CNC machining titanium and its alloys:seven key problems and solutions

Introduction: Why is titanium alloy difficult to machine?

Titanium alloy its viscous lightweight, high strength, corrosion resistance, high temperature resistance, excellent performance, is widely used in aerospace, medical, marine, automotive and high-end industrial fields. However, the processing of this “perfect material” is far from ideal. Compared with aluminum and other common metals, titanium alloy has poor sex, low modulus elastic steel, high strength, easy to knife and other characteristics, to the CNC machining titanium alloy has brought great challenges.

This paper will focus on CNC machining titanium alloys in the common seven key issues for in-depth analysis, and put forward practical solution strategies to help manufacturing enterprises and machining technologists to improve the efficiency and processing quality.

1. Tool fatigue fast -- material and tool matching and optimization

(1) Problem Analysis:

The high strength and low thermal conductivity of titanium alloys cause the temperature in the cutting area to rise sharply, making it difficult for the heat to dissipate. The tool is subjected to a huge thermal load and fatigues very quickly, especially under high-speed cutting or continuous processing conditions.

(2) Solution:

Choose high-performance tool materials: It is recommended to use micro-carbide (ultra-fine grain), ceramic tools or coated CBN tools with higher hardness.

Tool coating optimization: The use of TiAlN, AlTiN or Si-based nano-coatings significantly improves heat and alkali resistance.

Tool Geometry Adjustment: Sharp cutting edge, small rake angle and negative chamfer design are adopted to reduce cutting force and prevent chipping of the tool tip.

2. In the process of CNC machining titanium metal, the chip safeguard is difficult to control--reasonable chip removal efficiency and safety

(1) Problem analysis:

Titanium alloy chips are highly tough and have a small bending radius, and are prone to producing long, ribbon-like chips that get stuck on the spindle or workpiece, which not only affects the processing quality but may also cause equipment damage or processing interruption.

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(2) Solution:

Use chipbreaking groove or chipbreaking tool, such as “W” type or “S” type chipbreaking structure;

Equip high pressure coolant system (30~70 bar or more) to flush away chips quickly;

Setting up the cycle shut-off and cut-off function in the program to ensure the machining safety and efficiency;

When machining deep holes or cavities, take the cutter in layers and steps to reduce the gathering of chips.

3. Heat gap, high cutting temperature - cooling countermeasures can not be ignored

(1) problem analysis:

The thermal conductivity of titanium is low, about 1/6 of that of carbon steel. The heat generated in the cutting zone is mainly concentrated on the rake face of the tool, causing local overheating, edge ablation, and deterioration of the workpiece surface.

(2) Solution:

Adopt high-pressure cooling system and use special titanium machining coolant;

When CNC machining titanium, it is recommended to use MQL micro combined with lubrication air cooling, which is suitable for environmentally friendly dry machining;

In the finishing stage, control the cutting speed and feed rate to reduce heat input;

Appropriate setting of intermittent machining or skip-step cutting in the machining program to control heat accumulation.

4. Easy to stick the knife - coating selection and edge shape optimization

(1) Problem analysis:

Titanium alloys tend to have chemical affinity with cutting tools under high temperature conditions, forming built-up edge (BUE) at the tool tip, which not only destroys the cutting angle, but also aggravates tool wear and leads to a decrease in surface quality.

(2) Solution:

Avoid the use of sharp, non-chamfering cutter, choose “passivation” treatment after the knife;

Coating priority to AlTiN, TiSiN, DLC, with good oxidation resistance;

CNC machining titanium, control cutting speed should not be too high, reasonable matching feed rate local overheating;

The use of specialized titanium tool brands to enhance reliability.

5. CNC machining titanium, the workpiece is easy to deformation - clamping and path critical

(1) Problem Analysis:

Titanium alloy has a low modulus of elasticity (about 1/2 of steel), and is prone to elastic deformation under the action of cutting force, which affects the machining dimensions and assembly accuracy, especially in thin-walled structures is more obvious.

(2) Solution:

Adopt a rigid fixture system (e.g., full package clamp, hydraulic clamp, vacuum adsorption);

The machining path should avoid repeated machining of an area several times to reduce uneven heat input;

Consider pre-stress mounting clamping method or low-stress roughing method for workpieces with large size or complex structure;

Programming with a smooth milling strategy cutting force to reduce the cutting force direction change.

Precision machining of titanium alloy parts - automotive field

6. CNC machining titanium parts with poor surface quality - finishing strategy should be refined

(1) problem analysis:

Common defects on the surface of titanium alloy machining are: obvious knife lines, substandard finish, local blackening or bluing, micro-cracks, etc., which directly affects the subsequent assembly and performance of the parts.

(2) Solution:

The finishing tool is designed with a large front angle and a small arc radius;

Try to adopt the machining strategy of small feed, small depth of cut and high torque;

The use of high-performance CNC machine tools to ensure machine thermal stability and vibration control;

Post-treatment can add low-pressure shot blasting, polishing or electroplating cleaning to further improve the surface.

7. High cost, low efficiency - the overall process optimization is the key

(1) problem analysis:

Titanium alloy raw materials are expensive, and the tool consumption is fast and the efficiency is low during processing, which easily leads to material waste and high processing costs, affecting the overall profit margin of the enterprise.

(2) Solution:

Adopt roughing and finishing separation strategy, roughing priority use of lower-cost tools;

Batch programming and standardized machining process to improve consistency and processing beat;

For different titanium varieties (such as TC4, TA15, etc.) set exclusive processing parameters;

Try to introduce five-axis linkage machining technology to reduce the number of clamping and improve efficiency.

8. Conclusion: CNC machining titanium challenges can be broken by technology

CNC machining titanium alloy is indeed difficult, but through the systematic combination of material awareness, tool selection, process optimization, equipment matching and experience accumulation, it is entirely possible to achieve high precision, in addition, controllability of titanium parts production.

The complexity of titanium alloy, we should be oriented from the perception of the direction of active design, from the “difficult to process” thinking to “engineering mass production” perspective. For manufacturing companies, titanium processing technology breakthroughs, not only improve the performance of parts, but also enhance the core competitiveness of the brand.