CN105598418B - A kind of aluminum alloy automobile chassis casting metal type low-pressure casting forming method for rapid pressurization after holding pressure - Google Patents

Abstract

The invention discloses a kind of Quick-pressurizing method after aluminium alloy automobile chassis casting metal-mold low-pressure casting shaping pressurize, the method a liter liquid, fill type and crystallization pressurization stages, continue existing aluminium alloy automobile chassis casting low-pressure casting process, rise hydraulic coupling, mold filling pressure and crystallization Pressure control in 15~21kPa, 25~35kPa and 80~100kPa.In crystallization packing stage and between the release stage, the Quick-pressurizing stage after pressurize is increased.According to casting structure feature and solidification sequence, the multiple characteristic portions of setting.After determining that characteristic portion A starts solidification, start increase crystallization dwell pressure to 150~1000kPa, pumping rate is 10~40kPa/s；Packing stage, characteristic portion B, characteristic portion C and characteristic portion D consecutive solidifications are subsequently entered, after characteristic portion D solidifications terminate, continues 10~60s of pressurize.The inventive method causes that solidification feeding effect and mechanical castings are significantly improved, while avoiding the defects such as aluminium liquid splashing, casting fin burr, significantly reduces the requirement to mould structure and casting mold mold clamping force.

Description

A kind of aluminum alloy automobile chassis casting metal mold low pressure casting supercharging method

technical field

The present invention relates to a method of manufacturing aluminum alloy automobile chassis castings by adopting a low-pressure casting process, more particularly, it is a method for preparing aluminum alloy automobile chassis castings that continues to be rapidly pressurized after entering the crystallization and pressure-holding stage according to the solidification time in sequence , Metal mold low-pressure casting forming method of rapid pressurization after holding pressure.

Background technique

In recent years, with the improvement of automobile lightweight requirements, the application of aluminum alloy structural parts in automobiles has become more and more extensive. Taking the chassis suspension system as an example, the application ratio of aluminum alloy front/rear steering knuckles is close to 50%, and the application ratio of aluminum alloy in swing arms and control arm parts has also reached about 30%. In 1995, the BMW 5 Series used an all-aluminum suspension, which reduced the mass of the suspension system by 15%; the front and rear axles were made of aluminum alloy, reducing the weight by 65kg. Middle and high-end models use more aluminum alloy parts, while the application of aluminum alloy materials on low-end models is greatly restricted due to price reasons. Cost reduction has become the direction of efforts of automobile aluminum alloy parts manufacturers.

Commonly used materials for casting and forming aluminum alloy automobile chassis components are A356 and A380, etc. Commonly used casting processes include gravity metal mold casting, low pressure casting, high pressure casting, differential pressure casting, high vacuum die casting and semi-solid casting. The differential pressure casting process is mostly used to produce high-quality castings such as steering knuckles and control arms with complex shapes, large cross-section changes, and no casting defects such as shrinkage cavities and porosity.

The common features of differential pressure casting and low-pressure casting are: (1) the filling speed is controllable, the molten metal flows smoothly, and secondary inclusions are reduced; (2) the casting solidifies under pressure, the feeding effect is good, the structure is compact, and the density and mechanical properties are significantly improved. The difference is that differential pressure casting has two upper and lower pressure tanks, the lower pressure tank is a holding furnace and aluminum liquid crucible, and the upper pressure tank is a casting mold (sand mold or metal mold), while low pressure casting has only one lower pressure tank. type directly exposed to the atmosphere. Compared with low-pressure casting, differential pressure casting crystallizes and solidifies under a larger pressure environment, and the structure is more compact, but the operation inconvenience caused by the upper and lower tank structure of differential pressure casting, as well as the equipment brought by more complex structure and control system The price increase has caused the application of differential pressure casting to be far less popular than low pressure casting.

The low-pressure casting process can be used as a pressure-time curve on the surface of the molten metal to respond. A typical pressure (pressure difference)-time curve includes seven different process stages, including liquid raising stage, mold filling stage, crusting pressurization stage, crusting pressure holding stage, crystallization pressurization stage, crystallization holding pressure stage, and pressure relief stage. . Metal mold low-pressure casting generally omits the encrustation stage. Therefore, the metal mold low-pressure casting process includes five stages: liquid raising, mold filling, crystallization pressurization, crystallization pressure holding and pressure relief.

