ENGRAVED ROLL MARKING STAMPS

When a component or a part is marked with a steel stamp, the process is basically cold forging; the material is being moved around or compressed. As a result, for a stamp to be durable and effective in producing a clear mark, it must be hard, have sharp edges and a smooth surface along the entire relief angle of the character.

Over the past 20 years, the EDM process has been applied to the manufacture of steel marking stamps in an effort to produce stamps faster and at a lower cost. Those objectives were really never met, and the result has been a loss in stamp tool life and mark readability. Production-proven tests have shown that ultra high-speed milled (up to 50,000rpm) engraved stamps that are double-pass milled will typically last twice as long, and in some instances up to eight times as long as EDM stamps. Columbia Marking Tools, marking stamp producer, uses a proprietary ultra high-speed engraving and milling system to provide highquality marking stamps, which in many cases is a lower cost process than EDM technology.

Often, manufacturers do not fully understand the quality issues related to stamps produced with the EDM process. When the difference can be visually demonstrated, the benefits become obvious and improved quality is a given.

Because steel marking stamps are considered secondary operation tools, it's not uncommon to find stamps operating for up to six months without being replaced. Combine this situation with the increased use of more environmentally-friendly, watersoluble lubricants and release agents and you'll find compacted dirt in the character grooves, especially on EDM stamps.

Manufacturers of hand tools, for and during the process, carbon in the steel material disintegrates and decarburization occurs. It's important to remember, it's the carbon in the steel that makes it ‘tool steel'.

One of the Snap-On sockets that has been marked with a Columbia engraved roll marker.

As a result,EDM processing the surface automatically reduces stamping die life as much as 20%. Because the EDM surface layer is untempered, it can cause premature failure where high impact to tensile stresses are encountered. In simpler terms, the EDM processed surface works like sandpaper, where build-up naturally occurs on the rough surface during stamping action, and grabs onto the surface dirt. This happens on closed characters like Ps, Os, Ds and As, which ultimately causes character blowout or severe premature wear, so that the characters appear missing or washed out. And when characters are small, the problem is compounded that much more.

As the issue of overall part quality has evolved, manufacturers continue to search for improvements for every operation in the manufacturing process, and that has included part marking. For some of those manufacturers, one area of improvement that has added value, but not cost, has been replacing EDM stamps with those that have been engraved with a precision ultra highspeed milling process.