Saturday, January 23, 2010

Inkjet Printing

As the name suggests an Inkjet Printer is essentially a normal printer that prints in 3D. 3D printers can produce full colour, highly detailed, accurate models for communication and design evaluation. Multiple inkjets sweep across the surface of the layer and print the image of a single cross section onto the powder. The printer contains a bay with support material and a platform that moves in X and Z axes, the inkjet moves in axes X and Y. Where the binder is printed, the powder is glued together, then the powder-spread roller comes along the building tray distributes and regularizes the powder layer to be glued and the inkjet print heads is reloaded with binder. A new layer of powder is spread in surface to be glued. After the end of the model construction, it is vacuum cleaned to remove not glued powder. This rapid prototyping process do not offers great resistance to the model so it must be infiltrated. Parts are porous, and it is only necessary for the infiltrate to penetrate one-quarter inch to one-half inch in order to give the part a durable shell.

Laminated Object Manufacturing

Michael Feygin, the inventor of Laminated Object Manufacturing (LOM) first heard of RP in 1984 when he came across a article in a magazine about lasers been used to make models. Trying to imagine how this technology would work led him to using paper as a demonstration. From this LOM was invented. Over the next three years the process was developed with funding from the Department of Energy, Illinois. In 1985 Helisys was founded and released they’re first machine, the LOM-1015 in 1990.

LOM applications are sometimes limited due to the fact that models are made from paper and glue. However they have many applications such as visualisation patterns for sand & investment casting, moulds for vacuum forming, aerodynamic, analysis of bio-medical research, etc. LOM models generally can’t be used for physical testing or any sort of application involving heat.

The traditional LOM machines work by lying down a sheet of paper or plastic laminated to a previously laid layer and bonded the layers using a hot roller. The roller applies heat and pressure causing the adhesive on the sheet to activate and stick the layers together. A CO2 laser is then used to cut out the shape of that layer. Around the object the unused material is diced by the laser in a crosshatch pattern causing small pieces called “tiles” — this allows for easy removal. This unused material is used as support.

Fused Deposition Modelling (FDM)

Fused Deposition Modelling (FDM) was invented by Scott Crump. In 1988 Scott and his wife Lisa Crump founded Stratasys and released the first FDM machine (the 3D-Modeler) in 1990.

An FDM machine builds on a layer-by-layer basis by laying down a filament of thermoplastic material (generally ABS plastic). The material is unwound from a spool and fed through a heated nozzle just above the materials melting point. When it makes contact with the building board it solidifies immediately.

As mentioned FDM primarily uses ABS filament, it’s extremely durable, accurate, and keeps most of the fine detail from a drawing. It also produces some of the most hardwearing prototypes available on the market. Stratasys offer their ABS filament in a number of colours. The standard colour is white but also comes black, blue, green grey (light & steel), red, yellow, and also custom colours if so required. Stratasys also offer two other types of filament, polycarbonate (PC) and polyphenylsulfone (PPSF).

Accuracy of Rapid Prototyping

The accuracy and surface finish of a Rapid P:rototyping model is determined by its layer thickness.

RP is good on flat surfaces but can be poor on curved surfaces. RP models are left with a ladder shaped pattern along these curves. However layer thickness determines the time it takes to build a model. The idea of RP is that the user can have a model in their hand in rapid time. If it took too long to produce a small model, then it wouldn’t be rapid. The thinner the layer the more accurate the part will be, but this also means it will take longer to produce.

Rapid Manufacturing

Another concept of Rapid Prototyping is Rapid Manufacturing (RM). RM is the direct production of products using Rapid Prototyping technologies. The thought of being able to eliminate tooling and moulding costs for certain parts of your product has been of interest to companies for some years now. However at the moment there are several limitations with RP and RP components including speed, mechanical properties, surface finish and repeatability. Saying this there have been several good examples of RM in recent years and many involving the automotive industry. WilliamsF1 are a long-term user of SLA. They use it to build parts to test in their wind tunnel, but RM has also proved beneficial. For example after one of the races in the 2005 championship, Williams had to redesign the hydraulic and electrical cables under the driver’s legs. The problem was that the clips used to hold down these cables no longer fitted and there wasn’t time to get a new set moulded. So Williams used their SLA machine to build them. They concluded that the mechanical strength of these clips were strong enough and could be used in the future. Another good example of RM is in the hearing aid industry. Hearing aids can now be made to fit the exact shape of a person’s ear.

RP applications

1)Visualisation: The ability to feel and see a product before it goes into manufacturing is priceless. Rapid prototypes can be used as visual aids for engineers, designers, and manufacturers. It allows for increased communication between all parties and helps determine the cost of a good.

2)Form-fit and function testing: Component sizes and functionality can be verified to ensure they work their intended purpose.

3)Functional models: Allows for components to be physically tested.

4)Presentation models are important for organisations to win contracts and business.

5)Casting models: Casting moulds can be made in order to build full-scale replicas of the part.

6)Rapid tooling: A Rapid Prototype model is used to quickly make a mould, or uses the Rapid Prototyping process directly to fabricate a tool for a limited volume of prototypes.

7)Products for designers and jewellers: Some high fashion designers (e.g. Assa Ashuach) are using Rapid Prototyping to produce intricate shaped objects as fashion accessories.

8)Scaffolds for biomedical industry: Rapid prototyping is showing signs that it will be able to produce scaffolds for the biomedical industry. This could mean the end of the tedious process of trying to mould these scaffolds.

9)Visualisation tool for surgeon: 3D models can be made of parts of the human body. These models can even be personalised for the person being operated on. 3D scanners can replicate the exact break or fracture obtained by the person. Surgeons can then use these models to prepare for operations.

10)Rapid Manufacturing: Direct production of products using Rapid Prototyping technologies.

11)Ergonomic studies: Build the basic shape of the object and see how it feels in your hand.

Intoduction to Rapid Prototyping

Over the past twenty years Rapid Prototyping (RP) has been one of the most important techniques introduced to reduce the time for new product development. RP is a process of producing a model using a layer-by-layer deposition of material. With RP, designers can build a physical model of a component within hours, when before it could have taken weeks. Chiu et al. believes that “A diagram serves better than one thousand words for description, whereas a solid model serves better than one thousand diagrams for illustration”.

Charles Hull first imagined the idea of Rapid Prototyping in September 1982 when he was vice president of UVP Inc., which specialised in products that involved UV light. He developed the first feasible stereolithography RP machine in February 1983 and applied for a basic patent in August 1984. After acquiring the exclusive rights of UVP Inc. money was raised and 3D systems founded by Charles Hull and Raymond Freed in March 1986. The first machine commercially sold was in early 1988.

Rapid Prototyping is essentially the building of models in layers. These models can be built in various materials such as plastic, paper, metal and even rubber. The developments in rapid prototyping materials over the past few years has being staggering and are showing no sign of slowing down. Rapid prototyping simplifies the building of complex objects easy because of its layer-by-layer process. However these models are generally only useful as prototypes and not final products, but as mentioned with the developments of materials this could all change in the near future. In general rapid prototyping processes produce little waste material; this is seen to be very attractive in certain industries that use expensive materials extensively (e.g. aerospace).

Rapid Prototyping improves communication between all interested parties and enables them to understand the design. Thrimurthulu et al. classifies Rapid Prototyping as “an important technology as it has potential to reduce the manufacturing lead time of the product up to 30–50% even when the relative part complexity is very high”. Having a model in your hand allows the designer/manufacturer to detect any flaws in product design and therefore make design changes before the decisions are made to have high cost moulds manufactured.