METHOD FOR EVALUATING STABILITY OF COOLING EFFECT OF COOLING SYSTEM FOR LOW-PRESSURE CASTING OF ALUMINUM ALLOY WHEEL HUB

Description

FIELD OF THE INVENTION

The present disclosure relates to the technical field of low-pressure casting of automobile wheel hubs, in particular to a method for evaluating the stability of the cooling effect of a cooling system for low-pressure casting of an aluminum alloy wheel hub.

BACKGROUND OF THE INVENTION

An integrally cast aluminum alloy wheel hub integrates a hub, a spoke, and a rim, has high strength, high dimensional accuracy, easy assembly, and beautiful appearance, and is widely used in high-end motorcycles and cars. Low-pressure casting is widely used in the production process of aluminum alloy wheel hub castings due to the advantages of smooth filling, high crystallization pressure (0.1-0.15 MPa), and easy complete automation.

In order to further improve the production efficiency and improve the mechanical properties of aluminum alloy wheel hubs, it is often necessary to cool a metal mold used in low-pressure casting. Common cooling methods include various cooling forms such as full air cooling, local water cooling, full water cooling and water mist mixing, and different manufacturers have been exploring cooling forms and cooling processes suitable for their own plants. The stable control of the temperature of a mold in the production process is critical to the stability of the aluminum alloy wheel hub castings because the shrinkage cavity and shrinkage porosity, misrun and coarse grains of castings significantly affect the mechanical properties of wheel hub castings, and this series of defects is greatly influenced by a temperature field.

In the low-pressure casting mass production of the aluminum alloy wheel hub castings, the same temperature acquisition point exhibits different temperature curves at different cycles even with the same cooling process setting due to various factors such as fluctuations in a flow rate of a cooling medium and inconsistent production cycle durations. Meanwhile, since the metal mold used in low-pressure casting of aluminum alloy wheel hubs tends to have a large number of temperature acquisition points, these temperature acquisition points influence each other. On the other hand, when the mold contains a cooling system, the stability of the cooling effect of the cooling system is critical to the control of the mold temperature and the stability of the quality of the aluminum alloy wheel hub. However, the production cycle of each aluminum alloy wheel hub casting has differences in a series of conditions such as the initial mold temperature, the flow rate of the cooling medium, a temperature curve, and a cycle duration, resulting in difficulty in satisfying the harsh conditions required by a single-factor control variable method in the process of measuring the stability of the cooling effect of the cooling system. Therefore, how to evaluate the stability of the cooling system is an important problem to further improve the quality stability of castings.

Therefore, in view of the problems existing in the prior art, by virtue of the active research and improvement of designers of the present disclosure based on years of experience in the industry, the present disclosure provides a method for evaluating the stability of the cooling effect of a cooling system for low-pressure casting of an aluminum alloy wheel hub.

SUMMARY OF THE INVENTION

An object of the present disclosure is to provide a method for evaluating the stability of the cooling effect of a cooling system for low-pressure casting of an aluminum alloy wheel hub in view of the defects in the prior art that the production cycle of each aluminum alloy wheel hub casting has differences in a series of conditions such as the initial mold temperature, a flow rate of a cooling medium, a temperature curve, and a cycle duration, resulting in difficulty in satisfying the harsh conditions required by a single-factor control variable method in the process of measuring the stability of the cooling effect of the cooling system.

To achieve the object of the present disclosure, the present disclosure provides a method for evaluating the stability of the cooling effect of a cooling system for low-pressure casting of an aluminum alloy wheel hub, including:

• • performing Step S1: selecting a mold object that can be used for evaluating the stability of the cooling effect of the cooling system;
  • performing Step S2: arranging a thermocouple, and acquiring temperature data;
  • performing Step S3: changing an initial temperature at a temperature measuring point of the thermocouple, and further acquiring real-time temperature data;
  • performing Step S4: extracting characteristic temperature data, and performing linear regression between an initial temperature value and a characteristic temperature value; and
  • performing Step S5: performing temperature data fluctuation analysis, and quantitatively measuring the stability of the cooling effect of the cooling system by using a maximum value and a minimum value of deviation of discrete points from a fitting curve.

