TOOL PATHS: WEAK LINK NO MORE

Cutting tool and machine tool technologies have become more sophisticated over the years, but some experts believe full productivity gains have not been made because of the inherent shortcomings in the off-line generation of tool paths.

Ongoing research at Phoenix, AZ?s GateWay Community College involving tool path software provider Celeritive Technologies, Inc. (Cave Creek, AZ) and high-performance tool manufacturer Helical Solutions LLC (Gorham, ME) clearly shows that a high-quality cutting tool, driven by innovative tool path programs can increase metal removal rates as much as 10 times.

?No matter how sophisticated a machine tool is, it can?t do anything without a tool and a tool path,? says Glenn Coleman, chief product officer and co-founder of Celeritive Technologies, designers of the VoluMill tool path software used in the Gateway testing. ?The tool path has always been the weak link in the chain, typically forcing the use of cutting parameters that err on the side of caution rather than productivity.?

According to Scott Tiehen, Helical Solutions? national sales manager, ?These cautionary tool parameters are detrimental to the tools? performance and fate. High-performance geometries are designed for optimum speeds and feeds and ensure a customer a heightened return on their cutting tool investment. With the use of VoluMill, we discovered that not only does our tooling experience all of these characteristics, it also takes on a whole new aspect of affordability, consistency and predictability allowing for maximum return on investment.?

When numerical control came along some five decades ago, programmers tried to replicate what a skilled machinist could do turning crank handles. Problems become obvious every time there?s a sharp corner in the tool path, where the load on the tool increases because the tool is bearing into more material.

?There have been many attempts over the years to improve upon the traditional tool path,? recalls Coleman. ?Most of those, however, are still based on the fundamental pick-geometry-and-offset-it method. There are detect-and-adjust approaches out there that try to help along a path that has flaws, but our approach is to generate the tool path so that the flaws are never there in the first place.?

There are four problem areas that limit machining throughput when using traditional tool paths:
(1) The initial full cut
(2) Stepping over between cuts
(3) Feeding into new areas of the part, and
(4) Overloading in corners

VoluMill is a revolutionary new programming tool path technology that catches up with the cutting tools and machine tools by utilizing existing CAD/CAM functionality for geometry and input/output functions, allowing customers to continue using their CAM system of choice. It dynamically manages cutting strategies, feed rate and depth of cut, and minimizes force and heat build up in both the part and the tool by maintaining the programmed material removal rate. It is 100 percent compatible with all geometries and part/stock boundaries, cutting styles, materials and cutting tools with support for an unlimited number of islands, tapered walls, variable pocket depths and variable island heights found in the most widely used CAD/CAM software.

?What we have done with tool path technology,? explains Coleman, ?is devise a different way of driving the tool through the material. We?ve developed a path that will ensure a consistent load on the cutting tool. We?ve embedded ways to address all instances of the problem areas indigenous to traditional tool path technology. As necessary, the tool path technology makes dynamic adjustments to the depth of the cut and/or the feed rate so as to never exceed the pre-set volume of material being removed at any given time.? The results are metal removal rates that are five or ten times faster than traditional tool paths.

To prove these claims, Celeritive Technologies joined forces with Helical Solutions, a manufacturer of high-quality, high-performance cutting tools, at GateWay Community College (GWCC), where the two-year-old Manufacturing & Design Technology Department prides itself on being available to industry for research of this type. ?We call our program ?integrated technology? as it combines the disciplines of design, CAD/CAM, CNC programming and operations, tool holding and work holding,? notes Gateway?s program director Dave Zamora. ?We are fortunate to have a variety of machine tools to work with ranging from two-axis to simultaneous five-axis models. We enroll approximately 300 students each year, primarily in our technology certification programs for new students and those interested in upgrading their manufacturing skills.

?With these resources, we?re able to benchmark machining technology more than someone in the industry because they?re hard pressed to make parts every day,? continues Zamora. ?We are an educational research facility for area companies to benchmark manufacturing processes and tooling, and my students learn extreme material removal parameters and they learn variations in work holding to create an optimal setup, which can then be transferred to the production shop. We love this environment to be able to share this technology with our students and our industry.

?VoluMill and Helical challenged us to use the new high-speed machines that we have and we wanted to push the machining envelope,? adds Zamora. ?We found the tool path software to be straightforward and highly productive for generating part programs. Helical Solutions advised us on how aggressive we could be in speed and feeds and provided the coated carbide test tools.?

?The VoluMill tool path allowed us to pocket (rough mill) with a five-flute Helical tool,? says Zamora (see Milling Test #1). ?We also could utilize the same tool for the finishing pass, allowing a combination that may help customers reduce their tool inventory by roughing and finishing with a single cutter.?

Zamora recalls, ?Despite the fact that this test was conducted without coolant, Helical?s cutters and cutting parameters ran smoothly and the heat was carried off in the chips, keeping the part cool.? (see Milling Test #2)

?We ran this test at the maximum feed rate the machine tool would allow,? Zamora says (see Milling Test #3). ?Still, the spindle load meter registered only 10 percent of the available horsepower, a testament to the productivity of well-designed cutting tools and an efficient tool path.?

THE PRODUCTIVITY EQUATION
Lasting productivity improvements in metal cutting encompass all of the disciplines at work at GateWay?s Manufacturing & Design Technology Department. There is no ?silver bullet.? Helical Solutions is application-driven, knowing that a single carbide substrate with a common coating material won?t achieve the best results every time. The right combination of tool length, rake angles, clearance angles, edge sharpness and a multitude of coating processes are needed and provided by the company.

VoluMill represents a new way of thinking about machine tool programming. By using a machine?s optimum metal removal rate, it can increase productivity while removing unnecessary stress and strain on the machine, cutter, tool holder and fixture. These benefits lead to longevity of equipment, cutting tools, increased cutting precision and more. Moreover, there is no need to ?tweak? part programs on the machine and one-off runs become productive as well.

?Don?t overlook other items like coolant, high-quality, balanced tool holders and well-designed fixtures,? offers Tiehen. ?Eliminating vibration and adding lubricity go a long way toward higher metal removal and longer life. In all, testing at Gateway proved that milling efficiency can be increased by 75 percent or more by using the right tools and programming techniques. Depending on how much milling the work-piece requires versus drilling, tapping, boring and so on, overall cycle times can be reduced by one-quarter or more. That?s a great payback for a small investment in quality cutting tools and efficient programming.?

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Celeritive Technologies, Inc., 28248 N. Tatum Boulevard, B-1 Suite 148, Cave Creek, AZ 85331, 888-253-6701, Fax: 805-222-3055, www.celeritive.com.

Helical Solutions LLC, 29 Sanford Drive, Gorham, ME 04038, 207-854-5581, Fax: 866-350-5968, www.1helical.com.