Injection mold temperature is one of key factors affecting quality, production efficiency and cost control of injection molding process. During injection molding process, stability and control accuracy of mold temperature have a decisive influence on performance and appearance quality of product.

1. Flow and molding of plastics
Temperature of mold directly affects flow behavior of plastics. In high-temperature molds, viscosity of plastics decreases, fluidity increases, and it is easy to fill mold cavity. However, too high mold temperature may cause plastic to flow too quickly, causing excessive internal stress or flow marks in parts, may even affect mechanical properties and appearance quality of plastic due to thermal degradation. On the contrary, at lower mold temperatures, fluidity of plastics is poor, which may lead to insufficient filling or rough surface of parts.
2. Cooling and shrinkage of parts
Mold temperature determines cooling rate and shrinkage rate of plastic in mold cavity. Speed of cooling directly affects crystallinity of plastic and final structure of product. Too fast cooling may cause greater internal stress inside product, which may lead to quality problems such as warping and cracking; while too slow cooling may cause deformation of product or excessive internal stress. Mold temperature will also affect shrinkage rate of plastic, which in turn affects size and appearance of product.
3. Mold life and maintenance
Excessive mold temperature may cause thermal fatigue and wear of mold, thereby shortening service life of mold. If mold temperature is too low, condensation may occur between plastic and mold surface, resulting in appearance problems such as water marks and poor gloss on the surface of product.

1. Preheating and insulation
Preheating mold before production is an effective measure to ensure stable mold temperature. Preheating can eliminate temperature difference between mold and plastic, allowing plastic to better adapt to mold temperature, while reducing impact of cooling water on mold temperature. For large or complex injection molds, insulation can be performed during production intervals to maintain stability of mold temperature.
2. Control cooling water flow and temperature
Cooling water flow and temperature are important factors affecting mold temperature. Proper adjustment of cooling water flow and temperature can effectively control mold temperature. During production process, cooling water flow and temperature should be checked regularly to ensure that they are within range specified by process to ensure stability and accuracy of mold temperature.
3. Heating and cooling system maintenance
Heating and cooling system is core part of controlling mold temperature. Regular inspection and maintenance of heating and cooling system to ensure its normal operation can avoid mold temperature fluctuations caused by system failures. At the same time, for molds using hot runner technology, special attention should be paid to maintenance and care of hot runner system.
4. Reasonable production plan arrangement
Irrational production plan arrangement may lead to large mold temperature fluctuations. Continuous production is conducive to maintaining stability of mold temperature.

 

1. Optimization of mold cooling system
(1) Number of mold water channels should be as large as possible (uniform mold temperature).

 

(2) Distance between mold water channel and surface of mold cavity should be as close as possible.
(3) Water (oil) in mold should flow along shape of injection molded part.
(4) Arrangement of mold water channel should match shape of mold cavity as much as possible.
(5) Diameter of mold water channel should be as large as possible (water channel aperture is generally 10-14mm).
(6) Distance between water channel and cavity should not be less than 10mm (generally 15-20mm).
(7) Distance between water channels (center distance) is generally 3-5 times diameter of water channel.
(8) Cooling should be strengthened near runner and gate (water should be supplied from near runner).
(9) Temperature difference between inlet and outlet water temperatures should be as small as possible (within 3 degrees).
(10) When wall thickness of injection molded part is consistent, distance between water channel and mold cavity should be same.
(11) When wall thickness of injection molded part is different, cooling should be strengthened at wall thickness.
(12) Cooling water channel should be avoided as much as possible at weld line of injection molded part.
(13) Cooling water channels should also be opened on the inside of slider.
(14) Four corners of square injection molded part should be cooled.
(15) Cooling water channels should also be opened for guide pins/guide sleeves of larger molds.
(16) Distance between cooling water channel and ejector pin hole, screw hole should not be too close (need to be greater than 5mm).
(17) When water channel passes through insert, an "O" type sealing ring should be added (to prevent insert sleeve from leaking).
(18) Increase number of cooling water channel inlets and outlets to shorten length of water flow, reduce temperature difference between inlet and outlet water.
(19) For plastics with poor fluidity (high viscosity) or thin walls, a heating device should be installed.
(20) Cooling of slender cores should use a cooling surround core or use materials with high thermal conductivity (such as beryllium bronze) to make slender cores.
(21) Add a thin copper rod to thicker part (diameter greater than 8mm) inside core, then connect one end of thin copper rod in parallel to cooling water channel in mold plate.
(22) Inlet and outlet water hole interfaces should be located in a position that does not affect mold opening operation, and should be located on same side (behind injection molding machine) as much as possible.
(23) Inlet and outlet holes of small mold water channel should not be too close to avoid difficulties in installing nozzle and fixing water pipe.
(24) Inlet and outlet nozzles of cooling water channel cannot be directly opposite to position of injection molding machine's Green column to avoid difficulties in installing water pipe.
(25) Water inlet should not be opened at position of injection molding part's weld line.
(26) For multi-cavity precision injection molding parts, each cavity should be temperature controlled separately using a mold temperature controller.
(27) Heat insulation boards should be installed on the outside (four sides) and bottom of high-temperature mold (to prevent heat loss).