3D Printing Overview

Terminology

Figure 1: CAD image of a teacup; additional rendering shows differences in final build due to differences in layer thicknesses. (Reprinted with permission from Gibson, I., Rosen, D. & Stucker, B. Additive Manufacturing Technology. in Additive Manufacturing Technologies 1–18, 2015. DOI:10.1007/978-1-4939-2113-3 Copyright 2015 MDPI)

3D printing is the colloquial term for the rapid prototyping process formally known as additive manufacturing or rapid prototyping. Rapid prototyping (RP) is used generally across different industries to refer to a process in which different versions of a product are generated, evaluated, and improved upon in a relatively rapid and iterative manner until the final product is formed. However, the meaning of this term has also been extended to cover business development and software solutions (e.g., startup culture). It is thus beneficial to use the more specific terminology, additive manufacturing, or AM, which is the term that is generally agreed upon under ASTM standards. This terms covers iterative prototyping involving a manufacturing process that builds products or product parts designed using Computer-Aided Design (CAD) software by adding materials in layers (Figure 1). This distinguishes AM from other rapid-prototyping processes, such as injection molding or subtraction processes, as well as from uses of the term RP in various other industries.

History

3D printing has no singular specific inventor. The idea of 3D printing first emerged from sci-fi writer Murray Leinster in 1945 when he published the short story "Things Pass By," where he described a machine that could take drawings and replicate them using melted plastic.. The first patent submitted for 3D printing was in 1971 by Johannes F. Gottwald. Gottwald's patent detailed a liquid metal extruder that would take melted metal and print 3D objects. However, his patent would expire due to lack of resources. In 1981, Dr. Hideo Kodama would submit a patent for a laser beam curing process. Due to lack of funding, Kodama's patent would never go through.

In 1984, Charles W. Hull would file a patent for a 3D printing system, and, unlike everyone who had tried before him, it would get approved in 1986. Hull invented a Stereolithography (SLA) 3D printing method where thin layers of material cured by ultra violet light were printed in layers to form a 3D structure. This technology was commercialized by 3D Systems in 1989. In the same year, S. Scott and Lisa Crump patented their invention of fused deposition modeling (FDM), which feeds a plastic filament into a heated extruder and precisely lays down the heated material, and co-founded Stratasys, Ltd. In the early 1990s, a series of patents were filed for early versions of powder sintering printing technologies, which became the core technology of Z Corp; Z Corp was later acquired by 3D Systems.

Since then, development and innovation in the field has occurred at an increasingly rapid pace. Novel technologies include two-photon polymerization, which can print at the molecular level as well as contour crafting, which makes it possible to print large-scale concrete structures. Other technologies include food printing and bioprinting which could make it possible to print out human organs. Furthermore, the expiration of many early 3D printing patents has allowed the general public to co-opt additive manufacturing, catalyzing the start of the RepRap movement, an open-source arm of the 3D printing movement.

General Workflow

Figure 2: General workflow from CAD to final part (Reprinted with permission from Gibson, I., Rosen, D. & Stucker, B. Additive Manufacturing Technology. in Additive Manufacturing Technologies 1–18, 2015. DOI:10.1007/978-1-4939-2113-3 Copyright 2015 MDPI)

The specific of additive manufacturing varies across the different printing technologies, but the general process from design to final product remains similar. The general manufacturing stages are as follows (Figure 2).

1. CAD: Any printed part needs to start as a fully-defined 3D solid and/or surface representation on a computer somewhere. This can be generated in a CAD/CAM software, or it can be reverse engineered from 3D scanning data.
2. File Transfer to Printer: Nearly every 3D printer on the market accepts the STL file format, and most CAD software is able to output as an STL. Once this file conversion is done, the file is transferred to the machine, where further adjustments to size, position, and orientation of the part may be done before it is ready to build. Many printers also accept G-code, a programming language telling a printer the steps of printing decided by the user to create objects.
3. File Transfer: Nowadays, printers have access to Bluetooth and WiFi connectivity allowing direct upload of files to printer from PC or phone, but conventionally, an SD card or USB that is formatted is required for the printer to read the build code.
4. Machine Setup: Setup of the machine includes check leveling the bed, changing the filament, and calibrating the print settings to the material specifications.
5. Build: Start the build process after setup is complete. The bed will heat up to set temperature for bed adhesion, and the nozzle will heat up to extrusion temperature. The extruder will dispose a small amount of filament to make sure its unclogged, and the build process begins.
6. Remove: After the build is done, the bed will cool down, and the print can be easily removed.
7. Post-Processing: Following the build, parts may need to undergo post processing and/or cleaning to improve mechanical properties and clear out support materials and/or structures. These processes vary between the different printing technologies. After this is done, the part is ready to test or use.
8. Application: The build is ready to be implemented for its use.