We recently hired a new wire guy and he seems to have good experience but he likes to bead blast carbide punches and die sections. He also likes to bead blast the snot out of steel anything. He claims it removes recast. I'm pretty sure I understand recast and we very seldom cut anything with less then 5 passes for tooling a with some parts being cut with 8 passes. I've never really seen the need to bead blast unless maybe 1 cut surface. My question is how much recast could possible be left on a 5 pass or 8 pass technology? I guess we could send out samples to lab. But I also wanted to see what you all think about bead blasting.
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Bead blasting carbide
- Thread starter JTB3
- Start date
- Replies 11
- Views 3,857
implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Hi JTB3:
As a rule, I avoid bead blasting because it dubs off all the corners I usually want to keep sharp.
Also, if you're doing 5 to 8 wire passes, you are presumably doing so to hit the precision and finish you need.
Whacking it with abrasive afterward defeats the whole purpose of doing all the passes in the first place; both in terms of precision and in terms of finish.
It's totally uncontrolled, it's going to contaminate the surfaces with glass bead residues and all the other crap that accumulates in the abrasive reservoir, and it has no benefit whatsoever.
On the subject of recast thickness and HAZ thickness, Brian Pfluger from Makino posted a link recently to a study Makino did on recast layer thickness from modern generators.
It's MICRONS, and fractions of microns.
Not only that, if you truly needed to completely remove recast and had to certify you had done so, waving the job under the bead blaster for a couple of minutes is surely not the way.
Your new wire guy does not know what he's talking about.
I'd stop him from doing what he's doing.
He's fucking up your parts and wasting his time.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
As a rule, I avoid bead blasting because it dubs off all the corners I usually want to keep sharp.
Also, if you're doing 5 to 8 wire passes, you are presumably doing so to hit the precision and finish you need.
Whacking it with abrasive afterward defeats the whole purpose of doing all the passes in the first place; both in terms of precision and in terms of finish.
It's totally uncontrolled, it's going to contaminate the surfaces with glass bead residues and all the other crap that accumulates in the abrasive reservoir, and it has no benefit whatsoever.
On the subject of recast thickness and HAZ thickness, Brian Pfluger from Makino posted a link recently to a study Makino did on recast layer thickness from modern generators.
It's MICRONS, and fractions of microns.
Not only that, if you truly needed to completely remove recast and had to certify you had done so, waving the job under the bead blaster for a couple of minutes is surely not the way.
Your new wire guy does not know what he's talking about.
I'd stop him from doing what he's doing.
He's fucking up your parts and wasting his time.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
Thank you Marcus for your reply. I feel exactly the same way and 100% agree with you on your points made. But just checking to make sure I'm not crazy before I let him know how I feel about the bead blast issue and while we are on the subject of people being dumb asses this guy has been setting up all his jobs with diffusion annealed wire. And it's mostly tooling and precsion tolerance work. im well aware of the all types of wire and there intended purpose, trying to cut precsion tooling work with this type of wire is just a bad idea in general. What has me most perplexed is this guy came from a very well know tool and die shop. Witch leads me to believe that either this guy is full of shit or the shop he worked for isn't what it used to be and apprently its run by idiots.
Thanks again for your insight.
Keep on burning!
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
On carbide your guy may be correct.
See I was always told not to bead blast carbide because it can damage the surface.
Actually the part was a punch with very small outside radius and my thoughts are that bead blasting is just eroding the surface in a non controlled manner and causing poor geometric accuracy in the punch. I checked the punch straight off the machine and it showed much different results after it was hit with about 40 psi bead blast.
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
At 40 psi normal bead blasting will put a .0005/.001 radius on a sharp corner piece of carbide if applied for 30 seconds to a minute continuously on one spot. The speed of this varies with carbide grade.
Now if you load your bead blaster with actual diamond grit and run at 120 psi you can get it up to .003/.004 radius.
Tried by many and abandoned by all this is a painfully slow process of edge honing carbide.
If you are seeing dimensional variation other than this small corner break when bead blasting you can rest assured that what came off was not good carbide.
The problem with EDM on carbide no matter how many passes is leaving a cobalt depleted skin where the carbide particles are still hanging out there but the binder is gone. You can get a very nice looking surface but it has no integrity.
Sort of just the opposite of a cobalt enriched grade.
(Thermal cracking is another EDM problem but most experienced people know how to avoid this.)
One really needs a SEM to evaluate this although you can see it a bit at 2000x with a good metallurgical scope if you know what you are looking for.
We bead blast carbide at 60 psi for brazing to clean it and never see a size change on a flat surface. Some coating houses do the same.
