Embedded casting method for embedded metal

Abstract

The invention provides an embedded metal pre-embedded casting method, and belongs to the technical field of casting, the method comprises the following steps: firstly, manufacturing a silicon rubber mold, processing and roughening the surface of a copper accessory, accurately fixing the copper accessory in the mold through a stainless steel positioning pin, and designing a 5-8mm pouring gate and a 1-2mm exhaust channel on the mold; then, the mold is installed on a centrifugal casting machine at the speed of 800-1200 rpm, and a molten tin material is injected into the mold; a three-stage cooling process is adopted after casting, rapid cooling is matched with 28-32 Hz micro-vibration from 280 DEG C, medium-speed cooling is conducted at the speed of 8 DEG C per minute when the temperature reaches 180 DEG C, slow cooling is conducted at the speed of 2 DEG C per minute when the temperature reaches 90 DEG C, and intermittent tapping is conducted for 3-5 seconds every 5 minutes during the period; and finally, the pouring gate is removed, polishing treatment is conducted, and the problem that the interface bonding strength is insufficient in different metal composite casting is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of casting, and in particular relates to an embedded metal pre-embedded casting method. Background Art

[0002] Copper-tin composite components are widely used in the fields of electronics, communications equipment and precision machinery. Traditionally, centrifugal casting is mainly used to achieve the composite combination of copper accessories and tin materials. Traditional centrifugal casting technology uses the centrifugal force generated by high-speed rotation to press molten metal into the mold and solidify it. It has been widely used in the fields of automotive parts, power device connectors, electronic component heat dissipation bases, etc. This process is simple and efficient, suitable for mass production, but it has obvious shortcomings in the manufacture of dissimilar metal composite components.

[0003] When the traditional centrifugal casting process of dissimilar metals is used to process materials with significantly different thermophysical properties such as copper and tin, because the melting point of copper (1084℃) is much higher than that of tin (232℃), the thermal expansion coefficient is nearly twice as different, which leads to the formation of obvious thermal stress concentration areas at the interface during the solidification process. These stress concentration areas make it easy for the bonding interface to produce microscopic separation, which seriously affects the bonding strength and service life of the product. Especially under the conditions of thermal cycling or mechanical vibration, the problem of insufficient interface bonding strength is more prominent, becoming a major hidden danger to product reliability.

[0004] At present, the industry often tries to improve this problem by increasing the casting temperature, extending the solidification time or increasing the physical / chemical treatment of the surface, but these methods often have the disadvantages of narrow process window, high energy consumption, low efficiency or limited improvement effect. Especially for micro-precision parts with high dimensional accuracy requirements and complex structures, how to significantly improve the bonding strength of dissimilar metal interfaces while ensuring production efficiency has always been a core technical problem that needs to be solved urgently in this field. In other words, there is a problem in the prior art that the interface bonding of the two metals is not strong enough during the composite casting process of copper-tin composite parts. Summary of the invention

[0005] In view of this, the present invention provides an embedded metal pre-embedded casting method, which can solve the problem of insufficient firmness of the interface bonding between two metals in the composite casting process of copper-tin composite parts in the prior art.

[0006] The present invention is implemented as follows: The present invention provides an embedded metal precast casting method. The centrifugal casting process adopts a three-stage cooling process after casting. In the first stage, rapid cooling is implemented to a predetermined temperature and slight vibration is applied. In the second stage, it is cooled to a second predetermined temperature at a predetermined rate. In the third stage, the temperature is controlled to a third predetermined temperature at a predetermined rate lower than that in the second stage. The whole process is accompanied by intermittent light tapping assistance. The slight vibration promotes the mutual diffusion and penetration between two metal atoms by generating uniform slight amplitude vibration, forming a wider and more stable transition zone. At the same time, tiny bubbles in the melt quickly gather and are discharged, improving the interfacial bonding strength of the copper-tin composite part.

[0007] Among them, the production of the silicone rubber mold includes making a master model according to the product design drawing, and making a split mold using silicone rubber material to ensure that the mold has sufficient elasticity and the surface accuracy reaches within 50 μm.

[0008] Among them, the processing of the copper fitting includes processing the copper fitting according to the design requirements, with the precision controlled within 30 μm, and roughening the surface of the copper fitting to increase the bonding strength with the tin material.

[0009] Among them, the roughening treatment forms a microscopic uneven structure on the surface of the copper fitting through chemical corrosion or mechanical sandblasting, increasing the surface area and mechanical interlocking effect, and improving the adhesion and strength of the bonding interface with the tin material.

[0010] Among them, the centrifugal casting is carried out by installing the sealed mold on the rotating platform of the centrifugal casting machine, adjusting the rotation speed to 800 - 1200 revolutions per minute to make the mold uniformly stressed; heating the tin material to 350 °C to ensure complete melting and good fluidity, and then starting the centrifugal casting machine to inject the molten tin material into the mold from the reserved pouring gate.

[0011] Among them, in the first stage, it is rapidly cooled to 280 °C, in the second stage, it is cooled to 180 °C at a rate of 8 °C per minute, and in the third stage, the temperature is slowly controlled to 90 °C at a rate of 2 °C per minute.

[0012] Among them, the three-stage cooling process is a hierarchical temperature control method designed according to the metal solidification characteristics. The rapid cooling stage quickly reduces the temperature to make the metal initially solidify. The slight vibration assistance eliminates the bubbles in the initial stage of crystal nucleation. The normal cooling stage makes the crystal growth uniform. The slow cooling stage eliminates the internal stress through low-temperature heating to ensure the stability of the copper-tin bonding interface.

[0013] Among them, the intermittent light tapping assistance is to apply slight tapping to the outer wall of the mold every 5 minutes during the cooling process for 3 - 5 seconds, promoting the discharge of bubbles during the solidification process, improving the arrangement structure of metal crystals, and increasing the internal density of the casting and the metal interfacial bonding strength.

