Part Removal Efficiency In a 600 mm Plus World

“Just cut it off.” Sounds simple, right? This process is not pretty, fancy or fun like the engineering, design and execution of creating a part through additive manufacturing (AM) in metal.

In the full cycle of direct metal laser sintering (DMLS) or laser powder bed fusion 3D printing, part removal or “cutoff” is the recurrently forgotten step; an afterthought and rightfully so. I mean, who cares how you get the part off the plate as long as it’s off?

Manufacturers tend to focus on more urgent matters once a build is complete, such as heat treating, powder removal, inspection, density testing and postprocessing. Why is part removal overlooked? A cutoff doesn’t need to be extremely accurate, as the part almost always undergoes additional postprocessing. However, this quiet, overlooked afterthought could be a silent cost killer in the making.

The Size Challenge

Metal AM saw a substantial shift in 2021 with the advent of platforms with build plates measuring 600 mm or larger from Velo3D, SLM Solutions and GE Additive’s Concept Laser.

While these printers have proven to be game changers in terms of their capacity to print part sizes and quantities never before seen, they are quickly revealing shortcomings in the manufacturing process. Past jumps from 250 mm to 300 or 400 mm did not cause quite the same commotion despite the fact they shared similar postprocessing methods.

The shift to platforms 600 mm and larger enables part weights and sizes that few additive manufacturers are able to safely and effectively handle. Removing these large parts from the build plate is a major challenge many providers face now. 

How do you take a platform and a part of this magnitude and ensure it is safely handled, fixtured and affordably removed from its build plate? All of these factors must be considered in tandem with accuracy, to avoid scrapping a costly part.

The Removal Process Is Not Set In Stone

The first thing to consider is the need for establishing a cutting method as well as a machine that are actually capable of handling 600 mm platforms. Hand tools and cutoff wheels will not prevail in the ever-evolving additive world. Wire EDM or bandsaws will be the only options with the capability to complete the job.

Traditional bandsaws offer low purchase and operating costs, but at the expense of inaccurate cuts. In other words, bandsaws get the job done quick and dirty. This process is fairly effective on builds up to 300 mm, some even on 400 mm applications.  However, the drawback of a bandsaw is magnified at 600 mm. 

The cost of a saw this large and the fixturing required to hold parts as well as plates will make a bandsaw no longer the low-cost option users have been familiar with. Large saws are costly and have higher maintenance expenses. The issues with cutting hardened materials like titanium and Inconel with a saw grow substantially at 600 mm. 

For instance, there is the increased risk of a blade wandering. This can lead to scrapping a part, the build plate or both. While bandsaws remain an available option, they are far from the ideal solution.

Now, let’s turn to the world of electrical discharge machining (EDM). This process utilizes a small wire to cut through even the hardest materials with incredible accuracy. The challenge for EDM as it is usually applied comes with the 600 mm or taller cut heights. These are a death sentence for traditional brass EDM wire. 

Machines using this wire require a submerged work tank and optimal flushing conditions to achieve an acceptable and reliable cut speed.  The enclosed, submerged tank brings challenges with loading and holding of massive plates and parts within them. Brass wire EDM machines able to handle significant size are costly. Add on the cutting costs of $12 or more per hour, the chance of wire breaks and cutting delays, and brass wire EDM hits a similar roadblock as seen with the bandsaws.

The New Frontier

As plate size continues to grow, it becomes more and more difficult for manufacturers to handle. Fortunately, there is an emerging third option for EDM technology and it has the potential to be a game changer for postprocessing.

Molybdenum EDM, also referred to as “fast wire” EDM, has been growing in use in the United States. The technology is focused on the metal AM market for additive cut offs. Unlike brass EDM, these machines exclusively use molybdenum wire to reciprocate through the machines at high speeds. 

This technology does not require optimal flushing, a submerged tank or the highly complicated hardware found in brass EDM. Additionally, it operates for well under $2 per hour.

The technology is complementary with AM. EDM Performance Accessories introduced its HB Series Moly Cut EDM in 2016. While this technology has been applied to part removal with plates up to 500 mm, the emerging 600-mm and larger plates are where we are finding the biggest advantages for efficacy and safe handling of these larger plates and workpieces.

Molybdenum EDM is unaffected by tall or interrupted cuts found in most 600 mm cutoffs. The two main factors here are material type and thickness, which simplify the cut technology selection for operators. The machines utilize high wire speeds to create a flushing effect though the cut gap. The wire runs both up and down for 30 to 40 hours of cutting time on the same piece of wire.

Reusing the EDM wire for this time period and doing so on a simplified EDM machine results in cutting costs below $2 per hour, while cycle time increases to about two to three times that of brass EDM in many cases. The advantage for 600 mm printers is a potential 80% reduction in postprocessing costs and hours (perhaps days) of time savings on every build plate.

Handling and Safety Measures

Our largest model, HB1200, was introduced specifically for handling larger AM build platforms. What sets this machine apart is its massive, open work area and weight handling ability. The machine bed is accessible from all four sides and virtually open overhead (besides the small upper head column).  This enables operators to utilize the booth overhead for crane or fork truck plate loading.  Four-sided access without a submerged tank is beneficial for easier and safer plate loading. This facilitates a secure work environment for operators while tending to large, heavy plates.

When fixturing parts, it’s not uncommon for the fixturing alone to weigh in at over 600 pounds to accommodate the plates. When handling parts and plates of 600 by 600 mm and over 1.2 meter tall, having enough space and weight capacity to build proper fixturing is critical.

Unfortunately, no machine offers a one-size-fits-all answer. Different plate systems, from the round Velo3D plates to square and rectangular plates of other manufactures, have different fixturing needs. Plus, the work might be one large rocket component or 200 smaller production parts to catch. 

For this reason, we also build custom fixtures, and have developed a list of cutoff considerations for use in the design process. Considerations include: