1. The concept of drilling and the drill bit and drilling characteristics
1.The concept of drilling
The inner hole surface is one of the main surfaces on the part. According to the different role of the part in the mechanical product, the inner hole of different structure has different precision and surface quality requirements..According to the relative connection relationship between holes and other parts, they can be divided into matching holes and non-matching holes; according to their geometric characteristics, they can be divided into through holes, blind holes, stepped holes, tapered holes, etc.; according to their different geometric shapes , Can be divided into round holes, non-round holes, etc..Since the hole processing is the processing of the inner surface of the part, it is difficult to observe and control the processing process, and the processing difficulty is much greater than the processing of open surfaces such as outer round surfaces..The hole processing process mainly has the following characteristics:
(1) Hole processing tools are mostly fixed-size tools, such as drills, reamers, etc. The changes in shape and size caused by tool wear will directly affect the accuracy of the processed hole.
(2) Due to the limitation of the size of the hole to be processed, the cutting speed is difficult to increase, which affects the processing productivity and surface quality.
(3) The structure of the tool is limited by the diameter and length of the hole size, and the rigidity is poor.
(4) During hole processing, the tool generally works in a semi-closed space, which makes it difficult to remove chips; it is difficult for the coolant to enter the processing area and the heat dissipation conditions are not good..Drilling is a method of making holes in solid materials with a drill. In the drill press Bu. Drilling, the workpiece is fixed, the drill bit rotates (the spindle movement is called the main movement), while the axis moves downwards (called the feed movement).Due to the poor rigidity and poor orientation of the drill bit structure, it affects the processing quality, and the drilling is rough processing.
2.drill The tools used by fitter to drill are usually drill press and rock drill bits.Drilling machines commonly used by fitters for drilling are: bench drilling machines, straight drilling machines, radial drilling machines, etc..These devices have been introduced before, so I won’t repeat them here..The drill is the main cutting tool used for drilling. It consists of a shank, a neck and a cutting part. The shank is the clamping part of the drill, which is used to connect with the machine tool and play the role of centering and power transmission. The drill shank has There are two types of taper shank and straight shank. Generally, a straight shank with a diameter less than 13mm is a straight shank, which transmits less torque; a taper shank with a diameter greater than 13mm is a taper shank, which can transmit a larger torque.The neck is used for retreating the grinding wheel when grinding the drill bit.The specifications, materials and trademarks of drill bits are generally engraved on the neck.The working part of the twist drill is divided into two parts: cutting and guiding. The working part is the main part of the drill. The front end is the cutting part, which is responsible for the main cutting work. The rear end is the guiding part, which guides the drill and is also the backup for the cutting part. section.The material of the working part is generally made of high-speed steel, the hardness after quenching can reach HRC62-68, and the material of the handle is generally made of 45 steel.The twist drill has two symmetrical spiral grooves, which are used to form cutting grooves, and are used for conveying cutting fluid and chip removal.The cutting part of the front end has two symmetrical main cutting edges, the angle between the two edges is called the front angle, generally 116-118 degrees.The intersection of the two top surfaces is called a chisel.The two blades on the guiding part play a guiding role when cutting, and the fork can reduce the friction between the drill bit and the hole wall of the workpiece.The cutting part of a standard twist drill consists of five edges (two main cutting edges, two secondary cutting edges and one chisel edge) and six sides (two rake faces, two flank faces and two secondary flank faces).
2. Drilling characteristics
When drilling, the drill bit is cut in a semi-closed state, with high speed, large cutting amount, and difficult chip removal. Therefore, drilling has the following characteristics:
(1) The friction is more serious and requires greater drilling force;
(2) A lot of heat is generated, and heat transfer and heat dissipation are difficult, so the cutting temperature is relatively high;
(3) The high-speed rotation of the drill bit and the resulting higher cutting temperature can easily cause serious wear of the drill bit;
(4) Extrusion and friction during drilling are prone to cold work hardening of the hole wall, which makes the next process more difficult;
(5) The drill bit is slender and has poor stability. It is prone to vibration and deviation during drilling;
(6) Low machining accuracy.
Three, drilling operation methods and steps
Correctly draw a line on the surface of the workpiece and punch the sample punch hole. Before drilling, the punch hole in the center of the hole should be punched and then punched a bit larger, so that the chisel edge of the drill bit falls into the cone pit of the punch hole in advance, so that the drill The drill is not easy to deviate from the center of the hole when making a hole.
1.Choice of drilling machine
There are many types of drilling machines, but they can be roughly divided into bench drilling machines, vertical drilling machines, and radial drilling machines..The bench drilling machine is generally used to drill holes with a diameter of D<13mm on small workpieces. It adopts belt drive and variable speed to use five-stage tower wheels. Changing the V-belt in different installation positions of the two tower wheel grooves can make the spindle gain 5 Speed.Vertical drilling machines and radial drilling machines are mainly used to drill holes on larger workpieces. Generally, the maximum drilling diameter is 25, 35, 40, 50mm. The transmission of straight drilling machines is gear transmission..The drilling machine is equipped with positive and negative switches. When the drilling machine is in use, the speed must be stopped before changing the speed. The speed can be adjusted after the standby machine is stopped. Special attention; the fitter is strictly prohibited to wear gloves when using the drilling machine to drill. Female students must wear a work cap.
