CI ring and bush heated together, in one operation

The problem

Alloy wheel production pre-heats cast iron rings and bushes before assembly. The fit depends on how much each component has expanded, which depends on its actual temperature. Too cold and it will not assemble; too hot and you risk the component and waste the cycle.

An oven treats every part in the batch identically regardless of how it arrived. A part that has been sitting warm and a part off a cold rack get the same treatment and finish at different temperatures, so the fit varies.

And doing the ring and the bush as two separate operations doubles the handling for an assembly that goes together immediately afterwards anyway.

Our approach

We built a medium frequency machine to heat one bush and one CI ring together in a single operation with temperature control.

Medium frequency is the right band here rather than high, because pre-heating wants the section heated through and uniformly expanded, not a hot skin over a cold core. Lower frequency penetrates further.

The fully automatic version is a PLC controlled vertical heating station with an inbuilt DM water cooling system, working on measured temperature rather than a fixed time, so every part reaches the set temperature whatever it started at.

What this achieves

Closed loop control on measured temperature means the starting condition of the part stops mattering, which is the actual source of fit variation on this process.

Heating the ring and the bush together removes an entire handling operation from an assembly line, which is usually worth more than the heating time it saves.