Magnesium alloy semi-solid injection molding system and magnesium alloy semi-solid injection molding method

Abstract

The invention relates to a magnesium alloy semi-solid injection molding system and a magnesium alloy semi-solid injection molding method. The magnesium alloy semi-solid injection molding system comprises an injection unit, a mold, a cooling system, a detection unit and a control unit. The mold is provided with a plurality of cooling subareas, and the cooling subareas are divided according to the wall thickness of a casting corresponding to a mold cavity. The cooling system comprises a plurality of cooling channels and a plurality of flow adjusting pieces, the cooling channels are arranged in the mold, and the cooling channels and the flow adjusting pieces are arranged in a one-to-one correspondence mode. The detection unit is used for obtaining the solid fraction of the magnesium alloy slurry in the cavity of the mold in real time. The control unit is in communication connection with the detection unit and the flow adjusting part, and the control unit and the cooling system adjust the cooling rate of each cooling channel according to the control instruction. The state of the slurry can be sensed in real time, cooling behaviors of all areas of the mold can be dynamically and accurately regulated according to the state, and the production quality of magnesium alloy semi-solid castings is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of semi-solid injection molding, in particular to a magnesium alloy semi-solid injection molding system and a magnesium alloy semi-solid injection molding method. BACKGROUND

[0002] The magnesium alloy semi-solid injection molding is an advanced near-net forming technology, and the core of the technology is that magnesium alloy slurry containing a certain proportion of solid phase particles is injected and filled into a mold cavity under high-speed shearing and finally solidified and formed. The technology has the advantages of liquid casting and solid forging, can effectively reduce internal defects of castings and refine grains, so that complex components with dense structure and excellent mechanical properties are obtained, and the technology has wide application prospects in the fields of automobile, aerospace and 3C product light weight.

[0003] However, the precise control of the process is extremely challenging, and in particular, the solidification behavior of the slurry in the mold directly determines the quality of the final product. The cooling system of the existing mold mainly adopts a preset and fixed cooling mode, or is switched on and off according to a simple time sequence after filling. Such a static and open-loop control strategy has the following significant shortcomings: firstly, it cannot respond to the real-time and spatial dynamic changes of the solid phase rate of the slurry during the filling and pressure maintaining process, resulting in a mismatch between the cooling intensity and the actual solidification demand, which easily causes local overheating or overcooling, and causes defects such as coarse grains, shrinkage, porosity or hot cracking; secondly, for complex castings with uneven wall thickness, uniform cooling rate cannot realize the coordinated sequential solidification of each region, and the thick wall area forms a hot spot due to insufficient cooling, and the thin wall area hinders the feeding due to rapid cooling, which seriously restricts the further improvement of the overall performance and consistency of the castings. SUMMARY

[0004] Therefore, it is necessary to provide a magnesium alloy semi-solid injection molding system and a magnesium alloy semi-solid injection molding method, which can realize real-time sensing of the slurry state and dynamic and accurate regulation and control of the cooling behavior of each region of the mold, and improve the quality of magnesium alloy semi-solid casting production.

[0005] The technical scheme is as follows: a magnesium alloy semi-solid injection molding system, comprising: an injection unit; a mold provided with a plurality of cooling sub-zones, the plurality of cooling sub-zones are divided into a thin-wall zone and a thick-wall zone according to the wall thickness of a casting corresponding to a cavity of the mold; a cooling system comprising cooling channels and flow regulating members, the cooling channels are arranged in the mold, and the cooling channels and the flow regulating members are a plurality of and one-to-one corresponding, at least one cooling channel is arranged corresponding to each cooling sub-zone, and the cooling rate of each cooling channel is independently regulated by the flow regulating member; a detection unit for acquiring the solid phase rate of magnesium alloy slurry in the cavity of the mold in real time; and a control unit in communication connection with the detection unit and the flow regulating member, the control unit sends a control instruction to the cooling system according to the real-time solid phase rate signal transmitted by the detection unit, and the cooling system adjusts the cooling rate of each cooling channel according to the control instruction.

[0006] In one of the embodiments, in the mold, the mold wall thickness ≤1cm is a thin-wall zone, the density of the corresponding cooling channel is 1.2-1.5 pieces / cm2, the mold wall thickness >3cm is a thick-wall zone, and the density of the corresponding cooling channel is 0.5-0.8 pieces / cm2; and the inner diameter of the thin-wall zone cooling channel is 6-8mm, and the inner diameter of the thick-wall zone cooling channel is 10-12mm.

