For me, as an offset printer, I was relieved to note that the colour wasn't very good, registration was on a par with early colour newspapers and the toner had the feel of a relief map. Indigo stepped up the quality and gave a planographic finish, and others followed. Laser quality can be on par with litho. Inkjet had always offered considerable potential but the dye-based inks tended to spread when being absorbed into the surface of papers. This meant that colour control was difficult. The development of pigmented inks, some using ultraviolet curing, meant that colour reproduction quality on a range of stocks improved, but the result was not planographic. For some applications this was not a problem and there is a whole sector that uses this perceived drawback as the enabling mechanism to provide a new niche.

The 3D printing process

Instead of trying to reduce the size of the droplets, this market looks to increase the size to deposit a range of materials onto a base in order to build up a tangible three-dimensional model from a computer aided design (CAD) system or scanner. This technology is increasingly being used by organisations in a wide range of sectors to provide rapid prototyping and modelling. There has long been a need for prototypes allowing designers and marketers to see how their product will look and for engineers to test the properties of the device. As CAD packages became increasingly sophisticated they were used to produce more than drawings. For example, stereolithography is able to create solid plastic objects with detailed internal structures in a matter of hours. Such a machine has four parts:

• A tank filled with a liquid photoreactive monomer that polymerises when exposed to UV radiation, hardening into a polymer;
•  A perforated platform immersed in the tank that moves up and down in the tank during the process;
• An ultraviolet laser;
• A washer and finishing chamber.

The process involves 'slicing' the CAD model into thin layers, only 0.1mm in thickness. The laser then exposes the monomer in the tank, hardening it to replicate the slice. The platform then drops down into the tank at steps of 0.1mm and the laser paints the next slice, repeating layer by layer, until the prototype is complete. On completion it is washed and postcured in a UV chamber to harden the model. Depending on the size and number of objects being created it will take a minute or two for each layer and a run might take 6-12 hours, over several days for large objects. Machines can cost £250,000 (e353,500) with final items some e200-3,000 per model.

Stereolithography was invented by Chuck Hall, founder of Californian rapid prototyping provider 3D Systems, in 1986. The company now sells solid imaging solutions across the world, helping reduce the time and cost of designing products and facilitating direct and indirect manufacturing. As well as stereolithography, 3D Systems markets the SLS (selective laser sintering) product line for metal parts, and the MJM (multi-jet modelling) InVision 3-D printer product line.

Inkjet for 3D

There are several other suppliers of three-dimensional printers that use inkjet. The technology was invented at Boston's Massachusetts Institute of Technology (MIT), the original patents were from mechanical engineering professor Emanuel Sachs and materials scientist Michael Cima. They used electrostatic ink jets to spray polymer binder onto powders, selectively hardening slices of a CAD-defined object, layer by layer. Successive layers of powder are deposited on top, and the process is repeated until an object is completed. Overhangs and complex internal structures are possible as the part is temporarily surrounded and supported by loose powder, which is then shaken and removed from the finished part for reuse. In the words of Professor Sachs: "It's basically a process for printing with materials. Instead of red and blue ink, you have, say, aluminum and nickel."

The original process works by the printer spreading a thin layer of powder (starch or plaster) across a moveable fabrication piston, then an inkjet printhead prints a binder of the cross-section of the part being created. This binds the powder into a solid and the process is repeated, the fabrication piston drops, making room for the next layer.

There are several variations available, using materials including metals, polymers, foundry sand, starch, plaster, all of which provide a wide range of costs and finishes. When completed the model is not very strong, it can be handled carefully and examined.

The material is porous and can be infiltrated with a variety of waxes, urethanes and resins, depending on the desired part characteristics to produce a range of material properties. Instead of solidifying selected portions of powder, alternative techniques of fused deposition modelling (FDM) may be considered. This involves extruding a thermoplastic material such as acrylnitrile butadene styrene (ABS) through a nozzle mounted on an X, Y table.

Working like a plotter, the model is then drawn one layer at a time until the part is complete. A support structure is automatically created to support any overhangs in the model using a different material that can be easily identified and removed by hand or with simple tools. An alternative method of generating and subsequently removing support involves producing a soluble support structure that simply dissolves away, leaving a clean model. Parts are ready for use straight from the machine, as support removal normally takes only a few minutes.

ABS is the standard thermoplastic substrate used on most FDM devices.

It is strong, stable, can be glued, machined, painted and so is good for making functional parts or finished patterns. ABS parts are suitable for functional testing immediately but they can also be finished to resemble production parts, used as patterns for sand casting, vacuum casting etc. Alternatives to ABS can be used if parts are required in other materials including casting wax, high-impact ABS and flexible plastics.

