Near Solidus Forming (NSF): Semi-Solid Steel Forming at High Solid Content to Obtain As-Forged Properties

Abstract

Near solidus forming (NSF) of steels is a novel process under the umbrella of semi-solid forming technologies midway between classical hot forging and semi-solid technologies. This article presents the work done at Mondragon Unibertsitatea to develop this technology and demonstrates the great potential of the NSF process. The study proves the capability of the process to reduce raw material consumption by 20%, reduce forming loads from 2100 t to 300 t, and reduce forming steps from three to one, to obtain as-forged mechanical properties, as well as the excellent repeatability of the process. The work demonstrates that manufacturing commercial steel components in a single step using several off-the-shelf alloys is possible thanks to the flowing pattern of the material, which enables near-net shaping. In the first part of the article, a general overview of the semi-automated near solidus forming cell, together with a description of the NSF manufacturing trials, is provided, followed by the presentation and discussion of the results for the selected steel alloys.

Preliminary Study on the Capability of the Novel Near Solidus Forming (NSF) Technology to Manufacture Complex Steel Components

“…The deformation tooling that goes into the press was also self-designed, consisting of two-die closing die system ( Figure 2 c) attached to the press table and an injection punch attached to the ram ( Figure 2 b). For a more detailed description of the cell go to [ 17 ].…”

“… ( a ) The NSF cell of Mondragon University, ( b ) the self-designed NSF tooling for high melting point alloys [ 17 ] and ( c ) schematic drawing of the dies and expulsion system. …”

“…These problems have been proposed to be addressed through using Near Solidus Forging (NSF) technology. Previous works assessed how the manufacturing of large batches of components without observing any severe die damage has been possible, attaining as-forged properties [ 14 , 15 , 16 ], using off-the-shelf alloys and reducing by nearly 10 times the force required to fabricate the component by conventional hot forging [ 17 ]. This mainly comes from the optimization of the working conditions and equipment.…”

“…The material is heated up to temperatures below the steel solidus temperature and then deformed in a press in closed die system. This produces a part that has comparable mechanical properties to conventional forging with an ultimate tensile strength of 1073 MPa compared to the 1030–1130 MPa required for 42CrMo4 [ 17 ]. According to the best of the author’s knowledge, at the moment, there are no other studies on processes at the same conditions as NSF.…”

“…The NSF process therefore certainly offers the benefits to mechanical properties whilst also utilizing much lower specification forging presses (400t compared to 3000–4000t in hot forging). This, together with the material consumption reduction due to the avoidance of flash generation and the possibility to reduce the machining allowances, permits the attainment of a cost reduction of the order of 10–15% [ 17 ].…”