ALLES CNC knows that working with NC machining every day like ours has a deep impression on machining accuracy, but how much do you know about the "tolerance level" used to express machining accuracy?
Today, ALLES CNC decrypts the precision of CNC processing technologies such as truck, milling, planer, grinding, drilling and boring.
Tolerance grade is to determine the grade of dimensional accuracy, which is divided into 20 grades according to national standards. From IT01, IT0, IT1, IT2 to IT18, the bigger the number, the lower the tolerance grade (processing accuracy), the larger the tolerance range (tolerance value), and the less difficult the processing.
According to the different functions of product parts, the processing accuracy needed to be achieved is different, and the processing form and process chosen are also different. This paper introduces the processing accuracy of turning, milling, planer, grinding, drilling, boring and other common processing forms.
According to the different functions of product parts, the processing accuracy needed to be achieved is different, and the processing form and process selection are also different. The machining accuracy of turning, milling, planer, grinding, drilling and boring are introduced.
IT Standard Tolerance Level Table
Note: When the basic size is less than 1 mm, there is no IT14 to IT18.
- 01 -
Workpiece rotation, turning tool in the plane for straight or curve movement of the cutting process. Turning is generally carried out on lathes to process the inner and outer cylindrical surface, end face, conical surface, forming surface and thread of the workpiece.
Turning accuracy is generally IT8~IT7, and surface roughness is 1.6~0.8 um.
1) Rough turning strives to improve turning efficiency by using large cutting depth and large feed without reducing the cutting speed, but the machining accuracy can only reach IT11, and the surface roughness is Ralpha 20-10um.
2) Semi-finish and finish turning should adopt high speed and small feed and cutting depth as far as possible. The machining accuracy can reach IT10~IT7, and the surface roughness is Ralpha 10~0.16 um.
3) High-speed finish turning of non-ferrous metal parts on high-precision lathes with fine-grinded diamond turning tools can make the processing accuracy reach IT7-IT5, and the surface roughness is Ralpha 0.04-0.01 micron. This kind of turning is called "mirror turning".
- 02 -
Milling refers to the use of rotating multi-edged cutting tools to cut workpieces, which is a highly efficient processing method. Suitable for processing plane, groove, various forming surface (such as spline, gear and thread) and special surface of die. According to the same or opposite direction of the main motion speed and the feed direction of the workpiece in milling, it can be divided into forward milling and reverse milling.
The milling accuracy can generally reach IT8~IT7, and the surface roughness is 6.3~1.6 um.
1) Machining accuracy IT11~IT13 and surface roughness 5~20 um in rough milling.
2) Semi-finish milling accuracy IT8-IT11, surface roughness 2.5-10 um.
3) The precision of finishing milling is IT16~IT8, and the surface roughness is 0.63~5 micron.
- 03 -
Planing is a kind of cutting method which uses planing cutter to make horizontal relative linear reciprocating motion to the workpiece. It is mainly used for the shape processing of the workpiece.
Planing accuracy can generally reach IT9~IT7, and surface roughness is Ra6.3~1.6 um.
1) The roughing accuracy can reach IT12~IT11, and the surface roughness is 25~12.5 um.
2) The precision of semi-finish planer can reach IT10~IT9, and the surface roughness is 6.2~3.2 um.
3) The precision of finish planer can reach IT8~IT7, and the surface roughness is 3.2~1.6 um.
- 04 -
Grinding refers to the processing method of cutting redundant materials on workpieces with abrasives and abrasives. It belongs to finishing process, which is widely used in mechanical manufacturing industry.
Grinding is usually used for semi-finishing and finishing. The precision can reach IT8-IT5 or higher. The surface roughness is generally 1.25-0.16 um.
1) The surface roughness of precision grinding is 0.16-0.04 um.
2) The surface roughness of ultra-precision grinding is 0.04-0.01 um.
3) The surface roughness of mirror grinding can be less than 0.01 um.
- 05 -
Drilling is a basic method of hole processing. Drilling is often carried out on drilling machine and lathe, as well as on boring machine or milling machine.
The accuracy of drilling is low, generally only up to IT10, and the surface roughness is generally 12.5-6.3 um. After drilling, reaming and reaming are often used for semi-finishing and finishing.
- 06 -
Boring is a kind of internal diameter cutting technology with tool to enlarge hole or other circular contour. Its application range generally ranges from semi-rough processing to finishing processing. The tool used is usually a single-edge boring tool (called boring bar).
1) Boring accuracy of iron and steel materials can generally reach IT9~IT7, and surface roughness is 2.5~0.16 um.
2) The accuracy of precision boring can reach IT7~IT6, and the surface roughness is 0.63~0.08 um.
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