What Is the Role of Slicing in 3D Printing?

Humans are gifted with senses that help make decisions and perform activities. Like humans, machines have methods of processing information. Machines also use tools at their disposal to translate a set of instructions into formidable actions. That is how all machines work, and 3D printing is no different.

“3D printing, also called additive manufacturing, turns digital files into physical objects by building them up layer-by-layer. Imagine a cucumber sliced into paper-thin slivers by a mandolin and then put back together.”

Whenever we talk about 3D printing, we hear certain terms repetitively. “Slicing” is one such word that cannot be ignored. It is the intermediate and most important step in the process of 3D printing. In this article, we will try to understand the role slicing plays in 3D printing. 

Here is a list of sub-topics that will be part of this discourse:

1. What is Slicing? 
2. Components of a Slicing Software
3. Features of a Slicing Software
4. FDM vs SLA Slicer
5. The ultimate list of Slicer Softwares

1. What is Slicing? 

The act of converting a 3D model into a set of instructions for the 3D printers is called Slicing. Quite literally, it ‘slices’ the 3D model into thin layers, and further determines how each layer should be printed (the tool path) to get minimum time, best strength, and so on. 

A slicer software takes a 3D CAD model, which is generally an STL format file, and converts it into a g-code that gives commands to the printer. Following are the three major types of settings that can be controlled in a slicer software:

1. Print settings: layer heights, shells, infill percent, and speed
2. Filament settings: filament diameter, extrusion multiplier, the temperature of the extruder, and print bed
3. Printer settings: nozzle diameter, print bed shape (L x W), and Z offset

In the next few sections, we will delve into some of these Slicer settings that will directly impact the 3D print quality of the models.

2. Components of a Slicing Software

It is important to understand how data flows in the 3D printing process.

Like every software, we can divide it into two components: front-end and back-end, or GUI and logic. The front-end consists of the parts that the user directly interacts with. This is where the user visualizes the CAD, as well as the gCode and tool path. The back-end components contain algorithms or instructions for the code execution. Let us look at the components of the Slicer software.

Front End

GUI is the graphic user interface. It has all the tools that help the user interact with the 3D model. As you can see in the picture below, the graphic user interface of a free web-based software named Buildbee enables the user to move, scale, rotate, and change the settings for the 3D model. 

What is an STL File?

The main function of the slicing software is to work with the STL format file. It stores the visual image of the 3D model. It stands for “STeroLithography,” sometimes also called Standard Triangle Language or Standard Tessellation Language. It has information regarding the surface geometry of the model. In a nutshell, it encodes the model description for the slicer to pick up and display the visuals.

The word “tessellation” is associated with STL files as it breaks down complex 3D structures into 2D models. In the image below, we see that a sphere can be represented using a bunch of small squares or triangles. 

Certain tessellation rules help in giving a good 3D print quality:

1. Vertex to vertex rule: every triangle must share 2 vertices of its adjacent triangle.
2. Orientation rule: the direction of the normal vector has to point outwards, and the vertices are listed in anti-clockwise order while viewing the object.
3. All positive octant rule: the coordinates of the model must be all positive.

Things to keep in mind while exporting the STL:

• Angle control: gaps between the triangles prevent angle deviation and improve print resolution. 
• Chordal deviation: a parameter called the chord height (the maximum distance between the surface of the design and the STL diagram) needs to be maintained. The chord tolerance is set between 0.01 and 0.001 mm as a standard.
• Binary/ASCII: STL files can be shared in two types of encoding, binary and ASCII. Binary files are small and ASCII files are large in size. 

Back End: The logic

The back-end handles:

1. Reading the STL
2. Slicing the STL into layers and determining the tool path to print the object
3. Writing the G-code

What is G-code?

The most important component of the slicing process is the g-code. Based on the user inputs, the back-end generates an optimized code to print the object. A g-code is nothing but the set of commands to execute the print action. It helps in providing instructions to the machine controller, and a 3D slicer generates this G-code automatically. 

A deeper understanding of the G-code can help one troubleshoot issues while 3D printing. There are two types of commands: “G” and “M”. Here is the basic syntax of the code:

Slicing Algorithm: Understanding the G-code

We can convert the facets from the STL file into separate segments through a slicing algorithm. The algorithm looks at the G-code and extracts the information accordingly. It helps in understanding the G-code to slice the model into smaller parts. 