[0007] In one of the embodiments, the detection unit comprises a temperature sensor, a microwave sensor and a processing module, the temperature sensor is used for detecting the temperature of the gate zone, the thick-wall zone and the thin-wall zone of the mold respectively, the microwave sensor is used for detecting the dielectric constant of the slurry, the processing module is electrically connected with the temperature sensor and the microwave sensor respectively, the processing module is used for storing the relationship data of the solid phase rate-temperature-dielectric constant of the magnesium alloy, and the real-time solid phase rate is calculated according to the real-time temperature data and the dielectric constant data.

[0008] In one of the embodiments, the solid phase rate calculation model is: φ=[1-(T1-T s ) / (T y –T s )]*(1+k*ε1); wherein φ is the real-time solid phase rate, unit %, T1 is the real-time temperature of the slurry collected by the sensor, unit ℃, T s is the preset solidus temperature, unit ℃, T y is the preset liquidus temperature, unit ℃, ε1 is the real-time dielectric constant of the slurry collected by the microwave sensor, unit F / m, and k is the dielectric constant correction coefficient, and k is a constant.

[0009] In one of the embodiments, the control unit is configured to: collect the readings of the temperature sensors of each zone, calculate the local solid phase rate of each zone according to a pre-stored solid phase rate calculation model, and then calculate the real-time average solid phase rate for global control by weighted averaging of the local solid phase rates according to the weight coefficients of the zones, wherein the weight of the gate zone is 0.2, the weight of the thick wall zone is 0.5, and the weight of the thin wall zone is 0.3.

[0010] In one of the embodiments, the control unit is configured to: when detecting that the real-time solid phase rate of the slurry drops to a first threshold value, control the flow adjusting member corresponding to the thin wall zone of the mold to increase the cooling rate of the region to a preset first cooling rate interval; when detecting that the real-time solid phase rate of the slurry is higher than a second threshold value, control the flow adjusting member corresponding to the thin wall zone of the mold to decrease the cooling rate of the region to a preset second cooling rate interval; wherein the lower limit value of the first cooling rate interval is greater than the upper limit value of the second cooling rate interval.

[0011] A magnesium alloy semi-solid injection molding method, the magnesium alloy semi-solid injection molding method using the magnesium alloy semi-solid injection molding system of any one of the above, comprising the following steps:

[0012] Injecting and filling the magnesium alloy semi-solid slurry into the cavity of the mold;

[0013] Real-time detecting and calculating the solid phase rate of the slurry in the cavity;

[0014] Comparing the real-time solid phase rate with a preset solid phase rate threshold value;

[0015] According to the comparison result, adjusting the cooling rate of different cooling zones by controlling the flow adjusting member, when the real-time solid phase rate drops below the first threshold value, increasing the cooling rate of the thin wall zone to a first cooling rate interval; when the real-time solid phase rate rises above the second threshold value, decreasing the cooling rate of the thin wall zone to a second cooling rate interval; for the thick wall zone, when the real-time solid phase rate is below a third threshold value, controlling the cooling rate to be lower than that of the thin wall zone; the third threshold value is between the first threshold value and the second threshold value, wherein the range of the first threshold value is 60% to 65%, and the range of the second threshold value is 75% to 80%.

[0016] In one of the embodiments, the step of comparing the real-time solid phase rate with a preset solid phase rate threshold value specifically comprises: the control unit compares the real-time solid phase rate with the first threshold value and the second threshold value, if the real-time solid phase rate is less than or equal to the first threshold value, controls the flow adjusting member of the thin wall zone to adjust the cooling rate to 15 to 20 ℃ / s, and if the real-time solid phase rate is greater than the second threshold value, controls the flow adjusting member of the thin wall zone to adjust the cooling rate to 5 to 15 ℃ / s.

[0017] In one embodiment, the control unit is a PID, and the target cooling rate V t is a set point, and the real-time cooling rate V a calculated according to the temperature change rate of the cooling medium loop port is a process variable, and the control unit outputs a control signal to the flow regulating member arranged on the cooling partition loop, and the control algorithm is: u(t) = K p *e(t) + K i *∫e(t)dt + K d *de(t) / dt;

[0018] wherein u(t) is the controller output, e(t) is the error, and e(t) = V t -V a , K p is a proportional coefficient, K i is an integral coefficient, and the unit is ,K d are differential coefficients, and the unit is s.

