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3 Steps to Shutting Up Tool Chatter

Cutting tools undergo a great deal of force during the machining process, which cause vibrations – also known as chatter or harmonics. Avoiding these vibrations entirely is not possible, though minimizing them is pivotal for machining success. Vibrations become damaging when proper machining steps are not followed. This leads to strong, part-ruining chatter. In these situations, parts have what is known as “chatter marks,” or clear vibration marks along the surface of a part. Tools can experience an increased rate of wear due to excess vibration.

Tool Chatter can be kept at bay by following three simple, yet often overlooked steps:

1. Select the Right Tool for Your Job

It seems elementary, but selecting the best tool for your application can be confusing. With so many different geometric styles for tooling – overall length, length of cut, reach, number of flutes – it can sometimes be difficult to narrow down one specific tool for your job. Oftentimes, machinists opt for general purpose tooling that can perform a variety of operations, overlooking the option that’s optimized for one material and job.

Opting for Material Specific Tooling is helpful, as each material has different needs. For example, steels are machined differently than aluminum materials. Everything from the chip size, to chip evacuation, is different. Variable Helix or Variable Pitch designs help to minimize chatter by reducing harmonics, which are caused by the cutting edge having repeated contact with the workpiece. In order to reduce harmonics, the time intervals between flute contact with the workpiece are varied.

Overall length is another important factor to consider when deciding on a tool for your job. The more overhang, or length the tool hangs from the spindle, the less secure the spindle-to-tool connection is, and the more vibration. Ensuring that your tool is only as long as needed for your operation is important to minimizing chatter and harmonics. If machining deep within a part, opt for reached tooling or an extended reach tool holder to help solidify the connection.

2. Ensure a Secure Connection

When it comes to secure tool holding approaches, both the tool shank and the collet are important. A loose tool, unsurprisingly, has more ability to move, or vibrate, during machining. With this in mind, Helical offers Shank Configurations to help the connection including the ToughGRIP Shank, which replaces a smooth, mirror-like surface with a rougher, coarser one for increased friction. Helical is also a licensee of the HAIMER Safe-Lock™, added grooves on the shank of a tool that work opposite of the spindle rotation, securely fastening the tool in place.

Machinists must also know the different types of collets available to them to identify if a better solution might be necessary. For example, Hydraulic Tool Holders or Shrink Fit Tool Holders promote a stronger connection than a Mechanical Spindle Tightening method.

For more information, see Key Tool Holding Considerations

3. Choose a Chatter Minimizing Strategy

How a tool is run can mean the difference between stellar job results and a ruined part. This includes both the parameters a tool is run at, as well as the direction by which it rotates – either a Conventional Milling or a Climb Milling technique.

Conventional Milling

In this method, the chip width starts from zero and increases gradually, causing more heat to diffuse into the workpiece. This can lead to work hardening, creating more headaches for a machinist.

tool chatter

Climb Milling

Most modern machine shops will use a climb milling technique, or when the chip width starts at its maximum and decreases during the cut. Climb Milling will offer a more consistent cut than traditional methods, and puts less stress on the tool. Think of it like weight lifting – doing the heavy lifting will be easiest at the beginning of your workout. Similarly, a cut in which the thickest chip is removed first helps the tool maintain its strength. Because the chip cutting process is more swift, vibrations are minimized.

decrease tool chatter

For more information, see Climb Milling Vs. Conventional Milling

In Conclusion

Vibrations are unavoidable during the machining process, but minimizing them can mean the difference between successful machining and scrapped parts. Following three simple rules can help to keep your chatter and harmonics under control, including: Selecting the right tool, ensuring a secure machine-tool connection, and using it in a climb milling strategy. Both Harvey Tool and Helical Solutions have tools that can help, including shank modifications and Variable Helix or Variable Pitch end mills.

Work Hardening and When It Should Scare You

Work hardening is often an unintentional part of the machining process, where the cutting tool generates enough heat in one area to harden the workpiece. This makes for a much more difficult machining process and can lead to scrapped parts, broken tools, and serious headaches.

