The science and technology of composite materials - Curious

In an advanced society like ours we all depend on composite materials in some aspect of our lives. Fibreglass was developed in the late s and was the first modern composite. It's still the most common, making up about 65 per cent of all the composites produced today. It's used for boat hulls, surfboards, sporting goods, swimming pool linings, building panels and car bodies. You may well be using something made of fibreglass without knowing it.

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Composites made from metal oxides can also have specific electrical properties and are used to manufacture silicon chips that can be smaller and packed more densely into a computer. This improves the computer&#;s memory capacity and speed. Oxide composites are also used to create high temperature superconducting properties that are now used in electrical cables.

Nowadays many composites are made for functions other than simply improved strength or other mechanical properties. Many composites are tailored to be good conductors or insulators of heat or to have certain magnetic properties; properties that are very specific and specialised but also very important and useful. These composites are used in a huge range of electrical devices, including transistors, solar cells, sensors, detectors, diodes and lasers as well as to make anti-corrosive and anti-static surface coatings.

As for fibreglass, it&#;s made from plastic that has been reinforced by filaments or fibres of glass. These filaments can either be bundled together, and woven into a mat, or they are sometimes cut up into short lengths which are randomly oriented in the plastic matrix.

Composites have been made from a form of carbon called graphene combined with the metal copper, producing a material 500 times stronger than copper on its own. Similarly, a composite of graphene and nickel has a strength greater than 180 times of nickel.

Another well-known composite is concrete. Here aggregate (small stones or gravel) is bound together by cement. Concrete has good strength under compression, and it can be made stronger under tension by adding metal rods, wires, mesh or cables to the composite (so creating reinforced concrete).

Humans have been using composite materials for thousands of years. Take mud bricks for example. If you try to bend a cake of dried mud, it will break easily but it is strong if you try to squash, or compress it. A piece of straw, on the other hand, has a lot of strength when you try to stretch it but almost none when you crumple it up. When you combine mud and straw in a block, the properties of the two materials are also combined and you get a brick that is strong against both squeezing and tearing or bending. Put more technically, it has both good compressive strength and good tensile strength .

Composites exist in nature. A piece of wood is a composite, with long fibres of cellulose (a very complex form of starch) held together by a much weaker substance called lignin. Cellulose is also found in cotton and linen, but it is the binding power of the lignin that makes a piece of timber much stronger than a bundle of cotton fibres.

Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart &#; they do not dissolve or blend into each other.

Making a composite

Most composites are made up of just two materials. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). In the case of mud bricks, the two roles are taken by the mud and the straw; in concrete, by the cement and the aggregate; in a piece of wood, by the cellulose and the lignin. In fibreglass, the reinforcement is provided by fine threads or fibres of glass, often woven into a sort of cloth, and the matrix is a plastic. 

Examples of various forms of glass reinforcements to be used in the creation of fibreglass. Image source: Cjp24 / Wikimedia Commons.

The threads of glass in fibreglass are very strong under tension but they are also brittle and will snap if bent sharply. The matrix not only holds the fibres together, it also protects them from damage by sharing any stress among them. The matrix is soft enough to be shaped with tools, and can be softened by suitable solvents to allow repairs to be made. Any deformation of a sheet of fibreglass necessarily stretches some of the glass fibres, and they are able to resist this, so even a thin sheet is very strong. It is also quite light, which is an advantage in many applications. 

Over recent decades many new composites have been developed, some with very valuable properties. By carefully choosing the reinforcement, the matrix, and the manufacturing process that brings them together, engineers can tailor the properties to meet specific requirements. They can, for example, make the composite sheet very strong in one direction by aligning the fibres that way, but weaker in another direction where strength is not so important. They can also select properties such as resistance to heat, chemicals, and weathering by choosing an appropriate matrix material. 

Choosing materials for the matrix

For the matrix, many modern composites use thermosetting or thermosoftening plastics (also called resins). (The use of plastics in the matrix explains the name 'reinforced plastics' commonly given to composites). The plastics are polymers that hold the reinforcement together and help to determine the physical properties of the end product. 

Thermosetting plastics are liquid when prepared but harden and become rigid (ie, they cure) when they are heated. The setting process is irreversible, so that these materials do not become soft under high temperatures. These plastics also resist wear and attack by chemicals making them very durable, even when exposed to extreme environments. 

Thermosoftening plastics, as the name implies, are hard at low temperatures but soften when they are heated. Although they are less commonly used than thermosetting plastics they do have some advantages, such as greater fracture toughness, long shelf life of the raw material, capacity for recycling and a cleaner, safer workplace because organic solvents are not needed for the hardening process. 

