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2005-03-0 1 13:56:57
The developed countries of automobile industry, such as the United States, Germany and Japan, are committed to developing green and high-performance engines, which are developing in the direction of supercharging, supercharging and intercooling, high power, high reliability and low emission. Crankshaft, as the heart of engine, is facing severe challenges of safety and reliability, and traditional materials and manufacturing processes can no longer meet its functional requirements. Therefore, various professional crankshaft manufacturers are scrambling to introduce new technologies and new processes to improve manufacturing technology. The progress and future development trend of crankshaft manufacturing technology are introduced from the aspects of casting technology, forging technology, machining technology, heat treatment and surface strengthening technology of crankshaft blank.
* Li Shandong Binzhou Crankshaft Co., Ltd. Technology Center
Crankshaft is an important part of engine to bear impact load and transmit power, and it is the most difficult to ensure the machining quality among the five major parts of engine. Due to the harsh working conditions of the crankshaft, the requirements for crankshaft materials, blank processing technology, accuracy, surface roughness, heat treatment, surface strengthening and dynamic balance are very strict. If the quality of any link is not guaranteed, it will seriously affect the service life of the crankshaft and the reliability of the whole machine. Developed countries in the world automobile industry attach great importance to the processing of crankshafts and constantly improve the processing technology of crankshafts. With China's entry into WTO, domestic crankshaft manufacturers have realized the urgency of the situation and introduced a lot of advanced equipment and technology in order to improve the overall competitiveness of products, especially in the past five years, the manufacturing technology level of crankshafts has been greatly improved.
At present, there are two kinds of crankshaft materials for automobile engines: ductile iron and steel. Because of its good machinability, ductile iron can obtain ideal structural shape, and like steel crankshaft, it can be subjected to various heat treatments and surface strengthening treatments to improve the fatigue strength, hardness and wear resistance of crankshaft. The cost of nodular cast iron crankshaft is only about 1/3 of that of quenched and tempered steel crankshaft, so nodular cast iron crankshaft has been widely used at home and abroad. According to statistics, the proportion of automobile engine crankshafts made of ductile iron is 90% in the United States, 85% in Britain and 60% in Japan. In addition, Germany, Belgium and other countries are also widely used. The trend of using nodular cast iron crankshaft in China is more obvious. More than 85% crankshafts of small and medium-sized power diesel engines are made of ductile iron, and the crankshafts of engines with power above 160kW are mostly made of forged steel.
Development of crankshaft manufacturing technology/process
Casting technology of 1 nodular cast iron crankshaft blank
Following the production of QT800-2, QT900-2 and other brands of nodular cast iron crankshafts, Guangxi Yuchai and others have been able to stably produce QT800-6 brand crankshafts after tackling key problems, laying the foundation for replacing steel with iron.
(1) smelting
Obtaining pure hot metal with high temperature and low sulfur is the key to produce high quality ductile iron. In China, cupola is the main production equipment, and molten iron has not been pre-desulfurized; Secondly, there is less high-purity pig iron and poor coke quality. At present, the melting method of pre-desulfurization outside the double furnace has been adopted. Hot metal is melted in cupola, desulfurized outside the furnace, and then heated in induction furnace to adjust its composition. At present, vacuum direct reading spectrometer has been widely used in the detection of hot metal composition in China.
(2) Modeling
The air impact molding process is obviously superior to the clay sand molding process, and high precision crankshaft castings can be obtained. The sand mold made by this process has the characteristics of no rebound deformation, which is especially important for multi-throw crankshaft. At present, some crankshaft manufacturers in China have introduced air impact molding technology from Germany, Italy, Spain and other countries. However, only a few manufacturers have introduced the whole production line, such as Wendeng Tianrun Crankshaft Co., Ltd., which introduced the German KW casting production line.
2. Forging process of steel crankshaft blank.
In recent years, China has introduced a number of advanced forging equipment, but due to the small number, mold manufacturing technology and other facilities can not keep up, and some advanced equipment has not played its due role. Generally speaking, there are many old common forging equipment that need to be reformed and updated. At the same time, backward technology and equipment still dominate, and advanced technology is applied but not universal.
3, machining technology
At present, domestic crankshaft production lines are mostly composed of ordinary machine tools and special machine tools, with low production efficiency and automation. Rough machining equipment mostly uses multi-tool lathe to turn crankshaft main journal and crankshaft journal, which has poor quality stability and is easy to produce large internal stress, and it is difficult to achieve reasonable machining allowance. In finishing, MQ8260 crankshaft grinder is generally used for rough grinding-semi-fine grinding-fine grinding-polishing, and manual operation is usually used, so the processing quality is unstable.
