Guide: The high-volume, high-quality requirements and special solutions determined by the form of the workpiece and the unique process make the crankshaft machining a “super league” for metalworking in the automotive industry.

In an internal combustion engine, the function of the crankshaft is to convert the reciprocating motion of the piston into a rotary motion. This means severe acceleration and deceleration, with high bending deformation, high torque and vibration shock, resulting in very high and variable stresses.

Such extreme stresses require careful design and calculation, selection of suitable materials, and batch processing. These stresses are concentrated at the fillet radius between the support journal and the counterweight web as well as on the oil holes, so special attention needs to be paid to the machining of these locations.

Today's market requires automakers to supply smaller engines while still meeting higher power and speed requirements, which further increases the load and stress on the crankshaft. As a result, manufacturers are constantly looking for higher strength materials for these parts, often including high alloy metals.

Ductile iron is the standard material for lower load engines (mainly gasoline engines), while high horsepower engines (including most diesel engines) use more expensive alloy steel forgings. Steel grades used in crankshafts are typically subjected to various heat treatments such as quenching and tempering. In some special high-end applications, including racing cars, the crankshaft may be machined directly from round steel.

Due to the above conditions, crankshaft machining has become the most demanding high-volume metal cutting process. The crankshaft production line has also become the largest consumer of hard alloys throughout the automotive manufacturing process.

A simple way to machine both ends of the crankshaft and the journal is to turn on a conventional lathe or turning center. This obviously requires ample space between the shank and the surface of the machined journal. The benefits of this approach include the ability to use standard machine tools, tools and blades for high flexibility and low cost.

A special machine with turning and pulling capability allows the journal to be machined on the center of the crankshaft. The inserts for roughing and finishing can be mounted on the same cutter head at the same time, and a special shape can be machined in one complete cutting stroke. Other benefits include repeatable positioning accuracy, good machined surface quality, low tolerances, extended tool life, reduced tool utilization due to tool change times, and reduced machining time. The disadvantages of the car drawing process are the high cost of special machine tools and tools, and the need to use a large number of blades. A more specialized turning method is the use of multi-toothed blades to achieve cost-reducing efforts that facilitate iron filing control and the absence of broaching.

Regardless of the method used, the overall objectives of crankshaft machining include iron filing control, extended tool life, reduced cycle times and improved product quality. The crankshaft is usually produced in large quantities by a production line consisting of several special machine tools. However, the one-piece machining method can also be used in some special turnkey projects, such as racing engine crankshafts and marine diesel crankshafts.

External and internal milling represents another method, especially for link neck machining. If the counterweight has a large margin to remove, the milling cutter disc with the bladed blade is an attractive option. For these applications, Sandvik Coromant has over 40 years of experience. Oil hole drilling and milling are the most expensive processes for producing hard alloys in crankshaft production.

In crankshaft oil holes, the hole depth is usually 20 times the diameter, so this is a very difficult machining task. The most used tools include gun drills and carbide drills lubricated with oil mist. High-quality finishing is also essential because of the potential for stress concentration around the borehole.

Crankshaft application center

The competency center works with original equipment manufacturers and machine tool builders around the world in projects in around 20 countries. Emerging markets are expanding in this industry, especially in China, where the center recently opened new branches.

Crankshaft machining is one of the most demanding areas in automotive manufacturing. The key requirements for all machining methods are the same, including iron filing control, extended tool life, reduced cycle times and improved product quality.