-element dA2 of the thermoplastic material is given by equation (i):

[0100]

[0101] In the formula, q 1→2 σ is the heat flux density projected by the infrared device onto the surface of a thermoplastic micro-element; σ is the Stefan-Boltzmann constant; ε1 is the emissivity of the infrared device; T1 is the absolute temperature of the infrared device.

[0102] Assume ① the thermoplastic material is a diffuse gray body, and the emissivity J of the surface of the thermoplastic material micro-element is... A2 It is the total outward radiation density of the surface of a thermoplastic material element, expressed by equation (ii):

[0103] J A2 =qA2→trans +q A2→refle (ii)

[0104] In the formula, q A2→trans The emitted heat flux density of thermoplastic materials is numerically equal to the heat flux density of the infrared absorption device on the micro-element surface of the thermoplastic material; q A2→refle Thermoplastic materials reflect heat flux density.

[0105] The angular coefficient χ of the thermoplastic micro-element surface dA2 with respect to the infrared device A1 1,2 It can be calculated using the integral form, as shown in equation (iii):

[0106]

[0107] A portion of the radiation emitted by the thermoplastic material is absorbed by the infrared device and then emitted back by the infrared device to the thermoplastic material's heat flux density q. re_ref As shown in equation (iv):

[0108] q re_ref =(J A2 ·α1)χ 2,1 ε1α2 (iv)

[0109] In summary, the net emissivity of a thermoplastic material micro-element is given by equation (v):

[0110] J A2_net =J A2 +q re_ref (v)

[0111] The net heat flux density of the thermoplastic material micro-element surface receiving radiation from an infrared device and emitting and reflecting a portion of the radiation is given by equation (vi):

[0112] q A2_net =q 1→2 +J A2_net (vi)

[0113] Integrating equation (vi), we obtain the total radiative flux of the infrared interception device for thermoplastic materials as shown in equation (vii):

[0114]

[0115] The progressive convective heat transfer model with air under natural cooling is characterized by natural convection heat transfer between the thermoplastic material and air. Therefore, the heat flux q of the thermoplastic material to air under natural convection heat transfer is established. 2→气 For equation (viii):

[0116] q 2→air =h(T) s -T ∞(viii)

[0117] In the formula, h is the convective heat transfer coefficient, and T s For thermoplastic materials, T ∞ Let be the air temperature above the thermoplastic material; the heat conduction model and boundary conditions inside the thermoplastic material, in a two-dimensional Cartesian coordinate system, the governing Fourier equation for general transient heat conduction inside the thermoplastic material is as shown in equation (ix):

[0118]

[0119] In the formula, ρ is the density of the thermoplastic material, and C p Here, Q represents the specific heat capacity of the thermoplastic material, T is the temperature of the thermoplastic material over time, x and y are the Cartesian coordinates, t is time, k is the thermal conductivity of the thermoplastic material, and Q is the temperature of the thermoplastic material. vol(x,y) This model represents volumetric heat generation in thermoplastic materials. The boundary conditions are characterized by the total heat flux consisting of infrared thermal radiation and natural convection, as shown in equation (x):

[0120] -n·(-kΔT) (x,y,t) =q A2_sum +q 2→air (x)

[0121] By using a two-dimensional transient heat transfer module to solve equations (i) to (x), a predictive formula for the healing strength of thermoplastic materials under infrared conditions can be obtained as a function of the specific heat capacity of the thermoplastic material, the feed rate, the crystallization rate (for semi-crystalline thermoplastic materials), and the total radiative flux, as shown in equation (xi):

[0122]

[0123] Where T c It refers to the healing strength of thermoplastic materials, V. c It is the feed rate of the infrared device, V q It represents the crystallization rate of thermoplastic materials; p, m, and n are constants.

[0124] Furthermore, regarding the predictive formula for healing strength, the constant p in the formula is related to the properties of the thermoplastic material, the constant m is related to the geometrical relative position of the thermoplastic material and the infrared device, and the constant n is related to the boundary conditions of the thermoplastic material. Specifically, the constant p is related to the properties of the thermoplastic material and is adjusted to an appropriate value based on the type and percentage of modifiers (such as plasticizers, coupling agents, etc.) and reinforcing fibers (such as glass fibers and carbon fibers) added to the thermoplastic material; the constant m is related to the vertical angle θ between the infrared device's radiation surface and the thermoplastic material, and the vertical distance R from the center region of the infrared device to the thermoplastic material. The structure and assembly position of the infrared device determine the vertical angle θ and the vertical distance R, which further determine the solid angle Ω and angular coefficient χ subtended by the infrared device on the thermoplastic material, and further determine the constant m; the constant n is related to the boundary conditions of the thermoplastic material, which are determined by external conditions such as the area of ​​the thermoplastic material heated by the infrared device, the natural convection heat flux, and the substrate temperature. The predictive formula (xi) can be understood as improving the healing strength T of the thermoplastic material. c The primary approach is to increase the total radiation flux, including increasing the power and density of the infrared heat source. Secondly, different process parameters should be set to match the feed rate and crystallization rate. For example, when using a large feed rate, the vertical angle θ between the infrared device's radiation surface and the thermoplastic material and the vertical distance R should be reduced, and the heating area of ​​the infrared device should be increased to reduce the natural convection heat flux.