[0014] Among them, the micro-vibration is an auxiliary process that generates uniform and small-amplitude vibrations at the initial stage of metal solidification by connecting an electromagnetic vibrator to the mold base. The working frequency range of the electromagnetic vibrator is 20 - 60 Hz, and the optimal frequency range for casting tin-copper assemblies is 28 - 32 Hz. The amplitude is adjusted between 0.05 - 0.8 mm.

[0015] Among them, the electromagnetic vibrator is powered by a single-phase 220V power supply, with a power requirement of 500 - 800W. It can select continuous vibration or pulse vibration mode according to the needs of the casting process. Usually, it works continuously for 15 - 20 seconds during the first-stage cooling and then repeats after an interval of 30 seconds. The entire system is linked by PLC control and temperature monitoring to achieve automatic triggering of the vibration sequence according to the temperature threshold.

[0016] Through the synergistic effect of precise surface roughening pretreatment of copper, three-stage precise temperature control cooling, and micro-vibration, the present invention significantly improves the interfacial bonding strength of copper-tin composite parts. The micro-vibration system in this technical solution acts at the initial stage of metal solidification, generating precisely controlled vibrations of 28 - 32 Hz, effectively promoting the mutual diffusion and penetration of the two metal atoms at the copper-tin interface, and forming a wider and more stable transition zone. At the same time, the microscopic concave-convex structure formed by surface roughening treatment enhances the mechanical interlocking effect, and the cooperation of micro-vibration and three-stage cooling process ensures that the interfacial bonding is not damaged during the release of thermal stress. The intermittent tapping assistance technology further optimizes the stress distribution during solidification and effectively avoids the generation of microcracks. By systematically integrating a number of innovative process parameters and technical means, the present invention establishes a complete solution for dissimilar metal composite casting, successfully solving the core technical problem of insufficiently firm interfacial bonding of copper-tin composite parts. Brief Description of the Drawings

[0017] Figure 1 It is a flowchart of the method of the present invention. Detailed Embodiments

[0018] To make the purpose, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

[0019] As Figure 1 shown, it is a flowchart of an embedded metal precast casting method provided by the present invention. This method includes the following steps:

[0020] S01. Make the main model according to the product design drawing, and make the split mold using silicone rubber material to ensure that the mold has sufficient elasticity and the surface accuracy reaches within 50μm;

[0021] S02. Process the copper fittings according to the design requirements, control the precision within 30 μm, and roughen the surface of the copper fittings to increase the bonding strength with the tin material;

[0022] S03. Install the processed copper fittings inside the silicone mold at the predetermined positions, and fix them with positioning pins to ensure that the copper fittings do not displace during the casting process;

[0023] S04. Seal and connect the assembled silicone mold, and reserve a pouring gate channel and an exhaust channel on the mold. Control the diameter of the pouring gate channel within 5 - 8 mm;

[0024] S05. Install the sealed mold on the rotating platform of the centrifugal casting machine, adjust the rotation speed to 800 - 1200 revolutions per minute to make the mold evenly stressed;

[0025] S06. Heat the tin material to 350 °C to ensure complete melting and good fluidity, then start the centrifugal casting machine and inject the molten tin material into the mold from the reserved pouring gate;

[0026] S07. After casting, adopt a three - stage cooling process. In the first stage, implement rapid cooling to 280 °C and apply micro - vibration. In the second stage, cool down to 180 °C at a rate of 8 °C per minute. In the third stage, use a low - temperature heating device to slowly control the temperature to 90 °C at a rate of 2 °C per minute. The whole process is accompanied by intermittent light tapping for assistance;

[0027] S08. Conduct post - treatment on the casting, including removing the remaining material of the pouring gate and surface polishing to make the copper - tin bonding part have a smooth transition;

[0028] S09. Optionally, it also includes conducting finished - product quality inspection, including appearance inspection, dimension measurement, and bonding strength test, to ensure that the copper - tin materials are firmly bonded and there are no porosity defects.

[0029] Among them, the roughening treatment is specifically to form a microscopic concave - convex structure on the surface of the copper fittings through chemical corrosion or mechanical sanding, increase the surface area and mechanical interlocking effect, and improve the adhesion and strength of the bonding interface with the tin material.

[0030] Among them, the positioning pin is specifically a stainless - steel cylinder with a diameter of 2 - 3 mm, which is used to accurately fix the position of the copper fittings during the casting process and prevent the copper fittings from shifting during the high - speed rotation process.

[0031] Among them, the exhaust channel is specifically a small channel with a diameter of 1 - 2 mm, which is set at the top or side of the mold and is used to discharge the air and gas inside the mold during the casting process to prevent porosity defects in the casting.

[0032] Among them, the three-stage cooling process is specifically a hierarchical temperature control method designed according to the metal solidification characteristics. In the rapid cooling stage, the temperature is quickly reduced to make the metal initially solidify. Micro-vibration is used to assist in eliminating bubbles in the initial stage of crystal nucleation. In the normal cooling stage, the crystal growth is made uniform. In the slow cooling stage, internal stress is eliminated by low-temperature heating to ensure the stability of the copper-tin bonding interface.

[0033] Among them, the intermittent light tapping assistance is specifically to apply slight tapping to the outer wall of the mold every 5 minutes during the cooling process for 3 - 5 seconds, promoting the discharge of bubbles during solidification, improving the arrangement structure of metal crystals, and enhancing the internal density of the casting and the bonding strength of the metal interface. It can be achieved through an electromagnetic tapper, a pneumatic tapping device, or a mechanical cam system, or manually operated with a rubber hammer. After each operation for several seconds, it is repeated after a fixed interval.

[0034] Among them, micro-vibration is specifically an auxiliary process in which an electromagnetic vibrator is connected to the mold base to generate uniform micro-amplitude vibration at the initial stage of metal solidification. The working frequency range of this electromagnetic vibrator is 20 - 60 Hz (preferably, the optimal frequency range for casting tin-copper assemblies is 28 - 32 Hz). The amplitude can be adjusted between 0.05 - 0.8 mm (by default, an amplitude of 0.1 - 0.3 mm is used). The equipment is powered by a single-phase 220 V power supply, and the power requirement is 500 - 800 W. It can select continuous vibration or pulse vibration mode according to the needs of the casting process. Usually, it works continuously for 15 - 20 seconds during the first-stage cooling and then repeats after an interval of 30 seconds. The entire system is linked with PLC control and temperature monitoring to automatically trigger the vibration sequence according to the temperature threshold.

