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Original title: Drilling, reaming, reaming, boring, honing, broaching … Drill through the hole! ☞ This is Article 9972 posted by Metalworking (mw1950pub) Guided reading Hole is an important surface on box, bracket, sleeve, ring and disk parts, and it is also a surface often encountered in machining. In the case of the same requirements for machining accuracy and surface roughness, it is more difficult to machine holes than to machine cylindrical surfaces, resulting in low productivity and high cost. Productivity is low and costs are high because: 1. The size of the tool used for hole machining is limited by the size of the hole to be machined, and the rigidity is poor, so it is easy to produce bending deformation and vibration; 2. When a hole is machined with a fixed-size cutter, the size of the hole is often directly determined by the corresponding size of the cutter, and the manufacturing error and wear of the cutter will directly affect the machining accuracy of the hole; 3. When processing holes, the cutting area is inside the workpiece, the chip removal and heat dissipation conditions are poor, and the processing accuracy and surface quality are not easy to control. Common hole processing methods include drilling, reaming, reaming, boring, broaching, grinding and finishing. Below I will give you a detailed introduction to several hole processing processes to solve the problem of hole processing: Drilling and reaming Drilling Drilling is the first process of machining holes in solid materials, and the diameter of the hole is generally less than 80mm. There are two ways of drilling: one is the rotation of the drill; the other is the rotation of the workpiece. The errors produced by the above two drilling methods are not the same. In the drilling method of drill rotation, when the drill is deviated due to the asymmetry of the cutting edge and the insufficient rigidity of the drill, the center line of the hole to be machined will be deviated or not straight, but the hole diameter is basically unchanged. In the drilling method of workpiece rotation, on the contrary, the deviation of the drill will cause the hole diameter to change, but the hole center line is still straight. Two ways of drilling A) Drill rotation B) Workpiece rotation Commonly used drilling tools include: twist drill, center drill, deep hole drill, etc., of which the most commonly used is the twist drill with a diameter specification of Φ0.1 ~ 80mm. The structure of a standard twist drill in which the shank is the holding part of the drill and is used to transmit torque; the shank of the drill is available as a straight shank for small diameter drills and as a taper shank for large diameter drills. Expand the full text Structure of standard twist drill A) Taper Shank B) Straight Shank Due to the limitation of the structure, the bending stiffness and torsional stiffness of the drill bit are low, and the centering is not good, so the accuracy of drilling is low, generally only up to IT13 ~ IT11; the surface roughness is also large, Ra is generally 50 ~ 12.5 μm; but the metal removal rate of drilling is large, and the cutting efficiency is high. Drilling is mainly used to process holes with low quality requirements, such as bolt holes, threaded bottom holes, oil holes, etc. Holes with high requirements for machining accuracy and surface quality shall be reamed, reamed, bored or ground in subsequent machining. Reaming Reaming is the further processing of a drilled, cast, or forged hole with a reaming drill to enlarge the hole diameter and improve the quality of the hole. Reaming can be used as a pre-processing before finishing the hole,dhd drill bit, or as the final processing of a hole with low requirements. Reaming The reamer is similar to the twist drill, but has more teeth and no chisel edge. Reamer Compared with drilling, reaming has the following characteristics: (1) The reaming drill has many teeth (3-8 teeth), good guidance and stable cutting; (2) that ream has no chisel edge and has good cutting condition; (3) The machining allowance is smaller, the chip groove can be made shallower, the drilling core can be made thicker, and the strength and rigidity of the cutter body are better. The reaming accuracy is generally IT11 ~ IT10, and the surface roughness Ra is 12. 5 ~ 6.3 μm. Reaming is often used to machine holes less than 30 mm in diameter. When drilling a hole with a larger diameter (D ≥ 30mm), a small drill bit (0.5 ~ 0.7 times the diameter of the hole) is used to pre-drill the hole first, and then a reaming drill of the corresponding size is used to ream the hole, so as to improve the processing quality and production efficiency of the hole. In addition to machining cylindrical holes, counterbores of various special shapes (also known as drills) can also be used to machine various countersunk seat holes and countersunk end surfaces.
