Structural characteristics and application mode of

2022-10-21
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Structural characteristics and usage of BTA Deep Hole Drill

BTA Deep hole drill is a typical structure of internal chip removal deep hole drill. It is improved on the basis of single edge internal chip removal deep hole drill. Its cutting edge is in the shape of double-sided staggered teeth, and the chips are cut from both sides and enter the drill rod discharge hole through the double-sided chip removal hole. BTA Deep hole drill has uniform cutting force distribution, good chip separation and chip breaking performance, stable and reliable drilling, and good straightness of the deep hole drilled

1. Structural characteristics of BTA Deep hole drill

bta deep hole drill has the following structural characteristics:

(1) the tool body is distributed with external blade, medium like artificial limb, leaves constituting floating Christmas tree, beehive and supplies for astronauts in space, internal blade, guide block and two-sided chip removal hole, and is connected with hollow drill pipe through shallow tooth multi head rectangular thread on the tool body

(2) the drill core part is replaced by the inner blade of the fried dough twist drill, which overcomes the shortcomings of the fried dough twist drill, such as long horizontal blade and large axial resistance; Because the drill core is offset by a certain distance relative to the drilling axis, the cutting edge at the drill core is lower than the cutting edge at the center during processing, so a guide mandrel will be formed to make the drill bit have better guidance, which is not easy to deflect during drilling. When the guide mandrel grows to a certain length, it will break itself and be discharged with the chips

(3) the main blade adopts an asymmetric segmented, municipal and county-level measurement department, which generally does not establish the wrong arrangement form of this measurement standard, which can ensure reliable chip separation and avoid cracks when grinding the chip curling groove and chip separation groove with an integral cemented carbide blade

(4) several different grades of cemented carbide can be used as the blade material to meet the different requirements of the structure of each part for wear resistance and strength. For example, the cutting speed of the core part is low, the cutting force is large, and it is easy to collapse under the extrusion of chips. Hard alloy blades with good toughness can be selected; Cemented carbide blades with good wear resistance can be selected for the outer edge of the drill bit

2. Processing principle of BTA Deep hole drill

bta deep hole drill's working condition on the ordinary lathe: the processed workpiece is positioned by the V-shaped iron on the lathe carriage and clamped by the bolt pressing plate. When drilling, the drill pipe is clamped by the special chuck in the spindle and rotates under the drive of the spindle, and the workpiece is fed by the action of the carriage belt. A liquid feeder is installed on the workbench of the machine tool and is sealed and connected with the left end of the workpiece through an O-ring. Pressurized cutting fluid is injected from the liquid inlet of the liquid feeder and flows into the cutting area through the gap between the outer diameter of the drill pipe and the hole wall to cool the tool. The cuttings are discharged from the drain tank from the inner hole of the drill pipe through the liquid outlet of the special chuck together with the cutting fluid. Cutting fluid can be emulsified with a concentration of 5%; Cutting parameters can be selected: v=60 ~ 90m/min, s=0.035 ~ 0.23mm/r. Because the drill pipe is slender and easy to deform, a movable center support is installed on the guide rail of the machine tool, which can support any position of the drill pipe. The liquid feeder is connected with the carriage through the connecting plate, and makes feeding movement with the workpiece

3. Key points of deep hole machining

because deep hole machining has different characteristics and adverse factors from ordinary hole machining, the following points should be paid attention to when using BTA Deep Hole Drilling:

(1) deep hole machining cannot directly observe the cutting condition of the tool, so the chip removal and tool wear can only be judged by listening to the sound, looking at the chip, observing the machine load and cutting fluid pressure

(2) deep hole machining is difficult to dissipate heat, so an effective and reliable cutting heat cooling method must be adopted. (3) It is difficult to remove chips in deep hole machining. If chip blockage occurs, it is very easy to damage the tool. Therefore, the cutting parameters must be reasonably selected to ensure reliable chip breaking and smooth chip removal

(4) the hole is prone to deflection during deep hole machining, so the guiding device and measures should be considered in the structural design of the tool and the liquid feeder

(5) during deep hole machining, the length, poor rigidity and easy vibration of the drill pipe will directly affect the machining accuracy and production efficiency, so it is very important to reasonably select the cutting parameters

among the above problems, chip removal, guidance and cooling are the most important. These problems are solved, which can not only ensure the drilling accuracy, but also prolong the tool life and improve the machining efficiency. Therefore, in the deep hole processing, the following technological measures can be taken according to the specific processing requirements:

(1) pre drill a shallow hole with the same diameter as the drill before drilling, which can play a guiding and centering role during drilling. This step is particularly necessary when machining small holes with high straightness requirements

(2) when installing and debugging the machine tool, try to ensure that the central axis of the workpiece hole coincides with the central axis of the drill pipe

(3) reasonably select the cutting amount according to the workpiece material to control the degree of chip curl and obtain C-shaped chips that are conducive to chip removal. When machining high-strength workpiece, the cutting speed V should be appropriately reduced. The size of the feed rate has a great influence on the formation of chips. On the premise of ensuring chip breaking, a smaller feed rate can be used

(4) in order to ensure chip removal and cooling effect, cutting fluid should maintain appropriate pressure and flow. High pressure and small flow can be used when processing small diameter deep holes; Low pressure and large flow can be used when machining large diameter deep holes

(5) when starting drilling, first turn on the cutting fluid pump, and then start the lathe for cutting; When the drilling is over or there is a fault, stop the tool feeding first, then stop, and finally turn off the cutting fluid pump

4. Deep hole processing example

drill a deep hole with an aperture of 20+0.2mm and a depth of 1500mm on a workpiece with an outer diameter of 100mm and a material of 27SiMn. The surface roughness of the hole wall requires Ra1.6 μ m。 BTA Deep hole drill (20mm in diameter) produced by Chengdu deep hole processing center is selected for processing. The blade brand is yt798, and the drill pipe material is 45 steel (quenching and tempering treatment, HB240 ~ 280); Select cutting parameters: v=60m/min, s=0.21mm/r; The cutting fluid is 5% emulsion, the cutting fluid pressure is 2.5mpa/m2, and the hydraulic pump flow is 80L/min

processing precautions: ① its processing technology is simple, and the end face of the workpiece should be perpendicular to the axis line of the workpiece to ensure reliable end face sealing; ② Before formal processing, a shallow hole with a diameter of 20mm is pre drilled on the hole position of the workpiece, which can play a guiding and centering role during drilling; ③ In order to ensure the machining life of the cutting tool, it is best to adopt automatic feeding and feeding; ④ If the guide sleeves in the liquid feeder and movable center support are worn, they should be replaced in time to avoid affecting the drilling accuracy

the long-term application practice of BTA Deep Hole Drill shows that the workpiece material has a great impact on the deep hole drilling quality and processing efficiency, among which 27SiMn material has the best machinability, followed by 45 steel material; 40Cr material is difficult to process, and it is not easy to form C-shaped chips, which is easy to cause drill pipe blockage and drill bit damage. Therefore, when processing 40Cr material, quenching and tempering treatment (HB240 ~ 260) can be carried out in advance to reduce the processing difficulty. During drilling, pay attention to observe the wear of the back corner of a batch of innovative resources gathered on each blade of the tool. When the wear of the back corner exceeds 0.3mm, it should be re sharpened or replaced with a new drill bit. If it continues to be used, it will increase the cutting force, block the drill pipe and damage the tool

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