Often being the most challenging and also the final operation, you can't afford failing when parting off. Watch this episode for tips on how to make parting off trouble-free and successful.
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Transcript:
Parting off is one of the most challenging applications in metal-cutting and always used on turning centres, sliding head lathes and multi-spindle machines with a bar feeder. It is often one of the final operations and as a lot of time has already been invested into the almost-finished component, a tool failure at this stage can prove extremely expensive. Therefore it is worthwhile focussing a little extra on this area; and in this episode we will discuss the main guidelines to ensure trouble-free and successful parting off.
There are three main stages of the parting plunge, including the main long cut through the bar, the approach toward the end of the cut and the short stage just before reaching the component centre. As the tool is fed deeper, chip evacuation becomes essential but even if good external-coolant setups are used, chips can still get in the way to cause heavy loads and poor component finish. Internal, over- and-under, high precision coolant channeled through the tool provides the highest machining security. With over-coolant taking care of chip control and under-coolant prolonging tool life and increasing surface speed by between 30- and 50%.
Effective parting systems include inserts with a specially-developed channel to ensure coolant reaches the right position on the cutting edge. The geometry can then fold and curl the chip, making it narrower than the groove so that it evacuates without becoming trapped.
We recommend starting with the first-choice grade and recommended speeds and feeds for the material being machined. A speed that is too low can form a built-up edge on the insert, while a feed that is too low increases time in cut and risks more insert flank wear.
As the tool reaches the component centre, cutting speed decreases below the recommended value, causing a built-up edge and high loads on the insert. To avoid insert breakage and poor chip control, reduce feed by 50-75%, two millimeters before the centre. This small change in programming provides a large increase in tool life.
Always set up the tool with the shortest possible overhang, the recommended maximum being 8- to-10 times the insert width. To avoid tool breakage and rapid flank wear it is also essential to maintain the centre-height setting to a tolerance of plus or minus .1 of a millimetre or .004 of an inch.
So there you have it, a short guide to getting the most from your parting-off operations. To summarize, here are three main points to remember:
- use the first-choice tool- and cutting data recommendations
- use high precision coolant whenever possible
- always reduce feed at the component centre
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