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the requirements of carbide drawing molds
Apr 24, 2018

Based on the relevant knowledge about the requirements of carbide drawing molds, combined with our many years of production experience, we analyze and summarize the following aspects in many aspects, hoping to help you understand the nature of the demand points of carbide drawing molds. In the development of new types of cemented carbide materials, iron-nickel-cobalt has become popular in the past few years. For example, the high-strength and toughness carbides equivalent to YG15, YG2O, and YG25 developed by the Hunan Provincial Metallurgical Materials Co., Ltd. have received better results in the use of cold-die and cold-extrusion dies. The Tianjin Cemented Carbide Research Institute also used iron. Nickel-on-cobalt has developed quite a GY (15-20) cemented carbide mold material, which is equivalent to YG2O in terms of roll forging of standard parts and steel ball cooling piers. The new research hotspots in recent years are fine-grained, ultra-fine crystals, and even nanocrystalline carbides and graded cemented carbides. Gradient cemented carbides have gradients in composition, gradients in structure, etc. In addition, metal melt penetration treatment methods are also used to produce graded cemented carbides, such as graded cemented carbide top hammers. Fine-grained and ultrafine-grained carbides have also been introduced, such as the fine-grained YG8 wire drawing die, which is 3 times the normal wire drawing die when drawing <1 mm less steel wire. In addition, there are inlaid cemented carbide hot work molds, which have achieved very good results in rolling mills and wire rods. Carbide blanks made of a material have a long service life and some are short after being processed into a mold. After anatomical analysis, the problems were found in design, processing, assembly, and welding.


1. Hard alloy mold design technology


The drawing die is a relatively simple die. Before the 1980s, China had been using the "straight line" theory of the former Soviet Union. After 1980s, some manufacturers cited the "smooth transition" technology theory proposed in the 1950s.


In recent years, Chinese scholars have carried out the theoretical analysis of angle design and ring groove wear of drawing dies, proposed the concept of maximum and minimum drawing angles, and analyzed the mechanism of uneven wear of metal molds during the process of tensile deformation. The researchers of the Guangdong Institute of Technology conducted anatomical analysis of the hard alloy molds for the small-sized bolts of the cold pier, and found that the secrets of the domestic molds were low (2 to 4 million times) and the life of the Japanese molds (9 to 10 million times) was high. The key technology is the design of the angle. That is, the Japanese mold uses a double-convex design at the central contact point between the bottom of the core and the bottom surface of the inner hole of the mold sleeve. Its advantage is that it can make the most stressful center place guarantee to press tightly, and when the void left around is available for interference fit, it will store the extra metal that is extruded from the hole wall. The cemented carbide die used for the Ml2 nuts of the cold piers in the Shenyang Bridge Plant was changed from the original hexagonal design to the six-piece trimming insert. The average life expectancy is 500,000 pieces/model, and the high grade is 1.2 million pieces/this author thinks this kind of design is more reasonable. First, it saves cemented carbide compared to the overall structural design model; second, it is simple to assemble; third, it is easy to replace the mold. Damage to a valve can be replaced.


2. Effect of processing and assembly technology on carbide die


The dimensional accuracy and shape accuracy of carbide die are achieved by grinding. Because the grinding force of hard alloy is 2-3 times of the grinding force of general steel. Therefore, the power of the grinder is required to be large and the rigidity is high. As for the current level of machine tools in our country, there is no special grinder for machining cemented carbide. It often causes machining errors, and the cumulative effect of errors will seriously damage the service life of the mold. In the EDM process, due to the instantaneous high temperature of 10,000°C or the liquid medium during the discharge, the mold material undergoes a change in the metallographic structure of the surface, and may also be carburized (carbon in the working fluid). Infiltration of metal (copper tungsten electrode) and even micro-cracks, no doubt affect the life. The insert is designed to allow the alloy to withstand greater impact and crush loads. Whether it is hot or cold inserts, the clearance requirements are tight. General cold pressure insert set selection 0.03-0.05mm of the amount of interference, hot pressure insert set 0.08-0.1Omm, the cavity sleeve heating 700-800 °C, carbide take about 300 °C. After the hot press is completed, it is placed in a 600 box furnace for 2 hours to eliminate the stress.

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