Guojian Xu

Fiber laser welding of 780MPa high strength steel

A 2kW Ytterbium fiber laser, YLR-2000, was used for welding of 780MPa grade high strength steel. In the present work, this high strength steel is a kind of heat rolled, fine microstructure low carbon high strength steel used for welded constructions. The effects of defocusing distance, welding speed, shielding gas and its flow rate on cross section bead shape and penetration were studied in continue wave laser beam welding. The effects of frequency and duty cycle on the cross section bead shape and penetration were also studied in pulse fiber laser beam welding. In the fiber laser welding, square wave and triangle wave power output were adopted. The results showed that the pulse frequency and duty cycle of laser power had affected the bead shape and penetration in square wave Fiber laser welding. The pulse frequency of laser power had not effect on the bead width and penetration in triangle wave fiber laser welding. The microstructures of weld metals in different heat input were observed by optical microscopy. The hardness of welds was also tested and compared among welds welded at different welding speeds, in other words, in different heat inputs.A 2kW Ytterbium fiber laser, YLR-2000, was used for welding of 780MPa grade high strength steel. In the present work, this high strength steel is a kind of heat rolled, fine microstructure low carbon high strength steel used for welded constructions. The effects of defocusing distance, welding speed, shielding gas and its flow rate on cross section bead shape and penetration were studied in continue wave laser beam welding. The effects of frequency and duty cycle on the cross section bead shape and penetration were also studied in pulse fiber laser beam welding. In the fiber laser welding, square wave and triangle wave power output were adopted. The results showed that the pulse frequency and duty cycle of laser power had affected the bead shape and penetration in square wave Fiber laser welding. The pulse frequency of laser power had not effect on the bead width and penetration in triangle wave fiber laser welding. The microstructures of weld metals in different heat input were observed by optical micros...

Cladding of Stellite-6 and vanadium carbide on carbon steel using a yttrium–aluminum–garnet laser robot system

In the present work, a laser robot system was setup for cladding and repairing machinery parts using pulsed 300 W Nd:yttrium–aluminum–garnet laser facility, six-axis robot, optical fiber, powder feeding system with a special nozzle for powder supply. A mild steel plate was deposited with powder mixtures of Stellite-6 alloy and vanadium carbide (VC). The shape of clad layer, microstructure, and its wear performance were investigated by changing the weight fraction of VC in the range of 0%–100%. The microstructure observation showed that as the weight fraction of VC in the powder mixture increases, the amount of primary solidified VC phase, penetration depth, and crack susceptibility increased. This also increased the hardness and wear resistance of the clad layer. Depending on the weight fraction of VC in the powder, the resultant microstructures can be divided into two types—hypoeutectic structure containing primary Co-rich γ phase with eutectic mixture and hypereutectic structure containing primary VC, c...

Crack behavior and characteristics of laser clad layer with powder mixture of CO-based alloy and WC

A powder mixture of Stellite-6 and tungsten carbide (WC) in the range of 0wt%∼47wt%WC with a normal multi-layer cladding and novel multi-layer cladding were deposited on mild steel (JIS-SM400B) plates by a 2.4kW cw CO2 laser. In the normal multi-layer cladding, the WC weight fractions at each layer are constant In the novel multi-layer cladding, the WC weight fractions at each layer are varied by controlling the disk rotation speed of the feeder. The microstructure, hardness and wear resistance of the clad layer were investigated by an X-ray diffractometry, energy dispersion spectroscopy (EDS), scanning electron microscope (SEM), laser microscope, Vickers hardness tester and wear tester. According to the analyzed results, the microstructure of the clad layer belonged to a hypoeutectic structure. In addition, the undissolved tungsten carbides dispersed in the matrix of the Co-based alloy. The Vickers hardness increases with the increase of WC weight fraction. Using a WC constant weight fraction in the third layer, the clad layers of normal multi-layer cladding and novel multi-layer cladding have almost same wear resistance. On the other hand, to decrease the crack sensitivity of clad layer, the influence of a preheating temperature and WC weight fraction in the normal multi-layer cladding and novel multi-layer cladding on the crack sensitivity was investigated comparatively. As the result, the cracks of clad layer made with the powder mixture of Stellite-6 and WC belonged to a quasi-cleavage fracture type crack. In the novel multi-layer cladding with gradual increase of WC particles clad at three subsequent layers shifts the critical amount of WC at which cracking appears to the higher level, or that it reduces the required preheating temperature.A powder mixture of Stellite-6 and tungsten carbide (WC) in the range of 0wt%∼47wt%WC with a normal multi-layer cladding and novel multi-layer cladding were deposited on mild steel (JIS-SM400B) plates by a 2.4kW cw CO2 laser. In the normal multi-layer cladding, the WC weight fractions at each layer are constant In the novel multi-layer cladding, the WC weight fractions at each layer are varied by controlling the disk rotation speed of the feeder. The microstructure, hardness and wear resistance of the clad layer were investigated by an X-ray diffractometry, energy dispersion spectroscopy (EDS), scanning electron microscope (SEM), laser microscope, Vickers hardness tester and wear tester. According to the analyzed results, the microstructure of the clad layer belonged to a hypoeutectic structure. In addition, the undissolved tungsten carbides dispersed in the matrix of the Co-based alloy. The Vickers hardness increases with the increase of WC weight fraction. Using a WC constant weight fraction in the thir...