The crystallization supercharging pressure directly affects the effect of solidification and feeding. The higher the crystallization supercharging pressure, the better the effect of solidification and feeding, which is more conducive to eliminating defects such as shrinkage cavities and porosity, and improving tissue density. The crystallization boost pressure of low-pressure casting is generally 50-80kPa, and it increases to 80-150kPa under special conditions.

For low-pressure casting of aluminum alloy metal molds, the limitation of the mold clamping force, the overflow and splash of aluminum liquid caused by the gap between the molds, the flash and burrs of castings, etc. are considered in actual production, which limits the further improvement of castings by increasing the crystallization boost pressure. Feasibility of tissue density and mechanical properties.

Contents of the invention

Aiming at the problem that it is difficult to achieve high crystallization supercharging pressure in the low-pressure casting of aluminum alloy automotive chassis castings with complex shapes and variable cross-sections such as steering knuckles, control arms, and sub-frames, combined with the structural characteristics of such castings and the sequential solidification process According to the requirements, a pressure method for low-pressure casting molding of aluminum alloy casting metal molds with rapid pressurization after crystallization and pressure holding according to the solidification sequence is proposed to further reduce casting defects such as shrinkage cavities and porosity, and improve the microstructure of castings. density and mechanical properties.

The present invention relates to a metal mold low-pressure casting forming method for rapid pressurization after holding pressure. The metal mold low-pressure casting at least includes a liquid raising stage, a mold filling stage, a crystallization pressurization stage, a crystallization pressure holding stage, and a pressure relief stage. ; characterized by:

According to the solidification sequence of the characteristic parts, a rapid pressurization stage after holding pressure is added between the crystallization holding pressure stage and the pressure relief stage;

According to the structural characteristics and solidification sequence of the casting, a plurality of characteristic parts are set, and the characteristics can be characteristic part A, characteristic part B, characteristic part C, and characteristic part D;

The steps of the rapid pressurization stage after the pressure holding are:

(A) After the characteristic part A begins to solidify, start to increase the crystallization holding pressure to 150-1000kPa, and the pressurization speed is 10-40kPa/s;

(B) Characteristic part B begins to solidify;

(C) The characteristic part C begins to solidify;

(D) After the solidification of the characteristic part D, continue to maintain the pressure for 10-60s and then release the pressure.

A kind of metal type low-pressure casting molding is used to prepare the aluminum alloy automobile chassis casting by the rapid pressurization method after holding the pressure, and it is characterized in that following steps are arranged:

Step 1, liquid ascending stage;

Adjust the pressure in the liquid-raising stage to 15-21kPa, and the liquid-raising speed to 1.8-2.0kPa/s;

Step 2, the filling stage;

Adjust the filling pressure in the filling stage to 25-35kPa, and the filling speed to 0.4-1.0kPa/s, so that the aluminum liquid enters the cavity from the gate until the cavity is completely filled;

Step 3, crystallization pressurization stage;

After the second step, the molten aluminum is completely filled with the mold, and the pressure is rapidly increased to 80-100kPa in 5-7s;

Step 4, crystallization and pressure holding stage;

After the boost pressure reaches 80-100kPa, it enters the stage of crystallization and pressure holding;

Step 5, rapid pressurization stage after pressure holding;

(A) When the characteristic part A begins to solidify, start to increase the crystal holding pressure to 150-1000kPa, and the pressurization speed is 10-40kPa/s;

(B) Characteristic part B begins to solidify;

(C) The characteristic part C begins to solidify;

(D) After the solidification of the characteristic part D, continue to hold the pressure for 10-60s;

Step 6, pressure relief and deflation stage;

After Step 5, after the solidification of the aluminum alloy automobile chassis casting is completed, the gas pressure in the holding furnace is released, so that the unsolidified aluminum liquid in the riser pipe and the sprue mouth flows back into the holding furnace.

