CN101406925B - Ultrasonic vibration-assisted microthixotropic deformation method and device of semi-solid metal - Google Patents

Abstract

The invention discloses a method for the micro-thixotropy and molding of semisolid metal through the assistance of supersonic vibration. The lower end of a lower mould is provided with an electric heater of the lower mould; the lower mould is connected with a supersonic amplitude transformer; the lower mould is provided with a thermocouple of the lower mould; the upper end of a punching head is connected with an upper mould; the upper end of the upper mould is provided with an electric heater of the upper mould; the upper mould is connected with a pressure lever; and the upper mould is provided with a thermocouple of the upper mould. A semisolid metal blank material is remelted and heated to a solid-liquid coexisting region and is subjected to pressure machining; at the same time, supersonic vibration is applied to reduce friction and micro-molding resistance between the semisolid metal blank material and a micro-mould, strengthen the fluidity of the semi-solid metal material, improve the filling performance of the semisolid metal material in the micro-mould, and achieve good micro-molding effect. The method promotes the micro-thixotropy and molding of the semisolid metal, improves the efficiency of micro-molding, reduces equipment cost, avoids the disadvantages of hole contraction and the like in micro-machining process and improves the effects of micro-thixotropy and molding of the semisolid metal.

Description

Ultrasonic vibration-assisted microthixotropic deformation method and device of semi-solid metal

technical field

The invention relates to metal material microprocessing technology, in particular to an ultrasonic vibration-assisted semi-solid metal microthixotropic deformation method and device.

Background technique

In the early 1970s, scientists from the Massachusetts Institute of Technology discovered the rheological properties of semi-solid metals in experiments for the first time, and developed metal semi-solid forming technology, which is between solid metal forming and liquid metal forming. Combining the advantages of casting and plastic forming technology, it has significant advantages such as high efficiency and energy saving. Many scholars call it one of the most promising near-net shape technologies in the 21st century. Nowadays, scholars at home and abroad have carried out a lot of research work on semi-solid metal forming. The semi-solid processing technology of aluminum alloy and magnesium alloy is becoming more and more mature, and its research results have been applied to a large extent in the processing of parts in the automotive industry.

Semi-solid metal forming is a general term for forming processes for semi-molten or semi-solidified metals that coexist in solid and liquid states, mainly including thixoforming and rheoforming. It refers to direct semi-solid processing of the semi-solid metal slurry obtained by stirring under the condition of maintaining its semi-solid temperature, and thixoforming refers to cooling and solidifying the semi-solid slurry into a billet, according to the size of the product The material is blanked, reheated to semi-solid temperature, and then shaped. The thixoforming process is long, but it is convenient to organize specialized production and the quality is easy to control, so it has become the focus of semi-solid forming technology research, and most of the existing research and industrial applications use thixoforming technology .

When the metal blank is in a semi-solid state, it has a certain solid-liquid ratio. Compared with liquid die-casting, it has a certain viscosity. Therefore, it can avoid the disadvantages of splashing, turbulence and air entrainment during forming; it is easier to process than solid forging. The formation of fine features with low deformation force saves energy. Therefore, compared with the traditional forming process, semi-solid metal forming has a series of outstanding advantages: low forming temperature, good mechanical properties of formed parts, better integration of the advantages of solid metal die forging and liquid die-casting, and mass production of shapes Complex, high-performance and high-precision miniature components. The inherent advantages of semi-solid forming determine that semi-solid forming technology has the potential to be applied to the preparation of tiny parts, and it is expected to solve the problems of high cost and low efficiency that currently exist in microstructure processing technology, and provide a high-volume low-cost production of microstructure. A new method, however, so far semi-solid micro-forming technology is still rarely reported in the world. In 2004, Steinhoff et al. in the Netherlands first proposed the concept and method of micro-semi-solid forming (also known as: micro-thixoforming, Micro-Thixoforming) on pages 611-619 of Volume 75 of the magazine "Steel Research International", but So far there is no further report on the research and application of this technology. Gap-Yong Kim and others from the University of Michigan in the United States studied the micro-thixotropic deformation technology of semi-solid aluminum alloys at the micro/mesoscopic scale in their doctoral dissertation research. The main research results were published in "Transactions of the ASME" in 2007. It was reported on pages 246-251 of Volume 129 of Journal of Manufacturing Science and Engineering.

From the current research reports on semi-solid metal micro-forming technology, it can be found that the development of semi-solid metal micro-forming technology is still in its infancy, the technology is not yet mature, and the filling effect of micro-forming is not ideal.

The main problems are:

(1) During the microthixotropic forming process of semi-solid metal, the forming effect is not stable enough, and the forming consistency of some of the same structural features in the same processing process is not good enough;

(2) There are still problems such as shrinkage cavity and non-dense grain structure in the semi-solid metal microthixotropic deformation structure, and the microstructure morphology of the manufactured workpiece also needs to be improved;

(3) The processing efficiency and energy consumption of semi-solid metal microthixotropy still need to be improved.

In order to promote the semi-solid metal micro-forming method to industrial application, thereby providing a method suitable for large-scale, low-cost and high-efficiency processing of metal microstructure features, it is necessary to improve the existing semi-solid metal micro-thixotropic forming technology. very necessary.

