Application status and development trend of cranks

Application status and development trend of engine crankshaft manufacturing technology

at present, the developed countries of the world automotive industry attach great importance to the processing of engine crankshaft, and constantly improve the crankshaft processing technology through various means. With China's entry into WTO, domestic crankshaft manufacturers have also realized the seriousness of the situation. In order to improve the overall competitiveness of products, they have introduced many advanced processing equipment and manufacturing technology, which has greatly improved the manufacturing technology level of crankshaft

material analysis of engine crankshaft

at present, the materials of automotive engine crankshaft include ductile iron and steel. Due to the good cutting performance of nodular cast iron, it can obtain ideal structural shape, and as with steel crankshaft, it can be subject 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 nodular cast 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 nodular cast iron in large quantities. The trend of using nodular cast iron crankshafts in China is more obvious. More than 85% of medium and small power engine crankshafts are made of nodular cast iron

as far as high-power automotive diesel engine crankshafts are concerned, forged steel crankshafts have high comprehensive mechanical properties. Forged steel crankshafts are used in many high-speed and high-power four stroke diesel engines without exception. Steel die forged crankshafts are also used for engines with a displacement of more than 1.6 L

process analysis of engine crankshaft

at present, most of the older crankshaft production lines in China are composed of ordinary machine tools and special machine tools, with relatively low production efficiency and automation. Rough machining equipment mostly adopts multi tool lathe to turn crankshaft main journal and connecting rod journal. The quality stability of the process is poor, which is easy to produce large internal stress, and it is difficult to obtain reasonable machining allowance. Generally, crankshaft grinder is used for finishing, which is usually operated manually. The processing quality is unstable and the consistency of size is poor. The main feature of the old production line is that there are many ordinary equipment. There are 35~60 equipment in a production line, which leads to long production cycle and large space occupation, and it is entirely dependent on the decomposition process of multiple equipment and the sharing of surplus to improve production efficiency. In order to fully enhance the competitiveness of enterprises, many advanced crankshaft processing equipment and technology have been introduced in recent years. According to the crankshaft machining process, it can be generally divided into European and American type process scheme and Toyota type process scheme

European and American process plan

(1) domestic special machine tools are used to mill the front and rear end faces and drill central holes. Domestic CNC lathes are used to rough and finish the front and rear end excircles, the thrust surface on the main journal, and the circular arc grooves on the main journal and connecting rod journal. Adopt the domestic oblique cutting end face cylindrical grinder to grind the front and rear excircles and end faces

(2) the rough machining of main journal and connecting rod journal adopts the imported new external cutting and milling machine; The precision machining adopts the imported new double grinding wheel grinder (which can grind both the main journal and the connecting rod journal). The imported rolling machine is used to roll the arc grooves of the main journal and connecting rod journal, and the imported polishing machine is used to polish the main journal and connecting rod journal

(3) adopt imported CNC machine tools to process the hole system on the front and rear end faces. The imported CNC drilling machine is used to process the straight and inclined oil holes on the journal. The imported dynamic balance testing machine is used to conduct dynamic balance test on the crankshaft

the following is the European and American process scheme of engine crankshaft

① brief description of machining process of key parts:

main journal: turning → grinding → polishing

connecting rod journal: external milling → grinding → polishing

thrust surface: finish turning

oil hole: gun drill - → manual deburring - → high pressure cleaning

front and rear end faces: turning → grinding

cleaning: alternate cleaning twice, clean once after drilling oil hole, and finally clean once

finally, the crankshaft is comprehensively tested

② machining process of engine crankshaft:

milling two end faces, drilling center holes - → rear end of the car, No. 2-5 main journals - → front end of the car, No. 1 main journal and No. 1-5 main journal undercut - → milling No. 1-4 connecting rod journal and undercut - → drilling oil holes - → cleaning - → main journal, connecting rod journal excircle quenching - → magnetic particle flaw detection rolling main journal Connecting rod journal fillet - → front and rear end hole system processing - → fine turning thrust surface - → grinding main journal, connecting rod journal - → grinding flange excircle and end face - → grinding front excircle and end face - → dynamic balancing and weight removal - → polishing main journal, connecting rod journal and oil seal excircle - → magnetic particle flaw detection - → cleaning - → comprehensive inspection of crankshaft

Toyota process plan

this plan divides the whole process of crankshaft processing into 44 processes, using 57 sets of various equipment and 7 manipulators. Among them, there are 24 cutting processes, 1 high-frequency quenching process, 3 cleaning processes, 1 dynamic balance and correction process, 1 key pressing process, 1 heating and pressing gear process, 1 quality center hole measurement process, 1 oil hole penetration inspection process, and 1 gear inspection process; There is one connecting rod journal detection process, one main journal and connecting rod journal detection and printing process, and seven workpiece transfer processes

(1) mill the front and rear end faces and drill the center hole. The equipment used is similar to that made in China, but the difference is that the center hole drilled is a mass center hole rather than a geometric center hole, and after the completion of this process, a mass center hole benchmark balance tester is used for the preliminary detection of crankshaft dynamic balance. Adopt double turret CNC lathe to rough and finish the front and rear end excircles. The rough machining of the thrust surface on the main journal, the main journal and the circular arc groove on the connecting rod journal adopts a single axis CNC lathe. Adopt the oblique cutting end face cylindrical grinder to finish the front and rear end excircles and end faces. Use the thrust surface grinder to finish the thrust surface. After heat treatment, a special machine tool is used to correct the mass center hole

