Published 3/18/2022

Universal CAD/CAM Yields Ultra Precise Micro Molds

Mold builder uses CAD/CAM and IT software package to improve its micro mold tool design and machining.

Edited by Christina Fuges, Editorial Director, MoldMaking Technology

Innovation in Plastic Staple Zippers

PK0 plastic staple zippers are the smallest zippers that the company develops for baby and children’s clothing. The teeth injected directly onto the surrounding textile tape are made from Polyoxymethylene POM plastics for extreme durability and flexibility. In addition, since it is made of plastic, it offers an infinite range of color combinations from the strap to staple color, including novel glow-in-the-dark variants.

Even using the latest CAD/CAM, the entire design and development process for the PKO series still took 18 months. The zipper must meet demanding standards and the transverse strength is significant. Here the zipper has to withstand a force of 200 Newtons over a length of 1 inch. The final production mold includes a clever sliding section that can be interactively swapped to shape either the zipper start, middle and end sections, allowing for continuous molding regardless of zipper length (see Figure 1).

This injection mold for the PK0 plastic staple zippers were designed and machined with Pictures by PC.

Precision Mold and Electrode Machining

With products becoming increasingly complex, such as the PK0 zipper, the advanced machining strategies from Schott, such as trochoidal high-performance cutting (HPC) and high-speed finishing (HSC), are essential for the optimal cutting of hard tool steels and copper electrodes.

“Without good CAD/CAM software such as with Pictures by PC, the ever more complex construction and moldmaking processes are no longer possible,” Kellner says. As a result, the PK0 zipper has a very high level of precision (see Figure 2). Each tooth is 2 mm wide, 3 mm long and 2.4 mm high. The smallest corner radius on the tooth is a tiny 0.1 mm, with the gap between the cramps being approx. 0.9 mm. Using the milling strategies, they machined precise molds and electrodes in hard materials using tools as small as 0.2mm in diameter.

This shot illustrates the precision of the electrode for the PK0 zipper mold.

One of the main strengths of the Heiligenstadt-based company is its ability to manufacture the zipper clasps and grip plates according to exact customer requirements, such as logos and lettering. The flexible handling of the personalized graphics is made easier with the 2D vector graphic tools and the import of various other graphic formats. Typesetting and manipulation also meet the highest typographical requirements. The machining of the personalized 2D customer branding directly onto the 3D molds and electrodes is facilitated by the industrial engraving and carving toolpaths.

“The seamless transition to the CAM module offers great advantages, especially when it comes to lettering. This enables us to project logos and lettering onto free-form surfaces without any problems and thus mill and engrave the electrodes for die-sinking of the mold inserts. In addition, a great advantage of the CAM module is the many machining strategies that are available as standard,” Kellner says.

Kellner notes the free support and the large number of standard postprocessors available from Schotte Systeme. He believes the software forms a cornerstone of the company’s success.

Award-Winning Miniature Mold Design

Heiligenstädter Reißverschluß won the 2020 Zinc Die Casting Prize at the Euroguss exhibition in Nuremberg. Their award-winning cast part “suitcase” was a decorative zinc die-cast suitcase designed for a special series of collectible wooden figurines. Required to be an exact scale replica, the suitcase (measuring 20 x 14 x 7.5mm) included extra fine details, such as the case corners, that when scaled down, resulted in a protrusion from the case body of just 0.2mm.

To cast such fine undercut details without imprint marks, the company used Pictures by PC to design an intelligent solution of inclined ejectors that both formed and ejected the undercut regions of the suitcase corners, eliminating the need for mechanical sliders. The CAD/CAM’s high machining precision and surface finish (galvanized gold-plated) were compared during judging to ‘a watchmaker’s work.

“The cast part impressively shows that even the smallest quantities are interesting for zinc die casting. We machine everything in-house using our Pictures by PC CAM software, including the milling of the mold cores and ejectors,” Kellner says.