Replace Grinding with CBN Inserts and Hard Turning

You can replace grinding with CBN Inserts and Hard Turning with a little bit of research. In the vast majority of cases hard turning with PCBN can replace a grinding operation. Finish turning of hardened components can achieve similar tolerances and surface finishes. Hard turning with PCBN also offers several environmental and cost benefits over grinding. These include greater process flexibility, reduced machine time, lower energy consumption, optional use of coolant and swarf recycling possibilities.

What is Hard Turning?

What is hard turning?

Hard turning is defined as the process of single point cutting of part pieces that have hardness values over 45 Rc. Typically, however, hard turned part pieces will be found to lie within the range of 58-68 Rc. The hard turning process is similar enough to conventional “soft” turning that the introduction of this process into the normal factory environment can happen with relatively small operational changes when the proper elements have been addressed.

Hard turning is best accomplished with cutting inserts made from either CBN (Cubic Boron Nitride), Cermet or Ceramic. Since hard turning is single point cutting, a significant benefit of this process is the capability to produce contours and to generate complex forms with the inherent motion capability of modern machine tools. High quality hard turning applications do require a properly configured machine tool and the appropriate tooling. For many applications, CBN tooling will be the most dominant choice. However, Ceramic and Cermet also have roles with this process.

The range of applications for hard turning can vary widely, where at one end of the process spectrum hard turning serves as a grinding replacement process, and can also be quite effective for pre-grind preparation processes. The attractiveness of the process lies in the performance numbers. A properly configured hard turning cell would typically demonstrate the following:

• Surface finishes of 0.00011" (.003 mm)
  
• Roundness values of .000009" (.00025 mm)
  
• Size control ranges of .00020" (.005mm)
  
• Production rates of 4- 6 over comparable grinding operations

Hard turning is a technology-driven process that requires certain performance features of the machine tool, workholding, process and the tooling.

Improving Internal Turning In A Blind Hole

Haven't posted lately, but today have time for a quick tip or two.

It doesn't matter if your using carbide inserts, ceramic inserts, or CBN Inserts, internal turning in a blind hole brings about the problem of chip evacuation. When the cutting tool reaches the rear side wall, chips may be caught between the wall and the insert. This may cause the insert to break.

Here are two solutions I found from a carbide insert manufacturer that can eliminate cutting tool breakage:

First Solution
1. Start by grooving at the rear wall.
2. Continue by turning from the inside toward the outside.

Second Solution
Start by grooving at the rear wall. Pull the tool back to the outside. Turn the final diameter from outside toward the groove.

Carbide Insert Designation/Identification

So you have a blue, green, yellow, clear box sitting on your desk, that one of the guys in the shop dropped off and said I need some more of these. Simple enough you think, I'll just order right off the box, problem is the box is smudged, and all you know is that it is and 80 degree carbide insert something or other.

Not that this ever happens. However, if you find yourself in this situation down the road, a good place to start is the ANSI designation chart for carbide inserts. This handy chart tells you whether that carbide insert is an 80 degree diamond, 55 degree diamond, or other. The insert thickness, insert tolerance, radius, clearance, hole type, and whatever other conditions may be listed at the end.

An example of a part # would look something like this: CNMA-432T DR-50


From looking at the insert designation chart, it tells me that this insert is:

1. 80 Degree diamond
2. Clearance of 0 degrees
3. Tolerance of =/-.002 to .005
4. Has a hole in it
5. Size is 1/2"- Number of 1/8ths of an inch in I.C. when I.C. is 1/4 inch and over
6. Thickness is 3/16" -Number of 1/16ths of an inch in thickness for I.C. of 1/4 inch and over
7. Has a corner radius of 1/32"
8. Has a chamfer cutting edge or K-Land


Now I know that is a lot of detail, but you get my drift. Use the sheet as a quick reference for turning tools and before you know it, it will no longer be necessary.

Thanks for reading.

-B

Calculating Speeds and Feeds for Cutting tools

I get asked quite often about things such as recommended speeds and feeds, how to calculate speeds and feeds, how to convert speeds and feeds...get the point yet?

