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Mark Twain famously wrote, "Thunder is good, thunder is impressive; but it is lightning that does the work." So too it is with many tools, especially those used for molding or pressing large parts. Such tools can be impressively huge, made from masses of materials, and take much time to build. But it is only the front surface of the tool that does the work. This is the basic idea behind Surface Generation Ltd.'s Subtractive Pin Tooling (SPT^TM) technology.

The company, a UK start-up, creates large tools for aerospace, automotive, marine and other applications which require parts with surfaces that must be aerodynamically, aesthetically and structurally precise. Rather than milling the tools for such parts out of solid blocks of material, Surface Generation mills just the tops of an array of disposable pins. The pins are individually vertically positioned to provide a foundation for the tool that uses the minimum amount of material. According to the company, the result is an enormous savings in the time and material required for machining. Lead-times are said to be reduced as much as 90%.

Tooling surfaces can be made from almost any material including plastics, metals, ceramics or wood. Such tools also permit the addition and subtraction of material, and local alteration of working surfaces. This can facilitate rapid design iterations and also allows re-use of up to 90% of molds, according to the company.

Surface Generation believes SPT^TM will be useful in such processes as: compression and fiber glass molding, metal pressing, pattern making, expanded polystyrene and vacuum forming. The SPT^TM process is said to be highly scaleable and is constructed from off-the-shelf technology. It can be retrofitted to existing machine tools.

The company says the SPT^TM process allows machine tools to produce previously impossible forms. One example is high aspect ratio cavities. To form these, surrounding pins are depressed, allowing pins located in the cavity interior to be machined. The surrounding pins are then again raised to form a surface with a deep cavity. See the picture below.

Another example is flipping surfaces inside out to quickly make a matched tool. By rotating pins through 180 degrees and re-positioning them vertically, concave surfaces are made convex. Large parts can also be 'flattened' by lowering all the pins to the same height (e.g. on a dome), machining them in place, and then vertically re-positioning them to their intended locations. This allows small milling machines to produce large parts.

The technology is not a layered manufacturing method, per se, but it can be expected to offer competition to RP-based methods of creating tools for similar applications, and it may also make direct fabrication using additive technologies less attractive for others.

For more info Contact: Surface Generation Ltd. The Pera Innovation Park Nottingham Road Melton Mowbray Leicestershire LE13 0PB United Kingdom 0044 (0)870 013 1235 Tel 0044 (0)870 013 1236 FX Ben Halford, CEO ben.halford@surface-generation.com

Above is shown a CAD representation of a cowling with features that are deeper than possible to make with the milling machine available. Below, using a layering technique, it's possible to create this shape using SPTTM.