Weld lines result

The Weld Lines result displays the angle of convergence as two flow fronts meet.

The presence of weld lines can indicate a structural weakness and/or a surface blemish.

Tip: Overlay the Fill time result and step through the animation to 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. They can cause structural problems and make the part visually unacceptable.

Weld lines are unavoidable when the flow front splits and comes together around a hole, or has multiple gates. Consider the processing conditions and position of the weld lines to determine whether the weld lines are high quality. Avoid weld and meld lines; particularly avoid weld lines in areas that require strength or a smooth appearance.

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 weld line. A weld is good if the temperature of the melt at the weld line as it forms is no more than 20 C below the injection temperature.

Use this result

Move weld lines 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.
• 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.
• 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.

While you solve one problem, you can introduce other problems to the injection molding process. Carefully consider all the relevant aspects of the mold design specification before you choose an option.

Things to look for

The Weld Lines result helps you identify the following problems:

Structural problems

If the weld line is of a low quality, the part can fracture or deform at a weld line. 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 (for example, the bottom of the part), it is less problematic.