In this rule of thumb post, we discuss the difference between a weld line and a meld line in polymer injection moulding as well as how we can apply effective troubleshooting.
In
short: the angle at which the converging polymer flow front meets in the tool
again determines the difference between weld line and meld line.
A weld
line is formed if the angle is less than 135°.
A meld line is formed if the angle is greater than 135° and the polymer
molecules are more uniform compared to the orientation formed after a weld
line. This is demonstrated in the picture below.
It is
important to understand the flow fronts and the flow angle for achieving proper
weld lines. Such an understanding allows the use of multiple submarine gates rather
than fan gates to be used. Prediction of weld lines prior to the tool being cut
allows the optimization of the part design and gate location which in turn reduces
tool development time. Consideration of material, filler and pigmentation is important
and this is why discussion with the technical team at your material supplier at
the early stages are useful.
 |
| Rule of Thumb: Weld Line vs Meld Line |
Troubleshooting
of weld and meld lines
Weld
and meld lines can cause a decrease in mechanical properties and are often
clearly visible on the surface. An effective way of troubleshooting them is to
move them in a non-functional / non-visible area. This can be achieved by
changing the gate position or part thickness. Furthermore the allover quality
can be improved by increasing the melt and mould temperature. This facilitates
a better interfusion of the flow fronts. Also injection speed can help as well
as an optimization of the runner system design.
Thank
you for reading and #findoutaoutplastics
Greetings,
Herwig
Juster
Interested to talk with me about your plastic selection and part design needs - here you can contact me
Literature:
[1] https://knowledge.autodesk.com/support/moldflow-insight/learn-explore/caas/CloudHelp/cloudhelp/2017/ENU/MoldflowInsight/files/GUID-099634AE-DB7A-41BA-B70C-5A23FB013B06-htm.html
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