Efficient processing of coarse cylinder bores in aluminum engines, fine boring
The cast iron cylinder liner is precast on the blank. The processing of the thick, thin and partial bores of the cylinder bores are concentrated in the same process, which is the bottleneck of the processing of the all-aluminum engine cylinder block production line. For this reason, the use of new cutting theory to reasonably optimize the cutting tool can not only reduce production costs, but also achieve low power consumption and efficient processing.
The engine is made of all aluminum, which has the advantages of light weight, good heat dissipation, and low energy consumption. This process uses many new processes, such as casting the main oil passage and cutting the connecting rod. The production line adopts a flexible design concept, and the processing equipment is mainly a processing center.
The 1.8T oil cylinder production line is a fully flexible production line, and all processing equipment except the honing machine is a processing center. The engine block is entirely made of aluminum, and the cast iron cylinder liner is precast into a blank. Since aluminum alloy is an easy-to-process material with high processing efficiency, while cast iron is a general-purpose material with general processing characteristics, the workability of the two materials is very different. Therefore, the rough machining of the cylinder bore becomes the bottleneck of the cylinder production line, which limits the production capacity of the cylinder production line.
Detailed analysis of the specific conditions of the rough machining of the cylinder bore to obtain a better machining plan and improve the efficiency of the rough machining of the cylinder bore.
The actual machining of the thick cylinder bore is as follows. The processing uses a 3-blade file (see Figure 4), the lead angle is 75°, the rake angle is 0°, and the blade is made of CBN material.
Specific cutting parameters: cutting speed=400m/min, tooth feed=0.18mm, cutting depth=2.5mm, processing time 42.5s.
Several different processing methods are designed for trial cutting. After analyzing the test results, there may be two main reasons that limit the efficiency of cylinder bore processing.
1. Stuffy vibration
The cutting vibration generated when the cylinder bore is rough increases with the increase of the cutting speed, which limits the increase of the cutting speed. In addition, cutting vibration can easily damage the blades and frequently change tools, resulting in slower start-up speed of the equipment.
2. The spindle load is too high
The 1.8T series engine is an all-aluminum engine, and the machining is mainly made of aluminum. In order to save energy and reduce installed capacity, the production line does not use high-power processing centers. Therefore, the machine tool runs at full load when machining cast iron cylinder bores. Due to the limitation of machine power, increasing the feed rate or increasing the number of cutting blades cannot improve the material removal rate.
Reduce cutting force, eliminate cutting vibration, and improve processing efficiency. We worked with a tool manufacturer to design a new type of boring tool for rough machining of cylindrical holes (see Figure 5). Compared with the traditional boring tool, the new boring tool has the following advantages:
1. Positive cutting
It is generally believed that the cutting tool for processing brittle materials such as cast iron should adopt a negative rake angle to increase the strength of the tool and prevent the tool from chipping and damage. However, among the various geometric parameters of the tool, the rake angle has the greatest influence on the cutting resistance. Under the same other conditions, the larger the rake angle of the tool, the smaller the cutting force.
With the improvement of machine tool stability and the emergence of various new tool materials, large rake angle tools can now handle brittle materials, so the new file adopts a positive 10° rake angle. Compared with traditional boring tools with a 0° rake angle or a negative rake angle, a positive rake angle produces less cutting force. It can effectively reduce the cutting force without reducing the cutting parameters. This not only makes the cutting lighter, but also effectively reduces the generation of cutting vibration.
2. 90° lead angle
The radial cutting component is the main source of cutting vibration. The larger the radial component, the easier it is to cause cutting vibration. The new boring tool adopts a 90° lead angle, which will not produce a radial cutting component on the main cutting edge. Compared with a tool with a smaller lead angle, the radial cutting component is significantly reduced, and the cutting process is more stable.
Blade Clip Method
When using cemented carbide inserts such as CBN or cermet, the normal clamping method cannot make a positive rake angle on the insert, and making a positive rake angle on the tool will increase the difficulty of installing and adjusting the insert.
Compared with traditional clamping inserts, vertical inserts can easily manufacture inserts with large rake angles, and the inserts can withstand higher cutting resistance and improve tool reliability. The rake face of the vertical insert is not in contact with other parts or tool parts, but the chip flute design is limited and easy to optimize. In most cases, the vertical insert has better chip breaking effect, more reasonable chip removal space, smoother chip removal and easier to obtain a stable processing process than the conventional clamping type insert. Therefore, the blades of the new boring cutter are installed in a vertical clamping manner.
The material and structure of the blade
Ceramic tool is a new material tool in modern metal cutting. It has the characteristics of high hardness, high strength, high red hardness, high wear resistance, excellent chemical stability, and low friction coefficient. In recent years, the use of various additives and the application of fine particles have significantly improved the fracture toughness and impact resistance of ceramic blades. Ceramic models that can be rough processed under impact load are now on the market. Ceramic inserts can also be used for rough machining, because the drilling process is continuous cutting, and there is no impact during the cutting process. Compared with CBN tools, ceramic tools have a lower coefficient of friction and lower cutting resistance under the same conditions. Therefore, the new boring tool does not use CBN inserts, but chooses ceramic inserts that promote stable cutting.
Give the ceramic blade sufficient strength. After some comparative tests, it was found that the blade adopts a W-shaped blade with a blade angle of 80°, with a nose radius of 0.8mm, and the blade and the tip have dulled the bottom. The passivation blade not only eliminates the microscopic defects of the cutting edge, effectively prolongs the tool life, but also increases the strength of the cutting edge and improves the stability of the cutting process.
According to the characteristics of the new type of boring tool, various machining parameters are used for comparative experiments, and the final machining parameters are determined as follows. Cutting speed=500m/min, feed per tooth=0.12mm; the cutting depth is uncontrollable and unadjustable. When the new boring cutter increases the number of cutting edges and cutting speed, the processing time is shortened to 30.5 seconds, and the processing efficiency is increased by 39%. The anti-vibration measures adopted in all aspects of the new tool improve the stability of the processing process, basically eliminate abnormal damage to the blade, reduce the number of tool changes, and speed up the equipment start-up speed. Based on the above two factors, the production efficiency of the coarse-bore OP20 process has increased by about 6%.
By analyzing the effectiveness of the new boring tool, the superior performance of the new tool material has been fully utilized. Using the new cutting theory to properly optimize the tool can not only reduce production costs, but also achieve low power consumption and efficient processing.
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