Gradient complex heat treatment process for injection molding machine mold plate castings

Abstract

The present application relates to injection molding machine template casting heat treatment technical field, disclose a kind of gradient composite heat treatment process for injection molding machine template casting, comprising: the injection molding machine template casting austenitizing heating of including nodular cast iron matrix and carbon fiber reinforced phase;Periodically modulate induction current in preset austenitizing temperature interval, utilize the thermal expansion difference of matrix and reinforced phase to generate alternating mismatch strain field, drive interface microzone local plastic deformation to induce dislocation multiplication, build dislocation strengthening interface layer, adjust interface stress to be residual compressive stress distribution;Injection molding machine template casting is implemented gradient cooling quenching, the present application utilizes interface dislocation strengthening mechanism to convert microcrack tensile stress into residual compressive stress, effectively passivates interface stress concentration effect, improves the fatigue resistance of casting under alternating load, cooperates and optimizes hardness gradient and inhibits interface peeling.

Description

Technical Field

[0001] This invention relates to a gradient composite heat treatment process for injection molding machine template castings, belonging to the field of heat treatment technology for injection molding machine template castings. Background Technology

[0002] Currently, large injection molding machine template castings are typically composed of a ductile iron matrix and reinforcing phases to form a composite structure. These components are subjected to high-frequency alternating mold-locking loads during service. Existing technologies for processing such thick castings generally employ a secondary reheating and quenching process, using an external energy field to achieve microstructural transformation and relying on the medium to adjust the cooling rate to obtain performance gradients. In terms of structural optimization, the industry often changes the geometry of the template to reduce weight and costs. For example, Chinese invention patent CN202491373U discloses an injection molding machine template that uses V-shaped grooves with raised sides and recessed center, along with reinforcing ribs, between adjacent tie rod holes to create a non-solid structure on the four circumferential walls of the template, reducing weight while ensuring mechanical properties. However, such improvements are limited to overall morphological optimization. When the template evolves into a heterogeneous composite structure, the process of controlling the internal microstructure stress of the material still faces bottlenecks.

[0003] However, heavy castings exhibit significant thermal inertia. The elastic modulus and coefficient of thermal expansion differ between the ductile iron matrix and the internal reinforcing phase. During forced cooling, the surface phase transformation generates volumetric expansion stress, while the core region experiences contraction pressure due to hysteresis in heat conduction. These heterogeneous stresses converge at the heterogeneous interface, leading to stress collisions that can easily induce micron-level peeling cracks. To avoid the risk of cracking, the industry typically adopts a remedial measure of reducing the cooling rate, resulting in a cooling rate below the critical lower limit of martensitic transformation. This causes the hardened layer to fail to meet performance standards, creating a physical constraint between hardness indicators and structural integrity. Although attempts have been made to introduce multi-channel segmented cooling or closed-loop temperature control, the intrinsic thermal resistance in the depth direction of the casting makes it difficult for external energy compensation to penetrate into the matrix, thus preventing real-time and synchronous control of latent heat of phase transformation and structural stress.

[0004] Therefore, the technical problem to be solved by this invention is how to utilize the physical and thermal characteristics of the component itself to construct an interface stress self-locking mechanism and realize the active coupling of phase change sequence and strain field within a single process cycle to ensure the structural stability of complex irregular castings during the gradient strengthening process. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A gradient composite heat treatment process for injection molding machine template castings, comprising the following steps:

[0006] Step S1: Place the injection molding machine template casting in an induction heating furnace for austenitizing heating at a temperature of 800°C to 900°C. The injection molding machine template casting includes a ductile iron matrix and a carbon fiber reinforcing phase distributed within the ductile iron matrix.

[0007] Step S2: After the temperature of the injection molding machine template casting reaches the preset austenitizing temperature range, the frequency and amplitude of the excitation current of the induction coil are adjusted to make the temperature of the injection molding machine template casting perform a preset number of cycles of cyclic heating within the preset austenitizing temperature range. The physical mismatch between the thermal expansion coefficient of the carbon fiber reinforced phase and the thermal expansion coefficient of the ductile iron matrix is ​​used to generate a cyclic alternating thermal strain field at the heterogeneous interface where the carbon fiber reinforced phase and the ductile iron matrix come into contact.

[0008] Step S3: The alternating thermal strain field drives the matrix structure in the micro-region surrounding the carbon fiber reinforced phase to undergo local micro-plastic deformation. This induces high-density dislocation multiplication and cross-entanglement in situ to construct a dislocation-strengthened interface layer at the heterogeneous interface. The deformation strengthening energy inside the dislocation-strengthened interface layer is used to force the tensile stress state at the micro-notch inside the injection molding machine template casting to be transformed into a residual compressive stress distribution. This residual compressive stress distribution suppresses the tendency of interface delamination between the carbon fiber reinforced phase and the ductile iron matrix and passivates the stress concentration effect of the injection molding machine template casting under load conditions.

