Annular Cutter: A Professional Tool to Overcome the Challenges of Drilling Stainless Steel

In the field of industrial machining, stainless steel has become a key material in manufacturing due to its excellent corrosion resistance, high strength, and good toughness. However, these same properties also pose significant challenges for drilling operations, making stainless steel drilling a demanding task. Our annular cutter, with its unique design and outstanding performance, provides an ideal solution for efficient and precise drilling in stainless steel.

Ⅰ. Challenges and Core Difficulties in Drilling Stainless Steel

1.High Hardness and Strong Wear Resistance:
Stainless steel, particularly austenitic grades like 304 and 316, has high hardness that significantly increases cutting resistance—over twice that of regular carbon steel. Standard drill bits dull quickly, with wear rates increasing by up to 300%.

2.Poor Thermal Conductivity and Heat Accumulation:
The thermal conductivity of stainless steel is only one-third that of carbon steel. The cutting heat generated during drilling cannot dissipate quickly, causing localized temperatures to exceed 800°C. Under such high-temperature and high-pressure conditions, alloy elements in stainless steel tend to bond with the drill material, leading to adhesion and diffusion wear. This results in drill bit annealing failure and workpiece surface hardening.

3.Significant Work Hardening Tendency:
Under cutting stress, some austenite transforms into high-hardness martensite. The hardness of the hardened layer can increase by 1.4 to 2.2 times compared to the base material, with tensile strength reaching up to 1470–1960 MPa. As a result, the drill bit is constantly cutting into increasingly harder material.

4.Chip Adhesion and Poor Chip Evacuation:
Due to the high ductility and toughness of stainless steel, chips tend to form continuous ribbons that easily adhere to the cutting edge, forming built-up edges. This reduces cutting efficiency, scratches the hole wall, and leads to excessive surface roughness (Ra > 6.3 μm).

5.Thin Plate Deformation and Positioning Deviation:
When drilling sheets thinner than 3mm, the axial pressure from traditional drill bits can cause material warping. As the drill tip breaks through, unbalanced radial forces may lead to poor hole roundness (commonly deviating by more than 0.2mm).

These challenges make conventional drilling techniques inefficient for stainless steel processing, calling for more advanced drilling solutions to effectively address these issues.

Ⅱ. Definition of Annular Cutter

An annular cutter, also known as a hollow drill, is a specialized tool designed for drilling holes in hard metal plates such as stainless steel and thick steel sheets. By adopting the principle of annular (ring-shaped) cutting, it overcomes the limitations of traditional drilling methods.

The most distinctive feature of the annular cutter is its hollow, ring-shaped cutting head, which removes only the material along the hole's perimeter rather than the entire core, as with conventional twist drills. This design dramatically enhances its performance, making it far superior to standard drill bits when working with thick steel plates and stainless steel.

Ⅲ. Core Technical Design of the Annular Cutter

1.Three-Edge Coordinated Cutting Structure:
The composite cutting head consists of outer, middle, and inner cutting edges:

• Outer Edge: Cuts a circular groove to ensure precise hole diameter (±0.1mm).
• Middle Edge: Bears 60% of the main cutting load and features wear-resistant carbide for durability.
• Inner Edge: Breaks the material core and aids in chip removal. The uneven tooth pitch design helps prevent vibration during drilling.

2.Annular Cutting & Chip-Breaking Groove Design:
Only 12%–30% of the material is removed in a ring shape (core retained), reducing cutting area by 70% and lowering energy consumption by 60%. Specially engineered spiral chip grooves automatically break chips into small fragments, effectively preventing ribbon-shaped chip entanglement—a common issue when drilling stainless steel.

3.Central Cooling Channel:
Emulsion coolant (oil-to-water ratio 1:5) is directly sprayed to the cutting edge through a central channel, reducing the temperature in the cutting zone by over 300°C.

4.Positioning Mechanism:
The center pilot pin is made of high-strength steel to ensure accurate positioning and prevent drill slippage during operation—especially important when drilling slippery materials like stainless steel.

Ⅳ. Advantages of Annular Cutters in Drilling Stainless Steel

Compared to traditional twist drills that perform full-area cutting, annular cutters remove only a ring-shaped section of the material—retaining the core—which brings revolutionary advantages:

1.Breakthrough Efficiency Improvement:
With a 70% reduction in cutting area, drilling a Φ30mm hole in 12mm-thick 304 stainless steel takes just 15 seconds—8 to 10 times faster than using a twist drill. For the same hole diameter, annular cutting reduces workload by over 50%. For example, drilling through a 20mm-thick steel plate takes 3 minutes with a traditional drill, but only 40 seconds with an annular cutter.

2.Significant Reduction in Cutting Temperature:
Central cooling fluid is directly injected into the high-temperature zone (optimal ratio: oil-water emulsion 1:5). Combined with layered cutting design, this keeps the cutter head temperature below 300°C, preventing annealing and thermal failure.

3.Guaranteed Precision and Quality:
Multi-edge synchronized cutting ensures automatic centering, resulting in smooth, burr-free hole walls. Hole diameter deviation is less than 0.1mm, and surface roughness is Ra ≤ 3.2μm—eliminating the need for secondary processing.

