Hardenability of Steel

Many types of steel have a beneficial response to a method of heat treatment known as quenching. One of the most important criteria in the selection process of a workpiece material is hardenability. Hardenability describes how deep a metal can be hardened upon quenching from high temperature, and can also be referred to as the depth of hardening.

Steel At Microscopic Scale:

The first level of classification of steels at a microscopic level is their crystal structure, the way in which atoms are arranged in space. Body-Centered Cubic (BCC) and Face Centered Cubic (FCC) configurations are examples of metallic crystal structures. Examples of BCC and FCC crystal structures can be seen below in Figure 1. Keep in mind that the images in Figure 1 are meant to display atomic position and that the distance between the atoms is exaggerated.

depiction of BBC and FCC crystal structures in steel
Figure 1: Example of a BCC crystal structure (left) and FCC crystal structure (right)

The next level of classification is a phase. A phase is a uniform portion of a material that has the same physical and chemical properties. Steel has 3 different phases:

  1. Austenite: Face-Centered cubic iron; also iron and steel alloys that have the FCC crystal structure.
  2. Ferrite: Body-centered cubic iron and steel alloys that have a BCC crystal structure.
  3. Cementite: Iron carbide (Fe3C)

The final level of classification discussed in this article is the microstructure. The three phases seen above can be combined to form different microstructures of steel. Examples of these microstructures and their general mechanical properties are shown below:

  • Martensite: the hardest and strongest microstructure, yet the most brittle
  • Pearlite: Hard, strong, and ductile but not particularly tough
  • Bainite: has desirable strength-ductility combination, harder than pearlite but not as hard as martensite

Hardening at Microscopic Scale:

The hardenability of steel is a function of the carbon content of the material, other alloying elements, and the grain size of the austenite. Austenite is a gamma phase iron and at high temperatures its atomic structure undergoes a transition from a BCC configuration to an FCC configuration.

High hardenability refers to the ability of the alloy to produce a high martensite percentage throughout the body of the material upon quenching. Hardened steels are created by rapidly quenching the material from a high temperature. This involves a rapid transition from a state of 100% austenite to a high percentage of martensite. If the steel is more than 0.15% carbon, the martensite becomes a highly strained body-centered cubic form and is supersaturated with carbon. The carbon effectively shuts down most slip planes within the microstructure, creating a very hard and brittle material. If the quenching rate is not fast enough, carbon will diffuse out of the austenitic phase. The steel then becomes pearlite, bainite, or if kept hot long enough, ferrite. None of the microstructures just stated have the same strength as martensite after tempering and are generally seen as unfavorable for most applications.

The successful heat treatment of a steel depends on three factors:

  1. The size and shape of the specimen
  2. The composition of the steel
  3. The method of quenching

1. The size and shape of the specimen

During the quenching process, heat must be transferred to the surface of the specimen before it can be dissipated into the quenching medium. Consequently, the rate at which the interior of the specimen cools is dependent on its surface area to volume ratio. The larger the ratio, the more rapid the specimen will cool and therefore the deeper the hardening effect. For example, a 3-inch cylindrical bar with a 1-inch diameter will have a higher hardenability than a 3-inch bar with a 1.5-inch diameter. Because of this effect, parts with more corners and edges are more amendable to hardening by quenching than regular and rounded shapes. Figure 2 is a sample time-temperature transformation (TTT) diagram of the cooling curves of an oil-quenched 95 mm bar. The surface will transform into 100% martensite while the core will contain some bainite and thus have a lower hardness.

graph of sample time temperature transformation
Figure 2: Sample time temperature transformation (TTT) diagram also known as an isothermal transformation diagram

2.  The composition of the steel

It’s important to remember that different alloys of steel contain different elemental compositions. The ratio of these elements relative to the amount of iron within the steel yield a wide variety of mechanical properties. Increasing the carbon content makes steel harder and stronger but less ductile. The predominant alloying element of stainless steels in chromium, which gives the metal its strong resistance to corrosion. Since humans have been tinkering with the composition of steel for over a millennium, the number of combinations is endless.

Because there are so many combinations that yield so many different mechanical properties, standardized tests are used to help categorize different types of steel. A common test for hardenability is the Jominy Test, shown in Figure 3 below. During this test a standard block of material is heated until it is 100% austenite. The block is then quickly moved to an apparatus where it is water quenched. The surface, or the area in contact with the water, is immediately cooled and the rate of cooling drops as a function of distance from the surface. A flat is then ground onto the block along the length of the sample. The hardness at various points is measured along this flat. This data is then plotted in a hardenability chart with hardness as the y-axis and distance as the x-axis.

diagram of Jominy end quench specimen for hardened steel
Figure 3: Diagram of a Jominy end quench specimen mounted during quenching (left) and post hardness testing (right)

Hardenability curves are constructed from the results of Jominy Tests. Examples of a few steel alloy curves are shown in Figure 4. With a diminishing cooling rate (steeper drop in hardness over a short distance), more time is allowed for carbon diffusion and the formation of a greater proportion of softer pearlite. This means less martensite and a lower hardenability. A material that retains higher hardness values over relatively long distances is considered highly hardenable. Also, the greater the difference in hardness between the two ends, the lower the hardenability. It is typical of hardenability curves that as the distance from the quenched end increases, the cooling rate decreases. 1040 steel initially has the same hardness as both 4140 and 4340 but cools extremely quickly over the length of the sample. 4140 and 4340 steel cool at a more gradual rate and therefore have a higher hardenability. 4340 has a less extreme rate of coolness relative to 4140 and thus has the highest hardenability of the trio.

chart of hardenability for 4140, 1040, and 4340 steel
Figure 4: Hardenability charts for 4140, 1040 and 4340 steels

Hardenability curves are dependent on carbon content. A greater percentage of carbon present in steel will increase its hardness. It should be noted that all three alloys in Figure 4 contain the same amount of carbon (0.40% C).  Carbon is not the only alloying element that can have an effect on hardenability. The disparity in hardenability behavior between these three steels can be explained in terms of their alloying elements. Table 1 below shows a comparison of the alloying content in each of the steels. 1040 is a plain carbon steel and therefore has the lowest hardenability as there are no other elements besides iron to block the carbon atoms from escaping the matrix. The nickel added to 4340 allows for a slightly greater amount of martensite to form compared to 4140, giving it the highest hardenability of these three alloys. Most metallic alloying elements slow down the formation of pearlite, ferrite and bainite, therefore they increase a steel’s hardenability.

