https://cdn.mtdcnc.global/cnc/wp-content/uploads/2021/05/17143144/Figure-1-Modular-fixed-torque-keys-provide-effective-options-for-securing-milling-inserts-640x360.jpg
    Tooling

    In a high-speed spin

    • By MTDCNC
    • May 18, 2021
    • 4 minute read

    High-speed machining (HSM) has not only led to a significant difference between machine tools but has also brought awareness to the high-speed spindle. This has now become one of the most important and central components of high-speed machine tools.
    Operating a spindle with high rotation speed and gaining the optimal balance between the provided speed and torque is the main task of high spindle engineering. When machining, the spindle is not in direct contact with the workpiece but interacts with it through another technological system – the cutting tool. This connection acts as a conductor and should transform the impressive capabilities of a high-speed spindle into improved machining results.

    Another element between the cutting tool and the spindle is the toolholder. Poor performance of this small assembly may reduce the function of the spindle to zero. High-speed rotation generates centrifugal forces. In HSM, when compared with traditional machining methods, these forces grow exponentially and turn into a significant load on a cutting tool. In indexable milling, high centrifugal forces may cause insert clamping screws to break, inserts to loosen and a cutter body to fail. Formed fragments can not only damage a machine and a machined part but can be very dangerous to the operator.

    In such conditions, cutting tool manufacturers are compelled to consider the design necessary to ensure the reliability of their products. Hence, the focus on indexable milling should consider secure insert mounting and a robust body structure.
    Let us start with a clamping screw, the smallest and weakest element of a whole technological system with a great impact on the system’s reliability. Applying dynamometric keys controls the tightening of the clamping screw. (Fig. 1). However, ensuring the torque is tightened sufficiently is not enough. Intelligent design is directed to minimise the dynamic load on the clamping screw.
    ISCAR’s HSM90S FAL-22 milling cutters are intended for efficient milling of aluminium at high speeds. They carry large-size inserts that enable up to 22mm depth of cut. The cutter insert pocket has a protruding ridge on the seat surface, and the lower face of the insert has a matching groove that fits into a ridge when assembled. (Fig. 2). This eliminates insert radial displacement due to strong centrifugal forces at high-speed milling and improves load distribution on the insert clamping screw. The cutter design facilitates reliable milling in a rotational speed range of up to 31,000rpm.

    To reduce centrifugal forces, a cutter body should be axially symmetric and highly balanced. There are international and national standards and norms that specify tool balancing grades. When designing indexable milling tools for HSM, it is important to ensure the mass distribution of the body is symmetrical with the body axis. As this theoretical balance relates to a virtual object, it cannot replace the physical balancing of a real body if needed but can substantially diminish the mass unbalance of a future product making the “physical” balance much easier.

    Normally, the overhang-to-diameter ratio for solid carbide endmills is greater when compared with indexable tools. Such a feature, in combination with a flute shape that weakens a tool cross-section, demands specific attention to the vibration strength of a SCEM. To improve chatter stability, engineers often make a tooth angular pitch unequal, and a flute helix variable. This violates the principle of axial symmetry and may give a reverse result. Therefore, an optimal, intelligent design for solid carbide endmills requires engineer ingenuity and appropriate compromising (Fig. 3).

    Having highly engineered a balanced vibration-proof tool is half the battle. We have already mentioned the toolholder that is mounted on a high-speed spindle. So, what’s the use of an ideal tool if a larger toolholder is not suitable for HSM? In HSM, the dynamic characteristics of the tool cannot be separated from a toolholder. For example, balancing the tool should be done in assembly with the toolholder. Modern CAD/CAM systems ensure estimating the dynamic behavior of various products based on their 3D models. Providing such models for cutting tools, toolholders and various accessories is a typical feature of today’s tool manufacturer. In fact, ISCAR is proud to acknowledge that in recent years it has significantly expanded its digital twin assembly options in the e-catalog.

    https://cdn.mtdcnc.global/cnc/wp-content/uploads/2021/05/17143144/Figure-1-Modular-fixed-torque-keys-provide-effective-options-for-securing-milling-inserts-640x360.jpg

    In a high-speed spin

    High-speed machining (HSM) has not only led to a significant difference between machine tools but has also brought awareness to the high-speed spindle. This has now become one of the most important and central components of high-speed machine tools.
    Operating a spindle with high rotation speed and gaining the optimal balance between the provided speed and torque is the main task of high spindle engineering. When machining, the spindle is not in direct contact with the workpiece but interacts with it through another technological system – the cutting tool. This connection acts as a conductor and should transform the impressive capabilities of a high-speed spindle into improved machining results.

    Another element between the cutting tool and the spindle is the toolholder. Poor performance of this small assembly may reduce the function of the spindle to zero. High-speed rotation generates centrifugal forces. In HSM, when compared with traditional machining methods, these forces grow exponentially and turn into a significant load on a cutting tool. In indexable milling, high centrifugal forces may cause insert clamping screws to break, inserts to loosen and a cutter body to fail. Formed fragments can not only damage a machine and a machined part but can be very dangerous to the operator.

    In such conditions, cutting tool manufacturers are compelled to consider the design necessary to ensure the reliability of their products. Hence, the focus on indexable milling should consider secure insert mounting and a robust body structure.
    Let us start with a clamping screw, the smallest and weakest element of a whole technological system with a great impact on the system’s reliability. Applying dynamometric keys controls the tightening of the clamping screw. (Fig. 1). However, ensuring the torque is tightened sufficiently is not enough. Intelligent design is directed to minimise the dynamic load on the clamping screw.
    ISCAR’s HSM90S FAL-22 milling cutters are intended for efficient milling of aluminium at high speeds. They carry large-size inserts that enable up to 22mm depth of cut. The cutter insert pocket has a protruding ridge on the seat surface, and the lower face of the insert has a matching groove that fits into a ridge when assembled. (Fig. 2). This eliminates insert radial displacement due to strong centrifugal forces at high-speed milling and improves load distribution on the insert clamping screw. The cutter design facilitates reliable milling in a rotational speed range of up to 31,000rpm.

    To reduce centrifugal forces, a cutter body should be axially symmetric and highly balanced. There are international and national standards and norms that specify tool balancing grades. When designing indexable milling tools for HSM, it is important to ensure the mass distribution of the body is symmetrical with the body axis. As this theoretical balance relates to a virtual object, it cannot replace the physical balancing of a real body if needed but can substantially diminish the mass unbalance of a future product making the “physical” balance much easier.

    Normally, the overhang-to-diameter ratio for solid carbide endmills is greater when compared with indexable tools. Such a feature, in combination with a flute shape that weakens a tool cross-section, demands specific attention to the vibration strength of a SCEM. To improve chatter stability, engineers often make a tooth angular pitch unequal, and a flute helix variable. This violates the principle of axial symmetry and may give a reverse result. Therefore, an optimal, intelligent design for solid carbide endmills requires engineer ingenuity and appropriate compromising (Fig. 3).

    Having highly engineered a balanced vibration-proof tool is half the battle. We have already mentioned the toolholder that is mounted on a high-speed spindle. So, what’s the use of an ideal tool if a larger toolholder is not suitable for HSM? In HSM, the dynamic characteristics of the tool cannot be separated from a toolholder. For example, balancing the tool should be done in assembly with the toolholder. Modern CAD/CAM systems ensure estimating the dynamic behavior of various products based on their 3D models. Providing such models for cutting tools, toolholders and various accessories is a typical feature of today’s tool manufacturer. In fact, ISCAR is proud to acknowledge that in recent years it has significantly expanded its digital twin assembly options in the e-catalog.