Method of improving drilling precision

One, the precision of the line

Because the position accuracy of drilling depends on the accuracy of the marking and the accuracy of the location of the bit relative to the center of the hole, before drilling, we must first familiarize ourselves with the technological requirements of the drawing, determine the working procedure, calculate the technological dimensions of each part and finish the datum plane. Because the line of line has a certain width, the error of the line is usually around 0.2mm, the larger the aperture is, the greater the error. Therefore, in order to improve the marking accuracy, we should select the sharp edge vernier calipers to ensure that the groove marks on the center line of the holes on the workpiece surface are deeper and finer. Crossed prior to a height vernier calibration, according to the position of hole size, draw the cross center line hole with vernier caliper, the lines must be clear and accurate, and once completed, can not be repeated two times of lines crossed, will increase the width of the lines, which does not guarantee the accuracy of the positioning hole center, row after the application of vernier caliper or steel ruler test. In order to reduce the size deviation detection hole center and the standard position, after passing inspection should also take the hole center line as the center of symmetry, draw the size of the hole with a height vernier test circle or test box, as when drilling test line, generally can be divided into 2 3 sizes of the square lattice or round inspection inspection the test box, should be slightly larger than the pore size, small test box should be smaller than the aperture is greater than the transverse edge of the drill. Because it is difficult to locate the center of a circle by using the plan, it is often used to check the box in the work. During the drilling process, the location accuracy is ensured by caliper measuring hole and datum plane. In order to reduce the number of correct position of the bottom hole, shorten the processing time of operation, so, after finished punching line after the eye to carefully check the position accuracy, and correct the deviation in time.

Two. The clamping of the workpiece

Before installing the workpiece, we should first clean the table of the drilling machine, the surface of the fixture and the base surface of the workpiece. Because the phenomenon of tool or workpiece falling down on the work surface often occurs in daily work, resulting in the flatness error of the table, so the stone table is applied before the clamping. The requirements of the workpiece clamping firmly, and with 0 level precision square or 0.02mm level measurement of vertical and horizontal degrees, with shims to adjust, if use clamp clamping the workpiece with the high precision clamp, because in the process of drilling must use vernier caliper measurement tool to measure the position accuracy, in order to facilitate the measurement. The workpiece is clamped in the clamp on the jaw should be higher than a certain size. Due to the problem of drilling accuracy and the elastic deformation of drill bits, the drill bit must be as short as possible when clamping, so as to improve the rigidity and strength of the bit, so as to ensure the accuracy of its location accuracy and dimensional accuracy.

Three. The calibration of the positioning hole

It is an important link to ensure the accuracy of the drilling position. Punching must wear sharp and round, the first vertical punching gently a bit, and then from the angle of the cross line of careful observation, whether in cross point, determine the correct and then hit is large, so that the drill bit accurate centering centering, accurate, in order to ensure drilling position accuracy otherwise it will increase the difficulty and the number of correct reaming.

In the work is often used in an operating method without center punching: mark the line on the workpiece and the inspection and check after the inspection, is directly in the drilling clamp is provided with a tap M4 M6 clamped on a drill chuck, started drilling, carefully observe the coaxiality of the tap and drill tip chuck, if a larger swing re clamping is looking to tap the tip of the cross line alignment, to start drilling drilling, first gently under pressure, there will be a small standard cone pit, pit inspection and inspection of four square tapered edge distance is equal, if there is deviation, corrected repeat the previous work, the cone pit slightly expanded, until in the tolerance range.

Then replace it with a small drill or center drill to drill a small hole. The diameter of the bit is too small, and the strength is weak, so it is easy to break in the process. When drilling and enlarging the deviation, the drill bit is bent and deflected, which leads to the reverse direction to rectify the deviation, which increases the position error of the original hole. Because the center drill can better position and ensure sufficient stiffness and strength, so in the center of drilling bottom hole drill is appropriate.

The bottom hole drilling measurements after passing center drill hole 60o, and again with the position accuracy of inspection or inspection inspection hole of the round square, followed by a larger drill enlarging hole reaming process, if the front process deviation at this time will be corrected, if the offset is small, while in the hole the workpiece to the opposite direction with a force to correct the offset. If the offset should be larger in the opposite direction or center punching with a chisel chisel groove, reducing the cutting resistance, the bit offset, achieve the purpose of correction. Remainder the residual amount of 0.5mm - 1mm in the hole.

