Thread milling cutter: core tools and technical analysis of modern thread processing

As the core element of mechanical connection, thread is widely used in aerospace, automobile manufacturing, energy equipment and other fields. Although traditional thread processing methods (such as tapping and turning) are mature, they are gradually showing their limitations under the requirements of high precision, high efficiency and complex working conditions.

As an advanced thread processing tool, thread milling cutter has become a "changer" in modern manufacturing industry with its flexibility and high precision advantages. This article will deeply analyze the structural principle, technical characteristics and application scenarios of thread milling cutter, and provide you with a systematic technical guide.

1. Definition and core advantages of thread milling cutter

(1) Basic concept

Thread milling cutter is a precision tool based on CNC milling principle, which processes thread features on the surface of workpiece through multi-blade rotation and spiral interpolation motion. Its core principle is to use the three-axis linkage function of the machine tool (X/Y axis circular feed + Z axis linear feed) to make the tool move along the spiral trajectory and realize thread forming through successive cutting of the blade.

Compared with traditional taps and turning, thread milling cutters break through the limitation of single rotational motion and realize flexible control of thread parameters (pitch, tooth profile, and rotation direction) through CNC programming. They are particularly suitable for processing high-precision and complex structure threads. The following is a description of the advantages of thread milling cutters:

High precision: The processing accuracy can reach IT6-IT7 level, and the thread diameter error is ≤0.01mm.

Strong adaptability: It can process blind holes, deep holes, and large diameter threads (such as wind power bolts M120×6).

Efficient production: A single tool can process threads of different pitches and diameters, reducing tool change time.

Low cutting force: Layered cutting reduces load and is suitable for thin-walled parts and difficult-to-process materials (such as titanium alloys).

(2) Comparison with taps and turning

Indicator	Thread Milling Cutter	Tap	Thread Turning Tool
Machining Accuracy	IT6-IT7	IT7-IT8	IT7-IT9
Surface Roughness	Ra0.8-1.6	Ra1.6-3.2	Ra1.6-6.3
Material Compatibility	All metals/non-metals	Mainly ductile materials	Bar stock/shaft parts
Chip Control Performance	Excellent (multi-edge chip breaking)	Prone to clogging (blind holes)	Depends on grinding quality
Tool Life	High (coating protection)	Low (single-edge stress)	Medium (single-edge wear)
Machining Efficiency	Highest (multi-edge coordinated)	Low (rotation + feed)	Medium (single-edge reciprocation)
Cost	High (equipment requirements)	Low (simple tools)	Medium (requires high-precision machine tools)

2. Structure and classification of thread milling cutters

(1) Analysis of tool structure

A typical thread milling cutter consists of the following core components:

Cutter body: Usually made of high-strength alloy steel or cemented carbide, with integrated coolant channels (internal cooling design).

Cutting edge:

Integral type: Carbide blade and cutter body are integrally formed, with strong rigidity (suitable for small diameter processing).

Invertable type: Multiple carbide blades are installed and can be replaced after wear (economical, suitable for large threads).

Chip groove: Spiral groove design (30°~45° helix angle) optimizes chip removal and cutting stability.

Coating: TiAlN (high temperature resistance), DLC (friction reduction) and other coatings increase service life by 2~3 times.

(2) Mainstream classification methods

1) Classification by processing type

Internal thread milling cutter: used for processing nuts and valve body threads, with a diameter range of Φ3~Φ200mm.

Parts processed by internal thread milling cutter

External thread milling cutter: used for processing screw and shaft external threads, and can process continuous threads up to 2 meters.

Face thread milling cutter: used for processing threads on flange end faces and conical surfaces, with the tool axis and workpiece axis at a certain angle (15°-30°), and conical thread forming is achieved through spiral interpolation, which is commonly used in the processing of oil pipeline connection parts.

2) Classification by structural design

Type	Characteristics	Typical Applications
Solid Carbide	High rigidity, suitable for small-diameter threads (Φ3–Φ20mm)	Micro threads for medical devices
Indexable Insert Type	Replaceable inserts, low cost, suitable for large pitch (Pitch＞4mm)	Wind power bolts, oil pipeline threads
Multi-Tooth Type	Multi-edge design for high efficiency, but small chip space	Mass production of standard threads (e.g., M12)
Single-Tooth Type	High flexibility, capable of machining variable pitch threads	Aerospace special-shaped threads

3) Classification by material and coating

Material Type	Hardness (HV)	Heat Resistance (℃)	Typical Application Materials	Coating Configuration	Life Ratio (vs. HSS)
High-Speed Steel (HSS)	800–900	600	Low-carbon steel, aluminum alloys	No coating or TiN	1x
Cemented Carbide (WC-Co)	1400–1800	1000–1400	Stainless steel, alloy steel	TiAlN (hardness 3000HV)	3–5x
CBN	3000–4500	1400	Hardened steel (>HRC45)	Al₂O₃ composite coating	10–15x
PCD	7000–8000	700	Non-ferrous metals, non-metallic materials	Native diamond coating	20x+

3. Core processes and technical parameters of thread milling

(1) Detailed explanation of the processing flow

Take the processing of M24×3 internal thread as an example:

Prefabricated bottom hole: drill to Φ21mm (D=24-3×1.0825≈21).