The front end of the drill is often provided with a guide post, which is guided by a machined hole. Countersink Reaming Reaming is one of the finish machining methods of holes, which is widely used in production. For smaller holes, reaming is a more economical and practical processing method than internal grinding and fine boring. Reamer Reamers are generally divided into hand reamers and machine reamers. The handle part of the hand reamer is a straight handle, the working part is longer, and the guiding function is better. Hand reamers are divided into integral type (Figure a) and adjustable outer diameter type (Figure B). Machine reamers can be divided into those with shanks (Fig. C,down the hole bit, Φ1 ~ 20 mm for straight shanks, Φ10 ~ 32 for taper shanks) and those with sleeves (Fig. D). The reamer can be used to machine not only circular holes, but also tapered holes with a taper reamer (Figure e). Reamer Reaming technology and its application The reaming allowance has a great influence on the reaming quality. If the allowance is too large, the load of the reamer is large, the cutting edge is quickly dulled, it is not easy to obtain a smooth processing surface, and the dimensional tolerance is not easy to guarantee. If the allowance is too small, the tool marks left by the previous process cannot be removed, and naturally there is no effect on improving the quality of hole processing. To avoid built-up edges, lower cutting speeds (V < 8 m/min for HSS reamers in steel and cast iron) are usually used for reaming. The value of the feed is related to the diameter of the hole to be machined. The larger the diameter is, the larger the value of the feed is. When machining steel and cast iron with high-speed steel reamers, the feed is usually taken as 0.3 ~ 1mm/R. When reaming, proper cutting fluid must be used for cooling, lubrication and cleaning to prevent built-up edge and remove chips in time. Compared with hole grinding and boring, reaming has high productivity and is easy to ensure the accuracy of the hole, but reaming can not correct the position error of the hole axis, and the position accuracy of the hole should be guaranteed by the previous process. Stepped holes and blind holes are not suitable for reaming. The dimensional accuracy of reaming is generally IT9 ~ IT7, and the surface roughness Ra is generally 3.2 ~ 0.8 μm. For holes with medium size and high precision requirements (such as IT7 precision holes), the drilling-reaming process is a typical processing scheme commonly used in production. Boring Boring is a method of enlarging a preformed hole with a cutting tool. Boring can be done either on a boring machine or on a lathe. Boring method There are three different ways of boring. (1) The workpiece rotates and the cutter makes feeding motion. The process is characterized in that the axial lead of the processed hole is consistent with the rotary axis of the workpiece, the roundness of the hole mainly depends on the rotary accuracy of a machine tool spindle, and the axial geometric shape error of the hole mainly depends on the position accuracy of a tool feed direction relative to the rotary axis of the workpiece. This boring method is suitable for processing holes with coaxiality requirements with the surface of the outer circle. Boring mode of workpiece rotation and tool feed (2) The tool rotates and the workpiece makes feeding motion. The spindle of the boring machine drives the boring cutter to rotate, and the worktable drives the workpiece to feed. (3) The cutter rotates and makes feeding motion. When the boring mode is adopted for boring, the overhang length of the boring bar is changed, the stress deformation of the boring bar is also changed, the aperture close to the spindle box is large, and the aperture far away from the spindle box is small, so that a taper hole is formed. In addition, as the overhang length of the boring bar increases, the bending deformation of the spindle caused by its own weight also increases, and the axis of the hole to be machined will bend accordingly. This boring method is only suitable for machining shorter holes. Boring with both rotary and feed tool 1 — Boring bar 2 — Boring cutter 3 — Workpiece 4 — Worktable 5 — Spindle High speed fine boring (diamond boring) Compared with general boring, diamond boring is characterized by small cutting depth, small feed and high cutting speed. It can obtain high machining accuracy (IT7 ~ IT6) and smooth surface (Ra is 0.4 ~ 0.05 μm). Diamond boring was originally machined with diamond boring tools, but now it is generally machined with cemented carbide, Borehole Drill Bits ,dth drilling hammer, CBN and artificial diamond tools. It is mainly used for processing non-ferrous metal workpieces, as well as iron castings and steel parts.
