Two previous posts discussed 3D printing.  This technology is currently being used in the hearing aid industry, as it is in many other industries, for modeling, and even for some product fabricating, especially earmolds and custom-molded shells for in-ear products.  A previous post described Stereolithography (SL) and Selective Laser Sintering (SLS).  This post describes two additional 3D printing processes likely to be encountered, Fused Deposition Modeling (FDM) and Multi-Jet Modeling (MJM).

To review, four different types of 3D printing processes likely to be encountered, are:

  • Stereolithography (SLA)
  • Selective Laser Sintering (SLS)
  • Fused Deposition Modeling (FDM)
  • Multi-Jet Modeling (MJM)

 

Fused Deposition Modeling (FDM)

This additive manufacturing technology is used to model, prototype, and for production purposes.  Although it works by creating an object layer by layer, it differs somewhat from the others in the way the forming materials are used. 

In the FDM process a plastic filament is unwound from a coil and supplies material to an extrusion nozzle (Figure 1). The nozzle is heated to melt the thermoplastic material to a semi-liquid state, and has a mechanism which allows the flow of the melted plastic to be turned on and off. The nozzle is mounted to a mechanical platform, which can be moved in both horizontal and vertical directions (X and Y coordinates).  As the nozzle is moved over the table in the required geometry, it deposits a thin bead of extruded plastic to form each layer. The plastic hardens immediately after being squirted from the nozzle and bonds to the layer below.  Following hardening of a layer, the printer head only then moves vertically (Z-axis) to generate the next layer.  Two materials are used by FDM to complete the printing; a modeling material and a support material. The former constitutes the final product, while the latter acts as scaffolding.

FDM 3D printing utilizing the extrusion of thermoplastic material is easily the most common and recognizable 3D Printing process.  Because the process is clean and easy-to-use, FDM is suitable for office use.  (Video of FDM).

Figure 1. Illustration showing the fused-deposition modeling process, where molten thermoplastic material is deposited in specific patterns. (Reproduction)

Multi-Jet Modeling (MJM)

Multi-Jet Modeling (MJM), also sometimes referred to as thermojet, or Material Jetting, works on the principle of a 3D printer utilizing multi-jets.  Therefore, the modeling is starkly similar to that of an ink jet printer, but tends to use liquid photopolymers which are cured with a pass of UV light as each layer is deposited. The process is a type of a rapid prototyping process that can create wax-like 3D plastic models, layer by layer.

MJM printers have a head that has dozens of linear nozzles that sprays a colored glue-like substance onto a layer of resin powder (Figure 2). Due to the fact that this technology does not have the same kind of limitations as SLA, it is able to produce exceptionally detailed objects with thickness as fine as 16-microns. However, they aren’t as tough as those created using SLA.  (Video)

Figure 2.  MJM 3D printing modeling is similar to that of an ink jet printer, but tends to use liquid photopolymers which are cured with a pass of UV light as each layer is deposited.  (Reproduction)

This process allows for the simultaneous deposition of a range of materials, meaning that a single part can be produced from multiple materials having different properties and characteristics.  MJM printing is very precise and produces accurate parts having a very smooth finish.

Summary

All types of 3D printers build objects layer by layer.  The major difference lies in the technique they use to lay down and solidify the raw materials, as well as the nature of the raw materials themselves. Similarly, they require a file format of the 2D slices obtained from the blueprint.  Some are clean and simple enough to be used in the home or office, while others are limited to industrial applications.  Regardless, rapid advancements in 3D printing bring this technology within the reach of all kinds of modeling and production applications.

When will the first hearing aids be made using 3D printing?  This may be some time from now, but in the meantime, modeling, prototypes, and custom in-ear shells and earmolds are already being made using 3D printing.

Featured Image: http://3dinsider.com/3d-printing-guide/

A previous post opened a conversation about 3D printing.  This technology is currently being used in the hearing aid industry, as it is in many other industries, for modeling, and even for some product fabricating, especially earmolds and custom-molded shells for in-ear products.

