The two types of plasma welding are:
- Transferred arc plasma welding: In this method, the arc is formed between the tungsten electrode and the workpiece, and the plasma is transferred to the welding area.
- Non-transferred arc plasma welding: Here, the arc is formed between the tungsten electrode and a water-cooled nozzle, and the plasma jet is directed towards the workpiece.
Introduction
Plasma Welding: An Overview
Plasma welding refers to a process where an electric arc forms between a tungsten electrode and the workpiece. A plasma welding unit typically operates at 15 to 400 amps, providing considerable control for welding at low current, especially in situations where precision is necessary.
Industrial Significance of Plasma Welding
Plasma welding plays a pivotal role across various industries, notably in the automotive, aerospace, and manufacturing sectors. This is due to the high-quality, precision welds that the process can create, allowing for the manufacture and repair of highly sensitive components and assemblies.
Automotive Industry
In the automotive industry, plasma welding is essential in the production of key components, such as fuel injectors and transmission systems. Its precision is critical in manufacturing parts that must meet exacting dimensions and tolerances. For instance, the typical dimensional tolerance in a fuel injector part may be as small as +/- 0.05 mm, showcasing the fine precision that plasma welding allows.
Aerospace Industry
The aerospace industry often uses plasma welding for the production and repair of turbine engine components. These parts often need to withstand extreme temperatures and pressures.
Manufacturing Industry
Plasma welding’s versatility shines in the manufacturing industry, where it’s used in a wide range of applications, from medical equipment production to stainless steel processing. For example, in stainless steel processing, plasma welding increases productivity by up to 25% due to its high speed and deep penetration capabilities, compared to traditional welding methods.
Cost Implications of Plasma Welding
While plasma welding provides substantial advantages in terms of quality and precision, it comes with higher costs compared to other welding techniques. The typical cost of a plasma welding system ranges from $15,000 to $30,000 depending on the specifications, power, and accompanying accessories. In terms of operational costs, plasma welding consumes approximately 0.3 to 0.7 liters of gas per minute, translating to an average monthly expense of around $50 to $100, depending on the gas prices and usage intensity. However, given its advantages and the potential cost savings from reduced rework and increased component lifespan, the higher initial cost often justifies itself in industries where precision and quality are paramount.
Fundamentals of Plasma Welding
Plasma welding can be considered an advanced version of Tungsten Inert Gas (TIG) welding. Despite their similarities, plasma welding’s unique mechanics and principles set it apart, offering distinct advantages in various applications.
Plasma Welding Process Overview
In plasma welding, the process starts with an electric arc that is formed between the tungsten electrode and the workpiece. This electric arc is then tightly constricted by a fine-bore ceramic nozzle, forming a columnar or cylindrical plasma arc. The process is typically performed in the range of 0.1 to 400 Amperes, with the welding torch moving at a speed of about 0.5 to 25 millimeters per second, depending on the specific application and the thickness of the material being welded.
Working Principles and Mechanics
The principles behind plasma welding involve physics and thermodynamics. The heat required for welding comes from the electric arc that forms a plasma.The plasma welding process employs this plasma to transfer an electric arc to a workpiece with a force and heat intensity greater than those found in traditional welding methods. This results in faster welding speeds and deeper weld penetration. The temperature of the plasma arc in a typical plasma welding process can reach up to 22,000 degrees Celsius, which is approximately four times hotter than the surface of the sun.
Plasma Arc Formation
Plasma arc formation is the heart of the plasma welding process. This unique characteristic allows for high-quality, high-speed, and high-precision welding, especially in automated applications.
Types of Plasma Welding
There are two main types of plasma welding, differentiated by the manner in which the plasma arc is formed and used: transferred arc plasma welding and non-transferred arc plasma welding, also known as TIG plasma welding.
Transferred Arc Plasma Welding
Transferred Arc Plasma Welding is a subtype of plasma arc welding where the plasma arc is transferred from the electrode to the workpiece. It operates in a similar fashion to shielded metal arc welding, but with a key difference: the high-density plasma arc provides greater energy concentration, allowing for higher welding speeds and deeper penetration.
Mechanism and Characteristics
In the mechanism of transferred arc plasma welding, the workpiece itself becomes part of the electrical circuit. The temperature of the plasma arc in transferred arc plasma welding can reach up to 28,000 degrees Celsius, making it suitable for welding thick and high-density materials.
Applications and Advantages
It is particularly advantageous for welding components with thicknesses of 1.5 mm or greater, thanks to its deep penetration. Additionally, it offers benefits such as low distortion, fewer sparks, and less fume production compared to other welding methods.
Non-Transferred Arc Plasma Welding (TIG Plasma Welding)
In contrast to transferred arc plasma welding, non-transferred arc plasma welding, often referred to as TIG plasma welding, doesn’t involve the workpiece in the electrical circuit. Instead, the arc forms between the electrode and the nozzle, creating a plasma that heats the workpiece.
Process Explanation
The process starts with the arc forming between the tungsten electrode and the constricting nozzle, causing the gas to ionize and form a plasma. The temperature of the plasma in non-transferred arc welding typically reaches about 16,000 to 20,000 degrees Celsius, making it ideal for welding thinner materials.
