What is the role of metal 3D printing in industrial furnace and boiler repair?

1. Repairing complex structures: going beyond the physical constraints of traditional craftsmanship
High-temperature corrosion, thermal stress cycling, or mechanical wear can cause local failures in the main parts of industrial furnaces and boilers, such as combustion chambers, heat exchange tubes, and grates. Welding and spraying are traditional repair methods that are constrained by the way they work and are hard to use on complex geometries like thin-walled structures, internal flow channels, or uneven surfaces. For instance, the boiler superheater header needs 56 precise steam holes to work. In traditional sand casting, the core must be positioned, but the molten iron at high temperatures can move the core, which causes the hole position to move too much. After that, hand drilling correction is needed, which costs a lot of money and takes a lot of time.
Digital modelling and layer-by-layer stacking production have entirely solved this challenge with metal 3D printing technology. The Boro Casting Company used 3D sand printing technology to cut the time it took to put together the mould for the superheater header from 14 hours to 3.5 hours on the Tyseley steam locomotive repair project in the UK. This saved 67% of the expenditures. Also, it was possible to make 56 steam holes at once without any extra work. This case shows that 3D printing can accurately place complicated cores, get rid of quality problems that come from core movement in older procedures, and cut energy use by 30% in places that don't bear weight using topology optimisation design while still making sure strength.

2. Customising the performance of materials: meeting the repair needs of very harsh working circumstances
Industrial furnaces and boilers work in very difficult conditions, and their parts have to be able to handle a lot of stress, like high temperatures (>1000 °C), high pressures (>10MPa), oxidation, and corrosion. Nickel-based and cobalt-based alloys are examples of traditional repair materials that are stable at high temperatures. However, it is hard to find a balance between their many qualities, such as wear resistance and thermal shock resistance. Metal 3D printing can precisely customise the properties of materials by changing the way the powder is made and controlling the process parameters.
For example, when fixing aircraft engine turbine blades, the IN718 nickel-based alloy powder made by Platinum Technology Company, by controlling the powder particle size distribution (D50=45 μ m) and oxygen content (<50ppm), along with selective laser melting (SLM) technology, achieves a persistent strength of ≥ 900MPa at a high temperature of 650 ℃, meeting the extreme working conditions requirements of aircraft engines. Xi'an Jiaotong University developed the WC Co hard alloy composite powder for use in boilers. It is printed on the cutting teeth of a tunnelling machine using laser selective sintering (SLS) technology. It has a hardness of HRC68, is three times more resistant to wear than traditional forged parts, and can last up to 12 months. This kind of material innovation shows that 3D printing may improve the composition and microstructure of materials in a specific way dependent on the specific working conditions of the area being repaired, like temperature gradient and stress distribution. This is called "on-demand repair."
3. Digitising the whole process: rebuilding and fixing the industry's efficiency model
The old way of fixing things takes more than 10 steps, such as finding the problem, getting spare parts, machining, and heat treatment. It takes several months and is based on human experience, which leads to big changes in quality. The "digital twin+intelligent manufacturing" mode of metal 3D printing technology speeds up the repair procedure to less than 72 hours and makes it possible to follow the entire process.
The repair process can be broken down into four steps:
Intelligent detection: The SICK Ranger3 high-speed 3D camera scans components at a frame rate of 46kHz with an accuracy of 0.02mm. It automatically finds the size and location of defects like cracks and wear.
Reverse modelling: Using Geomagic Design X software to turn point cloud data into CAD models that can be changed, along with topology optimisation techniques, to use less material while still being strong;
Additive manufacturing: Using SLM or electron beam melting (EBM) technology, repair layers are printed based on model slicing data. The thickness of each layer can be regulated between 20 and 50 μm, which allows for micrometer-level size control.
Post-processing: Hot isostatic pressing (HIP) gets rid of internal pores and raises the density to 99.95%. Then, surface polishing is done to fulfil assembly accuracy standards.
When Rolls Royce used this technique to fix spare parts for aircraft engines, it cut the global inventory value from $4.2 billion to $1.8 billion and cut the time it took for customers' planes to be back in the air from 72 hours to 8 hours. This saved the airline more than $500 million a year in operational costs.