NC (Numerical Control)
NC is a technology that uses digital signals to automatically control objects (such as the motion of the machine tool and its working process), referred to as numerical control.
NC technology refers to the automatic control technology that uses numbers, letters and symbols to program a certain working process.
NC system refers to the organic integrated system of software and hardware modules that realize the functions of NC technology. It is the carrier of NC technology.
CNC System (Computer Numerical Control System)
CNC (Computer Numerical Control) system refers to the numerical control system with computer as the core.
CNC Machine Tools
CNC machine refers to a machine tool that uses CNC technology to control the machining process, or a machine tool equipped with a CNC system.
The term numerical control is a widely accepted and commonly used term in the machine tool industry. Numerical Control (NC) enables an operator to communicate with machine tools through a series of numbers and symbols.
NC which quickly became CNC (Computer Numerical Control) has brought tremendous changes to the manufacturing industry. New machine tools in CNC have enabled industry to consistently produce parts to accuracies undreamed of only a few years ago. The same part can be reproduced to the same degree of accuracy any number of times if the CNC program has been properly prepared and the computer properly programmed. The operating commands which control the machine tool are executed automatically with amazing speed, accuracy, efficiency, and repeatability.
The machine is connected to a computer, the computer will tell it where to move. First, the CNC operator should do the toolpath creation, the operator uses a software program to draw the shapes and create the tool path that the machine will follow.
The ever-increasing use of CNC in industry has created a need for personnel who are knowledgeable about and capable of preparing the programs which guide the machine tools to produce parts to the required shape and accuracy. With this in mind, the authors have prepared this textbook to take the mystery out of CNC - to put it into a logical sequence and express it in simple language that everyone can understand. The preparation of a program is explained in a logical step-by-step procedure, with practical examples to guide the user.
CNC technology consists of three parts: machine tool body, CNC system and peripheral technology.
The machine tool body is mainly composed of basic parts such as bed, column, guide rail, working table and other supporting parts such as tool holder and tool magazine.
The numerical control system is composed of input / output equipment, computer numerical control (CNC) device, Programmable Logic Control (PLC), spindle servo drive device, feed servo drive device and measuring device. Among them, the CNC device is the core of the numerical control system.
Peripheral technology mainly includes tool technology (mainly refers to tool system), programming technology, and management technology.
CNC: Computer Numerical Control.
G-Code: A universal numerical control (NC) machine tool language that specifies axis points to which the machine will move.
CAD: Computer Aided Design.
CAM: Computer Aided Manufacturing.
Grid: The minimum movement, or feed, of the router head. Head automatically moves to next grid position when button is toggled in continuous or step mode.
PLT (HPGL): Standard language for printing vector-based line drawings, supported by CAD files.
Toolpath: User-defined, coded route which the cutter follows to machine the workpiece. A “pocket” toolpath cuts the surface of the workpiece; a “profile” or “contour” toolpath cuts completely through to separate the workpiece shape.
Step Down: Distance in Z-axis that the cutting tool plunges into the material.
Step Over: Maximum distance in X or Y axis that cutting tool will engage with uncut material.
Stepper Motor: A DC motor that moves in discrete steps by receiving signals, or “pulses” in a particular sequence, thus resulting in very precise positioning and speed control.
Spindle Speed: Rotational speed of cutting tool (RPM).
Conventional Cut: Cutter rotates against direction of feed. Results in minimal chatter but can lead to tearout in certain woods.
Subtractive Method: The bit removes material to create shapes. (Opposite of additive method.)
Feed Rate: Speed at which the cutting tool moves through the workpiece.
Home Position (Machine Zero): Machine-designated zero point determined by physical limit switches. (It does not identify actual work origin when processing a workpiece.)
Climb Cut: Cutter rotates with direction of feed. Climb cutting prevents tearout, but can lead to chatter marks with a straight-fluted bit; a spiral-fluted bit will reduce chatter.
Work Origin (Work Zero): The user-designated zero point for the workpiece, from which the head will perform all it's cutting. X, Y and Z axes are set to zero.
