Mold design affects the quality of aluminum die casting
Mold design affects the quality of aluminum die casting
The development of science and technology, the requirements for the safety and aesthetic appearance of the die casting products are constantly improved. The quality of the parts varies according to the use. Today, I will give you some information about how mold design affects the quality of aluminum die casting. How to produce high quality parts, it is of great significance to save materials, energy and shorten manufacturing hours and improve economic efficiency.
1. Factors affecting the quality of die-casting parts
There are many factors influencing the quality of die casting, such as the type and quality of die casting machine, the rationality of the geometry of die casting parts, the rationality of the technical requirements, the structure of the mould and the technical level of the operator.
1. Design of die casting parts
Designers should first fully understand the use of user requirements and working conditions, the force situation of die casting, and then select the appropriate material according to the requirement and working environment, understand the material performance of die casting, etc. When designing, pay special attention to make the die casting structure simple in order to meet the requirement of use. The wall thickness is suitable and uniform, and the necessary deviation is left, otherwise it will lead to defects such as pits, stomata, shrinkage, undercast, tear, crack and deformation of die casting.
The requirement of the dimension precision of die casting should be reasonable, otherwise, the design of mould, mould processing, process conditions and management will cause unnecessary trouble, which will cause a large number of unqualified products.
2. Selection of mold structure, machining precision and mold material
The die casting is made of die casting, and no doubt the design, processing and selection of mould materials are closely related to the product quality. The mold structure is not reasonable, no matter what measures taken from the process, it is difficult to make the product qualified.
In addition, the machining precision of die materials, die traces, surface roughness, machining, heat treatment of tiny cracks, nitriding layer thickness and mold assembly, etc., will affect the product quality and die life.
3. Shrinkage of castings
The shrinkage rate of the casting material is usually given by the mean percentage or the percentage of the percentage of the casting material. The average shrinkage of the material is usually selected. For high precision die casting, mold design, select material shrinkage rate should pay special attention to, when necessary, to test the mold, on the test mould, after the data you need to design and manufacture of mould for mass production.
4. Formulation and implementation of die casting process
The formulation and execution of die casting process is related to the quality of mould, die casting equipment and the technical level of operators. Under the condition of existing die casting equipment in China, it is difficult to achieve stable, reliable and accurate control for die casting process parameters. The basic control die casting process is the process of combining die casting equipment, die casting material and mould etc. The process and main parameters are not strictly enforced, which can cause the die-casting parts to be shrinkable, deformed, undercast, and not qualified.
2. The relationship between die casting quality and mold
The mould is the main tool of die casting, therefore, when designing the mould, it is necessary to make the structure of the mould and the parts of the die structure reasonable, easy to manufacture, easy to use, safe and reliable. In order to make the mould not deformed in die casting, the metal liquid is stable in the mould, which can evenly cool the casting, and it can be cast without failure. In addition, according to the production batch, material condition and so on reasonably choose the appropriate mold material.
1. The structure of mould and mould parts should be reasonable
From the point of view of strength, the mould parts are designed to be good overall, durable, not easy to damage in use, not easy to deform. However, if the die-casting parts are complex and the parts of the die are complex, the mould can be difficult to process and the machining accuracy is not high. If the mould parts are made into combination, the machining is greatly simplified and easy to obtain high machining precision, which can obtain high quality die-casting parts.
2. Decision of cavity number
To determine the number of cavity, it is necessary to consider the equipment ability, the difficulty of mould processing, the production batch size and the precision of casting. Especially in the multi-cavity mould, because of the difficulty of the mould processing, the size accuracy error is large, the flow channel configuration is not easy to achieve the balance, the performance of each cavity castings is inconsistent. The die casting requires high precision and complex geometry, preferably one cavity. Small castings are based on the situation.
3. Design of pouring system
Gating system is not only the liquid metal die casting filling type of channel, and the transfer of the melt flow rate and pressure and exhaust conditions, die-casting type thermal stable factors such as regulation, therefore, must analyze casting gating system design structure characteristics, technical requirements, kinds of alloy and its features, consider the type and characteristic of die casting machine, etc., so as to reasonable design of gating system.
4. Design of exhaust system
The mould shall have overflow groove and exhaust passage with sufficient overflow range, which is important to ensure product quality. It is often overlooked that the overflow channel is blocked by the incoming metal. In order to make the metal liquid flow into the deeper part of the overflow tank, it will ensure that the air vent is connected in the longest time. In addition, the overflow tank shall have a top rod to exclude the metal in the overflow tank.
5. Mold temperature
The temperature of die casting mould is an important factor affecting casting quality. Improper mould temperature, not only affect the quality of die casting, both inside and outside (such as blow hole, shrinkage cavity, porosity formation of castings, mucous membrane, coarse grains and other defects), also affect the casting dimension accuracy, even deformation of the casting, the die-casting die appear crack, make the casting surface is difficult to remove the mesh burr formation, affect the quality of die casting's appearance. In the case of aluminium alloy, alloy in 670-710 ℃ temperature pouring into the mould. In the long-term production practice, the optimal temperature of the die should be controlled by 40% of the casting temperature. Aluminum alloy die-casting die temperature is 230-280 ℃, the mould temperature in the range to obtain high quality castings.
The mold is generally not used for gas or electric heating, and the preheating cooling device is used for heating and cooling of the mold.
6. Determination of forming part dimensions
When calculating the size of die casting parts, the shrinkage rate of the die casting material should be in line with the actual conditions, otherwise the production will not be qualified. When necessary, the dimensions of the die casting are calculated by testing the test mould. For high-precision products, even the thermal expansion of die casting parts material and the influence of the environment on the product size accuracy should be taken into account.
7. Determination of the position of the parting plane
The position of the parting surface will affect the mould processing, exhaust and product ejection. Usually, the parting surface will leave a trace line on the product, affecting the product's surface quality and dimensional accuracy. Design the parting surface position, therefore, in addition to considering the mould product, mould processing, such as exhaust problem, can put the parting surface position on the product surface quality is not high, or dimensional accuracy is not high.
8. Mould cannot deform
Often due to improper mold structure is not reasonable or mold material selection, cause mould in use rupture, deformation, resulting in the product is unqualified, therefore, in the design of the mould, proper measures must be taken to ensure the quality of the products.
Usually, the pressure inside the mold is 70-100mpa, so that the mold is not deformed and misshapen, the cavity should be fully thick, the plate and plate of the installation core should be sufficiently thick, and the cushion should be added when necessary. The shape core and the cavity should be installed reliably, the type core and the installation hole side roughness should be appropriate, the roughness can not be too low, the perforation core should be fixed on both sides, to prevent the product side wall thickness, side wall thin. The core of the blind hole in the product should be strengthened by the feeding port, quantity and core, so as to make the core balance.
The pressure mold can be used to check the strength of the cavity and pad. The strength and stiffness of the wall thickness are checked, and the stiffness of the pad is checked. In addition to adopting certain guarantee measures on the structure of the mould, the mould materials with small deformation and good strength are selected. In addition, there is a gap between the guide column and the guide sleeve, or the wear of the guide column and guide sleeve in the use process will affect the quality of the product. Especially the product with high dimensional accuracy, in order to ensure product accuracy, can be set up on the parting, die cone coordinate setting part, or place set up around the cavity 2-4 locating rod, positioning and enhancing role, in order to prevent the moving dislocation, mold, the large, mass production mode is more important.
The launching system should set up the guide pillar to prevent the work from being uneven, which can be worn by the single side to ensure that the product has a uniform force and the product is not deformed at the top.
