Application of advanced ceramics coating in mold materials
Die is the tool that makes the blank into a specific shape and size under the action of external force. It can be said that no mold, there is no modern industry, the development level of the mold industry is a key indicator to measure the level of the whole country's manufacturing industry, so it is also known as the "mother of industry". In electronics, automobiles, motors, electrical appliances, instruments, meters, home appliances and communications products, 60 to 80 percent of the parts are dependent on mold forming. The high precision, high complexity, high consistency, high productivity and low consumption of moulds are incomparable to other manufacturing methods. For example, in the most common automobile, automobile cover parts formed by stamping die, automobile interior parts formed by injection mold, and various engine transmission parts formed by precision forging all show the precision and efficiency of the mold industry.
Fig.1 the new mould of yinbaoshan applied on Peugeot 3008 (picture source: yinbaoshan new mould)
However, the traditional mold processing is generally carried out in harsh environment, alternating temperature, stress conditions make the mold prone to various fatigue damage; In addition, the severe friction between metal plastic flow and mold cavity makes mold wear become one of the important failure forms. Therefore, the development of new high hardness, high wear resistance, high strength of the mold material has been concerned.
Figure 2 jiangsu senwei precision forging automobile parts produced by block extrusion process, which can process various complex shape parts, but high deformation temperature and forming force, posing great challenges to mold materials
(photo by sen wei precision forging)
As early as the 1990s, boron carbide ceramics have been used in mold materials in China. The boron carbide drawing die developed by mudanjiang boron carbide research institute is made of boron carbide powder with high purity and ultra-fine particle size, which is pressed under high temperature and high pressure. It has high hardness and good abrasion resistance and can be used as the main wear-resisting component of the drawing equipment in the cable industry.
However, ceramic materials have high hardness, high temperature resistance, non-stick mold and other advantages at the same time, the application of the biggest difficulty is the brittleness of ceramics, as a brittle material, its fracture toughness is low, almost can not withstand tensile stress, this defect limits its application as a whole mold. In order to solve this problem, ceramic materials can be combined with metal materials to ensure high hardness and wear resistance, as well as good plasticity and toughness of metal materials. It can also be used as a surface coating material, which is attached to the surface of traditional mold materials to form a "tough outside but tough inside" mold. These two "learning from each other" methods have been widely used.
In 2017, xiong wei and his colleagues at the jiangxi institute of mechanical science unveiled a metal-ceramic mold using a hot extrusion process. In this study, W, Ti and other metal carbides are added into the mixture of metal-ceramic materials. After dry pressing, cold isostatic pressing, no pressure sintering, mechanical processing and other processes, a new generation of w-ti metal-ceramic hot extrusion die is developed, which breaks through the traditional technology of producing hot extrusion die with high alloy steel. The test results show that the service life of w-ti hot extrusion die is 7.5 times that of traditional alloy steel.
(tip: the extrusion process requires a very high mold, and the common extrusion pressure is above 2000MPa. Therefore, the research on new mold materials, the relevant literature often falls in the development of new extrusion mold materials. The initial mass extrusion of steel has been considered difficult to achieve, because there must be ultra-high strength of the mold material to withstand such a large extrusion pressure, cold extrusion for the first time mass production of steel parts is world war ii, Germany used a new alloy tool steel and phosphating saponification technology to achieve. Traditional extrusion is carried out at room temperature. In recent years, some high-strength materials must be squeezed at high temperature, which puts forward higher requirements for mold materials.
In addition, early studies generally used hot-press sintering method to prepare cermet, which used metal particles to toughen alumina ceramic mold to overcome the brittleness of ceramic materials. In addition to the toughening technology of alumina ceramics, central south university, together with aluminum corporation of China, has developed a new mold material using metal Ti to strengthen silicon nitride ceramics, and believes that silicon nitride has better red hardness, wear resistance and comprehensive mechanical properties than aluminum oxide, and is one of the most ideal materials for manufacturing hot extrusion molds.
A ceramic coating that is hard on the outside but tough on the inside
Compared with the research and development of new mould materials of cermet, the theory of ceramic coating is simpler and the actual operating cost is lower. Current methods include chemical vapor deposition (CVD) and physical vapor deposition (PVD), the latter of which is more widely used. PVD technology is an arc discharge technology with low voltage and large current under vacuum condition, which makes use of gas discharge to evaporate the target material and ionize both the evaporated substance and the gas, and USES the acceleration effect of electric field to deposit the evaporated substance and its reaction products on the workpiece.
Table 1. Brief analysis of PVD coating dies
Name of the mould
0.5 mm stainless steel
Life expectancy increased by more than nine times
Powder metallurgy die
WC + Co powder
Life expectancy increased by more than 12 times
Deep drawing mould
Carbon titanium nitride
Low carbon steel
Solve die strain problem
Die casting mould
Chromium nitride aluminum
6063 aluminum alloy
Solve sticky material problem
Swiss company Hatebur is one of the world's leading die equipment suppliers. It is the first company to apply titanium nitride coating through PVD to the punch of cold extrusion die. (small tip: in the extrusion process, general PVD coating method of titanium nitride can only be used under 450 ℃, the temperature is cold extrusion friction, material and the temperature of the mold interface has been able to achieve; And if you want to use warm extrusion, in order to prevent the loss of coating, often by CVD method, so working temperature can reach above 800 ℃. In addition, the use of CVD method of titanium carbide coating, the working temperature can reach 950 ℃ to 1100 ℃)
In November 2017, the third in the whole country "Internet +" contest of college students' innovative undertaking, xi 'an jiaotong university "originality cloud tu" project won the gold medal, and is considered by the organizing committee is the most valuable project undertaking, at present, the company started being Pre - A round of funding, intends to transfer shares 10%, mainly used for the contract of building and construction of professional team. It is reported, "originality cloud tu" project initiated by xi 'an jiaotong university doctoral Qian Dan after 85, currently rely on independent research and development of coating technology, expert team in colleges and universities, and research and development platform, developed including titanium nitride, titanium nitride carbon, chromium, chromium nitride aluminum nitride series of ceramic PVD coating technology, replacing the traditional metal or alloy plating coating method, for the mould put on "soft" hedgehog armour.
FIG. 4 sample of craftsmanship cloud coating using PVD method (picture source: craftsmanship cloud coating)
In general, the application of traditional steel or hard alloy die materials has been very mature, but in some more severe working conditions, performance and life is facing great challenges. As noted in the tip, the traditional cold extrusion technology is warm extrusion direction, in the warm extrusion process, because the temperature is higher, traditional materials red hardness difference problem increasingly exposed, adopt ceramic material coating after the hard material performance, longevity, reducing the frequent replacement mold, have achieved better economic benefits. In contrast, the application of ceramic materials reinforced by metal particles in industry is rarely reported, mainly because the price of monolithic ceramic metal mold is still very expensive, and the service life prediction is only limited in the laboratory. However, the development of combined concave die, so that the mold has a more flexible form, for the need to face the high temperature and pressure of the mold part, can be used to strengthen the ceramic material, and the rest of the remaining parts, still use relatively cheap traditional materials. In addition, the demand for stainless steel, heat resistant alloy steel is driving the development of hot forming technology, in the face of high deformation resistance, high temperature processing environment, metal ceramic mold is still worth looking forward to.
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