Better Understanding for Better Results

The thinking behind their research is simple, as Dr. Smith explains: "If you know exactly what a machine can do, then you can do a better job writing the part program." Quite simply put, the work that Dr. Smith and his colleagues are doing helps end users take the guesswork out of program writing.

For example, Smith says his group conducts cutting tests for different tools to determine which speed is optimal for each, and to determine the kind of depths of cut they can achieve. Using that information, the researchers at the University of North Carolina at Charlotte have built a database that lists the findings for each tool. Now, when they write the part program, they have the database as a reference point. This process results in part programs that work right the first time and that fully utilize the machine's capabilities. "We are not developing part programs by trial and error," Smith states.

Although Dr. Smith has been working on this program with the A55 DELTA for about three years, he has been involved with other projects involving Makino equipment in the past. During his involvement in an offset program with Boeing, Smith's group was assigned the task of selecting a machine for high-speed work in a Malaysian research facility. The machine chosen was required to meet a rigid set of criteria. Ultimately, that machine was the Makino A55.

Makino's A55 DELTA High-Speed Machining Center

Smith noted that Makino designed the A55 DELTA for maximum productivity and reduced part processing time. With faster spindle speeds, cutting feeds, and tool and pallet changes, the A55 DELTA reduces processing time and raises machine productivity for both high-volume production and high-flex machining operations.

The A55 DELTA features quick installation with simple, three-point leveling and no special foundation requirements for installation; and the A55 DELTA's easy relocation allows for better asset utilization. It offers a 1.8 second, 180° pallet index, along with simultaneous positioning of X, Y and Z axes to minimize out-of-cut time.

Precision is key with the A55 DELTA, according to Smith. Geometric intelligence cuts rework and out-of-tolerance rejection rates, allowing for the use of a single tool to bore varying diameters and pitches, and eliminating undercut and overshoot. Moreover, core cooling of ball-screws helps maintain tight accuracies during continuous, high-volume production.

The Repeatability Factor

In his years of involvement with the A55 DELTA at the University of North Carolina- Charlotte, Dr. Smith has identified one benefit to the machining center that he finds to be the most critical-- repeatability. Repeatability is increasingly at issue with machine tool users. Repeatability is achieved when, each time a process is repeated using the same setup, the results look exactly the same dynamically. Smith cites the A55 DELTA's spindle as a leading factor in the machining center's superior repeatability. "It has got a very robust spindle," he says. "Dynamically, the results look the same, and that is one of the really attractive qualities of the A55."

Smith goes on to explain the importance of repeatability in high-speed machining applications. "If I want to make the best use of my machine," he states, "then I need to know what all the tools can do. We have equipment and tests that we perform that tell us for every tool in the magazine what speed it should run and how big a cut it can make. And as long as I write a part program within those bounds, then the program will run right the first time, and I know that I am fully using the machine's capabilities. If I do not do that, then I am hunting. I make my best guess, I try it, then make adjustments based on the problems that arise. Eventually I get a program that works and I stop making adjustments. I am happy because I have a program that works, but that does not mean that I am really fully utilizing the machine's capabilities."

On the other hand, Smith states, "If I really know what all the tools can do, then I can write a program that allows me to use them all very well. But one of the requirements for that is that the tool dynamically looks the same every time I put it in the spindle." That is where repeatability comes into play.

Smith notes that repeatability is partly an effect of the machine itself and partly the responsibility of the user. The user is responsible for making the setup length of the tool the same each time. Repeatability is not possible when the user switches out holders, for instance. And it is the machine tool builder's responsibility to make sure all the spindles look the same. "If I have to replace a spindle, for instance," says Smith, "number two should look like number one." Spindle appearance should not change over time. "Repeatability of the machine means I want it to look the same every time I use it."

Machining Center Users: Three Possible Scenarios

According to Smith, there are three possible scenarios for machining center users. In the best case scenario, "You've used measurements or cutting tests, you know what each tool on your machine can do very well, and you've shared that information with the programmers so that they use that information to respect the limits when writing the program." The second possibility, according to Smith, is less positive. In this scenario, "You get into chatter problems every day because you're pushing the envelope and often end up outside the envelope because you don't know exactly where the envelope is."

Another possible scenario, Smith says, occurs when users don't realize the full potential of their machine and its tools. "A third scenario is that you are underutilizing your machine. Even if it's running 24-hours a day, you may be underutilizing it if it's not making the kind of cuts that it could." Dr. Smith approximates that most users of machine tools fall into this last category. "They may struggle because they don't know exactly what they can do so much so that, when they eventually do get a part program to work, they are so happy just to have it working that they don't touch anything else."

This sort of "ignorant bliss" can spell lost time in machining. For instance, if a machine is making a cut 1/4" deep that could be made 1/2" deep, the program takes twice as long to run and the machine is under-used by a factor of two. And that lost time is valuable in today's high-speed machining environment.

Designed for Speed

This is a machine designed for speed. Tool change for the A55 DELTA is unsurpassed, meaning the A55 DELTA effectively reduces non-cut time. Tool change is just 0.9 second with a standard spindle, and 0.7 second with the optional HSK spindle, and a chip-to-chip time of 3.4 seconds.

The A55 DELTA also initiates precision work faster than linear accelerated centers. Cycle time is improved, with bell-shaped acceleration achieving 14,000 rpm in just 2.8 seconds, and configuration capability to 20,000 rpm for even smaller tool applications. Bell-shaped acceleration/deceleration on the axis drives allows the A55 DELTA to reach maximum traverse and feed rate faster and hold it longer, while reducing shock loading.

The speed of the A55 DELTA puts it in the right range for many aluminum applications, meaning it lends itself easily to aerospace applications, like the ones being tested at UNC Charlotte. Most of the work that Smith's group conducts is geared toward aerospace manufacturing applications. Their work has been featured in publications from The American Society of Mechanical Engineers, the Society of Manufacturing Engineers, and The International Institution for Production Engineering Research.

Their concepts are adopted into practice by their interactions with the end users of the machines. The group shares their findings with product users to help them maximize their machine's potential. Among those who are making use of the research results that have come out of Smith and his colleagues' work, Boeing, St. Louis tops the list. To learn more about the work being done at Boeing, St. Louis in the area of high-speed machining, see the Radical Departures article "Boeing's Phantom Works Explores Issues of High-Speed Machining and Metal Cutting Dynamics."

If you're interested in learning more about Dr. Smith's views on machine dynamics, read the Radical Departures article "Understanding Machine Dynamics: Process Implications and Requirements for Successful High-Speed Machining."

Copyright © 2001 - 2010 by Makino, Inc. All rights reserved.