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Drilling

The method of making holes in a workpiece with a drill is called drilling. The accuracy of the drilling is generally IT10~IT11, and the surface roughness is Ra50~12.5um, so it can only be roughed and the precision of the hole is not high. Drilling is mainly used for making prefabricated holes before assembly, repair, and tapping.

Drilling equipment and tools

Drilling is done by hole processing equipment and drilling tools.

• Drilling equipment. Commonly used hole processing equipment includes bench drilling machines, vertical drilling machines, radial drilling machines, and hand drills, etc. The structure is shown in the figure.

Among them, the bench drill is abbreviated as bench drill, which is a small type of drilling machine, which generally processes holes with a diameter of less than 12mm.

A vertical drilling machine is abbreviated as a vertical drill. Generally used to drill holes on medium-sized workpieces, the maximum drilling diameter is 25mm, 35mm, 40mm, 50mm.

The spindle speed range and feed rate of the radial drilling machine are large, and the processing range is wide. It can be used for drilling, reaming, reaming, and other hole processing.

When working, the workpiece is installed on the machine base 1 or on the worktable 2 [see Figure(c)], and the headstock 3 is installed on the rocker arm 5 that can move back around the vertical column 4 and can swing along the horizontal rail on the arm reciprocates. Since the main shaft gearbox can move in a wide range on the rocker arm, and the rocker arm can rotate 360° around the column, the main shaft 6 can be adjusted to any position within the machining range of the machine tool. When processing porous workpieces on a rocker drill machine, the workpiece does not move, just adjust the position of the rocker arm and the headstock on the rocker arm.

After the main shaft is moved to the required position, the rocker arm can be locked on the column with an electric expansion brake, and the headstock can be fixed on the rocker arm with an eccentric locking device.

The electric hand drill is a portable electric tool. When assembling large-scale workpieces, when the drilling machine cannot be used for drilling due to the shape of the workpiece or the processing position, the electric hand drill can be used for processing.

The voltage of the electric drill is single-phase (220V, 36V) or three-phase (380V). There are 5 specifications for electric drills using single-phase voltage: 6mm, 10mm, 13mm, 19mm, and 23mm; and three specifications for electric drills using three-phase voltage: 13mm, 19mm, and 23mm. The specification of the electric drill refers to the maximum drilling diameter of 45 steel. For materials such as non-ferrous metals and plastics, the maximum drilling diameter can be larger than the original specifications when drilling.

• Drilling tools. Commonly used drilling tools mainly include flat drills, center drills, twist drills, etc.

Among them: the flat drill bit is a special drill bit with a simple structure and easy to manufacture. The disadvantage is that it has poor guidance and is not easy to remove chips. It is suitable for drilling shallow holes.

The center drill is specially used to drill the center hole on the end face of the workpiece. There are two shapes: one is an ordinary center drill; the other is a double cone center drill with a 120° protective cone.

The twist drill gets its name because the working part of the drill is shaped like a twist. It is the most used and most widely used drilling tool in production. Holes of ф0.1~80mm can be processed with twist drills.

Figure 1-41 shows the structure of a twist drill, which consists of a working part, a neck, and a handle, and is made of high-speed steel. Among them: the working part is composed of the cutting part and the guiding part. The cutting part mainly plays the role of cutting the workpiece. The structure of the cutting part of the twist drill is shown in Figure (c). The guiding part ensures the correct direction of the drill bit when drilling, smoothing the whole wall, and the cutting part. The backup part of the twist drill; the neck of the twist drill is used as an undercut during grinding. The drill’s specifications, materials, and trademarks are also printed on the neck; the shank of the twist drill has two types: straight shank and tapered shank. Generally, drills with a diameter of less than 13mm are made of straight shank [see Figure-(b)], and those with a diameter of more than 13mm are made of taper shank [see Figure(a)]. The shank is the clamping part of the twist drill. It is connected to the main shaft of the drilling machine through a clamp and plays the role of centering and torque transmission.

Drilling operation

The operation steps of drilling are generally scribing, tripping, and drilling of holes.

