What Is The CNC Lathe Machining Process?

The core of CNC lathe machining lies in "precision control + step-by-step cutting". Below is a detailed breakdown of each link, including specific operations, key parameters and precautions, helping you fully grasp the professional process.

Pre-Machining Preparation (Fundamental for Machining Precision)

Drawing Analysis & Process Planning

Core Task: Analyze part drawings to clarify key requirements — dimensional tolerances (e.g., ±0.01mm), geometric tolerances (roundness, cylindricity), surface roughness, and special features (threads, keyways, inner holes, etc.).

Process Planning Points: Determine machining sequence (external turning first, then internal boring; rough machining first, then finish machining), tool path (avoid interference), and clamping method (special fixtures for mass production, universal chucks for small batches).

Programming Practice: Import drawings into CAD/CAM software (e.g., Mastercam, UG) to generate tool paths, which are automatically converted into G-codes (e.g., G01 for linear cutting, G02 for circular cutting) and M-codes (e.g., M03 for spindle forward rotation, M08 for coolant on). Transfer programs to the lathe's CNC system via USB or network.

Material & Tool Selection (Compatibility Directly Affects Machining Results)

Material Selection:

Metal Materials: Carbon steel (easy to cut, low cost), stainless steel (corrosion-resistant, requiring high-hardness tools), aluminum alloy (lightweight, higher cutting speed applicable), copper alloy (good thermal conductivity, easy to control surface finish).

Non-Metal Materials: Engineering plastics (e.g., POM, PEEK), requiring special tools to reduce deformation.

Tool Selection:

By Machining Type: External turning tools (for cylindrical surfaces, end faces), internal boring tools (for round holes, stepped holes), threading tools (for metric/inch threads), parting tools (for workpiece separation or grooving).

By Material: Carbide tools for steel parts (high wear resistance), diamond-coated tools for aluminum parts (anti-sticking).

Clamping & Calibration (Key to Reducing Positioning Error)

Clamping Methods:

3-Jaw Chuck: Suitable for circular/hexagonal workpieces, automatic centering, quick clamping (commonly used in mass production).

4-Jaw Chuck: Suitable for irregular workpieces, adjustable individual jaws for higher positioning accuracy.

Center Clamping: Suitable for long shaft parts (e.g., transmission shafts), supported by centers at both ends to reduce workpiece deformation.

Calibration Steps: Use a dial indicator to check workpiece end runout and radial runout (error controlled within 0.005mm). Ensure spindle speed stability and tool firmness to avoid loosening during machining.

Core Machining Process (Achieve "Forming + Precision" in Stages)

Rough Machining (Efficiently Remove Surplus Material)

Core Goal: Quickly remove excess material to approach the final shape, prioritizing efficiency over high precision.

Key Parameters:

Cutting Speed: 80-120m/min for steel parts, 200-300m/min for aluminum parts (low speed causes tool sticking, high speed accelerates tool wear).

Feed Rate: 0.2-0.5mm/r (higher feed rate means higher efficiency but poorer surface roughness).

Depth of Cut: 2-5mm (appropriate increase for rough machining to reduce cutting times).

Operation Points: Turn on the cooling system (emulsion or cutting oil) to lower cutting temperature, remove chips, and protect tools and workpieces.

Semi-Finish Machining (Transitional Correction)

Core Goal: Correct dimensional deviations and surface irregularities after rough machining, leaving uniform stock (0.1-0.5mm, adjusted by part precision requirements) for finish machining.

Key Parameters: Cutting speed 10%-20% higher than rough machining, feed rate reduced to 0.1-0.2mm/r, depth of cut controlled at 0.5-1mm.

Notes: Inspect key dimensions (e.g., outer diameter, inner hole depth), adjust programs or tool offsets in time to avoid insufficient or excessive finish machining stock.

Finish Machining (Guarantee Final Precision)

Core Goal: Meet drawing requirements for dimensional accuracy (IT6-IT8 grade, up to IT5 grade for high-precision parts) and surface roughness (Ra0.8-3.2μm, mirror finish up to Ra0.4μm or below).

Key Parameters:

Cutting Speed: 150-200m/min for steel parts, 300-400m/min for aluminum parts (high-speed cutting improves surface finish).

Feed Rate: 0.05-0.1mm/r (low feed rate reduces cutting marks).

Depth of Cut: 0.1-0.3mm (light cutting to avoid workpiece deformation).

Operation Points: Turn off spindle backlash compensation (reduce vibration), ensure sufficient cooling, and prevent chips from scratching the machined surface.

Special Feature Machining (Implemented as Needed)

Thread Machining: Use threading tools programmed by pitch (e.g., 1.5mm), adopt "multiple passes" (decreasing depth of cut each time) to avoid tool overload and ensure complete thread profile.

Grooving: Use parting tools to cut grooves at specified positions (groove width determined by tool width), with step-by-step depth cutting to prevent groove wall inclination.

Taper/Curved Surface Machining: Achieve via G01/G02/G03 code linkage to control tool trajectory, requiring pre-verification of tool paths to avoid interference.

Post-Machining Treatment (Ensure Qualified & Usable Parts)

Quality Inspection (Comprehensive Verification)

Dimensional Inspection: Use calipers (for general dimensions), micrometers (for high-precision dimensions, accuracy 0.001mm), and internal dial gauges (for inner hole dimensions) to inspect key sizes.

Geometric Tolerance Inspection: Use roundness meters (for roundness), parallelism meters (for end face parallelism), and runout testers (for radial/end runout) to verify geometric accuracy.

Surface Quality Inspection: Measure surface roughness with a profilometer, and visually check for scratches, burrs, or tool sticking marks.

Surface Treatment (Enhance Performance & Appearance)

Basic Treatment: Remove burrs (with files or deburring machines), clean oil stains (with kerosene or special cleaning agents), and rust prevention (apply anti-rust oil or passivation treatment).

Advanced Treatment: Conduct electroplating (zinc plating, chrome plating for improved wear resistance and corrosion resistance), anodizing (aluminum parts only, increasing surface hardness and aesthetics), or polishing (enhancing surface finish for precision fittings) as required.

Packaging & Warehousing

Classified Packaging: Package parts separately by model and specification, wrapped in bubble film or pearl cotton to avoid collision and wear during transportation.

Labeling & Recording: Mark part name, dimensions, batch number, and quantity on packages for easy subsequent traceability and warehousing management.