Hot Processing vs. Cold Processing: How Processes Affect Accuracy, Strength, and Cost

Manufacturing needs a balance between precision, strength and cost. All three are necessary to make a part, and all three must be balanced for a successful manufacturing process.

There are many ways to change materials, but hot working and cold working are two of the most important ones, especially for metals and alloys. These two methods are used to change the properties of the materials, but they differ in precision, strength and cost.

What is Hot working？

Hot Working: An Overview

Hot working is when materials are formed at high temperatures. These temperatures are above the recrystallization temperature of the materials. The temperature used is usually between 0.5 and 0.75 times the melting point of the material.

Metals become more ductile when heated. Heating them to higher temperatures makes them easier to deform. They won’t break or crack easily this way. Hot working also gives materials more ductility. This means materials can change shape and size a lot before breaking. So hot working is very good for making complex parts. It uses heat to shape the metal into these parts.

Common Hot Working Processes

Forging: It is a process to shape metal. It uses a hammer or press to apply compressive force. This process is usually done at higher temperatures. Forging can make strong and durable parts. Examples include auto engine parts and aerospace-related parts.

Casting: It involves smelting metals first. Then the melted metal is poured into a mold. The mold helps make the metal into the required shape. Casting is often used for complex items. Examples include engine compartments and turbine blades.

Hot Rolling: First, the metal is heated. Then it is sent through rollers. The rollers help form the metal into thin sheets or plates. These can also be made into structural shapes. Hot rolling is widely used in industries. It is used to make steel beams, pipes and plates. These products are used in construction and manufacturing.

What is Cold working？

Cold Working: An Overview

Cold working is the process of shaping metals or other materials. It is done at or near room temperature. Usually, this temperature is below the metal’s recrystallization temperature.

Cold working does not involve heating the material. So, it needs much more force to shape the metal. Compared with hot working, cold working requires far more force to deform the material.

Since there is no heat, the material’s grains stay in their original positions. This is why cold working and hot working produce different results when shaping materials.
Cold working also causes work hardening. Because of this, the material becomes stronger and harder.

Common Cold Working Processes

Cold Rolling: It is a process that makes metal thinner. The metal is passed through rollers at room temperature. Cold rolling is mainly used to make thin metal sheets or strips. It is widely applied to metal parts that need precise size and good surface quality.

Drawing: In this process, a material (such as wire or tubing) is pulled through a die. This makes the material’s diameter smaller and its length longer. People often use drawing to make items like wires, rods and tubes.

Extrusion: It involves forcing a material through a die. This creates a continuous shape, such as pipes, rods or structural profiles. Cold extrusion uses cold extrusion components. These components are used in the electronics industry or precision industry.

How hot working and cold working impact precision？

Hot Working and Its Influence on Precision

Hot working happens above the material’s recrystallization temperature. This temperature is about 50% to 75% of the material’s melting point.

The heat makes the metal more ductile. So it is easier to shape the metal. This allows big changes to the metal’s shape.

Hot working gives the material good shapeability. But it has difficulty providing accurate measurements for the material.

Cold Working and Its Influence on Precision

Cold working is different. It lets people control dimensions much better. It is also much more precise than hot working.

Cold working is done at or near room temperature. This eliminates many problems caused by high heat. These problems include uneven cooling when the material cools down, and tools wearing out because of heat.

So cold working processes usually make parts with tighter tolerance. They also create parts with smoother surface finishes. For this reason, cold working is often used when very tight dimensional control is needed.

How hot working and cold working impact strength？

Hot Working and Its Impact on Strength

Hot working processes involve materials. These materials are worked at a higher temperature. This temperature is usually above the material’s recrystallization threshold.

At high temperatures, the material becomes more ductile. So it is easier to deform the material. But the material’s strength will decrease.

When the heating process is done, the metal’s grains grow larger. As a result, the material loses strength. This makes it weaker than cold-worked metal.

Cold Working and Its Impact on Strength

Cold working is the opposite of hot working. It usually makes metal stronger. It does this through a process called strain hardening or work hardening.

Cold working is done near room temperature. So there is no recrystallization. And there is no stress relief either.

When the material deforms, dislocation lines build up inside its crystal structure. These lines make the material resist more deformation. This leads to a significant strengthening effect.

Strength data for hot and cold working support

From the learning and industrial application of hot work and cold work, we can see that they have different strengths. For example, in some material comparison research on the mechanical properties of cold-drawn steel wire and hot-rolled wire, researchers found that the tensile strength of the cold-drawn wire was approximately around 700mpa compared to 450mpa for hot rolled wire (source: Journal of Materials Engineering). The difference is big, this means that cold working makes things stronger, special strong when they are to stay strong and don’t change shape if put under lots of pressure.

