When choosing cemented carbide drills, the dimensional accuracy requirements of drilling must be considered first. Generally speaking, the smaller the aperture to be processed, the smaller the tolerance. Therefore, drill manufacturers usually classify drills according to the nominal diameter of the hole being machined. Among the above four types of cemented carbide drills, solid cemented carbide drills have higher machining accuracy (the tolerance range of φ10mm solid cemented carbide drills is 0～0.03mm), so it is a better choice for machining high-precision holes ;The tolerance range of welded cemented carbide drills or replaceable cemented carbide crown drills is 0～0.07mm, which is more suitable for hole processing with general accuracy requirements; drills with cemented carbide indexable inserts are more suitable for heavy-duty rough machining Although its processing cost is usually lower than other types of drills, its processing is also relatively low, with a tolerance range of 0～0.3mm (depending on the length to diameter ratio of the drill), so it is generally used for hole processing with low precision , Or complete the finishing of the hole by replacing the boring blade
The stability of the drill bit itself should also be considered. For example, solid carbide drills are more rigid, so they can achieve high machining accuracy. The cemented carbide indexable insert drill bit has poor structural stability and is prone to deflection. Two indexable inserts are installed on this drill bit. The inner insert is used to machine the center part of the hole, and the outer insert is used to machine the outer edge from the inner insert to the outer diameter. Since only the inner blade enters the cutting at the initial stage of processing, the drill bit is in an unstable state, which can easily cause the drill body to deviate, and the longer the drill bit, the greater the amount of deflection. Therefore, when using a cemented carbide indexable insert drill with a length of more than 4D for drilling, the feed should be appropriately reduced at the beginning of the drilling phase, and the feed rate should be increased to the normal level after entering the stable cutting phase .
The welded cemented carbide drill bit and the replaceable cemented carbide crown drill bit are composed of two symmetrical cutting edges with a self-centering geometric edge type. This high-stability cutting edge design makes it unnecessary when cutting into the workpiece Reduce the feed rate, except when the drill is installed obliquely and cut in at a certain angle to the surface of the workpiece. At this time, it is recommended to reduce the feed rate by 30% to 50% when drilling in and out. Because the steel drill body of this kind of drill bit can produce small deformation, it is very suitable for lathe processing; while the solid carbide drill bit is more brittle, it is easier to break when used for lathe processing, especially when the drill bit is not well centered. This is especially true at times.
Chip removal is a problem that cannot be ignored in drilling. In fact, the most common problem encountered in drilling is poor chip removal (especially when machining low-carbon steel workpieces), and this problem cannot be avoided no matter what kind of drill is used. Processing workshops often use external coolant injection to assist chip removal, but this method is only effective when the depth of the processed hole is smaller than the diameter of the hole and the cutting parameters are reduced. In addition, a suitable coolant type, flow rate and pressure must be selected to match the diameter of the drill bit. For machine tools without a cooling system in the spindle, coolant pipes should be used. The deeper the hole to be processed, the more difficult it is to remove chips and the greater the coolant pressure required. Therefore, the minimum coolant flow recommended by the drill manufacturer should be ensured. If the coolant flow is insufficient, the machining feed must be reduced.
Post time: Sep-07-2021