Теплопроводность: определение, формула и справочник по материалам

Choosing an engineering material is rarely just a question of strength or hardness. If a component generates heat, transfers heat, experiences repeated thermal cycling, or must maintain tight dimensional accuracy as temperature changes, thermal conductivity can become one of the most important material properties to evaluate.

Thermal conductivity describes how readily heat can travel through a material. It influences the performance of heat sinks, cooling plates, electronic housings, battery components, heat exchangers, molds, motor housings, aerospace hardware, and many other precision parts. It can also affect how heat behaves while the material itself is being machined.

This guide explains what thermal conductivity means, how it works, its formula and units, the factors that influence it, how common engineering materials compare, and what the property means when selecting a material for CNC machining.

What Is Thermal Conductivity?

Thermal conductivity is a material’s ability to transfer heat from a region of higher temperature to a region of lower temperature.

When two areas of the same material are at different temperatures, thermal energy naturally flows toward the colder area. Thermal conductivity indicates how easily that transfer occurs.

• High thermal conductivity means heat moves through the material relatively easily.
• Низкая теплопроводность means the material slows the movement of heat.

Copper and aluminum are examples of metals with relatively high thermal conductivity. This is one reason they are frequently used for heat sinks, heat spreaders, cooling plates, and heat exchangers.

Many polymers and insulating materials have much lower thermal conductivity. In those applications, slowing heat transfer can actually be the desired function.

Therefore, high thermal conductivity is not automatically better than low thermal conductivity. The correct material depends on what the component is supposed to do.

How Does Thermal Conductivity Work?

Heat transfer in solids occurs because energy is transferred through the material at the atomic and microscopic level.

When one section of a solid is heated, atoms in that area gain energy and vibrate more intensely. These vibrations interact with neighboring atoms and transfer energy toward cooler regions.

In metals, heat transfer involves both lattice vibrations and mobile electrons. The presence of free electrons helps explain why many metals are much better thermal conductors than typical plastics.

In polymers, ceramics, and other non-metallic materials, heat transport depends more heavily on molecular and lattice interactions. Their internal structures can make energy transfer considerably less efficient.

The precise mechanism varies with material composition, crystal structure, temperature, and other conditions, which is why thermal conductivity should always be treated as a material-specific property rather than a universal constant.

Why Is Thermal Conductivity Important?

Thermal conductivity tells engineers how effectively a material can either distribute heat or limit its movement.

Рассеивание тепла

Components that must remove heat generally benefit from relatively high thermal conductivity. Typical applications include:

• Heat sinks
• Liquid cooling plates
• Электронные корпуса
• Battery cooling components
• Motor housings
• Теплообменники
• Thermal spreaders
• Mold inserts

A thermally conductive material can distribute localized heat across a larger area, reducing hot spots and making cooling systems more effective.

Thermal Insulation

Other applications require the opposite behavior. A component may need to prevent heat from reaching another part of an assembly.

Low-conductivity materials can therefore be useful for:

• Thermal barriers
• Electrical equipment insulation
• Furnace insulation
• Protective structures
• Temperature-sensitive assemblies

Material selection should consequently begin by determining whether the design must conduct heat or resist heat transfer.

What Is the Thermal Conductivity Formula?

Heat conduction is commonly described using Fourier’s law. For one-dimensional heat flow:

q = -kA(dT/dx)

Where:

• q = rate of heat transfer
• k = thermal conductivity
• A = cross-sectional area through which heat flows
• dT/dx = temperature gradient through the material

The negative sign indicates that heat travels in the direction of decreasing temperature.

For a flat section with constant thermal conductivity and steady-state heat flow, the relationship can be simplified to:

Q̇ = kA(T₁ – T₂) / L

Where:

• Q̇ = heat-transfer rate
• T₁ = temperature on the hot side
• T₂ = temperature on the cold side
• L = material thickness or heat-flow distance

This equation demonstrates an important engineering relationship. Heat transfer increases when thermal conductivity, temperature difference, or heat-transfer area increases. Increasing the distance that heat must travel reduces the heat-transfer rate.

How Is Thermal Conductivity Determined?

Engineers normally do not determine a material’s thermal conductivity from a simple theoretical calculation. It is generally measured experimentally under controlled conditions.

Material suppliers and engineering databases therefore provide thermal conductivity values for particular grades and temperatures.

Fourier’s law becomes especially useful after the thermal conductivity is known, because engineers can then estimate heat flow through a component.

This distinction is important. A value calculated for one operating condition should not automatically be treated as the conductivity of the material under every possible condition.

What Is the Unit of Thermal Conductivity?

The SI unit of thermal conductivity is:

W/(м·К)

Where:

• W = watts
• m = meters
• K = kelvin

The imperial unit may also be expressed as:

BTU/(hr·ft·°F)

A higher W/(m·K) value generally indicates that heat can pass through the material more readily.

