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Ask the Stamping Expert: What is the best method for selectively removing burrs from stamped holes?

Q: We receive high-volume, high-precision, low-cost stamped parts from a vendor. The oval-shaped parts come with burrs that we need to remove from the inner holes, but we cannot round the outside part edges. The cold-rolled steel parts have two sets of holes with different diameters stamped through the 0.088- to 0.092-in.-thick flat stock. What method can we use to remove those burrs?

Note from Ask the Expert columnist Tom Vacca: This topic is outside my area of expertise, so I am deferring to Steven Jacobsen, process development engineering supervisor for Micro Co.

A: The component deburring operation often is overlooked during high-speed stamping process development and quoting. The specific type of burr removal required can very costly when manufacturing any steel component. Understanding the various available options and their relative cost-benefit ratios will help you choose the right process for the job.

In this case you are looking for localized deburring that will target the stamped holes at the center of the part. Burrs not removed from this area will cause varying plating buildup, increased scrap, and poor process control.

Localized deburring is achievable, but at what cost?

The simplest solution to this problem is to remove the burrs with mechanical deburring methods such as hand tools or localized bead blasting. This will target the features but leave the outside edges of the component untouched. However, hand deburring is not cost-effective for a relatively low-margin flat blanked component.

Mass finishing is perhaps the most common deburring technology in use today. In this process components are deburred through tumbling or vibration in a vessel of specific media. The media acts on the workpiece abrasively to remove burrs and polish or descale surfaces.

This process can be scaled to work in relatively large batches, so it is cost-effective. Media sizes, shapes, and compositions can be chosen for the application to address specific areas of the component more aggressively than others. Consult with a mass finishing expert to engineer specific media and parameters required.

Another option is electropolishing. This process deburrs through an electrochemical reaction that dissolves burrs and polishes the surface. The workpieces are placed on a rack in an electrolyte bath, and a current is applied between the solution and workpieces. The amount of removal is proportional to the processing time and current applied.

While not specifically targeting the inner holes, electropolishing will have the greatest material removal rate on burrs that have the largest amount of current flowing through the smallest cross-sectional area. In this way, only the burrs are removed and, in general, edges are not rounded. Although this process is suitable for a variety of materials, it is better suited for higher-cost components because of processing times and the required labor for racking, processing, and electrolyte waste disposal.

Another option is thermal deburring. This process can deburr large quantities of components efficiently with no edge rounding. It uses a pressurized vessel filled with a mixture of oxygen and a combustible gas, which is then ignited in a controlled manner. The extreme heat generated can reach localized temperatures of up to 6,000 degrees F. The ratio of mass to surface area of the burrs causes the burrs to reach temperatures higher than their ignition point, and they are vaporized within milliseconds.

Because of this extremely short processing time, the rest of the part is not affected. Any oxides resulting from the combustion process can be removed using acidic aqueous washes before additional finishing, plating, or cleaning operations.

The capital costs for thermal deburring are very high, but an increasing number of vendors are employing this service on a contract basis. As a result, the cost per unit for processing in bulk is kept in line with expectations for high-volume, low-cost stamping.

About the Author
Micro Co.

Thomas Vacca

Micro Co.

Has a shop floor stamping or tool and die question stumped you? If so, send your questions to kateb@thefabricator.com to be answered by Thomas Vacca, director of engineering at Micro Co.