Laser Metal Deposition Process, Solidification Mechanism and Microstructure Formation

This paper presents the usage of vibration in laser direct deposition of Ti64. The vibration is used to refine the crystalline structure of the deposition. The vibration device vibrates in the laser deposition system along the Z axis. A design of experiments approach is applied in studying the effect of vibration on the deposited material. Vibration during deposition led to grain refinement and an increase in microhardness over that of samples from no-vibration. Also, vibration frequency is a significant factor. From the experiment results, it is found that a vibration frequency greater than 20Hz is desirable.

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Vision-based defect detection in laser metal deposition process

Rapid Prototyping Journal ◽

10.1108/rpj-04-2012-0036 ◽

2014 ◽

Vol 20 (1) ◽

pp. 77-85 ◽

Cited By ~ 24

Author(s):

Shyam Barua ◽

Frank Liou ◽

Joseph Newkirk ◽

Todd Sparks

Keyword(s):

Defect Detection ◽

Detection System ◽

Vision System ◽

Low Cost ◽

Deposition Process ◽

Metal Deposition ◽

Cooling Curve ◽

Laser Metal Deposition ◽

Content Type ◽

Melt Pool

Purpose – Laser metal deposition (LMD) is a type of additive manufacturing process in which the laser is used to create a melt pool on a substrate to which metal powder is added. The powder is melted within the melt pool and solidified to form a deposited track. These deposited tracks may contain porosities or cracks which affect the functionality of the part. When these defects go undetected, they may cause failure of the part or below par performance in their applications. An on demand vision system is required to detect defects in the track as and when they are formed. This is especially crucial in LMD applications as the part being repaired is typically expensive. Using a defect detection system, it is possible to complete the LMD process in one run, thus minimizing cost. The purpose of this paper is to summarize the research on a low-cost vision system to study the deposition process and detect any thermal abnormalities which might signify the presence of a defect. Design/methodology/approach – During the LMD process, the track of deposited material behind the laser is incandescent due to heating by the laser; also, there is radiant heat distribution and flow on the surfaces of the track. An SLR camera is used to obtain images of the deposited track behind the melt pool. Using calibrated RGB values and radiant surface temperature, it is possible to approximate the temperature of each pixel in the image. The deposited track loses heat gradually through conduction, convection and radiation. A defect-free deposit should show a gradual decrease in temperature which enables the authors to obtain a reference cooling curve using standard deposition parameters. A defect, such as a crack or porosity, leads to an increase in temperature around the defective region due to interruption of heat flow. This leads to deviation from the reference cooling curve which alerts the authors to the presence of a defect. Findings – The temperature gradient was obtained across the deposited track during LMD. Linear least squares curve fitting was performed and residual values were calculated between experimental temperature values and line of best fit. Porosity defects and cracks were simulated on the substrate during LMD and irregularities in the temperature gradients were used to develop a defect detection model. Originality/value – Previous approaches to defect detection in LMD typically concentrate on the melt pool temperature and dimensions. Due to the dynamic and violent nature of the melt pool, consistent and reliable defect detection is difficult. An alternative method of defect detection is discussed which does not involve the melt pool and therefore presents a novel method of detecting a defect in LMD.

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Optimization of Thin Walls With Sharp Corners in SS316L and IN718 Alloys Manufactured with Laser Metal Deposition

10.20944/preprints202011.0483.v1 ◽

2020 ◽

Author(s):

Juan Carlos Pereira ◽

Herman Borokov ◽

Fidel Zubiri ◽

Mari Carmen Guerra ◽

Josu Caminos

Keyword(s):

Layer Thickness ◽

Energy Deposition ◽

Deposition Process ◽

Metal Deposition ◽

Powder Materials ◽

Laser Metal Deposition ◽

Thin Walls ◽

Directed Energy ◽

Position Parameter ◽

Sharp Corners

In this work, the manufacture of thin walls with sharp corners has been optimized by adjusting the limits of a 3-axis cartesian kinematics through data recorded and analyzed off-line, such as axis speed, acceleration and the positioning of the X and Y axes. The study was carried out with two powder materials (SS316L and IN718) using the directed energy deposition process with laser. 1 mm thick walls were obtained with only one bead per layer and straight/sharp corners at 90º. After adjusting the in-position parameter G502 for positioning precision on the FAGOR 8070 CNC system, it has been possible to obtain walls with minimal accumulation of material in the corner, and with practically constant layer thickness and height, with a radii of internal curvature between 0.11 and 0.24 mm for two different precision configuration. The best results have been obtained by identifying the correct balance between the decrease in programmed speed and the precision in the positioning to reach the point defined as wall corner, with speed reductions of 29% for a programmed speed of 20 mm/s and 61% for a speed of 40 mm/s. The walls show minimal defects such as residual porosities, and the microstructure is adequate.

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