[0035] The reason why the micro-vibration technology can significantly improve the quality of embedded metal precast casting is mainly because it acts on the metal solidification process through four mechanisms simultaneously: on the one hand, micro-vibration can disrupt the dendrite growth during the solidification of the metal melt, promote the formation of more crystal nuclei, and finally obtain a fine and uniform grain structure, improving the mechanical properties of the casting; on the other hand, the vibration energy causes the tiny bubbles in the melt to quickly aggregate and float upward, and efficiently discharge through the reserved exhaust channels, reducing the porosity defect rate inside the casting; at the same time, at the copper-tin contact interface, micro-vibration promotes the mutual diffusion and penetration between the two metal atoms, forming a wider and more stable transition zone, increasing the bonding strength compared with the traditional non-vibration process; in addition, the periodic vibration during solidification helps to evenly release the internal stress generated by the metal shrinkage, significantly reducing the tendency of later deformation and micro-cracks, and is particularly suitable for composite casting of dissimilar metals such as copper and tin with a large difference in thermal expansion coefficients.

[0036] The specific implementation manners of the above steps are described in detail below. The specific implementation manner of step S01 is to first perform the main model design based on the three-dimensional digital model of the product, complete the optimization of the model geometric parameters by using a computer-aided design system, and control the accuracy within 50 μm. The material of the main model is selected as epoxy resin, and the high-precision machining of the model is realized through a numerical control machining center. Then, the surface of the main model is processed to a mirror finish, and the surface roughness is controlled below Ra0.4. Next, a two-component room-temperature vulcanizing silicone rubber is prepared, and a medium-hardness model with a Shore hardness of 28-35 is selected, and it is fully mixed according to the ratio of the base rubber to the curing agent of 100:3, and vacuum degassing treatment is carried out to remove the bubbles introduced during the mixing process. The treated silicone rubber is poured into a pre-prepared molding box, and during the pouring process, it is injected at a low speed and evenly to avoid generating new bubbles. The main model is slowly placed into the silicone rubber to ensure that no bubbles are wrapped, and the thickness of the silicone rubber is maintained within the range of 15-20 mm to ensure sufficient elastic strength. During the curing process of the silicone rubber, the temperature is controlled within the range of 22-25 °C, the relative humidity is controlled within the range of 40%-60%, and the curing time is 8-12 hours. After curing, the silicone rubber mold is divided along the preset parting line, and the main model is carefully taken out to obtain a parting mold with high surface accuracy and sufficient elasticity. The purpose of this step is to fabricate a high-precision and high-elasticity silicone rubber parting mold, provide an accurate cavity structure for the subsequent installation of copper fittings and the casting of tin materials, and ensure that the geometric accuracy and surface quality of the final product meet the design requirements.

[0037] The specific implementation of step S02 is to determine the geometric parameters and machining accuracy requirements of the copper fitting according to the design drawings, and create a three-dimensional digital model of the copper fitting using parametric modeling technology. Select electrolytic copper material with a purity of more than 99.9%, and perform rough machining through a CNC milling machine and a precision lathe, with the machining allowance controlled within 0.2 mm. Use a five-axis linkage machining center to complete the precision machining of the copper fitting, adopt a stepped feed rate control strategy, with an initial feed rate of 0.05 mm / s, and reduce it to 0.01 mm / s in the finish machining stage to ensure that the machining accuracy is controlled within 30 μm. After machining, perform a heat treatment annealing process on the copper fitting, control the temperature at 550 - 600 °C, hold for 1 - 2 hours and then cool with the furnace to eliminate the internal stress generated during the machining process. After annealing, perform roughening treatment on the surface of the copper fitting using two complementary methods: chemical etching method and mechanical sandblasting method. Chemical etching uses a mixed solution of ammonium sulfate and potassium persulfate, with a ratio of 3:1 and a concentration of 15% - 20%, and the etching time is controlled within 3 - 5 minutes to form microscopic etching pits with a depth of 5 - 8 μm. Mechanical sandblasting uses alumina sand grains with a particle size of 120 - 180 mesh, and the spraying pressure is controlled at 0.4 - 0.6 MPa to form a uniformly distributed surface microscopic uneven structure, and the surface roughness Ra value reaches 3.2 - 6.4 μm. After roughening treatment, perform ultrasonic cleaning on the copper fitting to remove the residual substances on the surface, and then perform anti-oxidation treatment by coating a solder flux protection layer with a thickness of 2 - 3 μm to improve the wettability with tin material. The function of this step is to prepare precision copper fittings and improve the copper-tin interface bonding strength through surface roughening treatment, optimize the microscopic contact area and mechanical interlocking effect, and lay a foundation for good metal bonding in the subsequent casting process.

[0038] The specific implementation of step S03 is to first clean the inside of the silicone mold to ensure that there is no dust and impurity residue. Determine the accurate position of the copper fitting in the mold according to the product design drawing, and use the three-dimensional coordinate method to mark the positioning points, with the coordinate accuracy controlled within 0.05 mm. Select a stainless steel positioning pin with a diameter of 2 - 3 mm, and the length is determined according to the thickness of the copper fitting, generally controlled at 1.5 - 2 times the thickness of the copper fitting. Pre-drill positioning holes at the corresponding positions of the silicone mold, with the hole diameter slightly smaller than the diameter of the positioning pin (generally 0.1 - 0.2 mm smaller), and utilize the elastic characteristics of the silicone material to ensure the tight fit between the positioning pin and the mold. Place the processed copper fitting at the predetermined position in the mold, and use a laser locator for position calibration, with the deviation controlled within 0.1 mm. Insert the stainless steel positioning pin through the positioning hole reserved on the copper fitting to firmly fix the copper fitting inside the silicone mold. The end of the positioning pin contacts the inner wall on the other side of the silicone mold to form a support point to prevent the displacement of the copper fitting due to centrifugal force during the casting process. Check the sealing performance between the edge of the copper fitting and the silicone mold to confirm that there is no gap. If necessary, use an appropriate amount of silicone rubber sealant for encapsulation treatment. Use a three-dimensional measuring instrument to recheck and verify the position of the installed copper fitting to ensure that the position deviation is controlled within the design tolerance range. The purpose of this step is to ensure that the position of the copper fitting in the mold is accurate and firmly fixed, preventing displacement due to centrifugal force during the high-speed centrifugal casting process, thereby ensuring the precise positioning of the copper fitting in the final product and meeting the product function and assembly requirements.