• Underline. According to the position and size requirements of the hole on the drawing, draw the centerline of the hole on the workpiece, punch the sample in the center, and draw the circumference of the hole according to the diameter of the hole. When drilling a hole with a larger diameter, you should also draw several inspection circles of varying sizes, as shown in Figure (a), so that you can check and correct the position when starting the drill. When the position and size of the drill hole are required to be high, in order to avoid the deviation caused by punching the center sample, you can also directly draw several boxes of unequal sizes with the centerline of the hole as the center of symmetry, as shown in Figure 1- As shown in (b), it is used as the inspection line when drilling, and then the center sample is punched to a large size. In order to accurately center the drill.

• Starting the drill. When starting the drill, start the drilling machine and align the drill bit to the center of the hole to drill a shallow hole, observe whether the drilling position is correct, and continuously correct it so that the shallow hole circumference is coaxial with the scribed circle. During the correction, if the deviation is small, the workpiece can be forced to move in the opposite direction of the deviation while drilling to achieve the purpose of gradual correction; if the deviation is large, as shown in Figure (a), it can be Make a few punches in the correct direction or use an oil groove to chisel several grooves, as shown in Figure (b), to reduce the drilling resistance here and achieve the purpose of correction. Regardless of the method used, the calibration must be completed before the taper pit diameter is smaller than the hole diameter. This is an important part of ensuring the accuracy of the drilling position. Otherwise, if the hole position is still offset, it will be difficult to perform the correction.

• Drilling of holes. When the drilling reaches the required drilling position, the workpiece can be pressed to drill the hole. When feeding, do not use too much force, otherwise, it will easily cause the drill bit to bend and cause the axis to be skewed when drilling, as shown in Figure.

In addition, when drilling small diameter (diameter <4mm) holes or deep holes, the feed force should be smaller, and the drill must be retracted frequently to avoid chip blocking and twisting the drill bit. Generally, when the drilling depth reaches 3 times the diameter, the drill must be retracted to remove chips. When the hole is about to be drilled, the feed force must be reduced. Manual feed is used, and the tool is gently fed until the drill is penetrated to prevent sudden feed If it is too large, it will increase the cutting resistance, cause the drill to break, or cause the workpiece to rotate with the drill and cause an accident. This is especially important for thin workpieces. If you cannot drill a through-hole, you can check whether the drilled depth is accurate through the length of the drill bit and the actual measured size. When drilling holes on the unmachined surface of the workpiece or on the hard surface of the material, the manual feed should be started at the beginning. Holes with a bore diameter greater than 30mm must be drilled twice. First, drill the hole with a drill bit of 0.5 to 0.7 times the hole diameter, and then ream the hole with a drill bit of the required hole diameter.

When drilling, the operating procedures should be strictly followed, and it is strictly forbidden to operate with gloves; when testing is required during the drilling process, the machine must be stopped before testing; when drilling, the handle end (moving pliers body) of the machine tool should be placed on The left side of the drill press workbench to prevent the flat vise from falling and hurting people due to excessive torque.

Method of drilling

When drilling holes on different metal components, different drilling methods should be used in a targeted manner.

• Drill holes in cylindrical workpieces. Drill a hole perpendicular to the axis and passing through the center of the cylinder on the outer circle of parts such as shafts or sleeves. Before drilling, you can use a centering tool (usually a V-shaped iron) to clamp on the drilling machine spindle, align the center of the drilling machine spindle and the center of the V-shaped iron where the workpiece is installed, and fix the position of the V-shaped iron with a pressure block. Then lay the cylindrical workpiece to be drilled in the V-shaped iron and adjust it to be in a horizontal position. After moving the big drill bit to the center of the hole, clamp the workpiece for trial drilling and drilling. If the alignment work is serious and careful, the symmetry between the drilling center and the centerline of the workpiece can be controlled within 0.1mm.
• Drill oblique holes. There are three types of inclined hole drilling: drilling on an inclined surface, drilling an inclined hole on a flat surface, and drilling a hole on a curved surface. They have a common feature: the center of the hole is not perpendicular to the end face of the hole. When drilling, you can cut the drilled part out of the platform or file out of the platform, or mill out the platform with an end mill [see Figure (a)], and then use a small diameter drill or center drill to drill out one Shallow pit or shallow holes can be drilled when appropriate; 3 group drills of the same height can also be used to drill oblique holes [see Figure (b)].

• Drill semi-circular holes. When drilling a semicircular hole, because one side of the drill is forced to deflect to the other side due to the radial force, the drill will bend or break, and the drilled hole will not be vertical. To prevent the above situation, when the semicircular hole is at the edge of the workpiece, two identical workpieces can be drilled together; when the outer part is a semicircular hole, the same material can be used to fill the hole again, as shown in Figure.

