Research On Shaped Tube Electrochemical Drilling Deep Small Holes

Deep small holes are widely used in the fields of aerospace, weapons, machinery, medical equipment and instruments. Currently, deep holes are mainly machined by mechanical drilling, laser machining, EDM, etc.. However, traditional mechanical machining tend to cause hot deformation and is difficult to manufacture high strength or high hardness materials; while laser machining and EDM may produce recast layer or micro cracks. Shaped tube electrochemical drilling does not have problems like cold work hardening layer, electrode loss, heat recast layer, burrs or flashes, and the processing range is not limited by strength, hardness, toughness, melting point and thermal conductivity of materials. Therefore, it has important research value to use shaped tube electrochemical drilling to manufacture deep small holes.The device for shaped tube electrochemical drilling deep small holes was designed and assembled. In our processing scheme, the workpiece was fixed and the electrode feed was realized by the extrusion of two rollers. The feeding device was controlled by PLC, and different feeding control modes were achieved by programming. Positive electrolyte flow type was adopted and the electrode clamp was designed. In order to improve the machining precision, a rectangular wave pulse power was chosen as the processing power source. A pressure holding structure was built at the outlet of the deep small hole, which could avoid short circuit and improve the processing stability. Sidewall insulation was achieved by using organic coatings of FA-8 resin, which could effectively alleviate the taper problem of deep small holes.Flow field simulation of the machining gap was conducted using COMSOL Multiphysics to analyze the relationship between the inlet pressure and the machining stability. Tests showed that too small or too large electrolyte inlet pressure might lead to deterioration of processing stability, finally determine the inlet pressure of the electrolyte is 0.4MPa.Shaped tube electrochemical drilling of deep small hole was carried out to study the influence rules of current, pulse frequency, duty cycle and feed rate on the quality of machined holes, and the effects of each processing parameter on surface roughness, radial overcut and taper were also analyzed. According to the results, when the feed rate was 0.66 mm/min, the current was 1.5 A, the pulse frequency was 10 kHz and the duty cycle was 0.5, the processing effect was relatively better. A deep hole with average diameter of 196.2 mm, depth of 30 mm, depth to width ratio of 15.3, roughness of 1.081 urn and taper of 0.074 degrees was fabricated. In addition, in the process of lengthened test, processability of FA-8 resin insulation technology in the side wall was explored, and a deep small hole with diameter of 1.939 mm, length of 60 mm, roughness of 1.349 ?m, taper of 0.092° degrees and depth to width ratio of 31 was successfully manufactured.