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ALEX DEN OUDEN |
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Oude techniek en werktuigbouw, industriële geschiedenis en archeologie |
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The laminated objects manufacturing method creates models from layers of paper or polyester laminate, bonded together. The paper, coated with a thin layer of heat-sensitive adhesive, is supplied on a roll. It passes up over a vertically moving table to a take-up reel. At the start of each layer, a heated roll passes over the newly exposed sheet of paper causing it to adhere to the previous layer. Papers of varying thickness can be used.
First, a CO2 laser beam directed by an X-Y device and mirrors, cuts a rectangle free from the bulk of the paper. Next, the shape of the layer is cut into this rectangle with the laser. The waste paper, surrounding and within the model, is cut into small squares, to make it easier to (later) remove them from the model.
When a layer is finished, the table on which the workpiece is supported, lowers one step (one paper thickness) and the paper is advanced to supply fresh material for the next layer. The cycle then starts again.
The laser motion is controlled directly by the computer on the basis of a 3D CAD model of the product to be manufactured. The system software has a scaling facility and thus can compensate for shrinkage. In other words, it can produce foundry patterns suitable for e.g. sand casting directly from the original shape. There is no need to first correct this for shrinkage. The software allows production of several models at the same time, from the same roll of paper.
The speed of cutting only depends on the peripheral length of each cross section rather than on the total surface area as is the case with alternative technologies. Therefore, parts with thick walls are produced in LOM just as fast as those with thin walls. To prevent problems due to variations in paper/adhesive thickness, the height of the workpiece is measured and fed back to the computer. The profile to be cut is calculated to be exactly appropriate to the actual height of the model at that stage of build.
The waste material is left in place until the model is finished. The cubes could be removed during the process, but as long as they are left, they provide stability to the model. The bonding roller every time passes over a complete sheet and thin sections remain adequately supported. The size of the cubes can be varied to suit the detail required. They are removed (with hammer and chisel) after the model is taken from the machine.
Overall accuracy is ± 0.13 mm, so a high degree of detail can be incorporated into the models. If necessary, they can be hand finished. The models exhibit characteristics similar to those of plywood, including strength and machinability. As the models are constructed at room temperature from laminates of solid material, there is no shrinkage. This ensures that the model has a predictable accuracy level.
These machines are free-standing, self-contained units, operating from a normal 240 Volts supply and requiring no special environmental considerations. The unit can be installed either on the shop floor or in an office.
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