climb cut or conventional cut.

[belearner]

Hi all.

99 % of programs in my shop are climb cut. Just wonder when and why we go for conventional cut.

Need help from all. Thanks.

[Salahuddin]

it was been covered

http://www.emastercam.com/cgi-bin/ultimate...t=026183#000000

 

for me I use climb cut 99% for the work I do on the cnc machines.

 

better for tool, better finish

[landscnc]

We do some hogmilling convetional on plates of 304 st that have been plasma cut this gets the tool under the hard surface of the burnt edges rather than cutting into that hard edge.

[Dave.L]

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We do some hogmilling convetional on plates of 304 st that have been plasma cut this gets the tool under the hard surface of the burnt edges rather than cutting into that hard edge.

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In the future, have them cut on a waterjet that you won't have the hard scale to deal with.

[3R!< W3NG3R]

Flame cut parts are the only ones we do conventional. Not very often too.

Mirrored parts sometimes when it isn't fussy and it is just easier for us lazy ones.

[Leigh @ Kodiak]

quote:

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In the future, have them cut on a waterjet that you won't have the hard scale to deal with

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Are there places in your area that waterjet cut at the same price as plasma?

[Dave.L]

quote:

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Are there places in your area that waterjet cut at the same price as plasma?

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Leigh, well that's a great question. I have only used waterjet for a few projects and that was about 5 years ago.

 

I would guess the price would be close. And, even if it was a little more, the savings in tooling should make it well worth it.

 

We never bring in plates with burn cuts. We specify saw cuts and if a vendor needs to burn, we require normalizing.

[jeff]

It's been a while, but wouldn't you also want to conventional cut on thin walled stuff?

[MACHINEMASTERG]

sometimes on plastic parts we climb mill the ruff pass and conventional machine the finish pass does a nicer job on the finish...also on chamfer milling passes it seems to wipe the pickup off the edge on my spring pass

[Nick Eaton]

Having glanced through the above thread and posts I think belearner might benefit from a general overview rather than indivdual examples, so here goes.

On the whole climb cutting allows you to balance the cutting forces and achieve a more accurate cut. There are exceptions.

Removal of an abrasive/hard skin is one. Waterjet can help on some matrials but nothing can be done about the nasty skin on Titanium extrusion and forged block. As mentioned above, with a conventional cut, you are entering virgin clean the material rather than constantly slamming into the nasty skin if you use a conventional cut.

Another technique I use frequently is rough conventional cutting vertical walls in aluminium. If you use one of the free cutting 90 degree shoulder insert mills such as Dapra there is nowhere for the chip to go when climb cutting a vertical wall and so the chip gets forced between the wall and the insert. This can cause material smearing and heat the part up from the friction (potential thermal distortion). Conventional cutting scoops the chip out and ejects it away from the wall. With a good free cutting insert you should only notice a 5 - 10% increse in tool pressure.

These are "special" circumstances and generally the choice of whether to use a conventional or climb cut is more to do with the dynamics of the chip formation.

On a climb cut the thickest part of the chip is made first, as the cutter advances the cutting edge impacts ahead of the direction of feed. The chip then thins out as the cut is completed.

On a conventional cut the thinnest part of the chip is formed first,as the cutter advances the cutting edge impacts behind the direction of feed, and the chip thickens through the cut.

Climb cutting, because of the initial high force impact followed by a falling off of force as the chip thins will have a tendancy to push the material away from the cutter.

Conventional cutting will tend to pull the material towards the cutter as the forces increase through the cut as the chip thickens.

A machined free standig wall will therefore tend to thicken towards the top (the flexible section of the wall) if you climb cut or thin out towards the top if you conventional cut.

The implications of these dynamics can be divided into two sections.

Physical/geometric implications are that a climb cut will have a tendancy to "hook" any corner or cusp and either have an unbalanced load surge or set up unwanted vibrations (chatter) in the system.

A good example of this would be trimming the ends of extrusion with a standig wall or leg. There is little or no flexiblity along the length of the part so you don't have to worry about sucking the part in and undercutting, so a good candidate for conventional cutting

Cusps can be a real problem in "tough" materials such as Titanium and Inconel for the above reasons.

Thermodynamic implications are more important for people in the aerospace machining world because many aeropace materials are "heat resistant", Aluminium, Titanium , Inconel and high chromium content stainless steel(324 - 348)are all heat resistant materials, i.e they do not conduct heat well.

When climb cutting the cross sectional area (and therefore the volume)of the chip is at its maximum when the majority of the heat is being generated, at the initial impact and shear. Maximum heat build up is just behind the cutting edge and slightly back on the chip side of the cutting edge. The higher the chip volume at this time the more heat will naturally flow into the chip and not the part, which can lead to distortion.

On a conventional cut large amounts of heat are being generated when the chip is thin. Frictional forces (which are converted to heat) are much greater as you push the cutting edge through the material at greater depth and the chip thickness increases. This can be OK in steel or heat conductive materials but can be a real problem in heat resistant materials as the excess heat will bleed into the part, again risking distortion.

This problem is magnified with insert cutters which generally have a nose a few thou. in radius (up front sharp free cutting inserts are an exception as mentioned above). So conventional cutting in tough heat resistant materials with inserts is a bit like trying to pierce the material surface with a ball bearing at an angle. The forces and and heat generated are great and the insert will rapidly break down.

Conventional cutting with inserts in Ti or Inconel will normally end in tears......

As the above implies conventional cutting is best done with HSS cutters as you can grind the edge sharper than carbide and thus reduce the above effect, you are also going slower so you are generating less heat.

Solid carbide is sort of half way between. Much sharper than inserts but not as sharp as HSS.

I conventional cut with solid carbide in Al if I am forced down that road and have even done so in Ti. But it is HARD on the cutters especially in tougher/harder materials.

So climb if you can and pay attention to detail when conventional cutting, and only do it when you are forced to.

A bit long winded but I hope this clarifies.

Cheers

Nick