In high-end manufacturing, the performance and accuracy of parts directly determine product quality, and the choice of materials is the foundation of all of this. Among numerous metal materials, oxygen free copper stands out due to its ultra-high purity and excellent performance, becoming an indispensable key material in fields such as aerospace, semiconductors, and precision machinery. This article will provide an in-depth analysis of the application, processing technology, precautions, and typical processing schemes of oxygen free copper in precision parts machining.

1、 Material characteristics of oxygen free copper: performance leap brought by high purity

Oxygen free copper, its core characteristic can be seen from its name - extremely low oxygen content. According to the standard, the oxygen content of oxygen free copper does not exceed 0.003%, the total impurity content is less than 0.05%, and the purity is over 99.95%. It is precisely this high purity that endows oxygen free copper with a series of excellent properties.

In terms of mechanical properties, after special manufacturing processes such as high temperature and high pressure, oxygen free copper has excellent strength and hardness, with a tensile strength of ≥ 290MPa and an elongation of over 30%. While ensuring high strength, it also has good toughness, which can meet the needs of various high-strength parts.

Oxygen free copper performs exceptionally well in terms of conductivity and thermal conductivity. Its conductivity reaches or exceeds 100% IACS, and its thermal conductivity is as high as 398W/(m · K), which is more than 15% higher than ordinary copper. This makes oxygen free copper an ideal material for transmitting electrical and thermal energy, especially suitable for applications that require strict electrical and thermal performance.

In addition, oxygen free copper also has excellent corrosion resistance. Due to its uniform single-phase structure, it reduces impurities such as copper oxide and greatly enhances the material's ability to resist corrosion. Moreover, oxygen free copper has excellent processing performance and can be processed into various complex shaped parts through various processes such as casting, extrusion, and stretching, meeting diverse design requirements.

From a microscopic perspective, oxygen free copper forms uniform equiaxed grains after high-temperature annealing, belonging to single-phase α - Cu grains with a grain size of up to ASTM grade 5. This structure ensures the isotropy of the material. Meanwhile, the pure lattice structure allows oxygen free copper to maintain stable performance in the extreme temperature range of -270 ℃ to 400 ℃.

2、 Manufacturing process of oxygen free copper parts: precise control from raw materials to finished products

1. High purity raw materials are the foundation

To manufacture oxygen free copper parts, the first step is to strictly screen the raw materials. Usually, cathode copper with a purity of up to 99.99% is selected, and the content of harmful impurities such as arsenic (As), antimony (Sb), bismuth (Bi) is further reduced through electrolytic refining to control it below 0.001%, ensuring the high purity of oxygen free copper from the source.

In the melting process, vacuum melting technology with a vacuum degree of 1 × 10 ⁻ ³ Pa is used, combined with inert gas protection, to minimize the oxidation of copper during the melting process and ensure the quality of the final product.

2. Diversified molding processes

In plastic processing, hot extrusion molding is one of the commonly used methods. Process copper into bars or plates at a 1:20 extrusion ratio within the temperature range of 850 ℃ to 900 ℃. During this process, the grains will fibrose along the flow direction, resulting in a 20% increase in material strength. Cold drawing deep processing, on the other hand, can produce ultrafine wires with a diameter of only 0.1mm through multiple passes of drawing (with a deformation of no more than 15% per pass), and can control the surface roughness to Ra<0.2 μ m.

For some complex thin-walled parts (wall thickness ≤ 0.5mm), vacuum suction casting technology is used, which uses negative pressure to suck copper liquid into the mold and forms it at a cooling rate of 50 to 100 ℃/s. In addition, investment casting is also a commonly used process, which can produce precision castings with dimensional accuracy up to CT4 level through ceramic shells and high-temperature calcination at 1200 ℃.

3. Surface treatment to enhance performance

In order to further improve the performance and appearance of oxygen free copper parts, surface treatment is essential. Electrolytic polishing is a commonly used method, which uses a mixture of phosphoric acid and sulfuric acid electrolyte to treat the surface of the part at a temperature of 50 ℃ to 60 ℃ with a current density of 20 to 30A/dm ², achieving a mirror like effect with a surface roughness Ra<0.1 μ m. In some high-frequency electronic components, cyanide free silver plating process is used to deposit a silver layer with a thickness of 5 to 10 μ m through sulfite system, making the contact resistance less than 1m Ω.

