As an important measure of the surface quality of gray cast iron, surface roughness not only directly determines the exquisite appearance of gray cast iron parts, but also has a great influence on the quality of machine equipment and the service life of gray cast iron parts. This article focuses on how to improve the surface roughness of gray cast iron parts from the three aspects of machine tools, cutting tools, and cutting parameters. The information is provided by Halnn Superhard and shared with you for discussion.
1. Effect of machine tool on surface roughness of gray cast iron parts
The poor rigidity of the machine tool, the poor precision of the spindle, the loose fixation of the machine tool, and the large fit clearance of the various parts of the machine tool will all affect the surface roughness of the gray cast iron parts.
For example: if the runout accuracy of the machine tool spindle is 0.002mm, which is 2 microns, it is theoretically impossible to process workpieces with a roughness lower than 0.002mm. Generally, workpieces with a surface roughness of Ra1.0 are acceptable. processed out. Moreover, gray cast iron itself is a casting, so it is not easy to process a high surface roughness like steel. In addition, the condition of the machine tool itself is poor, and it is even more difficult to ensure the surface roughness.
The rigidity of the machine tool is generally set at the factory and cannot be modified. In addition to the rigidity of the machine tool, the clearance of the spindle can be adjusted to improve the precision of the bearing, etc., so that the clearance of the machine tool can be reduced, so that the gray cast iron parts can be processed with higher surface roughness. degree is guaranteed.
2. Effect of cutting tool on surface roughness of gray cast iron parts
Tool material, improper selection of geometric parameters, tool wear and other factors will affect the surface roughness.
(1) Selection of tool material
When the affinity between the tool material and the metal molecules of the processed material is high, the processed material is easy to bond with the tool to form built-up edge and scales. Therefore, if the adhesion is severe and the friction is serious, the surface roughness will be large, and vice versa. . In the same processing of gray cast iron parts, it is difficult for cemented carbide inserts to reach the surface roughness of Ra1.6. Stability and wear resistance, under the condition that the cutting speed is several times higher than that of cemented carbide, the surface roughness of Ra1.6 can be easily processed. At the same time, the tool life is dozens of times that of cemented carbide tools, and the surface brightness is increased by one Magnitude.
(2) Selection of tool geometric parameters
Among the tool geometric parameters that have a greater impact on the surface roughness are the main declination angle Kr, the secondary declination angle Kr' and the tool nose arc radius re. When the main and minor deflection angles are small, the height of the residual area of the processed surface is also small, so the surface roughness can be reduced; the smaller the minor deflection angle, the lower the surface roughness, but reducing the minor deflection angle will easily cause vibration, so reduce The secondary deflection angle should be determined according to the rigidity of the machine tool. The influence of the tool nose arc radius re on the surface roughness: when the stiffness is allowed, the surface roughness will decrease when the re increases, and increasing re is a good way to reduce the surface roughness. Therefore, reducing the main declination angle Kr, the secondary declination angle Kr', and increasing the radius r of the tool nose can reduce the height of the residual area, thereby reducing the surface roughness.
The engineer of the Halnn superhard cutting tool said, "The selection of arc angle of the tooltip is recommended to be selected according to the rigidity and roughness requirements of the workpiece to be processed. If the rigidity is good, try to choose a large arc angle, which can not only improve the processing efficiency but also improve the surface finish of machining; but when boring or cutting slender shafts or thin-walled parts, because of the poor rigidity of the system, a smaller radius of the tool nose arc is often selected.”
(3) Tool wear
Tool wear is divided into three stages: initial wear, normal wear, and severe wear. When the tool enters the stage of severe wear, the flank wear rate of the tool rises sharply, the system tends to be unstable, the vibration increases accordingly, and the variation range of the surface roughness also rises sharply.
In the field of gray cast iron, many parts are mass-produced, which requires high product quality consistency and production efficiency. Therefore, many machining companies choose to change the tool without waiting for the tool to reach the third stage of severe wear, which is also called mandatory. When changing the tool, the machining company will test the tool repeatedly to determine a critical point, which will not affect the overall production efficiency while ensuring the surface roughness and dimensional accuracy of the gray cast iron.
3. Effect of cutting parameters on surface roughness of gray cast iron parts
The different selection of cutting parameters has a great influence on the surface roughness, which should be paid enough attention to. Finishing is an important process to ensure the surface roughness of gray cast iron parts. Therefore, during finishing, the cutting parameters should mainly ensure the surface roughness of gray cast iron parts, and take into account productivity and necessary tool life. The cutting depth of finish machining is determined by the margin-left after rough machining according to the requirements of machining accuracy and surface roughness. Generally, the depth of cutting is controlled within 0.5mm. At the same time, under the condition that the rigidity of the machine tool permits, the cutting performance of the tool can be fully utilized, and a high cutting speed can be used for high-speed machining of gray cast iron parts.
4. The influence of other factors on the surface roughness of gray cast iron parts
For example, there are some casting defects in gray cast iron parts, unreasonable choice of cutting fluid, and different processing methods will affect the roughness of gray cast iron parts.
Halnn superhard tool engineer said, "In addition to the three major factors of machine tool, cutting tool and cutting parameters, factors such as cutting fluid, gray cast iron parts themselves, and processing methods also have a certain impact on the surface roughness of gray cast iron parts, such as When turning, milling, and boring gray cast iron parts, under the condition that the machine tool, cutting parameters and other factors are allowed, Halnn superhard CBN tools can also process the surface roughness of Ra0.8, but it will affect the tool life, the specific needs to be judged according to the actual processing situation."
5. Summary
In view of the fact that surface roughness has a relatively direct impact on the performance of machine parts, and the factors that affect the surface roughness in actual production come from many aspects, therefore, all factors should be taken into account, and the surface roughness should be made more economical and applicable according to the needs.