We deal with numerical control machining every day, I believe you must have a deep impression on the machining accuracy, but how much do you know about the "tolerance level" used to express the machining accuracy?
Tolerance level refers to the level to determine the accuracy of the size, which is divided into 20 levels according to the national standards, from IT01, IT0, IT1, IT2 to IT18.
Product parts according to the different functions, the need to achieve different processing precision, the choice of processing form and processing technology is different.This paper introduces the machining accuracy of several common machining forms such as turning, milling, planing, grinding, drilling and boring.
IT standard tolerance grade table
(click the picture to enlarge)
Note: if the basic size is less than 1mm, there is no IT14 to IT18
- 01 -
turning
Workpiece rotation, turning tool in the plane for linear or curve movement of cutting.Turning is generally carried out on a lathe to process the inner and outer cylinder, end face, cone face, forming face and thread of the workpiece.
The turning accuracy is generally IT8~IT7, and the surface roughness is 1.6~0.8 m.
1) the rough car strives to improve turning efficiency by using large cutting depth and large feed without reducing cutting speed, but the machining accuracy can only reach IT11, and the surface roughness is R ° 20~10 ° m.
2) semi-finished cars and fine cars try to use high speed but small feed and cutting depth, processing accuracy up to IT10~IT7, surface roughness R 10~ 0.16nm.
3) on a high-precision lathe, the high speed polishing of the diamond turning tool can make the processing precision reach IT7~IT5, and the surface roughness is R 0.04~0.01 dm-this kind of turning is called "mirror turning".
- 02 -
milling
Milling is the use of rotating multi - edge tool cutting workpiece, is a high - efficiency machining method.Suitable for machining planes, grooves, various forming surfaces (such as splines, gears and threads) and special shapes of molds.According to the direction of main motion velocity and the direction of workpiece feeding the same or opposite, it is divided into forward milling and reverse milling.
The machining accuracy of milling is generally up to IT8~IT7, and the surface roughness is 6.3~1.6 nm.
1) rough milling processing accuracy IT11~IT13, surface roughness 5~20 cm.
2) semi-finishing milling processing accuracy IT8~IT11, surface roughness 2.5~10 cm.
3) precision IT16~IT8, surface roughness 0.63~5 cm.
- 03 -
planing
Planing processing is a cutting method which USES planer to make horizontal relative linear reciprocating movement to the workpiece. It is mainly used for the shape processing of parts.
The machining accuracy is generally up to IT9~IT7, and the surface roughness is Ra6.3~1.6 ° m.
1) roughing machining accuracy can reach IT12~IT11, and surface roughness is 25~12.5 m.
2) the machining precision of semi-finishing plane can reach IT10~IT9, and the surface roughness is 6.2~3.2 m.
3) the precision of fine planing can reach IT8~IT7, and the surface roughness is 3.2~1.6 ° m.
- 04 -
grinding
Grinding refers to the process of excising excess material on the workpiece with abrasives and abrasives.
Grinding is usually used for semi-finishing and finishing with precision up to IT8~IT5 or higher. Surface roughness is generally 1.25~0.16 nm.
1) precision grinding surface roughness is 0.16~0.04 nm.
2) the surface roughness of ultra-precision grinding is 0.04~ 0.01m.
3) the surface roughness of mirror grinding can be less than 0.01μm.
- 05 -
drilling
Drilling is a basic method of hole processing. Drilling is often done on a drill press and lathe, as well as on a boring or milling machine.
The machining accuracy of drilling is relatively low, which can only reach IT10 in general. The surface roughness is generally 12.5~6.3 inch m.
- 06 -
boring
Boring is an inner diameter cutting process that USES a tool to enlarge the hole or other circular contour. Its application range generally ranges from semi-rough machining to finishing. The tool used is usually a single edge boring tool (called boring bar).
1) the boring accuracy of iron and steel materials is generally up to IT9~IT7, and the surface roughness is 2.5~0.16 ° m.
2) the machining accuracy of precision boring can reach IT7~IT6, and the surface roughness is 0.63~0.08 nm.