Analyze the parameter characteristics of CNC turning cast iron materials

Analysis of the Parameter Characteristics of CNC Turning Cast Iron Materials

Due to its high hardness, high brittleness and low thermal conductivity, cast iron materials need to have their parameters adjusted specifically in CNC turning to balance tool life, processing efficiency and surface quality. The following analysis is carried out from aspects such as cutting speed, feed rate, cutting depth, tool parameters and cooling and lubrication:

1. Cutting speed (Vc

Characteristics: The cutting speed of cast iron is usually lower than that of steel because of its poor thermal conductivity (about 1/3 of that of steel), and high-speed cutting is prone to cause overheating and wear of the tool.

The cutting speed of common gray cast iron is generally 50-150 m/min. For ductile iron or alloy cast iron, due to its higher hardness, the cutting speed can be reduced to 30-100 m/min.

Influencing factors:

Hardness: The higher the hardness (such as HT300), the lower the cutting speed needs to be to avoid chipping.

Tool materials: Hard alloy tools (such as K type) are suitable for medium and low-speed cutting, while ceramic tools can be used for high-speed cutting (but require cooling).

2. Feed rate (f)

Feature: When cutting cast iron, the feed rate should be moderate. If it is too small, the tool may rub against the hard points; if it is too large, it may cause vibration or chipping.

Range: The feed rate can be taken as 0.2-0.5 mm/r during rough machining, and reduced to 0.05-0.2 mm/r during finish machining.

Influencing factors:

Cutting edge strength of the tool: Cast iron often contains hard points (such as graphite and carbides), so tools with high cutting edge strength (such as negative rake Angle tools) should be selected.

Machine tool rigidity: Cast iron has a relatively large cutting force. It is necessary to ensure that the machine tool has sufficient rigidity to avoid vibration.

3. Cutting Depth (ap)

Features: The cutting depth of cast iron can be appropriately increased to reduce the frequency of tool changes, but it is necessary to avoid excessive cutting force that may cause deformation of the tool or workpiece.

Range: During rough machining, the cutting depth can be 2-5 mm, and during finish machining, it is 0.1-1 mm.

Influencing factors:

Workpiece rigidity: For thin-walled or slender cast iron shafts, the cutting depth should be reduced to avoid vibration.

Tool life: Increasing the cutting depth will accelerate tool wear. It is necessary to balance efficiency and life.

4. Tool parameters

Tool material:

Hard alloys: K-type (such as YG8) are suitable for cutting cast iron because of their good impact resistance and wear resistance.

Ceramic cutting tools: Suitable for high-speed cutting, but they need to be used in conjunction with coolant to avoid hot cracking.

Tool geometric parameters:

Rake Angle: Generally, it is taken as -5° to 5°. A negative rake Angle can enhance the edge strength and reduce the risk of chipping.

Relief Angle: Take 5°-10° to reduce the wear of the rear tool face.

The main deflection Angle is set at 45°-90° to control the radial cutting force.

Edge treatment: Chamfering or negative chamfering can enhance the tool's impact resistance.

5. Cooling and lubrication

Feature: When cutting cast iron, it is necessary to cool it thoroughly to reduce the tool temperature, but the coolant selected should avoid reacting with the graphite in the cast iron.

Cooling method:

Emulsion: Suitable for general cast iron cutting, it can effectively cool and reduce tool wear.

Dry cutting: For some high-hardness cast irons (such as alloy cast irons), dry cutting can be adopted, but it needs to be combined with a powerful dust collection device.

Precautions: Avoid using extreme pressure cutting fluids containing sulfur or chlorine to prevent corrosion of the cast iron surface.

6. Processing strategy

Layer-by-layer cutting: For cast iron parts with large allowances, layer-by-layer cutting is adopted to reduce cutting force and vibration.

Chip breaking control: Cast iron chips are fragile, but the chip shape needs to be controlled through the geometric parameters of the tool (such as chip breaking grooves) to avoid entanglement.

Vibration suppression: Use vibration-reducing knife rods or optimize the clamping method (such as one clamping and one top) to reduce vibration.

7. The influence of cast iron type on parameters

Gray cast iron: It has good cutting performance, and the cutting speed can be at a relatively high value.

Ductile iron: It has high hardness and good toughness, so the cutting speed and feed rate need to be reduced.

Alloy cast iron: It contains alloying elements such as chromium and molybdenum, has higher hardness, and the cutting parameters need to be further reduced.

Summary

When CNC turning cast iron materials, the parameter Settings need to comprehensively consider the material properties, tool performance and machine tool conditions. The key points include:

Cutting speed: moderately low to avoid overheating.

Feed rate: Moderate, avoid friction or vibration from hard points.

Cutting depth: Adjust according to the rigidity of the workpiece to avoid deformation.

Tool selection: K-class cemented carbide is preferred, and the negative rake Angle enhances the strength of the cutting edge.

Cooling and lubrication: Ensure adequate cooling to prevent corrosion.

By reasonably adjusting the parameters, efficient and stable cutting processing of cast iron can be achieved.