2.Choice of drill bit
The choice of twist drill is mainly based on two points, one is the diameter of the workpiece to be drilled, and the other is the drilling material.
3.Installation and removal of drill
The straight shank drill bit can be inserted into the drill chuck and tightened with the drill chuck key. The drill chuck cannot be hit to avoid damage to the chuck and the drill press.The taper shank drill bit should be installed when it is consistent with the Morse taper hole of the drilling machine spindle. If the taper is inconsistent, a drill sleeve (taper sleeve) can be used; the taper drill can be removed by an inclined iron blow when disassembling, and the bit cannot be directly hit.
4.Correctly choose the clamping method of the workpiece
Safety accidents in drilling are mostly caused by the wrong clamping method of the workpiece.Therefore, attention should be paid to the clamping of the workpiece.Due to the large cutting force during drilling, the workpiece must be clamped and not loosened.The clamping is closely related to the shape of the workpiece. The clamping method of the workpiece when the fitter is drilling is as follows:
(1) For drilling small parts and thin plate parts, the workpiece can be placed on the positioning block.Bench vise Clamp the workpiece;
(2) For small and flat workpieces or medium-sized parts, flat-nose pliers can be used to clamp. When clamping, the surface of the scribed workpiece should be perpendicular to the drill bit; when the hole diameter is more than 8mm, the flat-nose pliers must be fixed with bolts and pressure plates ;
(3) For workpieces that are drilled on the side of cylindrical workpieces, V-shaped iron can be used to clamp the workpiece. When clamping, the axis of the drill bit should be perpendicular to the symmetry plane of the V-shaped body to ensure that the center line of the drilled hole passes through the axis of the workpiece line;
(4) For large workpieces and other workpieces that are not suitable for clamping with a vise, they can be directly fixed on the drilling machine table with the pressure plate screw;
(5) For large workpieces, in addition to compaction during drilling, jacks should also be used to prevent deformation of the workpieces;
(6) Drilling mold clamping positioning can be used for drilling large quantities of workpieces.
5.drilling
Select the appropriate speed first to check whether the drilling machine is running normally; then slowly cover the drill shaft handle, and align the drill bit with the punch hole that has been drilled in advance, and prepare to start drilling; when starting the drill, wait until the drill bit rotates smoothly before touching the workpiece On the surface, align the drill bit to the center of the hole (sample punching hole), and first try to drill a shallow hole with a diameter of about 1/4, then observe whether the drilling position is correct, such as the drilled cone hole and the drilled hole circle line If you don’t agree, you should take care of it in time.The so-called borrowing means that if the drilled cone pit is less offset from the circle of the drilled hole, the workpiece can be moved (the workpiece is pushed in the opposite direction of the offset while drilling) or the drilling machine spindle can be moved (shaking) When drilling with the arm drilling machine) to borrow the right; if there is a lot of deviation, you can punch a few punches in the positive direction or use the oil groove to chisel several grooves.When drilling, the feed force should not be too large, so as not to skew the axis of the drilling.Frequent drilling and chip removal.When drilling a deep hole, if the depth of the drill bit reaches 3 times the diameter, the drill bit must withdraw once for chip removal. Afterwards, the drill bit must withdraw for chip removal once every certain depth is drilled..Continuous drilling should be prevented, so that the chips will be blocked in the spiral groove of the drill bit and the drill bit will be broken.When the drilling is going to penetrate, the feed must be reduced, if automatic feed is used, it should be changed to manual feed.Add enough lubricating fluid during the drilling process to dissipate heat, cool down the drill bit, reduce friction, improve the processing quality of the hole and extend the service life of the drill bit.When the hole cannot be drilled, the stop limit of the drilling machine can be adjusted according to the required drilling depth. When the required hole depth is not high, the gauge can also be used to limit.The drill bit must be sharpened in time after being blunt.
Fourth, the precautions for drilling
Special requirements:
(1) Before drilling, check whether the equipment is safe and secure, and whether the workpiece is clamped firmly;
(2) When installing the fixture on the workbench or directly installing the work piece, the chips and dirt on the work surface must be wiped off, otherwise the fixture or work piece cannot be placed straight;
(3) When drilling, pay attention to the operation, and wear protective glasses when drilling.To prevent drilling chips from damaging eyes;
(4) It is not allowed to wear gloves to operate and use cotton yarn heads. The cuffs must be tightened to prevent the drill from curling up the gloves and hurting fingers; female students must wear work caps; small workpieces and thin workpieces cannot be directly supported by hands to avoid injury.
(5) When drilling through holes, iron should be lined under the workpiece to prevent damage to the worktable. When the hole is about to be drilled, the feed force should be minimized;
(6) When the drilling machine spindle speed is changed, the drill bit is changed, and the workpiece is assembled and disassembled, it must be stopped after the machine is stopped;
(7) Use a brush to remove the chips, do not wipe with your hands or blow with your mouth, and must be done after parking;
(8) The head is not allowed to be too close to the rotating spindle, the spindle should be allowed to stop naturally when parking, do not brake by hand, nor can reverse braking.
Five, the method of grinding the standard twist drill
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