And it was also found that with researching the cold rolled steel we could increase yield strength to be between 30 – 50% of the amount of hot rolled steel depending on the deformation applied to cold rolling it (source: Steel Processing Research Journal). And so they show it does really help make things stronger with cold working, especially when you want something to be strong but don’t care as much about if its stretchy.

How hot working and cold working impact cost change？

Hold Working and Its Impact on cost change

Hot working processes need more energy than cold working. This is because hot working has to heat materials to very high temperatures.

Processes like forging, casting and hot rolling involve high temperatures. These high temperatures can increase both direct and indirect costs a lot.

The main cost factor for hold working is

1. Energy Consumption

Heating materials to very high temperatures uses energy. For example, heating metals over 1000°C needs large ovens called furnaces. These furnaces need a lot of energy.

Maintaining such high temperatures also needs lots of power. This makes operating costs higher.

According to the Energy Efficiency in Manufacturing from the Industrial Research Institute, hot working needs about 30% more energy than cold working.

Higher energy use leads to higher production costs. This is especially true when energy prices change a lot or are expensive.

2. Equipment and Maintenance Costs

Equipment for hot working must handle high heat. It also needs to be strong machines.

This equipment includes furnaces, rollers and molds. They work in very hot conditions all the time. So they get damaged a lot.

More damage means more maintenance. This costs a lot of money.

For example, molds used in casting wear out quickly. They need to be updated often. Hot rolling equipment also wears out because of high temperatures and mechanical force. This leads to more maintenance and replacement costs.

3. Material Waste

Hot working almost always produces more waste than cold working.

In hot forging and casting, more material is used than needed. The excess material has to be removed. Sometimes the material has to be reworked to get the right shape.

When the material cools down, it may develop internal tension. This means more cutting or grinding is needed. This causes even more material waste.

Casting depends on quality molds and cooling effects. These factors affect the number of good products. Some castings are rejected because of porosity or shrinkage. This also increases waste.

4. Labor Costs

Hot working needs more workers. This is because of its high working temperatures and material handling needs.

Some hot working processes may be automated. But there are still tasks that need people. For example, pouring liquid metal into molds during casting, or moving pieces in forging.

These extra workers increase labor costs. Cold working is usually more automated and less dangerous. So it has lower labor costs compared to hot working.

Cold Working and Its Impact on cost change

Cold working does not cost as much energy as hot working. But it still has its own costs.

Cold working is done at or near room temperature. So it does not need much energy to heat materials to very high temperatures.

However, cold working is still quite expensive in some aspects. This is especially true for machinery and tools.

The main cost factor for cold working is

1. Equipment and Tooling Costs

Cold working needs specific machines and tools. These include drawing dies, rolls and extrusion presses.

All these machines and tools must handle great force.

Cold working usually uses less energy. But the equipment that applies the required force to materials can be expensive.

Rolls and dies for cold rolling or cold drawing need to be made of hard materials. Tungsten carbide is one such material. This helps them stay sharp and keep the exact size.

Over time, these tools need to be replaced or reconditioned. This adds more ongoing costs to cold working.

2. Material Costs and Waste

Cold working usually produces less material scrap than hot working. The reason is that materials do not need to be heated and cooled.

But cold working still involves some trimming. So some metal is lost during the process. This is especially common in cold drawing or extrusion.

For example, when metal is cold-drawn through a die, some material is lost on the edges. This lost material must be trimmed off or recycled.

The waste from cold working is not as bad as that from hot working. But it still adds up quickly. High-precision products also need extra high-quality materials, which increases costs.

3. Labor Costs

Cold working generally has more automated processes than hot working. So it can save on labor costs.

Processes like cold rolling, extrusion and drawing do not need much manual operation on machines. So the demand for skilled workers is not very high.

Even so, cold working still needs some oversight and quality control. This means there are still extra labor costs.

Workers need to make sure the material is straight. They also need to check that the material has the desired attributes, such as correct size and surface quality.

4. Processing Speed

Cold working has one advantage: it is often faster than hot working for some purposes.

Cold working does not require heating materials to high temperatures. So the total cycle time can be shorter.

This faster speed leads to higher throughput. This is especially true when producing large batches. Higher throughput reduces the per-unit cost.

Conclusion: Making the Right Choice

Choosing between hot working and cold working requires considering several factors. These factors include precision, strength, cost and production volume.

Hot working is most suitable for mass-producing complex parts. Cold working is good for making precise parts with higher strength.

In addition, technologies like AI, automation and additive manufacturing are developing. These technologies will bring greater optimization, higher efficiency and lower costs.

Manufacturers must first figure out their specific needs. Then they should choose the process that balances performance, cost and precision best.