Manufacturing: Metal Forming

Sheetmetal Forming - Fine Blanking

Fine blanking produces complex 'net shape' finished parts in just one or two operations. It can replace castings, forgings, fabrication and all subsequent machining operations. Consequently, it can be very cost-effective. Fine blanking is used primarily in the automotive components industry where quality is paramount, and the volumes can justify the cost of the press and tools.

The process, which is essentially a hybrid between stamping and cold extrusion, was developed in Switzerland in the 1920s for the watch and clock industry.

Advantages -

1. Repeatability - the closely toleranced design of the tool, and the fact that all operations are contained within the tool, so that special features are created as the basic component is produced, which lead to inherent quality and reliability
2. Cleanly sheared edges - with little or no edge break, eliminating the need for shaving, broaching, or profile grinding.
3. Tolerance on holes and profiles - infinitely better than conventional pressing because of the inherent characteristics of the process and the tooling
4. Flatness and surface finish - the fact that both sides of the component are supported at all times ensures a flatness standard which cannot be matched by conventional pressing, thus avoiding the need for planishing and other flattening processes.
5. Additionally, many advanced features such as gear teeth, ratchets and splines can all be formed without the need for hobbing, broaching etc.
6. Counter sinks, half shears, coined sections, self rivets or location point welding projections and many other shapes can all be made at the same time as the part is blanked, thus maintaining uniformity of position, component to component, and batch to batch.

The cost of fine blank tooling is, size for size, a little higher than conventional press tooling, but less than powder metal sintering tooling. All competent fine blanking companies have their own tool design and manufacturing facilities. The normal practice is for customers to own the tooling, which they pay for on satisfactory completion of a sample inspection.

A fine blank press does not run as fast as a conventional press and consequently for simple components such as brackets, where tolerances are not that tight and edge finish and cosmetic appearance not so important, conventional pressing or stamping has the economic advantage. When tight tolerances have to be held and where edge finish or flatness is important, or special features such as small holes, countersinks or half shears have to be added, fine blanking comes into its own. Basically, if a conventional high-volume pressing requires a secondary operation such as flattening, drilling, broaching, welding or hand finishing, it is likely that a fine blanked component will be better value.

By virtue of being able to produce a 'net shape' to drawing without any further machining, fine blanking is almost always less expensive than forging or casting and subsequent machining. Clearly there are many complex three-dimensional shapes where fine blanking is not appropriate, but with some forethought and creative design, a product can be designed that takes advantage of the economic benefits of fine blanking.