Weld and meld lines result

The Weld and meld lines result shows where weld and meld lines are likely to occur on your model.

This result is generated at the end of a Fill analysis.

Weld and meld lines are a weakness or visible flaw created when two or more flows meet and converge while filling a part. The presence of weld or meld lines may indicate a structural weakness and/or a surface blemish. The only difference between a meld line and weld line definition is the angle at which they are formed.

A meld line is typically formed by parallel flows. Meld lines tend to be stronger and generally less visible than weld lines. The quality of the meld line is dependent on the material type, the type and amount of fillers, and the pressure and temperature at the meld line.

Weld lines are formed at lower angles. Weld lines can cause structural problems, and they can also make the part visually unacceptable. Therefore weld and meld lines should be avoided if possible. However, weld lines are unavoidable when the flow front splits and comes together, around a hole, or has multiple gates. Look at the processing conditions and the weld line position to decide if the weld lines will be of a high quality. Avoid weld lines in areas which need strength, or need to appear smooth.

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 good weld typically occurs when the melt temperature where the weld line is formed is no more than 20°C below the injection temperature.

Using this result

Weld and meld lines can cause structural problems, and they can also make the part visually unacceptable. However, some weld and lines are unavoidable, so you need to look at the processing conditions and the weld/meld line position to decide if they will be of a high quality.

To move weld lines, change the fill pattern to make the flow fronts meet at a different place:

• Alter gate positions.
• Change the part thickness.

To improve the quality of weld lines:

• Increase the melt temperature, injection speed, or packing pressure. This will allow the flow fronts to weld to each other better.
• 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, so the weld line is created with a higher flow front temperature and is packed with more pressure.
• Move injection locations to make flow front 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 runner system design.
• Reduce runner dimensions and maintain the same flow rate to use shear heating to increase the melt temperature at the flow front.

Solving one problem can often introduce other problems to the injection molding process. Each option requires consideration of all relevant aspects of the mold design specification.

Things to look for

This 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 will be more of a problem in areas of the part which will be 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), this may not be a problem.

Note: Changes such as these can only be made using a licensed Autodesk Simulation Moldflow Adviser or Autodesk Simulation Moldflow Insight product.