Machinability of copper and its application in modern industry

As one of the earliest metals used by humans, copper occupies an important position in the industrial field due to its excellent electrical conductivity, thermal conductivity and ductility. However, pure copper has limitations in strength, hardness and corrosion resistance, and it is difficult to meet the complex working conditions of modern industry.

By forming alloys with elements such as zinc, tin, beryllium and aluminum, copper has derived a series of materials such as brass, bronze and beryllium copper, which not only retain the basic advantages of copper, but also have diversified processing properties, becoming a key material in the fields of electronics, automobiles, aerospace and so on. This paper will analyze the machinability of copper, its processing technology and its application in modern industry.

1. Analysis of the machinability of copper

The following will introduce several common copper alloys and their characteristics to verify the machinability of copper.

(1) Brass

1) Composition and classification:

With zinc as the main alloying element, the zinc content is 5% - 45%, and it is divided into ordinary brass (Cu - Zn) and special brass (adding lead, tin, aluminum and other elements).

2) Machinability advantages

Cutting performance: Leaded brass (such as HPb59-1) has a cutting resistance of only 1/3 of pure copper, and the tool life is increased by 2-3 times. It is suitable for automatic lathe processing of precision gears, valves and other parts.

Cold processing performance: Ordinary brass (such as H68) has an elongation of up to 40%, and can be cold-rolled into 0.1mm thin-walled pipes or stretched into 0.5mm precision springs, but when the zinc content exceeds 39% (such as H59), cold processing requires annealing.

3) Typical applications:

Automobile wiper gearbox, watch escapement wheel, bathroom faucet valve core, etc.

(2) Bronze

1) Composition and classification:

Traditionally, tin is the main alloying element, and modern multi-element alloys such as aluminum bronze, silicon bronze, and lead bronze have been developed.

2) Machinability advantages

Casting performance: Tin bronze (such as ZCuSn10Pb1) has a wide crystallization range and good fluidity, which is suitable for complex thin-walled castings, with a minimum wall thickness of 2mm.

Wear resistance: Lead bronze (such as ZCuPb30) contains 30% lead, forming a "hard matrix-soft particles" wear-resistant structure, which is suitable for manufacturing high-speed heavy-duty bearings.

Machining adaptability: Aluminum bronze (such as QAl9-4) has high strength and low plasticity, and needs to be processed with carbide tools, which can meet the precision requirements of precision gears.

3) Typical applications:

Ship propellers (aluminum bronze), injection molding machine screw nuts (lead bronze), engineering machinery bearing sleeves (tin bronze).

(3) Beryllium copper

1) Composition:

Age-strengthened alloy containing 1.6%-2.0% beryllium.

2) Machinability advantages

Heat treatment strengthening: first carry out 780-810℃ solid solution treatment, low hardness can be cold processed; then undergo 300-350℃ aging treatment to improve hardness and elastic limit.

Precision processing capability: The linear expansion coefficient is close to that of silicon chips, and the cold stamping forming accuracy can reach ±0.005mm, which is suitable for manufacturing high-precision connectors.

3) Special precautions:

Beryllium is toxic, and the dust concentration needs to be controlled during processing. Heat treatment must be carried out in a closed furnace.

4) Typical applications:

Aerospace high-reliability relay springs, 5G base station high-frequency connectors, and precision injection mold cores in the mold industry.

2. Copper alloy processing technology and process

(1) Cutting processing

Brass: Use high-speed steel tools, cutting speed 100-200m/min, feed rate 0.1-0.3mm/r.

Bronze: Carbide tools (such as YG8, YT15) are required, cutting speed is 50-80m/min, and emulsion cooling is used.

Beryllium copper: High-speed steel tools can be used before aging. After cold working, the hardness increases, and cubic boron nitride tools are required, with a cutting speed of 30-50m/min.

(2) Plastic processing

Cold working: Applicable to brass and beryllium copper before aging, including cold rolling, cold drawing, cold heading, etc. The deformation of brass strip cold rolling is controlled at 20%-30% per pass, and the intermediate annealing temperature is 550-650℃.

Hot working: Aluminum bronze and high-lead bronze require hot forging or hot rolling, heating temperature is 850-950℃, and rapid cooling after hot working.

(3) Casting process

Sand casting: used for large parts of tin bronze and aluminum bronze, with a pouring temperature of 1100-1200℃ and a dimensional accuracy of CT10-CT12.

Centrifugal casting: suitable for lead bronze bearings, with a rotation speed of 500-1000r/min and an internal defect rate of less than 1%.

Die casting process: The die casting temperature of brass die castings is 750-850℃, the mold life can reach more than 50,000 times, and the surface accuracy is Ra3.2μm.

Copper castings

(4) Heat treatment and surface treatment

Annealing: Brass requires stress relief annealing at 200-300℃ after cold working; bronze requires homogenization annealing at 800-900℃ after casting.

Aging strengthening: Beryllium copper aging treatment requires strict temperature control (±5℃), and the time error does not exceed 15 minutes.

Surface treatment: Copper alloys are easily oxidized and require electroplating or passivation treatment. Brass needs to be pickled before electroplating, and beryllium copper needs to be dehydrogenated at 180℃×2h after surface treatment.

3. Demonstrating the machinability of copper - Application areas in modern industry

(1) Electronic information industry

Connectors and connectors: Brass occupies more than 70% of the ordinary connector market; beryllium copper is used for high-end connectors, such as HDMI 2.1 plug shrapnel.

Integrated circuit lead frame: Silicon bronze is suitable for manufacturing 0.2mm thick lead frame to avoid solder joint cracking.

Heat dissipation device: Brass fins are used for 5G base station radiators to increase the heat dissipation area.

(2) Automobile industry

Engine system: Lead bronze is used to manufacture connecting rod bearings, and aluminum bronze is used to manufacture exhaust valve seat rings.

Electrical system: Brass terminals are used for automobile wiring harnesses, and beryllium copper relay springs ensure circuit reliability.

Brass Terminals

Thermal management system: Brass thin-walled tubes are used for automobile water tanks to reduce thermal resistance.

(3) Aerospace and defense

Aerospace engine parts: Beryllium copper is used to make high-temperature springs, and aluminum bronze is used to make landing gear bushings.

Missile and satellite components: Silicon bronze is used to make waveguide components, and beryllium copper is used to make gyro frames for inertial navigation systems.

Marine defense equipment: Tin bronze is used to make submarine propellers.

(4) Machinery manufacturing and mold industry

Precision gears: Aluminum bronze gears are used for high-precision reducers.

Injection molds: Beryllium copper mold cores shorten the injection molding cycle and are suitable for precision plastic parts.

Measuring tools and cutting tools: Silicon bronze gauge blocks are used as length measurement reference parts.

4. Conclusion

The machinability of copper is deeply coupled with alloy composition design and processing technology. Brass, bronze, and beryllium copper meet the needs of precision machining, heavy-duty wear resistance, and high-end equipment, respectively, making them a metal material system covering multi-scale industrial components.