Low-pressure casting process capable of regulating and controlling pouring gate feeding capacity through temperature

Abstract

According to the low-pressure casting technology for regulating and controlling the pouring gate feeding capacity through the temperature, the heat conduction sleeve is arranged between the conventional liquid lifting assembly and the pouring gate, the temperature rise of the heat conduction sleeve is controlled through the induction heater, the temperature of molten metal passing through the heat conduction sleeve is regulated and controlled, the controllability is high, and the feeding capacity to a cavity can be adjusted at different casting stages. The casting process provided by the invention has the advantage of high feeding efficiency, the size of the used pouring gate is far lower than that of the prior art, and the investment of a single set of mold is reduced. And meanwhile, the filter screen made of a high-heat-conduction material is arranged, heat of the induction heater can be rapidly transferred, molten metal is not prone to being solidified on the surface of the filter screen, and then the cleaning-free effect is achieved. The pouring gate is located on the inner side of the cavity, only a small part of molten metal is solidified on the inner surface of a casting after forming is completed, the time for sawing the pouring gate in the conventional technology is saved, and the production efficiency of the casting is greatly improved.

Description

Technical Field

[0001] The invention relates to a low-pressure casting process, in particular to a low-pressure casting process with temperature-controlled gate shrinkage compensation capability. Background Art

[0002] The low-pressure casting process is a common workpiece casting method. The working principle is that the molten metal in the insulation furnace rises to the part cavity of the metal mold under pressure, and then solidifies and forms under a low-pressure environment. Figure 1 and Figure 2 That is, a low-pressure casting mold for an automobile steering knuckle is shown, and a molding cavity of the casting is formed between an upper mold and a lower mold.

[0003] Shrinkage compensation for castings is a problem that must be faced during the casting process. This is because the structure and wall thickness distribution of the parts cannot always be in an ideal state. If the local location is thick and solidifies slowly, a hot spot will be formed inside the part. It is often necessary to increase the shrinkage compensation effect at the front end of the filling after cooling at this location. In short, the front end of the filling at this location requires a higher part temperature to form a temperature gradient.

[0004] Common feeding methods include Figure 1 As shown in the figure, a gate is set between the bottom of the cavity and the liquid riser as a transitional shrinkage zone for casting molding. The molten metal enters the part cavity through the gate. After the cavity is filled, pressure is still provided to the gate to help shrink the part body. The classic casting pressure curve is shown in Figure 8 As shown, it can be roughly divided into liquid rising, filling, solidification, pressure relief, etc. In order to ensure that the gate has sufficient shrinkage compensation capacity, it is necessary to ensure that the gate has a certain quality to form a temperature gradient. Figure 2 It can be clearly seen that the bottom gate is large in volume. Generally, the weight of the gate accounts for 15-25% of the weight of the casting. This part of the gate needs to be removed by sawing after molding, which affects the processing efficiency of the casting. Since each part needs to be sawed, even if the gate can be recycled and remelted after sawing, there will be a certain amount of burning. At the same time, due to the thickness of the gate, the actual acquisition rate of the part is low. In the later stage of casting, it takes a certain amount of time to cool the gate, which increases the process cycle time. Long-term heating and cooling adjustments will also increase the fatigue state of the gate area, and there is a risk of mold cracking. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a low-pressure casting process with temperature-controlled gate shrinkage compensation capability. First, a metal mold is prepared: the metal mold comprises an upper mold and a lower mold arranged opposite to each other, a liquid riser component connected to a heat preservation furnace is provided at the bottom of the lower mold, a diverter cone is installed at the bottom of the upper mold, and a gate is formed between the liquid riser component and the diverter cone;

[0006] A heat-conducting sleeve made of heat-conducting metal is arranged between the gate and the liquid riser assembly, and the centers of both ends of the heat-conducting sleeve are respectively connected to the liquid riser assembly and the gate; an induction heater connected to the control center is also included, and the induction coil ring of the induction heater is arranged in the heat-conducting sleeve, and the temperature of the metal liquid passing through the heat-conducting sleeve is controlled by electromagnetic induction;

