Looking to learn about 3D printing technologies for metal casting? Read our beginner’s guide.
In this article, we’ll provide an overview of traditional casting technologies and how they are changing with the use of 3D printers. We’ll also find out what 3D printers available on the market today are suitable for injection molding.
What is Casting?
A foundry refers to a factory where castings are produced by melting metal, pouring liquid metal into a mold, and then allowing it to solidify. The end product of foundry production is castings, i.e., future parts or blanks. The castings can weigh a few grams to several hundred tons.
Castings are mainly used in factories that produce machine tools. The production method stands out from others through the following:
1) You can obtain products with a mass of several grams to hundreds of tons. These items can be of complex geometry and have various mechanical and operational properties.
2) You can obtaining products whose materials or dimensions make them impossible or unprofitable to create through other methods.
3) Castings are as close as possible in size and shape to finished products. This is unlike the case with blanks obtained by volumetric hot stamping or forging.
Castings vs. Traditional Technology
In traditional casting process, the master model can be made by hand or by machining. However, some forms cannot be implemented manually. To produce master models, five-axis CNC machining centers are used. This significantly increases the possibility of creating items of various complex shapes.
However, making such a stencil or master model is very expensive. Therefore, this option of obtaining a casting is relevant for mass production but not economically feasible in small and medium production. For these two latter options, it would be better to use a 3D printer.
Graph showing how the cost of a model depends on the number of produced copies, and where use of additive technologies will be more rational.
Casting Production by Using Additive Technologies
One of the issues foundry technologists have to address is how to minimize labor-intensive operations when machining workpieces. This is solved by the fact that the castings should be as close as possible to the parameters of the required part, which also saves money and time. Here, innovations come to the rescue, in the form of additive technologies.
Additive technologies speed up the technical process, bypassing the traditional first steps in casting manufacturing technology. Through the technologies, manufacture can obtain the required casting model or mold in one operation.
In the red area – the traditional casting process, in the green and blue – casting using additive technologies – production time is reduced by 2-6 times.
Direct metal printing of products, which is used in many modern industries, is more expensive from an economic point of view than traditional casting. Therefore, 3D printing models through melting and burning, as well as the synthesis of molds and cores ready for casting, is of particular interest.
Injection molding using additive technologies is more cost-effective than direct printing.
Areas of Application
3D-printed master models and injection molds are used in jewelry factories, in production of dental molds and orthopedic products, in design offices, for R&D, in training centers and prototyping centers.
Geometrically complex castings resulting from the use of additive technologies are used in film and television to quickly produce unusual props of complex shape.
Casting scenery using sand molds printed on a 3D printer.
3D Printers and Technologies for 3D Printing Foundry models
To obtain injection models, 3D printing is used using FDM (FFF), SLS, SLA, DLP technologies. These technologies make it possible to print models for subsequent melting or burning out of the injection mold formed around it. Wax is used for investment models, while PMMA, CAST plastic and special photopolymers are used for burnt models.
The main advantage of using 3D printing technologies is that there is no need to prepare special equipment, e.g. molds. Other advantages include low ash content of materials during burnout.
The prepared 3D model is immediately sent for printing and, after a little post-processing, is ready for use.
FDM (FFF): Layer by Layer Deposition
FDM is 3D printing method widely known to professionals and amateurs of additive technologies.
The filament material for FDM printing of burnt-out models is a special plastic or a composite with a high wax content.
Recommended 3D Printer: PICASO 3D Designer X
PICASO 3D Designer X is an FDM printer with a build area of 200 x 200 x 210 mm. The unit can print materials such as ABS, PLA, HIPS, PVA, ULTRAN 630, ULTRAN 6130, ASA, ABS/PC, PET, PC, FRICTION, CAST, RELAX , ETERNAL, FLEX, RUBBER, SEALANT, PETG, AEROTEX, CERAMO, WAX, SBS, SBS PRO, PROTOTYPERSOFT, PRO-FLEX, TOTAL PRO, NYLON and PEEK at speeds up to 100 cm³/h and with layer thicknesses from 10 µm.
Polymaker Polycast is a wax filament for printing models for metal casting. This filament is suitable for any FDM printers.
AVAILABLE ON AMAZON
When the filament burns out, the minimum ash content remains – less than 0.01%. The material is well post-processed by polishing, using a solvent or flame. Wax models do not differ in properties from standard ones and can be used in foundry production.