[0009] Step S4: Perform gradient cooling quenching treatment with a gradient cooling rate distribution on the injection molding machine template casting with residual compressive stress distribution.

[0010] Preferably, when performing step S2, the fluctuation frequency of the input current of the induction heating furnace is set to 0.1Hz to 5.0Hz, and the temperature amplitude of the periodic heating is controlled within the range of 10°C to 50°C below the phase transformation point of the ductile iron matrix, with the number of cycles being 5 to 15.

[0011] Preferably, step S4 includes: acquiring preset thermal resistance distribution data of different depth sections of the injection molding machine template casting, and setting a non-uniform cooling temperature field path according to the preset thermal resistance distribution data; reserving a heat conduction time window before quenching to induce carbon atom migration on the surface of the ductile iron matrix, and using the residual heat in the core of the injection molding machine template casting to perform heat compensation on the surface.

[0012] Preferably, in a non-uniform cooling temperature field path, the temperature amplitude of periodic cyclic heating satisfies the following quantization constraint rule: ,in, For temperature amplitude, The yield strain of the ductile iron matrix within the preset austenitizing temperature range. The coefficient of thermal expansion of the ductile iron matrix. is the coefficient of thermal expansion of the carbon fiber reinforcing phase.

[0013] Preferably, in step S4, during gradient cooling quenching, a pulse pressure is applied to the quenching medium to generate fluid disturbance, and the vapor film in the concave geometry of the injection molding machine template casting is peeled off by the fluid dynamic pressure.

[0014] Preferably, the frequency of the pulse pressure is set to 20Hz to 100Hz, and the pressure amplitude is set to 0.2MPa to 1.0MPa; the pulse pressure is used to create turbulence at the abrupt change in the cross-section of the injection molding machine template casting.

[0015] Preferably, during step S4, the quenching medium is attached to the surface of the injection molding machine template casting to form a medium film; after step S4, the latent heat of vaporization of the medium film is used for thermal balance control, and the heat conducted from the core of the injection molding machine template casting to the surface is absorbed through the phase change heat absorption process of the medium film.

[0016] Preferably, the current frequency of the induction heating furnace in step S1 is set according to the thickness of the injection molding machine template casting: a current frequency of 100Hz to 500Hz is used for areas with a thickness greater than 200mm, and a current frequency of 1kHz to 10kHz is used for areas with a thickness less than 200mm.

[0017] Preferably, after performing steps S1 to S4, the microhardness within a 10mm depth range of the surface layer of the injection molding machine template casting is 45HRC to 55HRC, and the dislocation density in the dislocation strengthening interface layer is increased by 2 to 3 orders of magnitude compared with the original as-cast matrix.

[0018] Preferably, the process also includes step S5: aging the injection molding machine template casting after gradient cooling and quenching treatment by placing the injection molding machine template casting in an environment of 550℃ to 600℃ for 4 to 8 hours, then furnace cooling to 200℃ at ≤40℃ / h and air cooling to stabilize the microstructure within the dislocation strengthening interface layer and release local micro-stress.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. In gradient composite heat treatment, subcritical alternating thermal cycle pretreatment is used to generate alternating thermal strain by utilizing the absolute difference in thermal expansion coefficients at the heterogeneous phase interface. This drives the interface matrix to undergo local microplastic work and induces high-density dislocation proliferation. A dislocation-rich plastic self-locking encapsulation layer is constructed in situ around the reinforcing phase, transforming the tensile stress state at the micro-notch into a residual compressive stress field. This passively reduces the notch sensitivity naturally present inside the composite component from a physical source, thereby improving the fatigue resistance of the casting when subjected to high-frequency, high-tonnage alternating loads.

[0021] 2. Based on the thermal resistance characteristics of the component in the depth direction, an asymmetric phase transformation dynamic path is constructed. Combined with the static window of heat conduction before quenching, a trace carbon migration of the surface austenite is induced. With the directional feedback of residual heat from the core to the surface, a continuous and smooth hardness gradient distribution is formed between the surface tempered martensite and the core structure. This avoids interface peeling caused by abrupt changes in structural stress, and achieves system synergy between a high wear-resistant surface and a high toughness core without changing the material composition.

