Introduction to Common Types of Milling Operations

Milling is one of the most common machining processes in the metalworking and fabrication industries. You may be surprised to learn that milling is not just one procedure in itself, but there are many types of milling operations, each with different complexities that make it more suitable for the needs of the finished part. Let’s take a look at some of these operations.

1.Slot Milling

In this process, the width of the tool is less than the width of the workpiece: it is used to make slots in the workpiece. Thin tools make thin slots. To cut a workpiece in half, a very thin slot can be made to penetrate the depth of the workpiece. Another name for this process is “saw milling”.

2.Vertical Milling

Vertical milling machines have a spindle in a vertical position or parallel to the column, mounted on a sliding head for increased complexity. The most common tool used in vertical milling is an end mill or flat end mill. In some cases, it may also refer to a round end mill.

3.Horizontal Milling

Horizontal milling machines are best suited for machining flat surfaces, dovetails, keyways, and gears. These machines are best suited to operating in the milling process, where the metal is fed into the milling cutter against the direction of the milling cutter’s rotation. Compared to vertical milling, horizontal milling allows for the greatest force to be applied to the jaws holding the workpiece.

4.Side Milling

Side milling is the best choice when the goal is to machine a flat vertical surface on the workpiece. The depth of cut can be controlled by rotating the table’s vertical feed screw.

5.Group Milling

When two or more milling cutters are used together on a single spindle and cut horizontal surfaces, this is known as gang milling. The usual approach is to mount milling cutters of different diameters, shapes, and/or widths on the spindle. The potential combinations of cutters are endless and determined by the needs of the job.

6.Straddle Milling

Straddle milling is the best choice when you need to machine two or more parallel vertical surfaces at once. The process is accomplished by mounting two side milling cutters on the same spindle and placing them apart so that they straddle the workpiece.

7.Up (and Down) Milling

Also known as conventional milling, up-cut milling is when the cutter rotates against the table feed direction. This is in contrast to down-cut milling, where the cutter rotates with the table feed direction. What is the difference between the two? In up-cut milling, the chip load on the teeth increases gradually, while in down-cut milling, the chip load on the teeth decreases.

8.Profile milling

The profile milling process allows for the machining of special contours consisting of curves and straight lines (or possibly only curves) in one cut. This can be done with a profile milling cutter (a milling cutter shaped to the cutting contour) or a fly cutter ground specifically for this purpose. The more common profile milling involves milling a semi-circular groove in the workpiece.

9.Face milling

In face milling, the size and nature of the workpiece dictate the type and size of tool required. The teeth on the periphery of the tool do most of the work, but if the tool is properly ground, the face teeth remove a small amount of excess material left behind by the elasticity of the workpiece or tool, producing a better finish.

10.Turret milling

Turret milling is accomplished with drilling, cutting, and shearing. The spindle is stationary during milling, while the table moves along the X and Y axes. This process is typically used for “lighter” operations.

As you can see, the world of milling is diverse and encompasses many different techniques, tools, and results. The next time you think about milling a part, remember that an experienced machinist has a variety of methods available to get the job done.