Hot Forging

Meaning of Hot Forging:

Hot forging is one of the metal manufacturing processes to heat the metal billet above its recrystallization temperature using heat conduction heating, electromagnetic induction heating, or electric heating, and then forge so that the billet undergoes plastic deformation to make forgings with specific shapes, sizes, and mechanical properties. Hot forging is a necessary process, and hot forgings are widely used. The hot forging process can process a lot of metals and has irreplaceable advantages.

Types of Hot Forging:

If the billet temperature we use for forging is above its recrystallization temperature, We call this forging process a type of hot forging. For example: die forging is called hot die forging when a billet above its recrystallization temperature is used for die forging. 

Raw Materials Hot Forging Can Process:

We can use hot forging to process most metals, such as carbon steel, stainless steel, other alloy steels, copper alloys, and special alloys. Different hot forgings will use different blank shapes. Choosing the suitable original form from the bar, ingot, powder, and liquid of raw materials according to the size of the forging can not only save costs but also make the forgings have better Mechanical properties and better precision.

Hot Forging Heating Methods:

The purpose of heating is to make the metal billet have higher metal plasticity and lower deformation resistance so that it is easy to form and obtain a good forging structure. Therefore, hot forging will have higher productivity, ensure the quality of forgings and save energy consumption.

According to the different heat sources used, the heating methods of metal blanks can be divided into two categories: flame heating and electric heating.

Flame Heating:

Flame heating uses a large amount of heat energy generated by fuel (coal, coke, heavy oil, diesel, and gas) combustion to heat the billet.

The Specific Heat Transfer Process:

When the heating temperature is lower than 600-700°C, the surface heating method of the billet is mainly convective heat transfer. When the heating temperature exceeds 700-800°C, the surface heating method of the billet is mainly radiation heat transfer, supplemented by convection heating. Generally, when ordinary forging furnaces are heated at high temperatures, radiation heat transfer accounts for more than 90%, and convective heat transfer only accounts for 8% to 10%. The heating method inside the billet is heated by heat conduction.

Advantages and Disadvantages of the Flame Heating Method:

Advantages:

The source of fuel is convenient

The furnace is easy to build

Lower heating costs

Wide range of adaptation to blanks

Disadvantages:

The working conditions are poor

The heating speed is slow

The heating efficiency is low

The heating quality is difficult to control, etc

Electric Heating：

Electric heating is to heat metal blanks by converting electrical energy into heat energy. Among them are induction electric heating, contact electric heating, resistance furnace heating, and salt bath furnace heating.

1. Induction Electric Heating (Eddy Current Heating)

Electromagnetic inductors can generate alternating magnetic fields after being supplied with alternating current. Under the action of the alternating magnetic field, the alternating eddy current is generated inside the billet under the effect of the alternating magnetic field generated by the inductor passing the alternating current. The metal blank is heated directly due to eddy currents and magnetization heating (below the magnetic transition point).

For large-diameter blanks, to increase the heating speed, a lower current frequency should be selected to increase the depth of current penetration; for small-diameter blanks, due to the smaller cross-sectional size, a higher current frequency can be used, which can improve the heating efficiency.

Advantages and Disadvantages of Induction Electric Heating:

Advantages:

The heating speed is fast, and the eddy current heating can heat the billet to the required temperature faster

The faster heating speed can reduce the surface oxidation and decarburization of the billet, and most billets do not need gas protection

After the billet is heat-treated by induction heating, there is a thicker area of toughness under the surface-hard layer, which will have better compressive internal stress, and the fatigue resistance and breaking capacity of the billet has been improved

The heating equipment is easy to install on the production line, and it is easy to realize mechanization and automation

It is easy to manage, can reduce transportation costs, and save man costs. And improve production efficiency

It is easy to use, simple to operate, and can be started or stopped at any time. And no preheating is required

High utilization rate of electric energy, environmental protection and energy saving, safe and reliable, and suitable working conditions for workers

Disadvantages:

The equipment is more complex

The cost of one-time input is relatively high

Induction components (induction coils) have poor interchangeability and adaptability

It is not suitable for application on workpieces with complex shapes

2. Contact Electric Heating

After the billet is connected to the power supply, when the current passes, heat will be generated due to the resistance of the billet itself, thereby heating the billet.