(2) roughen the main journal and connecting rod journal with an internal cutting and milling machine. Adopt turning and drawing machine tool to semi finish the main journal. Adopt multi wheel grinder for semi fine grinding and fine grinding of main journal. The connecting rod journal is finely ground with a single grinding wheel grinder. Adopt abrasive belt polishing machine to superfinish the main journal and connecting rod journal. Special (rolling) machine tools are used to finish the arc grooves on the main journal and connecting rod journal

(3) use a single axis CNC machine tool to process the hole system on the front and rear end faces and the straight and inclined oil holes on the journal. The dynamic balance test of crankshaft is carried out by dynamic balance testing machine

(4) some manipulators are equipped on the production line

(5) after the crankshaft is processed and finally cleaned, a special machine is equipped to detect and mark the dimensions of the main journal and connecting rod journal

(6) use the quality tracking and recording system to record the quality records in the whole processing process

application of engine crankshaft manufacturing technology

today's automotive engine manufacturing technology is developing towards high-speed, intelligent, composite and environmental protection. Its development is characterized by intensified competition. How to continuously improve production efficiency, reduce manufacturing costs, provide customers with high-quality products at competitive prices, and timely meet the growing needs of users has become the focus of common concern of all enterprises. The flexibility of engine production is required to be improved, and it is required to launch new products or convert new models in time according to the needs of the market. When the market has a demand for a certain product, we must seize the opportunity to produce products that meet the needs of the market. In engine manufacturing, a large number of parts need to be cut, which is characterized by high technology intensity, large production batches and fast manufacturing pace. The cutting tools used in engine manufacturing not only require good cutting performance and long working life, but also require high stability. At the same time, they also need to have a high performance price ratio. Metal cutting and cutting tool technology are the most active factors in the process of machining, It has become one of the key technologies to improve production efficiency and processing quality and reduce manufacturing costs

based on the above situation, since the beginning of the 21st century, efficient processing technology and equipment have been rapidly applied in the automotive manufacturing industry, and the production efficiency has been greatly improved. The number of production equipment in the engine crankshaft production line is rapidly decreasing. There are only about 13 sets of equipment in the whole line of the car engine crankshaft production line (including heat treatment, avoiding the subsequent loss of surface strengthening caused by unqualified parts), The product turnover line is short, the processing efficiency is high, and the quality management is easy

in the mid-1990s, foreign countries developed a new type of CNC high-speed crankshaft external milling machine tool, which made the crankshaft rough machining process to a new level. Compared with NC High-speed crankshaft external milling, internal milling has the following disadvantages: it is not easy to set 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 long, but internal milling is used to process forged steel crankshaft, which is easy to break chips and process easily. NC High-speed crankshaft external 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, less tool change times, higher machining accuracy and better flexibility. The disadvantage of NC High-speed external milling is that it cannot process the crankshaft with countersunk grooves in the axial direction. The structure and application of crankshaft high-speed external milling cutter

the use of domestic CNC grinding machines for crankshaft finishing has been quite common, and the machining accuracy of products has been improved to a considerable extent. In order to meet the increasing processing requirements of crankshaft, high requirements are put forward for crankshaft grinder. With the application of modern drive and control technology, measurement control, CBN (cubic boron nitride) grinding wheel and advanced machine tool components, conditions have been created for the high-precision and efficient grinding of crankshaft grinder. A kind of follow-up grinding process called connecting rod journal reflects the concrete results of the comprehensive application of these new technologies. This follow-up grinding process can significantly improve the grinding efficiency, machining accuracy and machining flexibility of crankshaft connecting rod journal. During the follow-up grinding of the connecting rod journal, the crankshaft rotates with the main journal as the axis, and all connecting rod journals are ground under one clamping. In the grinding process, the grinding head realizes reciprocating swing feed and tracks the eccentric rotating connecting rod journal for grinding. To realize the follow-up grinding, the x-axis must not only have high dynamic performance, but also have enough tracking accuracy to ensure the shape tolerance required by the connecting rod journal. The application of CBN grinding wheel is an important condition to realize the follow-up grinding of connecting rod journal. Due to the high wear resistance of CBN grinding wheel, the diameter of the grinding wheel is almost unchanged in the grinding process, and 600~800 crankshafts can be ground at one time. CBN grinding wheel can adopt very high grinding speed. Generally, the grinding speed of up to 120~140m/s can be adopted on crankshaft grinder, and some can even be higher, with high grinding efficiency

development trend of engine crankshaft manufacturing technology

Application of new tool materials

the improvement of cutting tool performance provides the possibility for the development of high-efficiency and high-speed machining. In addition to high-speed steel and cemented carbide, the development of superhard materials has played an important role. PCD and PCBN create conditions for cutting, dry cutting and hard cutting of difficult to machine materials

in order to meet the needs of high-speed, high-efficiency and dry cutting of crankshaft processing, coated tools are widely used at present. The coated materials are developed from tin to Al2O3 and Ti