How Many Different Parts from a Single Tool?

How many product variants can be moulded from one tool? Ken Symonds, design manager with Allibert Handling, the U.K. subsidiary of French plastics group Sommer Allibert, says "How about 64?" But it could be more.

What Symonds refers to as his "baby" is an attached lid, nestable container for secure distribution of goods, typically in the automotive and pharmaceutical industries. Its ancestor, launched five years ago, was a single-colour product. The first significant variation along the evolutionary chain was to offer two different heights-a third was added later-without removing the tool from the press. Incorporation of a lock-and-link mechanism meant that a job that could take all day was cut to a couple of hours-simply a matter of taking one plate out and replacing it with a thicker one. Symonds describes it as "a concertina effect."

The container's twin half-lids were then being moulded separately. To cut costs, Symonds proposed moulding both container and lids from the same tool. But then, Allibert holds a patent on a single-barrel two-colour process. Why not use this to create simultaneously a container in one colour and lids in another? The attraction was a run with a low break-even point.

At Allibert's manufacturing plant in Gloucester, the two-colour process is incorporated in an 850-ton Battenfeld moulding machine, which then had a hot runner system developed in-house by Allibert. This called for outside help since, if any complications emerged during the later development of this increasingly elaborate project, their technical resolution would have been down to Allibert. So Mold-Masters was called in to modify one of its hot runner designs and then perform the necessary flow analysis and establish the pressure ratios.

Two-colour costs are competitive, since they are the same as single colour. Label holders on the box sides are created with "a very precise collapsing core mechanism," says Symonds. Two other collapsing cores create special recesses in the container to form the basis for a tamper-evident seal. A further 16 collapsing cores, eight on either side of the container, create engagement points for the hinge pins. Symonds says Allibert is the only company to produce a box with twin lids that requires no additional hinges or axes.

Pins on the mould create small indentations on the container rim that ensure the box is presented precisely for robot transfer from the moulding machine.

But what about those variants? Symonds invites anyone of a mathematical bent to work them out. Here's the range: