Factors that should be considered in selecting carbide drill bits

It has always been believed that drilling is carried out at low feed and cutting speeds, which was once true under machining conditions using ordinary drill bits. Nowadays, with the advent of carbide drill bits, the concept of drilling has changed.

In fact, choosing the right carbide drill bit can greatly improve the drilling productivity and reduce the cost of single hole processing.

Carbide bits are divided into four basic types:

Solid carbide bits, carbide indexable inserts, welded carbide bits and replaceable carbide crown bits. So, what do you need to pay attention to when choosing carbide drill bits?

Carbide bit

1. Machining accuracy

When selecting carbide drill bits, the dimensional accuracy requirements of the drilling holes should be considered. In general, the smaller the machining aperture, the smaller the tolerance. Therefore, carbide drill bit manufacturers usually classify drill bits according to the nominal diameter of the hole to be machined. Among the above four kinds of cemented carbide bits, the overall cemented carbide bit has high processing accuracy (the tolerance range of φ10mm overall cemented carbide bit is 0~0.03mm), which is the choice for machining high-precision holes; Welded carbide bits or replaceable carbide crown bits have a tolerance range of 0~0.07mm, which is more suitable for hole machining with general accuracy requirements. Carbide bit indexable bits are more suitable for heavy roughing. Although the machining cost is usually lower than other bits, the machining accuracy is relatively low, and the tolerance range is 0 to 0.3 mm (depending on the length to diameter ratio of the bit). Therefore, it is generally used for hole processing with lower accuracy requirements, or to replace the boring tool for hole processing.

2. Processing stability

When selecting carbide drill bits, in addition to the drilling accuracy requirements, the stability of the processing machine should also be considered. The stability of the machine tool is crucial to the safe service life and drilling accuracy of the drill bit, so the working condition of the machine spindle, fixture and accessories needs to be carefully checked.

Welded carbide bits and replaceable carbide crown bits are self-centering geometric blades consisting of two symmetrical cutting edges. This highly stable cutting edge design eliminates the need to reduce feed speed when cutting into the workpiece, unless the bit is mounted at an Angle and cut into the workpiece surface.

3. Scrap removal and coolant

Chip removal is an important problem in drilling. In fact, the common problem encountered in drilling is poor chip removal (especially when processing low carbon steel workpieces), no matter what kind of carbide drill can not avoid this problem. The machining shop usually uses external injection coolant to assist chip removal, but this method is only effective when the depth of the machining hole is less than the hole diameter and the cutting parameters are reduced. In addition, the appropriate coolant type, flow rate and pressure is selected to match the bit diameter. For machines not equipped with a cooling system on the spindle, coolant pipes should be used. The deeper the hole is processed, the more difficult it is to remove chips, and the greater the coolant pressure required. Therefore, the coolant flow recommended by the carbide drill bit manufacturer should be ensured. If the coolant flow rate is insufficient, the processing feed rate should be reduced.

4. Processing cost per hole

Productivity or processing cost per hole is an important factor affecting drilling. In order to increase productivity, carbide drill bit manufacturers are working hard to research machining methods that can integrate various operating procedures and develop drilling tools that can achieve AG feed and high-speed machining.

The newly developed replaceable carbide crown bit has good machining economy. After the carbide bit wears out, the user does not need to replace the entire bit body, only needs to replace the carbide crown, and the purchase cost is only equivalent to the cost of welding or grinding the whole carbide bit again. Hard alloy crown is easy to replace and has high repeatability accuracy. One drill body can be equipped with multiple crowns in the machining shop to process holes of different apertures. This modular drilling system reduces the cost of cataloging bits with diameters from 12 to 20 mm and saves on spare tool costs for welding or regrinding monolithic carbide bits.