First we need to understand the basic process, which is having a mold core or cavity created typically on a high-quality machine and placed in the molding machine. The mold is heated up, the plastic resin is injected, and the mold is cooled. The finished part is then ejected from the mold and the process is repeated.

This particular video is showing a molding machine with the core and cavity opening. You can see the plastic part being ejected from the cavity. Obviously, that is the objective of every molding process: to create a molded part.

Traditionally, if you get into low-temperature and high-temperature molding, problems are associated with both. Low-temperature molding results in a short molding time. In addition, you get into resin flow issues because you are trying to get the resin to flow at a low mold temperature. You tend to use higher pressure to force the resin through the mold. The risks are that you get weld lines because of the blending or flow. You get poor surface finish and, of course, because of higher pressures, you get potentially more flash.

This is a video that shows what happens with low mold temperatures. It shows rather quickly the potential of producing weld lines. In contrast, in high-temperature molding, one of the difficulties or problems that you have is that a longer molding time is going to cost you time with the part. However, you can mold at a lower pressure so there's less flash. It is also believed that you could have a longer tool life and your cavity will last longer. You get good resin flow because of the higher temperatures, which means that you are typically going to have better product appearance. However, the risks with a higher temperature could lead to the potential for product warping. You can get some sink marks and with warping comes some dimensional rejects and problems.

In this particular clip, you can see that at a higher flow there is no weld line. But it takes a longer amount of time to heat up the cavity and consequently much longer to cool down.

A traditional manufacturer of cores and cavities of mold heating and cooling method was achieved by straight-line drilled holes in the core and cavity. The reason they were very easy to manufacture was because of very limited mold complexity and production time, which meant that was the lowest-cost method of producing the cores and cavities. However, note that the distance to the molding surface varied dramatically to the actual surface of the cavity, so it resulted in unbalanced surface temperatures. You will notice here that the delta T or the heat transfer of the large heat area is much closer and is very high compared to the very thick area of the cavity of the small T.

Here is an example of a straight channel kind of a schematic. Notice that the drilled holes are actually the beginning of the heat-up cycle where you will see the cavity. Basically, here comes the temperature trying to heat the mold. You will detect that certain areas of the cavity are very hot when others are still very cool. They are still green, so consequently the surface area of the cavity varies dramatically. Likewise, once the part is molded, we are going to try to cool down the cavity so we can take out the part. You will see again that the temperature can vary dramatically because of the distance between the actual surface of the cavity and the feed lines.

To attack this problem, a lot of mold manufacturers went to what we refer to as a 2D, or two-dimensional method for handling mold heat and cooling. It is more advanced than the traditional drill-straight-holes methodology. Now what you have to do is angle the holes in order to minimize the distance between the cooling holes and the cavity. It is still relatively easy to manufacture, but, in many cases, it means that you have to reposition the mold components to produce the intersecting holes in order to add mold complexity in production time. As a result, that means a 2D mold is going to be a little more expensive than the traditional straight-line mold. However, the distance in the molding surfaces, although it improves, is still unbalanced and you are still going to get differentials and unbalanced mold surface temperatures.

This clip shows a 2D weldless mold. You can see where the holes are and that there is more shape to the contour of the cavity. As we heat up the cavity, even though it is 2D, there are areas of the surface of the mold that get hotter much faster than other areas. As a result, you are going to have a very unbalanced surface finish inside the cavity, which is going to potentially lead to issues with surface finish with weldless and seamless molding.

The optimum solution would be to produce a heating and cooling plate so that it is in the net shape of the mold. With this particular design, you can see that the blue in this is the heating and cooling cross and the cavity will be equal distance. All of the heating and cooling points are a uniform distance from the heat and cool supply and cavity.

Here we have an example of a 3D weldless mold. Note that the mold heats and cools much more uniformly because the supply of the heat and the cooling is uniformly close to the mold surface. Basically what this permits us to do is use steam in order to warm the cavity and use chilled water to cool the cavity. It allows us to provide a much more efficient means of heating and cooling the mold surfaces. It also gives us uniform distance between the heating and the cooling to allow the best possible thermal transfer characteristics. This provides optimal control over the mold surface temperature.

In this case, we've taken a thermograph of the surface of the 3D weldless mold. You'll notice that the entire surface changes temperature relatively uniformly. That means as we're heating the cavity it does so uniformly and once the resin flows in, it flows uniformly, then cools uniformly, preventing seams and weld lines, giving excellent flow and surface characteristics of the part. In order to produce a weldless mold, there's an additional part that's needed. Typically, you have a core and cavity. In a weldless mold, we have an intermediate plate. That plate goes in between the core and cavity to provide flow channels behind the core/cavity, in order to get heating and cooling to the surface of the core.

Here we're looking at a weldless 3D mold taken apart, so you can see the components. The real question becomes, in a 3D wedless mold, how do you manufacture that intermediate plate? It has the molded part features on one side, and the net-shape cooling cavity on the other, where the high-temperature steam and cooling water pass through. That becomes a manufacturing challenge. Here you can see a 3D weldless mold-the core and cavity being placed together with the intermediate plate already in position. This intermediate plate is extremely important to the weldless process. It serves on the one side as the characteristics of the molded part. On the other side, it is the passageway for the hot and cold, to heat and cool the molding surface. It's a critical component, in addition to the traditional core and cavity.

To help ensure the best heat transfer characteristics of the intermediate plate, we want to increase the surface area for heat transfer. In order to do that, we want to increase the fluid flow area, which we do by adding a series of channels consistent with the part profile, maintaining uniform distance from the cooling or heating to the mold surface. This helps increase the fluid flow area, increases the surface area, and heats and cools uniformly.

If you look at this video, you can see the complexity needed for the intermediate plate. You can see all the passageways and surface characteristics.