Positive extrusion test method for plastic forming friction coefficient and friction factor

Abstract

The invention relates to a positive extrusion test method for a plastic forming friction coefficient and a friction factor. The positive extrusion test method comprises the following steps of 1) preparing a tensile specimen by using a to-be-tested material and measuring a yield stress Y at a to-be-tested temperature; 2) preparing a cone-shaped mold with a cone angle [theta] and the diameter of a large end port and a small end port being D0 and D respectively, by using the same material to the to-be-tested mold; 3) preparing a cylinder specimen with the diameter of d by using the to-be-tested material, wherein d value is between D0 and Dl; 4) extruding a specimen coated by a lubricating agent downward in the cone-shaped mold on a material testing machine at a constant speed and recording a value when extrusion load F starts to be stable; 5) calculating the friction coefficient and the friction factor according to formulas disclosed by the invention; and 6) repeating the above steps for 3-5 times, and taking an average value as a result. The positive extrusion test method is in no need of measuring geometrical shapes after a test specimen is deformed, has no abnormal deformations such as compressive instability and the like, is simple in specimen process and needs no theoretical calibration curve. Besides, the positive extrusion test method has high test precision, convenient operation and high efficiency, and can be used for tests at various temperatures and speed conditions.

Description

technical field [0001] The invention belongs to the field of metal plastic forming, in particular to a method for testing the friction coefficient and friction factor of plastic forming. Background technique [0002] During metal plastic forming, the workpiece is in contact with the mold and deformed under high pressure. There is always friction between the contact surface of the workpiece and the mold that prevents the flow of material. Usually, friction has a great negative impact on plastic forming, such as causing mold wear and workpiece scratches, increasing deformation resistance, changing the stress state in the deformed body, and generating residual stress. In practice, lubrication measures are often used on the contact surface between the tool and the deformed metal, that is, a certain amount of lubricant is applied to reduce the influence of friction. Due to the continuous deformation of the metal and the constant change of the friction surface during the forming ...

AI Technical Summary

Problems solved by technology

The main problem of this method is that it is difficult to accurately determine the position of the neutral plane and accurately measure the data, so there are few practical applications

[0015] In view of the problems of large errors and inconvenient operation in the existing measurement methods of the friction coefficient (factor) of plastic forming, it is necessary to find a measurement method for μ and m that can obtain high measurement accuracy and is easy to implement

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