Production Machining

AUG 2018

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

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Page 33 of 91

As with chip shape, there is no correct size of chip, but small is almost always better. e chip should fit correctly into the tool flutes, slot, groove or bore. is consideration is especially critical when dealing with small part boring. Another argument for small chips is their influence on floor space: Can work cells be placed closer together with smaller chip bins? Could more space be available for additional production equipment? How much time is dedicated to removal and recycling? e surface finish of the chip can also tell an interesting story. When a new job, material or process is being run, the chips should be examined. Chips with ragged, serrated edges often indicate an unstable process. Finally, the color of the chip is also meaningful. For ISO P group steels, a blue-violet color will usually indicate the cutting speed is set such that most of the heat is being trans- ferred to the chip. For materials with low heat exchange rates, a big difference in color can mean the speed is too high. e chips are not only the by-product of machining—they are also often a great indicator of overall process conditions. Chipbreakers Long, stringy chips are undesirable, so the goal in any tool design is to break the chip up by changing its path/curl. While in broad terms there are three options for chip control, the most effective way is typically by incorporating a chipbreaker. Modestly priced and offering high returns, chipbreakers can either be built into the cutting face of the tool or brazed/clamped onto the cutting tool. In some cases, the holder of the cutting tool can be used as a chipbreaker. Clearance angles and rake angles are important to chip formation and control. Clearance angles are used to decrease the amount of rubbing of the tool against the workpiece and are always positive or zero, never negative. Rake angles control the sharpness or bluntness of the tools and can also be used as part of a chipbreaker, as in the case of a positive rake face. When using chipbreakers, maintaining the right amount of both heat and pressure is most important for efficient machining. Generating too much heat can lead to plastic deformation of the insert edge, and too little heat results in reduced benefit of material softening in the shear zone. Too much pressure can cause mechanical fatigue of the cutting edge, and with too little pressure, the chip may stay continuous. Chipbreakers are offered in a variety of configurations. Tooling manufacturers develop each configuration either to meet a specific need within the industry or to be used in more general applications. To make sure all applica- tions are covered, a shop should consider manufac- turers and holder platforms that have a large number of chipbreaker options. is strategy is especially important when a shop machines multiple types of material and has a highly variable product mix. High-Pressure Coolant High-pressure coolant can serve as a highly effec- tive chip control solution. It has an intermediate cost because of additional equipment purchase and maintenance effort, but it provides a lot of benefit with improved tool life and stability. e high heat cycling causes the workpiece material to fatigue rapidly and is aided by the pressure stream to facilitate breaking. For maximum effectiveness, the coolant stream should be as close to the cutting zone as possible. Some inserts, such as the Horn 3V geometry, have coolant holes in the insert to facilitate application directly on the cut zone. e high-pressure unit should be sized appropriately relative to the machine coolant reser- voir to avoid the need for cooling units that otherwise would be needed to limit heat buildup. Process Considerations Finally, process and programming changes can be applied, usually at moderate cost because of the involvement of multiple aspects of components processing. ese :: Grooving tools differ from turning in that the chip only has one path away from the component. The chip control geometry must reduce the width of the chip and curl at the same time. Long, stringy chips are undesirable, so the goal in any tool design is to break the chip up by changing its path/curl. CUTTING TOOLS 32 PRODUCTION MACHINING :: AUGUST 2018

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