Ceramics, carbon and metals are used as the matrix for some highly specialised purposes. For example, ceramics are used when the material is going to be exposed to high temperatures (such as heat exchangers) and carbon is used for products that are exposed to friction and wear (such as bearings and gears). 

An electron microscope image, in false colour, of a magnesium matrix composite reinforced with titanium aluminium carbide. Image source: ZEISS Microscopy / Flickr.

Choosing materials for the reinforcement

Although glass fibres are by far the most common reinforcement, many advanced composites now use fine fibres of pure carbon. There are two main types of carbon that can be used &#; graphite and carbon nanotubes. These are both pure carbon, but the carbon atoms are arranged in different crystal configurations. Graphite is a very soft substance (used in &#;lead&#;pencils) and is made of sheets of carbon atoms arranged in hexagons. The bonds holding the hexagons together are very strong, but the bonds holding the sheets of hexagons together are quite weak, which is what makes graphite soft. Carbon nanotubes are made by taking a single sheet of graphite (known as graphene) and rolling it into a tube. This produces an extremely strong structure. It&#;s also possible to have tubes made of multiple cylinders &#; tubes within tubes. 

Carbon fibre composites are light and much stronger than glass fibres, but are also more expensive. Of the two, graphite fibres are cheaper and easier to produce than carbon nanotubes. They are used in aircraft structures and in high performance sporting equipment like golf clubs, tennis rackets and rowing boats, and are increasingly being used instead of metals to repair or replace damaged bones. 

Even stronger (and more costly) than carbon fibres are threads of boron. Nanotubes of boron nitride have the additional advantage of being much more resistant to heat than carbon fibres. They also possess piezoelectric qualities, which means they can generate electricity when physical pressure is applied to them, such as twisting or stretching.

Polymers can also be used as the reinforcement material in composites. For example, Kevlar, originally developed to replace steel in radial tyres but best known for its use in bullet-proof vests and helmets, is a polymer fibre that is immensely strong and adds toughness to a composite. It is used as the reinforcement in composite products that require lightweight and reliable construction (eg, structural body parts of an aircraft). Even stronger than Kevlar is a substance made from a combination of graphene and carbon nanotubes.

Source: NASA Goddard / YouTube. View

Source: NASA Goddard / YouTube. View video details and transcript

Choosing the manufacturing process

Making an object from a composite material usually involves some form of mould. The reinforcing material is first placed in the mould and then semi-liquid matrix material is sprayed or pumped in to form the object. Pressure may be applied to force out any air bubbles, and the mould is then heated to make the matrix set solid. 

The moulding process is often done by hand, but automatic processing by machines is becoming more common. One of these methods is called pultrusion (a term derived from the words 'pull' and 'extrusion'). This process is ideal for manufacturing products that are straight and have a constant cross section, such as bridge beams. 

In many thin structures with complex shapes, such as curved panels, the composite structure is built up by applying sheets of woven fibre reinforcement, saturated with the plastic matrix material, over an appropriately shaped base mould. When the panel has been built to an appropriate thickness, the matrix material is then cured. 

Sandwich composites

Many new types of composites are not made by the matrix and reinforcement method but by laying down multiple layers of material. The structure of many composites (such as those used in the wing and body panels of aircraft), consists of a honeycomb of plastic sandwiched between two skins of carbon-fibre reinforced composite material.

A honeycomb composite sandwich structure from NASA. Image source: NASA / Wikimedia Commons.

These sandwich composites combine high strength, and particularly bending stiffness, with low weight. Other methods involve simply laying down several alternating layers of different substances (for example, graphene and metal) to make the composite. 

Copper, renowned for its electrical and thermal conductivity, plays a pivotal role in modern manufacturing and is a common material used in CNC machining. This guide delves deep into the world of copper machining, unraveling its intricacies, techniques, and applications. It&#;s not just about shaping a metal; it&#;s about harnessing copper&#;s unique properties to create components essential to various industries.

What is Copper Machining?

Copper machining refers to the process of cutting, shaping, or modifying copper material using various techniques to achieve desired geometries and dimensions. This process is crucial in producing highly precise and intricate copper parts used in numerous applications.

Key Aspects of Copper Machining:

• Exceptional electrical and thermal conductivity

• Ability to create complex shapes and precise dimensions

• Versatility in applications ranging from electronics to aerospace

How does Copper Machining work?

Copper machining works by removing material from a copper workpiece to achieve the desired shape and size. This can be done through various methods like milling, turning, drilling, and more, each suitable for different types of designs and requirements.

What are the Common Techniques for Copper Machining?

Copper machining involves a variety of techniques, each selected based on the project&#;s specific needs. These techniques cater to different design requirements and application areas.

CNC Milling

CNC milling, a cornerstone in copper machining, uses rotating cutting tools to carve out copper. This method&#;s precision is unmatched, making it ideal for complex parts and detailed designs.

