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CNC MACHINES AND DETAILS OF THEIR OPERATIONS

Computer numerical control (CNC) machines are modern machines operating with a digitized data. They take instructions from computer and CAM software programs. In other words, a computer and CAM program are used to control, automate and monitor the movement of the machine.     CNC machining is a manufacturing process in which pre-programmed computer software dictates the movement of the industrial machine. It can be used to control range of complex machinery like the lathe, grinders, routers, and milling operations, etc. CNC machining makes a single set of prompt action to be carried out in 3-dimensional cutting tasks.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

CNC machine can be a lathe, milling machine, router, welder, grinder, waterjet or laser cutter, sheet metal stamping machine, robot, or any type of machine. The key factor of such machine is the means of control which is based on CNC. Its control supersedes that of manual control where operators are needed to prompt and guide the commands of machining tools via levers, buttons and wheels. Visually, a CNC system might resemble a regular set of computer components, but the software programs and consoles employed in themachining operation distinguish it from all other forms of computation.

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Large industrial CNC machines usually make use of a computer in an on-board dedicated controller. While the small ones may be controlled from an external computer. The drive components and series of motors in the machines work or operate according to the CNC controller command in order of the programmed jobs using the motions of the necessary machines’ parts. In large industrial CNC machines, a sophisticated feedback system is usually employed to constantly monitor and adjust the cutter’s speed and its positions.

In other words, when a CNC system is activated, the desired cuts are programmed into the software and dictated to corresponding tools and machinery, which carry out the dimensional tasks as specified.  In its programming, the code generator within the numerical system will often assume the mechanisms are flawless, not minding the possible errors especially when the machine is directed to cut in more than one direction simultaneously, the placement of a tool in a numerical control system is outlined by a series of inputs known as the part program.

AUTOMATION METHOD BEFORE THE USE OF CNC METHOD

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Before the present use of the computer controlled methods, the earlier machining automations were carried out using numerical controlled system called ‘NC’ system. It is a system that uses a program in the form of inputted codes on punch cards. Hence, the machine reads the punch card codes to executive its commands. Meanwhile, the CNC system is quite different since its commands are fed into the machine using a program in a computer. And the necessary codes can be generated in the program by the computer input hardware such as keyboards and mouse.  Because of the above reason, CNC offer more expansive computational and operational capacity. Besides, the system can be updated, modified or have new code inclusion at any time unlike the NC system that is static and lack other features.

For practical purpose, small CNC machines are available currently in the engineering field as model maker-hobbyist style desktop CNC machines. They are generally light in weight, less rigid, less accurate or precise, slower in operation and less expensive than the industrial type. They are good for machining objects out of softer materials such as plastics, foam, and wax. In reality, some of them can run like a printer e.g. the practical 3D printing machines.

Some of the practical type have their own closed command system and perhaps even dedicated CAM software. Only few can accept standard G-code as input. Some of them can be made for industrial use however, they will be limited to doing precise small works.

CAD/CAM & HOW CNC MACHINING WORKS

Computer Aided Machining (CAM), is simply the use of various software packages to create toolpaths and NC code to run a CNC controlled machine using a 3-dimensional computation model data known as Computer Aided Designs (CAD). The combination of the two systems in an industrial automation technology is called the CAD/CAM machining.

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CAM does not run the CNC machine rather it creates codes for it to follow. In other words, it is not an automatic system that spits out the correct NC code from any CAD model rather it requires knowledge and experience in running the program, developing machining strategies, and knowing what tools and operations to use in each situation so that best result can be obtained. The same is obtainable it the 3D modeling system.

MACHINING CODES USE BY THE CAM PROGRAMS

CNC machining makes it possible to pre-program the speed and position of machine tool functions and run them using software repetitively in predictable cycles. Due to such ability, the process has been adopted in different manufacturing sectors especially in the making metal and plastic related products.

The numerical code use in CNC is referred to as the CAM language, some of the popular codes are; the G-code and the ISO-code which are alphanumeric programming language developed in the early 7os for CNC  machines. The codes control all aspects of the CNC machinemachine parts movement including its speed, feed rate, and axis coordination, etc. as it is being understood by the machine itself.  However, the G-code has been considered as the standard since each manufacturer can modify certain parts such as auxiliary functions, creating a situation where some of the code may work in one CNC machine and will not work in another.

Some CNC machine manufacturers, have developed their own programming languages. Therefore, to translate such language into a universal code that any CNC machine could understand, a postprocessor software will be used for that purpose. It translates the CAM software’s internally calculated paths into specific NC code. Once configured correctly, it outputs the appropriate code for the chosen machine such that any CAM system can output code for any CNC machine theoretically. It is an extension software of CAM system.

Modern production of parts using the CNC machines has become a fully-automated system where a pre-programmed software is used to specify dimensions for a given part set into place and then converted into actual finished product with computer aided manufacturing (CAM) software.

The position control is determined through an open loop or closed loop system. The open loop signal runs in a single direction between the controller and motor while in the closed loop system, the controller is capable of receiving feedback which makes error correction possible. The closed-loop system can rectify irregularities in velocity and position.

During the machining operation, the movement is usually directed across X and Y axes. The tool in turn is positioned and guided via stepper or servo motors, which replicate exact movements as determined by the G-code. If the force and speed are minimal, the process can be run through open-loop control. For everything else, closed-loop control is necessary to ensure the speed, consistency and accuracy required for industrial applications, such as network.

CNC creates consistency in parts production such that uniform parts could be made in mass which ordinarily may be impossible with a manual production system. It harnesses, all variety of machine tools such as drills and cutters, combined with several different functions into one cell. Some may have robotic handles in addition, to pick and drop specific pieces of the parts during its production, since one software controls all the actions in the production operations, there are orderliness and uniformity in the parts produced.

 

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Originally posted 2018-09-24 09:40:41.

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