[0019] In one embodiment, the range of K p is 3-10, the range of K i is 0.003-0.01 , and the range of K d is 5-50 s.

[0020] The beneficial effects of the present application are:

[0021] The above magnesium alloy semi-solid injection molding system, in the working process, the injection unit injects the semi-solid magnesium alloy slurry into the mold cavity; the mold is divided into multiple cooling partitions according to the wall thickness of the casting, to ensure that the cooling requirements of different wall thickness areas are matched; in the cooling system, each cooling partition corresponds to at least one independent cooling channel, and the flow and temperature of the cooling medium (such as ethylene glycol aqueous solution) are controlled through a dedicated flow regulating member (such as an electromagnetic flow valve), and then the cooling rate of each partition is independently regulated; the detection unit captures the solid phase rate of the slurry in the cavity in real time, and transmits the data to the control unit; the control unit analyzes the solid phase rate signal through a preset logic, sends instructions to the corresponding flow regulating member, and dynamically adjusts the cooling rate, so that the cooling rhythm of each cooling partition matches the solidification state of the slurry. This is beneficial to break through the limitation that the traditional mold cannot adapt to the wall thickness difference of the casting, and through the linkage of partition independent cooling and solid phase rate, the problems of cold shut in the thin-walled area due to too fast cooling and shrinkage in the thick-walled area due to too slow cooling are avoided, and the overall density and mechanical property consistency of the casting are improved; and the closed-loop control reduces manual intervention and reduces process fluctuations caused by experience operation, which is beneficial to improve production stability and improve casting quality.

[0022] The magnesium alloy semi-solid injection molding method combines the hardware capability of the system with scientific process strategies, not only regulates according to the change of the solid phase rate in the time dimension, but also implements a coordinated rather than unified cooling strategy in the space dimension for regions with different structural characteristics (thin wall, thick wall). The thick wall region maintains a lower cooling rate than the thin wall region for most of the time, ensuring the smoothness of the feeding channel, while considering the time sequence of the solidification process and the spatial differences of the casting structure. Through coordinated regulation, the globally optimal solidification effect is achieved. In addition, by limiting key thresholds and controlling actions, clear and executable process procedures are provided for on-site engineers, ensuring efficient conversion and stability of product quality. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the accompanying drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0025] Figure 1 A flow chart of the magnesium alloy semi-solid injection molding method described in an embodiment. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned purposes, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a variety of ways other than those described herein, and skilled in the art can make similar improvements without departing from the scope of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0027] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0028] In addition, the terms "first", "second", etc. are used herein only to describe different instances, and are not used to denote or imply relative importance or a number of indicated technical characteristics. Thus, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly and specifically limited.

[0029] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0030] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be directly above or obliquely above the first feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be directly below or obliquely below the first feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0031] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or there can be a middle element. When an element is referred to as "connected" to another element, it can be directly connected to the other element or there can be a middle element. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes, and do not represent the only implementation.

[0032] The embodiment of the present application provides a magnesium alloy semi-solid injection molding system, which comprises an injection unit, a mold, a cooling system, a detection unit and a control unit. The mold is provided with a plurality of cooling partitions, and the plurality of cooling partitions are divided into a thin-wall area and a thick-wall area according to the wall thickness of the corresponding casting of the mold cavity. The cooling system comprises cooling channels and flow regulating members, the cooling channels are arranged in the mold, and the cooling channels and the flow regulating members are one-to-one corresponding. Each cooling partition is provided with at least one cooling channel, and each cooling channel independently regulates the cooling rate through the flow regulating member. The detection unit is used for acquiring the solid phase rate of the magnesium alloy slurry in the cavity of the mold in real time. The control unit is in communication connection with the detection unit and the flow regulating member, and the control unit sends a control instruction to the cooling system according to the real-time solid phase rate signal transmitted by the detection unit, and the cooling system adjusts the cooling rate of each cooling channel according to the control instruction.

