So you’ve set up your 3D printer and you’re ready to start producing plastic items.
Everyone knows that the inside is not completely filled and is of varying degrees of hollowness. This hollowness inside is what allows for the movement of the print, as well as its strength and finished weight.
The best infill pattern for 3D printing will depend on a number of factors and the intended usage of the finalized project.
Each infill pattern will require a different amount of effort, time, and materials. You should consider all of these factors most highly when choosing an infill style.
If you choose the wrong infill style this can lead to a wealth of issues with your finished product.
The structural integrity can be compromised, the print quality could be reduced, or it can simply be inappropriately designed for the intended purpose.
It can be confusing to work out which infill style is best suited to your design needs, but there is no need to fret any more.
We have created a guide to assist you through every step of the way, meaning you will never be confused as to which infill style to use again.
What are the parts of a 3D printed project?
The different parts of a 3D printed project are shown in the diagram below. As you can see, there are 4 distinct sections of a 3D print.
Image from: https://www.3dhubs.com/knowledge-base/selecting-optimal-shell-and-infill-parameters-fdm-3d-printing/
You can customize each of these layers to suit your design and creation needs. The top and bottom layers are also part of the shell.
The top layer is the area of the printed project that is exposed to the outside. As the name suggests, it is found on the top of the finished product, underneath the print nozzle. This tends to be the most high-quality print finish on the entire project.
The bottom layer is essentially the same as the top layer, just closest to the build plate. The outer shell layers are the same but exposed to the sides of your print area.
The infill is the internal structural component of your printed project. The way you design this layer alters the strength and structural integrity of the finalized piece.
Shells
The shells are printed in a variety of thicknesses depending on the requirements of the project. They are printed in many layers to gradually build up the thickness and strength. Particularly for fused deposition modeling (FDM), these layers creating the shell are printed first.
By increasing the number of layers, you get a more solid and durable print product, but you do not need to use more material for infill purposes.
Your 3D printing program should have a setting to allow you to manipulate the shell thickness of varying areas. This means that sections of your model with a weaker structure can be granted additional strength from a thicker shell.
If you plan to chemically smooth or sand your project once it has been printed to create a more polished finish, you should increase the shell thickness.
The smoothing process will thin out and destroy some of the shell layers which can lead to the structural integrity being compromised. By designing the shell to counteract this thinning, you can create a higher quality finished product.
You should design the shell of your project to be a multiple of the nozzle diameter in thickness. This reduces the likelihood of holes and gaps appearing in the shell of your project.
The shells will be created without spacing resulting in a stronger final product. 3D printers commonly choose the shell width to be equal to twice the diameter of the print nozzle or around 0.8 mm.
The downside to increasing shell thickness seems fairly obvious. More materials will need to be used and the printing process will take a longer time to complete. This increases the cost of your project overall.
Infill
This is typically a much lower density than the printing of the shells. The standard FDM printing programs will create infills with a density that falls somewhere between 18 and 20%.
The benefit to this lower density printing is that it will allow the project to be completed faster and using less material. Both of these factors reduce the cost of creating the 3D print.
Infill percentages range from 0% (completely hollow shell) to 100% (a solid structure).
What impact does the infill pattern have?
The infill layers allow the project to be printed to suit your design without using a lot of resources or time. Using a more hollow infill pattern reduces the printing time, the cost of printing, the number of raw materials required, and the functionality of the finalized piece.
The strength of a 3D print depends massively on the infill percentage. The percentage chosen depends on the intended use of the final piece. Most designs will function well with a standard 20% infill but this can be changed to increase the structural strength.
The infill also plays an important job in how protruding features connect to your printed model. Let’s consider snap-fit connections, which are often weak at the base.
If the infill density is low then the cantilever is more prone to snapping. This is because the connection is over a short area and so cannot withstand much pressure. If the infill density is increased then more of the object’s body is connected to the cantilever, making the connection stronger.
The infill pattern and density are also important if you plan on drilling or using screws in conjunction with the 3D print.
It is wise to have an infill density of at least 50% if you plan on screwing into it to ensure a strong connection. If the infill density is low then a weak connection will be made and the join will not be secure.
If you are planning to use bolts and clearance holes with your 3D print, then it is often preferred to choose a low infill density. The combination of the thick shells and the infill pattern will create compressive strength. This makes it ideal for anchoring bolts.
