Deep drilling is a difficult machining operation, it often presents problems related to chip evacuation and efficiently cooling and lubrication of the cutting zone. Minimum quantity of lubrication (MQL) is an ecological alternative to wet machining. It provides better lubrication, however, it has low cooling effect and the chips are not removed away from the cutting zone by coolant. In this paper a combination of cutting speed, feed-rate and tool geometry is determined to produce smaller chips and lower workpiece temperature for deep drilling of SAE 4144 M steel under MQL lubrication condition. Full factorial design of experiment was used to plan the set of the experiments. Tool wear behavior and cross sections of the drilled holes were compared to a pressurized oil condition. Split point geometry, lower cutting speed and higher feed-rate resulted in the best chip shape and relatively low workpiece temperature in deep drilling of SAE 4144 M with MQL. The worn drill presented microchipping, adhered workpiece material on the rake face and exposed substrate resulted from abrasion of TiNAl coating. MQL resulted in longer tool life and more surface defects compared with the pressurized oil condition.

Purpose Deep drilling of hardened steels is a difficult machining operation because of the high wear level of tools. This paper aims to present the main wear mechanisms observed in physical vapor deposition (PVD)-coated twist drills during deep drilling of SAE4144M steel under minimum quantity lubrication, assessed in the production of injection holders. Design/methodology/approach Two PVD coatings were tested: TiAlN and AlCrN, industrially processed, the last one being a multilayer coating. The workpiece was heat treated for a hardness of 39 HRC to be applied in a diesel engine component. The tests were performed in an industrial environment for a fixed number of holes. Two levels of cutting speed and feed rate were selected for the experiments. In addition, minimum quantity of lubrication (MQL) was compared with conventional lubrication. Scanning electron microscope was used to reveal the wear mechanisms. Findings Spalling of PVD-coating was revealed for conventional lubrication, while adhesion was observed in MQL conditions. The use of multilayered AlCrN-based coating promoted a significant reduction of adhered material on the twist drill, which is the reason for this selection in industrial operation. Practical implications Results showed that the MQL regime can be applied for this industrial application. Originality/value A detailed description of wear mechanisms, which allows a suitable selection of coating and machining variables was found for a very difficult operation, using a more economic process in terms of lubrication.

No abstract

No abstract