Manufacturing technology of the hottest assembled

2022-08-24
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Manufacturing process of assembled camshaft

at present, most engine manufacturing enterprises use integral camshaft, some of which are made of medium carbon low alloy forged steel (after high-frequency quenching), and some are made of nodular cast iron. The machining process of integral camshaft includes rough machining, semi finishing machining and finishing machining. The automatic line multi station machine tool is used in production, which has large equipment investment, large area of production line and high production cost. The assembled camshaft only needs semi finishing and finishing, and the cam, gear and shaft sleeve can be made of different materials, so the product quality can be reduced by 30% - 50%; Flexible production, small equipment investment, small floor area of production line and low production cost

1 process flow of assembled camshaft

the process flow of assembled camshaft is straightening → machining center holes, threaded holes and drive holes on two end faces (processed by two machining centers in parallel) → axle journal, gear blank Front dead end face and guide hub → grinding journal and guide hub → gear hobbing → press pin → grinding cam (3 grinding machines are processed in parallel) → cam quenching → deburring → straightening Journal → camshaft journal and cam polishing → cleaning → comprehensive inspection

the cam, shaft sleeve, eccentric ring, gear and other parts in the assembled camshaft are successively connected to form a complete camshaft. The assembly process is to manually assemble all camshafts. The components include cam, main journal and gear blank, which are put into the installation loading box. The steel pipe is threaded into the holes of each component, and the initial positioning is carried out in the installation loading box. After starting the equipment, the feeding box enters the equipment. First, use the tooling probe to detect the parts in place and verify whether the cam is placed correctly. After the verification is passed, use the manipulator to load the camshaft to the camshaft ball pressing station, and then start the positioning block of each component to accurately position the cam, journal and gear. After it is in place, clamp all parts at the same time, and extend the ejector rod to pass the steel ball with a diameter greater than the inner diameter of the pipe through the inner diameter of the whole steel pipe. The camshaft components outside the steel pipe are elastically deformed with the steel pipe under the expansion and extension force of the steel pipe, and finally form an assembled camshaft. This camshaft assembly process is called in pipe rolling expansion method

2 camshaft assembly process method

2.1 hot sleeve method

at room temperature, there is interference between the hole of the external part and the outer diameter of the internal steel pipe. Before assembly, heat the external part (CAM, shaft sleeve) and cool the internal steel pipe to eliminate the interference. This process method completes the connection process in a short time, and has high accuracy in the dynamic display of the axial ruler: the inch and angle position in the experimental process

2.2 internal hydroforming (Ihu)

the hardened cam ring and the steel pipe are deformed to form an axial connection by using the internal high pressure. The axial positioning of the cam is achieved by pressing the steel pipe material out by about 1/10 mm next to the cam. The fabricated camshaft made by Ihu process has been successfully used in the v6tdi car diesel engine that Audi put into mass production in 2003. Ihu assembled camshaft is composed of isothermal quenched cam and steel pipe plug installed on precision steel pipe with wall thickness of 2.5 mm or 3.0 mm

the cam with equal wall thickness on the whole circumference is placed in a special equipment, which can ensure the axial alignment with the cam centerline and the cam angle position. The steel pipe is pushed through the cam so positioned, and a vacuum grabber puts the pre positioned parts on the hydraulic press with Ihu tool. The shape of the die cavity of Ihu tool is exactly consistent with the contour of the finished blank shaft. After the liquid medium is injected into the pipe, both ends of the steel pipe are sealed with axial plugs. By increasing the pressure in the pipe, the whole steel pipe is plastically deformed until it fits on the Ihu tool. At this time, the connection between the steel pipe and the cam produces force connection and shape connection

2.3 rolling expansion method in pipe

using the sliding rolling principle, the thin-walled steel pipe locally expands in the external parts with holes. A rolling tool with rolling interference can be used to pass through the inner tube to make the inner tube plastic expand. The assembled camshaft of the engine of Shanghai General Motors Co., Ltd. uses the steel ball to expand inside the steel pipe