[0007] The upper mold is controlled to be pressed downward to form a cavity for forming the molten metal between the upper mold and the lower mold, wherein the cavity is connected to the gate; the molten metal is introduced into the cavity according to the following steps:

[0008] S1, liquid rising stage: fill the holding furnace with gas to control the molten metal to rise to the bottom of the cavity along the liquid rising component; at the same time, start the induction heater to preheat the molten metal through the heat conducting sleeve;

[0009] S2, filling stage: maintain the gas pressure on the liquid surface of the holding furnace until the molten metal fills the entire cavity, and keep the heat-conducting sleeve heated during the filling process;

[0010] S3, solidification stage: the air pressure is increased and maintained, so that the molten metal gradually solidifies under low pressure. During the solidification process, the temperature of the heat-conducting sleeve is gradually increased until the molten metal in the cavity is completely solidified.

[0011] S4, pressure relief stage: release the gas pressure on the liquid surface, and the unsolidified metal liquid in the liquid riser and the gate begins to flow back; maintain the temperature of the thermal sleeve until the gate is cooled down and turn off the induction heater.

[0012] Furthermore, the metal mold further comprises a filter screen for filtering the molten metal, the filter screen is arranged on the inner side of the heat-conducting sleeve, and the outer side of the filter screen is in contact with the inner wall of the heat-conducting sleeve.

[0013] Furthermore, the filter screen is made of a heat-resistant metal material with a thermal conductivity of not less than 120 W / (m*K).

[0014] Furthermore, the filter screen is a molybdenum alloy filter screen.

[0015] Furthermore, in the pressure relief stage of step S4, circulating water is introduced into the upper mold to cool the diverter cone and the gate.

[0016] Furthermore, the splitter cone is made of a metal material with a thermal conductivity of not less than 80 W / (m*K).

[0017] Furthermore, the diverter cone is made of tungsten steel material.

[0018] Furthermore, the gate is formed on the inner side of the cavity.

[0019] Furthermore, in steps S1 and S2, the heat-conducting sleeve is preheated by controlling the induction heater so that the molten metal can maintain the initial molten aluminum filling temperature.

[0020] Furthermore, in step S3, the temperature of the molten metal in the pouring gate is controlled by an induction heater to be 10° C. higher than the melting point.

[0021] The present invention provides a low-pressure casting process with temperature-controlled gate shrinkage compensation capability. A heat-conducting sleeve is provided between a conventional liquid-rising component and a gate. The heat-conducting sleeve is controlled to heat up by an induction heater, and the temperature of the molten metal passing through the heat-conducting sleeve is regulated. The controllable capability is strong, and the shrinkage compensation capability of the cavity can be adjusted at different stages of casting. The casting process provided by the present invention has the advantage of high shrinkage compensation efficiency. The size of the gate used is much lower than that of the prior art, which reduces the investment in a single set of molds. At the same time, the small-sized gate can reduce fatigue cracking caused by cooling water cooling and extend the life of the mold.

[0022] The present invention is also provided with a filter screen made of a high thermal conductivity material, which can quickly transfer the heat of the induction heater, and the metal liquid is not easy to solidify on the surface of the filter screen, thereby achieving a cleaning-free effect.

[0023] The gate of the present invention is located on the inner side of the cavity. After molding is completed, only a small portion of the molten metal solidifies on the inner surface of the casting. This portion of the casting surplus can be processed in the necessary machining stage later, eliminating the time of sawing the gate in conventional technology and greatly improving the production efficiency of the casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a low-pressure casting mold in the prior art;

[0025] Figure 2 It is an exploded schematic diagram of a low-pressure casting mold in the prior art;

[0026] Figure 3 It is a schematic diagram of the appearance of the low-pressure casting mold of the present invention;

[0027] Figure 4 Schematic diagram of a low-pressure casting mold of the present invention;

[0028] Figure 5 It is a schematic diagram of the positions of the diverter cone and the gate in the mold cavity of the present invention;

[0029] Figure 6 It is a schematic diagram of the explosion of the gate and runner of the present invention;

[0030] Figure 7 is a schematic diagram of the position of the induction coil of the present invention;

[0031] Figure 8 It is a pressure curve diagram of low pressure casting in the prior art;

[0032] Fig. 9 It is a pressure curve diagram of low-pressure casting provided by the present invention;

[0033] Fig.10 It is the temperature control gradient diagram of the induction heater of the present invention.

