The injection cycle of an oil pressure drove injection molding machine refers to the period from the beginning of mold closing to the end of the next mold closing. Injection molding is a cyclic process. The molding cycle is mainly composed of material storage time, injection pressure holding time, cooling time, mold opening and closing time, and ejection and withdrawal time. In this process, the cooling of the product and the measuring and storing of the screw is carried out at the same time, and the larger value of the two is taken in the calculation of the molding cycle (the cooling time generally includes the storing time).
Storage time and injection holding time shall be determined according to polymer properties, product shape, and quality requirements (appearance, size, etc.). It is related to many factors such as injection pressure, injection rate, screw rotation, back pressure, and temperature, and the shortest time should be sought under the premise of ensuring quality. When estimating the storage time of injection parts, 65-85% of the maximum plasticizing capacity (g/s) of the injection molding machine is generally taken. The injection process is usually divided into three stages (slow – fast-slow).
The formula is：
T=W/20~50%V + t
T: Total injection time;
W: Total amount of glue shot (the unit weight of the product is X) + the weight of the nozzle);
V: Maximum injection speed of the injection molding machine;
T: Timebase required for starting and stopping of the screw;
The holding time starts after the cavity is filled and ends at the end of the holding time. The length of holding time generally depends on the requirements of the product for appearance shrinkage, size, and deformation. Cooling time refers to the time from the end of holding pressure to the opening of the mold. The length of cooling time is affected by the shape of the product, the thickness of the wall, the design of cooling water for the mold, the temperature of the mold, the properties of the melt, and other factors. The cooling time should be shortened as far as possible on the premise of obtaining a better quality. When the product is fixed, the design of cooling water is the key factor affecting the cooling time.
The opening and closing time is affected by the machine, mold structure, and other factors. The core-pulling structure (row position), opening and closing rack drive mechanism and three-plate mold (fine nozzle) mechanism will affect the opening and closing time. Generally, the opening and closing times are 4~8S for 80T~200T, 6~10S for 200T~500T, and 8~15S for 500T~1000T.
The ejection time is affected by ejection speed, ejection stroke, and ejection method (automatic, manual, and mechanical hand). Automatic ejection is generally only used for products with low appearance requirements (internal parts) or small size, and the ejection time is generally 0.5-2s. When the product is picked up by the mechanical hand, the mold can start to close the moving parts after the product leaves the mold range. The time of item extraction is generally 3~8S, which is 1~3S slower than manual product extraction.