Four different types of 3D printing processes likely to be encountered, are:

  • Stereolithography (SLA)
  • Selective Laser Sintering (SLS)
  • Fused Deposition Modeling (FDM)
  • Multi-Jet Modeling (MJM)


Stereolithography (SLA)

This 3D printing process is generally considered the pioneer of all other 3D printing processes.  It was introduced and patented in 1988 by Charles W. Hull, the founder of 3D Systems.  This process makes use of a vat of liquid photopolymer resin that is cured by a UV laser (Figure 1, and described previously).  The laser solidifies the resin layer by layer, creating the entire object.

The SLA printer consists of four main parts:

  • A printer filled with a liquid plastic (resin)
  • A perforated platform that is able to move down and up
  • A UV laser
  • A computer to control both the laser tracings and the platform

As described in a previous post, in the SLA process, a thin layer of plastic (often between 0.05 and 0.15 mm) is exposed above the platform.  Into this thin layer of plastic (resin), the laser “draws” the pattern of that slice of the object as depicted in the design files from the computer.  The touch of the laser onto the resin hardens it relative to the path of the laser.  Then, a new layer of resin flows over the hardened resin as the platform is lowered slightly.  This process continues, layer-by-layer until the entire object has been constructed.  The resultant object is generally smooth.  Because of the nature of the SL process, it requires support structures for some parts, specifically those with overhangs or undercuts. These support structures are designed into the CAD file and are removed manually when the product is complete.  The quality of the object depends on how complex the SLA machine is.

Figure 1.  Stereolithography employs an ultra-violet laser beam to cure liquid photo polymer in layers.  A platform starts one layer depth below the surface of the polymer material and the laser cures the first layer based on thin data slices of the object from a computer.  The platform is lowered by one-layer depth and the next layer is cured.  The process is repeated until the object is completed.


Selective Laser Sintering (SLS)

One of the most commonly used 3D printing techniques is that of Selective Laser Sintering (SLS).  In this process, tiny particles of ceramic, glass, or plastic are fused together by the heat of a high-power laser to form 3D objects.  Like all other 3D printing processes, it starts with designing of a 3D model using CAD software.  The files are then converted to an appropriate format recognized by the 3D printer.

Instead of a liquid resin tank, as used in SLA, SLS uses powder materials, usually plastics like nylon, to print the 3D objects.  The computer controlled laser is instructed to print the appropriate object by tracing a cross-section of the object onto the raw material (powder).  The heat from the laser is equal to, or slightly below, the boiling point of the particles.  As in all prototyping processes, the parts are built upon a platform that adjusts in height equal to the thickness of the layer being built.

As soon as the initial layer of the object is formed, the platform of the 3D printer drops by no more than 0.1mm (example) and a new layer of the powder is placed over the previous layer. This layer is then exposed to the laser to harden the material in that layer.  Additional powder is deposited by rolling it onto the platform on top of each solidified lay and sintered.  This process continues layer-by-layer until the object is created.  The powder is maintained at an elevated temperature so that it fuses easily when exposed to the laser.  The finished product must then be allowed to cool before being removed from the printer.  Figure 2 shows the process, and a video showing the process at this link.

SLS uses a moving laser beam to trace and selectively sinter powdered polymer and/or metal composite materials into successive cross-sections of a three-dimensional part.  Unlike SLA, special support structures are not required because the excess powder in each layer acts as a support to the part being built.

Selective Laser Sintering (SLS) was developed and patented (1989) at the University of Texas in Austin, by Carl Deckard, an undergraduate student, along with his professor, Joe Beaman.  The process was acquired by 3D Systems in 2001.

Figure 2.  A CAD file that has the data of thin slices of an object to be fabricated is passed through a laser and draws the image of that slice into the powder, where it hardens as drawn by the laser.  That layer is then dropped slightly, and the leveling roller pushes another layer of powder over that image.  This new layer is again exposed to the heat of the laser with the image of the next slice from the CAD program, and this layer is then formed.  This layering process continues until the object is completed.

A following post will describe Fused Deposition Modeling (FDM) and Multi-Jet Modeling (MJM) 3D printing.