The various 3D printers are not as widely used as the more established stereolithography but the lower cost and quick turnaround of 3D printing has aided industrial engineering and prototyping by improving product development, with more models created before the design is finalised. Generally speaking, the mechanical properties of parts by 3D printers are inferior compared to SLA. However, most commercially available 3D printers produce parts much faster than other RP technologies.

The Wohlers Report provides detailed analysis of the rapid prototyping industry. It reported that the 3D printer market grew from 656 units in 2002 to 1,032 units in 2003 - a 57 per cent increase. The leading supplier is the Massachusetts company Z Corporation, that has some 30 per cent market share with its range of machines.

Z Corporation

Z Corporation has over 900 customers in a range of industries including packaging, automotive, footwear, consumer products, consumer electronics and education. Leading brands include Sony, Fisher-Price, NASA, Lockheed Martin, Motorola, Northrop Grumman, Adidas, Ford and Disney.

Harley-Davidson Inc. recently purchased a ZPrinter 310 System for their Industrial Design and Concept Development teams. Packaging users include Constar, Clorox, Pechiney Plastics and PET Packaging producing glass and plastic packaging for the health care, household and chemical, automotive, and beverage industries.

New packaging design has to be functional, economical and innovative. Clear and effective communication is necessary to satisfy customers and simplify the design process. The traditional method of using 3D screen renderings limits communication and forces compromises or extensions late in the design process.

Z Corporation markets three different model printers, employing the powder binding process and using inkjet head technology from HP. Additionally the high-end printers allow models to be produced in full-colour with a Cabot Corporation Inkjet pigment system. This allows for communication of important information including engineering data, labelling and highlighting as well as appearance simulation. Marina Hatsopoulos, CEO of Z Corporation, believes the colour capability is a key advantage for their products, allowing the aesthetics of a prototype to be produced as a three-dimensional proof.

For the engineering community, colour allows finite element analysis plots to be created on models, for example making plastic bottles with stress plots to highlight regions most susceptible to stress forces when the bottles are hot-filled or stacked for transport. Colour can also be used to separate individual components of a complex assembly when produced as a single piece. Using colour slows down the process to two layers per minute compared to the monochrome six layers per minute.

Z Corporation's proprietary software accepts output from CAD systems as solid models in STL, VRML and PLY file formats as input. ZPrint software features 3D viewing, text labelling, scaling functionality and the ability to provide colour output. Powder, binder and printheads are consumed in the part printing process. The strength of the part may be enhanced using a range of infiltrants. Depending on the geometry and infiltrant choices, the cost of these consumables range between e1.00-2.10 per cubic inch of finished part; any excess powder not used can be fully recycled. The company offers the capability of creating negative parts in a plaster-ceramic composite suitable for casting low-temperature metals that can be used for moulding the part in the material that will be used.

Other competitive suppliers of 3D printers tend to be based in the US and include 3-D Systems Inc., Stratasys, Soligen, Sanders Prototype Inc. and Dimension Printing. The Dimension system is advertised in the UK at a cost of £18,975, including delivery, installation, training and 12 months' maintenance for a machine capable of producing models up to 203 x 203 x 305mm. The printer can be installed in an office as a standard network device. It is controlled by Catalyst software that automatically imports files from most leading CAD systems. It orients the part, slices the file, generates support structures (if necessary), and creates a precise deposition path to build the model. Multiple models can be packed within the build envelope to maximise efficiency. Catalyst provides queue management capabilities, build time, material status and system status information.

Applications of 3D printing

There are many industries using 3D printing: consumer appliances, architecture, automotive, education, footwear, forensics, medical modelling, molecular modelling and packaging. The primary application for rapid prototyping is widely used in many engineering and manufacturing applications, with interest in packaging growing. Pechiney Plastic Packaging (formerly the plastic packaging operations of American National Can Company) uses Z Corporation printers to help deliver innovative flexible packaging for food, meat, dairy, health care and specialty products, as well as plastic bottles for food and beverage. The Pechiney Bottles Group specialises in multilayer barrier plastic containers for food and beverages in PET as well as polyolefin resins (HDPE and polypropylene). The majority of their business is in custom bottles, containers with either a special shape or for products with sensitive packaging requirements for an adequate shelf life. The use of 3D printing helps reduce the development time for these custom bottles.

There are other specialist applications that involve design and manufacture of functional models in medical and forensic applications, even entertainment. One company, Therics, prints pharmaceutical pills and medical implants with the technology and their materials.

The 3D inkjet techniques allow colour printing and potential personalisation, even variable data across a wide range of substrates. There are early adopters in packaging and there are specialist service providers in the US acting as bureaux and full service providers, such as Solidworks, Autodesk, Solid Edge and Rhinoceros. The technology is an interesting new development that has not been considered by many in the print industry yet, but offers a potential opportunity to provide new services.