Work Hardening Overview

During machining, the friction between the tool and the workplace generates heat. The heat that is transferred to the workpiece causes the structure of the material to change and in turn harden the material. The degree to which it is hardened depends on the amount of heat being generated in the cutting action and the properties of the material, such as carbon content and other alloying elements. The most influential of these alloying elements include Manganese, Silicon, Nickel, Chromium, and Molybdenum.

While the hardness change will be the highest at the surface of the material, the thermal conductivity of the material will affect how far the hardness changes from the surface of the material.

titanium

Often times, the thermal properties of a material that makes it appealing for an application are also the main cause of its difficulty to machine. For example, the favorable thermal properties of titanium that allow it to function as a jet turbine are the same properties that cause difficulty in machining it.

Major Problems

As previously stated, work hardening can create some serious problems when machining. The biggest issue is heat generated by the cutting tool and transferring to the workpiece, rather than to the chips. When the heat is transferred to the workpiece, it can cause deformation which will lead to scrapped parts. Stainless Steels and High-Temp Alloys are most prone to work hardening, so extra precaution is needed when machining in these materials.

work hardening

One other issue that scares a lot of machinists is the chance that a workpiece can harden to the point that it becomes equally as hard as the cutting tool. This is often the case when improper speeds and feeds are used. Incorrect speeds and feeds will cause more rubbing and less cutting, resulting in more heat generation passed to the workpiece. In these situations, machining can become next to impossible, and serious tool wear and eventual tool breakage are inevitable if the tool continues to be fed the same way.

How To Avoid Work Hardening

There are a few main keys to avoiding work hardening: correct speeds and feeds, tool coatings, and proper coolant usage. As a general rule of thumb, talking to your tooling manufacturer and using their recommended speeds and feeds is essential for machining success. Speeds and feeds become an even bigger priority when you want to avoid heat and tool rubbing, which can both cause serious work hardening. More cutting power and a constant feed rate keeps the tool moving and prevents heat from building up and transferring to the workpiece. The ultimate goal is to get the heat to transfer to the chips, and minimize the heat that is transferred into workpiece and avoiding any deformation of parts.

While friction is often the main culprit of heat generation, the appropriate coating for the material may help combat the severity. Many coatings for ferrous materials reduce the amount of friction generated during cutting action. This added lubricity will reduce the friction on the cutting tool and workpiece, therefore transferring the heat generated to the chip, rather than to the workpiece.

Proper coolant usage helps to control the temperature in a cutting operation. Flooding the workpiece with coolant may be necessary to maintain the proper temperature, especially when machining in stainless steels and high-temp alloys. Coolant-fed tools can also help to reduce the heat at the contact point, lessening work hardening. While coolant-fed tools are typically a custom modification, saving parts from the scrap heap and using more machine time for the placement part will see the tool pay for itself over time.

Optimize Roughing With Chipbreaker Tooling

Chipbreaker End Mills feature unique notch profiles, creating a serrated cutting edge. These dividers break otherwise long, stringy chips into small, easily-managed swarf that can be cleanly evacuated from the part. But why is a chipbreaker necessary for some jobs, and not others? How does the geometry of this unique tool impact its proper running parameters? In this post, we’ll answer these questions and others to discover the very real benefits of this unique cutting geometry.

How Chipbreaker Tooling Works

As a tool rotates and its cutting edge impacts a workpiece, material is sheared off from a part, creating chips. When that cutting process is interrupted, as is the case with breaks in the cutting portion of the tool, chips become smaller in length and are thus easier to evacuate. Because the chipbreakers are offset flute-to-flute, a proper, flat surface finish is achieved as each flute cleans up any excess material left behind from previously passed flutes.

Benefits of Chipbreaker Tooling

Machining Efficiency

When chips are removed from the part, they begin to pile in the machine. For extensive operations, where a great deal of material is hogged out, chip accumulation can very rapidly get in the way of the spindle or part. With larger chips, accumulation occurs much faster, leaving machinists to stop their machine regularly to remove the waste. As any machinist knows, a stopped machine equates to lost money.

Prolonged Tool Life

Inefficient chip evacuation can lead to chip recutting, or when the the tool impacts and cuts chips left behind during the machining process. This adds stresses on the tool and accelerates rate of wear on the cutting edge. Chipbreaker tooling creates small chips that are easily evacuated from a part, thus minimizing the risk of recutting.

Accelerated Running Parameters

A Harvey Performance Company Application Engineer recently observed the power of a chipbreaker tool firsthand while visiting a customer’s shop in Minnesota. The customer was roughing a great amount of 4340 Steel. Running at the parameters below, the tool was able to run uninterrupted for two hours!

Helical Part No. 33737
Material 4340 Steel
ADOC 2.545″
RDOC .125″
Speed 2,800 RPM
Feed 78 IPM
Material Removal Rate 24.8 Cubic In/Min

Chipbreaker Product Offering

Chipbreaker geometry is well suited for materials that leave a long chip. Materials that produce a powdery chip, such as graphite, should not be machined with a chipbreaker tool, as chip evacuation would not be a concern. Helical Solutions’ line of chipbreaker tooling includes a 3-flute option for aluminum and non-ferrous materials, and its reduced neck counterpart. Additionally, Helical offers a 4-flute rougher with chipbreaker geometry for high-temp alloys and titanium. Harvey Tool’s expansive product offering includes a composite cutting end mill with chipbreaker geometry.

In Summary

Chipbreaker geometry, or grooves within the cutting face of the tool, break down chips into small, manageable pieces during the machining process. This geometry can boost shop efficiency by minimizing machine downtime to clear large chips from the machining center, improve tool life by minimizing cutting forces exerted on the tool during machining, and allow for more accelerated running parameters.

Speeds and Feeds 101

Understanding Speeds and Feed Rates

NOTE: This article covers speeds and feed rates for milling tools, as opposed to turning tools.

Before using a cutting tool, it is necessary to understand tool cutting speeds and feed rates, more often referred to as “speeds and feeds.” Speeds and feeds are the cutting variables used in every milling operation and vary for each tool based on cutter diameter, operation, material, etc. Understanding the right speeds and feeds for your tool and operation before you start machining is critical.

It is first necessary to define each of these factors. Cutting speed, also referred to as surface speed, is the difference in speed between the tool and the workpiece, expressed in units of distance over time known as SFM (surface feet per minute). SFM is based on the various properties of the given material. Speed, referred to as Rotations Per Minute (RPM) is based off of the SFM and the cutting tool’s diameter.

While speeds and feeds are common terms used in the programming of the cutter, the ideal running parameters are also influenced by other variables. The speed of the cutter is used in the calculation of the cutter’s feed rate, measured in Inches Per Minute (IPM). The other part of the equation is the chip load. It is important to note that chip load per tooth and chip load per tool are different:

speeds and feeds formula

 

  • Chip load per tooth is the appropriate amount of material that one cutting edge of the tool should remove in a single revolution. This is measured in Inches Per Tooth (IPT).
  • Chip load per tool is the appropriate amount of material removed by all cutting edges on a tool in a single revolution. This is measured in Inches Per Revolution (IPR).

A chip load that is too large can pack up chips in the cutter, causing poor chip evacuation and eventual breakage. A chip load that is too small can cause rubbing, chatter, deflection, and a poor overall cutting action.

Material Removal Rate

Material Removal Rate (MRR), while not part of the cutting tool’s program, is a helpful way to calculate a tool’s efficiency. MRR takes into account two very important running parameters: Axial Depth of Cut (ADOC), or the distance a tool engages a workpiece along its centerline, and Radial Depth of Cut (RDOC), or the distance a tool is stepping over into a workpiece.

The tool’s depth of cuts and the rate at which it is cutting can be used to calculate how many cubic inches per minute (in3/min) are being removed from a workpiece. This equation is extremely useful for comparing cutting tools and examining how cycle times can be improved.

speeds and feeds

Speeds and Feeds In Practice

While many of the cutting parameters are set by the tool and workpiece material, the depths of cut taken also affect the feed rate of the tool. The depths of cuts are dictated by the operation being performed – this is often broken down into slotting, roughing, and finishing, though there are many other more specific types of operations.

Many tooling manufacturers provide useful speeds and feeds charts calculated specifically for their products. For example, Harvey Tool provides the following chart for a 1/8” diameter end mill, tool #50308. A customer can find the SFM for the material on the left, in this case 304 stainless steel. The chip load (per tooth) can be found by intersecting the tool diameter on the top with the material and operations (based on axial and radial depth of cut), highlighted in the image below.

