English 
Español 
हिन्दी 
العربية 
Português do Brasil 
Русский 
日本語 
Deutsch 
한국어 
Français 
Türkçe 
Polski 
Tiếng Việt 
Italiano 
简体中文 Multi-point drills were once essential tools for China’s manufacturing industry more than half a century ago. Improved from standard twist drills, this special cutting tool has supported industrial development for decades with its excellent chip separation, low drilling force, long service life and high machining quality.
However, with CNC machine tools and imported alloy drills becoming standard workshop equipment, this tool representing traditional Chinese craftsmanship has gradually faded from industrial vision. This paper systematically reviews the modern upgrading paths of multi-point drills in tool materials, structural design, grinding processes and practical applications. The research shows that multi-point drills still hold irreplaceable practical value in the machining of difficult-to-cut materials and special structural parts.
Modern Upgrade of Multi-point drill Materials
Material Iteration and Structural Adaptation
Multi-point drill materials have gradually shifted from high-speed steel to cemented carbide. The low toughness of cemented carbide fails to match the original geometric structure of traditional drills, so targeted structural optimization is required for practical application. Directly adopting high-speed steel drill tip structures on cemented carbide multi-point drills easily causes edge chipping. Optimized geometric parameters can solve this problem, including an inner edge rake angle of -15°, a chisel edge length of 0.5–1.0 mm, and a chisel edge inclination angle of 85°. After optimization, drilling force drops by 10%–20%, tool service life is greatly prolonged, and drilling efficiency increases 2 to 3 times, with improved hole roundness and surface quality. The optimized cemented carbide multi-point drills applicable to dry drilling of high-strength steel, providing reliable structural references for special-condition drill development.
Figure 1 Edge structure of integral cemented carbide multi-point drill
Table 1 Main parameters of integral cemented carbide multi-point drill
TiN Coating Technology for Wear Resistance Improvement
Coating treatment is an effective method to improve the wear resistance of high-speed steel multi-point drills. After TiN coating, the average drilling capacity of multi-point drills reaches 548.4 holes, nearly ten times the service life of uncoated drills. TiN coating has high hardness and good high-temperature stability, which reduces friction and adhesion wear on the tool land. Uncoated drills easily form wear grooves during cutting and fail in advance. The test results verify the significant life-enhancing effect of TiN coating on multi-point drills, and provide experimental support for the application of coated multi-point drills in machining difficult-to-cut materials.
Figure 2 Wear curve comparison between uncoated and TiN-coated multi-point drills
Overall Upgrade of Multi-point drillGrinding Technology
The grinding process of multi-point drills has gone through continuous technical upgrades. In the early stage, multi-point drills were completely manually polished by bench grinders. This processing method has low precision, random errors and poor consistency, and highly depends on worker experience, failing to meet the requirements of precision and standardized production. With the development of mechanical processing technology, manual grinding has been replaced by multi-axis CNC grinding. At present, the grinding technology has entered a flexible intelligent stage supported by robots and parallel mechanisms.
Multi-axis CNC Precision Grinding Technology
Manual grinding of the crescent groove on cemented carbide multi-point drills has low precision and large errors. Six-axis CNC grinding equipment is widely used to solve this problem. The machine tool realizes high-precision grinding of complex crescent groove surfaces through the coordinated movement of X, Y, Z, rotation, swing and tilt axes. Equipped with complete software and hardware CNC systems, the equipment can realize automatic and precise grinding of standard multi-point drills, greatly improving processing quality and production efficiency. It shows prominent application advantages of multi-axis CNC grinding equipment in precision tool machining.
Figure 3 Structure of six-axis CNC grinding machine
High-precision six-axis CNC grinders can precisely control the grinding process of optimized cemented carbide multi-point drills. They ensure structural stability and processing consistency of improved drills, providing reliable technical support for structural design, process implementation and large-scale engineering application of cemented carbide multi-point drills.
Robot Flexible Grinding Technology
The flexible grinding system based on robot clamping, combined with automatic detection technology, realizes full-automatic grinding of multi-point drills. With the flexible movement performance of robots and high-precision sensors, the system eliminates manual errors and ensures consistent grinding quality of multi-point drills in different batches.
Figure 4 Assembly of robot clamping fixture for drills
Figure 5 Different tool setting postures of multi-point drills in robot flexible grinding system
High-precision Forming Grinding Technology Based on Parallel Mechanism
Parallel mechanism precision forming technology has been gradually applied to the research and development of multi-point drill grinding equipment. Relying on the high-precision motion control ability of parallel mechanisms, the equipment can efficiently complete the forming and grinding of complex curved surfaces of multi-point drills and accurately reproduce complex spatial structures. This technology effectively improves grinding precision and efficiency, providing new technical ideas for the research and upgrading of high-end precision grinding equipment.
Figure 6 Structural diagram of grinding machine based on parallel mechanism
Electric Discharge Green Machining Technology
The complex curved crescent grooves and chip dividing grooves of multi-point drills bring challenges to conventional automatic grinding. Electric discharge machining (EDM) serves as an efficient green processing method for multi-point drills. This non-contact machining technology uses precision electrodes to machine cemented carbide, which accurately reproduces the complex geometric features of inner edges, chisel edges and crescent grooves with strong adaptability. Different from traditional grinding, EDM produces no dust or oil mist pollution. It effectively supports green and intelligent manufacturing for small-batch, high-complexity multi-point drill production.
