Mold Cooling Channels

Mold Cooling Channels (Water channels) is one of the important systems in plastic mold, Water Cooling lines plays the role in molding process that could improve distortion, tolerance, cycle time, sink mark, and so on, poor Cooling Channels will never able to got high quality molding parts.

How a part cools has a dramatic effect on part quality and dimensional accuracy.  The ideal part is of uniform thickness cooled in a mold of uniform temperature.  This assures that the part shrinks at the same rate in all directions.  As we move away from the ideal conditions, we induce variable shrinkage in the part.

The areas that freeze first will be pulled on by the areas that shrink last.  This induces molded in stress and warp in the part.  The cooling plots show areas where this will occur.  The cooling quality plot highlights the problem areas in the part.  The Surface Temperature Variance and the Freeze Time Variance plots show the magnitude and areas of differential cooling.

The plots show you where heat tends to stay in a part due to its geometry (Surface Temperature Variance) and its thickness (Freeze Time Variance).  Keep in mind that the Adviser results are ISO thermic.  This means that the walls of the mold are kept at a constant temperature.  This differs from actual conditions in which the tool is coldest near the water lines and warmer between them.

Surface Temperature Variance Results

The Surface Temperature Variance result highlights areas where the part’s geometry will cause local heat concentrations. The high surface temperature variance areas in the part  are usually  interior regions with deep cores.  This is due to the fact that there is not sufficient thermal mass to remove the heat.  Therefore these areas are natural “hot spots” that are difficult to cool.  Bubblers and heat pins are often used to improve the cooling in these areas.

Note that the core pin that forms the inside of the part shown below is hotter than the outside.  This is because it has the same heat load as the outside surface but has less thermal mass.  Also note that it is hotter at the center of the pin.  This is because the sink is at each end of the pin, forcing the hottest area to the center.

Freeze Time Variance Results

The freeze time variance result displays the time required for each element of the model to freeze completely. The Freeze Time Variance results indicate places on the part that might require a redesign, such as reducing the thickness of a wall, or places in the mold that will require additional cooling capacity.

The fastest and first to cool is the thin rim of the part (-2.95).  The second area is the thin area of the tube (0.63).  The third is the thick section of the tube (4.22).  To resolve these issues the flange was thickened and  a flat was added to the thick section to thin that area.  These changes were important to minimize warping and differential shrinkage in this tight tolerance part.

What problems can poor cooling channels quality cause?

• Excessive warping and/or sink  in areas with large cooling variances.
•  Short shots or poor weld line formation in colder areas.
• Increased molded in stresses.

Types of Mold Cooling Channels

Cooling channel configurations can be serial or parallel. Both configurations are illustrated in Figure 1 below.

FIGURE 1. Cooling-channel configurations

Parallel cooling channels

Parallel mold cooling channels are drilled straight through from a supply manifold to a collection manifold. Due to the flow characteristics of the parallel design, the flow rate along various cooling channels may be different, depending on the flow resistance of each individual cooling channel. These varying flow rates, in turn, cause the heat transfer efficiency of the cooling channels to vary from one to another. As a result, cooling of the mold may not be uniform with a parallel cooling-channel configuration.

Typically, the cavity and core sides of the mold each have their own system of parallel cooling channels. The number of cooling channels per system varies with the size and complexity of the mold.

Serial cooling channels

Cooling channels connected in a single loop from the coolant inlet to its outlet are called serial cooling channels. This type of cooling-channel configuration is the most commonly recommended and used. By design, if the cooling channels are uniform in size, the coolant can maintain its (preferably) turbulent flow rate through its entire length. Turbulent flow enables heat to be transferred more effectively. Heat transfer of coolant flow discusses this more thoroughly. However, you should take care to minimize the temperature rise of the coolant, since the coolant will collect all the heat along the entire cooling-channel path. In general, the temperature difference of the coolant at the inlet and the exit should be within 5ºC for general-purpose molds and 3ºC for precision molds. For large plastic molds, more than one serial cooling channels are required to assure Cooling-channel Configuration uniform coolant temperature and thus uniform mold cooling.

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Mold Cooling channels to improve the plastic molding part quality

A single fundamental rule of injection molding is that hot material enters the mould, where it cools rapidly by cooling channels in the mold to a heat at which it stiffens enough to keep the pattern of them. The heat of the plastic mold tooling is for that reason important as it governs a portion of the general molding cycle.

