Session: 02-07-02: Advanced Material Forming: Roll Forming

Paper Number: 71851

Start Time: Thursday, 05:10 PM

71851 - Friction Assessment in Hot Forging Operations Using Large-Scale Ring Compression Test 

The ring compression test is the most extended experiment for friction characterization in metal forming processes. However, these experiments are commonly carried out under laboratory conditions with small specimens and highly controlled conditions, which may not accurately represent the industrial forging operations. A small size specimen does not provide enough surface area for the oxide scale formation and heat transfer, and these phenomena are critical in industrial processes. Then, friction characterization results more conveniently and accurately by using large-scale specimens. The friction was determined by reverse engineering, using commercial finite element (FE) code Qform, which is a commercial code for specific metal forming applications. Finite element models were adjusted considering both the final ring dimensions as well as the load-stroke during the entire experiment. The numerical model is a classic J2 rigid-plastic model, and the material is assumed to obey Misses law.  The material's properties, such as plastic flow curves, were determined previously using the cylindrical compression test, and these curves were introduced into de software. A mesh sensitivity analysis was conducted to determine the suitable spatial discretization, and refinement sections were set-up in the inner and outer cylindrical surfaces in order to accurately catch the final diameters. The compression anvils were modeled as rigid bodies, but thermal conduction is considered between plates and specimens.

The design of experiments (DOE) matrix included different factors and levels such as temperature, deformation speed, and high reduction. The temperatures were 900, 1100, and 1200 °C, the deformation speeds were 20, 80, and 150 mm/s, and the degree of deformations were 40, 60, and 80% in high reduction. The main effect of the parameters as mentioned above and their interactions are studied. The experiments were conducted to determine the friction and heat transfer in a real crankshaft's forging process. To determine that, ring specimens were done in a servo-hydraulic press, using compression plates made with the same material, thermal treatment, and surface coating as real forging dies used in the crankshaft pre-forming operation. A general response analysis was performed to establish the sensitivity of different friction models. The temperature effect was higher than the deformation speed; however, these two factors have a strong interaction effect. On the other hand, from the FE models' results, it was confirmed that the inner diameter reduction is highly sensitive to the coefficient of friction. However, the load-stroke behavior is shown to be less sensitive to changes in the friction, although it varies when different friction models are used.

Presenting Author: Diego Gomez University of Guanajuato

Authors:

Elias Ledesma University of Guanajuato
Diego Gomez University of Guanajuato
Ryutaro Hino Hiroshima University
Hiroshi Hamasaki Hiroshima University
Eduardo Aguilera Hiroshima University
Ismael Ruiz CIE PEMSA