Introduction of copper alloy die-casting process
Edit: 管理员 Date: 2018-07-31
The definition of copper alloy die-casting processing in metal die-casting workpieces is the process of organically combining and applying the three die-casting production factors of die-casting copper alloy, die-casting mold and die-casting machine. Copper alloy die-casting: the copper alloy solution is injected into the die-casting die by the die-casting die temperature machine, and the copper alloy die-casting can be taken out after cooling and molding.
Requirements for copper alloy die-casting processing materials:
1. When the heat temperature is not high, it has good fluidity and is convenient to fill complex cavities to obtain castings with good surface quality.
2. The linear shrinkage rate and crack tendency are small to avoid cracks in the casting and improve the dimensional accuracy of the casting.
3. The crystallization temperature range is small to avoid shrinkage cavity and porosity and improve the casting quality.
4. It has certain high temperature strength to avoid deformation or fragmentation when casting is pushed out.
5. It has high strength at room temperature to meet the production requirements of large thin-walled complex castings.
6. The tendency of physical-chemical interaction with metal cavity is small, so as to reduce the mucosa and mutual alloying.
7. It has good processing function and certain corrosion resistance.
The method of copper alloy die-casting processing: injection specific pressure and injection speed, pouring temperature and molding temperature.
1. Injection specific pressure and injection velocity
The selection of injection specific pressure shall be determined according to the structural characteristics of different alloys and castings; For the selection of filling speed, generally for castings with thick wall or high internal quality requirements, lower filling speed and higher boost pressure should be selected; For castings with thin wall or high surface quality requirements and complex castings, high proportion and high filling speed should be selected.
2. Die casting temperature
The die-casting temperature refers to the average temperature of the liquid metal when entering the mold cavity from the pressure setting. Because it is not convenient to measure the liquid metal temperature in the pressure chamber, it is generally expressed by the temperature in the holding furnace.
Die casting temperature is too high and shrinkage is large, which makes the casting easy to produce cracks, large grain size, and can also cause mold sticking; If the source of die casting is too low, it is easy to produce defects such as cold shut, surface pattern and insufficient pouring. Therefore, the die-casting temperature should be considered at the same time as the pressure, die-casting mold temperature and filling speed.
3. Die casting mold temperature
In continuous production, the temperature of die-casting die often rises, especially for die-casting high melting point alloy, which rises rapidly. High temperature not only causes the liquid metal to stick to the mold, but also causes the casting to cool slowly and make the grain coarse. Therefore, cooling measures should be taken when the temperature of die casting die is too high. The general cooling method is to use compressed air, water or chemical medium for cooling. However, with the continuous improvement of the die-casting process, at present, copper alloy die-casting manufacturers have begun to use die-casting die temperature machines to control the temperature of copper alloy die-casting dies. The advantages of using copper alloy die-casting mold warming machine: 1) At the beginning of the die-casting process, the die-casting mold warming machine can preheat the die-casting mold in advance. It can not only reduce the preparation time before die casting, but also greatly reduce the rejection rate of low pressure castings. 2) The die-casting mould temperature machine uses heat transfer oil to heat and cool the die-casting mould, which can greatly improve the service life of the die-casting mould. Because the die casting mold temperature machine can control the temperature of the heat transfer oil to plus or minus 1 degree, this can prevent the mold from cracking due to excessive local temperature difference caused by using cooling water to directly cool the mold. 3) The independent temperature control of different positions of die casting mould can be realized by using the multi-circuit die casting mould temperature machine.
Advantages of copper die-casting processing:
1. Good product quality: the dimensional accuracy of castings is high, which is generally equivalent to level 6~7, or even up to level 4; Good surface finish, generally equivalent to grade 5~8; The strength and hardness are relatively high. The strength is generally 25~30% higher than that of sand casting, but the elongation is reduced by about 70%; Stable size and good interchangeability; It can die cast thin-walled and complex castings.
2. High production efficiency: high machine productivity, for example, the domestic J Ⅲ 3 horizontal cold air die-casting machine can cast 600~700 times per eight hours on average, and the small hot chamber die-casting machine can cast 3000~7000 times per eight hours on average; The die-casting mould has a long service life and a pair of die-casting moulds.
3. Excellent economic effect: due to the advantages of accurate size of die castings and smooth surface. Generally, it is used directly without mechanical processing, or the processing volume is small, so it not only improves the metal utilization rate, but also reduces a large number of processing equipment and working hours; The casting price is easy; Combination die casting can be used for other metal or non-metallic materials. It can save both assembly time and metal.
