Introduction
CNC lathes are one of the most widely used CNC machine tools. They are primarily used to machine symmetrical rotating parts, such as shafts, inner and outer cylindrical surfaces of disc-like parts, inner and outer conical surfaces with arbitrary taper angles, complex rotating inner and outer curved surfaces, and cylindrical and conical threads.
Even the most common turning of contours has different processes. In the SINUMERIK CNC system, all these process options are covered by the three categories of “transverse turning”, “longitudinal turning (also called “reciprocating turning”)” and “grooving”. Let’s take a look at them together.
Characteristics of transverse turning:
- In transverse turning, the direction of movement of the turning tool is parallel to the axis of rotation of the workpiece.
- The tool moves from right to left if the machine is equipped with a main spindle and from left to right if the machine is equipped with a sub-spindle.
- Transverse turning can be used to machine both external and internal holes. However, when machining internal holes, a pilot hole must be pre-drilled first.
- In addition to machining the outer circle, end face machining is also possible.
Longitudinal turning, grooving and cutting
Characteristics of longitudinal turning of the side and end faces (also called “reciprocating cutting ” ) :
When longitudinally turning the side of a workpiece, the feed direction of the longitudinal turning tool is perpendicular to the axis of rotation of the workpiece.
In longitudinal turning of the workpiece end face, the feed direction of the longitudinal turning tool is parallel to the workpiece axis.
Sliding turning tools have three cutting edges, which allows the material removal process in the radial and axial directions to be as uninterrupted as possible.
Grooving knives and slitting knives have different blade shapes and tool body shapes.
Features of groove cutting on the side and end faces:
- When grooving, cutting is performed only in the infeed direction.
- The side grooving process is performed perpendicular to the axis of rotation.
- The face grooving process is performed parallel to the axis of rotation.
- Grooving tools can only withstand forces applied perpendicular to the tool axis.
- Grooving is the process used to produce grooves. Usually (but not always) the groove to be produced is as wide as the grooving tool.
Characteristics of cutting process:
- At the end of the machining process, the workpiece is cut off by a cutter.
- The cut-off cycle consists of an “assistance cut” and the actual cut-off process. The assistance cut ensures better chip evacuation.
- Parting off requires the tool to be fed beyond the center of rotation of the workpiece.
- It is often necessary to reduce the spindle speed before parting to provide better control over the rotating part being parted.
Turning case study using SINUMERIK Operate
As shown in the following three pictures, it is impossible to complete the processing of this handle part using only one cutting process, because the tool will not be able to process it in place or interference will occur when it reaches the position marked by the orange circle in the picture.
Groove cutting process:
Longitudinal turning process:
Transverse turning (or “reciprocating turning”):
Therefore, we need to combine the two processes of transverse turning and longitudinal turning to obtain the simulation effect shown below.
Note: Grooving and reciprocating turning are optional functions on the 828D PPU240 system. Option number (extended technology functions): 6FC5800-0AP58-0YB0.
Conclusion
Transverse turning:
- Allows for higher infeeds, i.e. larger chip cross-sections.
- Higher feed rates are possible during roughing.
- Perfect chip removal.
- Not all contours can be processed by transverse turning using limited tools, and more tool changes may be required during the process.
Longitudinal turning:
- Avoids empty cutting strokes.
- Reduced tool changing operations.
- High flexibility in application.
- Due to tool limitations, not all contours can be machined.
- Chip evacuation is sometimes not optimal (chips may get stuck).
When to use which process?
Longitudinal turning is generally used for machining parts with deep grooves and 90ยฐ corners, which can only be machined using this process.
Transverse turning is generally used for streamlined contour structures with arc transitions.
