3D Printing:

A method by which material is melted, cured, jetted, chemically bonded, or sintered in layers, eventually creating a solid, three-dimensional object.


Fused Deposition Modeling (FDM)


A prototype version of PasCo's favorite printer, the MAX Metal, featuring counterweighted flying extruders Two-Color Printing E3D Cyclops nozzle printing an early version of the Rostock effector A Hall-Theta Z probe in a mount designed in-house A 4½" depth gauge for a candle factory, printed in blue PET-G A "power box" for a 3D printer: illuminated switch, fuse, and IEC plug Meanwell PSU mounted with a pair of custom brackets

In this 3D printing method, plastic filament is forced by an extruder (motorized drive) into a hot end (melter) that is mounted to a robot that moves it in a three-dimensional space. The bottom of the hot end has a nozzle with a small, round opening (typically 0.3 to 0.5mm across) that allows plastic to be deposited in a controlled manner. FDM is the most common 3D printing method used today. It was patented in the 1980s. In the 2000s, as patents began to expire, the open-source RepRap movement began to produce hobbyist-level 3D printers. Ten years later, thousands of varieties have been produced.


Machines

Pasadena Coherent uses custom-built Rostock MAX Metal printers. The build volume is cylindrical (12" across) and about 11" tall. (The vast majority of 3D-printed objects are a fraction of that size.) Each machine is capable of printing in two colors (of the same material) simultaneously. In-house testing indicates that positional accuracy is very good, with positional accuracy better than 100 microns.

PasCo's printers have the following advantages:

  • All-metal Trick Laser MAX Metal frames.
    These all-aluminum frames are produced by a master machinist. They are designed for easy assembly with very high accuracy, which is critical for the positional accuracy of the machine. Unlike some other 3D printers, MDF and Lexan are not used for any of the structural components. Thus, there is no concern of expansion or contraction from humidity or minor temperature changes, and the frame is far tougher than it could be otherwise.

  • 32-bit controllers with heuristic calibration.
    Linear delta robots like these can be very difficult to calibrate by hand. Fortunately, PasCo's printers run Smoothieware with special heuristic calibration firmware.

  • Counterweighted flying extruders.
    These dramatically shorten the distance the filament has to travel from the extruders to the hot end, reducing retraction artifacts and spiderwebbing. The counterweight system takes over 95% of the weight of the extruders off the drivetrain, enabling faster and more accurate moves. (It also makes it a lot safer, too.)

  • E3D all-metal hot ends.
    E3D has earned its reputation, and that reputation is good. It produces a variety of high-quality hot ends and nozzles. PasCo uses the V6 for single extrusion, and Cyclops for multi-extrusion. Hardened steel nozzles allow for tough materials such as metal-fill and carbon fiber.

In order to ensure proper dimensions in finished objects, PasCo's machines are carefully calibrated:

  • The extruder steps-per-millimeter value is carefully calibrated with a micrometer.
  • Each and every spool of material is measured with an outside micrometer in ten separate locations to ensure the correct value is entered for the filament diameter.
  • For high-accuracy jobs, filament flow can be dialed in further by printing a hollow, single-walled object and measuring the wall width.

Other things to keep in mind:

  • Parts that need to fit together should be designed with about 20 microns, or 0.8 thou, of tolerance (gap between interfacing parts). That will provide a good interference fit.
  • FDM-printed holes usually come out slightly smaller than designed. Always design small holes (for screws, axles, etc.) 100 microns larger than they need to be. If the fit tolerance is critical, it may be necessary to test several iterations of your design.
  • Take overhangs into account during the design. Gravity has a definite impact on them. Any overhangs over ~50 degrees (depending on material and whether part cooling fans can be used) will require support structures. Because of the size of the two-color hot end, it is not possible to use part cooling with two-color prints.
  • FDM printers do not print knife-sharp edges. Because filament comes out of a round hole, corners will be ever-so-slightly rounded. This should be taken into account for parts that must fit together.


Characteristics

  • Used to produce a wide variety of moderately accurate (usually within ~100 microns) 3D objects using cheap (~$20/kg and up) plastic filament.
  • Objects are "drawn" layer by layer on a flat build surface at the bottom of the printer, with each layer fusing to the one below.
  • Quality/Speed tradeoff: Slower printing = higher quality.
  • Object shells (outer skin) are solid, whereas the interior (infill) is usually filled partially in a lattice pattern.
  • Between layers, and between "islands" in each layer, the printer retracts the filament very slightly. This reduces the nozzle's tendency to ooze hot plastic as it does so. This increases print quality, but isn't always perfect. Small blemishes may be left by this process. Support structures (if necessary) may also leave blemishes. You may want to wet-sand these with increasingly fine-grit sand paper to achieve a better finish.

Pre-Processing

  • STL file is loaded into a slicer called KISSlicer, which generates shell, infill, and support structures (if necessary), and then outputs G-code for the printer.
  • Many objects will require support structures so that any overhanging areas don't sag during the printing process.
  • G-code from the slicer is uploaded directly to the 3D printer, or to a program running on a computer. This process can take anywhere from a few seconds to a few minutes.

Printing

  • The printer will home itself and begin to warm the hot end and heated print surface. This may take anywhere from a few seconds to several minutes, depending on whether the print surface was previously warmed up.
  • The operator manually removes any excess (oozing) filament from the tip of the hot end right before printing begins.
  • Once the print is in progress, the operator must periodically monitor the print to ensure that nothing has gone wrong. On a well-tuned printer, most prints will succeed.
  • Depending on the size of the object, the print could take anywhere from a few minutes to a day or longer. Most smaller objects will finish in an hour or less.

