Choosing the Right Diffusion Welding Equipment for Your Application

Classification and Composition of Diffusion Welding Equipment

Classification of Diffusion Welding Equipment

(1) Classification by Vacuum Level

Based on the vacuum level or limit that the workspace can achieve, diffusion welding equipment can be divided into four categories: low vacuum (above 10-1Pa), medium vacuum (10-3~10-1Pa), high vacuum (<10-5Pa) welding machines, and protective gas diffusion welders.

Depending on the situation of the weld in the vacuum, it can be divided into diffusion welders where the entire weld is in a vacuum and partial vacuum diffusion welders. Partial vacuum diffusion welding machines only protect the welding area and are primarily used for welding large workpieces.

(2) Classification by Heat Source Type and Heating Method

Based on the heat source and heating method used during diffusion welding, welding machines can be divided into induction heating, radiation heating, contact heating, electron beam heating, glow discharge heating, laser heating diffusion welding machines, etc. The most widely used in practice are high-frequency induction heating and resistance radiation heating.

Composition of Diffusion Welding Equipment

Diffusion welding equipment generally includes a heating system, a pressure system, a protection system, and a control system.

(1) Heating System

The heating system is divided into induction heating, radiation heating, contact heating, etc. Induction heating or resistance heating is commonly used to heat the weld either partially or entirely. High-frequency induction diffusion welding equipment uses a high-frequency power supply for heating, with a working frequency of 60~500kHz. Due to the skin effect, equipment in this frequency range can only heat smaller workpieces.

For larger or thicker workpieces, to shorten induction heating time, it is best to use low-frequency welding equipment of 500~1000Hz. When welding non-conductive materials like ceramics, indirect heating should be used. A cylindrical graphite conductor can be added between the workpiece and the induction coil, utilizing the heat generated by the graphite conductor for welding heating.

Resistance heating vacuum diffusion welding equipment uses resistance radiation heating. The heating body can be made of tungsten, molybdenum, or graphite. The vacuum chamber should have a uniform heating zone made of high-temperature resistant materials to maintain uniform temperature.

(2) Pressure System

To achieve close contact between the workpieces being welded, a certain pressure must be applied during diffusion welding. The yield strength of the material decreases at high temperatures, and to avoid overall deformation of the workpiece, pressure is applied to cause microscopic local deformation at the contact surface. For ordinary metal materials, the pressure applied in diffusion welding is relatively small, ranging from 1~100MPa.

For hard-to-deform materials like ceramics and high-temperature alloys, or materials with a rough surface finish, higher pressure is used when the diffusion welding temperature is lower. The pressure system is divided into hydraulic, pneumatic, mechanical, and thermal expansion pressure systems. Automatic pressure control diffusion welding equipment is usually equipped with a pressure sensor to achieve pressure measurement and control.

Currently, most diffusion welding equipment uses hydraulic and mechanical pressure systems. In recent years, hot isostatic pressing (HIP) technology, which uses a pneumatic system to evenly apply the required pressure to the workpiece from all directions, has been used both domestically and abroad.

(3) Protection System

The protection system is a vacuum system or controlled atmosphere that protects the workpiece from oxidation during the heating and pressurizing process. At present, diffusion welding equipment generally uses vacuum protection. The vacuum system is usually composed of a diffusion pump and a mechanical pump.

The mechanical pump can reach a vacuum level of 1.33×10-3Pa, and with the addition of a diffusion pump, it can reach a vacuum level of 1.33×10-6~1.33×10-4Pa, which can meet almost all welding requirements. The size of the vacuum chamber should be determined based on the size of the workpiece. The larger the vacuum chamber, the higher the requirements for the vacuum system to reach and maintain a certain vacuum level.

The vacuum chamber should have a uniform heating zone made of high-temperature resistant materials to maintain the set temperature. The vacuum chamber shell needs cooling.

(4) Control System

The control system mainly controls temperature, pressure, vacuum level, and time. A limited number of devices can also measure and control displacement.

Temperature measurement uses nickel-chromium-nickel-aluminum, tungsten-rhenium, platinum-platinum-rhodium thermocouples, the measurement range is 20~2300℃, and the control accuracy is ±(5~10)℃. Pressure measurement and control are usually carried out through a pressure sensor.
The control system often uses computer-programmed automatic control, which can display, store, and print welding parameters.

