Machine for producing dental prostheses employs bespoke zero-point workholding

Headquartered in Austria, Amann Girrbach manufactures innovative equipment to produce not only dental prostheses such as abutments, crowns, veneers and bridges, but also dentures. In its latest production system, the Ceramill Matik, the company has introduced a zero-point clamping system from Roemheld group company Stark Spannsysteme. It ensures enhanced repeatability when positioning raw material for 5-axis milling of the complex profiles that characterise the prostheses. The workholding products are available in the Britain and Ireland through Roemheld UK, Hitchin.

Intended for extended periods of unattended production overnight and at weekends, the new machine is an intelligent solution that combines three operations in one – milling at up to 100,000 rpm, cleaning and automatic storage.

Marcel Humml, Senior Manager Operational Excellence responsible for R&D said, “The Ceramill Matik incorporates a 5-axis machining centre with a 36-workpiece changer, whereas other products on the market have a maximum of 12 workpiece positions and are considerably more expensive.”

He said that the company’s aim was to bring increased efficiency to the dental laboratory. To make this work, a system was needed that could autonomously and consistently handle tools with radio frequency ID from a 27-position magazine, as well as store and handle diverse workpiece materials such as metals, polymers, zirconium dioxide and ceramics. Accurate location of the material blanks, each of which also has a readable RFID chip, prior to machining is only possible if a zero-point system is used.

Michael Netzer from Stark Spannsysteme’s technical sales department helped to draw up a specification sheet for Amann Girrbach with key parameters such as workpiece size, clamping force and required repeatability of positioning. Analysis showed that the optimal zero-point clamping system would be a STARK.basics.S Pneumatic. A week later, Mr Netzer delivered one to Amann Girrbach.

It is well suited to the application due to its high-quality, stainless tool steel construction and compact, modular, maintenance-friendly design. Spring force clamping with pneumatic release provides fail-safe workholding. Positioning is simple and reliable via an integrated recess in the STARK.basic.S and a corresponding locator in the holder.

Since cleaning was a high priority in this application, the decision was taken to use a zero-point variant with blow-off, an extended nozzle ensuring effective removal of debris. The cylindrical recess therefore remains free from swarf and due to optimal application of clamping force, no flexing or lifting is possible and high positioning accuracy is guaranteed.

Humml added, “When testing the Stark zero-point system, we concluded that we would like to have a few modifications. We did not want any visible screws and we preferred the sides to be exposed so that water and dirt could run off better.

“Due to our compact holder size, we also requested a smaller support surface to save space. All of these modifications were duly made by Stark in the customised solution they provide to us.

“The cooperation with Stark during the development phase of Ceramill Matik was unbeatable – the relationship really couldn’t have been better.”

Netzer concluded, “Our zero-point product was designed for metal machining on a factory floor and was not originally intended for a small production centre producing fine, delicate parts.

“However we were happy to make the necessary adaptations to support automation in the dental sector.”