Peter Zelinski has been a writer and editor for Modern Machine Shop for more than a decade. One of the aspects of this work that he enjoys the most is visiting machining facilities to learn about the manufacturing technology, systems and strategies they have adopted, and the successes they’ve realized as a result. Pete earned his degree in mechanical engineering from the University of Cincinnati, and he first learned about machining by running and programming machine tools in a metalworking laboratory within GE Aircraft Engines. Follow Pete on Twitter at Z_Axis_MMS.
What machining capability is the right complement to additive manufacturing? For Star Prototype, the answer is a UMC-750 five-axis vertical machining center from Haas Automation (seen here when it was newly purchased in June 2015) programmed using Delcam’s PowerMill software.
The British-owned company based in Guandong Province, China, combines metal 3D printing and five-axis machining to quickly deliver complex, low-volume components that might previously have required the work of two separate suppliers. It calls this service AddSub Manufacturing.
“Many metal 3D printed parts are no longer used as prototypes but as complex low-volume manufactured components,” says Gordon Styles, president of Star Prototype. “As a result, many of these parts need certain high-precision features that are virtually impossible to produce with 3D printing alone.”
The company uses a Renishaw AM250 direct metal laser melting machine to produce dense, complex metal parts in titanium, stainless steel and aluminium. The challenge of machining those parts is not the amount of stock to remove, because the parts are so near to net shape. The machining challenge instead comes from the geometric complexity that additive permits, which led to the five-axis machine purchase. (Indeed, the connection between complex machining and additive manufacturing is a point Delcam recently highlighted in a test case with additive production.)
Star uses five-axis machining to add features to additive parts such as mating faces, precision bores and tapped holes. Whenever possible, the company says, parts are built on the AM250 in a useful orientation for machining, with supports designed so that the build plate can be transferred directly to the five-axis machine.
Chatter is self-excited vibration. We often think of controlling chatter as a challenge that relates to milling. However, chatter can be a factor in turning, too. This video from Haas Automation describes “Spindle Speed Variation,” a parameter in the company’s CNC that addresses chatter on lathes.
As the name implies, this parameter allows the lathe spindle speed to automatically vary. The user sets the speed variation envelope (say, ±100 rpm) along with the period of time for cycling through this range (in increments of 0.1 second). In the video, a lathe running at 2,000 rpm ±100 rpm is seen under a strobe light. The strobe picks up the speed variation, making it look as though the spindle is rocking back and forth.
This solution works to overcome chatter because chatter is speed-specific. Certain spindle speed values resonate with the overall machining system. Varying the rpm potentially stabilizes the cut because it means that the lathe spends only an instant at a time at any problematic speed.
The video illustrates the impact by showing the turning of a long bar, unsupported by a tailstock. The bar chatters when turned at consist speed, but then can be turned precisely and quietly once the variable speed is turned on.
A small slice of the infographic. Click on the link below to see the entire illustration.
MMS’s outreach to future manufacturing professionals typically focuses on careers in machining. A closely related field is welding, and the Tulsa Welding School has recently produced a detailed infographic summarizing the work, opportunities and compensation in this field. Most of the jobs are in manufacturing, but the illustration points out the traveling job opportunities as well. It also notes the increasing extent to which welding work involves automation. For the benefit of a young person in your life who might make a good welder or welding technician, find the complete infographic here.
I’ve noticed how some shops here and there have improved their lighting, recognizing that both the accuracy and the psychology of the shop stand to improve with better ambient light.
3V Precision has arguably taken the next step, giving thought to ambient sound. In this Tacoma, Washington, job shop, there are no competing radios at different toolboxes, or boomboxes struggling to be heard over the machines. Instead, a sound system appropriate to the shop’s noise and acoustics has been installed with speakers mounted high above the machines. Two of those speakers are visible in this photo. As the machine tools run here, upbeat music playing through them can be heard at a level that does not seem loud, but nevertheless comes through clearly enough to sing along.
The music is selected by shop owner Peter Boucher, and he keeps it light. Read more about Mr. Boucher, 3V Precision and this shop’s attention to employees.
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.