Abstract: In order to reduce the weight index, fuel consumption index and exhaust emission index of engine unit power, we have studied and developed the cylinder and cylinder head products of lost-die casting in-line four-cylinder two-valve lower cam diesel engine. By optimizing the design of the product structure process, the casting process and the performance of the cast iron material, the technical performance index of each set of cylinder and cylinder lost foam casting products meets the design requirements and the production cost is greatly reduced.
I. Overview
The manufacturing level of the engine block and cylinder head is one of the important indicators to measure the manufacturing level of a country, and it represents to a large extent the development level of a country's automobile industry. Continuously improving engine power, reducing fuel consumption and reducing exhaust emissions are inherent requirements of the automotive industry's own development and an objective requirement for the external environment. The selection of aluminum alloy materials has effectively reduced the weight of the engine and even the entire vehicle, and promoted the development of the automotive industry. However, advances in automotive technology have placed higher norms on raw materials, energy conservation, and environmental protection, making the engine's specific power (k W / displacement · L) larger and larger, resulting in engine blocks and cylinder heads. The working temperature has generally increased, and the operating temperature in many local areas has exceeded 200 °C (normal working temperature is about 105 °C). On the one hand, the mechanical properties of aluminum alloys will drop rapidly and become overwhelmed; on the other hand, such high temperatures make The lubrication and thermal conductivity of the oil is weakened, while the cast iron material still works well at this temperature and exhibits excellent performance.
At present, the measures to solve the low mechanical properties of aluminum alloy at high temperature and normal temperature are to cast gray cast iron at the joint of the cylinder block, the cylinder head connecting bolt and the joint between the cylinder block and the bearing cap to strengthen the screw or gray cast iron connection. board. In doing so, on the one hand, the technical difficulty of casting and the weight of parts are increased, and the manufacturing cost is increased. On the other hand, due to the difference in expansion coefficient between aluminum alloy and gray cast iron, fatigue cracks and cast-in-place pieces are easily generated under engine working conditions. Loose defects.
Throughout the whole process of forming a cast product, the energy consumption of aluminum alloy is higher than that of cast iron; while the anti-vibration, self-lubricating and high-temperature mechanical properties of cast iron products are much larger than those of aluminum alloy. Therefore, it can be foreseen that ordinary gray cast iron, high-grade auto parts such as cast iron, alloy cast iron, vermicular cast iron and ductile iron will be more and more people's attention. Especially for the vermicular graphite iron castings, as a new engine material, the vermicular graphite cast iron has an increase in tensile strength of about 75%, an elastic modulus of nearly 40%, and a fatigue strength of almost twice that of gray cast iron. The replacement of the engine block produced by the gray cast iron with the vermicular graphite cast iron can reduce the weight by at least 10%, and at the same time greatly reduce the fatigue deformation and the pollutant emissions of the diesel engine. Absorbent graphite cast iron material has been widely used in high-power diesel engine parts. It has the strength close to ductile iron, has anti-vibration, thermal conductivity and casting performance similar to ordinary gray cast iron, and has better plasticity than ordinary gray cast iron. And fatigue resistance. In short, from the practical application of current alloy materials, the mechanical properties and high temperature performance of cast iron parts can meet the future development requirements of automotive engines.
The basic principle of lost foam casting is to use the same foam shape as the shape of the required casting, and add the alloy shrinkage rate instead of the mold to shape. The foam pattern is not taken out as a solid mold, after pouring the molten metal to vaporize it. Form castings.
Compared with traditional sand casting, lost foam casting has the following advantages:
(1) The process of sand mixing and core making has been eliminated, which eliminates the operations of binning, demoulding, trimming, lower core and combined boxing in the traditional molding process, which greatly simplifies the falling sand, casting cleaning and sand treatment processes. Shortened production cycle.
(2) On the one hand, due to the high rigidity of the mold under negative pressure, the cast iron piece is easy to realize self-feeding, thereby reducing the size of the riser required for the casting; on the other hand, the assembly freedom of the foam model cluster is large, and it is easy to realize one. The multi-piece casting is used to improve the process yield.
(3) The machining allowance of the lost foam casting is small (2.5~3.5mm), the wall thickness uniformity is high, and the internal cavity with the hole diameter larger than 7mm can be directly cast. The weight of the casting is reduced by 8% compared with the ordinary sand casting. 12%.
(4) There is no need for binders and additives (pulverized coal, bentonite, water) in the dry sand mold. It not only saves a lot of raw materials, but also helps the old sand recycle and reduce environmental pollution.
Anhui Quanchai Group Co., Ltd. introduced a complete lost foam casting production line and related production technology from the United States in 1994, including pre-foaming machine, molding machine, gluing machine, manipulator, dry sand molding and negative pressure casting production line. After more than 10 years of digestion and absorption and arduous exploration, it has independently researched and developed two series of 7 varieties of lost foam casting ordinary gray cast iron and high grade cast iron diesel engine parts and components.
This paper focuses on the key technologies and applications of the in-line four-cylinder two-valve lower cam diesel engine block and cylinder head lost foam casting process.
Second, the foam model structure process design
The structural complexity factor of the automobile engine cylinder block and the cylinder head lost foam model is one level, and it is difficult to foam it at one time in the actual production process. With reference to the self-structure of the part and the characteristics of the lost foam casting process, the product foam model is processed into pieces, and the structural process design of each die is carried out to facilitate foam forming. The number of pieces in each product foam model and the merits of the process design of the die structure are directly related to the success or failure of the lost foam casting process and the level of production efficiency.
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