[0022] 3. Periodic pressure pulses are used to induce fluid cavitation in the quenching medium. The micro-jet generated by the collapse of cavitation bubbles mechanically peels away the stable vapor film in the concave geometric dead corners, breaking the heat conduction bottleneck in the fluid dynamic shadow area. This synchronizes the cooling rates of different parts of the irregularly shaped component, reduces the peak stress superposition caused by phase change timing disorder at the interface between thick and thin walls, improves the uniformity of the microstructure of complex irregularly shaped components, and eliminates the risk of quenching cracking. The latent heat of boiling vaporization of the residual medium film is used to construct a passive temperature clamping mechanism. The excess heat conducted from the core to the surface is automatically absorbed through the medium phase change process, locking the surface tempering temperature within a constant range near the boiling point of the medium. This solves the problem of secondary softening of the microstructure caused by excessive thermal inertia in ultra-large components. Without relying on external precision temperature control equipment, the gradient heat treatment process ensures extremely high implementation stability and performance consistency for components of different tonnages. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the core steps of the gradient composite heat treatment process for injection molding machine template castings of the present invention.

[0024] Figure 2 This is a diagram illustrating the key technical elements and strengthening mechanism of the gradient composite heat treatment process of this invention.

[0025] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0027] A gradient composite heat treatment process for injection molding machine template castings includes the following steps:

[0028] Step S1: Place the injection molding machine template casting in an induction heating furnace for austenitizing heating at a temperature of 800°C to 900°C. The injection molding machine template casting includes a ductile iron matrix and a carbon fiber reinforcing phase distributed within the ductile iron matrix.

[0029] Step S2: After the temperature of the injection molding machine template casting reaches the preset austenitizing temperature range, the frequency and amplitude of the excitation current of the induction coil are adjusted to make the temperature of the injection molding machine template casting perform a preset number of cycles of cyclic heating within the preset austenitizing temperature range. The physical mismatch between the thermal expansion coefficient of the carbon fiber reinforced phase and the thermal expansion coefficient of the ductile iron matrix is ​​used to generate a cyclic alternating thermal strain field at the heterogeneous interface where the carbon fiber reinforced phase and the ductile iron matrix come into contact.

[0030] Step S3: The alternating thermal strain field drives the matrix structure in the micro-region surrounding the carbon fiber reinforced phase to undergo local micro-plastic deformation. This induces high-density dislocation multiplication and cross-entanglement in situ to construct a dislocation-strengthened interface layer at the heterogeneous interface. The deformation strengthening energy inside the dislocation-strengthened interface layer is used to force the tensile stress state at the micro-notch inside the injection molding machine template casting to be transformed into a residual compressive stress distribution. This residual compressive stress distribution suppresses the tendency of interface delamination between the carbon fiber reinforced phase and the ductile iron matrix and passivates the stress concentration effect of the injection molding machine template casting under load conditions.

[0031] Step S4: Perform gradient cooling quenching treatment with a gradient cooling rate distribution on the injection molding machine template casting with residual compressive stress distribution.

[0032] Preferably, when performing step S2, the fluctuation frequency of the input current of the induction heating furnace is set to 0.1Hz to 5.0Hz, and the temperature amplitude of the periodic heating is controlled within the range of 10°C to 50°C below the phase transformation point of the ductile iron matrix, with the number of cycles being 5 to 15.

[0033] Preferably, step S4 includes: acquiring preset thermal resistance distribution data of different depth sections of the injection molding machine template casting, and setting a non-uniform cooling temperature field path according to the preset thermal resistance distribution data; reserving a heat conduction time window before quenching to induce carbon atom migration on the surface of the ductile iron matrix, and using the residual heat in the core of the injection molding machine template casting to perform heat compensation on the surface.

[0034] Preferably, in a non-uniform cooling temperature field path, the temperature amplitude of periodic cyclic heating satisfies the following quantization constraint rule: ,in, For temperature amplitude, The yield strain of the ductile iron matrix within the preset austenitizing temperature range. The coefficient of thermal expansion of the ductile iron matrix. is the coefficient of thermal expansion of the carbon fiber reinforcing phase.

[0035] Preferably, in step S4, during gradient cooling quenching, a pulse pressure is applied to the quenching medium to generate fluid disturbance, and the vapor film in the concave geometry of the injection molding machine template casting is peeled off by the fluid dynamic pressure.

[0036] Preferably, the frequency of the pulse pressure is set to 20Hz to 100Hz, and the pressure amplitude is set to 0.2MPa to 1.0MPa; the pulse pressure is used to create turbulence at the abrupt change in the cross-section of the injection molding machine template casting.

[0037] Preferably, during step S4, the quenching medium is attached to the surface of the injection molding machine template casting to form a medium film; after step S4, the latent heat of vaporization of the medium film is used for thermal balance control, and the heat conducted from the core of the injection molding machine template casting to the surface is absorbed through the phase change heat absorption process of the medium film.

[0038] Preferably, the current frequency of the induction heating furnace in step S1 is set according to the thickness of the injection molding machine template casting: a current frequency of 100Hz to 500Hz is used for areas with a thickness greater than 200mm, and a current frequency of 1kHz to 10kHz is used for areas with a thickness less than 200mm.