The advantages of the method for quickly pressurizing after holding pressure for the metal mold low-pressure casting molding of aluminum alloy automobile chassis castings of the present invention are:

(1) By adopting the method of the present invention to prepare A356 aluminum alloy automobile chassis castings, the effect of solidification and feeding is significantly improved. Compared with the existing low-pressure casting pressurization method, the tensile strength can be increased by 10-50% and the elongation rate can be increased by 25-50% under the condition that the mold structure and clamping force remain unchanged. Significantly reduces the requirements on the mold structure and mold clamping force, and at the same time avoids defects such as aluminum liquid overflow and splash, casting flash and burr.

(2) Adopting the method of the present invention to prepare high-quality aluminum alloy castings with complex shapes and variable wall thicknesses can achieve the density and mechanical performance indicators of differential pressure casting, while avoiding the inconvenience of operation caused by the upper and lower tank structures of differential pressure casting, As well as problems such as increased equipment prices brought about by more complex structures and control systems, it can better adapt to the low-cost and mass production requirements of aluminum alloy castings such as automotive chassis components.

Description of drawings

FIG. 1A is a schematic diagram of structural features of a rear steering knuckle of an automobile.

FIG. 1B is a pressure-time curve diagram of the rapid pressurization mode after pressure holding in Example 1. FIG.

Fig. 2A is a schematic diagram of structural features of a control arm for an automobile.

FIG. 2B is a pressure-time curve diagram of the rapid pressurization mode after pressure holding in Example 2. FIG.

FIG. 3 is a pressure-time curve diagram of the rapid pressurization mode after pressure holding in Example 3. FIG.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

For steering knuckles, control arms, sub-frames and other aluminum alloy automotive chassis castings with complex shapes and large cross-sectional changes, the principle of sequential solidification is usually adopted in differential pressure casting or low pressure casting. At the part, during the filling process, the high-temperature aluminum liquid flows out from the gate to fill the casting, and finally reaches the thinner part far away from the gate; during the solidification process, the thinner part far away from the gate solidifies first, and then gradually solidifies sequentially toward the gate , in order to achieve a good feeding effect.

In the present invention, according to the structural characteristics and solidification sequence of the casting, a plurality of characteristic parts are set, that is, the thin-walled part at the end farthest from the gate is selected as the characteristic part A, and the wall thickness abrupt change part farthest from the gate is selected as For characteristic part B, select the wall thickness mutation point close to the gate as characteristic part C, and select the center of the gate as characteristic part D.

What the present invention proposes is a kind of metal mold low-pressure casting method that increases pressure-holding and pressurizes quickly to prepare aluminum alloy automobile chassis castings (that is, a kind of aluminum alloy automobile chassis casting metal mold low-pressure casting forming with pressure-holding and rapid pressurization). method), the method of the present invention includes: a liquid raising stage, a mold filling stage, a crystallization pressurization stage, a crystallization holding pressure stage, a rapid pressurization stage after holding pressure, and a pressure relief and deflation stage. Specifically:

Step 1, liquid ascending stage;

Adjust the pressure in the liquid-raising stage to 15-21kPa, and the liquid-raising speed to 1.8-2.0kPa/s;

The compressed air of 15-21kPa is passed into the sealed holding furnace, and the aluminum liquid rises steadily along the riser pipe to the gate of the mold under the action of pressure, and flows into the mold;

Step 2, the filling stage;

Adjust the filling pressure in the filling stage to 25-35kPa, and the filling speed to 0.4-1.0kPa/s, so that the aluminum liquid enters the cavity from the gate until the cavity is completely filled;

Step 3, crystallization pressurization stage;

After the second step, the molten aluminum is completely filled with the mold, and the pressure is rapidly increased to 80-100kPa in 5-7s;

Step 4, crystallization and pressure holding stage;

After the boost pressure reaches 80-100kPa, it enters the stage of crystallization and pressure holding;

Step 5, rapid pressurization stage after pressure holding;

In the present invention, the rapid pressurization method after pressure holding varies depending on the size and structure of the aluminum alloy automobile chassis casting, the state of the mold and the cooling conditions.

The fast pressurization method after the described crystallization pressure holding refers to:

(A) When the characteristic part A begins to solidify, start to increase the crystal holding pressure to 150-1000kPa, and the pressurization speed is 10-40kPa/s;

(B) Characteristic part B begins to solidify;

(C) The characteristic part C begins to solidify;

(D) After the characteristic part D solidifies, continue to hold the pressure for 10-60s.