So far we have looked at the components that enable the slicing of a CAD output model. It is now time to look further into some more features that will help us print the best quality 3D objects. 

3. Features of a Slicing Software

Once you retrieve the STL file from the CAD software, there are certain settings in the software that you must cater to.

Orientation

After loading the STL file on the slicing software, we need to align the 3D model to the given space. As mentioned above, one has to follow the orientation rule. 

Layer Height (Object resolution)

The resolution of a 3D object is highly dependent on its layer height. Smaller layer heights give high resolution and smooth surface. However, the overall printing time could be more. 

Object Shells (Shell Thickness)

The outer layer that builds the wall of the object is called the object shell or perimeter. The strength of the object is dependent on the number of shells present. Higher shell count means higher strength! 

Infill

Density: Infill density is measured in percentage, ranging from 0 to 100%. An object with 0% will have a hollow interior and an object with 100% density will be solid. Objects with high density will have a longer printing time. The recommended shape for the infill for optimal speed and strength is a honeycomb structure. 

Types and Shapes: The design of the infill pattern can have an impact on the strength and flexibility of the 3D prints. Based on your requirements you can pick the infill type. For example:

• Functional prints: Cubic, octet, gyroid
• Figurine and model prints: Lines
• Standard prints: Grid or triangles
• Flexible prints: Concentric

Support Structures

In the process of 3D printing, one layer is printed over another existing layer. This means every layer needs an underlying layer to support it. If a model has an overhanging part, it still needs a supporting layer. This supporting layer is called the support structure. Slicer software has the ability to insert supports where needed, and they are easily detachable post-printing, though removing them cleanly is its own discipline, covered in our guide to finishing 3D prints. In the picture below, the blue color component is the support structure for the given 3D model. 

Rafts, skirts and brims

It is common for 3D printed objects to get stuck on their print beds. To avoid this, the slicer offers some good solutions: structures that make the detachment easier. 

1. Skirt (as shown in fig ‘a’): a single outline surrounding the part without touching the actual 3D object. 
2. Brim (as shown in fig ‘b’): a layer printed along the print bed that touches the actual 3D object. 
3. Raft (as shown in fig ‘c’): a series of layers printed before the model is printed. It serves as a detachable base for the 3D object. 

Slicing software gives us these simple techniques to avoid adhesion problems at the print bed, which is a common issue in 3D printing. 

Print speed

The slicer software has speed settings that can be adjusted based on the geometry of your 3D model. The slicer has default settings for the speed which may be lower than what you might want. The speed can also vary depending on the type of materials you use. Typically, for PLA or ABS the recommended print speed is 40 to 60 mm/s. 

The print speeds are categorized into two types: print moves and non-print moves. Below is a chart to help you understand the different types of print speeds. The travel speed under non-print moves refers to the speed at which the extruder moves from the end of one extrusion to the next. This is crucial in preventing oozing. 

Optimized Print Paths

An optimized printing path is crucial to 3D printing. It affects printing time, surface roughness and strength. Printing paths have a direct impact on the time taken to complete a print, and a path planning strategy can help optimize the overall process, resulting in shorter fabrication time. Slicer software has pre-defined print paths that one can select from. 

Temperature

One of the most important slicer settings is the temperature. It needs to be calibrated as per the print speed settings. It is important to increase the temperature if the print speed is set higher, because if the print speed is not matched to the temperature, it can lead to under-extrusion due to improper melting of filaments. High temperatures can lead to over-extrusion and result in blobs or zits. It is recommended to increase the temperature between 5 and 10 degrees Celsius for every 5 to 10 mm/s rise in print speed. 

Another important factor while controlling the temperature is the type of material used. Below is a list of materials with set values of temperatures used in 3D printing. 

Dealing with multiple extruders

Multi-nozzle, or multi-extruder, printers have two or more extruders. They are commonly used to print a 3D object with different materials, and the design can also help reduce the waste generated in typical single-extrusion methods. The printer will have a dedicated nozzle for a given material, and it is possible to dedicate one extruder to a certain region and another to a different region. Calibration of the nozzles is important here to avoid mistakes. Using slicing software, it is now easy to assign different roles to each extruder, a principle that scales up considerably in industrial printing infrastructure. 

