1. Cutting function
Main cutting edge: The two main cutting edges symmetrically distributed at the front end of the twist drill remove the material through rotational motion to form a hole. The geometric parameters of the cutting edge (such as the top angle and the back angle) directly affect the cutting efficiency and surface quality.
Top angle: Usually 118° (general steel) or 135° (hard material), which affects the cutting ability and heat dissipation.
Cross edge: Connects the two main cutting edges. Although it participates in a small amount of cutting, it mainly plays a centering role. An overly long chisel edge will increase the axial force and needs to be optimized through grinding.
2. Chip removal function
Spiral groove design: The spiral groove (chip groove) on the drill body discharges the chips along the groove during rotation to avoid clogging. The helix angle of the groove (usually 25°-35°) affects the chip removal speed and the balance of cutting force.
Material adaptability: Processing plastic materials (such as aluminum) requires a large helix angle to facilitate chip removal, while brittle materials (such as cast iron) can choose a smaller angle to enhance the edge strength.
3. Guiding and centering function
Blade (guide belt): a narrow edge distributed along the drill body, which contacts the hole wall to reduce vibration and deflection and ensure the straightness of the drill hole.
Centering challenge: The initial positioning of the chisel edge is easy to slide, especially on hard materials, and is often used with a center punch or pre-drilled guide hole.
4. Versatility
Material breadth: By adjusting the drill bit material (such as high-speed steel, carbide) and coating (TiN, TiAlN), metal, plastic, wood, etc. can be processed.
Special design: woodworking drill bits often have pointed tips to prevent tearing, and plastic drill bits use a small helix angle to reduce adhesion.
5. Adapt to different processing needs
Size range: diameters range from 0.1mm to tens of millimeters, and lengths are divided into standard and extended types to meet the needs of shallow holes to deep holes.
Deep hole processing: intermittent chip removal or internal cooling drills are required to avoid chip accumulation and drill breakage.
Precision control: After drilling, reaming or boring is often required to achieve high precision, because the tolerance of the twist drill itself is generally IT10-IT13.
6. Cooling and lubrication
Application of cutting fluid: reduce cutting temperature, extend drill life, and improve surface quality. Internally cooled drills reach the cutting zone directly through internal channels, which is more efficient.
Dry cutting adaptation: coated drills or materials such as cast iron can reduce the dependence on coolant, but the feed rate needs to be controlled to prevent overheating.
Additional considerations
Optimization of geometric parameters: the back angle reduces friction, and the helix angle balances chip removal and strength, which needs to be selected according to the material characteristics.
Clamping method: straight shank (drill chuck) is suitable for small diameters, and Morse taper shank transmits greater torque to ensure stability.
Maintenance and re-grinding: regular re-grinding restores cutting performance, and symmetry needs to be maintained to avoid hole diameter deviation.
Summary
Twist drills have become the main tool for drilling operations due to their efficient cutting, chip removal and guiding capabilities. Correct selection of drill parameters, processing parameters and cooling methods can significantly improve processing efficiency and quality. Understanding its functional principles can help optimize operations and extend tool life.
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