[0034] Reference numerals: upper mold 1, lower mold 2, cavity 3, liquid lifting component 4, diverter cone 5, gate 6, filter screen 7, induction coil 8, heat-conducting sleeve 9, net support 10, annular groove 11. DETAILED DESCRIPTION

[0035] Example 1: Figures 3 to 5 The low-pressure casting mold shown in the figure comprises an upper mold 1 and a lower mold 2 which are arranged opposite to each other, and a cavity 3 for forming a metal liquid is formed between the upper mold 1 and the lower mold 2. The upper mold 1 is driven downward by a vertically arranged driving mechanism to make the upper mold 1 and the lower mold 2 fit together. The bottom of the lower mold 2 is connected with a liquid riser assembly 4, which is generally composed of a liquid riser pipe and a ceramic core installed on the top of the liquid riser pipe. The other end of the liquid riser assembly 4 is connected to a metal liquid insulation furnace. The metal liquid in the insulation furnace flows into the cavity 3 through the liquid riser assembly 4 under the action of external pressure; after the metal liquid fills the cavity 3, it continues to be pressurized, and the metal liquid in the cavity 3 solidifies and forms under a low-pressure environment. A diverter cone 5 is installed at the bottom of the upper mold 1, and the lower end of the diverter cone 5 extends into the cavity 3. The side section of the diverter cone 5 generally presents an arc structure with a wide top and a narrow bottom. During the filling stage, the metal liquid can be diverted and filled from bottom to top along the outer arc of the diverter cone 5 to the inner side of the cavity 3.

[0036] The lower mold 2 has a gate 6 at the top of the liquid riser assembly 4, and the two ends of the gate 6 are connected to the liquid riser assembly 4 and the cavity 3 respectively. The molten metal flows to the gate 6 through the liquid riser assembly 4, and then is smoothly guided to the cavity 3 through the diverter cone 5, playing the role of shrinkage compensation of the cavity 3 during the solidification process of the molten metal. The mouth of the gate 6 generally presents an arc-shaped concave structure with a wide top and a narrow bottom according to the shape of the diverter cone 5 and the cavity 3, forming a shape with a reasonable wall thickness distribution, and ensuring the shrinkage compensation effect of the cavity 3 molding as much as possible.

[0037] Different from the prior art in which the gate 6 is provided to compensate the shrinkage of the cavity 3, the present invention is provided with a heating mechanism at the lower part of the gate 6 to change the temperature of the molten metal flowing through the gate 6 in real time to adjust the degree of compensation of the molten metal. The heating mechanism includes a heat-conducting sleeve 9 provided below the gate 6 in the lower mold 2, and the centers of both ends of the heat-conducting sleeve 9 are respectively connected to the liquid riser 4 and the gate 6, and the heat-conducting sleeve 9 can heat the molten metal at the runner before entering the gate 6.

[0038] The heat-conducting sleeve 9 of the present invention heats the runner by induction heating. The principle of induction heating is to generate an alternating magnetic field through an alternating current. Eddy currents will be generated inside the metal conductor in the alternating magnetic field, which will rapidly increase the temperature of the metal conductor. The induction heater has the advantage of fast heating speed. At the same time, the induction heater can control the heating program according to pre-set parameters and has a certain degree of automatic operation capability. Figure 6 and Figure 7 As shown, a ring-shaped heating cavity is provided in the heat-conducting sleeve 9, and an induction coil 8 of the induction heater is arranged in the heating cavity. The wire end of the induction coil 8 passes through the heat-conducting sleeve 9 and is connected to an external power supply.

