Molds’ cooling: importance and innovations

In the world of plastic injection molding, cooling is an important part of the process. It consumes the vast majority of the cycle time, and plays an important role in determining the profitability of a part. A cooling system that performs well and reliably for your application means higher quality products, but it is a reality hard to achieve. The pressures to reduce cycle time and increase cost-efficiency are growing more intensely by the day. 

 

Cooling is a critical part of the process. Even the smallest change in temperature can have a great impact on cycle time and the quality of your product. As the polymer melt cools, it tends to shrink towards the core side. The biggest concentration of material is in contact with this side. Therefore, more heat will escape through the core than through the cavity, which is why the core side requires more efficient cooling. If the gradient is too high, warpage is the inevitable result. Mold designers should strive for a differential of no more than 5ºC between the core and cavity. 

Mold cooling can account for more than two-thirds of the total cycle time in the production of injection-molded thermoplastic parts.
Figure 1- Part warpage due to (a) non-uniform cooling in the part, and (b) asymmetric cooling across the part thickness.

The two factors to be considered when thinking about new and innovative cooling cycles are speed and consistency. Shorter cycle times increase part warpage while longer cycle times reduce it, but add to total manufacturing costs. To solve this dilemma, the most employed method to cool the shaped charges faster is the use of cooling channels within the mould. These are used to let a fluid — usually water — flow and carry the heat out. Nowadays, straight channels by CNC machines are the most diffused solution to reduce the cooling time. However, the problem with this technology is that the cooling system does not conform to the part geometry, lowering the overall system efficiency. Consequently, this technical solution results in a relatively long production and lead time, as well as non-uniform cooling rates on the mould surface, causing hot spots as demonstrated in Figure 2.

Figure 2 – Non uniform cooling induced by straight cooling channels made by CNC machine

This last aspect frequently leads to part warpage and excessive deformation, behind acceptable tolerances leading to part scrap. The step forward to improving cooling system performance is represented by conformal channels. Conformal cooling technology is based on additive manufacturing techniques that enable the designing of cooling systems that conform to the geometry of the part. An example is shown in Figure 3. This solution provides a larger surface area for heat transfer between the mould cavity and the cooling channels, resulting in reduced cooling time and a relatively more uniform cooling, leading to less non-conformal parts.

conformal cooling channels
shows hotspots, a cause for warpage and scrap in injection molding production
Figure 3
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QTOOL: A NEW GENERATION OF INSERTS

 

At QTool we create innovative mould inserts that will allow companies to optimize goods’ production in order to lead to a performance in mass production processes never experienced before, and to contribute to reshore manufacturing to Europe and USA.

How?

Taking full advantage of the industry 4.0 tools and making additive manufacturing and conformal cooling benefits more accessible using innovation to break boundaries and leveling up the market.

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