[0039] The specific implementation of step S04 is to first clean the parting surface of the silicone mold to ensure that there is no impurity residue, and coat a layer of silicon-based mold release agent with a thickness of 5 - 10 μm to improve the subsequent demolding effect. Align the parting surfaces of the silicone mold and use a positioning pin hole system to achieve precise alignment, with the alignment accuracy controlled within 0.1 mm. Use a mold clamping device to apply uniform pressure to the silicone mold, with the pressure value controlled within the range of 0.1 - 0.15 MPa to ensure that the parting surface fits tightly without gaps. According to the product structure characteristics and casting process requirements, design a gate channel system with a conical structure, an inlet diameter of 8 mm, an outlet diameter of 5 mm, and a taper of 5° - 8°, which is beneficial for the filling of the molten metal and the subsequent removal of the gate. The position of the gate channel is selected at the non-critical part of the product and determined according to the principle of the shortest flow path and the minimum resistance. Design an exhaust channel at the high point of the mold with a slender structure, an inlet diameter of 2 mm, an outlet diameter of 1 mm, and a channel length of 15 - 20 mm to ensure smooth exhaust while preventing the overflow of the molten metal. The number of exhaust channels is determined according to the complexity of the product, generally every 100 cm 3The cavity volume is configured with 1 to 2 exhaust channels. High-strength nylon cable ties are used for multi-point fixation around the outside of the mold to ensure that the mold will not separate during high-speed rotation. The mold sealing performance is verified through an airtightness test. The test pressure is 0.2 MPa, the pressure holding time is 1 minute, and the pressure drop does not exceed 0.02 MPa. The purpose of this step is to complete the sealed assembly of the mold and design a reasonable gating system and exhaust system to ensure that the molten metal can completely fill the cavity during the casting process while effectively discharging gases, preventing defects, and laying a foundation for the production of high-quality castings.

[0040] The specific implementation method of step S05 is to first check the technical parameters and operating status of the centrifugal casting machine to ensure that the equipment is in good working condition. Clean the surface of the rotating platform of the centrifugal casting machine to remove impurities that may affect the mold installation. Install the sealed mold at the center position of the rotating platform and fix it with bolts. The tightening torque is controlled within 25 - 30 N·m to ensure a firm connection between the mold and the platform. Adjust the balance state of the mold on the rotating platform and measure it with a dynamic balance tester. The unbalance amount is controlled within 5 g·cm. If necessary, add balance weights for dynamic balance correction. Set the rotation speed parameter of the centrifugal casting machine. According to the product diameter size and mass distribution characteristics, determine the optimal rotation speed, generally controlled within the range of 800 - 1200 revolutions per minute. For small-diameter products (less than 50 mm), a higher rotation speed of 1000 - 1200 revolutions per minute is adopted, and for large-diameter products (more than 100 mm), a lower rotation speed of 800 - 900 revolutions per minute is adopted. Conduct an no-load test run to check the running stability of the rotating platform and the fixing reliability of the mold. The running time is not less than 1 minute. According to the centrifugal force distribution theory, calculate the centrifugal force magnitudes at different positions through the formula F = mω 2 r to ensure uniform stress and consistent density distribution at all parts of the casting. Adjust the acceleration and deceleration parameters of the centrifugal casting machine. The acceleration time is controlled within 5 - 8 seconds, and the deceleration time is controlled within 10 - 15 seconds to avoid impact on the mold caused by sudden acceleration and deceleration. The purpose of this step is to firmly install the mold on the centrifugal casting machine and adjust the optimal rotation parameters, so that the liquid metal remains uniform and dense during solidification through the principle of centrifugal force, improving the quality and performance of the casting.

[0041] The specific implementation of step S06 is as follows: First, select high-purity tin materials with a purity of over 99.9%, cut them into appropriate-sized blocks for easy melting and pouring. Use a temperature-controlled resistance furnace for heating, with the furnace temperature control accuracy of ±5°C. Place the tin material blocks into a graphite crucible, and coat the inner wall of the crucible with an anti-sticking agent to prevent the reaction between the molten tin and the crucible. At the initial stage of heating, the heating rate is controlled at 15 - 20°C per minute. After the temperature reaches 200°C, reduce the heating rate to 10°C per minute to avoid temperature overshoot. After the tin material is completely melted, stabilize the temperature at 350°C, which is about 120°C higher than the melting point of tin, to ensure that the tin material is completely melted and has good fluidity. In the molten state, add 0.3 - 0.5% of a flux to the molten tin to improve the wettability and fluidity of the molten tin and reduce the formation of oxides. Stir the molten tin with a graphite rod to make the temperature uniform and fully mix the flux. Use a vacuum degassing device to process the molten tin, control the vacuum degree at 5 - 10 Pa, and the degassing time is 2 - 3 minutes to remove the gas and impurities in the molten tin. Start the centrifugal casting machine to make the rotating platform reach the preset speed and operate stably. Use a pouring tool preheated to 250°C to quickly pour the molten tin material into the rotating mold from the reserved pouring gate, and complete the pouring within 3 - 5 seconds to ensure continuous and uninterrupted flow of the molten metal. During the pouring process, the temperature of the molten tin is monitored in real time through a thermocouple to ensure that the pouring temperature is stable within the range of 340 - 350°C. The function of this step is to pour the molten tin material into the high-speed rotating mold under the best temperature conditions, and use the principle of centrifugal force to evenly distribute and fill the cavity with the molten metal, creating conditions for good metallurgical bonding at the copper-tin interface.

