Today’s Reverse Engineering Cycle for Turbine Blades [Mechanical Engineering]

In today's turbine engine market, finding spare parts to keep legacy engines operating can be a Challenge. Reverse engineering and manufacturing Ls often die best solution tor providing cost effective aftermarket parts for overhauling and repairing existing gas turbine engines. Aftermarket parts typically provide the end user a 30-40% cost savings as compared to OEM options.

Widi today's technology, reverse engineering is a more precise method than previous mechanical practices. No longer do companies have to rely on legacy data or subjective manual measurements to reproduce parts.

The following six categories can be utilized to break down the reverse engineering process:

I. PRODUCT INVESTIGATION AND RESEARCH

First, by understanding the intended purpose and operational constraints of the original component the design team can determine the parameters that influence the final product.

On rotating turbine engine blades, these design decisions begin with a detailed investigation of weight characteristics, metallurgical analysis and vibrational interaction. In addition, there are also other considerations, including an investigation of die overall assembly and service histories before any reverse engineering can take place. This will allow the parameters of the project to be properly defined.

II. DATA COLLECTION

Once the parameters of the project have been outlined, empirical data is captured with traditional measuring equipment and the use of 3-Dimensional digital scanning.

Digital scanning may consist of either laser or structured light scanning. Laser scanning utilizes a laser single point or an oscillating beam in conjunction with a camera to triangulate the distance to the object. Points are created where the laser interfaces with the part and 3D point cloud data is created. In structured light scanning, such as white light scanning, a fringe pattern is projected on the part and multiple cameras utilize a focal distance to measure the variations from in the fringe to create the point cloud data.

Some scanning systems are portable, such as hand held units or tripod mounted systems, and others are fixed such as CMM mounted systems.The most important factor in selecting the system is matching the accuracy and precision of the system with the parts being scanned. Widi turbine blades the trailing edge radius typically dictates the precision of the system needed to accurately capture the geometry. White light scanning systems project millions of points per shot, and on small components can be accurate to +/- 0.0003." Many commercial laser scanners are accurate to within +/-0.001."

III. DATA PROCESSING

Once the point cloud data has been collected it will need to be processed and converted to a stereolithography (sd) file to begin the modeling process. This step requires evaluating die scanned meshed data and starting the process of converting the mesh to surfaces. The reverse engineering software is utilized to evaluate the mesh data to determine how the surfaces are created. The surface can be placed at a minimum, average or maximum level based on die topography of the mesh. Some software allows the creation of sketches direcdy on die mesh which can be extruded to create a solid body. Additionally bodies created (solid or surface) can be checked against the mesh data to insure die accuracy of the part.

IV. DATA PREPARATION

Any additional work required to process a fullyformed CAD model will depend on the application. For example, if we are looking for a space claim model or if we need to run finite element analysis (FEA), we'll utilize the format as received from the reverse engineering software.

However, if the application requires a fully parametric model and supporting drawings, the reverse engineered model needs to be transferred to a CAD package. The data can be manipulated to create nominal tolerance conditions, correct any symmetry issues and add geometric deßnitions in the model.

V. DATAVALIDATION ANDTOLERANCING

The CAD model must now be validated to emure it meets the specified requirements. For a turbine blade, the contours of the free form surfaces, and their relationship to the machined surfaces, can be inspected on a scanning CMM to compare the new CAD model to the physical OEM part. A secondary means of verification is to use validation software to compare the new CAD model to the original OEM scan data. Within the verification software there are multiple options of alignment to generate the comparisons. Alignment by the machined surfaces allows for die validation of the airfoils position relative to the root, or alignment by die airtbü surfaces to validate the accuracy of the lofted airfoil surfaces.

Using this validated CAD model, dimensional tolerances are established to generate manufacturing drawings.Typicaüy a part reverse engineered within the tolerance constraints of the OEM sample lot is acceptable, but sometimes additional requirements may be imposed. For turbine blades rotating at high RPM's in elevated temperature environments, the parts may also require bounding by frequency iâtigue and creep comparisons.

Understanding the nuances of die part's design intent, fabrication method, interaction with mating parts and their affect on downstream components will aid in developing realistic dimensional tolerances and critical to quality dimensions.

Vl. FABRICATIONANDFIRSTARTtCLEAPPROVAL

Once a physical part has been reproduced, qualifying the operational safety of the new component is one of the last steps in getting it to market. Many of the characteristics established and developed within the reverse engineering process will need to be verified with first article parts. This may include dimensional inspections, destructive analysis, and/or performance testing. To establish pass/fail criteria for first article testing, physical tesúng may also need to be performed on the OEM parts sample lot.

Having a good plan and knowing the final expectations will gready increase the success of a reverse engineering project,

About Triax Turbine Components

Triax Turbine Components (TTCI1 which acquired the assets of Dynamic Turbine LLC (DTLl and Triumph Precision Casting Corp (TPCCI, specializes in the reverse engineering service, investment casting, and the machining of hot section turbine engine components. TTC has extensive experience with producing "airfoil" shaped components and has manufactured blades and vanes fora wide range of aerospace and industrial gas turbine engines.

By Samuel Shock, Engineering Manager, Triax Turbine Components (www.triaxturbine.com)

Robert Wilburn, Project Manager