Core drills refer to productive instruments intended for the treatment of the ends of the bosses and holes adjacent to him.
In the form of the processed surface core drills can be divided into the following types:
Cylindrical core drills, are used to increase the diameter of the hole obtained by drilling, casting or by plastic deformation, improving surface roughness and the correction previously obtained the direction of the axis of the hole.
Conical core drills, used for machining of conical holes, to reduce the width of the shear layer, usually have teeth of a spiral direction structureslecture grooves are staggered.
Mechanical Zenker s-counterbores are used for the treatment of zachowania ends of the bosses and recesses in the holes for the head bolts. They usually have a front rail (often interchangeable). It should be noted that the presence of a front rail in this case contributes to system rigidity AIDS and reduces vibration during the cutting process.
Conical core drills — countersink is designed to remove the countersink chamfers. In this case, the tooth is usually taken straight direction.
Combined and special core drills use or for simultaneous processing of multiple surfaces, or holes complex profile.
Since the cylindrical counterboring, find more wide application, let us consider the main provisions for the appointment of the dimensions and design elements, as well as the main directions of improving the design of core drills.
So for standard taper shank core drills of high-speed steel total length L for diameters 12 to 25 mm is in the range from 170 to 260 mm. At the same time, if a core drill is special used for very specific items, with the purpose of increasing the rigidity of the system AIDS its length can be reduced by reducing the length of the working part with regard to the length of countersinking and stock for regrinding.
Width ribbons for core drills with a diameter from 10 to 80 mm is in the range from 0.8 to 2.0 mm, and the magnitude of the reverse taper, respectively, from 0.04 to 0.10 mm PA and 100 mm length of working part. At the same time, the tolerance of the PA diameter D of a vertical drill at the specified interval D is changed from 0.035 to 0.060 mm.
For carbide core drills when machining steel to ensure smoother insertion of the tool into the workpiece it is advisable to use the double grinding of the cutting angles of 30° and 60°. The main work to remove the allowance should be transitional cutting blade angle 30°.
on the Contrary, core drills, used for processing cast iron, you should assign 60°.
Number of teeth of the core drill shall be appointed on the basis of the tool diameter and the material its cutting parts, the magnitude of the allowance and other conditions of processing. Typically, the number of teeth is from three to four. Rarely, removal of large allowances, apply dvuhzubye, and the processing of holes of relatively large diameters megasurya core drills.
the Most simple solution to the question of streghetta of core drills, designed for machining through holes, is the creation of inclination of the cutting blade with a negative angle of 22-25° C, which allows completely abandon flute on the cylindrical part. In this’ case, even at large depths, the entire generated in the process, the chips are freely given in the form of tight spirals in the direction of movement of the core drill. On the contrary, the positive angle of the cutting blade or of the pen of a vertical drill 12° provides chip evacuation back, i.e. against the direction of feed of the tool.
the Optimal value for the tilt angle flute core drills of HSS is the angle of 15-20°.
core drills with a diameter of 40 mm to produce rationally design team with inserted knives. There are many methods of fastening the teeth of a sheath of high-speed steel and hard alloy in the housing of the tool.
core drills with ring shank for diameters above 40 mm perform Assembly.
cutting data when drilling holes with a diameter of 14 mm and a depth of 50 mm in workpieces made of steel 45 hardness HB = 170-229 and cast iron SCH 15-32 hardness HB = 163-229 the average, counterboring the following values:
cutting speed v = 4-6 m/min
the feed per tooth s: = 0,2—0,6 mm/tooth
depth of cut f = 0.3— 0.5 mm on a side.
it Should be noted that the lower value v m/min s mm/tooth mm t is, the smaller the roughness of surface finish and higher accuracy of the hole.
the allowance in excess of 5 mm, the processing is done in two passes using two core drills.
Use of core drills in serial and mass production provides a significant effect in economy of production, but at a unit cost of manufacturing additional tool significantly increases the cost of production.
According to: Gigalo N. I., Kiselev V. V. designing and manufacturing cutting tools