CNC Turning

In CNC turning, the copper piece rotates against a fixed cutting tool, primarily used for crafting cylindrical components. This technique is efficient and versatile, suitable for both internal and external machining.

Drilling

Drilling creates precise round holes in copper, essential for components requiring fastening or bolting. Both drill presses and milling machines can be utilized for this purpose.

Tapping

Tapping involves cutting threads within drilled holes, facilitating the insertion of bolts or screws. This process can be manual or CNC-driven for added precision.

Grinding

Grinding achieves fine finishes and exact dimensions using an abrasive wheel. This technique is often a finishing step, refining parts machined by other methods.

Electrical Discharge Machining (EDM)

For copper parts demanding extreme precision, EDM is the go-to method. It uses electrical sparks to meticulously shape copper, ideal for complex geometries.

Water Jet Cutting

Water jet cutting employs a high-pressure water stream, sometimes mixed with abrasives, to slice through copper. It&#;s especially beneficial for cutting thick copper sheets without heat distortion.

What is the Best Tool to Machine Copper?

The choice of the right tool is crucial in copper machining. The nature of copper, known for its malleability and conductivity, demands tools that can handle its unique properties while ensuring precision and quality.

General Guidelines for Effective Tools:

• Durability: Tools made from high-grade materials like carbide or high-speed steel (HSS) to resist wear.

• Precision: Sharp, well-designed tools for intricate designs and tight tolerances.

• Compatibility: Tools that work harmoniously with CNC machines for optimal performance in copper CNC machining services.

Different Grades of Copper Used in Machining

Pure Copper

Pure copper, also known as cathode copper, offers high electrical conductivity. It&#;s typically used in electrical applications but can be challenging to machine due to its softness.

Electrolytic Copper

With high purity, electrolytic copper is preferred for electronic applications. Its electrical and thermal conductivity make it an excellent choice for heat exchangers and wiring.

Oxygen-Free Copper

Known for its superb conductivity and ductility, oxygen-free copper is ideal for high-quality audiovisual equipment and vacuum electronics. Its low oxygen content reduces the risk of hydrogen embrittlement.

Free-Machining Copper

Free-machining copper alloys, like those containing lead, improve machinability. They are frequently used in applications where ease of machining is crucial, albeit with slightly reduced conductivity.

Best Copper Grade for Machining

When it comes to machining, selecting the right copper grade is paramount. Each grade offers unique properties, influencing its suitability for specific applications. For instance, free-machining copper grades, while easier to machine, might not offer the same conductivity as pure or oxygen-free copper.

Copper with Best Mechanical Strength

Among copper grades, those alloyed with elements like tin or zinc often exhibit superior mechanical strength. These grades are typically chosen for parts that demand durability alongside conductivity.

Precision and Tolerance in Copper Machining

Achieving high precision and maintaining tight tolerances are key in copper machining. Factors affecting precision include:

• Machine calibration and stability

• Tool quality and suitability

• Material properties of the copper grade

• Operator skill and experience

Understanding these factors and controlling them is crucial for quality copper machining, especially in precision-driven industries like aerospace and electronics.

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Applications of Copper Machining

Copper machining finds its place in a myriad of industrial applications, thanks to its excellent electrical and thermal conductivity. Here are some notable applications:

• Electrical Components:

  From wiring to connectors, copper&#;s conductivity makes it indispensable.

• Heat Exchangers:

  Leveraging its thermal properties for efficient heat transfer.

• Aerospace Components:

  Where strength and conductivity are both required.

Choosing the Right Copper Alloy for Specific Applications

Selecting the right copper alloy is a critical decision in machining projects. Factors to consider include:

• Required electrical or thermal conductivity

• Mechanical strength needed

• Specific application requirements like corrosion resistance or machinability

Primary Benefits and Challenges of Machining Copper

Advantages of Copper Machining

• Superior Conductivity:

  Both electrical and thermal.

• Versatility:

  Suitable for a wide range of applications.

• Recyclability:

  Copper can be recycled without loss of properties.

Challenges in Copper Machining

• Work Hardening:

  Copper can harden during machining, affecting tool life.

• Thermal Expansion:

  Managing heat generation during machining.

What are the Factors to Consider When Machining Copper?

Choosing the Right Copper Material Grade

The grade influences machinability, strength, and conductivity.

Designing for Manufacturability

Optimizing design to leverage copper&#;s properties while ensuring efficient machining.

Setting the Correct Feed Rate

Balancing speed and precision to minimize tool wear and achieve desired finishes.

Selecting the Appropriate Tool Material

Tools that can withstand copper&#;s unique characteristics, ensuring longevity and precision.

