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4-axis cutting with SINUMERIK Operate

Tangible productivity advantages - that’s what users gain from machining on the same machining profile simultaneously with two turning tools. Modern CNC controls make it possible to program this highly sophisticated machining task directly on the machine without the need for a CAD/CAM system.

Working efficiently with two tools

The prerequisite for four-axis turning, also known as balance cutting, is a turning machine with at least two independent tool carriers. As a rule, this involves one tool turret behind the rotation center and a second in front of the rotation center. The machine has to be designed in such a way that both tool carriers can be engaged on one workpiece simultaneously - one on the main spindle and one on the counter spindle. If both tool carriers are moved independently, two independent CNC programs are executed simultaneously, thus activating a multi-channel structure in the CNC control system.

In this respect, four-axis chip removal can be considered a special form of multi-channel machining: simultaneous machining with two identical tools (for example two 80-degree roughing inserts) on one machining profile of the workpiece. Balance cutting offers two significant advantages compared with machining using only one cutting insert: First, when machining long, thin components, the balancing of the cutting forces increases the dimensional accuracy, since the use of two opposite cutting inserts eliminates the distortion of the workpiece resulting from the cutting force. Second, the cutting volume per time is increased. There are two possible strategies for achieving these benefits: either synchronous or offset tool path control.

Everything in one channel

In synchronous path control, the cutting inserts are always exactly opposite each other. The two compound slides of the turrets therefore perform exactly the same movement in the respective x and z geometric axes. Because the cutting thickness is distributed equally on both cutting edges, the feed per revolution can be doubled. As a result, the chip volume per time is doubled in comparison with machining using only one cutting edge. But what happens in synchronous path control in the SINUMERIK CNC? First, the activation of the tool length corrections and the approach to the machining start point are carried out independently in both CNC channels. Next, the x and z axes of one channel (the following channel) are transferred to the guide channel and carried along position-synchronously. This means that the CNC sets responsible for the machining are processed only in the guide channel, and the following channel remains in the waiting position during the machining.

Synchronous path control is equally suitable for roughing and finishing. However, to avoid measuring inaccuracies, the two cutting inserts need to have a tool radius that is as identical as possible, because the guide channel’s tool radius correction also has an effect on the second tool carrier.

Separate CNC positioning sets for each tool

In offset path guidance, the two compound slides carry out different movements. In other words, in longitudinal turning, the cutting inserts work on different diameters, and in face turning, the cutting edges work at offset Z positions. In both cases, this results in a doubling of the effective tool feed rate. Due to the path offset, however, the CNC channels have to be synchronized for each feed, resulting in brief waiting times, which is why the cutting volume per time cannot be exactly doubled compared with machining using only one tool. The offset movements of the two compound slides generally require independent CNC programs in both CNC channels. The two CNC channels are synchronized with each other only during feeds by means of WAIT marks. Because the two cutting tools work with different feeds, offset path control is suitable only for roughing.

Cross-channel CNC programming

In order to enable such complex operations to also be programmed directly on the machine without a CAD/CAM system, Siemens has expanded the proven and efficient SINUMERIK Cycle952 contour machining cycle: the contour and the basic cutting parameters now need only to be programmed in the guide channel. What’s more, the CNC sequences required for the respective four-axis turning strategy are created fully automatically by the contour machining cycle. With just two parameters "on top," machining with one tool can be extended into highly productive balance cutting with two tools.

Video 4-axis turning

Watch the video to see more about 4-axis turning and balance cutting.

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