When drilling the cross seam screw holes and the hardness of the two materials on both sides of the seam is different, a rigid drill bit (as short as possible) should be used, and the punching hole should be slightly biased to the side of the harder material. When the drill bit has penetrated to a certain depth and has reached the middle of the contact surface on the softer side, then drill the bit into the contact surface.

• Drill double holes. There are 3 common double holes as shown in Figure. Since the two holes are relatively deep or far apart, the drill bit protrudes very long when drilling, it is easy to swing, and it is not easy to center, and it is also easy to bend to make the drilled hole tilt, and the concentricity cannot meet the requirements. At this time, the following methods can be used for drilling.

When drilling the double hole shown in Figure (a), you can first drill the small hole to the depth of the large hole with a shorter drill bit, then use a long small drill bit to finish the small hole, then drill the large hole, and then Spot the bottom plane of the large hole.

When drilling the double hole shown in Figure (b), first drill the upper hole, and then use a large sample punch with an outer diameter that matches the upper hole closely, insert it into the upper hole, and punch out the lower hole Then use the drill bit to align the punch hole to drill a shallow hole at a slow speed, confirm the correctness, and then drill at high speed.

When drilling the double hole shown in Fig(c), a long drill pipe can be made for mass production, the outer diameter of which is a dynamic fit with the upper hole. After drilling the large hole on the upper side, replace the extended drill rod with a small drill bit. The upper hole is used as a guide to drill the lower hole. You can also use the double hole method shown in Figure(b).

Sharpening of drill bits

The purpose of drill sharpening is to regrind the dull or damaged cutting part or regrind to meet the needs of different materials to meet the required geometric parameters so that the drill has good drilling performance. Whether the drill is sharpened correctly or not has a direct impact on the quality, efficiency, and service life of the drill. Manual sharpening of drill bits is carried out on a grinder. The grit size of the generally used grinding wheel is 46~80. When the grinding wheel rotates, the amount of runout must be strictly controlled. The sharpening method is as follows.

• Sharpening of the main cutting edge. When sharpening, use your right hand (or left hand) to hold the head of the drill bit as a positioning fulcrum (or lean on the grinder bracket), and hold the drill shank with your left (or right) hand to make the axis of the drill bit and the cylindrical surface of the grinding wheel The main cutting edge is in a horizontal position and lightly touches the circumferential surface above the centerline of the grinding wheel. Use the hand holding the drill head to apply pressure to the grinding wheel and position the drill to rotate around its axis. The hand holding the drill handle makes the drill rotate clockwise around the axis and swing up and down. The drill bit rotates around its axis in order to grind the entire flank surface, and the up and downswing are to grind a certain relief angle. The movements of the two hands must be coordinated well, and the swing angle must be changed with the subsequent angle because the back angle is not equal at different radii of the drill. Repeatedly sharpen it several times. After one main cutting edge is sharpened, turn 180° to sharpen the other main cutting edge. In this way, the top angle relief angle and the chisel bevel angle can be ground, as shown in Figure.

According to different drilling materials, the specific value of the drill tip angle 2ф can be selected according to Table.

After the main cutting edge is sharpened, check whether the apex angle 2ф is equal to the axis of the double-line drill bit, whether the two main cutting edges are symmetrical and equal in length, and each is a straight line; check whether the relief angle at the upper outer edge of the main cutting edge meets the required value Whether the bevel angle of the chisel edge is accurate.

• Sharpen the chisel edge. When grinding the chisel edge, the relative position of the drill bit and the grinding wheel is shown in Figure. When grinding, first make the back of the blade contact with the grinding wheel, and then rotate the drill bit to gradually move the grinding point to the center of the drill, thereby shortening the chisel edge. The rounded corners of the edge of the grinding wheel for grinding the chisel edge should be small, and the diameter of the grinding wheel should be smaller.

Reaming and countersinking

Reaming is an operation method of using a reaming drill or drill bit to expand the punched or drilled hole on the workpiece. Countersinking is a method of using a countersink drill on the surface of an existing orifice to process a sink or surface of the desired shape. Kind of hole processing method.

