Engine crankshaft manufacturing technology progress and future
The crankshaft is an important part of the engine that is subjected to impact loads and transmits power. It is the most difficult to guarantee the processing quality among 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, so that the manufacturing technology of the crankshaft has been greatly improved, especially It has developed more rapidly in the past five years.
At present, the crankshaft of the vehicle engine is made 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€.
The smelting 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 modeling 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. 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, combined with mold manufacturing technology and other facilities, some advanced equipment has not played its due role. In general, 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 cranking machine such as MQ8260 rough grinding - semi-finishing - fine grinding - polishing, usually by manual operation, the processing quality is unstable.
With the advent of trade globalization, manufacturers have realized the seriousness of the situation, have carried out technological transformations, and strive to enhance the competitiveness of enterprises. In recent years, many advanced equipments and technologies have been introduced, and the progress is very fast. As far as the current situation is concerned, these devices and technologies are basically dependent on imports. The following is an introduction to the situation of Harbin Dongan Power, FAW Dachai, Wendeng Tianrun Crankshaft, Binzhou Haide Crankshaft and other companies.
The crankshaft production line of Harbin Dongan Group is a fully automatic flexible water production line. The rough processing line consists of the German automatic machine line (LINDENMAIER), CNC machine-car pull, CNC high-speed follow-up milling (BOEHRINGER), fillet roller press (HEGENSCHEIDT-MFD) It is composed of a push-roller rolling machine and an EMA. The finishing line consists of a Japanese high-speed CNC CBN grinding machine (TOYODA), a dynamic balancing machine, a polishing machine (IMPCO-NACHI), a testing machine, and a washing machine.
The connecting rod journaling process adopts the numerical control high-speed follow-up machining technology. The whole line adopts high-speed CBN grinding wheel grinding technology, and the grinding line speed reaches 120m/s.
Through the introduction of advanced equipment from developed countries such as Germany, the United States and Italy, Wendeng Tianrun Crankshaft has established a large crankshaft production base with international advanced level, from CBN grinding machine, HAAS vertical and horizontal machining center, Italian SAILM grinding machine, Germany HELLER Machining lines consisting of crankshaft internal milling machines and SA-FINA polishing machines have begun mass production.
The rough and finishing processes of the FAW Dachai crankshaft production line are located in different workshops, thus ensuring the cleanliness of the finishing shop. Rough machining includes crankshaft quality centering machine, CNC internal milling machine and other equipment. The finishing equipment consists of imported advanced equipment such as British LANDIS and Japan TOYADA CNC crankshaft grinder.
After the technical transformation of Binzhou Haide Crankshaft, a CNC crankshaft machining production line was established. The roughing equipment consisted of CNC lathes, CNC crankshaft milling machines, etc. The finishing equipment consisted of CNC grinding machines, CNC belt polishing machines, and roller finishing machines. Composition, recently prepared to purchase key equipment such as Japan TOYADA machine CNC grinding machine, inspection equipment has the United States ADCOLE crankshaft CMM, roughness meter and other components. It is worth mentioning that Haide Crankshaft Company has taken the lead in applying the new technology of spheroidal graphite cast iron crankshaft fillet rolling and barrel finishing in the professional crankshaft manufacturers nationwide, and achieved good economic and social benefits.
It can be seen that the most advanced engine crankshaft manufacturing technology is machining equipment. The typical machining process is milling and grinding. The following is a brief introduction to the GF70M-T crankshaft grinder and the VDF 315 OM-4 high-speed follower milling machine.
GF70M-T crankshaft grinding machine is a special crankshaft grinding machine developed and produced by TOYADA machine in Japan. It is a CNC crankshaft grinding machine designed to meet the needs of multi-variety, low-cost, high-precision and mass production. The grinding machine adopts workpiece rotation and grinding wheel servo linkage control technology, which can complete all journal grinding by clamping without changing the center of the crankshaft, including follow-up grinding of the connecting rod journal; Static pressure guide rail, static pressure feed screw (sand wheel head frame) and linear grating closed-loop control, using the GC50 CNC control system produced by TOYADA machine, the roundness accuracy of grinding journal can reach 0.002mm; using CBN grinding wheel, grinding With a line speed of up to 120m/s and a double wheel head frame, the grinding efficiency is extremely high.
