Crankshaft machining process

Crankshaft machining process

2021-02-25 18:25:24 54

The crankshaft is the most important part of the engine. It takes the force from the connecting rod and transforms it into torque that is output through the crankshaft and drives other accessories on the engine. The crankshaft is subjected to the combined effect of centrifugal force of rotating mass, periodically changing gas inertia force and reciprocating inertia force, which makes the crankshaft subjected to bending and torsional load. Therefore, the crankshaft is required to have sufficient strength and stiffness, and the journal surface needs to be wear-resistant, work evenly and have good balance.

The wear and tear of the crankshaft in use is an important factor in determining whether the engine needs an overhaul. If the quality of the crankshaft is not guaranteed, it will seriously affect the life of the whole engine. Therefore, the crankshaft material and blank processing technology, precision, surface roughness, heat treatment and surface strengthening, dynamic balance and other requirements are very strict. Among them, crankshaft machining not only affects the quality of the crankshaft, but also has a close relationship with productivity and cost.


Crankshaft machining


The first thing to look at is what the crankshaft is made of, ductile iron or steel. Crankshaft machining is a very complex and demanding process, and the machining process can basically be divided into two parts: roughing and finishing.


Rough machining of crankshaft processing is the use of CNC lathes, CNC internal milling machines, CNC lathes and other advanced equipment for the main journal, connecting rod journal CNC turning, internal milling, turning - broaching processing, in order to effectively reduce the amount of crankshaft processing deformation.


The finishing of crankshaft machining is generally done by using CNC-controlled crankshaft grinder to finish grinding its journals. Such grinding machines will be equipped with functional requirements such as automatic dynamic balancing device for grinding wheels, automatic tracking device for center frame, automatic measurement, automatic compensation device, automatic dressing of grinding wheels, and constant linear speed to ensure the stability of grinding quality. The status quo of relying on imported high precision equipment is not expected to change in the near future.


Crankshaft polishing


In the past, the requirements for crankshafts were not so high, and the surface requirements could be met after finishing by grinding machines. The crankshaft grinding machine is a "metal cutting machine tool", and the grinding volume of the crankshaft grinding machine is often tens of microns or even several millimeters to complete the rough and fine grinding processes until the finished product is qualified. Therefore, more and more crankshaft processing companies have added polishing as a process.

The main journals, connecting rod journals and thrust surfaces of crankshafts all require super-finishing and polishing. In the early days, foreign crankshaft superfinishing has adopted the CNC abrasive belt polishing process, with the use of abrasive belts that are moisture-proof and electrostatically flocked (to ensure that the abrasive tips face outward). In order to be able to polish rounded corners and shoulders, the belt is slotted on both sides in order to fit with the processing surface.


This crankshaft grinding belt polishing machine can polish main journals, connecting rod journals, rounded corners, shoulders and thrust surfaces at the same time. Its structure are used to clamp type, each journal with 4 pieces of pad (in concave type) pressed sand belt; pad and sand belt according to the workpiece material and hardness selection; machine tool on the tape reel can ensure that each journal have a new section of sand belt (length adjustable) to participate in the work; polishing way to super-finishing principle. Its efficiency and effect are far better than oil stone. 


For polishing and grinding of ductile iron crankshaft, since the ferrite inside the ductile iron will form a protruding burr after grinding, the grinding steering of the shaft should be made opposite to the working steering, and the polishing steering is the same as the working steering. In this way, the burr can be effectively removed in polishing and avoid scratching the shaft tile when working.



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