[0033] In the working process of the magnesium alloy semi-solid injection molding system, the injection unit injects the semi-solid magnesium alloy slurry into the mold cavity; the mold divides a plurality of cooling partitions according to the wall thickness of the casting, so that the cooling requirements of different wall thickness areas are matched; in the cooling system, each cooling partition is provided with at least one independent cooling channel, the flow and temperature of the cooling medium (such as ethylene glycol aqueous solution) are controlled through the exclusive flow regulating member (such as an electromagnetic flow valve), and then the cooling rate of each partition is independently regulated; the detection unit captures the solid phase rate of the slurry in the cavity in real time and transmits the data to the control unit; the control unit analyzes the solid phase rate signal through a preset logic, sends an instruction to the corresponding flow regulating member, dynamically adjusts the cooling rate, and matches the cooling rhythm of each cooling partition with the solidification state of the slurry. Therefore, the magnesium alloy semi-solid injection molding system can break through the limitation that the traditional mold cannot adapt to the wall thickness difference of the casting, avoid the problems that the thin-wall area produces cold shut due to too fast cooling and the thick-wall area produces shrinkage due to too slow cooling, improve the overall density and mechanical property consistency of the casting, and reduce the process fluctuation caused by experience operation through closed-loop control and reduction of manual intervention, so that the production stability and the casting quality are improved.

[0034] In one embodiment, in the mold, the mold wall thickness ≤ 1 cm is a thin wall area, the corresponding cooling channel density is 1.2-1.5 pieces / cm2, the mold wall thickness > 3 cm is a thick wall area, and the corresponding cooling channel density is 0.5-0.8 pieces / cm2; and the inner diameter of the cooling channel in the thin wall area is 6-8 mm, and the inner diameter of the cooling channel in the thick wall area is 10-12 mm. According to the principle of heat transfer, the thin wall area has small heat capacity, and needs more intensive heat exchange area and faster heat exchange speed; the thick wall area has large heat capacity, and needs more sufficient cooling medium flow to take away heat. Thus, the channel parameters are designed according to the difference in cooling rate requirements of the casting wall thickness: thin wall area wall thickness ≤ 1 cm: large heat dissipation area, fast solidification speed, if the cooling capacity is insufficient, it is easy to leave liquid phase and cause shrinkage, so high-density channels and small inner diameter are used, the contact frequency of the cooling medium and the mold is increased, and the cooling efficiency per unit area is improved; thick wall area wall thickness > 3 cm: small heat dissipation area, slow solidification speed, if the cooling is too fast, it is easy to cause surface layer to solidify first and internal shrinkage, so low-density channels and large inner diameter are used, the cooling medium flow rate is reduced, and the cooling rate is slowed down, and time is reserved for internal slurry feeding. The cooling channel parameters match the wall thickness requirements, which is beneficial to avoid the double defects of insufficient cooling in the thin wall area and excessive cooling in the thick wall area; the differentiated design of the channel density and the inner diameter can reduce the cooling rate deviation of each area of the mold, and improve the density of the casting.

[0035] In one embodiment, the detection unit comprises a temperature sensor, a microwave sensor and a processing module. The temperature sensor is used to detect the temperature of the gate area, thick wall area and thin wall area of the mold respectively, and the microwave sensor is used to detect the dielectric constant of the slurry. The processing module is electrically connected with the temperature sensor and the microwave sensor respectively, and is used to store the solid phase rate-temperature-dielectric constant relationship data of the magnesium alloy, such as the solid phase rate-temperature-dielectric constant basic relationship data of AZ91D and AM60B, and calculate the real-time solid phase rate according to the real-time temperature data and dielectric constant data. The temperature sensor and the microwave sensor are combined to detect. The temperature sensor directly measures the temperature of the slurry. Since there is a difference in the dielectric properties of liquid and solid metals, the microwave sensor indirectly reflects the solid phase rate by measuring the dielectric constant of the slurry. The processing module fuses the three parameters to calculate a more accurate and more anti-interference real-time solid phase rate by using an improved mathematical model. A single temperature sensor may be out of alignment due to position lag or environmental interference. The introduction of dielectric constant as an auxiliary parameter forms data redundancy and complementarity. Even if the single sensor signal is temporarily abnormal, the system can correct or maintain stable output through another parameter, and the calculation result is more reliable. The dielectric constant is directly related to the viscosity and fluidity of the slurry, and can more essentially reflect the change of the solid-liquid two-phase, so that the judgment of the solid phase rate is more scientific. Compared with a single temperature sensor or a microwave sensor, multi-parameter fusion detection can further reduce the calculation error of the solid phase rate; the detection of the key areas such as the gate, thick wall and thin wall of the mold can avoid the overall misjudgment caused by local data, and provide accurate data support for subsequent partition cooling regulation.

[0036] Optionally, the temperature sensor can be a K-type thermocouple sensor, an infrared temperature measurement sensor, a PT100 or other temperature measurement sensor types. The microwave sensor can be a waveguide type microwave transmission sensor, a coaxial probe type microwave reflection sensor, a microstrip antenna type microwave sensor or other sensor types.

