December 2013 Design Tip



When in Doubt, Go With the Flow

Use ProtoFlow® analysis to improve your part

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


How does ProtoFlow help?

  • It aids in the positioning of the gate or gates on your part.
  • It shows the position of knit lines allowing you to improve the cosmetic and physical properties of your part (Figure 1).
  • It locates trouble spots that are hard to fill within the part.
  • It tells you whether or not we can fill your part with a selected material.

Figure 1: Flow analysis helps determine gate placement, locate knit lines and identify areas where gas trappings can occur. If needed, CSEs can recommend design modifications to improve the mouldability of the part.

Figure 1: Flow analysis helps determine gate placement, locate knit lines and identify areas where gas trappings can occur. If needed, CSEs can recommend design modifications to improve the mouldability of the part.


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.

Figure 2: The colour coding gets “hotter” as the pressure goes up. Gold, yellow and red represent high pressure and reduced flow. Blue and green colours mean flow is good and the part will have a wide process window to work with.

Figure 2: The colour coding gets “hotter” as the pressure goes up. Gold, yellow and red represent high pressure and reduced flow. Blue and green colours mean flow is good and the part will have a wide process window to work with.


Plastics with good flow characteristics include polypropylene, HDPE, LDPE and unfilled nylons. Resins such as PC and ABS/Polycarbonate tend to flow poorly.


ProtoFlow 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 mouldability. ProtoFlow, however, does not show areas of distortions or sink in your part.


Our Customer Service Engineers (CSEs) will run an initial flow analysis with our default material Makrolon 2458 (PC) if a material is not listed. Since it’s a difficult resin, a successful run through ProtoFlow often means that any other resins you select will work as well.


What if your part is not filling right? A CSE can provide solutions such as increasing the wall thickness of the part, adding multiple gates or different material options (Figure 3). Keep in mind that if you see Makrolon 2458 listed as the material and it’s not what you intend to use, CSEs can correct the material and run another simulation.

Figure 3: With the help of ProtoFlow analysis, slight modifications such as increasing wall thickness can be made to your CAD model to create better flow, and ultimately better parts.

Figure 3: With the help of ProtoFlow analysis, slight modifications such as increasing wall thickness can be made to your CAD model to create better flow, and ultimately better parts.


ProtoFlow analysis is automatically applied to a small percentage of parts where mouldability 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 ProtoFlow or our general capabilities, a Proto Labs CSE is available on +44 (0)1952 683047. For additional resources such as moulding and prototyping processes, resin options, video tutorials and more, check out protomold.co.uk.