How a DC motor armature is manufactured: the 9 steps

A brushed DC or universal motor armature passes through a fixed sequence of operations. The order does not change between manufacturers; what changes is how much of it is automated, how tightly each station is controlled, and how early defects are caught.

1. Shaft pressing

The shaft is pressed into the laminated core. The controlled variables are axial position and press force; a force curve outside the window usually means a wrong core stack height or a shaft outside tolerance.

2. End plate pressing

Insulating end plates are pressed onto both core faces so that the winding does not touch the lamination edges.

3. Commutator pressing

The commutator is pressed to its axial distance from the core with its tangs angularly aligned to the slots. Alignment error here shows up at winding as missed hooks.

4. Slot paper inserting

Insulation paper is cut, folded and pushed into every slot. Paper length and fold accuracy decide whether the paper stays put during winding.

5. Winding

Flyers wind each coil into its slot pair and hook the wire on the commutator tang. Tension, turn count and hook position are the controlled variables.

6. Commutator welding

Each tang is spot-welded or hot-staked to fuse the wire and copper. Joint resistance scatter is the failure mode to watch.

7. Slot wedge inserting

Wedges close the slot openings and hold the coils against centrifugal force.

8. Commutator turning

A diamond tool turns the commutator surface round and smooth. Runout left here becomes brush bounce in the finished motor.

9. Testing

Bar-to-bar resistance, surge and hi-pot tests confirm the winding and insulation. Results are logged per part or batch.

Where scrap comes from

• Commutator misalignment at pressing → missed hooks at winding
• Paper movement at winding → insulation failure at hi-pot
• Weld energy drift → resistance scatter at test
• Runout at turning → field returns, not factory scrap