Helical Solutions Teams up With Mastercam to Test Different Levels of Continuous Time In Cut (CTIC)

Don Grandt, Harvey Performance Company National Application Engineer, met up with Jesse Trinque at the Mastercam Manufacturing Lab to demo some Helical Solutions End Mills and discuss Continuous Time In Cut (CTIC).

Continuous Time in Cut (CTIC) is the amount of time that a tool is engaged with a material. When an end mill is in a cut for too long, the friction can build and surface foot can be sacrificed, greatly affecting the performance and wear of a tool.

Check out this video to watch Jesse and Don test out how different levels of CTIC directly affect tool life and performance. This series of tests, which were facilitated by Mastercam, were conducted in Okuma’s GENOS M560-V, and utilized tool paths from Mastercam. For tooling, a standard ½” Helical Solutions HEV-6, a 6 flute, variable pitch end mill with a .03” corner radius, was used to machine 17-4 stainless steel.

All tests used the same cutting parameters, setup, material, and tool, with altered CTIC.

Take a Deeper Dive Into CTIC

Tune into this episode of In The Loupe TV to learn how you can manipulate Continuous Time In Cut (CTIC) and surface foot to reduce heat in your machining applications.

We Partnered with Makino & Mastercam to Set MRR Standards with Helical Solutions’ HEV-C-6

Material removal rate (MRR) is the term for the measurement of material removed from a part during machining, over a set period of time, and is the key identifier in machine, tooling, and software efficiency. Radial depth of cut (RDOC) and axial depth of cut (ADOC) are critical elements to MRR, as they determine how and where your tooling is engaging with the workpiece. Applying High Efficiency Milling (HEM) strategies to your milling practice is the best place to start to increase MRR while also keeping tool wear and overall tool life in check.

Utilizing HEM with Helical Solutions’ HEV-C-6 chipbreaker with Mastercam software, Makino machinists were able to use a Makino PS105 VMC to achieve a new industry standard in MRR for 4140 steel alloy.

Setting a New Material Removal Rate Benchmark with Helical

Engineered for HEM, Helical’s HEV-C-6 was designed for optimal chip evacuation and reduced tool harmonics at high RPMs. Makino machinists utilized these features wit Mastercam’s highly effective tool paths, resulting in a very impressive MRR.

Watch the video below from Makino to see these impressive feats.

Inside the machine, the HEV-C-6 was spun at 10,695 RPM with Mastercam’s impressively efficient toolpaths to achieve an incredible 40in3 MRR. 

Harvey Performance Company National Application Engineer Don Grandt, who worked with Makino and Mastercam on this project, spoke of what went into this effort.

How did this project initially gain traction?

Makino saw a Helical Solutions email highlighting the HEV-C-6 end mill, and wanted to work with us and Mastercam to do a demo to show off the power of their PS105 Vertical Machining Center with a 1/2″ end mill. Using our tool, they were able to max out the horsepower on the machine to get unbelievable MRR.

What considerations were met as you attempted to set this new industry standard?

All tools can only be pushed to the limits of the machine and material. So the goal was to watch the machine’s spindle load to give 100% or greater efficiency of the machine. We also wanted to use a combination of radial step over, axial stepdown, and Feed per Minute to maximize the MRR, as well.

Why was Helical’s HEV-C-6 chosen for this project?

The HEV-C-6 was chosen for a couple of reasons. First, the email that Helical sent was boasting some impressive things about this tool, which intrigued Makino. The other reason was Mastercam was working with us in the past and had an idea that with their tool path (Dynamic), and Makino’s machine power and performance, that this could be an incredible collaboration.

What is next for the performance between these three brands?

We have pushed the limits of the Makino PS105 Machine with a half inch end mill so the sky is the limit with other machines in Makino’s arsenal with greater horsepower and performance. And as far as Mastercam is concerned, they evolve their software yearly with new tool paths and strategies that make it easier and easier on the tool.

For more information on this impressive feat, a webinar hosted by Makino, and featuring Don Grandt, can be found here. Cutting Tool Engineering (CTE) also featured this collaboration in their August 2021 issue as well, as in an accompanying blog post written by Jesse Trinque of Mastercam.

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.

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.