How to Machine a Crankshaft?

How to Machine a Crankshaft?

The crankshaft is one of the most critical components in an internal combustion engine. Its manufacturing process is complex and rigorous, requiring advanced equipment, strict quality standards, and specialized expertise. This article will provide a step-by-step guide to crankshaft machining, covering the entire process from raw material preparation to final quality inspection.

1. Raw Material Preparation

The processing begins with the selection and preparation of materials:

Common materials: carbon steel (45#), alloy steel (42CrMo).

Blank preparation: hot-rolled/cold-rolled → sawing → ultrasonic testing to detect internal cracks.

Reference equipment: WMTCNC CNC circular sawing machine (cutting accuracy ±0.2mm).

High-quality materials and precise pre-processing lay the foundation for subsequent processes.

2. Turning Processing

Turning is a fundamental process in crankshaft manufacturing:

Tasks: Remove surface defects, rough-turn the journal, and finish-turn the reference surfaces.

Precision requirements: Rough turning IT8, finish turning IT7; surface roughness Ra ≤ 3.2 μm.

Equipment: WMTCNC CK series CNC lathes (high stability, multi-station processing).

By establishing precise reference points, subsequent processes are ensured to meet strict tolerances.

3. Drilling Processing

The oil passages and bolt holes inside the crankshaft must be precision-machined:

Technical Challenges: Deep hole straightness ≤0.1mm/100mm, hole position accuracy ±0.05mm.

Solution: Gun drilling process + high-pressure internal cooling (80 Bar coolant).

Equipment: WMTCNC machining center (with deep hole drilling attachments available).

This step ensures the reliability of the lubrication channels, which is critical for the crankshaft’s service life.

4. Grinding (core process)

Grinding determines the final precision and surface quality of the crankshaft:

Objective: IT6 dimensional accuracy, roundness ≤0.005mm, radial runout ≤0.03mm, surface roughness Ra ≤0.4μm.

Process: Rough grinding (remaining allowance 0.2mm) → Fine grinding (remaining allowance 0.02mm) → Polishing.

Equipment: WMTCNC MK series CNC crankshaft grinding machine (with online measurement and automatic compensation).

This is the decisive process ensuring the reliable operation of the engine.

5. Heat Treatment

Heat treatment is used to enhance the strength and wear resistance of crankshafts:

Process sequence: carburizing → quenching → tempering.

Hardness requirements: surface HRC 58–62, core HRC 35–40.

Environmental control: independent furnace zone, temperature monitoring and alarm system.

Proper heat treatment ensures wear resistance of the surface layer and toughness of the core.

6. Final Quality Inspection

Each crankshaft must undergo rigorous quality inspection before delivery:

Conclusion

Crankshaft machining is a precise and systematic engineering process. From raw material preparation, turning, drilling, to grinding and heat treatment, every step is critical. Only by relying on advanced CNC equipment and strict quality control can the high precision and reliability of crankshafts be ensured.

At WMTCNC, we provide comprehensive crankshaft machining solutions for automotive, marine, and industrial engine manufacturers, including CNC lathes, crankshaft grinders, and machining centers, helping customers reduce costs and improve efficiency.

Contact WMTCNC today to obtain detailed equipment specifications and process solutions.