Disadvantages of copper alloy die-casting processing:
1. Due to the high speed of liquid metal filling the mold cavity and the unstable flow state during die casting, the general die casting method is adopted, and the casting is easy to produce air holes and cannot be heat treated;
2. For castings with complex concave, die-casting is more difficult;
3. High melting point alloy (such as copper, ferrous metal), low life of die casting mold;
4. It is not suitable for small batch production. The main reasons are the high manufacturing cost of die casting mould, the high production efficiency of die casting machine, and the uneconomical small batch production.
Defects and solutions of copper alloy die-casting processing:>>
1、 Mold spots often appear on the surface of die castings, which seriously affect the appearance quality of castings, mainly caused by release agents. At present, there are a large number of large and small manufacturers of release agents on the market, many of which have various quality problems, the most important of which is the corrosion effect on die castings. Generally, the die casting factory does not pay much attention to it. If the die casting is put for a long time, there will be white spots (frosty, black after removal) on the surface. In fact, corrosion has occurred. The main reason is that there are corrosive components in the release agent. Therefore, the selection of release agent must not only pursue low price, but also pay attention to cost performance.
The release agent generally does not penetrate into the die casting. However, the inferior release agent will cause corrosion on the surface of the die casting, and will penetrate into the interior; In addition, if the release agent has a large amount of gas, it will be involved in the die casting to form pores. If coating such as mold release paste is not used properly, defects such as slag inclusion will occur.
2、 The surface peeling of die castings often occurs after shot blasting, which is generally caused by the following reasons: 1. The mold or injection chamber (melting cup) is not cleaned; 2. The injection pressure is not enough (it is also necessary to pay attention to whether the dynamic die is yielding during injection); 3. There is a problem with the gating system, and there is turbulence in the alloy liquid entering the mold cavity; 4. Mold temperature, etc; 5. The molten metal splashes seriously during injection.
3、 Zinc alloy electroplating blisters. Poor electroplating can be caused by factors such as electroplating process and surface quality of die castings. The surface quality of die castings shall be good and free from defects such as porosity, cracks, pores, bubbles, shrinkage holes, cold lines, pinholes, etc., otherwise the surface of castings is easy to blister after electroplating, and the plating layer is separated from the substrate. When grinding and polishing before electroplating, be careful not to grind excessively. Because during the solidification process of die castings, a dense layer of hard and cold layer is formed on the surface due to rapid cooling, while the internal structure may have defects such as pores and shrinkage holes. Do not grind off this good surface layer during grinding, otherwise there will be pits, bubbles, etc. during electroplating. In addition, the polishing wheel should not be pressed too tightly and overheated to prevent the abrasive from sticking to the product, resulting in poor electroplating of the product.
4、 There are air holes in the die casting, and the reasons are as follows: 1. The metal flow direction is incorrect, and it has a positive impact with the casting cavity, resulting in eddy current, which surrounds the air and produces bubbles; 2. The inner gate is too small and the metal flow rate is too high. Before the air is discharged, the exhaust hole is blocked prematurely, leaving the gas in the casting; 3. The cavity is too deep, and it is difficult to ventilate and exhaust; 4. The design of exhaust system is unreasonable, and it is difficult to adjust the exhaust; 1. Correct the size and shape of the splitter cone to prevent the positive impact of metal flow on the cavity; 2. Increase the inner gate properly; 3. Improve mold design; 4. The exhaust groove shall be reasonably designed to increase air pockets.
5、 The metal liquid splashes outward in the process of die casting, and the causes are as follows: 1. The mold closing between the moving and fixed molds is not tight, and the gap is large; 2. Insufficient clamping force; 3. Die-casting machine, fixed mold mounting plate is not parallel; 4. The support plate has a large span. The injection force causes deformation of the sleeve plate. Spray material is produced. Adjustment method: 1. Reinstall the mold; 2. Increase clamping force; 3. Adjust the die-casting machine so that the movable and fixed die mounting plates are parallel to each other; 4. The support plate is added on the movable mold to increase the rigidity of the sleeve plate.
The relationship between the processing quality of copper alloy die-casting and the mold:
1. The mold structure should be reasonable, and the structure of mold parts should also be reasonable.
From the point of view of strength, the mold parts are designed to be good as a whole, firm and durable, and not easy to be damaged and deformed in use. However, if the shape of die castings is complex and the mold parts are complex, it will make the mold processing difficult and the processing accuracy is not high. If the mold parts are made into a combined type, the processing will be greatly simplified, and it is easy to obtain high processing accuracy, and then high-quality die castings can be obtained.