QDTD Acryclic Filament
QDTD Acrylic Filamnet is a polymethyl methacrylate (PMMA) filament for foundry production. The filament, commonly known as acrylic, has a high degree of transparency and low ash content.
AVAILABLE ON AMAZON
Models printed with this material are infused with a wax solution to create a smooth surface. Then, in the foundry for the model, a system of channels is created to uniformly supply the melt. The structure is then dipped into the molding mix, which is applied in several layers. This creates a strong print from the printed model and the gating system.
The printed model is then burned out of the mould and calcined in a furnace. After this, it can be used for casting.
Below are some examples of items created using PMMA filaments.
SLS – Selective Laser Sintering
SLS is used to manufacture master models of complex shapes, moderate accuracy and relatively large dimensions.
Below is an overview of how the technology works:
A working chamber is filled with an inert gas such as nitrogen. The chamber should have a platform coated with a roller rolls polystyrene powder with a particle size of 50-150 microns. A new layer is sintered on the platform with a CO2 laser (with a temperature of 100-120°C) along the section of the “body” of the CAD model. After this, the working platform is lowered by 0.1-0.3 mm, after which the next layer is printed.
The printed model does not require support because the material itself (surrounding powder) serves as a reference. Any unused material can be reused.
The model obtained on such a printer is filled with mold material, from which it is then burned out in a calcining furnace. During burning, combustible gases are released. These gases must be neutralized.
The mold may clog with the ash of a burnt model. Therefore, materials used to manufacture it are taken with a low ash content, in hundredths of a percent.
3DSystesm ProX SLS 6100
3DSystems ProX SLS 6100 is an SLS 3D printer with build times faster than other SLS printers in its price point, high performance nesting and high density capability for a 25% larger build volume capacity
PrimeCast 101 – Polystyrene Gray is a gray material based on polystyrene. The material is suitable for printing models for metal casting due to low melting point and dimensional accuracy of printed parts.
SLA – Stereolithography Laser Apparatus (Laser stereolithography)
This printing process is similar to SLS. However, instead of powder material, liquid material is used. The UV laser acts on the material, which cures selectively and in layers.
The materials used are light-sensitive resins and photopolymers. The working platform is lowered or raised (depending on the location of the light source) and the liquid is polymerized by a laser at given points.
Like is the case with powders, unused liquid material can be reused for printing subsequent models.
The resulting models have a high surface quality. Therefore, they do not need further machining.
Recommended 3D Printers
The UnionTech RSPro450 3D printer prints parts with a layer thickness of 30 microns and a size of 450 x 450 x 300 mm.
The Shining3D EP-A450 photopolymer printer prints objects up to 450×450×350 mm at a speed of up to 120 g/h.
XJRP SPS 450H
The XJRP SPS 450H 3D printer has a working chamber size of 450 x 450 x 350 mm and prints at a speed of 200 g/h.
Somos Element stereolithography resin was developed by DSM Additive Manufacturing specifically for casting models. The material does not contain antimony.
Printing with it allows you to achieve high-quality 3D models with a high degree of repeatability. The material has high strength, does not deform during storage and has a low ash content. The remaining material is easily removed, leaving the mold clean.
LCD (Liquid Crystal Display) and DLP (Digital Light Processing)
To cure the photopolymer, a DLP projector on DMD chips or an LCD screen is used. This is the main difference from SLA technology, which uses a UV laser.
Another difference is that the entire layer is projected, each pixel at the same time. Moreover, the layer is not drawn by a laser beam. This speeds up the process.
Models printed on such a printer require removal of supports and UV treatment. This means that post-processing for models obtained using this technology does not differ from those that are printed using SLA technology.
DLP printing allows you to get a model faster, but with a less smooth surface than an SLA printer.
The difference in detail when printing using SLA technology and DLP technology.
Flash Forge Hunter DLP
FlashForge Hunter DLP is a DLP printer with a layer thickness of 25-50 microns and a print area of 120×67.5×150 mm.
Printed model and finished casting made with FlashForge Hunter DLP printer
Photocentric Liquid Crystal Magna
The Photocentric Liquid Crystal Magna 3D printer is one of the largest LCD printers. It has a capacious working chamber – 510 x 280 x 350 mm and prints parts with a layer thickness of 25 microns.
The model is printed on a Photocentric Liquid Crystal Magna printer.
