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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 graphite parts. This “In The Loupe” post will examine graphite’s material properties, the 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.

graphite 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.

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 graphite 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.

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.

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

 

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 tooling

Harvey Performance Company, LLC.

 

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

material specific tooling

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

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.

University of Michigan Formula SAE Racing Team – Featured Customer

Formula SAE is a student design competition that began in 1980. The competition was founded by the SAE (Society of Automotive Engineers) branch at the University of Texas. Each year, hundreds of universities across the world spend months designing and manufacturing their best Formula style car before putting them to the test in competitions.

Alex Marshalek is the Team Captain of the University of Michigan’s Formula SAE team, MRacing. The team was originally founded in 1986, and has been very successful over the years. In the 2017 season, they finished 5th at the Formula SAE Michigan event, and took home a 1st place finish at Formula North. They are hoping to continue riding that momentum into another successful season in 2018.

Mracing

Alex reached out to Harvey Tool and Helical earlier this year, and after some conversation, the decision was made to sponsor their team’s efforts by supplying cutting tools and providing technical support. With competitions on the horizon and a new build coming over the summer, Alex was kind enough to find some time to talk with us about his experiences as a student learning the ropes in engineering, manufacturing, and design, the importance of quality tooling and maintaining a superior part finish for competition, and challenges he has faced during this process.

Hi Alex. Thanks for taking the time to talk with us today. When you were looking into college degree programs, what initially interested you in manufacturing and engineering?

I have always had an interest in Aerospace Engineering, but it was nothing more than a personal interest until I started college. My high school unfortunately did not have any machine shop or manufacturing type classes, so a lot of what I knew, I learned from my dad. My dad worked as a Mechanical Engineer at an axle manufacturing company, and he used to always be doing things around the house and showing me the basics of engineering and design.

When it came time to choose a school, I knew that Michigan had an impressive Aerospace Engineering department, and I liked the feel of the campus and community better than other schools I had toured.

How did you first get involved with the Formula SAE team?

I knew going into school that I wanted to get involved in a design team and advance my learning in that way. We have about a dozen different design teams at Michigan, but the Formula SAE team really stood out to me as a really cool project to get involved in.

I started with the team in Fall of 2016, helping out with the design and manufacturing of the vehicle’s suspension. Now, for the upcoming 2018 season, I am taking over the role of Team Captain. There will be a little bit less hands-on design and manufacturing work for me as it is more of an administrative/outreach role.

michigan racing

How does a typical FSAE season run?

So FSAE seasons are constantly running, and nearly overlapping with each other. For example, we are currently finishing up competitions from the 2018 season, but at the same time we are beginning the design of the vehicle for the 2019 season. Typically, the design work is done over the summer, and finalized in October. After that, the major manufacturing begins and lasts until about March, with spare parts and additions being added as we go. Testing begins in March, where we fine tune the vehicle and optimize the design for performance. Then, the rest of the Spring and early Summer is competition time, and the process starts all over again!

What sort of machines do you have in the shop?

Right now, we have three manual Bridgeport mills, two retro-fit CNC Bridgeport mills, 2 manual lathes, 1 retro-fit CNC lathe, and a Haas VF-2SS and Haas SL-20. For the vast majority of what we are machining, we are using the Haas. We do most of our work in Aluminum, with some parts made out of steel or titanium, and the Haas has been great for everything.

We are also using AutoDesk’s Fusion 360 software for our CAD/CAM, and we love it.

What has been the most difficult part of the build?

Time is really the biggest challenge. We are all full-time students, so time is already hard to find, but we also don’t have an overabundance of machinists so the operators can get overburdened. It all works out in the end and our machinists are great, but time management is truly the biggest challenge.

michigan formula sae

The composite materials we work with are also very challenging to machine. We constructed the vehicle’s monocoque (the structural “skin”, often seen in Formula One cars) out of carbon fiber. While we cut a lot of it on the water jet machine, we needed more precise holes than a water jet could offer, so we went to the Haas for that. We were using HSS drills and only getting 10-12 holes at a time before they wore out. However, we had Don Grandt (Harvey Performance Company Application Engineer) stop in the shop and he sent us a few Harvey Tool diamond coated drills, which should make this a much faster and more precise process!

You mentioned Don stopped in to give you guys a visit. What were some of your biggest takeaways?

