Hardness: an important performance index of mold materials and finished molds

In industrial production, mold steel is the main material of the die industry. The service life of the die and the accuracy, quality and appearance performance of the finished parts are not only related to the design technology and manufacturing accuracy of the die, but also related to the accuracy and manufacturing operation of the machine tool. Correct selection of die materials and correct execution of heat treatment process are also crucial. The heat treatment quality and service performance of molds are usually judged by hardness
Hardness is an important performance index of mold materials and finished molds. The stress state of the mold during operation is complex. For example, the hot working mold usually bears the alternating stress under the alternating temperature field, so it should have a good ability to prevent the mold from changing into a soft or plastic state, and still maintain the shape and dimensional accuracy of the mold in the long-term working environment. Generally, the hardness of finished molds is usually 59-60hrc for cold working molds and about 48hrc for hot working molds.
Wear resistance is also an important performance index of finished molds. When the part is formed, the metal moves relative to the surface of the mold cavity, which abrades the surface of the mold cavity, so that the size, shape, accuracy and surface roughness of the mold change and become invalid. The wear resistance of the mold is determined by the heat treatment of the mold, especially the surface heat treatment. The main basis for evaluating the wear resistance of the mold is also the hardness.
The hardness test of die steel is mainly aimed at three situations, namely, the hardness test of die steel materials, the hardness test of semi-finished dies after heat treatment, and the surface hardness test of dies requiring high wear resistance after heat treatment.
Die steel materials are mainly forged steel plates, steel blocks or steel bars, which are generally supplied in annealed state. Some plastic mold steels are also supplied in pre hardened state (quenching and tempering treatment), and users can directly process them into molds without subsequent heat treatment. Mold steel can be divided into carbon tool steel, alloy tool steel and high-speed tool steel according to the classification of steel. The Chinese standard stipulates the factory hardness requirements for all kinds of mold steel, and requires the annealing hardness of steel and the quenching hardness of samples to be tested. Metari hardness tester is widely used. It is fast and convenient to test. The test value can be automatically converted into Brinell hardness value, so it has been applied to a certain extent.
The die steel materials that have been machined should be quenched and tempered, and then refined and polished to become finished dies. The hardness test of the die after quenching and tempering is more important, because the material hardness is a very important quality index at this time, which determines the service life of the finished die to a great extent. Quenching and tempering die materials require the use of Rockwell hardness tester to test HRC Rockwell hardness value. The finished mold needs to have the best comprehensive mechanical properties, not only enough hardness, but also a certain toughness. Hardness and toughness are a pair of contradictions. In order to have a higher hardness under the condition of reasonable toughness, the best hardness value will be limited in a relatively narrow range, usually only 2-4 HRC units.
The hardness test of finished and semi-finished molds is a difficult problem to solve. There has never been an ideal solution. Only a few molds with small volume and weight can be moved to the bench Rockwell hardness tester for testing. The Leeb hardness tester provides a solution for the hardness test of finished and semi-finished molds. The Leeb hardness of molds can be tested first, and then converted to HRC Rockwell hardness. At present, Leeb hardness tester is the most widely used hardness testing method in the mold industry, and the mold industry is the most widely used field of meiteri hardness tester. As mentioned above, the reasonable hardness range of finished and semi-finished molds is relatively narrow, and the Leeb hardness tester cannot meet such accuracy requirements. But this is the current situation of the mold industry, there is no better solution.
For the mold with surface carburization, nitriding or laser quenching treatment, the surface hardness of the mold needs to be tested. The carburized layer is usually thick. When the thickness of carburized layer is greater than 0.8mm, Rockwell hardness tester can be directly used to test HRC hardness. When the thickness of carburized layer is 0.6-0.8mm, a scale of Rockwell hardness tester can be used. The test force of scale a is small, only 60kg (the test force of scale C is 150kg), so a shallow indentation can be pressed on the surface of the mold, which will not penetrate the hardened layer, and the hardness test is more accurate. The measured HRA hardness value can be easily converted into HRC hardness value by looking up the table. For thin carburized layer or nitrided layer, as long as the thickness is greater than 0.1mm, the surface Rockwell hardness tester can be used. The test force of the surface Rockwell hardness tester is only 15kg, 30kg or 45kg. The surface Rockwell hardness indentation is smaller. For example, when the mold hardness is 60HRC, the surface Rockwell hardness value is 90.6hr15n, and the indentation depth is equal to (100-90.6) x0.001mm=0.009mm. Such indentation is almost difficult to distinguish with the naked eye. Therefore, the surface Rockwell hardness tester can also test the finished mold, and the measured hardness value can also be converted into HRC hardness value.
Hardness is the most important property of die steel. In order to take into account other properties such as toughness, the best range of die hardness is a relatively narrow range. Therefore, how to use Mattel portable durometer on site to quickly and accurately test die hardness is of great significance in die manufacturing and use. It can improve the quality of mold products, improve the technical level of mold manufacturing, and extend the service life of molds.



About Huizhou Dj Molding Co., Ltd

Dj Mold is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.

Person: James Yuan
Company: Huizhou Dj Molding Company Limited
Add:  LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Tel: 86-752-6682869
Email: [email protected]

Site: https://www.jasonmolding.com/custom-injection-molding/


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