It is an important part of the engine, and its material is made of carbon structural steel or nodular cast iron. It has two important parts: main journal, connecting rod journal and other parts. The main journal is installed on the cylinder, the connecting rod journal is connected with the big end hole of the connecting rod, and the small end hole of the connecting rod is connected with the cylinder piston, which is a typical crank-slider mechanism. The lubrication of crankshaft mainly refers to the lubrication of bearing bush between rocker arm and two fixed points. This is usually pressure lubrication, and there is an oil passage in the middle of the crankshaft that communicates with each bearing bushing. After the engine is running, the oil pump will provide pressure oil for lubrication and cooling. The working process of the engine is that the combustion and explosion of the mixed compressed gas drive the piston to do linear motion, and the force is transmitted to the crankshaft through the connecting rod, and the linear motion is converted into rotary motion by the crankshaft. The rotation of the crankshaft is the power source of the engine. It is also the source power of the whole ship.
Development of crankshaft manufacturing technology/process
Casting technology of 1 nodular cast iron crankshaft blank
(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.
Liaoning Hongfa crankshaft production line has undergone technical transformation, mainly consisting of three CNC lathes (imported VT36, CAK6 163, CAK6 150) and two CNC internal milling machines (S 1-305B). Seven CNC crankshaft grinders (1 imported CBN grinding wheels 3L 1, 2 H 197B, 4h29b) and fluorescent magnetic particle flaw detectors and other finishing equipment; Eight vertical furnaces are used for stress relief, seven plasma nitriding furnaces are used for nitriding, and CIHM 12 automatic quenching machine tool and pusher tempering furnace produced by EFD company imported from France are used for quenching heat treatment. At the same time, the crankshaft comprehensive measuring instrument imported from the United States can detect the crankshaft in all directions, and the product quality is reliably guaranteed. At the same time, it has the production capacity of simultaneous processing of three production lines.
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 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.
Technological analysis of grinding burn of crankshaft thrust surface
When grinding the thrust surface of hardened steel crankshaft, the following three kinds of burns may occur:
1. Tempering burn
If the temperature in the grinding zone does not exceed the transformation temperature of quenched steel, but exceeds the transformation temperature of martensite, the tempered martensite structure of the metal on the surface of the thrust surface will be transformed into tempered structure (sorbite or bainite) with lower hardness, which is called tempering burn.
Step 2 put out burns
If the temperature in the grinding zone exceeds the phase transition temperature, coupled with the rapid cooling effect of the cooling liquid, the surface metal undergoes secondary quenching, resulting in secondary quenched martensite structure on the surface metal, and its hardness is higher than that of the original tempered martensite. Tempered structure (sorbite or torpedo) with hardness lower than that of original tempered martensite appears in its lower layer due to slow cooling, which is called quenching burn.
3. Annealing burns
If the temperature in the grinding zone exceeds the phase transition temperature, and no cooling liquid enters the grinding zone, the surface metal will produce annealed structure and the surface hardness will drop sharply. This kind of burn is called annealing burn. In crankshaft forming grinding, most of them belong to this kind of burn.
Ways to improve grinding burn
Grinding heat is the root cause of grinding burn, so there are two ways to improve grinding burn: one is to reduce the generation of grinding heat as much as possible; The second is to improve the cooling conditions, so that the generated heat is less transferred to the workpiece.
1. Crankshaft thrust journal with undercut groove
In figure 1, the crankshaft thrust journal has a deep undercut, which has been processed in the previous process, so it is not necessary to grind the undercut, only the thrust journal and two thrust surfaces are needed. In this case, even if the formed grinding wheel is used for grinding, as long as strong cooling, reasonable grinding allowance and good grinding wheel parameters are adopted, grinding burn defects can generally be avoided. When grinding the thrust journal with a narrow grinding wheel, the following schemes can be adopted: adjusting the program and angle grinding of the grinding wheel, so that the grinding wheel enters obliquely from the right side of the journal, grinds to the required size, and then quickly exits obliquely along the original angle direction; The grinding wheel enters obliquely from the left side of the journal, grinds to the required size, and then exits obliquely and quickly along the original angle direction; Make the grinding wheel quickly cut into the middle of the journal and grind to the required size, and then quickly exit. In the above grinding process, strong cooling should be carried out. At this point, the thrust journal and two sides have been ground.