After step 5, continue pressurization and solidification according to the rapid pressurization method after crystallization and pressure holding, so as to reduce casting defects such as shrinkage cavity and porosity of aluminum alloy automobile chassis castings, improve the feeding effect, and increase the microstructure density of aluminum alloy automobile chassis castings and mechanical properties.

Step 6, pressure relief and deflation stage;

After Step 5, after the solidification of the aluminum alloy automobile chassis casting is completed, the gas pressure in the holding furnace is released, so that the unsolidified aluminum liquid in the riser pipe and the sprue mouth flows back into the holding furnace.

Example 1

The rear steering knuckle of the car is made of A356 alloy and weighs 2.8kg. The pouring temperature is 710°C, the mold material is H13 steel, the initial mold temperature is 350°C, and the cooling method is a combination of 9-way water cooling and 3-way air cooling. The configuration and characteristic parts of the steering knuckle are shown in Figure 1A. The structure of Figure 1A refers to Modern Manufacturing Engineering, Issue 4, 2014, "Automotive Rear Steering Knuckle Lightweight Design and Test Verification", author Zhang Qi et al.

Referring to the pressure-time curve diagram of the rapid pressurization method after holding pressure shown in Figure 1B, the steps for preparing aluminum alloy automobile chassis castings by using the metal mold low-pressure casting molding and using the rapid pressurization method after holding pressure are as follows:

Step 1, liquid ascending stage;

Under the conditions of the liquid lifting pressure of 17kPa and the liquid lifting speed of 2.0kPa/s, the aluminum liquid rises steadily along the liquid rising pipe to the gate of the mold and flows into the mold;

Step 2, the filling stage;

Under the conditions of filling pressure of 28kPa and filling speed of 0.55kPa/s, liquid aluminum is filled into the cavity from the gate until the cavity is completely filled;

Step 3, crystallization pressurization stage;

After the molten aluminum is filled with the mold, the crystallization pressure is rapidly increased, and the pressure is boosted to 80kPa in 5.5s;

Step 4, crystallization and pressure holding stage;

After the boost pressure reaches 80kPa, start to crystallize and hold the pressure;

Step 5, rapid pressurization stage after pressure holding;

In the present invention, the crystallization and pressure-holding treatment is carried out in an improved way of rapid pressurization after pressure-holding, and its pressure-time curve is shown in FIG. 1B .

(A) The characteristic part A begins to solidify after 10s of mold filling, and at this time, increase the crystallization holding pressure to 380kPa at a speed of 25kPa/s;

(B) The characteristic part B begins to solidify after 13 seconds of filling;

(C) The characteristic part C begins to solidify after 19 seconds of filling;

(D) The characteristic part D is solidified 190s after the filling is completed, and the pressure is continued for 60s;

Step 6, pressure relief and deflation stage;

After step 5, the gas pressure in the holding furnace is released, so that the unsolidified aluminum liquid in the riser pipe and the sprue mouth flows back to the holding furnace.

Comparative Example 1

Steps 1 to 3 are the same as those in Embodiment 1, except that the process of rapid pressurization after pressure holding in step 5 is omitted.

Following step 3, after the pressurized pressure reaches 80kPa, start to crystallize and hold the pressure for 250s, and then release the gas pressure in the holding furnace, so that the unsolidified aluminum liquid in the riser and runner mouth flows back to the holding furnace.

The A356 alloy steering knuckle castings prepared in Example 1 and Comparative Example 1 were subjected to T6 heat treatment, and their tensile strength, yield strength and elongation properties were tested.

The mechanical properties of the steering knuckle prepared in Comparative Example 1 were measured by an Instron 8801 tensile testing machine: the tensile strength, yield strength and elongation were 246 MPa, 201 MPa and 8.0%, respectively.

The mechanical properties of the steering knuckle prepared in Example 1 were measured by an Instron 8801 tensile testing machine: the tensile strength, yield strength and elongation reached 333 MPa, 287 MPa and 11.9%, respectively.

Through comparison, it can be seen that the tensile strength, yield strength and elongation of the steering knuckle obtained by the method of the present invention are increased by 35.3%, 42.8% and 48.8%, reaching the mechanical performance index of differential pressure casting.

