The Science of Machining?
If You Don’t Know the Correct Measurement, It’s a Guessing Game To Find Optimum Machine Performance.
Aerospace machining has long been an experienced-based industry. If a problem occurs, the standard response is to decrease the speed and back off the depth of cut. So, the end result is that, while the part is eventually correct, no knowledge is gained from the process. An opportunity to gain additional information in order to improve the efficiency of the process has been lost.
According to Jerry Halley, considered by many to be an innovator of high-speed machining in aerospace, machining needs to become less of an art and more of a science. Halley, an associate technical fellow at Boeing Aircraft and Missiles Division in St. Louis, believes that in order to improve the industry, machining should avoid the trial and error process by being more deterministic and less of a craft or trade.
“If you don’t know the correct measurement, it’s a guessing game to find optimum machine performance,” Halley said. “A close collaborator of mine, Dr. Scott Smith at UNC Charlotte, explains that you have one of three options: one is exactly right and one overextends the machine capability and probably does significant damage. Or, if the cut is nice and the finish is good, it is very likely that you are under-utilizing the capability of that machine. What we see is that you can determine the correct measurement before you make the part.”
Getting the Most Out of the Machine
One key to this transformation is for operators to consistently run machines at optimum levels. Regardless of whether the operator is making one part or thousands, it is important to get the process parameters right the first time.
“We can take an A55 Horizontal Machining Center (HMC) from Makino, optimize the set of tools and significantly increase the performance for a particular family of parts,” said Halley. “We think very few people are running parts at the optimum levels they could. The more repeatable the parts, the more repeatable the assembly process. This allows us to gain added benefits when building the airplane as well as eliminating steps while realizing significant cost savings in our overall process.”
Another component of running the machine at the optimum level is to understand the science involved in the interaction between the tool tip and the work piece.
“You have a Makino MAG4 machine that is an incredible piece of equipment. Then an aerospace shop adds an inexpensive end mill and uses the wrong process parameters. You just destroyed the potential of this incredible machine you just bought. As a result, we have put a lot of effort into developing a very good understanding of what will happen at the tool tip,” said Halley.
By making measurements such as a frequency response function, it is possible to characterize the performance of the tool tip very effectively and to ultimately have the ability to understand what the tool is going to cut before the machine is turned on. Armed with this knowledge, machining becomes much more of a deterministic process rather than a guessing game.
One component of understanding the science of machining is to strive for the same tool performance wherever the machine is and whatever the conditions the machine is under. This is not so much a question of the machines’ capability but of operator education and shop culture.
Halley commented, “I use a Makino A99E, and I would like that same tool and the same tool holder to perform the same over a bunch of those machines. An A99E in California or Ohio or Malaysia, the same tool and the same tool holder ought to perform the same. This is not an issue of the machine’s performance or capabilities; it is an issue of user execution. We are not yet close to standardizing this. In terms of the capabilities of the machines, it is there for the taking. The question becomes one of discipline and how you control the tool, the tool holder and the process parameters.”
Halley added that a frequent cause for chatter and vibration is purchasing components of a machine based on price or other factors rather than the compatibility with the rest of the machine.
“As Scott Smith and I have discussed, a company will buy the tool from somebody, then buy the tool holder from somebody else, and they get the spindle from somebody else, and they get the machine from yet another vendor. The reality is, it is not these individual components that make a great machine, it is the integration of these components and proper choice of parameters. Right now, we guess at that combination.”
Halley also suggested that, while education is an important step towards uniform use of machines, another possibility is to bundle technology so as to not limit capabilities but make the process less complex.
Outsourcing: The New Frontier
Changes in machining involve becoming more familiar with the capabilities, functions and science of a machine tool. However, another rapidly changing area involves helping others realize the proper use of a machine when outsourcing. According to Halley, Boeing started divesting fabrication in St. Louis in January, 2001.
While it is still a fledgling idea for Boeing, Halley is quick to defend the benefits of outsourcing. “We just divested of fabrication this year. I think we understand the importance of it, and we are working hard to try to manage that activity and help our suppliers be better performers. In the end, we just want to produce a better flying product.”
While there are obvious financial advantages, the key to outsourcing successfully is to ensure that the quality of the product will not be affected. According to Halley, an effective way to do this is through sharing technology.
“I think we have been very open with the technology we have and the approach we take. We have always been pretty open about talking to our suppliers and trying to help them. If you do not own the fab and you are trying to influence the products that show up on your airplanes so you can assemble them better, that means that you have to tell people information, data and processes.”
Halley adds that another critical facet to successful outsourcing is carefully monitoring the progress, “We get metrics on the part before we start. We do the process development. We will look at those performance measures. When we are done, that will be a measure of our success. And we are working with our partners to administer the process.”
One issue that has arisen from this situation: if the supplier is manufacturing the product, do they handle R&D as well? According to Halley, the answer is yes, but on a very limited basis.
“The supplying community wants to do well, but they do not have the financial resources to do research. And they do not necessarily understand the full product requirement. So, we continue to do machining R&D, even though we no longer own a machining facility in St. Louis.”
Machining is still a craft-oriented industry. Understanding more about running a machine at an optimum level, maintaining an industry-standard for tool use and performance and finding cost-efficient methods of production while maintaining quality—such as outsourcing—are ways to transform machining into a science.