[0042] The specific implementation of step S07 is that after casting is completed, the three-stage cooling process is immediately started. This process is designed based on the theory of metal solidification kinetics and the principle of phase change control. In the first stage, rapid cooling is implemented. The temperature of the casting is rapidly reduced from the initial 340 - 350 °C to 280 °C, and the cooling rate is controlled at 40 - 50 °C per minute. At the same time, an electromagnetic vibrator is started to generate micro-vibrations with a frequency of 28 - 32 Hz and an amplitude of 0.1 - 0.3 mm. After the vibration lasts for 15 - 20 seconds, there is an interval of 30 seconds, and this is repeated 3 - 4 times. The electromagnetic vibrator uses the principle of electromagnetic induction to generate an alternating magnetic field in the electromagnet through an alternating current, driving the mold base to generate controlled vibrations. The vibration parameters are automatically adjusted by the PLC system according to the real-time temperature. When the temperature drops to 300 °C, the amplitude is reduced to 0.1 mm and the frequency is reduced to 25 Hz. In the second stage, a conventional cooling process is adopted. The temperature is reduced from 280 °C at a constant rate of 8 °C per minute to 180 °C. During this period, the mold rotates at a low speed (100 - 150 revolutions per minute) to ensure uniform temperature distribution. In this stage, the outer wall of the mold is tapped intermittently every 5 minutes for assistance. The tapping force is controlled at 2 - 3 N and lasts for 3 - 5 seconds. The internal bubble discharge and crystal arrangement adjustment are promoted through the transmission of external mechanical shock waves. In the third stage, a low-temperature heating and temperature control process is adopted. The temperature is reduced from 180 °C at a slow rate of 2 °C per minute to 90 °C, and the mold completely stops rotating. In this stage, a low-temperature heating device is used to apply slight heat compensation to the mold. The cooling curve is precisely controlled through the PID control algorithm, and the temperature fluctuation is controlled within the range of ±1 °C. The temperature gradient of each part of the casting is monitored in real time through an infrared thermal imager to ensure that the internal and external temperature difference does not exceed 15 °C. When the temperature drops to 90 °C, it is kept warm for 30 - 60 minutes to fully release the internal stress of the casting. The purpose of this step is to optimize the metal crystal structure, eliminate bubbles, reduce shrinkage defects, improve the copper-tin interface bonding quality, and ensure the internal structure of the casting is dense and uniform by precisely controlling the solidification process and cooling rate of the tin alloy, combined with micro-vibration and intermittent tapping techniques.

[0043] The specific implementation of step S08 is as follows: after the casting is cooled to room temperature, carefully remove the casting from the silicone mold. Adopt the progressive demolding method, starting from the non-critical parts first and gradually expanding to the whole to avoid damaging the surface of the casting. Use a precision sawing machine to cut off the excess materials of the gating and exhaust channels, and the cutting position is 1-2 mm away from the casting body, reserving the subsequent machining allowance. Use a precision milling machine to finish machine the position where the gating is cut off, and the machining parameters are: spindle speed 2000-2500 revolutions per minute, feed rate 80-100 mm / min, cutting depth 0.2-0.3 mm per pass until it is flush with the casting surface. Conduct meticulous treatment on the copper-tin bonding part, use a rotary grinding tool, and the grinding material is diamond powder with a mesh size of 1000-1500 to ensure that the copper-tin transition area is smooth and natural without obvious boundaries. Use a multi-stage polishing process to treat the surface of the casting. First, conduct wet grinding with 800-mesh, 1200-mesh, and 2000-mesh sandpapers in sequence, and then use a polishing wheel and polishing paste for final polishing until the surface reaches a mirror finish, and the surface roughness is controlled within Ra0.4. Conduct ultrasonic cleaning on the casting to remove the surface machining residues. The cleaning solution is an aqueous solution of a neutral cleaner, and the cleaning time is 3-5 minutes. After cleaning, conduct anti-oxidation treatment on the surface of the casting, and coat a protective agent with a thickness of 2-3 μm to extend the surface quality retention time of the casting. Use a precision three-coordinate measuring instrument to detect the key dimensions of the casting to ensure that they meet the design requirements, and the error is controlled within the range of ±0.05 mm. The function of this step is to remove the excess parts on the casting, conduct finish machining and beautification treatment on the surface, so that the product reaches the appearance and dimensional accuracy required for final use, especially to ensure a smooth transition at the copper-tin bonding part and avoid the formation of stress concentration points.

[0044] Step S09 is an optional step, and its specific implementation method is to adopt a multi-method and multi-dimensional quality inspection system to ensure that the castings meet the requirements of various technical indicators. First, conduct an appearance inspection. Use a 10x magnifying glass to comprehensively inspect the surface of the casting, with a focus on inspecting the copper-tin bonding area to confirm that there are no surface defects such as cracks, pores, and shrinkage porosity. The inspection standard is that the allowable defect area on the surface does not exceed 0.1% of the total area, and the size of a single defect does not exceed 0.2 mm. Use a digital microscope to magnify the copper-tin bonding interface by 50-100 times to observe whether the interface transition is smooth, whether the bonding is tight, whether the interface line is clear and continuous, and there is no obvious delamination or detachment phenomenon. Use a coordinate measuring machine to measure the dimensions. Take at least 5 measurement points for the key dimensions of the casting to form a dimensional measurement report, and all dimensional tolerances are controlled within the design requirements, generally controlled within ±0.05 mm. Conduct a bonding strength test. Adopt the push-pull test method. Use a fixture and a universal material testing machine to apply an increasing load to the copper-tin bonding part, record the load-displacement curve, and the bonding strength value is not less than 40 MPa. Conduct cross-section metallographic analysis on some samples. Prepare copper-tin interface metallographic samples. After grinding, polishing, and etching, observe the interface microstructure under a metallographic microscope. The thickness of the interface diffusion layer should be within the range of 5-15 μm, and the structure is dense without pores. Use an ultrasonic flaw detector to conduct non-destructive testing on the inside of the casting. The detection sensitivity is not less than the equivalent of a 0.5 mm standard flat-bottom hole, and the internal defect rate of the casting does not exceed 2%. Conduct X-ray fluoroscopy on some samples to observe the integrity of the internal structure and the copper-tin bonding state, without obvious defects and loose areas. The purpose of this step is to comprehensively evaluate the key indicators such as the appearance quality, dimensional accuracy, internal structure, and bonding strength of the casting through a series of scientific detection means, ensure that the product meets the design and use requirements, and provide quality assurance for subsequent applications.

