Tech Front - Tooling Choices Lead to Thread Milling Solutions
When most people talk about the question of tool life, they’re referencing extending the time of use of a particular tool. It can be more helpful to take a look at the big picture and examine the question of tool life from a technological perspective," said Jeff Dei, president, Carmex Precision Tools LLC (Richfield, WI). "In effect, if tool life is too short, you might be using the wrong tool. For instance, over the years, many of our customers have come to us because they were regularly breaking taps. By altering the approach from tapping to thread milling, they were able to derive a better result and eliminate the question of tap life.
"Even in cases where the customer has opted for thread milling, however, it is essential that the tool selected meet the highest quality standards in order to ensure the best results and the longest life," said Dei, citing the example of a high-precision specialty shop Apex CNC Swiss located in western Pennsylvania. Production capabilities of the latest generation of Swiss-style machines has necessitated a new generation of tools capable of standing up to the rigors of high-speed, high-pressure coolant and high-volume production. Apex CNC Swiss has to meet the challenges of high-precision complex parts machined in hard materials and exotic alloys.
"One of the challenges facing Apex CNC Swiss involved an electronic circuit board standoff in 303 stainless which was machined on a Star SR-20RIII machine," said Chuck Fluharty, co-owner. The 0.180" (4.6-mm) deep hole being threaded required a 0–80 thread. Using a competitor’s tool, between 200–300 parts were machined before tool failure. When the manufacturer’s technical support was contacted, Apex was advised that it was normal. Apex then searched for a better solution. When Apex switched to the Carmex mini mill-thread design, production soared to over 2000 parts, and they were able to do 500 additional parts in 17-4 stainless.
"The advantage of longer tool life doesn’t stop with having to purchase fewer tools over time. Even more important, once we had established that we could trust the Carmex tool for longer production runs, we were able to spend less time monitoring the machine and changing tools, and that resulted in even further savings, including untended operation up to four-hour cycles," said Fluharty.
Another case of switching to thread milling involved a shop owner who was machining a critical part for a radar component. Made of titanium alloy 6 Al-4V, the part required 683 blind holes. Because of the tapping operation, his customer had to allow a tap deviance of 0.040" (1.0 mm) in depth to allow for the thread clearance. This meant that the holes had to go from a depth of 0.150–0.190" (3.8–4.8 mm). The 2-56UN thread’s major diameter was 0.086" (2 mm), and the drill diameter 0.070" (1.8 mm). Repeatability was nearly impossible on his CNC equipment, and the shop owner literally came in every Saturday to tap the holes by hand. When he started talking to Carmex, he was breaking his taps after only 20 holes—"an extraordinarily short tool life," said Dei.
By re-examining his technology, and switching to thread milling, he was able to accomplish the threading of 683 holes with a single thread-mill on his CNC equipment. Despite the number of passes, the wear factor between the first and the last holes could only be measured in tenths, and the customer was able to get the thread detail back to its original 0.150" (3.8 mm) full thread depth.
When it comes to individual tool life, three of the major factors involved are tool design or geometry, cutting tool substrate and coating. Carmex realized early on that a helical design, what Dei calls "our Helical Advantage," eased entry of the thread-mill into the hole, reduced chatter, and created a better finish. This reduction in stress and vibration results not only in better performance but an increased wearability and longer overall use.
"One of the most rapidly changing aspects of tooling at present involves composition, and by that, I mean both the basic carbide or other underlayment and the coating deposited thereon," said Dei. "Just as we’ve seen an evolution in carbide grades, there has been a corresponding rapid development in coating materials and technology. When it comes to carbide, our engineers and designers match the grade according to a wide field of parameters, including size of the tool, the application, the material being cut, and the speeds and feeds involved.
