An Introduction to 3D Printing as Additive Manufacturing
Additive manufacturing is the process by which techniques of adding material to a working area and building upon existing material are employed to create a final product consistently and reliably. Although modern techniques like 3D printing are talked about mostly when addressing additive manufacturing, the term has been applied to many techniques dating back to when blacksmithing was the primary metal forming method. Modern autonomous 3D printing methods use 3D modeling software to translate models into printing instructions that are often established layer by layer.
Subtractive manufacturing implies the process of removing material from formed raw material in a controlled manor. Historically, subtractive manufacturing received its roots from carving and sharpening of wood, stone, and bone. Modern traditional subtractive manufacturing methods rely on high precision computer operated machinery and an entire industry focused on cutting methods in an attempt to more easily accommodate design engineering expectations.
In most cases, due to the maturity of the subtractive manufacturing industry focused mostly on CNC (computer numerical control) machining, it is cheaper and quicker to design for these techniques.
Design projects requiring unique weight management specifications, airflow and cooling requirements, acoustics, strength, etc., traditional subtractive manufacturing and welding may not offer enough flexibility. In more complex design, additive manufacturing, more specifically 3D printing, offers more flexibility and less restrictions than most engineers are used to in industry.
History of Additive Manufacturing
Early and late history of ceramic and pottery forming as well as construction introduced new methods of manufacturing that relied on additive building. Additive manufacturing’s debut into modern history originated from blacksmithing, the art of cutting and forming metal into useable objects by treating the material with heat.
Metal castings, an additive manufacturing technique developed by foundries, are created by melting metal into its molten form and pouring the resultant fluid into a formed mold. Mass production of complex shapes and parts/products both large and small was revolutionized by the introduction of metal casting and injection molding. Major materials such as plastics, iron, aluminum alloys, steel alloys, copper alloys and more can be molded at scale.
The most notable form of additive manufacturing is welding, primarily defined as the joining of two pieces of metal. Modern welding consists of using filler metal in order to repair parts by building upon the base metal or to create a more reliant connection than simply fusing the base metal. Buildup of weld filler metal layer by layer to repair or build a 3D object is the basic premise behind metal 3D printing.
Metal 3D Printing
Additive manufacturing as applied to 3D printing refers to the automated process of translating digital 3D modeling data into a physical 3D part layer-by-layer from dispensed material. Current metal 3D printing machines use SLS, SLM, and DMLS style printing.
SLS – Selective Laser Sintering – Process of using an automated laser to sinter compacted layers of powdered material (typically nylon-based) to form a 3D part. Once the base layer is sintered, a new layer of compacted powdered material is dispensed and the laser then sinters the new powder to the previously sintered material. This process is fast and functional, not requiring additional supports due to the powder bed acting as a support.
DMLS – Direct Metal Laser Sintering – Similar to SLS printing, DMLS uses metal powder and a higher powered laser to sinter the material. Common metal powder include stainless steel, titanium, aluminum, and Inconel. Disadvantages of DMLS printing are likeliness of surface porosity that can be removed during post processing.
SLM – Selective Laser Melting – Process of using high powered lasers to fuse metal powders together by locally melting the material, a process similar to standard welding. SLM printing generally produces a stronger part with less risk of porosity, but requires more design parameters. More heat causes more thermal stresses which can hinder manufacturing and result in poor quality parts or print failure.
Each process is performed using a high powered and extremely accurate laser, 3D modeling data, and dispensed metal in the form of a very fine powder. As the metal powder is dispensed (either as a layer or selectively as the laser is operational) the laser either melts or sinters as dictated by the locations in the 3D model. Sintering metal powder will solidify the particles and fuse the material together without welding, whereas melting will introduce different bead size, surface finish, and porosity within the finished product. The primary use-case of 3D printing additive manufacturing besides rapid prototyping is the development of designs and products that are ultimately impossible to build using traditional subtractive manufacturing methods or castings.
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