Weld lines result

The Weld lines result displays the angle of convergence as two flow fronts meet. The presence of weld lines may indicate a structural weakness and/or a surface blemish.

Tip: By overlaying the Fill time result and stepping through the animation, you can see how the flow fronts converge.

The term “weld line” is often used to mean both weld and meld lines. The only difference between them is the angle at which they are formed; weld lines form at lower angles than meld lines. Weld lines can cause structural problems and make the part visually unacceptable, but they are unavoidable when the flow front splits and comes together around a hole, or if the part has multiple gates.

Consider the processing conditions and position of the weld lines to determine whether the weld lines will be high quality. Weld and meld lines should be avoided, particularly weld lines in areas that require strength or a smooth appearance.

Note: For Midplane or Dual Domain studies, this result is the same as a custom weld line plot with a meeting angle of 135 degrees. For a different meeting angle, create a custom weld line plot and specify the meeting angle.

Processing conditions help to determine the quality of weld or meld lines. Weld line strength is influenced by the temperature at which the weld line is formed and the pressure exerted on the weld until the part freezes; pressure is 0 at the time the weld line forms. Typically a “good” weld will occur if the temperature of the melt at the weld line as it forms is no more than 20°C below the injection temperature.

Using this result

Weld lines can be moved by changing the fill pattern to make the flow fronts meet at a different place. To move weld lines:

Alter the gate locations.
Change the thickness of the part.

To improve the quality of weld lines:

Increase the melt temperature, injection speed, or packing pressure. This will enable the flow fronts to weld to each other more effectively.
Increase the diameters of gates and runners to make it easier to pack the part.
Move injection locations to make weld lines form closer to the gates. The weld line is then created with a higher flow front temperature and is packed with more pressure.
Move injection locations to make flow fronts meet more obliquely, turning the weld line into a meld line.
Place a vent in the area of the weld line. This will remove air traps, which could further weaken the weld line.
Optimize the design of the runner system.
Reduce runner dimensions and maintain the same flow rate. Shear heating can then be utilized to increase the melt temperature at the flow front.

Solving one problem can introduce other problems to the injection molding process. Carefully consider all the relevant aspects of the mold design specification before choosing an option.

Things to look for

The Weld Lines result helps you identify the following problems:

Structural problems: The part may be more likely to fracture or deform at a weld line, especially if the weld line is of a low quality. This weakness is a more serious problem in areas of the part that are subject to stress.
Visual defects: A weld line can cause a line, notch, or color change on the surface of the part. If the weld line is positioned on a non-critical part surface, such as the bottom, this may not be a problem.