LCD: Liquid Crystal Display (used on the controller).
U Disk: External data storage device that is inserted into a USB interface.
1. Improve Processing Accuracy.
CNC machine tools are highly integrated mechatronic products, which are composed of precision machinery and automatic control systems. They have high positioning accuracy and repeat positioning accuracy. The transmission system of the machine tool and the structure of the machine tool have high rigidity and heat. Stability; measures to reduce errors were adopted when designing the transmission structure, and it was automatically compensated by the CNC system. Therefore, the CNC machine tool has a higher processing accuracy, especially the consistency of parts processing in the same batch, and the product quality is stable The pass rate is high, which is incomparable with ordinary machine tools.
2. Improve Production Efficiency.
CNC machine tools can use a larger amount of cutting, which effectively saves processing time. CNC machine tools or machining centers also have automatic speed change, automatic tool change and other automatic operation functions, which greatly shorten the auxiliary time, and once a stable processing process is formed, there is no need to perform inter-process inspection and measurement. Therefore, the productivity of CNC machining is 3-4 times higher than that of ordinary machine tools, or even more.
3. Improve Adaptability.
The CNC machine tool performs automatic processing according to the CNC program of the processed parts. When the processing object changes, as long as the CNC program is changed, there is no need to use special process equipment such as masters and templates. This is helpful to shorten the production preparation cycle and promote product replacement.
4. Improve the Machinability of Parts.
Some mechanical parts formed by complex curves and curved surfaces are difficult to process or even impossible to complete with conventional techniques and manual operations, and can be easily realized by CNC machine tools using multi-coordinate axes linkage.
5. Improve Economic Efficiency.
CNC machine tools (especially machining centers) mostly use process concentration, and one machine is multi-purpose. In the case of one clamping, most parts of the parts can be processed. One CNC machine tool or machining center can replace several ordinary machine tools. This can not only reduce clamping errors, save auxiliary time between transportation, measurement, and clamping between processes, but also reduce the types of machine tools, save machine tool area, and bring higher economic benefits.
From the perspective of CNC technology and equipment applications in the world, its main application areas are as follows:
1. Manufacturing industry.
The machinery manufacturing industry is the earliest industry to apply CNC technology, and it is responsible for providing advanced equipment for various industries of the national economy. The main applications are the development and production of high-performance five-axis high-speed vertical machining centers for modern military equipment, five-axis machining centers, large-scale five-axis gantry milling, etc .; CNC machine tools for flexible processing production lines for engines, gearboxes, and crankshafts in the automotive industry And high-speed machining centers, as well as welding, assembly, painting robots, plate laser welding machines and laser cutting machines, etc .; high-speed five-coordinate machining centers for machining propellers, engines, generators and turbine blade parts in the aviation, marine and power generation industries, heavy duty Turning and milling complex machining center, etc.
2. Information industry.
In the information industry, from computer to network, mobile communication, telemetry, remote control and other equipment, it is necessary to adopt manufacturing equipment based on super-precision technology and nanotechnology, such as wire bonding machines for chip manufacturing, wafer lithography machines, etc. These equipment The control of the need to use CNC technology.
3. Medical equipment industry.
In the medical industry, many modern medical diagnosis and treatment equipment have adopted numerical control technology, such as CT diagnostic instruments, whole body treatment machines and minimally invasive surgical robots based on visual guidance, orthodontics and dental restoration in stomatology are required. Using high-precision CNC machine tools to produce teeth.
4. Military equipment.
Many modern military equipment use servo motion control technology, such as automatic aiming control of artillery, tracking control of radar and automatic tracking control of missiles.
5. Other industries.
In the light industry, there are printing machinery, textile machinery, packaging machinery and woodworking machinery that use multi-axis servo control; in the building materials industry, there are CNC waterjet cutting machines for stone processing, CNC glass engraving machines for glass processing, CNC sewing machine used for Simmons processing and CNC embroidery machine used for clothing processing; in the art industry, more and more crafts and artworks will be produced using high-performance five-axis machining centers.