Crankshafts are widely used in engines. Currently, the materials for automotive engines are mainly ductile iron and steel. Due to the good cutting performance of ductile iron, various heat treatments and surface strengthening treatments are performed to improve the fatigue strength, hardness and wear resistance of the crankshaft. Ductile iron crankshafts have lower cost, so ductile iron crankshafts have been widely used at home and abroad. Below we will introduce the crankshaft manufacturing technology.
Crankshaft manufacturing technology:
1. Casting technology of ductile iron crankshaft
The acquisition of high-temperature, low-sulfur, pure molten iron is the key to producing high-quality ductile iron. The domestic production equipment is mainly based on cupola, and the molten iron is not pre-desulfurized; the second is high-purity pig iron and poor coke quality. At present, a double-external pre-desulfurization smelting method has been adopted, which uses a cupola to melt molten iron, desulfurizes it 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.
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, which is especially important for the multi-turn crankshaft. At present, some crankshaft manufacturers in China have introduced airflow impact molding processes from Germany, Italy, Spain and other countries. However, only a few manufacturers have introduced the entire production line.
2. Forging technology of steel crankshaft
In recent years, a number of advanced forging equipment have been introduced in China, but due to the small number, combined with mold manufacturing technology and other facilities, some advanced equipment has not played its due role. In general, there are many old 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. Mechanical processing 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 crankshaft grinding machines such as MQ8260 for rough grinding – semi-finishing – fine grinding – polishing, usually by manual operation, and the processing quality is unstable.
4. Heat treatment and surface strengthening treatment technology
The key technology for heat treatment of the crankshaft is surface strengthening treatment. Ductile iron crankshafts are generally normalized and prepared for surface preparation. Surface strengthening treatments generally use induction hardening or nitriding. Forged steel crankshafts are journaled and rounded. The imported equipment includes AEG automatic crankshaft quenching machine and EMA quenching machine.