2.4 positioning method of cam pressure suit

this process rolls on the outside of the steel pipe for the first time, but different models process grooves in the circumferential direction. Axial grooves are processed in the holes of the cam, and then the processed cam is sleeved on the steel pipe and pushed in from the axial direction. Because there is interference between the outer diameter of the steel pipe and the cam hole, plastic deformation will occur when the cam is pushed onto the steel pipe, and there are some tapers on the surface of the steel pipe and the cam hole, It is very firm after being pushed in. ThyssenKrupp adopts this method in the assembly process of assembled camshaft in Dalian

3 manufacturing process characteristics of assembled camshaft

a. rough machining of blank parts is omitted, and the process flow is simple. The machining allowance of each part of the assembled camshaft is small and the precision is high. Unlike the integral camshaft, it can reach the required shape only after a large number of rough machining and complex processes are carried out from the blank parts (castings or forgings). The assembled camshaft only needs semi finishing and finishing after assembly, which shortens the whole process

b. small machining allowance, convenient for high-efficiency production. Each cam adopts precision casting parts, so the machining allowance is small. The equipment has short processing time and high production capacity, which is conducive to large-scale production. For example, the cam is precision cast according to the final shape, which reduces the grinding allowance and shortens the grinding time

c. different materials can be used for different parts to improve product performance and processing performance. The engine has different performance requirements for different parts (shaft sleeve, cam, gear), and the assembled camshaft can adopt different materials on different parts. For example, the cam adopts powder metallurgy or cast steel, and the camshaft adopts cold drawn steel pipe. This is not only conducive to optimizing product performance, but also conducive to improving camshaft processing performance and optimizing cost

d. meet the requirements of flexible tracking of gauge line for multiple products. Many kinds of camshafts can be produced by changing different journals and grinding different cam profiles. The basic parameters of this series of products are consistent, including journal, cam base circle radius, steel pipe diameter, shaft direction, length spacing, etc. the production line only needs to change the journal mold in the installation box and switch the grinder program

4 fabricated camshaft processing shock resistance test on explosion-proof equipment is one of the main type tests specified in GB 3836.1 (2) 010. Process development direction

A. flexible production line layout. The production line layout adopts unit automation module. There are gantry manipulator loading and unloading in the unit, and a position is reserved in the bottleneck unit for expansion. Unit transportation can be automated or manual, which is conducive to the improvement of the starting rate of the production line

b. flexible products. The material and structure of camshaft can be changed flexibly according to the product design needs to meet the market requirements more, and provide a variety of products through the change of journal and cam profile

c. use of high-speed grinding and high-speed grinding CBN (boron nitride) tools. It can greatly improve the grinding efficiency and reduce the number of equipment used. The grinding force is small, the machining accuracy of parts is high, and the surface roughness of workpiece is reduced. The service life of grinding wheel is extended and the production cost is reduced

d. multi wheel grinding and the use of two wheel heads. Using multi wheel grinding while increasing the wheel speed is another method to reduce the processing beat, such as grinding the outer diameter of the journal while grinding the cam with multiple wheels, and synchronously machining the cam with two wheel heads on one grinder

e. use of measuring instrument. In order to ensure dimensional stability, the key equipment of assembled camshaft processing increasingly uses the function of detection and automatic compensation

f. use of materials such as powder metallurgy

g. process in a centralized manner. This method is to concentrate the process contents of turning, milling, drilling and grinding respectively, and adopt the manufacturing unit composed of flexible equipment for centralized processing. In this way, the number of workpiece clamping and the auxiliary time of loading and unloading transportation will be minimized, which is conducive to reducing errors and improving production efficiency

h. the equipment unit can adopt double spindles or double machine tools to reduce the processing beat. For example, a grinding unit can combine two grinding machines, share a set of control system, and transport the workpiece through the built-in gantry loading and unloading device. Compared with using two independent machine tools, it not only saves equipment costs, but also greatly reduces the floor area, and each grinder can use multiple spindles to complete the grinder combination. Lathes and machining centers can also adopt the method of double spindle to improve efficiency. ThyssenKrupp Group has established an assembly Camshaft Factory in Dalian to provide assembly camshafts for engine manufacturing enterprises

with the assembly camshaft, the engine performance is improved, the fuel economy is significantly improved, the emission is reduced, the vibration is reduced, and the manufacturing cost is also reduced. At present, the assembled camshaft has been more and more welcomed by engine manufacturing enterprises. (end)

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