What are the different types of infill patterns?
This is by no means a conclusive list of infill patterns, however, these are the most commonly used options.
Concentric
This is a 2D infill pattern that creates waves inside the printed product. The shape of these waves is similar to the external structure of the walls.
The resultant pattern is visually similar to the ripples a stone makes on the surface of water when it is thrown in.
Cross / cross 3D
The cross pattern is 2D and is made of layers and grids of cross shapes. They are spaced out which allows for flexibility and manipulation in the finished product.
Cross 3D is the 3D version of this infill pattern. As the project gets taller and taller, the lines move at inclines. This results in a firmer and more rigid finished product.
Cubic
This is a 3D infill style. It is constructed of many different cubes, stacked on top of one another and tilted with one of the corners facing downward.
The paths of the pattern cross one another within the layer. This is also sometimes referred to as a honeycomb infill pattern.
The pattern generates a lot of air pockets within the structure. This allows for excellent heat insulation and also helps the finalized project float on the surface of water.
It can be printed very rapidly and has a great deal of strength in all directions. It is the strongest multipurpose infill pattern.
There is a variation on this style known as Cubic subdivision. It is a variant that appears visually similar but requires less material to create.
Gyroid
This is another 3D infill style. It is quick to print, doesn’t need a huge amount of materials, and does not cross itself within any one later.
It is shaped in a way that it too creates air pockets. These are really well suited to being filled with a liquid or even resin.
It has a lot of strength in all directions and is relatively lightweight.
Rectangular
This is the standard infall pattern used by 3D printing programs. There is a lot of strength in all directions like honeycomb infills. It is slightly slower to print, but it requires the least bridging of any infill styles.
Bridging is when a flat and horizontal section of the print product must be generated in mid-air. It is essentially ‘bridging the gap’ between 2 printed areas on your project.
Triangular / diagonal
This style of infill is used when strength needs to be built in the direction of the project’s walls. They are the slowest of the infill types to print.
The triangular infill pattern is incredibly strong, particularly when weight is applied perpendicular to the face of the product.
This infill style is particularly useful for bridging gaps between walls of thinner components. Without this style of infill, there may not be much insulation between the components which leads to a loss in strength.
Trihexagons
This is a 2D infill pattern that generates a combination of hexagonal and triangular shapes.
This is used as the hexagonal shape uses relatively less materials compared to their strength than triangles alone.
The sides of each hexagon are also shorter. This causes less issues with bowing as the lines are able to cool more rapidly.
Wiggle
This infill pattern allows for movement and manipulation of the final project. It is ideal when used with softer materials such as nylon and rubber.
Lines / zig zags / rectilinear
These are the fastest of the infill patterns to print.
They have a relatively low infill density and are best suited for projects that do not require a great deal of strength. This is a very useful infill pattern to use on prototypes as less materials are used.
A 2D grid is created by the print nozzle, printing only one axis per layer. With line infill patterns, many lines per layer are made. With zig zag infill patterns, the infill is one constant line.
Infill line direction
The standard setting for this is 45 degrees. This allows the motors on the X and Y axes to print at the same rate at the maximum speed possible.
If you wish to increase the strength or flexibility of a certain area of your print, we recommend changing the infill line direction.
Gradient infill v gradual infill
A gradient infill is where the infill density ramps up as the print nozzle moves closer to the shell. This will make the product strong and rigid while reducing the amount of materials required to create it.
A gradual infill follows similar principles but with a different execution. Gradual infills change the infill density near the top and bottom of the print.
This means that effectively you can have a larger infill density when you reach the top of the print than you do in the middle. This is used to save time and resources without compromising on strength.
Infill patterns for models
Models and small figurines do not require a great deal of internal strength.
Nothing will be resting on or supported by them, so all the infill needs to do is help to hold the weight of the model’s walls and support the structure from collapsing.
These types of creations tend to have an infill density ranging from around 0 to 15%. This is commonly found when using line or zig zag infill patterns.
Infill patterns for standard 3D prints
These tend to have an infill density ranging from 15 to 50%, depending on the amount of stress they are likely to be put under once formed.
For low stress products, you should opt for a rectangular, triangular, or trihexagonal infill style. These will guarantee you the best results for this type of project.
Be aware that these infills take a longer time to create. Including them could increase your print time by up to 25%.
