Part Details Review
| Abatement Options |
Processing parameters conducive to increase weld line strength, such as increasing the melt and the mold temperature, are effective to various degrees. Vent pins at the weld line location help in evacuating the trapped air. Special processes, such as "Multi-Live Feed Injection Molding" and "Push-Pull Molding" can also help. When weld lines cannot be avoided, an effective design practice is to try to place the weld lines in the areas where they will have the least impact on cosmetic and structural properties.
Designers today have better tools to predict, prior to tool construction, the location of weld lines and to place them away from the aesthetically important surfaces and areas subjected to external stresses. Mold filling simulation software has been used for many years to predict and modify weld locations to improve part quality and strength.
In addition to predictive analysis the following design alternatives may offer help as well:
- Consider sequential valve gates for large parts requiring multiple gates. Sequential gate opening can be used to completely eliminate the weld lines.
- Provide an overflow well to form a meld line instead of a weld line (butt weld) at the end of fill (see figure 1). Alternatively, if possible, instead of the overflow well, relocate the gate next to the hole to direct the weld line into a stronger area.
- Use techniques like relocating the gate, adjusting the part thickness locally, or designing flow leaders to move the weld lines away from the sensitive areas.
- Relocate the gate such that the weld line is under compression rather than tension when the part is loaded. The example in figure 2 shows the gate relocation at 90° from the existing location to form a weld line which will be under compressive load. Use this alternative if you are not able to simply rotate the part by 90° relative to the load.
