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How to Optimize Results While Machining with Miniature End Mills

 The machining industry generally considers miniature end mills to be any end mill with a diameter under 1/8 of an inch. This is also often the point where tolerances must be held to a tighter window. Because the diameter of a tool is directly related to the strength of a tool, miniature end mills are considerably weaker than their larger counterparts, and therefore, lack of strength must be accounted for when machining with them. If you are using these tools in a repetitive application, then optimization of this process is key.

Key Cutting Differences between Conventional and Miniature End Mills

Runout

Runout during an operation has a much greater effect on miniature tools, as even a very small amount can have a large impact on the tool engagement and cutting forces. Runout causes the cutting forces to increase due to the uneven engagement of the flutes, prompting some flutes to wear faster than others in conventional tools, and breakage in miniature tools. Tool vibration also impacts the tool life, as the intermittent impacts can cause the tool to chip or, in the case of miniature tools, break. It is extremely important to check the runout of a setup before starting an operation. The example below demonstrates how much of a difference .001” of runout is between a .500” diameter tool and a .031” diameter tool.

The runout of an operation should not exceed 2% of the tool diameter. Excess runout will lead to a poor surface finish.

Chip Thickness

The ratio between the chip thickness and the edge radius (the edge prep) is much smaller for miniature tools. This phenomena is sometimes called “the size effect” and often leads to an error in the prediction of cutting forces. When the chip thickness-to-edge radius ratio is smaller, the cutter will be more or less ploughing the material rather than shearing it. This ploughing effect is essentially due to the negative rake angle created by the edge radius when cutting a chip with a small thickness.

If this thickness is less than a certain value (this value depends of the tool being used), the material will squeeze underneath the tool. Once the tool passes and there is no chip formation, part of the plowed material recovers elastically. This elastic recovery causes there to be higher cutting forces and friction due to the increased contact area between the tool and the workpiece. These two factors ultimately lead to a greater amount of tool wear and surface roughness.

Figure 1: (A) Miniature tool operation where the edge radius is greater than the chip thickness (B) Conventional operation where the edge radius is small than the chip thickness

Tool Deflection

Tool deflection has a much greater impact on the formation of chips and accuracy of the operation in miniature operations, when compared to conventional operations. Cutting forces concentrated on the side of the tool cause it to bend in the direction opposite the feed. The magnitude of this deflection depends upon the rigidity of the tool and its distance extended from the spindle. Small diameter tools are inherently less stiff compared to larger diameter tools because they have much less material holding them in place during the operation. In theory, doubling the length sticking out of the holder will result in 8 times more deflection. Doubling the diameter of an end mill it will result in 16 times less deflection. If a miniature cutting tool breaks on the first pass, it is most likely due to the deflection force overcoming the strength of the carbide. Here are some ways you can minimize tool deflection.

Workpiece Homogeny

Workpiece homogeny becomes a questionable factor with decreasing tool diameter. This means that a material may not have uniform properties at an exceptionally small scale due to a number of factors, such as container surfaces, insoluble impurities, grain boundaries, and dislocations. This assumption is generally saved for tools that have a cutter diameter below .020”, as the cutting system needs to be extremely small in order for the homogeny of the microstructure of the material to be called into question.

Surface Finish

Micromachining may result in an increased amount of burrs and surface roughness when compared to conventional machining. In milling, burring increases as feed increases, and decreases as speed increases. During a machining operation, chips are created by the compression and shearing of the workpiece material along the primary shear zone. This shear zone can be seen in Figure 2 below. As stated before, the chip thickness-to-edge radius ratio is much higher in miniature applications. Therefore, plastic and elastic deformation zones are created during cutting and are located adjacent to the primary shear zone (Figure 2a). Consequently, when the cutting edge is close to the border of the workpiece, the elastic zone also reaches this border (Figure 2b). Plastic deformation spreads into this area as the cutting edge advances, and more plastic deformation forms at the border due to the connecting elastic deformation zones (Figure 2c). A permanent burr begins to form when the plastic deformation zones connect (Figure 2d) and are expanded once a chip cracks along the slip line (Figure 2e). When the chips finally break off from the edge of the workpiece, a burr is left behind (Figure 2f).

Tool Path Best Practices for Miniature End Mills

Because of the fragility of miniature tools, the tool path must be programmed in such a way as to avoid a sudden amount of cutting force, as well as permit the distribution of cutting forces along multiple axes. For these reasons, the following practices should be considered when writing a program for a miniature tool path:

Ramping Into a Part

Circular ramping is the best practice for moving down axially into a part, as it evenly distributes cutting forces along the x, y, and z planes. If you have to move into a part radially at a certain depth of cut, consider an arching tool path as this gradually loads cutting forces onto the tool instead of all at once.

Machining in Circular Paths

You should not use the same speeds and feed for a circular path as you would for a linear path. This is because of an effect called compounded angular velocity. Each tooth on a cutting tool has its own angular velocity when it is active in the spindle. When a circular tool path is used, another angular velocity component is added to the system and, therefore, the teeth on the outer portion of tool path are traveling at a substantially different speed than expected. The feed of the tool must be adjusted depending on whether it is an internal or external circular operation. To find out how to adjust your feed, check out this article on running in circles.