2. Determination of cavity number
To determine the number of cavities, it is necessary to consider the equipment capacity, the difficulty of mold processing, the size of production batch, and the precision requirements of castings.
3. Design of gating system
The gating system is not only the channel for liquid metal to fill the die casting mold, but also has the regulating function on the flow rate and pressure transmission of molten liquid, the exhaust conditions, and the thermal stability of the die casting mold. Therefore, the design of gating system must analyze the structural characteristics, technical requirements, alloy types and characteristics of castings, and also consider the type and characteristics of die-casting machine, so as to design a reasonable gating system.
4. Exhaust system design
The mold shall be equipped with overflow groove and exhaust channel with sufficient overflow range, which is very important to ensure product quality.
5. Mold temperature
The temperature of the die-casting die is an important factor affecting the quality of the casting. Improper die temperature not only affects the internal and external quality of the die-casting, but also affects the dimensional accuracy of the casting and even the deformation of the casting, causing cracks in the die-casting die, forming a network burr on the surface of the casting that is difficult to remove, and affecting the appearance quality of the die-casting.
Molds are generally not heated by gas or electricity, but by preheating and cooling devices. These devices preheat and cool the mold with heat transfer oil as the medium as required.
6. Determination of formed part size
When calculating the size of die-casting parts, the shrinkage rate of die-casting materials selected should conform to the actual situation, otherwise the products produced will be unqualified.
7. Determination of parting surface position
The position of parting surface will affect mold processing, exhaust, product demoulding, etc. Generally, the parting surface will leave a trace line on the product, which will affect the surface quality and dimensional accuracy of the product. Therefore, when designing the parting surface position, in addition to taking into account the product demoulding, mold processing, exhaust and other issues, the parting surface position can be placed where the product surface quality requirements are not high or the dimensional accuracy is not high.
8. The mold cannot be deformed
Due to the unreasonable mold structure or improper selection of mold materials, the mold is often cracked and deformed during use, resulting in unqualified products. Therefore, appropriate measures must be taken to ensure the quality of products during design.
Dongguan Dahetan Machinery Equipment Co., Ltd. specializes in the production of: die-casting mould thermostat dual-temperature die-casting mould thermostat magnesium alloy die-casting mould thermostat aluminum alloy die-casting mould thermostat copper alloy die-casting mould thermostat zinc alloy die-casting mould thermostat
Daheda originated from Taiwan, and has focused on industrial refrigeration equipment and industrial temperature control equipment for 15 years; A supplier of heating and cooling design solutions and solutions!
Requirements for copper alloy die-casting processing materials:
1. When the heat temperature is not high, it has good fluidity and is convenient to fill complex cavities to obtain castings with good surface quality.
2. The linear shrinkage rate and crack tendency are small to avoid cracks in the casting and improve the dimensional accuracy of the casting.
3. The crystallization temperature range is small to avoid shrinkage cavity and porosity and improve the casting quality.
4. It has certain high temperature strength to avoid deformation or fragmentation when casting is pushed out.
5. It has high strength at room temperature to meet the production requirements of large thin-walled complex castings.
6. The tendency of physical-chemical interaction with metal cavity is small, so as to reduce the mucosa and mutual alloying.
7. It has good processing function and certain corrosion resistance.
The method of copper alloy die-casting processing: injection specific pressure and injection speed, pouring temperature and molding temperature.
1. Injection specific pressure and injection velocity
The selection of injection specific pressure shall be determined according to the structural characteristics of different alloys and castings; For the selection of filling speed, generally for castings with thick wall or high internal quality requirements, lower filling speed and higher boost pressure should be selected; For castings with thin wall or high surface quality requirements and complex castings, high proportion and high filling speed should be selected.
2. Die casting temperature
The die-casting temperature refers to the average temperature of the liquid metal when entering the mold cavity from the pressure setting. Because it is not convenient to measure the liquid metal temperature in the pressure chamber, it is generally expressed by the temperature in the holding furnace.
Die casting temperature is too high and shrinkage is large, which makes the casting easy to produce cracks, large grain size, and can also cause mold sticking; If the source of die casting is too low, it is easy to produce defects such as cold shut, surface pattern and insufficient pouring. Therefore, the die-casting temperature should be considered at the same time as the pressure, die-casting mold temperature and filling speed.
