INTRODUCTION

MỘT CNC router is a router whose tool paths can be controlled via computer numerical control. It is a computer-controlled machine for cutting various hard materials, such as wood, composites, aluminium, steel, plastics, and foams. It is one of many kinds of tools that have CNC variants. A CNC router is very similar in concept to a CNC milling machine.

CNC routers come in many configurations, from small home-style “desktop” CNC routers to large “gantry” CNC routers used in boat-making facilities. Although there are many configurations, most CNC routers have a few specific parts: a dedicated CNC controller, one or more spindle motors, AC inverters, and a table.

CNC routers are generally available in 3-axis and 5-axis CNC formats.

The CNC router is run by a computer. Coordinates are uploaded into the machine controller from a separate program. CNC router owners often have two software applications—one program to make designs (CAD) and another to translate those designs into a program of instructions for the machine (CAM). As with CNC milling machines, CNC routers can be controlled directly by manual programming, but CAD/CAM opens up wider possibilities for contouring, speeding up the programming process and in some cases creating programs whose manual programming would be, if not truly impossible, certainly commercially impractical.

CNC routers can be very useful when carrying out identical, repetitive jobs. A CNC router typically produces consistent and high-quality work and improves factory productivity.A CNC router can reduce waste, frequency of errors, and the time the finished product takes to get to market. A CNC router gives more flexibility to the manufacturing process. It can be used in the production of many different items, such as door carvings, interior and exterior decorations, wood panels, sign boards, wooden frames, mouldings, musical instruments, furniture, and so on. In addition, the CNC router makes thermo-forming of plastics easier by automating the trimming process. CNC routers help ensure part repeatability and sufficient factory output.

NUMERICAL CONTROL

Numerical control technology as it is known today emerged in the mid 20th century. It can be traced the year of 1952, the U.S Air Force, and the names of john parsons and the Massachusetts institute of technology in Cambridge, MA, USA. It was not applied in production manufacturing until the early 1960`s. the real boom came in the form on CNC, around the year of 1972, and decade later with the introduction of affordable micro computers. The history and development of this fascinating technology has been well documented in many publications. In the manufacturing filed, and particularly in the area of metal working, Numerical Control technology has caused something of revolution.

Even in the every days before computers became standard fixtures in every company and in many homes, the machine tools equipped with Numerical Control system found their special place in the machine shops. the recent evolution of micro electronics and the never ceasing computer development , including its impact on Numerical Control , has brought significant changes to the manufacturing sector in general and metalworking industry in particular.

DEFINITION OF NUMERICAL CONTROL

In various publication and articles, many descriptions have been used during the years, to define what Numerical Control is. Many of these definitions share the same idea, same basic concept, just use different wording.

The majority of all the known definitions can be summed up into relatively simple statement: Numerical control can be defined as an operation of machine tools by the means of specifically coded instructions to the machine control system.The instructions are combinations of the letters of alphabet, digits and selected symbols, for example, a decimal point, the percent sign or the parenthesis symbols. All instructions are written in a logical order and a predetermined form.

The collection of all instructions necessary to machine a part is called an NC program, CNC program, or a part program. Such a program can be stored for a future use and used repeatedly to achieve identical machining results at any time.

Terminology

Absolute zero

This refers to the position of all the axes when they are located at the point where the sensors can physically detect them. an absolute zero position is normally arrived at after a home command is performed.

Ball screw

A ball screw is a mechanical device for translating rotational motion to linear motion. it consists of a re-circulating ball bearing nut that races in a precision threaded screw.

CAD

Computer-aided design (CAD) is the use of a wide range of computerbased tools that assist engineers, architects and other design professionals in their design activities.

CAM

Computer-aided manufacturing (CAM) is the use of a wide range of computer-based software tools that assist engineers and CNC machinists in the manufacture or prototyping of product components.

Program zero

This is the reference point 0,0 specified in the program. in most cases it is different than the machine zero.

Rack and pinion

A rack and pinion is a pair of gears which convert rotational motion into linear motion.

Spindle

A spindle is a high frequency motor fitted with a tool holding apparatus.

Spoilboard

It is also known as the sacrificial board, it is the material used as a base for the material being cut. it can be made of many different materials, of which MDF and particleboard are most common.

Tool loading

This refers to the pressure exerted onto a tool while it is cutting through material. Tool speed It is also called the spindle speed, this is the rotational frequency of the spindle of the machine, measured in revolutions per minute (RPM).

SAFETY RELATED TO CNC WORK

One the wall of many companies is a safety poster with a simple, yet powerful message: The first rule of safety is to follow all safety rules. The heading of this section does not indicate whether the safety is oriented at the programming or the machining level. The season is that the safety is totally independent. It stands on its own and it governs behaviour of everybody in a machine shop and outside of it. At first sight, it may appear that safety is something related to the machining and the machine operation, perhaps to the setup as well. That is definitely true but hardly presents a complete picture. Safety is the most important element in programming, setup, machining, tooling, fixturing, inspection, chipping, and-you-name it operation within a typical machine shop daily work. Safety can never be overemphasized. Companies talk about safety, conduct safety meeting, display posters, make speeches, call experts. This mass of information and instructions is presented to all of us for some very good reasons. Quite a few are passed on past tragic occurrences – many laws, rules and regulations have been written as a result of inquests and inquire into serious accidence. At first sight, it may seem that in CNC work, the safety is a secondary issue. There is a lot of automation; a part program that runs over and over again, tooling that has been used in the past, a simple setup, etc. All this can lead to complacency and false assumption that safety is taken care of. This is a view that can have serious.

In programming, observation of safety rules is also important. A tool motion can be programmed in many ways. Speeds and feeds have to be realistic, not just mathematically “correct”. Depth of cut, width of cut, the tool characteristics, all have a profound effect on overall safety.All these ideas are just a very short summery and a reminder that safety should always be taken seriously.