Hello and welcome back to our latest article about additive manufacturing (AM)! In the previous article, we took a closer look at different additive manufacturing processes for polymers. We talked about solidifying liquid and applying solid polymeers. Today we will talk about the slicer, the different methods of slicing a component, and the resulting layers. We will also look at the structure of a layer and the functions that each different part of a layer fulfills. Figure 1 gives you an overview of the AM process.
Figure 1: Additive manufacturing (AM) process flow, taken from 
The slicer is a software component that uses algorithms to slice 3D geometry into individual slices which are called layers. In figure 1, this is the step between steps 2 and 3. These layers can be printed sequentially and are built in such a way that each layer must cover the previous one so that in the end all layers are fused, the overall structure holds and no gaps in the part are present. For each layer, the tool path and printing parameters are calculated. These are defined by the material, the printing technique, and the part geometry.
Layers can have different forms – if the part is hollow, most layers are too since only the outside wall needs to be printed. These outside walls are called the perimeter. If the part is solid, they require an infill that is inside of the perimeter and printed separately. Usually, the perimeter is printed before the infill. There are many different strategies to fill in a perimeter:
Figure 2: Different infill patterns, taken from 
These infill patterns come in different shapes. These shapes vary in strength, the amount of material, and printing time. We will not go into detail on these patterns. If you are interested, here is a good source on patterns on all3dp.com.
Another important parameter is density. The density parameter controls, how much material is placed in the infill. The higher the density, the more material is used for the infill. A density of 0 means that the layer is hollow. This means, for a functional or industrial part, high density and patterns that provide durability and strength are required. Prototypes and proofs-of-concept may use less material since them being optimally durable and strong is often not required. More importantly, these need to be produced fast.
Extra layers below the very base of the printed component (the printer bed), are often used to ease the retrieval of the part from the printer or to alleviate problems of the material not sticking to the printer bed (due to fluctuations of the heating or the material flow on the start of the machine).
Additional printed layers that are not part of the resulting component, may be used as a socket from which the part may be taken. It is not that important how well the socket sticks to the printer bed, as these additional layers can easily be removed afterward.
Utilizing additional layers to alleviate these problems is a great benefit of using this technology since it effectively counters variances at the start of the system. Most industrial systems have these variances and using more complex technologies (for instance AFP) would require either a longer and more complicated starting strategy or additional finishing steps.
There are two scenarios of parts that are manufactured, either they are built from the bottom-up on a flat surface, or they are manufactured on a curved surface, for instance, if a part will be attached to the surface of another part in an assembly. Modern, load-oriented designs or bionics are rarely perfectly flat.
Slicing a component into flat layers works straightforward. Starting from the very bottom, the 3D geometry is intersected with a horizontal plane. This process is repeated in certain intervals (moving the plane up) until the whole part is sliced. The geometry of the intersection is used to define the perimeter and infill of the layer.
If the base of the part is not flat, this strategy needs to be adapted. Instead of incrementally intersecting the part with a plane, an additional surface is necessary: The curved surface that the part will be placed on. This surface will be used to intersect the part instead of the horizontal plane. Additionally, a slicing direction is required. The result of the slicing is a set of layers that are inertly curved just like the base surface is. See this example of the slicing process of a part on a curved surface:
In this video, you can see how the different layers are generated. The surface is moved along the direction of the blue arrow in the center and intersected with the geometry of the part. The resulting layers consist of a perimeter (blue) and an infill (white).
Our CAESA Composite TapeStation for digital process chain of Automated Fiber Placement (AFP) and Automated tape Laying (ATL) also includes a 3D printing module. Unlike common slicing software (2.5D printing), the module allows users to create paths for parts sliced on arbitrarily curved surfaces (Real 3D printing) and transfer them via post-processors into machine programs for robotic or gantry-based 3D printers. In the context of a machine simulation, the software also allows the programs created to be checked for collision-free operation.
We hope that this article gave you a lot of insight into one of the most important processes of 3D printing. By now you have learned about the different types of layers and infills and how these are generated by the slicer. We will see you again next time with an exciting project!
Until then, stay safe and stay tuned.
 Dr. Wei Jun “Opportunities and Applications of 3D Additive Manufacturing” Singapore Institute of Manufacturing Technology, 11 Apr 2013