Michael A. Langerman

Non‐Dimensional Characterization of the Friction Stir/Spot Welding Process Using a Simple Couette Flow Model Part I: Constant Property Bingham Plastic Solution

A simplified model for the material flow created during a friction stir/spot welding process has been developed using a boundary driven cylindrical Couette flow model with a specified heat flux at the inner cylinder for a Bingham plastic material. Non‐dimensionalization of the constant property governing equations identified three parameters that influence the velocity and temperature fields. Analytic solutions to these equations are presented and some representative results from a parametric study (parameters chosen and varied over ranges expected for the welding of a wide variety of metals) are discussed. The results also provide an expression for the critical radius (location of vanishing material velocity) as functions of the relevant non‐dimensional parameters. A final study was conducted in which values for the non‐dimensional heat flux parameter were chosen to produce peak dimensional temperatures on the order of 80% of the melting temperature for a typical 2000 series aluminum. Under these conditi...

Thermal Imaging of Laser Powder Deposition for Process Diagnostics

Thermal imaging is an important tool for future developments in Laser Powder Deposition (LPD). Thermal imaging of the LPD process is typically used for the verification of mathematical models describing the process and/or dynamic melt pool control. The research discussed here shows how thermal imaging can be used to improve our understanding of the connection between deposition parameters, thermal gradients, and final part quality. Data gathered from melt pool and bulk-part thermal images were used to correlate deposition parameters to final part quality. The results presented here are for applications in internal barrel cladding and laser brazing.Copyright

Numerical Simulation of Laser Glazing and Laser Deposition Processes Using Coupled Temperature-Displacement FEM Models

Predicting the changes in the temperature, displacement and stress fields during Laser Powder Deposition (LPD) is of particular importance. To create a FEM model of LPD, it is convenient to consider first Laser Glazing (LG) since it does not involve the addition of material. Once an adequate approach has been identified to model the thermal aspects associated with the effect of the laser, the complexity of adding material can be included. In this paper coupled temperature-displacement FEM models of LG and LPD developed using the commercial FEM code ABAQUS/Standard are presented. In the case of LG, a model based on the sequentially coupled thermo-mechanical theory was used to predict the temperature distribution, deformations and stresses in a rectangular plate on which the laser moved along a straight path. The results for the temperature distribution were validated using Rosenthal’s solution and experiments performed using the same material and processing parameters. For LPD, the model was developed using fully coupled thermo-mechanical theory and it was limited to thin-wall builds deposited on a plate with dimensions comparable to the wall thickness. To add material, new elements were sequentially introduced in the mesh. Qualitatively, the results obtained with the model were promising.Copyright

Preliminary Design of a Calorimeter for Experimental Determination of Effective Absorptivity of Metal Substrates During Laser Powder Deposition

A thermal model of the laser powder deposition (LPD) process has been developed and tested. Results obtained from the model, however, are dependent upon the magnitude of the laser energy absorbed during the process. Although spectral absorptivities of metal surfaces are described in literature, during the LPD process, the powder increases the energy delivered to the substrate. There are no published data regarding this affect. Therefore, the SDSM&T Additive Manufacturing Laboratory (AML) is developing a calorimeter to experimentally investigate the affect of the powder on laser energy absorption at the metal substrate. The preliminary design is described in this paper with discussion on measures being taken to increase the accuracy of experimental data.Copyright

Thermal Control of Laser Powder Deposition: Heat Transfer Considerations

Laser based solid free-form fabrication is an emerging metallurgical forming process aimed at rapid production of high quality, near net shape products directly from starting powders. Laser powder deposition shares, with other free-form technologies, the common characteristic that part fabrication occurs directly from a 3-D computer aided design (CAD) model. The microstructure evolution and resulting material properties of the component part (strength, ductility, etc.) fabricated using laser deposition are dependent upon process operating parameters such as melt pool size, laser power, head (manipulator) speed, and powder flow rate. Presently, set points for these parameters are often determined through manual manipulation of the system control and trial and error. This paper discusses the development of a path-planning, feed-forward, process-driven control system algorithm that generates a component part thermal history within given constraints, thereby assuring optimal part quality and minimizing final residual stresses. A thermal model of the deposition process drives the control algorithm. The development of the thermal model is the subject of this paper. The model accounts for temperature-dependent properties and phase change processes. Model validation studies are presented including comparisons with known analytic solutions as well as comparisons with data from experiments conducted in the laser laboratory at SDSM&T.Copyright

