The difficulties of horizontal welding technology are stated in this paper. On the basis of analyzing the defects occurred during horizontal welding technology as well as several corresponding methods are adopted nowadays. Control measures for horizontal welding technology high efficiency can be summed up to two types: weld pool quick solidification control measure and weld pool stable shape measure. The development history of their research and application is reviewed. And the mechanism of producing weld defects is deeply analyzed. The prospects and development of horizontal welding technology are elaborated.

Fig. 9. The macro-morphology and the corresponding microstructure from traverse cross-section built with different technological parameters. V s and V f refer to the laser scanning speed and the powder feeding rate, respectively. The laser power P is 2 kW for all the specimens.creased, the duration of the laser beam interaction on the powder and the substrate becomes shorter, which results in less heat input of the laser cladding. After certain a threshold of the laser scanning speed, energy available will be insufficient to fuse the powder to the substrate, and an incomplete fusion appears. A relatively weak bonding between the layer and the substrate will be formed. This phenomenon is undesired. By adjusting the processing parameters, this phenomenon will be eliminated. Similarly, under a given laser scanning speed, the powder feeding rate also exists a threshold. When the powder feeding rate is higher, the powder flux shields the laser beam. The energy which melts the substrate mostly comes from that of permeated from the cladding powders is so small that it causes insufficient substrate melting, the metallurgical bonding between the cladding layer and the substrate can't also achieved. The laser cladding process doesn't realize. In a word, on condition that other technological parameters hold immutable, a given laser scanning speed corresponds with a critical powder feeding rate and a given powder feeding rate also corresponds with a critical laser scanning speed. Furthermore, the critical powder feeding rate decreases accompanying the increase of the laser scanning speed at the same technological condition. Similarly, the critical laser scanning speed decreases with the increase of the powder feeding rate. In practice, the adjustment of the powder feeding rate should limit within the critical powder feeding rate at a given scanning speed and the adjustment of the scanning speed should limit within the critical scanning speed at a given powder feeding rate. A good matching of the scanning speed and the powder feeding rate is necessary in laser cladding. The Microhardness of Cladding LayersThe microhardness is an important index to evaluate the material properties. It is possible to understand the mechanical properties of the cladding layer by means of the microhardness across the layer, at least on a rough scale. The microhardness measurement across the transverse cross-section of the sample was carried out using microhardness tester. Figure 10 exhibits the effects of the laser scanning speed and the powder feeding rate on microhardness distribution of the transverse section of the sample. Horizontal ordinate represents the vertical distance from the substrate to the measuring point of the sample and vertical ordinate represents the Vickers hardness of the measuring point. From Fig. 10, it can be observed that with the increasing of the distance, the hardness profiles all present increasing trend. It is apparent that the microhardness of the laser cladding layer is much higher than that of the substrate and...

The technological and economic advantages of laser welding of plastics in comparison to the traditional welding process and research situation are analyzed in this paper. Process methods of this technology are reviewed as well as the range of application for these manners is compared. The technological challenges facing the further development of the technology and the critical issues needing to be solved are deeply investigated. It is pointed out that efficient prevention of plastics distortion and cracking as well as control of internal structure and defects are currently the two bottleneck obstacles challenging the further development and industrial applications of the revolutionary advanced manufacturing technology. The developments of laser welding technology of plastics in the future are also forecasted.

The basic principle and the characteristics of magnetically controlled welding technology are introduced in this paper. The specific applications of domestic and foreign magnetically controlled welding technology in welding process are comprehensively analyzed at the moment, including the effect rule of external magnetic field on arc shape, metal droplet transfer, molten pool, weld microstructure, mechanical properties. And the key problems needing to be solved are deeply investigated. The developments of magnetically controlled welding technology in the future are also forecasted.