"Coatings likewise have come a long way, and our latest PVD-BLU has met with enthusiastic acceptance in applications ranging from heavy-duty threading in the energy sector, to our new line of tools for Swiss-style machines. BLU is a new harder submicron substrate with the latest nanocomposite coating-AlTiN/SiN. BLU can be used for heat-resistant materials like Inconel, Hastelloy, Monel or other nickel-based materials as well as titanium and austenitic stainless steels," said Dei. ME
For more information from Carmex Precision Tools LLC., go to www.carmexusa.com, or phone 262-628-5030.
is Quick and Accurate
Unilock zero-point clamping systems from BIG Kaiser Precision Tooling Inc. (Hoffman Estates, IL) are designed for quick, efficient part loading for low and high-volume production runs for almost anything manufactured or assembled. Zero-point clamping enables datums to be transferred along with the part when parts are moved from machine to machine, eliminating the need to indicate the part setup on the next machining process. The savings in setup time alone, not to mention accuracy, can be substantial.
Originally, zero-point clamping was developed to prove out copper or graphite electrodes that were machined on milling machines and were then mounted on a supporting plate that was transferred to an EDM machine," said Gerard H. Vacio, BIG Kaiser Precision Tooling Inc. "The intent of zero-point clamping initially was to be able to share the same datum systems from the milling machine that was going to make the electrode as the datum system on the quill of the EDM machine on which it was going to be used."
The technology worked so well for sinker EDMs that many wondered why it wouldn’t work on other manufacturing processes. "Zero-point clamping would involve taking the coordinate system and geometry form right over to the mill, to the lathe, or to the grinder by replacing the concept of the T-slot table or a grid plate with something that had only one XYZ location. Whenever the datum was transferred to a machine, you always knew exactly where it would be," said Vacio.
"The zero-point clamping system is called zero point because when there are multiple receivers on the machine table any one can be designated the zero point in establishing the coordinate system," said Vacio. "Any time you have to locate something specifically in 3D space you can do that by establishing two fixed points underneath that component. With three or more receivers on the table, any one can be selected as the XY coordinate datum and be the zero point. A second location orients about zero and the remaining locations provide downward clamping force for stiffness and rigidity. Zero-point systems allow you to look at a blueprint, determine design intent, then find a way to pick which one of the receivers on your machine table will do the best job of establishing location based on your print," said Vacio.
All zero-point clamping systems aren’t created equal. "Unilock incorporates design improvements to enable handling large tables, larger work areas, larger parts, and heavier cuts. The retention knob that hangs off of the bottom of the fixture plate was shortened for rigidity and positioned closer to the cutting area. A wedge design for surface-to-surface gripping has replaced the ball bearing for better contact, allowing more downward energy to be applied for clamping," said Vacio.
BIG Kaiser’s Unilock system includes chucks and components for virtually any application, including thin-walled tombstones, the face of fourth or fifth-axis rotary tables, large diameter heavy-duty applications, large-diameter flange designs, and even through-hole rotary tables for lathes or mills. For five-axis machine tables, flexible workholding is achieved by surrounding Unilock zero-point quick change receivers with a grid pattern. "The benefits of five-axis machines are greatest when workholding is based on the size and shape of the workpiece and not by the limitations of the table interface," said Vacio.
"By providing multiple workholding opportunities, Unilock users can quickly integrate most workholding products and keep their machine spindles up and running," said Vacio. If the optimal work zone is directly over the center of the machine table, low-profile grid plates with integrated Unilock zero-point clamping systems are available, out of the box, as turnkey solutions. Offering capscrew and dowel pin technology intermixed with Unilock zero-point chucks baseplates allows rapid loading of virtually any workholding product including five-axis vises and dovetail clamping solutions."
Quick-change solutions are available for five-axis machine tables as well as fourth and fifth-axis tables on three-axis machining centers. "Workpieces can be pulled down onto the table to maximize the available envelope. If the workpiece needs to be elevated above the table and that feature isn’t built into the workholding component, Unilock can be used to raise the workholding or the workpiece for complete five-sided access. Unilock clamping knobs can also be attached directly to the bottom of the workpieces and within 25 mm of the machining edge. Unilock zero-point clamping chucks can also be surface mounted directly to the machine table, and five-axis clamping products, DoveTail Grip and FirstClamp can also be directly affixed to a machine table or a grid plate or processed in Unilock chucks," said Vacio. ME
For more information from BIG Kaiser Precision Tooling, go to www.bigkaiser.com, or phone 847-228-7660.
This article was first published in the April 2013 edition of Manufacturing Engineering magazine. Click here for PDF.