7th March 2016
Additive Manufacturing (3D Printing)
Additive manufacturing is a relatively new fabrication technique where products are created layer-by-layer rather than traditional manufacturing processes which involve subtracting material (i.e. machining or stamping). This is commonly achieved with the use of a high powered laser which is directed around a melted ford of the desired material. The laser is guided by computer based on the CAD geometry of the desired product defined by the engineer, solidifying areas of the melted material as it goes.
The process is still in its infancy in industry but has the potential to bring significant advantages to the manufacture of many products. Advantages of the technique include:
• Building products in layers can minimise or even eradicate wasted material as the product isn’t machined down from a larger part.
• Layering products allows for more complex shapes to be constructed as single pieces of material thus negating the need to include additional joining processes which can lead to costs and time saving.
• Can be used with a variety of materials including both plastics and metals.
Additive manufacturing is closely aligned with the drive for lightweight design as is could allow complex geometry taken directly from a freeform optimisation processes to be manufactured without the need for as much engineering interpretation of the topology results.
3D printing is a common term to describe all additive manufacturing processes but in reality, 3D printing is often used in the prototyping stage of the design cycle. The printing technology allows manufacturers to visualise products in a tangible format which can have many advantages in the early development stages and require CAD geometry as an input to be able to reproduce the physical part. Recent advances have even allowed for single printed parts to have different colours across the product, adding to the realism and allowing for easy identification of separate components.
Peter Marsh, FT manufacturing editor, talks to Abe Reichental of US-based 3D Systems to find out how 3D printing works and if it really is a ‘disruptive technology’
Selective Laser Sintering (SLS)
This technique uses a high power laser to fuse together particles of plastic, metal, ceramic, or glass powders into a solid product. The laser fuses powdered material by scanning cross-sections generated typically from a CAD model on the surface of a powder bed. After each scan, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed. SLS has an advantage over some other methods in that a number of products can be ‘printed’ at the same time on the same bed of powder which can increase productivity.
Fused Deposition Modeling (FDM)
In this technique, a plastic filament or metal wire supplies material to an extrusion nozzle which can turn the flow on and off. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions controlled by a computer-aided manufacturing (CAM) package. The model or part is produced by extruding small beads of material, one on top of another to build the part up in layers. A number of materials can be produced including ABS polymers, polycarbonates, polycaprolactone and waxes, with different trade-offs between strength and temperature properties.
Stereolithography uses a vat of liquid ultraviolet photopolymer resin and a laser to build 3D objects up layer by layer. For each layer, the laser beam traces a cross-section of the part pattern on the surface of the liquid resin. The ultraviolet laser light solidifies the shape and joins it to the layer below. After each layer is complete, the product is lowered by one layer and the process starts again. To complete the process, the object is placed into a chemical bath and then cured in an oven. Some hand finishing is required as this technique often needs supporting structures to be added to the CAD model to avoid collapse during the print. The process is fast but the added steps can make it a costly solution.
Laminated Object Manufacturing (LOM)
LOM builds layers of adhesive-coated paper, plastic, or metal laminates by gluing them together layer by layer and then cut to shape with a knife or CNC or laser cutter. The process is low cost due to the use of more readily available materials but this comes at a trade off with accuracy.
Electronic Beam Melting (EBM)
This technique manufactures parts by melting metal powder layer by layer with an electron beam in a vacuum. Unlike some metal sintering techniques, the parts are fully dense, void-free, and extremely strong. As such, EBM is often used as a rapid manufacturing process rather than just a prototyping exercise. CAD model data is read in and lays down layers of powdered material that are melted together with the use of a computer controlled electron beam. The process takes place under vacuum, which makes it suited to manufacture parts in reactive materials such as titanium.
Inkjet Head 3D Printing
An inkjet-like printing head moves across a bed of powder, depositing a liquid binding material in the shape of a section of the object. A fresh layer of powder is spread across the top of the model, and the process is repeated. When the model is complete, unbound powder is automatically removed. Currently, parts can be built on a printer at a rate of around 1 vertical inch per hour.