Don was great. He stopped by and we gave him a tour of the facility and showed off some of the parts we were designing. We talked shop for quite a bit, and he gave us a bunch of great tips and tricks we could use to really optimize our machining. As I mentioned, he also went through the catalogs with us and helped us find exactly what we need for tooling. The Harvey Tool diamond coated drills are going to be a life saver for carbon fiber. I guess the biggest takeaway was just all of the knowledge we received from Don and how helpful that was to have someone direct from the tooling manufacturer sharing everything we knew with us.

Now that you have the Harvey and Helical tools in the shop, how have they helped you complete this project and get a leg up on your competition?

One of the most impressive things for us have been the finishing end mills we received. The Helical finishers for Aluminum are giving us some of the best finishes we have ever seen. For us, that is a point of pride. We not only want to have the fastest and most well-designed vehicle, but we also want to have the best looking parts. Subpar finishes reflect poorly on the entire build, and first impressions mean a lot in these competitions.

We have also been blown away by the Chipbreaker roughers. We absolutely love those tools and push them to the limits with great results. In fact, the first time we ran them, we used Machining Advisor Pro to dial in our speeds and feeds, and the numbers seemed insane to us. We were nervous, but we pushed the button and let it run. It was amazing to see that we could push a tool that fast without tool failure.

How has your experience been using Machining Advisor Pro?

We use Machining Advisor Pro every time we picked up the Helical end mills. MAP was actually one of the main reasons we were looking for Helical to sponsor us. We had heard a lot about MAP and your level of technical support, which was important to us as we are learning more about manufacturing and machining. Machining Advisor Pro has quickly become one of our best learning tools in the shop.

The nice thing about MAP is that is takes a look at all of the parameters. A lot of applications only give you numbers on your speeds and feeds, but MAP takes a look at the depth of cut, chip thinning, engagement angle, and all of the other parameters that are so essential to a successful run. As a result, we have been able to get very aggressive with the end mills. We are not a huge production shop, so cycle times are not as important, but we still want to get the most out of our tools in the least amount of possible time.

So, let’s break down some specs. What are you all working with on this year’s build?

Right now our car features a 4 cylinder Honda 600 CBR engine, with a Turbo and 600cc displacement. We are one of the few teams that run a turbo in competition. As we mentioned, the monocoque is completely carbon fiber, and the car features a full aero package with an undertray. The max speed is around 80 MPH, and the car weighs 420 pounds without the driver.

Once the build is complete, how does a typical competition work?

Most of the Formula SAE competitions are multi-day events, with a few static events, and then dynamic events where the car is running. For static events, we first have a Design portion. We validate and argue for our design in front of judges who are engineers in the industry. Then, we get into a Cost presentation, as one of the goals is to build the cheapest possible car with a high level of performance. That balance of cost vs. performance is a critical part of the build. The last static event is a Business presentation, where we introduce a business/manufacturing plan on how to get this design to a production level of 100 units in a year.

For the dynamic events, we have 4 different tests. First, we have the Accel Run, which is a 75 meter sprint, and the fastest cars win. From there we go to the Skip Pad event, which is centered on turning radius and the stiffness of the chassis as we do tight figure eight turns with the car.

University of Michigan FSAE

Then we have the AutoCross, a one lap race, which determines our placement in the final event; Endurance. For the Endurance event, we drive the cars around a 22km track, and the goal is to finish the race without any mechanical or design failures in the quickest time possible. Only around 50% of participants actually complete this event. If a single part falls off, or breaks, you are disqualified. Many times we see things like the suspension, powertrain, or wings falling off. It is disappointing when it happens, but it allows us to easily identify any flaws and fix them for the next event.

What is next for you after school? Any future plans or goals?

I am currently majoring in Aerospace Engineering, and would like to stay within that industry. I am leaning towards working on aircraft. Designing either aircraft structures or the aerodynamics would be very cool. I really like the size and scale of working on commercial aircraft, but I could see myself doing something more specialty like working in Defense as well.


Alex and his team had a very successful 2018 season. They recently placed 9th overall in a competition at the Michigan International Speedway. In the dynamic events, they placed 4th in Skidpad, and 7th in Autocross. The high placement in the Autocross event allowed them to race head to head against top teams in the world, and they ended up placing 4th in Endurance out of 104 cars!

The MRacing team also competed at Formula North, a competition in Ontario, Canada, where they achieved a top ranking of 2nd place overall. They passed all of the technical inspections on the first try and placed 1st in Acceleration, 2nd in Skidpad and Endurance, 3rd in Autocross, and 4th in Efficiency.

michigan fsae

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.