Slotting with a Miniature Tool

Do not approach a miniature slot the same way as you would a larger slot. With a miniature slot, you want as many flutes on the tool as possible, as this increases the rigidity of the tool through a larger core. This decreases the possibility of the tool breaking due to deflection. Because there is less room for chips to evacuate with a higher number of flutes, the axial engagement must be decreased. With larger diameter tools you may be stepping down 50% – 100% of the tool diameter. But when using miniatures with a higher flute count, only step down between 5% – 15%, depending on the size of the diameter and risk of deflection. The feed rate should be increased to compensate for the decreased axial engagement. The feed can be increased even high when using a ball nose end mill as chip thinning occurs at these light depths of cut and begins to act like a high feed mill.

Slowing Down Your Feed Around Corners

Corners of a part create an additional amount of cutting forces as more of the tool becomes engaged with the part. For this reason it is beneficial to slow down your feed when machining around corners to gradually introduce the tool to these forces.

Climb Milling vs. Conventional Milling

This is somewhat of a tricky question to answer when it comes to micromachining. Climb milling should be utilized whenever a quality surface finish is called for on the part print. This type of tool path ultimately leads to more predictable/lower cutting forces and therefore higher quality surface finish. In climb milling, the cutter engages the maximum chip thickness at the beginning of the cut, giving it a tendency to push away from the workpiece. This can potentially cause chatter issues if the setup does not have enough rigidity.  In conventional milling, as the cutter rotates back into the cut it pulls itself into the material and increases cutting forces. Conventional milling should be utilized for parts with long thin walls as well as delicate operations.

Combined Roughing and Finishing Operations

These operations should be considered when micromachining tall thin walled parts as in some cases there is not sufficient support for the part for a finishing pass.

Helpful Tips for Achieving Successful Micromachining Operations

Try to minimize runout and deflection as much as possible.This can be achieved by using a shrink-fit or press-fit tool holder. Maximize the amount of shank contact with the collet while minimizing the amount of stick-out during an operation. Double check your print and make sure that you have the largest possible end mill because bigger tools mean less deflection.

  • Choose an appropriate depth of cut so that the chip thickness to edge radius ratio is not too small as this will cause a ploughing effect.
  • If possible, test the hardness of the workpiece before machining to confirm the mechanical properties of the material advertised by the vender. This gives the operator an idea of the quality of the material.
  • Use a coated tool if possible when working in ferrous materials due to the excess amount of heat that is generated when machining these types of metals. Tool coatings can increase tool life between 30%-200% and allows for higher speeds, which is key in micro-machining.
  • Consider using a support material to control the advent of burrs during a micro milling application. The support material is deposited on the workpiece surface to provide auxiliary support force as well as increase the stiffness of the original edge of the workpiece. During the operation, the support material burrs and is plastically deformed rather than the workpiece.
  • Use flood coolant to lower cutting forces and a greater surface finish.
  • Scrutinize the tool path that is to be applied as a few adjustments can go a long way in extending the life of a miniature tool.
  • Double-check tool geometry to make sure it is appropriate for the material you are machining. When available, use variable pitch and variable helix tools as this will reduce harmonics at the exceptionally high RPMs that miniature tools are typically run at.
Figure 3: Variable pitch tool (yellow) vs. a non-variable pitch tool (black)

TOMI Engineering INC – Featured Customer

Since its beginning in 1977, brothers Tony and Mike Falbo have made the focal point of TOMI Engineering to deliver quality, competitively-priced parts on time. TOMI Engineering has earned a reputation through the years as being a world-class manufacturer of precision machined components and assemblies for aerospace, defense, commercial and other advanced technology industries. They are fortunate to have the highest level of engineering, quality and programming personnel on staff, and, with over 40 years in the industry, there isn’t a problem TOMI hasn’t experienced.

With all the years of experience, TOMI Engineering has a lot of knowledge to share. We had the pleasure of sitting down with Tony and Mike Falbo to ask them about their experiences, techniques, tooling and a lot more.

How was TOMI Engineering INC started?

TOMI Engineering, Inc. began in 1977 when we (Tony and Mike) teamed up and got a loan from our father to purchase our first machine.  The machine was used in the garage of our parents’ home, which still resides in Tustin, California.  Forty years, 20 current machines, and countless parts later, TOMI Engineering proudly serves the defense, airline, medical and commercial industries.  We machine just about any type of product thrown our way.  Over the years, we have made wing tips for the F16 fighter jet, enclosures for GPS housings, manifolds that help transport fluids, support frames for Gulfstream, cabin brackets for Airbus, ammunition feeders for tanks, and many, many others.

At TOMI Engineering, we aim to be a one-stop shop for our customers.  Once we receive blueprints, we can program, machine, deburr, inspect, process and assemble most parts.  We utilize a mixture of 3-and-4-axis machines in order to increase efficiency, which helps us to cut down costs to our customer.  In our temperature-controlled assembly room, we can assemble bearings, bushings, rivets, nut plates, gaskets and sealants.  We also hope to add additive machining to our repertoire soon.

What machines are you currently using in your shop?

