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Within the classification of machine tools, machining centers are placed between the numerically controlled individual machines and the cell. Within these cells the individual machines are placed together with shared work piece storage units, measuring stations and handling equipment, and they are controlled by a central cell computer.
The prefix “machining” suggests that a machining center is the combination of several different manufacturing processes including drilling, milling, thread cutting or reaming. The work tools are changed automatically from an integrated tool magazine. Additionally, they contain a workpiece storage unit and a rotating table, which allows for processing of the workpiece on all sides.
They do not differ from in terms of their basic structure: the frame and main spindle clamp. Machining centers are often categorized as horizontal machining centers, vertical machining centers, or combined universal centers. Machine centers are particularly effective in their production of small and medium sized series, because they can quickly and easily be adjusted to undertake various tasks. The two main types of machining centers are 5 axis machining center and CNC machining center. Automated devices and flexible processing cells or systems can be integrated into machining centers for tool changing.
Background and Areas of Application for the Different Types of Machines in a Machining Centers
Machining centers are the answer for the increasing productivity demands in production technology. The integrated tool magazine enables the work piece to be processed on all sides without having to re-clamp it into the machine. The automatic workpiece feed significantly reduces idle time. These two features, along with numerical control, ensure that a largely automated process is possible. The capacity of a machining centre increases with the number of tools that can be automatically implemented. An increase in tools reduces the space requirements for chain magazines in relation to revolving magazines. The round shaped revolving or disk magazine usually has about 40 tools; when working with more than 40 tools, it is more common to use a chain magazine.
Magazines are available either as star or drum shaped designs, with either a vertical jointing direction or one parallel to the axis in vertical machining centers. The distance between the magazine storage and the spindle, and the magazine’s structure and jointing direction, influence the tool changing time. This is due to the various required movements and the distance the tool needs to travel during a tool change. Even the shape of the tool changer has a significant influence on the time required for tool changing. Double tool changers can simultaneously take up a tool from the main spindle and the magazine, and can switch both in one step. Simple changers require two steps for this tool change. It is also important to note that if there is no intermediary storage space for the tool, the positioning of the magazine on the old and subsequently the new tool has to happen during idle time.
The correct allocation of the tools used on the machine is decided through coding the work tools or the location of the magazine. If the location is coded, then the tools always have to be laid into the machine in the same order. If the tools are coded, then the machine will look for the right tool by reading the tool’s codes. It is possible to have a more flexible use of the magazine, with shorter tool switching times, through a combination of both encodings and electronic accounting through the controls.
The number of controllable movement axes (usually there are three translational and up to two rotational axes) is another important characteristic that determines the capacity of a machine center. The adjustable speed of the spindle, the length of the working and feed routes, and the size and capacity of the work table, are also important characteristics. If the intention is to use the work table of the machining center as a main spindle for turning the workpiece, then the speed and capacity of the rotary table is also an important feature to note.
Machining centers usually have a cross-bed design, or similar, type of machine bed. They are also commonly available in a travelling column design. The cross-bed design has at least one translational motion axis for the workpiece carrier. With the travelling column design, the workpiece carrier moves along all three main translational axes. The cross-bed has been expanded into a rectangle machine bed to provide surfaces for the tool changer, tool magazine and other additional features.
The flexibility of CNC machining centers is pushed even further through their modular structure. The capacity of the machine tool can be fitted to customer requirements. Additionally, the basic set up can be expanded by using components that can be combined with other machines. This allows manufacturers to offer a wider spectrum of machine tools.
Used Machining Centers for Sale
Find a suitable used machining center can be a tricky job as you need to check certain quality factors such as manufacturer, year of make, model and its drawbacks since the beginning of its production and available machine tools service representatives nearby from the manufacturers. It is advisable to choose used machining centers, and in particular used CNC machining centers for sale, from well known brands at a bit more extra cost than going for small or unknown brand that doesn't have any service on the call for the obvious reasons.
Machining Center Manufacturers
Important names include BIESSE, BURKHARDT & WEBER, CHIRON, CINCINNA, CMS, DMG MORI SEIKI (formerly DECKEL, MAHO, GILDEMEISTER), HECKERT HOMAG, HÜLLER HILLE, MORBIDELLI, SHW, STEINEL, WEEKE, as well as WERNER & KOLB.