Vertical Machining Center (VMC) is a machining center in which the spindle axis and the rectangular worktable are set vertically, which is suitable for processing workpieces with high accuracy and precision, even with multiple procedures and complex shapes. The spindle cartridge is mounted in a housing that moves vertically which is known as the z-axis and the workpieces of VMC are usually mounted on top of its table and perform standard 2.5 or 3 axis machining operations, using a 3D Cartesian coordinate system for its motion. It is utilized primarily as a metal cutting machine that is useful in cutting or shaping steel, aluminum, and other hard materials in a precision formed or machined surface. Aside from these, it can be also be used for milling, boring, drilling, carving, engraving, tapping, thread cutting, and more operations. It is used in various machinery manufacturing industries with high precision and mass production requirements such as aerospace, automobile, handicrafts, mold making, military products, electronic and electrical, light and textile, etc.
VMC has a simple structure, small floor area, and can be equipped with multiple adjustments. Its versatility, adaptability, and low cost made it one of the most popular machines that can be easily found in shops all over the world. It has been around for more than 150 years, in its most basic form. It went through a lot of renditions and the later ones added power and hydraulic feeding devices to make the system more automated, until computer numerical control (CNC) which is a process that involves the use of computers to control machine tools was added for more automation in operation, repeatability, tool selection/changing, and contour control. To describe the CNC milling and drilling machines with an automatic tool changer and a table that clamps the workpiece in one place, the term “machining center” was coined. Then, the term VMC was born after all these developments, taking the “milling” machine to a whole new level of productivity.
Commonly, VMC machines have three axes: the x, y, and z-axis – in which the cutter stays in the vertical direction. An axis is described as the number of motors that can be individually driven for positional control of the tool; in which for x-axis is from left to right, y-axis is front to back, and the z-axis is up and down. However, VMCs are not limited to three axes, a 4th or even a 5th axis can be added to increase the benefits of the VMC. Ancillary equipment increases the flexibility and capability of VMC machines, including spindle speeders, angle heads, tool- and part-probes, quick-change workholding devices, and rotary indexers to enable four- or five-axis machining work. With the 4th axis being added, the cutter can rotate around the x-axis which allows the VMC machine to drill holes in the front and back of the product, and the 5th axis can add complexity to the machine.
Some of the main components of VMC are: a rotating spindle which is perpendicular to the table or working surface and can hold a variety of cutting tools. It also has a movable work table which the workpiece is attached to – either directly or through a variety of fixtures like milled aluminum plates or hard clamping vices. Then, it has a tool changer that greatly increases a VMC’s productivity because it allows for the automatic computer-controlled selection of tools for a variety of tasks from rough cutting to fine hole boring. A coolant system is also needed to keep parts and cutters cool and lubricated. The coolant system most VMCs use is a mixture of soluble oil and water but it can be a variety of other liquids too. A variety of chip conveyors and chip augers are employed as well to evacuate the chips from the work zone, which increases productivity and reduces downtime from manually shovelling out waste chips. Full covers or enclosures can also be added to reduce the splash/splatter caused by milling operations and protect the operators and environment from the machining process. Lastly, the use of shuttle tables or other automatic part loading systems is a great addition to significantly increase productivity, decrease downtime, and increase the spindle “ON” time of most VMC systems.
The staple machinery of VMC in machine shops is still the 3-axis machine, unlike the horizontal machining center (HMC) that usually comes with a 4th axis. However, there are still a lot of advantages it can offer and some of these are simpler set-up and easier to manage. It is also less costly, versatile, economically efficient, effective, and widely used in the market because the debugger is easier. Aside from these, the functionality of VMC has significantly improved by adding table and spigot table configuration for the fourth and fifth axis, more pallet changers, more tools, and high speed spindles which are helpful for more complex productions. And with the technology evolving, it gives way to more advanced features to increase the productivity of the VMC, given that the machine is also well taken care of.
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