S. Gerardis

Complete qualification methodology for coatings of precision glass molding tools

Fritz KlockeKyriakos GeorgiadisFraunhofer Institute for Production Technology17 Steinbachstrasse, Aachen, GermanyandFraunhofer Project Center for Coatings inManufacturing17 Steinbachstrasse, Aachen, GermanyE-mail:kyriakos.georgiadis@ipt.fraunhofer.deOlaf DambonFraunhofer Institute for Production Technology17 Steinbachstrasse, Aachen, GermanyKonstantinos Dionysios BouzakisStefanos GerardisGeorgios SkordarisFraunhofer Project Center for Coatings inManufacturing17 Steinbachstrasse, Aachen, GermanyandAristoteles University of ThessalonikiLaboratory for Machine Tools and ManufacturingEngineeringThessaloniki, GreeceAbstract. Precision glass molding is the technology of choice for theproduction of complex-shaped optical components. Protective coatingscan significantly extend the lifetime of the molding tools, but the coatingproperties have to be exactly customized for individual application condi-tions. The current biggest challenge is to ensure the reliability of newlydeveloped coatings without resorting to extensive and expensive practicaltesting. However, the usual coating qualification methods either cannot beused or don’t provide meaningful results. In this work a new three-tier,application-specific methodology for the qualification such coatings is pre-sented. First, the basic characterization of coating properties is discussed,takingintoaccountthespecificcharacteristicsofthecoatingsusedforpre-cision glass molding tools. In the second step, application-specific testingmethods are devised, based on the analysis of the loads during glassmolding. Finally, a new machine for testing the lifetime of the coatedmolding tools is proposed. Three case studies are presented wherenanoscratch, nanoimpact and glass contact tests are performed withPt-Ir, TiAlN, and CrAlN-coated samples in combination with various glasstypes, showcasing the usefulness of the proposed three-tier methodology.

Chip Length Effect on the Wear of Coated Cemented Carbide Inserts in Milling

The effect of the developed chip length on the coated tool’s cutting performance was investigated. Milling experiments at various cutting speeds and chip lengths were performed, which resulted to different tool wear developments. To explain these results, a FEM simulation of the cutting process was conducted and the related chip geometries were predicted and compared to the corresponding experimental ones. Based on these results, the Coulomb friction coefficient between chip and tool rake was appropriately adjusted to achieve a sufficient correlation between experimental and computational data. By additional FEM calculations, the mechanical and thermal loads of the cutting edge were estimated and insight was provided concerning the effect of chip length on coated tool stresses and film fatigue fracture. The obtained results revealed that the chip length reduction improves the cutting performance of coated tools and a significant increase of the removed material volume and material removal rate as well can be achieved.

Evaluation of PVD Coated Tools’ Life in Milling Ti6Al4V, Based on Impact Tests at Ambient and Elevated Temperatures

A methodology based on FEM-calculations and experimental tests for predicting coated tool efficiency in milling Ti6Al4V by coated cemented carbide inserts is introduced. The used coatings were: (Ti,Al,Si)N and (Ti,Al)N films. The stress-strain curves and the fatigue critical loads of the coatings were determined by nanoindentations and impact tests respectively at various temperatures, employing FEM-supported procedures developed for results evaluation. The milling investigations were conducted at various cutting speeds. The stress and temperature fields in the cutting edge region were obtained by FEM calculations of the milling process. These results facilitated the explanation of the coated inserts’ cutting performance versus the cutting speed. The cutting tests at various cutting speeds and the impact tests at ambient and elevated temperatures revealed that the tool life and the film impact resistance versus the temperature are not linear. Moreover, a sufficient correlation of the coatings’ impact resistance at various temperatures with their cutting performance at corresponding cutting speeds was revealed. In this way, an adaption of the cutting conditions to the films’ temperature-dependent strength can lead to a considerable cutting performance improvement.

Erratum to “Application in milling of coated tools with rounded cutting edges after the film deposition”

In the above published article (b) Fraunhofer Project Center Coatings in Manufacturing, in Centre for Research andTechnology Hellas (CERTH), Thessaloniki, Greece and (c) Fraunhofer Institute for Production Technology (IPT), Aachen, Germany is one legal entity Fraunhofer Project Center Coatings inManufacturing, in Centre for Research and TechnologyHellas (CERTH), Thessaloniki, Greece and in Fraunhofer Institute for Production Technology (IPT), Aachen, Germany CIRP Annals Manufacturing Technology 58 (2009) 722