With the advent of trade globalization, manufacturers have realized the seriousness of the situation and have carried out technological transformation to enhance the competitiveness of enterprises. In recent years, many advanced equipment and technologies have been introduced and made rapid progress. As far as the current situation is concerned, these equipment and technologies basically rely on imports. The following are Harbin dongan power, FAW Dachai, Wendeng Tianrun Crankshaft and Binzhou Hyde Crankshaft.
The crankshaft production line of Harbin Dongan Group is a fully automatic flexible production line. The roughing production line consists of German special plane automatic line (Lindenmaier), CNC lathe-lathe, CNC high-speed external milling (Bollinger), fillet rolling machine (Hagen Stedt -MFD), thrust surface lathe-lathe and quenching machine tool (EMA). The finishing production line consists of Japanese numerical control high-speed CBN grinder (TOYODA), dynamic balancing machine, polishing machine (IMPCO-NACHI), detector, cleaning machine, etc. The connecting rod journal is machined by CNC high-speed servo machining technology, and the whole line is grinded by high-speed CBN grinding wheel, and the grinding linear speed reaches120 m/s. ..
Wendeng Tianrun Crankshaft has established a large crankshaft production base with international advanced level by introducing advanced equipment from Germany, America, Italy and other developed countries. The machining production line consisting of CBN grinder, Haas vertical and horizontal machining center, Italian SAIMP grinder, German Heller crankshaft internal milling machine and Sa -FINA polishing machine has started mass production.
The roughing and finishing processes of FAW Dachai crankshaft production line are located in different workshops, which ensures the cleanliness of the finishing workshop. Rough machining includes crankshaft quality centering machine, CNC internal milling machine and other equipment, and finishing equipment consists of imported advanced equipment such as LANDIS in Britain and TOYADA CNC crankshaft grinder in Japan.
After technical transformation, Binzhou Hyde crankshaft has established a CNC crankshaft processing production line. Rough machining equipment consists of CNC lathe, CNC crankshaft milling machine and other equipment. Finishing equipment includes CNC grinder, CNC belt polisher, roller polisher and other equipment. In the near future, it is planned to purchase key equipment such as TOYADA machine CNC grinder in Japan. The testing equipment consists of American ADCOLE crankshaft CMM (see Figure 3) and roughness meter. It is worth mentioning that Hyde Crankshaft Company took the lead in applying the new technology of nodular cast iron crankshaft fillet rolling and rolling polishing among the national professional crankshaft manufacturers, and achieved good economic and social benefits.
It can be seen that the fastest progress in engine crankshaft manufacturing technology is machining equipment, and the typical machining process is milling and grinding. The following briefly introduces GF70M-T crankshaft grinder and VDF 3 15 OM-4 high-speed external milling machine, and their advanced degree can be seen:
GF70M-T crankshaft grinder is a special crankshaft grinder developed and produced by TOYADA Machine Tool Company of Japan. It is a CNC crankshaft grinder designed to meet the needs of multi-variety, low cost, high precision and mass production. The grinding machine applies the servo linkage control technology of workpiece rotation and grinding wheel feed, and can grind all journals, including the follow-up tracking grinding of connecting rod journals, by one-time clamping without changing the rotation center of crankshaft. Closed-loop control of hydrostatic spindle, hydrostatic guide rail, hydrostatic feed screw (grinding wheel spindle box) and linear grating is adopted, and GC50 numerical control system produced by Toyo Machine Tool in Japan is adopted, and the roundness accuracy of grinding journal can reach 0.002mm；; Using CBN grinding wheel, the grinding linear speed is as high as 120m/s, and the grinding efficiency of spindle box with double grinding wheels is extremely high.
VDF 3 15 OM-4 high-speed external follow-up milling machine is a flexible CNC milling machine specially designed and manufactured for automobile engine crankshaft by Boehringer Company of Germany. The equipment applies the servo linkage control technology of workpiece rotation and milling cutter feed, which can track and mill the crankshaft connecting rod journal at one time without changing the crankshaft rotation center. VDF 3 15 OM-4 high-speed follow-up external milling adopts an integrated composite structure bed, and both ends of the workpiece are driven by electronic synchronous rotation, which has the characteristics of dry cutting, high machining accuracy and high cutting efficiency. Siemens 840D CNC system is adopted, and the basic parameters of parts can be input on the man-machine interface to automatically generate equipment operation instructions. Various crankshafts with a length of 450 ~ 700 mm and a rotary diameter of less than 380mm can be processed, and the diameter error of connecting rod journal is 0.02 mm ..
