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    Accidents happen and some things are unpredictable. But when it comes to high-precision CNC turning, there’s no margin for error. Therefore, understanding and eliminating BUE is an important part of the machining process.

    What is BUE??

    The acronym stands for “build-up edge.” It’s the accumulation of materials that get stuck to the tool’s tip while the workpiece is turning. It can be caused by many different factors and may affect the outcome of a precision CNC project. That’s because too much build-up edge can separate the tool from the chip.

    Contrary to popular belief, this stuff is not due to normal wear and tear. When a build-up edge forms, it’s because the workpiece materials are being deposited at the cutting edge during the turning process. Thus, those deposits transform the geometry of the cutting edge, and thereby reduce its ability to create clean, sharp cuts.

    Essentially, rapid turning causes the cutting tool and the workpiece material to share properties. In other words, the hardness of the workpiece and that of the cutting edge end up being too similar to accommodate efficient tooling. Therefore, it’s important for CNC machine shops and their clients to understand the measures that must be taken to prevent this.

    What causes BUE?

    In CNC turning, cutting tools remain stationary. That means the workpiece is what rotates using a collet holder or clamped chuck. Since many manufacturing operations are performed on a lathe, specific geometries and tolerances are required for different materials. In general, the workpiece harness equals the surface smoothness (or lack thereof).

    The other machining conditions that most commonly cause build-up edge are as follows:

    #1. Low Cutting Speeds

    When low cutting speeds are used to machine certain materials, a build-up edge can accumulate on the tool’s rake face. Therefore, higher cutting speeds may reduce frictional forces and the subsequent build-up that forms.

    #2. Improper Feed Speeds

    High feed speeds may help prolong the lifespan of cutting tools and reduce BUE, but they produce better surface finishes as well. According to studies, high feed speeds combined with high cutting speeds create the least issues possible.

    #3. Wrong Rake Angles

    Tool rake angles and material properties can also influence chip formation. Plus, the workpiece deformation behaviors often dictate the types of chips used. So, wrong rake angles combined with low cutting speeds and improper feed speeds can produce problems quickly.

    #4. Insufficient Heating

    Proper heat generation is important when machining parts because each material has different properties. Too much heat can change the way a material behaves, while too little heat may make tooling less effective and chip removal more difficult.

    Also, if the proper parameters and tolerances aren’t applied correctly during a process, material build-up may occur more rapidly than expected.

    The effects of BUE

    In short, too much build-up edge can cause many-dimensional inaccuracies and may even result in a part or component being completely scrapped. It produces a shoddy surface finish too, and those things combined can drive up the cost of any machining project. However, a build-up edge is one of the easiest things to identify and manage for a skilled machinist.

    Issues are usually visible to the naked eye. No eye loupe or microscope is generally needed. Because the term refers to machined materials being pressure welded to the cutting tool, finding evidence of BUE is as simple as looking for excess material on the rake face of the cutting tool. Machinists might also discover it just by observing the inaccuracies of their processes.

    Unmitigated build-up edge can create a lot of problems for a CNC machine shop, including these:

    • Poor lifespan on cutting tools
    • Longer lead times
    • Component uniformity variations
    • Subpar surface finishes
    • Part quality reduction

    It’s also frustrating to deal with when tight tolerances are required, so the machinists at Pioneer Cuts take special care of all their CNC equipment to provide precision work at lightning speeds. In fact, we frequently use microscopes and eye loupes to weed out the following things and help prevent unnecessary hiccups:

    • Normal wear and tear
    • Cratering
    • Thermal cracking
    • Chipping

    By understanding the causes and effects of build-up edge, CNC machinists and their clients can solve problems and meet deadlines more efficiently.

    How to reduce BUE in CNC turning applications

    Here are the top six ways highly-skilled machinists minimize the build-up edge in their CNC turning applications:

    #1. Increase the cutting and feed speeds.

    Rev up the cutting speeds, especially when tooling with carbide inserts, because chips won’t have as much time to adhere to the tool that way.

    #2. Introduce coatings and lubricants.

    Try inserting polycrystalline diamond (PCD) to significantly decrease the material accumulation in high-precision CNC turning projects.

    #3. Minimize the heat.

    Machining produces a lot of heat but cutting fluids can help minimize that and thereby reduce the amount of built-up edge that accumulates on the tooling components.

    #4. Focus the coolant on the cutting edge.

    Point the coolant toward the tool’s cutting edge to prevent excess heat build-up and subsequent issues. Also, increase the coolant concentration level if possible.

    #5. Select the best tools.

    Choose free-cutting tools with sharp, diligently maintained geometries and refined surfaces. Keep in mind that chip breaker geometry may help limit chip adherence even more.

    #6. Double-check your approach.

    It’s always crucial to closely monitor and check a tooling project’s running parameters to ensure everything is compatible with the chosen application.

    For more information on how to further reduce the CNC build-up edge for more accurate tooling, consult with a Pioneer Cuts professional.

    The takeaway

    Scrap materials and loose chips are all part of the machining process. But so are heat, friction, and pressure. Together, those conditions may cause a build-up edge to develop, thereby reducing the accuracy of your CNC turning applications. To minimize the presence of BUE, machinists must follow specific steps and maintain vigilance with their tools.

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