Table 1: Shows the alloying contents of 4340, 4140, and 1040 steel

Type of Steel: Nickel (wt %): Molybdenum (wt %): Chromium (wt %):
4340 1.85% 0.25% 0.80%
4140 0.00% 0.20% 1.00%
1040 0.00% 0.00% 0.00%

There can be a variation in hardenability within one material group. During the industrial production of steel, there are always slight unavoidable variations in the elemental composition and average grain size from one batch to another. Most of the time a material’s hardenability is represented by maximum and minimum curves set as limits.

Hardenability also increases with increasing austenitic grain size. A grain is an individual crystal in a polycrystalline metal. Think of a stained glass window (like the one seen below), the colored glass would be the grains while the soldering material holding it altogether would be the grain boundaries. Austenite, ferrite, and cementite are all different types of grains that make up the different microstructures of steel. It is at the grain boundaries that the pearlite and bainite will form. This is detrimental to the hardening process as martensite is the desired microstructure, the other types get in the way of its growth. Martensite forms from the rapid cooling of austenite grains and its transformation process is still not well understood. With increasing grain size, there are more austenite grains and fewer grain boundaries. Therefore, there are fewer opportunities for microstructures like pearlite and bainite to form and more opportunities for martensite to form.

colorful glass representing austenite
Figure 5: The colorful glass pieces represent grains of austenite which transforms into the desirable martensite upon quenching. The black portions in between the color portions represent grain boundaries. Sites where pearlite or bainite will form upon quenching.

3. The method of quenching

As previously stated, the type of quench affects the cooling rate. Using oil, water, aqueous polymer quenchants, or air will yield a different hardness through the interior of the workpiece. This also shifts the hardenability curves. Water produces the most severe quench followed by oil and then air. Aqueous polymer quenchants provide quenching rates between those of water and oil and can be tailored to specific applications by changing the polymer concentration and temperature. The degree of agitation also affects the rate of heat removal. The faster the quenching medium moves across the specimen, the greater the quenching effectiveness. Oil quenches are generally used when a water quench may be too severe for a type of steel as it may crack or warp upon treatment.

metalworker quenching casts in an oil bath
Figure 6: Metalworker quenching casts in an oil bath

Machining Hardened Steels

The type of cutter that should be chosen for processing tools chosen for machining a workpiece after hardening depends on a few different variables. Not counting the geometric requirements specific to the application, two of the most important variables are the material hardness and its hardenability. Some relatively high-stress applications require a minimum of 80% martensite to be produced throughout the interior of the workpiece. Usually, moderately stressed parts only require about 50% martensite throughout the workpiece. When machining a quenched metal with very low hardenability a standard coated solid carbide tool may work without a problem. This is because the hardest portion of the workpiece is limited to its surface. When machining a steel with a high hardenability it is recommended that you use a cutter with specialized geometry that is for that specific application. High hardenability will result in a workpiece that is hard throughout its entire volume. Harvey Tool has a number of different cutters for hardened steel throughout the catalog, including drills, end mills, keyseat cutters, and engravers.

Shop Harvey Tool’s Offering of Fully Stocked End Mills for Hardened Steels

Hardened Steel, Summarized

Hardenability is a measure of the depth to which a ferrous alloy may be hardened by the formation of martensite throughout its entire volume, surface to core. It is an important material property you must consider when choosing a steel as well as cutting tools for a particular application. The hardening of any steel depends on the size and shape of the part, the molecular composition of the steel, and the type of quenching method used.

Grappling With Graphite: A Machining Guide

Despite being a softer material, graphite is actually one of the most difficult materials to machine. There are many considerations machinists need to make in terms of tooling, coolant use, and personal safety when it comes to machining these parts. This “In The Loupe” post will examine the material properties, key machining techniques to consider, and tips for properly selecting cutting tools to achieve success in this tricky material.

What is Graphite?

While graphite is an allotrope of carbon, the two terms are not simply interchangeable. Carbon is an element that can form into several different allotropes including graphite, diamond, and fullerite. Graphite happens to be the most stable form of carbon, and is the most common, as carbon naturally occurs as graphite under standard conditions.

Graphite is most recognized for its superior conductivity and resistance to high heat and corrosion. This makes it a common material in high heat, high-pressure situations in the aerospace, electrode, nuclear, energy, and military industries.

graphite cnc material

Even though graphite can handle intense high-pressure situations with ease, it is actually a very soft, abrasive, and brittle material. This can cause serious challenges when machining, as graphite can eat up cutting tools, and severely minimize a tool’s usable life. However, with the proper tooling and techniques, there are ways to optimize graphite machining to be more cost-effective than the competition.

Graphite Machining Techniques

Since graphite is such a soft and brittle material, special consideration needs to be made when machining to avoid chipping it. To get a good cut, it is recommended that you take light chip loads and use lower feed rates in graphite. If you were to take a heavy cut at a fast feed rate, you would start chipping the graphite and could cause it to fracture completely. To give a comparison point, chip loads for graphite are similar to those for Aluminum materials, but with less than half the feed rate.