Super-short times laser welding of thermoplastic resins using a ring beam optics

A ring beam optics was developed for a circular seam welding of the automotive parts using a 2 kW fiber laser. The characteristics of the ring beam optics were investigated by a Primes Beam Monitor. As a result, with increase of focal length of collimating lens, the outer diameter of the ring beam was hardly changed, however the inner diameter of the ring beam decreased. Therefore, the width of the ring beam was increased in the experiment. A distance (L12) between first axi-cone lens and second axi-cone lens increases, the outer diameter and inner diameter of the ring beam increases simultaneously. And the width of the ring beam was almost fixed. Moreover, it was confirmed that the intensity distribution of the ring beam becomes uniform by adjusting the coaxial performance of collimating lens, first axi-cone lens, and second axi-cone lens. After the ring beam optics connects to the fiber laser facility, a transparent thermoplastic resin and opaque thermoplastic resin with a circular seam was welded by a ...

Characteristics of the laser clad metal made with powder mixture of Co-based alloy and vanadium carbide

A powder mixture of Co-based alloy (Stellite-6) and vanadium carbide (VC) was deposited to substrates of SM400B mild steel and SUS304 stainless steel using a 2.4 kW cw CO2 laser. The mechanism of crack for clad metal was investigated by changing the VC weight fraction in the range of 0%–56%. The microstructures of the clad layer for matrix of Co-based alloy can be classified into two types—hypoeutectic structure (0–12 wt % VC) and hypereutectic structure (13–56 wt % VC). The wear resistance and Vickers hardness of the clad layer increased with increase of VC weight fraction. The cracks of the clad metal that occurred below 573 K depend on measurement results of a temperature sensor. The fractography of the clad metal belonged to a quasicleavage fracture due to the brittle microstructures by an increase of the VC weight fraction. The crack sensitivity increased with the increase of the VC weight fraction. On the other hand, compared with substrate SM400B, substrate SUS304 showed lower crack sensitivity due...

Cladding of stellite 6 and VC powder on carbon steel using a YAG laser robot system

In the present study, a laser robot system was set up for cladding and repairing of mechanical parts using a pulsed 300W YAG laser facility, a 6-axis robot, an optical fiber of 5m in length, a powder feeding system and a special nozzle for powder supply. Stellite 6 alloy and vanadium carbide (VC) mixed powder were cladded on carbon steel (SM400B) plate. The characteristic of laser cladding of the mixed powder was investigated using the automatic system. The shape, microstructures and performances of the clad layer were investigated by changing VC volume fraction from 0% to 100%. The experimental results showed that crack susceptibility, hardness distribution, primarily solidified (V, W)C phases, and wear resistance of clad layer increased with VC volume fraction in the 0%VC ∼ 80%VC range. The microstructure can be divided into two domains of hypoeutectic and hypereutectic by changing VC volume fraction.In the present study, a laser robot system was set up for cladding and repairing of mechanical parts using a pulsed 300W YAG laser facility, a 6-axis robot, an optical fiber of 5m in length, a powder feeding system and a special nozzle for powder supply. Stellite 6 alloy and vanadium carbide (VC) mixed powder were cladded on carbon steel (SM400B) plate. The characteristic of laser cladding of the mixed powder was investigated using the automatic system. The shape, microstructures and performances of the clad layer were investigated by changing VC volume fraction from 0% to 100%. The experimental results showed that crack susceptibility, hardness distribution, primarily solidified (V, W)C phases, and wear resistance of clad layer increased with VC volume fraction in the 0%VC ∼ 80%VC range. The microstructure can be divided into two domains of hypoeutectic and hypereutectic by changing VC volume fraction.

Clack behavior and microstructure of clad layer in laser cladding of stellite 6 and WC powder

The Nd: YAG laser robot cladding system, which consists of 6-axis robot, powder supply equipment and special powder delivery nozzle, are used for laser cladding of Stellite 6 + WC mixed powder. The Stellite 6 + WC mixed powder were cladded on mild carbon steel plate (SM400B). Small penetration depth, cracking behavior, microstructures, Vickers hardness, and wear resistance were investigated. Ductility-dip crack, Vickers hardness and wear resistance were increased with WC volume fraction in the range of 0%∼90%. The microstructures of clad layer can be divided into hypoeutectic (0%∼40%WC) and hypereutectic (50%∼100%WC) one.The Nd: YAG laser robot cladding system, which consists of 6-axis robot, powder supply equipment and special powder delivery nozzle, are used for laser cladding of Stellite 6 + WC mixed powder. The Stellite 6 + WC mixed powder were cladded on mild carbon steel plate (SM400B). Small penetration depth, cracking behavior, microstructures, Vickers hardness, and wear resistance were investigated. Ductility-dip crack, Vickers hardness and wear resistance were increased with WC volume fraction in the range of 0%∼90%. The microstructures of clad layer can be divided into hypoeutectic (0%∼40%WC) and hypereutectic (50%∼100%WC) one.