Rapid prototyping

From Free net encyclopedia

Rapid prototyping also describes a software engineering methodology.

Image:3dprinter.jpg Rapid prototyping, also known by other names such as additive fabrication and solid freeform fabrication, is the automatic construction of physical objects using additive processes including stereolithography, selective laser sintering, and fused deposition modeling. The first techniques for rapid prototyping became available in the 1980s and were used to produce models and prototype parts. Today, they are used for a much wider range of applications and are even used to manufacture production quality parts in relatively small numbers. Some sculptors use the technology to produce complex shapes for fine art exhibitions.

In brief, Rapid Prototyping takes virtual designs (from computer aided design or from animation modeling software) processes them by transforming them into cross sections, still virtual, and then forms or manufactures each cross section in physical space, one after the next until the model is finished. It is a wysiwig process (what you see is what you get) where the virtual model and the physical model correspond almost identically. The process is similar to the construction of a topographical model where the layers correspond to the elevations in the model.

There are two main methods of rapid prototyping, which are derived from similar approaches in sculpture. In additive prototyping, the machine reads in data from a CAD drawing, and lays down successive micrometer or millimeter-thick layers of liquid plastic, powdered plastic or some other engineering material, and in this way builds up the model from a long series of cross sections. These layers which correspond to the virtual cross section from the cad model are glued together or fused (often using a laser) automatically to create the final shape. This is similar to the ancient technique of coil building a ceramic pot. The primary advantage to additive construction is its ability to create almost any geometry (excluding trapped negative volumes). One drawback is that these machines make smallish parts, typically smaller than an engine block. Monumental parts can be made by automatically carving foam with a hot wire one layer at a time. Several companies have built large scale machines to do this automatically, but most market the product rather than the machine.

The subtractive method is older and less efficient. In this technique the machine starts out with a block of plastic or wax and uses a delicate cutting tool to carve away material, layer by layer to match the digital object. This is similar to a computer numerical control (CNC) device such as a lathe or a mill. The subtractive method (and CNC) is older and tried and true. It is similar in concept to a sculptor carving a block of marble or wood where they chip away at the surface of the model until the form of the project begins to emerge. Complex shapes and forms with undercuts are more difficult to accomplish with the subtractive method. Typically these are made in parts and fit together. Subtractive technologies are capable of doing large scale projects.

The standard interface between CAD software and rapid prototyping machines is the STL file format.

Today its possible to make very high solutions in layers of mikrometer and below [1], uv curing materials are based on Sol-Gel materials, acrylates, epoxies and others.

The word "rapid" is relative: construction of a model with contemporary machines typically takes 3–72 hours, depending on machine type and model size. Used in micro technologies "rapid" is correct, the products made are ready very fast and the machines can build the parts in parallel.

Advances in technology allow the machine to use multiple materials in the construction of objects. This is important because it can use one material with a high melting point for the finished product, and another material with a low melting point as filler, to separate individual moving parts within the model. After the model is completed, it is heated to the point where the undesired material melts away, and what is left is a functional plastic machine. Although traditional injection molding is still cheaper for manufacturing plastic products, soon rapid prototyping may be used to produce finished goods in a single step.

Other advances may include machines that are both additive and subtractive. Some consider the lamination technologies (laminated object manufacture) to already be dual strategy machines.

Lab tests have shown that prototyping machines can also use conductive metals as a building material, and conceivably in the future could assemble small electronics like mobile phones in a single process. Today its possible to make mems and integrate bare dies at microTEC Germany.

Due to the high degree of flexibility and adaptability required by many rapid prototyping techniques, these applications typically require the use of robots or similar mechanisms.

As of 2005, the cheapest rapid prototyping machines cost about US$ 25 000 and are therefore still beyond the reach of most consumers.

However, there are currently several schemes to improve rapid prototyper technology to the stage where a prototyper can manufacture its own component parts (see RepRap). The idea behind this is that a new machine could be assembled relatively cheaply from raw materials by the owner of an existing one. Such crude 'self-replication' techniques could considerably reduce the cost of prototyping machines in the future, and hence any objects they are capable of manufacturing.

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