To give you an idea of speeds and feeds for graphite, here is an example using a 1/4″ Harvey Tool CVD Diamond Coated, 4 flute Square End Mill. If that tool was running at a standard RPM of 12,000 at 780 SFM, the recommended chip load would be .00292 for a feed rate of 140 IPM.

electrode machining

In terms of machine setup, the one major tip to remember is to always avoid using coolant. Graphite is a fairly porous material, and so it can absorb coolant and act as a “coolant sponge,” which will cause problems with finished parts. Inside the machine and on the tooling, the coolant can actually react with the graphite dust and create an abrasive slurry, which will cause problems while machining. A vacuum system is recommended for clearing material while machining graphite. Otherwise, coated tools should be able to run dry.

Another thing to note when machining graphite is that because graphite does not produce chips, but rather a cloud of very abrasive dust, it can be harmful to operators and machines without proper care. Operators should be wearing a protective mask to avoid inhaling the graphite dust. Proper ventilation and maintaining air quality in the shop is also key for the protection of machinists when working in graphite.

Since the graphite dust is also extremely conductive, it can easily damage non-protective circuits inside your CNC machine, which can cause major electrical issues. While coolant is not recommended, a vacuum system can help to remove the dust, keeping it from accumulating too much inside the machine and preventing serious problems.

Increase Your Graphite Machining Efficiency – Tap Into Harvey Tool’s Speeds and Feeds Charts Today

Cutting Tools for Graphite Machining

As previously mentioned, graphite is a notorious cutting tool-killer due to its extremely abrasive nature. Even the highest quality carbide end mills, if left uncoated, will wear quickly on most jobs. This extreme wear may force a tool change during an operation, which could lead to an imperfection in the part when trying to restart the operation where the worn tool left off.

graphite cutting tools

When selecting a cutting tool for graphite machining, the coating and cutting edge is the most important consideration. Flute count, helix angles, and other key features of the tool geometry ultimately come second to the coating when purchasing tooling.

For graphite machining, a CVD (Chemical Vapor Deposition) diamond coating is recommended whenever possible to maximize tool life and tool performance. These coatings are grown directly into the carbide end mill, improving the hardness and leaving the tool with a coating layer that is 5 times thicker than a PVD Diamond Coating. While not the sharpest edge, the CVD diamond coating provides much longer tool life than other diamond coatings due to the thicker diamond layer.

Even though initial tooling costs may be higher with CVD coated tools versus uncoated tools, since CVD coated tools see considerably longer tool life than uncoated tools, this makes the cost per part shrink significantly. In difficult, abrasive materials like graphite, the uncoated carbide tool will last a short time before the abrasiveness of the graphite completely wears down the cutting edge. Having a CVD coated tool will give you a leg up over the competition, keep your machine running with less downtime for tool changes, and ultimately deliver substantial cost savings.

end mills for graphite
CVD Diamond Coated End Mill from Harvey Tool

Overall, graphite can be a difficult material to machine, but with the right cutting tools and proper speeds and feeds you will be making quality parts in no time. Harvey Tool offers a wide selection of CVD coated end mills in various diameters, reaches, and lengths of cut to ensure you have what you need for any job that comes your way.

High Efficiency Milling for Titanium Made Easy With Helical’s New HVTI Cutter

Titanium is a notoriously difficult material to machine, especially in aggressive toolpaths, such as those associated with High Efficiency Milling (HEM). Helical Solutions’ new line of tooling, the HVTI-6 series of end mills for titanium, is optimized specifically for this purpose, and proven to provide 20% more tool life than a competitor’s similar tool.

At face level, these new Helical end mills for titanium feature corner radius geometry, 6 flutes, and are Aplus coated for optimal tool life and increased cutting performance. But there is much more to these end mills than the typical geometry of standard 6 flute tools. The HVTI-6 was designed with a combination of a unique rake, core, and edge design that give it a leg up over standard 6 flute tools for milling titanium while cutting HEM toolpaths. Click here to watch the HVTI-6 in action!

End Mills for Titanium

The design of the HVTI-6 was the result of significant testing by the Harvey Performance Company Innovation and New Product Development teams. These teams spent many months testing tools, doing in-depth analysis on materials and tool geometry, and pushing these tools through dozens of hours in the cut at testing sites across the country.

The new HVTI-6 cutter experienced higher metal removal rates (MRR) and 20% longer tool life while performing HEM in Titanium when compared to a standard 6 flute tool offered by a Helical Solutions competitor. This type of tool life improvement will produce huge cost savings on tooling, as well as shortened cycle times and lower cost per part.

Helical HVTI Titanium

The Harvey Performance Innovation team targeted Titanium grade Ti6Al4V for their testing, which accounts for the vast majority of the Titanium being machined in North America. The test part was designed and programmed to allow for a more defined agility test of the tool, taking the tool into key geometry cutting exercises like tight corners, long straight line cuts, and rapid movement.

Many hours were spent with Lyndex-Nikken, manufacturers of high-quality rotary tables, tool holders, and machining accessories, at their Chicago headquarters. By working with the team at Lyndex-Nikken, the Harvey Performance Company team was able to test under optimal conditions with top-of-the-line tool holders, work holding, and machining centers. Lyndex was also available to provide their expert support on tool holding techniques and were an integral part of the testing process for these tools. Video of the impressive test cuts taken at the Lyndex facility can be seen below.

WATCH THE HVTI IN ACTION

In these tests, the HVTI end mills for titanium was able to run HEM toolpaths at 400 SFM and 120 IPM in Ti6Al4V, which served as the baseline for most of the testing.

While the standard 6 flute tools offered by Helical will still perform to high standards in Titanium and other hard materials (steels, exotic metals, cast iron), the HVTI-6 is a specialized, material-specific tool designed specifically for HEM toolpaths in Titanium. Advanced speeds and feeds for these new tools are already available in Machining Advisor Pro, and the complete offering is now available in the Helical CAM tool libraries for easy programming.

