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.
Tech Manufacturing runs the spindles hard on its five-axis profilers. The Missouri shop uses these machines to take heavy cuts at high speed for machining large aircraft parts. Periodic spindle replacement is a fact of life and an acceptable cost for this shop.
But the problem was that spindle failure was occurring by surprise. Analysis of machine performance data revealed spindle replacement to be the leading cause of unplanned maintenance downtime for the shop. If this event could instead be planned maintenance downtime, so the shop could schedule spindle replacement within its workflow, then that change would represent a meaningful efficiency improvement. In short, the shop needed to find a way to predict that a spindle was about to fail.
The team members here searched for the telling clue. They tried periodic tap testing. They tried drawbar force tests.
The reliable indicator proved to be temperature.
Just after a milling cycle, the temperature inside one of the profiler’s spindle tapers is generally about 120°F (49°C). But observation of this temperature over time revealed that it reliably increases as the spindle begins to near the end of its life. The increase comes early enough that the shop has time to order a new spindle and schedule the needed replacement.
Now, the shop watches this indicator. Employees routinely measure spindle temperature in search of this increase. They use a digital thermometer for this measurement, but it is possible that this precise device is not even needed. Now that the team members running the profilers are aware of this effect, they can often detect it in the heat of the toolholders when they are manually changing out tools between jobs.
Transforming unplanned spindle replacement into planned maintenance was part of a broad process improvement effort for Tech Manufacturing. Read more about that effort.
Open capacity at 3D-Machine can sometimes involve large-capacity machines, such as the one seen here. The shop uses the distributed manufacturing platform to obtain business from unknown companies without any of its own sales efforts.
MakeTime, the young company connecting buyers and sellers of machining services through a distributed manufacturing platform, describes itself as a “virtual machine shop of CNC machining services from qualified U.S. suppliers.” (In a nod to the popular lodging rental website Airbnb, the company also describes itself as “AirCNC.”) We first wrote about MakeTime in detail in this article, which is still essentially correct. But one important change is this: The company no longer requires shops involved in the platform to spend time on bidding. To improve efficiency, MakeTime now generates fair-market pricing for every job, with buyer and seller simply choosing whether to accept that price.
Removing bidding helps reinforce a point the company takes pains to stress: It’s not an RFQ site. Instead, the idea underlying MakeTime is capacity matching. Buyers upload machining projects, while sellers (machine shops) list their machine tools and their windows of open capacity. MakeTime’s automated process then puts the jobs and capacity together. In addition to performing costing, MakeTime also provides for file preparation, payment management, materials procurement and logistics scheduling. The company does not charge a fee, but collects a percentage of the payment for each successful job.
A recent press statement from the company included two quotes from users of the platform. From a machine shop:
“MakeTime has helped us grow our business without hiring outside salespeople,” says Greg Richardson, owner of 3D-Machine, a Georgia-based independent machine shop. He says the platform also “enables us to tap into a much larger customer base.”
And from a buyer of machined parts:
“Before MakeTime, we were doing most of our production overseas and trying to juggle expectations with different vendors,” says William Davidson, owner of Hybrid Racing, a Louisiana-based aftermarket auto parts supplier. “Now we’re able to move some of our production back to the U.S. because I can get my parts quicker while remaining cost-competitive.”
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.