Second of Six Parts on Additive Manufacturing Overview for manufacturers
Blog Written by: Hutch Hutchison, Principal, Technology and Engineering, FuzeHub
This week we will see How AM Works:
HOW DOES ADDITIVE MANUFACTURING WORK?
I guess I would trace the origins of Additive Manufacturing (3-D Printing) back to August of 1977 when Canon engineer Ichiro Endo discovered thermal inkjet printing, where a computer algorithm guided the placement of thermally-induced ink droplets to form an image on paper. This discovery has gotten a lot of mileage in the world, and we take for granted that when we send a file to our printer from a computer, we get a precise representation of the image, in two dimensions, in full color! So consider what happened, the print head laid down a single layer of ink, to form an image.
Now consider that a 3-D printer does little more than this, accurately print a part, but one layer at a time, and of a material that is more “solid” than ink, such as plastics, metals, or even organic materials. So, Here’s how it works: Starting with a 3-D CAD model of the object, a version of that CAD model produces a special computer program (similar to programming a Computer Numeric Control (CNC) Machine) that ‘slices’ the part model into single layers that the head prints successively out of plastic or other solid material. This file is a “.stl” file. Similar to the CNC analogy, the .stl file guides the “toolpaths” that the head takes to form each layer. The smarter .stl applications not only guide the toolpaths, but also select materials and placement of (removable) supports if the layer has an appendage that is not adequately supported during the build and/or cure time. The files also guide the orientation of the part, for maximum efficiency. In contemporary machines, an engineer or designer can intervene and program the.stl file for efficiency or accommodate a different material.
Armed and guided by the .stl file, the 3-d printer head scans back and forth across the build platform, depositing, fusing, binding, even cutting material to build a part, in as small as tenth of millimeter layers, with wall thicknesses as small as tenths of millimeters to solid.
I hope you get the idea from this simple analogy. The rapid growth of 3-D printing, given how relatively simple it is to make solid parts by “printing” has spawned several methods, all acting on the same, computer-guided principle. For example, the first such 3-D Print method, as we saw last week, was called Stereo Lithography. In this case, a vat of photosensitive polymer liquid material feeds a layer onto a build platform, which is on a movable (up and down) platform. The .stl file controls a UV laser to expose only the material that comprises the first layer of the part, thus hardening only the exposed portion. The platform drops the predetermined layer thickness amount, and another layer of the liquid is formed for exposure by the computer-guided laser beam. Both build material and support material are exposed during a layer build, so that the part is supported until fully cured. As the part grows, layer by layer, when the last layer is complete, it is removed from the printer and the entire part is put in a UV cure oven, for a predetermined period, to fully solidify. The cured part then has the support material removed, and is now ready for finishing, including painting if necessary. Stereo Lithography was very popular as a prototype tool for many years, but has not really caught on, due to material aging issues, as a viable additive manufacturing tool.
This video shows the Stereo Lithography process better than I have described it:
FUSED DEPOSITION MODELING
Let’s take a look at another very popular means of 3-D Printing, called fused deposition modeling (FDM). In this case, the CAD file guides the print head, which is connected to a spool or other feed of various plastics, including ABS. The print head heats the plastic line to a viscous state and extrudes a continuous, flow of material onto the build platform, again one layer at a time. The FDM process is very popular in the “maker” community, basically hobbyists, who build their own 3-D printers from companies such as Maker Bot, in Manhattan, which sells a kit of parts for around $1000. On the other end of the price spectrum, Stratasys, an old name in AM, makes several models of FDM processors, capable of turning out plastic parts in sizeable build volumes up to 3’ X 3’ X 2’ – that’s a big part. Here is a video of the FDM process, to clarify:
So that covers what I wanted to talk about this week. Come back next week, we will take on the main reason that 3-D Printing is becoming Additive Manufacturing – METALS! We will look at the process of Selective Laser Sintering, which is the process of fusing metal powders to form parts. You’ll love it!