Browsing by Subject "process control"

Now showing 1 - 5 of 5

DC-Gain Layer-to-Layer Stability Criterion in Laser Metal Deposition Process
(University of Texas at Austin, 2015) Sammons, P.M.; Bristow, D.A.; Landers, R.G.
In Laser Metal Deposition (LMD), a blown powder metal additive manufacturing process, functional metal parts are fabricated in a layer-by-layer fashion. In addition to the inlayer dynamics, which describe how the process evolves within a given layer, the additive-fabrication property of LMD creates a second set of dynamics which describe how the process evolves from layer-to-layer. While these dynamics, termed layer-to-layer dynamics, are coupled with both the in-layer dynamics and the process operating conditions, they are not widely considered in the modeling, process planning, or process control of LMD operations. Because of this, seemingly valid choices for process parameters can lead to part failure – a phenomenon commonly encountered when undergoing the laborious procedure of tuning a new LMD process. Here, a layer-to-layer stability condition for LMD fabrications is given, based on the shape of the powder catchment efficiency function, which provides insight into the layer-to-layer evolution of LMD processes and can be useful in process planning and control. The stability criterion is evaluated for various operating points, allowing stable and unstable operating regions to be identified. Simulation results are presented showing both stable and unstable layer-to-layer LMD fabrications. The simulated behavior successfully predicts the results seen in both stable and unstable experimental depositions.
Development of Powder Bed Fusion Additive Manufacturing Test Bed for Enhanced Real-Time Process Control
(University of Texas at Austin, 2015) Vlasea, M.L.; Lane, B.; Lopez, F.; Mekhontsev, S.; Donmez, A.
Laser powder bed fusion (PBF) is emerging as the most popular additive manufacturing (AM) method for producing metallic components based on the flexibility in accommodating a wide range of materials with resulting mechanical properties similar to bulk machined counterparts, as well as based on in-class fabrication speed. Although this approach is advantageous, the current limitations in achieving predictable and repeatable material and structural properties, geometric and surface roughness characteristics, and the occurrence of deformations due to residual stresses results in significant variations in part quality and reliability. Therefore, a better understanding and control of PBF AM processes is needed. The National Institute of Standards and Technology (NIST) is developing a testbed to assess in-process and process-intermittent metrology methods and real-time process control algorithms, and to establish foundations for traceable radiance-based temperature measurements that support high-fidelity process modeling efforts. This paper will discuss functional requirements and design solutions to meet these distinct objectives.
Examination of the LPBF Process by Means of Thermal Imaging for the Development of a Geometric-Specific Process Control
(University of Texas at Austin, 2019) Pichler, T.; Schleifenbaum, J.H.
The development of process parameters for the Laser Powder Bed Fusion (LPBF) process is typically carried out by the manufacturing and metallurgical analysis of geometrically primitive test specimens (e.g. cubes). The process parameters identified in this way are used for the manufacturing of parts which are characterized by a high geometric complexity and a combination of solid and filigree component areas. Due to the discrepancy between the parameter development on primitive specimens and applications with complex parts, a geometric-specific process control is to be developed. In the context of this work different sample geometries are manufactured from Ti6Al4V by LPBF and the process is monitored by thermal imaging. The influence between component geometry and process parameters on the thermal behavior is shown.
A High Temperature Polymer Selective Laser Sintering Testbed for Controls Research
(University of Texas at Austin, 2015) Fish, S.; Kubiak, S.; Wroe, W.; Booth, J.; Bryant, A.; Beaman, J.
High Temperature Polymers under development over the last decade show great promise for Additive Manufacturing (AM) applications in aviation, medicine, and other fields based on their high strength and high temperature qualities. Selective Laser Sintering (SLS) of these materials, derived generally from the Poly Ether Ketone Ketone class of polymers is still somewhat immature however, and certifiably repeatable SLS parts with certifiable mechanical properties remain elusive. One barrier to this is the limited number and high cost of SLS machines capable of operating at the high ~300-350C temperatures needed to build with low internal thermal stress and tight process controls. Another barrier is the lack the instrumentation in the few machines available, to develop critical feedback control and associated flexibility in the thermal management of the material from feedstock to cooled part/part-cake. This paper describes the development and initial testing of a new laboratory SLS machine with the flexibility required in deriving optimal process control for polymer SLS including these high temperature polymer powders. With such a system validated for SLS operation, we will embark on multiple control development approaches to improve part/material property performance.
Investigation of Advanced Process Control Methods for Exposure Controlled Projection Lithography
(University of Texas at Austin, 2014) Zhao, Xiayun; Rosen, David W.
The DMD based Exposure Controlled Projection Lithography (ECPL) process has promising applications in fabrication of microfluidics and micro optics components. Unlike a conventional layer-stacking projection stereolithography process, ECPL cures a 3D feature by projecting radiation through a stationary, transparent substrate by varying exposure patterns and durations implemented by a sequence of DMD bitmaps. Due to the unavailability of an in situ metrology for cured part dimensions, unmeasurable time-varying disturbances such as oxygen inhibition and light source fluctuations, and the complex chemical & physics interactions in photopolymerization, a common practice in stereolithography process planning is to use experimental characterization and statistics models in an open-loop mode, which yields poor accuracy. This paper reviewed existing process control methods for ECPL and defined a need for advanced control methods. As a first proposal for advanced control methods to mask projection stereolithography, the paper surveyed relevant processes and put forward a hierarchical framework of advanced control methods for ECPL, including evolutionary cycle-to-cycle (EC2C) and adaptive neural network (ANN) backstepping control methods. The goal is to identify some advanced control methods, which are capable of tracking the process dynamics by online updating the model parameters with real-time measurement feedback. Such closed-loop control methods are promising to be able to improve the process precision and robustness.