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moldmakingtechnology.com 29 Machine-hammer peening is applied through the operation of a controllable electro-magnetic hammer head imparting rapid reciprocal motion of a striker ball against a workpiece surface. This image demonstrates the before and after of a mold surface being peened. or eliminate hand polishing. Cusp height, or the distance from the top of the microscopic "hill" to the bottom of the "valley," is a measure of the milled surface roughness and is recorded in micromillimeters or microinches. A general rule is that the closer the milled pitch distance is from sidestep to sidestep, the lower the cusp height will be. Ball nose endmills with larger diameters also reduce cusp height at the same pitch since cut- ters with larger radii produce wider tool paths. In theory, this method makes sense. However, in practice, it is a costly exercise because these cutting operations require a lot of machining time and use accurate, rigid, expensive machine tools with high spindle speeds, feeds and processing capacity. These cutting operations also require expensive con- sumable cutting tools that actually "cut" the steel as opposed to simply sliding, scraping or dragging them over the surface. Also, the use of improper cutters can cause surface defects. Simply put, cutting alone can never achieve perfect smooth- ness. So, despite the best final milling practices, polishing remains a necessary finishing process for achieving customer- required surface qualities. Nevertheless, moldmakers today can choose a different polishing strategy. Automated technology that is capable of enhanced surface quality can replace manual polishing. This mechanized system also facilitates faster milling operations, which reduces costs and accelerates job completion. Automated Polishing Peening is the process of working a metal's surface to improve its material properties, using mechanical means, such as hammering, blasting with shots (shot peening) or blasting of light beams (laser peening). Peening itself is not a new treatment, as Ancient Egyptians practiced it to improve the strength and durability of their chest armor and spear tips. They understood that a cold- working process produced better results than heat treating their metals. Today, this process uses automation to hammer and control each point of impact. An electronically-con- trolled hammer head produces machine-hammer peening, and a CNC machine or a robot controls the head positioning, executing CAM software that is programmed specifically for peening applications. A separate moveable console unit on rollers contains a computer and a 110-volt power supply that converts DC for the hammer head. Electromagnets in the conical-shaped head create a powerful Lorentz force (or the force exerted on a charged particle moving with velocity through an electric