How to correctly select these three elements is a major content of the metal cutting principle course. Metal processing WeChat has excerpted some key points and the basic principles for selecting these three elements:
(I) Cutting speed (linear speed, circumferential speed) V (m/min)
To select the number of revolutions per minute of the spindle, you must first know how much the cutting linear speed V should be. The choice of V: depends on the tool material, workpiece material, processing conditions, etc.
Tool material:
For cemented carbide, V can be higher, generally more than 100 m/min, and technical parameters are generally provided when purchasing blades:
What material can be processed and how much linear speed can be selected. High-speed steel: V can only be lower, generally not more than 70 m/min, and in most cases less than 20~30 m/min.
Workpiece material:
High hardness, low V; cast iron, low V, when the tool material is carbide, it can be 70~80 m/min; low carbon steel, V can be more than 100 m/min, non-ferrous metal, V can be higher (100~200 m/min). Hardened steel, stainless steel, V should be lower.
Processing conditions:
Roughing, low V; finishing, high V. Poor rigidity system of machine tools, workpieces, and tools, low V. If the S used in the CNC program is the spindle revolutions per minute, then S should be calculated based on the workpiece diameter and cutting line speed V: S (spindle revolutions per minute) = V (cutting line speed) * 1000 / (3.1416 * workpiece diameter) If the CNC program uses a constant line speed, then S can directly use the cutting line speed V (m/min)
(II) Feed (cutting amount)
F mainly depends on the surface roughness requirements of the workpiece. During fine machining, the surface requirements are high, and the feed rate is small: 0.06~0.12mm/spindle revolution. During rough machining, it can be larger. It is mainly determined by the tool strength, generally it can be more than 0.3. When the tool main clearance angle is large, the tool strength is poor, and the feed rate cannot be too large. In addition, the power of the machine tool and the rigidity of the workpiece and the tool should also be considered. The CNC program uses two units of feed rate: mm/min and mm/spindle revolution. The units used above are mm/spindle revolution. If mm/min is used, the formula can be used for conversion: feed rate per minute = feed rate per revolution * spindle revolutions per minute
(III) Cutting depth (cutting depth)
During fine machining, it can generally be less than 0.5 (radius value). During rough machining, it is determined according to the workpiece, tool, and machine tool. Generally, a small lathe (machining diameter is less than 400mm) turns 45 steel in the normalized state, and the radial cutting depth generally does not exceed 5mm. In addition, it should be noted that if the lathe spindle speed change adopts ordinary frequency conversion speed regulation, then when the spindle speed is very low (lower than 100~200 rpm), the motor output power will be significantly reduced, and the cutting depth and feed amount can only be very small.
