Using Mold Flow Analysis to Improve Injection Molding Design

Use our free mold flow analysis to improve the moldability of your parts

Injection molding resin flow analysis
Figure 1: Flow analysis helps determine gate placement, locate knit lines, and identify where gas trappings can occur.

Designing a good injection-molded part is dependent on many factors. Proper flow of the resin into the mold is one of them. Our mold flow analysis is a proprietary software program that was created by Protolabs to digitally simulate flow of resin through your part geometry. The resulting data that emerges will essentially help you design a part that will mold better.

What is Mold Flow Analysis?

Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. By understanding material fill, injection mold designers can better position gates, anticipate where knit lines will appear, and locate difficult to fill spots in the mold. It can also aid in material selection since fill will vary by resin.

The analysis also examines how resins flow with certain temperatures and injection pressures (Figure 2). As material cools it begins to harden which is why gate pressure increases. The higher the pressure, the more difficult the fill, which translates to greater concern about weak knit lines (contributing to poor part integrity), flash, sink, and shorts.

How Material Flow Differs by Resin

Depending on a material's properties, it will flow into the mold differently. Plastics with good flow characteristics include:

  • polypropylene
  • K-Resin
  • HDPE
  • LDPE
  • unfilled nylons.

Resins such as PC and ABS/polycarbonate tend to flow poorly.

Our mold flow analysis works to pinpoint issues that can arise from these difficult flowing materials as well as other issues like thin walls and complicated geometries, providing solutions to improve flow and moldability.

A finished injection-molded part
Using mold flow analysis can lead to modifications in your design, creating better parts, as in this finished part.

Our applications engineers will run an initial flow analysis with our default material Lexan 940 (PC) if a material is not listed. Since it’s a difficult resin, a successful flow analysis often means that any other resins you select will work as well.

What if your part is not filling right? An applications engineer can provide solutions such as increasing the wall thickness of the part, adding multiple gates, or recommending different material options. Keep in mind that if you see Lexan 940 listed as the material and it’s not what you intend to use, applications engineer can correct the material and run another simulation.

Our mold flow analysis is automatically applied to a small percentage of parts where moldability issues are immediately present but flow analysis is also available upon request. And better yet, it’s free, all in an effort to help you design better parts and help us get them to you as fast as possible.

If you have any questions about your injection molding quote or our general capabilities, a Protolabs application engineer is available at 877-479-3680. You can also try the mold flow analysis by viewing our sample injection molding quote. For additional resources such as molding and prototyping processes, resin options, video tutorials, and more, check out