Contents of the invention

In order to overcome the disadvantages of the above-mentioned semi-solid metal microthixotropic deformation method, the object of the present invention is to provide a semi-solid metal microthixotropic deformation method and device assisted by ultrasonic vibration. Utilize the guiding effect of ultrasonic waves, remove gas, enhance the fluidity of semi-solid metal materials, reduce the resistance of micro-forming, increase the density of materials, etc., to achieve the auxiliary effect on the micro-thixotropic forming process of semi-solid metals, so as to obtain good results. Excellent semi-solid metal workpiece micro-forming effect, improving the micro-thixoforming efficiency.

The technical solution adopted by the present invention to solve its technical problems is:

One, a kind of ultrasonic vibration assisted semi-solid metal microthixotropic deformation method, this method comprises the following steps:

(1) Place the semi-solid metal blank whose internal structure is spherical crystal on the lower die, preheat it with an embedded electric heater and keep the temperature of the punch and the lower die rising to 250-350°C;

(2) The induction coil heats the temperature of the semi-solid metal billet, and controls the solid phase fraction or liquid phase fraction of the billet to the solid-liquid coexistence area;

(3) Press down the punch with a fine feature structure on the lower surface and apply a forging load to start the press processing. The forging pressure is 50kN ~ 70kN. At the same time, turn on the power ultrasonic generator, through the ultrasonic horn and the lower die Direct connection, apply ultrasonic vibration with a power of 300-500W and a frequency of 15-20kHz to the micro-thixotropy processing of semi-solid metal, and complete the micro-thixotropy process of semi-solid metal blanks with the assistance of ultrasonic waves ;

(4) Complete the ultrasonic vibration-assisted microthixotropy forming process of semi-solid metal, stop ultrasonic vibration and mold heating;

(5) After raising the punch, take out the semi-solid metal microthixomorphic deformed parts.

2. An ultrasonic vibration-assisted semi-solid metal microthixotropy forming device:

An electric heater for the lower die is provided at the lower end of the lower die, and the lower die is connected to the ultrasonic horn. A thermocouple of the lower die is installed in the lower die. There is an upper mold electric heater, the upper mold is connected with the pressure rod, and the upper mold thermocouple is installed in the upper mold.

In the method and device for microthixotropic deformation of semi-solid metal assisted by ultrasonic vibration, the lower surface of the punch with micro-featured structure is provided with an array of circular holes with a diameter and a depth of 0.8 mm to 1 mm.

The beneficial effects that the present invention has are:

The invention applies ultrasonic vibration to the microthixotropy forming process of semi-solid metal for the first time, improves the microthixotropy deformation effect by utilizing various auxiliary functions of ultrasonic vibration, shortens the process time, improves the process quality and reduces the manufacturing cost. It is of great significance to promote the development and application of semi-solid metal micro-thixotropic deformation methods, so as to obtain a high-efficiency, low-cost, high-quality metal microstructure feature processing method.

Description of drawings

Fig. 1 is a schematic diagram of an ultrasonic vibration-assisted semi-solid metal microthixotropic deformation device (during induction heating).

Fig. 2 is a schematic diagram of an ultrasonic vibration assisted semi-solid metal micro-thixotropic deformation device (during thixotropic deformation).

In the figure: 1. Ultrasonic horn, 2. Lower die electric heater, 3. Screw, 4. Punch, 5. Bolt, 6. Upper die electric heater, 7. Pressure rod, 8. Upper die, 9 . Upper mold thermocouple, 10. Lower mold, 11. Semi-solid metal blank, 12. Lower mold thermocouple, 13. Induction coil.

Detailed ways

As shown in Fig. 1 and Fig. 2, the present invention is provided with lower mold electric heater 2 at the lower end of lower mold 10, and lower mold 10 is connected with ultrasonic horn 1, and lower mold thermocouple 12 is installed in lower mold 10, and lower surface The upper end of the punch 4 with micro-featured structure is connected with the upper die 8, the upper end of the upper die 8 is provided with an upper die electric heater 6, the upper die 8 is connected with the pressure rod 7, and the upper die thermocouple 9 is installed in the upper die 8.

The lower surface of the punch with the fine characteristic structure is provided with an array of circular holes with a diameter and a depth of 0.8 mm to 1 mm.

