With the development of science and technology, the requirements for the safety and beauty of die casting products are increasing. According to the use of different parts of the quality evaluation is different. Today hand small make up to tell you how mold design affects the quality of aluminum die casting.
How to produce high quality parts is of great significance to save materials, energy, shorten manufacturing hours and improve economic efficiency.
Factors affecting die casting quality
There are many factors that affect the quality of die casting parts, such as the type and quality of die casting machine, the rationality of die casting geometric structure and technical requirements, the structure of die and the technical level of operators, etc.
1. Die casting design
Designers should first fully understand the user's operating requirements and working conditions, the stress of the die casting, and then choose the appropriate material according to the operating requirements and working environment, to understand the die casting performance of the material. In the design, special attention should be paid to make the die casting structure as simple as possible under the premise of meeting the use requirements. The thickness of the wall should be uniform and the necessary deviation of the die should be maintained, otherwise the defects such as pits, air holes, shrinkage, undercasting, tensile marks, cracks and deformation will appear on the die casting pieces.
The requirement of dimension accuracy of die casting parts should be reasonable, otherwise it will cause unnecessary trouble to mold design, mold processing, process conditions formulation and management, and will cause a large number of unqualified products.
2. Mold structure, machining accuracy and mold material selection
Die casting is die casting, there is no doubt that mold design, processing, mold material selection and product quality is closely related. Unreasonable mold structure, no matter what measures are taken from the process, it is difficult to make the product qualified.
In addition, mold materials, mold processing accuracy, surface roughness, machining marks, heat treatment of small cracks, nitriding layer thickness and improper assembly of the mold, will affect the quality of products and mold life.
3. Shrinkage of casting materials
The average shrinkage of the casting material is usually chosen when it is given in the form of an average percentage or a percentage with a range of variations. For high-precision die castings, special attention should be paid to the shrinkage rate of selected materials when designing molds. If necessary, test molds can be made first. After obtaining the required data from the test molds, design and manufacture of molds for mass production can be started.
4. Formulation and implementation of die casting process
The formulation and implementation of die casting process is related to the quality of die casting equipment and the technical level of operators. It is difficult to control the die casting process parameters stably, reliably and accurately under the condition of existing die casting equipment in China. The realization of basic control of die casting technology is a process of combining and applying die casting equipment, die casting materials and molds. Lax execution of the process and main parameters will lead to shrinkage, deformation, undercasting, unqualified dimensions, etc.
The relationship between die casting quality and die
Die casting is the main tool, therefore, in the design of die, we should pay attention to make the overall structure of die and die parts structure reasonable, easy to manufacture, easy to use, safe and reliable. In order to keep the die from deformation in die casting, the liquid metal flow in the die is stable, the casting can be cooled evenly, and the die casting can be done automatically without fault. In addition, according to the production of batch, material and other reasonable selection of appropriate mold materials.
1. The structure of molds and mold parts should be reasonable
From the point of view of strength, the mould parts are designed as a whole, which are strong and durable, not easy to be damaged and deformed in use. However, if the shape of the die casting is complex, the mold parts are also complex, it will make the mold processing difficult, the processing precision is not high. If the die parts are made into a combination, the machining can be greatly simplified, and high machining accuracy can be easily obtained, thus high quality die castings can be obtained.
2. Determination of cavity number
To determine the number of cavity, we should consider the equipment capacity, mold processing difficulty, production batch size, casting precision requirements, etc. Especially for multi-cavity mold, due to the difficulty of mold processing, large dimensional accuracy error, difficult to achieve balance of runner configuration, the performance of each cavity casting is inconsistent. When die casting requires high precision and complicated geometry, it is better to have one cavity per mold. Small castings as appropriate.
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. Exhaust system design
The mold should be provided with enough overflow channel and exhaust channel, which is important to ensure product quality. People often ignore the phenomenon of premature blockage of the overflow channel by the incoming metal liquid. A reasonable structure should be adopted to make the metal liquid flow into the deeper part of the overflow tank first and ensure that the vent hole is always open for the longest time. In addition, the overflow tank shall be provided with material ejector bar to eliminate the metal in the overflow tank.
5. Mold temperature
The temperature of die casting mould is an important factor affecting casting quality. Improper mold temperature will not only affect the internal and external quality of the die casting (such as the defects of pores, shrinkage holes, loose, mucous membrane, coarse grains, etc.), but also affect the size accuracy of the casting, and even the casting deformation, causing cracking of the die casting, forming network burrs on the casting surface that are difficult to remove, and affecting the appearance quality of the die casting. Take aluminum alloy as an example, the alloy was poured into the casting mold at the temperature of 670-710℃. In the long-term production practice, it is concluded that the optimal temperature of the mold should be controlled at 40% of the casting temperature. The die casting temperature of aluminum alloy is 230-280℃, which is beneficial to obtain high-quality and high-yield castings.
The die is generally heated without gas or electricity, but with preheating and cooling devices, which preheat and cool the die using oil as the medium required.
6. Determine the size of molding parts
When calculating the size of die casting parts, the shrinkage rate of die casting materials should be in line with the reality, otherwise it will lead to unqualified products. If necessary, the dimension of the die casting is calculated after being measured by the test mold. For high-precision products, the thermal expansion of die casting parts, preservation of products after die casting and the influence of using environment on the dimensional accuracy of products should even be taken into account.
7. Determination of parting surface position
Parting surface location, will affect the mold processing, exhaust, product demoulding. Usually, the parting surface will leave a trace line on the product, affecting the surface quality and dimensional accuracy of the product. Therefore, when designing the position of parting surface, the position of parting surface can be put in the place where the quality requirement of product surface is not high, or the size accuracy is not high, in addition to the problems of product demoulding, mold processing and exhaust gas.
8. The mold shall not be deformed
Often because the mold structure is not reasonable or the mold material selection is improper, causes the mold in the use the crack, the deformation, then causes the product to be unqualified, for this, when the design mold, must take the appropriate measure to guarantee the product quality.
Normally, the pressure in the die casting is 70-100mpa. In order to prevent the mold from deformation and dislocation, the cavity should be fully thick. The plate and backing plate of the mold core should be fully thick. The core and cavity shall be installed reliably, the side roughness of the core and installation hole shall be appropriate, and the roughness shall not be too low. The core of the through-hole shall be fixed on both sides to prevent the product from having thick and thin walls on one side. For the blind hole core of the product, we should also find a way from the position of the inlet, the quantity and the reinforcement of the core to make the core bear the same force.
The die casting die can be used to check the strength of mold cavity and backing plate. Check the strength and stiffness of the cavity wall thickness and the stiffness of the backing plate. In addition to the structure of the mold to take some measures to ensure, but also to choose small deformation, good strength of the mold materials. In addition, there is a gap between the mold guide column and guide sleeve, or the wear of guide column and guide sleeve in the use process will affect the quality of products. Especially for the products with high dimensional accuracy, in order to ensure the accuracy of the products, the matching part of the cone surface of moving and fixing die can be set on the parting surface, or 2-4 positioning rods can be set around the cavity to play the role of positioning and strengthening, so as to prevent the dislocation of moving and fixing die, which is more important for large-scale and mass production.
The ejector system shall be equipped with guide pillars to prevent the work of the push rod from being unstable and subject to unilateral wear, so as to ensure the product to bear uniform force and not to deform the product during ejector.