Wire EDM and milling machines with multiple axes can make complex parts in a single setup. This boosts production, slashes labor costs, while giving a company a competitive edge.

Electric discharge machining

As a brief refresher, a wire electric discharge machine (EDM) works by submerging conductive part stock in a dielectric fluid, then placing the stock near a taut wire carrying an electric current. This creates a tiny electrical spark that precisely erodes away the material. Part accuracies are between ±0.0001 in. to ±0.00005 in. Surface finishes depend on wire quality and dielectric and ambient temperatures, as well as the machine's rigidity, its movement accuracy, and spark-control precision. Wire EDM works well making small and complex parts and ones from brittle materials.

Most wire EDM machines have what's called XYUVZ control. The XY axes relate to lower-head movement in the X and Y direction and UV axes relate to upper-head movement in the same direction. The Z-axis moves the upper head up or down before XYUV movement starts.

A scenario for these machines often goes like this: An operator clamps a part directly to the worktable and makes a cut. He then unclamps the part, turns it, and re-clamps it for the next cut. For a more automated approach, operators can perform what's called turn-and-burn operations. Here, an operator clamps a part to a manual indexer mounted on the worktable. The indexer allows rotating and cutting parts without unclamping them, but the devices are not controlled by the machine. Wire EDMs also work with programmable indexers. These mount to worktables and connect for power and control into a built-in port on the machine. The devices can be programmed to turn an arbitrary fixed rotation speed to index a part to some angle before machining recommences.

What we call turn-while-burn increases the flexibility of conventional turn-and burn operations and is an option that turns parts mounted on a rotary, servo-controlled B-axis. The B-axis can index a part to a required angle before EDM cutting. Or, in true turn-while-burn mode, the indexer can be synchronized with XYUV movement. Turn-while-burn has the indexer motor rotating at different rates during machining, usually with feedback from (and relative to) the X and Y cutting speeds. This arrangement can generate complex “twisted” or helix parts.

High-speed machining

High-speed machining (HSM) at, for example, a 42,000-rpm spindle speed provides faster machining speed, better accuracy, and a more polished surface finish than that from conventional milling. Part accuracies are between ±0.001 in. to ±0.0001 in.

In the past, HSM was limited to 3-axis machining. Here, the top head spindle holds a rotating cutting tool (such as an endmill) that cuts a part clamped on a stationary work table. Adding two more axes, here called B and C, made simultaneous 5-axis HSM a reality. Basically, the B-axis controls the center of the table rotation around a line parallel to the Y axis, while the C-axis controls the center of the table rotation around a line parallel to the Z axis.

This seemingly complex arrangement is easier to understand by mentally separating things into two areas, that is, 3-axis (X, Y, and Z) + 2-axis (B and C). For example, to determine the function of additional rotary axes (A, B, and C), assign them in alphabetical order to the linear axes X, Y, and Z. Thus, an A-axis associates with the X-axis, B goes with Y, and C with Z. In simultaneous 5-axis milling, as the cutting tool travels in 3D space, the part can rotate simultaneously in B and C in synchronized rotary motion or at an indexed and tilted orientation, similar to EDM. Other manufacturers may assign axes in different configurations.