Alluring Deburring

APRIL 2008 / VOLUME 60 / ISSUE 4 By Dr. LaRoux K. Gillespie Using magnetic abrasive finishing for deburring produces parts that perform well and look great. C ustomers won’t accept precision parts with rough surfaces, microcracks, recast metal, burrs, metallurgical phase changes, visible scratches or damaging residual stresses. Yet grinding, EDMing, laser machining, conventional cutting and even polishing can produce these unwanted side effects. However, magnetic abrasive finishing or polishing (MAF or MAP) processes can remove these defects and provide highly polished surfaces (Figure 1). EDMed surfaces typically exhibit recast metal subsurface damage. This can cause parts to be rejected. Subsequent processes such as reaming, honing, lapping and grinding must be used, but they too can create problems to a lesser degree. MAF, however, does not create additional quality problems and is one of the least complicated processes for removing material to provide a true base-metal surface. Equipment is Part Dependent The equipment needed for deburring with MAF depends on part geometry. For example, a small lathe can typically be used for MAF of cylindrical surfaces, while a milling machine performs MAF on flat surfaces, recessed pockets, rectangular parts and parts with both flat and cylindrical surfaces. In MAF, a magnetic field is created by rotating the part opposite a fixed magnet or rotating the magnet around a fixed part. These magnets attract abrasive grains of different sizes and materials, such as silicon carbide, which come into contact with and finish the part’s surface. The abrasive grains are mixed with small amounts of metalworking fluid, such as distilled water, SAE30 motor oil or kerosene. The fluid helps retain the abrasive, adds lubricity and cools the parts. It also reduces abrasive impregnation and improves finishes. Some abrasives have metal cores that respond to the magnetic field. If abrasives without this core are used, loose magnetic grit (such as iron filings) is added to create a medium that responds to the magnetic field. The magnetized grit Magnetic Abrasive MagneticFinishing abrasive finishing Magnetic abrasive barrel finishing Metal pin media Magnetic abrasive spindle finishing Iron base particles + abrasive particles Conventional Magnetic abrasive cylindrical finishing (lathe applications) Magnetic abrasive prismatic finishing (machining center applications) Vibratory assist Ultrasonic assist Chemical Electrolytic Continuous field Pulsating field Magnetic abrasive rheological finishing Magetic abrasive float polishing Conventional Electrolytic Abrasive flow L. Gillespie Figure 1: There are several types of magnetic abrasive finishing (MAF), which can be divided into groups and subgroups. MAF float polishing and rheological finishing are primarily processes for semiconductor and ceramic parts. Other processes can accommodate metal, glass and ceramics. Alluring Deburring (continued) and coolant medium carries the abrasive particles along with it. An MAF setup for deburring does not need to be precise or rigid to produce mirror finishes because the magnetic field directs the loose abrasive grains. These grains act as self-sharpening tools because different edges rotat