After entering the 21st century, great changes have taken place in the crankshaft of the engine in terms of manufacturing processes and tools. Leading the multi-knife turning process and manual grinding process for more than half a century, it is gradually withdrawing from the historical stage due to low processing accuracy and poor flexibility. High-speed, high-efficiency composite processing technology and equipment rapidly enter the automobile and parts manufacturing industry, and high-speed and high-efficiency composite machining technology has been applied to a considerable degree in crankshaft processing and production, and will be its inevitable development trend.
Crankshaft processing technology equipment
At present, the older crankshaft production lines in China are mostly composed of ordinary machine tools and special machine tools, and their production efficiency and automation are relatively low. Roughing equipment generally uses multi-knife lathes to turn crankshaft main journals and connecting rod journals. The process quality is poor in stability, and it is easy to produce large processing stress, making it difficult to achieve a reasonable machining allowance. The general machining of crankshafts such as the MQ8260 crankshaft grinding machine is generally used for rough grinding, semi-finishing grinding, fine grinding and polishing. Usually, manual operation is used, and the machining quality is unstable and the dimensional consistency is poor.
One of the main features of the old-fashioned production line is that there are too many common equipments. According to the calculation of the ductile iron crankshaft, a production line has 35 to 40 devices. The author has examined a domestic forged steel crankshaft production line. Roughing adopts ordinary external milling machining of the main shaft and the connecting rod neck, and then the numerically controlled finishing main shaft and the connecting rod neck, and then passes through multiple grinding procedures and transfers to the finishing machining. Process. Therefore, this production line has more than 60 sets of equipment, resulting in long product turnaround lines and a large area of â€‹â€‹site occupancy. Its production efficiency is entirely enhanced by the number of equipment breakdown processes and margins.
The current car engine crankshaft manufacturing industry is facing the following problems:
1. Multi-variety, small-batch production;
2. The delivery time is greatly shortened;
3. Reduce production costs;
4. The emergence of difficult-to-cut materials has made the processing more difficult. There are many issues that need to be addressed in the processing, such as hard-cutting;
5. To protect the environment, it is required to use less or no cutting fluid to achieve dry cutting or quasi-dry cutting;
It is based on the above situation that since the 21st century, high-speed, high-precision, high-efficiency composite processing technology and equipment have been rapidly applied in the automotive crankshaft manufacturing industry, and production efficiency has been greatly improved, so production equipment in the engine crankshaft production line The number is reduced. I have seen in a car engine crankshaft production line, the entire line of equipment (including heat treatment, surface hardening) only about 13 sets of equipment, product turnover line is short, high processing efficiency, easy quality control management.
Development of Crankshaft Compound Machining Technology
In the late 1980s, Germany's BOEHRINGER and HELLER developed a complete crankshaft car-turning machine. This machining process combines the crankshaft turning process with the crankshaft pull process, resulting in high production efficiency, good machining accuracy, and high flexibility. With high automation and short tool change time, it is especially suitable for the machining of undercuts and crankshafts. After machining, the crankshaft can be directly ground, eliminating the need for rough grinding. Therefore, crankshaft car-vehicle pull processing technology is currently one of the popular machining processes in crankshaft rough machining in the world.
The new CNC high-speed crankshaft outside milling machine that appeared in the mid-1990s made the crankshaft roughing process reach a new level. Comparing CNC internal crankshaft milling with CNC high-speed crankshaft external milling, internal milling has the following disadvantages: it is not easy to align the tool, the cutting speed is low (usually not more than 160m/min), the non-cutting time is long, the machine tool investment is large, and the process cycle time is Longer. The CNC high-speed crankshaft milling has the following advantages: high cutting speed (up to 350m/min), short cutting time, short process cycle time, small cutting force, low workpiece temperature rise, high tool life, and tool change times Less, higher processing accuracy and better flexibility. Therefore, CNC high-speed crankshaft external milling will be the development direction of crankshaft roughing.