Figure 7 EDM processing of multi-point drill tip
Application Advantages of Multi-point drills in Difficult-to-cut Materials and Special Working Conditions
Multi-point drills have unique and irreplaceable advantages in machining difficult-to-cut materials and complex special working conditions. Through structural optimization, parameter matching and process improvement, multi-point drills adapt to various complex drilling scenarios. They solve the common defects of standard twist drills such as poor chip separation, serious wear, low hole quality and large cutting impact, and greatly improve processing stability and precision under complex working conditions.
Application in Stainless Steel Drilling
Stainless steel drilling is prone to chip winding, tool adhesion and severe tool wear. The optimized cemented carbide multi-point drill tip can effectively solve these problems. Matching key geometric parameters including tip height, arc radius, outer edge length and outer edge angle can realize efficient and high-precision stainless steel drilling. Under conventional cutting conditions, multi-point drills with optimized parameters achieve the lowest axial force and torque. The chips present a short spiral shape with good chip breaking performance. The tool has minor flank wear and no edge chipping. Optimized geometric parameters significantly improve the chip separation and breaking ability of multi-point drills and reduce tool wear, which is suitable for batch drilling of viscous stainless steel materials.
Figure 8 Optimized cemented carbide multi-point drill tip structure
Figure 9 Spiral-shaped short chips
Low-damage Drilling Application in Fiber Composite Materials
Glass fiber reinforced polymer (GFRP) often suffers outlet delamination and tearing during drilling. Multi-point drills can achieve low-damage hole making through structural optimization. Key parameters including inner edge angle, outer edge angle and tip height effectively control machining defects. Within reasonable parameter ranges, the unique chisel-edge-free and negative-rake-angle structure of multi-point drills reduces axial thrust, while outer edges form complete circular chips to avoid material tearing. Appropriate cutting heat also softens the resin matrix and further suppresses delamination. Related tests prove that feed speed, spindle speed and outer edge relief angle exert coupled nonlinear influences on hole quality, requiring collaborative multi-parameter optimization. This method provides effective parameter guidance for precision low-damage drilling of composite materials.
Processing tests show that feed speed, spindle speed and outer edge relief angle have coupling and nonlinear effects on outlet damage, which requires multi-parameter collaborative optimization. This study provides reliable parameter guidance and design ideas for low-damage precision drilling of composite materials.
Figure 10 Outlet stage of GFRP drilling with multi-point drill
Figure 11 Circular cutting chips
Precision Deep Hole Drilling Application in Alloy Steel
Deep hole drilling of alloy steel faces problems such as large axial force, poor chip removal and rapid tool wear. The optimized cemented carbide deep-hole multi-point drill based on the “three-tip and seven-edge” structure has prominent processing advantages. Grinding crescent grooves on the flank forms a composite structure with inner edges, arc edges and outer edges, shortens the chisel edge and optimizes cutting edge parameters. Compared with ordinary deep-hole twist drills, the optimized multi-point drill has lower axial force and torque. The fine and broken chips are discharged smoothly, solving the deep-hole chip removal problem. It also reduces inner hole surface roughness and tool wear, extending tool service life and meeting the precision deep-hole machining requirements of alloy steel.
Figure 12 Tip structure of deep-hole multi-point drill
a) Ordinary deep-hole twist drill
b) Optimized deep-hole multi-point drill
Low-impact Drilling Application in Brittle Thin-walled Non-metallic Materials
Drilling brittle thin-walled materials such as hard plastic and bakelite easily causes cracking and tool jamming due to large instantaneous cutting impact. The optimized multi-point drill with a large vertex angle, small relief angle and short chisel edge can effectively reduce penetration impact torque. This classic three-tip seven-edge structure lowers torque fluctuation and shortens drilling time, avoiding workpiece damage. The chisel edge length is the dominant factor affecting drilling stability, and shortening the chisel edge significantly improves processing performance. In addition, spiral surface flank grinding delivers better results than plane grinding, offering a practical design for stable low-impact drilling of brittle non-metallic thin-walled parts.
Figure 13 Impact comparison between ordinary drill and optimized multi-point drill for brittle thin-walled materials
High-strength Manganese Steel Drilling Application
Drilling of ZGMn13 high manganese steel easily causes tool chipping and hole wall thermal cracking with poor processing stability. The clamped cemented carbide multi-point drill can adapt to the machining demands of this high-strength wear-resistant material. Through material selection and orthogonal optimization of inner edge angle, arc radius and inner edge rake angle, the drill improves chip morphology and reduces axial force and torque. The clamped structure avoids high-temperature welding defects of traditional welded drills, improves tool reliability and hole quality, and reduces processing energy consumption and tool cost, which meets the requirements of green manufacturing.
Conclusion
Although integral cemented carbide drills and indexable U-drills have become mainstream hole-processing tools in modern manufacturing, multi-point drills show unique advantages in high-end and complex machining scenarios for intelligent manufacturing. With the integration of cemented carbide substrate, advanced coating technology and AI-driven parameter optimization, multi-point drills will evolve from empirical manual tools into intelligent cutting units for modern precision machining.