The following table calculates the speeds and feeds for this tool and material for each operation, based on the chart above:

speeds and feeds

Other Important Considerations

Each operation recommends a unique chip load per the depths of cut. This results in various feed rates depending on the operation. Since the SFM is based on the material, it remains constant for each operation.

Spindle Speed Cap

As shown above, the cutter speed (RPM) is defined by the SFM (based on material) and the cutter diameter. With miniature tooling and/or certain materials the speed calculation sometimes yields an unrealistic spindle speed. For example, a .047” cutter in 6061 aluminum (SFM 1,000) would return a speed of ~81,000 RPM. Since this speed is only attainable with high speed air spindles, the full SFM of 1,000 may not be achievable. In a case like this, it is recommended that the tool is run at the machine’s max speed (that the machinist is comfortable with) and that the appropriate chip load for the diameter is maintained. This produces optimal parameters based on the machine’s top speed.

Effective Cutter Diameter

On angled tools the cutter diameter changes along the LOC. For example, Helical tool #07001, a flat-ended chamfer cutter with helical flutes, has a tip diameter of .060” and a major/shank diameter of .250”. In a scenario where it was being used to create a 60° edge break, the actual cutting action would happen somewhere between the tip and major/shank diameters. To compensate, the equation below can be used to find the average diameter along the chamfer.

Using this calculation, the effective cutter diameter is .155”, which would be used for all Speeds and Feeds calculations.

Non-linear Path

Feed rates assume a linear motion. However, there are cases in which the path takes an arc, such as in a pocket corner or a circular interpolation. Just as increasing the DOC increases the angle of engagement on a tool, so does taking a nonlinear path. For an internal corner, more of the tool is engaged and, for an external corner, less is engaged. The feed rate must be appropriately compensated for the added or lessened engagement on the tool.

non-linear path

This adjustment is even more important for circular interpolation. Take, for example, a threading application involving a cutter making a circular motion about a pre-drilled hole or boss. For internal adjustment, the feed rate must be lowered to account for the additional engagement. For external adjustment, the feed rate must be increased due to less tool engagement.

adjusted internal feed

Take this example, in which a Harvey Tool threadmill #70094, with a .370” cutter diameter, is machining a 9/16-18 internal thread in 17-4 stainless steel. The calculated speed is 2,064 RPM and the linear feed is 8.3 IPM. The thread diameter of a 9/16 thread is .562”, which is used for the inner and outer diameter in both adjustments. After plugging these values into the equations below, the adjusted internal feed becomes 2.8 IMP, while the external feed becomes 13.8 IPM.

adjusted external feed

Click here for the full example.

Conclusion

These calculations are useful guidelines for running a cutting tool optimally in various applications and materials. However, the tool manufacturer’s recommended parameters are the best place to start for initial numbers. After that, it is up to the machinist’s eyes, ears, and experience to help determine the best running parameters, which will vary by set-up, tool, machine, and material.

Click the following links for more information about running parameters for Harvey Tool and Helical products.

How to Avoid Composite Delamination with Compression Cutters

Composites are a group of materials made up of at least two unique constituents that, when combined, produce mechanical and physical properties favorable for a wide array of applications. These materials usually contain a binding ingredient, known as a matrix, filled with particles or fibers called reinforcements. Composites have become increasingly popular in the Aerospace, Automotive, and Sporting Goods industries because they can combine the strength of metal, the light weight of plastic, and the rigidity of ceramics.

Unfortunately, composite materials present some unique challenges to machinists. Many composites are very abrasive and can severely reduce tool life, while others can melt and burn if heat generation is not properly controlled. Even if these potential problems are avoided, the wrong tool can leave the part with other quality issues, including delamination.

While composites such as G10 and FR4 are considered “fibrous”, composites can also be “layered,” such as laminated sheets of PEEK and aluminum. Layered composites are vulnerable to delamination, when the layers of the material are separated by a tool’s cutting forces. This yields less structurally sound parts, defeating the purpose of the combined material properties in the first place. In many cases, a single delaminated hole can result in a scrapped part.