[0039] Preferably, after performing steps S1 to S4, the microhardness within a 10mm depth range of the surface layer of the injection molding machine template casting is 45HRC to 55HRC, and the dislocation density in the dislocation strengthening interface layer is increased by 2 to 3 orders of magnitude compared with the original as-cast matrix.

[0040] Preferably, the process also includes step S5: aging the injection molding machine template casting after gradient cooling and quenching treatment by placing the injection molding machine template casting in an environment of 550℃ to 600℃ for 4 to 8 hours, then furnace cooling to 200℃ at ≤40℃ / h and air cooling to stabilize the microstructure within the dislocation strengthening interface layer and release local micro-stress.

[0041] Example 1: During the heat treatment of an injection molding machine template casting comprising a ductile iron matrix and a carbon fiber reinforcing phase, the casting is subjected to high-frequency alternating clamping force under service conditions. Its stress characteristics manifest as strain concentration at the interface between the carbon fiber reinforcing phase and the ductile iron matrix. Due to the difference in elastic modulus and thermal expansion coefficient between the two phases, under alternating loads, each carbon fiber end evolves into a fatigue notch similar to the root of a fastener thread. This makes the component highly susceptible to fatigue crack initiation at the heterogeneous interface and propagation along the phase boundary during long-term operation. The injection molding machine template casting is placed in an induction heating furnace. The excitation current generated by the induction coil heats the casting to a preset austenitizing temperature range. After reaching the preset temperature, the temperature of the injection molding machine template casting is periodically cyclically heated within the preset austenitizing temperature range by adjusting the frequency and amplitude of the excitation current of the induction coil. The input current fluctuation frequency of the induction heating furnace is set to 0.1Hz to 5.0Hz, the temperature fluctuates within the range of 10℃ to 50℃ below the phase transformation point, the number of cycles is 5 to 15, and the temperature amplitude is... Satisfy the formula ,in For temperature amplitude, The yield strain of the ductile iron matrix within the preset austenitizing temperature range. The coefficient of thermal expansion of the ductile iron matrix. The coefficient of thermal expansion of the carbon fiber reinforcing phase is used to generate an alternating thermal strain field at the heterogeneous interface by utilizing the physical mismatch of the two phases' thermal expansion coefficients. This drives the local matrix structure at the interface to undergo plastic deformation, thereby inducing dislocation multiplication and constructing a dislocation-reinforced interface layer at the heterogeneous interface.

[0042] Select ductile iron matrix Using a reference point, the values ​​are determined according to the material batch. The balance power of the induction heating furnace is set to maintain a constant output to the preset austenitizing temperature. A triangular wave or sine wave is superimposed to modulate the current fluctuation, ensuring the injection molding machine template casting... The nearby temperature range is experiencing cyclical oscillations, among which... Yield strain The temperature intensity response matrix stored in the control unit is determined by real-time interpolation. The response matrix is ​​constructed from high-temperature compression test data of the same material standard sample in the temperature range of 700℃ to 950℃, based on the real-time surface temperature feedback from the infrared thermometer. locking The numerical values ​​are adjusted, and the pulse width of the excitation current is adjusted to achieve quantitative input of the thermal strain field to the dislocation multiplication driving force of the heterogeneous interface; an asymmetric phase transition path is established by utilizing the thermal resistance characteristics of the injection molding machine template casting in the depth direction; a heat conduction time window of 3s to 15s is reserved before quenching to induce carbon atom migration in the matrix surface; the entire injection molding machine template casting is immersed in PVA / PAG quenching liquid to perform gradient cooling quenching treatment; during the cooling process, periodic pressure pulses with a frequency of 20Hz to 100Hz and a pressure amplitude of 0.2MPa to 1.0MPa are applied to the quenching medium; the vapor film attached to the concave geometric part of the injection molding machine template casting is peeled off by hydrodynamic pressure to synchronize the cooling rate; and the injection molding machine template casting is subjected to periodic pressure pulses with a frequency of 20Hz to 100Hz and a pressure amplitude of 0.2MPa to 1.0MPa. When the thin-walled region of the part reaches the martensitic transformation endpoint and the thick-walled region does not undergo a non-martensitic phase transformation, the rapid cooling operation is interrupted. In-situ self-tempering is performed by utilizing the internal heat flow conducted from the thick-walled region to the thin-walled region of the injection molding machine template casting. After performing the above process steps, the tensile stress state at the micro-notches inside the injection molding machine template casting is transformed into a residual compressive stress distribution. The microhardness within a 10mm depth range of the surface layer of the injection molding machine template casting reaches 45HRC to 55HRC. The dislocation density in the dislocation-strengthened interface layer is increased by 2 to 3 orders of magnitude compared to the original as-cast matrix. Through the organizational control of the inherent thermal strain field to counteract the phase transformation stress, the heterogeneous interface exhibits higher peel resistance and fatigue strength when subjected to injection molding impact.

