Friday, 1 July 2016

3D printing Processes

When discussing 3D printing technologies, it is important to understand that 3D printers have varying grades and levels. While some were the early birds in terms of their date of production and when they started working both commercially and in non commercial capacity.

3D printing has many different types of printing processes which i will discuss in details. These processes are as listed below:

StereoLithography (SL)
Fused Deposition Modelling / Extrusion / FFF
Digital Light Processing (DLP)
Laser Sintering / Laser Melting
Inkjet: Binder Jetting and Material Jetting
Selective Deposition Lamination (SDL)
Electron Beam Melting

StereoLithography (SL) :

This 3D printer was probably the first 3D printer in the market, it was the earliest bird to the market, as it was the first 3D printer to be commercialized and made available to the market for purchase and use.

I will be using the short form of this printer, SL, a laser based process which works with photo-polymer resins (highly viscous substance), going into reaction with this laser and thereafter, it is UV cured to form a very solid and accurate parts.

It is a complex process, but can simply be explained thus, the photo-polymer resin is held in a vat with a movable platform inside.

A laser beam is directed in the X-Y axes across the surface of the resin according to the 3D data supplied to the machine (which is the .stl file), and the resin hardens precisely where the surface was exposed to the laser. Once the layer is completed, the platform within the vat drops down by a fraction (in the Z axis) and the subsequent layer is traced out by the laser.

StereoLithography 3D printing process

This continues until the entire object is completed and the platform can be raised out of the vat for removal.

Now due to the nature of the SL process, it requires support structures for some of its parts, specifically those with overhangs or undercuts and theses structures need to be manually removed.

Curing here seems a little different from the curing we know in medicine, this one involves subjecting the part that was exposed to laser to intense light in an oven-like machine to fully harden the resin.

This particular 3D printer is generally accepted as being one of the most accurate 3D printing processes with excellent surface finish. However limiting factors include the post-processing steps required and the stability of the materials over time, which can become more brittle.

Fused Deposition Modelling / Extrusion / FFF:

This 3D printer is currently an industry grade 3D printing process which works by melting plastic fillament that is deposited , through a hot extrude, a layer at a time, unto a built platform according to the 3D data supplied to the printer.

3D printing Process with FDM

Now each of this layer hardens as it is deposited and it bonds to the previous layer.

The developer of this technology (Stratasys) has developed a range of proprietary industrial grade materials for his Fused Deposition Process (FDP) that are suitable for some production applications.The FDM / FFF processes require support structures for any applications with overhanging geometries.

For FDM, this entails a second, water-soluble material, which allows support structures to be relatively easily washed away, once the print is complete. Support structures, or lack of it, have generally been a limitation to the entry level FFF of 3D printers. However, as the systems have evolved and improved to incorporate dual extrusion heads, it has become less of a problem.

In terms of models produced, the FDM process from Stratasys is an accurate and reliable process that is relatively office/studio-friendly, although extensive post-processing can be required to improve its performance relative to other printers in the market.

Digital Light Processing (DLP):

DLP is another 3D printing process, which like the Setrolithography process utilizes the photopolymers. Remember i talked about the light source of SL as the UV, well that is the major difference between the two types of printing processes.

Digital Light Process

DLP- makes use of light sources like arc lamp, with a liquid crystal display panel or a DMD (Deformable Mirrow Device), which is applied to the entire surface of the vat of photopolymer resin in a single pass, thus making it faster than SL. Note also that like SL, DLP produces highly accurate parts with excellent resolution, but has similar fault, which include the same requirements for support structures and post-curing.