Tool path planning:

Spiral interpolation: The tool rotates around the hole center while feeding along the Z axis (one pitch rises 3mm per revolution).

Layered cutting: 3~4 radial cuts, each cutting depth is 0.5~1mm.

Cutting parameter setting:

Speed ​​(n): 1500~2000rpm (linear speed vc≈80~120m/min).

Feed speed (vf): n×feed per tooth (fz=0.05~0.1mm/z)×number of teeth.

For example: 4-tooth milling cutter, fz=0.08mm/z → vf=1500×0.08×4=480mm/min.

(2) Key technical parameters

Parameter	Formula/Recommended Value	Description
Cutting Speed (vc)	\( v_c = \frac{\pi \times D \times n}{1000} \)	\( D \) = Tool diameter (mm), unit: m/min
Feed per Tooth (fz)	0.03–0.15 mm/tooth (adjust based on material hardness)	Smaller values for harder materials, larger values for softer materials
Radial Cutting Depth (ae)	≤ 30% of tool diameter	Prevents excessive tool load and ensures stable machining
Axial Cutting Depth (ap)	Pitch × number of thread starts	For single-start threads, \( a_p = \text{pitch} \) (mm)

4. Selection and use strategy of thread milling cutter

(1) Five selection factors

1) Workpiece material:

Stainless steel: Select TiAlN coating, helix angle 35°~40° (taking into account both chip removal and strength).

Titanium alloy: Use sharp cutting edge and large chip groove design to reduce cutting heat.

2) Thread specifications:

Small pitch (Pitch＜2mm): solid carbide milling cutter.

Large pitch (Pitch＞4mm): indexable insert milling cutter.

3) Machine tool performance:

High-speed machine tool (spindle＞10000rpm): solid carbide tool is preferred.

Ordinary machine tool: indexable type is more economical.

4) Cooling method:

Internally cooled tool: suitable for deep hole processing (depth-to-diameter ratio＞3:1).

Externally cooled tools: general scenarios, low cost.

5) Processing batch:

Small batch and multiple varieties: single-tooth or double-tooth milling cutter, high flexibility.

Mass production: multi-tooth comb cutter, 50% efficiency improvement.

(2) Precautions for use

1) Clamping rigidity:

Tool holder runout must be less than 0.01mm (hydraulic tool holder or heat shrink tool holder is recommended).

2) Cutting fluid selection:

Emulsion: general processing, concentration 8%~10%.

Oil-based cutting fluid: difficult to process materials (such as high-temperature alloys), reduce tool adhesion.

3) Path optimization:

The feed adopts arc cutting (radius = 0.5×pitch) to avoid tool vibration.

When retracting, the axial lift is 0.1mm to prevent scratching the processed surface.

5. Typical application scenarios and case analysis

(1) Aerospace field: engine blade locking thread

Challenge: titanium alloy (TC4) blind hole thread, depth 50mm, precision H2 level

Solution:

Tool: Solid carbide internal cooling milling cutter (Φ8mm, 6 blades).

Parameters: n=6000rpm, vf=800mm/min, layered cutting (0.3mm per layer).

Result: Thread accuracy reaches H1 level, tool life 200 holes/blade.

(2) Energy equipment: Offshore wind power flange bolts

Challenge: M64×4 external thread, material 34CrNiMo6, length 2m, straightness ≤0.1mm/m.

Solution:

Tool: Indexable insert external thread milling cutter (diameter Φ50mm, 3 blades).

Parameters: n=400rpm, vf=300mm/min, cooling pressure 10MPa.

Result: Processing efficiency is increased by 3 times, which is better than traditional turning process.

6. Summary

As a landmark tool in the era of CNC machining, the technological evolution of thread milling cutters deeply reflects the demand for efficient, flexible and high-precision machining in the field of precision manufacturing. From the single application of early integral tools to the diversified development of modern machine-clamped and intelligent tools, thread milling cutters have become indispensable key equipment in high-end fields such as aerospace, automobile manufacturing, and electronic information.