Marginal Problem Of Machining Length Of Micro Holes And Corresponding Solutions
Jan 22, 2019


Gun drill represents advanced and efficient hole processing technology. One of the main processing directions is to process deep holes with a diameter of less than 40 mm and a large aspect ratio. The common hole depth is 10-150 times of the tool diameter. With the advancement of tool and machine tool technology, gun drills are more and more used in the processing of micro deep holes below 3 mm. In the processing of oil pump nozzles, medical instruments, mold barrels, special cutters, hydraulic and other industries, gun drill systems are typical processing means of small diameter deep holes and precision shallow holes. At present, in the processing of water-cooled holes of special cutters, surgical instruments and moulds, micro-diameter deep holes with super-large aspect ratio are more common.


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German TBT integral carbide gun drill (_1.4mm; _1.7mm)

      In the process of gun drilling, with the increase of the ratio of length to diameter and the decrease of diameter, the difficulty of processing will increase in varying degrees. Because of the processing principle of gun drill system, the need of automatic forced chip removal and the unique technological structure, the machining elements such as tool rigidity, cutting hydraulic force flow rate and zero length of auxiliary mechanism of machine tool are highly demanded in the processing of deep holes with large aspect ratio. Especially when the hole is less than 3 mm, the performance is particularly prominent. The data show that under the same pressure level, the unit time flow rate of cutting oil reaching the cutting zone through the cooling passage of gun drill pipe will decrease nonlinearly when the drilling depth exceeds 40 times of the length-diameter ratio, which is only 60%-70% of the normal level. The chip breakage, chip removal and tool lubrication in the process of machining are different greatly. Beneficial impact.


     When the diameter is less than 3 mm, especially when the hole is less than 2 mm, the ultimate processing depth is about 30-40 times longer than the length-diameter ratio. The whole carbide gun drill with imported brand welding-free technology is used with all the cutters (both the cutter head and the cutter stem are carbide). The maximum unsupported hanging length of the drill pipe allowed by the cutter is usually about 60-80 times of the diameter of the cutter.

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        In order to obtain better safety and reliability in the case of larger processing depth when processing diameter is less than 3 mm, the following suggestions are proposed:


1. Consider two-way feeding or two-time clamping and turning to drawing depth dimension.

2. Integral carbide gun drill is adopted, which is divided into two stages to reduce the processing difficulty of the second stage long cutter.

3. Ensuring the uniformity and consistency of the material structure during machining can greatly improve the tool life and processing efficiency, and reduce the tool accidental breakage rate.

4. Under the current technological and technological conditions, the maximum effective length of the universal carbide tool rod that can be customized globally (excluding no chip removal groove and reinforcing section) has great limitations, such as that the diameter of 1.5 mm will not exceed 500 mm, which also becomes an important condition to limit its maximum drilling depth, and there should be no mass customization and processing examples.

5. Special machine tools should be used to ensure the effective length of the cutter rod as small as possible through the design of the box and drive handle structure in the special machine tools.


          When the processing diameter is more than 3 mm, the ultimate processing depth is generally about 150 times of the length-diameter ratio. The tools used are welded carbide gun drills, and the support distance of the drill pipe is usually about 40 times of the diameter of the tool. For the processing of holes above this specification, high quality welding gun drills can be made. The drill depth corresponding to the specification of the tool, using the drill pipe support, can be processed to the required dimension depth at one time.


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