|
looking at how the part fills may give clues to issues seen
Definitions: Short Shot: 1) to be not full or completely packed out 2) not full in that some cavities in multicavity tool may not be full while others are. Results: the results or outcome of an action
In the previous section the short shot test was explained and some examples were given. To further the discussion the area that has to be known is what did your short shot test produce.
The photo shown below was produce as a short shot, and it appears to have multiple issues and is being used as an example.
Area A: this is a windowing effect in that the area appears encapsulated and shall close and the question that remains is it sealed, what happened to the air
Area B: While it is observed that there is a weld line across the area are these recesses are used for an O-ring or other type of seal and is this an area of concern for leakage. In this case knowing the function and application of the product is of great concern.
Area C: A window effect, again where is the air to go? Is a line or mark in the part permissible per cosmetics and is there an issue if a pin hole remains, or does this limit the speed of injection due to burning in this area due to too fast of a fill.
Area D: As should be in a part of this design opposite the gate is a weld line, is it permitted and is the tool vented in this area specifically for this?
Area E: Fill down a shaft (or so it appears) it is uneven, and a weld line is forming, but more importantly is this possibly causing the core to deflect? Is a uniform wall needed and specified.
In reviewing all the above, what process conditions can be changed which may assist the part being molded? To answer those one may need to know what material composition is and requirements for the part / application. Testing at various fill rates and or mold temperatures may be suggested. If a multicavity tool are all parts filling in same pattern? Is it a critical part? Might we have only had an issue with only one cavity versus all cavities?
Another possibility is to run a shear viscosity curve type study but instead of filing to 95% fill only to 80% or so and then adjust the fill rate to see if possibly the pattern at some specific fill rate appears better suited to make acceptable parts. The test shows a series of short shots produced in a systematic order under different fill rates.
Please understand this part was used to illustrate what to look for and think about.
SLSILVEY
21061014
| 