Wires are drawn from steel wire rods with high carbon content. The typical manufacturing process of a motor tyre bead (MTB) wire is shown in Figure 1 and explained further.
- In the Pre-Drawing stage, the diameter of wire rods is reduced from 5.5 mm to 3.25 mm by wire drawing process by passing through a sequence of carbide die box. The average line speed is 12 m/s.
- In the Patenting stage, the pre-drawn wires are heat-treated to remove inherent stress in the wires, induced due to the wire drawing process.
- In the subsequent stage of Finished wire drawing, the diameters of the wires are reduced from 3.25 mm to 0.965 mm by wire drawing through a sequence of carbide die box at a line speed of 20 m/s.
- In the next stage, the wire surfaces are cleaned and passed through bronze coating baths to generate uniform bronze coated wires. The average line speed is 425 m/min.
- In the final stage, the wires are straightened and coiled on spools and packaged.
We always strive to have uniform surface appearance without any surface abnormality such as die marks (refer Figure 2) or other mechanical damage (refer Figure 3) appearing on the wire surface. Wires that have surface abnormality are sold at lower rates.
To detect the surface abnormalities, a small portion of the wire is cut from one end of the finished wire spool (refer Figure 4) and sent to the lab for offline visual tests. Defects are located by rotating the cut sample & observing it from various angles. Most of the time, defects are present only on one side of the wire. This method of sampling and testing is not only manual but does not represent the entire length of the wire coiled on the spool.
Thus, a solution is sought which can accurately identify such surface abnormalities online, as and when they occur across the various process steps and generate alerts & reports. This will enable us to quickly take preventive/corrective actions.
The proposed solution should meet the following criteria:
- The system should provide enough data for us to do root cause analysis of the surface abnormalities.
- Elimination of manual inspection, which is being done currently at the final stage.
- There is a variation in wire surface colors at each process stage.
- Very high line speed – up to 20m/s
- The small diameter of the wires – 0.965 mm
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