Developing Metalworking Fluids for Titanium Cutting

Abstract

Economical titanium cutting remains a challenge in manufacturing, especially with the titanium use rising. The productivity is low and tool wear is high. Metalworking fluids have a major influence on the tool wear. The working mechanism of metalworking fluids is poorly understood. New products are therefore developed in expensive trial-and-error cycles. The development process of new metalworking fluids for titanium should be made easier, more target-oriented, and less expensive. In this thesis, the whole fluid development chain from concept to machining tests with the final product is analyzed and optimized. The causes of tool wear in titanium cutting are investigated. Therefrom, the required properties of the metalworking fluid to mitigate wear are derived. Tribological laboratory tests are developed. As they are not able to replace the testing of a newly developed metalworking fluid in a real cutting situation, cutting tests are optimized as well. The test repeatability has one of the biggest leverages on the expenses of a full-scale cutting test. Disturbances are therefore identified and eliminated. It is found that notch wear can be attributed to tribo-chemical binder degradation. Crater wear in contrast can be attributed to the dissolution of carbide grains. Strategies to mitigate both types of wear are discussed. The tendency for notch wear can be assessed with an in-process tribometer. In full scale turning tests, the tool life standard deviation could be reduced by a factor of three by compensating the influence of the initial cutting edge radius. In full scale milling tests, the resolution of the tool life measurement could be increased at a decreased workpiece material consumption by using a force-based tool life criterion and single-fluted milling tools. The exact conditions a metalworking fluid meets close to the cutting edge remain unclear. Therefore, full-scale cutting tests are still needed before launching a new metalworking fluid. The methods to evaluate metalworking fluids are developed in an industrial environment and are directly adaptable by metalworking fluid producers. The methods are easy to use and can be automated.