Really, sometimes finding information on speeds and feeds on cutting tools is like searching for a diamond in the rough.

But fear no more, you have come to right place for all the speeds and feeds you can handle.

Hold on to your hats it's a wild and bumpy ride.

If your just getting in to machining and want some good calculators for speeds and feeds, you should try American Machinist. They have calculators for:

Tool Life Speed Adjustments - This calculator shows you a range of cutting speeds for different tool lives.

Speeds/Feeds Conversion - This calculator converts different expressions of speeds and feeds to other units of measure.

If using calculators on the web isn't your thing, I found a pretty cool webiste today that has a desktop Machinist's Calculator. It isn't free like at American Machinist, but you don't have to be online to use it, plus they are offering a free 30 day trial. I always like freebies!

The next bit of information came from another site I stumbled upon today while searching for speeds and feeds. This is what they have to say about speeds and feeds:

"Selecting spindle speeds and feed rates can be difficult, particularly if you're not accustom to working with CNC machines. Although you can't beat years of experience, we've compiled a short list of recommended spindle speeds and feed rates. The most commonly used materials are listed, then divided according to the CNC machine. All values are modeled around the use of engraving or .25-inch diameter cutters and in most cases should suffice for most jobs. However, do remember that these rates are only approximate values; they do not take into account factors such as tooling material types, diameters, and profiles. With this in mind, we recommend performing a test cut, then changing the values according to any factors that may affect the machining of your design."

So if you are looking for speeds in feeds for steel to wood turning, this is place to check out:

Speeds and Feeds/Spindle Speeds

As always, happy machining.

I am out...B

Finding Cutting Tools

Today I was searching for a cutting tool for a customer, an SJC something or other, hold on, must lean over desk to get part #.....ah yes, here it is and SJC63E4-CX90. Apparently is was a insert they had, but did not have the tool holder....so my job was to find out what sort of tool holder this insert goes into.

How did that work, you ask? Well if I'm writing about it, it obviously hasn't gone to well...but then again I'm no rocket scientist...I sell cutting tools (inside joke for those in the know).

So after multiple searches in both Google and Yahoo returning the same results, a light bulb went off, ah ha, I should just go to the manufacturers site, oh boy was that a bad idea. Not only were the links all crazy, but I think the site could use some updating. There was nothing there to help me find what I wanted. Oh it was great if you already know what you want, what this company makes, and how their tools work.

Am I starting to rant? That is never a good thing, so let me get to point.

And the point is....ready? I bet I have you on the edge of your seat right now...(the rambling thing again....)

The point is that sometimes in today's world it is easier to call the manufacturer direct to get an answer to your question. Because after all of my today's generation, tech savyness (sp?), multiple searches to page 5, (really?). It was the old fashion, pick up the phone, someone answers (not voicemail), ask a question, that ended up working. I was told the insert was old, and the holder was obsolete.

I suppose if it's not in the search engine, it doesn't exist....

I am out.

-B

Machining with CBN Inserts - Hard Turning with CBN Inserts

Hard Turning with CBN Insert
Hard Turning Definition

David Richards define “Hard Turning “ as machining hardened steels above 40 HRc, not hard in terms of “difficult”. Alloy Steels with a hardness below 40 HRc are not generally machined using CBN inserts because other tool materials work as well or better and cost less. Soft materials often stick to PCBN cutting tools causing “build up” on the cutting edge. This results in poor surface finish and tool life. The geometry of PCBN tools used for machining hardened steel is very blunt with no chip groove geometry to provide swarf control, not ideal for machining soft steels. However, some steels with a high alloy content and 30+ HRc are successfully finish machined with DR-50 because nothing else will do the job. If there is no adhesion, reliable size control and consistent surface finish can more than justify the cost of the tools.

Aluminum Alloy Machining
Aluminium alloys cannot be machined with CBN inserts. PCBN has a trace content of Aluminium nitride. Aluminium builds up on the cutting edge very quickly causing rapid tool wear and poor surface finish.

Cast Iron Machining
Cast iron and Iron based hard facing alloys with a significant ferrite content are not machined with CBN inserts. The soft gooey ferrite sticks to the CBN insert cutting edge causing rapid wear and poor surface finish.

