Development Trend Of Crankshaft Manufacturing Technology in The Future

Crankshaft is one of the key components of automotive engines, and its performance directly affects the life of the vehicle. During operation, the crankshaft is subjected to heavy loads and constantly changing bending moments and torques. The common forms of failure are bending fatigue fracture and journal wear. Therefore, the crankshaft material is required to have high rigidity, fatigue strength, and good wear resistance.

1. Foundry Technology

(1) Smelting

For the melting of high grade cast iron, large capacity intermediate frequency furnaces or variable frequency intermediate frequency furnaces will be used for melting, and direct reading spectrometers will be used to detect the composition of molten iron. The treatment of nodular cast iron adopts subcontracting, develops new types of nodularizing agents, and adopts advanced inoculation methods such as flow inoculation, in mold inoculation, and composite inoculation. The parameters of the melting process are controlled by microcomputer and displayed on screen.

(2) Styling

Lost foam casting will be developed and promoted. In sand casting, box less injection molding and extrusion molding will receive attention and continue to be promoted and applied in new or rebuilt plants. The original high-voltage molding line will continue to be used, and some key components will be improved to achieve automatic core assembly and core removal.

2. Forging technology

The development direction of forging crankshaft production is automatic lines based on hot die forging presses and electro-hydraulic hammers. These production lines will generally adopt precision shearing and blanking, roll forging (cross wedge rolling) billet making, and medium frequency induction heating.

3. Machining technology

For rough machining of crankshaft, advanced equipment such as CNC lathes, CNC internal milling machines, and CNC broaching machines will be widely used for CNC turning, internal milling, and turning broaching of the main journal and connecting rod journal, in order to effectively reduce the deformation of crankshaft processing. CNC controlled crankshaft grinding machines will be widely used for crankshaft finishing to finish machining its journals.

This grinding machine will be equipped with automatic dynamic balancing device for grinding wheels, automatic tracking device for center frame, automatic measurement, automatic compensation device, automatic dressing of grinding wheels, constant linear speed, and other functional requirements to ensure stable grinding quality. The current situation of high precision equipment relying on imports is not expected to change in the short term.

4. Heat treatment technology and surface strengthening technology

(1) Medium frequency induction hardening of crankshaft

The crankshaft medium frequency induction hardening will adopt a microcomputer controlled closed-loop medium frequency induction heating device, which is characterized by high efficiency, stable quality, and controllable operation.

(2) Crankshaft soft nitriding

In order to improve the quality of the crankshaft in mass production, a microcomputer controlled nitrogen based atmosphere gas soft nitriding production line will be adopted in the future. The nitrogen based atmosphere gas soft nitriding production line consists of a front cleaning machine (cleaning and drying), a preheating furnace, a soft nitriding furnace, a cooling oil tank, a rear cleaning machine (cleaning and drying), a control system, and a gas preparation and distribution system.

(3) Surface Strengthening Technology for Crankshaft

Nodular cast iron crankshaft fillet rolling strengthening will be widely used in crankshaft processing. In addition, composite strengthening processes such as fillet rolling strengthening and journal surface hardening will also be widely used in crankshaft processing. Forged steel crankshaft strengthening methods will increasingly use journal and fillet hardening.

Main causes of crankshaft fracture:

(1) The engine oil deteriorates after long-term use; Serious overloading and overloading have resulted in long-term overload operation of the engine and the occurrence of a tile burning accident. The crankshaft suffered severe wear due to the burning of the engine tiles.

(2) After the engine has been repaired, the vehicle has not passed the running-in period, which means it is overloaded and overloaded. The engine has been overloaded for a long time, causing the crankshaft load to exceed the allowable limit.

(3) Overlay welding was used in the repair of the crankshaft, which damaged the dynamic balance of the crankshaft and did not undergo balance verification. The imbalance exceeded the standard, causing greater vibration of the engine and causing the crankshaft to fracture.

(4) Due to poor road conditions and severe overloading and overloading of vehicles, the engine often operates within the critical rotational speed of torsional vibration, and the damper fails, which can also cause torsional vibration fatigue damage and fracture of the crankshaft.