Tips on selecting 3D printers

This feature is part of a series of features for the 2011 Make Parts Fast Handbook.

cover art_opt, Make Parts Fast Handbook, 2011A 3D printer can be used to analyze form, fit, feel, function, or some combination of these features. But it can do more. Today’s printers also function as manufacturing equipment, producing one of a kind parts, like hearing aids, medical instruments, orthodontic parts, and prosthetics, as well as small numbers (typically less than 10,000 units) of end use parts.

In general, 3D printing systems will let you:

• Analyze form—examine how the model looks off the screen in multidimensional reality.

• Analyze fit—determine whether parts will fit together in and after assembly.

• Analyze feel—examine how the finished product will likely feel in your hands.

• Analyze function—Determine whether the design meets operational and performance requirements.

• Control costs—3D printers can reduce the number of design iterations, as well as reduce the cost of creating multiple design iterations.

• They can reduce the need to develop tooling and fixtures. They can eliminate manufacturing steps through innovative design and validate a part’s “produce-ability.” They help you validate the design more quickly. And they can reduce the number of post processing steps for manufactured parts.

• Enable faster feedback—Printers can produce your model in hours.

Materials play a key role in whether a printer operates as a prototype machine or as a small factory, or both. The range and number of materials for these systems continues to expand. While many doubt the ability to use parts from Additive Manufacturing (AM) machines as final products, several documented cases show that even the aerospace industry uses AM machines to make parts for planes.

A printer for nearly every need

3D printers are available in a range of printing processes to suit application need and material choice.

In Ink jet printing layers of a fine powder, such as plaster, cornstarch, or resins, are selectively bonded by “printing” an adhesive from the inkjet printhead.

In a photopolymer system the machine feeds liquids, usually some type of photopolymer through an ink-jet type printhead. UV light, which can be mounted in the printhead, cures each layer as it is deposited. Many of these systems use a large printhead to cover a wide area. Depending on the material used, layer thicknesses can be very thin, resulting in very fine, crisp detail.

Several 3D printers use multiple jets to deposit UV-curable liquid and build a part in raster fashion. These systems are either feeding the same material through a number of jet print heads or feeding different material through multiple heads. One brand of printer can make multi-colored parts using colored binders.

Most versions of this type of printer use a support material to stabilize the part during the build step. Supports are generated by the computer program, and are often made of wax or some other material that melts away or washes away to reveal the parts.

In film transfer imaging (FTI), a thin layer of material is dispensed onto a reciprocating film carriage. At each reciprocating movement, the cartridge brings a fresh layer of material onto the build surface, which is then cured with UV flash photography one layer at a time.

A relatively new introduction into the 3D printer market involves building parts additively but using a high-resolution Digital Light Processor (DLP) projector to solidify the liquid photopolymer. This process results in durable plastic parts that mimic injection molding for accuracy, material properties, detail, and surface finish. These systems “image” an entire cross-section at once, so they can build at twice the speed of machines with comparable performance.

Selecting the right additive system

You have more than 40 additive-manufacturing systems you can choose from for your prototyping and manufacturing needs, from 3D printers to sophisticated SLA/SLS systems. How do you narrow that down to a reasonable number without reading every brochure on every system?

No system will have every convenience that you need. Some require more processing on the back end, some on the front end; some require support structures, some don’t. Depending on your personal preference, such factors can be just part of the process or a major inconvenience.

The charts in our selector guide are meant to help you at least narrow your focus to several machines. Then you can examine system claims more closely for your particular application needs. Some vendors provide a lot of information; some do not. Where there are blanks, please contact that particular vendor.

But a listing of numbers does not tell the whole story for any AM system. So, here is a little background information to consider for each of the major categories shown in the charts.

The application will, of course, be a key factor—whether you are building a part for concept examination, to test for function, or as an end-use product.

Then you will need to consider material. If you’re examining a product for concept, you may not need a rugged material. Several good quality, low cost systems will suit concept needs. Of course, if you are examining a part for use in the aerospace industry, you may want it made of a sintered metal, which, once it passes its tests, can then go right into production.

Build size will narrow your choice. Nearly every one of the more than 40 systems currently available has a different size tray for building parts. A common build size is just under 12 in. by 12 in. by 8 in. This size not only suits larger parts, it suits multiple parts easily.

Depending on the application, features like part accuracy will further narrow your choice. Accuracy is a highly subjective parameter; it depends on the part geometry, the material, the end use of the part, and so on. To help you determine a system’s potential accuracy, we have listed the layer thicknesses. But keep in mind that these numbers are dependant on other listed parameters. All the vendors will suggest that you run a trial part before making your final choice.

Finish is another subjective category. It is best to try a part on a system to determine if it will have the finish you need.

Throughput, or build speed, depends on the material you are using for your part, the geometry of the part, and the fineness of detail. In general, the finer the detail, the longer it will take to build your part. Most systems, however, have sufficient material capacity to operate over a weekend; and those that don’t are very clear about that feature.

Price is only one factor in your choice, and it is not the most important factor. Initial purchase price does not take into account the cost of ongoing use, purchase of materials, any training, waste, and so on. Price is not necessarily an indicator of quality or value; that all depends on your needs.

Not all brochures give you this information either. We spoke with each manufacturer about these selection criteria. Information on machine size, weight, laser parameters are available in nearly all brochures; so once you’ve narrowed your choice, that information is easy to find.

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