Reverse Flow and Supplier Development

Why it matters

Reverse flow is material going back from the point of use or delivery for inspection, repair, re-evaluation or suitable handling. When a returned part is taken off the accounting record or off usable stock, it does not physically disappear from the system. It is moved, set apart, examined and waits for a decision. A part judged suitable can be accepted again; a reworked part requires a final inspection; for an unusable part, an authorized closing action is also needed. If the durations and space needs of these stages are not recorded, the load of the return becomes invisible. While the forward-flow plan counts only new orders, the same resources can fill up with return work. Reverse flow is therefore examined with its own quantity balance and capacity calculation.

The number of returns does not explain the whole quality loss. Some parts are truly defective; some come back because the wrong material was sent or because the acceptance definition did not match. Returns in which no defect is found also create inspection and transport load. For each return, the claimed cause must be separated from the verified finding. A condition the buyer calls nonconforming may not be reproducible under the supplier's inspection condition; this difference needs to be investigated. A repeat return of the same part creates a new physical load, but its link to the first defect must also be kept. The number of return events, the number of unique parts and the number of defective units are not the same concept. If improvement rates are compared without this distinction, the result can be misleading even if the numbers are added up correctly.

Supplier development is not just asking for defective parts to be sorted out faster. It is necessary to understand together the condition under which the problem arose, test the correction in a limited trial and show that the acceptance result has been preserved. If the final inspection has been removed while rework time shortens, the apparent capacity gain may not come from real quality assurance. Conversely, extra inspection at the supplier can reduce returns but may create more work in the whole system. For this reason, the added and reduced work at both the buyer and the supplier is kept visible. Minutes removed from one side's record may have moved to the other side. A joint improvement decision separates a shift of load from a real reduction in load. When the acceptance condition of the part does not stay the same, old and new results cannot be compared directly.

Transport is not explained by the number of vehicles alone either. The quantity, weight, distance, set-aside space and re-shipment requirement of a return create different loads. A large number of small parts carried in a single vehicle and the same number of heavy parts do not create the same physical load. On the other hand, multiplying kilograms by kilometers is not directly a monetary cost or an environmental impact calculation. These claims are not made unless the necessary coefficients are given. In this lesson the inspection and rework minutes, the weight carried and the distance are calculated together. Each result is presented with its own unit. The final decision should show that no open return remains, where the physical quantity went and by what evidence the development was accepted.

Formula