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using cbn inserts for efficient re-profiling of rail wheels

Re-profiling of rail wheels is one of the most economical methods of maintaining the efficiency and safety of railroad cars. Although train wheels are made of steel which is hardened to give it more strength and reduce the rate of wear, the wheels could require repair due to drag braking and the large amount of weight they bear. As soon as defects are observed on the train wheels, they need to be re-profiled using suitable polycrystalline cbn inserts that can meet the strict machining requirements for rail wheels.

In most countries, regulatory agencies specify very strict quality standards for re-profiling of worn out train wheels. This helps to prevent the derailing of trains which use these re-furbished wheels. Therefore, the shape, dimensions, and grade of the cutting tools and pcbn inserts must comply with very tight tolerance specifications. Even with hardened heat-treated wheels and intermittent disruptions in the cutting process, the tools and inserts used for machining must deliver exceptionally accurate surface finish.

Turning of Rail Wheels
Re-profiling of train wheels is frequently done while the wheels are still assembled to the train, using an underfloor lathe. Operations required for most mounted rail wheels usually include, wheel turning, and wheel boring. To obtain excellent results, turning of train wheels is normally performed in three phases: roughing, medium machining and finishing. At each of these phases, cutting can be done economically with standard inserts. For example the LNMM and RCGA series can be used for roughing and medium machining. Two of this type of inserts may be combined in a single cutter to machine the thread and flange in a single pass. For medium machining and finishing of the wheel thread, the CNMM will provide a high quality surface.

Boring of Rail Wheels
The re-boring of wheels allows for a perfect fit between the wheel and the axle. It enables the train to have a balanced and safe ride devoid of unwanted vibration. Inserts used for the roughing stage include SNMG, a square-shaped insert with multiple cutting edges and a chip breaker. Other commonly used inserts for boring are the RNMG and RCMH series. These inserts are frequently used with L-shaped boring cutters designed specifically for boring of rail wheels.

Cutting Conditions
Specific machining conditions may be recommended for the re-profiling of rail wheels. For instance a cutting depth of 5 – 12 mm, a feed rate 1.5 mm/rev and a cutting speed of 50m/min is recommended for turning of the external thread and flange using the LNMM insert series. But the actual cutting speed, depth and feed rate depend on the type of faults, defects and problems encountered on each wheel. Examples of problems that need to be tackled include: flat areas caused by drag braking, mismatched wheels that can lead to excessive wear on the side with the flange, excessive roll-over, mushrooms, accidental torch burns, and excessive heating of rotating wheels.

Conclusion
To achieve the best results from wheel re-profiling, the wheels should be carefully studied to discover all the defects on it. Then the appropriate polycrystalline cbn inserts should be selected to handle each machining operation at the roughing, medium, and finishing stages.

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