How does a CNC turning machine work?
Computer Numerical Control (CNC) technology enables machinery to be almost fully autonomous. A CNC turning machine follows coded programmed instructions to process material to meet certain specifications. The codes are converted into electrical signals designated to activate turning motors in the machine. Once programmed, the entire process can be completed without an operator controlling the machine.
In order to understand how a CNC machine works, let’s examine some of the specific functions that can be programmed.
CNC Programming
The CNC program is a sequential listing of instructions that the machine will execute. These instructions contain all the information required for machining the part.
The most commonly used programming language for CNC machines is called G-code or RS-274. It controls movements in the automated machining tools. G-code works in tandem with another programming language called M-code. While RS-274 commands specific movements, M-codes control miscellaneous functions.
The G-code describes the machine motion functions like rapid positioning, circular or linear feed, and fixed cycle. It also indicates the offset value to be used.
The M-code commands miscellaneous functions that are required for machining the part but do not correspond to machine movements. It controls spindle start and stop, tool change, coolant, and program stop among other machining operations.
In turn, each code contains variables identified with other letters and defined by the programmer for each specific function. For example, F defines feedrate, S the spindle speed, T the selected tool, (X,Y,Z) the movement of the axis and so on. However, these letters will vary depending on the CNC machine and program.
Motion Control
All CNC machines share one characteristic in common: they have two or more programmable directions of motion called axes. An axis of motion can be linear (in a straight line) or rotary (in a circular path). The complexity of a CNC machine can often be measured by the number of axes. As a rule of thumb, the greater the number of axes, the greater the complexity.
The axes of a CNC machine carry out the movements necessary for the manufacturing process. Commonly, the linear axes are denoted by the letters X, Y, and Z. Rotary axes are A, B, and C. There are two main G-code systems that tell the CNC machine how to read dimensions and movements along the axes:
G Code G90 (Absolute value): the coordinates of the destination point uses the point of origin or datum position as reference.
G Code G91 (Incremental positioning): the coordinates of destination point uses the current point as a reference. The tool uses the last position of the tool as the origin point.
Programmable Accessories
A CNC machine would not be very useful if it only had a single motion control. Nearly every machine can be programmed to perform a variety of different functions. In order to carry out complex functions, CNC machines have to be equipped with the appropriate programmable accessories and tools. A CNC machining center will have at least the following programmable :
Automatic Tool Changer: most machining centers can have many different tools stored within the CNC machine. When required, the tools can be automatically placed on the spindle for corresponding machining.
Spindle speed and activation: the spindle speed is measured in revolutions per minute (RPM) and it can be specified to rotate clockwise, counterclockwise or stopped.
Coolant: machining metals often requires coolant to lubricate and cool the parts while they are being processed. The coolant can be turned on and off during the machining process.
CNC controller
The controller on a CNC lathe is a key component that interprets the program and drives the series of commands in sequential order. It activates the appropriate functions of the CNC machine, drives the axes, and follows the instructions necessary to machine the material. In short, the CNC controller is the brains of the lathe.
In addition to interpreting the CNC program, the controller serves several other functions. For example:
- Identify and correct errors in the program.
- Perform accuracy checks to ensure the machine is working properly.
CAM Program
DNC System
Once the CNC program has been written (either manually or with the assistance of CAM software), it must now be loaded into the controller. This is done via a DNC (Distributed Numerical Control) system
DNC software allows multiple CNC machines to be connected to the computer containing the CNC program. Traditionally, the transfer of programs was carried out using a rudimentary serial communications protocol. However, technological advances allow for CNC controllers to be connected in a network via ethernet cables.
CNC turning is a complex process that requires experience in manufacturing and programming. Marvo is specialized in high-quality CNC turning. Our machinery is state-of-the-art and our fast turnaround times will help you increase productivity for your business. If you’d like to know more about our CNC machining services, feel free to reach out to us!