When it comes to fixtures, it is believed that auto parts fixtures are a topic that will never fade. The solution of various special-shaped workpieces and clamping problems is a bitter tear for fixture enterprises. Now, with the acceleration of the overall production cycle of manufacturing industry, the improvement of fixture structure is one thing for fixture enterprises, and the process transformation of clamping parts is also a very important part. Today, let’s take a look at the process optimization of “popular contestant” cylinder head of auto parts!
1、 Cylinder head overview
Cylinder head is one of the key components of automobile engine, which is located on the upper part of engine. It is firmly combined with cylinder block by means of bolt, cylinder pad. The cylinder head is used to close the cylinder and build the combustion chamber of the engine. At the same time, it is used as the assembly matrix of the valve train and related parts of the engine. The processing technology of the cylinder head is very complex, and its main characteristics are as follows: first, the cylinder head of automobile engine is usually hexahedron, which is a porous thin-walled part, and the thinnest part of the hole wall is only 3.5 μ The number of holes can reach 100. Second, the strength and rigidity of the cylinder head are required to be high. Only when it meets the standard can the gas run stably under the combined action of thermal stress and pressure. The above processes have high machining accuracy requirements, and the machining quality directly affects the performance of the engine.
Fig. 1 hexahedral porous thin wall part
2、 Detailed description and optimization of processing technology
2.1: manufacturing materials
In the field of engine production, we usually use gray cast iron, aluminum alloy and vermicular graphite cast iron as cylinder head materials. At present, vermicular graphite cast iron or gray cast iron is commonly used in diesel engines, while aluminum alloy is widely used in gasoline engines. A small number of small diesel engines in the market also use aluminum alloy materials. Aluminum alloy has good thermal conductivity, which is helpful to improve the compression ratio and the engine efficiency. Driven by the concept of energy saving and environmental protection, people’s requirements for energy saving and emission reduction of automobile engine are constantly improving, which drives the continuous optimization of automobile engine materials including cylinder head. In the past, the cracks between the valves of the four valve cylinder head of diesel engine occurred from time to time. Later, with the application and popularization of vermicular graphite cast iron, this problem has been well solved.
In the field of cylinder head processing, due to the different characteristics of gray cast iron, aluminum alloy and vermicular graphite cast iron, the processing efficiency is also different. In terms of processing efficiency, vermicular graphite cast iron has the lowest efficiency, while aluminum alloy has the highest efficiency.
2.2: production line and process
In the field of automobile engine cylinder head processing, there are three kinds of production line layout of vermicular cast iron or gray cast iron cylinder head commonly used in diesel engine
① It is a special equipment production line. It has the advantages of high processing efficiency and low tool cost, and is usually used for mass production of shaped cylinder head; The disadvantage is that once the product design needs to be changed, the transformation cost is very high.
② Machining center + special equipment production line is usually used for products with continuous small adjustment and change, and its transformation cost can be well controlled.
③ The flexible production line composed of machining centers is usually used to produce unshaped engine products or products with low output. Its disadvantage is that the operating cost of cutting tools is high. In today’s aluminum alloy cylinder head processing technology, the production line is usually a flexible manufacturing system composed of machining center. The main shaft of the equipment mostly adopts motorized spindle, and the speed of the main shaft is usually set at more than 7 000 R / mm. For flexible machining line, vertical machining center can be used for top and bottom surface machining, while horizontal machining center can be used for four side surface machining. Based on the cost analysis of flexible machining line, vertical machining is more cost-effective, so it is more popular with users. In the cylinder head processing, strengthening the configuration of vertical machining center can undoubtedly obtain better cost advantage.
For the general layout of the production line, the centralized process unit usually adopts “U” type wiring. At the same time, many factors such as logistics, investment and output comprehensive cost, ergonomics optimization and so on must be fully considered in the process scheme design.
