EDM Strategies for Odd Pockets
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By Ann Mazakas The wire EDM market thrives on complex shapes that are difficult, if not impossible, to cut by any other means. However, that challenge can become a real chore when geometry is too complex to remove easily in one piece. One option is to remove sections of material bit by bit with cumbersome geometric manipulations and multiple machining operations. A better choice is to let a computeraided manufacturing (CAM) system perform an intelligent calculation of the geometry and then generate the simplest, most intuitive wire path possible to effortlessly remove a complex shape. Cutting to the Core The first step in the analysis of a complex profile is to identify the two basic areas that need to be cut: • The core • The shell The core represents the largest area that can be removed with simple 2-axis wire path. The shell is the remaining area between the core and the desired outer profile. Divide and Conquer A classical approach to problems of great complexity is to “divide and conquer”. This technique proves itself time and time again because, quite simply, it works. To know how to divide and conquer requires a skillset that involves in-depth knowledge of the capabilities of wire EDM, knowledge of the different cutting processes that can be applied, and the experience to know which cutting processes will work best based on the geometry of the given workpiece. For a skilled programmer working without assistance from an advanced CAM system, it could take several hours to produce the correct geometry and generate the wire path for an odd shape with complex tapers. Working with the assistance of a CAM system that uses advanced algorithms to analyze all the shapes involved and then use that analysis to calculate the most efficient wire path can reduce that time to minutes. That’s time that can be spent burning metal instead of burning brain cells. ESPRIT uses the logic of “divide and conquer” to analyze and split complex pockets into smaller, separately defined zones that can be easily cut with adaptive 4-axis EDM strategies. Two areas on the model are initially identified: the core and the shell. The core represents the largest area that can be easily removed with vertical wire path. The remaining shell area can then be removed with 4-axis no-core pocketing wire path.

The core area can be removed with either a 2-axis contouring wire path or burned with 2-axis no-core pocketing. Then, the entire shell area is burned with 4-axis no-core pocketing wire path. As with the core, the user can choose how the shell area is removed. This choice will mostly depend on the shape of the cavity. When the thickness between the core and the outer profile is relatively uniform, the entire shell is burned with an advanced morphing techique that gradually adapts the shape of the wire path from the inner core to the shape of the outer profile. When the thickness between the...

The “No Core” strategy burns the entire shape with no-core pocketing wire path from the inside out. This wire path also uses an advanced morphing technique to adjust the shape of the wire path to the shape of the inner and outer profiles. Getting there from here A common issue with complex pockets is that the geometry simply does not allow the wire to be threaded in a standard vertical orientation. In that case, the wire must pass through a tilted thread hole at the start of the operation. In ESPRIT, the features for 4-axis EDM can be modified to tilt the thread angle. The user can add a...

When an area cannot be reached without causing a violation between the wire and the part, each zone of the pocket can be connected to a calculated inner profile. In a single CAM function, wire EDM programmers can have the options they need to machine virtually any complex shape in an intuitive and effortless way. This can only be accomplished when the software developer does an in-depth analysis of each step in the process programmers use to generate wire path. It also requires real-world experience working with the EDMs that are used today on the shop floor and by partnering with machine...