1. The unique nature of making energy equipment makes quality control more important.
There are three main things that make making energy equipment difficult. First, the materials have very extreme properties. For example, gas turbine blades have to be able to handle temperatures of 1500 °C and stress of 300 MPa. Second, the structures are very complicated. For instance, the steam generator in a nuclear power plant has tens of thousands of fine pipes. Third, the service environment has gotten tougher. For example, offshore wind power equipment needs to be able to withstand salt spray corrosion and typhoon damage. These traits make quality control in metal 3D printing three times as hard:
Control of the stability of material properties: Under harsh working circumstances, the printed parts must not fail in ways like creep and fatigue fracture. For instance, gas turbine blades made with Inconel 718 nickel-based alloy need hot isostatic pressing (HIP) treatment to get rid of internal pores and make the blades last more than twice as long as ordinary castings.
Geometric precision closed-loop control: For precise parts like the control rod drive mechanisms in nuclear power reactors, the size tolerances must be kept within ± 0.05mm. One company has added a laser interferometry measurement system to its SLM equipment so that it can fix errors in shape and position in real time while printing. This has raised the crucial dimension qualification rate from 82% to 97%.
Complete coverage of finding defects: The technology behind industrial CT scanning can find micro hole faults with a diameter of 0.02mm or greater and create 3D models of printed products. A company that makes wind power equipment set up a defect database and utilised machine learning algorithms to smartly look at CT images. This cut the time it takes to find defects from 4 hours to 20 minutes.
2. The Whole Process Quality Control System's Four Pillars
(1) Control of material performance at the source
Three checks on the quality of the powder: Set up a system to manage batches of powder so that you can test the chemical composition (using ICP-AES detection), the particle size distribution (using the laser diffraction method), and the flowability (using a Hall current meter) on each batch of metal powder. One company that makes energy equipment says that the D50 particle size of 316L stainless steel powder should be between 25 and 35 μm, the Hall flow rate should be less than or equal to 25s/50g, and the oxygen content should be less than or equal to 0.05%.
Building a material database: Make a process parameter database with 12 alloys that are often used in the energy area. This database should include important information like the shape of the melt pool and the likelihood of different powder batches to spheroidise at certain energy densities. For instance, the database reveals that the best density (99.2%) and tensile strength (320MPa) for the AlSi10Mg aluminium alloy may be reached with a laser power of 350W and a scanning speed of 1200mm/s.
(2) Control of the printing process in real time
Simulation of interaction between multiple physical fields: We utilise ANSYS Workbench software to do thermal mechanical coupling simulations on the printing process and figure out how the residual stress would be spread out. A company that makes nuclear power equipment utilised simulation optimisation to alter the printing orientation from the Z-axis to a 45° angle. This cut the Z-axis shrinkage rate from 0.8% to 0.3% and made interlayer peeling problems much less common.
Use of a closed-loop control system: Put an infrared thermometer and a melt pool monitoring camera in SLM equipment so that it can give you real-time information on the size (error ± 10 μ m) and temperature (error ± 5 ℃) of the melt pool. If the molten pool's width goes over the predetermined value by 15%, the system automatically changes the laser power and scanning speed to keep the molten pool stable.
(3) Exact control of post-processing technology
Optimising the heat treatment process: A two-stage annealing procedure has been devised for Ti6Al4V titanium alloy printed parts. The first step is to change the β phase at 920 °C for 2 hours. The second step is to refine the α+β phase structure at 730 °C for 4 hours. The printed parts' fatigue strength went up by 40% after this processing, reaching 680MPa.
Integration of surface modification technology: Micro arc oxidation (MAO) technique makes a 50 μm thick ceramic coating on the surface of parts that are likely to corrode, including offshore wind turbine gearbox bearings. This increases the duration they can resist salt spray corrosion from 500 hours to over 2000 hours.
(4) Smartly improving quality control
A mixture of non-destructive testing technologies: Set up a three-level testing system that includes "industrial CT, ultrasonic phased array, and eddy current testing." First, use industrial CT (resolution 10 m) to scan the whole gas turbine combustion chamber, which is 200 mm in diameter. Then, use ultrasonic phased array fine testing (resolution 0.1 mm) to check any regions that look suspect. Finally, use eddy current testing to check for cracks on the surface.
How to use digital twin technology: Make digital copies of printed parts and keep track of how they are doing in real time. A specific company has added a fatigue life prediction algorithm to their digital twin model. This can give a 6-month early notice of certain equipment breakdown risks and cut down on unplanned downtime by 65%.
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