3. Die casting mold temperature
In continuous production, the temperature of die-casting die often rises, especially for die-casting high melting point alloy, which rises rapidly. High temperature not only causes the liquid metal to stick to the mold, but also causes the casting to cool slowly and make the grain coarse. Therefore, cooling measures should be taken when the temperature of die casting die is too high. The general cooling method is to use compressed air, water or chemical medium for cooling. However, with the continuous improvement of the die-casting process, at present, copper alloy die-casting manufacturers have begun to use die-casting die temperature machines to control the temperature of copper alloy die-casting dies. The advantages of using copper alloy die-casting mold warming machine: 1) At the beginning of the die-casting process, the die-casting mold warming machine can preheat the die-casting mold in advance. It can not only reduce the preparation time before die casting, but also greatly reduce the rejection rate of low pressure castings. 2) The die-casting mould temperature machine uses heat transfer oil to heat and cool the die-casting mould, which can greatly improve the service life of the die-casting mould. Because the die casting mold temperature machine can control the temperature of the heat transfer oil to plus or minus 1 degree, this can prevent the mold from cracking due to excessive local temperature difference caused by using cooling water to directly cool the mold. 3) The independent temperature control of different positions of die casting mould can be realized by using the multi-circuit die casting mould temperature machine.
Advantages of copper die-casting processing:
1. Good product quality: the dimensional accuracy of castings is high, which is generally equivalent to level 6~7, or even up to level 4; Good surface finish, generally equivalent to grade 5~8; The strength and hardness are relatively high. The strength is generally 25~30% higher than that of sand casting, but the elongation is reduced by about 70%; Stable size and good interchangeability; It can die cast thin-walled and complex castings.
2. High production efficiency: high machine productivity, for example, the domestic J Ⅲ 3 horizontal cold air die-casting machine can cast 600~700 times per eight hours on average, and the small hot chamber die-casting machine can cast 3000~7000 times per eight hours on average; The die-casting mould has a long service life and a pair of die-casting moulds.
3. Excellent economic effect: due to the advantages of accurate size of die castings and smooth surface. Generally, it is used directly without mechanical processing, or the processing volume is small, so it not only improves the metal utilization rate, but also reduces a large number of processing equipment and working hours; The casting price is easy; Combination die casting can be used for other metal or non-metallic materials. It can save both assembly time and metal.
Disadvantages of copper alloy die-casting processing:
1. Due to the high speed of liquid metal filling the mold cavity and the unstable flow state during die casting, the general die casting method is adopted, and the casting is easy to produce air holes and cannot be heat treated;
2. For castings with complex concave, die-casting is more difficult;
3. High melting point alloy (such as copper, ferrous metal), low life of die casting mold;
4. It is not suitable for small batch production. The main reasons are the high manufacturing cost of die casting mould, the high production efficiency of die casting machine, and the uneconomical small batch production.
Defects and solutions of copper alloy die-casting processing:>>
1、 Mold spots often appear on the surface of die castings, which seriously affect the appearance quality of castings, mainly caused by release agents. At present, there are a large number of large and small manufacturers of release agents on the market, many of which have various quality problems, the most important of which is the corrosion effect on die castings. Generally, the die casting factory does not pay much attention to it. If the die casting is put for a long time, there will be white spots (frosty, black after removal) on the surface. In fact, corrosion has occurred. The main reason is that there are corrosive components in the release agent. Therefore, the selection of release agent must not only pursue low price, but also pay attention to cost performance.
The release agent generally does not penetrate into the die casting. However, the inferior release agent will cause corrosion on the surface of the die casting, and will penetrate into the interior; In addition, if the release agent has a large amount of gas, it will be involved in the die casting to form pores. If coating such as mold release paste is not used properly, defects such as slag inclusion will occur.
2、 The surface peeling of die castings often occurs after shot blasting, which is generally caused by the following reasons: 1. The mold or injection chamber (melting cup) is not cleaned; 2. The injection pressure is not enough (it is also necessary to pay attention to whether the dynamic die is yielding during injection); 3. There is a problem with the gating system, and there is turbulence in the alloy liquid entering the mold cavity; 4. Mold temperature, etc; 5. The molten metal splashes seriously during injection.
3、 Zinc alloy electroplating blisters. Poor electroplating can be caused by factors such as electroplating process and surface quality of die castings. The surface quality of die castings shall be good and free from defects such as porosity, cracks, pores, bubbles, shrinkage holes, cold lines, pinholes, etc., otherwise the surface of castings is easy to blister after electroplating, and the plating layer is separated from the substrate. When grinding and polishing before electroplating, be careful not to grind excessively. Because during the solidification process of die castings, a dense layer of hard and cold layer is formed on the surface due to rapid cooling, while the internal structure may have defects such as pores and shrinkage holes. Do not grind off this good surface layer during grinding, otherwise there will be pits, bubbles, etc. during electroplating. In addition, the polishing wheel should not be pressed too tightly and overheated to prevent the abrasive from sticking to the product, resulting in poor electroplating of the product.