To heat a billet of a specific size to the required temperature, it is necessary to calculate the required electric current according to the resistance of the billet. If the electric current is large and the voltage is also, it is easy to cause a short circuit. We need specific transformers to step down the voltage and increase the current.

Advantages and Disadvantages of Contact Electric Heating:

Advantages:

Fast heating speed

Less metal burning loss

The heating temperature range is not limited

High thermal efficiency

Less power consumption

Low cost

The equipment is simple

Easy to operate

Disadvantages:

The surface roughness, shape, and size of the billet have strict requirements, especially since the billet end must be regular and not be distorted

It is also difficult to measure and control the heating temperature

Suitable for overall or partial heating of long blanks

Hot Forging Process:

An advanced and strictly managed hot forging factory will have a complete forgings manufacturing process. It can provide safety in the entire production process, improve the yield of orders, and shorten the orders' production time. The forge will generally start the orders' production according to the following forging process.

Drawing Design:

For factories, drawing design can be provided, design drawings according to your ideas, make hot forging solutions, and complete your orders. OEM hot forging factories need formulating solutions and complete production according to your drawings or samples. 

Mold Making:

After the forging factory receives the drawings or samples, it will formulate solutions and quotations and ensure that they can satisfy you. The forge will start making the molds after receiving the down payment. The mold material will be selected according to the materials of the forging. After the mold is made, samples will be produced and sent to customers for testing. After the forgings' samples pass the test, the hot forging factory will start the order mass production.

Purchase of Raw Materials:

After the sample passes the test, the hot forging factory will purchase raw materials.

Forging Billet Blanking:

No matter what shape the billet is, we need to cut it to a specific size, which can better complete the heating of the billet and the subsequent process.

Forging Billet Heating:

Use flame heating or electric heating to heat the billet to a specific temperature.

Billet Performing:

Use free forging, roll forging, and other pre-forming forging processes to forge the billet into a predetermined shape, which is convenient for the next step of forming.

Forming:

Using form forging processes such as die forging to process the billed into a specific shape.

Finishing:

For forgings with special needs, heat treatment is also required.

After the forging cools down, start the finishing machining of the forging.

For forgings with flash, we need to cut off and grind flash. Forgings may also require some machining to adjust the shape of the forging to improve accuracy and surface quality.

Surface Treatment:

Some forgings also need surface treatment, such as polishing, galvanizing, spraying, blueing, etc.

And that's it: a finished forging is complete.

Advantages and Disadvantages of Hot Forging:

Advantages:

The recrystallization process eliminates the strain-hardening effect as the metal deforms

Parts are more malleable, which makes them suitable for more industries

Forgings have a non-porous surface quality and can be polished and other surface treatments

Hot forging is more efficient when working with harder metals such as steel

Disadvantages:

We carry out hot forging in a high-temperature environment. So we require stricter operation management. Otherwise, there will be potential safety hazards for personnel and equipment

The material is prone to oxidation at high temperatures, resulting in scale, fouling on the surface, and poor smoothness and flatness

After the hot forging is completed, the forging material will shrink during the cooling process. Dimensions and accuracy of forgings are affected

High-temperature operation requires high equipment and maintenance costs.

Hot Forging Service

Hot forging service is the process in which the forging factory uses hot forging technology to complete the order production according to the drawings and requirements provided by customers. After you send the forgings drawing to the metal processing service provider, the manufacturer will determine whether hot forging can be used to complete the order according to the drawing and complete the quotation according to raw material processing, production cost, and other factors. After some negotiation with the customer, the contract is signed, and the service begins.

A better hot forging service provider will have these six characteristics:

1. Any information about the customer will not be disclosed to others without permission, and a confidentiality agreement will be signed with the customer

2. Have a complete supply chain to provide service support. They can finish the production of orders and provide packaging, transportation, after-sales, and other services

3. The factory has excellent production capacities and can complete orders faster under the premise of ensuring product quality

4. Have a quality control center to guarantee product quality

5. Can provide more professional freight consulting services, optimize freight routes, reduce freight costs, and provide other freight-related services

6. With after-sales service, when there are quality problems with the product, we can put forward a better solution centered on you