Thermal conductivity is most commonly represented by the symbol k, although engineering literature may also use κ или λ.

What Factors Affect Thermal Conductivity?

Thermal conductivity is not necessarily a single fixed value under every condition. Several factors can change how effectively a material transfers heat.

1. Temperature

Thermal conductivity can change considerably with temperature.

For many metals, thermal conductivity may decrease as temperature rises because increased lattice vibration increases scattering of heat-carrying electrons. Other materials can behave differently, and some non-metals may show increasing or decreasing conductivity depending on their structure and temperature range.

This is why material data should always be checked at a temperature relevant to the actual application.

2. Material Composition

Pure metals and their alloys can have very different thermal conductivity values.

Adding alloying elements may improve strength, corrosion resistance, hardness, or heat-treatment response while reducing conductivity. This creates an important engineering tradeoff.

For example, a designer may prefer a high-purity copper grade when maximum thermal transfer is important, but choose an aluminum alloy when lower weight, strength, machinability, and thermal performance need to be balanced.

3. Density

The spacing and concentration of atoms or molecules influence how energy moves through a material. Dense, continuous structures can often transfer thermal energy more effectively than highly porous structures.

Density alone, however, should not be used to predict conductivity because composition and structure can have an equally important effect.

4. Pressure

Pressure can alter density, molecular spacing, and even the phase or structure of certain materials. Under extreme conditions these changes may modify thermal conductivity.

Pressure is generally less important for ordinary CNC components than temperature and material composition, but it becomes relevant in specialized thermal and high-pressure applications.

5. Crystal and Microstructure

Grain boundaries, crystal orientation, phases, and microstructural features can interfere with the movement of electrons and lattice vibrations.

Consequently, processing history and heat treatment may influence thermal behavior even when the nominal alloy designation remains unchanged.

6. Porosity

Voids and pores commonly lower effective thermal conductivity.

This occurs because gases trapped inside pores generally conduct heat much less efficiently than the surrounding solid material.

Porosity is one reason foams and many insulation materials can have extremely low thermal conductivity.

7. Impurities

Impurities can disrupt regular crystal structures and interfere with mechanisms that transport heat.

Material purity can therefore be particularly important in applications requiring very high thermal or electrical conductivity.

Thermal Conductivity of Common Engineering Materials

The following values are representative engineering values intended for comparison rather than design certification. Actual conductivity varies with exact grade, temperature, heat treatment, material condition, direction, and testing method.

The difference between metals and engineering plastics can span several orders of magnitude. However, even materials within the same family can vary substantially.

For example, different aluminum alloys do not all have the same thermal conductivity. Likewise, stainless steel families differ from one another according to their alloy content and microstructure.

Always confirm the exact grade rather than relying on a generic value for “aluminum,” “steel,” or “plastic.”

What Does High Thermal Conductivity Mean?

High thermal conductivity means heat can spread relatively quickly through a material.

This characteristic is desirable when the design must remove heat from a hot area or distribute temperature more evenly.

Common applications include:

• Heat sinks
• Теплообменники
• Electronic enclosures
• Cold plates
• Battery thermal-management components
• Thermal spreaders

However, conductivity should never be considered alone.

Copper offers excellent heat transfer but is much denser than aluminum. Aluminum may therefore provide a better balance where weight is critical. Stainless steel conducts heat much less efficiently but can offer superior corrosion resistance in aggressive environments.

The best engineering material is the one that satisfies the complete set of requirements, not simply the one with the highest thermal conductivity.

What Does Low Thermal Conductivity Mean?

Low thermal conductivity means heat travels through the material relatively slowly.

This can be beneficial when a component must isolate one area of an assembly from another or prevent unwanted heat transfer.

Applications can include:

• Thermal barriers
• Электроизоляция
• Protective housings
• Furnace insulation
• Components surrounding heat-sensitive electronics

Low conductivity is therefore not a material defect. In many products, it is a deliberately selected functional property.

What Material Has the Highest Thermal Conductivity?

Diamond is well known for exceptionally high thermal conductivity, and advanced carbon materials such as graphene can also exhibit extraordinary thermal transport under specific conditions.

That does not mean they are automatically the best materials for a machined thermal component.

Engineering design also requires consideration of:

• Manufacturability
• Raw material availability
• Геометрия
• Mechanical strength
• Joining methods
• Стоимость
• Вес
• Surface requirements

For conventional CNC-machined thermal components, copper and aluminum are therefore often much more practical choices.

Thermal Conductivity vs. Thermal Resistivity

Thermal conductivity and thermal resistivity describe opposite aspects of heat transfer.

Теплопроводность indicates how easily heat passes through a material.

Thermal resistivity indicates how strongly the material resists conductive heat transfer.

