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Surface Treatment 28 MoldMaking Technology —— JANUARY 2018 By Thomas Pickhardt and Brian Guild VIDEO Access the related video under the Videos tab at MMT online. Machine-Hammer Peening Automates Mold Polishing Images courtesy of Accurapuls Canada Inc. H igh-quality, smooth surfaces are essential in mold manufacturing. Customers insist on it, but the pro- cesses for achieving these surfaces are costly and diffi- cult. Polishing is one such finishing process that requires abra- sive rubbing or a chemical action to produce a smooth, shiny surface and to diffuse reflections. The challenge for moldmak- ers is the labor-intensive nature of these operations that are completely dependent on the personal skill and expertise of an experienced mold polisher. The bottom line is that polishing requires a lot of time and skill, is prone to costly errors and delays and causes frustration. A polishing automation solution eliminates hand work, accelerates milling operations and controls surface geometries. System components for machine-hammer peening include the peening hammer and striker, spindle adapter, flex cable, air hose, computer, CAM software, control console, handheld pulse generator, machine tool and workpiece. Polishing Basics An unpolished, milled sur- face that is magnified 1,000 times has the appearance of miniature peaks and valleys. To reduce this roughness, a polisher rubs the surface using coarse grit, then progresses to finer grit and eventually buffs with compound pastes. Repeated abrasive rubbing over the surface literally "wears" the peaks down until they are flat or shallow hills, and the surface becomes smooth. A polisher uses hand stones, emery cloth and honing compounds to achieve the required grade of smoothness. However, since the pol- isher physically removes the material in this process, the polisher often compromises the dimensional outcomes and surface geometries, ren- dering them "unknown" and impossible to repeat. Control over the finished product is lost. Surface inspection becomes a subjective opinion and can lead to customer disputes or dissatisfaction. What is more, overworking the surface can lead to defects, such as orange peel, scratching and pitting. Polishers must take great care to avoid these flaws. Many mold manufacturers today address these risks by finish-milling the surfaces as smoothly as possible to minimize