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Technical : 10.1 Burrs vs. Parting Line Flash

10.1 Burrs vs. Parting Line Flash

We occasionally receive notice of a discrepancy described as “burrs” on various locations of the products we manufacture, and have been asked to clarify some definitions for inspection departments.

The term “burr” is ordinarily used in the context of metalworking operations such as lathe turning or milling operations. This condition ordinarily occurs where metal is removed via some process involving a cutting tool. Less than ideal circumstances such as dull cutting tools, improper feed rate, poor machine-ability of the metal, improper cutting bit material, etc., are the main sources of “burrs”. Now given these burrs are metal, they themselves become a source of a whole range of problems such as: dangerous sharp edges that pose a hazard to assemblers, fit and interference problems, wear and damage problems when burrs break off and enter potentially harmful areas of application. These situations can be prevented with good metalworking procedures, and monitored by incoming inspection by referring to appropriate notes on the drawings as is currently done.

Parting Line Flash (PLF) on the other hand is a condition inherent to all plastics molding operations. The molding procedure requires the dies to assemble and disassemble during the molding cycle. The dies are assembled to form a cavity which the plastic resin is forced into. The dies are then disassembled and the plastic part is removed. Some of the components move against each other, requiring a certain minimum clearance between them. Those areas where clearance must exist, also provide very small cavities for the plastic resin to be forced into. When the dies are disassembled what remains of the resin forced into the clearance cavity of the assembled dies, is called “flash”. Stated another way, this resin remaining where the dies separate and move “apart”, is called PLF (Parting Line Flash). As stated earlier this is a required condition for the molding process. Note: In some interference geometries, flash is a desired component.

PLF is monitored by incoming inspection to the following parameters: 1)The flash must be tightly adhered to the main body of the part. It must require sharp cutting or scraping tools to remove. It must not be easily loosened or removed by hand. 2)The flash must not protrude from the main body of the part by more than .015" or in such a way that hampers the performance or function of the finished part. These situations are prevented with a de-flashing operation we perform as a final step in our manufacturing process which minimizes but not entirely removes, the condition.

Although these two conditions (burrs and PLF) appear similar to the untrained eye, they are indeed quite different. Consequently when incoming inspection refers to a condition described as “burrs” when in actuality it is PLF, we are at the situation currently being addressed: Incorrect or inappropriate usage of terminology.

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Plastic Injection Molding Services

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Plastic Injection Molding Services
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