Copyright 2017 - RD Prototype Division
Stereolithography(SLA) Machine
Fused Deposition Modeling(FDM) Machine Machine
Stereolithography  (SLA)

​ Unlike the desktop printer you use to print documents, SLA machines don't extrude ink or some other liquid onto a surface. Instead an SLA machine starts with an excess of liquid plastic, some of which is cured, or hardened, to form a solid object. 

  SLAs have four main parts: a tank that can be filled with liquid plastic (photopolymer), a perforated platform that is lowered into the tank, an ultraviolet (UV) laser and a computer controlling the platform and the laser. In the initial step of the SLA process, a thin layer of photopolymer (usually between 0.05-0.15 mm) is exposed above the perforated platform. The UV laser hits the perforated platform, "painting" the pattern of the object being printed. The UV-curable liquid hardens instantly when the UV laser touches it, forming the first layer of the 3D-printed object.

  Once the initial layer of the object has hardened, the platform is lowered, exposing a new surface layer of liquid polymer. The laser again traces a cross section of the object being printed, which instantly bonds to the hardened section beneath it. This process is repeated again and again until the entire object has been formed and is fully submerged in the tank.  The platform is then raised to expose a three-dimensional object. After it is rinsed with a liquid solvent to free it of excess resin, the object is baked in an ultraviolet oven to further cure the plastic. 

  Objects made using stereolithography generally have smooth surfaces, but the quality of an object depends on the quality of the SLA machine used to print it. The amount of time it takes to create an object with stereolithography also depends on the size of the machine used to print it. Small objects are usually produced with smaller machines and typically take between six to twelve hours to print. Larger objects, which can be several meters in three dimensions, take days.

Fused Deposition Modeling  (FDM)

​ Objects created with an FDM printer start out as computer-aided design (CAD) files. Before an object can be printed, its CAD file must be converted to a format that a 3D printer can understand — usually .STL format.

FDM printers use two kinds of materials, a modeling material, which constitutes the finished object, and a support material, which acts as a scaffolding to support the object as it's being printed.  During printing, these materials take the form of plastic threads, or filaments, which are unwound from a coil and fed through an extrusion nozzle. The nozzle melts the filaments and extrudes them onto a base, sometimes called a build platform or table. Both the nozzle and the base are controlled by a computer that translates the dimensions of an object into X, Y and Z coordinates for the nozzle and base to follow during printing.

In a typical FDM system, the extrusion nozzle moves over the build platform horizontally and vertically, "drawing" a cross section of an object onto the platform. This thin layer of plastic cools and hardens, immediately binding to the layer beneath it. Once a layer is completed, the base is lowered — usually by about one-sixteenth of an inch — to make room for the next layer of plastic.

Printing time depends on the size of the object being manufactured. Small objects — just a few cubic inches — and tall, thin objects print quickly, while larger, more geometrically complex objects take longer to print. Compared to other 3D printing methods, such as stereolithography (SLA) or selective laser sintering (SLS), FDM is a fairly slow process. 

Once an object comes off the FDM printer, its support materials are removed either by soaking the object in a water and detergent solution or, in the case of thermoplastic supports, snapping the support material off by hand. Objects may also be sanded, milled, painted or plated to improve their function and appearance.
Room Temperature Vulcanization  (RTV) 

  Injection molding has long been the best method of bulk production, while 3D printing has recently become the best choice for early stage prototyping.  But when and how should you make the switch from single volume production with 3D prints to high volume production? With small run production it can be hard to find the balance between upfront costs, production costs, and quality, but silicone molds can be an effective way to bridge the low-volume chasm.

  Silicone molding – most commonly known as room temperature vulcanizing (RTV) molding – offers a great solution for small batch production. The mold material has no problem retaining tiny and detailed features and tolerances similar to those in your 3D printed parts (minimum features 0.025"/0.6mm).  First, a pattern of the item to be manufactured must be produced. You may be starting with an existing item you wish to reproduce, in which case the silicone can be applied directly (assuming the material is suitable).
A pattern will be made with 3D printing. 3D printing the mold pattern has shown to reduce lead times up to 90% and reduce costs up to 70%, depending on the geometry of your original part.  Once the pattern is ready, the silicone is mixed with curing agent and poured over the pattern; curing can take up to 24 hours and the resulting mold is strong and flexible and then ready to use almost immediately.

  Urethanes, a type of thermoset plastic, are the most commonly used casting material and offer a wide range of mechanical, visual and electrical properties; post production work can be reduced to almost nil.  The mold can be used for runs of up to 100 parts, although typically the usage range is between 15-30 units per mold, depending on the casting material and part geometry.