[0037] Further, the temperature sensor can also be other quantities to further dynamically monitor the temperature of other positions of the mold.

[0038] In one embodiment, the solid phase rate calculation model is: φ=[1-(T1-T s ) / (T y –T s )]*(1+k*ε1); wherein φ is the real-time solid phase rate, unit is %, T1 is the real-time temperature of the slurry collected by the sensor, unit is ℃, T s is the preset solidus temperature, unit is ℃, T ywherein T is preset liquidus temperature, unit is ℃, ε1 is real-time dielectric constant of the slurry collected by the microwave sensor, unit is F / m, k is dielectric constant correction coefficient, and k is a constant. The model is divided into two parts: temperature basic calculation and dielectric constant correction. The temperature basic calculation is based on the solid-liquid phase line temperature of the magnesium alloy. The theoretical solid phase rate is calculated by the difference between the real-time temperature T1 and the solid-liquid phase line, that is, [1-(T1-T s ) / (T y -T s )], which reflects the core influence of temperature on the solid phase rate. The dielectric constant ε1 and the correction coefficient k are introduced, wherein k is preset for a specific magnesium alloy, such as k=0.02 for AZ91D alloy and k=0.018 for AM60B alloy. The factors that cannot be covered by temperature, such as the roundness of solid phase particles and the microwave fluctuation of liquid phase composition, are compensated. The theoretical solid phase rate is dynamically calibrated by the term (1+k*ε1), so that the calculation result is more consistent with the actual slurry state. This is conducive to correcting the defects of the traditional single temperature model that ignores the microstate of the slurry, further improving the calculation accuracy of the solid phase rate, and the model structure is simple and can be directly embedded in the control unit for real-time operation without complex data processing, which is suitable for the high rhythm production demand of industrial field.

[0039] Specifically, if it is AZ91D alloy, the preset solidus temperature T s is 470℃, and the preset liquidus temperature T y is 595℃; if it is AM60B alloy, the preset T s is 465℃, and the preset T y is 590℃.

[0040] In one embodiment, the control unit is configured to: collect the readings of the temperature sensors in each subarea, calculate the local solid phase rate of each subarea according to the pre-stored solid phase rate calculation model; and then calculate the real-time average solid phase rate for global control by weighted averaging of the local solid phase rates according to the weight coefficients of the subareas, wherein the weight of the sprue area is 0.2, the weight of the thick wall area is 0.5, and the weight of the thin wall area is 0.3. The control unit does not simply take the arithmetic mean of all sensor readings, but uses a weighted average algorithm. This algorithm recognizes that different areas have different influences on the overall quality of the casting. Therefore, by giving higher weights to key areas, the finally calculated global average solid phase rate can better represent the overall solidification process of the casting and the state of the key risk points.

[0041] Specifically, the weight of the gate area is set to 0.2: as the slurry inlet, it reflects the initial solid phase rate state, but the slurry flow has less effect on subsequent solidification after flowing through, so the weight is the lowest; the weight of the thick wall area is set to 0.5: the solidification period is the longest, and it is easy to produce shrinkage due to insufficient cooling, so the solid phase rate change directly determines the overall solidification progress, and the weight is the highest; the weight of the thin wall area is set to 0.3: the solidification speed is fast, and it is easy to produce cold shut due to too fast cooling, which has a significant effect on the surface quality and local strength of the casting, so the weight is the second; through the weighted sum of the local solid phase rate and the corresponding weight, the real-time average solid phase rate reflecting the overall slurry solidification state of the mold is obtained, which avoids the over-regulation or insufficient regulation caused by single area data (such as only measuring the thin wall area), makes the global solid phase rate calculation more in line with the actual solidification priority, and avoids the problem that the thick wall area shrinkage is not timely regulated due to excessive attention to a certain area; the regulation is targeted to improve, which is beneficial to reduce the performance deviation of each area of the casting, thereby reducing the scrap rate.

