In this episode of “AM in 10,” we’re looking at the “how, what and why” of how additive manufacturing can be used in the mould and dye industry, specifically, the additive manufacturing of conformal cooling channels in injection moulding. Knowing when and where to use additive manufacturing (AM) is a key skill for AM designers and engineers. Although AM is currently unable to achieve “mass production”, additive manufacturing can be used successfully, combined with other manufacturing processes. Watch the video or read on to find out more.
Injection moulding and cooling channels
Injection moulding is a common manufacturing method that can be used to achieve mass production of parts. Molten plastic is injected into a mould, which is then cooled, after which the final part is ejected to achieve the final component. A closer look at the injection moulding cycle shows that up to 80 per cent of the time taken to create a part is dedicated to the cooling of the plastic. By adding cooling channels into moulds, the cycle time can be reduced, and create parts more efficiently.
In the traditional method, cooling channels are created by drilling holes in straight lines into the part and a conductive liquid is added through these channels to extract heat from the mould. However, the design freedoms of additive manufacturing mean that we can further improve the cooling and efficiency of these moulds by creating more complex channels.
What is the point of moving to AM instead of conventional cooling channels?
As always in this video series, we first need to answer the question, why? What is the point of moving from conventional cooling channels that are drilled, to additive manufacturing of conformal cooling channels in injection moulding, and adding this extra complexity into the process?
One key reason is that producing cooling channels that conform to the surface can give better cooling results to the part, and this allows us to produce more efficient and cheaper parts.
However, speed and cost are not the only drivers here. By creating a more uniform temperature across the mould, conforming cooling channels made with the AM process allows us to create parts with:
- better surface finish
- better dimensional tolerance and accuracy
- less warping
These three things combined mean that there’s a reduced scrap rate and therefore greater profitability of that mould overall.
Additive manufacturing of conformal cooling channels in injection moulding is generally more expensive overall. However, we don’t necessarily need to create the whole mould from additive manufacturing. We can create inserts to that mould using AM and machine the rest.
Therefore, knowing where and when to use AM is a key part of the overall mould design. We must consider very carefully how we design specifically for AM.
Benefits of AM for conformal cooling
Uniform temperature distribution over the part
Gen3D’s flow module has design accelerators that improve the design of conformal cooling channels. When we’re creating cooling channels, we want to create a uniform temperature distribution over the part. To do that we require a uniform distance of that cooling channel away from a surface. Inside Gen3D’s flow module, we have the simple option to add a conform property to a fluid channel. This means that we can create a uniform distance of that channel away from any surface that we click on.
Above, (and even better in the video), you can see that now that I’ve created this conform relationship, I can drag this fluid channel over the surface and as I’m dragging, we still have this uniform offset away from the surface. This means we will get a uniform cooling distribution over the surface.
Another benefit is the ability to move from just regular circular channels to customised channels such as capsule shapes which means that we can get better cooling across an entire surface.
Above, you can see that we’ve blended from a circular fluid channel into a capsule-shaped channel, and as we create this helix up the cylinder section of this part, we can get good and uniform distribution across the entire surface of this part.
Additional complexity to increase turbulence
Additive manufacturing also allows us to create additional complexity inside the cooling channels. Things, like the ability to add fins or lattice structures in combination with these fluid channels, allows us to increase the turbulence of the fluid going through these channels.
Increased turbulence and movement of the water as it circulates through the conformal cooling channels promotes extra cooling and heat transfer and, again, improves the cooling efficiency of the mould tool itself. This is something that can only be done using additive manufacturing and isn’t possible to produce using conventional cooling methods.
Challenges associated with additive manufactured parts
There are a number of challenges associated with AM parts when it comes to conformal cooling.
Surface finish is one. Additive manufacturing processes such as DMLS which is commonly used for creating these conformal cooling inserts cannot yet produce the surface finishes that are required for end-use parts in injection moulding. Therefore, most DMLS moulds go through post-processing, such as EDM or CNC machining to achieve the required surface tolerances.
This means the cost of the mould tool itself will increase because we’re adding an additional process, the AM process into the workflow of the design.
However, it’s important to consider the total return on investment of the entire mould tool itself.
Let’s say that the additive manufacturing mould tool is 10 to 20 per cent higher in cost to produce compared to the conventional tool. If we can reduce the cycle time by 10 to 15 per cent across the entire cycle of the mould, the return on investment of moving to additive manufacturing can be significant. In fact, using additive manufactured models can be more profitable over the lifetime of that mould.
Another challenge is fouling and the build-up of unwanted material inside of the mould, which reduces the thermal efficiency. With conventional channels that are drilled, as fouling increases, we can run the drill back and remove any material build-up. However, with the conformal nature of AM channels, it can be difficult to go in and remove any of that additional material.
Therefore it’s important when using additive manufacturing mould tools, to use conditioned water that’s been treated before going through the mould. Other techniques such as abrasive flow machining can be used to clean the channels after printing, or if there’s been a buildup of filing material over the mould’s lifetime.
The future of additive manufacturing of conformal cooling channels in injection moulding
My prediction is that there will be more optimisation and automation of the design of these moulds as multi-physics generative design methods come in. We’ll exploit the benefits of multi-scale additive manufacturing in the design of mould tools. We might see the addition of lattice structures or topology optimisation to reduce the material usage and the use of porous materials that can be used for increased venting inside of the mould.
One of the hurdles we have to overcome is education. Many injection mould toolmakers see conventional cooling as the default and are unfamiliar with the advantages of additive manufacturing processes. As education about additive manufacturing grows, we’ll see more toolmakers introduce additive manufacturing into their moulds. This means we’ll see more case studies exploiting the benefits of additive manufacturing in the injection moulding industry.
If you’re interested in learning more about how Gen3D’s flow module can help you design better conformal cooling channels inside of the moulds and dyes, get in contact at www.gen3d.com and one of our applications engineers or sales representatives will happily give you a live demo of the software.