CNC router speeds prototype production

Edited by the Engineeringtalk editorial team Jun 3, 2008

Each Isel CNC router is constructed from extruded aluminium profiles, has four ground and hardened steel shafts plus eight re-circulating bearings in each axis.

The improved accuracy and faster turnaround made possible by a computer numeric controlled (CNC) router has helped generate a 30% increase in sales at a manufacturer of plastic prototypes by increasing the repeat business.

Previously, the company manually cut parts out of plastic sheet stock and glued them together when making prototypes.

While this method resulted in a reasonable facsimile of a part it was slow and lacked the high level of accuracy that some customers needed.

With the CNC router, designs are now carved out of plastic blocks, which are then used to produce silicone moulds for urethane castings.

The cast prototypes generated directly from CAD data are more accurate than the previous 'pieced-together' models.

The manufacturer provides prototypes to companies that design and sell injection-moulded parts.

In the past these companies ordered very expensive steel moulds used to mass produce their plastic products so they could evaluate prototypes of new designs to make sure they were acceptable.

The CNC approach saves them the cost of modifying a mould or building a new one by letting them uncover problems with new products before they invest in the moulds.

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 of CNC routers that could cut plastic directly from the client's CAD data and would remove the accuracy restrictions imposed by human limitations.

Even if the pieces were just cut by the computer-controller router rather than by hand the increase in accuracy would be significant.

However the comapny wanted to try a new process for producing prototypes that would also eliminate the need to assemble separate pieces.

With a CNC router the company could program the machine to cut away the shape of the CAD geometry from a block of butter board plastic and create a silicon mould from that cavity.

Filling the mould with urethane provides a highly accurate wax model that looks just like it came out of an injection moulding machine.

This approach gives companies the best window into how their products would actually appear once they were mass produced.

Of the two options in CNC equipment, the first was a heavy machining centre primarily designed for metalworking, which was accurate but very expensive.

The Isel CNC router was more affordable and included a number of high-end features that would allow it to produce parts with the level of accuracy wanted.

Each router is constructed from extruded aluminium profiles, has four ground and hardened steel shafts plus eight re-circulating bearings in each axis.

This shaft-and-bearing system produces very smooth, play-free motion and an extremely rigid system that produces high-quality cuts.

The machine uses anti-backlash ball screws like those used in high-end machining centres.

It has excellent power transmission due to the rolling ball contract between the nut and screws.

This type of contact ensures low friction, low wear and a long life.

The ball screws also make it possible to produce parts to the machine resolution of 0.013mm.