what is the working principle of cutting tools in excavation

Excavation is one of the most fundamental activities in mining, construction, tunneling, and infrastructure development. At the heart of every excavation operation lies a critical component: the cutting tool. Understanding how cutting tools work—their mechanical principles, material composition, and interaction with different geological formations—is essential for selecting the right equipment and maximizing operational efficiency. This article explores the working principles of various cutting tools used in excavation, from PDC cutters and tricone bits to road milling teeth and rock drilling tools.

The Core Working Principle: Mechanical Energy Transfer

All cutting tools in excavation operate on a shared fundamental principle: the conversion of mechanical energy into rock or soil fragmentation. Whether driven by rotation, percussion, or a combination of both, the cutting tool applies concentrated stress to the material being excavated. When this stress exceeds the material's compressive or tensile strength, fractures initiate and propagate, causing chips or fragments to separate from the parent mass.

The specific mechanism by which this fragmentation occurs depends on the tool design, the material properties of both the tool and the formation, and the operational parameters such as weight on bit, rotation speed, and torque. Broadly, cutting tools employ three primary fragmentation mechanisms: shearing, crushing, and impact. Many modern tools combine these mechanisms for optimal performance across varying ground conditions.

PDC Cutters: Shearing and Scraping Action

PDC (Polycrystalline Diamond Compact) cutters are among the most widely used cutting elements in modern drilling and excavation. A PDC cutter consists of a tungsten carbide substrate with a thin layer of synthetic polycrystalline diamond bonded to its working face. The diamond layer provides exceptional hardness and wear resistance, while the carbide substrate offers toughness and impact resistance.

The working principle of PDC cutters relies primarily on shearing. As the drill bit rotates, the PDC cutter engages the rock at a shallow depth of cut. The diamond cutting edge slices through the formation, shearing off layers of material in a manner similar to a lathe machining metal. This shearing action is highly efficient in soft to medium-hard formations such as shale, sandstone, limestone, and claystone. The cutting efficiency depends on the rake angle, depth of cut, and the cutter's exposure above the bit body. PDC bits equipped with these cutters can achieve penetration rates significantly higher than conventional roller cone bits in suitable formations, because shearing requires less energy than crushing.

TY Drilling Bits supplies a comprehensive range of PDC bits featuring both steel body and matrix body designs. Steel body PDC bits offer flexibility and toughness, while matrix body bits provide superior wear resistance through a tungsten carbide powder matrix infiltrated with a copper alloy binder. The 3-blade and 4-blade configurations available from TY Drilling Bits are optimized for water well drilling, mining, and geological exploration applications.

Tricone Bits: Crushing and Chipping Mechanism

Tricone bits, also known as roller cone bits, operate on a fundamentally different principle from PDC bits. Instead of shearing, they rely on crushing and chipping to break rock. A tricone bit features three rotating cones, each studded with rows of tungsten carbide inserts (TCI) or milled steel teeth. As the bit rotates, the cones roll along the bottom of the borehole, and the individual inserts or teeth strike the rock with concentrated point loads.

The working principle can be broken down into several stages. First, the weight applied to the bit forces the carbide inserts into the rock, creating localized stress concentrations that exceed the rock's compressive strength. This causes the formation of a crushed zone directly beneath each ｉｎｓｅｒｔ. As the cone continues to rotate, the ｉｎｓｅｒｔ moves out of contact, and the sudden release of pressure creates tensile fractures that radiate outward from the crushed zone. Finally, the offset between cones creates a scraping component that helps remove chips from the borehole bottom. This combination of crushing, chipping, and scraping makes tricone bits exceptionally effective in hard, abrasive formations like granite, quartzite, and basalt where PDC bits may experience rapid wear.

TY Drilling Bits offers TCI tricone bits in sizes ranging from 3 inches to 12 1/4 inches, suitable for water well drilling, oil and gas exploration, and hard formation drilling. The tungsten carbide inserts are carefully graded and shaped to match specific formation hardness levels, ensuring optimal penetration rates and bit life.

Carbide Drag Bits: Scraping and Plowing

Carbide drag bits represent one of the simplest yet most cost-effective cutting tool designs for excavation. These bits feature large tungsten carbide cutting elements brazed or pressed into a steel body. Unlike PDC bits that use a thin diamond layer, carbide drag bits rely on solid tungsten carbide tips that are shaped into chisel or conical profiles.

The working principle of carbide drag bits is primarily scraping and plowing. As the bit rotates, the carbide cutting edges dig into the formation and drag through it, displacing and removing material in a continuous scraping motion. This action works best in soft to medium formations such as clay, mudstone, unconsolidated sandstone, and soft shale. The step drag bit design—where cutting elements are arranged in a stepped pattern—improves penetration by creating multiple cutting stages, with each step removing a portion of the formation. TY Drilling Bits manufactures carbide drag bits in sizes from 60mm to 203mm, including chevron drag bits and step drag bits, all designed for efficient water well and groundwater drilling applications.

Road Milling and Trencher Cutting Tools: Rotational Cutting

In surface excavation applications such as road milling, trenching, and foundation work, cutting tools take the form of conical picks, also known as point-attack tools. These tools consist of a hardened steel body with a tungsten carbide tip brazed onto the working end. The tip is typically conical or bullet-shaped, and the tool is mounted in a holder that allows it to rotate freely during operation.

The working principle of conical picks combines indentation and tensile spalling. When the tool engages the pavement or rock surface, the carbide tip creates a highly concentrated point load. This localized stress causes the material to crush and form a compacted core beneath the tip. As the tool advances, tensile cracks radiate from this crushed zone, and chips of material spall away from the surface. The free rotation of the tool in its holder ensures even wear around the tip circumference, maintaining a self-sharpening effect that prolongs tool life. TY Drilling Bits supplies a full range of road milling teeth compatible with Wirtgen and Caterpillar machines, as well as trencher teeth and holders for various trenching applications.

Rock Drilling Tools: Percussive and Rotary Drilling

Rock drilling tools encompass a broad category of equipment used for drilling blast holes, anchor holes, and exploration boreholes in hard rock formations. The most common types include thread button bits, DTH (Down-The-Hole) hammer bits, and tapered button bits.

Thread button bits work on the principle of percussive drilling. A rock drill or drifter delivers high-frequency hammer blows to the bit through a series of drill rods. The impact energy is transmitted through the bit body to the tungsten carbide buttons on the bit face. Each button concentrates the impact force into a small contact area, creating stress levels that far exceed the rock's compressive strength. The rock fractures, and the bit rotates slightly between blows to index the buttons to fresh rock. Compressed air or water flushes the cuttings from the hole. This percussive mechanism is highly effective in hard, brittle rock formations.

DTH hammer bits combine percussion with rotation. The hammer assembly is located directly behind the bit at the bottom of the hole, eliminating energy losses through the drill string. High-pressure air drives a piston that strikes the bit directly, while the drill rig simultaneously rotates the entire assembly. The carbide buttons on the bit face crush and chip the rock with each impact, and the exhaust air carries cuttings to the surface. TY Drilling Bits offers a complete selection of thread button bits (R25, R32, T38, T45, T51) and DTH hammer bits for various hammer models including DHD, Cir, and QL series.

Key Factors Affecting Cutting Tool Performance

Choosing the Right Cutting Tool for Your Excavation Project

Selecting the appropriate cutting tool requires a thorough understanding of the ground conditions, project requirements, and equipment capabilities. The table below summarizes the key characteristics of different cutting tool types: