CNC lathe setup: structure and function
Turning is one of the machining processes. Turning is characterized by the cutting movement performed by the workpiece. The auxiliary movement - i.e. feed and infeed - is generated by the tool with the aid of a longitudinal and cross slide. If very slim workpieces are being machined, they can be supported with a steady rest. The design of a CNC lathe has evolved over the past few decades: from a simple lathe, which is usually set and operated manually, to a modern CNC machine.
In addition to the main spindle and the turret (tool carrier), these include the following options:
- A counter spindle for 6-sided complete machining
- Driven tool positions on the turret
- A Y-axis for off-center machining
High-tech on the inside: what makes CNC machines so special
The letters NC are synonymous with the English word "Numerical Control". They describe the control of a machine by entering numbers. If this control is carried out with the aid of a computer, it is referred to as "Computerized Numerical Control", i.e. CNC machines. These CNC controls are used to control and regulate machine tools, including lathes. In addition to the CNC, lathes always consist of a frame, a lathe bed, a so-called headstock, the tool slide, a counter spindle for a 6-sided and a Y-axis for off-center machining and an optional tailstock as well as a steady rest.
Design of CNC lathes: from simple to complex
Lathes are used worldwide and in a wide range of industries. Experience has shown that each industry has its own standards, procedures, norms and regulations for its production. This results in different requirements for the operation and control of a CNC lathe. The following example illustrates this: If a lathe is used in high-volume production for the automotive sector, for example, and components with little variance are manufactured, the machine is operated and programmed relatively little. The focus here is on high efficiency, short non-productive times, maximum process stability and therefore component quality. On the other hand, in mold making or contract manufacturing, for example, production is often carried out with a greater number of variants and in small batches. This requires more frequent operation of the machine. In order to provide the industry with the greatest possible number of machining options, machine tool manufacturers such as DMG MORI are continuously developing CNC lathes. For example, there are now lathes with more than one turret (2 ¾) for holding several tools and the B-axis function - an interpolating movement of the tool. The horizontal and vertical movements of the tool that are possible here allow the machining of complex components.
Types of components
Regardless of the place of use or the technical production requirements, the structure of CNC lathes is made up of the following components:
- Frame: load-bearing element (usually made of gray cast iron) that supports all moving and fixed elements of a machine. It guarantees stability and strength, prevents vibrations and ensures accuracy.
- Lathe bed: base plate on which a machine is mounted. The lathe bed provides a stable and level base so that tool slides and other moving parts can move smoothly.
- Headstock: contains the main spindle that rotates a workpiece. The headstock is responsible for the precise rotation of a workpiece. It can also accommodate different clamping devices (chucks, collets).
- Counter spindle: is a second spindle that rotates in the opposite direction to the main spindle. It enables workpiece machining from 6 sides without having to reclamp the workpiece. Machines with a counter spindle are now standard: The NLX 2500 SY700 - a universal lathe with Y-axis and counter spindle - is now one of the best-selling machines from DMG MORI.
- Driven tool positions in the turret: can be moved by a motor to increase precision.
- Y-axis: for off-center machining enables complex workpieces to be machined off-center.
- Feed drive: is responsible for the movements of the tool slide and other moving parts along the desired axes. It ensures precise and controlled movements during the turning process.
- Tool slide: carries the cutting tool and moves it precisely along the desired axes to machine the workpiece. The slide can be moved in several directions and therefore enables different cutting processes.
- Tailstock: is the counterpart opposite the headstock and supports it. The tailstock can be moved along the machine bed. It has a rotating center to keep the workpiece stable.
- Steady rest: additional support to stabilize long workpieces during processing. This also prevents the workpiece from bending or swinging.
- CNC control technology: supplies and converts digital data into machine data to achieve a fully automatic sequence of all functions within a machining operation.
- Coolant/lubricant: independent circuit within a machine to lubricate and cool moving components using so-called cooling lubricants. They are relevant for machine safety and component quality.
This is how a turning process works
Before the turning process - i.e. CNC machining - starts, a previously created program with machining sequences or motion sequences is loaded by the operator. The workpiece is also clamped in the spindle. The choice of cutting tools is based on the turning task and the workpiece material. Once all the tools have been defined, they are clamped in the turret - a tool holder for several tools. The CNC lathe is now ready for the CNC machining process, during which the workpiece rotates and the cutting tool removes material from the workpiece according to the specified parameters.
Many variants: different turning processes
Simple turned parts are given their shape by a feed movement in the direction of the axis of rotation or perpendicular to it. The different turning processes are named according to the directional feed movement.
- Long turning: The turning tool moves parallel to the workpiece axis (usually from left to right) with the aim of turning a cylindrical component to a specific diameter.
- Facing: The tool moves perpendicular to the workpiece axis with the aim of machining an end face or a shoulder. The direction of movement of the turning tool depends on the task and the cutting edge.
- Turning: The tool moves parallel or perpendicular to the workpiece axis.
- Piercing: Turning process for producing certain groove shapes.
- Cutting: Special form of recess turning in which the workpiece or a section of it is completely separated from the blank. The main cutting edge of the tool can not only be inclined, but also straight.
- Cut out: Description of grooving, in which the feed direction of the grooving tool is parallel to the workpiece axis.
- Profile turning: The main cutting edge of the turning tool has the profile shape to be produced. - Taper turning: Long turning with decreasing diameter and thus creating a conical shape.
- Thread turning: Long turning process in which the feed rate is the decisive factor in determining the thread pitch.
- Shape turning: Individual feed and cutting movements create a specific shape.
- Copy turning: Here, the workpiece shape is picked up from a template and transferred to longitudinal and cross slides.
Horizontal or vertical: lathe designs
The position of the spindle defines the machine type: In vertical machines, the spindle is vertical and the workpiece is clamped horizontally or suspended. In horizontal machines, the spindle is horizontal and the workpiece is held upright. For very large workpieces with large diameters such as large flanges (> 1 m), for example, it may make sense to carry out machining on a vertical lathe. In addition to easier clamping (depositing by means of lifting technology from above), the forces that occur can be managed much better with this design. Machines of this type are usually designed in portal or gantry construction. Horizontal lathes are usually designed as a console column or cross table design. These CNC lathes are used to machine particularly long workpieces. DMG MORI also has machines for horizontal production turning in its portfolio.
In addition, so-called turn-mill machines are now also standard in everyday industrial use. This term covers technologies in which the machining spectrum is extended by an automatic tool change and often a milling spindle with its own drive unit and/or additional equipment. The diversity and rich variety of CNC lathes, universal lathes and the aforementioned horizontal versions make DMG MORI a manufacturer of machine tools that can reliably cover the entire spectrum of turning tasks.