Aerospace increasingly relies on metal additive manufacturing (AM) to create weight-saving components with complex geometries, different material properties, and minimal setup times. To construct each part, advanced 3D printers melt, or partially melt, ultra-fine layers of metal powder on build plates. After each metal part is finished, it’s cut from the build plate.
However, one production bottleneck in AM is any residual metal must be entirely removed before the build plate can be reused. This requires precisely resurfacing the build plate so it’s flat, level, and correctly textured prior to printing the next part. Unfortunately, traditional methods of accomplishing this task have significant drawbacks and have become a production bottleneck.
Advanced precision rotary surface grinders used in metalworking and glass grinding to create perfectly flat, parallel surfaces are ideally suited to remove any residual metal from the build plate surface, restoring it to precise dimensions.
“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,” says Doug Hedges, chief technology officer of Deerfield Beach, Florida-based Beehive3D Inc., an AM provider for industries such as aerospace, defense, and turbine technologies. The AM contract manufacturer currently has five U.S. locations and is expanding nationally.
It’s critical in Beehive3D’s laser powder bed fusion process to resurface the build plate to precise process tolerances prior to reuse. “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 explains.
Since the metal part is essentially welded to the build plate, it’s typically cut off with wire electrical discharge machining (EDM) or a bandsaw. However, both methods remove a thin layer of the build plate surface, gradually reducing its thickness until it’s no longer usable.
The alternative is to cut close to the part, leaving material that must be removed later. With EDM and bandsaws, the process can take hours and hard materials such as Inconel tend to strain-harden, further increasing the difficulty. Some shops address the issue with CNC milling, possibly taking hours and limiting equipment availability for actual production. Exceptionally hard AM materials, Inconel and titanium, further lengthen 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 build plate as possible while providing necessary resurfacing of the build plate,” says Erik Lawson, engineering manager at Winona, Minnesota-based DCM Tech, a designer and builder of industrial rotary surface grinders.
Today, surface grinders are designed with more advanced sensors and controls that automatically maintain very tight tolerances, removing material down to within 0.0001" 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, eliminating variability among resurfaced build plates while 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 almost any operator can successfully manage. 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 the pressure of the spindle motor and 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 any operator can use to make necessary adjustments without programming. This capability enhances processing flexibility, so it’s easy to adjust any grinding factor to prevent an issue from recurring.
For routine processes, the use of a variety of grind recipes with sets of parameters for different AM construction builds can further 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 doesn’t 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 explains.
One aspect that expedites production is accommodating grinding of extremely hard residual material from build plates. 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.
Beehive3D currently uses DCM Tech IG series rotary surface grinders at some of its locations and plans to add more in the future. Hedges finds value in working with an expert vendor that can tailor the rotary surface grinder to 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 such as DCM Tech gives us the flexibility we need to efficiently remove a range of metal remnants from the build plates,” Hedges says.
Also important is the ability to alter parameters through the grind cycle to handle 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 adjust to each on contact. Once the grinder cuts through the residual part material and reaches the plate, the grinding abrasive must work completely differently; the rotary grinders automatically make that transition.
The advanced unit’s grind recipes can also 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 properly adhere to the surface during buildout.
“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’s no reason to take it to a secondary operation,” Hedges says. “An operator can simply clean it with alcohol or a solvent, let it dry, and it’s ready to use again.”
Automation saves time, steps
The automation from advanced rotary grinders allows operators to set up the machine and then attend to other tasks. The machine doesn’t need to be constantly monitored because it has built-in load monitoring.
“Unlike older style machines, the advanced rotary grinders don’t need constant operator input or oversight. This allows the operator to multitask and minimizes the risk of error,” Hedges says.
Automation also eliminates the need for operators to manually dress abrasives 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.
“Advanced rotary grinders with an auto dress option free operators from needing to do it manually, making operation easier and less time consuming,” Hedges says. “The option can be particularly helpful with hard materials such as Inconel, which can require more frequent dressing of abrasives.”
As metal AM production ramps up, manufacturers who take advantage of sophisticated, automated rotary surface grinders to efficiently remove excess materials and resurface build plates will outperform those using slower, less precise conventional methods.