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Research Papers

Variable Powder Flow Rate Control in Laser Metal Deposition Processes

[+] Author and Article Information
Lie Tang

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 1870 Miner Circle, Rolla, MO 65409-0050ltx8d@mst.edu

Jianzhong Ruan

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 1870 Miner Circle, Rolla, MO 65409-0050jzruan@mst.edu

Robert G. Landers

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 1870 Miner Circle, Rolla, MO 65409-0050landersr@mst.edu

Frank Liou

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 1870 Miner Circle, Rolla, MO 65409-0050liou@mst.edu

J. Manuf. Sci. Eng 130(4), 041016 (Jul 22, 2008) (11 pages) doi:10.1115/1.2953074 History: Received October 29, 2007; Revised May 06, 2008; Published July 22, 2008

This paper proposes a novel method, called variable powder flow rate control (VPFRC), for the regulation of powder flow rate in laser metal deposition processes. The idea of VPFRC is to adjust the powder flow rate to maintain a uniform powder deposition per unit length even when disturbances occur (e.g., the motion system accelerates and decelerates). Dynamic models of the powder delivery system motor and the powder transport system (i.e., 5m pipe, powder dispenser, and cladding head) are constructed. A general tracking controller is then designed to track variable powder flow rate references. Since the powder flow rate at the nozzle exit cannot be directly measured, it is estimated using the powder transport system model. The input to this model is the dc motor rotation speed, which is estimated online using a Kalman filter. Experiments are conducted to examine the performance of the proposed control methodology. The experimental results demonstrate that the VPFRC method is successful in maintaining a uniform track morphology, even when the motion system accelerates and decelerates.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Powder delivery system schematic

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Figure 2

Powder flow rate control system hardware schematic

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Figure 3

Powder delivery system motor measured and modeled responses to command voltage step signals. Note that responses are nearly identical.

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Figure 4

Powder delivery system dc motor model and experimental rotation speed frequency responses

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Figure 5

Infrared emitter-detector pair setup used for powder transport system modeling

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Figure 6

Infrared sensor feedback and dc motor rotation speed for step command voltage signals

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Figure 7

Steady-state powder flow rate versus steady-state dc motor rotation speed

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Figure 8

Powder delivery system comprehensive model

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Figure 9

Powder delivery system closed-loop control system block diagram

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Figure 10

Circular part (left) and measured motion system speed profile for one layer (right). The commanded speed is 254mm∕min and the radius is 25.4mm.

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Figure 11

Circular part deposition (left) and three-dimensional scan (right) using constant powder flow rate (pr=8.25g∕min)

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Figure 12

Circular part powder flow reference (top) directly calculated from motion system measured speed profile, powder flow rate reference first time derivative (middle), and powder flow rate reference second time derivative (bottom) for one layer

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Figure 13

Circular part tracking error (top), command voltage (middle), and disturbance estimate (bottom) on the third layer for VPFRC with powder flow rate reference directly calculated from motion system speed

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Figure 14

Circular part deposition (left) and scanned three-dimensional result (right) using VPFRC with powder flow rate reference directly calculated from motion system speed

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Figure 15

Circular part modified powder flow reference (top) determined experimentally, powder flow rate reference first time derivative (middle), and powder flow rate reference second time derivative (bottom) for one layer

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Figure 16

Circular part tracking error (top), command voltage (middle), and disturbance estimate (bottom) on the third layer for experiment with modified powder flow rate reference

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Figure 17

Circular part deposition (left) and three-dimensional scan (right) using VPFRC with modified powder flow rate reference

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Figure 18

Height profiles for circular parts

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Figure 19

Fish-shaped part (left) and measured motion system speed profile for one layer (right). Arrows indicate direction of motion, and the commanded speed is 254mm∕min.

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Figure 20

Fish-shaped part deposition (left) and three-dimensional scan (right) using constant powder flow rate (8.25g∕min)

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Figure 21

Fish-shaped part powder flow reference (top) directly calculated from motion system measured speed profile, powder flow rate reference first time derivative (middle), and powder flow rate reference second time derivative (bottom) for one layer

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Figure 22

Fish-shaped part tracking error (top), command voltage (middle), and disturbance estimate (bottom) on the third layer for VPFRC with powder flow rate reference directly calculated from motion system speed

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Figure 23

Fish-shaped part deposition (left) and three-dimensional scan (right) using VPFRC with powder flow rate reference directly calculated from motion system speed

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Figure 24

Fish-shaped part schematic showing modified powder flow rate reference parameters

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Figure 25

Fish-shaped part modified powder flow reference (top) determined experimentally, powder flow rate reference first time derivative (middle), and powder flow rate reference second time derivative (bottom) for one layer

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Figure 26

Fish-shaped part tracking error (top), command voltage (middle), and disturbance estimate (bottom) on the third layer for VPFRC with modified powder flow rate reference

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Figure 27

Fish-shaped part deposition (left) and three-dimensional scan (right) using VPFRC with modified powder flow rate reference

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Figure 28

Height profiles for the fish-shaped part

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