Universal milling machines are milling based machine tools that use spinning cutting tools driven by milling spindles to remove materials as it advances a tool into one or several workpieces under the control of a computer numerical control system. Different from conventional milling machines, universal milling machines are much more versatile in regard to the machining capacity as well as the phase processing.
Universal milling refers to a standalone machine tool that is able to perform types of machining processes, such as turning, drilling, and milling. Most of the universal milling machines were used to be manually controlled since the multitasking nature makes those machining impossible to be set on NC controllers. With the CNC technology, many universal milling machines are now controlled by computer programs with coordinative axis movements, achieving all kinds of cutting tasks.
The concept of CNC universal milling is derived from traditional CNC milling machines, or say, programmed CNC milling machinery. That is, there is a blurred line in between whether a milling-based machine is a mere milling machine or one universal milling machine. There exists a wide spectrum of milling-based cutting machinery. Conventional manual milling machines stand at the one end of the spectrum and multiple axis universal milling machines with automation system equipment stand at the other end. The gradient tells how time passed and how the milling technology progresses with the various inventions involving different kinds of machining processes.
Conventional milling machines and basic lathes are all designed at least with three axes, namely, the x, y, and z-axis. They both can be designed vertically or horizontally as their basic machine structure. However, these are unilateral functional, so either horizontal milling or vertical milling is too narrow for manufacturers who need multi-tasking milling machines.
That is the reason why CNC machining centers and CNC universal milling machines are thus made. They are designed to do more than milling but also drilling, boring, turning, and even some simple polishing process. For doing so, both vertical and horizontal milling machines are added with some additional axes like the fourth axis and even the fifth axis in order to empower the machining capacity. In some advanced versions, there are sixth and even higher synchronized axis added to the universal milling machines so that the overall machining directions and tilting angles can be maximized.
The additional two or even three tools of the axis are normally installed as the working table. Working tables of universal milling machines can be rotated, tilted, rose, moving forward and backward, or other movements for machining purposes. They are normally activated by servo motors rather than hydraulic units because the high-end machining tasks request a higher resolution that cannot tolerate even the smallest tolerance usually made on hydraulic motors.
So, inside the universal milling machines, the box-in-box guideways are normally be replaced by linear guides and the spindles are of higher torque forces rather than high speed but lower torque counterparts. Only with the higher torque, can the machine do more versatile multi-tasking machining without further vibration.
To make the machine universal in machining, an automatic tool changer is a must-have for the change of tooling systems. The ATC is more like a robotic arm that can hold and transfer tools vertically or horizontally. Some may even do both directions. The automatic tool changer helps the spindles of universal milling machines to connect with different machining tools, achieving different types of cutting, including abrasive cutting. After the ATC takes the used tools, it will be put them in a storage space called a tool magazine. Tool magazines are designed with many different kinds of shapes, such as disc, rectangular, square, etc.
The stored tools are then put into their coded stations in the chained units that will record their own position. All the contacted metal tools are worn out at the end, so there have to be technicians who remove those worn-out tools and take them out for either re-sharpen or recycle. This mechanism ensures the milling quality of the universal milling machines to be kept within a certain level of standards and tolerance.
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