The VDF 315 OM-4 high-speed external milling machine is a flexible CNC milling machine designed and manufactured by BOEHRINGER of Germany for the crankshaft of automobile engines. The machine uses the workpiece rotary and milling cutter feed servo linkage control technology, which can change the crankshaft rotation without clamping at one time. The center follows the link pin journal of the crankshaft. VDF 315 OM-4 high-speed follow-up milling adopts integrated composite structure bed, electronically synchronous rotary drive at both ends of the workpiece, featuring dry cutting, high machining precision and high cutting efficiency; using SIEMENS 840D CNC control system, equipment operation In the man-machine interface, the machining program can be automatically generated by inputting the basic parameters of the parts. It can process various crankshafts with a length of 450 to 700 mm and a rotary diameter of 380 mm. The diameter of the connecting rod journal diameter is ±0.02 mm.
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.
According to foreign data, the spheroidal graphite cast iron crankshaft is compounded with a rounded rolling process and ion nitriding to increase the fatigue strength of the entire crankshaft by more than 130%. Some domestic manufacturers have also carried out this practice in recent years and achieved good results.
For the crankshaft fillet rolling process, the machine tool produced by HEGENSCHEIDT-MFD AUTOMATIC in Germany uses the patented technology of variable pressure rolling and correction. It is a good rounded rolling device, but it is expensive. At present, domestic research in this area has also achieved certain results. The research and development and application of "Crankshaft fillet rolling strengthening and rolling straightening technology" of Dongfeng Motor Co., Ltd. has solved the problem of introducing domestic enterprises into foreign technology. The problem was won the second prize of the Science and Technology Progress Award of the former State Bureau of Machinery Industry.
Development trend of crankshaft manufacturing technology
Casting technology
Smelting For the melting of high-grade cast iron, a large-capacity intermediate frequency furnace will be used for smelting or variable-frequency intermediate frequency furnace smelting, and a direct reading spectrometer will be used to detect the molten iron composition. Ductile iron treatment adopts subcontracting to develop a new variety of spheroidizing agent, and adopts advanced gestation methods such as gestation, intra-type gestation and compound gestation. The parameters of the melting process enable microcomputer control and screen display.
Modeling lost foam casting will be developed and promoted. In sand casting, boxless injection molding and extrusion molding will be valued and will continue to be promoted in new or rebuilt plants. The original high-pressure molding line will continue to be used, and some of the key components will be improved to achieve automatic core and lower core.
2. Forging technology
The automatic line with hot forging press and electro-hydraulic hammer as the main engine is the development direction of forged crankshaft production. These production lines will generally adopt precision shearing, roll forging (cross wedge rolling), medium frequency induction heating, finishing hydraulic press. Advanced technology such as precision pressing, and equipped with a robot, conveyor belt, and a die changer with a rotary table to form a flexible manufacturing system (FMS). FMS automatically replaces workpieces and molds and automatically adjusts parameters for continuous measurement during operation. Display and record data such as forging thickness and maximum pressure and compare with the set value to select the best deformation to obtain a quality product. The entire system is monitored by the central control room for unmanned operation.
3. Machining technology
Crankshaft roughing will use CNC lathes, CNC internal milling machines, CNC broaching machines and other advanced equipment to perform CNC turning, internal milling and car-broaching on the main journal and connecting rod journals to effectively reduce the deformation of crankshaft machining. Crankshaft finishing will extensively use a CNC-controlled crankshaft grinder to finish the journal. The grinding machine will be equipped with the automatic dynamic balancing device of the grinding wheel, automatic tracking device of the center frame, automatic measurement, automatic compensation device, automatic dressing of the grinding wheel, constant line speed and other functional requirements to ensure the stability of the grinding quality. High-precision equipment relies on the status quo of imports and is not expected to change in the short term.
4. Heat treatment technology and surface strengthening technology
The intermediate frequency induction quenching of the crankshaft medium frequency induction hardening crankshaft will adopt the microcomputer monitoring closed loop intermediate frequency induction heating device, which has the characteristics of high efficiency, stable quality and controllable operation.
Crankshaft Soft Nitriding For high-volume production of crankshafts, in order to improve product quality, a microcomputer-controlled nitrogen-based atmosphere gas soft nitriding line will be used in the future. The nitrogen-based atmosphere gas soft nitriding production line consists of a front washing machine (cleaning and drying), a preheating furnace, a soft nitriding furnace, a cooling oil tank, a post-cleaning machine (cleaning and drying), a control system, and a gas-making gas distribution system.
Crankshaft surface strengthening technology Ductile iron crankshaft fillet rolling strengthening will be widely used in crankshaft machining. In addition, the composite strengthening process such as round roll rolling strengthening and journal surface quenching will also be widely used in crankshaft machining, and forged steel crankshaft reinforcement. More will be used for journal and fillet quenching.
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