Solid models by 3D fax

Contributing editor Rex Narraway takes a look at the latest rapid prototyping tools and technologies

The ability for designers to quickly visualise 3D models of their parts is now a reality, thanks to the development of rapid prototyping machines.

One of the pioneering companies in this area is Sanders Prototype Incorporated (SPI) which now offers a range of ModelMaker 3D plotting systems based on the printing process.

The machines use a dual inkjet system riding on a programmable X-Y drive carriage which deposits both ProtoBuild – a thermoplastic material used for the final part geometry – and ProtoSupport wax to support overhanging geometry. The profile is traced out onto a platform in a series of uniformly-spaced micro-droplets, placed with an accuracy of 7 micro m to give the part an accuracy of 25 micro m and making it possible to use it directly for investment casting or plastic moulding.

Volume production of the first ModelMaker began in 1995 with the current ModelMaker II introduced in 1997. Since that time, a number of other RP companies have entered the field with new machines.

One machine, introduced earlier this year, is the Thermojet from 3D Systems which is classed as an office printer and intended for use by the design engineer. Dr Richard Balanson, president and chief operating officer of 3D Systems, envisages that smaller and less expensive machines will be built in the future, aiming at personal office and, ultimately, home use.

`Tomorrow, with future generations of Thermojet,’ he said, `we could just as easily custom-design and `print’ a chess set or a toy, create a model of a new invention, or download a file from the Internet to print out a replacement for a broken plastic appliance part. That’s when we enter the realm of personal manufacturing.’

Thermojet is a multi-jet wax-printing device that exploits the concept of solid object imaging to produce detailed models at 300dpi resolution for testing fit, form and function. At £36, 000, though, it will probably be some years before the concept can be developed for home use.

Another American RP company, Stratasys, is aiming at a similar market with a machine designated Genisys Xs. Having a footprint the size of an office printer, the machine is claimed to give 3D prints in a matter of minutes `with the ease and simplicity of printing paper documents’.

It uses Stratasys Autogen software to scale the original part, slice the data and construct the model using the fused deposition modelling (FDM) process. Prototypes are built from a high-strength polyester compound which can be sanded, painted or drilled, as required.

In line with most manufacturing systems, a key factor in the development of RP machines is productivity and, ultimately, this depends on how quickly the model can be constructed. This summer, Z Corporation launched a machine into the UK market which offers a new concept claimed to make it operate at between 3 and 10 times the rate of traditional machines. Again classed as 3D printer, Z402 is available from Umak and can be plugged directly into the printer port of a PC or CAD system. It produces a model by spraying layer-upon-layer of starch and cellulose powder, inter-spaced by layers of binder fluid, onto a movable platen. The material has been specially developed for the Z402 by Ciba Specialty Chemicals in conjunction with the Z Corporation. Part build rate is up to 50mm/h inside a working volume of 250 by 200 by 200mm, and there is no need for post-processing work.

To date, the process has been used by NASA, Kodak, Toyota and Pratt and Whitney, for aluminium and titanium investment casting, sand castings and prototype components. In addition, Motorola engineers have been able to design cell phone parts, 3D print and revise the concepts, all in a single day.

Manufacturers of more traditional RP machines are also looking at ways to increase the speed of the process employed. For instance, the latest stereolithography machine from 3D Systems, SLA 7000, offers four times the model-building speed of its predecessors whilst its capability of depositing layers of nearly half the thickness produces a smoother finish.

In the case of fused deposition modelling, Stratasys has come up with a system of magnetically-positioned floating extrusion heads to increase the speed of its new flagship, the FDM Quantum, by more than five times over standard FDM machines. Launched early this year, the machine uses a technique similar to one used in the placement of surface-mounted electronic chips and has been designated the Magnadrive system.

The machine incorporates two extrusion heads: one for constructing the model from ABS; the other for depositing the support material, both being supported on an air cushion. Each head is driven in the X and Y axes by magnetic impulses so there are no mechanical parts in the drive system, boosting reliability and accuracy.

Stratasys has also enhanced the productivity of its latest automated FDM 3000 machine – capable of building models of up to 254 by 254 by 406mm in ABS, ABSi, investment casting wax or elastomer – by incorporating a facility known as WaterWorks. Support structures can be generated using software for WaterWorks, SupportWorks or Break-Away Support System. If WaterWorks is selected, once the model has been completed, a water-based solution is used to flush away the features used to support the model while it is being constructed, leaving a clean, smooth surface finish.

