×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Drilling 316 Stainless Steel
3

Drilling 316 Stainless Steel

Drilling 316 Stainless Steel

(OP)
We have a project to improve the yield of a drilling process on an older CNC machining center and I'm looking for some knowledge sources of current best practices on drilling 316SS.

Our biggest defect is a .1874+/-.0004 ID hole that sometimes ends up oversized. The drilling steps for these holes are: center drill, mill, turbo drill, ream. We use a recycled (filtered) Moly-D cutting oil that has been drawn from another CNC machine used for tapping. The oil is not pressure fed.

We have made these parts for years and have considerable experience at it, but haven't paid much attention to advancements outside our company.

So, what are my questions?

I would like to know some good sources of knowledge of drilling 316 stainless (i.e. vendor catalogs, associations, handbooks, etc.)?

Also, I want to test the validity of using recycled oil that is uncontrolled, but our "experts" believe to be more than adequate for the application. How can we test cutting oil? What are the best practices in PM of oils?

If anyone can give me some guidance or advice I would be grateful. Thanks.

 

RE: Drilling 316 Stainless Steel

2

Authoritative references on machining:

Machinery's Handbook Twenty Sixth Edition http://www.industrialpress.com/mh.htm

ASM HANDBOOK Volume 16 Machining http://www.asminternational.org


Good on-line references on machining:

Manufacturing Center http://www.manufacturingcenter.com/online_book/default.asp

American Machinist http://metalworking.penton.com/

Production Machining http://www.production-machining.com/

Modern Machine Shop http://www.mmsonline.com/

Cutting Tool Engineering http://www.ctemag.com/

Society of Manufacturing Engineers http://www.sme.org

I recommend you perform a search for "stainless steel drilling" on the SME site (http://www.sme.org/cgi-bin/storefront/search/2///)-- between their Manufacturing Engineering magazine and the journal articles, transactions, etc. there will be quite a bit of information.  Also, SME has several books on machining-- I don't how they compare to Machinery's or ASM Vol 16:
http://www.sme.org/cgi-bin/storefront/prodgrp/B/B11000/MEMBNUM/SME/

RE: Drilling 316 Stainless Steel

Although the sources provided by TVP are a good beginning, you probably will not find the proper answer to your questions there.  The problem is that these recommendations are toooooo general and thus do not account for you particular case.

I would recommend the following sequence to combat the problem:

1.    Check your re-sharpening practice.   The key issue here is that the drill should have exactly the same angles and length of both lips.  It this is not the case, the drill drifts so you have an oversized hole.
2.    Since you CNC machine is old, the excessive spindle runout might be the case.  Even small runout results in hole oversizing (drilling and reaming).
3.    Check you drill holder.  The drill holder may contribute a lot in the mentioned runout so its runout adds to that of the spindle.
4.    There is no simple method to check the quality of the cutting fluid (coolant).  The rule of thumb is to keep it clean (particle size should be <20mictometers).  In any case, the coolant for your application should have high percentage of sulfur and chorine – this is mandatory.
5.    You have not mentioned the depth of drilling.  If it is >5D, you have a problem with chip removal and coolant access to the cutting lips.    

Viktor
http://viktorastakhov.tripod.com

RE: Drilling 316 Stainless Steel

(OP)
Thanks TVP and Viktor for your helpful replies!

On the cutting oil:
We do filter it periodically, however, I'm concerned that other substances are added to the solution over time (i.e. parts cleaning solvents, lube oils from gear boxes, etc.). There must be some point where the fluid reaches a point of ineffectiveness. Is this simply a case of needing a steady source of cooling liquid, or are there other important properties, like viscosity?

On the hole size:
The holes we have the most trouble with are just over 5D and they're through holes. We've suspected chip removal as an issue. Is the solution a matter of programming the the drill to come out more often? Or how is this problem best approached?


Please forgive my ignorance (not stupidity) on this subject. I'm a mech engr and Six Sigma Black Belt, but new to CNC machining.

Again, thanks for your great help!

RE: Drilling 316 Stainless Steel

As Viktor mentioned, chip removal becomes a problem at larger depths, especially with stainless steel, due to its tendency to gall.  One solution is to program the drill to "come out more often".

The quality of the lubricant is a more difficult question.  You should definitely be using a sulfochlorinated cutting oil if you want the optimum performance.  Viscosity is recommended to be less than 300 SUS at 38 C (100 F) in order to permit the necessary flow.  I am not an expert when it comes to lubricants and the degree to which contamination becomes an issue.

RE: Drilling 316 Stainless Steel

Viscosity is really good signal of (potential) chemical degradation of oil.

You can measure it periodically, and acceptable tolerance range should be obtained from oil manufacturer.

The other occasion : inter-reaction of oil additives with surrounding chemicals is far too complex for this purpose.

RE: Drilling 316 Stainless Steel

In an earlier life we did a lot of small, deep drilled holes stainless parts in a twin drill machine (Snow). The biggest problem w/ Stainless is heat - get too much and you're done. I modified the oiling system with a larger flood nozzle where the drill entered the part, and a smaller flow on the drill tip while it was retracted. This increased drill bit life about 10x and allowed changes to drill geometry to combine operations.  Worked fine until somebody in the shop decided it didn't need that much coolant and went back to one small line.... drill bits failed in a day again. There was also a programmed chip clearing stroke as the bit got deeper into the part, which retracted the drill just out of the hole (into the large oil flow) for a second to clear chips.
For hand drilling there was a product called Anchor Lube that worked very well. Don't know if its still around.

Keep the wheels on the ground
Bob
showshine@aol.com

RE: Drilling 316 Stainless Steel


  In most general maching applications, recycled oil works as good as any 1980's oils.  Also to be considered is the source of the recycled oil;  no one wants to end up with old PCB cooling oil in the system.  However; Rocool has several tapping compounds that work great on 304 SS so I assume 316 should work better.  I once had expensive synthetic oil verses recycled cheap oil compared with running a race in a jogging suit verses a three peice suit, both will finish but jog suit wins. The finest finished goods are as good as the ingredients.

RE: Drilling 316 Stainless Steel

Anothe option when drilling deep holes and having issues with chip clearance is to try parabolic flute(?) drill bits, these have a more agressive spiral for removng chips a lot easier and tend to have a more accurate hole drilled.

They have worked well for us in our dealings with 316 and 316L SS

RE: Drilling 316 Stainless Steel

Dear Yahnozha

As far as I know, a “parabolic” chip removal flute does not form straight cutting edge when intersected with a conical flank surface.  The problem is that the flute counter is not a ”flat” curve, i.e. it does not belong to the plane perpendicular to that containing drill axis.  Therefore, the design of a milling tool (or profiling a grinding wheel) for the drill flute is not that simple as it seems to be.  The problem is that the line of intersection of two curved surfaces, namely, the flute and the flank, should be the straight cutting edge.  Unfortunately this issue is not well understood.  Would you please elaborate more on the parabolic chip removal flute.  Thank you.

Viktor
http://viktorastakhov.tripod.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources