Understanding The Importance Of Cooling Times In Injection Molding

Cooling time and cooling rate are two important factors affecting the cost and quality of your injection molding operation. Because over 75 percent of the operation cycle time is attributable to cooling, achieving the right cooling process and rate can be a make or break in your output (defective or defect-free), cost per unit and part ejection. 

For every molding engineer, achieving a shorter cycle time without compromising on part quality should be the top operational KPI. A firm understanding of cooling time and cooling rate brings us one step closer to this. Today’s blog takes a shallow dive to the basic understanding of cooling times and cooling rates, the factors affecting these two parameters and the benefits of attaining faster cooling rates and lower cooling times. 

The cooling stage begins immediately after the holding stage. During injection molding, the cooling stage is where the liquified resin material solidifies into the physical essence of the shape in the mold cavity. Cooling commences when the material exists the injection nozzle. The liquid resin begins to lose the heat that was involved in the injection to the environment and the internal temperature gradually begins to fall. Cooling time should only be estimated after packing and holding has been completed. The cooling process becomes complete when the temperature of the part is no longer falling. At this point the molding operation can be concluded as any further time spent cooling the part is simply an overrun to operation time and costs. 

Cooling Rate 
The cooling rate of any injection molding operation is simply the rate at which the liquified resin loses heat per unit time till it is completely re-solidified. The higher the rate of cooling, the lower the cooling time. Consequently, the injection molding cycle and operational cost will be lower when there is a faster cooling rate. The cooling rate of any injection molded part is dependent on the mold cavity pressure, the mold temperature, the mold surface area, the material thickness and the material used in constructing the mold. 

Cooling Time 
The cooling time is a function of a number of variables. It is defined as the time taken to lower the temperature of the liquified resin to a temperature where it can be ejected. It hinges on factors like cooling rate, material type, heating temperature, holding time, part thickness and injection time. The cooling time begins just after the cavity has been completed and lasts up to the point of ejection.

Achieving Higher Cooling Rates and Lower Cooling Times 
There is an inverse relationship between cooling rate and cooling time. Achieving optimal cooling performance in injection molding will help you in the following ways: 

i.    Reduce operational cost and cost per part
ii.    Lower the chances of part defect and rejections
iii.    Optimize the parts produced per operation 
iv.    Avoid molded-in stress 
v.    Improve dimensional stability 

One of the keys to achieving optimal cooling rates is to tackle heat dissipation and cooling from the plastic old design phase. Ensure that you work closely with your mold experts to determine the best cooling channels and mold temperature parameters. The downside to insufficient mold cooling is the production of defective parts, waste and significantly higher operation costs. Poor mold design and cooling channels can also cause part errors like sinking, warping and shrinking. Generally, the key to achieving the best cooling is to engineer your process to accommodate efficient heat dissipation. This will improve the quality of your molded parts, lower costs (as cooling takes over 75% of the injection molding cycle) and reduce part defects. 

First Part Injection Molding Services in China
FirstPart offers excellent quality, plastic injection molding services for a wide array of plastic part projects in China. We also offer low-volume manufacturing that serve small quantities from 50 to 10000 parts for small and medium scale establishments. Away from low-volume manufacturing, all our factories boast of an always-running mass production capacity for CNC3D printing and PVC injection molding services. Our engineers are always available to advice on the best processes, materials and design optimization to ensure cost-savings, quick turnaround and the production of parts that are 100 percent defect and issue free. Feel free to request a free quote now and submit your design for a free evaluation and contact us on how to get started on your next projects.