[0125] In this work, infrared heat transfer models, convective heat transfer models, and heat conduction models are used to evaluate the overall heat conduction trend and heat distribution characteristics of thermoplastic materials under the action of infrared devices. The required heat flux density of the thermoplastic material is then extracted to further guide the structural design of the infrared device, including setting the infrared heat source power, circumferential spacing, and vertical distance between the infrared device and the thermoplastic material. Secondly, the specific heat capacity C of the thermoplastic material is considered. P and crystallization rate V q Material property correction constants are used as compensation for actual infrared heating healing repair, and finally the feed rate V is set. c The strength of the thermoplastic material after repair is calculated using an infrared healing intensity prediction formula. The method involves a host computer calculating the total radiant flux required by the thermoplastic material and receiving real-time thermal image field signals from an infrared camera. The host computer compares the current infrared image field heat with the total radiant flux and outputs a signal to a temperature control PID controller. The temperature control PID controller then regulates the on / off state of a solid-state relay to control the infrared heat source temperature to meet the energy requirements of infrared healing repair.

[0126] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for infrared healing repair of thermoplastic materials, characterized in that, Includes the following steps: S1: Analyze the infrared heat transfer principle and actual working conditions to pre-establish several assumptions for mathematical modeling; S2: An infrared heat transfer model is established based on the structural characteristics of the infrared device. The effective radiation surface of the infrared device is equivalent to a planar or spherical region. The heat flux density of the infrared device intercepted by the micro-element on the surface of the thermoplastic material is as follows: ， In the formula, This refers to the heat flux density projected by the infrared device onto the micro-surface of the thermoplastic material. It is the Stefan-Boltzmann constant. The emissivity of the infrared device, The absolute temperature of the infrared device. Let A1 be the area of ​​the thermoplastic material micro-element surface, A1 be the total area of ​​the equivalent annular region of the infrared device's effective radiation, d be the inner diameter of the infrared device, θ1 be the vertical angle between the micro-element ring and the thermoplastic material micro-element surface, θ2 be the vertical angle between the thermoplastic material micro-element surface and the micro-element ring, and r be the distance from the micro-element ring to the thermoplastic material micro-element surface. S3: Establish a convective heat transfer model between thermoplastic materials and air under natural cooling; S4: Establish a heat conduction model and boundary conditions within the thermoplastic material, and finally establish an infrared healing strength prediction model.

2. The infrared healing repair method for thermoplastic materials according to claim 1, characterized in that, The assumptions stated in S1 are as follows: ① Assume that both the infrared device and the thermoplastic material are diffuse-radiative gray bodies, i.e., their emissivity is... equal to absorption rate Furthermore, the absorption rate is the same across the entire surface of the thermoplastic material; ② Assume that the radiation intensity projected by the infrared device is uniform and equal in space; ③ Assume the infrared device covers a closed space, and do not consider radiation leakage losses to the surrounding area; ④ Assume that the radiation and absorption capacity of the air gas in the gap between the device and the thermoplastic material at high temperature is negligible, that is, assume that they are transmissive. ⑤ Assume that higher-order reflection and absorption by infrared devices and thermoplastic materials are negligible; ⑥ It is assumed that heat transfer on the surface of thermoplastic materials mainly occurs through radiation from the infrared device to the surface of the thermoplastic material and natural convection between the air and the thermoplastic material. ⑦ Assume that heat transfer within thermoplastic materials mainly occurs through thermal conduction; ⑧ Assume that the thermoplastic material has been dried before printing, meaning there is no excess moisture inside.

3. The infrared healing repair method for thermoplastic materials according to claim 1, characterized in that, Assuming the thermoplastic material is a diffuse-radiative gray body, the emissivity of the thermoplastic material's micro-element surface... It is the total outward radiation density of a thermoplastic material element, expressed as equation (ii): ， In the formula, The emitted heat flux density of thermoplastic materials is numerically equal to the heat flux density of the infrared absorption device of the thermoplastic material micro-element surface. For thermoplastic materials to reflect heat flux density; Angular coefficient of thermoplastic micro-element face to infrared device Calculated using the integral form, as shown in equation (iii): ， Where D is the outer diameter of the infrared device, and R is the vertical distance from the center of the annular region to the micro-element surface of the thermoplastic material; A portion of the radiation emitted by the thermoplastic material is absorbed by the infrared device, and then emitted back by the infrared device to the thermoplastic material's heat flux density. As shown in equation (iv): ， in, The reflectivity of the infrared device, The reflectivity of thermoplastic materials.