The author saw two equipments of German BOEHRINGER company in the Fiat car crankshaft production line of Jiangsu South Asia Automatic Vehicle Co., Ltd. One of them was a multi-crankshaft crankshaft-car pulling machine, and the other one was a CNC high-speed crankshaft outer milling and experienced a â€œcutting ironâ€ in person. Like mud" feeling. According to experts, crankshaft car-turning machine tools are particularly suitable for crankshafts that have sinker grooves on the journals and do not need to be machined on the side of the balancer block; high-speed external milling, on the other hand, cannot handle crankshafts that have an undercut groove in the axial direction. The milling machine is Germany's BOEHRINGER's VDF 315 OM-4 high-speed follow-up milling machine. It is a flexible CNC milling machine specially designed and manufactured by Germany's BOEHRINGER company for the crankshaft of automotive engines. The machine uses workpiece rotation and milling cutter feed servo linkage control technology. , Can be clamped at one time without changing the crankshaft rotary center, and follow the crankshaft connecting rod journal. VDF 315 OM-4 high-speed follow-up milling adopts the composite material integrated structure bed, and the workpieces are synchronously driven by both ends of the electrons. It has the features of dry cutting, high machining accuracy and high cutting efficiency. The milling machine uses SIEMENS 840D CNC control system. Through the input of the basic parameters of the parts can be automatically generated by the processing program, can be processed length 450 ~ 700mm, rotary diameter of 380mm within the various crankshaft, connecting rod journal diameter error of Â± 0.02mm.
From the above, it can be seen that the more popular processes for crankshaft roughing are: the main spindle adopts the car pulling process and high-speed external milling, the connecting rod neck adopts high-speed external milling, and tends to follow the high-speed follow-up milling, all adopt dry cutting. Due to the high price of such equipment abroad and the high cost of product processing, some domestic machine tool manufacturers (such as Qinghai No. 2 Machine Tool Manufacturing Co., Ltd.) have successively developed CNC crankshaft lathes, CNC high-speed crankshaft millers, and CNC crankshaft lathes and other special machines. machine tool.
The grinding of crankshafts using domestic CNC grinding machines is quite common, and the accuracy of product processing has been considerably improved. In order to meet the increasing processing requirements of crankshafts, high demands are placed on crankshaft grinding machines. In addition to high static, dynamic stiffness and high machining accuracy, modern crankshaft grinding machines require high grinding efficiency and more flexibility. In recent years, crankshaft grinding machines have been required to have stable machining accuracy. For this reason, Cp â‰¥ 1.67 is specified for the process capability coefficient of the crankshaft grinding machine, which means that the actual machining tolerance of the crankshaft grinding machine is required to be less than half of the crankshaft given tolerance. With the application of modern drive and control technology, measurement and control, CBN (CBN) grinding wheels and advanced machine parts, it has created conditions for high-precision, high-efficiency grinding of crankshaft grinding machines. A process called follow-up grinding of the connecting rod. It is the concrete results of the comprehensive application of these new technologies. This follow-up grinding process can significantly improve the crankshaft connecting rod neck grinding efficiency, machining accuracy and processing flexibility. In the follow-up grinding of the connecting rod neck, the crankshaft rotates with the main journal as the axis, and all the connecting rod necks are ground in one clamping. In the grinding process, the grinding head feeds back and forth and tracks the eccentrically rotating connecting rod neck for grinding. To achieve follow-up grinding, in addition to the high dynamic performance of the X-axis, it must also have sufficient tracking accuracy to ensure the required shape tolerances for the connecting rod neck. The application of CBN grinding wheel is an important condition for the follow-up grinding of the connecting rod neck. Due to the high wear resistance of the CBN grinding wheel, the diameter of the grinding wheel during the grinding process is almost constant, and 600 to 800 crankshafts can be ground at a single dressing. CBN grinding wheels can also be used with very high grinding speeds. Grinding speeds of up to 120 to 140 m/s can be used on crankshaft grinding machines, and grinding efficiency is high.