As we discussed last week, quality control is almost always perceived as a cost—one of those “necessary evils” that every manufacturer must accept. In reality, however, quality control should begin long before the actual machining process: with supplier selection, incoming material inspection, storage conditions, and even the management of cutting tools.
Within this framework,
an important part of process control takes place in an area that is often regarded as purely logistical: the warehouse.
The reason is straightforward. Most of today’s engineering materials are produced from recycled scrap. Although they fully comply with the applicable standards governing chemical composition, every production batch contains slightly different proportions of alloying and residual elements such as nickel, copper, iron, magnesium, and lead. Each remains within the specified limits, yet the overall composition inevitably varies from batch to batch.
The material’s manufacturing history also plays a role. A 40 mm bar, for example, may have been cold drawn from a 100 mm billet or from a 200 mm billet, resulting in different residual stresses within the material. What we commonly refer to as raw material is, in reality, already a semi-finished product with its own manufacturing history.
For relatively non-critical components, these differences may have little practical significance. However, in industries such as aerospace, medical devices, or automotive, they become much more important because they influence tool wear, dimensional stability, and the material’s response to subsequent heat treatments or finishing operations.
For this reason, materials intended for critical applications may undergo additional laboratory testing—including metallographic examination, chemical analysis, and verification of mechanical properties against specification requirements. These tests are not necessarily performed on every batch, but whenever the application demands them.
There is, however, another aspect that should never be underestimated.
Even the most rigorous documentation system loses much of its value if human error occurs later in the process.
Two 20 mm steel bars manufactured from different grades of steel are virtually indistinguishable by visual inspection alone. In many cases, the only immediate identification is the color code painted on the end of the bar—blue, red, or green depending on the material family. While useful, this is not an infallible identification system.
This is precisely where the physical organization of the warehouse becomes an integral part of the overall quality system.
At MICROingranaggi, for example, we never store materials of the same diameter but with different chemical compositions in the same drawer or storage location. A 20 mm carbon steel bar and a 20 mm alloy steel bar are always kept separate.
The reason is not that the color markings are unreliable. Rather, we do not want operators to rely on memory or on a simple visual marking to distinguish between different materials.
Physically separating materials significantly reduces the risk of selecting the wrong bar without realizing it. It is therefore far more than an organizational choice—it is a genuine process control measure.
Needless to say, this becomes especially critical in high-risk applications. Using a steel grade different from the one specified for an aircraft valve actuation mechanism, for example, may lead to premature corrosion or mechanical failure, turning what initially appears to be a purely metallurgical issue into a functional and potentially safety-critical problem.