• Reaming. When the processed aperture is large, a hole with a smaller diameter can be drilled first, and then a large-diameter hole can be processed by a reaming method to obtain a higher hole processing quality. Commonly used reaming methods include reaming with a twist drill and reaming with a reaming drill. There are two types of reaming drills: high-speed steel reaming drills and cemented carbide reaming drills. Figure (a) is a high-speed steel reaming drill; Figure (b) is a cemented carbide reaming drill.

When reaming, if a twist drill is used to ream the hole since the chisel edge of the drill bit does not participate in cutting, the axial force is small, and the feed is labor-saving. However, because the rake angle at the outer edge of the drill bit is large, it is easy to pull the bit from the drill sleeve. The rake angle at the outer edge of the drill bit should be trimmed to be smaller, and the feed rate should be properly controlled. When reaming a hole with a reaming drill, the feed rate can be selected to be larger.

• Countersink. Machining a counterbore with a certain depth and a larger diameter on the machined hole is called a counterbore. Common twist drills can be used for countersinking, or special cylindrical countersinks, tapered countersinks, or end-face countersinks can be used. The figure shows countersinks and their applications.

When countersinking, the cutting speed should be lower than that of drilling, generally 1/3~1/2 of the drilling cutting speed. At the same time, because the axial resistance of the countersinking drill is small, the feed force should not be too large and should be uniform. When polygonal vibration marks appear on the surface of the counterbore, the processing should be stopped immediately and trimmed in time. In order to control the depth of the countersinking, the feed depth of the drilling machine spindle can be adjusted with the depth gauge and positioning nut on the drilling machine before the countersinking and then locked.

Reaming processing

Reamer. The reamer is the main tool for reaming. The reamer is composed of a handle, a neck, and a working part, as shown in Figure. The structure of the reamer is composed of a working part, a neck, and a handle. The working part has a cutting part and a calibration part. The main structural parameters are diameter (D), cutting cone angle (2ф), rake angle (γ0), relief angle (α0) of the cutting part and the calibration part, the edge width of the calibration part (f), the number of teeth (z), etc.

Reamers can be divided into hand reamer and machine reamer according to different usage methods. Among them: the handle of the hand reamer is made into a square tenon shape so that the wrench or reamer can be inserted, and the reaming can be reamed by rotating the reamer with the wrench or reamer by hand. The working part of the hand reamer is longer, and the entering angle is small, generally 40’~4°; the machine reamer has two kinds of taper handle and straight handle. The machine reamer is characterized by a shorter working part, a longer neck, and a larger entering angle. The entering angle of the standard machine reamer is 15°.

According to the material of the cutting part, the reamer can be divided into two types: high-speed steel reamer and cemented carbide reamer. Generally speaking, the machine reamer is made of high-speed steel, and the hand reamer is made of high-speed steel or high-carbon steel. Reamers can be divided into straight groove reamer, cone reamer, and spiral groove reamer according to different external shapes. A spiral groove reamer is especially suitable for reaming inner holes with key grooves.

A Cone reamer is used for reaming conical holes, as shown in Figure, it is a 1:50 conical reamer used for reaming conical positioning pinholes.

1:10 taper reamer is a reamer used for reaming the holes on the coupling; Morse taper reamer is used for reaming No. 0-6 Morse taper holes, and its taper is approximately 1:20; 1:30 taper reamer is used to ream the taper hole of the sleeve tool.

Reaming operation. Reaming is the finishing process after drilling and reaming. The accuracy of reaming is mainly guaranteed by the structure and precision of the tool. Therefore, when reaming, you should first choose the correct reamer, and then choose the appropriate reaming. Allowance, reaming speed and feed rate, cooling lubricant, etc.

• Choice of the reamer. According to the different operation methods, the reaming is divided into two types: hand reaming and machine reaming. Among them: hand reaming is the reaming made by putting a wrench or reaming bar on the dumpling knife by hand; machine reaming is the machine reaming. Reaming by installing on a drill press or a lathe. Machine reaming is a reaming performed by installing a machine reamer on a drill press or a lathe.

When choosing a reamer, it should be selected according to different processing objects. The following aspects can be considered: If the batch of workpieces with larger holes is larger, the machine dumpling knife should be selected; if the taper hole is reamed, the corresponding choice should be based on the taper requirements and diameter of the hole. Cone dumpling knife; if reaming holes with key grooves, you should choose a spiral groove reamer; if reaming non-standard holes, you should choose an adjustable reamer.

