In turning processing, especially for finishing, how to choose a tool?
Determine the entering angle of the tool
Among the entering angles of conventional tools, the ones suitable for finishing are generally between 90° and 95°, especially 91°, 93°, and 95° which are most used. The entering angle of close to 90° makes the cutting force follow the axis of the workpiece, and no vertical force is applied to the workpiece to avoid vibration and deformation (thin-walled parts processing is especially important). The entering angle is generally guaranteed on the tool bar.
Determine the angle of the tool tip and select the tool shape
Generally, our commonly used blade forms mainly include:
Round blade (beginning with R), 90 degree square blade (beginning with S), 80 diamond blade (beginning with C), 80 degree convex triangular blade (beginning with W), 60 degree triangular blade (beginning with T), 55 degree diamond blade (beginning with D) ), 35 degree diamond blade (beginning with V).
These tool shapes basically cover more than 90% of conventional turning inserts. These types of inserts are arranged in terms of tool strength: R, S, C (W), D, V. R blade has the highest strength and V the lowest. But the higher the strength, the greater the resistance and the greater the risk of vibration. Therefore, we often choose R, S, C (W) for roughing. For finishing, we will choose D and V. The profiling ability required for finishing is also the best for V and the worst for R.
Determine the rake angle and back angle of the tool
The negative rake angle tool has good rigidity and is not easy to chip, which is suitable for rough machining, while the positive rake angle blade cuts lightly and is more suitable for finishing. There is a matching relationship between the rear angle and the rake angle. Generally, the negative rake angle blade is basically a 0 degree rear angle. And the positive rake angle insert has 5°(B), 7°(C), 11°(P) three commonly used clearance angle combinations (referring to turning only).
CC/CP (C type positive rake angle blade 7°/11° clearance angle), DC (D type positive rake angle blade 7° clearance angle), VC/VB (V type positive rake angle blade 7°/5° clearance angle ), WB/WC (W-type positive rake angle insert 5°/7° clearance angle), these combinations are also the insert shapes used in conventional finishing (the front and rear corners are determined)
Combining the three, the tool form for conventional finishing is as follows:
95° entering angle arbor + CC blade
93° entering angle arbor + WB/WC/DC/VC/VB blade
91° entering angle arbor + DC/VC/VB blade
Among them, the 93° entering angle toolholder +DC is the best finishing plan recommended by individuals (referring to the turning radial direction only). This plan is equipped with suitable cutting parameters and the processing effect should be one of the best in turning at present. I have tried 1.6 roughness of several different materials, and 0.8 roughness of another steel part is because of the inner hole and the diameter of the shank is limited, so I can only use 95° entering angle shank + CC blade.
Of course, the above options are not the only ones. Under the working conditions of medium and large diameter solid materials that can reach high linear speed, the blade with 0° clearance angle (ISO code N) can also produce better roughness, but the roughness at this time is more dependent on thick oxidation. Aluminum CVD coated blades are "ground" at high linear speeds. This roughness is basically about one grade different from the roughness processed by the tool selected above. In other words, the CN blade can be turned to 1.6, and the DC blade can be turned to 0.8.
Commonly used blades in inner hole precision turning are TC/TP (T-type positive rake angle blade 7°/11° clearance angle), the corresponding toolholder combination 91° entering angle toolholder + TC/TP blade, inner hole diameter For fine turning over 16, DC blades can basically be used, but there are two types of DC, 07 and 11. The 07 blade can process 16-20 inner holes, and the DC11 blade can be used for 25 and above. For precision turning with an inner hole of about 10-16, either CC blades or TC/TP blades can be used. For those with an inner hole less than 10, generally only CC blades are more suitable. Japanese CC blades can achieve 5.5-6mm.