To learn more about the HVTI 6 Flute End Mills for Titanium, please visit the Helical Solutions website. To learn more about HEM techniques, download the HEM Guidebook for a complete guide on this advanced toolpath.

An In-Depth Look at Helical’s Tplus Coating for End Mills

When working with difficult-to-machine materials, such as Inconel, stainless steel, or hardened steels, utilizing an effective coating is important for sustaining the life of your tool and perfecting the outcome of your part. While looking for the right coating, many machinists try out several before finding a solution that works – a process that wastes valuable time and money. One coating gaining popularity in applications involving tough materials is Helical SolutionsTplus coating. This post will explore what Tplus coating is (and isn’t), and when it might be best for your specific job.

tplus coating on helical end mill

What is Helical Solutions’ Tplus Coating?

Helical’s Tplus coating is a Titanium-based, multi-layered coating that is applied by a Physical Vapor Deposition (PVD) process. This method of coating takes place in a near-vacuum and distributes micron-thick layers evenly onto a properly prepared tool.  Tplus is a premium, multi-layered, titanium coating that increases edge strength, wear resistance, and tool life.

tplus coating specification chart

When Should a Machinist Use Tplus Coating?

When Working in Difficult to Machine Materials

Tplus coating works great in difficult-to-machine materials such as Inconel, stainless steel, hardened steels, and other alloyed steels with a hardness up to 65 Rc. It provides high hardness (44 GPa) for your tool, creating stronger cutting edges and resulting in extended tool life.

When Working in High Temperature Applications

When you are running an application in a ferrous material where extreme heat and work hardening are a possibility, Tplus is a great solution, as it’s designed to withstand high temperatures (up to 2,192°).

Helical Solutions’ 7 Flute Tplus End Mill

In Dry Machining Applications

In the absence of coolant, fear not! Tplus coating is a viable option since it can handle the heat of machining. The low coefficient of friction (0.35) guarantees great performance in dry machining and allows the coated tool to move throughout the part smoothly, creating less heat, which is extremely beneficial in applications without coolant.

In Large Production Runs

In high production runs is truly where this coating excels, as its properties allow your tool to remain in the spindle longer – creating more parts by avoiding time in swapping out a worn tool.

Machining Precious Metals

Precious metals can be particularly difficult to machine due to their wide range of material properties and high cost if a part has to be scrapped. The following article will introduce these elements and their alloys as well as provide a guide on how to machine them effectively and efficiently.

About the Elements

Sometimes called “noble” metals, precious metals consist of eight elements that lie in the middle of the periodic table (seen below in Figure 1). The eight metals are:

  1. Ruthenium (Ru)
  2. Rhodium (Rh)
  3. Palladium (Pd)
  4. Silver (Ag)
  5. Osmium (Os)
  6. Iridium (Ir)
  7. Platinum (Pt)
  8. Gold (Au)

These elements are some of the rarest materials on earth, and can therefore be enormously expensive. Gold and silver can be found in pure nugget form, making them more easily available. However, the other six elements are typically found mixed in the raw ore of the four metals they sit below on the periodic table: Iron (Fe), Cobalt (Co), Nickel (Ni), and Copper (Cu). These elements are a subset of precious metals and are generally called Platinum Group Metals (PGM). Because they are found together in raw ore, this makes mining and extraction difficult, dramatically increasing their cost. Because of their high price tag, machining these materials right the first time is incredibly important to a shop’s efficiency.

machining metals

Figure 1: Periodic table with the 8 precious metals boxed in blue. Image source: clearscience.tumblr.com

Basic Properties and Compositions of Precious Metals

Precious metals have notable material properties as they are characteristically soft, ductile, and oxidation resistant. They are called “noble” metals because of their resistance to most types of chemical and environmental attack. Table 1 lists a few telling material properties of precious metals in their elemental form. For comparison purposes, they are side-by-side with 6061 Al and 4140 Steel. Generally, only gold and silver are used in their purest form as the platinum group metals are alloys that consist mainly of platinum (with a smaller composition of Ru, Rh, Pa, Os, Ir). Precious metals are notable for being extremely dense and having a high melting point, which make them suitable for a variety of applications.

Table 1: Cold-worked Material Properties of Precious Metals, 4140 Steel and 6061 Aluminum 

precious metals

Common Machining Applications of Precious Metals

Silver and gold have particularly favorable thermal conductivity and electrical resistivity. These values are listed in Table 2, along with CC1000 (annealed copper) and annealed 6061 aluminum, for comparison purposes. Copper is generally used in electrical wiring because of its relatively low electrical resistivity, even though silver would make a better substitute. The obvious reason this isn’t the general convention is the cost of silver vs. copper. That being said, copper is generally plated with gold at electrical contact areas because it tends to oxide after extended use, which lowers its resistivity. As stated before, gold and the other precious metals are known to be resistant to oxidation. This corrosion resistance is the main reason that they are used in cathodic protection systems of the electronics industry.

Table 2: Thermal Conductivity and Electrical Resistivity of Ag, Au, Cu, and Al 

machining metals

Platinum and its respective alloys offer the most amount of applications as it can achieve a number of different mechanical properties while still maintaining the benefits of a precious metal (high melting point, ductility, and oxidation resistance). Table 3 lists platinum and a number of other PGMs each with their own mechanical properties. The variance of these properties depends on the alloying element(s) being added to the platinum, the percentage of alloying metal, and whether or not the material has been cold-worked or annealed. Alloying can significantly increase the tensile strength and hardness of a material while decreasing its ductility at the same time. The ratio of this tensile strength/hardness increase to ductility decrease depends on the metal added as well as how much is added, as seen in Table 3. Generally this depends on the particle size of the element added as well as its natural crystalline structure. Ruthenium and Osmium have a specific crystal structure that has a significant hardening effect when added to platinum. Pt-Os alloys in particular are extremely hard and practically unworkable, which doesn’t yield many real-world applications. However, the addition of the other 4 PGMs to platinum allow for a range of mechanical properties with various usages.

