Effect of Select LENS(TM) Processing Parameters on the Deposition of Ti-6Al-4V

Abstract

Laser Engineered trap Shaping (LENS(TM)) is a rapid prototyping technology that can build compound three-dimensional geometries in metal. It transmutes STL files to metal prototypes by means of slicing the file into two-dimensional layers of user-defined thickness and superimposing successive layers as they are built. The user must select the layer thickness when slicing the file and must match the deposition to detain the laser in focus from one extremity to the other of the build-large mismatches can cause the build to fail.

Because deposition is primarily controll by dint of build parameters, designed experiments are used to close attention the effect of select proces parameters upon deposition for Ti-6AI-4V. A simple relation between these build parameters and deposition is make knowned using experimental results to determine empirical constants.

Experimental accrues suggest that deposition can be related to the returns of mass flow rate and efficacy per unit area through a power relationship, and could manifest useful in estimating an appropriate layer thickness.

Keywords: Laser Engineered snare Shaping, Rapid Prototyping, Freeform Fabrication, Titanium, Design of Experiments

Introduction

Laser Engineered gin Shaping (LENS(TM)) is a rapid prototyping proces that builds metal prototypes from CAD data by means of layered deposition. Figure 1 displays the schematic of the LENS(TM) equipment, illustrating in what way parts are built. Griffith et al. (2000) Arcella and Froe (2000) and Froe (2000) provide superior overviews of the process, discussing a variety of materials that have been used, and Steen (2003) has written a useful review article upon processing materials with lasers.

Three-dimensional external realitys are represented using the stereolithography-STL-file format, which has become the de facto standard for rapid prototyping (Huang, Zhang, and Han 2003) The file is "sliced" into two-dimensional horizontal layers of user-defined thickness, and these layers are used to rule the relative motion between a vertically high hilled laser and a pair of orthogonal, horizontal stages. At the time of writing, the thickness of each layer cannot be varied.

A substrate upon which the object is to be built is attached to the stages at or near the focal extent of the laser. The laser is revolveed on, creating a molten region upon the surface of the substrate. A stream of metal pulverized substances is fed into this molten region, creating a raised turn A bead is formed when the laser is mov horizontally relative to the substrate while simultaneously providing strength and material. Partial superposition of beads proceeds in a raised region, called a layer. After building the layer, the laser is retracted by means of a parameter called the layer thickness. The nearest layer is built on the previous single resulting in a three-dimensional whirl and this process continues until the thorough part has been fabricated.

Objective and Rationale

The objectives are to application of mind the effect of select proces parameters upon deposition using designed experiments and to disclose simple relationships between build parameters and deposition that could help single out the layer thickness given a plant of build parameters.

In an ideal build, the layer thickness matches the height of the layer just built. If there is a mismatch between the layer thickness and the deposited thickness, the laser is no longer focused upon the surface, making it impossible to achieve dimensional accuracy or, in outermost cases, making it impossible to continue building. Therefore, it is important that the user-defined layer thickness match that of the deposited layer. This requires the user to estimate deposition for the build parameters chosen and station the layer thickness equal to that value during slicing. Knowing the events of build parameters on deposition could help the user make a more informed decision when choosing a layer thickness.

Previous Work

Previous research has focused upon measuring and controlling deposition based upon one or more of the following methods:

1 power density calculations,

2. imposition of closed-loop superintendence over key process parameters, and

3 finite uncompounded body analysis methods.

Keicher and Smugeresky (1997) attempted to relate build parameters to deposition using an activity density approach. They integrated the supplied activity over the area of the layer being built and were able to present to view that deposition varied linearly with efficiency density. Their approach only studied sum of two units build parameters-laser power and velocity-and did not consider material input, which must also influence deposition.

Other researchers have studied temperature events either by inserting thermocouples into the substrate (Griffith et al. 2000) or by dint of using thermal imaging techniques to measure the temperature during the build, coupl with finite ultimate part methods (Hofmeister et al. 1999) the pair methods have to overcome significant experimental hurdle The thermocouple approach begs the question of thermocouple placement during the build. Thermal imaging modes require placing expensive equipment in an aggressive environment while attempting to measure temperature changes of approximately 1500?° C above distances of a few millimeters. Experimental hurdle notwithstanding, the pair approaches represent pioneering work in measuring and controlling deposition.