Our 21,250 square foot facility houses 20 CNC machines.  Most of our machines are Kitamura, OKK and Okuma.  The purchase dates of these machines range from 1987 to December of 2019.  With our large machine diversity, we can machine parts smaller than a penny, and as large as 30 x 60 inches. Most of the material that makes its way through our shop is aluminum.  Whether it is 6061 or aircraft grade 7000 series, we aim to have most of our parts be aluminum.  However, we do see a large amount of 6AL-4V titanium, along with 17-4 and 15-5 steel. We are currently utilizing Mastercam 2020 for most of our programming needs and are staying up to date with software upgrades and progression.

What sets TOMI Engineering apart from the rest of the competition?

We believe our greatest asset is our experience.  Here at TOMI, we have been machining parts since 1977.  In those 40-plus years, a lot of parts have come and gone through our doors and we have helped our customers solve a large array of problems.  Most of our machinists have been with us for over 10 years, while some are approaching 20 years!  Our programmers easily boast over 60 years of experience! With so many of our employees working together for so many years, it has really helped everyone to understand what helps us quickly machine our products, while being held accountable to the high standards of AS9100. 

Where did your passion for machining start?

We grew up with machines in our garage and it wasn’t until we needed money to pay for college that our dad realized he could show us the basics of operating a milling machine, which allowed us to pay our tuition while working at home in the evenings and weekends. Machining was more of a necessity than a passion at the time. However, after nearly 40 years in the business, it has been amazing to see the strides in technology from a Bridgeport Mill to the multi-axis lights-out machining that is available today.

My favorite part of the job has always been the flexibility it has allowed me. I had the opportunity to watch my kids grow up and be a part of their lives by going to their school plays, coaching them, and being home at night to help them with anything they needed. Most importantly, I’ve had the opportunity to work with my brother, my business partner, who also shares the same ideals about being with family, so we could always cover for each while the other was gone and spending time with their family. The business would not have worked without both of us understanding the importance of each other’s input. The challenge of running a business keeps me going, and working with all of the different personalities was an added bonus.

Who is the most famous contact that you have worked on a project with? What is the most interesting product youve made?

At TOMI, we do not work with specific individuals, so we can’t really name drop.  However, a vast majority of our work is for Airbus, Boeing, or the military. So it’s pretty gratifying to say that we supply parts to some of the biggest companies in the world and that our work helps to defend this country.

The most interesting product we have made here at TOMI is a GPS housing for a defense contractor.  This part encompasses everything that we can do at TOMI: precision machining, complex/multi detail assemblies, gasket assembly, and pressure testing fluid transportation components. 

Why is high quality tool performance important to you?

High quality tool performance is important to us in many ways.  Purchasing high quality tools allow us to constantly achieve premium surface finishes, push our machines to the high speeds and feeds that they are capable of, and enjoy noticeably longer tool life.

Every part, day-in and day-out, is different.   Because of our vast array of products, our tools are always changing.  But when we are picking out Helical End Mills for Aluminum, we always go with their 3-flute variable helix cutters, and we have always been happy with them.

What sort of tolerances do you work in on a daily basis?

The tolerances we typically work with are ± tenths of an inch, as well as very tight true position cal louts. We can hold and achieve these close tolerance dimensions through our very experienced Mastercam programmers, as well as our superior quality department.  Our quality inspectors have over 30 years of experience in the industry and utilize two Zeiss Contura G2 coordinate measuring machines (CMMs).  While in their temperature controlled environment, the CMMs are capable of measuring close tolerance dimensions and are used to generate data for inspection reports.

Are you guys using High Efficiency Milling (HEM) techniques to improve cycle times? What advice do you have for others who want to try HEM?

Yes, we are using HEM techniques to improve cycle times while roughing to increase our MRR while increasing tool life. If you have CAM/CAD software that supports HEM, then go for it!  Machine Advisor Pro (MAP) is VERY helpful with the suggested speeds and feeds as a starting point.  Over time though, and through experience, we have learned that every single machine is a bit different and often needs a different approach with speeds and feeds.  Start with a smaller than suggested RDOC and physically go out to your machine and see how it sounds and what is going on.  Then, start increasing and find that sweet spot that your particular machine runs well on.  Many programmers in the industry will not take the time to go out and watch how their part is sounding and cutting on the machine and going out and doing that is the best way to really find out what you and the machine are capable of achieving.

If you could give one piece of advice to a new machinist ready to take the #PlungeIntoMachining, what would it be?

Ask questions!  Don’t be afraid to talk to programmers and fellow coworkers about what is trying to be achieved and WHY the programmer is holding tolerances a certain way.  Learn from them and watch what every cutter is doing during your cycles.  The more you learn, the more you can contribute to the machining process and move up in your business.  Sometimes it takes just one good suggestion about the machining approach that can change the set-up process from aggravating to very easy.  Lastly, be open minded to new ideas and approaches.  As we said earlier, there are a ton of ways to make good parts in a constantly evolving industry.

Please take the time to check out the TOMI Engineering INC website or follow them on social media!

