A burr (also known as a “flash”) is an unwanted raised edge or small piece of material left after a part has been worked in a manufacturing process. It can be metal, rubber, plastic or really any other material used in manufacturing. Machining operations such as grinding, drilling, milling, turning, tapping, slotting etc. cause burrs in machining operations. As you can see in the picture on the right, burrs give plastic a messy, unfinished appearance. But with a little elbow grease, those same parts will be crisp-looking and ready for use!
The process of removing the unwanted piece is called deburring. Deburring often accounts for a substantial portion of manufacturing costs. There are four types of burrs formed by machining operations: Poisson burr, rollover burr, breakout burr, and tear burr. Let’s take a closer look at the different kinds of burrs and deburring processes.
Types of Burrs
1) Roll-over Burr
The rollover burr is the most common type of burr. It is basically a chip that is bent rather than sheared, resulting in a comparatively large burr. This type of burr is also known as an exit burr because it is usually formed at the end of a cut in face-milling.
2) Tear Burr
A tear burr is the result of material tearing loose from the work piece rather than shearing .
3) Cut-off Burr
The cut-off burr is a projection of material left when the work piece falls from the stock before the separating cut has been completed.
4) Poisson Burr
The Poisson burr is a result of a material’s tendency to bulge at the sides when compressed, causing permanent plastic deformation.
Types of Deburring
While there are many types of deburring processes, the ones described below are used specifically on plastic materials.
1) Manual Deburring
Manual deburring is the most common type of deburring as it allows for the greatest flexibility. The tools used for manual deburring are generally low in cost. Manual deburring allows for instant inspection and generates the best quality without stressing the materials being worked on. Manual deburring is commonly used on plastics as well as on metals and other materials. The negative sides to this process are the expense of maintaining staff and the possibility of human error.
2) Cryogenic Deburring and Deflashing
Cryogenic deflashing and deburring is one of the most efficient and least expensive processes used to remove flash from injection molded parts and machined components. Using liquid nitrogen, components are lowered to a temperature that allows the material to become brittle. Then, utilizing a cryogenic deflashing machines the flash and burrs are easily removed without altering the finish on the parts. This process can be completed on a wide variety of materials, including rubber, plastic, silicone and light metal die castings. Cryogenic deflashing of rubber and plastic parts removes unwanted residual mold flash that is found on molded parts after removal from the mold. Flash is typically found in areas where the mold comes together or apart, when the liquid mold material escapes from the mold cavity during production. Cryogenic deflashing does not degrade the parts or harm their finish. Only the flash is removed and the shape of the part is retained. Edges stay sharp and recessed areas are completely cleaned of flash. Plastics can be deflashed with great precision.
3) Mechanical Deburring
This is a process that mechanically grinds or sands the burr off a manufactured part. It can be used on materials like PVC that do not produce a smooth finish when deburred by hand. This process can be time consuming and the quality of the finish is not guaranteed.
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