PDA

View Full Version : What about sparks?



A.K. Boomer
04-27-2008, 09:57 AM
A friend sent this to me and I watched it and was wondering about all the sparks, I always thought it was a bad sign whenever machining? could this be normal for some materials?:confused:


http://www.amazon.com/gp/blog/post/PLNK1D9884FEA6IT6

japcas
04-27-2008, 10:41 AM
It's normal when "hard turning" Boomer. Coolant added to the cut can cause cracking of the insert in those conditions. Insert life isn't nearly as good when compared to normal turning conditions but if it gets the job done, insert life isn't a concern. Still quicker than grinding. Generally sparks coming from a cut on a softer material means that the insert is breaking down.

dalee100
04-27-2008, 11:31 AM
Hi,

It's looks like the material in the annealed state in the video and I didn't see any sparks. A different video maybe?

Still, for dry machining with carbide and enough spindle Hp, sparks can be OK, even desirable. As japcas said, the cost of the insert edge maybe minor compared to the cost of coolant and maintenance of the coolant, and may be detrimental in the case of hard machining.

The thing I've noticed with machining like that is, the inserts will take it, (if the proper ones are selected for the job), but the insert seats tend to erode fairly quickly. This is due to the very high temps generated during machining. So those tools with replaceable seats are better choices if you want to do such work.

dalee

Forrest Addy
04-27-2008, 11:51 AM
Sparks are normal in steel and zero nickel alloys over a certain surface speed and they increase with surface speed. Some steel and insert combinations promote some fancy fireworks.

As it happens iron is a chemically active metal. Steel wool will burn when ignited for example; a jet of hot oxygen will cut steel like a hot knife in butter, then then there is rust. Any combination that produces finely divided hot steel dust will generate sparks. Since there is tearing and laminar slip in chip formation, metal dust will be generated. You can smell it under certain circumstances.

Heat steel dust up to 800+ degrees with agressive machining parameters and you will get sparks. I recall cutting 4140 at 1200 SFM dry with ceramic tooling producing showers of sparks and fountains of chips with coruscating edges. Pretty too.

If you get an hour or so of cutting time per insert corner you're running things pretty well.

An old wood industry executive once told me that there's a practical limit to the sharpness attainable in a cutting edge in carbon steel because of spontaneous oxidation. That's why you have to stop straight razors before shaving and why HSS is so much more durable in wood than carbon steel. That's what he said anyway.