Titan Ring Design – Featured Customer

Officially started in 2015, Titan Ring Design is a high quality machine shop that designs rings, as well as mechanical tie clips, art based designs, and freelance custom designs. While working at a machine shop that produced top notch parts for just about every type of field you can imagine, now owner of Titan Ring Design, Trevor Hirschi, noticed that the machining industry is mostly about cranking out a mass quantity of the highest quality parts as quickly as possible. This often resulted in compromised tolerances and part finishes, something Trevor aimed to change. Quality always comes first in his projects.

Whether you are looking for a band for an upcoming wedding, looking to replace or upgrade your current wedding ring, or just want something unique and beautiful, Trevor’s designs are different than anything else. Trevor was able to take the time and answer some questions for us about his business, machining techniques, tooling, and a lot more.

How was Titan Ring Design started?

Titan Ring Designs is a part time, passion/hobby business of mine that I sort of started at the time I was ring shopping for a wedding ring back in 2013. I didn’t like what was available on the market and was inspired by a former Oakley designer to machine my own. I had been introduced to machining in High School at a technical college and had been working as a machinist since graduating in 2007, so I decided to make my own wedding ring. It sort of snowballed into my business in 2015, after finally deciding to make it official with a business license and some sales. Some further work experience in California for McWhinney Designs brought me greater motivation and encouragement to keep going and helped me get to where I am today. I now offer several different CNC Milled [wedding] rings, as well as a mechanical tie clip, some occasional art based designs, and freelance custom design and mill work. I also teach machining full time  at the same tech college I graduated from in my own education and enjoy sharing my knowledge and love for machining with those interested in the career.

What capabilities does your shop have?

Custom Design in CAD/CAM, 3axis CNC Mill work, Small Scale Lathe Work, Tumbling, Finishing, Assembling, 3D Printing/Rapid Prototyping. I cut 6-4 Titanium primarily, but also work with Stainless Steel for fasteners, Aluminum and some Steel for fixtures, and Polycarbonate for prototyping ideas. I teach machining technology full time, so I have access to SolidWorks, MasterCam, Fusion360, and NC Simul. We currently have a Haas OfficeMill 3axis, Levin High Precision Instrument Maker’s Lathe, Prusa i3 MK2S 3D Printer in the shop.

What sets Titan Ring Design apart from the competition?

There are lots of people making interesting rings today, but most are done on lathes. Anyone can make a round part on a lathe. Very few of them make rings on a mill, and I feel that gives the opportunity to be creative and allows you to think outside the box more. I try to stand out in that field by offering something that makes you think about the value of the design process more by interrupting and challenging the norm. I also like to take on work that is outside of jewelry, but still highly design related. Most other ring makers stick with just rings.

What is your favorite part of the job and what other passions do you have?

Making cool stuff! Most machinists only end up making whatever comes through the shop, which can be cool, but most of the time you have no idea what you’re making, just some part for Customer X, Y, or Z. Being a small, design centered business, I get to come up with ideas for what to make next, and most of the time I start out making something that wasn’t ever intended to be marketed, it was simply something I wanted for myself that I found others were interested in too. I discovered machining in high school and fell in love with it when I started making parts for my dirt bikes and truck. I’ve been hooked ever since but I do have other passions. I’ve always had a big interest in LED lighting and flashlights. I’m perpetually working on different ideas for making one of my own, which will happen eventually. I’m also a bit of a health-nut and enjoy being outdoors and spending time with my family.

Who is the most famous contact that you have worked on a project with?

I made a ring for an NFL player once, but I don’t follow football and his name didn’t stick out to me so I’ve forgotten who he was. I also had the privilege of working for McWhinney Designs and made some truly remarkable products in the openable wedding ring niche market. I gained more skill in design, machining, craftsmanship, and engineering while working for Jeff McWhinney. We’re good friends and often work together to help each other when one of us gets stumped on something.

What is the most difficult project you have worked on?

I was commissioned to design from the ground up and machine was a custom set of all-titanium cabinet door handle pulls for a very high end wine cabinet. Each handle was an assembly of 32 pieces, all machined from billet 6-4 Titanium. They required over 400 individual CAM toolpath operations, 35 unique machine setups, and well over 300 hours to complete, including finishing and assembly. More than anything, it was extremely time intensive in programming, set up, and machine time. The design was a fair bit challenging in my mind and initial modeling, but didn’t compete with what it took to actually produce them. I grossly underestimated and underbid the job. But in the end, I really enjoyed making a truly one of a kind, Tour-De-Force product, even if it was completely overkill for its purpose. I enjoy making that kind of stuff, and the lessons you learn from it.

What is your favorite project you have worked on?

It’s really simple and was initially designed just because I wanted it for myself, but I have a mechanical titanium tie clip that I really enjoy making. It’s quite unique in that, as far as I know, to this day, it is the only CNC machined mechanical titanium tie clip you’ll find anywhere in the world. It puts a little bling in your formal attire, for those times you have to go full suit and tie.

Why is high quality tool performance important to you?