2. Crankshaft thrust journal without undercut
As shown in Figure 2, the crankshaft thrust journal has no undercut, so it is necessary to grind the thrust journal, two thrust surfaces and two formed fillets when grinding. In this case, even with narrow grinding wheel and strong cooling, it is difficult to avoid grinding burn defects. The following two grinding methods are used to describe the solution:
(1) form grinding. In form grinding, the main causes of burns are annealing burns caused by the accumulation of grinding heat and the inability of coolant to enter. Annealing burn reduces the hardness of the crankshaft thrust surface, produces annealed structure on the surface, worsens the wear resistance of the thrust surface and seriously affects the running stability of the engine. According to the main factors that cause burns, this paper starts from three aspects: selecting appropriate grinding wheel, selecting reasonable grinding allowance and improving cooling conditions.
① Select a suitable grinding wheel. The thrust surface of hardened steel crankshaft has high hardness and large area, and sand grains are easy to become dull. In order to avoid a lot of grinding heat generated by the grinding wheel, the hardness of the grinding wheel should be soft, so that the grinding wheel can fall off in time and keep the self-sharpening of the grinding wheel. There are many air holes on the grinding wheel with soft structure, which can contain chips and avoid the blockage of the grinding wheel, and can also bring cooling liquid or air into the grinding area, thus reducing the temperature of the grinding area.
On the premise of ensuring the roughness of crankshaft thrust surface, it is advisable to choose coarse-grained grinding wheel to achieve higher removal rate; In addition, the grinding wheel must be finely balanced, so that the grinding wheel is in a good balance state when working; The grinding wheel must be trimmed in time to keep sharp; There are many factors that affect the dressing frequency of grinding wheel, including the purity and type of materials to be ground and the cleanliness of cooling liquid. The diamond support of dressing grinding wheel must be firm. If there is 0.5 ~ 0.6 mm wear on the diamond surface, it means that the diamond has become dull and should be replaced in time. Strictly control the gap between the grinding wheel transmission system and the grinding wheel spindle; The tension of the grinding wheel drive belt is properly adjusted.
② Choose reasonable grinding allowance and grinding parameters. In production practice, surface burns and cracks of workpieces are often reduced by increasing workpiece speed and reducing radial feed. There is a grinding method with experience of 0. 1mm, that is, in the final machining allowance of 0. 1mm, the feed rate is gradually reduced, which can remove the surface damage layer produced by the first two grinding strokes and reduce grinding burn.
According to the above theory, we adopt multi-process grinding of crankshaft thrust journal in production practice, which is divided into rough grinding, semi-fine grinding and static grinding. After multi-step grinding, the crankshaft thrust journal diameter allowance is 0. 15 ~ 0.25mm, and the thrust surface unilateral allowance is 0.04 ~ 0.07 mm. Forming grinding combined with strong cooling can effectively avoid the occurrence of burn defects. It is worth mentioning that selecting a reasonable grinding allowance can also prevent the flare shape of the thrust surface (to prevent burns, a softer grinding wheel is generally selected, and the abrasive particles fall off in pieces and tend to appear conical surface).
(3) Improve cooling conditions and implement strong cooling. The cooling liquid must be effective and sufficient, and the cooling liquid must be sprayed to the grinding area; Generally, the flow rate is 40 ~ 45L/min to realize full cooling; The general pressure is 0.8 ~ 1.2n/mm2 to wash away the chips stuck on the grinding wheel; Keep the coolant pure and filter it properly to remove debris, abrasive particles and other dirt in the coolant; Coolant containers should be large enough to avoid mixing too much gas or foam; In order to prevent the temperature of the coolant from rising or falling sharply, it is generally enough to control the volume of the cooling system and the room temperature of the workshop. However, the radiator should be used under special storage conditions.
(2) Grinding with a narrow grinding wheel (the width of the grinding wheel is lower than that of the thrust journal). When grinding with narrow grinding wheel, the burn prevention measures adopted in form grinding can be applied to this grinding method, but narrow grinding wheel grinding can have more choices in grinding wheel feeding mode. One is radial cutting and grinding, and improper adjustment will cause the bell mouth shape mentioned above; The other is oblique grinding. Step 1, the grinding wheel enters obliquely from the right side of the journal, grinds to the required size, and then quickly retreats obliquely along the original angle direction; Step 2, the grinding wheel enters obliquely from the left side of the journal, grinds to the required size, and then quickly exits obliquely along the original angular direction; Step 3, make the grinding wheel quickly cut into the middle of the journal and grind it to the required size, and then quickly push it out. Working procedure grinding allowance and cooling mode are the same as those of forming grinding.