Accurate Additive Manufacturing Requires Machine Simulation

Originally titled 'Know What to Expect Before Starting with Additive Manufacturing'

Machine simulation can help to provide a clear picture of the additive manufacturing process from the first to the last step.

As with other segments of the manufacturing industry, 3D printing is making significant inroads into the mold, die and toolmaking market. Whether it is mold inserts with conformal cooling channels, mold repairs, rapid prototype and bridge tooling, or 3D-printed “show-and-tell” models for quoting and customer approval purposes, those who have made the leap to additive are finding it an important tool in the manufacturing toolbox.

 

 

Yet challenges exist because metal additive powder-bed and spray-deposition technology are still relatively new. The correct “recipe” of laser parameters, such as traverse speed and power levels, material feed rates and gas flow, are often a best guess or are determined by slow trial-and-error on the machine tool. The behavior of the feedstocks and powders that you would use with 3D printers is similar.

Additively manufactured part geometries are in a constant state of flux as designers and engineers learn the best ways to leverage this new technology. Warping from thermally induced internal stress and the occasional “crashed build” is not uncommon. Then, once the product leaves the 3D printer, secondary machining processes are usually needed to ream and tap holes or skim-cut critical surfaces.

To make matters worse, there is no chance to open the door and peek in on the burgeoning workpiece as there is with a CNC machining center or lathe. Therefore, it behooves machine owners, programmers and operators to know what to expect before pushing the cycle start button and to have a clear idea of the manufacturing process from the first step to the last. The best way to accomplish this is with machine simulation software.

Determining the Need for Machine Simulation

Some people argue that machine simulation software is all about collision checking, and because the additive manufacturing process is always working on the top layers of the workpiece, there is very little of the crash potential that is common in traditional machining.

While that statement is valid for some additive machines, the reality is much deeper. On metal-based additive machines especially, build rates are quite slow. You might spend tens or even hundreds of hours printing a part only to find that you missed something during the design process, used an incorrect recipe of additive parameters or wish that you had built something differently.

Then there is the question about which would be faster: building a part additively or through traditional fixturing and machining. More effective cost quoting up front is necessary for your shop to answer this question correctly and with confidence.

Why would you not want to spend a few minutes simulating the build ahead of time to make sure that your expensive machine tool does not just waste thousands of dollars building something that will head straight to the recycling bin? Simulation also provides one final chance to review the “as-printed” design. If there is a question, you can revisit the build parameters or consult with the customer and avoid the unpleasant phone call you might otherwise have to make later.

If there is a question, you can revisit the build parameters or consult with the customer and avoid the unpleasant phone call you might otherwise have to make later.

Moving to the Next Level

Hopefully, your shop is already leveraging toolpath simulation software to verify and optimize traditional machine tools. If that is the case, then you already know that the best way to verify how a machine will react to one of your tool paths is to simulate the actual post-processed G-code that will drive the machine. No more do you wonder whether an unexpected hiccup in the post-processor will send a half-inch ballnose end mill careening into the workpiece. Gouging and uncut material is clearly identified as are wasted motion and less-than-ideal machining values.

These benefits extend to additive manufacturing as well. Building a part that does not match the intended design and errors like leaving voids and unexpected material are clearly visible. Laser activity, including things like gas flow, wattage and powder deposition, is no longer a guessing game. You can maintain detailed build history for archival purposes or to conduct a post-build forensic analysis in the event of a failure. You can quickly reveal the precise identification of root-cause NC program, tool (additive or subtractive) and block of NC code with a single mouse click.

There are even more reasons to simulate with a hybrid additive machine. Collision avoidance comes back into play but takes on a new level of complexity as metal is added to and subtracted from the workpiece. You can watch the entire manufacturing process virtually. You can stop and restart it at any time, rewind or fast-forward as you need, zoom into problem areas and visualize each discrete step of the hybrid additive machining cycle.

Those who can determine most quickly when and how to utilize this technology to make better parts, faster, and at a lower cost will be the ones to define success.

Looking Ahead

Maybe you are not ready yet, and the thought of spending a million dollars or more for completely new manufacturing technology (that is, at least, new to you) has you lying awake at night. With simulation, you can eliminate much of the mystery. Simulation models for all major additive and hybrid machine tools usually are available. Just plug in your 3D model and some NC code to start kicking the tires. You can easily validate build speeds and machining capabilities before the first dollar of hard-earned cash ever leaves your checking account.

Take that a step further. Say you have a new machine but are still grappling with how to quote additively produced molds and tooling. Simulation provides accurate cycle times, material statistics, power consumption and more while identifying potential problem areas. You can experiment with different production strategies and determine the best approach. That way, it is easier to determine which part features your shop should print and which part features your shop should machine. You can visualize and validate end-to-end all of the “hand-shakes” made along the entire manufacturing process, including steps like additive and subtractive processes, secondary machining and post-build finishing, which possibly could help you avoid costly rework.

Leaving Old School Ways Behind

You may be thinking, Hold on. We have been doing this for 30 years. Our moldmaking techniques have been laboriously (and sometimes painfully) refined. Why would we upset our applecart by investing in a technology that is still rapidly evolving, is quite expensive and for which very few people can operate and program the machinery?

Similar questions were posed when the first paper-tape NC lathes and mills hit the showroom. Maybe you were not an early adopter back then either, but can you imagine a world without CNC machine tools now? The same will be said about additive manufacturing and probably much sooner than anyone can imagine. Those who can determine most quickly when and how to utilize this technology to make better parts, faster and at a lower cost will be the ones to define success.

Machine simulation makes 3D printing on CNC additive and hybrid machines safer and much less scary. And, for those who are not afraid of anything, it makes the entire manufacturing process, including auxiliary operations, far more efficient and profitable. You have come this far, so why not take the extra step? Get simulating.

You have come this far, so why not take the extra step? Get simulating.

About the Contributor

Gene Granata is Vericut product manager for CGTech.

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