Because I cut mostly titanium, tools wear out quickly if you don’t have a rigid set up, the right coolant, proper feeds & speeds, and of course, high quality tooling. Harvey Tool makes such a wide variety of micro tooling that works so well in the industry of making small titanium parts, where I like to fit into. I’ve used a fair spread across Harvey’s offering and have always been impressed with performance and the feeds and speeds guides are top notch too. I had an application that required a .0035” internal corner radius which landed me with a .007” end mill. It’s still hard to comprehend tooling in this league. My machine actually recommends only tooling under 1/4” shank size, so I don’t get into Helical’s range too often. But I’ve used Helical 1/2” end mills extensively at other job shops and they are definitely made for eating metal. I was using another tool brand’s key cutters for some undercut hinges and would wear through them much more often than I thought was reasonable. When I finally decided to try Harvey’s key cutters, I was blown away with how much longer they have lasted me. Truly a game changer!

If you could give one piece of advice to a new machinist ready to take the #PlungeIntoMachining, what would it be?

Be creative. Machining is such a rewarding career that has limitless possibilities of what you can achieve. Follow your passion and have fun with it! If you end up in a dead end shop doing something you don’t like, go somewhere else. There are so many shops that need help right now and chances are good that you can find a better shop that suits your style.

Is there anything else you would like to share with the In The Loupe community?

To those machine shops out in industry, do whatever you can to be supportive of your local trade schools that are teaching the upcoming machinist workforce. They really need your support and in turn will bring you the employees you depend on.

Please take the time to check out Titan Ring Designs website or follow them on Instagram @titanringdesigns

Chipbreaker Tooling: Not Just for Roughing

When many people think about solid carbide tools with chip breakers, they are usually tooling up for a roughing application. While the chip breaker tool is a great choice for such applications, it can be utilized in a number of other areas too. In this post, we’ll examine many other benefits of the chip breaker style of tooling.

High Efficiency Milling (HEM)

High Efficiency Milling (HEM) uses CAM software to program advanced toolpaths that reduce cutting forces. These tool paths employ smaller end mills with a higher number of flutes (for a stronger core) running at higher speeds and feeds. This strategy includes a light radial depth of cut (RDOC), high axial depth of cut (ADOC), and a controlled angle of engagement.

Helical’s chipbreaking tools include serrated indents along the edge of flute for the entire length of cut. Because HEM utilizes heavy axial depths of cuts, these tools are able to break long chips into smaller ones. In addition to improving chip control and reducing cutting resistance, chipbreaker tools also help in decreasing heat load within the chips. This delays tool wear along the cutting edge and improves cutting performance. 

Check out this testimony from a Helical Solutions customer:

“We were able to get going with the 7 flute tools with the chipbreaker. I have to say the difference was INCREDIBLE! We can now rough the entire part with one tool. Also, the operator doesn’t have to open the door to clear chips hardly at all. We were able to rough and finish a 4.15 dia. bore 2 inches deep through the part without having to clear chips at all. Before we had to clear the chips out at least 15-20 times. Many thanks for your support.”

Slotting

When slotting, a major concern is chip control. A large buildup of chips can cause the recutting of chips, which adds a lot of heat back into the tool. Chip buildup can also cause a heavy amount of chattering. Both of these conditions are detrimental to tool life. A chip breaking tool can help reduce chip build-up when slotting which will extend tool life. Remember when slotting that 4 flute tools should be utilized in steel. For aluminum and other non- ferrous materials, a 3 flute tool is best.

Trochoidal Slotting

Trochoidal slotting is a form of slotting that uses HEM techniques to form a slot. Trochoidal milling implements a series of circular cuts to create a slot wider than the cutting tool’s cutting diameter. Using the logic listed in the earlier paragraphs of this article, a chipbreaker should be used when performing this operation.

Advantages of Trochoidal Slotting:

Decreased cutting forces

Reduced heat

Greater machining accuracy

Improved tool life

Faster cycle times

One tool for multiple slot sizes

Finishing

A little known fact about Helical’s chipbreaker style tool is that the chip breakers are offset flute to flute, which allows for a quality finish on the walls of the part. When utilizing light depths of cuts, high-quality finishes can be achieved.

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.

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.

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.

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.

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.

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.

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.

Summary:

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.

New Dublin Ship Fittings – Featured Customer

New Dublin Ship Fittings was established in 2017 by Lucas Gilbert, and is located on the scenic south shore of Nova Scotia, Canada.  Lucas began his career with a formal education in machining and mechanical engineering. In the early 2000’s, Lucas got into the traditional shipbuilding industry made famous in the region he grew up in, Lunenburg County, Nova Scotia. It is then when Lucas identified the need for quality marine hardware and began making fittings in his free time. After some time, Lucas was able to start New Dublin Ship Fittings and pursue his lifelong dream of opening a machine shop and producing custom yacht hardware.

Lucas was our grand prize winner in the #MadeWithMicro100 Video Contest! He received the $1,000 Amazon gift card, a Micro-Quik™ Quick Change System with some tooling, and a chance to be In the Loupe’s Featured Customer for February. Lucas was able to take some time out of his busy schedule to discuss his shop, how he got started in machining, and the unique products he manufactures.

How did you start New Dublin Ship Fittings?

I went to school for machine shop and then mechanical engineering, only to end up working as a boat builder for 15 years. It was during my time as a boat builder that I started making hardware in my free time for projects we were working on. Eventually, that grew into full-time work. Right now, we manufacture custom silicon bronze and stainless fittings only. Eventually, we will move into a bronze hardware product line.