[0039] The heat-conducting sleeve 9 of the present embodiment is composed of two metal fixtures with L-shaped cross-sections, which are assembled up and down. The relative circumferences of the two metal fixtures enclose the heating cavity for storing the induction coil 8. The metal fixtures are made of highly heat-resistant mold steel material, which can quickly receive the heat generated by the heating induction coil 8 and at the same time provide external shielding for the induction coil 8.

[0040] The principle of the present invention is to increase the temperature of the molten metal at the runner by induction heating, thereby increasing the degree of shrinkage compensation of the molten metal. It is not necessary to reserve a large amount of molten metal for shrinkage compensation as in the prior art, so the space occupied by the gate 6 can be greatly reduced. In addition, unlike the prior art in which the gate 6 is formed below the cavity 3 and the redundant gate 6 needs to be sawed off along the bottom of the cavity 3 after casting, the gate 6 in this embodiment occupies a smaller space and can be further arranged on the inner side of the cavity 3. A small amount of molten metal is formed at the gate together with the cavity 3. This part of the casting surplus can be removed in the later inherent machining process without sawing the lower gate 6.

[0041] The diverter cone 5 of the present invention is made of a heat-conducting material with a high thermal conductivity, such as a tungsten steel alloy with a thermal conductivity of not less than 80W / (m*K), and its thermal conductivity is twice that of ordinary mold steel. In the late solidification of the molten metal, circulating water will flow through the inside of the diverter cone 5 for cooling. Due to the small volume of the gate 6 and the improvement of the material of the diverter cone 5, the heat in the middle area of ​​the cavity 3 and the gate 6 will be quickly taken away, greatly reducing the cooling time of the gate 6. After the gate 6 solidifies, the mold can be opened to take out the parts and enter the next cycle. In each low-pressure casting cycle, the conventional casting process usually takes about 50-70 seconds to cool the gate 6 in the late solidification period, while the device provided by the present invention can reduce the cooling time of the gate 6 to about 10-20 seconds.

[0042] Because there may be oxide slag inside the molten metal, or impurities dropped from the crucible or degassing consumables, or residues after alloy or refining agent treatment, in the prior art, a Figure 2The filter screen 7 is shown. There are usually two ways to set the filter screen 7: one is to set a disposable glass fiber filter screen, which is placed manually, and the sawed gate 6 is allowed to be put into the furnace for remelting; the other is a metal filter screen placed by a robot, but the gate cannot be reused due to iron contamination. The former solution cannot ensure that the filter screen 7 is placed correctly or not missed, and the latter has the problem of low material utilization.

[0043] Like the prior art, the present invention is provided with a filter screen 7 for filtering the molten metal, and the filter screen 7 is arranged in a ring in the runner of the heat-conducting sleeve 9 to fully cover the flow area of ​​the molten metal. The filter screen 7 is made of a metal material with high heat resistance and high thermal conductivity, such as a molybdenum alloy material with a thermal conductivity of not less than 120W / (m*K). After being heated by the induction coil 8, the filter screen 7 can be quickly heated up by the heat-conducting sleeve 9, thereby accelerating the flow speed of the molten metal through the induction coil 8. The position of the filter screen 7 is preferably set at the nozzle position close to the side of the gate 6. After passing through the filter screen 7, the molten metal directly flows into the gate 6, heating the molten metal at the gate 6, thereby improving the shrinkage compensation efficiency.

[0044] The conventional filter screen 7 is usually a disposable filter structure, fixed in the gate 6 by an external net holder 10, and replaced each time casting. In this embodiment, an annular groove 11 is further provided on the inner peripheral surface of the heat-conducting sleeve 9, and the annular groove 11 serves as a net holder for supporting the filter screen 7. The filter screen 7 is fixedly installed in the annular groove 11, which can reduce the number of replacements and prevent the filter screen 7 from being missed or tilted.

[0045] Example 2: This example uses the mold provided in Example 1 to manufacture a steering knuckle casting for an automobile under a low-pressure environment. The aluminum grade of the casting is A356, with a yield strength of ≥220Mpa, a tensile strength of ≥290Mpa, and an elongation of ≥8%.

