CNC MachinesComputer numerical control (CNC) machines are automated milling machines that make industrial components without human assistance. This is possible because CNC machines are fed a series of instructions that are delivered to an internal computer controller. These instructions are in the form of codes that belong to the numerical control programming language.The code used to program CNC machines is generically called Gcode. However, Gcode instructions are only part of the programming language. Specifically, Gcodes give CNC machines the coordinates from which to hold and engage the machining tool in order to cut and shape metal to certain specifications. The entire series of codes used to operate CNC machines also include Mcodes and TCodes, which manage the CNC machine and drill tool, respectively. Tooling speed and feed controls are dictated by SCodes and FCodes, while X, Y, and Zcodes determine absolute position.A standardized set of control codes for CNC machines was developed in the early 1960s in the U.S. by a trade organization known as the Electronic Industries Alliance. Roughly 20 years later, the system was revised and dubbed RS274D. Although these codes are still used across the country to assist computeraided manufacturing (CAM), variations and additions exist among operators and manufacturers of CNC machines. In fact, operators of specific CNC machines need to be educated about the differences between manufacturer’s models to avoid a conflict in programming compatibility.CNC machines have evolved considerably since their initial introduction into the manufacturing industry. The earliest CNC machines received code instructions through hardwired controllers, which meant that the programming format could not be altered. However, later models were programmed via mainframe cables and floppy disks, which permitted variations in programming. At present, most CNC machines are tied into a network of computers and receive operating and tooling instructions via a software file containing the ".NC" extension. Although, the file extension varies with each machine shop, depending on its ISO certification protocols.Today, CNC machines have graduated to encompass entire "cells" of tooling machines that can operate independently of each other. They are driven by the direct upload of CAM software files, eliminating the need for design plans to be physically drawn up. Modern CNC machines are also capable of running overnight or for several days without human supervision. In fact, CNC machines are now so sophisticated that they can dial the chief operator’s cell phone to notify him or her when a tool part breaks, and still complete other parts of the program. These features make it possible to produce thousands of parts while the machine shop is closed or while the operator is performing other tasks. Advantages and disadvantages of using CNC machinesAdvantages:
*AccuracyWhen programmed correctly, CNC machines are usually 100% correct with what they produce. They: 1. produce parts to maximise accuracy 2.provide good positional accuracy and repeatability 3.provide a high degree of quality because of their accuracy and their ability to reuse programs.*SimplicityCNC machines are not all that difficult to use once you learn how. For example: 1.complex jigs and fixtures are not required in all areas 2.since fewer jigs are used, the actual storage requirements are reduced 3.lower tooling costs since there is less need for complex jigs and fixtures 4.once the first piece has passed inspection, minimal inspection is required on subsequent parts 5.advanced machine control and programming capabilities allow for complex machining operations to be more easily accomplished.*TimeUsing CNC machines effectively reduces the amount of time take to produce furniture items. CNC machines: 1. enable the operator to make changes or improvements with a minimum of delay or expense 2.reduce waste as errors due to operator fatigue, interruptions and other factors are less likely to occur 3.improve production planning as they can often perform work at one setting that would normally require several conventional machines 4.reduce lead time as a result of lower tooling costs. Disadvantages:*CostAs with any business, costs are always a factor. CNC machinery: 1.costs quite a lot more than conventional machinery 2.does not eliminate the need for expensive tools 3.parts (ie machines and tooling) are costly and their purchase requires extensive justification. 4.is expensive to repair.
*ErrorsCNC machines do not totally eliminate errors. Operators can still push the wrong buttons, make incorrect alignments and fail to locate parts properly on a jig. Conventional Machines: Conventional machining is collection of materialworking processes in which powerdriven machine tools, such as saws, lathes,milling machines, and drill presses,are used with a sharp cutting tool to mechanically cut the material to achieve the desired geometry. Machining is a part of the manufacture of almost all metal products, and it is common for other materials, such as wood and plastic, to be machined. A person who specializes in machining is called a machinist . A room, building, or company where machining is done is called machine shop.Much of modern day machining is controlled by computers using computer numerical control (CNC) machining.