Laser metal cladding rechnology
05-14-2014, 09:01 AM
|Laser metal cladding rechnology
[/font]Know-how of choosing laser cladding machine and the advantages of fiber delivery semi-conductor laser machine
There are two parts about laser cladding:
1. Metal deficiency repair ,such as abration,indentation,corrosion,scratch, damage due to pulling;
2. Surface modification on the parts which require improving hardness,abration resistance,corrossion resistance, heat resistance and change of non-magnetic.
Most customers who are looking for laser cladding machine may need one that will perform both of two fuctions mentioned above. There are three technical prameters in the process of laser cladding. Firstly, relatively high power density on the surface will melt powder(including[font=Arial] some refractory powder like ceramic power and WC) and metal base, forming a molten pool,so that metallurgical bonding is achieved. Second, large facular with fast cladding speed is qualified for repairing or hardfacing large-sized parts or large-area defect.Small facular is more suitable for repairing kinds of high-accuracy parts, thin-wall parts or componetnts that have the problem of thermal deformation. There are 3 catagories of laser cladding machines in the market,eg:CO2 lasers, semi-conductor lasers and YAG lasers.
The wavelength of CO2 lasers is 1064nm, which is 10 times as long as that of the semi-conductor/YAG ones,on the basis of the same output powe. Besides, CO2 laser is 1/3 of the latter in terms of power desnity, but 3 times in terms of heat affected area.In order to increase the surface power density, output power should be boosted,this is why the output power of most CO2 lasers used for cladding in the market is high. On one hand,the procurement cost of CO2 lasers increases,on the other hand,large-sized CO2 laser machine is not proper for onsite refurbishment and not easy to be equipped with manipulators or supporting tools. Running cost and maintenance cost of CO2 lasers is high and frequent replacement of quick-wear parts is expensive. Especially,CO2 laser may lead to large heat affected areaand deformation easily, which need insulation treatment during and after cladding.Therefore,CO2 lasers are not the optimum machine for laser metal cladding.
YAG laser, pulse laser with low heat affected area, can repair thin-wall,small-sized and high precision and easily-deformed components.YAG laser is simple in structure, easy to get repaired and low price for its spare parts is more suitable for the start up company in metal maintenance field. Also it is the first choice for the company without heavy work. However, the disadvantage of low electro-optical conversion rate of 5% make it impossible to produce high power laser machine of more than 1000w due to the limit of luminous theory. With low output power and cladding effeciency,YAG is not qualified to repair parts of large-size or with large-defected area.The directly delivery semi-conductor laser machine in today’s market is 2000-6000w, with compact size,low weight,and 50% electro-optical conversion rate, 808nm/ 976nm/ 1064nm of wavelength,which solve the problem of large size,heavy weight and long wavelength of CO2 lasers. But there are two fatal disadvantages about directly delivery semi-conductor laser machine:
It is difficult to shape laser beam to very small size,that is the reason why this machine fails to repair thin-wall,small-size, high accuracy and easily-deformed worlpiece.
2. Laser directly points at the base metal and the reflected light from the molten pool will greatly damage bars,which serve as luminous medium.Some company claimed that they have worked out a way of solving the problem of thermal radiation with the technology of reflective light,but the reality is that this tech is not mature after market test. We can often see large-scale goods return happens a lot. The best laser-fiber semi-conductor laser machine is very expensive and its quality beam is a waste for cladding process,which doesn’t need tiny facular of less than 1mm. High price of quick-wear part and long after-sale period of fiber semi-conductor laser can not meet the reuirement of continuity of cladding process. A characteristic of repairing is that refurbishment of most defected parts may delay the production in an enterprise,which thus causes huge loss.
One way to solve the all problems mentioned above is to choose fiber delivery semi-conductor laser machine. The advantages of it are as following:
1. small facular delivered by fiber can repair thin-wall,small-sized,high precision and easily-deformed workpiece;
2. facular through fiber is delivered uniformly,no slug,low splashing,smooth result surface,no gas hole.
3 this machine can be equipped with long fiber. Compact and light laser head is easily to be used with different supporting tools and match with mechanical hands.
4. Laser is delivered by fiber, so the problem of damage on laser device caused by reflected light is settled.
5.This machine is compact in size,light in weight, is simple to operate, is free-maintenance with similar price of directly delivery laser machine.
Currently, the manuifacturers of fiber delivery semi-conductor laser machine is DILAS from Germany and RichCause Technology Com.,Ltd.
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