Production Machining

AUG 2018

Production Machining - Your access to the precision machining industrial buyer.

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Chipbreaker Lingo Understanding the terminology and important features of the functional chip geometry can help in learning the ins and outs of chip control. Interference Geometry: The form pressed or ground into a grooving insert that creases the chip. This form is used in grooving to ensure the width of the chip is less than the width of the groove. Talus: A protrusion that extends toward the radius of the tool, functioning to redirect the flow of the chip back toward the material. The talus cannot intersect with the cutting edge, but the closer it is, the smaller the minimum depth capability. Hone: Protects the cutting edge from damage while also playing a role in shearing the material. The size of the hone defines the amount of pressure at the cutting edge. Plateau: The height of the insert plateau over the cutting edge height will define how aggressively the chipbreaker will behave. Normally, a shallow plateau is made for short chipping material. Primary Rake: Located immediately behind the hone, this angle defines how positive- cutting the geometry is. More ductile work materials such as aluminum benefit from high rake angles because of increased shear pressure. A high primary rake equals a sharper tool. Secondary Rake: This angle defines the curl of the chip. More positive secondary rakes lead to deeper overall chipbreaker depths and tighter chip control. The distance the secondary rake runs from the cutting edge determines how long the chip can flow before it hits the plateau and changes direction. Clearance: High clearance angles will also shear the material more efficiently in ductile materials. High clearance angles also make the tool sharper, thus limiting the max feed. Chip Groove: The features on an insert that function to direct and/or change the shape of the chip. The standard ISO turning insert follows much of the same conventions with respect to chip terminology. The narrower the chip groove, the tighter the chip. Each chip groove is designed to curl and break the chip, but not over-compress it. Forming: In forming operations, chips are created along a shear plane on the workpiece that is perpendicular to the feed direction. The chips move along the cutting face of the tool (orthogonal cutting). Different from single-point turning, multiple features are being cut, but the cutting face of the tool is engaging at different times. Broaching: Like forming, broach tools consist of a clearance angle and a face angle, which replaces the rake angle. Chips form at the points/ teeth of the broach, run along the face of the broach and curl toward either the bottom of the hole (for internal broaching) or the back of the workpiece (for external broaching). Workpiece Chip Top Rake Angle Form Clearance Angle strategies also bring high benefit through improved tool life and stability. Tool alignment is a good place to start. Center height is critical for chip control, because if the cutting tool edge is not positioned correctly, the chipbreaker may not provide optimal results and excessive tool wear will become an issue. Above center causes friction and vibration, and below center causes vibration and increased shearing zone. Machine alignment should be inspected regularly and frequently, because machine crashes and maintenance issues that lead to misalign- ment often go unreported. Tooling with high stability is important, making use of a highly rigid setup. If the insert rolls when indexing, the cutting height, and thus the chip control, can be affected. ere should be as much material as possible under the cutting edge. If the insert is pushing off at each revolution, chip control will be difficult. Modular tooling can reduce deflection by shortening the overall length from the tool turret to the cutting edge. For almost all ISO turning inserts, depth of cut (DOC) is critical to chip control. As a common rule of thumb, the depth should be at least 2/3 of the radius size. For the best results, the depth should be 1 to 2 mm (0.039 inch to 0.079 inch) past the radius. One common misconception is that the larger the depth, the poorer the tool life. e fact is that when adjusting feed, cutting speed or DOC, it is DOC that has the least effect on tool life. For this reason, increasing The Fundamentals of Chip Control productionmachining.com :: 33

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