Using Compression Cutters in Composite Materials

Composite materials are generally machined with standard metal cutting end mills, which generate exclusively up or down cutting forces, depending on if they have right or left hand flute geometry. These uni-directional forces cause delamination (Figure 1).

delamination

Conversely, compression cutters are designed with both up and down-cut flutes. The top portion of the length of cut, closest to the shank, has a left hand spiral, forcing chips down. The bottom portion of the length of cut, closest to the end, has a right hand spiral, forcing chips up. When cutting, the opposing flute directions generate counteracting up-cut and down-cut forces. The opposing cutting forces stabilize the material removal, which compresses the composite layers, combatting delamination on the top and bottom of a workpiece (Figure 2).

compression cutters

Since compression cutters do not pull up or press down on a workpiece, they leave an excellent finish on layered composites and lightweight materials like plywood. It is important to note, however, that compression cutters are suited specifically to profiling, as the benefits of the up and down-cut geometry are not utilized in slotting or plunging operations.

Something as simple as choosing a tool suited to a specific composite material can have significant effects on the quality of the final part. Consider utilizing tools optimized for different composites and operations or learn how to select the right drill for composite holemaking.

Introduction to High Efficiency Milling

The following is just one of several blog posts relevant to High Efficiency Milling. To achieve a full understanding of this popular machining method, view any of the additional HEM posts below!

High Speed Machining vs. HEM I How to Combat Chip Thinning I Diving into Depth of Cut I How to Avoid 4 Major Types of Tool Wear I Intro to Trochoidal Milling


High Efficiency Milling (HEM) is a strategy that is rapidly gaining popularity in the metalworking industry. Most CAM packages now offer modules to generate HEM toolpaths, each with their own proprietary name. In these packages, HEM can also be known as Dynamic Milling or High Efficiency Machining, among others. HEM can result in profound shop efficiency, extended tool life, greater performance, and cost savings. High performance end mills designed to achieve higher speeds and feeds will help machinists to reap the full benefits of this popular machining method.

High Efficiency Milling Defined

HEM is a milling technique for roughing that utilizes a lower Radial Depth of Cut (RDOC) and a higher Axial Depth of Cut (ADOC). This spreads wear evenly across the cutting edge, dissipates heat, and reduces the chance of tool failure.

This strategy differs from traditional or conventional milling, which typically calls for a higher RDOC and lower ADOC. Traditional milling causes heat concentrations in one small portion of the cutting tool, expediting the tool wear process. Further, while Traditional Milling call for more axial passes, HEM toolpaths use more passes radially.

For more information on optimizing Depth of Cut in relation to HEM, see Diving into Depth of Cut: Peripheral, Slotting & HEM Approaches.

High Efficiency Milling

Built-In CAM Applications

Machining technology has been advancing with the development of faster, more powerful machines. In order to keep up, many CAM applications have developed built-in features for HEM toolpaths, including Trochoidal Milling, a method of machining used to create a slot wider than the cutting tool’s cutting diameter.

HEM is largely based on the theory surrounding Radial Chip Thinning, or the phenomenon that occurs with varying RDOC, and relates to the chip thickness and feed per tooth. HEM adjusts parameters to maintain a constant load on the tool through the entire roughing operation, resulting in more aggressive material removal rates (MRR). In this way, HEM differs from other high performance toolpaths, which involve different methods for achieving significant MRR.

Virtually any CNC machine can perform HEM – the key is a fast CNC controller. When converting from a regular program to HEM, about 20 lines of HEM code will be written for every line of regular code. A fast processor is needed to look ahead for the code, and keep up with the operation. In addition, advanced CAM software that intelligently manages tool load by adjusting the IPT and RDOC is also needed.

HEM Case Studies

The following example shows the result a machinist had when using a Helical Solutions HEV-5 tool to perform an HEM operation in 17-4PH stainless steel. While performing HEM, this ½” diameter, 5-flute end mill engaged the part just 12% radially, but 100% axially. This machinist was able to reduce tool wear and was able to complete 40 parts with a single tool, versus only 15 with a traditional roughing toolpath.

The effect of HEM on a roughing application can also be seen in the case study below. While machining 6061 aluminum with Helical’s H45AL-C-3, a 1/2″, 3-flute rougher, this machinist was able to finish a part in 3 minutes, versus 11 minutes with a traditional roughing toolpath. One tool was able to make 900 parts with HEM, a boost of more than 150% over the traditional method.

