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form profile milling of rails with pcbn inserts and solid cbn inserts

The principal objective in the production of girder and flat bottom rails is to achieve long and safe service life. However, all rails have to bear a great deal of stress on a daily basis. The type of steel used for most rail tracks has a tensile strength of up 1500 N/mm2. Hence, it poses a major challenge while machining it. Strong, robust and versatile cutting tools and inserts are therefore needed to effectively mill different sections of the rail track. Polycrystalline cubic boron nitride and solid cbn inserts are the hardest cutting tools available after diamonds and they provide a high level of process reliability and productivity when machining railroad tracks.

Profile milling of railroad tracks involves the milling of the top face, bending point, contact edge, and bottom contact face with cutters that have been designed specifically for rail track machining. The machining process should be sub-divided into three: roughing, medium or semi-finishing and finishing. Appropriate tool inserts must be used to increase productivity and ensure excellent surface finish.

Roughing and Semi-roughing Inserts
For roughing milling operations, round, square, rectangular, parallelogram shaped inserts are suitable for taking off a large portion of material at a high speed. For example, the round RCGT insert series works well in end mills that are designed for roughing of rail tracks made of steel and titanium alloys. This indexable insert allows a large cutting depth (with a cutting edge of over 20 mm) and it can be used with milling cutters that have a positive insert location.

Medium Machining Inserts
Other important cutting inserts include the 85-degree parallelogram-shaped ADCT and ADKT inserts. These inserts have two cutting edges and they can be used for medium machining. Due to their compatibility with various forms of milling cutters, they may be used in form milling cutters for various kinds of profiles, especially for precise machining of the rail profile at the area of transition between the rail head and the grooves.

Finishing Inserts
Another set of inserts that may be used for medium or finishing operations is the CNHU series. This set of inserts allow various depths of cut; their cutting edge length ranges from 10 mm to 16 mm. With the aid of these indexable diamond-shaped inserts which have an 80-degree rake angle, a double-sided countersunk hole and multiple chip breakers, high cutting efficiency can be achieved. It is possible to use it with various milling cutters and achieve high metal removal rates with cutters that have an optimized number of cutting edges.

Milling the Rail Head
Special milling cutters are usually used to machine railroad track heads in order to achieve a high level of accuracy. These cutters are made with various diameters so they can cover virtually all the rail profiles in existence today. Each of these cutters has stable insert seats that hold pcbn inserts with very little tolerance.

For efficient milling of rail heads, helical milling cutters are frequently used with square-shaped inserts. Polycrystalline cbn inserts such as the SDET and SDPT insert series may be used. They are indexable inserts with 4 cutting edges and a clearance angle of 15 degrees which makes them ideal for efficient high speed cutting.

Conclusion
Selecting suitable inserts for milling of rail road tracks requires a careful study of the rail profile. After a form milling cutter that can efficiently machine the rail track has been identified, appropriate pcbn inserts like those discussed above should used to create the desired surface finish.

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