curved hole in a solid block of metal
A Relatively Curved Space
How to make a curved hole in a solid block of metal? This was the question facing engineers at Weiss Kunststoffverarbeitung GmbH & Co. KG, Illertissen, Germany. An automotive subcontractor for whom the company has been producing heavy duty polyamide chain tensioners for car engines over many years wanted to integrate the oil dipstick by feeding it through the tensioner.
This good idea, however, presupposes that a curved hole is incorporated into the mold. Temperature control was also a critical aspect. Says Stefan Martini, a project engineer at Weiss: "In the area around the through-hole for the dipstick, the thickness of the workpiece had to be doubled for strength reasons. This meant that, if warpage was to be avoided in this area, accurate, conformal cooling during the injection process would be necessary."
To solve the problem of the curved hole, this section of the mold is made in two halves, which are then pinned together and hard soldered. Since the curvature, at least, is uniform, a curved slide can be used during injection molding to generate the cavity for the dipstick. Modern CAD and simulation tools were deployed to place the cooling channels in such a way that, despite the heterogeneous wall thicknesses, a uniform process temperature results.
Since temperature control is an important process parameter, Weiss integrated sensors into the mold surface to monitor the pressure and temperature in-line at especially critical points. The sensors are connected to the machine and process controller direct, such that any part which overshoots or undershoots specified values is immediately identified as a "fail" upon being removed from the mold and so can be rejected. Thanks to this interplay of rugged "hardware" – the mold weighs some 2.5 t – and high-precision sensors, these sophisticated parts are now produced to a high level of quality and have proved fit for purpose in practice.
WEISS Kunststoffverarbeitung GmbH & Co
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