[0043] Example 2: In the test verifying the stability and fatigue service life of the heterogeneous interface of the injection molding machine template casting, the test platform included an induction heating unit with a power of 500kW, equipped with an infrared temperature measurement closed-loop control system with a response time of less than 10ms, and a spray quenching device with pulse pressure output capability. The pressure pulse generator had an adjustment range of 0.1MPa to 1.5MPa and a frequency response range of 10Hz to 150Hz. The test data came from the actual measurement and acquisition of standard samples by the physical experimental platform. The measuring instruments included a digital display hardness tester with a resolution of 0.1HRC and a residual stress analyzer based on the X-ray diffraction principle with a spatial resolution better than 50μm. Force analyzer; In the experimental parameter settings, the value of the input current fluctuation frequency depends on the balance between the electromagnetic induction skin effect and the thermal conductivity of the matrix. When heating a 100mm thick casting sample, if the fluctuation frequency exceeds 5.0Hz, the Joule heat generated by the induced current will be excessively concentrated on the surface, resulting in the thermal strain field failing to cover the deep heterogeneous interface. If the frequency is below 0.1Hz, the energy conversion gradient per unit time is insufficient to induce local plastic deformation of the matrix. Based on the above trade-off logic, this experiment sets the input current fluctuation frequency to 2.0Hz to ensure that sufficient physical mismatch stress to drive dislocation multiplication is generated within an effective heating depth of 15mm.

[0044] To verify the synergistic effect of the proposed solution, an experiment was conducted with a control group, a partially deficient group, and the present invention sample group. The control group underwent conventional overall austenitization followed by spray quenching; the partially deficient group underwent austenitization and gradient cooling but removed the periodic cyclic heating step; and the present invention sample group underwent a complete gradient composite heat treatment process with 10 cycles. During the initial experimental phase, initial interface state data were obtained for the three groups of samples. This showed that the average original residual tensile stress at the interface between the carbon fiber reinforcement phase and the ductile iron matrix was distributed between 85 MPa and 110 MPa, and the initial dislocation density observed by transmission electron microscopy was [data missing]. During the heating stage, to simulate a real industrial electromagnetic environment, Gaussian white noise with a signal-to-noise ratio of 20dB is superimposed on the control signal as an environmental disturbance. The prototype of this invention uses a closed-loop control system to correct the excitation current amplitude in real time. After experiencing 10 periodic temperature fluctuations, the average dislocation density in the heterogeneous interface micro-region jumps to [value missing]. The dislocation density of some missing groups remains at [a certain level]. The jump in the intermediate eigenvalue nearby confirms the excitation effect of the alternating thermal strain field on lattice defects.

[0045] In the final cooling stage, the cooling path was controlled using surface fluid pressure data fed back from sensors. Under the condition of a cooling pressure pulse of 0.5 MPa and a frequency of 50 Hz, the cooling rate of the surface layer of the sample group of this invention remained stable at 45℃ / s. Actual measurement data showed that the proportion of microcracks in the control group reached 15.2% after quenching, while no microcracks were detected in the sample group of this invention. Fatigue performance indicators were obtained by conducting cyclic tensile fatigue tests under a load of 100 kN on the three groups of samples, with the average fatigue life of the control group being [missing data]. Next, the fatigue life of the partially missing group was The fatigue life of the sample group of this invention reached [number missing]. Secondly, data comparison shows that the deformation strengthening effect generated by the dislocation strengthening interface layer and the microstructural constraint effect generated by the gradient hardness distribution have a nonlinear correlation. The improvement in fatigue life exceeds the sum of the contributions of any single process feature, verifying the key role of the dislocation strengthening interface layer in suppressing local notch sensitivity. To establish the rationality of the parameter boundaries, an out-of-range control group was introduced into the experiment, with the temperature amplitude... The temperature was set at 65℃, exceeding the upper limit of 50℃. Monitoring results showed that when the temperature amplitude was too large, unexpected phase transformations frequently occurred on the surface of the ductile iron matrix, leading to lattice distortion and thermal stress damage in the matrix. The residual stress on the sample's surface changed from compressive stress to tensile stress of 120 MPa, and the fatigue life plummeted. This study demonstrates that the temperature amplitude range defined by this invention is the optimal working window for achieving thermomechanical coupling strengthening. Once this range is exceeded, the physical mismatch stress will transform from a strengthening factor into a destructive factor. Finally, through dissection analysis of the sample group of this invention, it was confirmed that its microhardness at a depth of 10 mm reached 52.4 HRC, and the peak residual compressive stress was stable at 320.5 MPa. The test results provide a closed-loop confirmation of the technical logic of reversing the interfacial stress state through periodic thermal cycling, providing a basis for improving the reliability of large composite castings.

