The highest machining accuracy that can be achieved by turning, milling, planing, grinding, drilling and boring

Machining accuracy is mainly used to characterize the fineness of products, and it is a term to evaluate the geometric parameters of machined surfaces. Machining accuracy is measured by tolerance grade, and the smaller the grade value, the higher its accuracy.

There are 20 tolerance grades from IT01, IT0, IT1, IT2, IT3 to IT18, in which IT01 indicates that the machining accuracy of this part is the highest, and IT18 indicates that the machining accuracy of this part is the lowest. General factory and mine machinery belongs to IT7 grade, and general agricultural machinery belongs to IT8 grade. According to the different functions of product parts, the machining accuracy needs to be different, and the machining form and technology chosen are also different. This paper introduces the machining accuracy that can be achieved by several common machining forms such as turning, milling, planing, grinding, drilling and boring.

1.Turning
The workpiece rotates, and the turning tool moves in a straight line or curve in the plane. Turning is generally carried out on a lathe to process the internal and external cylindrical surfaces, end surfaces, conical surfaces, forming surfaces and threads of workpieces.

The turning accuracy is generally IT8—IT7, and the surface roughness is 1.6-0.8 μ m.

1) Rough turning strives to improve turning efficiency by using large cutting depth and large feed rate without reducing cutting speed, but the machining accuracy can only reach IT11 and the surface roughness is rα 20-10μ m.

2) Semi-finish turning and finish turning should adopt high-speed and small feed and cutting depth as far as possible, and the machining accuracy can reach IT10—IT7, and the surface roughness is rα 10-0.16μ m.

3) High-speed finish turning of nonferrous metal parts with finely polished diamond turning tools on high-precision lathe can make the machining accuracy reach IT7—IT5 and the surface roughness is Rα0.04—0.01μm m. This turning is called “mirror turning”.

2. Milling
Milling refers to cutting a workpiece with a rotating multi-edge tool, which is an efficient processing method. Suitable for machining planes, grooves, various forming surfaces (such as flower keys, gears and threads) and special shapes of molds. According to the same or opposite direction of the main movement speed and the workpiece feeding direction during milling, it can be divided into forward milling and reverse milling.

The machining accuracy of milling can generally reach IT8—IT7, and the surface roughness is 6.3-1.6 μ m.

1) The machining accuracy of rough milling is IT11—IT13 and the surface roughness is 5-20μ m.

2) The machining accuracy of semi-finish milling is IT8—IT11, and the surface roughness is 2.5-10μ m.

3) The machining accuracy of finish milling is IT16—IT8, and the surface roughness is 0.63-5μ m.

3. Planing

Planing is a cutting method that uses a planer to make a horizontal relative linear reciprocating motion on the workpiece, which is mainly used for the shape processing of parts.

Generally, the precision of planing can reach IT9—IT7, and the surface roughness is Ra 6.3-1.6 μ m.

1) Roughing accuracy can reach IT12—IT11, and the surface roughness is 25-12.5μ m.

2) The precision of semi-finish planing can reach IT10—IT9, and the surface roughness is 6.2-3.2 μ m.

3) The precision of finish planing can reach IT8—IT7, and the surface roughness is 3.2-1.6 μ m.

4. Grinding
Grinding refers to the processing method of removing excess materials from the workpiece with abrasive and abrasive tools, which belongs to finishing and is widely used in machinery manufacturing industry.

Grinding is usually used for semi-finishing and finishing, the accuracy can reach IT8—IT5 or even higher, and the surface roughness is generally 1.25-0.16 μ m.

1) The surface roughness of precision grinding is 0.16—0.04μm m.

2) The surface roughness of ultra-precision grinding is 0.04—0.01μm m.

3) The surface roughness of mirror grinding can reach below 0.01μm m.

5 .Drilling
Drilling is a basic method of hole processing. Drilling is often carried out on drilling machine and lathe, or on boring machine or milling machine.

The machining accuracy of drilling is low, generally only reaching IT10, and the surface roughness is generally 12.5-6.3 μ m. After drilling, reaming and reaming are often used for semi-finishing and finishing.

6. Boring
Boring is a kind of inner diameter cutting technology to enlarge holes or other circular contours with tools, and its application range is generally from semi-rough machining to finish machining. The tools used are usually single-edged boring tools (called boring bars).

1) The boring accuracy of steel materials can generally reach IT9—IT7, and the surface roughness is 2.5—0.16μm m.

2) The machining accuracy of precision boring can reach IT7—IT6, and the surface roughness is 0.63-0.08 μ m.

 

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