Industries like aerospace and automotive rely increasingly on metal additive manufacturing (AM) operations to create critical parts expeditiously – weight-saving components with complex geometries, different material properties, and minimal set-up times. To construct each part, 3D printers melt, or partially melt, ultra-fine layers of metal powder on build plates. After each metal part is finished, it is cut away from the build plate.
However, a notable production bottleneck in metal AM (or metal 3D printing) is that any residual metal must be removed entirely before the build plate can be re-used. This requires precisely resurfacing the build plate so that is completely flat, level, and correctly textured prior to printing the next part. Unfortunately, standard surfacing methods present significant drawbacks and have become a production bottleneck in the metal AM process.
Enter advanced precision rotary surface grinders, which have long been used in metalworking and glass grinding to create perfectly flat, parallel surfaces. The equipment is ideally suited to the AM process and quickly and accurately removes any residual metal from the build plate surface, restoring its precise dimensions.
The most advanced rotary surface grinders even offer automation that allows minimally experienced operators to set them up and then attend to other tasks. This comprehensive approach is helping to exponentially speed build plate resurfacing, boost AM production, and improve quality.
“With advanced rotary surface grinders, our AM build plate resurfacing process is significantly more efficient, precise, and flexible. Incorporating the units in our process will help us handle high expected growth in the AM market,” according to Doug Hedges, chief technology officer of Beehive3D Inc., a metal AM supplier to industries like aerospace, defense, and turbine technologies. The Deerfield Beach, Fla.-based contact manufacturer currently has five U.S. locations, and it’s expanding nationally.
Hedges said resurfacing the build plate to precise tolerances prior to reuse is critical in Beehive3D’s laser powder bed fusion process. “Not only do you have remnants of metal on the build plate, but also portions of the build plate can become bowed or distorted, so it needs to be resurfaced after each use to keep it flat and parallel,” Hedges said.
Since the metal part is essentially “welded” to the build plate, typically it is cut off with electrical discharge machining (EDM) wire or a bandsaw. However, both those approaches involve removing a thin layer of the build-plate surface, gradually reducing its thickness until it is no longer usable. And most of the cuts are not entirely flat or level, either.
The alternative is to cut close to the part, but this leaves material that must be removed from the build plate later. With EDM and bandsaws, the process can take hours and hard materials like Inconel tend to strain-harden, increasing the difficulty further.
Some shops address the issue with a CNC milling machine, but this also can take hours of production time and limit the availability of the equipment for actual production. Exceptionally hard AM materials like Inconel and titanium further extend the required milling time.
A more efficient alternative uses advanced precision rotary surface grinders to remove unwanted residual material with a large rotary grinding wheel surface.
“The goal is to remove just the residual AM part material and as little of the building plate as possible while providing necessary resurfacing of the build plate,” explained Erik Lawson, engineering manager at Winona, Minn.-based DCM Tech, a designer and builder of industrial rotary surface grinders.
Today, surface grinders are designed with advanced sensors and controls that automatically maintain very tight tolerances, making it possible to remove material to within one ten-thousandth of an inch of the final thickness. The equipment can achieve tighter dimensional tolerances, flatness, parallelism, and surface finish on build plates in much less time than other methods. The rotary surface-grinding process eliminates variability among resurfaced build plates in addition to increasing production and quality, batch after batch.
More advanced units such as DCM Tech’s IG series offer variable-speed grinding with automation and controls that allow virtually any operator to manage a unit successfully. These units can control the initial contact between the abrasive wheel and the build plate, which in the past had to be finessed by the operator. Advanced sensor technology detects vibration and can automatically fine-tune not only the pressure of the spindle motor but how quickly it moves the wheel down onto the build plate. When the machine senses the abrasive wheel has contacted the build plate, it automatically begins the grind cycle.
The most advanced units offer simple controls – including a touchscreen human-machine interface (HMI) – that even unsophisticated operators can use to make any necessary adjustments without programming. The HMI controls allow operators to enter virtually any requirement into a touchscreen. This capability enhances processing flexibility, so it is easy to adjust any grinding factor to prevent an issue from reoccurring.
For routine processes, the use of a variety of grind “recipes” with sets of parameters for different AM construction builds can speed production, enhance quality, and aid in quick changeover.
“Different grind recipes can be set for different customers, material types, or construction builds so complex programming or data does not need to be entered at the start of each job. A new recipe can be created for job variations, such as a different finish for a specific AM material,” Lawson explained.
One aspect that expedites production is the operator’s ability to accommodate grinding of extremely hard residual material like Inconel or titanium from build plates. Typically this involves working with an expert vendor that can tailor the surface grinder’s abrasives to accommodate different types of metals and alloys, as well as the materials used for the build plate.
Currently, Beehive3D uses DCM Tech IG series rotary-surface grinders at some of its locations and plans to add more in the future. CTO Dough Hedges finds value in working with an expert vendor that can customize the rotary surface grinder to Beehive3D’s specific needs.
“Using the proper abrasives and feed rates can reduce finishing time and facilitate an efficient, repeatable process. Working with an expert in abrasive use like DCM Tech gives us the flexibility we need to efficiently remove a range of metal remnants, such as aluminum, titanium, and Inconel, from the build plates,” says Hedges.
Also important is the ability to alter the parameters through the grind cycle, to handle both the printed metal or alloy and the material used for the build plate. The material characteristics of the printed part residue and the build plate are very different, so the rotary grinder must appropriately adjust to each of these on contact. Once the grinder cuts through the residual part material and reaches the actual plate, the grinding abrasive must work completely differently. The rotary grinders automatically make that transition.
The advanced unit’s grind recipes also can be set to accommodate required build-plate textures. This eliminates the need to “roughen up” a build plate in a separate process so the AM part will adhere properly to the surface during build-out.
“Instead of trying to tailor a build-plate finish by running it through a mill or an abrasive blaster, after grinding with an IG machine there is no reason to take it to a secondary operation,” Hedges said. “An operator can simply clean it with alcohol or a solvent, let it dry, and it is ready to use again in the AM process.”
According to Hedges, the automation provided by advanced rotary grinders allows operators to set up the machine and then attend to other tasks. The machine does not need to be monitored constantly because it has built-in load monitoring.
“Unlike older style machines, the advanced rotary grinders do not need constant operator input or oversight. This allows the operator to multi-task and it minimizes the risk of error,” he said.
Automation also eliminates the need for operators to dress abrasives manually on the grinding wheel to renew a good abrasive surface. Without automation, over time the wheel can become clogged with residue from the AM material.
When operators manually dress abrasives, on most machines they hold a tool under the grinding wheel abrasive. The tool applies abrasion and knocks off all used or clogged abrasives until the grinding wheel has a nice, new abrasive surface. Operators frequently need to repeat the process, sometimes as often as every 10 minutes depending on the materials ground, which can be labor intensive and decrease productivity.
“Advanced rotary grinders with an auto dress option free operators from needing to do it manually, making operation easier and less time-consuming,” Hedges said. “The option can be particularly helpful with hard materials like Inconel, which can require more frequent dressing of abrasives.”
As metal AM production is adopted more widely, manufacturers that take advantage of sophisticated, automated rotary surface grinders to remove excess part materials and resurface build plates will outperform those using slower, less precise conventional methods.
Del Williams is a technical writer in Torrance, Calif. He writes about health, business, technology, and educational issues, and he holds an M.A. in English from C.S.U. Dominguez Hills.