CNC Machining 101, Part I
Basic operator training for computer numerical control (CNC)-equipped machine tools should focus on the four key areas of CNC-machine tool operation: components, direction of motion, accessories and programmable functions. In this installment, we'll cover the first two of those.
Components and vital statistics
In order to maximize the efficiency of a CNC-based machine tool, the operator must be familiar with the machine's basic components. On a universal-style slant bed turning center, for example--used by many industries including automotive and aerospace--the operator should know the locations and basic functionality of the bed, way system, headstock and spindle, turret, tailstock and workpiece holding device.
Likewise, operators must be familiar with the machine's operating characteristics and other specifications including: maximum revolutions per minute; number of spindle ranges and cut-off points for each range; spindle and axis-drive horsepower; maximum travel distance for each axis; number of tools the machine can hold; way construction type such as square, dovetail or linear bearing; and fastest traverse rate and cutting speed.
Beyond the classroom, the best operator resource for this information is typically the machine tool builder's technical manual. The more time an operator spends learning these basic functions, the less time it takes to achieve a comfort level with the machine, and the more quickly the unit can be put to its maximum use.
The XYZs of motion axes
Knowing the axes, or programmable motion directions, and the axes reference points of a CNC-machine tool are also critical for efficient operation. While the axis names may vary from machine to machine, they are always named by a letter address. The common axis names are X, Y, Z, U, V and W for linear axes; rotary axes are typically named A, B and C.
Most CNC-equipped machine tools use precise points along an axis as a starting or reference point for that axis. This point is referred to in a variety of ways: zero return position, grid zero position or home position. Whatever its name, the reference position is required by many controls to provide an accurate point of reference. CNC controls that use a reference point for each axis require that the machine be manually moved to its reference point in each axis as part of the power-up procedure. Once this process is completed, the control is in sync with the machine's position.
During programming, both a letter address and an axis destination is used to delineate movement commands in one or multiple axes. The position X3.752 directs the machine to move the X axis to a position of 3.752 inches from the zero point in X, assuming the absolute programming mode is used.
These are just some of the basics that CNC machine tool training and self-study programs must cover. Next month, in the final installment, we'll look at machine tool accessories and programming functionality.
Tom Wood is the training services manager at GE Fanuc Automation (Charlottesville, VA). For more information, call (800) GEFANUC.