The concept of precision gear die


1. Concept and application of precision gear mold

1) Precision gear refers to very high parameter size and performance requirements. Parameters include addendum circle outer diameter, tooth root circle outer diameter, modulus, index circle diameter (also known as common normal), index circle tooth thickness, pressure Angle, helical gear inclination angle, gear ring run-out tolerance, etc.; performance includes material selection and accuracy requirements on other assembly dimensions.

2) In terms of application, representative products such as internal transmission parts of printers and copiers, commonly used are VCD drive brackets. If the gears do not meet the precision requirements, the in and out of the bracket will be unstable, accompanied by vibration or swing With a horrible move and a very loud voice, we can have a perceptual understanding of the precise concept and its necessity.

3) Precision gears are graded in accuracy. The national standard is that the higher the grade, the more precise, and the Japanese standard is that the smaller the grade, the more precise. According to the JIS standard, most precision mold factories can only achieve Grade 4 and Grade 5 gears. The level of 3 plastic gears is already quite high.

2. Types of precision plastic gears:

1) From the axial inclination angle of the tooth: spur gear, helical gear, combined spur gear, combined helical gear and combined spur helical gear. The concept of combination is that spur gears or helical gears are distributed in steps in the axial direction, and injection molded at one time.

2) In terms of transmission, there are two main types: meshing transmission gears and belt transmission gears.

3. Selection of mold embryo:

The accuracy of the mold blank directly affects the manufacturing and injection accuracy of the mold, and also affects the life of the mold. Experience has shown that the accuracy of general mold blanks is generally difficult to meet the requirements of precision gear molds.

4. the selection of plastic materials:

There are two main types: POM and PA (PA+GF%). Other raw materials, such as polysulfone, are not excluded. The most fundamental reason why POM and PA materials are preferred: POM and PA products have good self-lubricating properties.

Other common reasons: good wear resistance, good impact resistance and fatigue resistance; secondly, POM products have high rigidity and excellent creep resistance; PA products have good toughness, and GF% can be added if necessary to enhance their rigidity. Generally, POM gears can be used for meshing transmission, and PA gears are used for meshing transmission with POM gears.