Everyone is familiar with hole processing, but what is the difference between drilling, reaming, and boring? Today I will talk about it.
DRILLING
- 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 to drill holes: one is drill rotation; the other is workpiece rotation. The deviation caused by the above two drilling methods are not the same. In the drilling method with the drill bit rotating, when the drill bit is deflected due to the asymmetry of the cutting edge and insufficient bit rigidity, the center line of the processed hole will be deviated or It is not straight, but the hole diameter is basically unchanged; while in the drilling method where the workpiece rotates, the opposite is true. The deviation of the drill bit will cause the hole diameter to change, and the hole center line is still straight.
Commonly used drilling tools include twist drills, center drills, deep hole drills, etc. The most commonly used one is twist drills with a diameter of Ф0.1~Ф80mm.
Due to structural limitations, the bending and torsional rigidity of the drill bit are low, and the centering is not good, the drilling accuracy is low, generally only IT13 ~ IT11; the surface is also rough, Ra is generally 50 ~12.5μm; 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, and oil holes. For holes that require high machining accuracy and surface quality, they should be achieved by enlarge drilling, reaming, boring or grinding in the subsequent processing.
- Enlarging the upper part of hole
Enlarging a hole is to use a countersink to further process a hole that has been drilled, cast or forged to enlarge diameter and improve the processing quality of the hole. The enlarging hole process can be used as pre-processing before finishing the hole, or as Final machining of less demanding holes. Countersinks are similar to twist drills, but have more teeth and no chisel.
Compared with drills, countersink has the following characteristics: (1) A countersink has a large number of teeth (3-8 teeth), good guidance, and the cutting is relatively stable; (2) The countersink has no chisel edge and has good cutting conditions; (3) The machining allowance is small, the chip pocket can be made shallower, the drill core can be made thicker, and the strength and rigidity of the tool body are better. The precision of countersink bit is generally IT11~IT10, and the surface roughness Ra is 12.5~6.3. Countersink is often used to process holes with a diameter less than Ф100mm. When drilling a hole with a larger diameter (D ≥30mm), a small drill bit (diameter 0.5~0.7 times of the hole diameter) is often used to pre-drill the hole, and then use the corresponding size of countersink to ream the hole, which can improve processing quality and production efficiency of holes.
In addition to reaming cylindrical holes, you can also use various special-shaped reaming drills (also known as countersink drills) to process various countersunk seat holes and countersinking. The front end of the countersink often has a guide post, which is guided by a machined hole.
REAMING
Reaming is one of the finishing methods of holes, which is widely used in production. For smaller holes, reaming is a more economical and practical processing method compared to internal grinding and fine boring.
- Reamer
Reamers are generally divided into two types: hand reamer and machine reamer. The handle of the hand reamer is a straight shank, the working part is longer, and the guiding effect is better. The hand reamer has two structures: an integral type and an adjustable outer diameter. The machine reamer has two kinds of structures: a shank and a sleeve type. The reamer can not only process circular holes, but also taper holes can be processed by taper reamer.
- Reaming technology and its application
The reaming allowance has a great influence on the quality of reaming. If the allowance is too large, the load of the reamer is large, the cutting edge is quickly blunt, it is not easy to obtain a smooth processing surface, and the dimensional tolerance is not easy to guarantee; the allowance is too small, the machining trace left by the previous process cannot be removed, and naturally there is no effect of improving the quality of hole processing. Generally, the margin of rough hinge is 0.35~0.15mm, and the margin of fine hinge is 01.5~0.05mm.
In order to avoid build-up edge, the reaming is usually processed at a lower cutting speed (v ＜8m/min when processing steel and cast iron with HSS reamer). The feed is related to the diameter of hole to be machined. The larger the aperture, the greater the value of the feed. The feed is usually 0.3~1mm/r when HSS reamer is processing steel and cast iron.
When reaming, it is necessary to use appropriate cutting fluid for cooling, lubrication and cleaning, in order to prevent the generation of built-up edge and remove the chips in time. Compared with hole grinding and boring, reaming has high productivity and easy to ensure the accuracy of the hole; but reaming cannot correct the position error of the hole axis, and the position accuracy of the hole should be guaranteed by the previous process. Reaming is not suitable for machining stepped holes and blind holes.
