Closed-loop control of variable width deposition in laser metal deposition

In laser metal deposition (LMD) technology, multi-track overlapping is usually used for the deposition of the unequal width thin-walled part. In the present study, a single-track deposition with the variable width method was proposed to improve deposition accuracy and efficiency, and reduce repeated heating. The hollow laser beam internal powder feeding nozzle was applied to realize variable laser spot deposition. Based on the developed deposition height sensor, a closed-loop control system and PI controller were developed and tested. A segmented deposition height control method was developed. The unequal width thin-walled part was divided into several segments along the scanning direction, and each segment was matched with different laser spot sizes. The segments were controlled to have unequal widths, but with an equal height. A thin-walled part with a width range of 5.08–2.14 mm and a “blade-shaped” part with a width range of 6.18–2.64 mm were deposited. The control curves of most segments were stable and convergent. The microstructure and properties of the formed part varied with wall width. All width areas achieved the compact and small size of the grains, as well as high microhardness.