4、 There are air holes in the die casting, and the reasons are as follows: 1. The metal flow direction is incorrect, and it has a positive impact with the casting cavity, resulting in eddy current, which surrounds the air and produces bubbles; 2. The inner gate is too small and the metal flow rate is too high. Before the air is discharged, the exhaust hole is blocked prematurely, leaving the gas in the casting; 3. The cavity is too deep, and it is difficult to ventilate and exhaust; 4. The design of exhaust system is unreasonable, and it is difficult to adjust the exhaust; 1. Correct the size and shape of the splitter cone to prevent the positive impact of metal flow on the cavity; 2. Increase the inner gate properly; 3. Improve mold design; 4. The exhaust groove shall be reasonably designed to increase air pockets.
5、 The metal liquid splashes outward in the process of die casting, and the causes are as follows: 1. The mold closing between the moving and fixed molds is not tight, and the gap is large; 2. Insufficient clamping force; 3. Die-casting machine, fixed mold mounting plate is not parallel; 4. The support plate has a large span. The injection force causes deformation of the sleeve plate. Spray material is produced. Adjustment method: 1. Reinstall the mold; 2. Increase clamping force; 3. Adjust the die-casting machine so that the movable and fixed die mounting plates are parallel to each other; 4. The support plate is added on the movable mold to increase the rigidity of the sleeve plate.
The relationship between the processing quality of copper alloy die-casting and the mold:
1. The mold structure should be reasonable, and the structure of mold parts should also be reasonable.
From the point of view of strength, the mold parts are designed to be good as a whole, firm and durable, and not easy to be damaged and deformed in use. However, if the shape of die castings is complex and the mold parts are complex, it will make the mold processing difficult and the processing accuracy is not high. If the mold parts are made into a combined type, the processing will be greatly simplified, and it is easy to obtain high processing accuracy, and then high-quality die castings can be obtained.
2. Determination of cavity number
To determine the number of cavities, it is necessary to consider the equipment capacity, the difficulty of mold processing, the size of production batch, and the precision requirements of castings.
3. Design of gating system
The gating system is not only the channel for liquid metal to fill the die casting mold, but also has the regulating function on the flow rate and pressure transmission of molten liquid, the exhaust conditions, and the thermal stability of the die casting mold. Therefore, the design of gating system must analyze the structural characteristics, technical requirements, alloy types and characteristics of castings, and also consider the type and characteristics of die-casting machine, so as to design a reasonable gating system.
4. Exhaust system design
The mold shall be equipped with overflow groove and exhaust channel with sufficient overflow range, which is very important to ensure product quality.
5. Mold temperature
The temperature of the die-casting die is an important factor affecting the quality of the casting. Improper die temperature not only affects the internal and external quality of the die-casting, but also affects the dimensional accuracy of the casting and even the deformation of the casting, causing cracks in the die-casting die, forming a network burr on the surface of the casting that is difficult to remove, and affecting the appearance quality of the die-casting.
Molds are generally not heated by gas or electricity, but by preheating and cooling devices. These devices preheat and cool the mold with heat transfer oil as the medium as required.
6. Determination of formed part size
When calculating the size of die-casting parts, the shrinkage rate of die-casting materials selected should conform to the actual situation, otherwise the products produced will be unqualified.
7. Determination of parting surface position
The position of parting surface will affect mold processing, exhaust, product demoulding, etc. Generally, the parting surface will leave a trace line on the product, which will affect the surface quality and dimensional accuracy of the product. Therefore, when designing the parting surface position, in addition to taking into account the product demoulding, mold processing, exhaust and other issues, the parting surface position can be placed where the product surface quality requirements are not high or the dimensional accuracy is not high.
8. The mold cannot be deformed
Due to the unreasonable mold structure or improper selection of mold materials, the mold is often cracked and deformed during use, resulting in unqualified products. Therefore, appropriate measures must be taken to ensure the quality of products during design.
Dongguan Dahetan Machinery Equipment Co., Ltd. specializes in the production of: die-casting mould thermostat dual-temperature die-casting mould thermostat magnesium alloy die-casting mould thermostat aluminum alloy die-casting mould thermostat copper alloy die-casting mould thermostat zinc alloy die-casting mould thermostat
Daheda originated from Taiwan, and has focused on industrial refrigeration equipment and industrial temperature control equipment for 15 years; A supplier of heating and cooling design solutions and solutions!
13602318867