Design Considerations for Effective Copper Machining

When designing for copper machining, consider:

• Complexity of the Part:

  Ensuring the design is feasible with available machining techniques.

• Material Properties:

  Accounting for copper&#;s physical characteristics in the design phase.

• Tolerances and Finish:

  Balancing precision requirements with copper&#;s machinability.

Key Safety Tips for Copper Machining

In copper machining, safety is paramount. Key practices include:

• Proper Ventilation:

  To manage copper particles and dust.

• Regular Tool Maintenance:

  Ensuring tools are in optimal condition.

• Adherence to Safety Protocols:

  Following guidelines for machine operation and material handling.

Common Problems and Solutions in Copper Machining

Copper machining, while offering numerous benefits, also presents its own set of challenges, such as burr formation, work hardening, and tool wear. Addressing these issues is crucial for maintaining the quality and efficiency of the machining process.

• Burr Formation:

  Often a result of improper tooling or machining parameters. Solutions include using sharp tools, optimizing feed rates, and employing proper cooling techniques.

• Work Hardening:

  Copper can harden unexpectedly during machining. Countermeasures include using lower cutting speeds and ensuring continuous, uninterrupted cuts.

• Tool Wear:

  Due to copper&#;s softness and high thermal conductivity, tools can wear quickly. Using carbide or polycrystalline diamond (PCD) tools can help increase tool life.

What Are the Costs Involved in Copper Machining?

Cost Factors in Copper CNC Machining

Costs in copper machining vary based on several factors:

• Material Grade:

  Different copper grades, like oxygen-free or electrolytic copper, have varying prices.

• Complexity of Machining:

  More intricate designs require more time and precision, increasing costs.

• Tooling and Equipment:

  Advanced tools and machines can add to the overall expense.

Costs can range from moderate for simpler tasks to significantly higher for complex or high-precision machining.

Comparing Costs of Different Copper Machining Techniques

Each machining technique comes with its own cost implications:

• CNC Milling and Turning:

  Generally more cost-effective for mass production.

• EDM and Water Jet Cutting:

  Higher costs due to the precision and equipment involved.

• Drilling and Tapping:

  Relatively lower costs, suitable for simpler operations.

How to Ensure Quality in Copper Machining Processes?

Quality in copper machining is non-negotiable. Key quality control measures include:

• Regular Inspection:

  Frequent checks during the machining process to ensure tolerances and specifications are met.

• Tool Maintenance:

  Ensuring tools are sharp and well-maintained to avoid defects.

• Process Optimization:

  Continuously refining machining parameters for optimal results.

• Integration of 3D Printing:

  Complementing traditional machining with additive manufacturing for complex designs.

The Economic Impact of Copper Machining

Copper machining holds significant economic importance. Its applications in critical industries like electronics, aerospace, and automotive underscore its economic value. The cost-effectiveness of machining copper, especially when compared to other materials, contributes to its widespread use and industrial significance.

Why is Copper Machining Important in Modern Manufacturing?

Copper machining is integral to modern manufacturing due to its:

• Versatility:

  Used in a wide range of products, from electrical components to decorative items.

• Conductivity:

  Essential in electrical and thermal applications.

• Machinability:

  Offers a balance of workability and durability, making it a preferred choice in many sectors.

Alternatives to CNC Machining for Copper

While CNC machining is prevalent, alternative methods include:

• Hand Machining:

  For simpler or one-off projects.

• Laser Cutting:

  For precise, non-contact cutting of thinner copper sheets.

• Stamping and Forming:

  Cost-effective for producing copper parts in large volumes.

Environmental and Health Considerations in Copper Machining

Copper machining, like any industrial process, poses environmental and health considerations. Proper disposal of copper chips and coolants is crucial to minimize environmental impact. Health aspects involve ensuring adequate ventilation and protective equipment to safeguard against copper dust and particles.

Conclusion

In summary, copper machining is a sophisticated and essential part of modern manufacturing. Its versatility, conductivity, and machinability make it a valuable material across various industries. Despite its challenges, advancements in machining technologies continue to enhance its applications and efficiency.

3ERP is a leading provider of copper machining services and capable of producing parts in various coatings and finishes depending on your project requirements.

We produce corrosion-resistant copper machined parts and can handle solid copper bars, copper-nickel alloys, and CNC turning or milling of copper alloy materials.

Frequently Asked Questions About Copper Machining

1. Is Copper Easy to Machine?

Copper is generally considered easy to machine, but it requires proper tooling and parameters to manage its softness and potential for work hardening.

2. How to Optimize Machining for Different Copper Alloys?

Optimizing machining for different copper alloys involves selecting the right tools, adjusting machining speeds and feeds, and considering the specific properties of each alloy, such as hardness and conductivity.

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