Optionally, in the step S1, a mold corresponding to an aluminum alloy wheel hub casting that is stably produced is selected as the mold object for evaluating the stability of the cooling effect of the cooling system.

Optionally, cooling process parameters are maintained unchanged during a stability evaluation test of the cooling effect of the cooling system.

Optionally, the opening time and the closing time of each cooling pipeline, and a flow rate of a cooling medium in each cooling pipeline are set to be kept unchanged during a production cycle of the aluminum alloy wheel hub.

Optionally, in the step S3, the initial temperature at the temperature measuring point of the thermocouple is changed by closing one of cooling pipelines and acquiring temperature data at a preset cycle.

Optionally, the number of continuous production cycles during which each single cooling pipeline is closed and the number of continuous production cycles during which each single cooling pipeline is reopened are not particularly limited.

Optionally, the number of continuous production cycles during which each single cooling pipeline is closed is equal, and the number of continuous production cycles during which each single cooling pipeline is reopened is equal.

Optionally, in the step S4, characteristic temperature values on a temperature curve before mold opening are selected for analysis.

Optionally, in the step S5, the smaller a span between a maximum value and a minimum value of deviation of discrete points from a linear regression curve, the more stable the cooling system.

In summary, the method for evaluating the stability of the cooling effect of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure has the following prominent substantive features and notable progress:

• • (1) performing analysis based on the temperature data can intuitively reflect the stability of the cooling effect of the cooling system, and avoids a complex mapping relationship between the stability of the flow rate and the stability of the cooling effect compared with the analysis of the stability of the flow rate of the cooling medium;
  • (2) the difficulty of testing under the condition that the initial temperature of the mold cannot be consistent is overcome, and instead, temperature data acquisition and analysis are performed by using the same cooling process setting at a differentiated initial temperature of the mold, and the test method is easy to implement; and
  • (3) by analyzing a relationship between the initial mold temperature and the characteristic temperature value under the cycle, and selecting the temperature value on the temperature curve before mold opening of low-pressure casting of the aluminum alloy wheel hub casting as a characteristic temperature value, the complexity of curve analysis is avoided, and the influence of non-mold cooling process factors on the cooling effect stability analysis result during the processes such as mold opening.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart of a method for evaluating the stability of the cooling effect of a cooling system for low-pressure casting of an aluminum alloy wheel hub according to the present disclosure;

FIG. 2A is a schematic diagram showing cooling pipelines of a top mold of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure;

FIG. 2B is a schematic diagram showing cooling pipelines of a bottom mold of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure;

FIG. 2C is a schematic diagram showing cooling pipelines of a side mold of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure;

FIG. 3 is a schematic diagram showing cycles of acquiring temperature data by a thermocouple according to the present disclosure;

FIG. 4 shows a low-pressure casting process of an aluminum alloy wheel hub and a pressure curve thereof;

FIG. 5A is a graph showing a relationship between a characteristic temperature value (a maximum temperature value) and an initial temperature value at a certain temperature measurement point on a mold; and

FIG. 5B is a graph showing a relationship between a characteristic temperature value (a temperature value at 180 s) and an initial temperature value at a certain temperature measurement point on the mold.

DETAILED DESCRIPTION OF THE INVENTION

The technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some but not all of the embodiments of the present disclosure. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without making inventive step belong to the scope of protection of the present disclosure.

