1. What is spiral milling? Core principles and definitions disassembled
Many machining practitioners will wonder: what is the difference between helical milling and traditional drilling and milling? In fact, the essence of spiral milling is to realize the composite process of hole processing or contour processing by rotating the tool around its own axis while feeding along the spiral trajectory, and its core lies in the collaborative control of "spiral interpolation movement".
The differences are significant compared to traditional processes:
| Process type: | Cutting method | Cutting force distribution | Chip evacuation effect | Machining accuracy |
| Conventional drilling | Axial feed + drill rotation | Concentrated on the tip of the drill bit, the radial force is large | Relying on the chip removal groove, it is easy to block | Hole diameter accuracy ±0.05mm |
| Conventional milling | Radial cutting is the main focus | Unilateral force is easy to vibrate | Chips are dispersed and require high-pressure cooling | High contour accuracy but low hole processing efficiency |
| Spiral milling | Axial + radial compound cutting | Uniform dispersion reduces peak cutting force by 30%-50% | The spiral trajectory guides the orderly discharge of chips | The hole size accuracy can reach ±0.01mm |
From a technical point of view, the synergy between axial and radial cutting is key: the axial direction is responsible for the depth removal of the material, and the radial direction enables hole wall finishing by means of a small offset between the tool and the workpiece. The advantage of low cutting force machining stems from the fact that the contact area between the cutting edge and the material is always in dynamic changing, avoiding the "hard hit" of traditional drilling. In terms of chip formation and ejection mechanism, spiral chips formed by spiral trajectories are not easy to wind around the tool, especially suitable for deep hole machining - measured data from an aerospace parts factory shows that the chip clogging rate of holes with a 10:1 diameter ratio is reduced from 28% to 3% in traditional processes using spiral milling.
2. The core advantages of spiral milling: why is it the preferred choice for high-end manufacturing?
1. Four core process advantages
- Higher processing accuracy: Through the spiral interpolation movement, the roundness and cylindricity of the hole can be controlled within 0.005mm, far exceeding the 0.02mm standard of traditional drilling;
- Extended tool life: Dispersion of cutting force reduces tool wear rate by 40%-60%, taking titanium alloy machining as an example, the life of carbide spiral milling cutters can reach 3 times that of traditional drill bits;
- Wide material adaptability: especially good at difficult materials (such as titanium alloys, composite materials, superalloys), solving the problems of material hardening and tool chipping in traditional processes;
- Worry-free deep hole machining: Deep hole helical milling can easily handle holes with a depth-to-diameter ratio of more than 15:1 without the need for additional chip evacuation aids.
2. Typical application scenarios
- Aerospace parts processing: The machining of titanium alloy holes in the receiver of an aircraft engine increased the machining efficiency by 50% and the scrap rate was reduced from 8% to 1.2% after spiral milling.
- Medical device manufacturing: cobalt-chromium alloy hole machining for orthopedic implants needs to meet the requirements of high precision and surface roughness Ra≤0.8μm, and spiral milling is perfectly achieved by optimizing cutting parameters;
- New energy equipment processing: High-strength steel deep hole machining of wind power gearboxes, using the low vibration characteristics of spiral milling, avoids the occurrence of hole wall cracks.
3. Optimization of key process parameters: a guide from theory to practice
To maximize the advantages of helical milling, the following core parameters need to be precisely controlled and optimized in combination with actual scenarios:
1. Core parameter selection logic
| Parameter type | Influencing factors | Recommended range: | Optimize your strategy |
| Helical angle selection | Material hardness, hole diameter | 10°-30° | Choose a small angle (10°-15°) for hard materials, and a large angle (20°-30°) for soft materials. |
| Supply rate | Tool diameter, rotational speed | 0.1-0.3mm/r | Dynamic adjustment based on cutting force feedback to avoid vibration |
| Rotational speed | Material cutting speed, tool diameter | 5000-15000rpm | Calculated by formula n=1000vc/(πd) (vc is the cutting speed) |
| Cooling lubrication strategy | Material properties, processing depth | Oil Mist Cooling / High Pressure Cooling | Titanium alloy processing is prioritized with high-pressure cooling (pressure ≥ 10MPa) |
2. Practical optimization skills
- Tool path planning: Preferentially choose a clockwise spiral trajectory to reduce tool chatter; Deep hole machining adopts the "segmented feed + retraction chip removal" mode, with 1mm retreat for every 3-5mm machining;
- Cutting force and vibration control: Simulate cutting force distribution through CAM software to predict vibration risks; In actual processing, the combination of "low speed + high feed" is used to reduce the peak cutting force;
- Improved machining stability: increase the rigidity of the spindle (recommended spindle runout ≤ 0.003mm), optimize the clamping method of the fixture, and avoid deformation of the workpiece.
