Lightweight Design And Wire Laser Additive Manufacturing For Pile Leg Chord Pipe Of Jack-up Offshore Platform

The jack-up offshore platform has a trussed pile leg structure,and the stable triangle structure is formed between the pile legs through the connection of chord pipe,rack plate and brace pipe.The traditional chord pipe is a semi-circular structure with groove on both sides and is connected to the rack substrate by symmetrical welding.The steel used in the pile leg is a kind of marine high-strength steel,which has high construction cost.The large weight of platform reduces the towing ability of the platform.Domestic manufacturing level is limited and mainly dependent on import.Honeycomb structure is a kind of porous thin-wall structure with low density and higher stiffness,which has been widely used in engineering.In this paper,the lightweight design of JU2000 E ship type pile leg chord pipe is carried out according to the honeycomb sandwich structure,and the finite element analysis is made compared with the traditional chord pipe.The source program was written to generate the path file that can be read directly by the robot.The relationship between the influence of the process parameters on the macroscopic morphology of the single-pass deposition layer was explored and the best parameters were selected for wire laser additive manufacturing of honeycomb chord pipe.The following results were obtained:The structural design of the honeycomb chord pipe was completed.Firstly,the shape of the honeycomb cell was determined to be hexagonal,based on the following: hexagonal honeycomb has the lowest material consumption,hexagonal cross-section is isotropic in cross-section,hexagonal net cross-section has the highest load-bearing capacity and hexagonal honeycomb is the most widely used.Using the width-to-diameter ratio of 0.2 and the single-pass forming width of high-strength steel as the basis,the initial choice of edge length of 40 mm and wall width of 6 mm was modeled.The strength and stiffness were calculated by using ANSYS and compared with the results of traditional chord pipe calculations.The results showed that the maximum static stress of 6mm wall width honeycomb chord was 191.8MPa,the maximum strain was 0.959 mm and the destabilizing load was 422 t,which could not meet the requirements.The 8mm wall width honeycomb chord had the static stress of 150.17 MPa,the maximum strain was 0.75 mm and the destabilizing load was 481.16 t,which could meet the requirements.Path planning scheme of honeycomb structure additive manufacturing was obtained.The path file of the commercial printer is G code,which cannot be read and used by the robot.The laser wire requires some special external control instructions,which need to be added.For this design,the source program can generate the scanning path read by the robot.The honeycomb structure is arranged regularly,and the model can be segmented to design a path of unit length.The starting point of the path and the print coordinate axis are determined according to the robot travel.As the side view of the honeycomb structure is semicircular and the top view is asymmetric,the increasing height and the constant change of the path need to be taken into account.Python language is used to write the source program,and Easy GUI module is used to realize parameter interaction.The Y coordinate is set as the independent variable,the coordinate interval is judged,and the corresponding statements are executed to generate the scan path.The low power laser was used to ablate the substrate to check the path accuracy and the appropriateness of instructions.The scanning paths of different layers were checked and the results were correct.The honeycomb structure was fabricated by wire laser additive manufacturing technology.In order to match the width of thin wall,the relationship between single channel deposition morphology and parameters of high strength steel should be explored.In the case of single variable,the laser power increases,the width of the sedimentary layer increases,and the height decreases.When the wire feeding rate increases,the width of the deposited layer changes little,but the height increases.As the scanning rate increases,the width and height of the deposit decreases.By improving the laser power and wire feed rate,reduce the scanning rate to meet the requirements.Change the spot diameter method to adjust the width of the deposit layer.The spot diameter is 10 mm.Determine the forming parameters for laser power4200 W,scanning rate 2.3m/s,wire feed rate 20mm/s.Firstly,the printing test of the path per unit length was carried out.After optimizing the parameters,multiple layers were deposited and the increase height of layer is 1.5mm.Then the whole honeycomb chord pipe was deposited.Finally,the outer cover plate of chord pipe was deposited.The structural design of the honeycomb string tube was completed.