Thursday, April 19, 2007

CNC machinery and tools


A CNC machine tool is a powered mechanical device used to fabricate metal components of machines by the selective removal of metal. The term machine tool is usually reserved for tools that used a power source other than human movement, but they can be powered by people if appropriately set up. Many historians of technology consider that the true machine tools were born when direct human involvement was removed from the shaping or stamping process of the different kinds of tools. For instance, they consider that lathe machine tools were invented around 1751 by Jacques de Vaucanson because he was the first to mount the cutting instrument on a mechanically adjustable head, taking it out of the hands of the operator.
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CNC Routers

CNC Router
A router is a woodworking tool used to rout out (hollow out) an area in the face of a piece of wood. It was a tool particularly used by pattern makers and staircase makers and consisted of a broad-based wooden hand plane with a narrow blade projecting well beyond its base plate gaining it the nickname Old Woman's Tooth. Since about 1960, it has been replaced by the modern spindle router, which was designed for the same work, although the first electric hand routers appeared in the years just after World War I. Further refinement produced the plunge router, invented by Elu (now part of deWalt) in Germany in the late 1940s. This is even better adapted for many types of work. Today, traditional hand-powered routers are often called router planes. Modern routers are often used in place of traditional moulding planes or spindle moulder machines for edge decoration (moulding) of timber. Related to the router, is a smaller lighter version designed specifically for trimming laminates. It can be used for smaller general routing work. For example with an appropriate jig it can be used recessing door hinges and recessing lock faceplates etc. A wood CNC Router is similar to a metal CNC mill with the following differences:The wood router typically spins faster — up to 24,000 RPM It typically uses smaller tools — typical shank size 20 mm or at most 25 mm. It typically uses smaller toolholders MK2 (Morse taper #2 - on older machines),ISO-30, HSK-63 or the tools just get held in a collet tool holder affixed directly to the spindle nose. ISO-30 and HSK-63 are rapid-change toolholding systems. HSK-63 has begun to supplant the ISO-30 as the rapid change standard in recent years Some wood routers have multiple separate heads that can come down simultaneously or not. This design is generally not as easy as a toolchanger with ISO-30 or HSK-63, though it is easier to maintain. A wood router table is controlled in the same way as a metal mill, but there is a lot of CAM software specifically for wood routers. Wood with different grain must be approached with unique strategies, and wood CAM software is less likely to need to have hog-out strategies than the metal ones. Wood routers are frequently used to machine other soft materials such as plastics at high speed.

CNC Milling machine

CNC Milling
A milling machine is a machine tool used for the complex shaping of metal and other solid materials. Its basic form is that of a rotating cutter or endmill which rotates about the spindle axis (similar to a drill), and a movable table to which the workpiece is affixed. That is to say the cutting tool generally remains stationary (except for its rotation) while the workpiece moves to accomplish the cutting action. Milling machines may be operated manually or under computer numerical control (see CNC). Milling machines can perform a vast number of complex operations, such as slot cutting, planing, drilling, rebating, routing, etc. Cutting fluid is often pumped to the cutting site to cool and lubricate the cut, and to sluice away the resulting swarf.
There are two main types of mill: the vertical mill and the horizontal mill. In the vertical mill the spindle axis is vertically oriented. Milling cutters are held in the spindle and rotate on its axis. The spindle can generally be extended (or the table can be raised/lowered, giving the same effect), allowing plunge cuts and drilling. There are two subcategories of vertical mills: the bedmill and the turret mill. In a turret mill the spindle remains stationary during cutting operations and the table is moved both perpendicular to and parallel to the spindle axis to accomplish cutting. In the bedmill, however, the table moves only perpendicular to the spindle's axis, while the spindle itself moves parallel to its own axis. Also of note is a lighter machine, called a mill-drill. It is quite popular with hobbyists, due to its small size and lower price. These are frequently of lower quality than other types of machines, however.
Most CNC milling machines or machining centers are computer controlled vertical mills with the ability to move the spindle vertically along the Z-axis. This extra degree of freedom permits their use in engraving applications, and also allows to create 2.5D surfaces such as relief sculptures. When combined with the use of conical tools or a ball nose cutter, it also significantly improves milling precision without impacting speed, providing a cost-efficient alternative to most flat-surface hand-engraving work.