Therefore:

• Higher thermal conductivity corresponds to lower thermal resistivity.
• Lower thermal conductivity corresponds to higher thermal resistivity.

Both are properties of the material itself.

Thermal Conductivity vs. Thermal Resistance

Thermal conductivity should not be confused with thermal resistance.

Thermal conductivity is primarily an intrinsic property of a material, while the thermal resistance of a component also depends on its geometry.

For simple one-dimensional conduction:

R = L / (kA)

This means thermal resistance depends on:

• Material conductivity
• Part thickness
• Heat-transfer area

Two parts made from exactly the same material can therefore have different thermal resistance if their geometry is different.

This distinction matters in real component design. Selecting a conductive material cannot compensate for every poor thermal geometry, just as changing thickness can substantially affect thermal performance without changing the material.

Why Does Thermal Conductivity Matter in CNC Machining?

Thermal conductivity does not only affect the finished component. It can also influence what happens while the material is being cut.

Cutting Heat

CNC milling and turning generate heat through plastic deformation of the material and friction between the workpiece, chip, and cutting tool.

The workpiece material influences where this heat goes.

Materials capable of conducting heat effectively can distribute a larger portion of the thermal energy through the workpiece and chip. Materials with low conductivity can allow a greater concentration of heat to remain close to the cutting zone.

Срок службы инструмента

High temperatures at the cutting edge can accelerate several tool-wear mechanisms.

This is particularly relevant when machining materials that combine low thermal conductivity with high strength or difficult chip behavior.

Titanium alloys are a common example. Their thermal behavior is one of several reasons titanium machining requires careful control of cutting speed, tool engagement, coolant delivery, tooling, and toolpath strategy.

However, thermal conductivity alone does not determine machinability. Hardness, tensile strength, ductility, work hardening, abrasiveness, microstructure, tool geometry, and cutting parameters also contribute.

Thermal Expansion and Dimensional Accuracy

Thermal conductivity and thermal expansion are different material properties, but they interact during precision manufacturing.

If machining generates localized heating, the workpiece may temporarily change dimensions. Measurements made while the component is significantly warmer than the inspection environment may therefore differ after the part returns to a stable temperature.

For tight-tolerance components, manufacturers may need to manage:

• Выделение тепла
• Cutting parameters
• Coolant application
• Machining sequence
• Part stabilization
• Inspection temperature

This becomes particularly important for thin walls, long features, precision fits, and components with strict geometric tolerances.

Поверхностная отделка

Excessive cutting-zone temperatures can also accelerate tool wear or encourage material adhesion to the cutting edge.

As the condition of the tool changes, surface finish and dimensional consistency can deteriorate.

Thermal management during machining is therefore part of maintaining repeatable part quality.

Thermal Conductivity of Common CNC Machining Materials

Медь

Copper is one of the most thermally conductive metals commonly available for conventional manufacturing.

Copper alloys are used for heat exchangers, busbars, electrical contacts, cooling components, and other parts where rapid heat or electrical transfer is important.

Pure and high-conductivity copper grades generally provide better thermal performance than more heavily alloyed copper materials, although machinability and mechanical properties may differ.

Алюминий

Aluminum combines relatively high thermal conductivity with low density and generally good CNC machinability.

This balance makes aluminum particularly useful for:

• Heat sinks
• Электронные корпуса
• Cold plates
• Optical equipment
• Аэрокосмические конструкции
• Battery components

However, the exact conductivity can vary considerably between alloy series and tempers. A thermal design should therefore specify the actual aluminum grade rather than assume every aluminum alloy performs like pure aluminum.

Латунь

Brass generally offers lower thermal conductivity than high-purity copper but often provides excellent machinability, good corrosion resistance, and useful mechanical properties.

It is widely used in precision turned parts, fittings, valves, connectors, and fluid-handling components.

Нержавеющая сталь

Austenitic stainless steels have substantially lower thermal conductivity than copper and many aluminum alloys.

Nevertheless, stainless steel may still be the better design choice when corrosion resistance, strength, hygiene, temperature resistance, or chemical compatibility is more important than maximum heat transfer.

This illustrates why material selection cannot be based on a single property.

Титан

Titanium alloys such as Ti-6Al-4V have relatively low thermal conductivity compared with aluminum and copper.

During machining, heat can remain concentrated close to the cutting interface. Combined with titanium’s other machining characteristics, this makes cutting strategy and thermal control particularly important.

At the same time, titanium provides excellent strength-to-weight performance and corrosion resistance, making it indispensable in aerospace, medical, chemical, and other demanding applications.

Инженерные пластмассы

Most unfilled engineering plastics have much lower thermal conductivity than metals.

Materials such as PEEK, POM, nylon, and PTFE may therefore provide useful thermal isolation in addition to properties such as low weight, chemical resistance, electrical insulation, or low friction.