The commonly used cutting parameters of diamond boring are: The back cutting depth pre-boring is 0.2-0.6mm; The final boring is 0.1mm; The feed rate is 0.01-0.14mm/R; The cutting speed is 100-250m/min when the cast iron is machined; 150-300m/min when steel is processed; 300-2000m/min when processing nonferrous metals; In order to ensure high machining accuracy and surface quality of the diamond boring machine, the machine tool (diamond boring machine) must have high geometric accuracy and rigidity. The spindle of the machine tool is usually supported by precision angular contact ball bearings or hydrostatic sliding bearings. High-speed rotating parts must be accurately balanced. In addition, the movement of the feed mechanism must be very stable to ensure that the worktable can do stable low-speed feed movement. Diamond boring has good processing quality and high production efficiency, and is widely used in the final processing of precision holes in mass production, such as engine cylinder holes, piston pin holes, spindle holes on the spindle box of machine tools, etc. However, it should be noted that when diamond boring is used to process ferrous metal products, only boring cutters made of cemented carbide and CBN can be used, and boring cutters made of diamond can not be used, because the affinity between carbon atoms in diamond and iron group elements is large, and the tool life is low. Boring Cutter Boring cutters can be divided into single-edge boring cutters and double-edge boring cutters. The structure of a single-edged boring tool (as shown in the figure) is similar to that of a turning tool, with only one main cutting edge. When boring a hole with a single-edged boring tool, the size of the hole is guaranteed by the operator adjusting the position of the boring tool head. Single edge boring cutter A) Through hole single blade boring cutter B) Blind hole single blade boring cutter The double-edged boring cutter has two symmetrical cutting edges, which is equivalent to two symmetrically installed turning tools participating in cutting at the same time; the dimensional accuracy of the hole is guaranteed by the size of the boring cutter itself. The floating boring cutter shown in the figure is a kind of double-edged boring cutter. The boring blade is inserted into the groove of the boring bar, and its position is automatically balanced by the back force acting on the two cutting edges, which can eliminate the error caused by the installation error of the boring cutter or the deflection of the boring bar. However, it is similar to reaming, which can only ensure the dimensional accuracy and can not correct the position error of the hole axis before reaming. Floating boring cutter Technological Characteristics and Application Range of Boring Compared with the drilling-expanding-reaming process, the hole size is not limited by the size of the cutter, and the boring process has a strong error correction ability, which can correct the deviation error of the original hole axis through multiple passes, and can keep a high position accuracy between the boring hole and the positioning surface. Compared with external turning, the machining quality and production efficiency of boring are not as good as external turning because of the poor rigidity of the arbor system, large deformation, poor heat dissipation and chip removal conditions, and relatively large thermal deformation of the workpiece and tool. From the above analysis, it can be seen that boring has a wide range of processing and can process holes of different sizes and different precision grades. For holes and hole series with large diameter and high requirements for size and position precision, boring is almost the only processing method. The machining accuracy of boring shall be grade IT9 ~ IT7. Boring can be carried out on boring machines, lathes, milling machines and other machine tools, which has the advantages of flexibility and is widely used in production. In order to improve the efficiency of boring in mass production, boring dies are often used. Honing hole Honing principle and honing head Honing is a method of finishing a hole by using a honing head with a grinding bar (oilstone). When honing, the workpiece is fixed, and the honing head is driven by the spindle of the machine tool to rotate and make reciprocating linear motion. In the honing process, the grinding bar acts on the surface of the workpiece with a certain pressure to cut off a very thin layer of material from the surface of the workpiece, and the cutting track is a cross reticulation. In order to ensure that the motion track of the abrasive grains is not repeated, the number of revolutions per minute of the rotary motion of the honing head and the number of reciprocating strokes per minute of the honing head shall be prime numbers with each other. Principle of honing A) Shaping motion B) Development diagram of abrasive strip grinding trajectory C) Resultant speed The cross angle of the honing path is related to the reciprocating speed and circumferential speed of the honing head, and the size of the angle affects the processing quality and efficiency of honing. In order to facilitate the discharge of broken abrasive particles and chips, reduce the cutting temperature and improve the processing quality, sufficient cutting fluid should be used during honing. In order to ensure that the wall of the hole to be processed can be uniformly processed, the stroke of the sand strip should exceed a section of overtravel at both ends of the hole.