[0045] Specifically, the principle of the present invention is as follows: The technical principle of the present invention is based on the comprehensive application of material interface science, metal solidification kinetics, and vibration energy transfer theory, and solves the problem of the bonding strength of dissimilar metal interfaces through a multi-level collaborative mechanism. First, the surface roughening treatment of the copper fitting increases the surface area and the complexity of the microscopic morphology at the microscopic level, providing a physical basis for subsequent metal bonding. The microscopic concave-convex structure formed after roughening not only increases the effective contact area but also creates an "anchor point" effect conducive to mechanical locking, fundamentally improving the initial conditions of interface bonding.

[0046] The micro-vibration technology is the core innovation of the present invention. Its working principle mainly enhances the interfacial bonding strength through three key mechanisms: First, the vibration energy promotes the mutual penetration and diffusion of two metal atoms at the interface, forming a wider transition zone and a metallurgical bonding layer; Second, the vibration disrupts the conventional dendritic growth pattern during solidification, prompting the metal to form a finer and more uniform grain structure, reducing grain boundary segregation and the generation of brittle phases at the interface; Third, under the action of periodic vibration, the thermal stress generated during solidification is released in a timely manner, avoiding the generation of interfacial microcracks caused by stress concentration.

[0047] The three-stage cooling process and the micro-vibration system form a precisely coordinated process synergy. In the first stage, rapid cooling and micro-vibration cooperate to establish an initial bonding state. In the second stage, medium-speed cooling ensures the stable formation of the interfacial transition zone. In the third stage, ultra-low-speed temperature control effectively eliminates residual internal stress and prevents the interfacial thermal stress from damaging the formed bond. The intermittent tapping assistance technology promotes the self-healing of microdefects and the uniform distribution of stress by introducing periodic mechanical disturbances without damaging the overall solidification structure.

[0048] In summary, through the systematic integration of multiple process innovations, the present invention has established a set of dissimilar metal composite casting technology systems with internal logical consistency. Each process link supports each other and has complementary functions, thus successfully solving the core technical problem of insufficient interfacial bonding of copper-tin composite parts at both the theoretical and practical levels.

[0049] The following provides a specific Example 1 of the present invention: Technicians need to design and manufacture a high-precision and high-strength copper-tin composite bearing housing, which requires a copper alloy guide sleeve to be precisely embedded in the tin matrix to meet the wear resistance and electrical conductivity requirements under special working conditions. Technicians use the inlaid metal precast casting method for production and manufacturing, and the specific implementation process is as follows.

[0050] Technicians first conduct the main model design based on the three-dimensional digital model of the product, complete the three-dimensional parametric modeling of the bearing housing using UG software, with the accuracy controlled within 35μm. The main model uses epoxy resin material and is processed with high precision through a five-axis CNC machining center, with the surface roughness reaching Ra0.32. Subsequently, a two-component room temperature vulcanizing silicone rubber is prepared, and a model with a Shore hardness of 32 is selected. It is mixed in a ratio of 100:3 of base rubber and curing agent and degassed in a vacuum environment of -0.08MPa for 5 minutes. The silicone rubber is injected into the molding box, and the injection speed is controlled at 20cm 3 / min, and the thickness of the silicone rubber is maintained at 18mm. It is cured for 10 hours at an ambient temperature of 23°C and a relative humidity of 55% to obtain a parting mold with a surface accuracy of 42μm.

[0051] According to the design requirements, the process personnel processed an electrolytic copper sleeve with a purity of 99.95%. The geometric dimensions are an outer diameter of 45.00 mm, an inner diameter of 35.00 mm, and a height of 28.00 mm. The machining accuracy is controlled within 27 μm. The copper sleeve was finish-machined on a five-axis machining center with a feed rate of 0.03 mm / s. After machining, it was annealed at 580 °C for 1.5 hours. The surface of the copper sleeve was roughened by chemical etching method, using a 3:1 mixed solution of ammonium sulfate and potassium persulfate (concentration 18%) for etching for 4 minutes to form microscopic etching pits with a depth of about 6.5 μm. At the same time, 150-mesh alumina sand grains were used for mechanical sandblasting under a pressure of 0.5 MPa to form a uniform surface micro-concave and convex structure, and the surface roughness Ra value reached 4.8 μm. The treated copper sleeve was ultrasonically cleaned for 30 minutes and then coated with a soldering flux protective layer with a thickness of 2.5 μm.

[0052] The process personnel pre-drilled positioning holes with a diameter of 2.5 mm inside the silicone mold and selected a stainless steel 304 positioning pin with a diameter of 2.4 mm and a length of 45 mm. A three-coordinate measuring device was used to determine the accurate position of the copper sleeve in the mold, establish a coordinate system and mark the positioning points, and the coordinate accuracy was controlled within 0.03 mm. The copper sleeve was placed at the predetermined position in the mold, and a laser locator was used for position calibration with the deviation controlled within 0.08 mm. The positioning pin was inserted to firmly fix the copper sleeve. The tightness between the edge of the copper sleeve and the silicone mold was checked, and a small amount of silicone rubber sealant was used for encapsulation treatment to ensure no gap.