4.Extended Tool Life and Reduced Costs:
The carbide cutting head withstands the high abrasiveness of stainless steel. Over 1,000 holes can be drilled per regrind cycle, reducing tool costs by up to 60%.

5.Case Study:
A locomotive manufacturer used annular cutters to drill 18mm holes in 3mm-thick 1Cr18Ni9Ti stainless steel base plates. The hole pass rate improved from 95% to 99.8%, roundness deviation decreased from 0.22mm to 0.05mm, and labor costs were reduced by 70%.

Ⅴ. Five Core Challenges and Targeted Solutions for Drilling Stainless Steel

1.Thin-Wall Deformation

1.1Problem: Axial pressure from traditional drill bits causes plastic deformation of thin plates; at breakthrough, radial force imbalance leads to oval-shaped holes.

1.2.Solutions:

• Backing Support Method: Place aluminum or engineering plastic backing plates under the workpiece to distribute compressive stress. Tested on 2mm stainless steel, ovality deviation ≤ 0.05mm, deformation rate reduced by 90%.
• Step Feed Parameters: Initial feed ≤ 0.08 mm/rev, increase to 0.12 mm/rev at 5mm before breakthrough, and to 0.18 mm/rev at 2mm before breakthrough to avoid critical speed resonance.

2. Cutting Adhesion and Built-Up Edge Suppression

2.1.Root Cause: Welding of stainless steel chips to the cutting edge at high temperature (>550°C) causes Cr element precipitation and adhesion.

2.2.Solutions:

• Chamfered Cutting Edge Technology: Add a 45° chamfer edge 0.3-0.4mm wide with 7° relief angle, reducing blade-chip contact area by 60%.
• Chip-Breaking Coating Application: Use TiAlN coated drill bits (friction coefficient 0.3) to reduce built-up edge rate by 80% and double tool life.
• Pulsed Internal Cooling: Lift drill every 3 seconds for 0.5 seconds to allow cutting fluid penetration at adhesion interface. Combined with 10% extreme pressure emulsion containing sulfur additives, temperature in cutting zone can drop by over 300°C, significantly reducing welding risk.

3. Chip Evacuation Issues and Drill Jamming

3.1.Failure Mechanism: Long strip chips entangle the tool body, blocking coolant flow and eventually clogging the chip flutes, causing drill breakage.

3.2.Efficient Chip Evacuation Solutions:

• Optimized Chip Flute Design: Four spiral flutes with 35° helix angle, increased flute depth by 20%, ensuring each cutting edge chip width ≤ 2mm; reduces cutting resonance and cooperates with spring push rods for automatic chip clearing.
• Air Pressure Assisted Chip Removal: Attach 0.5MPa air gun on magnetic drill to blow away chips after each hole, reducing jamming rate by 95%.
• Intermittent Drill Retraction Procedure: Fully retract drill to clear chips after reaching 5mm depth, especially recommended for workpieces thicker than 25mm.

4. Curved Surface Positioning and Perpendicularity Assurance

4.1.Special Scenario Challenge: Drill slipping on curved surfaces like steel pipes, initial positioning error >1mm.

4.2.Engineering Solutions:

• Cross Laser Positioning Device: Integrated laser projector on magnetic drill projects crosshair on curved surface with ±0.1mm accuracy.
• Curved Surface Adaptive Fixture: V-groove clamp with hydraulic locking (clamping force ≥5kN) ensures drill axis parallel to surface normal.
• Stepwise Starting Drill Method: Pre-punch 3mm pilot hole on curved surface → Ø10mm pilot expansion → target diameter annular cutter. This three-step method achieves verticality of Ø50mm holes at 0.05mm/m.

5.Combating Work Hardening

5.1.Optimization:

Drill Point Angle Adjustment: Increase drill point angle from standard 118° to 130°-135° to enhance cutting edge strength and extend tool life.

Chip-Breaking Groove for Large Diameter Drills: Recommended for drills >8mm diameter to improve chip evacuation.

6.Stainless Steel Drilling Parameter Configuration and Cooling Fluid Science

6.1 Golden Matrix of Cutting Parameters

Dynamic adjustment of parameters according to stainless steel thickness and hole diameter is the key to success:

Data compiled from austenitic stainless steel machining experiments.

Note: Feed rate < 0.08 mm/rev aggravates work hardening; > 0.25 mm/rev causes insert chipping. Strict matching of speed and feed ratio is necessary.

6.2 Coolant Selection and Usage Guidelines

6.2.1.Preferred Formulations:

• Thin Plates: Water-soluble emulsion (oil:water = 1:5) with 5% sulfurized extreme pressure additives.
• Thick Plates: High-viscosity cutting oil (ISO VG68) with chlorine additives to enhance lubrication.

6.2.2.Application Specifications:

• Internal Cooling Priority: Coolant delivered through drill rod center hole to the drill tip, flow rate ≥ 15 L/min.
• External Cooling Assistance: Nozzles spray coolant onto chip flutes at a 30° inclination.
• Temperature Monitoring: Replace coolant or adjust formulation when cutting zone temperature exceeds 120°C.

