Go blow laser melting!

{TECH}

Integrated gas flow & synchronous laser scanning in powder bed fusion

Introduction

Metal AM processes, in particular laser powder bed fusion, receive a lot of criticism because of the supposed high cost of production. Nearly all LPBF machines run with significant proportions of unproductive time during the powder deposition phase, or re-coating as it is more commonly referred to. One way that can cut process time is to have bi-directional coating systems, thus allowing for more layers per hour. The process can be further improved if the system is capable of laser melting simultaneously as it recoats each layer. However, in most systems the gas flow in the system is usually perpenicular to the direction of coating. This then introduces all sorts of issues to gas recirculation, and the flow dynamics in the process chamber.

Hence, could there be imrovements by introducing a system that allows gas flow to be in the same axis of travel as the coater mechanism?

Idea of Operation

Imagine a coater mechanism that has a axial gas port, runnig across the length of the recoater, that allows inert gas to backflow over the area that it has just deposited.
Then combine this with a continuous-synchronous single linescan raster scan strategy to control laser melting at the trailing side of the coater mechanism.

A recoater configured with two-sided parallel axial gas ports could then enable bi-directional laser melting, and the possible result could be the optimum throughput for any given process combination of selected alloy powder, laser parameters, and layer thickness.

Gas flow

An axial gas port could be arranged in the most simplistic manner to produce a continuous flow of gas, for example as a laminar stream, over the trailing powder bed area.
An exhaust port parallel to the coater could be devised with a pump to collect the gas and any process fumes, and ejected matter from the interaction of the laser and the powder bed. This exhaust port could be in the form of a secondary travelling device in synchronous motion to the coater mechanism with sufficient separation to allow for laser scanning and melting in the gap separating coater and exhaust. Alternatively, the exhaust port, or ports, could be at a fixed position in the side walls of the process chamber with suitably designed openings to allow efficient collection of the gas and any process fumes, and ejected matter from the interaction of the laser and the powder bed.

Controlling gas flow

The axial gas port, or ports, introducing the gas to the process, and controlling the exhaust, could be part of an adjustable mechanism such that the angle of injection, or extraction, over the process area could be changeable dependent on the position of the coater over the entire process powder bed area. Additionally, the flow rate could be continuously adjustable also dependent on the position of the coater over the entire process powder bed area.Optimal perfornance would depend on the correct callibration of gas flow for any given build application for each variable combination of build geometry, alloy powder and laser process parameters.

Raster scanning

Don't have to say anything about single line raster scanning strategies, since there's a whole lot of histroy covering this already!