By adjusting the spiral angle from 25° to 15°, the feed rate was reduced from 0.25mm/r to 0.18mm/r, and the vibration amplitude was reduced from 0.012mm to 0.004mm, and the machining accuracy was improved by 67% by adjusting the helix angle from 25° to 15°, the feed rate was reduced from 0.25mm/r to 0.18mm/r, and high-pressure cooling was enabled.
4. Special tools and equipment: "hardware guarantee" for spiral milling
1. Key requirements for special tools
- Tool design: The special spiral milling cutter should have a spiral cutting edge, chip removal groove and center positioning tip to ensure the accuracy of the trajectory;
- Material selection: Preferential selection of cemented carbide and coating tools, the coating type is matched according to the material - TiAlN coating for processing steel parts, diamond coating for processing aluminum alloys;
- Structural parameters: The tool diameter should be 0.1-0.2mm smaller than the target aperture to ensure uniform radial cutting allowance.
2. Equipment functional requirements
- Multi-axis linkage CNC machine tools: at least have 3-axis linkage function, and 5-axis linkage is recommended for high-end applications to achieve helical milling of complex curved surfaces;
- High rigidity spindle system: spindle speed fluctuates ≤±5rpm, insufficient rigidity will lead to excessive hole roundness;
- CAM programming support: Spiral interpolation programming function is required, and it is recommended to use software such as Mastercam and UG to generate optimized tool paths.
- Dynamic milling function: Some high-end machine tools are equipped with dynamic milling modules, which can adjust cutting parameters in real time and improve processing stability.
Equipment upgrade case of a mold factory: After upgrading the traditional 3-axis machine tool to a 5-axis linkage CNC machine tool, the processing efficiency is increased by 80% with a special spiral milling cutter to process the deep holes in the mold cavity, and the surface quality does not need to be polished.
5. Yigu Technology's view
As a key process in the field of high-end manufacturing, the core value of spiral milling lies in solving the pain points of difficult materials and high-precision hole machining. As the requirements for processing quality and efficiency continue to increase in aerospace, medical device and other industries, the application scenarios of spiral milling will continue to expand. When introducing this process, enterprises should not only pay attention to the procurement of equipment and tools, but also pay attention to the optimization of process parameters and the training of operators. In the future, functions such as intelligent cutting parameter planning and real-time monitoring of tool wear combined with AI technology will become the development direction of spiral milling technology, helping enterprises further reduce production costs and enhance product competitiveness.
6. FAQ
- What diameter hole is spiral milling suitable for?
A: The general application range is φ2-φ50mm, and special customized tools can process tiny holes below φ1mm or large diameter holes above φ100mm.
- How does the machining cost of spiral milling compare to traditional drilling?
A: The initial investment in tools and equipment is high, but in the long run, the processing cost can be reduced by 20%-30% due to the longer tool life and lower scrap rate.
- How does helix milling avoid delamination in composite processing?
Answer: Choose a small helix angle (10°-15°), low feed rate, adopt a "bottom-up" cutting direction, and use a vacuum adsorption fixture to reduce workpiece deformation, which can effectively avoid delamination.
- Can a normal 3-axis machine achieve helical milling?
A: Yes, but the machine needs to support the spiral interpolation function, and the machining accuracy and efficiency are slightly lower than those of 5-axis machines, making it suitable for simple hole machining scenarios.
