Banca de DEFESA: DIEGO CHIARELLO

APPLICATION AND PERFORMANCE OF DLC THIN FILM IN THERMOPLASTIC INJECTION MOLD EXTRACTOR PINS

Thin Films; DLC; Pin and Bushing; Injection Molds; Tribology

In this work, extractor pins of thermoplastic polymer injection molds, originally produced in AISI H13 steel and gas nitrided, were coated with a thin film of DLC (Diamond Like Carbon), making a tribological pair with extractor bushings of AISI P20 and AISI H13 steels quenched and tempered. The DLC thin film was deposited in a PECVD (plasma enhanced chemical vapour deposition) chamber with electrostatic confinement. A device that simulates the extraction system of an injection mold was used to test the wear behavior of the proposed pin-bushing pairs, as a function of the increase in the number of cycles. Different materials and lubrication conditions were tested, looking for more efficient alternatives to the current system that uses gas nitrided pins and white grease for molds as a lubricant. Optical microscopy and Scanning Electron Microscopy (SEM) were used for the microstructural characterization of the samples and analysis of the DLC layer. Wear on the pins was quantitatively evaluated by mass loss and by measuring the layer thickness in SEM after 100,000 cycles. Analysis of the roughness variation of the topography of the samples by SEM was carried out to verify the impacts of the wear test on the surface of the samples. The hardness and adhesion of the DLC film were measured through nanohardness and nanoscratch tests, respectively. In addition, the samples were analyzed by nanohardness, GDOES (glow-discharge optical emission spectroscopy), and the friction coefficient, by scratching test. The mass loss results show that for the samples without the use of lubricating grease, the wear rate was considerably lower. The pins with the least wear were those of the PS and HS sets, both without the use of grease, which showed a mass loss of 5,400 and 5,467 mg, respectively. These results prove the possibility of using DLC coated pins without the use of lubricating grease in injection mold extractor systems and that this still provides a considerable reduction in the wear rate. The DLC film presented a uniform layer, with an average thickness of 3.34 μm and no gaps between the film and the substrate after its deposition. The main wear mechanism for DLC lubricated systems was abrasion, due to the abrasive paste created with DLC particles and the grease. Therefore, the condition of pins with DLC without the grease had a better performance in the bench tests.