Abstract Scope |
Introduction: Robots have performed gas metal arc welding (GMAW) and other-directed energy deposition (DED) processes for decades. Applying these processes for building three dimensional structures, conformal cladding complex surfaces, and welding-based repair have been done for years. Robotic DED additive manufacturing (AM) provides digital automation of these and additive manufacturing applications. Robotic DED utilize computer-aided design (CAD) files and computer-aided manufacturing (CAM) solvers to “digitally” manufacture AM components. DED AM components are grouped into categories of complexity ranging from linear extrusions to artistic artisan features. In this project, different DED categories were demonstrated using different robotic DED systems. These components and their classification groups are listed below:
• Lattice structure – linear extrusion
• Pipe coupler – surface of revolution
• Propeller blade – varying cross-section
This presentation will introduce each component, and walk through the digital environment, to the production of the component.
Experimental Approach: Multiple components were produced per the classifications listed above. Each component was produced using a digital data workflow (DDW) process. This involved processing a CAD design of the part using DED computer aided manufacturing (CAM) software, and then post-processing the digital build file for the physical system. The DDW will be described in the steps below.
The CAD component surfaces were used to calculate the additive toolpaths. Additive toolpaths were further defined and organized into levels and sets. This allowed the solver to differentiate what needs to be built and separates the build platform. Other items addressed were the form of the component. Sharp edges were avoided when possible and replaced with radiuses. Features that were easy to machine were also removed.
The second step, component pre-forming was used to add additional stock to the component to account for machining and weld process tolerances. In some cases, a shell of the component was produced, as a hollow form was not previously possible.
Setting up the component in the digital work cell involved importing the model into the solver’s environment. Typically, this involved repositioning the component onto a build platform, a tilt/turn positioner, or a rotary chuck. The robot reach was analyzed in the system, as well as the line of sight of the component being built.
2D path planning trajectory was used to simulate the build layer by layer. The platform needed to be specified as well at the region to be deposited. Based off the component structure, a path planning strategy was selected. These varied from a raster pattern, profile only, profile offset, or a combination from the CAM software tool list. In this step, several DED parameters were inputted such as contact tip to work distance, weld bead step over, torch angle, and layer thickness. Once the 2D path plan was calculated, additional modifications were made such as travel direction and bead sequence.
Next trajectory process planning was then applied along with sequencing of operations. Detailed process parameter was applied along every point of the toolpath. Processes that can be controlled can varied from DED parameters to external peripheral control. Sequencing was applied at this time where items such as interpass temperature checks, feed wire clipping, and interpass cleaning.
The last part of this process involved the simulation and output of the robotic program. The CAM solver used the digital twin to calculate multi-axis additive toolpaths. In this step it checked to ensure the robot had range of motion to produce the component and check the robot paths for singularities. Once this was complete the software compiled the physical robotic code using the DED CAM post processor.
Results and Discussion: Three components of increasing complexity were produced which included a lattice structure, a pipe coupler, and a propeller blade.
The first component was the lattice structure. It was a 10-in. x 10-in. x 1-in. build consisting of four 5-in. x 5-in. squares that shared a common wall, and one outer bead that was common to all four squares. This was produced on a Fanuc robotic system using a Fronius TPS power supply. It was produced using ER308L wire on a 304L build platform. The build strategy consisted of a single DED procedure with integral starts and stops using a pattern finish strategy. This build was completed fully automatically by utilizing an IR spot sensor to ensure the inter-pass temperature limit was not exceeded.
The second component was the pipe coupler. It was an 8-in to 6-in pipe reducer, with an initial angle of 45-deg, that was 6-in tall. This was produced on a Motoman robotic system using a Fronius TPSi power supply. It was produced using MIL 100S-1 on a HY-80 platform. The build strategy consisted of a single DED procedure with integral starts and stops. It was a 3-bead wide wall and was solved using a medial axis offset strategy. This build was done in a semi-automatically by utilizing an IR spot sensor to keep pre-heat and interpass temperature in range.
The third and final component was a high-skew propeller blade. The height was 12-in tall, with a base that was 4.5-in x 2-in. The was also produce on a Motoman robotic system listed above. It was produced using ER CuNiAl on a C63200 platform. The build strategy consisted of multiple DED procedures with integral starts and stops. It was on average a 3-bead wide solution and was solved using the regional parameter offset strategy. It was determined at 8-in in height that the DED material was sagging off the front edge angle of the blade. The platform was then rotated by 20-deg and 20-deg wedge was deposited. After this was completed, it was rotated another 40-deg to continue the deposition. This component was scanned using a 3D structure light and determined to meet minimum material conditions.
Conclusion: This project produced several product categories including linear extrusions, surface of revolutions, and varying cross-sections. These components included a lattice structure, pipe coupler, and a propeller blade. By producing such a wide variety of shapes, it was concluded that robotic DED AM can produce shapes of varying complexity. |