We also 220 grit glass bead blast used inserts to remove the burnt on coolant and such. This allows us to see the actual carbide and it's wear without removing any carbide itself.
Not sure what abrasive or grit you are using so your mileage may vary.
Bob
Now if you load your bead blaster with actual diamond grit and run at 120 psi you can get it up to .003/.004 radius.
Tried by many and abandoned by all this is a painfully slow process of edge honing carbide.
If you are seeing dimensional variation other than this small corner break when bead blasting you can rest assured that what came off was not good carbide.
The problem with EDM on carbide no matter how many passes is leaving a cobalt depleted skin where the carbide particles are still hanging out there but the binder is gone. You can get a very nice looking surface but it has no integrity.
Sort of just the opposite of a cobalt enriched grade.
(Thermal cracking is another EDM problem but most experienced people know how to avoid this.)
One really needs a SEM to evaluate this although you can see it a bit at 2000x with a good metallurgical scope if you know what you are looking for.
We bead blast carbide at 60 psi for brazing to clean it and never see a size change on a flat surface. Some coating houses do the same.
We also 220 grit glass bead blast used inserts to remove the burnt on coolant and such. This allows us to see the actual carbide and it's wear without removing any carbide itself.
Not sure what abrasive or grit you are using so your mileage may vary.
Bob
implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Hi Carbide Bob:
I'm really curious why you are endorsing bead blasting carbide that's been wire EDM cut.
How do you believe it would improve the performance of carbide punches and die sections?
After all they're cutting tools just like end mills, so the edge geometry matters and I've had the same experience that JTB3 has had about the bad effects of abrasive blasting on the sharpness of the punch edges.
Wire cut parts are already inferior to ground ones due to cobalt depletion at the edges; bead blasting them only makes this worse and forces a face grind to restore the sharpness of the punch and die edges after the blasting.
If you believe that face grind is a necessary part of creating excellent punches and dies, I'd be prepared to do it in order to make the best possible tools, but I can't yet see what the benefit is.
I'm arguing it cannot be to remove the recast; the wire finishing passes do that.
One of the things about wirecutting carbide that's not all that widely known except by carbide WEDM specialists is that the wirecutting strategy is supremely important in a way that's simply not true for wirecutting steel.
The underlying reason is that sintered carbide is so full of stress that a poor die design or poor cutting strategy carries a big risk of cracking the carbide, and we're not talking just microcracks in the recast layer.
JTB3 alludes to this when he talks about 5 to 8 wire passes; the first cuts are typically strategic stress relief cuts, the intermediate cuts block out the form and the final ones create precision and finish and remove the microcracks and macro cracks created from the roughing.
The corollary benefit of all these passes is that the recast layer is minimized, because the finish passes have so little spark energy that virtually no new recast is formed and all the roughing recast is cut away during semifinishing.
So blasting the carbide doesn't remove undesirable recast but only degrades the punch and die corners, and if done with enough enthusiasm, will dig out tungsten grains from the surface and ruin the punch surface geometry as JTB3 has pointed out.
I can't see any upside to bead blasting; but you have huge experience with carbide and I'd love to know your reasoning.
So what am I missing??
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
EDIT: Looks like you type faster than I do.
OK your comments are well reasoned and fair, but a point that sticks out to me is that you are referring to as sintered or ground surfaces when you make the observation that a bead blast at 40 PSI will not change the surface of the carbide.
The corollary to this as you also correctly comment is that the carbide left on the surface of a wire EDM cut punch is not "good carbide" and you are right; however we have to accept that reality whenever we choose to wire cut a punch with a water dielectric.
Best possible punches have ground geometry...no argument there, and the next best thing is probably oil dielectric in the wire machine, but the geometry even of a typical wire cut punch is still very important and my experience is that it doesn't do well when bead blasted.
So which way to compromise??
Cheers
MC
I'm really curious why you are endorsing bead blasting carbide that's been wire EDM cut.
How do you believe it would improve the performance of carbide punches and die sections?
After all they're cutting tools just like end mills, so the edge geometry matters and I've had the same experience that JTB3 has had about the bad effects of abrasive blasting on the sharpness of the punch edges.
Wire cut parts are already inferior to ground ones due to cobalt depletion at the edges; bead blasting them only makes this worse and forces a face grind to restore the sharpness of the punch and die edges after the blasting.
If you believe that face grind is a necessary part of creating excellent punches and dies, I'd be prepared to do it in order to make the best possible tools, but I can't yet see what the benefit is.
I'm arguing it cannot be to remove the recast; the wire finishing passes do that.
One of the things about wirecutting carbide that's not all that widely known except by carbide WEDM specialists is that the wirecutting strategy is supremely important in a way that's simply not true for wirecutting steel.