Four. The grinding of a bit

In order to ensure its rigidity, strength and guidance performance, standard twist drills produce only minor rear angles of the steering taper and zero degree in the manufacturing process. The friction between the secondary angle and the wall of the hole is serious, which affects the size accuracy and roughness of the hole. Drilling with standard twist drill on a conventional drilling machine is usually IT10 IT11, and the surface roughness is Ra25 - 100 m, so the standard twist drill has no advantage of finishing, and belongs to rough machining tool. If a higher surface roughness is obtained and a higher aperture precision is needed, the geometric parameters of the standard twist drill must be sharpened. Compared with reamers, drill bits have similar characteristics. For example, if there are two main cutting edges and auxiliary cutting edges, the secondary cutting edges are spiral, with edge and chamfering, which can increase the smoothness of cutting. The cutting angle and the surface roughness of the drill are improved and improved with reference to the requirements of the hinge blade. In order to reduce friction between the edge and the hole wall, avoid scraping of the chip to the hole wall, avoid centering instability and vibration during drilling, avoid cutting tumors, reduce cutting deformation and residual area. Basically, there is a condition similar to the hinge edge, so a hole with high precision can be drilled, and the drill can be sharpened from the following aspects:

The first 1 main cutting edge angle unchanged, grinding out second vertex and a cutting edge, the length of the new cutting edge at 3 4mm, second vertex according to the workpiece of different materials in general 50O 75o, after the angle is not too large in 6O 8O, so as to avoid vibration, affect the accuracy of the hole. The angle of both sides of the cutting edge must be symmetrical, so that a rough and finishing joint cutting edge can be formed, which can reduce cutting thickness and cutting deformation, improve the ability of light repair, improve the heat dissipation condition, and improve the surface roughness of holes. Connect the new cutting edge and the edge of the fine oil stone out of arc transition edge R0.2 0.5mm, can increase the cutting edge strength, reduce the residual area height.

2, the width of the front edge of the drill bit is narrowed. According to the diameter of the drill bit, it usually stays between 0.1 and 0.3, and the length is about 4mm - 5mm, so as to increase the side rear angle of the edge and reduce the friction between the edge and the hole wall.

3 the edges of the edges are grate into the edges of the spiral milling cutter. The value of the auxiliary rear angle changes with the diameter of the bit, the greater the diameter, the higher the edge, the larger the rear angle, and vice versa, the better the 4o___8o is. The intersecting between the rear and the worn edge of the blade is used for grinding the circular arc with a fine oil stone. The front and rear face of each cutting edge is lapping with fine oil stone, making the roughness of the cutting edge up to Ra0.4, so as to ensure the higher hole wall smoothness in the drill hole.

4 grinding out the negative edge angle, the general inclination angle of the blade from -10 to -15 degree, making the chip flow to the surface to avoid scratching the hole wall, which is beneficial to improve the surface roughness of the hole.

5 the edge of the largest drilling diameter should be controlled within the nominal range of the aperture.

Five, the reasonable cutting amount of the cutting amount, mainly refers to the cutting speed and feed speed. The reasonable cutting amount directly affects the production efficiency, the machining precision, the surface roughness and the life of the bit.

The main factor that affects the roughness of the hole surface is the feed speed, and the cutting speed is the main factor that affects the life of the bit. Therefore, a reasonable amount of cutting should take into account the factors such as hardness, strength, pore size, depth and roughness of the workpiece.

When the material hardness is high, the strength is large, and the aperture is large, cutting speed is not too high. When the material hardness is low and the strength is small, the cutting speed can be improved correspondingly.

The cutting amount of drilling tool for carbon tool steel, cast steel and alloy tool steel should be reduced by 1/5 to 1/3 than that of common carbon steel. The cutting amount of drilling stainless steel should be reduced by about 1/2, and the feed rate of drilling iron castings should increase by 1/5 while cutting speed should be reduced by 1/5.

During drilling, some materials will produce hardened layer, such as stainless steel, and the feed amount should be larger to reduce the bit wear.

The higher the precision of the hole, the choice of the cutting amount corresponding to smaller, when drilling small holes, the use of manual feed.

Six. Select the appropriate cutting fluid

Because of the contact friction between drill and workpiece, the cutting heat and cutting deformation occur during drilling process, which seriously affects the cutting ability of drill bit, even leads to annealing of bit, so that drilling can not continue, and the production efficiency is reduced. In the drilling process, should according to the different requirements of different properties and accuracy of processing materials, proper selection of cutting fluid, enhance lubrication, avoid cold hardening and achieve better roughness, will greatly improve the cutting force of drill and the service life, but also improve the drilling machining precision and work efficiency.

The general drilling is a rough machining process, and cooling is the main purpose of using the cutting fluid. As a result, 3% - 5% emulsified oil-water solution is often used when processing general holes.

When drilling in a material with high hardness and strength, molybdenum disulfide can be added to the cutting fluid to reduce friction and cutting load.

Drilling on materials with high plasticity and toughness can add a proper amount of mineral oil to the cutting fluid to increase the lubricating ability to avoid the production of the chip.

In order to improve the precision to get better surface roughness, oil and vulcanized cutting fluid should be selected to improve the accuracy of drilling holes.

Seven. Other matters of attention

A drilling machine with higher precision should be selected for drilling. If the radial deviation of the spindle of the drilling machine is larger, the drill can be clamped with a floating drill chuck.

Try to use the new or precision level close to the required bit. The bit is as short as possible to increase