Filled polymers can behave very differently. Carbon, graphite, metal, or ceramic fillers may significantly increase thermal conductivity, so the exact material grade must be confirmed.

How to Choose a Material Based on Thermal Conductivity

Thermal conductivity should be treated as one part of a broader material-selection process.

1. Define the Thermal Function

First determine whether the component is intended to conduct, spread, retain, or block heat.

2. Define the Operating Temperature

Use conductivity values that correspond as closely as possible to the expected operating temperature. Room-temperature data may not accurately represent performance at several hundred degrees Celsius.

3. Check Mechanical Requirements

Compare conductivity with:

• Yield and tensile strength
• Твердость
• Устойчивость к усталости
• Износостойкость
• Impact performance

4. Consider Weight

Copper can provide superior thermal conductivity, but aluminum may be more attractive where component mass must be minimized.

5. Evaluate Corrosion Resistance

A highly conductive material is of little benefit if it cannot survive moisture, chemicals, saltwater, coolant, or another service environment.

6. Consider Machinability

The thermal properties that make a material perform well in service do not necessarily make it easy to machine.

Tool wear, chip control, achievable tolerances, wall thickness, surface finish, and production volume should also be considered.

7. Evaluate Total Cost

The lowest raw material price does not always produce the lowest finished-part cost.

Material utilization, machining time, tool consumption, finishing, scrap risk, inspection, and part life all contribute to total manufacturing cost.

A practical decision therefore balances thermal performance, mechanical performance, manufacturability, and cost.

Limitations of Thermal Conductivity as a Design Parameter

Thermal conductivity is extremely useful, but it does not describe the complete thermal behavior of a component.

Conductivity Changes With Temperature

A material’s thermal conductivity may change as operating temperature changes. Comparing two materials using data measured at different temperatures can therefore produce misleading conclusions.

Thermal Conductivity Describes Conduction

Real systems can transfer heat by:

• Conduction
• Convection
• Radiation

Thermal conductivity primarily concerns conduction through the material.

The performance of an actual component may additionally depend on airflow, coolant flow, surface emissivity, contact resistance, interfaces, coatings, fasteners, thermal compounds, and assembly conditions.

Good thermal design therefore considers the entire heat-transfer path rather than just the conductivity value listed on a material datasheet.

Frequently Asked Questions About Thermal Conductivity

Is higher thermal conductivity always better?

No. High thermal conductivity is beneficial when heat must be transferred or dissipated. Low thermal conductivity is beneficial when heat must be isolated or retained.

What is a good thermal conductor?

Copper and aluminum are common engineering metals with relatively high thermal conductivity and are frequently used for heat-transfer components.

Is stainless steel a good thermal conductor?

Compared with copper and aluminum, common austenitic stainless steels have relatively low thermal conductivity. Stainless steel is usually selected for other benefits such as corrosion resistance, mechanical performance, hygiene, or durability.

Does thermal conductivity change with temperature?

Yes. Thermal conductivity is temperature dependent, and the direction and magnitude of the change depend on the material.

What is the difference between thermal conductivity and heat capacity?

Thermal conductivity describes how readily heat moves through a material. Heat capacity describes how much thermal energy is required to change the material’s temperature. A material can have high heat capacity without having high thermal conductivity, and vice versa.

Does thermal conductivity affect CNC machining?

Yes. It affects how heat generated during cutting is distributed between the cutting zone, workpiece, chip, and surrounding material. However, machinability is also controlled by many mechanical and metallurgical properties.

Does high thermal conductivity mean low thermal resistance?

For components with the same geometry, increasing thermal conductivity reduces conductive thermal resistance. However, thermal resistance also depends on thickness and heat-transfer area.

Which CNC material is best for heat dissipation?

There is no universal answer. Copper can provide very high thermal conductivity, while aluminum frequently provides a better combination of conductivity, low weight, machinability, availability, and cost. The final selection should also consider strength, corrosion resistance, geometry, operating temperature, and manufacturing requirements.

Заключение

Thermal conductivity measures how readily heat travels through a material, but its engineering importance extends far beyond a single number on a datasheet.

Material grade, composition, temperature, structure, porosity, geometry, and operating conditions all influence the final thermal performance of a component. For CNC-machined parts, thermal properties can also influence cutting-zone temperatures, tool life, dimensional stability, and manufacturing strategy.

A successful material choice therefore balances thermal conductivity with strength, corrosion resistance, weight, machinability, dimensional requirements, and total cost.

For components that require controlled heat dissipation, thermal isolation, tight tolerances, or demanding material performance, Tuofa CNC Германия can evaluate both material properties and CNC manufacturability before production. Matching thermal requirements with an appropriate alloy, machining strategy, and part geometry can help reduce manufacturing risk while improving finished-part performance.