[0046] Example 3: During the heat treatment of a heavy-duty injection molding machine template casting with a thickness of 150mm and containing a carbon fiber reinforced phase of 15% by volume, due to the large thermal inertia of the component's cross-section, there is a thermal conduction hysteresis between the surface and deep layers. This causes the induced heat flux density at the heterogeneous interface at a depth of 15mm to be easily constrained by the electromagnetic skin effect during temperature fluctuation strengthening. Without power compensation calibration, the dislocation multiplication rate of the deep matrix will be lower than that of the surface layer. To establish the process benchmark under this specific condition, an initial state definition procedure based on impedance evolution characteristics is implemented. Three armored thermocouples with a measurement accuracy of 0.1℃ and a response time of 5ms are respectively embedded on the surface, at a depth of 15mm, and at a depth of 30mm of the injection molding machine template casting. During the output of the reference power by the induction heating furnace, the controller monitors the change in system load impedance by collecting the phase difference between the voltage and current at the heating coil terminals. When the impedance curvature undergoes a step shift and the sensor reading at 15mm reaches 742.5℃, the phase transformation start point of the ductile iron matrix is ​​determined. The point is used as the reference value for periodic cyclic heating.

[0047] Based on this, an adaptive adjustment method based on power density compensation is implemented, whereby the controller of the induction heating furnace adjusts the control based on the real-time collected surface temperature. The excitation current modulation calculation is performed by dynamically correcting the output voltage of the inverter circuit through an adjustment factor K, thereby adjusting the actual output power of the induction heating furnace. Satisfy the formula ;in To maintain the balanced power required for the preset austenitizing temperature, the austenitizing temperature is set to 800℃ to 900℃ based on the composition of the ductile iron matrix. η represents the power fluctuation depth, which is determined by the target temperature amplitude. In this embodiment, η is set to 0.25, and f is the fluctuation frequency of the input current. For the heating time, f was calibrated to 1.5Hz for a 150mm wall thickness component to ensure that the alternating thermal strain field covered the heterogeneous interface at a depth of 15mm, utilizing the electromagnetic wave penetration law. After implementing the above calibration and adjustment procedures, the temperature fluctuation synchronization rate deviation at different detection points was less than 1.2℃ during 12 cyclic heating cycles of the injection molding machine template casting, offsetting the energy fluctuations caused by environmental impedance drift. Dissection characterization data showed that the dislocation density distribution within the dislocation strengthening interface layer at a depth of 15mm was uniform, and its measured value was... Furthermore, the fatigue crack initiation resistance in this region under a 100kN load is consistent with the surface microstructure; by using a power modulation algorithm to counteract the skin effect through controlled strengthening, the microstructure integrity of ultra-thick composite castings across the entire cross-section was achieved, eliminating the risk of early failure of large components under complex alternating stress fields; the wall thickness exceeds In a thick cross-sectional area of ​​mm, the induction heating control unit collects the excitation voltage U and current I at both ends of the resonant tank circuit and calculates the phase difference monitoring system's inductive reactance change. The phase transition point offset is calibrated online using the hysteresis loss inflection point generated by the evolution of permeability μ with the lattice arrangement state. A power regulation operator ζ is introduced to compensate for the deep energy attenuation caused by the skin effect. impedance response slope With the aspect ratio of carbon fiber reinforcing phase Fluctuation adjustment: The control system identifies the load impedance characteristics during the frequency sweep phase and matches the corresponding pulse frequency from the offline adjustment matrix to adjust the load across the thick cross-section. An alternating thermal strain field is generated at a depth of mm to drive local microplastic deformation of the matrix, eliminating the unevenness of the hardened layer structure caused by the limitation of electromagnetic penetration depth.

[0048] Example 4: When the injection molding machine template casting is in a state where the phase transformation point shift is caused by the fluctuation of the ductile iron matrix composition, the mapping relationship between the induction excitation power and the strain field intensity of the heterogeneous interface deviates. Before performing heat treatment, on-site calibration is performed using characteristic response samples. In the induction heating furnace, a pulse current with a frequency of 0.1Hz to 10.0Hz is applied through the control unit. At the same time, the characteristic loops of the magnetic field strength H and magnetic induction intensity B on the surface of the casting are collected using a magnetic probe. The inflection point of hysteresis loss when the permeability μ changes with the lattice arrangement is used to determine the batch of materials. A characteristic function ψ=U / I, composed of excitation voltage U and current I, is established to characterize the system inductive reactance, and this inductive reactance data is used as a feedback operator to correct the power amplitude of periodic cyclic heating.

