CNC Milling and CNC Punching: What are the Differences?

August 6, 2019

CNC Milling and CNC Punching, the Computer Numerical Control prefix does imply a link, but aren’t they two different machining processes? Controlled by computer codes, CNC Miling involves the use of a “milling” cutter. Unlike that subtractive material shaving machine, CNC Punching equipment processes sheet metal feedstock. The punching turret or head drops down to strike free a blank and leave behind a geometrically precise opening.

What Do They Have in Common?

That’s easy enough to answer. The CNC label is there on both machines, so they both have that control system in common. A 3D model is stored in a computer’s workspace. The shape of that part, plus its various holes and shaped openings, are then translated into machine instructions. That’s the G-code, the machine programming language that tells a tool to carry out a movement or tooling operation. At any rate, whatever the automated equipment, there’s a G-code that’ll tell it to punch or mill, or whatever. Okay, let’s leave the codes behind; we’re headed over to the factory floor.

Describing the CNC Punching Process

There’s a moving table, which is shifting a section of sheet metal along the X and Y-axis. When a punch point aligns, the automated punch head drops down and strikes. Arrays of shaped openings are struck on the sheet metal. They’re positioned mere millimetres apart as the table moves incrementally to the left, then it moves slightly down to begin a whole new line of openings. Using a special turret attachment, CNC Punching machines can even switch tools while a job is underway.

Switching Over to a CNC Milling Machine

If punching tools create perfect 2D blanks, what can a CNC Milling machine do? Well, the tool head isn’t static, isn’t driven by a powerful piston. Unlike CNC Punching equipment, the cylindrical tool is spinning. It lowers daintily to cut and sculpt sections of metal away from a workpiece. Like a sculptors’ chisel, it subtracts shavings until the profile of a dimensionally accurate part is fully revealed. Better yet, though, the milling head can work at an angle so that it can process intricate workpiece geometries.

CNC (Computer Numerical Control) systems are automated. They manipulate tool heads and workpiece retaining tables. For CNC Punching, expect X-Y table movement. The punch and die align, the table moves again, then a ram strikes. Intricate openings are precisely placed using this technique. As for the CNC Milling machinery, its hardened bit spins while cutting. Mounted on a multi-axis framework, a workpiece remains stationary while the tool head moves on three axes. On advanced machines, even angular strokes present little challenge to top-tier CNC Milling equipment.

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