CNC lathes

CNC Lathe
CNC Lathe and turningCNC lathes are rapidly replacing the older production lathes (multispindle, etc) due to their ease of setting and operation. They are designed to use modern carbide tooling and fully utilize modern processes. The part may be designed by the Computer-aided manufacturing (CAM) process, the resulting file uploaded to the machine, and once set and trialled the machine will continue to turn out parts under the occasional supervision of an operator. The machine is controlled electronically via a computer menu style interface, the program may be modified and displayed at the machine, along with a simulated view of the process. The setter/operator needs a high level of skill to perform the process, however the knowledge base is broader compared to the older production machines where intimate knowledge of each machine was considered essential. These machines are often set and operated by the same person, where the operator will supervise a small number of machines (cell). The design of a CNC lathe has evolved yet again however the basic principles and parts are still recognisable, the turret holds the tools and indexes them as needed. The machines are totally enclosed, due in large part to Occupational health and safety (OH&S) issues. With the advent of cheap computers, free operating systems such as Linux, and open source CNC software, the entry price of CNC machines has plummeted. For example, Sherline makes a desktop CNC lathe that is affordable by hobbyists. Most CNC Swiss style lathes today utilize two spindles. The main spindle is used with the guide bushing for the main machining operations. The secondary spindle is located behind the part, aligned on the Z axis. In simple operation it picks up the part as it is cut off (or parted off) and ejects it into a bin, eliminating the need to have an operator manually change each part, as is often the case with standard CNC turning centers. This makes them very efficient, as these machines are capable of fast cycle times, producing simple parts in one operation in as little as 10-15 seconds. This makes them ideal for large production runs of small diameter parts.

CNC Machining Centers

Machining Center
CNC Machining Center. The introduction of CNC machines radically changed the manufacturing industry. Curves are as easy to cut as straight lines, complex 3-D structures are relatively easy to produce, and the number of machining steps that required human action have been dramatically reduced. With the increased automation of manufacturing processes with CNC machining center, considerable improvements in consistency and quality have been achieved. CNC automation reduced the frequency of errors and provided CNC operators with time to perform additional tasks. CNC automation also allows for more flexibility in the way parts are held in the manufacturing process and the time required to change the machine to produce different components. A more recent advancement in CNC interpreters is support of logical commands, known as parametric programming. Parametric programs incorporate both G-code and these logical constructs to create a programming language and syntax similar to BASIC. Various manufacturers refer to parametric programming in brand-specific ways. For instance, Haas (machining center) refers to parametric programs as macros. GE Fanuc refers to it as Custom Macro A & B. While Okuma refers to it as User Task 2. The programmer can make if/then/else statements, loops, subprogram calls, perform various arithmetic, and manipulate variables to create a large degree of freedom within one program. An entire product line of different sizes can be programmed using logic and simple math to create and scale an entire range of parts, or create a stock part that can be scaled to any size a customer demands. A horizontal machining center has the same sort of x–y table, but the cutters are mounted on a horizontal arbor across the table. A majority of CNC vertical machining also feature a degree rotary table that allows milling at shallow angles. While endmills and the other types of tools available to a vertical mill may be used in a horizontal mill, their real advantage lies in arbor-mounted cutters, called side and face mills, which have a cross section rather like a circular saw, but are generally wider and smaller in diameter. CNC machining center.

CNC Plasma Cutting Machines

Plasma cutting machine
Plasma cutting is a process used to cut steel and other metals (or sometimes other materials) using a plasma torch. In this process, an inert gas (in some units, compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut, turning some of that gas to plasma. This plasma is sufficiently hot to melt the metal and moving sufficiently fast to blow molten metal away from the cut. The result is very much like cutting butter with a hot jet of air. Plasma cutters have also been used in CNC machinery. Manufacturers such as Retro Systems and Plasma CAM build CNC cutting tables, some with the cutter built in to the table. The idea behind CNC tables is to allow a computer to control the torch head making clean sharp cuts. Modern CNC plasma equipment is capable of multi-axis cutting of thick material, allowing opportunities for complex welding seams on CNC welding equipment that is not possible otherwise. For thinner material cutting, plasma cutting is being progressively replaced by laser cutting, due mainly to the laser cutter's superior hole-cutting abilities. A specialized use of CNC controlled Plasma Cutters has been in the HVAC industry. Software will process information on ductwork and create flat patterns to be cut on the cutting table by the plasma torch. This technology has enormously increased productivity within the industry since its introduction in the early 1980's. A typical HVAC cutting machine is Plasma Automation's Vicon Cutting Table Plasma cutters use a number of methods to start the pilot arc, depending on the environment the unit is to be used in and its age. Older cutters use a high voltage, high frequency circuit to start the arc. This method has a number of disadvantages, including risk of electrocution, difficulty of repair, sparkgap maintenance, and the large amount of radio frequency emissions. Plasma cutters working near sensitive electronics, such as CNC hardware or computers, use the contact start method. The nozzle and electrode are in contact. The nozzle is the cathode, and the electrode is the anode. When the plasma gas begins to flow, the nozzle is blown forward. A third, less common method is capacitive discharge into the primary circuit via a Silicon Controlled Rectifier. PC: plasma cutting machines also plasma systems cutting or plasma.