Evaluation of lubrication and friction in cold forging using a double backward-extrusion process

Identification of a friction model for the bearing channel of hot aluminium extrusion dies by using ball-on-disc tests

“…At elevated temperatures, the adhesive friction plays a dominant role, due to the strong atomic or chemical interactions, especially under 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 12 high contact pressures [1][2][3]36]. This is mainly due to the following reasons: at elevated temperatures, the atoms in both materials in contact are highly activated, which aids the interdiffusion at the surface layers of the materials and a strong chemical bonding tends to be established.…”

“…3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 In general, field test is to estimate the friction coefficient or factor by using extrusion friction tests. Based on the material flow response to the friction force, some novel extrusion friction tests have been developed, including double backward extrusion [1], combined forward rod-backward can extrusion [2] and combined forward conical / straight can-backward straight can extrusion [3]. These tests were designed with highlighted friction sensitivity indicated by extrudate lengths, and the lubricants can be evaluated and the global friction coefficient or factor on the workpiece/tooling interface can be determined quantitatively with the aid of FE simulations.…”

“…It was found that many practical problems in the hot extrusion industry, such as wear of the extrusion dies [1][2][3][4], surface quality of the extruded profiles [5], die lines and pick up [6] etc., are related to the strong adhesion between the hot aluminium and the die due to strong chemical and atomic interactions between hot aluminium and steel, which is the main reason for the excessively high friction observed during hot aluminium extrusion [1][2][3]7]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 In the past years, efforts have been made to study the tribological phenomenon of the extrusion process and the developed friction testing techniques can be classified as three different groups, namely, field tests; simulative tests (or physical simulation tests) and tribological tests.…”

“…Hence, simulative tests have been proposed and conducted. The block on cylinder tests [1,7] were developed to simulate the contact between the workpiece and extrusion die, and the wear mechanisms in the bearing channel region were studied. The results revealed that adhesive wear and abrasive wear…”

Friction Coefficient in Hot Compression of Cylindrical Sample

“…In practice, direct predicting the friction coefficient at a random strain level is difficult because of the difficulty with measuring the related parameters of specimens simultaneously in the working process; researchers often simply assume that the friction coefficient is constant or independent of the strain level. 7) Details regarding the evolution behavior of friction coefficients during the hot forging processes have not yet been clarified. The surfaces of the sample contain hills and valleys when viewed on a microscopic scale.…”