We deal with CNC 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 machining accuracy?
Tolerance level refers to the level of accuracy of the size. The national standard is divided into 20 levels. From IT01, IT0, IT1, IT2~IT18, the higher the number, the lower the tolerance level (machining accuracy), the allowable range of tolerance (tolerance) The larger the value, the smaller the processing difficulty.
According to the different functions of the product parts, the machining precisions that need to be achieved are different, and the selected processing forms and processing techniques 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.
IT standard tolerance scale
Note: When the basic size is less than 1mm, there is no IT14 to IT18
– 01 –
The workpiece rotates and the turning tool performs a straight or curved movement in the plane. Turning is generally carried out on a lathe to machine the inner and outer cylindrical faces, end faces, conical faces, forming faces and threads of the workpiece.
The turning precision is generally IT8~IT7, and the surface roughness is 1.6~0.8μm.
1) Roughing is to improve the turning efficiency by using large cutting depth and large feed rate without reducing the cutting speed, but the machining accuracy can only reach IT11, and the surface roughness is Rα20~10μm.
2) The semi-finished and refined cars should adopt high speed and small feed rate and cutting depth as much as possible. The machining precision can reach IT10~IT7 and the surface roughness is Rα10~0.16μm.
3) On the high-precision lathe, the fine-grained diamond turning tool high-speed finishing car with colored metal parts can make the machining precision reach IT7~IT5 and the surface roughness is Rα0.04~0.01μm. This turning is called “mirror turning”. “.
– 02 –
Milling refers to the use of a rotating multi-blade tool to cut a workpiece, which is a highly efficient machining method. Suitable for processing planes, grooves, various forming surfaces (such as splines, gears and threads) and special shapes of the mold. According to the same or opposite direction of the main moving speed direction and the workpiece feeding direction during milling, it is divided into down milling and up milling.
The machining accuracy of milling is generally up to IT8~IT7, and the surface roughness is 6.3~1.6μm.
1) Machining accuracy during rough milling IT11~IT13, surface roughness 5~20μm.
2) Machining accuracy during semi-finishing milling IT8~IT11, surface roughness 2.5~10μm.
3) Machining accuracy during finishing milling IT16~IT8, surface roughness 0.63~5μm.
– 03 –
Planing is a cutting method that uses a planer to horizontally reciprocate the workpiece horizontally. It is mainly used for the shape processing of parts.
The accuracy of planing is generally up to IT9~IT7, and the surface roughness is Ra6.3~1.6μm.
1) The roughing processing precision can reach IT12~IT11, and the surface roughness is 25~12.5μm.
2) The precision of semi-precision machining can reach IT10~IT9, and the surface roughness is 6.2~3.2μm.
3) Precision machining can reach IT8~IT7 with surface roughness of 3.2~1.6μm.
– 04 –
Grinding refers to the processing method of using abrasives and abrasive tools to remove excess materials on the workpiece. It belongs to the finishing industry and is widely used in the machinery manufacturing industry.
Grinding is usually used for semi-finishing and finishing, with an accuracy of IT8~IT5 or higher, and the surface roughness is generally 1.25~0.16μm.
1) Precision grinding surface roughness is 0.16~0.04μm.
2) Ultra-precision grinding surface roughness is 0.04~0.01μm.
3) The surface roughness of mirror grinding can be less than 0.01μm.
– 05 –
Drilling is a basic method of hole machining. Drilling is often carried out on drill presses and lathes, or on a boring machine or milling machine.
Drilling has a low processing precision, generally only achieves IT10, and the surface roughness is generally 12.5~6.3μm. After drilling, reaming and reaming are often used for semi-finishing and finishing.
– 06 –
Boring is an internal diameter cutting process that uses tools to enlarge holes or other circular contours. Applications range from semi-roughing to finishing. The tools used are usually single-edged boring tools (called masts).
1) The precision of the boring of steel materials is generally up to IT9~IT7, and the surface roughness is 2.5~0.16μm.
2) The precision of precision boring can reach IT7~IT6, and the surface roughness is 0.63~0.08μm.
Post time: Feb-21-2019