Importance of Tooling to HEM

Generally speaking, HEM is a matter of running the tool – not the tool itself. Virtually every tool can perform HEM, but using tooling built to withstand the rigors of HEM will result in greater success. While you can run a marathon in any type of shoes, you’d likely get the best results and performance from running shoes.

HEM is often regarded as a machining method for larger diameter tooling because of the aggressive MRR of the operation and the fragility of tooling under 1/8” in size. However, miniature tooling can be used to achieve HEM, too.

Using miniature tooling for HEM can create additional challenges that must be understood prior to beginning your operation.

Best Tools for HEM:

  • High flute count for increased MRR.
  • Large core diameter for added strength.
  • Tool coating optimized for the workpiece material for increased lubricity.
  • Variable Pitch/Variable Helix design for reduced harmonics.

Key Takeaways

HEM is a machining operation which continues to grow in popularity in shops worldwide. A milling technique for roughing that utilizes a lower RDOC and higher ADOC than traditional milling, HEM distributes wear evenly across the cutting edge of a tool, reducing heat concentrations and slowing the rate of tool wear. This is especially true in tooling best suited to promote the benefits of HEM.

High Speed Machining Vs. HEM

The following is just one of several blog posts relevant to High Efficiency Milling. To achieve a full understanding of this popular machining method, view any of the additional HEM posts below!

Introduction to High Efficiency Milling I How to Combat Chip Thinning I Diving into Depth of Cut I How to Avoid 4 Major Types of Tool Wear I Intro to Trochoidal Milling


Advancements in the metalworking industry have led to new, innovative ways of increasing productivity. One of the most popular ways of doing so (creating many new buzzwords in the process) has been the discovery of new, high-productivity toolpaths. Terms like trochoidal milling, high speed machining, adaptive milling, feed milling, and High Efficiency Milling are a handful of the names given to these cutting-edge techniques.

With multiple techniques being described with somewhat similar terms, there is some confusion as to what each is referring to. High Efficiency Milling (HEM) and High Speed Machining (HSM) are two commonly used terms and techniques that can often be confused with one another. Both describe techniques that lead to increased material removal rates and boosted productivity.  However, the similarities largely stop there.

High Speed Machining

High speed machining is often used as an umbrella term for all high productivity machining methods including HEM. However, HEM and HSM are unique, separate machining styles. HSM encompasses a technique that results in higher production rates while using a much different approach to depth of cut and speeds and feeds. While certain HEM parameters are constantly changing, HSM uses constant values for the key parameters. A very high spindle speed paired with much lighter axial depths of cut results in a much higher allowable feed rate. This is also often referred to as feed milling. Depths of cut involve a very low axial and high radial components. The method in general is often thought of as z-axis slice machining, where the tool will step down a fixed amount, machine all it can, then step down the next fixed amount and continue the cycle.

High speed machining techniques can also be applied to contoured surfaces using a ball profile or corner radius tool. In these situations, the tool is not used in one plane at a time, and will follow the 3 dimensional curved surfaces of a part. This is extremely effective for using one tool to bring a block of material down to a final (or close to final) shape using high resultant material removal rates paired with the ability to create virtually any shape.

High Efficiency Milling

HEM has evolved from a philosophy that takes advantage of the maximum amount of work that a tool can perform. Considerations for chip thinning and feed rate adjustment are used so that each cutting edge of a tool takes a consistent chip thickness with each rotation, even at varying radial depths of cut and while interpolating around curves. This allows machinists the opportunity to utilize a radial depth of cut that more effectively uses the full potential of a given tool. Utilizing the entire available length of cut allows tool wear to be spread over a greater area, prolonging tool life and lowering production costs. Effectively, HEM uses the depths associated with a traditional finishing operation but boosts speeds and feeds, resulting in much higher material removal rates (MRR). This technique is typically used for hogging out large volumes of material in roughing and pocketing applications.

In short, HEM is somewhat similar to an accelerated finishing operation in regards to depth of cut, while HSM is more of a high feed contouring operation. Both can achieve increased MRR and higher productivity when compared to traditional methods. While HSM can be seen as an umbrella term for all high efficiency paths, HEM has grown in popularity to a point where it can be classified on its own. Classifying each separately takes a bit of clarification, showing they each have power in certain situations.

