Hot Forging-Based development of mining drill bit preforms: experimental and numerical analysis

Abstract Low-alloy steel drill bits are commonly used in the mining industry for boring holes into rocks. They are characterized by high hardenability and a good combination of mechanical properties, with minimal additions of alloying elements. As product quality improves, the market becomes more competitive. Significant growth in the use of engineering development tools has also occurred, leading to improved performance in rock drilling, oil and mineral exploration, and the search for gemstones. Due to the constant cyclical mechanical stresses applied, the expected life of drill bits is often reduced by fatigue or mechanical wear, indicating that the market consistently requires the availability of new drill bits. This work aimed to demonstrate the suitability of hot forging as a substitute for machining to manufacture the specific profile of the drill bit preform used in rock drilling. A mining-industry partner selected AISI 8640 steel, as it is widely used for drilling applications. Tests were performed with AISI 8640 as a modeling material, and the results from the forging process were used to evaluate the punch movement and consequent metal flow, as well as the filling of the part’s cavity within the forging dies. The results obtained using Elementary Plasticity Theory (EPT) allowed verification of the physical experiment with AISI 8640 steel forged parts. Following this evaluation, numerical modeling was performed and compared with the hot forging process. Formation of the hollow cavity b within the part and the head of the preform in the same step was assessed. As a result of this optimized process, the reduction in the initial height of the billet and the preform formation were analyzed, with the finishing of the drill bit contingent upon the machining process. This hot forging demonstrated improved material utilization compared to the machining process, highlighting the benefits of deformation through simulations.