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)

Titanium Machining Cost Savings with Helical Solutions

When the manufacturing team at Geospace Technologies was looking for better tool life and improved performance on a Titanium CNC milling job, they turned to Harvey Performance Company and local Application Engineer Mike Kanigowski to dial in some Helical Solutions End Mills. With Mike’s help, Geospace Technologies, led by Lead Mill Programmer Tranquilino Sosa, achieved massive success and cost-savings, which led them to completely shift their tooling repertoire to Helical’s high-performance end mills in their shop.

Struggling with Tool Life

Prior to switching to Helical, Geospace Technologies was experiencing trouble with tool life on a job that required both roughing and finishing toolpaths on a Titanium (Ti-6AL-4V) part. For their roughing pass, Geospace was using a competitor’s 4 flute, 3/8” diameter end mill with a 30° helix angle and TiALN coating. In traditional roughing toolpaths, this tool was running at 1,750 RPM with a 10 IPM feed rate. The tool would take four step downs, three with an axial depth of cut of .200”, and a final pass at .100” for a total depth of .700”.

When finishing, the team used a 1/2” version of the same competitor tool, running at 900 RPM with an 8 IPM feed rate. This would take two passes, one at .400” deep and the last down to the bottom of the part at .700”.

geospace technologies

With this strategy and tooling, the team was creating high-quality parts at a cycle time of 15 minutes and 22 seconds per part, but were only seeing the roughing tool last for 60 parts on average, and the finishing tool for around 120 parts. This was causing tool costs to be higher than they would like, and costing the team precious time with frequent tool changes.

Sosa had seen some of the success that other shops were having with Titanium milling using Helical Solutions end mills, and so they reached out to Kanigowski to see how Helical could help them lower their cost per part while achieving an even better finish.

Dialing in Tool Selection

When Mike got in touch with the team at Geospace, he knew there were some immediate benefits to changing the toolpaths used in this job. Using their ESPRIT software, the team was able to dial in a new program using high efficiency milling (HEM) toolpaths through ESPRIT’s “Profit Milling” technology.

With HEM toolpaths in place, Geospace was going to need new high performance tools to take full advantage of the programming adjustments. After much testing and evaluating several options from Helical’s extensive line of end mills for Titanium, Geospace settled on two solid tools.

Helical offers many different options for Titanium milling in HEM toolpaths. During testing, the team at Geospace decided on Helical EDP 59424, a 3/8” diameter, 7 flute, corner radius end mill. This tool features variable pitch geometry and offset chipbreakers for optimal chip evacuation, reduced harmonics, and minimized tool pressure, as well as Helical’s Aplus coating for high temperature resistance, decreased wear, and improved tool life.

7 flute chipbreaker
7 Flute Chipbeaker Tools Fresh Off the Grinder

When looking at the finishing toolpath, Geospace decided on Helical EDP 82566, a 3/8”, 6 flute, square end mill from Helical’s well known HEV-6 product line. This tool featured a variable pitch design to help mitigate chatter and leave a superior finish. While Helical also offers several tools for finishing toolpaths in Titanium, during testing this tool provided Geospace with the best finish for their specific part geometry.

HEV-6
Example of a Tool from Helical Solutions HEV-6 Tooling Line

Experiencing the “Helical Difference”

With the new tools in place, Sosa’s team reached out to Helical for help dialing in speeds and feeds. The Helical tech team was able to get them set up on Machining Advisor Pro, an advanced speeds and feeds calculator developed by the experts behind Helical Solutions tooling. With this “miracle worker” application in their arsenal, the team was able to easily dial in their new tools for their specific material grade, depth of cut, and machine setup.  

The team saw immediate positive results and cost-savings on this job. They were able to increase their roughing toolpaths to 4,500 RPM and 157 IPM. The finishing path remained largely the same, but resulted in a much improved final part. In total, cycle time dropped from 15 minutes and 22 seconds per part to 12 minutes and 17 seconds per part, which was great, but the improvement in tool life was where Sosa was most impressed.

titanium end mills

With the new Helical end mill in the shop, Geospace was able to run both tools for 580 parts with very minimal wear on the tool. This was a nearly 1000% improvement in tool life for their roughing passes and a 483% improvement in tool life for the finishing operation. In total, one roughing tool was able to last more than 42 hours in the cut before needing to be replaced.