Referring to FIG. 1, FIG. 1 is a flowchart of a method for evaluating the stability of the cooling effect of a cooling system for low-pressure casting of an aluminum alloy wheel hub according to the present disclosure. The method for evaluating the stability of the cooling effect of a cooling system for low-pressure casting of an aluminum alloy wheel hub includes:

Step S1 is performed: a mold object that can be used for evaluating the stability of the cooling effect of the cooling system is selected;

• • referring to FIGS. 2A-2C, FIG. 2A is a schematic diagram showing cooling pipelines of a top mold of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure. FIG. 2B is a schematic diagram showing cooling pipelines of a bottom mold of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure. FIG. 2C is a schematic diagram showing cooling pipelines of a side mold of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure. As a specific embodiment, a mold corresponding to an aluminum alloy wheel hub casting that is stably produced is selected as a research object according to actual conditions. A plurality of cooling pipelines 1 and temperature measuring points of a thermocouple (not shown) are arranged on the mold. The number and distribution of the cooling pipelines 1 and the temperature measuring points of the thermocouple are based on the structure of the aluminum alloy wheel hub casting and the corresponding mold, so as to meet the production requirements. Cooling process parameters are maintained unchanged during a stability evaluation test of the cooling effect of the cooling system. That is, the opening time and the closing time of each cooling pipeline 1, and a flow rate of a cooling medium in each cooling pipeline 1 are set to be kept unchanged during a production cycle of the aluminum alloy wheel hub.

Step S2 is performed: a thermocouple is arranged, and temperature data is acquired;

• • the mold is mounted on a low-pressure casting machine, and the thermocouple is mounted on the mold, and the other end of the thermocouple is connected to a computer, while the cooling pipelines 1 communicate with a joint arranged on the mold. After communication, mold heating is started to be performed, and after stable production, data acquisition is performed by the thermocouple.

Step S3 is performed: an initial temperature at a temperature measuring point of the thermocouple is changed, and real-time temperature data is further acquired;

• • referring to FIG. 3, FIG. 3 is a schematic diagram showing cycles of acquiring temperature data by a thermocouple according to the present disclosure. In the stable production process, since the change of the temperatures at the temperature measuring points of the thermocouple is small, it is unlikely to use the temperatures as a data set for analysis of the stability of the cooling effect, and a data set for analysis needs to be further expanded. Based on this, in the present disclosure, the initial temperature value of the mold at the temperature measuring point of the thermocouple under the condition that the production cycle is changed is used, and temperature data under the cycle is then acquired for analysis. In particular, the initial temperature of the mold is changed by closing one of the cooling pipelines 1 and acquiring temperature data at a preset cycle.

For a non-limiting example, 17 cooling pipelines 1 are arranged on a selected mold, only one of the cooling pipelines 1 is closed after stable production, 5 production cycles are continued in this state, and then the closed cooling pipeline 1 is reopened, and 3 production cycles are continued in this state. Subsequently, the remaining 16 cooling pipelines 1 are sequentially subjected to the above operations. Those skilled in the art can easily know that under the stability evaluation test of the cooling effect of the cooling system, there are a total of 51 production cycles with the same cooling process parameter setting, and there are a total of 85 production cycles during which only one pipeline is closed, and temperature data of the 51 production cycles with the same cooling process parameter setting is selected as data for analysis of the stability of the cooling effect. Obviously, the number of continuous production cycles during which each single cooling pipeline is closed and the number of continuous production cycles during which each single cooling pipeline is reopened are not particularly limited. The number of continuous production cycles during which each single cooling pipeline is closed is equal, and the number of continuous production cycles during which each single cooling pipeline is reopened is equal. In view of the temperature change and the efficiency of the test, preferably, the number of continuous production cycles during which each single cooling pipeline and the number of continuous production cycles during which each single cooling pipeline is reopened are 3-5.

Step S4 is performed: characteristic temperature data is extracted, and linear regression between an initial temperature value and a characteristic temperature value is performed.

Referring to FIG. 4, FIG. 4 shows a low-pressure casting process of an aluminum alloy wheel hub and a pressure curve thereof. According to the step S1 to the step S3, temperature data at temperature measuring points of the thermocouple on a mold with different initial mold temperatures under the same cooling process are obtained to further extract characteristic temperature points from the acquired temperature data. Since the low-pressure casting process can be divided into stages such as liquid raising, filling, pressurizing, pressure maintaining, pressure relief, and mold opening according to a time sequence, in order to eliminate the influence of environmental factors on the fluctuation in the temperature of the mold, characteristic temperature values on a temperature curve before mold opening are selected for analysis.