Comparison with Transferred Arc Welding
Compared to transferred arc welding, non-transferred arc plasma welding operates at lower temperatures, thus it offers less penetration and is suitable for welding thinner materials. However, it does provide a finer degree of control and lower heat input, which can be beneficial in applications requiring precise and intricate welds, such as in the electronics or medical equipment manufacturing industries.
Suitable Applications
Despite its lower heat input and penetration compared to transferred arc welding, its ability to achieve fine, high-quality welds makes it highly valuable in specific industrial applications.
Equipment and Setup for Plasma Welding
The correct setup for plasma welding requires an understanding of its key equipment, including the welding torches, power sources, and gas selections.
Plasma Welding Torches and Components
The primary tool for plasma welding is the torch. Plasma welding torches have a unique design that includes a tungsten electrode, a water-cooled body, and a ceramic nozzle.
The tungsten electrode serves as the source of the arc. Standard diameters of the tungsten electrode for plasma welding range from 1.0 mm to 2.4 mm.
The ceramic nozzle plays a crucial role in forming the plasma arc. It has a small orifice which constricts the arc and focuses it on the workpiece. Typical inner diameters for the nozzle range from 0.5 mm for micro-plasma welding to 2.0 mm for standard plasma welding.
Power Sources and Settings
The power source for plasma welding is typically a direct current (DC) supply with a capability of delivering between 0.1 to 400 Amperes. The power setting used depends on the material type and thickness. For example, welding a 3 mm thick stainless steel workpiece would typically require a power setting of around 100 Amperes.
The majority of power sources for plasma welding are inverter based, providing a high-frequency start to initiate the pilot arc without touching the workpiece. This high-frequency start ensures a consistent and reliable arc start every time, critical for automated welding applications.
Gas Selection and Flow Rates
Gas selection and flow rate are also critical to the plasma welding process. The shielding gas typically used is Argon due to its stable arc characteristics.
The flow rate for the plasma gas usually ranges from 0.5 to 4.0 liters per minute, depending on the current and nozzle diameter. Too high a flow rate can lead to turbulence in the arc, while too low a flow rate can result in an unstable arc. Therefore, correct setting of the gas flow rate is essential for a stable and high-quality welding process.
Materials Suitable for Plasma Welding
The selection of the material largely depends on the requirements of the specific application and the characteristics of the material itself.
Ferrous Metals
Ferrous metals include those containing significant quantities of iron, such as carbon steel, stainless steel, and alloy steel. Plasma welding is particularly advantageous for welding these metals because it provides deep penetration and high welding speed, which can enhance productivity and weld quality.
Carbon steel, with similar thicknesses, would require slightly higher power settings, between 130 to 400 Amperes, due to its higher thermal conductivity and melting point
Non-Ferrous Metals
For a thickness of 1.5 mm to 8 mm, the recommended power setting ranges between 70 to 250 Amperes. A thickness of 0.8 mm to 4 mm would typically require a power setting of 70 to 200 Amperes.
Exotic Alloys
Their high melting points and strong resistance to heat and corrosion make plasma welding an excellent choice.
Welding Procedures and Techniques
The overall success of plasma welding depends on several factors, including preparation, joint design, the welding parameters, and control of the weld pool and heat input.
Preparation and Joint Design
Surfaces must be free from dirt, oil, rust, and paint. This is because any contaminants can potentially cause weld defects such as porosity or inclusions.
The design of the joint also plays a significant role.
Plasma Welding Parameters
| Material | Thickness (mm) | Current (Amperes) | Gas Flow (L/min) | Travel Speed (mm/min) |
|---|---|---|---|---|
| Stainless Steel | 3 | 100 | 2 | 250 |
Control of Weld Pool and Heat Input
Control of the weld pool and heat input is critical in plasma welding, and travel speed. It is important to balance these parameters to prevent excessive heat input that can lead to warping or distortion of the workpiece.
Comparison with Other Welding Processes
Each process has its unique strengths and weaknesses, and the choice depends on the specific requirements of the welding operation.
Plasma Welding vs. TIG Welding
Plasma welding and TIG (Tungsten Inert Gas) welding are both high-quality welding processes that use a non-consumable tungsten electrode. However, they differ in several aspects.
Plasma welding offers greater control over the heat input and a more focused arc, resulting in higher welding speeds and deeper penetration.
On the other hand, TIG welding equipment tends to be less costly. The average cost for a professional TIG welding setup might be around $2,000, while a plasma welding setup can cost up to $8,000, making the initial investment higher for plasma welding.
Plasma Welding vs. MIG Welding
MIG (Metal Inert Gas) welding is a more straightforward process that uses a consumable wire electrode, making it faster and easier to use than plasma welding. However, it often doesn’t offer the same degree of precision and control.
Therefore, for thin or delicate materials, plasma welding might be a better choice.
Cost-wise, MIG welding equipment is typically cheaper than plasma welding equipment. A typical MIG welding setup might cost around $1,200, while, as mentioned earlier, a plasma welding setup can go up to $8,000.
Plasma Welding vs. Laser Welding
Laser welding, like plasma welding, provides high energy density, resulting in high welding speeds and deep penetration. Both processes offer excellent precision and control, making them suitable for a wide range of applications.
However, laser welding equipment is generally more expensive, with average costs for professional-grade equipment starting at $15,000. This is significantly higher than the cost for a plasma welding setup.