Where did your passion for marine hardware come from?

I’ve always loved metalworking. I grew up playing in my father’s knife shop, so when I got into wooden boats, it was only a matter of time before I started making small bits of hardware. Before hardware, I would play around making woodworking tools such as chisels, hand planes, spokeshaves, etc.

What can be found in your shop?

The shop has a 13”x 30” and 16”x 60” manual lathe, a Bridgeport Milling Machine, Burgmaster Turret Drill Press, Gang Drill, Bandsaw, 30-ton hydraulic press, #2 Hossfeld Bender, GTAW, and GMAW Welding Machines, as well as a full foundry set up with 90 pounds of bronze pour capacity. We generally only work in 655 silicon bronze and 316 stainless steel.

What projects have you worked on that stand out to you?

I’ve been lucky to work on several amazing projects over the years. Two that stand out are a 48’ Motorsailer Ketch built by Tern Boatworks, as well as the 63’ Fusion Schooner Farfarer, built by Covey Island Boatworks. Both boats we built most of the bronze deck hardware for.

I’ve made many interesting fittings over the years. I prefer to work with bronze, so I generally have the most fun working on those. I’m generally the most interested when the part is very
challenging to make and custom work parts are often very challenging. I’m asked to build or machine a component that was originally built in a factory and is difficult to reproduce with limited machinery and tooling, but I enjoy figuring out how to make it work.

Why is high-quality tooling important to you?

When I first started I would buy cheaper tooling to “get by” but the longer I did it, the more I realized that cheaper tooling doesn’t pay off. If you want to do quality work in a timely fashion, you need to invest in good tooling.

What Micro 100 Tools are you currently using?

Currently, we just have the Micro 100 brazed on tooling but we have been trying to move more into inserts so we are going to try out Micro’s indexable tooling line. After receiving the Micro-Quik™ Quick Change System, we are looking forward to trying out more of what (Micro 100) has to offer. This new system should help us reduce tool change time, saving us some money in the long run.

What makes New Dublin Ship Fittings stand out from the competition?

I think the real value I can offer boat builders and owners over a standard job shop is my experience with building boats. I understand how the fitting will be used and can offer suggestions as to how to improve the design.

If you could give one piece of advice to a new machinist what would it be?

The advice I would give to new machinists is to start slow and learn the machines and techniques before you try to make parts quickly. There is a lot of pressure in shops to make parts as fast as possible, but you’ll never be as fast as you can be if you don’t learn the processes properly first. Also, learn to sharpen drill bits well!

5 Things to Know About Helical’s High Feed End Mills

Helical Solutions‘ High Feed End Mills provide many opportunities for machinists, and feature a special end profile to increase machining efficiencies. A High Feed End Mill is a High Efficiency Milling (HEM) style tool with specialized end geometry that utilizes chip thinning, allowing for drastically increased feed rates in certain applications. While standard end mills have square, corner radius, or ball profiles, this Helical tool has a specialized, very specific design that takes advantage of chip thinning, resulting in a tool that can be pushed harder than a traditional end mill.

Below are 5 things that all machinists should know about this exciting Helical Solutions product offering.

1. They excel in applications with light axial depths of cut

A High Feed End Mill is designed to take a large radial depth of cut (65% to 100% of the cutter diameter) with a small axial depth of cut (2.5% to 5% diameter) depending on the application. This makes High Feed End Mills perfect for face milling, roughing, slotting, deep pocketing, and 3D milling. Where HEM toolpaths involve light radial depths of cut and heavy axial depths of cut, High Feed End Mills utilize high radial depths of cut and smaller axial depths of cut.

2. This tool reduces radial cutting forces

The end profile of a High Feed End Mill is designed to direct cutting forces upward along the axis of the tool and into the spindle. This reduces radial cutting forces which cause deflection, allowing for longer reach tools while reducing chatter and other issues that may otherwise lead to tool failure. The reduction of radial cutting forces makes this tool excellent for use in machines with lower horsepower, and in thin wall machining applications.

3. High Feed End Mills are rigid tools

The design and short length of cut of High Feed End Mills work in tandem with the end geometry to produce a tool with a strong core, further limiting deflection and allowing for tools with greater reach lengths.

4. They can reduce cycle times

In high RDOC, low ADOC applications, High Feed End Mills can be pushed significantly faster than traditional end mills, saving time and money over the life of the tool.

5. High Feed End Mills are well suited for hard materials

The rigidity and strength of High Feed End Mills make them excellent in challenging to machine materials. Helical’s High Feed End Mills come coated with Tplus coating, which offers high hardness and extended tool life in high temp alloys and ferrous materials up to 45Rc.

In summary, High Feed End Mill tools with specialized end geometry that utilizes chip thinning and light axial depths of cut to allow for significantly increased feed rates in face milling, slotting, roughing, deep pocket milling, and 3D milling applications. The end profile of a High Feed End Mill applies cutting forces back up into the spindle, reducing radial forces that lead to deflection in long reach applications. Combining this end geometry with a stubby length of cut results in a tool that is incredibly rigid and well suited for harder, difficult to machine materials.