Check out the video below to see HEM in action!

 

Tackling Titanium: A Guide to Machining Titanium and Its Alloys

In today’s manufacturing industry, titanium and its alloys have become staples in aerospace, medical, automotive, and firearm applications. This popular metal is resistant to rust and chemicals, is recyclable, and is extremely strong for its weight. However, there are several challenges that must be considered when machining titanium and selecting the appropriate tools and parameters for the job.

Titanium Varieties

Titanium is available in many varieties, including nearly 40 ASTM grades, as well as several additional alloys. Grades 1 through 4 are considered commercially pure titanium with varying requirements on ultimate tensile strength. Grade 5 (Ti6Al4V or Ti 6-4) is the most common combination, alloyed with 6 percent aluminum and 4 percent vanadium. Although titanium and its alloys are often grouped together, there are some key differences between them that must be noted before determining the ideal machining approach.

Titanium 6AL4V

Helical Solutions’ HVTI End Mill is a great choice for high efficiency toolpaths in Titanium.

Titanium Concerns

Workholding

Although titanium may have more desirable material properties than your average steel, it also behaves more flexibly, and is often not as rigid as other metals. This requires a secure grip on titanium workpieces, and as rigid a machine setup as is possible. Other considerations include avoiding interrupted cuts, and keeping the tool in motion at all times of contact with the workpiece. Dwelling in a drilled hole or stopping a tool next to a profiled wall will cause the tool to rub – creating excess heat, work-hardening the material, and causing premature tool wear.

Heat Generation

Heat is a formidable enemy, and heat generation must be considered when selecting speeds and feeds. While commercially pure grades of titanium are softer and gummier than most of its alloys, the addition of alloying elements typically raises the hardness of titanium. This increases concerns regarding generated heat and tool wear. Maintaining a larger chipload and avoiding unnecessary rubbing aids with tool performance in the harder titanium alloys, and will minimize the amount of work hardening produced. Choosing a lower RPM, paired with a larger chipload, can provide a significant reduction in temperature when compared to higher speed options. Due to its low conduction properties, keeping temperatures to a minimum will put less stress on the tool and reduce wear. Using high-pressure coolant is also an effective method to reduce heat generation when machining titanium.

cutting tools for titanium

These camshaft covers were custom made in titanium for Mitsubishi Evos.
Photo courtesy of @RebootEng (Instagram)

Galling and Built-Up Edge

The next hurdle to consider is that titanium has a strong tendency to adhere to a cutting tool, creating built up edge. This is a tricky issue which can be reduced by using copious amounts of high pressure coolant aimed directly at the cutting surface. The goal is to remove chips as soon as possible to prevent chip re-cutting, and keep the flutes clean and clear of debris. Galling is a big concern in the commercially pure grades of titanium due to their “gummy” nature. This can be addressed using the strategies mentioned previously, such as continuing feed at all times of workpiece contact, and using plenty of high-pressure coolant.

Titanium Solutions

While the primary concerns when machining titanium and its alloys may shift, the methods for mitigating them remain somewhat constant. The main ideas are to avoid galling, heat generation, work hardening, and workpiece or tool deflection. Use a lot of coolant at high pressure, keep speeds down and feeds up, keep the tool in motion when in contact with the workpiece, and use as rigid of a setup as possible.

In addition, selecting a proper tool coating can help make your job a successful one. With the high heat being generated during titanium machining operations, having a coating that can adequately deal with the temperature is key to maintaining performance through an operation. The proper coating will also help to avoid galling and evacuate chips effectively. Coatings such as Harvey Tool’s Aluminum Titanium Nitride (AlTiN Nano) produce an oxide layer at high temperatures, and will increase lubricity of the tool.

As titanium and its many alloys continue to grow in use across various industries, more machinists will be tasked with cutting this difficult material. However, heat management and appropriate chip evacuation, when paired with the correct coating, will enable a successful run.

machining titanium

Most Common Methods of Tool Entry

Tool entry is pivotal to machining success, as it’s one of the most punishing operations for a cutter. Entering a part in a way that’s not ideal for the tool or operation could lead to a damaged part or exhausted shop resources. Below, we’ll explore the most common part entry methods, as well as tips for how to perform them successfully.


