FDM 3D printers are the most universal hobby 3D printer of today. But do you know what does exactly FDM 3D printing mean? In this article, let’s learn about the FDM rapid prototype process, characteristics, materials available, benefits, as well as limitations of this widely used 3D printing technology.
What Is FDM Prototyping Service?
Fused Deposition Modeling (FDM) is one of the most common additive manufacturing technologies of today (the other two common processes are SLA and SLS. Read: SLA vs. SLS: Which to Use for Prototyping). In FDM，objects are built by selectively depositing molten material layer by layer in a predetermined path. The thermoplastic polymer with long filaments is the most used material in this process. But how does the FDM rapid prototype process work? Roughly three procedures:
Firstly, a spool of thermoplastic filament is added into an FDM printer. The filament will then be fed into the extrusion head and melt once the nozzle has been heated to the required temperature.
Secondly, the extrusion head is attached to a 3-axis system, this system allows the head to move in the X, Y, and Z directions. In this area, the melted material is extruded into thin stands and deposited layer by layer in the predetermined place. It cools and solidifies there. Sometimes, a cooling fan is attached to the extrusion head to accelerate the cooling.
Thirdly, after a layer is completed, the build platform moves down. The printer then deposits a new layer. Repeat this process until the part is completely printed.
Characteristics of FDM Rapid Prototype Process
Warping
Much like the SLS rapid prototype process, warping is also one of the common defects in FDM. The size of extruded material decreases when it cools in solidification. It is because different areas of the print cool down at various rates and their size also varies from speed. The difference in cooling rate leads to the accumulation of internal stress, thereby pulling the bottom layer upwards and causing warping.
Therefore when you want to use FDM to create your prototypes or parts, here are some features that should be avoided in your design:
1. Avoid designing large flat areas in your models. Using FDM prototyping service for creating models, prototypes, or parts of large flat areas is not the perfect option, because this kind of design is more likely to warp.
2. Avoid thin protruding features in your design if you want to use FDM to create your parts. This design is also more prone to warping. You could add some sacrificial material at the edge to increase the surface that touches the build platform. And sharp corners are usually easier to warp than rounded shapes. So if you intend to use FDM prototyping service to make your parts, try to use rounded corners in your design.
3. Material selection is also important. In most cases, ABS tends to warp more easily than PLA or PETG as it has a higher glass transition temperature and a relatively higher coefficient of thermal expansion.
Layer Adhesion
Good layer adhesion is important for the FDM part. In FDM, the bond strength of different layers is always lowered than the base strength of the material, which means that FDM parts have the inherently anisotropic characteristic - their strength in XY-plane is always larger than that in Z-axis. Besides, when printing, the melted material is pressed against the previous layer, causing the wavy surface of the FDM printed object. If such features as holes or threads are required, the post-processing is essential. Here are some common post-processing methods: sanding and polishing, cold welding, priming and painting, vapor smoothing, metal plating, and epoxy coating.
Support Structure
If you want to use FDM prototyping service to print prototypes or parts with overhangs, then a support structure is required. However, the surface printed on support is often of poorer quality than other areas of the print. Therefore, the support structure is not recommended.
Material Available In FDM Prototyping Service
An extensive range of materials is available in the FDM prototyping service. FDM printers can work with commodity thermoplastics such as PLA and ABS, engineering plastics, including PA, TPU, and PETG, as well as high-performance thermoplastics like PEEK and PEI.
The materials used will have a great impact on the mechanical properties and precision of printed parts, as well as their prices.
ABS and PLA are the most common materials for FDM printing. They are similar in cost. If the aesthetics are of great importance to your printed prototypes or parts, PLA is the ideal FDM material. This material is easier to print as it requires low printing temperature, which makes it more suitable for parts with fine details. And ABS is better suited for prototypes or parts requiring excellent strength, ductility, thermal stability, as well as machinability. One downside of this material is that it is more prone to warping. (>>>> 3D Printing Materials Guide: ABS or PLA)
Benefits & Limitations of FDM Prototyping Service
When you intend to use the FDM prototyping service to create prototypes or parts, it would be better to keep in mind the advantages and limitations of this service as it will help you reach the best result.
Below is the summary of the main advantages and limitations of this common 3D rapid prototype process:
Advantages:
1. FDM is the most economical way to produce custom-made thermoplastic prototypes or parts.
2. With high productivity and availability, the lead times of FDM printed parts are short (could be as fast as 24-hour delivery).
3. An extensive range of thermoplastic materials is available. FDM is suitable for building prototypes as well as functional parts.
Limitations:
1. When compared to other 3D printing methods, FDM rapid prototype process delivers lower accuracy in dimension and resolution. It is not suitable for making parts requiring intricate details.
2. The layer lines could be obvious. Post-processing is thus often needed for a smooth finish. And the surface of FDM printed parts is inherently anisotropic.