When it comes to a combination of size, complexity and fast build, the patented laminated object manufacturing process used on the LOM-1015Plus and LOM-2030H machines from Helysis is still commanding much attention, especially from the automotive industry. Recent refinements to the larger 2030H machine have included a servo-based X-Y motion control and improvements to the software algorithms which give a 30% reduction in part build times over previous LOM machines.

In addition, the company has recently broadened its range of materials with the new LXP 050 LOMPlastic. It comprises a polyester film coated with a polyethylene co-polymer and combines the advantages of greater moisture resistance, improved flexibility and higher mechanical strength, over the traditionally-used paper.

In the LOM process, a laser beam is used to cut out layers from a spool-fed roll of sheet material as it is passed across the model and bond them to the stack of previously cut layers to build up the prototype model. As the cut is made, so the areas around the model are cut into cubes allowing the model to be broken away immediately after it is taken from the working area.

One of the best examples of the process capability is a model of a gearbox housing that was used on Volkswagen’s Passat and Golf ranges. It was fully detailed with all fillets, draft surfaces and hole features and, in all, it contains in excess of 3000 features.

Arguably, of all the RP processes, laser sintering systems come closest to what most engineers would regard as true production machines. Laser sintering basically involves applying a layer of powder on a movable platform and fusing specific areas depicted in the 3D computer model with the aid of a CO2 laser, lowering the platform by the equivalent of a layer, then repeating the process.

At last year’s Euromold exhibition, EOS, whose machines are available in the UK from HK Technologies, introduced a machine offering direct laser sintering of metal powder for the first time. Called Eosint M 250 Xtended it uses a new steel powder, DirectSteel 50-V1, to build tool inserts with good detail resolution and a smooth surface finish. It employs the DirectTool process which was developed in conjunction with the Finnish company Electrolux Rapid Development to provide a direct route to metal tooling.

It can be used to construct tool inserts directly from metal powders in a matter of a few hours, and the material of the end-product has a tensile strength up to 500N/mm2.

Since Euromold 98, the material range has been extended by the addition of two other metal powders – DirectSteel 50-V2 and DirectSteel 100-V3 – offering successive increases in build speed at the expense of a slight deterioration in surface finish.

Amid claims for the most productive system for processing thermoplastics using laser sintering techniques, EOS has developed its Eosint P 350 machine. Not only does it offer a high building speed of 25mm/h in the Z axis but it is capable of constructing several parts simultaneously, inside a volume of 340 by 340 by 600mm. Since the process obviates the need for supports, a considerable amount of cost is saved.

A FLEXIBLE PROCESS

One of the virtues of this process is that, in addition to designing models, it can be used to create functional prototypes in plain or glass-filled polyamide with integral hinges or snap-fitted features. Alternatively, polyester powder can be used to produce components either directly or to build investment casting patterns for metal parts.

EOS also manufactures Series S machines which incorporate a double-laser design for the direct production of components used in casting.

Another company to use laser sintering is DMT which uses the process in its range of SinterStation selective laser sintering (SLS) machines which are on sale in UK via the company’s European subsidiary, DTM. Typical of the machines is the Sinterstation 2500Plus which can accommodate plastics, metal or ceramic powders in a build chamber measuring 381 by 330 by 457mm.

To date, a wide range of resins have been able to be worked with SLS, including: standard nylon, glass-filled nylon and polycarbonate, plus a range of powdered metal material known as RapidSteel. One of the latest to be introduced is RapidSteel 2.0 Metal which can be processed by SLS to give a polymer-coated stainless steel part. When placed in a furnace, the polymer binding is removed and the steel particles are lightly sintered to about 60% dense. The `brown’ part is then returned the furnace and infiltrated with bronze to produce a fully dense, steel/bronze composite which, when finished and mounted, can be used as an insert for plastic injection moulding or diecasting. The time required for the preparation of mould-ready inserts ranges from five to 15 working days, according to complexity, and upwards of 100,000 injection moulded plastic parts or 200-500 aluminium, zinc or magnesium diecastings can be produced before replacement is required.

For short runs of around 100 to 400 parts, DTM now offers a copper/polyamide material. This is suitable for the production of injection mould inserts for polyethylene, polypropylene, glass-filled polypropylene, polystyrene, ABS, PC/ABS, and other common plastics.

{{Sanders Prototype Incorporated Tel: +1 603 429 97003D Systems Tel: +49 6151 357 304Stratasys Tel: +1 612 937 3000Stratasys (In UK) Laser Lines Tel: 01295 267 755Z Corporation Tel: +1 617 628 2732In UK: UMAK Limited at Tel: 0121 766 8844Ciba Specialty Chemicals Tel: 01223 832121Helisys Tel: +1 310 891 0600HK Technologies Tel: 01788 577288DMT Tel: +1 303 652-0200}}