Photopolymer Daylight Precision Castable is designed for making casting molds for jewelry. The printer has high precision and detail. The surface of the products is clear and smooth. After burning, the material does not leave ash, and does not deform during polymerization.
3D Printers for Making Molds
You can quickly get a high-quality casting mold using Binder Jetting and SLS technologies. 3D printers using these technologies print molds from special foundry sand.
Binder Jetting Technology
This technology allows you to print a sand mold with a complex geometry without any additional processing. After printing, you can start casting immediately.
The main advantage of Binder Jetting technology is that there is no need for any special conditions for the operation of such a printer. You can print at room temperature.
In this case, the material used is sand. The sand is distributed over the working platform using a roller. Next, the print head applies a bonding adhesive on top of the powder. The platform is lowered through the thickness of the model layer and the object is formed where the sand is associated with the liquid (i.e. glue).
The unused material, by analogy with SLS technology, is a support for a future model.
The principle device of a printer with Binder Jet technology.
Casting molds printed using Binder Jet technology.
The sand 3D printer FHZL PCM1500 prints models with an accuracy of ±0.3 mm, with a layer thickness of 200 microns. The machine has a build volume of 1500 x 1000 x 700 mm.
The Sand 3D printer, FHZL PCM2200, has an even larger working chamber of 2200 x 1000 x 800 mm. The machine prints with quartz, calcined, synthetic and chromite sand parts with a layer thickness of 200 microns.
ExOne S-Max Pro
This industrial 3D printer, ExOne S-Max Pro, prints prototypes and molds from sand with a layer thickness of 260 microns. The dimensions of the printed models should not exceed the dimensions of the working chamber – 10400 x 3520 x 2860 mm.
The ExOne S-Print is an industrial 3D printer with a working chamber of 800 x 500 x 400 mm. The machine prints products with a layer thickness of 240 microns.
SLS Printing of Casting Molds
The main difference from the previously mentioned SLS technology is the use of foundry sand pre-clad with a polymer as a printing material. The material is laser sintered and then cleaned. The resulting form is placed in a calcining oven for curing, which takes place at a temperature of 300-350 ° C.
The main difference from the Binder Jet technology is the higher detail of the finished mold. However, it takes more time to get the finished form due to the need for additional processing.
Solar 3D Printing
Another interesting sand printing technology is known as Solar Sinter. The technology was developed by a German engineer, designer and artist Markus Kaiser. Solar 3D printing is great for creating sand molds at a very low precision.
If your business is located in the desert, then this is the best option since sand and sunlight are all around, i.e., on a standard nine-hour shift. You only need to bring your own printer with a computer to start printing.
The printer is equipped with a Fresnel lens, which concentrates sunlight into a beam. The lens makes it possible to melt sand at a temperature of 1400-1600°C. A solar tracker tracks the position of the sun and rotates the lens towards it. There are also photocells to power the electric drives of the installation.
The main plus of this technology is saving on electricity, materials and rent of premises. However, perhaps even more important is the concept.
Such a printer, both due to the specifics of the application and the low accuracy of the resulting models, can hardly be used for industrial needs. However, for artists and artisans, it will be a real find.
Printing injection molds on it is perhaps a dubious occupation, but art objects are the very thing.
Removing the model from the working area of the solar 3D printer is done using a tablespoon. You can use a plug, but the speed will be slower.
But seriously, who knows where technology will go next? Sometimes crazy projects open up new possibilities in our daily lives.
The introduction of 3D printing makes casting process cheaper and faster. With 3D printing, you can produce models and molds for casting with complex geometry and various dimensions, without losing the accuracy of the resulting casting.
You can use printers working on FDM(FFF), SLS, SLA/DLP, Voxeljet technologies to obtain lost-wax and burnt-out models. The materials used have a low percentage of ash content, and printing models is faster than making them manually or using a CNC machine.
An example of a process chain for obtaining a casting using an investment model
For casting molds, Binder Jetting and SLS printing technologies with a material suitable for the molds are suitable.
Additive technologies in casting are applicable where it is necessary to obtain a master model or mold for future casting cheaply and quickly, e.g., to design offices and pilot plants. The technologies are also applicable in mass production.
If micron accuracy is not required, the difference in speed and cost of work makes them much more attractive than machining on a CNC router.
Today, you can order a casting made of metal or plastic and look at the result of using 3D printing in casting.
Contact us for advice on choosing a 3D printer to integrate into your foundry or foundry equipment.