Milling is the machining process of using rotary cutters to remove material from a workpiece by feeding the cutter into the workpiece. It is a technique with a variety of applications, from small to large scale. Milling machines are a commonly used tool in the manufacturing process. There are two main types of mills, vertical mills and horizontal mills.
Vertical milling uses cutting heads mounted on a vertically oriented spindle. Typically, depending on the mill, the spindle can extend, or the table raised and lowered, allowing for plunge cuts and drilling. Different mills can control movement in different ways. With bed mills, the spindle can be raised or lowered and the bed moved horizontally. On another note, turret mills perform in a slightly different way; the spindle is static and the bed moves both horizontally and vertically. Turret mills are more versatile than a bed mil, but impractical for larger parts. Large, heavy pieces are difficult for a machine operator to raise and lower, which makes bed mills more appropriate.
Horizontal mills also employ a spindle to mount the cutting surfaces; however, the spindle orients horizontally instead of vertically. Depending on the machine’s manufacturer, vertical and horizontal mills can share tools. Mazak is a great example of this. Additionally, horizontal mills have the ability to load parts on a vice outside of the machine while milling parts, allowing for quick turnaround time and high output. This design makes horizontal mills exceptional for high yield production. Notably, some horizontal beds are rotatable to enable milling at multiple angles on multiple faces of the workpiece.
Which one should I choose?
Because of the lower initial cost of vertical mills, around $80,000 versus $250,000 for horizontal machines, many machine shops choose a vertical machine as their first mill. Vertical mills also have a smaller footprint, taking up less floor space. Unlike horizontal mills, chip evacuation is not as efficient when using a vertical mill. This added difficulty can shorten tool life.
Horizontal mills have the ability to execute parts with fewer operations. Due to the ease of chip removal, horizontal mills produce more refined finishes in a shorter time. This leads to a greater throughput. The gravity-assisted chip evacuation also helps preserve the life of a tool.
Both mills have their uses. The part design dictates the appropriateness of a vertical or horizontal machine. The size, shape, and number of planes should all be taken into consideration. If a part is heavier and requires milling on multiple sides, horizontal milling may be preferred. If there are sinking dies, vertical milling might be the way to go. Regardless of the part’s design, milling machines are immeasurably useful all around. With the introduction of CNC milling centers, even complex jobs are accomplishable.