Everything You Always Wanted to Know . . . Additive Manufacturing

Chapter 9: From Digital to Physical – Rapid Prototyping and Milling

Up to now we’ve been discussing putting physical objects into the realm of the digital, but before we finish this series we need to talk about another common application for our 3D scanning and modeling processes. Chapter Nine focuses on creating physical objects from digital data.

Important Terminology

Additive Manufacturing – the process of making a physical object from 3D digital data by layering materials; also known as rapid prototyping and 3D printing.

Milling – a subtractive process of removing material to create a physical object directly from 3D digital data by the cutting away from existing solid material.

Applications

You may be asking, why do I need a physical replication of my digital model? After all, we just spent a series of entries talking about turning your physical parts into various digital formats. But there are many good reasons to create new physical models of your data. Here are a few:

* Scaling: Making enlargements, reductions, or even exact size replicas...we can do it all. After a Digital Model has been created, there are few boundaries as to how big or how small we can replicate your object or part.
* Restoration: Our technology enables us to capture accurate 3D data that can be used for manufacturing to completely restore any object that has been damaged by weather, neglect, natural disasters, etc. such as historical monuments and artifacts or aged aircraft and automotive parts.
* Manufacturing Prototype: With a digital model, Direct Dimensions can create a physical prototype that can be used for testing or to manufacture final pieces, such as milling a foam sculpture for a bronze casting pattern or creating a finished prototype as a concept model for a new consumer product.

And now we can talk about the best ways to create the physical models.

Additive Manufacturing (AM)

There are a variety of additive manufacturing equipment manufacturers and processes on the market. Regardless of the type of AM, the various machines read the 3D data most typically in an STL file format. We discussed this format in earlier editions. The software within the machines then generates the layering instructions and directs the deposition of successive layers of material needed to build up the physical part. Essentially this part is created from cross sectional layers. The layers are fused together automatically and ultimately create the final shape, an exact physical replica of the 3D model. Additive manufacturing is an umbrella term that covers many of the following processes.

* One of the earliest and most common types of AM is called Stereolithography (also known as SLA). SLA builds pieces using a laser and a vat of UV-curable liquid resin. Each thin layer of resin is solidified and secured to the layer below with every pass of the UV laser. SLA is good for producing models, patterns, and prototypes. A downside to SLA is that it generally requires support structures to be included in the build, which is part of the SLA process.
* Another AM process is Selective Laser Sintering (also known as SLS). Unlike SLA, SLS can utilize a wide variety of materials such as plastics, metals, and ceramics although post processing may be required. SLS does not require support material while building since it is built and incased within the raw material. SLS uses these materials in a powder format and, by fusing the powder together, creates the layers needed to build the part. SLS is increasingly being used to create final parts for when mass scale production isn’t necessary.
* Similar to Stereolithography is Fused Deposition Modeling (also known as FDM). FDM, trademarked and marketed by Stratasys, also uses the additive platform build concept. Rather than raw liquid or powder, FDM uses thermoplastic materials which are applied through a heated nozzle that places a single thermoplastic bead at a time. These beads fuse together and harden as cooled. The plastics used in FDM are known for their strength and high heat resistance, making them good for product testing.
* Perhaps the most similar to regular 2D printing is the concept of 3D Inkjet Printing. The only rapid prototyping technique that can print in multiple colors, 3D printing also uses a powder base material, but rather than sintering the powder, an inkjet releases a dot of adhesive mixed with coloring, allowing the layers to be built with colors. While the final model is not generally as strong as the other three techniques it is usually cheaper and faster and the colored prints allow for good representation of final concepts. Recently 3D printing has been used commercially to create personalized figurines from World of Warcraft and Rock Band avatar characters.

The primary advantage to additive fabrication is its ability to create almost any shape or geometric feature relatively quickly and inexpensively. We generally say that for a small part, you can’t beat the price to complexity ratio. However the overall volume within a single build is generally limited for AM and for larger parts we recommend milling.

Milling

Milling is best described as a subtractive manufacturing technique. Most often used in the creation of metal production parts, tools, and molds for virtually any industry, an engineer, or even an artist, counts this as a well-tested valuable method. More advanced Computer Numerical Control (CNC) milling machines, like the various additive manufacturing machines, use a 3D CAD file to create a physical reproduction of the digital model. Unlike AM, CNC milling machines can utilize an extremely diverse range of materials including:

* Metals
* Stones
* Woods
* Waxes
* Plastics
* Even Glasses!

Milling steel or aluminum is a common option to make durable tooling. And stone and wood are common for sculpture and historical restoration projects.

Where is this all going?

We are almost done with our “Almost Everything You Always Wanted to Know About 3D Scanning” series. Don’t be surprised if we add additional chapters now and then; the field is constantly changing and growing. We wrap up this series next with talking about the immediate future of these technologies, including desktop (or home) scanning and manufacturing.