D2 Machining
Interrupted cutting D2 tool steel is very difficult and unpredictable. D2 contains up to 14% Chromium and was designed to be used at 50-56 HRc. If the material is hardened to +60 HRc and not tempered very carefully, Chromium Carbide formation at the grain boundaries makes the material impossible to machine with interrupted cutting.

HSS Machining
Interrupted cutting of High Speed Steel – HSS is temperature resistant and does not soften in the shear zone. Interrupted cutting Nitrided steel is difficult. When continuous cutting, the super-hard surface is machined away by a part of the cutting edge that is not controlling surface finish and size. When interrupted cutting, the entire cutting edge impacts with a superhard surface resulting in poor tool life.

Hard Facing Alloy Machining
Hard facing alloys – Stellite (Cobalt/Chrome Alloys)and Colmonoy (Nickel/Chrome alloy) with more than 20% Chrome is not practically machined with PCBN – Tool life is too short. Chromium cannot be machined using PCBN. PCBN can be used to remove hard Chromed plated surfaces and expose a hardened steel base material, but it is not possible to machine within the Chrome.

High Temperture Alloy Machining
Machining high temperature alloys – Inconel, Hastalloy, Waspalloy, Titanium, Nimonics etc are not machined with PCBN. Tool life is negligible due to chemical affinity.

The information for the article was given thanks to:

David Richards Engineering Corporation

http://www.drengus.com/

and

David Richards Engineering Limited

http://www.dreng.co.uk/

Machining Cast Iron With CBN Inserts

CBN can provide a cost effective and highly productive alternative to hard metal or ceramic cutting tools for the machining of cast irons. In general terms, the following factors should be considered when applying CBN to an iron component:

Cast iron is not generally very hard (less than HRc.30) but tends to be abrasive. CBN is therefore employed because of its abrasive resistance. Unless the iron has been chilled or deliberately heat treated, the cutting action will be such that the CBN will not be required to anneal the material being cut in the shear zone. Grey cast irons are often fully pearlitic in structure - Grade 14 & 17 are common. In this case, the best results are gained using DR - 100/80 at surface speeds above 400 m/min. if the machine tool or component limit the speed available to less than 400 m/min, DR - 50 becomes more cost effective. Tool life and component quality improvements are often dramatic and more than justify the increased cost of the CBN tools. if the grey cast iron is not fully pearlitic and more free ferrite is present within the structure, the machinability of the iron becomes more difficult to predict. As the level of “soft and sticky” ferrite increases, the tool is more likely to suffer adhesion pick up which will alter the cutting action, resulting in premature wear of the tool. DR-50 becomes more likely to provide good results as the level of free ferrite increases and a short trial will soon determine the most suitable PCBN material.

Fully ferritic grey cast irons are not generally cost effective PCBN applications. S.G. irons are generally soft (less than HRc.30 ) and fully ferritic. PCBN is therefore not generally as efficient as other cuttingtool materials. There has, however, been a tendency to produce S.G. irons (nodular irons) with a pearlitic structure. This has resulted in some nominally S.G. irons machining surprisingly well with PCBN, DR-50 tending to be more successful. Low alloy irons commonly used in the automotive industry can be machined with CBN, but the performance is again dependant on the level of free ferrite in the structure of the iron.

Hardened irons, either heat treated or alloyed and heat treated, are machined in the same manner as hardened steels and are therefore more predictable. Cutting speeds recommended are lower - less than 200 m/min. It must be remembered that cast iron of a given specification produced by a foundry on one day may have a different machinabilty to that produced the next day. Once the benefits of machining with CBN have been determined, it may be considered worthwhile ensuring that castings supplied to the machine shop have a suitable microstructure to guarantee consistent PCBN tool performance. if the structure or grade of cast iron is unknown, a simple trial will soon determine the suitability of PCBN as a cutting tool.

You can find inserts for cast iron at the companies listed.

The information for the article was given thanks to:
David Richards Engineering Corporation
http://www.drengus.com
and
David Richards Engineering Limited
http://www.dreng.co.uk