As can be seen from FIG. 4, in the production process of the aluminum alloy wheel hub casting, the pressure relief operation is started to be performed at 170 s and all the cooling pipelines 1 are closed at 180 s, and the highest value of the temperature curve and the temperature value at 180 s can be selected as characteristic temperature values. It should be noted that the temperature value at a certain time from the beginning of a cycle is taken as the characteristic temperature value, and this time has different values according to the actual production process (that is, it is not necessarily 180 s). Preferably, the time corresponding to the temperature value at a certain time from the beginning of a cycle is distinguished from the time corresponding to the highest temperature value.

Referring to FIG. 4, in conjunction with FIGS. 5A-5B, FIG. 5A is a graph showing a relationship between a characteristic temperature value (a maximum temperature value) and an initial temperature value at a certain temperature measurement point on a mold. FIG. 5B is a graph showing a relationship between a characteristic temperature value (a temperature value at 180 s) and an initial temperature value at a certain temperature measurement point on the mold. According to the extracted characteristic temperature value data, a scatter plot of data for characteristic temperature values versus initial temperature values at different positions is drawn, and a linear regression is performed on the scatter plot.

Step S5 is performed: temperature data fluctuation analysis is performed, and the stability of the cooling effect of the cooling system is quantitatively measured by using a maximum value and a minimum value of deviation of discrete points from a fitting curve.

For a stable cooling system, under the same cooling process conditions, the initial temperature is the same and its corresponding characteristic temperature value is the same. As can be seen from FIGS. 5A-5B, the characteristic temperature value deviates from a theoretical value due to instability of the cooling system. Obviously, taking the maximum value and the minimum value of deviation of the discrete points from the fitting curve is a quantitative representation of the instability of the cooling system on the fluctuation of the cooling effect, and this index is used to quantitatively measure the stability of the cooling effect of the cooling system. The smaller a span between a maximum value and a minimum value of deviation of discrete points from a linear regression curve, the more stable the cooling system.

More intuitively, for example, in FIGS. 5A-5B, for the temperature measuring points of the thermocouple, deviation of the highest temperature value and the initial temperature value from the fitting curve is in the interval range (−5.1° C., 8.3° C.), and deviation of the temperature value at 180 s and the initial temperature from the fitting curve is in the interval range (−4.6° C., 8.4° C.), illustrating that when the initial temperature is the same, the cooling system can ensure that the deviation of the characteristic temperature value at that point is controlled within a range. The smaller the interval span, the more stable the cooling system.

In summary, the method for evaluating the stability of the cooling effect of the cooling system for low-pressure casting of the aluminum alloy wheel hub according to the present disclosure has the following prominent substantive features and notable progress:

• • (1) performing analysis based on the temperature data can intuitively reflect the stability of the cooling effect of the cooling system, and avoids a complex mapping relationship between the stability of the flow rate and the stability of the cooling effect compared with the analysis of the stability of the flow rate of the cooling medium;
  • (2) the difficulty of testing under the condition that the initial temperature of the mold cannot be consistent is overcome, and instead, temperature data acquisition and analysis are performed by using the same cooling process setting at a differentiated initial temperature of the mold, and the test method is easy to implement; and
  • (3) by analyzing a relationship between the initial mold temperature and the characteristic temperature value under the cycle, and selecting the temperature value on the temperature curve before mold opening of low-pressure casting of the aluminum alloy wheel hub casting as a characteristic temperature value, the complexity of curve analysis is avoided, and the influence of non-mold cooling process factors on the cooling effect stability analysis result during the processes such as mold opening.

It will be understood by those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit or scope of the present disclosure. Therefore, if any modifications or variations fall within the scope of protection of the appended claims and their equivalents, the present disclosure is deemed to encompass these modifications and variations.