Foundation, Concrete and Earthquake Engineering

Hollow Drill

Hollow drill bit is more suited to portable tool hole processing tool. However, hollow drill bit manufacturing process more complicated, and can not be processed blind hole, and therefore the use of metal cutting are not common, usually only in the processing of some large diameter or precious metal workpiece through-hole drilling equipment, power is limited or when the use of .

Here's hollow design of the cutting bit to make a brief analysis of the impact.
1. A front-line impact of change on the drill bit cutting

Anterior horn of the cutting force under the influence of change in angle will affect the extent of chip deformation of the material, thereby cutting force change. Larger chip deformation, cutting force greater; chip deformation smaller, the smaller the cutting force. The current angle is 0 ° ~ 15 ° within the scope changes, the changes in cutting force correction factor ranging from 1.18 to 1. Anterior horn of the impact of increased durability drill bit anterior horn, the tip will reduce the intensity and volume of cooling the same time, the situation will affect the tip force.

Hollow Drill Bits
The current angle is positive when the tip under tensile stress; the current angle is negative, tip compressive stress. Such as the choice of anterior horn is too large, although the increase drill sharpness, reducing the cutting forces, but the tip tensile stress suffered by a larger tip strength decreased, easy to break. A number of bits in the cutting trials were too large due to anterior horn damage. However, due to be processed materials, high hardness and strength, combined with a portable drilling rig machine spindle and a lower rigidity, such as pre-selected angle is too small, the increase of cutting forces during drilling spindle will vibrate, processing, apparent surface vibration pattern, drill durability will be reduced.
2. Posterior horn of the impact of change on the drill bit cutting

Increased posterior horn can be reduced and the cutting flank friction between materials, reducing the strain on the machined surface. However, if the posterior horn is too large, it will reduce the edge strength and heat dissipation. A direct impact on the size of the posterior horn drill durability. In the drilling process, the drill wear in the form of the main phase transition mechanical abrasions and wear. Consider mechanical abrasion wear and tear, when the cutting life is constant, the greater the posterior horn, cutting time can be longer; consider the phase-change wear and tear, posterior horn larger drill bit will reduce the cooling capacity. Bit worn, with the gradual flank wear band widening, cutting power gradually increased, the friction heat generated will gradually increase, so that drill bit temperature, when the temperature rises to drill phase transition temperature, the drill will occur rapid wear and tear.

3. Bit design of the grinding process of

Hollow drill small amount of processing volume is small, so the design should take into account bit processing technology issues, as far as possible commonly used machining equipment and tools used to achieve machining and grinding. Chip flow through the rake face, so the shape of the rake face a direct impact on the performance chip shape and chip removal. Chip in the outflow of the process of being the rake face extrusion and friction, and further deformation. Chip the greatest extent of the underlying metal deformation and slippage along the rake face, so that the bottom length of the chip is longer, to form a variety of curling shapes. Using hollow drill hole, we hope ribbon cuttings or debris into the debris in order to facilitate chip removal. To facilitate the processing and grinding, the rake face must be designed as a flat, and do not open chip-breaker. The rake face in use does not require re-grinding. Flank is the most likely to re-grinding the hollow drill bit face, but also the fastest surface wear and tear, so hollow drill grinding is grinding flank to achieve. Deputy Vice-flank divided into internal and external vice flank flank. Severity grinding point of view, re-grinding inside and outside is not easy to achieve, Vice flank, so Vice-flank grinding should be designed to not re-form. Based on the above analysis, the hollow drill bit blade designed for the form shown in Figure 1. Processing of Practice has proved that fully meet the design re-use requirements and tool grinding requirements.

4. Cutting fluid used and the impact of drill cutting

The main characteristics of the hollow drill holes within the core working hours will not be cut, so hollow drill twist drill cutting significantly reduced compared with the required drilling and cutting power in less heat generated. High-speed steel hollow drill hole, because of processing zones of temperature on the hardness of a great impact drill, so drilling process must be used coolant temperature. We started using an external spray cooling method, but drill the horizontal axis station processing, cooling fluid is not easy to enter the blade part of the drill bit, coolant consumption of a larger cooling effect is not ideal. The re-engineering to change the drill spindle structure, the external spray cooling an internal spray cooling, cooling fluid from the hollow core drill bits were added, so that coolant can smoothly reach the drill bit cutting section, thereby significantly reducing the cooling fluid consumption, improved cooling effect.

5. Hollow drill bit to use effects

Well-designed hollow drill bit should also meet the requirements in the following aspects: ease of manufacturing, to adopt common tools and common tooling; easy re-sharpening can be carried out using common grinding wheel grinding machine; high production efficiency, long service life; low price. Basically, we developed the hollow drill bit to achieve the above requirements. In actual use, the drill durability is stable up to 50 minutes, diameter tolerance, surface roughness, Deng Jun reached the design requirements. Because only re-grinding flank, posterior horn bit easier to control, in the ordinary wheel machine grinding can be easily implemented.

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