On-Machine Metrology Drives Efficiencies In Large-Scale Additive Manufacturing
In the cornfields of southern Indiana, Thermwood Corp. is making unique large-scale additive manufacturing (LSAM, known as “L-sam”) equipment that are achieving singular breakthroughs for aerospace, mold-making, and a growing number of interested manufacturers. Used to produce large= to very-large-sized components from reinforced thermoplastic composite materials, LSAM equipment can make industrial tooling, masters, patterns, molds and production fixtures for a variety of industries including aerospace, automotive, foundry, and marine.
The LSAM equipment and process are a remarkable and unique mix of machine design and material science. They lay down a large bead of thermopolymer at room temperature, which as the company describes is essentially an exercise in controlled cooling. Polymer cooling and not print head output determines print speed. Print head output determines how large a part you can print in the layer time available. LSAM print heads are available that can print well over 500 pounds per hour, which makes really large parts possible. Thermwood makes LSAM machines in sizes from 10-ft. (3m) X 10-ft. (3m), up to 10-ft. (3m) X 100-ft (30m). work areas that both print and trim thermopolymer components.
Dubbed Vertical Layer Printing (VLP), large print beads plus Thermwood’s patented compression wheel create solid, fully fused, virtually void-free printed structures that can sustain vacuum in a pressurized autoclave at elevated temperature without the need for expensive coatings.
High-Efficiency Process, High-Quality Parts
In 2019, Boeing, on behalf of the Air Force Research Laboratory (AFRL) contacted Thermwood to evaluate LSAM for reducing the cost and time in fabricating autoclave-capable tooling for producing composite aerospace components. The initial demo tool would be for fuselage skin for an AFRL concept.
Among LSAM’s attractions was that the process offered capable tooling in a matter of days compared to the weeks or months required for conventional machining. The large-format LSAM equipment also could print large components, thereby reducing assembly time and cost. Boeing and AFRL chose to 3D-print a section of a large tool to evaluate LSAM functionality. The mid-scale tool (four feet in length vs 10 ft. for the final tool) was printed on Thermwood’s LSAM Additive Manufacturing demonstration machine using a 40-mm print core running 25% carbon-fiber-reinforced polyethersulfone (PESU).
The initial test tool has the same width, height, and bead path as the final mold, incorporating all major features of the final mold, but compressed in length. The mid-scale tool set a milestone achievement as the first high-temperature tool printed using VLP. It required 5 hours and 15 minutes print time with a print weight of 367 lbs (166 Kg). After final machining, the tool was probed for surface profile and tested for vacuum integrity. The tool passed the room-temperature vacuum test and achieved dimensional surface profile tolerances. The full-scale tool will weigh approximately 1400 pounds and require 18 hours to print.
Boeing and the Air Force are carefully documenting all operational parameters of the project to transition the technology to production programs. Additive-manufactured autoclave tooling offers significant advantages over traditional methods of producing these tools, namely 3D printed tooling is less expensive and can be fabricated in days or weeks rather than months while delivering all the production benefits.
LSAM Printing Tooling LSAM Machining of Printed Tooling
Not Only Capture the Data, But Adjust the Process
Manufacturing such parts efficiently is a breakthrough, but a critical portion includes measuring them to confirm a good part, maintain quality control, and confirm conformance to customer and industry (in this case, government) standards. Large parts like the AFRL tooling do not have the luxury of being taken off the production equipment, transferred to a coordinate measuring machine (CMM) for measurement, then returned to the LSAM for adjustment and finishing.
Machining and Probing Printed Tooling on LSAM equipment.
In Thermwood’s case, advanced measurement software, CAPPSNC, from Applied Automation Technologies enables machine tools themselves to perform measurements like a CMM and use that real-time feedback to adjust machining parameters like work offsets as they change.
CAPPSNC provides capabilities to quickly develop measurement programs offline and run these programs directly on CNC machine tools in a similar fashion to a CMM. Measurement results are used to adjust machining process parameters such as calculating precise work offsets, dynamic tool compensations and other critical data feedback in an automated process, together with providing complete part inspection and SPC reports without the need to take the part off the machine and to a CMM lab.
CAPPSNC connects with the machine tool via an ethernet cable, can read and write to any controller parameter and has a live connection with the machine tool controller. What really makes the software powerful is its ability to convert the calculated metrology data it collects into machining parameters and directly update the controller. It runs outside the machine tool controller yet works as part of the machining process. Using such closed-loop feedback to provide correction for the machining process allows the system to be self-adapting to factors that affect the machining process and the quality of products being machined.
What really makes the software powerful is its ability to convert the calculated metrology data it collects into machining parameters and directly update the controller
Benefits All Around
Metrology is the most relevant information about machined parts; having control over this data, easily creating it, converting it into meaningful parameters and distributing it to systems where they are needed ultimately reduces the cost to manufacture these parts. The benefits are realized at each stage of the part-manufacturing process:
- Pre-Process: Preparing part setup on the machine before starting the machining process can be challenging, costly and time-consuming. Automation that quickly measures a part location can eliminate the need to have expensive fixtures and manual part setup. Parts that requires a six-degrees-of-freedom coordinate setup are particularly difficult to set up with the standard work offset. A part measurement that produces a best-fit coordinate system can automatically be converted into a work offset that locates the part in 3D space and gets the machine ready for processing.
- In-Process: Many variables may affect finished part quality during machining. As discussed, cutting tool wear—as well as the actual cutting tool shape under pressure during the cut process—affects how the part form will be generated. Although there are other methods of calculating tool wear and offsets, these are static methods and do not include tool deformation under cutting pressure. Final shape and size measurement can help calculate dynamic tool offset for these changes. An automated, cut-measure-cut closed-loop-metrology-controlled process can achieve parts that are always in tolerance regardless of the complexity of their shapes.
- Post-Process: Data collected by many machining centers can be visualized for how tactual manufacturing throughout the factory is working. Intelligent algorithms that can work with the data can calculate optimum manufacturing parameters ultimately creating a factory wide artificial intelligence system.
“By printing large components and trimming them on the same machine, Thermwood is accomplishing very exciting results for their customers,” says AAT3D senior applications engineer Chris Affer. “Many process parameters can affect the final part. CAAPSNC helps adjust production in real time and refines the part in space so more good parts are produced.”
Adds Duane Marrett, Thermwood vice president of marketing, “We have customers that require accuracy of point location on their components and measuring in place. CAPPSNC is comparable with our machine control, which we supply and program ourselves, and it generates G-code that allows us to add automated measuring processes and process adjustment to our production.”
Data-driven manufacturing is a relatively new term that emphasizes a fundamental truth. Data is the lifeblood of manufacturing and the source of process improvement. Adaptive machining is the process whereby metrology data generated at the machine tool is collected and fed back to the NC control to adjust and refine machine tool processes in real time automatically. Add that new production systems such as LSAM are evolving before our eyes and generating new levels of production efficiency and part quality, it becomes clear that adaptive machining is an enabler of both high-quality parts and real process improvement.
For more information on LSAM: www.thermwood.com
For more information on CAPPSNC: www.aat3d.com