Laser Melting(Laser cladding)technology is an emerging surface modification technology. It has the advantages of low dilution rate, small heat affected zone, metallurgical bonding with the base surface, relatively small distortion and deformation of cladding parts, and easy automation of the process.
The application of laser cladding technology to mold surface treatment can greatly improve the mechanical properties of the surface of parts such as hardness, wear resistance, corrosion resistance, fatigue resistance, etc., and greatly improve the service life of the material. At the same time, it can also be used to repair molds, saving a lot of processing costs.
I. Laser Melting – Laser Melting Define
Laser cladding emerged in the 1980s and is an advanced laser surface modification technology. It adds a cladding material with specific functions on the surface of the substrate by presetting or synchronously, and uses a high energy density (104~106W/cm2) laser beam to irradiate the cladding material to fuse with the thin layer on the surface of the substrate It becomes a metallurgically combined additive cladding layer, which significantly improves the wear resistance, corrosion resistance, heat resistance, oxidation resistance and fatigue resistance of the surface of the base material.
Compared with surfacing, spraying, electroplating and vapor deposition, laser cladding has the following advantages:
- The heat-affected zone of cladding is small, the deformation of the workpiece is small, and the yield of cladding is high.
- The dilution rate of the fused cladding layer is low, the melting amount of the base material is small, and the dilution rate of the fused cladding layer is low.
- The layer grains are small and the structure is dense, so its physical and chemical properties are better (for example, the hardness is generally relatively high, and the wear resistance, corrosion resistance and other properties are also better)
- The coating is well combined with the substrate, and the quality of the fusion coating is stable
- It is suitable for many cladding materials with large changes in particle size and content
- The laser melting process is easy to realize automatic production.
II. Materials for Laser Cladding
At present, iron-based, nickel-based, cobalt-based, aluminum-based, titanium-based, magnesium-based and other metal-based composite materials can be prepared by laser cladding technology. Classified by function: single or simultaneous coatings with multiple functions can be prepared, such as: wear resistance, corrosion resistance, high temperature resistance, etc., as well as special functional coatings. From the perspective of the material system that constitutes the coating, it has developed from a binary alloy system to a multi-component system. The alloy composition design and multifunctionality of multi-system systems are important development directions for the preparation of new materials by laser cladding in the future.
III. Laser cladding process flow
The main process flow of synchronous powder feeding laser cladding is: substrate surface pretreatment—feeding laser melting—post-processing
IV. Equipment for Laser Ablation
With the development of control technology and computer technology, laser cladding technology is more and more intelligent and automated. At present, TRUMPF provides a five-axis linkage CNC laser fusion system that integrates a disc laser, an optical fiber transmission optical path system, an automatic adjustable powder conveying system, a laser spot diameter adjustable fusion cladding processing head, an offline programming software and a whole-process parameter detection system. TruLaser Cell7000, a cladding machine tool, and TruLaser Robot, a six-axis linkage robot laser cladding system.
Compared with the traditional laser cladding equipment, the lasers used are CO2 lasers and lamp-pumped YAG lasers. TRUMPF uses a new generation of fiber-conducting disc lasers.
TRUMPF provides coaxial powder feeding heads for up to 4KW lasers and range axis powder feeding heads for 10KW lasers. It is worth mentioning that the cladding processing head provided by TRUMPF has the function that the spot diameter can be adjusted in real time from 0.3mm to 7mm. In this way, the diameter of the laser spot can be adjusted by programming during processing, which can not only ensure high processing accuracy of laser cladding, but also ensure high cladding efficiency.
V. Application of laser cladding in mold remanufacturing
Using laser cladding technology, high-performance surfaces can be made on low-cost metal substrates, which can replace a large number of advanced alloys to save precious and rare metal materials, improve the performance of substrates, and reduce energy consumption. It is very suitable for It has broad development space and application prospects in the remanufacturing of molds that are locally vulnerable to wear, impact, corrosion and oxidation.
With the rapid growth of the domestic auto market, competition has become more intense, and the average lifespan of new models has been shortened from the previous 5-6 years to 2-3 years. This brings unprecedented challenges and opportunities to the manufacture of automobile molds. The development cycle of a complete set of automobile molds is generally about 1 year, and the cost is high. But usually the new model is only a small change on the basis of the previous model of the same series. Therefore, using laser cladding technology to partially fuse the original automobile mold, the old mold can be remanufactured into a mold for a new model, which greatly shortens the development time of new model molds, saves a lot of development costs, and produces significant economic benefits. benefit.
VI. Precautions for laser cladding in mold remanufacturing
Laser cladding is a complex physical and chemical metallurgical process, and the parameters in the cladding process have a great influence on the quality of the cladding parts. The process parameters in laser cladding mainly include laser power, spot diameter, defocus amount, powder feeding speed, moving speed, molten pool temperature, etc. It has a great influence on the dilution rate of the cladding layer, cracks, surface roughness and the compactness of the cladding parts. In addition, the pretreatment before cladding and the temperature control during cladding will also affect the quality of laser cladding. These are all things that need to be paid attention to in the remanufacturing of molds by laser cladding.