Eliminating the need for a tool change every 60 parts was also a significant time-saver. Constant tool changes were causing serious machine downtime, which was eliminated with the longer tool life experienced with the Helical end mills. What seems like a minor inconvenience will truly add up to dozens of hours in saved time over the course of a few months for Sosa’s team.

titanium machining tool wear
A Closeup of the 7 Flute Chipbreaker After 42 Hours In The Cut

Geospace was thrilled with the results they saw on this Titanium job, as they had never experienced long tool life in Titanium with any other competitor brand. Sosa and his team are excited to continue using Helical Solutions product across all of their other jobs going forward and to continue working with Kanigowski and the Helical tech team on dialing in tool selection and speeds and feeds on future projects.

Please see below for a head-to-head breakdown of the Helical end mills’ performance in terms of total costs and productivity gained versus that of the competitor. These numbers are measured per 1,000 parts, taking into account tooling costs, tool change time, labor costs, running parameters, and cycle times.


titanium machining cost savings

Save Time With Quick Change Tooling

Making a manual tool change on any CNC machine is never a timely or rewarding process. Typically, a tool change in a standard holder can take up to 5 minutes. Add that up a few times, and suddenly you have added significant minutes to your production time.

As CNC machine tool and cutting tool technology has advanced, there are more multi-functional tools available to help you avoid tool changes. However, sometimes it just isn’t feasible, and multiple tool changes are needed. Luckily, Micro 100 has developed a revolutionary new method to speed up tool changes significantly.

What is the Micro-Quik™ Tooling System?

Developed in Micro 100’s world-class grinding facility in Meridian, Idaho, the Micro 100 Micro-Quik™ tooling system is held to the same standards and tight tolerances as all of the Micro 100 carbide tooling.

The quick change tooling system allows for highly repeatable tool changes that save countless hours without sacrificing performance. This system combines a unique tool holder with a unique tool design to deliver highly repeatable and accurate results.

Each quick change tool holder features a locating/locking set screw to secure the tool and a locating pin which helps align the tool for repeatability. Removing a tool is as simple as loosening the set screw and inserting its replacement.

During tool changes, the precision ground bevel on the rear of the tool aligns with a locating pin inside the tool holder. The distance from this locational point to the tip of the tool is highly controlled under tight tolerances, meaning that the Micro-Quik™ tooling system ensures a very high degree of tool length and centerline repeatability. The “L4” dimension on all of our quick change tools, as seen in the image above, remains consistent across the entire product line. Check out the video below for a demonstration of the Micro 100 Micro-Quik™ system in action!

Quick Change Tooling Benefits

The most obvious benefit to using Micro 100’s Micro-Quik™ system is the time savings that come with easier tool changes. By using the quick change holders in combination with quick change tooling, it is easy to reduce tool changes from 5 minutes to under 30 seconds, resulting in a 90% decrease in time spent swapping out tools. This is a significant benefit to the system, but there are benefits once the tool is in the machine as well.

As mentioned above, the distance from the locational point on each tool shank to the tip of the tool is highly controlled, meaning that regardless of which type of tool you insert into the holder, your stick out will remain the same. This allows you to have confidence in the tooling and does not require additional touch offs, which is another major time saver.

By removing additional touch-offs and tool changes from your workflow, you also reduce the chances for human or machine error. Improper touch-offs or tool change errors can cause costly machine crashes and result in serious repairs and downtime. With the Micro 100 Micro-Quik™ system, initial setups become much easier, allowing you to hit the cycle start button with total confidence for each run.

By making a few simple changes to your tool holding configurations and adopting the Micro-Quik™ system, your shop can save thousands in time saved, with less machine downtime and increased part production. To learn more about the Micro 100 Micro-Quik™ cutting tools and tool holders, please visit (URL here to quick change page).