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Model Repair

Because simply flagging up structural flaws in a model isn’t enough, we are also proud to present our Model Repair tool! It goes together with the Model Analyzer tool like an awesome superhero-and-sidekick duo, spotting 3D model crimes and taking them down like the team they are. The Model Repair tool will flip your inverted triangles, fill in gaps, stitch bad edges and trim your uneven surfaces.

Common errors in 3D models

The Materialise Cloud Model Analyzer indicates the errors your 3D model contains. Then the Model Repair tool comes in to fix those errors, leaving you with a perfect design that’s ready for printing. It’s a tool that is based on Magics, Materialise’s state-of-the-art data preparation software, so you know that you’re in good hands.

Inverted Normals

There are two sides to any 3D model: the outside, which is the side you’ll be able to see once it’s been printed, and the inside, which you would only be able to see if you cut a hole through the side of your design. The triangles making up the body of your design also have an inner side and an outer side, and the outer side is called the “normal”. If a normal inadvertently gets flipped, so that it faces inward, the printer will get confused and think that the entire inside of your model needs to be filled in since the inside can now also be considered as the outside of the model. Essentially, it won’t know where to stop printing and which parts it needs to leave hollow.

The Materialise Cloud Model Analyzer detects the inverted normals and the Model Repair tool flips them automatically.

illustration for inverted normals

Holes

Sometimes triangles are missing, leaving a gap in your design. This is also confusing for the printer, as it won’t have enough information to print the part properly. It tends to deal with these gaps in a similar way to the way it deals with inverted normal: your printer won’t know where the design begins or ends and it will end up printing only the contour (and neglect the inside of each slice) or it will continue to print when it should stop.

It’s important to note that it’s completely possible to print a design with intentional holes; these holes just need to be properly defined with correctly placed triangles.

illustration for holes

Redundant triangles

When designing a more complex model, you will probably need to combine two shapes or subtract a part of your model (i.e. applying Boolean operations). As a result, the internal geometry of your model is no longer optimal, and you’ll need to clean up the redundant triangles that overlap each other. It isn’t a fatal flaw – but it will cost the printer more time and material to print your model. It’s also extremely tricky to spot on a finished model, as there could be layers upon layers of hidden redundant triangles worked into your design without you noticing. Luckily, the Model Repair tool will get rid of them in no time.

examples of redundant triangles

Bad Edges

When two or more triangles aren’t connected to each other, we refer to it as “bad edges”. Another variant of this phenomenon is called “near bad edges” and occurs when two triangles are close to one another, but with edges that don’t completely touch. This isn’t always visible on your screen, so it’s always best to be careful and let the Model Repair tool do its work.

illustration for bad edges

When you have a whole series of bad edges, it’s referred to as a “bad contour”.

illustration for bad contour

Stitching edges

In theory, bad edges can also simply be considered as gaps in the design, as the triangles that surround the gap can’t connect to an edge anymore. When your design contains bad edges, it means that you don’t have a watertight design (more information about the term “watertight” can be found on the Model Analyzer webpage). You need to stitch these bad edges to get a manifold, printable model.

Multiple Shells

Not the kind you find on a beach, in 3D Printing a shell is basically a group of connected triangles which forms an autonomous 3D object in your file. These shells can overlap one another or be separated by space. A frequent problem with shells is when they have inverted triangles, or when the triangles on intersecting shells touch each other but one side is face the wrong direction.

Noise shells

Another phenomenon can occur, where a shell is so small that it becomes unnecessary. These types of shells are called “noise shells” or “orphaned shells” as they barely have any volume. Think of it as a wrinkle in an otherwise smooth piece of fabric that needs to ironed out. The easiest way to remove noise shells is by flipping inverted triangles, and finally the remaining useful shells in your design will need to be unified into a single, solid volume. It is not necessarily a bad thing if your design has multiple shells – but the print time will increase significantly.

Not too much, not too little

To make this all a little more clear visually, imagine drawing the outline of a shape on a piece of paper. If you trace the same outline a second time, it will become thicker, much like the way a 3D printed object gets thicker and stronger the more shells it is printed with. When printing a hollow design (a fairly standard practice as the model will be lighter and more cost-effective), the most common tactic is to print an outer shell (called an “outline”) and an inner shell (called an “insert”). The inner layer is composed of inverted normals in order to signal to the computer that it is designing a hollow model, and besides, a design with a single shell won’t be strong enough and is likely to be printed badly. Too many shells are also bad for the object, and the maximum recommendation is five.

If you’re having trouble with shells, don’t fear. Materialise Cloud’s Model Repair tool automatically fixes the shells in your 3D model and ensures that you end up with the correct amount.

examples of overlapping and unified shells

Intersecting and Overlapping Triangles

Another common problem that novices in 3D Printing may come across is triangles cutting each other. When triangles intersect, you will have to cut off the sharp edge and trim the triangles to obtain a unified design. If you forget to do this, the 3D printer will get confused again about the inside and outside of your model and will not know what part of the bounding box to fill up, resulting in a failed print.

example of overlapping triangles

Triangles can also overlap. When this happens an edge of a triangle is shared by more than two faces. In this case the printer will have a hard time calculating the production path. It’s not clear to the machine what it needs to do, so it can slice your model in a way that the laser or nozzle simply continues to print your model with two identical edges on top of one another. Materialise Cloud removes the duplicates that are part of the overlapping triangles, thereby getting rid of the calculation problem and ensuring that you have a unified solid model.

ShrinkWrap to the Rescue

For files with very bad quality, the automatic repair of flipped triangles, bad edges, holes and rough surfaces may not be sufficient. In that case, Materialise Cloud applies one of Materialise’s impressive fixing tools, called ShrinkWrap. This complex algorithm will place a thin layer around your model that shrinks afterwards and repairs difficult errors, while keeping details intact.

illustration for ShrinkWrap

A Repaired 3D Model

All in all, the most important thing to remember is that you need a watertight 3D model to print your design and that a design can seem manifold on your screen without being it in reality. The Materialise Cloud Model Repair tool can repair files of the worst quality, without any manual effort on your part. You start out with a file riddled with errors and get a solid, watertight design back!