Abrasive media depends on job and machine.
It might seem like flat deburring is as simple as putting a part into a single-head machine and watching it emerge burr-free, but there often is more to it than just that. Consider edge burrs sticking up on leading and trailing plate edges. On a single-head machine, the wide-belt abrasive cuts the burr off but sometimes leaves a portion of that burr lying flat on the leading edge; this is what’s known as a secondary burr, which extends horizontally off the part. That may or may not be acceptable for the job. Regardless, that sharp secondary burr can cut into the hands of material handlers, press brake operators, and others.
In this situation, a multihead machine may work better. After the initial abrasive belt (rotating with the material feed) cuts the burrs off, a barrel brush rotating in the opposite direction softens the leading-edge burr. This produces a burr-free part that’s safe to handle.
A flat-part deburring machine can have one or more heads that hold various abrasive tools. The most common are a wide-belt abrasive that rotates around a drum; a cylindrical barrel brush positioned horizontally across the machine width; and discs that rotate over the material surface. Each belt and brush combination can be configured for the application and can include several custom abrasive media.
The drum that holds the wide-belt abrasive has a specific hardness rating, as do barrel brushes and other finishing media. Application requirements—including material type, thickness, and desired finish—dictate the hardness of the wide-belt-abrasive drum as well as the brushes. Some of the softest contact drums are 30 durometer (a little harder than a bicycle gel seat). Generally, the softer the durometer rating of the heads, the more of a radius is put on a part edge.
A machine may require multiple heads to eliminate all burrs. In this case, a wide-belt abrasive cuts the burrs but also leaves a secondary, lateral burr. To eliminate this, a barrel brush removes the secondary burr and softens the plate’s leading edge.
Abrasive media, feed speed, motor horsepower, and drum hardness determine the amount of stock that can be removed in one pass. A hard, wide-belt-abrasive drum with an aggressive abrasive and high horsepower may remove 0.02 mm of material or more, while a rotary brush may not remove a significant amount, except at that radius on the part edges.
Grit size also plays a role, especially in achieving a specific grain finish. Generally, coarse grains remove more material. On a four-head machine, the first belt might be 60 grit; the second would be 100 grit; the third would be 150 grit; and the finishing belt would be 180 grit. That 150-grit belt may be able to put a No. 3 finish on the part, while that 180-grit belt may put a No. 4 finish. (Unfortunately, when it comes to finishes, no manufacturing-wide standard exists. A No. 3 finish for one automotive customer may be different from a No. 3 finish in the appliance industry.)
Used in combination, multiple heads and brushes—running with and against the material feed—can eliminate most if not all edge burrs on flat part profiles. If laser-cut parts have tiny edge burrs in slots only 1,5mm wide, chances are some combination of abrasive media will eliminate burrs wwith slots. If a part has burrs on the top and bottom edges, passing it through the machine twice should eliminate them (though some specialized, high-volume machines do have abrasive media above and below the workpiece, effectively eliminating all burrs in one pass).
Put simply, finishing and deburring machines are designed to remove imperfections that remain attached to workpieces after they’ve been modified by another machine. These undesirable raised edges are commonly known as burrs, and they fall into one of two categories:
- Mechanical burrs result from operations like shearing, stamping, or folding.
- Thermal burrs, often called slag or dross, are caused by heat-generating machines like laser cutters.
There are a variety of factors that can lead to the formation of burrs including the type and thickness of the metal being worked, condition of the die, blade clearance, and pressure or power exerted by the machine.
Understanding the Differences between Deburring and Finishing
- Deburring involves removing any raised edges or small pieces of material that remain attached to a workpiece after it’s been modified.
- Finishing is done to alter the surface of a workpiece, getting rid of any scaling and pitting to enhance its quality or prepare it for a next step like painting.
Other common operations done with finishing machines can include calibration and stock removal (a machining operation done to achieve higher material removal rates and decrease variations), slag grinding (targeting slag produced by thermal cutting machines), and edge rounding (any action that breaks the edge of a metal part, but especially those that form an edge radius).