Table 3: PGM material properties (Note: the hardness and tensile strength are cold worked values) 

machining metals

Platinum and its alloys are biocompatible, giving them the ability to be placed in the human body for long periods of time without causing adverse reactions or poisoning. Therefore, medical devices including heart muscle screw fixations, stents, and marker bands for angioplasty devices are made from platinum and its alloys. Gold and palladium are also commonly used in dental applications.

Pt-Ir alloys are noticeably harder and stronger than any of the other alloys and make excellent heads for spark plugs in the automobile industry. Rhodium is sometimes added to Pt-Ir alloys to make the material less springy (as they are used as medical spring wire) while also increasing its workability. Pt and Pt-Rh wire pairs are extremely effective at measuring temperatures and are therefore used in thermocouples.

Machining Precious Metals

The two parameters that have the most effect when machining are hardness and percent elongation. Hardness is well-known by machinists and engineers across the manufacturing industry as it indicates a material’s resistance to deformation or cutting. Percent elongation is a measurement used to quantify material ductility. It indicates to a designer the degree to which a structure will deform plastically (permanently) before fracture. For example, a ductile plastic such as ultrahigh molecular weight polyethylene (UHMWPE) has a percent elongation of 350-525%, while a more brittle material such as oil-quenched and tempered cast iron (grade 120-90-02) has a percent elongation of about 2%. Therefore, the greater the percent elongation, the greater the material’s “gumminess.” Gummy materials are prone to built-up edge and have a tendency to produce long stringy chips.

Tools for Precious Metals

Material ductility makes a sharp cutting tool essential for cutting precious metals. Variable Helix for Aluminum Alloy tools can be used for the softer materials such as pure gold, silver, and platinum.

machining metals

Figure 2: Variable Helix Square End Mill for Aluminum Alloys

Higher hardness materials still require a sharp cutting edge. Therefore, one’s best option is to invest in a PCD Diamond tool. The PCD wafer has the ability to cut extremely hard materials while maintaining a sharp cutting edge for a relatively long period of time, compared to standard HSS and carbide cutting edges.

machining metals

Figure 3: PCD Diamond Square End Mill

Speeds and Feeds charts:

machining metals

Figure 4: Speeds and Feeds for precious metals when using a Square Non-ferrous, 3x LOC

machining metals

Figure 5: Speeds and Feeds for precious metals when using a 2-Flute Square PCD end mill

What to Know About Helical Solution’s Zplus Coating

Non-ferrous and non-metallic materials are not usually considered difficult to machine, and therefore, machinists often overlook the use of tool coatings. But while these materials may not present the same machining difficulties as hardened steels and other ferrous materials, a coating can still vastly improve performance in non-ferrous applications. For instance, materials such as aluminum and graphite can cause machinists headaches because of the difficulty they often create from abrasion. To alleviate these issues in non-ferrous machining applications, a popular coating choice is Helical Solution’s Zplus coating.

zplus coating

What is Helical Solutions’ Zplus Coating?

Helical’s Zplus is a Zirconium Nitride-based coating, applied by a Physical Vapor Deposition (PVD) process. This method of coating takes place in a vacuum and forms layers only microns thick onto the properly prepared tool. Zirconium Nitride does not chemically react to a variety of non-ferrous metals, increasing the lubricity of the tool and aiding in chip evacuation.

zplus coating specification chart

When Should a Machinist Use Helical Solution’s Zplus?

Working with Abrasive Materials

While Zplus was created initially for working in aluminum, its hardness level and maximum working temperature of 1,110°F enables it to work well in abrasive forms of other non-ferrous materials, as well. This coating decreases the coefficient of friction between the tool and the part, allowing it to move easier through more abrasive materials. This abrasion resistance decreases the rate of tool wear, prolonging tool life.

Concerns with Efficient Chip Evacuation

One of the primary functions of this coating is to increase the smoothness of the flutes of the tool, which allows for more efficient chip removal. By decreasing the amount of friction between the tool and the material, chips will not stick to the tool, helping to prevent chip packing. The increased lubricity and smoothness provided by the coating allows for a higher level of performance from the cutting tool. Zplus is also recommended for use in softer, gummy alloys, as the smooth surface encourages maximum lubricity within the material – this decreases the likelihood of those gummier chips sticking to the tool while machining.

Large Production Runs

Uncoated tools can work well in many forms of non-ferrous applications. However, to get a genuinely cost-effective tool for your job, the proper coating is highly recommended. Large production runs are known for putting a lot of wear and tear on tools due to their increased use, and by utilizing an appropriate coating, there can be a significant improvement in the tools working life.

3 flute corner radius end mill for aluminum

When is Zplus Coating Not Beneficial to My Application?

Finishing Applications

When your parts finish is vital to its final application, a machinist may want to consider going with an uncoated tool. As with any coating, ZrN will leave a very minor rounded edge on the tip of the cutting edge. The best finish often requires an extremely sharp tool, and an uncoated tool will have a sharper cutting edge than its coated version.

What to Know About Harvey Tool’s TiB2 Coating

Aluminum and magnesium alloys are common materials found in machine shops worldwide, and are known as an “easier” material to machine. However, machinists can still experience hiccups while machining this material if they are not prepared with the proper tooling.. When working with aluminum and magnesium alloys, it is important to choose a coating that will work to extend your tool’s life and aid in the removal of chips. A popular choice for this material bucket is Harvey Tool’s TiB2 coating.

Explore More TiB2 Tooling With Harvey Tool’s End Mills for Aluminum

What is Harvey Tool’s TiB2 Coating?

