Production Machining

AUG 2018

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

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Page 32 of 91

Insert Positioning Insert Support :: Stability is key to a successful process, with plenty of support under the insert. C hip control issues often lead to other problems such as shortened tool life, conveyor stoppages and poor surface finishes, while also creating safety hazards. ese concerns cost shops countless hours of production time. But certain strategies can be implemented to help shops recognize potential pitfalls, allowing them to take control of their chips, resulting in longer tool life and better productivity. At this year's Precision Machined Products Association (PMPA) National Technical Conference, Edwin Tonne, training and technical specialist at Horn USA Inc., and Rob Somma, form tools/inserts engineer at Somma Tool Co. Inc., provided an in-depth look at the best ways to read chips and presented creative strategies for best practices in managing chip breakage. Following are key points from the presentation. Identifying Chip Features While chips may sometimes be viewed in a negative light, they do bring advantages to the cutting operation when properly handled. In almost every metalcutting process, excess heat is generated. e excess heat only has a few paths of escape: the environment, the workpiece, the cutting tool and the chip. For steels using the optimum cutting speed, dry machining will result in about 75 percent of the heat leaving with the chip, 10 percent in the material and 15 percent transmitted to the cutting edge. Heat-resistant alloys will realize less benefit, but even a modest 25 percent leaving with the chips will help with tool life. e appearance of the chips can also provide a second line of sight (of sorts) for the operator when the windows to the workzone are obscured by coolant, scratches or tool turrets. If chip control is good at the start of a run, but then the chip bin begins to fill up with long, stringy chips, the cutting edge could be damaged. Other changes during the operation may indicate built-up edge (BUE) of the top rake. e machinist would then know to increase the speed or select a coating with better lubricity or less chemical affinity. When it comes to chip shape, there is no right or wrong answer, but the industry accepted shapes are 6s and 9s. ese shapes generally indicate the chip is breaking under its own momentum, on the part shoulder or other areas that do not cause damage to the unused cutting edges or part surface. e 6 and 9 shapes are also desirable because that means the chips are not too tight. If the chip is too tight, especially in difficult alloys such as titanium and nickel-based materials, extremely high pressure and excess heat is generated. :: Chipbreaker geometries are offered in a variety of configurations suited to meet the needs of the application. A chipbreaker should be selected that is strong enough for the required feeds and free-cutting enough to reduce heat. The Fundamentals of Chip Control :: 31

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