End Mill Performance & Spindle Torque

Many times when machinists look at cutting tool speeds and feeds, they are often misled into believing that they should be concerned with horsepower. The real driving force is not horsepower, it’s TORQUE. In order to maximize your speeds and feeds you should have a good understanding of how your CNC machine develops and holds torque.

Torque is the measure of how much immediate rotational force a spindle drive motor can generate. The image at the right shows Relationship between force F, torque τ,linear momentum p, and angular momentumL in a system which has rotation constrained in one plane only (forces and moments due to gravity and friction are not considered).

End Mills in the Old School

Traditionally, a 1” diameter end mill would require high torque and low speed , while a 1/4” diameter end mill would require high speed and low torque. Generally speaking, different end mill diameters & geometries have different requirements for both Horsepower and Torque. 

Destiny End Mills

However, as a general rule most of our end mills are designed to be run at high RPM regardless of diameter. We prefer high speed AND high torque. Our tool geometry is optimized for high speed machining. 

A while back we talked about our tooling geometry and how our end mills can have up to 3 rake face in the cutting edge of the tool. As the tool enters the cut and takes the first 3-5 revolutions (and remember you can be running up to 18,000 Revolutions Per Minute) there is a tremendous amount of cutting force placed upon the tool and you can notice your HP meter jump as the tool enters the cut multiple times. This entry is when the torque curve on your CNC machine is the most important.  Older CNC machines where designed to quickly reach peak torque between 1200 - 3000 RPM and then drop off. Newer, high speed machining centers hold constant torque.

Think of it like this. When a hydrofoil starts off from the dock it's not up to speed so it requires both HP and torque until the hull of the boat lifts off the surface. At that point a couple important changes happen in power consumption because the ship has "lifted" from the surface: The coefficient of friction has dropped dramatically. Similarly, once our tools are "in the cut" the chip formation "lifts" from contact with the gullet of the tool (the 'core diameter"). Horsepower is not quite as important as maintaining torque in the cut especially as you interpolate around a corner in a full slotting application.

We like Constant Torque

Spindle Torque Efficiency

Because of the unique geometry, our tools perform best under constant torque.  Take a look at the torque curve for your CNC machine. If you have a 10,000 RPM spindle motor and the torque drops from it’s constant peak at 8200 RPM then 8200 RPM would be your maximum RPM. Take this into consideration FIRST when calculating the specific speeds and feeds.

The Diamond Back Rougher

Our Diamond Back Rougher is designed for maximum Metal Removal Rates (MRR) in Non Ferrous Applications. Although the chart below depict a maximum chip load per tooth (IPT) value, your maximum may be lower due to Machine Horsepower, Machine Torque, Toolholder and/or workholding. 

The “General Operating Range” is based upon 2X diameter (ADC / DOC)  in full diameter (RDC / WOC) SLOTTING.   The minimum Chip Loads remain constant for all applications, however, the maximum chip loads can vary for side milling applications in Finishing, Heavy Roughing  & Light roughing.

Diamond Back Rougher Chip Load range for Non Ferrous "N" type materials

Our Philosophy on End Mills: Coatings

We've spent a great deal of time insuring that our coatings work in conjunction with all the other aspects of our end mills.  We have three primary coatings for our tools. Here's some details on what they are and where to apply them for your cutting material applications.

Black Stealth

Black Stealth Coating MoS2

Molybdenum Disulfide (MoS2). The easiest way to understand our Stealth coating is to think of the coating as being ‘clear’ and not ‘black.’ As soon as the tool enters the cut many people comment that the “color has worn off.”  We can assure you that this is not the case. There’s several physical and chemical changes that cause this visual change and space does not permit here to explain the science. That’s part of the reason we call it “stealth” because you can’t see it any more!  What’s important is the this coating has a lower co-efficient of friction than just about everything else on the market. Our geometry works ideally with this coating. Used for our Viper and DiamondBack series tools which are for all Non Ferrous Alloy milling (N)

