Marking the exhaust pipes of these famous motorcycles with their model names can be tricky. Find out how embossing—or metal squeezing—is getting the job done:

From the pages of IEN Online

Embossing — or as it is sometimes called, semi-coining — is a method of marking that is essentially metal squeezing. The process requires a great deal of know-how and experience in not only the way certain metals move under pressure without affecting metal thickness, but also how stretching and compressing affects the height of the design lines. Materials that can be successfully embossed include gold, silver, low carbon mild steels, brass, bronze, and copper. The advantage of embossing is that complicated designs with smooth surfaces can be economically and accurately reproduced in metal parts at good production rates. Limitations involve the difficulty in maintaining uniform part thickness and the creation of sharp impressions.

Embossing marking die manufacturer Columbia Marking Tools, Inc, Mt Clemens, MI, has provided many of the marking tools used to emboss the model names that decorate the exhaust pipes of Harley-Davidson motorcycles. Columbia designs and manufactures metal and plastic marking equipment including stamps, roll marking dies, roll marking and impact marking machines, numbering heads, and special marking machines.

“Many times we are not given a great deal of preliminary information when we are asked to make an embossing die,” notes Tom Phipps, Columbia’s CEO. “Some of the products we work on are prototypes and we may only be given the type of material, the thickness, the approximate shape, and maybe some rough diameter dimensions. This can be pretty tricky when the part to be marked has severe tapers and bends like those found on motorcycle exhaust pipes. There is a good deal of extrapolation of basic dimensional information that we have to do, and this requires a great deal of experience and know-how.”
Steel dies with matching male and female die configurations are generally used for embossing. The die material is selected and matched to the application and hardness of the part to be marked. For example, higher cost, longer wearing die steels can be justified if the required production rate is high. If the part temperature is too high, it may draw the hardness out of the die. As a starting point, oil-hardened die steels are typically used. Some applications may require air-hardened or even high-speed steels with fine grain powder metal technology. Columbia Marking Tools stocks over 21 die steel grades.
For embossing, the idea is not to compress/forge the steel, but to flow the metal. Metals are viscous and will flow under pressure without tearing or reducing the metal thickness. However, they all perform differently, and the real skill is in producing the depressed side (shoulder) wall of the embossed shape. The highest pressure in a given squeezing operation is required to set the part at the bottom of the press stroke. As movement takes place, metal fluidity decreases and pressure to sustain the movement must be increased. As a result, both lateral and vertical movements can be achieved.

“For the Harley-Davidson exhaust pipe application,” Phipps adds, “40 tons of hydraulic pressure was required to emboss the convex and concave logo dies. Much testing and design engineering time was required to produce the internal mandrel, which holds the female convex die. The mandrel had to be open on one end and reach 18 in. into the exhaust pipe with just the right amount of flex, while remaining rigid enough to prevent any distortion to the exhaust pipe or logo. In these types of embossing applications, the die shoe and the precision embossing depth stop pins are all keyed and doweled so they are all ready to go right into the customer’s press.”


Columbia Marking Tools, Inc
Mt Clemens, MI
800-469-6275
www.columbiamt.com

*Reprinted from IEN Online March 2004