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Method of testing the coefficient of friction of thin plates and strips of metallic materials أداة الاختبار –

Author:QINSUN Released in:2023-09 Click:100

Test method for the coefficient of friction of thin sheets and strips of metal materials

Task source
According to the first batch of industrial standard revision project plans of the Ministry of Industry and of Information Technology in 2010, \"Friction Testing Industrial Standard \"Method\" of Coefficient of Metal Material Sheets and Thin Strips was drafted by Wuhan Iron and Steel (Group) Company, University of Science and Technology Huazhong Technologies and Metallurgical Industry Standards Research Institute.

Writing process and solicitation of opinions
Friction is widely present in production and real life, and constitutes one of the research areas of solid mechanics. When there is relative motion or a tendency for relative motion between two objects in contact with each other, a mechanical force that impedes the relative motion will be generated on the surface.e of contact, called friction force. The two objects rubbing against each other are called friction pairs. According to the wordIonic state of the friction pair, friction can be divided into static friction and kinetic friction. The first refers to friction when the two objects in contact with each other tend to move relative to each other and are in a critical state of rest. The latter refers to friction when the two objects in contact with each other cross the critical state of rest. Friction occurs when relative motion occurs.

The coefficient of friction refers to the ratio between the friction force between two contact surfaces and the vertical force acting on one of the surfaces. The coefficient of friction is generally related to the roughness of the contact surface and has nothing to do with the size of the contact area. . Depending on the nature of the movement, it can bere divided into static friction coefficient and kinetic friction coefficient. The maximum resistance of the two contact surfaces at the beginning of the relative movement is the static friction force, and the ratio to the normal force is the static friction coefficient. The ratio of the resistance when two contact surfaces move relative to each other at a certain speed to the normal force is the coefficient of kinetic friction. It should be emphasized that the friction coefficient corresponds to a set of friction torques and is linked to the material and roughness of the two contact objects that make up the friction torque. It makes no sense to just talk about the coefficient of friction of a certain material.

Most researchers believe that the essence of friction is caused by intermolecular cohesion on the contact surface of objects. However, in fact, for two objects in contact with each other,only microscopic protrusions on the surfaces are in contact with each other, and most places are not in contact. Therefore, the actual contact area is much smaller than the apparent contact area (i.e. what we measured on the sample area). Friction resistance is proportional to the actual contact area (not proportional to the apparent contact area). Generally, the actual contact area is proportional to the positive pressure on the surface, so the friction force is proportional to the positive pressure. The cohesive attraction between molecules on the contact surface between different materials is different, which will affect the friction between objects, so the friction coefficients between different materials are also different.

Friction plays a negative role in most situations, causing wear of products and parts, leading to surface damage, material loss and part failure. This not only consumes energy and materials, but also reduces the operating efficiency of equipment. , and it will accelerate the disposal of equipment, cause frequent replacement of parts, and cause huge economic losses. In the field of sheet metal forming, friction conditions also affect sheet metal forming performance, one of the important parameters. During the forming process, the sheet metal and the molds together form a friction pair. The friction state between the two will directly affect the forming limit, springback and surface quality of the workpiece. Excessive friction will cause the sheet metal to fail during the forming process. Defects will occur in the mold, and scratches and \"bond tumors\" will occur on the surface of the mold, which will worsen thewear of the mold and will affect the life of the mold. In the numerical simulation of sheet metal stamping forming, the friction coefficient is also a necessary input parameter, and it is also an important factor affecting the accuracy of the numerical simulation.

Since the 1990s, the country has issued five relevant standards in the field of friction, which have played a very good guiding role in the standardization of industrial testing methods. However, over time, many gaps have gradually emerged in the implementation of the above-mentioned standards. For example, the automobile brake lining standard (GB5763-1998) and the automobile clutch surface standard (GB/T5764-1998) and relevant foreign standards are very different in terms of technical concepts, determination of friction performance level and testing methods, which restricts the export of friction materialsChinese tion to foreign markets; the products of the standard on asbestos friction pads for industrial machinery (GB/T11834-2000). The name contains the word \"asbestos\", which is obsolete; some test items for friction linings are still blank; the quality of fixed-speed friction testing machines is uneven, and the comparison and reproducibility need to be verified; some clauses of the standard are obsolete and waiting behind. However, there are currently no international or national standards for testing methods for the friction properties of metal sheets. Only a few large automobile manufacturers and steel mills have formulated corresponding corporate test specifications. Therefore, it is very necessary to formulate industrial standards for the field of sheet metal forming and battery. Detect the friction performance between sheet metal and molds through dhe testing methods. There is a need to standardize testing methods between laboratories so that they can be used under uniform conditions. Providing practical and usable test results is of great importance. When formulating this standard, the principles of revising China\'s friction material standards have been fully implemented: it should reflect the technical level of the industry, promote technological progress, and benefit the development of the industry . At the same time, the situation in the automobile industry should be taken into account and the problems of adequacy with the requirements and standards of the automobile industry should be taken into account.

The standard “Metal Sheet and Strip Method for Friction Coefficient” (Metal Sheet and Strip Method for Friction Coefficient) is mainly aimed at the field of sheet metal forming in the inautomotive industry and can be considered as a reference for other industries. This test method is designed to identify contact properties between stamped steel plates and stamping dies. It is used to detect the sliding friction coefficient between a sheet metal (0.2~2mm) and a standard mold. This parameter can be used to evaluate the surface quality of the steel plate, and can also be directly used in numerical simulation software to design parts and adjust the stamping process. The standards are highly operational. They adapt to the requirements of the current development of mechanical property testing technology towards complete, detailed, precise and reliable measurement.

This test method specifies in detail the method of measuring the sliding friction coefficient of sheet metal strips, and clarifies the experimental principle of this test method; the selectionon sample size and sampling focus; and machining the sample. Methods ; sample preparation methods and requirements; test equationequipment, test requirements, test steps and processes; methods of analyzing and processing test results, how to issue test reports and many other contents. There are no excessive requirements for the selection of lubricating oil and only relevant instructions are given during sample preparation. The aim is to broaden the applicability of this standard. A point that is easily overlooked when calculating the coefficient of friction is that there is a two-fold relationship between the tensile force of the testing machine and the one-sided friction force during the experiment. Relevant explanations and key reminders were carried out separately in the test results processing section.
In July 2010, the CommitteeNational Standardization Administration officially issued a document accepting that Wuhan Iron and Steel Co., Ltd. would be responsible for drafting and formulating the industrial standard for “Test Method of Sliding Friction Coefficient of Sheet Metal Strips”. project number 2010-0281T-YB. Subsequently, the Standards Development Working Group was established to discuss and formulate a work plan.

After receiving the formulation task, I began to prepare the draft standard for comments, collected, analyzed and studied relevant international and foreign materials, and mastered the current status and methods testing coefficient of friction test methods for various materials. Development direction, and based on national conditions and development trends, a draft of this standard is proposed.