Harvey Tool’s TiB2 coating is a Titanium Diboride, ceramic-based coating that provides superb erosion resistance during machining. TiB2 is added to a tool by a method called Physical Vapor Deposition (PVD), which is conducted in a vacuum where particles are vaporized and applied onto a surface, forming thin layers of material onto the properly-prepped tool. This method enables the coating to be corrosion and tarnish resistant.

TiB2 Coating Specification chart

TiB2 is identified in Harvey Tool’s product catalog with a “-C8” following the sku number. It can be found offered in Harvey Tool’s lines of Variable Helix End Mills for Aluminum Alloys and Miniature High Performance Drills for Aluminum Alloys.

When Should a Machinist Use TiB2 Coating?

Chip Evacuation Concerns

TiB2 has an extremely low affinity to aluminum, which helps with the chip evacuation process. Simply, chips of a material are able to evacuate through chip valleys easier if they don’t have a high affinity to the coating being used. TiB2 coating does not chemically react with aluminum and magnesium, which allows for smoother chip evacuation, as the chips do not stick to the coating and create issues such as chip packing. This is a common machining mishap that can cause both part and tool damage, quickly derailing a machining operation. By using a coating that increases the lubricity of the tool, chips will not have a surface to stick to and will more smoothly evacuate from the flutes of the tool.

Large Production Runs

While an uncoated tool may work fine in some applications, not all applications can succeed without a tool coating. When working with large production runs where the tools need to hold up through the process of machining large numbers of parts, using a coating is always recommended because they extend the life of your tool.

When is TiB2 Coating Not Beneficial to My Application?

Extremely Abrasive Materials

During the PVD coating process, tools can reach a temperature in excess of 500° F, which can cause the toughness of the carbide to drop slightly. This process does not normally compromise the performance of the tool due to the coating being placed over the carbide. The coating then protects the slightly weakened edge and increases tool performance in recommended materials. Micro-fractures only start appearing when the tool is being run incredibly fast through highly abrasive materials, leading to a decrease in the life of the tool.

Extremely Soft Materials

The coating, while only a few microns thick at most, still provides an ever-so-slight rounded edge to the cutting edge of the tools it is placed on. It is important to take this into consideration, as using the sharpest tools possible when working with materials such as soft plastics is recommended. The sharpest edge possible decreases the likelihood of any “pushing” that might occur on the material and increases the likelihood of proper “shearing” when machining.

When Finish Is Vital

If your part’s finish is imperative to the final product, an uncoated tool may work better for your application. A coating, like stated above, creates a microscopic rounded surface to the cutting edge of the tool. When running tools at finishing speeds and feeds in materials like aluminum, a sharp edge can create the difference between a finished part that does – or does not – pass final inspection.

How Material Specific Tooling Pays Off

A machinist is faced with many questions while selecting the proper tool for their job. One key decision that must be made is whether a material specific tool is appropriate and necessary for the application that’s going to be performed – whether the benefits of using this type of tool outweigh the higher price tag than that of a tool designed for use in a variety of materials. There are four main categories to consider when deciding whether a material specific tool is your best bet: internal tool geometry, coatings, material removal rates (MRR), and cost.

When to Utilize Material Specific Tooling

Are you a machinist in a shop that deals primarily with one type of material? Or, do you generally change materials frequently throughout the day? Further, how many parts do you make at a time? These are questions you must ask yourself prior to making a tooling decision.

Material Specific Tooling is best utilized where several parts are being machined of the same material. For instance, if your shop is machining 1,000 plastic parts, it would be in your best interest to opt for a tool designed for this material as your tooling would not only last longer but perform better. If machining flexibility is paramount for your shop, if you’re only machining a few parts, or if part finish is not of high importance, a regular end mill may suffice.

Pros and Cons of Material Specific Tooling

There are pros and cons to purchasing a Material Specific Tool.

Pros:

  • Tool geometry designed for the material you’re working in to achieve the best results.
  • Coating optimized for the material you’re cutting.
  • More aggressive speeds and feeds, and boosted MRR as a result.
  • Increased tool life.

Cons:

  • Higher upfront cost, though long term savings are possible if used in proper situations.
  • Less opportunity for flexibility. While most end mills may be suitable for use in many jobs and many machines, Material Specific End Mills are engineered for use in specific materials

Special Benefits of Material Specific Tooling

A Unique Internal Tool Geometry

Many manufacturers supply tooling designed for use in specific material buckets. For instance, Harvey Tool has distinct catalog sections for material specific tooling for Hardened Steels, Exotic Alloys, Medium Alloy Steels, Free Machining Steels, Aluminum Alloys, Plastics, Diamond Tooling for Non-Ferrous Materials, and Composites. The special geometry of tools found in these sections is optimized to allow the tool to perform optimally in its select material group.

For instance, a machinist may be faced with a dilemma while preparing to machine a plastic part. While an end mill found in Harvey Tool’s Miniature End Mill section could certainly machine this material, Harvey Tool’s end mill offering designed to machine plastics feature a high rake, high relief design. This is ideal for plastics because you want to effectively cut and form chips while the strength of the tool is less of a concern. The high rake and high relief creates a sharp cutting edge that would quickly break down in metals. However, in plastics, this effectively shears the material and transfers the heat into the chip to produce a great finish in your part.

material specific tooling

Harvey Performance Company, LLC.

Specific Coatings & Substrates for Optimal Performance

One key benefit of opting for a material specific tool is the ability to utilize the best coating option available for that material. Tool coatings serve many functions, including improved lubricity, increased tool life, and a higher-quality part finish. In addition, coated tools can typically be run around 10% faster than uncoated tools.

While many manufacturers will specially coat a standard end mill at your request, this takes added time and cost. In its Material Specific catalog sections, Harvey Tool offers coated tools stocked and ready to ship. For instance, their Hardened Steels and Exotic Alloys categories utilize AlTiN Nano coating. This is a unique nanocomposite coating that has a max working temperature of 2,100° F and shows improved performance in materials such as Hardened Steels, Titantium Alloys, and Inconel, among others.