4. The infrared healing repair method for thermoplastic materials according to claim 3, characterized in that, The net emissivity of a thermoplastic micro-element surface is given by equation (v): ， The net heat flux density of the thermoplastic micro-element surface receiving radiation from an infrared device and emitting and reflecting a portion of the radiation is given by equation (vi): ， Integrating equation (vi), we obtain the total radiative flux of the infrared interception device made of thermoplastic material as shown in equation (vii): 。 5. The infrared healing repair method for thermoplastic materials according to claim 1, characterized in that, In S3, a progressive convective heat transfer model between the thermoplastic material and air under natural cooling is established. The heat transfer between the thermoplastic material and air is natural convection. Therefore, the heat flux of the thermoplastic material to air under natural convection heat transfer is established. For example (viii): ， In the formula, h is the convective heat transfer coefficient. Temperature for thermoplastic materials, This refers to the air temperature above the thermoplastic material.

6. The infrared healing repair method for thermoplastic materials according to claim 4 or 5, characterized in that, In S4, a heat conduction model and boundary conditions are established inside the thermoplastic material. In a two-dimensional Cartesian coordinate system, the governing Fourier equation for general transient heat conduction inside the thermoplastic material is as shown in equation (ix): ， In the formula It refers to the density of thermoplastic materials. It is the specific heat capacity of thermoplastic materials. It refers to the temperature of thermoplastic materials over time. It is a Cartesian coordinate position. It is time. The thermal conductivity of thermoplastic materials, It is the volumetric heat generation of thermoplastic materials; The total heat flux consists of infrared thermal radiation and natural convection, and the model boundary conditions are as shown in equation (x): ， Equations (i) to (x) are solved using a two-dimensional transient heat transfer module to obtain a predictive formula for the healing strength of thermoplastic materials under infrared conditions, which is related to the specific heat capacity of the thermoplastic material, the feed rate, the crystallization rate, and the total radiation flux, as shown in equation (xi): ， in It refers to the healing strength of thermoplastic materials. It is the feed rate of the infrared device. It is the crystallization rate of thermoplastic materials. It is the volumetric heat generation of thermoplastic materials in the (x,y) Cartesian coordinate system, where p, m, and n are constants.

7. A thermoplastic material infrared healing and repair device, used to implement the thermoplastic material infrared healing and repair method according to any one of claims 1-6, characterized in that, The system includes an infrared heat source, terminals, a support plate, a multi-port retaining ring, an arc-shaped reflector, an outer ring, an inner ring, a top cover, a thermocouple, a temperature control PID controller, a high-temperature wire, a solid-state relay, an infrared camera, and a host computer. The infrared heat source components are spaced circumferentially. The terminals are in contact with the leads at the ends of the infrared heat sources. The support plate has multiple holes and lugs, through which the infrared heat source passes and is fixed. The multi-port retaining ring has multiple slots for fixing to the lugs of the support plate. The arc-shaped reflector is mounted on the infrared heat source. The outer ring has equally spaced threaded holes circumferentially. The inner ring... The bottom of the ring is fixed by inserting a multi-hole retaining ring; the top cover is arranged above the arc-shaped reflector and has holes for connecting the wiring terminals; the thermocouple temperature measuring terminals are arranged below the infrared heat source; the temperature control PID receives the thermocouple signal and switches the circuit on and off to control the temperature; one end of the high-temperature wire is connected to the wiring terminal; the AC contact of the solid-state relay is connected to the high-temperature wire, and the DC contact is connected to the temperature control PID to realize contactless circuit on and off; the infrared camera's thermal imaging field of view covers the infrared heat source and maintains a certain distance; the host computer samples the infrared camera's thermal image and feeds it back to the temperature control PID; each infrared unit is controlled independently by the host computer and the temperature control PID without interference.

8. The infrared healing and repair device for thermoplastic materials according to claim 7, characterized in that, The circumferential spacing of the infrared heat source is determined based on the heat flux density of the infrared device; the greater the heat flux density, the greater the spacing.

9. The infrared healing and repair device for thermoplastic materials according to claim 7 or 8, characterized in that, The circumferential spacing of the infrared heat source is controlled between 5mm and 10mm.

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