The developed countries of the automobile industry such as the United States, Germany, and Japan are all committed to developing green, high-performance engines. The engines are developing in the direction of supercharging, supercharging, intercooling, high power, high reliability, and low emissions. As the heart of the engine, the crankshaft is facing serious challenges of safety and reliability. Traditional materials and manufacturing processes can no longer meet its functional requirements. Therefore, professional crankshaft manufacturers are rushing to introduce new technologies and new processes to improve the manufacturing technology. The article introduces the progress and future development trend of crankshaft manufacturing technology from the aspects of casting technology, forging technology, machining technology, heat treatment and surface strengthening technology of crankshaft blank.
The crankshaft is an important part of the engine that is subjected to impact loads and transmits power. It is most difficult to guarantee the quality of machining in the five major parts of the engine. Due to the harsh working conditions of the crankshaft, the requirements for crankshaft material and blank machining technology, precision, surface roughness, heat treatment, surface strengthening and dynamic balance are very strict. If the quality of any of these links is not guaranteed, it can seriously affect the service life of the crankshaft and the reliability of the whole machine. The developed countries of the world's automobile industry attach great importance to the processing of crankshafts and continuously improve the crankshaft processing technology. With the addition of the WTO, domestic crankshaft manufacturers have realized the urgency of the situation and introduced a large number of advanced equipment and technologies to improve the overall competitiveness of the products, which has greatly improved the manufacturing technology of the crankshaft, especially It has developed more rapidly in the past five years. Metal processing WeChat, the content is good, it is worthy of attention.
At present, the engine crankshaft of the vehicle has two types of ductile iron and steel. Due to the good cutting performance of ductile iron, a better structural shape can be obtained, and as with the steel crankshaft, various heat treatments and surface strengthening treatments can be performed to improve the fatigue strength, hardness and wear resistance of the crankshaft. The cost of ductile iron crankshaft is only about 1/3 of the cost of quenched and tempered steel crankshaft, so the ductile iron crankshaft has been widely used at home and abroad. Statistics show that the proportion of ductile iron used in automotive engine crankshafts is 90% in the United States, 85% in the United Kingdom, and 60% in Japan. In addition, Germany, Belgium and other countries have also adopted large quantities. The trend of using spheroidal graphite cast iron crankshafts in China is more obvious. More than 85% of the crankshafts of small and medium-sized power diesel engines use ductile iron, and the crankshafts of engines with power above 160 kW are mostly forged steel crankshafts.
Progress in crankshaft manufacturing technology/process
1. Casting technology of spheroidal graphite cast iron crankshaft
After the production of spheroidal graphite cast iron crankshafts, following several brands such as QT800-2 and QT900-2, Guangxi Yuchai and others have been able to stably produce QT800-6 grade crankshafts, which laid the foundation for the crankshaft “to iron-based steelâ€.
(1) Smelting
The acquisition of high-temperature, low-sulfur, pure molten iron is the key to producing high-quality ductile iron. Domestically, the production equipment mainly consists of cupola, and the molten iron is not pre-desulfurized; the second is high-purity pig iron and poor coke quality. At present, a double-addition pre-desulfurization smelting method has been adopted, which uses molten steel to melt molten iron, desulfurizes outside the furnace, and then heats up and adjusts the composition in an induction furnace. At present, the detection of domestic molten iron components has been generally carried out using a vacuum direct reading spectrometer.
(2) Modeling
The airflow impact molding process is obviously superior to the clay sand type process, and high-precision crankshaft castings can be obtained. The sand mold produced by the process has the characteristics of no rebound deformation and the like, which is particularly important for the crankshaft. At present, some crankshaft manufacturers in China have introduced airflow impact molding technology from Germany, Italy, Spain and other countries. However, only a few manufacturers have introduced the entire production line. For example, Wendeng Tianrun Crankshaft Co., Ltd. has introduced the German KW casting production line.
2. Forging technology of steel crankshaft blank
In recent years, a number of advanced forging equipment have been introduced in China, but due to the small number, and the mold manufacturing technology and other facilities can not keep up, some advanced equipment has not played its due role. Generally speaking, there are many old and forged forging equipment that need to be modified and updated. At the same time, backward technology and equipment still occupy a dominant position, and advanced technology has been applied but not yet widespread.
3. Machining technology
At present, most domestic crankshaft production lines are composed of ordinary machine tools and special machine tools, and the production efficiency and automation are relatively low. The roughing equipment mostly uses a multi-tool lathe to turn the crankshaft main journal and the neck, and the quality stability of the process is poor, and it is easy to generate large internal stress, and it is difficult to achieve a reasonable machining allowance. General finishing uses the crankshaft grinding machine such as MQ8260 rough grinding - semi-finishing - fine grinding - polishing, usually by manual operation, the processing quality is unstable.
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