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304L VAR machining

Lunchbox1029

Plastic
Joined
Feb 6, 2022
Hi guys,

I am having some trouble drilling in 304 L VAR. Background: using a Walter B4213 indexable insert drill (.656") in a Mori Sieki SL200 lathe, drilling 1.375" deep hole on center. Currently running 1100 RPM @ .0025 IPR per Walter app. Problem is the inserts deteriorate much much faster than I'd like. We are using the E57 inserts that should be sufficient for this material and condition. Sometimes we'll get 20 parts before the inserts give out, sometimes its two parts. We do not have high pressure coolant but do have good flow and volume running Blaser oil. I have used these drills in many, many other materials without issue but this VAR stuff is nasty.

This is a high volume part for us and for the lst 10+ years that we have been running them it has always been an issue. I just took over as lead for the lathe department and am looking for a solution without luck so far. I cannot seem to find much info about the VAR effects on machinability and my tool vendors have been less than helpful. Any insight will be much appreciated.
 
What is the cold work condition of the material? To me, VAR mainly affects the alloy cleanliness. In the annealed condition, VAR material may be softer and more gummy than "normal" material. In the work-hardened condition, chips may be a lot tougher to break due to there being fewer defects in the microstructure.
 
I think your speed is on the low side for indexable insert drill. That's probably not what you want to hear. You should be starting in the 350-400 sfm range since you don't have high pressure coolant.
 
I think your speed is on the low side for indexable insert drill. That's probably not what you want to hear. You should be starting in the 350-400 sfm range since you don't have high pressure coolant.
The vendor that originally turned us onto this drill said 2500rpm which is about 430sfm. That seemed really fast to me and we were going thru inserts like crazy so I turned it down to 1100rpm, which I got from Walter but you may be right about it being too slow. I just ordered some inserts with a different geometry to try out as well. I'll try it around 350sfm and see how it goes. My production manager is acting like 304L VAR is some mystical unobtainium that is just going to cut this way no matter what but I'm unconvinced. I'll keep experimenting and see what i can come up with.
 
I'm not familiar with Walter's grades and geometries. Are you using one designed for stainless (ISO M)? If so, then 400sfm should be a suitable speed for 304 or 316 SS.
With Sandvik's 880 drill and SS grade/geometry insert, I'm running 550 sfm in 316L. Feed rate is similar to yours for a 16mm drill (a few tenths higher).
I do get more unpredictable tool life out of the smaller indexable drills (14-17mm size range) than the larger ones (I have 14mm-50mm drills). I prefer using a replaceable tip drill in the 14-17mm range (Sandvik 870, Seco CrownLoc, Iscar SumoCham, etc...) even though it might be a bit slower than an insert drill.

Indexable insert drills run at a considerably higher speed/lower feed compared to solid carbide or replaceable tip drills. But, overall, the insert drill usually has a higher metal removal rate.
 
My production manager is acting like 304L VAR is some mystical unobtainium that is just going to cut this way no matter what but I'm unconvinced.
It is a somewhat oddball material. I didn't know it existed.

304 is generally a cheaper alternative to 316, but VAR can add significantly to the cost. So why not use 316L VAR? 🤔

Anyway, at .656, I'd be using a replaceable tip or solid carbide rather than indexable.
 
I was running that same drill the other day only .709 dia. Running fine in steel at 0.0027/rev then decided to flip inserts. First part sounded like gravel, so I dropped the feed to 0.0015 and just ran the rest out at that feed. Sounded to me like the chips weren't clearing fast enough. Not sure if you've played around with feed rates.

One thing we have done in the past is point the nozzle from locline into the back hole of the drill to get some thru coolant effect.

My Walter rep gives me great service. If I was having your issues, he would keep feeding me inserts and stay until the job was running correctly. Not sure why yours isn't doing the same for you.

That low carbon stainless can be nasty stuff at times. One tool rep told me to drop my surface footage in half when drilling 304L. Again, not sure how much you have played with feeds and speeds.
 
You said this is a high volume part for you. If that's the case, i would be calling Carpenter Stainless and getting a quote for their 304 VAR. Their material is usually a bit more expensive, but its consistent from batch to batch and will save you in the long run.
 
You said this is a high volume part for you. If that's the case, i would be calling Carpenter Stainless and getting a quote for their 304 VAR. Their material is usually a bit more expensive, but its consistent from batch to batch and will save you in the long run.
Material consistency has been a big part of the problem for us. My production manager is the one that orders all my materials and he swears that only one company make VAR material... I have no idea how accurate that is but hes 72 years old and arguing with him is futile. We are primarily a job shop so high volume to me on these is 10k parts per year. We mostly just struggle through them but Im trying to change that outlook shop wide. I will give them a call and see what the price difference is.
 
I was running that same drill the other day only .709 dia. Running fine in steel at 0.0027/rev then decided to flip inserts. First part sounded like gravel, so I dropped the feed to 0.0015 and just ran the rest out at that feed. Sounded to me like the chips weren't clearing fast enough. Not sure if you've played around with feed rates.

One thing we have done in the past is point the nozzle from locline into the back hole of the drill to get some thru coolant effect.

My Walter rep gives me great service. If I was having your issues, he would keep feeding me inserts and stay until the job was running correctly. Not sure why yours isn't doing the same for you.

That low carbon stainless can be nasty stuff at times. One tool rep told me to drop my surface footage in half when drilling 304L. Again, not sure how much you have played with feeds and speeds.
Yea i have muddled around with the speeds and feeds but havent had much luck. The new inserts just came in and im hoping they will help. And yes we have experienced the gravel sound with fresh inserts as well. I am running thru coolant as well as a nozzle. I dont have a walter rep, per say, just a local vendor that happens to sell walter tools.
 
Yea i have muddled around with the speeds and feeds but havent had much luck. The new inserts just came in and im hoping they will help. And yes we have experienced the gravel sound with fresh inserts as well. I am running thru coolant as well as a nozzle. I dont have a walter rep, per say, just a local vendor that happens to sell walter tools.
Where are you located? You could at least get some free lunch out of the deal.
 
Where are you located? You could at least get some free lunch out of the deal.
Ha!! Free lunch, now you're speaking my language. I'm pretty new to the lead role so my experience with vendors is basically non existent. I'm in Western Washington, just east of Seattle.
 








 
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