Dec 03,2025
Balance of multi-cavity mold: simultaneous optimization of runner, cooling and ejection
Multi-cavity molds are the embodiment of efficiency, but they are also a collection of challenges. The core objective is"Balancing"-ensuring that each cavity is filled, cooled and ejected under exactly the same conditions. Any small imbalance can be magnified in mass production into a huge difference in quality and waste.
Balance of the runner system: the cornerstone of packing consistency
Natural equilibrium (geometric symmetry)
H-type layout: the most classic balanced runner, from the main gate to the sub-gate runner length is exactly the same, is the preferred to achieve natural balance.
Radial layout: suitable for moulds arranged in a circle, also can achieve the same flow length.
Limitations: when the number of cavities or mold size is limited, may lead to the total volume of runner is too large, low material utilization.
Artificial Balance (asymmetric runner)
Application: when the cavity can not be arranged into a symmetrical structure (such as"Family mold" or a mold of different products) .
Through accurate calculation and CAE mold flow analysis, the length and diameter of each branch runner were adjusted, and the filling pressure and time of each cavity were balanced by the resistance difference of the runner itself.
Technical Points: manual balancing requires high design accuracy, and is usually only effective for specific materials and process parameters. After refueling or adjusting parameters, the balance may be destroyed.
Cooling system balance: consistency in thermal management
Runner balancing solves the"Fill" problem, but if the cooling is uneven, the product will still warp due to uneven shrinkage.
Parallel loop principle: all the cooling loops around the cavity should be in parallel, rather than in series, to ensure that each cavity can contact the inlet temperature of the coolant.
Symmetrical design: the layout of the cooling circuit should be symmetrical to the center of the mold, the number of waterways, diameter, and the distance from the cavity should be consistent.
Targeted cooling: for products of different weights in the family mold, the cooling of the large product area should be strengthened, and the cooling of the small product area should be weakened, so as to pursue the simultaneous solidification of all products.
The balance of ejection system: the guarantee of movement synchronism
The significance of ejecting balance: if the ejecting of the products in each cavity is not synchronized, the products that have been ejected may be stuck by the products that have not been ejected, resulting in the fracture of the thimble or the deformation of the products.
How to do it:
Roof guide pillar strengthening: increase the number and diameter of roof guide pillars to ensure that the ejector plate does not tilt during movement.
Thimble layout optimization: The thimble should be arranged symmetrically under each product to make the ejecting force uniform.
Independent ejection system: for super large or deep cavity products, we can consider to design independent ejection cylinder for each cavity or area, and control the ejection sequence and speed by program.
Special balance strategy of family mould
Family molds (one mold for different products) are the highest challenge in balancing technology. Its strategy:
Runner design: manual balancing must be used and separate gate sizes designed for each product.
Cooling design: design independent cooling loop for different products, and connect mold temperature machine separately to realize partition temperature control.
Process Window: the process window of the family mold is usually narrow, and the packing curve needs to be finely adjusted to set different packing pressure and time for different products to make up for the difference in flow length and wall thickness.
Conclusion:
Multi-cavity mold balance, is a design from the beginning of the end of the"Absolute fairness" of the pursuit. It requires engineers to use a combination of rheological, thermodynamic and mechanical dynamics knowledge, through the precise simulation of CAE tools and strict control of the manufacturing process, the three systems of runner, cooling and ejection are integrated into a coordinated and efficient production unit, and the scale benefit of 1 + 1 > 2 is finally realized.
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