Benefits & Drawbacks of High and Low Helix Angles

While many factors impact the outcome of a machining operation, one often overlooked factor is the cutting tool’s helix angle. The Helix angle of a tool is measured by the angle formed between the centerline of the tool and a straight line tangent along the cutting edge.

A higher helix angle, usually 40° or more, will wrap around the tool “faster,” while a “slower” helix angle is usually less than 40°.

When choosing a tool for a machining operation, machinists often consider the material, the tooling dimensions and the flute count. The helix angle must also be considered to contribute to efficient chip evacuation, better part finish, prolonged tool life, and reduced cycle times.

Helix Angles Rule of Thumb

One general rule of thumb is that as the helix angle increases, the length of engagement along the cutting edge will decrease. That said,
there are many benefits and drawbacks to slow and high helix angles that can impact any machining operation.

Slow Helix Tool <40°

Benefits

  • Enhanced Strength – A larger core creates a strong tool that can resist deflection, or the force that will bend a tool under pressure.
  • Reduced Lifting – A slow helix will decrease a part from lifting off of the worktable in settings that are less secure.
  • Larger Chip Evacuation – The slow helix allows the tool to create a large chip, great for hogging out material.

Drawbacks

  • Rough Finish – A slow helix end mill takes a large chip, but can sometimes struggle to evacuate the chip. This inefficiency can result in a sub-par part finish.
  • Slower Feed Rate – The increased radial force of a slow helix end mill requires running the end mill at a slower feed rate.

High Helix Tool >40°

Benefits

  • Lower Radial Force – The tool will run quieter and smoother due to better shearing action, and allow for less deflection and more stability in thin wall applications.
  • Efficient Chip Evacuation – As the helix angle increases, the length of cutting edge engagement will decrease, and the axial force will increase. This lifts chips out and away, resulting in efficient chip evacuation.
  • Improved Part Finish – With lower radial forces, high helix tools are able to cut through material much more easily with a better shearing action, leaving an improved surface finish.

Drawbacks

  • Weaker Cutting Teeth – With a higher helix, the teeth of a tool will be thinner, and therefore thinner.
  • Deflection Risk – The smaller teeth of the high helix tool will increase the risk of deflection, or the force that will bend a tool under pressure. This limits how fast you can push high helix tools.
  • Increased Risk of Tool Failure – If deflection isn’t properly managed, this can result in a poor finish quality and tool failure.

Helix Angle: An Important Decision

In summary, a machinist must consider many factors when choosing tools for each application. Among the material, the finish requirements, and acceptable run times, a machinist must also consider the helix angle of each tool being used. A slow helix end mill will allow for larger chip formation, increased tool strength and reduce lifting forces. However, it may not leave an excellent finish. A high helix end mill will allow for efficient chip evacuation and excellent part finish, but may be subject to increased deflection, which can lead to tool breakage if not properly managed.

Machining Advisor Pro Updated With New Improvements

Harvey Performance Company is excited to announce that Machining Advisor Pro, a cutting edge resource for generating custom CNC running parameters, has been updated with new features and improvements with the release of version 1.5.

Thousands of users have enjoyed the benefits of using Machining Advisor Pro (MAP) to dial in their running parameters for their Helical Solutions high-performance end mills, and with version 1.5, the Harvey Performance Company team has made customizing your speeds and feeds easier than ever. Much of the work done on MAP version 1.5 was the direct result of excellent user feedback, including some of the most innovative updates to the user experience since the launch of Machining Advisor Pro in 2018.

The new improvements to MAP include:

Improved Speed and Feed Sliders (Desktop)

The speed and feed sliders in the “Recommendations” section are now percentage-based. This allows users to more precisely adjust their running parameters while fine-tuning numbers for increased production or longer tool life. Previously, users could adjust their speed and feed values with dials, but without an exact measurement of the increase or decrease. With the new sliders, users can be more accurate, adjusting their speed and feed values by +/- 20% in one percent increments. Users can also type in percentage values to automatically adjust the sliders to their desired number.

machining advisor pro

Locking Depths of Cut

Inside of the “Parameters” section, users will now see a new button that allows them to lock their depths of cut. With this new feature, users have more control over the customization of their running parameters. In the past, the radial and axial depths of cut would adjust dynamically with each other based on the user adjustments to one of the values. Now users can lock the radial depth of cut (RDOC) and adjust the axial depth of cut (ADOC) without affecting the RDOC value, and vice versa.

Machining Advisor Pro Update

Enhanced Summary Section (Mobile)

On mobile devices, users will now see an enhanced “Summary” section at the completion of their job. The summary section will now include key metrics like material removal rate (MRR), as well as important parameters that apply to trochoidal slotting toolpaths. The summary section for chamfering toolpaths has also been updated to better reflect the necessary parameters for those tools.

Machining Advisor Pro Mobile

Smoother User Experience

In MAP version 1.5, users will be greeted with a much smoother user experience throughout the application. Due largely to user feedback, the Harvey Performance Company team has been hard at work to make sure that the major pain points within the application have been addressed. Much of the feedback centered around the “Tooling” section and the “Material” section and significant improvements have been made to each.