[0046] Reference Fig. 9 The low-pressure casting method of the steering knuckle includes the following pressurizing steps:

[0047] S1, liquid raising stage: gas is filled into the holding furnace, and the gas pressure is quickly increased to 100 Mbar. Under the action of gas pressure, the aluminum liquid rises along the liquid raising component 4 to the bottom of the cavity 3.

[0048] S2, filling stage: the aluminum liquid enters the cavity 3 smoothly through the gate 6, and the gas pressure on the liquid surface of the holding furnace is maintained until the aluminum liquid fills the entire cavity 3; the gas pressure is increased to 200Mbar in about 20s to speed up the filling speed of the aluminum liquid.

[0049] S3, solidification stage: increase the pressure to 550Mbar, and introduce cooling water into the diverter cone 5. The aluminum liquid gradually solidifies under the action of pressure; continue to maintain the gas pressure of 550Mbar, and the aluminum liquid continues to solidify and shrink in the cavity 3 until the aluminum liquid is completely solidified and fills the entire cavity 3.

[0050] S4, pressure relief stage: release the gas pressure on the liquid surface, so that the unsolidified aluminum liquid in the liquid lifting component 4 and the pouring gate 6 flows back to the holding furnace. After the pressure relief is completed, the mold is opened to take out the cast workpiece, and the next casting cycle is carried out again.

[0051] While the casting process is pressurized, the pouring channel is heated by the induction heater in Example 1. Fig.10 In steps S1 and S2, the induction heater is turned on to quickly increase the heating efficiency to 20%, and the aluminum liquid passing through the heat-conducting sleeve 9 is preheated and kept warm, so that the aluminum liquid at the runner can maintain the initial filling temperature, and the aluminum liquid fills the cavity 3 at a certain rate.

[0052] In the S3 solidification stage, the aluminum liquid begins to solidify under a pressurized environment, gradually improving the heating efficiency of the induction heater to 80%, maintaining the flow effect of the aluminum liquid at the runner, and then improving the shrinkage compensation effect of the aluminum liquid at the runner. The part located at the top of the cavity 3 is far away from the heat-conducting sleeve 9, and the casting begins to solidify and form from the top of the cavity 3. The position of the gate close to the heat-conducting sleeve 9 is finally formed, and the entire molding process is carried out step by step from top to bottom. The heating efficiency is gradually improved throughout the S3 solidification stage, which can be adapted to the molding process of the casting. The temperature of the aluminum liquid at the gate 6 is at least 10°C higher than the melting point, and the cavity 3 can be compensated for shrinkage stably and fully at all times, and will not solidify with the cavity 3 under a low-pressure environment; in the later stage of the solidification stage, the aluminum liquid in the cavity 3 has been completely solidified, and the formed part at the gate 6 is in good contact with the diverter cone 4, which can achieve rapid cooling of the gate 6. Further, for some larger gates 6, on the premise of ensuring that the cavity 3 is completely solidified, the arrival time of the peak temperature of the induction heater can be appropriately advanced.

[0053] In the S4 pressure relief stage, the heating efficiency is maintained at no less than 80%, so that the filter screen 7 is always in a high temperature state, which can speed up the reflux of the aluminum liquid at the gate and the runner. In the later stage of the pressure relief stage, the unsolidified aluminum liquid at the gate 6 has been basically discharged, and the aluminum liquid will not solidify at the filter screen 7, so that the filter screen 7 has a self-cleaning effect and does not need to be replaced every time casting. After waiting for the mold to cool down sufficiently, the mold can be opened to take out the casting and then the next cycle can be carried out.

