The Complete Material Selection Guide for 3D Printing

How-To Choose the Right Material for Your Application

Starting with the proper material selection is essential to getting the outcomes you want during extrusion and when 3D printing. You should choose your material based on its properties and its processability, not the possibilities you hope it’ll give you.

To help you along with your journey, we’ll take you through the different factors you should consider while giving you real-life examples, so you know how to go about the right material selection for your specific need. These factors include:

• • • Difficulty to 3D print or extrude the material
    • Features available with your 3D printer or extruder
    • Project requirements dependent on the material
    • Choosing the correct material grade
    • Complexities of using recycled plastic
    • Creating composite materials with the use of additives

Difficulty to 3D Print or Extrude the Material

Not all materials have the same processability or require the same settings for filament extrusion. For example, high-temperature polymers such as PEEK, PEKK, and PEI require special processing, transition, and purging techniques. Therefore, it’s important to know and learn these techniques before you start experimenting to avoid clogging your filament maker.

Polymers such as PP and HDPE are challenging to solidify as round filaments due to high crystallinity. While they are very safe to process with out equipment, they take time to master from the start

Crystallites that can affect the roundness of some polymers

Project Requirements Dependent on the Material

What do you want to achieve with your project?
Before you decide on a material, define your needs carefully. Your material selection may become a variable in your project, so if several materials meet all your needs, it would be wise to choose the one that’s easier to process at the end of the day.

Choosing the Correct Material Grade

When considering which polymer to choose for your application, it is essential to know the different grades available. The grade of a polymer corresponds to one specific reference of a polymer type by one manufacturer.

ABS is a family of hundreds of grades of the same plastic. Each grade is unique, and luckily, each is usually associated with a specific technical data sheet that can help you with filament manufacturing or 3D printing. To simplify things, we can divide them into categories of types of grades.

The main difference between the categories is the flowing behavior of the molten polymer, which we can quantify with a clear viscosity indicator: the Melt Flow Index (MFI) in g/10min.

The MFI test is quite simple. It’s done by measuring the mass of molten polymer that can be pushed through a hole under standardized conditions. The higher the MFI, the more fluid the plastic is, but the lower its viscosity.

 

The MFI values are only estimates and not exact settings. The scale gives a general indication of which grades are easier to transform into filaments, but it does not mean that only extrusion grades can be processed with filament makers. Quite the contrary, our material specialists have been able to process many injection-molding grades successfully.

There are usually no material-technical datasheets for manufactured items. In this case, the MFI is unknown.

The Challenges of using Recycled Plastics

Recycling plastics usually comes with a few more challenges than processing virgin plastics. These challenges include:

• Collecting and sorting the parts
• Shredding the plastic
• Keeping the batch clean
• No datasheet as reference

Although these extra steps can be time consuming, but don’t let that stop you from trying! We have successfully extruded recycled plastic several times and have learned that it works well when all parameters are controlled.

 

In order to create a composite, the additive must be mixed with the base polymer. There are two ways to ensure that the additive is dispersed throughout the polymer.

• Premixing the additive and polymer through extrusion
  Premixing the additive and polymer to form homogeneous pellets is usually done by twin-screw extrusion and making filament out of it. This method tends to let you achieve high additive proportions.
  
  
• Directly feeding the polymer and additive into the hopper
  By feeding the polymer and additive directly into the hopper of the filament maker*, the steps of mixing and filament production are combined. However, the risk of clogging the filament maker is higher.
  *This is possible with our filament makers; please note that this might not be possible with other filament makers.

When experimenting, it’s advisable to start with a small percentage of additives (usually 5%wt) and gradually increase the rate. The particle size of the additive is also crucial; sizes around 100 microns have been found to work very well.

Material Selection Summary

By choosing the right material and the right quality, you can achieve your goal effortlessly. A safe process allows you to quickly assess the workability of a particular grade and choose a different grade if necessary.

These guidelines can seem quite daunting, and you may focus on the limitations and constraints of material selection. But, in reality, they show the many opportunities and discoveries you can make in material selection and processing.