What Are The Effects Of Low Production Efficiency On The Cutting Force Of CNC Milling Machine?

When cutting metal with CNC milling machine, the cutting tool cuts into the workpiece and deforms the workpiece material into chips, which is called cutting force. Cutting force is an important basis for calculating cutting power, designing cutting tools, machine tools and machine tool fixtures, and formulating cutting parameters. In automatic production, the cutting process and the working state of cutting tools can also be monitored by cutting force.

Cutting Force And Cutting Power Of CNC Milling Machine

1. The source of cutting force of CNC milling machine.

On the one hand, the source of cutting force is the resistance caused by elastic deformation and plastic deformation in the process of chip formation. On the other hand, it is the friction resistance between chip and tool rake face and between workpiece and tool rake face.

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2. Cutting force and decomposition.

The total cutting force F during cutting is a spatial force. In order to facilitate measurement and calculation and meet the needs of machine tool, fixture and tool design and process analysis, f is often decomposed into three mutually perpendicular cutting components FC, FP and FF.

(1) The main cutting force FC is the projection of the total cutting force F in the main motion direction, and its direction is perpendicular to the base plane. FC is an important basis for computer bed power, tool strength, fixture design and selection of cutting parameters. FC can be calculated by empirical formula or unit cutting force KC (unit: n / mm): FC = kcad = kchdbd = kcapf.

(2) The back force FP is the component of the total cutting force F perpendicular to the feed direction. It is the main factor affecting workpiece deformation and causing system vibration.

(3) The feed force FF is the cutting component of the total cutting force to f in the feed direction. It is the main basis for designing and checking the feed mechanism of machine tool and the feed power of computer bed.

Cutting force is the total cutting force, f is decomposed into FC and FD, FD is decomposed into FP and FF, and their relationship is FF = fdsinkr, FP = fdcoskr.

3. Cutting power of CNC milling machine.

Cutting power refers to the power consumed by the cutting force in the cutting process, expressed in PM and in kW. When turning an excircle, it is the sum of the power consumed by the main cutting force FC and the feed force FF. Since the feed force FF consumes a small proportion of the power (only 1%5%), generally the power consumed by FF can be ignored, and FP does not do work, so pm=fc is obtained υ c × Where FC is the main cutting force (n), υ C is the cutting speed (M / s).

Considering the transmission efficiency of the machine tool, the motor rate PE of the machine tool can be calculated from the cutting power PM, that is, PE ≥ PM / where is the transmission efficiency of the machine tool, generally taken as 0.75 ~ 0.85.

Main Factors Affecting Cutting Force Of CNC Milling Machine

1. Influence of workpiece material of CNC milling machine.

The higher the strength and hardness of the workpiece material, although the cutting deformation decreases slightly, the total cutting force still increases. For materials with similar processing strength and hardness, if the plasticity is large, the friction coefficient with the tool is also large, so the cutting force increases; When machining brittle materials, the cutting force is small due to small plastic deformation and small friction between chip and tool rake face.

2. Influence of cutting parameters of CNC milling machine

(1) Back feed AP and feed F.

When f and AP increase, the cutting area increases and the main cutting force also increases, but the influence degree of them is different. In turning, when AP is doubled, the main cutting force is doubled; When f is doubled, the main cutting force increases by only 68% ~ 86%. Therefore, in the cutting process, if considering the main cutting force and cutting power, increasing the feed rate is better than increasing the back draft.

  • Cutting speed υ c.

Influence curve of cutting speed on cutting force when machining 45 steel (AP = 4mm, f = 0.3mm / R) with YT15 cemented carbide turning tool. When cutting plastic metal, in the area of chip accretion, the growth of chip accretion can increase the actual rake angle of the tool, reduce the chip deformation and reduce the cutting force; On the contrary, the reduction of chip buildup increases the cutting force. When there is no chip buildup, with the cutting speed υ C increases, the cutting temperature increases, the rake face friction decreases, the deformation decreases and the cutting force decreases. Therefore, high-speed cutting is often used in production to improve productivity. When cutting brittle metals, υ C increases and the cutting force decreases slightly.

3. Influence of tool geometric parameters on CNC milling machine

(1) Front corner. The rake angle has the greatest influence on the cutting force. When cutting plastic metal, the rake angle increases, which can reduce the extrusion deformation and friction of the material to be cut, smooth chip removal and reduce the total cutting force; When cutting brittle metals, the effect of rake angle on cutting force is not obvious.

(2) Negative chamfering. Grinding negative chamfering on the sharp cutting edge can improve the strength of the edge and improve the service life of the tool, but at this time, the deformation of the metal to be cut increases and the cutting force increases.

(3) Principal deflection angle. The influence of the main deflection angle on the cutting force is mainly through the change of the cutting thickness and the length of the tool tip arc curve to affect the deformation, so as to affect the cutting force. The main deflection angle has little effect on the main cutting force FC, but has an obvious effect on the proportion of the back force FP and the feed force FF. F’d is the reverse thrust of the workpiece to the tool. Since f’p=f’dcoskr, f’f=f’dsinkr, increasing the main deflection angle Kr will increase the feed force F’f and decrease the back force f’p. When turning a slender workpiece, a larger main deflection angle can be selected to reduce or prevent the bending deformation of the workpiece.

4. Other factors. Friction between cutting tools and workpiece materials

Under the same cutting conditions, the cutting force of high-speed steel tool is the largest, followed by cemented carbide tool and ceramic tool. Using cutting fluid in the cutting process can reduce the cutting force, and the higher the lubrication performance of cutting fluid, the more significant the reduction of cutting force. The greater the friction, the more serious the tool wear.

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