FDM vs SLA Slicing

FDM and SLA are the two most common techniques in 3D printing. Before you read further, check out our detailed coverage of FDM vs SLA printing techniques. 

FDM Slicing

The print movement of the extruder or nozzle in an FDM printer is confined to the X and Y axes, while it moves in Z for changing layers. FDM printers depend on multi-axis control, which needs attention to get the best printing accuracy. Temperature control settings (for heating and cooling of extruders and print beds) are important for FDM printers. Some of the best slicer software for FDM printers, with tested pre-defined algorithms to execute the G-code, are Cura (free) and Simplify3D (paid). 

SLA Slicing

In SLA printing, the build platform moves up and down to dip into the resin tank and form layers one after the other, so the movement is along the Z-axis for SLA printing. The major difference between FDM slicing and SLA slicing is that SLA printers do not use G-code as the output file; they have their own built-in slicing software. As SLA printers have no extruders, nozzle temperatures are irrelevant; instead, exposure time and lifting speeds are key parameters. There are a few third-party options common to SLA printers, including ChiTuBox and FormWare. 

The Ultimate List of Slicer Software

Version numbers move quickly, so this list focuses on what each tool is for rather than which release it is on.

1. Cura (free; enterprise tier paid): developed by UltiMaker and the most widely supported FDM slicer. Strong default profiles and a large community.
2. PrusaSlicer (free): the actively maintained successor to Slic3r. Excellent support generation and variable layer height. It has itself been forked into Bambu Studio and OrcaSlicer.
3. Simplify3D (paid): fine-grained control over supports and process settings, favoured for complex prints. A recent major relaunch rebuilt the slicing engine and added live print monitoring.
4. IdeaMaker (free): from Raise3D. Fast slicing, a clean interface, and texture-mapping features.
5. 3DPrinterOS (paid): cloud-based fleet management aimed at enterprises, schools and universities.
6. KISSlicer (free; pro tier paid): lightweight, with strong multi-extruder handling. A niche option now.
7. Repetier-Host (free): host software that bundles multiple slicing engines, particularly suited to RepRap-style printers.
8. OctoPrint (free): as much a print-farm and remote-control layer as a slicer, and a common integration point for other tools.
9. AstroPrint (free; premium paid): cloud-based slicing and print management.
10. IceSL (free): research-oriented, with procedural modelling built in.
11. ChiTuBox and FormWare (free and paid tiers): resin slicers for SLA and MSLA printers rather than FDM.

“C6 (free): our own slicer, built at Fabheads and usable from a browser with nothing to install. It was developed alongside our own continuous fiber printers, for a category of printing the tools above were not designed around. Try C6.”

Conclusion

This discussion on slicing software is important with regard to the 3D printing process. The slicing process is crucial in determining the print quality of your 3D models, so understanding its various aspects can help you manoeuvre 3D printing with ease. 

3D model slicing is the puzzle piece that completes the 3D printing process. Its role is definitive of the printing standards you set for your models. Despite all the knowledge on slicing settings, 3D prints can still find you in a sticky situation, so for those times, check out our article on fixing 3D print problems! 

Slicing settings will take a print a long way. But when a part has to carry a real structural load, the limit stops being the slicer and starts being the material, which is where continuous fiber printing and composite manufacturing come in. 

Building parts with continuous carbon fiber and want to see how slicing works for that process specifically? Explore C6.

Frequently Asked Questions

What is slicing in 3D printing?

Slicing is the process of converting a 3D model into a set of instructions (G-code) that a 3D printer can follow, breaking the model into thin layers and determining the path the printer takes to build each one.

What is G-code?

G-code is the set of commands a slicer generates to control a 3D printer (covering movement, temperature and extrusion) which the printer’s controller reads and executes layer by layer.

What is an STL file?

An STL file stores the surface geometry of a 3D model as a mesh of triangles, which a slicer reads to generate the toolpath and G-code needed to print it.

What does a slicer do?

A slicer takes a 3D CAD model, usually an STL file, and converts it into G-code. It controls three groups of settings: print settings such as layer height and infill, filament settings such as temperature, and printer settings such as nozzle diameter.

Which slicer software is best?

It depends on the printer and the part. Cura and PrusaSlicer are the most widely used free options for FDM, Simplify3D offers finer control for complex prints, and ChiTuBox and FormWare handle resin printing. Continuous fiber printing needs a slicer built for it.