The crankshaft is one of the key components of a car engine, and its performance directly affects the life of the car. The crankshaft is subjected to heavy loads and constantly changing bending moments and torques during operation. The common failure modes are bending fatigue fracture and journal wear. Therefore, the crankshaft material is required to have high rigidity and fatigue strength and good wear resistance
1. Casting technology
For the melting of high-grade cast iron, a large-capacity intermediate frequency furnace or a frequency conversion intermediate frequency furnace will be used for melting, and a direct-reading spectrometer will be used to detect the composition of the molten iron. The treatment of ductile iron adopts subcontracting to develop new varieties of nodulizers, and adopts advanced inoculation methods such as flow inoculation, in-mold inoculation and compound inoculation. The parameters of the melting process are controlled by a computer and displayed on the screen.
Lost foam casting will be developed and promoted. In sand casting, boxless injection molding and extrusion molding will receive attention and continue to be promoted and applied in new plants or remodeled plants. The original high-voltage molding line will continue to be used, and some of the key components will be improved to realize automatic core assembly and core setting.
2. Forging technology
Automatic lines with hot die forging presses and electro-hydraulic hammers as the main engine are the development direction of forging crankshaft production. These production lines will generally use precision shear blanking, roll forging (cross wedge rolling) billet, intermediate frequency induction heating, etc.
3. Mechanical processing technology
For crankshaft roughing, advanced equipment such as CNC lathes, CNC internal milling machines, CNC lathes and broaching machines will be widely used to perform CNC turning, internal milling, and turning-broaching of the main journal and connecting rod journal to effectively reduce the deformation of the crankshaft. Crankshaft finishing will be widely used CNC-controlled crankshaft grinder to finish grinding its journal.
This kind of grinding machine will be equipped with automatic dynamic balance device of the grinding wheel, automatic tracking device of the center frame, automatic measurement, automatic compensation device, automatic dressing of the grinding wheel, constant linear speed and other functional requirements to ensure the stability of the grinding quality. The current situation of high-precision equipment reliance on imports is expected to remain unchanged in the short term.
4. Heat treatment technology and surface strengthening technology
(1) Intermediate frequency induction hardening of crankshaft
The intermediate frequency induction hardening of the crankshaft will adopt a computer-controlled closed-loop intermediate frequency induction heating device, which has the characteristics of high efficiency, stable quality and controllable operation.
(2) Soft nitriding of crankshaft
For mass-produced crankshafts, in order to improve product quality, a microcomputer-controlled nitrogen-based atmosphere gas nitrocarburizing production line will be used in the future. Nitrogen-based atmosphere gas nitrocarburizing production line is composed of front cleaning machine (cleaning and drying), preheating furnace, nitrocarburizing furnace, cooling oil tank, post cleaning machine (cleaning and drying), control system and gas production and distribution systems.
(3) Crankshaft surface strengthening technology
Nodular cast iron crankshaft fillet rolling strengthening will be widely used in crankshaft machining. In addition, compound strengthening processes such as fillet rolling strengthening and journal surface quenching will also be widely used in crankshaft machining. Forged steel crankshaft strengthening methods will be more The ground adopts the shaft journal and fillet quenching treatment.
The main cause of crankshaft fracture:
- (1) The engine oil has deteriorated after long-term use; serious overload and overhang, causing long-term overload operation of the engine and occurrence of bush burning accidents. The crankshaft was severely worn due to the engine burning.
- (2) After the engine is repaired, the load has not passed the running-in period, that is, overload and overload, and the engine has been overloaded for a long time, causing the crankshaft load to exceed the allowable limit.
- (3) Surfacing welding was used in the repair of the crankshaft, which destroyed the power balance of the crankshaft, and did not perform balance verification. The unbalanced amount exceeded the standard, which caused the engine to vibrate greatly and caused the crankshaft to break.
- (4) Due to poor road conditions, the vehicle is seriously overloaded and overloaded, the engine often runs within the critical speed of torsional vibration, and the failure of the shock absorber will also cause the crankshaft torsional vibration fatigue damage and fracture.