Thin-Walled Preforms With Follow-Up Rolling in Laser Metal Deposition
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Solution Overview
Problem
Existing laser metal deposition technologies face challenges in preparing thin-walled preforms with wall thickness less than 2 mm due to the limit width of the molten pool, resulting in poor surface quality and convex/concave peaks, which lead to deformation and discontinuous formation during the process, causing issues with surface flatness and residual stress.
Innovation Solution
A method combining laser metal deposition with follow-up rolling, where the roller adjusts its speed and spacing to match the forming wall thickness, conducting integral or local rolling to rectify the deposited area, ensuring continuous formation and improving surface quality by synchronizing roller and laser head movements, and post-processing with hot isostatic pressing to eliminate defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high laser power is used to melt metal powder with minimum spot diameter greater than 1 mm, then the powder can be melted and deposited, but the limit width of the molten pool affects the forming wall thickness and makes it difficult to prepare thin-walled preforms with wall thickness less than 2 mm
Solution Approach 1:
A thin-walled preform with desired wall thickness is prepared in advance through laser metal deposition, and then a rolling device is introduced to apply rolling pressure to the deposited layer during the deposition process. This preliminary rolling action prevents excessive molten pool width formation while the deposition is still in progress, enabling thin-walled structures with wall thickness less than 2 mm to be successfully formed.
Solution Approach 2:
A rolling device is introduced as an intermediary between the laser deposition process and the final preform structure. The rolling device applies controlled pressure to the deposited metal layer, mediating the relationship between high laser power input and thin wall thickness output by mechanically constraining the molten pool width and promoting uniform consolidation.
2Productivity
If laser metal deposition is used to form preforms, then large-sized components can be manufactured with high forming speed, but the surface of the formed preform has convex and concave peaks due to interlayer overlapping, resulting in poor surface quality
Solution Approach 1:
The rolling device is introduced to perform preliminary smoothing and consolidation of the deposited layer while the deposition process is still ongoing. This preliminary action prevents the formation of severe convex and concave peaks by applying pressure to flatten and densify the metal layer before the next layer is deposited, thereby improving surface quality without sacrificing forming speed.
Solution Approach 2:
The rolling device operates continuously during the laser deposition process, maintaining continuous contact with the deposited layer to progressively smooth out surface irregularities as they form. This continuous rolling action ensures that surface quality is maintained throughout the entire deposition process rather than requiring post-processing intervention.
3Ease of manufacture
If thin-walled preforms with convex and concave peaks are prepared, then laser metal deposition can be used, but there is large frictional resistance between the preform and the forming die during hot gas bulging forming, which is not conducive to plastic deformation
Solution Approach 1:
The rolling device performs preliminary flattening and smoothing of the deposited layer surface during the deposition process itself. By applying rolling pressure to the metal layer while it is still hot and plastic, the surface convexities and concavities are eliminated before the preform undergoes hot gas bulging forming, thereby reducing frictional resistance with the forming die and facilitating plastic deformation.
4Reliability
If thin-walled preforms are prepared by existing laser metal deposition technology, then the process can be completed, but the convex and concave peaks generated by interlayer overlapping may have local residual stress in the deformation process, thereby easily leading to cracks
Solution Approach 1:
The rolling device applies preliminary compressive stress to the deposited layer during the deposition process, which helps to redistribute and reduce local tensile residual stresses that would otherwise concentrate at convex peaks and concave valleys. This preliminary stress management prevents the formation of stress concentrations that could lead to cracking during subsequent deformation processes.
Solution Approach 2:
The rolling pressure, which initially might seem to add complexity to the process, actually converts the harmful effect of surface irregularities and residual stress concentrations into a beneficial effect by densifying the metal layer, eliminating voids, and redistributing stresses uniformly throughout the deposited structure, thereby improving crack resistance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the production of thin-walled preforms with uniform wall thickness and improved surface quality, overcoming the limitations of existing technologies by allowing continuous formation and reducing residual stress, thus enhancing the accuracy and quality of the preforms for subsequent hot gas bulging processes.
Implementation Method 1
the laser beam acts on the surface of base material to form a molten pool on the surface of the base material
Implementation Method 2
laser melting, rapid solidification and layer by layer deposition
Implementation Method 3
uses the roller to conduct follow-up rolling on the deposited area completed by laser metal deposition
Implementation Method 4
conducting hot isostatic pressing on the formed thin-walled preforms under high temperature and high pressure conditions to eliminate micro-cracks, gas holes, unfused defects
Data Source
AI summary
Laser additive manufacturing and a method for preparing thin-walled preforms by laser metal deposition and follow-up rolling. This can solve the problems that when the existing laser metal deposition technology prepares the thin-walled preforms, the limit width size of a molten pool at high power affects the forming wall thickness of the preforms so that it is difficult to prepare preforms with wall thickness less than 2 mm, and the problems of poor surface quality and low accuracy of preforms due to convex and concave peaks caused by the interlayer overlapping, but also can solve the problems that a laser beam with a preset trajectory cannot act on the end surfaces of the preforms due to preform deformation caused by residual stress in a printing process so that the preforms cannot be continuously formed.