In order to achieve the purpose of standardization, we classify automobile gear hobs according to manufacturing accuracy. The main purpose of dividing the automobile gear hob according to the accuracy grade is to select the appropriate hob more accurately and reasonably. The choice of accuracy grade of automobile gear hob depends on the specific design accuracy requirements of parts. However, the actual results may depend largely on the equipment, preparation and design level, the grinding accuracy and inspection method of automobile gear hob. Control the deviation of hob in the manufacturing process as much as possible. Calibrate the eccentricity of the hob by installing the hole hob on the mandrel. On the bar hob, the surface is the calibration surface.
Usually, the tooth profile error of parts is caused by the deviation of automobile gear hob or the diameter jump of hob installed on gear hobbing machine. In addition, multi head hobs may also be caused by the cogging error of parts. Other deviations of parts are usually caused by machine faults, tools or other reasons. Higher precision automobile gear hobs can not improve these problems.
In foreign countries, involute metal cutting hobs are generally classified according to four standard grades. Single head hobs up to four head hobs are in this standard grade. We use this classification level and method here. The four categories are mainly as follows:
Class A: ultra precision grinding hob
Grade B: industrial fine grinding hob
Grade C: rough grinding hob
Grade D: Industrial rough grinding hob
In production, AA grade hob has higher accuracy than grade a hob. Grade AA hobs have been widely used in production in recent years. When the precision of processed parts is higher or the consistency of products is higher, we suggest to use Grade AA hobs to ensure. Grade AA hob only adopts single head design, and the tolerance is consistent with the standard grade tolerance.
The precision grinding hob of automobile gear is mainly carried out after the hob is quenched and the tool is deformed to improve the machining accuracy of the tool. The precision grinding is mainly carried out after the tool is heat treated to eliminate the quenching deformation and improve the accuracy. They are mainly used for forming hobs. When the part requires tooth profile, the specified class a hob is usually used. Class A and Class AA hobs have very similar tolerances, but Class AA is more suitable for machining applications with higher accuracy. Class B hobs are generally used when the tolerance requirements such as tooth profile are not very high. They are usually semi finished in many cases.
With the progress of manufacturing technology, the precision of grade C hob without fine grinding has been greatly improved. This hob is usually used for the pre machining of gear hobbing process. In many cases, customers will also consider adding shaving process after using these automobile gear hobs to ensure accuracy. However, when the requirements for gear accuracy are not particularly high, it can also be processed directly by C and D hobs.
Like all other industrial products, all auto gear hobs should have suitable accuracy to process different parts. However, there is no unified deviation standard for the deviation standard of automobile gear hob profile, and each manufacturer is also different. In the more mature enterprises that manufacture and use automobile gear hobs, they have established their own deviation standards. However, this is only limited to the needs of the enterprises themselves.