Machinability Assessment of Injection Mold Steels Subjected to Distinct Heat Treatment Conditions

The increasing demand for high-quality products with reduced delivery times has driven the adoption of increasingly complex manufacturing processes. However, the higher level of sophistication and efficiency of these processes tends to raise the cost of the final products, which makes the optimization of machining operations indispensable. In mould manufacturing, it is estimated that approximately 30% of the total cost of the final product is associated with the mould, and about 65% of this value is directly related to machining operations. These figures highlight the relevance of machinability and of properly defined cutting strategies to ensure the technical and economic feasibility of mould and die production. The aim of this study is to evaluate and compare the machinability of steels for plastic injection moulds under high-hardness conditions. End-milling tests were carried out using coated cemented carbide tools, with monitoring of tool life and surface roughness, and external cylindrical turning tests were performed with cemented carbide tools, in which cutting forces and cutting temperature were measured. The materials investigated were: VP50IM steel in the solution-treated and aged condition; N2711 steel in the quenched and tempered condition; and VP20ISO steel, also quenched and tempered. The main input parameters were cutting speed, feed and depth of cut. The results indicated that, in terms of tool life in milling, VP20ISO exhibited the best performance, followed by N2711 and, finally, VP50IM. On the other hand, VP20ISO generally produced the highest surface roughness values, whereas N2711 and VP50IM provided better surface finish under specific cutting conditions. The machining of N2711 required the highest cutting forces, while VP50IM presented the highest temperatures at the chip–tool interface, an effect mainly associated with its higher nickel content and microstructural features. In all conditions, flank wear was the predominant wear mode, and abrasive wear was the main wear mechanism. Overall, the chemical composition; particularly the nickel content and the presence of manganese sulphides, proved to be a key factor governing the machinability of the steels studied, directly affecting heat generation, cutting forces, surface roughness and tool wear rate.