Which 5-axis machining center is right for you? DMG MORI explains

With so many choices in 5-axis machining technology, how do you know which is best for your shop? First, consider the parts. Then, look at existing processes and potential 5-axis benefits.

There are plenty of reasons to take advantage of today’s 5-axis machining technology. First, it gives you access to all five sides of a prismatic workpiece. If for no other reason than being able to eliminate additional setups or processes, this technology can be justified in a wide range of applications, and at a surprisingly affordable cost. As the parts get more complex, the payback increases with the ability to generate intricate workpiece features or contours that cannot be machined efficiently, or at all, with a conventional three-axis machining center.

But with so many ways to go about 5-axis machining, how do know what is the best buy for your shop? DMG MORI’s general manager of Aerospace Center of Excellence, Jeff Wallace, offers some insight.

With some 47 models of 5-axis machines in a variety of configurations, he says, DMG MORI is well-positioned to address the transition to increasingly sophisticated 5-axis machining technology. Whether you’re looking to introduce five axes for the first time or need higher machining capacity, there are a wide variety of options to consider.

Why 5-axis machining?
Some people mistakenly think 5-axis technology is only for the most complex parts. While it certainly excels at that, a significant majority of the applications are simply used to enable the machining of five sides of a workpiece in a single setup. With three-axis machining, jobs might require two, three or more setups to get at all the features of the part. With the done-in-one approach, those additional setups are eliminated in addition to potential for error each time you reposition a part. The justification for a 5-axis machine on these grounds is simple, with dramatic reductions in total setup, machine time and reduced fixturing.

Another inherent advantage of 5-axis machining is it can use shorter tools because the tool/toolholder combination can be tipped away from otherwise interfering surfaces or features on the workpiece. This is particularly important in die/mould work where the use of toolholder extensions is common to reach deep cavity surfaces. A shorter tool results in less vibration, allowing for heavier or faster cutting, better surface finish and longer tool life.

Particularly for job shops, 5-axis machining enables complex parts to be cut from solid material that otherwise might have to be cast. This enables quick turnaround for short-run and prototype work on high-value parts. It’s a great opportunity to differentiate the shop from lower tech competitors and build a more profitable business.

Five-axis technology that fits the part
First, consider your parts. How big are they? How much do they weigh? What levels of accuracy do they require?

For example, if the parts are small to medium size, with today’s technology, a tilting-table-type machine is going to be the best bet. If the parts are large and heavy, an articulating head possibly on a gantry-style machine or a horizontal machining center may be the only option. This consideration alone will narrow your choices and help you compare features of various machine models within the required range.

Starting with 3+2 machining centers
The simplest and least expensive way to get at five sides of a part is with a 3+2 machine configuration. For small to medium machines, that typically means a three-axis machining center with a tilting rotary table to position the part. This of course can be accomplished with an auxiliary two-axis table on a standard three-axis machining center. But a machine with an integrated tilt table offers better machining performance and is easier to set up and programme.

With a 3+2 machining center, the fourth and fifth axes are locked down while the part is machined. Still, almost any plane of the workpiece can be presented to the spindle, and surprisingly complicated parts can be cut efficiently.

In DMG MORI’s case, a swivel rotary table is integrated into the CMX U series of 3+2 machines. With a C-frame construction, Wallace says, these universal machining centers also allow the spindle to be set in a vertical or horizontal orientation.

Moving up to full 5-axis machining
The next step up is adding full simultaneous contouring control to an otherwise similar machine configuration, represented by DMG MORI’s DMU series. The primary advantages of full 5-axis control are that you can now dynamically tilt the tool into the cut, away from interference zones, or keep the tool vector constant as it feeds across sloped or free flowing surfaces. These are the reasons why 5-axis machining is so widely used for aerospace components, orthopaedics and other parts with curving features.

For several other kinds of parts, 5-axis facilitates more efficient use of cutting tools. Tilting the cutter relative to the workpiece surface supports better utilisation of the milling flutes, often cut with the side rather than the end of a cutter.

Moreover, with a 3-axis process, there is little alternative to the ball nose end mill to generate contoured surfaces. To get a smooth surface requires multiple passes with very small step-overs, which takes a lot of machine time and may still require another secondary process to smooth the cusps. With 5-axis machining, you can even use a flat nose end mill to generate some of the contoured surfaces. In a process sometimes referred to as “sturtz milling,” the tool is tilted into the cut presenting the radius of the tool to the surface of the part.

The ability to access more features of a part is simply more pronounced with full 5-axis control, as the tool can dynamically tilt away from interference zones on the part. Full 5-axis control provides the opportunity to detail hard-to-reach features such as the corners of pockets or bosses and create smoother surfaces in the process. This capability can eliminate the need for secondary processes, such as sinker EDM in die/mould work.

Higher precision and production
Higher part precision requirements in production environments place higher demands on a machine’s construction and motion control system. Rising to these demands, DMG MORI’s NMV series is a vertical machine with the column (X and Y axes) travelling overhead in a “box-in-box” construction.

Another 5-axis machining platform option is DMG MORI’s DMU monoBLOCK series. This machining platform series offers a wide variety of options so that machines can be better configured for multiple applications. It can achieve even higher levels of precision with a cooling system that covers the servo motors and mounts, the C-axis gearbox and an internally cooled X-axis ballscrew. The machine features a multi-sensor system feeding a real-time control system that can compensate for small errors caused by thermal conditions, workpiece inertia, or other physical factors.

Software considerations
What still scares many people about 5-axis machining is the part programming. However, CAM systems have evolved in recent years and become much easier to use. These systems include features where programmers can create 5-axis toolpaths and still work largely within the 3-axis context in which they are accustomed. As a result, shops can employ familiar cutting strategies augmented by the additional workpiece features that 5-axis machining provides.

On the machine, controls have become much more user friendly. For example, DMG MORI’s CELOS control automatically checks for interference in 3D for spindles, tables, tools, workpieces and fixtures. Once a problem is detected, the machine will stop operation, whether it is in automatic or manual mode.

For more information contact Retecon Machine Tools on TEL: 011 976 8600 or visit www.retecon.co.za