[0049] When quenching and debugging injection molding machine template castings with wall thickness abrupt changes exceeding 50%, spatially discretized temperature measurement nodes are used to record data in order to determine the trigger boundary of the heat conduction time window. Twelve temperature sampling nodes are set in different wall thickness distribution areas of the casting to record the coupling curve of the surface temperature drop rate and the core energy release rate during the quenching medium spraying stage. The equivalent thermal conductivity at different depth sections is then used to determine the optimal temperature range. Construct a non-uniform cooling temperature field path, and when the monitoring system identifies that the real-time temperature of the thin-walled region meets the conditions... At that time, the control unit adjusts the spray pressure to 0.2MPa, uses the residual heat in the core of the thick-walled area to carry out thermal penetration into the thin-walled area, and corrects the parameters through the physical response characteristics of the material to make the component form a martensitic structure layer in different wall thickness areas and inhibit the peeling of heterogeneous interfaces.

[0050] Example 5: Aspect Ratio of Carbon Fiber Reinforcing Phase in Different Batches of Raw Materials In production tasks that generate discrete fluctuations of 10% to 25%, in order to offset the influence of raw material micro-geometric characteristic fluctuations on the uniformity of the dislocation strengthening interface layer, a standardized pre-calibration method is implemented. This involves using a scanning electron microscope to measure characteristic samples with different aspect ratio gradients and recording the impedance response slope of the characteristic samples during the heating process within a preset austenitizing temperature range. Establish a system based on aspect ratio The offline adjustment matrix formed by the power adjustment operator ζ, where the formula for calculating the power adjustment operator ζ is: Where ζ is the power regulation operator, The slope of the impedance response of the current sample. As the impedance response reference value under the standard length-to-diameter ratio, the data of the offline adjustment matrix is ​​stored in the control unit of the induction heating furnace. When the system identifies that the load inductive reactance of the current casting deviates from the reference value through the initial frequency sweep, the control unit corrects the pulse width adjustment factor of the excitation current according to the retrieved power adjustment operator ζ. Through parameter correction based on the physical properties of the components, the limitation of different raw material batches on the thermomechanical coupling strengthening effect is eliminated, so that the dislocation strengthening interface layer forms a consistent microstructure distribution on different cross sections.

[0051] When the system encounters a cooling dead zone caused by poor circulation of the quenching medium in the concave part of a large, irregularly shaped mold, an online compensation method based on cooling rate gradient feedback is implemented. Four auxiliary pressure sensors are installed in the concave geometric part of the injection molding machine mold casting to monitor the dynamic pressure head of the quenching medium flowing through the concave geometric part in real time. Simultaneously, the temperature drop rate is collected by temperature measurement nodes buried at corresponding depths. Perform a logical judgment; if the judgment result satisfies the logical condition, then... and ,in For the rate of temperature decrease, This represents the lower limit of the critical cooling rate for martensitic transformation. For dynamic pressure heads, To achieve the preset fluid head safety threshold, the control unit instructs the spray device to increase the medium circulation flow rate and raise the pressure pulse amplitude in the quenching medium by 20%. This utilizes fluid dynamic pressure to peel away the vapor film adhering to the surface of the concave geometric area. Through a dynamic compensation mechanism based on the evolution of local physical states, a hardness gradient distribution is constructed in the irregular morphology region of the injection molding machine template casting, ensuring that the microhardness difference of the component surface layer remains stable within 1.5 HRC and that no heterogeneous interface peeling occurs. During gradient cooling quenching, temperature measurement nodes located on the concave geometric area of ​​the injection molding machine template casting collect real-time temperature drop rates. The auxiliary pressure sensor monitors the dynamic pressure head of the quenching medium flowing through the zone. Logical judgment unit identification and hour, This represents the lower limit of the critical cooling rate for martensitic transformation. To preset the fluid head safety threshold, the control unit instructs the spray device to step up the medium pressure pulse frequency from 20Hz to above 50Hz. The high-frequency pressure wave induces cavitation in the fluid dynamics shadow region and peels off the stable vapor film attached to the surface. The latent heat of vaporization of the medium film remaining on the surface after quenching is used to construct a passive temperature clamping range, locking the surface tempering temperature in a constant range near the boiling point of the medium. The sensible heat is conducted from the core to the surface to achieve self-counteracting of the structural stress, stabilizing the surface martensite hardness difference within 1.5HRC and blocking the interface peeling path.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A gradient composite heat treatment process for injection molding machine template castings, characterized in that, Includes the following steps: Step S1: Place the injection molding machine template casting in an induction heating furnace for austenitizing heating at a temperature of 800°C to 900°C. The injection molding machine template casting includes a ductile iron matrix and a carbon fiber reinforcing phase distributed within the ductile iron matrix. Step S2: After the temperature of the injection molding machine template casting reaches the preset austenitizing temperature range, the frequency and amplitude of the excitation current of the induction coil are adjusted to make the temperature of the injection molding machine template casting perform a preset number of cycles of cyclic heating within the preset austenitizing temperature range. The physical mismatch between the thermal expansion coefficient of the carbon fiber reinforced phase and the thermal expansion coefficient of the ductile iron matrix is ​​used to generate a cyclic alternating thermal strain field at the heterogeneous interface where the carbon fiber reinforced phase and the ductile iron matrix come into contact. Step S3: The alternating thermal strain field drives the matrix structure in the micro-region surrounding the carbon fiber reinforced phase to undergo local micro-plastic deformation. This induces high-density dislocation multiplication and cross-entanglement in situ to construct a dislocation-strengthened interface layer at the heterogeneous interface. The deformation strengthening energy inside the dislocation-strengthened interface layer is used to force the tensile stress state at the micro-notch inside the injection molding machine template casting to be transformed into a residual compressive stress distribution. This residual compressive stress distribution suppresses the tendency of interface delamination between the carbon fiber reinforced phase and the ductile iron matrix and passivates the stress concentration effect of the injection molding machine template casting under load conditions. Step S4: Perform gradient cooling quenching treatment with a gradient cooling rate distribution on the injection molding machine template casting with residual compressive stress distribution.