Figure 2 engine cylinder head production line
3、 Difficulties and optimization of processing technology of aluminum alloy cylinder head
3.1: plane processing
From the internal structure of cylinder head, there are many large planes, and the inlet and exhaust surfaces, item surfaces and bottom surfaces are large planes. This requires that the flatness and surface roughness and other accuracy be kept high level, and then the machine tool shall have the ability to achieve high-precision machining, and achieve high tool adjustment accuracy and geometric accuracy. Before, the large plane of cylinder head was mainly processed by alloy blade. Now, because of the rough condition, diamond blade is usually used for processing. This process can optimize the cylinder head plane and improve the precision of the machining surface.
3.2: high precision hole processing
The cylinder head has high precision holes such as valve guide hole, camshaft hole and tappet hole, which are closely matched with each other. Therefore, the surface roughness, position and dimension precision of the cylinder head shall be strictly controlled during processing. When machining, the cylinder head valve guide and valve seat are fed at the same time. It is necessary to make it in place once to reduce the error and keep the coaxiality between the valve guide and the valve seat. Valve seat and cone with sealing fit requirements have strict requirements for roundness and runout; Some valve guide holes have the requirements of fit between moving parts, so the dimensional accuracy requirements are very high, and because of the different materials of the two, in the process of processing, we should pay attention to the selection of tool materials.
3.3: processing of bottom hole of valve guide
The size accuracy of the bottom hole of valve guide is very high. Therefore, the accuracy requirements should be considered during processing to avoid errors. Precision control should be paid attention to. Once the control is unstable, the coordination degree between valve guide and cylinder head will be affected, and the reliability of engine will be affected.
3.4: camshaft hole processing
As the longest hole in the cylinder head, if the camshaft hole is processed by turning head (or segmented processing), it can reduce the requirements of machine tools and equipment, and can basically guarantee the machining accuracy, but it can not meet the machining requirements of camshaft hole for coaxiality. Therefore, the molding should be guaranteed as much as possible during processing.
3.5: optimization of burr processing of cylinder head
As we all know, the aluminum alloy material used in cylinder head is plastic material, and burr is inevitable in the process. The key to solve the burr problem is: first, the proper parameters should be selected in the process, and the other is to improve the hardness of the workpiece materials. In the process of processing, high pressure water or nylon brush is usually used to remove and weaken burr. These operations are dangerous and need to ensure personal safety.
Figure 3 aluminum alloy and vermicular graphite cast iron cylinder block
4、 Key points of optimization of cylinder head machining process
Cylinder head machining is a system engineering. Through detailed experimental research, we summarize the following optimization points
First of all, in the overall design of the process, we should also consider the design of the inspection program after the processing, and carry out the corresponding inspection after completing a processing, so as to effectively control the process quality. Secondly, the internal structure of cylinder head is very complex, and the unstable distribution of internal stress may lead to deformation, which will affect the machining accuracy. Therefore, when we process the cylinder head, we usually follow the principle of “face before hole”, and release the stress by dispersing the fine machining and rough machining. Thirdly, the scratch on the joint surface of the cylinder head may damage the quality of the cylinder head and affect the efficiency of the engine. Therefore, in order to avoid this problem, we usually finish the joint surface to avoid subsequent damage. Fourth, with the development of automatic production, the degree of automation of some processing production lines is constantly improving. For these automatic production lines, it is necessary to attach fixture air jet and tool break detection to avoid loss.
Cylinder head is the key component of automobile engine assembly, and its process quality is related to the overall efficiency of automobile engine. The structure of cylinder head is complex, and the processing technology standard is high. Therefore, it is the consistent goal of the industry to continuously pursue the best processing technology. This paper introduces the processing and technology of cylinder head, analyzes the manufacturing materials and production line of cylinder head, deeply discusses the current mainstream processing characteristics of aluminum alloy cylinder head, and combs and analyzes the process difficulties from the plane processing, high-precision hole processing, valve guide bottom hole processing, camshaft hole processing, cylinder head burr optimization and other aspects, Finally, the key points of optimization of cylinder head machining process are summarized. In order to meet the development requirements of the automotive industry in the future, we should continue to strengthen the research on the optimization of the process quality of the cylinder head, especially the aluminum alloy cylinder head.