From design prototypes to prosthetic body parts, 3D printing is creating new possibilities in manufacturing. 3D printing machines currently produce everything from sand castings to titanium dental implants and turbine blades. The duck pictured above, Buttercup, was born with a terribly deformed foot which made her unable to walk. With the help of a custom 3D printed prosthetic, Buttercup can now walk normally.
Before taking a closer look at 3D printing or, as it’s formally termed, ‘additive manufacturing,’ let us examine conventional, or as it’s sometimes termed, ‘subtractive manufacturing’. This type of conventional manufacturing, as far as cutting plastics is concerned, is something that Craftech is well equipped to do. In subtractive manufacturing, sheets or rods of plastics are whittled down to produce finished fasteners.
Cutting metals like steel presents a greater challenge. When we cut steel, the fasteners usually spend some time in a CNC mill, where they are cut into shape by carbide end mills. The machine must be extra rigid to hold tight tolerances. By way of example, one of our mills, a small one by industry standards, weighs in at about 26,000 pounds. It uses a 35 horse power motor and has rigid box ways. When the machine is in fighting trim it can hold a thousandth of an inch easily. Holding tenths is also not out of the question since the spindle and ball screws are cooled to a consistent temperature and high pressure coolant can run through the spindle, allowing us to do things like gun drilling. A mill like that, if bought today, would cost around $350,000-$400,000. Its work envelope is approximately 20”x40”x26” high. Anyone who programs and runs one of these beasts always ultimately asks the same question: why couldn’t a machine simply lay down or fuse layers of metal into a finished part? Wouldn’t that be much simpler? That’s where 3D printing comes in.
When approaching a 3D printing project, one first needs access to a 3D modeling program, such as Solidworks or Inventor. The solid model made by such programs, as well as pricier programs like Sieman’s NX or Pro-E, can then be output in STL (stereolithography) format. The term ‘stereolithography’ was patented in 1984 by Charles W. Hull, the man who invented the language of modern 3D printing. The term is defined as "a system for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed."
The original goal for 3d printing was to be able to make extremely small objects with tremendous accuracy. This process is called microfabrication. In a way, 3d printing is the outgrowth of a combination of the CNC positioning system used in mills and EDM machinery with the technology, largely from the Semiconductor group of industries, which involved using beams to disturb the layer of resist on printed circuit boards, so as to produce 3d features. This early 3D printing technology was essentially lithography.
It didn’t take long before various processes, such as the LIGA process, could build real 3D structures with great accuracy. For example, a honeycomb structure 70 um high was built with 8 um thick cell walls. Other items, such as fully-functional pumps, locks, etc., have also been built this way.
Once these technologies were developed the stage was set for producing larger items. Let us now examine the top three technologies which have been developed for macro printing, or the 3D printing of visible objects with some mass.
1) Fused Deposition Modeling (FDM)
This method is really a type of extrusion which is usually used to make ABS or other plastic models. It can be also used with eutectic metals and even edible substances. Machines utilizing FDM can be relatively inexpensive. There are even do-it-yourself kits for those for whom accuracy is not a big factor. Some of you may be familiar with MakerBot, a common FDM machine.
2) Direct Metal Laser Sintering (DMLS)
Almost any metal alloy can be used to make models with this 3D printing technique. Post-Build issues blunt some of the effectiveness of any of these additive methods which rely on sintering by a beam. That is simply that they need post-build curing to ensure that the particles of the model adhere in such a way as to be at least reasonably close in strength to the actual metal being used. This also means more post-build time. To compensate for less than perfect bonding and/or dimensionality, some manufacturers are no producing units which combine additive and subtractive technologies to produce a finished part. Say you want to make a high tolerance part, such as an enamel covered metal tooth, or partial plate. The metal item is first formed. Then, without having to be physically moved, with all the loss of ccuracy that that implies, the item simply slides over to the subtractive (milling) unit, where the last few thousandths are removed and any polishing or other mechanical finishing done. Admittedly, this is an interim and awkward fusing of two technologies. Eventually additive manufacturing cells will lay down each layer atom by atom, erasing the need for any kind of finishing.
3) Selective Laser Sintering (SLS)
This process was also developed in the mid 1980’s. It is capable of sintering metals and plastics. Selective Laser Melting (SLM), on the other hand, does not rely on sintering. Rather it melts the material at a high enough temperature that a fully-formed, dense and strong object is formed through the process. Then there is EBM, or Electron Beam Melting. This process is conducted in a high vacuum, and is mainly used to form fully-dense, strong, titanium parts. It uses an electron beam to melt a thin wire, thereby laying down layer after layer of metal. It is also one of the most accurate processes. However, purchasing one large and powerful enough to even produce small mold cavities and cores could set the purchaser back $500,000 or more. What is today far more ubiquitous, are the small desktop 3D extrusion type printers.
The 3D scanner must also be mentioned as being an indispensable adjunct to the 3D modeling and printing. Sort of like a camera and digitizer in one, it can scan an object accurately enough that it can be immediately translated into a model. At one time the only way to accurately scan an object’s measurements was through the use of a coordinate measuring machine, or CMM. As recently as ten years ago, these machines cost well over $100,000. Although they still have their place in tool-making shops and other places where required accuracies are within tenths (.0001” or about ¼ micron), many models can be scanned with these new, relatively inexpensive 3D scanners. No doubt someone is also working on a scanner that will tell the prospective buyer whether the sweater they’re buying online will fit! In any case, the field of additive manufacturing and 3D scanning is one which currently shows unlimited promise.
Do you have experience with any of these 3D printing machines? Share your experiences below!
Looking to learn more about plastic manufacturing? Check out our complimentary glossary!