In CNC machining, tool life refers to the time that the tool tip cuts the workpiece during the entire process from the beginning of the machining to the tool tip scrapping, or the actual length of the workpiece surface during the cutting process.
1. Can the tool life be improved?
The tool life is only 15-20 minutes, can the tool life be further improved? Obviously, tool life can be easily improved, but only on the premise of sacrificing line speed. The lower the line speed, the more obvious the increase in tool life (but too low line speed will cause vibration during processing, which will reduce tool life).
2. Is there any practical significance to improve tool life?
In the processing cost of the workpiece, the proportion of the tool cost is very small. The line speed decreases, even if the tool life increases, but the workpiece processing time also increases, the number of workpieces processed by the tool will not necessarily increase, but the cost of workpiece processing will increase.
What needs to be understood correctly is that it makes sense to increase the number of workpieces as much as possible while ensuring the tool life as much as possible.
3. Factors affecting tool life
1. Line speed
Linear speed has the greatest impact on tool life. If the linear velocity is higher than 20% of the specified linear velocity in the sample, the tool life will be reduced to 1/2 of the original; if it is increased to 50%, the tool life will be only 1/5 of the original. To increase the service life of the tool, it is necessary to know the material, state of each workpiece to be processed, and the linear speed range of the selected tool. Each company’s cutting tools have different linear speeds. You can do a preliminary search from the relevant samples provided by the company, and then adjust them according to the specific conditions during processing to achieve an ideal effect. The data of the line speed during roughing and finishing are not consistent. Roughing mainly focuses on removing the margin, and the line speed should be low; for finishing, the main purpose is to ensure the dimensional accuracy and roughness, and the line speed should be high.
2. Depth of cut
The effect of cutting depth on tool life is not as great as linear velocity. Each groove type has a relatively large cutting depth range. During rough machining, the depth of cut should be increased as much as possible to ensure the maximum margin removal rate; during finishing, the depth of cut should be as small as possible to ensure the dimensional accuracy and surface quality of the workpiece. But the cutting depth cannot exceed the cutting range of the geometry. If the cutting depth is too large, the tool cannot withstand the cutting force, resulting in tool chipping; if the cutting depth is too small, the tool will only scrape and squeeze the surface of the workpiece, causing serious wear on the flank surface, thereby reducing tool life.
3. Feed
Compared with line speed and depth of cut, feed has the least impact on tool life, but has the greatest impact on the surface quality of the workpiece. During rough machining, increasing the feed can increase the removal rate of the margin; during finishing, reducing the feed can increase the surface roughness of the workpiece. If the roughness allows, the feed can be increased as much as possible to improve the processing efficiency.
4. Vibration
In addition to the three major cutting elements, vibration is the factor that has the greatest impact on tool life. There are many reasons for vibration, including machine tool rigidity, tooling rigidity, workpiece rigidity, cutting parameters, tool geometry, tool tip arc radius, blade relief angle, tool bar overhang elongation, etc., but the main reason is that the system is not rigid enough to resist The cutting force during processing results in the constant vibration of the tool on the surface of the workpiece during processing. To eliminate or reduce vibration must be considered comprehensively. The vibration of the tool on the workpiece surface can be understood as the constant knocking between the tool and the workpiece, instead of normal cutting, which will cause some tiny cracks and chippings on the tip of the tool, and these cracks and chipping will cause the cutting force to increase. Large, the vibration is further aggravated, in turn, the degree of cracks and chipping is further increased, and the tool life is greatly reduced.
5. Blade material
When the workpiece is processed, we mainly consider the material of the workpiece, the heat treatment requirements, and whether the processing is interrupted. For example, the blades for processing steel parts and those for processing cast iron, and the blades with processing hardness of HB215 and HRC62 are not necessarily the same; the blades for intermittent processing and continuous processing are not the same. Steel blades are used to process steel parts, casting blades are used to process castings, CBN blades are used to process hardened steel, and so on. For the same workpiece material, if it is continuous processing, a higher hardness blade should be used, which can increase the cutting speed of the workpiece, reduce the wear of the tool tip, and reduce the processing time; if it is intermittent processing, use a blade with better toughness. It can effectively reduce abnormal wear such as chipping and increase the service life of the tool.
6. Number of times the blade is used
A large amount of heat is generated during the use of the tool, which greatly increases the temperature of the blade. When it is not processed or cooled by cooling water, the temperature of the blade is reduced. Therefore, the blade is always in a higher temperature range, so that The blade keeps expanding and contracting with heat, causing small cracks in the blade. When the blade is processed with the first edge, the tool life is normal; but as the use of the blade increases, the crack will extend to other blades, resulting in a reduction in the life of other blades.
Post time: Mar-10-2021