[0042] In one embodiment, the control unit is configured to: when it is detected that the real-time solid phase rate of the slurry decreases to a first threshold value, control the flow adjusting member corresponding to the thin wall area of the mold to increase the cooling rate of the area to a preset first cooling rate interval; when it is detected that the real-time solid phase rate of the slurry is higher than a second threshold value, control the flow adjusting member corresponding to the thin wall area of the mold to decrease the cooling rate of the area to a preset second cooling rate interval; wherein the lower limit value of the first cooling rate interval is greater than the upper limit value of the second cooling rate interval. The control unit has a phased control strategy built-in. When the solid phase rate is lower than the first threshold value (such as 65%), it indicates that the slurry still has good fluidity, at this time, the cooling of the thin wall area is strengthened, which can make it quickly pass through the solidification interval and refine the structure. When the solid phase rate is higher than the second threshold value (such as 75%), it indicates that the casting has been basically formed and enters the late solidification period, at this time, the cooling rate is reduced overall, especially in the thin wall area, so that it is slowly cooled to release the internal stress generated by the solidification shrinkage. This is conducive to pursuing structure refinement in the early solidification period and preventing stress cracking in the late solidification period. This threshold value control logic can locate the main contradiction and its conversion node in the semi-solid forming process, and realize accurate management. In addition, this control strategy can effectively deal with the two common defects of coarse structure and hot cracking at the same time, thereby improving the performance while significantly improving the good product rate of the product.

[0043] An embodiment of the present application also provides a magnesium alloy semi-solid injection molding method, please refer to Figure 1 , the magnesium alloy semi-solid injection molding method, using the magnesium alloy semi-solid injection molding system of any one of the above, comprising the following steps:

[0044] S10: injecting and filling the magnesium alloy semi-solid slurry into the mold cavity;

[0045] S20: real-time detection and calculation of the solid phase rate of the slurry in the cavity;

[0046] S30: comparing the real-time solid phase rate with a preset solid phase rate threshold value;

[0047] S40: according to the comparison result, adjusting the cooling rate of different cooling sub-zones by controlling the flow adjusting member, when the real-time solid phase rate drops below the first threshold value, increasing the cooling rate of the thin-wall zone to the first cooling rate interval; when the real-time solid phase rate rises above the second threshold value, reducing the cooling rate of the thin-wall zone to the second cooling rate interval; for the thick-wall zone, when the real-time solid phase rate is below the third threshold value, controlling the cooling rate to be lower than the cooling rate of the thin-wall zone; the third threshold value is between the first threshold value and the second threshold value, wherein the first threshold value ranges from 60% to 65%, and the second threshold value ranges from 75% to 80%.

[0048] The above magnesium alloy semi-solid injection molding method combines the hardware capability of the system with the scientific process strategy, not only adjusts and controls according to the change of the solid phase rate in the time dimension, but also implements a coordinated but not unified cooling strategy in the space dimension for different structural feature zones (thin-wall and thick-wall). The thick-wall zone maintains a lower cooling rate than the thin-wall zone for most of the time, ensuring the smoothness of the feeding channel, while considering the time sequence of the solidification process and the spatial difference of the casting structure, and achieving the globally optimal solidification effect through coordinated control. In addition, by limiting the key threshold value and controlling the action, a clear and executable process procedure is provided for the on-site engineers, ensuring the efficient conversion of the invention and the stability of the product quality.

[0049] In one embodiment, the step S30 of comparing the real-time solid phase rate with a preset solid phase rate threshold value specifically includes: the control unit compares the real-time solid phase rate with the first threshold value and the second threshold value, if the real-time solid phase rate is less than or equal to the first threshold value, the flow adjusting member of the thin-wall zone is controlled to adjust the cooling rate to 15-20℃ / s; if the real-time solid phase rate is greater than the second threshold value, the flow adjusting member of the thin-wall zone is controlled to adjust the cooling rate to 5-15℃ / s. Such adjustment of the control unit with the solid phase rate threshold value as the control node can adapt to different solidification stage requirements. When the real-time solid phase rate ≤ the first threshold value: the liquid phase accounts for a high proportion in the slurry, and the thin-wall zone is prone to shrinkage due to excessive liquid phase and insufficient cooling, so the flow adjusting member of the thin-wall zone is controlled to increase the flow of the cooling medium, and the cooling rate is increased to 15-20℃ / s to accelerate the conversion of the liquid phase to the solid phase and inhibit shrinkage; when the real-time solid phase rate ≥ the second threshold value: the solid phase accounts for a high proportion in the slurry, and the thin-wall zone is prone to cold shut due to excessive solid phase and excessive cooling, so the flow adjusting member is controlled to reduce the flow, and the cooling rate is reduced to 5-15℃ / s to slow down the solidification speed and ensure the flowability of the slurry to fill small cavities. Through threshold-based dynamic control, the cooling rate is adapted in real time with the change of the solid phase rate, avoiding defects caused by single global cooling; which is conducive to reducing the shrinkage rate and cold shut rate of the thin-wall zone, and improving the stability of the tensile strength of the casting.

