There are many kinds of real drill bits, mainly according to their different uses and distinguish, that is, what kind of drill bits to drill. Common drill bits are twist drill, flat drill, deep hole drill, reaming drill, countersink drill, center drill, etc., the following in detail.
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Flat drill
The cutting part of flat drill is spade form, structure is simple, manufacturing cost is low, in cutting fluid leads into hole easily, but performance of cutting and discharge chip is poorer. Flat drill structure has two types of integral and assembled. The whole is mainly used for drilling 0.03 ~ 0.5 mm diameter micro hole. Prefabricated flat drill blade can be changed, can use internal cooling, mainly used for drilling 25 ~ 500mm diameter of large holes.
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Twist drill
Twist drill is the most widely used hole machining tool. The usual diameter range is 0.25 to 80 mm. It is mainly composed of bit working part and shank. The working part has two spiral grooves, shaped like a twist, hence the name. In order to reduce the friction between the guide part and the hole wall when drilling, twist drill from the drill tip to the handle direction gradually reduce the diameter of the inverted cone. The screw Angle of twist drill mainly affects the size of cutting edge Angle, edge edge strength and chip removal performance, which is usually 25° ~ 32°. Spiral grooves can be processed by milling, grinding, hot rolling or hot extrusion, and the front end of the drill bit forms a cutting part after grinding. The cutting Angle of the standard twist drill is 118, the bevel Angle of the cross edge is 40° ~ 60°, and the back Angle is 8° ~ 20°. Due to structural reasons, the rake Angle is large at the outer edge and gradually decreases to the middle, and the transverse edge is negative rake Angle (up to about -55°), which acts as extrusion when drilling.
In order to improve the cutting performance of twist drill, the cutting part can be ground into various shapes according to the properties of processed materials (such as group drill). Twist drill shank form has straight shank and cone shank two kinds, processing the former clip in the drill chuck, the latter inserted in the machine tool spindle or tail seat of the cone hole. The general twist drill is made of high speed steel. Insert welding carbide blade or crown twist drill for the processing of cast iron, hardened steel and non-metallic materials, such as the whole cemented carbide small twist drill for the processing of instrument parts and printed circuit boards.
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Deep hole drilling
Deep hole drilling is usually refers to the processing of hole depth to aperture ratio greater than 6. Commonly used gun drill, BTA deep hole drill, jet drill, DF deep hole drill and so on. Sleeve drills are also commonly used for deep hole machining.
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Center drill
The center drill is used for drilling the center hole of shaft type workpieces. It is essentially composed of screw Angle small twist drill and countersink drill, so it is also called compound center drill.
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Economic drill
Shaving drill has more cutter teeth, in order to form the hole end processing into the required shape, used for processing various countersunk head screw hole, or flat hole outer end face.
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Reaming drill
Reaming drill has 3 to 4 cutter teeth, its rigidity is better than twist drill, used to expand the existing hole and improve processing accuracy and finish.