AlTiN 

AlTiN Coating

Aluminium Titanium Nitride  This PVD coating has a gradually increasing percentage of aluminum added as it goes through the coating process. It gradually increases in the amount of Aluminum from the substrate interface until it reaches the outer surface of the coating, where there is a higher percentage (up to 65%) of aluminum in the film. As the tool heats up, the aluminum converts to aluminum oxide, staying in the film. This coating provides exceptional oxidation resistance and extreme hardness. AlTiN retains its hardness when the temperature is 800° to 930° C (1,470° to 1,700° F) This coating is ideal for dry machining environments. Used exclusively on our Raptor products for all P - Steels (blue), M - Stainless Steel (yellow), K - Cast Iron (red), and S - Hi-Temp Alloys Special Alloys & Titanium - (brown) materials. 

Please keep in mind that this coating CANNOT be used in Aluminum (N) machining because the Aluminum in it would have an affinity to itself and cause workpiece adhesion to the cutting tool.

X-Treme 

TiAlN Xtreme Coating

Titanium Aluminium Nitride (TiAlN) This monolayer PVD coating has high hardness and excellent thermal stability that protects against premature tool wear. It also has excellent oxidation resistance allows high speed and semi dry or dry machining operations. Used for our Cobra and Python series tools which are for all P - Steels (blue), M - Stainless Steel (yellow), K - Cast Iron (red), and S - Hi-Temp Alloys Special Alloys & Titanium - (brown) materials

Our Philosophy on End Mills: Tolerance

When we talk about tolerance we are actually referring to two components of our end mills.  Our shank diameters are held tighter than standard h6 industry specifications of -0.0001” / -0.0003”.  Our Viper and DiamondBack End Mills are held to -0.0001" / 0.0003" on diameter and shank. However, that is just part of the story...

We’ve really concentrated a lot of time on the grinding tolerance as well. When you look at our competitors under a microscope many times you will see that the primary and secondary grind finish looks like a washboard texture because of the wheel that was used to finish grind it with.  

End Mill performance in high speed machining is dependent upon the surface roughness (topography) of the rake face and and relief face of the end mill.  Better, smoother ground surfaces reduce the co-efficient of friction and permit the tool to perform better “in the cut”.  As we talked about in our previous posting with regard to geometry, we make every attempt to reduce the co-efficient of friction that a chip encounters as it is being formed into 6's & 9's in our end mills.  We take special care to insure that our wheels are re-dressed quite often to maintain consistent surface finish. And that has an impact on coating adhesion as well. We'll be discussing that in our next posting.

Our Philosophy on End Mills: Geometry

Take a close look at our end mills... under a microscope. What you will find is that they look much different than most all of our competitors. 

Edge Strength

Edge Strength: Eccentric relief between primary & secondary

There are numerous variables that have an impact of cutting tool performance and tool life. We designed the tools to be used in different conditions and different machines. We spent many years perfecting the length of the primary and secondary grind in combination with the eccentric relief on our tools. The Red arrow shows the direction of typical cutting tool forces. We’ve believe that we've engineered more edge strength into our tools than any other competitor on the market which means that you can run at higher chip loads.

Double Variable Helix

Double Variable Helix

Chatter has been a persistent problem in milling for many years. Typically most shops will reduce the RPM and/or Feed to reduce the amount of chatter. Chatter is a result of natural harmonics built within the tool which is operating at it's own natural frequency.  Because traditional end mills maintained a consistent helix angle along the length of the flute, the tools tended to get in "tune". Technically, called a Frequency Response Function (FRF).  

Unequal Flute Spacing on a Raptor 3/6

The Double Variable Helix design corrects for this problem with a number of  design elements which enable out tools to run at higher RPM chatter free:

• Variable Flute Spacing - Each flute is unequally spaced around the circumference of the end mill, creating an out-of-phase cutting action.
• Double Variable Helix - DVH - The helix angle changes along the cutting edge which further creates an out-of-phase cutting action. 

Heat kills

With the exception of hard milling, it's pretty common knowledge that the heat should be removed with the chip and the less heat transferred to the tool the longer the tool life.  

