PVD coating is a tool coating commonly used in industrial production, and it is also a tool coating with a long development time, which has a wide range of applications in cutting tools, moulds and dies, and other finishing industries. However, with the improvement of industrialised production level, the requirements on tool coatings are getting higher and higher. Although the preparation method is constantly progressing, however, the preparation process will still inevitably have certain shortcomings, which is also inevitable.

First, the common appearance of PVD coating preparation process shortcomings

1, large droplets

PVD coating preparation process, high-energy ion bombardment target material to obtain high stacking power conditions of the typical shortcomings, the general three-dimensional scale of the particles are more uniform, greater than 1.5um, is a serious impact on tool machining accuracy of the coating shortcomings of the tool's repeatability of the positioning accuracy and the appearance of the machined parts of the quality of the impact.

2、Tumour and flake protrusion

Is due to the particles in the vacuum chamber or the substrate appearance of the particles in the coating build-up once attached to the substrate appearance, followed by the build-up exists in the coating, often more flimsy coating shortcomings, shortcomings in the area of the scale is often much larger than the height in the use of easy to peel off.

3, empty pan or disc-shaped pit

PVD coating exists with the coating of the combination of foreign particles in the high stress effect of spontaneous fall, constituting the shortcomings of flooding; there is contamination between the substrate, in the vacuum chamber cooling due to thermal stress effect and fall constitutes a disc shaped pits or reveal the shortcomings of the substrate.

4、Pinhole or bubble

When the appearance of the substrate there is a narrow pit, the coating accumulation process in the pit side of the preferential growth, gradually constitute the coating pinhole shortcomings, and the appearance of the polishing process, the shortcomings of the appearance of a thin layer of the coating is ground off, exposed. Bubbles are 100-400nm micro-particles, vacuum chamber constitutes a sheet, when they pass through the plasma can get a charge, this ion can reach the substrate appearance, and in the effect of the charge is fixed in the substrate appearance, the stacking process constitutes a bubble-type shortcomings.

Second, the common methods to deal with the shortcomings of PVD coating appearance

1、Vacuum polishing

Vacuum chamber and internal components of the gas discharge, and the external surface area of the material is directly related. The atomic density of solid appearance is about 2×1019 m-2, considering the unevenness of the appearance, the practical solid appearance will adsorb a large number of gas molecules. Making the appearance flatter by polishing can greatly reduce the external surface area, thus cutting down the gas molecules adsorbed on the external surface. Polishing mainly has glass pill sandblasting and electrolytic polishing two kinds of techniques.

2, ultrasonic cleaning

Ultrasonic cleaning is the use of ultrasonic waves in the liquid cavitation effect, acceleration effect and direct flow effect on the liquid and dirt direct, direct effect, so that the dirt layer is lax, emulsification, stripping and reach the cleaning intention. To the liquid into the ultrasonic wave, the liquid's intense movement makes the local pressure difference. Low pressure part will occur a large number of bubbles, when the pressure from the beginning of the rise, these bubbles will be in an instant break, so that shock waves occur in the liquid. The shock wave will strip the oil from the solid exterior. The liquid used for ultrasonic cleaning is generally alcohol or acetone. Through the ultrasonic cleaning parts into the atmosphere, alcohol or acetone will immediately evaporate, will not leave scale on the exterior of the parts.

Third, TD treatment and PVD treatment - hardened layer and base material bonding force comparison

TD treatment hardened layer and base material metallurgical bonding, the use of not easy to fall off; PVD coating and base material similar to the combination of electroplating, belongs to the mechanical bonding, bonding and surface treatment processing equipment technology level has a lot to do. No matter what kind of processing technology is used, TD treatment hardened layer can withstand greater stress than PVD coating is not easy to peel off.

Fourth, TD treatment and PVD treatment-hardware stamping mould field application and effect comparison

TD treatment and PVD treatment can be used to improve the life of the mould and solve the problem of mould surface strain. TD treatment can be used for steel plate strength 590Mpa forming moulds and other occasions of greater force, PVD coating can be used for thin plate thickness, low strength occasions. High precision requirements of the mould can only be used PVD treatment.

In short, to improve the life of the mould workpiece, design + material selection + machining + pre-processing heat treatment + suitable surface treatment, do every step, in order to achieve or even exceed the expected service life.