[0054] Comparative Example 1: Using Figure 1 and Figure 2 The low pressure casting mold shown and Figure 8The steering knuckle was prepared according to the pressure curve shown in the figure, and the performance parameters of the steering knuckle casting were consistent with those in Example 2. The performance test of the mold after casting was carried out, and the comparative data shown in the following table were obtained:

[0055]

[0056] It can be seen from the data in the above table that the mold of Example 1 of the present invention and the casting method provided by Example 2 can effectively provide shrinkage compensation for the solidification of the molten metal in the cavity 3, form a gate that is much smaller than the prior art, reduce the time required to cool the cavity 3 after pressure relief, and thus reduce the reduction in the life of the mold due to cooling cracking. The embodiment of the present invention can eliminate the step of sawing the gate 6 after a single casting, and the filter screen 7 has a self-cleaning function, which can greatly simplify the low-pressure casting molding steps of the workpiece.

[0057] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability, characterized in that: First, a metal mold is prepared, wherein the metal mold comprises an upper mold (1) and a lower mold (2) arranged opposite to each other, a liquid riser assembly (4) connected to a heat preservation furnace is provided at the bottom of the lower mold (2), a diverter cone (5) is installed at the bottom of the upper mold (1), and a gate (6) is formed between the liquid riser assembly (4) and the diverter cone (5); A heat-conducting sleeve (9) made of heat-conducting metal is arranged between the gate (6) and the liquid riser assembly (4), and the centers of both ends of the heat-conducting sleeve (9) are respectively connected to the liquid riser assembly (4) and the gate (6); and an induction heater connected to a control center is also included, and the induction coil (8) of the induction heater is arranged in the heat-conducting sleeve (9), and the temperature of the metal liquid passing through the heat-conducting sleeve (9) is controlled by electromagnetic induction; The upper mold (1) is controlled to be pressed downward, so that a cavity (3) for molding molten metal is formed between the upper mold (1) and the lower mold (2), and the cavity (3) is connected to the gate (6); the molten metal is introduced into the cavity (3) according to the following steps: S1, liquid raising stage: filling gas into the heat preservation furnace to control the molten metal to rise along the liquid raising component (4) to the bottom of the cavity (3); at the same time, starting the induction heater to preheat the molten metal through the heat conducting sleeve (9); S2, filling stage: maintaining the gas pressure on the liquid surface of the holding furnace until the molten metal fills the entire cavity (3), and maintaining the heating of the heat-conducting sleeve (9) during the filling process; S3, solidification stage: the air pressure is increased and maintained, so that the molten metal gradually solidifies in a low-pressure environment, and the temperature of the heat-conducting sleeve (9) is gradually increased during the solidification process until the molten metal in the cavity (3) is completely solidified; S4, pressure relief stage: the gas pressure on the liquid surface is released, and the unsolidified metal liquid in the liquid riser (4) and the gate (6) begins to flow back; the temperature of the heat-conducting sleeve (9) is maintained until the gate (6) is cooled down, and the induction heater is turned off.

2. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 1, characterized in that: The metal mold further comprises a filter screen (7) for filtering the metal liquid. The filter screen (7) is arranged around the inner side of the heat-conducting sleeve (9), and the outer side of the filter screen (7) is in contact with the inner wall of the heat-conducting sleeve (9).

3. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 2, characterized in that: The filter screen (7) is made of a heat-resistant metal material with a thermal conductivity of not less than 120 W / (m*K).

4. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 3, characterized in that: The filter screen (7) is a molybdenum alloy filter screen.

5. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 1, characterized in that: During the pressure release phase of step S4, circulating water is introduced into the upper mold (1) to cool the diverter cone (5) and the gate (6).

6. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 1, characterized in that: The splitter cone (5) is made of a metal material with a thermal conductivity of not less than 80 W / (m*K).

7. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 6, characterized in that: The splitter cone (5) is made of tungsten steel material.

8. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 1, characterized in that: The gate (6) is formed on the inner side of the cavity (3).

9. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 1, characterized in that: In steps S1 and S2, the heat-conducting sleeve (9) is preheated by controlling the induction heater so that the molten metal can maintain the initial aluminum liquid filling temperature.

10. A low-pressure casting process with temperature-controlled gate shrinkage compensation capability as claimed in claim 1, characterized in that: In step S3, the temperature of the molten metal in the pouring gate (6) is controlled by an induction heater to be 10° C. higher than the melting point.

Images