Reaming allowance. Reaming allowance is the machining allowance in the diameter direction left by drilling or reaming for reaming. The machining allowance for reaming should be appropriate. The excessive reaming allowance will load the cutting edge of the reamer tooth. Increase, deformation increase, so that the precision of the reamed aperture size is low, and the surface roughness value is increased; and the margin is too small, the residual deformation in the drilling or reaming process is difficult to correct, and the original cutting traces cannot be removed, which affects the hole the shape accuracy and surface roughness. When reaming with a high-speed steel standard reamer, the reaming allowance is shown in Table.

• Cutting speed and feed rate of machine reaming. When reaming steel parts with high-speed steel reamer, the cutting speed v is 4-8m/min; when reaming cast iron parts, the cutting speed v is 6~8m/min; when reaming copper parts, the cutting speed v is 8~12m /min. When reaming steel and cast iron parts, the feed rate f is 0.5~1mm/r, and when reaming copper or aluminum, the feed rate f is 1~1.2mm/r.

• Selection of cooling lubricant. When reaming, in order to wash away the chips, reduce friction, reduce the temperature of the workpiece and the reamer, and prevent the generation of knife edges, the cooling lubricant should be selected correctly, and the cooling lubricant should be selected according to Table.

Manual reaming method. Manual reaming is a reaming method using manual reaming and manual reaming. A reasonable manual reaming operation can make the reaming accuracy reach the IT6 level.

• Manual reaming tool. Commonly used manual reaming tools include reaming hands and adjustable wrenches, as shown in Figure.

1. Hinged hand. Reamers are commonly known as reamers, which are special tools for clamping reamers and taps and pulling the reamers and taps. There are four commonly used types: fixed type, adjustable type, fixed T-shaped type, and movable handle type. Among them, the adjustable reaming hand can adjust the size of the square hole by turning the right handle or adjusting the screw nail. Within a certain size range, a variety of reamers and taps can be clamped. The T-shaped hinged hand is suitable for use when there is not enough space around the workpiece and the hinged hand cannot be rotated all around.
2. Adjustable wrench. The adjustable wrench is only used when the rotation of the general hinged hand is hindered and there is no flexible T-shaped hinged hand. The size of the wrench should be adapted to the size of the reamer. Large wrenches should not be used to pull small reamers. Otherwise, it is easy to break the reamer.

• Key points of manual reaming. The main points of manual reaming are as follows, as shown in Figure.  

1. The workpiece should be clamped upright, put the reamer into the bottom hole, and correct with a square from two vertical directions. After the direction is correct, press the reamer on the hole with the thumb down. The clamping force for thin-walled workpieces should not be too large to avoid flattening the hole.
2. When trying reaming, put on the reaming hand and use the left hand to press down the reamer and control the direction. Turn the reaming hand steadily with the right hand. After the cutting edge cuts a small section of the cone at the hole, check whether the direction of the reamer is correct. Correct in time.
3. In the process of reaming, the force of both hands should be balanced, the speed of rotating the reaming hand should be even, the reamer should maintain the vertical feed, not swinging left and right, to avoid the appearance of a bell at the orifice or enlarge the aperture. The force should be applied gently during the rotation, not too strong, and the force should be evenly controlled, and pay attention to changing the stop position of each reaming hand to prevent overlapping knife marks due to the reamer often stopping at the same place, so as to ensure a smooth surface.
4. The reamer is not allowed to be reversed, and the knife must be turned forward when retracting to avoid scratching the hole wall and damaging the reamer after the chips enter the blade. When retracting the knife, you must retreat while turning.
5. When reaming a tapered hole, a taper pin should be used to check the reaming depth.
6. Do not turn the reamer hard when it is stuck. The reamer should be withdrawn, the chips should be removed, the hole and the tool should be checked; when the reaming is continued, the feed should be slow to prevent it from being stuck in the original place.
7. For the reaming positioning pinhole, the two assembly parts must be aligned and fixed together. After the bottom hole is drilled by the combined drilling method, the hole will be compared without changing the original state. In this way, positioning accuracy and smooth assembly can be guaranteed. When the taper pinhole and taper pin match requirements are relatively high, first ream with an ordinary taper reamer, leaving a certain margin, and then use a correcting taper reamer for accuracy.
8. A reamer is a finishing tool, wipe it clean after use, and apply engine oil for storage.