Post-Processing

  • The print surface (a GeckoTek plate) is removed from the printer and flexed. This frees the bottom of the printed object.
  • Support structures (if any) are removed. They usually come off very easily, and can sometimes be removed without any cutting tools.
  • If desired, the customer can sand and paint the finished object.
  • Most materials do not require any specific post-processing at all.

Available Plastics

  • Polylactic Acid (PLA): Biodegradable, durable, easy to print with, moderately stiff, lower heat tolerance, lower shrinkage and better inter-layer bonding than ABS, responds well to part cooling fans.
  • PET-G: Harder, shinier, more durable, and higher heat tolerance than PLA. Less prone to retraction artifacts and spiderwebbing, too. This is PasCo's go-to material. It is recommended unless you specifically need something else.
  • Thermoplastic Urethane (TPU) / Elastomer (TPE): Rubbery. Flexible, compressible, and stretchy. Good for tires, compressible washers, and other "soft" applications.
  • Metal Fill: PLA embedded with tiny metal particles (bronze, steel, etc). Can be buffed and polished for a metallic sheen.
  • Carbon Fiber: PLA embedded with short-chopped carbon fibers. Suitable for use in drones and other applications requiring lightweight, strong construction. More brittle than standard PLA.
  • Conductive: This filament conducts electricity, albeit not as well as copper wire. Expect at least several ohms of resistance per inch.
  • ABS: The original 3D printing material. Tougher and more temperature-resistant than PLA, but requires high print surface temperatures and heated chambers for optimal printing. More prone to shrinking and warping. Pasadena Coherent can print small, simple objects in ABS, but generally recommends PLA or PET-G instead.

PLA, PET-G, and ABS are available in a wide variety of colors. TPU/TPE is available in a few colors. Metal Fill is the same color as the metal it's filled with, Carbon Fiber is black, and Conductive is white or off-white.



Stereolithography (SLA)


An effector for Rostock-type delta 3D printers Form 2 printing the effector and carriages with their support structures The effector, produced in clear resin on a Form 2, with ball joints installed

In this 3D printing method, an ultraviolet laser, steered by mirrors, is fired into a vat of resin. The resin is cured in distinct patterns, creating a solid three-dimensional object. Like FDM, it was patented in the 1980s. Due to its need for highly expensive resin, expensive and time-consuming post-processing, and ongoing patent issues, it enjoys only a tiny fraction of the popularity of FDM. Nevertheless, it excels in the production of small, extremely accurate objects.


Machines

Pasadena Coherent uses Form 2 printers from Form Labs. They are able to print at resolutions of 100, 50, and 25 microns. In-house testing indicates that dimensional accuracy is exceptional, with deviations of less than 25 microns.


Characteristics

  • Used to produce highly-accurate (as fine as 25-micron accuracy) 3D-printed objects using expensive resin ($150+ per liter) and vats ($60) that must be replaced after about two liters of material. Shipping is fairly expensive as well.
  • Objects are "drawn" upside-down, layer by layer, on a flat build surface that is lowered into the vat, with each layer fusing to the one above. After each layer, the build surface is lifted out of the vat, and a wiper moves across the vat surface to clear any debris.
  • Quality/Speed tradeoff: Slower printing = higher quality.
  • Objects are 100% solid.
  • Pre- and post-processing are much more time-consuming than FDM.
  • Support structures (required) will leave small blemishes. You may want to wet-sand these with increasingly fine-grit sand paper to achieve a better finish.

Pre-Processing

  • STL file is loaded into PreForm, which is a slicer.
  • Objects must be aligned such that there are no flat surfaces on the bottom, and such that any slanted surfaces have a sufficiently high angle to allow uncured resin to run off. Otherwise, uncured resin will "bloom" and create a very rough finish.
  • Objects with internal voids must have drainage channels so that uncured resin can escape. Otherwise, parts may explode during printing.
  • Objects must have complicated support structures planned and generated. This often requires ten minutes or more.
  • Generation of the printer's proprietary printing file, and transmission to the printer, can take many minutes.

Printing

  • The build platform is secured, and the correct resin tank and tray are loaded.
  • The printer automatically fills the resin tray, and slowly brings it up to about 30° C. This may take ten minutes or longer.
  • After the resin tank reaches temperature, the print begins automatically.
  • If the supports were placed properly, there should be no defects in the print, and it can be allowed to run unattended. The printer will automatically refill the resin tray from the tank as needed.
  • 25-micron resolution prints may take half a day or longer, depending on object size.

Post-Processing

  • After the print is complete, the build platform is removed, and the completed object is pried off by the bottom support structure. (The object itself is not damaged by this process.)
  • Support structures, which are usually quite dense, are painstakingly clipped off with edge cutters. This process usually takes 10-20 minutes.
  • The object is placed in an ultrasonic alcohol vat and agitated. This removes most of the excess (uncured) resin.
  • After ten minutes in the vat, it is transferred to a secondary alcohol vat, where it is manually agitated for twenty seconds and allowed to sit for two minutes.
  • After removal from the secondary vat, the object is placed either under UV lights or in direct sunlight. This finalizes the curing process.
  • Tiny bumps and blemishes will be left by the support structure attachment points. Customer may wish to sand these down. This can be done with increasing grits of sand paper to produce a smooth finish.

Available Resins

  • Full list is available here.
  • Standard: Black, white, grey, clear, and custom-dyed.
  • Tough: ABS-like. Shatter-resistant.
  • Durable: Polypropylene-like. Low modulus, high impact strength. Glossy finish.
  • High-Temp: Suitable for low-volume injection molding. HDT: 289° C @ 0.45 MPa.
  • Flexible: Simulates 80-durometer rubber.
  • Wax: Suitable for investment casting (not candles).
  • Dental: Suitable for dentures, retainers, drill guides, models, and other dental work. Some dental resins are bio-compatible.
  • Ceramic: Must be fired in a kiln.

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