Shenzhen Wuge Industrial Co., Ltd

Nickel titanium alloy wire (memory alloy wire) is widely used in medical, aerospace, electronics and other fields due to its unique shape memory effect and superelasticity. Bending process is one of the key technologies for its forming, which requires precise control based on material characteristics and process parameters. The following provides a detailed introduction from the aspects of process characteristics, equipment and tools, operating procedures, and application cases:

1、 Material characteristics of nickel titanium alloy wire

1. Shape memory effect: After solidification at high temperature (austenitic phase), deformation at low temperature (martensitic phase) can restore the original shape after heating.   

2. Superelasticity: In the austenitic state at room temperature, it can withstand significant deformation without permanent damage.   

3. Processing difficulties:

High hardness and strong toughness, conventional bending is prone to rebound or fracture.   

Sensitive to temperature, it is necessary to control the temperature rise during the processing.   

2、 Classification and Equipment of Bending Process

According to the processing temperature, nickel titanium alloy wire bending can be divided into two categories: cold bending and hot bending, with significant differences in corresponding equipment and processes:

1. Cold bending process

Applicable scenarios:

Small scale processing or simple shape forming at room temperature (such as springs, hook shaped structures).   

By utilizing the superelasticity of materials, the deformation is usually less than their elastic limit (about 8% strain).   

Equipment and tools:

Manual bending tools: such as bending pliers, customized molds (requiring wear-resistant materials such as hardened steel).   

CNC bending machine: suitable for complex curves or mass production, controlling the bending angle and path through programming.   

Operation points:

1. Clean the surface of the wire to avoid oil stains or impurities affecting the forming accuracy.   

2. Apply pressure slowly to avoid sharp bends that may cause internal stress concentration.   

3. For multi-stage bending, it needs to be carried out step by step, and the rebound amount should be checked after each step (the rebound rate of nickel titanium wire can reach 5% and 15%).   

4. If necessary, pre deformation treatment should be adopted: first slightly stretch the wire, and then bend it to reduce rebound.   

limitations:

Complex shapes are difficult to form in one go and require multiple adjustments.   

Large angle bending (such as>90 °) is prone to plastic deformation or fracture.   

2. Hot bending process

Applicable scenarios:

High precision complex shapes (such as the three-dimensional structure of medical stents) or scenes that require shape memory effect shaping.   

The plasticity of materials is improved at high temperatures, which can achieve large deformations (>10% strain).   

Equipment and tools:

Heating device: such as oven, hot air gun (temperature control accuracy ± 5 ℃), commonly used temperature range: 200, 500 ℃ (needs to be adjusted according to the alloy composition, nickel titanium alloy phase transition temperature is usually 60, 100 ℃, but the heat treatment temperature needs to be higher than the phase transition point).   

Customized mold: Made of high-temperature resistant materials (such as stainless steel or ceramics), the target shape needs to be designed in advance.   

Operation process:

1. Preheat the wire: Heat the nickel titanium wire evenly to the set temperature (such as 300 ℃), hold for 510 minutes, and homogenize the internal structure.   

2. Mold bending: Quickly place the hot wire into the mold, apply pressure to fix the shape, and hold for 13 minutes (to avoid overheating causing coarse grains).   

3. Cooling and shaping: air cooling or water cooling (depending on subsequent performance requirements, water cooling can retain more martensitic phase).   

4. Stress relief annealing (optional): If internal stress needs to be relieved, it can be annealed at 150200 ℃ for 30 minutes.   

Key advantages:

High molding accuracy and controllable rebound (by adjusting temperature and cooling rate).   

It can achieve complex three-dimensional shapes such as spiral and wavy shapes.   

3、 Common problems and solutions

1. Fracture at the bend

Reason: The bending radius is too small and the cold processing stress is concentrated.   

Solution: Increase the bending radius and preheat or anneal before hot bending.   

2. Rebound exceeds the tolerance

Reason: Insufficient consideration of material hyperelasticity or inadequate temperature control.   

Solution: Increase the bending angle during cold bending (e.g. target 90 °, bend to 100 ° first); Extend the holding time during hot bending.   

3. Surface damage

Reason: The mold is rough or the pressure is uneven.   

Solution: Polish the surface of the mold (roughness Ra ≤ 0.8 μ m) and use lubricant (such as graphite powder).   

4、 Application Cases

1. Medical field:

Vascular stent: a complex mesh structure formed by hot bending, which expands in vivo using shape memory effect.   

2. In the field of electronics:

Connector spring: Cold bent into high-precision elastic components, utilizing super elasticity to maintain contact pressure.   

3. Aerospace:

Expandable structural components: After hot bending and shaping, the folding and unfolding function is achieved through temperature triggered memory effect.   

The bending process of nickel titanium alloy wire needs to combine material characteristics (superelasticity, memory effect) with the target shape, select cold/hot processes, and accurately control parameters. Cold bending is suitable for simple shapes and small batch production, while hot bending is used for complex structures and high-precision requirements. By optimizing mold design, temperature control, and pressure parameters, high-quality molding can be achieved to meet the application needs of different fields.