While the melt runs more freely with a hot injection mould tools, a better cool period is required in advance of the solidified molding can be ejected. Alternatively, while the melt stiffens quickly in a cold tool, it might not exactly achieve the extremities of the cavity. A compromise among the 2 opposites must, for this reason, be accepted to gain the perfect molding cycle.

The operating temperature for the mould will hinge on a number of aspects which incorporate the next: model and grade of material to be molded; length of flow within the impression; wall portion of the molding; period of the feed method, etc.

It is often found helpful to utilize a somewhat higher temperature than is needed merely to fill the impression, as this tends to improve the surface finish of the molding by minimizing weld lines, flow points and other blemishes.

To hold the required temperature differential among the mould and plastic material, water (or other fluid) is distributed through cooling holes or channels within the plastic mould. These holes or channels are named flow-ways or water-ways and the complete system of flow ways is known as the circuit.

Through the impression filling phase the hottest material should be near the entry point, i.e. the gate, the coolest material could be at the point farthest from the entry. The heat of the coolant fluid, however goes up as it passes through the plastic mould.

Subsequently, to attain an uniform cool rate above the molding surface, it is necessary to locate the incoming coolant fluid next to “hot” molding surfaces and to choose the channels containing “heated” coolant fluid next to “cool” molding surfaces?

Nonetheless, as will likely be seen out of the next few debates, it is not constantly practicable to use the idealized technique and the designer must make use of a fair amount of sound judgment once laying out coolant circuits if avoidably pricey molds are to be avoided.

Items for the flow of water (or other fluids) are in a commercial sense available. These units are basically connected to the mould via manageable hoses, with the unit the mould’s temperature can be kept in close limits. Close heat manipulation is not available using the options strategy where the mold is interconnected to cold water provide.

This is basically the mould designer’s duty to offer suitable water cooling lines design within the mould. In general, the simplest methods are those in which holes are bored longitudinally through the mould. Nonetheless, this is exactly definitely not the best way for a particular mould.

When employing drillings for the flow of the coolant, even so, these mustn’t be positioned too close to the cavity (closer than 15 mm) as this is certainly possible to cause a labeled temp version across the impression, with resultant molding problems.

The design of a water circuit is frequently complicated from the feet that flow ways must not be drilled too close to any a few another hole in the similar mould plate. It shall be recalled that the mould plate has a sizeable amount of holes or recesses, to accommodate ejector pins, guide pillars, guide bushes, sprue bush, inserts, etc.

How close it is safe to the location in a cooling water flow way next to another hole relies to a large extent on the depth of the cooling flow way drilling required. While drilling deep water flow ways, there is a tendency for the bore to wander off its prescribed course. A rule which is often utilized is that for drillings about 149 mm deep the cooling channel really should not be closer than 3 mm to any other hole. For greater water flow ways this allowance is increased to 6 mm.

To get the greatest available situation for just a water circuit, it is a good exercise to lay the cooling circuit in at the earliest possible in the blueprint. The other mould items, for example, ejector pins, guide bushes, etc., can then be located accordingly.

Mold Cooling Channels manufacturing tips

This manufacturing tip is for plastic injection molds that have round inserts with o-rings and cooling channel on the outside.

When we put the insert with the o-ring into the hole in the insert sometimes we damages the o-ring, because the edge in the cooling hole is too sharp and the edge cuts away a part of the o-ring and damaged the o-ring, to avoid this issue we need to add small chamfer to the edge of the cooling hole in the insert plate, when the o-ring comes to the cooling hole the o-ring will not be damaged since the edge area is smoothly.

Below red cycle area, the edge is too sharp, it will damage the O-ring, if we add some chamfer at the pocket of O-ring, this issue could be solved.

Below areas are another type of case, at the open area of the cooling hole has a very sharp edge, this may cut the toolmaker’s hands if touch that area, to avoid this issue we need to add some radius and make this area roundness.

Cooling Chamfer

Step to make radius for this issue,

1. Find a hand grinder machine and choose a grinding pin that is round not a sharp one.

hand grinding machine

2. Checking on the drawing how big fillet you can make, if the fillet is too big maybe the water will go out under the o-ring, in this case, there is 1.5mm from the o-ring to the cooling hole so we can make a radius 1mm fillet all around the cooling hole.

3. Grind the fillet around the cooling hole by hand, be careful so that you don’t damage the surface around the cooling hole, below picture is good cooling chamfer should be.

good cooling channel