2. The gradient composite heat treatment process for injection molding machine template castings according to claim 1, characterized in that, When performing step S2, the fluctuation frequency of the input current of the induction heating furnace is set to 0.1Hz to 5.0Hz, and the temperature amplitude of the periodic heating is controlled within the range of 10°C to 50°C below the phase transformation point of the ductile iron matrix, with the number of cycles being 5 to 15.

3. The gradient composite heat treatment process for injection molding machine template castings according to claim 1, characterized in that, Step S4 includes: acquiring preset thermal resistance distribution data of different depth sections of the injection molding machine template casting, and setting a non-uniform cooling temperature field path according to the preset thermal resistance distribution data; reserving a heat conduction time window before quenching to induce carbon atom migration on the surface of the ductile iron matrix, and using the residual heat in the core of the injection molding machine template casting to perform thermal compensation on the surface.

4. The gradient composite heat treatment process for injection molding machine template castings according to claim 3, characterized in that, In a non-uniform cooling temperature field path, the temperature amplitude of periodic cyclic heating satisfies the following quantization constraint rule: ,in, For temperature amplitude, The yield strain of the ductile iron matrix within the preset austenitizing temperature range. The coefficient of thermal expansion of the ductile iron matrix. is the coefficient of thermal expansion of the carbon fiber reinforcing phase.

5. The gradient composite heat treatment process for injection molding machine template castings according to claim 1, characterized in that, In step S4, during gradient cooling quenching, pulse pressure is applied to the quenching medium to generate fluid disturbance, and the vapor film in the concave geometry of the injection molding machine template casting is peeled off by the fluid dynamic pressure.

6. The gradient composite heat treatment process for injection molding machine template castings according to claim 5, characterized in that, The frequency of the pulse pressure is set from 20Hz to 100Hz, and the pressure amplitude is set from 0.2MPa to 1.0MPa; the pulse pressure is used to create turbulence at the abrupt change in the cross-section of the injection molding machine mold casting.

7. The gradient composite heat treatment process for injection molding machine template castings according to claim 1, characterized in that, During step S4, the quenching medium is attached to the surface of the injection molding machine template casting to form a medium film. After step S4, the latent heat of vaporization of the medium film is used for thermal balance control. The heat conducted from the core of the injection molding machine template casting to the surface is absorbed through the phase change heat absorption process of the medium film.

8. The gradient composite heat treatment process for injection molding machine template castings according to claim 1, characterized in that, In step S1, the current frequency of the induction heating furnace is set according to the thickness of the injection molding machine template casting: a current frequency of 100Hz to 500Hz is used for areas with a thickness greater than 200mm, and a current frequency of 1kHz to 10kHz is used for areas with a thickness less than 200mm.

9. The gradient composite heat treatment process for injection molding machine template castings according to claim 1, characterized in that, After performing steps S1 to S4, the microhardness within a 10mm depth range of the surface layer of the injection molding machine template casting is 45HRC to 55HRC, and the dislocation density in the dislocation strengthening interface layer is increased by 2 to 3 orders of magnitude compared with the original as-cast matrix.

10. The gradient composite heat treatment process for injection molding machine template castings according to claim 1, characterized in that, It also includes step S5: aging treatment of the injection molding machine template casting after gradient cooling and quenching, placing the injection molding machine template casting in an environment of 550℃ to 600℃ for 4h to 8h, furnace cooling to 200℃ at ≤40℃ / h, and air cooling after removal from the furnace, in order to stabilize the microstructure within the dislocation strengthening interface layer and release local micro-stress.

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