[0053] When assembling the mold, the process personnel first coated a silicon-based mold release agent with a thickness of 8 μm, then aligned the parting surfaces of the silicone mold, and used a positioning pin hole system to achieve precise alignment with an alignment accuracy of 0.06 mm. A mold clamping device was used to apply a uniform pressure of 0.12 MPa to the silicone mold to ensure that the parting surfaces were closely fitted. A tapered gate channel was designed with an inlet diameter of 7.5 mm, an outlet diameter of 5.5 mm, and a taper of 6°. Two exhaust channels were designed at the top of the mold with an inlet diameter of 1.8 mm, an outlet diameter of 1.2 mm, and a channel length of 18 mm. High-strength nylon cable ties were used to fix the outside of the mold at 10 points, and the tightness of the mold was verified by a 0.2 MPa airtightness test. The pressure drop in 1 minute was 0.015 MPa, meeting the requirements.

[0054] Install the assembled mold at the center of the rotating platform of the centrifugal casting machine and fix it with M8 bolts. The tightening torque is 28 N·m. Use a dynamic balance tester to measure the balance state of the mold on the rotating platform. The initial unbalance is 7.2 g·cm, and it is adjusted to 3.8 g·cm by adding balance weights. Set the rotation speed of the centrifugal casting machine to 950 revolutions per minute according to the product diameter (about 60 mm), with an acceleration time of 6 seconds and a deceleration time of 12 seconds. Conduct an idle running test for 1.5 minutes to check the running stability of the rotating platform and the fixing reliability of the mold.

[0055] Before casting, the process personnel select high-purity tin material with a purity of 99.98% and cut it into blocks of about 50 g. Heat it using a temperature-controlled resistance furnace with a furnace temperature control accuracy of ±3°C. The initial heating rate is 18°C per minute. When the temperature reaches 200°C, reduce the heating rate to 8°C per minute. After the tin material is completely melted, the temperature stabilizes at 348°C. Add 0.4% rosin-based flux to the molten tin and stir it evenly with a graphite rod. Use a vacuum degassing device to process the molten tin with a vacuum degree of 7 Pa and a degassing time of 2.5 minutes.

[0056] As shown in Table 1, the process personnel made a detailed record of the key process parameters of this casting operation:

[0057] Table 1 Key Process Parameter Table for the Casting of Copper-Tin Composite Bearing Seats

[0058] Process parameters Parameter value Control accuracy Remarks Processing accuracy of copper sleeve 27μm ±3μm Five-axis linkage machining center Surface roughness Ra of copper 4.8μm ±0.5μm Chemical corrosion + mechanical sandblasting Mold parting accuracy 0.06mm ±0.01mm Positioning pin hole system alignment Purity of tin material 99.98％ - High-purity electrolytic tin Temperature of tin liquid 348℃ ±3℃ Temperature-controlled resistance furnace Flux addition ratio 0.4％ ±0.05％ Rosin-based flux Centrifugal speed 950r / min ±10r / min Variable frequency speed regulation system Micro-vibration frequency 30Hz ±1Hz Electromagnetic vibrator Micro-vibration amplitude 0.2mm ±0.03mm PLC control system Cooling rate in the first stage 45℃ / min ±3℃ / min Stop point at 280℃ Cooling rate in the second stage 8℃ / min ±0.5℃ / min Stop point at 180℃ Cooling rate in the third stage 2℃ / min ±0.2℃ / min Stop point at 90℃

[0059] After starting the centrifugal casting machine, the process personnel use a pouring tool preheated to 245°C to inject the molten tin material from the reserved pouring gate into the rotating mold within 4 seconds. During the pouring process, the thermocouple monitors the temperature of the molten tin and stabilizes it at 345°C in real time. After casting is completed, immediately start the three-stage cooling process for temperature control. In the first stage of rapid cooling, the temperature of the casting drops from 345°C at a rate of 45°C per minute to 280°C. At the same time, start an electromagnetic vibrator with a frequency of 30 Hz and an amplitude of 0.2 mm. After the vibration lasts for 18 seconds, it is interrupted for 30 seconds and repeated 4 times. In the second stage of conventional cooling, the temperature is reduced from 280°C at a constant rate of 8°C per minute to 180°C. During this period, the mold rotates at a low speed of 120 revolutions per minute. At the same time, the outer wall of the mold is tapped intermittently every 5 minutes for assistance, with a tapping force of 2.5 N and a duration of 4 seconds. In the third stage of low-temperature heating and temperature control, the temperature is reduced from 180°C at a rate of 2°C per minute to 90°C. The mold stops rotating completely, and a PID control system is used to precisely control the cooling curve, with the temperature fluctuation controlled within the range of ±0.8°C. When the temperature drops to 90°C, keep it warm for 45 minutes to fully release the internal stress of the casting.

[0060] After the casting is cooled to room temperature, the technicians carefully remove the casting from the silicone mold using a progressive demolding method to avoid damaging the surface of the casting. The excess material of the gate and exhaust channels is cut off using a precision sawing machine, and the cutting position is 1.5 mm away from the casting body. The position where the gate is removed is finely processed using a precision milling machine with the following processing parameters: spindle speed of 2,200 revolutions per minute, feed rate of 90 mm / min, and cutting depth of 0.25 mm per pass. The copper-tin joint is carefully treated using a rotary grinding tool with 1,200-mesh diamond powder as the grinding material to ensure a smooth and natural transition in the copper-tin area. Wet sanding is sequentially carried out using 800-mesh, 1,200-mesh, and 2,000-mesh sandpapers, and then final polishing is performed using a polishing wheel in combination with polishing paste to achieve a surface roughness of Ra 0.32. The casting is ultrasonically cleaned for 4 minutes and then coated with a 2.2-μm-thick silicone anti-oxidation protective agent.