Example 2

The lower control arm of the car is made of A356 alloy and weighs 2.4kg. The pouring temperature is 720°C, the mold material is H13 steel, the initial mold temperature is 250°C, and the cooling method is a combination of 6-way water cooling and 3-way air cooling. The configuration and characteristic parts of the control arm are shown in Figure 2A. The structure of Figure 2A refers to "Numerical Simulation and Process Optimization of Squeeze Casting of Automobile Control Arm", author Xing Zhiwei et al.

See Figure 2B for the pressure-time curve diagram of the rapid pressurization method after holding the pressure. The steps for preparing aluminum alloy automobile chassis castings by using the metal mold low-pressure casting molding method to quickly pressurize after holding the pressure are as follows:

Step 1, liquid ascending stage;

Under the condition that the liquid lifting pressure is 20kPa and the liquid lifting speed is 2.0kPa/s, the aluminum liquid rises steadily along the liquid rising pipe to the gate of the mold and flows into the mold;

Step 2, the filling stage;

Under the conditions of filling pressure of 30kPa and filling speed of 0.5kPa/s, liquid aluminum is filled into the cavity from the gate until the cavity is completely filled;

Step 3, crystallization pressurization stage;

After the molten aluminum is filled with the mold, the crystallization pressure is rapidly increased, and the pressure is boosted to 85kPa in 6s;

Step 4, crystallization and pressure holding stage;

After the boost pressure reaches 85kPa, start to crystallize and hold the pressure;

Step 5, rapid pressurization stage after pressure holding;

In the present invention, the crystallization and pressure-holding treatment is carried out in an improved way of rapid pressurization after pressure-holding, and its pressure-time curve is shown in FIG. 2B .

(A) The characteristic part A begins to solidify after filling the mold for 8s. At this time, the crystallization holding pressure is increased at a rate of 32kPa/s until the crystallization holding pressure reaches 950kPa;

(B) The characteristic part B begins to solidify after 12 seconds of filling;

(C) The characteristic part B begins to solidify after 17s of filling;

(D) The characteristic part D is solidified 130s after the filling is completed, and the pressure is continued for 30s;

Step 6, pressure relief and deflation stage;

After step 5, the gas pressure in the holding furnace is released, so that the unsolidified aluminum liquid in the riser pipe and the sprue mouth flows back to the holding furnace.

Comparative Example 2

Steps 1 to 3 are the same as those in Embodiment 2, except that the process of rapid pressurization after pressure holding in Step 5 is omitted.

After step 3, after the pressurized pressure reaches 85kPa, start to crystallize and hold the pressure for 165s, and then release the gas pressure in the holding furnace, so that the unsolidified aluminum liquid in the riser and sprue mouth flows back to the holding furnace.

The A356 alloy steering knuckle castings prepared in Example 2 and Comparative Example 2 were subjected to T6 heat treatment, and their tensile strength, yield strength and elongation properties were tested.

Instron 8801 model tensile testing machine was used to measure the mechanical properties of the control arm prepared in Comparative Example 2: its tensile strength, yield strength and elongation reached 256MPa, 199MPa and 8.2%, respectively.

The mechanical properties of the control arm prepared in Example 2 were measured by an Instron 8801 tensile testing machine: the tensile strength, yield strength and elongation reached 340 MPa, 289 MPa and 11.5%, respectively.

The tensile strength, yield strength and elongation of the control arm treated by the method of the invention are increased by 32.8%, 45.2% and 40.2%, reaching the mechanical performance index of differential pressure casting.

Example 3

The rear steering knuckle of the car is made of A356 alloy and weighs 2.8kg. The pouring temperature is 720°C, the mold material is H13 steel, the initial mold temperature is 350°C, and the cooling method is a combination of 9-way water cooling and 3-way air cooling. The configuration and characteristic parts of the steering knuckle are shown in Figure 1A.

