Material, mold, core making and inspection are the four basic aspects of engine block casting, which run through the whole process of engine block casting.
Gray cast iron is widely used in engine block castings in China, especially HT250. In order to meet the requirements of good machinability of cylinder block iron castings, and ensure the anti leakage and mechanical properties of cast iron castings, the application materials of cylinder block iron castings generally present the tendency of high carbon equivalent (CE = 3.9% – 4.05%) and low alloying. In order to ensure the high quality and stability of molten metal during pouring, the dual furnace melting process (cupola and induction furnace) is generally used in industrial production, and the pouring temperature is generally between 1350 ℃ and 1420 ℃. With the requirement of “energy saving and emission reduction” put forward by the state, the engine block casting is gradually developing towards the direction of lightweight and green, in order to meet the manufacturing concept of “low emission, zero pollution”.
In mold production, wet clay sand molding is the most widely used molding method for cylinder block iron castings. In order to meet the technical requirements of continuous production of large quantities of small cylinder block iron castings, a large number of manufacturers generally use various types of high-pressure automatic molding lines to meet the requirements of rapid casting of cylinder blocks, among which pneumatic and hydrostatic molding lines are typical. The advantages of this kind of production line are good molding performance, low energy consumption, low noise, less pollution, high efficiency and reliable operation. With the continuous innovation of sand mold molding technology at home and abroad, sand adding methods such as air impact plus compaction, air flow gain air impact plus compaction, static pressure plus compaction, active multi contact compaction, molding extrusion and other sand adding methods have been developed and widely used, which makes the mold hardness more uniform.
However, continuous production is impractical for large-scale, single piece and small batch of iron castings. The traditional casting process is complex, with many processes, long process and high cost, which can not respond to the market demand quickly. Therefore, rapid prototyping manufacturing technology emerges as the times require. Rapid prototyping manufacturing technology belongs to the category of additive manufacturing, mainly including three-dimensional lithography technology, layered solid technology, selective laser sintering technology, melt deposition technology, three-dimensional printing technology and thermoplastic material selective spraying technology. Rapid prototyping manufacturing technology is characterized by 3D CAD model driving and NC machining, and integrates advanced laser technology, advanced material technology and other modern scientific and technological achievements. It realizes seamless connection between digital design and digital manufacturing. It is an effective method to realize single piece and small batch agile manufacturing of large cylinder body iron castings to adapt to China’s national conditions. At present, this technology has been applied to some extent in the field of automobile engine block casting. Such as a Beijing Technology Center selective laser sintering technology to make mold. The thickness of the mold is generally 0.2mm, and the accuracy can be controlled within ± 0.25mm. The mold obtained by laser sintering can be cured twice after removing the floating sand, and the sand mold after secondary solidification has the same properties as the mold made by core shooting mechanism. Because most of the engine parts are made of sand casting, rapid prototyping manufacturing technology has become one of the most common and effective methods for engine prototype trial production and production.