Which aspects of CAD technology are most important for 3D printing?

Additive manufacturing (AM) is a process for making 3D objects of almost any shape by additively laying down successive layers of material under computer control. The AM technology began when Chuck Hull of 3D Systems® invented stereolithography in the 1980s for UV curing of photopolymers. In the 1990s, Stratasys® introduced metal sintering form of AM and called it fused deposition modeling (FDM).

Since the early work of 3D Systems® and Stratasys® in AM technology, 3D printing technology improved rapidly, and 3D printing machines have found many applications in architecture, construction, industrial design, automotive, aerospace, military, dental and medical industries, biotech (human tissue replacement), fashion, footwear, jewelry, eyewear, education, geographic information systems, food, and many other fields.

Within the past decade, a rapidly expanding hobbyist and home-use market emerged for 3D printing, due to the GNU open-source RepRap project (a British project) and the Fab@Home project, which is a syringe-based AM deposition model developed at Cornell University.

Because 3D printing is becoming increasingly popular, it is now common to print objects which were formerly manufactured by injection molding. For example, instead of buying a measuring cup from a store, a customer could download the 3D model for the cup from the web, and print it at home on a desktop printer.

How are 3D CAD technology and 3D printing related?

Two major CAD-related technologies are vital for 3D printing. They are:

• Representation of 3D objects in a file format, which can be transformed into instructions for 3D printers.
• CNC CAD technology, which creates machine instructions for creating 3D objects by additive manufacturing.

3D printed objects require an STL (STereoLithography) file format. This format, which is native to stereolithography CAD software, was developed by 3D Systems®. In order to create 3D printed objects, a 3D CAD model for the object should exist, preferably in binary STL format.

The STL file format describes only the surface geometry of a three-dimensional object. It does not describe representation of color, texture or other common CAD model attributes. The STL format can be written in either ASCII or binary form. The binary format is preferred, because it is more compact. The major components of an STL file format are definitions for triangles in terms of 32-bit floating-point numbers, which specify the normal and the x-y-z coordinates of each vertex of the triangle.

Two variations on the binary STL format are used to add color information.

The first variation adds 2 bytes to the end of the description for each triangle in order to store a 15-bit RGB color. The second variation uses the 80-byte header at the beginning of the STL file to represent the overall color of the entire part. In order to print a 3D object, the STL file is processed by software called a “slicer” which converts the model into a series of thin layers and produces G-code. The G-code specifies NC (Numerical Control) or CNC (Computer Numerical Control) instructions which are tailored for a specific 3D printer. The 3D printer follows the G-code instructions to lay down successive layers of liquid, powder, paper or sheet material to additively build the model from a series of cross sections. These layers correspond to the virtual cross sections from the CAD model, and the layers are joined or automatically fused to create the final shape.

Printer resolution describes layer thickness and x-y resolution in dots per inch (dpi) or micrometers (µm). Typical layer thickness is around 100 µm (250 dpi), although some machines produced by Objet® and 3D Systems® can print layers as thin as 16 µm (1,600 dpi). The x-y resolution is comparable to that of laser printers. The particles (3D dots) are around 50 to 100 µm in diameter. The proliferation of personal, open-source CNC software has made it possible for hobbyists and home-based 3D printers to print their own objects.

Why is 3D printing disruptive to conventional manufacturing methods?

3D printing has become a major market disruptor, which is ushering in a new industrial revolution. At the last Consumer Electronics Show (CES) held in 2014, there were over thirty 3D printing companies whose exhibits ranged from toys to tea cups and iPhone cases. The turnout at the 3D printing exhibits drew dense crowds that could not fit in the exhibit booths.

The following discussion lists some of the reasons why 3D printing is becoming disruptive.The majority of those who use 3D printing are professionals, hobbyists and home users. They are using desktop 3D printers for making toys, phone add-ons, and models of objects and fashion.

• Many companies are making plans to automate their factories to use AM technology, because it provides better efficiency, more accurate prototyping, cost savings, shorter time to market during product development, and improvement in supply chain performance.
• Two companies in the housing market estimate that giant 3D printers could build a 2,500-square-foot house in 20 hours. The enabling factors are that 3D printers could be utilized for electrical work, plumbing, tiling, finishing work, and painting.
• Because there will be less reliance on hard tooling (which is needed for manufacturing thousands of identical objects), 3D printing creates the opportunity to offer customized designs at lower cost, and to a far broader range of customers.
• The medical industry is using 3D printing to create medical models which make complex surgical procedures more manageable. Notably, surgeries involving the skull and spinal column are benefiting from 3D printed models. Also, studies are underway to create 3D printed medical implants embedded with antibacterial and chemotherapeutic medicines for smart drug delivery.

Summary

The two major CAD technologies that enabled 3D printing to make significant progress are the STL CAD format and CNC CAD technology.

The explosive growth in 3D printing will continue.

In the industrial marketplace, the two clear leaders in 3D printing are 3D Systems® and Stratasys®.

Because of open source software which translates STL files into 3D printer format, there will also be explosive growth in hobbyist-oriented and home-based 3D printers.

– The CAD Chief