The underlying reason is that sintered carbide is so full of stress that a poor die design or poor cutting strategy carries a big risk of cracking the carbide, and we're not talking just microcracks in the recast layer.
JTB3 alludes to this when he talks about 5 to 8 wire passes; the first cuts are typically strategic stress relief cuts, the intermediate cuts block out the form and the final ones create precision and finish and remove the microcracks and macro cracks created from the roughing.
The corollary benefit of all these passes is that the recast layer is minimized, because the finish passes have so little spark energy that virtually no new recast is formed and all the roughing recast is cut away during semifinishing.
So blasting the carbide doesn't remove undesirable recast but only degrades the punch and die corners, and if done with enough enthusiasm, will dig out tungsten grains from the surface and ruin the punch surface geometry as JTB3 has pointed out.
I can't see any upside to bead blasting; but you have huge experience with carbide and I'd love to know your reasoning.
So what am I missing??
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
EDIT: Looks like you type faster than I do.
OK your comments are well reasoned and fair, but a point that sticks out to me is that you are referring to as sintered or ground surfaces when you make the observation that a bead blast at 40 PSI will not change the surface of the carbide.
The corollary to this as you also correctly comment is that the carbide left on the surface of a wire EDM cut punch is not "good carbide" and you are right; however we have to accept that reality whenever we choose to wire cut a punch with a water dielectric.
Best possible punches have ground geometry...no argument there, and the next best thing is probably oil dielectric in the wire machine, but the geometry even of a typical wire cut punch is still very important and my experience is that it doesn't do well when bead blasted.
So which way to compromise??
Cheers
MC
implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Hi again Carbide Bob:
Another question I'd love to know your thoughts on:
in your opinion, is a wire EDM cut carbide punch or die made on a water dielectric WEDM machine a total waste of effort?
It seems to me to be a logical argument, given the fact that water dielectric WEDM machines will ALWAYS strip out the cobalt binder from the surface thereby wrecking the carbide.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
Another question I'd love to know your thoughts on:
in your opinion, is a wire EDM cut carbide punch or die made on a water dielectric WEDM machine a total waste of effort?
It seems to me to be a logical argument, given the fact that water dielectric WEDM machines will ALWAYS strip out the cobalt binder from the surface thereby wrecking the carbide.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
Not understanding the stress thing at all.
Carbide is sintered in the free state and shrinks 30% in volume during this process as the glue melts and the part collapses in on itself filling the voids. Any major cracks are from bad pressing or bad green work.
There should be no residual stress. None.
Yet we have all seen carbide break during processing. This is not a internal stress problem.
If a bead blast pulls particles out of the binder they were not going to say put in use anyways. Hence "not good carbide".
Yes there is a huge problem of maintaining a nice sharp edge. But is this edge still sharp after 5 minutes of use?
Would a .0002/.0005 radius on the edge work better or worse?
One evaluates a tool after it has been used a few times, not what it looks like in the package.
What is in the blaster and how it is applied makes a difference and for sure best not to spend time not needed.
Soda blasting is nicer to the edges while removing the grains that have no holding power.
IMO both sides of this are correct and you perfect the process as it works best for you and your customer.
I am all for not blasting just from a time and possibility of screwing things up side.
Bob
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
Guessing that you are referring to cobalt leaching from the water.
This is a very slow process in reality. If you dry the tools after processing you generally won't see a problem.
If you are "in the tank" for 6+ hours this could well be a worry.
Also of note is that your water will have cobalt in liquid phase contained which is easily absorbed through your skin unless you have inhibitors in the mix.
I am nowhere near the expert on WEDM that you are.
We only rough with a wire or hole popper and as a last resort so many less concerns, 98% of all work is grinding.
I make mostly parts like these below and while some of my competitors use edm for such none of these have any edm work done on them.
All ground and all ground in water.
Bob
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implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Hi Carbide Bob:
Attached below is a link to a rather simplistic article on the most popular theory about carbide and stress as it relates to cracking while being wire cut.
Stamping World - Carbide Corner - 241 EDM Tungsten Carbide
The culprit is claimed to be stress release and not thermal cracking; the justification for that belief is the idea that the thermal mass of the water in the EDM tank is so large that the temperature effects are extremely localized and have no effect, but the tungsten particles are bound into the cobalt at high temperatures and pressures so contraction cooling from that state leaves the whole microstructure quivering with tension and when you hack into that quivering ball with your wire it goes "doinnngggg".
Whether this is true or not; it is the common wisdom of the EDM world and the sudden cracking especially of die sections is common enough, that a reasonable amount has been written on what to do to minimize it, and that's entered the EDM folklore for better or worse.