We've taken a look at that very carefully and have designed our tools to form chips a bit differently.  Chips are formed in the outer rake face of the tools. Instead of the chip traveling all the way down into the gullet of the tools, which causes a lot of friction and heat, and then 6' & 9' formed against the core diameter, we have designed our tools to take a much heavier chip load that most competitors. 

By taking a heavier chip load the material is forced to turn on itself in the other rake face and eject from the cut without traveling down the entire length of the rake face. Think of it like throwing a tennis ball to a point 10 feet in front of you vs throwing it directly between your feet.

Our Philosophy on End Mills: Carbide Substrate

The most commonly used term for carbide is “Micro-Grain” but it does NOT really describe the differences that have evolved since the first development of “Micro-Grain” in the past 40-50 years. Fine, Ultra-Fine and Sub Micron grains are some of the current terminology that is used.

Two other commonly used terms are “toughness” and “wear resistance.” We’ve found that neither term can be used as a proper gage. Here’s why:

• Toughness - Fracture toughness is not only a characteristic of the material but also a function of the loading conditions. Carbide rod is measured for "toughness” before geometry has been ground into the tool and a finished, ground tool can vary as much as 300% in “fracture toughness” based upon geometry alone.
• Wear Resistance - Cutting tool wear is a result of complicated physical, chemical, and thermo-mechanical actions. Tool wear is caused by such mechanisms as adhesion, abrasion, diffusion & oxidation that all act together with predominant influence of one or more of them in different situations within the CNC machine, which is quite different from lab testing.

Cemented Carbide is similar to cement in more than name only. Cobalt is the “lime” that holds the Carbide “gravel” together. If a large chunk of carbide is exposed at the cutting edge it will fracture off just like a piece of gravel on a cement walkway edge. 

Destiny Tool Substrates compared to our competitors

Bottom Line: At Destiny Tool, through over a decade of testing, we have selected substrates that work together with our tools for optimal tool life and performance in specific materials. Our substrates range from a transverse rupture strength of 580,000 - 630,000 psi and vary in cobalt content from 10 -12% based upon the specific application that the tool was designed. You can trust that we’ve selected the correct substrate for your application material.

Manufacturer's Agents wanted!

We're preparing for the IMTS 2012 event and hoping to meet Manufacturer's Reps for much of the North American Market area. 

If you are a rep with cutting tool experience please plan on stopping by our IMTS booth W-2232 during the show so we can meet you and show you a little bit about our product offering. 

Our Manufacturer's representatives often assume the role of CNC Machining application consultants, offering wholesale, government and machine shop customers the best tooling recommendations from among our product offering.

Requirements

• No "Direct" to end-user sales
• Calling on Industrial Distributors accounts 
• Calling on Machine Tool Dealers and OEM's in their market area.
• Providing Technical support at End User accounts

Our independent agents typically make sales presentations and solve application problems for end users, industrial cutting tool distributors, machine tool dealers and, in some instances, Machine Tool Builders. 

Agents are expected to be able to demonstrate product samples, answer the client's questions, then make recommendations on which products best fit their client's needs.

A technical understanding and use and function of Surface Footage & Chip Load is required. Agents should have a working knowledge of coatings, ISO materials classification, competitive products lines and competitive distribution channels in their market area.

We are actively seeking agents with affiliated product lines that work in CNC milling machines such as rotary toolholders, work holding and no competitive cutting tool product lines.

Our products are targeted to specific material niches which include machining Aluminum and non ferrous alloys, Stainless Steels, Hi temperature alloys such as Titanium, Inconel, Kovar, Monel and other exotics.  Our target markets are aerospace, defense, performance automotive, wind, solar, and medical market segments.

Prospective agents should have a working knowledge of manufacturing facilities in their market area and who services them at the industrial distributor level. We are actively looking for industrial distributor partners to act as regional stocking distributors in a number of markets. Agents are expected to develop targeted industrial distributors to fulfill this role in their market area.