ADAPTING A FRESHMAN MANUFACTURING COURSE TO DIFFERENT LEARNING STYLES

AAaron Lalley P.E. Aaron Lalley is an instructor at the South Dakota School of Mines and Technology (SDSM&T). His current research includes chatter modeling of a machining process with fixture optimization. Prior to academia Aaron worked for 23 years as an engineer for Hutchinson Technology, Caterpillar, Midwest Precision Tool and Die, Unified Theory Inc. and Manufacturing Works in the areas of machine design, tool design, product design, CNC programming, HVAC, MRP, process development and product development. See more at: https://www.asee.org/public/person#sthash.WaxuWfqL.dpuf

Heat Transfer Considerations for Designing FSW Cryogenic Thermal Structures for Aerospace Applications

Research was conducted to investigate potential structural design configurations for aerospace cryogenic tank wall applications. The primary design considerations included the vibration damping characteristics under various flight loading conditions and the panel wall thermal resistance under different heat loads. The discussion herein is with regards to the thermal issue, specifically the heat transfer rates across two different panel wall designs that have attractive vibration damping characteristics. The heat transfer rates were evaluated analytically and verified with experimental data. One panel is a corrugated, serpentine-layered design fabricated using friction stir welding. The other panel is an “egg-carton” design fabricated using friction stir spot welding. An important thermal consideration for the cryogenic tank wall design is the minimum outer wall temperature attained during ambient storage or prior to launch. Of the two designs considered herein, neither wall provided sufficient thermal resistance to maintain outer wall temperatures above freezing under ambient conditions. One of the wall designs, however, performed somewhat better. It is shown that when configured with an outer layer of thermal plastic coating both designs could maintain an outer wall temperature within design constraints.Copyright

Modeling Heat Transfer Effects During Free-Form Fabrication: Multi-Dimensional Effects

Laser Powder Deposition (LPD) for additive fabrication is a relatively new technology that is currently being qualified for use in the manufacturing industry. Although this technology has significant advantages over conventional manufacturing processes, such as the reduced need for post-production part machining, the resulting component material properties (strength, ductility, etc.) are affected by process operating parameters such as laser power, head (manipulator) speed, and powder flow rate. Set points for these parameters are often based upon trial and error with process control requiring the oversight of a system operator. Additionally, thermal stresses that build up in the part and the substrate can lead to warping and separation of the part from the substrate. Although this latter effect has been investigated, no robust process control has been identified that will solve the problem. Therefore, to assure component part quality and to minimize residual stresses and attendant deformation, an intelligent laser deposition path planning control algorithm needs to be developed. Such control requires knowledge of the part thermal history. The process, however, is not amenable to direct experimental measurement, which has led to the need to develop accurate and reliable thermal models. Preliminary multi-dimensional results from one such model, discussed herein, show the need for process control and how such a model is central to developing an intelligent laser powder deposition path planning strategy.Copyright

Active control of heat induced deformation in a laser deposition process

This paper presents results of ongoing research that addresses possible geometric inaccuracies and structural deficiencies resulting from nonuniform heating and cooling of parts fabricated or repaired using laser powder deposition. An active-control method is investigated, in which piezoelectric (and/or mechanical) actuators provided on the substrate are used sequentially to deform and un-deform a substrate through deposition with the goal of minimizing the residual deformations/stresses in the part. Different actuation configurations are considered, and results based on linear theory are discussed. Initial experimental work is also described. Results to date indicate that the approach could be used to advantage in certain types of builds for active control/reduction of residual deformations/stresses in laser deposited parts.This paper presents results of ongoing research that addresses possible geometric inaccuracies and structural deficiencies resulting from nonuniform heating and cooling of parts fabricated or repaired using laser powder deposition. An active-control method is investigated, in which piezoelectric (and/or mechanical) actuators provided on the substrate are used sequentially to deform and un-deform a substrate through deposition with the goal of minimizing the residual deformations/stresses in the part. Different actuation configurations are considered, and results based on linear theory are discussed. Initial experimental work is also described. Results to date indicate that the approach could be used to advantage in certain types of builds for active control/reduction of residual deformations/stresses in laser deposited parts.

Laser Deposition Process Design Via Thermal Analysis‐Thermal Model Development

Research being conducted in the Laser Deposition Laboratory of the Advanced Material Processing center at the SDSM&T has as one objective the development of a path‐planning, feed‐forward, process‐driven control system algorithm that generates a component part thermal history within given constraints, thereby assuring optimal part quality and minimizing final residual stresses. These constraints are maximum temperature, temperature gradient, and cooling rate. A thermal model of the deposition process drives the control algorithm. The development of the thermal model is discussed herein. Results from the model are compared to known exact solutions and to experimental data. Results from these comparisons indicate that the model is appropriately accounting for underlying physical phenomena.