Special Hollow Drill Bit On The Cutting Performance Of The Design
Hollow drill bit is a more appropriate use of portable tool hole processing tool. However, the hollow drill bit manufacturing process more complicated and can not be processed blind hole, so the use of metal cutting are not common, usually in the processing of large diameter or precious metal workpiece hole or drilling equipment to use when the power is limited . Since there is no standard stereotypes hollow drill bit products, so most of the special materials used in processing need to be developed by the hollow drill bit.
We worked hard for processing the user to develop a special hollow drill bit processing materials. Code of material to be processed U-Mn, the main chemical components include: carbon (0.56% ~ 0.68%), manganese (1.35% ~ 1.65%), silicon (0.2% ~ 0.35%), etc.; material tensile strength ≥ 882N/mm2, higher hardness and wear resistance. The drill bit is used in the 17mm thick material on process? 30 +0.5 mm hole, a portable drilling rig power 30min, drill materials W6Mo5Gr4V2. In the development process of the hollow drill bit, bit by repeatedly adjusting the design parameters and drilling tests to finalize the drill bit geometric parameters: the former angle g = 12 °, after the angle a = 9 °, vice posterior horn of the a1 = 3 ° .
Following on the hollow design of the cutting bit to make a brief analysis of the impact.
1, before the angle change on the impact of drill cutting
Before the impact angle on the cutting force
Front will affect the chip material change in the degree of deformation, so that the cutting force change. Larger chip deformation, cutting force greater; chip deformation smaller, the smaller the cutting force. The current angle is 0 ° ~ 15 ° range of changes, the cutting force correction factor changes the range of 1.18 to 1.
Anterior horn of the durability of the bit
Increase the bit before the corner, the tip will reduce the intensity and volume of heat, will also affect the tip force conditions. The current angle is positive, the tip tensile stress; the current angle is negative, the tip compressive stress. Such as the use of the front is too large, although the increased bit sharp, reducing the cutting force, but the tip tensile stress suffered greatly reduce the tip strength, easy to break. In the cutting tests, many bits are due to excessive damage to the anterior horn. However, due to processing of materials by high hardness and strength, combined with a portable drill spindle and rigidity, low, such as the use of the front is too small, the increase of cutting force during drilling spindle will produce vibration, significant vibration Surface pattern, drill durability will be reduced.
2, after the angle change on the impact of drill cutting
Increase can be reduced after the angular flank and cutting material of friction between, reducing the strain on the machined surface. However, if the horn is too large, it will reduce the edge strength and heat dissipation.
Directly affect the posterior horn of the size of the drill durability. In the drilling process, drill the main form of mechanical abrasion and wear phase transition wear. Consider the mechanical abrasion and wear, when cutting life is certain, after the angle the greater the longer the cutting time available; consideration of phase transformations and wear, horn drill will increase the cooling ability. Bit worn, with the gradual flank wear band widening, cutting power gradually increased, the friction heat will gradually increase, so the bit temperature, when the temperature rose to drill the phase transition temperature, the drill will occur rapid wear.
3, bit design of the grinding process of
Hollow drill small amount of processing volume is small, so the design should take into account the bit processing problems, as commonly used machining equipment and tools used to achieve machining and grinding.
Chip out by the rake face, so the shape of the rake face shape and direct impact on chip performance chip removal. Chip in the process of being out of the rake face extrusion and friction, further deformation. The maximum deformation of the underlying metal chip, and to slip along the rake face, so that a longer length of the bottom chip to form a variety of curl shapes. When using hollow drill bit, hoping the chip into a scrap or ribbon cuttings, in order to facilitate chip removal. To facilitate the processing and grinding, must be designed for the flat rake face, and do not open chip-breaker. Does not require the use of the rake face regrinding.
Hollow drill flank is the side most likely to re-grinding is the fastest surface wear, so the grinding is grinding the hollow drill flank to achieve.
Within the Deputy Vice-flank into outer flank and flank vice. Heavier grinding point of view, re-grinding the inner and outer flank is not easy to achieve, vice, vice flank should be designed so as not re-form grinding.
4, cutting fluid use and the impact on the drill bit cutting
The main characteristics of the hollow drill holes within the core working hours is not cutting, so cutting the hollow drill bit significantly reduced compared to twist drills, drill the necessary power and cutting the heat generated is also small.
High-speed steel drill bit hollow, because of processing zones of temperature on the hardness of a great impact drill, the drilling process must be used coolant temperature (if no coolant, drill wear and tear will start the main phase transition and rapid wear wear). We started using external spray cooling method, but the bit-position horizontal axis machining, cooling fluid into the drill bit blade difficult part of a larger coolant consumption and cooling are not ideal. The re-designed to change the drill spindle structure, the external spray cooling spray into the internal cooling, the cooling liquid from the hollow core drill bits were added, so that the coolant can reach the bit to cut the part, thereby significantly reducing coolant consumption, improved cooling effect.
5, hollow drill bit to use effects
Hollow drill designed to meet the following aspects should also be asked: ① easy to manufacture, to use common tools and common processing tools; ② easy to re-grinding can be carried out using common grinding wheel machine; ③ high efficiency, long service life; ④ low prices.
We basically developed the hollow drill bit to achieve the above requirements. In actual use, the drill durability can be stable up to 50 minutes, diameter tolerance, surface roughness Dengjun meet the design requirements. Because only a re-grinding flank, posterior horn bit easier to control, in the ordinary grinding machine grinding can be easily implemented.
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