The Benefits and Limitations of Machining With an Angle Head
Far from being outdated by the latest machine tool technology, angle heads often prove an ideal complement by pushing done-in-one capabilities even further. Proper application, however, requires attention to their limitations as well as their benefits.
Even amid the ongoing proliferation of increasingly sophisticated multi-axis machine tools, the relatively simple angle head still plays a critical role in the production of complex-geometry parts. That’s the picture painted by sales data from Big Kaiser Precision Tooling, which reports robust use of angle heads among aerospace and energy industry customers in particular. During a recent presentation, engineering and product manager Alan Miller covered the advantages and the limitations of these tried-and-true accessories.
By adding another axis to an existing machining center, an angle head enables the tool to reach part features that would otherwise be inaccessible. That’s a key advantage for aerospace manufacturers contending with increasingly stringent delivery and accuracy requirements for parts with more sculpted, curved geometry than ever before. To meet that demand, these shops often turn to five-axis and multitasking machines that can eliminate multiple setups and the associated potential for stackup error. Still, without an angle head, features like internal scallops can prevent single-setup production on even the most flexible equipment, Mr. Miller says. Other parts, particularly in the energy industry, have complex internal features that could be impossible to produce any other way, even with multiple setups.
Given these possibilities, manufacturers often have high expectations for angle heads—expectations that must sometimes be tempered. It’s important to remember that an angle head is a spindle attachment, not a direct output from the spindle, Mr. Miller says. As such, its rigidity is inherently limited, as are horsepower and thrust (even the heaviest-duty units are limited to about 5 hp). Thus, users should take care with chip loads and cutting depths, and aggressive climb milling techniques with carbide tools simply aren’t practical in applications involving any material harder than 40 HRc. Conventional milling with high speed steel cutters is a better option to avoid deflection or chipping the tool. “If you could do it on a knee mill, an angle head can probably handle it,” Mr. Miller says. “But if it’s something that’s going to take a 20-hp cut on a milling machine to pull off, you should probably rethink what you’re doing.” He adds that cycle times should be limited to about 30 minutes with an angle head running anywhere close to maximum speed because the units rely on external coolant.
After determining that an angle head is a viable option, customers often raise questions about programming, Mr. Miller says. Although most CAM systems have built-in functionality for angle heads, users should keep in mind that many software packages use the older term “aggregate heads” to refer to the attachments. Shops without a CAM package can employ canned cycles as long as the machine’s CNC offers the functionality to select the proper plane for cutting. On FANUC controls, for example, axes can be “flipped” using the G17, G18 and G19 commands. The G68 command can also adjust the machine coordinate system if the head is not set up along a common machine axis, although he points out that this is much more complicated. Without a CAM system or a CNC capable of the aforementioned functions, programming by hand using G1 commands is the only option. In that case, macros can provide significant time savings if the same head is employed repeatedly in the same types of applications.
Another common difficulty with implementing angle heads involves stop blocks, which mount to the spindle and engage with the head’s locating pin to prevent it from rotating out of place during operation. These accessories require a precise fit with the spindle of a particular machine model, and attaining that fit often requires working with customers to design and dimension custom subplates, Mr. Miller says. Typically, proper mounting locations, bolt hole patterns and other needed dimensions can be found in the machine’s manual. The fact that many machine tool builders have standardized on pin designs from Big Daishowa, the Japanese designer of Big Kaiser’s angle heads, makes this process easier, he notes.
Far from being outdated by the latest machine tool technology, angle heads can push done-in-one capabilities even further. Proper application, however, requires attention to their limitations as well as their benefits.
Companies concerned about strict quality requirements regularly check toolholder tapers for wear or inaccuracy because these conditions can jeopardize the results of a critical operation. However, a shop can check tapers quickly and reliably with air gages. These devices can be used effectively without special operator training. For measuring taper in a production environment, few other methods can match the speed and performance of air, as multiple-circuit air jets can be placed in very small taper gages.
Collet toolholders are too important to the machining process to use them incorrectly. Follow this simple advice.
A reader recently asked about speed, feed rate and depth of cut when using small tools in steel.