online stress measurement during laser-aided metallic additive manufacturing

by:UMeasure     2020-04-14
In-situ measurement of residual stress is a challenge and a source of many defects in the additive manufacturing process (AM).
Usually, once a defect occurs, it is too late to save the product after the death measurement.
Most of the existing technologies are Predictive simulation and post-mortem analysis.
However, these techniques do not directly reflect the stress changes in the manufacturing process.
This paper introduces a kind of computer vision technology.
Stress monitoring system based on finite element method (FEM)
Techniques for estimating stress development within the sediment layer.
The system uses a CCD camera and a line laser beam to measure the height of the molten pool and the solidified layer to form a real
The time finite element model and the surface displacement between the two states are used to calculate the stress development during the solidification process.
The results show that there is no obvious shape change after solidification.
The shape of the molten pool is similar to that of the solid state.
The stress distribution obtained through online monitoring is similar to the traditional thermal-
Stress simulation. Laser-
Auxiliary metal additive manufacturing uses a laser as a heat source to melt the substrate, delivering the metal powder coaxial into the molten pool and depositing it on the substrate to form the various shapes required by the user.
This method is widely used in the repair, cladding and manufacturing of engineering components and works of art.
However, due to the complexity of the laser thermal history,
Based on the AM process, uneven heat shrinkage and expansion can produce a large amount of residual stress inside the solidified material.
These stresses may exceed the strength of the material and may lead to undesirable deformation and cracking. The stress-
The resulting defects often appear slowly and gradually, without obvious symptoms, and may erupt with very little external stimulation.
Therefore, it is essential to control the pressure during the AM process.
Due to the high temperature, plasma and Sparks will be generated during the laser process.
AM process based.
Traditional equipment is difficult to locate in the manufacturing process to measure stress.
The most commonly used methods at present are simulated and post-mortem stress tests.
Through 2D to 3D models, numerical simulation begins with pure temperature calculation.
Then, based on the temperature history, the stress calculation developed by P. Zhang and P.
Farahcommand is used to calculate the stress of laser cladding layer based on temperature field.
For more accurate calculation, H.
Qi and Xinran Zhao added solidification phase changes to the model, making the results more similar to the experimental data.
Another way to measure residual stress is to perform post-mortem analysis after manufacture and analyze with laser parameters. R. J.
Moat and Pratt, P measure stress in direct metal deposition using neutron diffraction (DMD)
Make blocks. U.
De Oliveira uses X
X-ray diffraction measurement of residual stress in Co-
Based on the laser cladding.
Although the numerical prediction and
Experimental measurements can help us better understand the device processes, which are difficult to save products when defects cause failures.
In addition, there is limited space for integrating X-
On the basis of the traditional method, the ray or neutron diffraction equipment is introduced into the system, and the time is insufficient, and the online simulation cannot be carried out.
Another way to monitor this process is to evaluate the strain evolution on the substrate.
Andreas adopted LVDT (
Linear Transformer
Meter measuring out-of-
Plane deformation at the center of the bottom surface of the substrate.
However, this method cannot directly reflect the real situation inside the sediment layer. M.
Digital image correlation for Biegler applications (DIC)
A technique for measuring distortion on a substrate.
This method has to spray the overlay in the target area, which makes it easier to detect distortion.
However, due to the changing shape of the overlay and the relatively high temperature, it is difficult to form a stable optical overlay, so it is difficult to apply it to the sediment layer.
In this article, we have developed a new method to monitor the stress evolution in the process of the device.
Based on computer vision and finite element analysis, the method can quickly predict the stress generated during laser deposition.
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