Shop Solutions: Dynamic Toolpaths Double Die Making
Progressive stamping die manufacturer LH Carbide (Fort Wayne, IN), a division of L.H. Industries, is a leading producer of progressive stamping dies used in manufacturing rotor and stator cores for electric motors. Because the high quality of these tools results in improved core motor manufacturing precision and productivity, reduced waste, and ultimately better electric motor performance, they are used by OEMs in a broad range of industries throughout the world.
“Like most manufacturers, our company experienced a severe downturn in orders post 9-11. As a result, staff levels declined and they still have not returned to pre 9-11 levels in some departments,” said Tom Neuenschwander, L.H. Industries vice president-technology. “Gradually, the company has recovered and in 2013 is experiencing record sales. CNC manufacturing productivity is keeping pace with demand by using Mastercam’s dynamic toolpaths to get more done with fewer people and at higher levels of quality.”
Progressive dies are sophisticated tools manufactured to a motor OEM’s specifications. They are assembled from 100 or more high-precision parts, mostly 2D, made from extremely hard materials like carbide or tool steel. The CNC department cuts the parts to near net shape so that they can be efficiently shuttled through a series of critical-precision downstream processes including heat treating, wire EDM, precision jig and surface grinding, and finally assembly.
During the course of the week, programmers receive hundreds of unique part designs detailed in SolidWorks. They use Mastercam X6 Mill from Mastercam/CNC Software Inc. (Tolland, CT) to create programs for the machining department’s nine Haas Automation VF2-VF9 mills, a CNC lathe and a Mazak Integrex seven-axis machining center. Parts destined for subsequent processes with long lead times must go to the head of the line to assure that they all arrive at assembly in time to meet the customer’s delivery requirements.
At the customer’s plant, the progressive die will be installed in a large stamping press (e.g., 350 ton) that operates at up to 400+ strokes per minute. With each down stroke of the press one, two, or three rows of 0.010–0.035" (0.25–0.89-mm) thick lamination steel are successively die cut, stacked, compressed and interlocked into unique rotor and stator cores that could be from 18 to 80 laminations high. In spite of the incredible pounding these tools take, they will endure for well over a million stamping cycles before requiring maintenance.
As the economy was heating up in 2011, it was becoming difficult to keep up with the volume of work that was being pushed through the manufacturing department. Neuenschwander said that early in 2011, two things changed that made a big difference. Up until that time, 10 machine operators did most of their own CNC programming. The company decided CNC programming should be a separate function, making it a full-time responsibility of their two most experienced programmers. This gave the dedicated programmers more time to focus directly on optimizing Mastercam programs for improved manufacturing productivity. Operators on the shop floor still have access to Mastercam for making some program adjustments and off-loading work from the primary programmers when work volumes spike.
About the same time, CAD/CAM Technologies (LH Carbide’s Mastercam reseller) introduced the company to a new kind of dynamic toolpath strategy that was developed by Mastercam to address the types of throughput and tool-wear problems that LH Carbide was facing.
The dynamic toolpath strategy goes against the conventional wisdom of aggressively hogging out parts with high stepover cuts using a very small portion of the tool’s flute length. Instead, stepovers are very slight but use as much of the flute as possible, often at spindle speeds as high as the particular machine can generate safely. To improve the precision of these cuts, the company is now using shrink-fit toolholders which keep the total runout of carbide tools to within a few tenths, which is very important for assuring clearance tolerances for precision punches within the die system.
Excessive forces on the tool are eliminated because the software thinks ahead to detect conditions that will result in the tool getting buried in the material (e.g. hitting a corner) and causing it to break or damage the part. Based on this foresight, the program automatically adjusts feeds and speeds to avoid these overloads. The dynamic toolpath algorithms are continually looking ahead and comparing options to decide such things as where to enter the part, where to go for the next cut and when to lift ever so slightly from the part during a dwell so that heat build-ups are avoided.
The dynamic toolpaths allow CNC equipment to run safely while cutting the hardest steel. They have helped reduce tool wear and tooling costs. The cost of prematurely worn and broken tools is always a concern. However, the more important advantage of this approach has been the ability to reduce the number of tool changes required for better equipment up-time.
LH has been introducing lighter duty CNC equipment with higher spindle speeds to its manufacturing operations. Some of these operate at spindle speeds up to 30,000 rpm. Dynamic toolpaths have improved productivity by as much as 100%. However, when the company began using dynamic toolpaths, there were a significant number of older 40-taper machines only capable of spindle speeds up to 7500 rpm. The dynamic paths allowed these mills to run smaller diameter tools at the highest feeds and speeds possible without placing excessive stress on tools and the less rigid spindles. Productivity on these machines went up substantially.
“This advanced computer-aided manufacturing technology is allowing us to get a higher volume of work done faster. Until the last few years, if we could complete the detail parts for a die in a week or a week and a half, we would be doing well. Recently, there have been times when we have produced two or three dies in a single week. Our customers have very tight delivery expectations and we are finding ways to give them what they need,” Neuenschwander said. ME
For more information from Mastercam/CNC Software, go to www.mastercam.com, or phone 860-875-5006.
This article was first published in the August 2013 edition of Manufacturing Engineering magazine. Click here for PDF.