In the tooling section, MAP will now automatically select a tool for you if you enter a valid EDP once you navigate outside of that section. If an invalid EDP number is entered, the intrusive error message has been removed and now will display “no results found” in the drop-down menu.

In the material section, MAP requires that a material condition be selected in order to generate accurate running parameters. In the past, this was not immediately clear and could lead some users to believe that the application was malfunctioning. In version 1.5, once a user leaves the material section without selecting a condition, a message will display in the material section to alert users of the missing material condition.

Open in MAP from HelicalTool.com

On the new HelicalTool.com website, users can now import a tool into MAP from the Tool Details page. Users reach the Tool Details page by clicking on a SKU in a product table, or searching for an EDP in the search bar. Once on the Tool Details page, users can select “Open in Machining Advisor Pro” under the Resources section, and MAP will open in a new window and import the tool’s information directly into MAP.

Helical Machining Advisor Pro


Users will see these updates immediately upon their next log-in to the application on a desktop computer and will need to ensure their app is updated to the latest version from the App Store or Google Play to see these changes reflected on mobile.

To get started with Machining Advisor Pro, click here to create an account.

To stay up-to-date on all of the latest improvements and news on Machining Advisor Pro and the Harvey Performance Company brands, join our email list.

If you have any feedback or questions about MAP, please contact Harvey Performance Company at [email protected].

Simplify Your Cutting Tool Orders

With the launch of the new Helical Solutions website, Harvey Performance Company is proud to introduce a new way to order Helical cutting tools. Now, users of our new website are able to send a “shopping cart” of Helical tools they’re interested in directly to their distributor to place an order, or share it with a colleague. Let’s dive into the details about this functionality and learn how you can take advantage of the time savings associated with sending a “shopping cart” to your distributor for simplified ordering.

Get Started with a HelicalTool.com Account

First, you must create an account on HelicalTool.com. Having an account on the Helical website allows you to save and edit “shopping carts,” which can be sent to a distributor to place an order; choose a preferred distributor; auto-fill your information in any important forms; and to manage your shipping information.

Create Helical Account

 

Now that you have an account, it is time to start creating your first “shopping cart.”

Creating a “Shopping Cart”

To begin creating a new shopping cart, simply click on the “My Carts” text in the top right menu. This will take you to the management portal, where you can add a new “shopping cart” by selecting “Create New Shopping Cart.”

Helical Solutions Order

Once complete, you can name your “shopping cart” anything you would like. One example might be creating a collection of tools for each of your jobs, or for different machines in the shop. In this case, we will name it “Aluminum Roughing Job.” You can create as many different “shopping carts” as you would like; they’ll never be removed from your account unless you choose to delete them, allowing you to go back to past tooling orders whenever you’d like.

Helical Solutions Website

Now that you have a “shopping cart” created, it is time to start adding tools to it!

Adding Tools to Your “Shopping Cart”

There are multiple ways to add tooling to your “shopping cart,” but the easiest method is by heading to a product table. In this example, we will be adding tooling from our 3 Flute, Corner Radius – 35° Helix product line. We want to add a quantity of 5 of EDP #59033 to our “shopping cart.” To do this, simply click on the “Add To Cart” icon located in the table row next to pricing and tool descriptions. This will open up a small window where we can manage our selection. The first step will be to choose which “shopping cart” we want to add this tool to, so we will select our “Aluminum Roughing Job” collection.

Helical Online Ordering

Since this tool is offered uncoated and Zplus coated, we need to select which option we would like from the drop down menu. For this example, we will select the Zplus coated tool. Now, we simply need to update our quantity to “5”, and click “Add To Cart.” That tool will now appear in your “shopping cart” in the quantity selected.

If you need more information on a tool, you can click on an EDP number to be brought to the tool details page, where you can also add that EDP to your collection.

If you know the EDP number you need and want to check stock levels, use our Check Stock feature to check quantities on hand, and then add the tools to your “shopping cart” right from the Check Stock page.

check stock

Now, it is time to send the “shopping cart” to place an order with your distributor!

Placing An Order With Your Distributor

Once you have completed adding tools to your “shopping cart,” navigate back to the My Carts page to review it. From here, you can update quantities, see list pricing, and access valuable resources.

On the right side of the My Cart screen, you will see an option to “Send to Distributor.” Click on the text to expand the drop down. If you have previously added a preferred distributor from your account page and they are participating in our Shopping Cart Program, you will see their information in this area.

If you have not yet selected a preferred distributor, select “Update My Distributor.” This will bring you to a new page where you can select your state and see all participating distributors in your area. Select one distributor as your preferred distributor, and then head back to the My Cart page.

Now that you have a distributor selected, you can do a final review of the “shopping cart,” and then simply click “Send Cart.” This will send an email order directly to your distributor with all of your shipping information, your list of tools and requested quantities, and your contact information. You will also receive a copy of this email for your records.

Helical Distributor

Within 1 business day, the distributor will follow up with you to confirm the order, process payment, and get the tools shipped out and on the way to your shop. No more phone calls or emails – just a single click, and your order is in the hands of our distributor partners.

To get started with this exciting new way to shop for Helical cutting tools, click here to begin creating an account on HelicalTool.com!