6.3 Six-Step Operation Process

• Workpiece clamping → Hydraulic fixture locking
• Center positioning → Laser cross calibration
• Drill assembly → Check insert tightening torque
• Parameter setting → Configure according to thickness-hole diameter matrix
• Coolant activation → Pre-inject coolant for 30 seconds
• Stepwise drilling → Retract every 5mm to clear chips and clean flutes

7. Selection Recommendations and Scenario Adaptation

7.1 Drill Bit Selection

7.1.1.Material Options

• Economical Type: Cobalt High-Speed Steel (M35)
  Applicable scenarios: 304 stainless steel thin plates <5mm thick, hole diameter ≤ 20mm, non-continuous operation such as maintenance or small-batch production.
  Advantages: Cost reduced by 40%, regrindable and reusable, suitable for budget-limited applications.
• High-Performance Solution: Coated Cemented Carbide + TiAlN Coating
  Applicable to: Continuous machining of 316L stainless steel thicker than 8mm (e.g., shipbuilding, chemical equipment).
  Hardness up to HRA 90, wear resistance improved 3 times, tool life > 2000 holes, TiAlN coating friction coefficient 0.3, reduces built-up edge by 80%, solves adhesion issues with 316L stainless steel.
• Special Reinforced Solution (Extreme Conditions): Tungsten Carbide substrate + Nanotube coating
  Nanoparticle reinforcement improves bending strength, heat resistance up to 1200°C, suitable for deep hole drilling (>25mm) or stainless steel with impurities.

7.1.2.Shank Compatibility

1.Domestic Magnetic Drills: Right-angle shank.

2.Imported Magnetic Drills (FEIN, Metabo): Universal shank, quick-change system supported, runout tolerance ≤ 0.01mm.

3.Japanese Magnetic Drills (Nitto): Universal shank only, right-angle shanks not compatible; require dedicated quick-change interface.

4.Machining Centers / Drilling Machines: HSK63 hydraulic tool holder (runout ≤ 0.01mm).

5.Handheld Drills / Portable Equipment: Four-hole quick-change shank with self-locking steel balls.

6.Special Adaptation: Conventional drill presses require Morse taper adapters (MT2/MT4) or BT40 adapters for compatibility with annular cutters.

7.2 Typical Scenario Solutions

7.2.1.Steel Structure Thin Plate Connection Holes

• Pain Point: 3mm thick 304 stainless steel thin plates prone to deformation; roundness deviation > 0.2mm.
• Solution:Drill bit: HSS right-angle shank (cutting depth 35mm) + magnetic drill with adsorption force > 23kN.

Parameters: Speed 450 rpm, feed 0.08 mm/rev, coolant: oil-water emulsion.

7.2.2.Shipbuilding Thick Plate Deep Hole Machining

• Pain Point: 30mm thick 316L steel plates, traditional drill takes 20 minutes per hole.
• Solution:

Drill bit: TiAlN coated carbide drill (cutting depth 100mm) + high-pressure cutting oil (ISO VG68).

Parameters: Speed 150 rpm, feed 0.20 mm/rev, stepwise chip evacuation.

7.2.3.Rail High Hardness Surface Hole Drilling

• Pain Point: Surface hardness HRC 45–50, prone to edge chipping.
• Solution:

Drill bit: Tungsten carbide four-hole shank drill + internal cooling channel (pressure ≥ 12 bar).

Assistance: V-type fixture clamping + laser positioning (±0.1mm accuracy).

7.2.4.Curved/Inclined Surface Positioning

• Pain Point: Slippage on curved surface causes positioning error > 1mm.
• Solution:

Three-step drilling method: Ø3mm pilot hole → Ø10mm expansion hole → target diameter drill bit.

Equipment: Magnetic drill integrated with cross laser positioning.

Ⅷ.Technical Value and Economic Benefits of Steel Plate Drilling

The core challenge of stainless steel drilling lies in the conflict between the material’s properties and traditional tooling. The annular cutter achieves a fundamental breakthrough through three major innovations:

• Annular cutting revolution: removes only 12% of the material instead of full cross-section cutting.
• Multi-edge mechanical load distribution: reduces load per cutting edge by 65%.
• Dynamic cooling design: lowers cutting temperature by more than 300°C.

In practical industrial validations, annular cutters deliver significant benefits:

• Efficiency: Single hole drilling time is reduced to 1/10 of that with twist drills, increasing daily output by 400%.
• Cost: Insert life exceeds 2000 holes, reducing overall machining cost by 60%.
• Quality: Hole diameter tolerance consistently meets IT9 grade, with near-zero scrap rates.

With the popularization of magnetic drills and advancements in carbide technology, annular cutters have become the irreplaceable solution for stainless steel processing. With correct selection and standardized operation, even extreme conditions such as deep holes, thin walls, and curved surfaces can achieve highly efficient and precise machining.

It is recommended that enterprises build a drilling parameter database based on their product structure to continuously optimize the entire tool lifecycle management.