Features

Speed equates to cost, so faster prototyping and production mean lower costs and faster time to market. Although this statement seems to be fairly easy, there are some considerations to make when thinking of additive manufacturing, also called 3D printing, where a three-dimensional object is created by laying down successive layers of materials from a digital model. Rapid prototyping has become an all-encompassing term for the use of a class of technologies to construct physical models using computer-aided design (CAD) data. This is exactly why medical device companies are exploring the use of a variety of types of additive manufacturing to help cut prototyping and production costs. Here’s a look at some of the different additive processes available, their materials, applications, and some design rules to keep in mind when designing for manufacturability.

Processes

Fig. 1 – Femoral components are shown raw in a bed of powder from a DMLS machine in cobalt chrome.
There are several additive processes all of which equate to certain needs, materials, and geometries, and all built directly from 3D CAD data.

The most recent technology is Direct Metal Laser Sintering (DMLS), an additive metal fabrication technology that fuses metal powder into a solid part by melting it using the focused laser beam. It can be used to build fully dense alloys within a matter of a few days. (See Figure 1)

After that, we have Stereolithography (SLA) and, although this is one of the first rapid prototyping processes available, it can not be used to build production grade materials. SLA requires the use of supporting structures that must be removed from the finished product manually. Although SLA can produce a wide variety of shapes, it is often expensive.

Another sintering process is Selective Laser Sintering (SLS) uses a high power usually pulsed laser to fuse small particles of plastic, metal, ceramic, or glass powders into a mass that has a desired three-dimensional shape. This technique can be used to build parts in Nylon-based materials that are production grade.

One of the most commonly used technologies is Stratasys’ Fused Deposition Modeling™ (FDM), which can be used to build production grade applications using acrylonitrile butadiene styrene (ABS) or polycarbonate (PC) materials. The technology is also known as fused filament fabrication. FDM is making a huge name for itself in the “do it yourself” market where retail consumers are purchasing small home-based systems for less than $1,500. Both FDM and SLS use melting or softening material to produce the layers, while SLA lays down liquid materials that are cured with different technologies.

Lastly, we have PolyJet™, a new photopolymer 3D printing process from Objet Ltd., that uses simultaneous jetting of multiple types of modeling materials to create a single piece 3D model. What is amazing about this process is the fact you can build multiple durometers on a single part thus mimicking overmold components. PolyJet technology allows the user to choose from more than 100 different build materials and can simultaneously build 14 different materials into a single model part.

Materials

Fig. 2 – Showing is a femoral trial used in total knee replacement manufactured with the DMLS technology, polished in a stainless material.
Each additive manufacturing process uses its own materials, some of which can include hundreds of options. Rather than including every single material, this compressed list describes the most commonly used materials for each process.

DMLS: PH1 Stainless Steel 15-5 (high corrosion resistance, sterilizability, hardness and strength), GP1 Stainless Steel 17-4 (high corrosion resistance, sterilizability, high toughness and ductility), MP1 Cobalt Chrome (high mechanical properties in elevated temperatures and with good corrosion resistance), Ti64 (combination of high mechanical properties and low specific weight), IN718 (chemical resistance with an elevated temperature) and MS1 Tooling Steel (heavy duty injection molds and inserts for molding all standard thermoplastics using standard injection parameters, with achievable tool life of millions of parts).

SLA: Accura 25 (polypro-like), Accura 60 (polycarb-like), Somos 11122 (ABS-like and can be transparent) and Somos NeXt (durable with high feature resolution).

SLS: Nylon 12 (durable and flexible), GF Nylon (durable and rigid) and Duraform Flex (rubber like material).

FDM: ABS-M30i (biocompatible ABS (ISO 10993 USP Class VI certified) material), PC (most widely used industrial thermoplastic), PC-ABS (superior mechanical properties) and Ultem 9085 (FST, high heat, chemical resistance, highest tensile and flexural strength)

PolyJet: Vero White (rigid and white), Vero Black (rigid and black), Tango Plus (flexible 27a and amber in color) and Tango Black (flexible 61a and black in color). Objet Connex printers can also produce multiple durometers depending on the geometry and application.

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