How Plastic and Resin 3D printers work

In Fused Deposition Modeling (FDM) also known as Fused Filament Fabrication (FFF), the filament is extruded in layers to create a 3D printed object. During printing, the material is fed through a hot extruder and by moving the nozzle in three directions the object can be printed.

  

Figure. A FDM printer.

A Resin 3D printer uses photopolymers as consumable materials. These are liquid materials that can react to light and be solidified. There are two types of Resin printers:

1) Using a laser beam printing the object line by line. This is called pure stereolithography (SLA).

2) Projecting the entire slice of the object using a digital projector. This process is called digital light processing (DLP).

DLP models are faster than SLA printers, since each layer hardens by projecting the entire image of one layer. A SLA or DLP printers uses an ultraviolet (UV) laser to harden the liquid materials; this process is called curing.

Figure 2. A Resin printer.

 

Materials

The Plastic 3D printers can print from the standard materials PLA and ABS up to a wide variety filament blends (mixed with wood, ceramics, metals, carbon fibres etc.). Also, a lot of exotic filaments are available in the market. The filaments can be found in two standardised diameters: 1.75 and 3.00 mm. However, some commercial 3D printers use filament boxes provided by the relative company. They are considered more expensive than standard spools but it is claimed that produce better quality.

 

In the Resin printers, regarding the materials and the colours, there are limited choices. It is recommended that the resin materials should not be from other companies.

 

Precision, smoothness and speed

In the FDM (plastic) 3D printers, the resolution depends on the nozzle diameter (0.2 up to 1.0 mm), the height layer and the precision of the extruder movements in the X and Y axis. The precision and smoothness are affected by a number of printing issues may occur such as warping, oozing or stringings and misalignment of layers.

 

The resin printers consistently produce higher resolution objects and are more accurate than FDM printers. The resolution is primarily determined by the optical spot size either of the laser or the projector, which is really small. SLA prints can produce objects with much better details than a FDM printer could have done (Fig. 1).

 

Figure 1. An object printed with FDM and SLA printers.

Adhesion/removal after 3D printing

In the FDM (plastic) 3D printers, the object can be removed easily. In some cases, a blue tape or specific glue is needed for better adhesion. Also, other tools such as palette knife can be used to remove the object.

 

In resin printers, it can be difficult to remove the printed model from the bed. Sometimes, there is a lot of resin on the bed that it has to be removed using a tool. It is more difficult to remove an object from an SLA printer than in a FDM printer.

 

Post-processing

In the FDM (plastic) 3D printers, there is no post-processing. There is only one case when it may be required when supports have been used and they have to be removed with a cutting tool or even with a hand.

In the resin printers, the printed objects are covered with resin which has to be removed in a bath of isopropyl alcohol. Also, supports have to be removed with a cutting tool.

 

Cost

For the common FDM (plastic) 3D printers, a lot of companies offer standardised filaments and the price for a spool with weight at 750-1000 gr can cost at 20-35 $. Specialised filaments are more expensive.

 

In the resin printers, the tank and the build platform may need to be changed after some printings. Also, the resins are much more expensive than the FDM’s spools and are offered only by the manufacturer of the printer.

 

Synopsis

 In Table 1, the cons and pros of a plastic and resin printer are demonstrated.

 

Plastic

Resin

Low-cost models

High-cost models

Large build volume

Limited build volume

Large variety of materials and colors

Limited variety of materials

Low printing speed

High printing speed

High strength and durability

Low strength and durability

Medium precision and very low smooth finish

High precision and smooth finish

Low post-processing

High post-processing

Table 1. A comparison between a FDM (plastic) and Resin printer.

 


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