Increased Material Removal Rates

Because Material Specific Tooling features optimal tool geometry for a job, running parameters are generally able to be more aggressive. Any machinist knows that Material Removal Rates (MRR), is the metric that’s most closely related to shop efficiency, as the more material removed from a part in a given period of time, the faster parts are made and the higher the shop output.

The following example compares running parameters of end mills from Harvey Tool’s Miniature End Mill and Material Specific End Mill Sections. You can notice that while key geometries between the two tools are identical, and are in use in the same material with the same operation, the chip load (+25%), linear feed rate (+33%), and depth of cut (+43%) are boosted. This allows for more material to be removed in a shorter period of time.

Miniature End Mill

Part Number: 836408

Description: 3 Flute 1/8 inch diameter 3x LOC Square Stub & Standard

Material: 6061 Aluminum

Application: Slotting

Speed: 10,000 RPM

Chip Load: .00124 IPT

Linear Feed: 37.2 IPM

DOC: .04375

Material Specific End Mill

Part Number: 942308

Description: 3 Flute 1/8 inch diameter 3x LOC Square Variable Helix for Aluminum Alloys

Material: 6061 Aluminum

Application: Slotting

Speed: 10,000 RPM

Chip Load: .00165 IPT

Linear Feed: 49.5 IPM

DOC: .0625

Harvey Performance Company, LLC.

Extensive Cost Savings

The following chart displays a cost analysis breakdown between a tool found in the Miniature End Mill section, item 993893-C3; and a tool found in the Material Specific End Mill section, item 933293-C6. When compared for the machining of 1,000 parts, the overall savings is nearly $2,500.

material specific tooling benefit chart

Material Specific Tooling Summarized

In conclusion, Material Specific End Mills have many benefits, but are best utilized in certain situations. While the initial cost of these tools are higher, they can work to save your shop time and money in the long run by lasting longer and producing more parts over a given period of time.

Slaying Stainless Steel: Machining Guide

Stainless steel can be as common as Aluminum in many shops, especially when manufacturing parts for the aerospace and automotive industries. It is a fairly versatile material with many different alloys and grades which can accommodate a wide variety of applications. However, milling steel can also be immensely difficult. Stainless steels are notorious end mill assassins, so dialing in your speeds and feeds and selecting the proper tool is essential for machining success.

Material Properties

Stainless steels are high-alloy steels with superior corrosion resistance to carbon and low-alloy steels. This is largely due to their high chromium content, with most grades of stainless steel alloys containing at least 10% of the element.

Stainless steel can be broken out into one of five categories: Austenitic, Ferritic, Martensitic, Precipitation Hardened (PH), and Duplex. In each category, there is one basic, general purpose alloy. From there, small changes in composition are made to the base in order to create specific properties for various applications.

For reference, here are the properties of each of these groupings, as well as a few examples of the popular grades and their common uses.

CategoryPropertiesPopular GradesCommon Uses
AusteniticNon-magnetic, outstanding corrosion and heat resistance.304, 316Food processing equipment, gutters, bolts, nuts, and other fasteners.
FerriticMagnetic, lower corrosion and heat resistance than Austenitic.430, 446Automotive parts and kitchen appliances.
MartensiticMagnetic, moderate corrosion resistance – not for severe corrosion.416, 420, 440Knives, firearms, surgical instruments, and hand tools.
Precipitation Hardened (PH)Strongest grade, heat treatable, severe corrosion resistance.17-4 PH, 15-5 PHAerospace components.
DuplexStronger mixture of both Austenitic and Ferritic.244, 2304, 2507Water treatment plants, pressure vessels.

Tool Selection

Choosing the correct tooling for your application is crucial when machining stainless steel. Roughing, finishing, slotting, and high efficiency milling toolpaths can all be optimized for stainless steel by choosing the correct style of end mill.

Traditional Roughing

For traditional roughing, a 4 or 5 flute end mill is recommended. 5 flute end mills will allow for higher feed rates than their 4 flute counterparts, but either style would work well for roughing applications. Below is an excellent example of traditional roughing in 17-4 Stainless Steel.

Slotting

For slotting in stainless steel, chip evacuation is going to be key. For this reason, 4 flute tools are the best choice because the lower flute count allows for more efficient chip evacuation. Tools with chipbreaker geometry also make for effective slotting in stainless steel, as the smaller chips are easier to evacuate from the cut.

stainless steel machining

Finishing

When finishing stainless steel parts, a high flute count and/or high helix is required for the best results. Finishing end mills for stainless steel will have a helix angle over 40 degrees, and a flute count of 5 or more. For more aggressive finishing toolpaths, flute count can range from 7 flutes to as high as 14. Below is a great example of a finishing run in 17-4 Stainless Steel.

High Efficiency Milling

High Efficiency Milling can be a very effective machining technique in stainless steels if the correct tools are selected. Chipbreaker roughers would make an excellent choice, in either 5 or 7 flute styles, while standard 5-7 flute, variable pitch end mills can also perform well in HEM toolpaths.

stainless steel

HEV-5

Helical Solutions offers the HEV-5 end mill, which is an extremely versatile tool for a variety of applications. The HEV-5 excels in finishing and HEM toolpaths, and also performs well above average in slotting and traditional roughing. Available in square, corner radius, and long reach styles, this well-rounded tool is an excellent choice to kickstart your tool crib and optimize it for stainless steel machining.

stainless steel machining

Running Parameters

While tool selection is a critical step to more effective machining, dialing in the proper running parameters is equally important. There are many factors that go into determining the running parameters for stainless steel machining, but there are some general guidelines to follow as a starting point.

