Characterization of friction coefficient at near solidus forming (NSF) conditions using T-shape compression test

Abstract

Amidst the escalating demand for sustainable manufacturing practices aimed at mitigating global emissions and waste, industries are actively seeking novel forming solutions to address these pressing global challenges. Near Solidus Forming (NSF) processes emerge as a promising alternative to confront such issues, offering the capability to fabricate intricate components reliably while minimizing material waste and energy consumption. This promising manufacturing process is still in its developmental stages for industrial applications, necessitating further exploration and understanding of various factors such as friction, heat transfer, and others. From the literature review, a lack of friction data at these temperatures has been identified. Therefore, this study is dedicated to the advanced characterization of the friction coefficient for Near Solidus Forging (NSF) operations. With that aim, T-shape experimental tests of 42CrMo4 alloy steel have been conducted at high temperatures (up to 1360 °C). Additionally, a lack of consensus on the correct T-shape testing and inverse analysis procedure has been noted. Consequently, apart from the experimental work, an in-depth analysis of the friction coefficient identification procedure has been conducted. As a result, a new geometrical output index is proposed, highly sensitive to the friction coefficient and therefore more reliable compared to state-of-the-art indexes. Furthermore, the influence of the selected geometrical output index and the consideration of sample-to-sample transfer and holding times were studied. Results showed that the increase in workload to consider the sample-to-sample transfer and holding times is not worthwhile, as assuming the average values lead to significantly less work with little impact in the final results (<5 % of error). The study also concludes that a friction coefficient of 0.25, 0.45 and 0.6 has been identified at temperatures of 1250 °C, 1300 °C and 1360 °C, respectively. Additionally, the result of thermal camera showed good agreement with the thermocouple data. Overall, in this study a robust and reliable T-shape testing, and friction coefficient identification procedure is proposed and validated.