Typical Diffusion Welding Equipment and Their Technical Parameters

There are many types of diffusion welding equipment currently in use in production. Here, we introduce a few commonly used diffusion welding equipment.

Vacuum Diffusion Welding Equipment

During diffusion bonding, to ensure that the bonding area and bonding metal are not affected by air, the bonding must be carried out in a vacuum or inert gas medium. The most commonly used method at present is vacuum diffusion bonding. Vacuum diffusion bonding can use high frequency, radiation, contact resistance, electron beam, and glow discharge methods to locally heat the workpiece.

The most commonly used diffusion welding equipment in industry uses induction and radiation heating methods. Figure 3-3 shows a schematic diagram of a vacuum diffusion welding machine structure, and Figure 3-4 shows an external view of the FJK-2 vacuum diffusion welding machine. Table 3-3 lists the main technical parameters of some vacuum diffusion welding equipment.

Figure 3-3 Schematic Diagram of a Vacuum Diffusion Welding Machine Structure

1 – High-frequency Power Source
2 – Pressurizing System
3 – Vacuum Chamber
4 – Diffusion Bonding Workpiece
5 – Induction Coil
6 – Mechanical Pump and Diffusion Pump

Figure 3-4 Exterior View of FJK-2 Vacuum Diffusion Welding Machine

Table 3-3 Main Technical Parameters of Some Vacuum Diffusion Welding Equipment

Equipment Model or TypeZKL-1ZKL-2Workhorse IIHKZ-40DZL-1
Heating Zone Dimensions/mmΦ600~Φ800Φ300~Φ400304×304×457300×300×300
Vacuum Level/PaCold State1. 33 ×10-31. 33 ×10 -31. 33 ×10-61. 33×10 -37.62 ×10-4
Hot State5 ×10-35 × 10 -36. 65 ×10-5
Pressure Capacity/kN245 (Max)58.8 (Max)30080300
Maximum Furnace Temperature/°C12001200135013001200
Furnace Temperature Uniformity/°C1000 ±101000 ±51300 ± 51300 ±101200 ±5

Superplastic Forming Diffusion Welding Equipment

This type of equipment consists of a press and specialized heating equipment, which can be divided into two main categories. One category is composed of a standard hydraulic press and a specially designed heating platform. The heating platform, made from ceramic refractory materials, is mounted on the metal surface of the press.

Superplastic forming diffusion molds and workpieces are placed between the two ceramic platforms, and the parts to be welded can be sealed in a vacuum container for heating. In the other category, the metal platform of the press is placed inside the heating equipment, as shown in Figure 3-5. Its platform is made from high-temperature-resistant alloys, and heating elements can also be installed within the platform to accelerate temperature rise.

This equipment has a vacuum air supply system, which uses a single mechanical pump for vacuum extraction, and the method of repeated vacuuming and argon filling is used to reduce the oxygen partial pressure on the surface to be welded and in the surrounding atmosphere.

Argon gas is supplied to the mold cavity with the workpiece or to the bag-type blank through a gas pressure regulator to obtain uniform and adjustable diffusion welding pressure and superplastic forming pressure.

Figure 3-5 Schematic Diagram of Superplastic Forming Diffusion Welding Equipment

1 – Lower Metal Platform
2 – Upper Metal Platform
3 – Furnace Shell
4 – Guide Simplification
5 – Pillar
6 – Hydraulic Cylinder
7 – Upper Mold
8 – Lower Mold
9 – Air Pipe
10 – Movable Furnace Bottom

Hot Isostatic Press Diffusion Welding Equipment

In recent years, in order to produce high-density ceramics and precision-shaped components, hot isostatic press equipment has gradually attracted attention in various industries. During diffusion welding, the workpiece to be welded is sealed in a thin bag and vacuumed, and then the entire bag with the workpiece (including fillers) is placed in a heating chamber for heating.

At the same time as high-temperature welding, high pressure is applied to the workpiece to increase its density or obtain the required component shape. Since the applied gas pressure is high, the equipment shell must be thick enough to withstand tens of MPa or even higher pressure.

This equipment can be used for powder metallurgy, defect healing of castings, preparation of composite materials, ceramic sintering, and diffusion welding of precision complex components.

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