In order to ensure the uniformity of honing allowance and reduce the influence of machine tool spindle rotation error on machining accuracy, floating connection is mostly used between honing head and machine tool spindle. The radial telescopic adjustment of the honing head grinding bar has various structural forms such as manual, pneumatic, hydraulic and the like. Process Characteristics and Application Scope of Honing (1) Honing can obtain high dimensional accuracy and shape accuracy, the machining accuracy is IT7 ~ IT6, and the roundness and cylindricity error of the hole can be controlled within the range of 3 ~ 5 μm, but honing can not improve the position accuracy of the machined hole. ② Honing can obtain high surface quality, the surface roughness Ra is 0.2 ~ 0.025 μm, and the depth of the deterioration defect layer of the surface metal is very small (2.5 ~ 25 μm). ③ Compared with the grinding speed, although the peripheral speed of the honing head is not high (VC = 16 ~ 60m/min), the reciprocating speed is relatively high (va = 8 ~ 20m/min) due to the large contact area between the sand bar and the workpiece, so the honing still has a high productivity. Honing is widely used for machining precision holes in engine cylinder bores and various hydraulic devices in mass production, and can process deep holes with a length-diameter ratio greater than 10. However, honing is not suitable for processing holes on non-ferrous metal workpieces with large plasticity, nor can it process holes with keyways, splines, etc. Pull the hole Broaching and broaching tool Broaching is a highly productive method of finishing. It is carried out on a broaching machine with a special broach. Broaching machine is divided into horizontal broaching machine and vertical broaching machine, with horizontal broaching machine being the most common. During broaching, the broach only moves in a straight line at a low speed (main motion). Generally, the number of teeth of the broach working at the same time shall not be less than 3, otherwise the broach will not work smoothly, and it is easy to produce annular ripples on the surface of the workpiece. In order to avoid breaking the broach due to excessive broaching force, when the broach is working, the number of working teeth should not exceed 6 to 8. There are three different broaching methods for broaching holes, which are described as follows: 1) Layered broaching The characteristic of this broaching method is that the broach cuts off the machining allowance of the workpiece layer by layer. In order to facilitate chip breaking, the cutter teeth are grinded with interlaced chip separating grooves. Broaches designed according to the layered broaching method are called ordinary broaches. Layered broaching A) Broaching pattern B) Profile of cutting part C) Chip 2) Block broaching The characteristic of this broaching method is that each layer of metal on the machined surface is removed by a group of cutter teeth (usually consisting of 2-3 cutter teeth) with basically the same size but staggered cutter teeth. Each blade cuts only a portion of a layer of metal. Broaches designed according to the block broaching method are called rotary broaches. 3) Comprehensive broaching This method combines the advantages of layered and block broaching. Block broaching is used for rough gear cutting and layered broaching is used for fine gear cutting. In this way, the length of the broach can be shortened, the productivity can be improved, and better surface quality can be obtained. A broach designed according to the integrated broaching method is called an integrated broach. Technological characteristics and application scope of broaching 1) The broach is a multi-edge tool, which can complete the rough machining, finish machining and finishing machining of holes in sequence in one broaching stroke, with high production efficiency. 2) The broaching accuracy mainly depends on the accuracy of the broaching tool. Under normal conditions, the broaching accuracy can reach IT9 ~ IT7, and the surface roughness Ra can reach 6.3 ~ 1.6 μm. 3) During hole broaching, the workpiece is positioned by the machined hole itself (the front guide of the broach is the positioning element of the workpiece), and it is not easy to ensure the mutual position accuracy between the hole and other surfaces by hole broaching; for the processing of rotary parts with coaxiality requirements on the inner and outer circular surfaces, the hole is often broached first, and then other surfaces are processed with the hole as the positioning reference. 4) The broach can process not only round holes, but also formed holes and spline holes. 5) Broach is a fixed-size tool with complex shape and high price, which is not suitable for processing large holes. Hole broaching is commonly used in mass production to process through holes on small and medium-sized parts with a hole diameter of Ф10 ~ 80 mm and a hole depth of no more than 5 times the hole diameter. Brief summary Drilling features: poor tool rigidity, difficult chip removal, cutting heat is not easy to discharge.
Reaming features: ① The cutting edge does not need to extend from the excircle to the center, avoiding the adverse effects of the chisel edge and its hard gas; ② Because AP is small, the cutting is narrow and easy to remove; at the same time, the chip groove can be made smaller and shallower, increasing the rigidity of the tool; ③ High productivity, better guidance, more stable cutting; ④ The processing quality of reaming is higher than that of drilling. Reaming features: good tool rigidity, good guidance, less reaming allowance, small cutting force, low VC, less cutting heat, that is, to reduce the heat and deformation of the workpiece, can be used for finishing. In addition, drilling, expanding and reaming can only guarantee the accuracy of the hole itself, but can not guarantee the dimensional accuracy of the distance between holes. This can be ensured by using a fixture or a boring clamp. ☞ Source: Ji Jia Xiao Zhuge ☞ Editor of this article: Jacy ☞ Media cooperation: 010-88379864 Disclaimer: If the video, pictures and text used in this article involve copyright issues,mining drill bit, please inform us at the first time. We will confirm the copyright according to the proof materials you provide and pay the remuneration according to the national standards or delete the content immediately! Disclaimer: If the video, pictures and text used in this article involve copyright issues, please inform us at the first time. We will confirm the copyright according to the proof materials you provide and pay the remuneration according to the national standards or delete the content immediately! Return to Sohu to see more Responsible Editor:. wt-dthtools.com