Research On Penetration Depth Of Laser-welded Cobalt-chromium Alloy

[Background]Because Cobalt-chromium alloy has excellent mechanical properties, biocompatibility and economy, it is Widely used in the manufacture for various restorations in dentistry. In the production of the long span fixed restorations, the segments after casting are welded to improve accuracy of the restorations. The connectors of the partial fixed denture usually have 4-10mm2 area. The frame of the removable partial denture has the thickness of 1-2mm. For the two types of restorations, the requirements of penetration depth are respective 1-2mm and 0.5-1mm. Compared with the other welding methods such as arc welding or resistance welding, the laser welding has no embedding, convenience, small heat affected zone, etc. The laser welding widely is used to dental field.[Objective]The present study shows that although laser welding technology has more advantages, but there are also some problems, such as welding parameters are not clear, which restrict the application of laser welding in dentistry. In order to solve this problem, the purpose of the experiment is based on the different parameters of laser welding to measure depth penetration of Co-Cr after welded. Provide a reference for the choice of parameters in the clinical application by revealing the relationship between various factors and penetration depth.[Method]Glass block made 48 volume of 6.0 mm x 6.0 mm x 10 mm3 as a casting, embedded and finished casting. Cooling to room temperature after casting, specimens were removed the embedding material, sandblasted. Silicon carbide abrasive paper 240-800 purpose will have its surface grinding smooth in turn. The welding surface the specimens were sandblasted with 50μmAl2O3 particles 10 seconds under the pressure of 0.4 Mpa. Finally specimens soaked in acetone solution were ultrasonic cleaning for 10 minutes, dried and preserved. The face of the two specimens 10×6 was relatively close contact no clearance, and fixed on the special jig. The cast alloy specimens were butted against each other and laser welded at their interface using various powers (1.0-2.5 kW) and spot diameters (0.3-1.2 mm) and pulse duration (2.4-18 ms). After welding, Stereo Microscope was surveyed welding surface morphology to measure the penetration depth by Photoshop software.[Result]1. The value ranges of depth penetration of the groups of spot diameter (0.3 mm, 0.6 mm and 0.9 mm) were 0.719-0.719 mm,0.5011.678 mm,0.3941.071 mm. Between each spot diameter of the same energy group, along with the rising power the depth penetration significantly increased (p<0.05).2. The value ranges of depth penetration of the groups of spot diameter (1.2mm) were 0.281-0.471mm. Between each spot diameter of the same energy group, along with the rising power penetration depth had no significant change (p> 0.05).3. The penetration depth under different power had significant difference (P< 0.05). The penetration depth under different power had obvious difference (P< 0.05); Along with the change of pulse time, the penetration depth values changed parallelly (P<0.05). spot diameter is the most critical factors for penetration depth, followed by power and pulse time, the ratio of F value of the influences is 68.894:29.616:14.398.[Conclusion]1. The formula of penetration depth is deduced: Penetration depth=0.353-1.02*spot diameter+0.527+0.046* power pulse time.2.Spot diameter of Co-Cr alloy after laser welding penetration depth influence significantly (p<0.05). The penetration depth value increased with the spot diameter decreases.3. The improvement of power could increase the penetration depth of laser welding Co-Cr alloy. Considering as the diversity of dentures, the convenience of operation, energy saving and service life of the welding equipment, author suggested the range of power is 1.5-2.0kW.