The dimensional accuracy of the reaming hole is generally IT9~IT7, and the surface roughness Ra is generally 3.2~0.8. For medium-sized holes with high precision requirements (such as IT7-level precision holes), the drilling-enlarging-reaming process is a typical processing plan commonly used in production.
BORING
Boring is a processing method that uses cutting tools to enlarge the prefabricated hole. The boring work can be done on a boring machine or a lathe.
1. Boring method
There are three different processing methods for boring:
- The workpiece rotates and the tool performs feed motion. Boring on a lathe mostly belongs to this boring method. The process characteristic is: the axis line of the hole after machining is consistent with the rotation axis of the workpiece, the roundness of the hole mainly depends on the rotation accuracy of the machine tool spindle, and the axial geometric error of the hole mainly depends on the tool feed direction relative to the rotation axis of the workpiece The location accuracy. This boring method is suitable for processing holes with coaxiality requirements with the outer circular surface.
- The tool rotates and the workpiece performs feed movement. The spindle of the boring machine drives the boring tool to rotate, and the worktable drives the workpiece to feed movement.
- The tool rotates and performs feed motion. This boring method is used for boring. The overhang length of the boring bar is changed, and the deformation of the boring bar is also changed. The aperture near the headstock is large, and the aperture far from the headstock is Small, forming a cone hole. In addition, as the overhang of the boring bar increases, the bending deformation of the spindle due to its own weight also increases, and the axis of the machined hole will be bent accordingly. This boring method is only suitable for processing shorter hole.
2. Diamond Boring
Compared with general boring, diamond boring is characterized by a small amount of back tooling, a small feed rate, and a high cutting speed. It can obtain high machining accuracy (IT7～IT6) and a very smooth surface (Ra is 0.4~ 0.05). Diamond boring was originally processed with diamond boring tools, and now it is generally processed with cemented carbide, CBN and synthetic diamond tools. Mainly used for processing non-ferrous metal workpieces, but also for processing cast iron and steel parts.
The commonly used cutting parameters for diamond boring are: the amount of back-cutting is 0.2~0.6mm for pre-boring, and the final boring is 0.1mm; the feed is 0.01~0.14mm/r; the cutting speed is 100~250m/min when machining cast iron. 150~300m/min for steel and 300~2000m/min for non-ferrous metals.
In order to ensure that diamond boring can achieve high machining accuracy and surface quality, the machine (diamond boring machine) must have high geometric accuracy and rigidity. Machine tool spindle support commonly used precision angular contact ball bearings or hydrostatic sliding bearings, and high-speed rotating parts. It must be precisely balanced; in addition, the movement of the feed mechanism must be very stable to ensure that the table can do a smooth low-speed feed movement.
Diamond boring has good processing quality and high production efficiency. It is widely used in the final processing of precision holes in mass production, such as engine cylinder holes, piston pin holes, and spindle holes on machine tool spindle boxes. But it should be noted that when using diamond boring to process ferrous metal products, only boring tools made of solid carbide and CBN can be used, and boring tools made of diamond cannot be used, because the carbon atoms in diamond have a large affinity with iron group elements , tool life is short.
3. Boring tool
Boring tools can be divided into single flute boring tools and 2F boring tools.
4.Process characteristics and application scope of boring
Compared with the drilling-enlarging-reaming process, the diameter is not limited by the tool size, and the boring has a strong error correction ability. The deviation of the original hole axis can be corrected through multiple passes, and it can make the boring and positioning surface maintain high position accuracy.
Compared with the turning of the outer circle, the boring system has poor rigidity, large deformation, poor heat dissipation and chip removal conditions, large thermal deformation of the workpiece and tools, and the processing quality and production efficiency of the boring are not as good as the turning of the outer circle.
Based on the above analysis, it can be seen that boring has a wide processing range, and can process holes of various sizes and different accuracy levels. For holes and hole systems with larger diameters, high size and position accuracy requirements, boring is almost the only processing method. The machining accuracy of boring is IT9～IT7. Boring can be carried out on machines, such as boring machines, lathes, milling machines, etc. It has the advantages of mobility and flexibility and is widely used in production. In mass production, boring dies are often used to improve boring efficiency.