3、 Key considerations during the processing: details determine success or failure

1. Precise control of hot working temperature and cooling

Temperature control is crucial during hot processing. If the temperature is below 700 ℃, oxygen free copper is prone to work hardening; And above 950 ℃, it will lead to coarse grains. Therefore, it is recommended to control the hot working temperature between 800 ℃ and 900 ℃. After extrusion molding, rapid water quenching treatment should be carried out with a cooling rate greater than 50 ℃/s to effectively prevent the precipitation of second phases and maintain the high conductivity of the material.

2. Strategies for Dealing with Cutting Difficulties

Due to the high plasticity of oxygen free copper, it is prone to tool sticking during cutting. To solve this problem, polycrystalline diamond (PCD) cutting tools can be used, with a rake angle set to 10 ° to 15 °, and combined with extreme pressure emulsion with a concentration of 8% to 10%.

The thermal deformation during the processing can cause fluctuations in dimensional accuracy. To address this, a stress relief annealing treatment at 180 ℃ for 2 hours can be performed after semi precision machining, and micro lubrication (MQL) technology can be used in the final processing.

In order to improve the problem of poor surface roughness caused by chip deposits, it is necessary to increase the cutting speed and control it at 200 to 300m/min, while reducing the feed rate and maintaining it at 0.05 to 0.1mm/r.

3. Strict environmental and tool requirements

Oxygen free copper processing has high environmental requirements, and the processing workshop needs to achieve ISO level 8 cleanliness to avoid dust particles contaminating the parts. In the selection of tools and lubricants, it is strictly prohibited to use lubricants containing sulfur or chlorine. It is recommended to use fully synthetic water-soluble cutting fluids with a pH value between 8.5 and 9.5.

4、 Typical application areas and processing solutions: customized processing under different needs

1. Semiconductor packaging lead frame

The semiconductor packaging lead frame requires a thickness of 0.15mm, a pin spacing of 0.2mm, and a surface roughness Ra<0.3 μ m. The specific processing plan is to use oxygen free copper strip with a hardness of 1/4H and a thickness of 0.2mm, which is formed by precision stamping (with a mold gap of 0.01mm), then subjected to electrolytic deburring treatment, and finally chemically plated with nickel and gold on the surface, with a nickel layer thickness of 5 μ m and a gold layer thickness of 0.1 μ m.

2. Aerospace heat dissipation components

Aerospace heat dissipation components usually have irregular porous structures, requiring thermal conductivity>380W/(m · K) and pressure resistance ≥ 10MPa. During processing, vacuum brazing is first used, with Ag Cu Ti alloy as the brazing material, to join complex structures at 850 ℃; Then use electrical discharge machining (EDM) to create microchannels with a diameter of 0.3mm; Finally, ultrasonic cleaning and potassium dichromate solution passivation treatment are carried out.

3. High end mechanical bearing cage

For high-end mechanical bearing cages with a diameter of 50mm, circular runout ≤ 0.02mm, and high wear resistance requirements, first prepare a φ 50mm rod (with a grain size of ASTM grade 6) through hot extrusion molding; Next, perform CNC turning with a speed set at 3000r/min and a feed rate of 0.08mm/r; Finally, surface boronizing treatment was carried out at 900 ℃ for 4 hours to increase the hardness to HV1200.

5、 Process optimization and quality control: the last line of defense to ensure product quality

To ensure the quality of oxygen free copper parts, it is necessary to establish a comprehensive testing system. Eddy current testing can screen for microcracks of ≥ 0.1mm inside materials, while X-ray diffraction is used to analyze residual stresses after processing, requiring residual stresses to be less than 50MPa.

In terms of performance verification, eddy current conductivity meter is used to test the conductivity, ensuring that the conductivity is ≥ 100% IACS; Conduct corrosion resistance testing by immersing in a 3.5% NaCl solution for 24 hours, with a required weight loss rate of less than 0.01g/m ².

With the continuous development of technology, oxygen free copper, with its unique properties, is driving precision parts processing towards higher precision and reliability. In the future, with the integration of vacuum metallurgy technology and digital processing technology, oxygen free copper is expected to play a greater role in cutting-edge fields such as quantum computing and new energy.

Article source: Internet

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