The chip flute structure of spiral point taps crucially influences chip breaking during continuous cutting. Its design strategy must balance chip morphology control, optimized chip evacuation paths, and cutting stability. The chip flute geometry directly influences the chip curling radius and fracture behavior. Conventional straight-flute taps often produce long, strip-shaped chips that easily entangle on the tap surface or clog the hole bottom. However, spiral point taps, through the coordinated design of the helix angle and flute curvature, subject the chips to combined axial and radial stresses during formation. As the chip flows along the spiral flute, its curvature gradually decreases, concentrating internal stress in specific areas. Ultimately, it fractures in a controlled manner before exiting the flute, forming short, curled chip segments. This design significantly reduces the probability of chip contact with the machined thread surface, preventing secondary scraping of the hole wall by long chips, thereby improving thread surface finish.
The matching of the spiral flute's helical direction with the cutting rotation direction is a key factor in chip breaking effectiveness. For right-hand thread machining, the chip evacuation direction of a right-hand spiral flute tap aligns with the tap feed direction, guiding the chips upward in a spiral pattern. This design not only reduces chip accumulation at the hole bottom but also controls the chip evacuation rate through the spiral flute's lead. When the chip evacuation rate and cutting speed are in dynamic equilibrium, the chips will curl further due to inertia before exiting the chip flute, leading to fractures due to gravity or coolant impact. In contrast, if the spiral direction does not match the cutting direction, chip evacuation resistance increases, resulting in the formation of continuous ribbon-like chips and poor chip breaking performance.
The cross-sectional shape of the chip flute has a direct impact on chip fracture behavior. Common spiral flute cross-sections include semicircular, trapezoidal, and compound curve shapes. Semicircular flutes offer low chip flow resistance but relatively weak chip breaking performance, making them suitable for machining materials with lower toughness. Trapezoidal flutes increase the contact area between the flute wall and the chip, enhancing chip deformation and promoting chip breaking. However, excessive contact pressure may cause the chip to adhere to the flute wall. Compound curved flutes combine the advantages of the first two. By optimizing the flute wall curvature and flute bottom angle, they ensure smooth chip flow while subjecting the chip to periodic deformation during discharge, ultimately achieving efficient chip breaking.
The cutting taper design of spiral point taps also enhances chip breaking. The cutting taper's rake angle and rake angle together determine the initial chip curl direction. When the rake angle is negative, the chip flows toward the machined surface of the workpiece, forming an angle with the spiral flute's chip discharge direction. This design increases bending stress in the chip, promoting early chip breakage. Furthermore, the tooth height distribution of the cutting taper also influences chip breaking performance. Typically, the tooth profile height gradually increases from the tip toward the calibration section. This design evenly distributes the thread removal across the cutting edge, preventing excessive chip deformation caused by localized cutting forces and thus maintaining consistent chip breaking.
The application of coolant significantly impacts the chip breaking performance of spiral point taps. During the continuous cutting process, coolant not only cools the chip but also alters its stress state by impacting the chip surface. When coolant is sprayed into the spiral flute at high pressure, the rapid cooling of the chip surface generates contraction stress, which, combined with the internal thermal stress, creates a compound stress field, further promoting chip breakage. Furthermore, the coolant's lubrication reduces friction between the chip and the flute wall, preventing the chip from sticking and forming elongated strips, thereby enhancing chip breaking performance.
Material properties impose distinct requirements on the chip breaking performance of spiral point taps. When machining plastic materials like mild steel, chips tend to form long ribbons, requiring increased chip deformation by increasing the helix angle or optimizing the flute curvature. When machining highly ductile materials like stainless steel, the chips exhibit high fracture toughness, requiring a combination of coolant impact and flute design to achieve forced chip breaking. When machining brittle materials like cast iron, chips are prone to fragmentation, but chip clogs in the flute must be prevented, requiring an appropriate increase in flute width and depth.
The spiral point tap's flute structure achieves precise control over chip breaking during continuous cutting through the synergistic effects of geometry, helix direction, cross-sectional design, optimized cutting taper, and coolant. This design not only improves machining efficiency and thread quality, but also extends tap life by minimizing chip damage to the machined surface, providing a reliable guarantee for high-precision thread machining.
