We mentioned before How to increase the service life of CNC inserts correctly. In this article, we will interpret the factors that affect the life of CNC cutting tools.
In addition to insert quality and workpiece material, linear speed, cutting depth, and feed rate are the fundamental factors affecting the insert life. But vibration and insert service life are also important reasons that can not be ignored. Let me explain these factors to you.
- Linear speed. The linear speed has the greatest influence on the tool life. If the linear speed is higher than 20% of the specified linear speed of the sample, the tool life will be reduced to 1 / 2 of the original value; if it is increased to 50%, the tool life will be only 1 / 5 of the original one. In order to improve the service life of the tool, it is necessary to know the material and state of each workpiece to be processed and the linear speed range of the selected tool. The linear speed of each company’s cutting tools is different. We can find out 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 linear speed in rough machining and finish machining are not consistent, rough machining is mainly to remove allowance, linear speed is low; finishing is to ensure dimensional accuracy and roughness, linear speed should be high.
- Cutting depth. The influence of cutting depth on tool life is less than that of linear velocity. Each groove has a relatively large range of cutting depth. In rough machining, the cutting depth should be increased as much as possible to ensure the maximum residual removal rate; while in the finishing process, the cutting depth should be as small as possible to ensure the dimensional accuracy and surface quality of the workpiece. But the cutting depth should not exceed the cutting range of groove. If the cutting depth is too large, the tool can not bear the cutting force, leading to tool edge collapse; if the cutting depth is too small, the tool only scrapes and extrudes on the surface of the workpiece, resulting in serious wear of the flank, thus reducing the tool life.
- Feed. Compared with the linear speed and cutting depth, the feed has the least effect on the tool life, but has the greatest impact on the surface quality of the workpiece. In rough machining, the removal rate of allowance can be improved by increasing feed rate; while in finish machining, the surface roughness of workpiece can be improved by reducing feed. If the roughness is allowed, the feed can be increased as much as possible to improve the machining efficiency.
- Vibration. There are many reasons for vibration, including machine tool rigidity, tooling rigidity, workpiece rigidity, cutting parameters, tool geometry, tool-point arc-shaped blade, blade relief angle, tool bar overhang elongation, etc., but it is mainly due to insufficient system rigidity. Can not resist the cutting force during processing, resulting in constant vibration of the tool on the surface of the workpiece during processing. To eliminate or vibration vibration must be considered comprehensively. The surface vibration of the workpiece can be understood as the constant knocking between the tool and the workpiece, rather than normal cutting, causing some tiny cracks and chippings on the tip of the tool, and these cracks and chipping lead to an increase in cutting force. The vibration is further aggravated, which in turn further increases the degree of cracks and chipping, which greatly reduces the tool life.
- Material of inserts. When processing the workpiece, we mainly consider the material, heat treatment requirements and intermittent processing. For example, the inserts for machining steel parts are not necessarily the same as those for processing cast iron, and the inserts with processing hardness of hb215 and HRC62; the inserts for intermittent machining and continuous processing are not the same. Steel insert is used to process steel parts, casting insert is used to process casting, CBN insert is used to process hardened steel, etc. For the same workpiece material, if it is continuous processing, a insert with higher hardness should be used, which can improve the cutting speed of the workpiece, reduce the wear of the tool tip and reduce the processing time; if it is intermittent processing, a insert with better toughness should be used, which can effectively reduce the abnormal wear such as chipping and improve the service life of the tool.
- Usage times of insert. A large amount of heat will be generated in the process of using the cutter, which will greatly increase the temperature of the insert. However, when it is not processed or cooled by cooling water, the temperature of the insert will decrease. Therefore, the insert is always in a high temperature range, which makes the insert constantly expand and contract, resulting in small cracks in the insert. When the insert is machined with the first edge, the tool life is normal; however, with the increase of insert use, cracks will extend to other inserts, resulting in the life of other inserts reduced.
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