[0061] The technicians conducted a comprehensive quality inspection on the produced copper-tin composite bearing seats, as shown in Table 2:

[0062] Table 2 Quality inspection results of copper-tin composite bearing seats

[0063]

[0064]

[0065] The technicians further compared the product performance differences between this process and the traditional embedded casting method, as shown in Table 3:

[0066] Table 3 Comparison of product performance between the new process and the traditional process

[0067] Performance indicators Traditional process This process Improvement ratio Bonding strength of copper-tin interface (MPa) 31.4 48.6 54.8％ Thickness of interface diffusion layer (μm) 4.2 10.5 150.0％ Internal defect rate (%) 3.8 1.3 -65.8％ Dimensional accuracy deviation (mm) 0.068 0.032 -52.9％ Production cycle (h) 24 16 -33.3％ Product yield rate (%) 88.5 97.2 9.8％

[0068] There are several main technical difficulties in the traditional embedded metal pre-casting method: First, the interfacial bonding strength between dissimilar metals is insufficient, resulting in easy delamination during use; second, the gas is not discharged sufficiently during the casting process, causing internal porosity defects; third, the cooling process control is inaccurate, leading to internal stress concentration and dimensional deformation. The traditional process usually adopts a single surface treatment method, a static casting process, and a natural cooling method, which cannot effectively solve these problems.

[0069] In contrast, the embedded metal pre-casting method adopted in the present invention has obvious advantages: First, through the composite surface treatment process combining chemical corrosion and mechanical sandblasting, the microscopic uneven structure on the copper surface is significantly increased, the mechanical interlocking effect is improved, and the bonding strength at the copper-tin interface is increased by 54.8%; Second, by using the centrifugal casting principle and combining with a carefully designed exhaust channel, the gas discharge effect during the metal liquid filling process is greatly improved, and the internal defect rate is reduced by 65.8%; Most importantly, the micro-vibration technology and the three-stage cooling process are innovatively introduced. The micro-vibration effectively promotes the bubble discharge and crystal nucleus formation in the initial solidification stage of the metal, while the precisely controlled cooling rate ensures uniform growth of metal crystals and full release of internal stress, increasing the product size accuracy by 52.9% and shortening the production cycle by 33.3%. In particular, the thickness of the interface diffusion layer increases from 4.2 μm in the traditional process to 10.5 μm, an increase of 150.0%, which means that a more solid metallurgical bond is formed between copper and tin, significantly improving the service reliability of the product under harsh working conditions such as high temperature and vibration.

[0070] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. An embedded metal precast casting method, comprising fabricating a silicone rubber mold, machining copper fittings, installing the copper fittings, sealing the mold, performing centrifugal casting, cooling the casting, post-treating and quality inspecting, characterized in that, The centrifugal casting process adopts a three-stage cooling process after casting. In the first stage, rapid cooling is implemented to a predetermined temperature and slight vibration is applied. In the second stage, it is cooled to a second predetermined temperature at a predetermined rate. In the third stage, the temperature is controlled to a third predetermined temperature at a predetermined rate lower than that in the second stage. The whole process is accompanied by intermittent tapping assistance. The slight vibration promotes the mutual diffusion and penetration between two metal atoms by generating uniform micro-amplitude vibration, forming a wider and more stable transition zone. At the same time, tiny bubbles in the melt are quickly aggregated and discharged, improving the interfacial bonding strength of the copper-tin composite part.

2. The embedded metal precast casting method according to claim 1, characterized in that, The production of the silicone rubber mold includes making a master model according to the product design drawing and making a split mold with silicone rubber material to ensure that the mold has sufficient elasticity and the surface accuracy reaches within 50 μm.

3. The embedded metal precast casting method according to claim 2, characterized in that, The processing of the copper fitting includes processing the copper fitting according to the design requirements with the precision controlled within 30 μm, and roughening the surface of the copper fitting to increase the bonding strength with the tin material.

4. The embedded metal precast casting method according to claim 3, characterized in that, The roughening treatment forms a microscopic concave-convex structure on the surface of the copper fitting through chemical corrosion or mechanical sandblasting, increasing the surface area and mechanical interlocking effect, and improving the adhesion and strength of the bonding interface with the tin material.

5. The embedded metal precast casting method according to claim 4, characterized in that, The centrifugal casting is carried out by installing the sealed mold on the rotating platform of the centrifugal casting machine, adjusting the rotation speed to 800 - 1200 revolutions per minute to make the mold evenly stressed. The tin material is heated to 350 °C to ensure complete melting and good fluidity, and then the centrifugal casting machine is started to inject the molten tin material into the mold from the reserved pouring gate.

6. The embedded metal precast casting method according to claim 5, wherein In the first stage, it is rapidly cooled to 280 °C. In the second stage, it is cooled to 180 °C at a rate of 8 °C per minute. In the third stage, the temperature is slowly controlled to 90 °C at a rate of 2 °C per minute.

7. The embedded metal pre-embedded casting method according to claim 6, characterized in that, The three-stage cooling process is a hierarchical temperature control method designed according to the metal solidification characteristics. In the rapid cooling stage, the temperature drops rapidly to make the metal initially solidify. The slight vibration assistance eliminates the bubbles in the initial stage of crystal nucleation. In the normal cooling stage, the crystal growth is made uniform. In the slow cooling stage, the internal stress is eliminated by low-temperature heating to ensure the stability of the copper-tin bonding interface.

8. The embedded metal precast casting method according to claim 7, characterized in that, The intermittent tapping assistance is to apply slight tapping to the outer wall of the mold every 5 minutes during the cooling process for 3 - 5 seconds, promoting the discharge of bubbles during solidification, improving the arrangement structure of metal crystals, and enhancing the internal density of the casting and the metal interfacial bonding strength.

9. The embedded metal pre-embedded casting method according to claim 8, characterized in that, The slight vibration is an auxiliary process that generates uniform micro-amplitude vibration at the initial stage of metal solidification by connecting an electromagnetic vibrator to the mold base. The working frequency range of the electromagnetic vibrator is 20 - 60 Hz, and the optimal frequency range for casting the tin-copper composite part is 28 - 32 Hz. The amplitude is adjusted between 0.05 - 0.8 mm.

10. The embedded metal precast casting method according to claim 9, wherein The electromagnetic vibrator is powered by a single-phase 220 V power supply with a power requirement of 500 - 800 W. It can select continuous vibration or pulse vibration mode according to the needs of the casting process. Usually, it works continuously for 15 - 20 seconds during the first-stage cooling and then repeats after an interval of 30 seconds. The whole system is linked with temperature monitoring through PLC control to achieve automatic triggering of the vibration sequence according to the temperature threshold.

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