Different types of CNC machines cover rather large variety. Number of installations is rapidly increasing, and the technology development advances at a rapid pace. It is impossible to identify all possible applications, they would make a long list. Here is a brief list of some of the groups CNC machines can be part of:
- Mills and Machining centers
- Lathes and Turning centers
- Drilling machines
- Boring mills and Profiles
- EDM wire machines
- Punch presses and Shears
- Flame cutting machines
- Water jet and Laser profiles
- Cylindrical grinders
- Welding machines
- Benders, Winding and Spinning machines, etc.
Without a doubt, CNC machining centers and lathes dominate the number of installations in industry. These two groups share the market just about equally. Some industries may have a higher need for a particular type of machines, depending on their needs. One must remember there are many models of lathes available and equally many different models of machining centers. However, the programming process for a vertical machine is similar to the one for a horizontal machine or even a simple CNC mill, for example. Even between different machine groups, there is a great amount of general applications, while the programming process is generally unchanged. For example, a contour milled with an end mill has a lot in common with a contour cut with a wire on an EDM machine.
Mills and Machining Centers
Minimum number of axes on a milling machine is three – the X,Y and Z axes. Part set on a milling machine is always stationary, mounted on a moving machine table. The cutting tool rotates, it can move up and down (or in and out), but it does not physically follow the tool path.
CNC mills – sometimes called CNC milling machines – are usually small, simple machines, without a tool changer or other automatic features. Their power rating is often low. In industry, they are used for tool room work, maintenance purposes, or small part production. They are usually designed for simple contouring, unlike CNC drills.
CNC machining centers are far more popular and efficient than drills and mills, mainly for their flexibility. The main benefit users get out of a CNC machining center is the ability to group several diverse operations into a single setup. For example, drilling, boring, counter boring, tapping, spot facing and contour milling can be incorporated into a single CNC program operation. In addition, the flexibility is enhanced by automatic tool changing, using pallets to minimize idle time, indexing to a different face of the part, using a rotary movement of additional axes, and number of other time saving features. CNC machining centers can be equipped with special software that controls cutting speeds and feeds, life of the cutting tool, automatic in-process gauging, broken tool detection, offset adjustment and other production enhancing and time saving devices.
There are two basic designs of a typical CNC machining center. They are vertical and horizontal machining centers. The major difference between the two types is the nature of work that can be done on them efficiently. For a vertical CNC machining center, the most suitable type of work are flat parts, either mounted to the table fixture, or held in a vise or a chuck. The work that requires machining on two or more faces (sides) in a single setup is more desirable to be done on a CNC horizontal machining center. A good example is a pump housing and other cubic-like shapes, often irregular. Some multi-face machining of small parts can also be done on a CNC vertical machining center equipped with a rotary table.
Programming process is the same, but an additional axis (usually B axis) is added to the horizontal version. This axis is either a simple table positioning axis (indexing axis), or a fully rotary axis for simultaneous contouring.
Lathes and Turning Centers
A CNC lathe in its basic form is a machine tool with two axes, vertical X axis and horizontal Z axis. The main feature of a lathe that distinguishes it from a mill is that the part is rotating about the machine center line. In addition, the cutting tool is normally stationary, mounted in a sliding turret. Cutting tool follows the contour of the programmed tool path. Many modern CNC lathes are much more than just turning centers – with a simple milling attachment, the so called live tooling, the milling cutter has its own motor and rotates while the spindle is stationary. More complex designs incorporate off-center milling, double spindles, double turrets, part transfer, and many other efficiency improving features. These machines are generally called the mill-turn centers or sometimes the turn-mill centers.
Modern lathe design can be horizontal or vertical. Horizontal type is far more common than vertical type, but both designs have their purpose in manufacturing. Several different designs exist for either group. For example, a typical CNC lathe of the horizontal group can be designed with a flat bed or a slant bed, as a bar type, chucker type or a universal type. Added to these combinations are many accessories that make a CNC lathe an extremely flexible machine tool. Typically, accessories such as tailstock, steady rests or follow-up rests, part catchers, pullout-fingers and a third axis milling attachment are popular components of CNC lathes. A CNC lathe can be very versatile – so versatile in fact, that it is often called a CNC Turning Center.