1. Gate: generally, 3-point or 6-point is used for balance. For micro gears, usually single point is used.
2. Mold cavity: usually for 1~4 cavities. Small gear can reach 6 or 8 cavities; Different shapes of gears could be 3 cavities. The most representative is 4 cavities.
3. Ejection: normally use center ejector sleeve and ejector pin. For the helical gear, a bearing must be added to assist the ejection. The position of the bearing has two types: on sleeve needle and sleeve core.
4. Parting surface tube location block: The parting surface tube location block must be installed with cylindrical parting surface tube location block.

5. In the precision of the ejector sleeve, ejector pin or the small center insert pin of the key position, the design accuracy usually requires a coaxiality of 0.02mm, and some of them have higher requirements. In addition, the upper end of the central ejector pin or insert pin should be designed as a cylindrical straight tube position, and insert the upper mold insert to position it to achieve a higher coaxiality of the front and rear mold gate positions.

6. The core and inserts are designed as cylindrical in order to ensure the coaxiality of the product. Material is generally selected SKD61, hardened to HRC52~56.
SKD61 is preferred because:
a. After the material is hardened, the heat treatment margin is small, and the cost and time are naturally saved in semi-finishing;
b. After hardening, the wear resistance is high, and the gear is demolded without draft angle, so wear resistance is naturally important;
c. As mold steel, with the temperature change, the steel performance is stable, suitable for long-term precision injection molding;
d. After hardening, the wear resistance is good, especially for POM decomposing formaldehyde gas.

However, if the hardness requirements are higher, cold work steel materials such as SKD51 and SKD11 will also be used. The core insert (needle) can be 8407.

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