Importance of casting molds in sand casting

- Aug 09, 2018-

The factory calls the casting mold "the mother of casting", which is a high-level summary of the role and status of the casting mold in casting production.

It is called “mother”. One of them is because in the factory, all the castings are made by molding the sand mold, and there is no casting mold without casting. Second, the castings always have the “hereditary” of the casting mold. The dimensional accuracy of the casting, the surface roughness and even some casting defects are directly related to the quality of the casting mold. (1) Dimensional accuracy The casting is made according to the mold, and the dimensional error of the mold is reflected on the casting without exception. Especially for some complex castings, due to the use of multiple molds (outer mold and core box), the cumulative error will seriously affect the dimensional accuracy of the casting. The picture shows the chain size diagram of the casting dimensional accuracy of a car cylinder (4 cylinders). The shaded frame in the figure is the casting process equipment, and the other frames are the process. It can be inferred from the figure that even if the accuracy of each set of tools can get 99 points, the score may be only 82.5 points in the box. This shows how important it is to pursue the “zero error” of the mold.

(2) Surface roughness The smooth surface of the mold not only improves the mold release, but also reduces the type (core) waste, improves the productivity, and can obtain a smooth cavity (or sand core), which is favorable for obtaining a smooth casting.

(3) Casting defects Some casting defects may be caused by poor quality of casting molds. For example, the surface of the casting mold has a negative degree of soiling and unevenness, which will result in poor mold release, damage to the surface of the mold and even blisters; mold installation deviation or positioning The pin (set) wear causes misshape, extrusion, and blisters; the random fabrication or installation of the gating system causes the slag flow to deviate from the process design requirements, which may cause defects such as porosity, shrinkage, and the like. In casting production, process-molding-equipment is an inseparable system, and good process design relies on casting molds. Similarly, a crappy process design may result in a well-processed mold being scrapped due to the inability to produce a qualified casting. The proper fit of the mold and equipment is just as important. Therefore, in the process of determining the process plan and designing the process, it is necessary to start the preparation of the mold and the equipment at the same time, that is, it is necessary to implement the parallel engineering. Because of this, some domestic enterprises have introduced core boxes at the same time as the introduction of core making machines, and introduced some complex molds (such as car cylinders), including process design. In the modern society where innovation is becoming the main theme of economic development, the product renewal cycle is shortening and new products are emerging one after another. This requires the manufacturing industry to adapt to it and develop rapidly. The mold industry, which is the basis of manufacturing industry, will inevitably develop. It can be said that the introduction of high-quality, high-precision molds as soon as possible is one of the primary and key factors to seize the market. Design and manufacturing technology of casting molds China is a big country in casting, but it is far from a casting power. China's casting technology level, casting quality, technical and economic indicators, etc. are far from the advanced countries, and manual and semi-mechanical modeling still occupy a large proportion. Similarly, China's casting process equipment is also far from the advanced countries. Wood molds and wood-plastic touches are still widely used. The processing of metal molds is still dominated by ordinary milling machines. The development of new products is often delayed due to long mold design and long manufacturing cycle, resulting in the loss of the market. Since the 1990s, the huge market demand, especially the rapid development of home appliances, automobiles and motorcycles, has greatly promoted the development of China's mold industry. The foundry mold industry has also undergone tremendous changes. These changes are reflected in the design and manufacturing technology. Have: 

1) Auto CAD is commonly used by designers;

2) CAD/CAM has been widely used in the foundry mold industry. Not only large companies, large factories such as FAW, Dongfeng Motor Corporation, Yituo Group, Yuejin Group, etc., some of the township professional casting mold factories that have risen in recent years, such as Xiangshan Many factories are also used freely;

3) Rapid prototyping of molds has entered the practical stage, the reliability and technical indicators of LOM, SLS and other methods have reached and exceeded the level of similar foreign products, and the price is only 1/4 to 1/3 of similar foreign products;

4) High-speed machining (referred to as HSM) The introduction of technology into the mold industry has improved the accuracy of the mold and greatly shortened the mold manufacturing time. Studies have shown that HSM processing time can be reduced by more than 30% for molds with a high degree of complexity. A factory processing diesel engine block casting mold, the original three-axis linkage CNC machine tool, the total processing time is 50.28h, using NURBS high-speed machining, the total processing time is only 6.756h;

5) CAE and reverse engineering have been applied by some enterprises and achieved obvious results. The solidification simulation in the early stage of product development greatly optimizes the process design and shortens the test time. The use of reverse engineering and digital (CAD/CAM) methods to make molds (especially complex molds) has short production cycle, high precision and good consistency. Many advantages such as low price.