What is the cycle time in injection molding?
Cycle time: Injection molding is a comprehensive process, which is related to the time of each procedure. So it directly affects the thermal history and time of the force acting on the polymer solids melt. And the product affects the product quality and production efficiency.
In the molding cycle, the main part is the injection holding time, cooling time, mold opening time, and demolding time. A complete cycle is composed of closing the door-closing the mold-injection holding pressure-screw measurement-cooling-opening the mold-ejecting the product-opening the door to take the parts (there is no option for fully automatic).
The molding cycle directly affects labor productivity and equipment utilization. Therefore, in the production process, the relevant time in the molding cycle should be shortened as much as possible under the premise of ensuring quality. In the entire molding cycle, the injection time and cooling time are the most important, they all have a decisive impact on the quality of the product. The filling time in the injection time is directly inversely proportional to the filling rate, and the filling time in production is generally about 3-5 seconds. The holding pressure time in the injection time is the pressure time for the plastic in the cavity. This accounts for a large proportion of the entire injection time, generally about 20-120 seconds (extra-thick parts can be as high as 5-10 minutes).
(1) Injection time
Injection time includes injection melt filling time and pressure holding time. The Injection mould filling time refers to the time taken by the screw to move forward quickly to push the plasticized melt into the mold and fill the cavity, generally 3 to 5 seconds. For products with high melt viscosity and fast cooling rate, the fast injection should be used to reduce the melt filling time.
Holding pressure time refers to the residence time after the screw is moved forward and injected. That is, the time for the melt to enter the mold cavity to cool down and to be filled by the injection pressure. This period of time accounts for a larger proportion of the total injection time, generally about 20 to 120 seconds. If the shape of the part is simple and the size is small, the holding time is short; when the large part has a large wall thickness, the holding time is long.
(2) Cooling time
cooling time refers to the cooling and solidification time of the product after the melt is filled. The length of the cooling time is related to the thickness of the product. The properties of the raw material, and the mold temperature. Generally, the product does not cause deformation when demolding, and the shorter the time, the better. The cooling time of the product is generally in the range of 30 to 120s.
The following formula expresses the total cycle time t for injection molding.
Formula 19 t = td + ti + tc
Whereas:
td: intermediate time
The sum of the time required to open and close the mold (referred to as the dry cycle in injection molding), to remove the molded product from the mold, to place inserts in the mold, and to apply a parting agent.
ti: injection time
The sum of the time required to fill the mold cavity with molten polymer and to replenish the mold with material to avoid voids and sink marks.
tc: cooling time
The time required to coagulate the molten polymer in the cavity and to cool to a temperature and solidify within the mold so that the ejector pins will not cause deformation or strain in the molded product during part release.
It is a complete time taken to produce a product. It includes Injection Time, Refilling Time, and Cooling Time. Basically, it’s the time between Mould close and Mould open in a production cycle.
