Sledge hammer head hardening, double station

The problem

A sledge hammer head has an awkward specification. The striking face must be hard enough to resist deformation under repeated impact. The body must stay tough, because a uniformly hardened hammer head can shatter, and a shattering hammer head is a safety incident rather than a quality problem.

So the requirement is selective hardening: a defined hard zone on the face, and a soft, tough body behind it. That is exactly what induction does and exactly what a furnace cannot.

The production problem was different. On a manual hardening cell for a part this size, the heating itself is a small fraction of the cycle. Most of it is the operator picking up the head, locating it, starting the cycle, waiting, and unloading. The power supply sits idle for most of the time it is switched on.

Our approach

We built a PLC controlled vertical scanner with two stations, allowing the operator to load one station while the other completes its heating cycle.

The machine carries an inbuilt DM water and quenching water cooling and circulation system, so the coil circuit and the quench circuit are separate and both are self-contained.

Doubling throughput this way costs one extra station and one extra fixture. Achieving the same throughput by adding a robot would have cost considerably more and added something else to maintain in a hand tool works.

What this achieves

The cycle is set by the machine rather than judged by the operator, so the hardened zone is in the same place on every head and the body stays tough.

The second station addresses the actual constraint rather than the assumed one. That is worth stating plainly, because the instinct on a slow cell is usually to specify more power, and more power would not have helped here at all.