So now everyone "knows" you don't just bomb around your profile with roughing, semifinishing and finish passes like you can with a D2 die; you do relieving cuts first, inspect the results for cracks, and then rough with a generous allowance, rough again with a standard stock allowance and then begin your semifinishing and finish skims.
With regard to cobalt leaching, my understanding is that the cobalt dissolves into the water at a fast rate as a consequence of two conditions unique to wire EDM.
The first is that the conductivity is actively held low by the presence of the DI resin which continuously strips out cobalt ions as they form and drives the further dissociation of cobalt because the system can never come to chemical equilibrium as long as the DI resin remains effective.
The second is the presence of localized high temperature and electrical current both of which drive dissociation faster than would be accomplished by the dissociation constant of cobalt in water alone.
That's apparently why wire cut carbide is noticeably inferior in physical properties to ground carbide and why time in the WEDM tank is not like time in the presence of normal water or water based coolants.
So given that oil based systems specifically made for wire cutting carbide are available (but very slow compared to a water based WEDM); one should logically assume that you cannot make as good a tool with water dielectric as you can with oil dielectric and if you are serious about making the best tooling possible it should be ground or cut on one of those specialized systems.
If you dare to use a normal water dielectric wire EDM you are cheating your customers if that logic is true.
The 64 million dollar question of course, is just how much worse is a tool cut with water based wire EDM?
Furthermore, going back to JTB3's original question, is crappy geometry from abrasive blasting away degraded carbide worse or is crappy carbide not removed from the wire cut surface worse?
It's an interesting question and I don't know of any publications where anyone's actually made comparisons.
I've made mostly custom milling and turning tools on my wire, not punch dies and not production tooling.
I do know even for my applications, that ground tools are better; they cut nicer and last longer.
If I abrasive blast them they're worse than if I don't
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
Attached below is a link to a rather simplistic article on the most popular theory about carbide and stress as it relates to cracking while being wire cut.
Stamping World - Carbide Corner - 241 EDM Tungsten Carbide
The culprit is claimed to be stress release and not thermal cracking; the justification for that belief is the idea that the thermal mass of the water in the EDM tank is so large that the temperature effects are extremely localized and have no effect, but the tungsten particles are bound into the cobalt at high temperatures and pressures so contraction cooling from that state leaves the whole microstructure quivering with tension and when you hack into that quivering ball with your wire it goes "doinnngggg".
Whether this is true or not; it is the common wisdom of the EDM world and the sudden cracking especially of die sections is common enough, that a reasonable amount has been written on what to do to minimize it, and that's entered the EDM folklore for better or worse.
So now everyone "knows" you don't just bomb around your profile with roughing, semifinishing and finish passes like you can with a D2 die; you do relieving cuts first, inspect the results for cracks, and then rough with a generous allowance, rough again with a standard stock allowance and then begin your semifinishing and finish skims.
With regard to cobalt leaching, my understanding is that the cobalt dissolves into the water at a fast rate as a consequence of two conditions unique to wire EDM.
The first is that the conductivity is actively held low by the presence of the DI resin which continuously strips out cobalt ions as they form and drives the further dissociation of cobalt because the system can never come to chemical equilibrium as long as the DI resin remains effective.
The second is the presence of localized high temperature and electrical current both of which drive dissociation faster than would be accomplished by the dissociation constant of cobalt in water alone.
That's apparently why wire cut carbide is noticeably inferior in physical properties to ground carbide and why time in the WEDM tank is not like time in the presence of normal water or water based coolants.
So given that oil based systems specifically made for wire cutting carbide are available (but very slow compared to a water based WEDM); one should logically assume that you cannot make as good a tool with water dielectric as you can with oil dielectric and if you are serious about making the best tooling possible it should be ground or cut on one of those specialized systems.
If you dare to use a normal water dielectric wire EDM you are cheating your customers if that logic is true.
The 64 million dollar question of course, is just how much worse is a tool cut with water based wire EDM?
Furthermore, going back to JTB3's original question, is crappy geometry from abrasive blasting away degraded carbide worse or is crappy carbide not removed from the wire cut surface worse?
It's an interesting question and I don't know of any publications where anyone's actually made comparisons.
I've made mostly custom milling and turning tools on my wire, not punch dies and not production tooling.
I do know even for my applications, that ground tools are better; they cut nicer and last longer.
If I abrasive blast them they're worse than if I don't
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
I do bow to your experience and knowledge here.
Not sure I get the high pressure thing. Much carbide is made on simple "pill presses", yes just like aspirin tablets.
Most carbide is now sintered in a vacuum not under pressure, the exception being sinter-hip grades.
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