In the realm of mechanical manufacturing for threaded components like bolts, nuts, and pipe joints, thread inserts stand out as essential cutting tools for achieving efficient and precise thread forming. Compared to traditional solid taps and dies, thread inserts feature an innovative indexable design – a single insert contains multiple cutting edges, allowing for rotation to a fresh edge once one becomes worn. This design delivers exceptional versatility, easy replacement, and consistent machining accuracy, making it the preferred choice for batch thread machining. They are widely compatible with various equipment, including lathes, CNC lathes, and turning centers.
I. What is a Thread Insert? Core Definition and Composition
1. Basic Definition
A thread insert is an indexable cutting tool specifically engineered for machining internal threads (within holes) or external threads (on shafts or cylindrical surfaces). Its spiral cutting edges accurately cut standard-compliant thread profiles—such as triangular, trapezoidal, or rectangular—directly onto the workpiece. The machining precision of the insert is critical, as it directly influences the thread's performance in areas like sealing, transmission efficiency, and connection reliability.
2. Core Composition
The performance of a thread insert hinges on its three fundamental components:
▷Substrate: The base material, typically cemented carbide (e.g., WC-Co alloy, hardness HRC89-92), is suitable for common materials like steel, cast iron, and non-ferrous metals. For challenging applications involving superalloys or titanium alloys, advanced substrates like cermets (Al₂O₃-TiC) or CBN (Cubic Boron Nitride) are employed to enhance wear and high-temperature resistance.
▷Coating: To extend service life and optimize cutting performance, inserts are often coated with functional layers. Common coatings include:
◇TiN (Titanium Nitride): A general-purpose coating that reduces friction, ideal for low-carbon steel and aluminum alloys, boosting lifespan 2-3 times over uncoated tools.
◇TiAlN (Titanium Aluminum Nitride): Offers high-temperature resistance (up to 800°C), making it excellent for medium/high-carbon steels and alloy steels with superior abrasive wear resistance.
◇AlCrN (Aluminum Chromium Nitride): An ultra-high temperature coating (up to 1100°C), perfect for superalloys (e.g., Inconel 718) and titanium alloys, preventing material adhesion.
◇DLC (Diamond-Like Carbon): Features an extremely low friction coefficient (0.05-0.1), ideal for non-ferrous metals like copper and aluminum alloys, effectively preventing chip adhesion.
▷Cutting Edge Design: The edge profile is tailored to the thread type—for instance, triangular edges for 60°/55° profiles or trapezoidal edges for 30° profiles. The edge preparation (dulling amount of 0.01-0.05mm) is carefully matched to the workpiece material's hardness, with larger hone values used for harder materials to prevent chipping.
3. Working Principle
The machining process involves the machine spindle rotating the workpiece while the thread insert feeds along the workpiece axis at a rate precisely matching the thread lead (axial travel per revolution). The insert's cutting edge progressively shears the material to form a continuous, precise thread form. The indexable design allows a single insert to be used across 3-4 cutting edges before replacement is needed, drastically reducing tool change downtime from 5-8 minutes (for solid taps) to just 1-2 minutes.
II. Thread Insert Model Classification: Standards and Functional Types
Thread insert models adhere to international standards (e.g., ISO 5680, ANSI B94.11M). They are classified based on key dimensions: thread standard, insert shape, accuracy grade, and installation method. The combination of these factors creates a comprehensive model identification system.
1. Classification by Thread Standard (Core Basis)
The thread standard dictates the insert's profile angle and pitch specification.
▷Metric Threads (ISO Standard): Feature a 60° profile angle with pitch in millimeters (e.g., M10x1.5). These are globally prevalent. Corresponding inserts often have a suffix like "M" or no special marking (e.g., Kennametal's TNMG160408-M).
▷Imperial Threads (ANSI Standard): Also have a 60° profile angle but use Threads Per Inch (TPI) (e.g., UNC 1/2-13). Common in North America, these inserts typically carry a "UN" suffix (e.g., Sandvik's CCMT09T304-UN).
▷Other Specialized Standards:
◇Pipe Threads (ISO 7/1, ANSI B1.20.1): Used for fluid conduits; profile angles are 55° (NPT) or 60° (G). Model suffixes include NPT or G (e.g., Iscar's WNMG080404-NPT).
◇Trapezoidal Threads (ISO 2904, GB/T 5796): Used in power transmission systems (e.g., lead screws); feature a 30° profile angle and larger pitches (e.g., Tr40x7). Models are marked with "Tr" (e.g., Zhuzhou Diamond's DNMG150608-Tr).
◇Aerospace Threads (MJ Standard): Feature a 60° profile with a rounded root for fatigue resistance. Models are identified with "MJ" (e.g., Guhring's SNMG120406-MJ).
2. Classification by Insert Shape (For Specific Applications)
The shape is determined by the cutting direction (internal/external) and workpiece geometry (deep hole/thin wall).
▷Triangular Inserts (Code C/T): The most versatile type, suitable for standard 60°/55° threads (e.g., M, UNC), accounting for over 70% of use. Examples include TNMG (with relief) and CNMG (without relief), e.g., TNMG160408-MF for external threads.
▷Square Inserts (Code S): Designed for rectangular or square threads (0° profile), used in heavy-load transmissions. Example: SNMG120404-UN for internal threads.
▷Round Inserts (Code R): Highly versatile; the radius can be adjusted for different pitches, ideal for large-pitch threads (P≥6mm) or thread repair. Example: RNMG200608-Tr for trapezoidal threads.
▷Special-Shaped Inserts: Include profiles like serrated (Code Z, 33° angle) for unidirectional loads or worm (Code W) inserts for worm machining. Example: ZNMG180612-W.
3. Classification by Accuracy Grade (For Dimensional Tolerance)
The accuracy grade corresponds to the thread's tolerance range, affecting fit and sealing.
▷Internal Thread Accuracy (e.g., 5H, 6H, 7H): A smaller number indicates higher precision. 5H is for precision instruments, 6H is general purpose, and 7H is for less critical applications.
▷External Thread Accuracy (e.g., 5g, 6g, 7g): 6g is the most common grade. 5g is for high-precision aerospace fits, while 7g is for agricultural or construction machinery.
▷Accuracy Marking: Often included in the model suffix, e.g., CNMG09T304-6g (6g external) or DNMG150608-5H (5H internal).
4. Classification by Installation Method (For Tool Holder Compatibility)
This affects the connection rigidity and stability in the tool holder.
▷Flat-Mounted Inserts (Code P): The insert sits on a flat tool holder seat. Simple design, best for shallow threads (depth ≤5mm). Example: PNMG160408-M.
▷Vertical-Mounted Inserts (Code V): The insert is mounted vertically in a pocket, offering better cutting force distribution for deep threads (depth >5mm) or thick-walled parts. Example: VNMG200612-NPT for deep NPT threads.
In summary, thread inserts represent a significant advancement in thread machining technology, offering unparalleled efficiency, consistency, and cost-effectiveness for mass production. Their indexable design, combined with a wide range of substrate materials, specialized coatings, and precise geometries, makes them adaptable to virtually any threading task—from standard metric and imperial threads to specialized pipe, trapezoidal, and aerospace profiles.
As a leading manufacturer of precision machining tools, we provide a comprehensive range of high-quality thread inserts designed to meet your most demanding application challenges. Explore our catalog to find the perfect solution for your needs, or for personalized assistance in selecting the right tool to maximize your productivity and machining quality.
