Machining centers are machine tools that are used to automatically repeat operations on a workpiece. Common operations include drilling, reaming, tapping, milling, and boring. Most machining centers are numerically controlled. A CNC machining center uses computerized numeric control (CNC) to manufacture complex parts in metal or other materials. Typically, a CNC machine center uses a program which conforms to the EIA-274-D standard, commonly called G-code. A drill center automates the drilling of holes in a workpiece. A milling center automates the cutting, shaping, finishing, or working of products manufactured in a mill. In facilities that use lean manufacturing practices, machining centers can be an integral part of workcell design.
Machining centers vary by how much xyz travel is required. For example, 5-axis machining provides the ability to machine complex shapes, undercuts and difficult angles in a single setup, which can reduce tooling cost and labor. Specifications for machining centers include table length, table width, longitudinal travel, cross travel, horsepower, drilling capacity in steel, drilling capacity in cast iron, x-axis travel distance, y-axis travel distance, spindle taper, T-slot size, number of T-slots, spindle speeds in revolutions per minute (rpm), power down feed, feedrates, feedrate for power downfeed, and head tilt-back degree. In a horizontal machining center, the tool rotates around the horizontal axis. A horizontal machine center is preferred if a large amount of material has to be removed, or there is less need for accuracy. A horizontal machining center can have a pallet system with dozens of tools in an automatic tool changer. In a vertical machine center, the tool rotates around the vertical axis. A vertical machining center used more commonly, largely because the workpiece is easier to mount. A CNC vertical machining center uses computerized numeric control.
Machining centers can carry the ETL Listed mark, which certifies that they conform to the National Fire Protection Association (NFPA) standard NFPA 79 and the Canadian equivalent, CAN/CSA C22.2 No. 73. Machining centers are covered by the American Society of Mechanical Engineers (ASME) standard ASME B5. 5-axis machining is covered by MIL-M-80263.