[0050] In one embodiment, the step of controlling the flow regulating member to adjust the cooling rate of different cooling sub-zones is specifically: the control unit is a PID, taking the target cooling rate V t as the set point, and the real-time cooling rate V a calculated according to the cooling medium loop port temperature change rate as the feedback value, and the control algorithm is: u(t) = K p *e(t) + K i *∫e(t)dt + K d *de(t) / dt; wherein, u(t) is the controller output, e(t) is the error and e(t) = Vt-Va, K p is the proportional coefficient, K i is the integral coefficient, and the unit is ,K d are the differential coefficients, and the unit is s. The PID controller takes the target cooling rate V t as the set value, the real-time cooling rate V a calculated based on the cooling medium loop port temperature change rate as the feedback value, and realizes accurate cooling control through the cooperation of the three links. Compared with traditional manual or on-off control, the PID control is beneficial to reduce the cooling rate fluctuation range, reduce the response time, improve the process consistency, and reduce the rework cost caused by parameter fluctuation.

[0051] Specifically, the range of K p is 3-10, the range of K i is 0.003-0.01 , and the range of K d is 5-50 s. The proportional link quickly responds to the error, the integral link eliminates the steady-state error, and the differential link predicts the change trend and suppresses the overshoot. Among them, the proportional link: according to the error e(t) = V t -V a quickly outputs the control signal, and the value of K p 3-10 can ensure the response speed to the error while avoiding excessive overshoot. The integral link: eliminates the static error through integral accumulation, such as the V a deviation from V t caused by long-term cooling medium temperature drift, and the value of K i is small to avoid the control lag caused by integral saturation. The differential link: according to the error change rate de(t) / dt, it predicts the trend in advance and suppresses the cooling rate fluctuation, such as instantaneous flow change, and the value of K dThe value is adapted to the cooling characteristics of magnesium alloy, so as to avoid excessive fluctuation of the cooling rate and cause internal stress of the casting. Finally, the opening of the flow adjusting member is controlled by the u(t) output signal, so as to realize stable control of the cooling rate. Thus, the optimized experience range of the temperature / heat flow control system with large inertia and slow process can guarantee the response speed and stability of the system, so as to ensure that the control system has sufficient rapidity to track the change of the solid phase rate and has good stability to avoid impact on the mold and the casting caused by the dramatic oscillation of the cooling rate, so that the whole dynamic regulation process is smooth, stable and reliable.

[0052] The technical features of the above embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combinations of the technical features do not contradict, they should be considered as the scope of the description.

[0053] The above embodiments only express several implementation manners of the present application, the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that, for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A magnesium alloy semi-solid injection molding system, characterized in that, The magnesium alloy semi-solid injection molding system includes: Injection unit; The mold is provided with multiple cooling zones, and the multiple cooling zones are divided into at least thin-walled zones and thick-walled zones according to the wall thickness of the casting corresponding to the mold cavity. A cooling system, comprising cooling channels and flow regulating components, wherein the cooling channels are disposed within the mold, and there are multiple cooling channels and flow regulating components that are configured in a one-to-one correspondence. Each cooling zone is provided with at least one cooling channel, and the cooling rate of each cooling channel is independently regulated by the flow regulating components. The detection unit is used to acquire the solid fraction of the magnesium alloy slurry within the mold cavity in real time; and The control unit is communicatively connected to the detection unit and the flow regulating component. The control unit sends control commands to the cooling system based on the real-time solid fraction signal transmitted by the detection unit. The cooling system adjusts the cooling rate of each cooling channel according to the control commands.

2. The magnesium alloy semi-solid injection molding system according to claim 1, characterized in that, In the mold, the mold wall thickness ≤ 1cm is the thin-walled area, and the corresponding cooling channel density is 1.2~1.5 channels / cm². The mold wall thickness > 3cm is the thick-walled area, and the corresponding cooling channel density is 0.5~0.8 channels / cm². The inner diameter of the cooling channel in the thin-walled area is 6~8mm, and the inner diameter of the cooling channel in the thick-walled area is 10~12mm.

3. The magnesium alloy semi-solid injection molding system according to claim 2, characterized in that, The detection unit includes a temperature sensor, a microwave sensor, and a processing module. The temperature sensor is used to detect the temperature of the gate area, thick-walled area, and thin-walled area of ​​the mold, respectively. The microwave sensor is used to detect the dielectric constant of the slurry. The processing module is electrically connected to the temperature sensor and the microwave sensor, respectively. The processing module is used to store the solid fraction-temperature-dielectric constant relationship data of the magnesium alloy, and calculate the real-time solid fraction based on the real-time temperature data and dielectric constant data.

