Purpose of making viscosity curve is to select an appropriate injection speed, which will not cause a large change in melt viscosity when there are small fluctuations in each parameter. Fluctuation between each mold should be as small as possible to ensure repeatability of product quality.

 

Refer to viscosity curve in the figure above, it can be seen that when injection speed is higher than 55mm/s, viscosity of melt is basically very stable. Therefore, setting injection speed to 65mm/s will ensure consistency of filling process. Slight fluctuation of parameter itself will not cause a great change in the viscosity of melt.
Of course, there are special situations where this optimized speed cannot be used, such as reducing gate halo. In this case, of course, appearance is priority, but optimized speed should be used as a reference for injection curve. For example, start passing gate at a low speed to reduce gate halo, and then quickly increase to this optimized speed.

This test is only required if there are multiple points, such as 2 points or multiple points. Purpose is to check maximum deviation percentage between holes in different filling stages.

 

Unbalanced filling may or may not be accepted, depending on product quality requirements. This information is best determined after appearance of shaping window (Step 4) is completed.

1. If product can be fully packed and molding window is large, check whether product dimensions are within tolerance, if they are, unbalanced filling is acceptable.

2. If molding window is very small, and there are burrs in the cavity that is filled first, but there are short shots or sink marks in other cavities, find out reason for imbalance in filling.

There are usually 4 main reasons for unbalanced filling:

1. Different runner sizes

2. Different gate size

3. Different exhaust sizes

4. Cooling is different, but this reason often has little effect when it is just turned on

There is also an imbalance caused by shearing, especially for 8-cavity cold runner molds.

 

Purpose of pressure drop test is to evaluate pressure loss in different stages of filling. This usually includes machine nozzle, vertical runner, main runner, secondary runner, gate and filling end.

 

Molding process should not use maximum pressure of machine. For example, if maximum pressure of machine is 180 Bar, then maximum pressure required for filling should not reach 180 Bar. If this is the case, it means that screw needs more pressure to reach set injection speed, but it cannot be achieved due to pressure limitations. This situation is called "pressure limitation".
Generally, injection process should not exceed 90% of maximum pressure of machine. In pressure drop curve made, if pressure is "limited" or more than 90% of machine pressure, find steeper section of pressure curve and try to reduce pressure loss here. For example, in picture on the right, pressure drop of secondary flow channel is large, which means that a lot of force is needed to promote flow of plastic in this section. Enlarging diameter of flow channel in this section will help reduce pressure.

 

Forming window is a very important test. Usually this appearance molding window is composed of holding pressure and material temperature (amorphous material), holding pressure and mold temperature (crystalline material).
Appearance molding window will tell you how much space is available to adjust process while getting a product with acceptable appearance. Ideal situation is to have a relatively large molding window. If forming window is relatively small, it will be easier to produce quality defects. For example, in the above figure, if forming window is relatively small, it is easier to have short shots or burrs due to fluctuation of process itself. A robust process is to have a relatively large forming window to compensate for fluctuations in process itself.
Appearance molding window will also provide upper and lower limits of material temperature/mold temperature, holding pressure allowed to be used in subsequent mold test due to adjustment of size or DOE test.

 

For cold runner molds or semi-cold runners (hot to cold), in order to ensure repeatability between molds, holding pressure must continue until gate is completely cooled.
After curve is generated, select a time after product weight stabilizes. In above figure, product weight will not increase after 7s, so for safety reasons and at the same time compensate for fluctuation of process itself, pressure holding time should be set to 8s.
It should be noted that extra 1s during holding pressure phase does not increase cycle time, because during this time, gate should have frozen and only hold cold runner for a short time, while product is already beginning to cool. Therefore, extra 1s should be subtracted from cooling time to ensure same cycle time.

 

Purpose of mold temperature map is to record instantaneous temperature distribution of mold surface after product is ejected. It can be used to confirm whether cooling water circuit is working or whether there is a "hot spot".
In addition, this information can also be used to solve problems later-for example, when product size is inconsistent, it can be used to confirm whether mold surface temperature is same as before.
Temperature measurement must use a contact pyrometer.
It should be noted that after the first startup or shutdown, mold temperature will gradually rise to a stable state. Therefore, measurement must be performed after mold temperature is stable (at least after 10 molds).
Above figure provides 5 frames, which can be applied to different molds according to situation. For example, if you are trying a set of 4-cavity molds, you need to record points measured at same position in each cavity in corresponding four corner boxes, leave middle box blank. If test is a single-cavity mold, all five of them need to be used, representing different measurement positions.