Generally speaking, when machining stainless steels a SFM of between 100-350 is recommended, with a chip load ranging between .0005” for a 1/8” end mill up to .006” for a 1” end mill. A full breakdown of these general guidelines is available here.

Machining Advisor Pro

Machining Advisor Pro is a cutting edge resource designed to precisely calculate running parameters for high performance Helical Solutions end mills in materials like stainless steel, aluminum, and much more. Simply input your tool, your exact material grade, and machine setup and Machining Advisor Pro will generate fully customizable running parameters. This free resource allows you to push your tools harder, faster, and smarter to truly dominate the competition.

Dial In Your Stainless Steel Machining Application With Helical Solutions’ Machining Advisor Pro

In Conclusion

Stainless steel machining doesn’t have to be hard. By identifying the proper material grade for each part, selecting the perfect cutting tool, and optimizing running parameters, headaches from milling steel can become a thing of the past.

Ideal Tooling for Machining Composites

Composite Materials

A material is classified as a composite if it is made up of at least two unique constituents that when combined yield beneficial physical and mechanical properties for a number of different applications. A binding agent that is the matrix material is filled with either particles or fibers of a second material that act as reinforcements. The combination of strength, weight, and rigidity make composites extremely useful for the automotive, aerospace, and power generation industry. Often the matrix material of particulate-reinforced composites is some form of plastic, and the reinforcement material is either glass or carbon particles. These are sometimes called “filled plastics,” and are typically very abrasive materials. Many composites are layered with varying fiber orientations, which increase the strength of the material and are called fiber-reinforced composites.

Common Problems When Machining Composites

  1. Delamination of composite layers
  2. Uncut Fibers
  3. Fiber tear-out
  4. Uneven tool wear
  5. Poor surface finish due to “competing” materials

These problems are all caused by unique conditions created by composite materials, and can be very tricky to correct.  The simple fact of cutting a combination of multiple materials at the same time introduces many factors that make it difficult to strike the right balance of the proper tool for the job and appropriate running parameters.  The following tool styles provide solutions for a wide array of composite concerns.  Composite Drilling Applications can face the same issues, and proper drill choice can help as well.

Straight Flute End Mill

Straight Flute Composite Cutters are designed to prevent delamination of layered materials by applying all cutting forces radially, eliminating axial forces from a typical helical cutting edge. Cutting action is improved with a high positive rake angle for shearing fibers and eccentric relief for improved edge life. Shallow ramping operations can be performed with this tool, but the largest benefits are seen in peripheral milling applications.

straight flute end mill

Compression Cutters

The Compression Cutter consists of an up cut and down cut helix. The top portion of the length of cut has right-hand cutting teeth with a left-hand spiral. The lower portion of the length of cut has right-hand cutting teeth with a right-hand spiral. This creates opposing cutting forces to stabilize the material removal process when cutting layered composites to prevent delamination, fiber pullout, and burs along the surface. Compression of the top and bottom of the workpiece keeps the layered bonded together.

compression cutter end mill

Chipbreaker Cutter

The Chipbreaker Cutter is ideally suited for roughing and profiling composites with a high percentage of fiber fill. The notch-like chipbreakers shear fibers and shorten chips for improved material evacuation. This specialized geometry is great for keeping chips small and avoiding “nesting” of stringy fibrous chips around the cutter.

chipbreaker for composite materials

Diamond Cut End Mill

Diamond Cut Composite Cutters come in two different geometries: End Mill Style and Drill Mill Style. Although the end mill style tool is center cutting, the drill mill style has a 140° point angle, making it more suitable for plunge cutting. This is great for clearing out pockets in the middle of composite sheets.

diamond cut end mill for composites

End Mills for Composites – Diamond Cut – End Mill Style

diamond cut drill mill for composites

End Mills for Composites – Diamond Cut – Drill Mill Style

Both the end mill and drill mill style share the same downcut geometry on the outside diameter. This diamond cut tool receives its name from the combination of left-hand and right-hand teeth. The tool is predominantly a downcut style – a geometry that allows for these tools to effectively rough and profile high fiber reinforced or filled composites, breaking up chips and shearing through fibers.

Diamond Cut vs. Chipbreaker Style

The diamond cut tools have a higher flute count, which some may intuitively think would lead to a better finish, but this is not the case as this line of tools contains right-hand and left-hand teeth. There is a trade-off between an increased ability to shear fibers and leaving a poorer finish. The chipbreaker style tool, although not as effective as shearing fibers, is ultimately designed for the same purpose but leaves a better finish as all of the flutes are facing the same direction.

Composite Finisher

The Composite Finisher has optimized geometry for finishing in composite. A slow helix and high flute count for more contact points ultimately renders a smooth finish by minimizing fraying of fiber-reinforced and layered materials.

finishing end mill for composites

Coating or No Coating?

Composite materials, especially those with glass or carbon fiber, can be particularly abrasive and have a tendency to wear down the cutting edge of carbide tools. If one is looking to achieve the best tool life and maintain a sharp cutting edge, then choosing an Amorphous Diamond coated tool is the best option. This thin coating improves lubricity and wear resistance over its uncoated counterpart. Using a tool with CVD diamond coating can be very beneficial in extreme cases, when fiber fill percentage is very large. This is a true diamond coating, and offers the best abrasion resistance, but a slightly less sharp cutting edge as it is a thicker coating. PCD diamond tooling offers the best tool life. If it a solid diamond wafer brazed to a carbide shank, and can maintain the sharpest edge of any diamond tooling. However, PCD is limited to straight flutes, and can come at a higher price.

Composite materials are being increasingly utilized in today’s manufacturing world for their impressive strength to weight ratio. This growth has stimulated innovative techniques of cutting composites seen in the tool choices above. Harvey Tool’s variety of geometries helps any machine shop tackle composite cutting applications and will continue to offer groundbreaking solutions to these types of manufacturing problems.