4, heat treatment and surface strengthening treatment technology
The key technology of crankshaft heat treatment is surface strengthening treatment. Generally, the nodular cast iron crankshaft is normalized to prepare for surface treatment, and the surface strengthening treatment generally adopts induction quenching or nitriding process. Forged steel crankshaft adopts journal and fillet quenching process. Imported equipment includes AEG automatic crankshaft quenching machine tool and EMA quenching machine tool.
According to foreign data, the fatigue strength of nodular cast iron crankshaft can be improved by more than 130% by combining fillet rolling technology with ion nitriding. Some domestic manufacturers have also done this in recent years and achieved good results.
In the aspect of crankshaft fillet rolling, the machine tool automatically produced by HEGENSCHEIDT-MFD in Germany applies the patented technology of variable pressure rolling straightening, which is a good fillet rolling equipment, but it is expensive. At present, domestic research in this field has also achieved certain results. The Research, Development and Application of Crankshaft Fillet Rolling Strengthening and Rolling Straightening Technology by Technical Research Institute of Dongfeng Motor Co., Ltd. solved the problem that domestic enterprises invested huge sums of money to introduce foreign technology, and this topic won the second prize of the former State Machinery Industry Bureau for scientific and technological progress.
Development trend of crankshaft manufacturing technology
1, casting technology
(1) smelting
For the smelting of high-grade cast iron, high-capacity intermediate frequency furnace or variable frequency intermediate frequency furnace is used for smelting, and the composition of molten iron is detected by direct reading spectrometer. The treatment of nodular cast iron is subcontracted, new varieties of nodulizer are developed, and advanced inoculation methods such as stream inoculation, in-mold inoculation and compound inoculation are adopted. The parameters of melting process are controlled by microcomputer and displayed on the screen.
(2) Modeling
Lost foam casting will be developed and popularized. In sand casting, boxless injection molding and extrusion molding will be paid attention to and will continue to be popularized and applied in newly built or rebuilt factories. The original high pressure molding line will continue to be used, and some key components will be improved to realize automatic core loading and core lowering.
2. Forging technology
The automatic production line based on hot die forging press and electro-hydraulic hammer is the development direction of forging crankshaft production. Generally, these production lines will adopt advanced technologies such as precision shearing blanking, roll forging (cross wedge rolling) blank making, medium frequency induction heating, fine pressing of finishing hydraulic press, and at the same time, they will be equipped with auxiliary machines such as manipulator, conveyor belt and mold changing device brought back to turntable to form a flexible manufacturing system (FMS). Through FMS, the workpiece and die can be automatically replaced, the parameters can be automatically adjusted, and continuous measurement can be made during the working process. Display and record the data of forging thickness and maximum pressure, and compare with the fixed value, select the best deformation and obtain high-quality products. The whole system is monitored by the central control room to realize unmanned operation.
3, machining technology
Advanced equipment such as CNC lathes, CNC internal milling machines and CNC broaching machines will be widely used in CNC turning, internal milling and broaching of main journal and connecting rod journal, so as to effectively reduce the machining deformation of crankshaft. CNC crankshaft grinder will be widely used in finishing crankshaft journal. This grinder will be equipped with automatic grinding wheel dynamic balance device, automatic tracking device of center frame, automatic measuring and compensation device, automatic dressing grinding wheel, constant linear speed and other functional requirements to ensure the stability of grinding quality. It is estimated that the current situation that high-precision equipment depends on imports will not change in the short term.
4, heat treatment technology and surface strengthening technology
(1) intermediate frequency induction quenching of crankshaft
The closed-loop medium-frequency induction heating device monitored by microcomputer will be used for crankshaft medium-frequency induction quenching, which has the characteristics of high efficiency, stable quality and controllable operation.
(2) Soft nitriding of crankshaft
For mass-produced crankshafts, in order to improve product quality, a microcomputer-controlled nitrogen-based atmosphere gas soft nitriding production line will be adopted in the future. The nitrogen-based atmosphere gas soft nitriding production line consists of pre-cleaning machine (cleaning and drying), preheating furnace, soft nitriding furnace, cooling oil tank, post-cleaning machine (cleaning and drying), control system and gas generation and distribution system.
(3) Crankshaft surface strengthening technology
Rolling strengthening of nodular cast iron crankshaft fillet will be widely used in crankshaft processing. In addition, the compound strengthening processes such as fillet rolling strengthening and journal surface quenching will also be widely used in crankshaft processing, and forged steel crankshafts will be strengthened by journal and fillet quenching.