Posted by: Matt Danford 22. January 2016

Five-Axis Blends Require Minding Ballnose Tolerances

Die stamping components like this one are relatively rare at Legacy Precision Molds, which, true to its name, specializes mostly in plastic injection molds. However, 3+2 toolpaths like the one used for this part are quite common—more common, in fact, than full simultaneous contouring. Only when the shop made that leap (from 3+2 to full five) did it discover a need for new ballnose tooling. 

At first, making the leap from 3+2 to full five-axis contouring didn’t look like a very promising development for Legacy Precision Molds (Grand Rapids, Michigan). Nine months after installing their first five-axis, a DMU 50 from DMG MORI, Tyler Vanree and the rest of the crew at this 14-employee shop were struggling to avoid blend lines on parts that would have posed no problems machining smooth on simpler equipment. As it turned out, however, the problem didn’t have anything to do with the shop’s newest machine, nor with its operators or programmers, VanRee says. Rather, the problem was with the cutting tools.

Not that there was anything wrong with those tools intrinsically. After all, ballnose cutters identical to those on the new five-axis machine had been employed on countless three-axis jobs over the years without issue. Yet, those designs simply wouldn’t stand up to the demands posed by five-axis machining, which requires a highly symmetrical ballnose profile to ensure smooth, line-free surfacing. These days, shop personnel insist that all tools employed for contouring have diameter and radius tolerances within ±0.0005 inch. At that level of precision, personnel can rest assured that machining will proceed exactly as planned even if different portions of the cutting edge engage the material at different points along the tool path.

Beyond tight tolerances, the shop appreciates the fact that Innova Tools VHM ballnose end mills are available with various neck lengths. This attribute saves time previously spent grinding shanks back, whether for rigidity, to ensure a tool fits in its heat-shrink holder, to better access features like vertical walls, or any of the above.  

Of course, other shops with other priorities and specialties might specify different tolerance requirements for ballnose cutters. Whatever the level of precision, Vanree emphasizes the importance of considering both tolerance figures—that is, both radius tolerance and diameter tolerance—and checking the math. Although these dimensions are interlinked (that is, one figure depends largely on the other), cutting tool manufacturers often specify tighter tolerances for ballnose radii than for diameters.

“If you had a 0.25-inch-diameter cutter and swung a perfect radius from one side to the other, that radius would measure 0.125 inch—half the diameter,” Vanree explains. “If you shrink the diameter, the radius will shrink with it. That’s why having looser tolerance on the diameter than the radius can complicate things when you’re trying to program the toolpath. So, we try to find tools where diameter and radius tolerance figures match up as well as possible.”

Legacy Precision Molds has learned plenty more lessons since bringing in its first five-axis machining center. To learn more, keep an eye on this blog and for our February issue, which will include a feature article on the shop’s experience. 

Posted by: Peter Zelinski 21. January 2016

Video: Accelerated Blisk Milling

CAM developer Delcam and cutting tool supplier Technicut produced this brief video illustrating the highlights of a machining cycle that generated a blisk from an 804-mm diameter disk of titanium 6-4 in 35 hours. The two companies say that cycle time is less than half of what would be required to machine this same part with conventional methods. In the cycle shown, several factors contributed to that productivity:

  • Roughing is performed in stages throughout the process. Lower sections of blades are left in their rough state to maintain stiffness while the upper portion is being machined.
  • Tool paths specific to blisk machining programmed in Delcam’s PowerMill use barrel cutters from Technicut for semi-finishing and finishing. Offering a larger radius at the cutting surface than ballnose cutters, barrel cutters achieve the same cusp height between passes as a ballnose tool with a stepdown that can be three to four times as large.
  • Initial rough machining operations between the blades use Technicut’s Titan X-Treme Ripper end mill not only to remove material quickly but also to relieve stresses in the material introduced by forging.

Blisks—one-piece bladed disks—are increasingly used in turbine engines in place of individual blades machined separately and fixed into a hub. The completed blisk in this video has 31 blades, each 84 mm long with a root radius of 4 mm and scallop height of 10 microns.

Posted by: Emily Probst 20. January 2016

Searching for Good News in the Manufacturing Skills Gap

While the current employment outlook is seemingly bleak, with a high number of manufacturers reporting a moderate to severe shortage of available, qualified production workers, there does appear to be a light at the end of the tunnel concerning the future of American manufacturing over the next decade.

So says Jon Iverson, CEO of Optis, in an article written in correlation to the company’s new qualitative research report, which looks into the state of American manufacturing to examine the current mood and make predictions for the future.

In the article , Mr. Iverson mentions three ways the manufacturing industry can begin to bridge the skills gap, ensuring a sustainable future.

  1. Use model-based definition. Design parts and automatically embed tolerances in the model. By doing so, product development can be streamlined.
  2. Use automation. Automating routine tasks enables personnel to concentrate on more intricate, complex and individualized procedures. According to the report, this will become increasingly important as manufacturers reshore to the United States, bringing more demand for operators and further impacting the skills shortage.
  3. Design more intuitive machines. A certain amount of “tribal knowledge” will be lost when the baby boomers retire. This insight needs to be “trained” into machines so less human intervention is necessary to make the future machine tool self-sufficient.

Posted by: Derek Korn 19. January 2016

“Swiss Automatic” Grinder…Made in Jersey

The CAM.2 microgrinding machine from Glebar uses a hydrostatic bushing to offer support very near the area of contact between the part and the grinding wheel. There’s pretty much no limit to the length of wire to be ground, as shown in these demonstration parts with tiny ground flats, tapers, threads and so on.

Glebar, a New Jersey manufacturer of OD grinders, plunge grinders and other types of grinders, developed an interesting technology for grinding long, small-diameter parts. We’re talking workpiece stock as small as 0.005 inch in diameter and a minimum grinding diameter of 0.0005 inch for applications such as medical guidewires that can range to 16-feet long.

The way it does that is by applying a concept that’s similar to a sliding-headstock, Swiss-type lathe and its signature guide bushing. Learn more.

Posted by: Jedd Cole 18. January 2016

Robots Assist with Repetitive Tasks

Click above to view the slideshow of January’s Modern Equipment Review Spotlight.

While the topic of robots and automation continues to spur intense development, innovation and debate, there’s no denying that robotics shine when applied in situations with repetitive tasks, such as load handling in production runs. A few of this month’s curated robot and automation products suit this sort of implementation. A different sort of application is exemplified by Perceptron’s AutoScan Collaborative RoboGauge, which performs automated 3D scanning by combining a FANUC robot with Perceptron’s Helix scanner.

Click the image above for a slideshow featuring these and other automation products, with links to more information. 

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