As shown in Figure 1 and Figure 2, the specific implementation process of the ultrasonic vibration-assisted semi-solid metal microthixotropic deformation method proposed by the present invention is as follows:

(1) As shown in Figure 1, the upper mold electric heater 6 and the lower mold electric heater 2 are set in the processing device to heat the punch 4 and the lower mold 10 respectively, and the upper mold thermocouple 9 and Lower mold thermocouple 12, and measure the temperature of upper mold 8 and lower mold 10 in real time respectively. Connect the upper mold electric heater 6 and the upper mold thermocouple 9, and the lower mold electric heater 2 and the lower mold thermocouple 12 to the multi-channel high-precision temperature controller to form two closed-loop temperature control systems. By setting the multi-channel temperature The relevant parameters such as the control temperature and the control strategy of the controller can achieve real-time feedback control of the temperature of the punch 4 and the lower die 10 . The material used for the punch 4 and the lower die 10 is hot work die steel H13. The punch 4 and the lower die 10 need to be preheated before ultrasonic vibration-assisted microthixotropy processing of semi-solid metal, and the temperature should be kept at about 300°C. The temperature of the head 4 and the lower mold 10 is too low compared with the secondary heating temperature of the semi-solid metal blank 11, which will cause the temperature of the semi-solid metal blank 11 to drop too fast during the processing process, causing the semi-solid slurry to quickly crust. Or increase the cold gap, thereby affecting the forming effect of the semi-solid metal microstructure, but if the mold temperature is too high, it is easy to stick to welding and accelerate the wear of the mold. Therefore, the temperature of the punch 4 and the lower mold 10 is controlled at about 300°C.

(2) As shown in Figure 1, after the preheating of the lower die 10 and the punch 4 is completed, an induction coil 13 is used to heat the semi-solid metal blank 11 placed on the lower die 10 to control the solid fraction or liquid phase of the blank From the fraction to the solid-liquid coexistence area, the semi-solid metal blank 11 can be processed by commonly used semi-solid aluminum alloys or magnesium alloys such as A356 and A357. After the induction heating is completed, the induction coil 13 is removed.

(3) As shown in Figure 2, after the semi-solid metal billet is heated to the solid-liquid coexistence area, the punch 4 is pressed down and the forging load is applied to start the press processing. The forging pressure is 50kN-70kN. Ultrasonic vibration-assisted semi-solid metal micro-thixoforming device can be refitted on the basis of ordinary presses, in which the upper die 8 and the pressure rod 7 are connected by bolts 5, and the micro-featured structure of the lower end of the punch 4 can be used according to the needs of the workpiece. The machining is completed by EDM. Turn on the ultrasonic generating device at the same time as the pressure processing starts, the power of the ultrasonic wave is 300-500W, and the frequency is 15-20kHz. Since the ultrasonic horn 1 is directly connected with the lower mold 10 through the screw 3, the effective transmission of ultrasonic vibration energy is ensured. Ultrasonic vibration is always applied during the micro-thixoforming process, so that the semi-solid metal blank completes the rapid micro-forming process with the assistance of ultrasonic waves. At the same time of pressure processing, it is still necessary to continuously heat the punch 4 and the lower die 10 through two closed-loop temperature control systems to maintain the punch 4 and the lower die 10 in a high temperature state, so as to ensure the semi-solid metal microthixotropy during the deformation process. The temperature is in the solid-liquid coexistence region.

(4) After the microthixotropy forming process is completed, stop the ultrasonic vibration and mold heating.

(5) After raising the punch, take out the semi-solid metal micro-formed workpiece, and repeat the above process to start the processing of the next workpiece.

Claims (4)

1. A microthixotropic deformation method of semi-solid metal assisted by ultrasonic vibration, is characterized in that, the method comprises the following steps: (1) Place the semi-solid metal blank whose internal structure is spherical crystal on the lower die, preheat it with an embedded electric heater and keep the temperature of the punch and the lower die rising to 250-350°C; (2) The induction coil heats the temperature of the semi-solid metal billet, and controls the solid phase fraction or liquid phase fraction of the billet to the solid-liquid coexistence area; (3) Press down the punch with a fine feature structure on the lower surface and apply a forging load to start the press processing. The forging pressure is 50kN ~ 70kN. At the same time, turn on the power ultrasonic generator, through the ultrasonic horn and the lower die Direct connection, apply ultrasonic vibration with a power of 300-500W and a frequency of 15-20kHz to the micro-thixotropy processing of semi-solid metal, and complete the micro-thixotropy process of semi-solid metal blanks with the assistance of ultrasonic waves ; (4) Complete the ultrasonic vibration-assisted microthixotropy forming process of semi-solid metal, stop ultrasonic vibration and mold heating; (5) After raising the punch, take out the semi-solid metal microthixomorphic deformed parts. 2. A method for micro-thixotropic deformation of semi-solid metal assisted by ultrasonic vibration according to claim 1, characterized in that: the lower surface of the punch with micro-featured structure has a hole diameter and a depth of 0.8mm ~1mm array of circular holes. 3. A microthixotropic deformation device assisted by ultrasonic vibration of semi-solid metal is characterized in that: the lower end of the lower die (10) is provided with a lower die electric heater (2), the lower die (10) and the ultrasonic horn ( 1) connection, the lower mold thermocouple (12) is installed in the lower mold (10), the upper end of the punch (4) with a fine feature structure on the lower surface is connected with the upper mold (8), and the upper end of the upper mold (8) is provided with The upper mold electric heater (6), the upper mold (8) is connected with the depression bar (7), and the upper mold thermocouple (9) is installed in the upper mold (8). 4. An ultrasonic vibration-assisted semi-solid metal micro-thixotropy forming device according to claim 3, characterized in that: the lower surface of the punch with the micro-featured structure has a hole diameter and a depth of 0.8mm ~1mm array of circular holes.

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