Investment in CNC router helps business to raise turnover

A manufacturer of plastic prototypes had previously formed these by manually cutting parts out of plastic sheet stock and gluing them together. While this method resulted in a reasonable facsimile of a part, it was slow and lacked the high level of accuracy that customers needed. With a new CNC (computer numerically controlled) router, designs are carved out of plastic blocks, which are then used to produce silicone moulds for urethane castings. The cast prototypes generated this way are more accurate than the previous 'pieced-together' models.

The manufacturer supplies prototypes to companies that design and sell injection-moulded parts. In the past, these companies ordered expensive steel moulds so they could evaluate prototypes of new designs. The CNC approach can save them the cost of modifying a mould or building a new one by enabling problems to be uncovered before mould tools are laid down.

Up until now, model makers used conventional tools such as a manual router and table saw to make the prototypes. After receiving a CAD model of the part from the client, they would break it down into component parts such as ribs, top, bottom and side panels and then cut these parts out of ABS plastic sheet stock by hand. The sheet stock used was as close as possible to the wall thickness of the part that was going to be injection-moulded. Once all the pieces were cut, they were glued together to represent the final product. This process took about five days and the resulting prototype was a close approximation of the final product.

An investigation was carried out to establish whether the CNC routers could cut plastic directly from the client's CAD data and remove the accuracy restrictions imposed by human limitations. Even if the pieces were just cut by the CNC router rather than by hand, the increase in accuracy would be significant. However, model makers wanted to try a new process for producing prototypes that would also eliminate the need to assemble separate pieces. With a CNC router, the machine could be programmed to cut away the shape of the CAD geometry from a block of butter board plastic and, from that cavity, create a silicone mould. By filling the mould with urethane, a highly accurate wax model could be produced. This approach would give companies the best preview of how their products would actually appear once they were mass-produced.

CNC options

Of the two options in CNC equipment, the first was a heavy machining centre primarily designed for metalworking and, although this would deliver the accuracy needed, the smallest machine was very expensive. The second option, an Isel CNC router, provided the best of both worlds - it was more affordable and included a number of high-end features that would enable it to produce parts with the level of accuracy required. Each router is constructed from extruded aluminium profiles, has four ground and hardened steel shafts plus eight recirculating bearings in each axis. This shaft-and-bearing system produces very smooth, play-free motion and a rigid system for high-quality cuts. The machine uses anti-backlash ball screws similar to those in high-end machining centres, as they have excellent power transmission characteristics due to the rolling ball contact between the nut and screws. This type of contact ensures low friction, low wear and long life. The ball screws also make it possible to produce parts to the machine resolution of 0.013mm.

The machine has been successful in speeding up the process, reducing waste, cutting costs, producing a superior product for the customer and so increasing the customer base. Furthermore, the customer has enjoyed a 30 per cent boost in sales by increasing the repeat business.