Infill patterns for functional 3D prints
When we say functional 3D prints we are referring to items that will be utilized for a practical purpose, such as a 3D printed shelf bracket.
These prints will likely be put under a great deal of stress and will need to be strong and incredibly durable. They will also require strength in a multitude of directions to ensure safety when in operation.
The best infill styles for functional 3D prints include cubic, quarter cubic, cubic subdivision, octet, and gyroid. These styles of infill will have a density of over 50%, making them very strong.
Infill patterns for flexible 3D prints
The infill density required for flexible 3D prints depends on the level of flexibility you wish to see in the finished product. It can range anywhere from 0 to 100% according to the desired outcome.
Good infill patterns for these types of prints include concentric, cross, and cross 3D. If you are using a flexible type of filament such as a soft PLA, it is wise to use a flexible infill pattern. This will help to preserve the flexibility of the material and the print as a whole.
What else influences the strength of your design?
Filament choice
It is wise to choose a filament from a reputable source as not all are created equally.
It may be tempting to cut down on costs by purchasing cheaper filaments but this is not a good idea. It can lead to imperfections and issues with your printed product and may cause damage to your printer.
There are also specialized filaments available depending on the characteristics you are after. As well as the standard PLA you can get PLA + and PLA blends. These blends often incorporate carbon fiber, wood, copper, and other materials.
Print orientation
The weakest areas on any print are the layer lines. Earlier we touched upon the concept of X, Y, and Z axes.
When a printed product has the majority of its strength in the XY direction instead of the Z axis, it is referred to as anisotropic. This strength difference can be up to 5x.
By rotating your printed object 45 degrees on your printer bed, you can potentially double its strength level.
Number of shells
This seems fairly obvious, but the more layers that you have on the outside of your printed product, the stronger it will be.
It is estimated that one additional shell layer could increase the strength by the same amount as including an additional 15% infill.
Thickness of shells
This will also increase the strength of your final piece as it means the shell layers will be thicker. This is particularly useful if you plan on sanding or chemically smoothing the exterior of your final product.
The shells are the first part of your object to be printed and play a critical role in determining the strength of the finished object.
Over extruding
This is a setting that you will need to play around with as you become more confident with 3D printing.
A little extra extrusion will increase the strength of your final print, but it can decrease the overall aesthetics.
The piece will also be less precise as the over extrusion increases, so take this into account too. Generally, between 10 and 20% over extrusion is a good level to be at.
What are some common infill problems?
Deformed infill
This occurs when your infill settings are not adjusted correctly. Check the infill print speed and gradually begin to reduce it. This could well solve the issues you are having.
Look at your skip settings - i.e., whether the infill has been set to skip layers. Reduce the skip settings and retry printing.
If you were trying to save materials in a previous print project, your extrusion width may be lessened. Set this back to 100% and see what happens.
If your infill is still struggling, you could consider adding a solid diaphragm between the layers. This will act as a support structure for future layers and make your final product much more solid.
You could also try increasing the print temperature in 5 degree increments. This will help to ensure that all of the plastic used is fully melted.
You should also look at the belts and pulleys on your machine. If they are loose it means that the angles produced by the printer are much less accurate. This could lead to deformities in the infill layers.
Infill is poking through the shell
This is really annoying and can add an unsightly finish to your product. Add some more outlines to prevent the infill layers from poking through the shell.
Manipulate the settings on your slicer program so that the outlines are printed prior to the infill layers. We would also recommend reducing the infill overlap amount.
Optimize your retraction settings. This is commonly a major factor in these kinds of issues. You can also recalibrate your extrusion parameters to ensure increased accuracy.
Weak or under extruded infill
If your final product appears spongy then this can be a sign of a weak infill. It is commonly caused by your print settings being slightly inaccurate.
It may not impact upon the aesthetics of your finished product as the shell will likely cover any issues. That being said, it is likely to greatly reduce the strength and stability of your print.
This issue can be fixed by reducing your extrusion settings. The print speed for infills and the extrusion multiplier is increased when compared to regular shell outline layers. If your printer is working its hardest in speed and extrusion volume, you will commonly see infill issues.
You can also try to reduce the layer height. The height should not exceed 75% of your print nozzle size. This means that if you have a 0.4mm nozzle, you should have layers of 0.3mm or less.
You could also consider increasing your print temperature. You should do this in increments of 5 degrees until the infill issues have been resolved.