4. The magnesium alloy semi-solid injection molding system according to claim 3, characterized in that, The calculation model for the solid fraction is: φ=[1-(T1-T s ) / (T y –T s )]*(1+k*ε1); where φ is the real-time solid fraction, in %, and T1 is the real-time temperature of the slurry collected by the sensor, in °C. s This is the preset solidus temperature, in °C (T). y ε1 is the preset liquidus temperature in °C, ε1 is the real-time dielectric constant of the slurry collected by the microwave sensor in F / m, and k is the dielectric constant correction coefficient, which is a constant.

5. The magnesium alloy semi-solid injection molding system according to claim 3 or 4, characterized in that, The control unit is configured to: collect the readings of the temperature sensors in each zone, calculate the local solid fraction of each zone according to the pre-stored solid fraction calculation model, and then calculate the real-time average solid fraction for global control by weighting the local solid fractions according to the weight coefficients of each zone, wherein the weight of the gate zone is 0.2, the weight of the thick-walled zone is 0.5, and the weight of the thin-walled zone is 0.

3.

6. The magnesium alloy semi-solid injection molding system according to claim 2, characterized in that, The control unit is configured to: when the real-time solid fraction of the slurry is detected to drop to a first threshold, control the flow regulating component corresponding to the thin-walled region of the mold to increase the cooling rate of that region to a preset first cooling rate range; when the real-time solid fraction of the slurry is detected to be higher than a second threshold, control the flow regulating component corresponding to the thin-walled region of the mold to decrease the cooling rate of that region to a preset second cooling rate range; wherein the lower limit of the first cooling rate range is greater than the upper limit of the second cooling rate range.

7. A method for semi-solid injection molding of magnesium alloy, wherein the method for semi-solid injection molding of magnesium alloy is characterized in that, The magnesium alloy semi-solid injection molding system according to any one of claims 1-6 includes the following steps: Magnesium alloy semi-solid slurry is injected and filled into the mold cavity; Real-time detection and calculation of the solid fraction of the slurry inside the mold cavity; The real-time solid fraction is compared with a preset solid fraction threshold; Based on the comparison results, the cooling rates of different cooling zones are adjusted by controlling the flow regulating device. When the real-time solid fraction drops below the first threshold, the cooling rate of the thin-walled zone is increased to the first cooling rate range; when the real-time solid fraction rises above the second threshold, the cooling rate of the thin-walled zone is decreased to the second cooling rate range; for the thick-walled zone, when the real-time solid fraction is below the third threshold, its cooling rate is controlled to be lower than that of the thin-walled zone; the third threshold is between the first threshold and the second threshold, wherein the range of the first threshold is 60%~65%, and the range of the second threshold is 75%~80%.

8. The magnesium alloy semi-solid injection molding method according to claim 7, characterized in that, Step: The comparison of the real-time solid fraction with the preset solid fraction threshold specifically includes: the control unit compares the real-time solid fraction with the first threshold and the second threshold; if the real-time solid fraction is less than or equal to the first threshold, the flow regulator in the thin-walled region is controlled to adjust the cooling rate to 15~20℃ / s; if the real-time solid fraction is greater than the second threshold, the flow regulator in the thin-walled region is controlled to adjust the cooling rate to 5~15℃ / s.

9. The semi-solid injection molding method for magnesium alloys according to claim 7, characterized in that, The control flow regulator adjusts the cooling rate of different cooling zones as follows: the control unit is a PID controller, with a target cooling rate V. t The setpoint is the real-time cooling rate V calculated based on the temperature change rate at the cooling medium circuit inlet. a As a process variable, the control unit outputs a control signal to the flow regulators installed on each cooling zone loop. The control algorithm is: u(t) = K p *e(t)+K i *∫e(t)dt+K d *de(t) / dt; Where u(t) is the controller output, e(t) is the error and e(t) = V t -V a K p K is the proportionality coefficient. i The integral coefficient is expressed in units of 1000 ppm. K d These are the differential coefficients, in units of seconds (s).

10. The magnesium alloy semi-solid injection molding method according to claim 7, characterized in that, K p The range is 3~10, K i The range is 0.003~0.01 K d The range is 5~50s.

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