Tools and dies used in metal forming are characterized by extremely high temperatures at the interface, high local pressures and large metal to metal sliding. These harsh conditions result in accelerated wear of tooling. This phenomenon becomes a serious issue when parts forged at complex and are expected to meet tight tolerances.
The objective of this dissertation is to develop a computer-based methodology for analyzing the requirements hot forging tooling to resist wear and plastic deformation and to create wear resistant surfaces to overcome these failure mode, to increase hot forging tool life.
The approach proposed and tested in the dissertation involves development of a FEM based approach to model material degradation caused by heat, load and sliding. This approach uses tempering parameters proposed by Holloman and Jaffe and published thermal softening behavior of tool steels to predict the drop in hardness of tool steels during service. Using a modified Archard’s model for wear that takes into account effect of temperature on hardness, this drop in hardness is then used to more accurately predict wear in hot forging tools, that are dominated by thermal softening.
Dissertation outlines development of a new cyclic contact test design to recreate intermittent tempering seen in hot forging. This test has been used to validate the use of tempering parameters in modeling of in-service softening of tool steel surfaces. The dissertation also outlines an industrial case study, conducted at a forging company, to validate the wear model. This dissertation also outlines efforts at Ohio State University, to deposit Nickel Aluminide on AISI H13 substrate, using Laser Engineered Net Shaping (LENS). Dissertation reports results from an array of experiments conducted using LENS 750 machine, at various power levels, table speeds and hatch spacing. Results pertaining to bond quality, surface finish, compositional gradients and hardness are provided. Also, a thermal – based finite element numerical model that was used to simulate the LENS process is presented, along with some demonstrated results.