Pre-Drilled Hole

Pre-drilling a hole to full pocket depth (and 5-10% larger than the end mill diameter) is the safest practice of dropping your end mill into a pocket. This method ensures the least amount of end work abuse and premature tool wear.

tool entry predrill

 


Helical Interpolation

Helical Interpolation is a very common and safe practice of tool entry with ferrous materials. Employing corner radius end mills during this operation will decrease tool wear and lessen corner breakdown. With this method, use a programmed helix diameter of greater than 110-120% of the cutter diameter.

helical interpolation

 


Ramping-In

This type of operation can be very successful, but institutes many different torsional forces the cutter must withstand. A strong core is key for this method, as is room for proper chip evacuation. Using tools with a corner radius, which strengthen its cutting portion, will help.

ramping

Suggested Starting Ramp Angles:

Hard/Ferrous Materials: 1°-3°

Soft/Non-Ferrous Materials: 3°-10°

For more information on this popular tool entry method, see Ramping to Success.


Arcing

This method of tool entry is similar to ramping in both method and benefit. However, while ramping enters the part from the top, arcing does so from the side. The end mill follows a curved tool path, or arc, when milling, this gradually increasing the load on the tool as it enters the part. Additionally, the load put on the tool decreases as it exits the part, helping to avoid shock loading and tool breakage.


Straight Plunge

This is a common, yet often problematic method of entering a part. A straight plunge into a part can easily lead to tool breakage. If opting for this machining method, however, certain criteria must be met for best chances of machining success. The tool must be center cutting, as end milling incorporates a flat entry point making chip evacuation extremely difficult. Drill bits are intended for straight plunging, however, and should be used for this type of operation.

tool entry

 


Straight Tool Entry

Straight entry into the part takes a toll on the cutter, as does a straight plunge. Until the cutter is fully engaged, the feed rate upon entry is recommended to be reduced by at least 50% during this operation.

tool entry

 


Roll-In Tool Entry

Rolling into the cut ensures a cutter to work its way to full engagement and naturally acquire proper chip thickness. The feed rate in this scenario should be reduced by 50%.

tool entry

 

Corner Engagement: How to Machine Corners

Corner Engagement

During the milling process, and especially during corner engagement, tools undergo significant variations in cutting forces. One common and difficult situation is when a cutting tool experiences an “inside corner” condition. This is where the tool’s engagement angle significantly increases, potentially resulting in poor performance.

Machining this difficult area with the wrong approach may result in:

  • Chatter – visible in “poor” corner finish
  • Deflection – detected by unwanted “measured” wall taper
  • Strange cutting sound – tool squawking or chirping in the corners
  • Tool breakage/failure or chipping

Least Effective Approach (Figure 1)

Generating an inside part radius that matches the radius of the tool at a 90° direction range is not a desirable approach to machining a corner. In this approach, the tool experiences extra material to cut (dark gray), an increased engagement angle, and a direction change. As a result, issues including chatter, tool deflection/ breakage, and poor surface finish may occur.

Feed rate may need to be lessened depending on the “tool radius-to-part radius ratio.”

corner engagement

More Effective Approach (Figure 2)

Generating an inside part radius that matches the radius of the tool with a sweeping direction change is a more desirable approach. The smaller radial depths of cut (RDOC) in this example help to manage the angle of engagement, but at the final pass, the tool will still experience a very high engagement angle.  Common results of this approach will be chatter, tool deflection/breakage and poor surface finish.

Feed rate may need to be reduced by 30-50% depending on the “tool radius-to-part radius ratio.”

corner engagement

Most Effective Approach (Figure 3)

Generating an inside part radius with a smaller tool and a sweeping action creates a much more desirable machining approach. The manageable RDOC and smaller tool diameter allow for management of the tool engagement angle, higher feed rates and better surface finishes. As the cutter reaches full radial depth, its engagement angle will increase, but the feed reduction should be much less than in the previous approaches.

Feed rate may need to be heightened depending on the “tool-to-part ratio.” Utilize tools that are smaller than the corner you are machining.

corner engagement