Conformal cooling is prevalent in moldmaking. A primary driver of conformal cooling is the ability of a cooling circuit to follow the contour of the plastic molding cavity surface, yielding consistent cooling. Another driver is getting water into places that conventional milling and drilling will not allow. However, both benefits require creativity when it comes to creating complex contours, avoiding dead spots and promoting turbulent flow.
Conformal cooling also remains the top application of additive manufacturing in moldmaking—conformally-cooled 3D-printed mold inserts or additive tooling. Many mold builders have adopted additive tooling to differentiate their mold performance from the competition, but many designers hold onto the subtractive mindset, so the cooling circuits still look very conventional despite eliminating cross-drilled waterline plugs. Here is where additive tooling shines, as it enables limitless design constraints. However, conformal cooling is a delicate balance of creativity and convention. Conventional mold design standards are still important for maintaining design discipline to create highly-efficient cooling circuits.
For example, to maintain consistent cooling across the mold surface, keep cooling circuits consistently spaced apart. It is important to note that cold spots are possible in a mold, which, just like hot spots, can negatively impact molding performance. Consistency is key.
Things start to get interesting when working with circuit profiles because numerous options are available to promote more surface area and turbulent flow. Some profiles have internal grooves to maximize surface area while others have spiraling ramps that promote turbulent flow.
Most of these designs do not consider the build process and create features requiring supports that can restrict the cooling circuit flow or create sharp corners where concentrated stress could cause cracking. Elliptical or elongated cooling circuits are the best option for maximizing flow, achieving optimal thermal transfer and squeezing in between narrow steel sections that need the most cooling .
A controversial cooling circuit design is splitting circuits into several smaller channels and feeding them with a larger circuit from the mold. For example, a great way to minimize the number of circuits in a mold is to use a large inlet (¼-inch or ⅜-inch NPT waterline) that you break off into multiple waterlines and then rejoin at the exit.
However, with this design a circuit can get blocked and go undiscovered until the molder is producing bad parts. When you use a single circuit, you can easily monitor the in-and-out for flow and quickly identify any issues.
Another consideration when using multiple lines is the DMLS powder getting in the lines after a build. Multiple lines make it difficult to determine if all the powder evacuates prior to heat treatment. If the powder gets stuck in the circuit, shops must then scrap the insert. You can mitigate the risk of splitting waterlines internally by limiting the split section to less than one-third of the overall circuit length. This rule of thumb helps to maintain the larger flow and then splits the circuit only in the critical location required, enabling the powder to evacuate without the risk of a blockage.
Once you have an optimal circuit design, conduct a cooling simulation study to confirm effectiveness and then run FEA analysis to confirm the insert’s integrity and sufficient steel conditions for injection pressures. Taking this approach to circuit design identifies the most appropriate solution for the mold design before building the inserts.
Conformal cooling is the process of using coolant channels in plastic injection mold tools which closely follow, or conform, to the shape of the part being molded. They differ from standard cooling channels in that they are not confined to the line-of-sight, straight holes that are created from conventional drilling or milling. Conformal cooling channels follow the twists and turns of complex part designs, and so offer much better cooling efficiency and faster cycle times.
Successful injection molding depends on both uniform heating and cooling of thermoplastic resin. While it’s relatively easy to heat the resin until it’s molten, it’s much more difficult to cool it quickly and at a uniform rate. But this is critical for creating a finished part that’s free from thermal stress and all the defects that it creates – weld lines, warpage, sink marks, etc.
Cooling is also important because thermoplastic resin doesn’t like to be molten for too long. The chemicals rapidly degrade and can quickly become useless.
Once the design has been optimized for efficient cooling, a tool or insert can be printed and post-finished in a matter of days, compared to weeks for conventional tools. The process also consumes less raw material.
Finished part quality using this type of tool can be far superior, with fewer molding defects. And because the tool heats and cools more quickly, cycle time is reduced. This can be a real cost savings for high volume production, and can more than make up for the cost of the tool in the long term.
In a typical mold, cooling is achieved by passing a fluid through channels inside the mold so that the heat is conducted out of the plastic part, through the metal tool and into the fluid in the cooling channel. Conventional cooling channels are machined in straight lines using machining operations like drilling or milling, which severely limits the reliable cooling equally across the mold.
This is where conformal cooling comes into play. It is an innovative technology that elevates the cooling channels to a different level and is transforming the die and mold-making industry.
In terms of production time reduction, the cooling phase which accounts for nearly 70 percent of the molding process, typically determines the length of the overall cycle time. Conformal cooling can reduce the cooling time to up to 40 percent depending on the part complexity.
If thorough engineering analysis such as flow analysis, computational fluid dynamics and finite-element analysis are further applied before designing the conformal cooling channels, cycle time can be further reduced.
In addition to increased productivity, the new technology can also improve product quality by minimizing warpage and shrinkage of plastic parts. This results in decreased scrap and promotes better surface quality of plastic parts.
These benefits help to achieve cost efficiency in the long run. As the chart below shows, even though the fixed costs of conventional tooling are low compared to conformal cooling, you will be able to achieve profit earlier due to cycle time reduction.
In a typical mold, cooling is achieved by passing a fluid through channels inside the mold so that the heat is conducted out of the plastic part, through the metal tool and into the fluid in the cooling channel. Conventional cooling channels are machined in straight lines using machining operations like drilling or milling, which severely limits the reliable cooling equally across the mold.
This is where conformal cooling comes into play. It is an innovative technology that elevates the cooling channels to a different level and is transforming the die and mold-making industry.