Ion nitriding technology of automobile mould

The application of ion nitriding technology can further improve the service life of automobile die, and form a layer of fatigue resistant Nitriding on the die surface which is higher than the hardness and strength toughness of the base material, so as to improve the ability of die to resist thermal deformation and wear, and greatly extend the die life.

Ion nitriding has the advantages of fast nitriding speed, good performance of nitriding layer, energy saving and environmental protection. It can effectively improve the wear resistance, fatigue strength, corrosion resistance and burning resistance of steel metal parts. It is widely used in modern manufacturing industry.

In recent years, some new plasma source and ion nitriding technologies have emerged, such as active screen and plasma source, which have obvious advantages in equipment and technology, and may become the development direction of ion nitriding technology.

Characteristics of automobile mould

Automobile molds are generally divided into two categories:

One is cold working die, such as automobile panel die;

The second is hot working die, such as some auto parts hot forging die.

1. Cold working die

In the automobile manufacturing industry, the large-scale cold working die is mainly the die of automobile covering parts, which is mainly made of cast iron or cast steel with large size and quality. The service life of these dies mainly depends on the die material, manufacturing and assembly accuracy, as well as the wear resistance of the die surface. In the automobile industry, the drawing die for large car panel is usually made of gray iron, nodular iron, alloy iron or cast steel. The overall dimension of the die is 5-6m, and the quality of the single die is 20-30t. And because of the development of modern car panel die toward high efficiency, long life and large-scale high precision, the shape of die is more and more complex, and the requirement of die is higher and higher. At present, ion nitriding technology has become the main means to extend the service life of large-scale cast iron new mold or repair old mold and improve the quality of die stamping parts. The production practice shows that the main factors affecting the quality of ion nitriding of cast iron die are the surface purification before nitriding, the surface processing after nitriding, the thickness of compound layer and the effect of sub surface hardening.

2. Hot working die

There are many kinds of automobile hot working dies, and the working conditions and failure forms of the dies are complex. When this kind of hot forging die works in the hot state, the working surface of the die shall bear repeated heating and cooling to produce certain thermal stress; at the same time, it shall bear different degrees of mechanical stress repeatedly, especially the great dynamic load stress, so that the internal of the die material is subject to alternating tensile and compressive stress, so as to generate lattice vacancy in the metal structure, and gradually form micro cracks, resulting in mold shape Cavity cracking. In addition, due to the poor cooling of the die, the phenomenon of die sticking will occur, which will increase the temperature of the die surface and the plasticity. Under the constant pressure stress and shear stress, the die cavity will deform. Generally speaking, the service life of automobile hot working die is relatively low. In order to prolong the service life of the die, it is necessary to select the die materials correctly, improve the quality of raw materials, adopt advanced heat treatment technology, improve the quality of heat treatment of the die, and the correct assembly and operation of the die are also important factors. Not all molds need or are suitable for surface strengthening treatment. Incorrect surface strengthening treatment may cause premature die failure.

Active screen ion nitriding technology

In 1999, Georges J of Luxembourg invented the active screen ion nitriding technology. The furnace body of the active screen ion nitriding equipment is anode, and the metal screen is cathode, which is connected with DC or pulse voltage. The workpiece is suspended in the metal screen, and the metal screen is formed by stainless steel wire. The principle is to connect the negative pole of the high-voltage power supply to the metal screen in the vacuum chamber, and place the processed workpiece in the metal screen. When the metal screen is connected to the high-voltage power supply, the gas in the low-voltage reaction chamber is ionized. Under the action of the electric field, the activated gas ions bombard the metal screen to heat up the metal screen; at the same time, under the ion bombardment, iron or iron nitride particles are continuously sputtered out, In the form of particles deposited on the surface of the workpiece, the nitrogen in the particles diffuses to the interior of the workpiece to achieve the purpose of nitriding. In the process of ion nitriding of active screen, the metal screen plays two roles: one is to heat the workpiece to the temperature required by nitriding treatment through radiation; the other is to provide iron or nitride particles of iron to the workpiece surface.

The characteristics of the active screen ion nitriding technology are: in the nitriding process, the workpiece is in suspension state, and the ion bombards the metal screen instead of the workpiece itself. Compared with conventional ion nitriding, this technology can deal with different shapes of workpieces, eliminate the edge effect and hollow cathode effect, and measure the temperature of workpieces conveniently.

Ion nitriding equipment

Ion nitriding equipment is generally composed of furnace body, air intake system, exhaust system, power system and control system.

Equipment parameters: the working parameters of the ion nitriding equipment vary with the size of the furnace body. The main parameters affecting nitriding process are total power of power supply, DC output voltage, maximum output current of rectifier, pulse output voltage, maximum peak current of pulse output, pulse frequency, etc. The whole system controls and completes the process automatically through the control system. The equipment is reliable and the treatment quality is stable.

Energy saving renovation of ion nitriding equipment: the energy consumed by ion nitriding mainly includes electric energy and thermal energy, and the renovation of energy saving equipment is mainly considered from the perspective of reducing the consumption of electric energy and thermal energy.

The application of ion nitriding technology can further improve the service life of automobile die. A layer of fatigue resistant nitriding layer with higher hardness and toughness than that of matrix material can be formed on the die surface. On the premise of reducing the initiation and propagation of thermal fatigue cracks on the die surface, the ability of ion nitriding to improve the thermal deformation and wear resistance of die can be fully exerted, and the die life can be greatly extended.