Referring to the pressure-time curve diagram of the rapid pressurization method after holding pressure shown in Figure 3, the steps for preparing aluminum alloy automobile chassis castings by using the metal mold low-pressure casting molding and using the fast pressurization method after holding pressure are as follows:

Step 1, liquid ascending stage;

Under the conditions of the liquid lifting pressure of 18kPa and the liquid lifting speed of 2.0kPa/s, the aluminum liquid rises steadily along the liquid rising pipe to the gate of the mold and flows into the mold;

Step 2, the filling stage;

Under the conditions of filling pressure of 26kPa and filling speed of 0.98kPa/s, liquid aluminum is filled into the cavity from the gate until the cavity is completely filled;

Step 3, crystallization pressurization stage;

After the molten aluminum is filled with the mold, the crystallization pressure is rapidly increased, and the pressure is boosted to 90kPa in 6s;

Step 4, crystallization and pressure holding stage;

After the supercharging pressure reaches 90kPa, start to crystallize and hold the pressure;

Step 5, rapid pressurization stage after pressure holding;

In the present invention, the crystallization and pressure-holding treatment is carried out in a rapid pressure-increasing manner after the improved pressure-holding, and its pressure-time curve is shown in FIG. 3 .

(A) The characteristic part A begins to solidify after 10s of mold filling, and at this time, the crystallization holding pressure is increased to 164kPa at a speed of 6.4kPa/s;

(B) The characteristic part B begins to solidify after 13 seconds of filling;

(C) The characteristic part C begins to solidify after 19 seconds of filling;

(D) The solidification of the characteristic part D ends 190s after the filling is completed, and the pressure is continued for 20s.

Step 6, pressure relief and deflation stage;

After step 5, the gas pressure in the holding furnace is released, so that the unsolidified aluminum liquid in the riser pipe and the sprue mouth flows back to the holding furnace.

With the A356 alloy steering knuckle casting that embodiment 3 makes, after T6 heat treatment, adopt Instron 8801 model tensile testing machine to test its tensile strength, yield strength and elongation performance: tensile strength, yield strength and elongation reach respectively 328MPa, 281MPa and 12.5%, reaching the mechanical performance index of differential pressure casting.

Claims (1)

1. A kind of aluminum alloy automobile chassis casting metal mold low-pressure casting forming method for rapid pressurization after holding pressure, said aluminum alloy automobile chassis casting metal mold low pressure casting at least includes a liquid lifting stage, a filling stage, and a crystallization supercharging stage , crystallization holding pressure stage and decompression stage; It is characterized in that: The aluminum alloy automobile chassis castings refer to steering knuckles, control arms, sub-frames or hub brackets; During the solidification process, the thinner part far away from the gate solidifies first, and then gradually solidifies sequentially toward the gate; according to the structural characteristics and solidification sequence of the casting, set multiple characteristic parts, that is, select the thinner part farthest from the gate. The wall is the characteristic part A, select the wall thickness sudden change part farthest from the gate as the characteristic part B, select the wall thickness sudden change part closer to the gate as the characteristic part C, and select the center of the gate as the characteristic part D; According to the solidification sequence of the characteristic parts, a rapid pressurization stage after holding pressure is added between the crystallization holding pressure stage and the pressure relief stage; Step 1, liquid ascending stage; Adjust the pressure in the liquid-raising stage to 15-21kPa, and the liquid-raising speed to 1.8-2.0kPa/s; Step 2, the filling stage; Adjust the filling pressure in the filling stage to 25-35kPa, and the filling speed to 0.4-1.0kPa/s, so that the aluminum liquid enters the cavity from the gate until the cavity is completely filled; Step 3, crystallization pressurization stage; After the second step, the molten aluminum is completely filled with the mold, and the pressure is rapidly increased to 80-100kPa in 5-7s; Step 4, crystallization and pressure holding stage; After the boost pressure reaches 80-100kPa, it enters the stage of crystallization and pressure holding; Step 5, rapid pressurization stage after pressure holding; (A) When the characteristic part A begins to solidify, start to increase the crystal holding pressure to 150-1000kPa, and the pressurization speed is 10-40kPa/s; (B) Characteristic part B begins to solidify; (C) The characteristic part C begins to solidify; (D) After the solidification of the characteristic part D, continue to hold the pressure for 10-60s; Step 6, pressure relief and deflation stage; After step 5, after the solidification of the aluminum alloy automobile chassis casting is completed, the gas pressure in the holding furnace is released, so that the unsolidified aluminum liquid in the riser pipe and the sprue mouth flows back into the holding furnace.