basic welding metallurgy SS 2

Summary

This video explains the fundamental principles of heat transfer during welding. It starts by illustrating how electrical energy is converted to heat, using examples like an electric lamp. The video then delves into how energy input, welding speed, and process efficiency affect the size and cooling rate of welds. It emphasizes the importance of understanding heat input per unit length and how different welding processes vary in efficiency. The transcript includes detailed tables and figures, highlighting the relationship between energy input and weld size, aiding in precise and effective welding practices.

Takeaways

• 😀 The script discusses the effects of heat on metal during welding, including the influence of heating and cooling on the welded object.
• 😀 An example of electrical energy conversion is given with a lamp, showing how electrical energy is converted to heat and light, and how similar principles apply to welding.
• 😀 The energy formula used for calculating the heat generated in welding is based on electrical current (ampere) and voltage, providing an energy output in joules per second (watt).
• 😀 The energy input in welding is dependent on the welding current, voltage, and the efficiency of the welding process, which varies by technique.
• 😀 Different welding processes have different energy efficiencies, with values ranging from 20% to 99%, depending on the method (e.g., SAW, SMAW, GTAW).
• 😀 Heat input is an essential parameter, affecting the uniformity of the weld and the size of the heat-affected zone (HAZ), with higher heat input typically leading to a larger HAZ.
• 😀 The script provides a formula for calculating energy input per unit length of the weld, which helps determine the heat distribution along the weld joint.
• 😀 Speed of welding affects energy input; slower speeds lead to higher energy input per unit length, which influences the quality of the weld.
• 😀 Efficiency is crucial in determining the actual heat input, as the energy delivered to the weld is affected by the process efficiency.
• 😀 A larger energy input generally results in a wider weld with a lower cooling rate, as shown in various figures and tables that illustrate these relationships in different welding techniques.
• 😀 The script also presents a comparison of welding techniques (e.g., SAW and SMAW) and how their energy input affects the size of the weld and the heat-affected zone.

Q & A

What is the primary focus of the script?

The primary focus of the script is to explain the effects of heat input in welding, how energy is transferred to the metal during welding, and the impact of this energy on the welded material, particularly in terms of temperature, cooling, and efficiency of different welding processes.

How does the electrical energy in a lamp relate to welding?

The script compares the energy conversion in a lamp (where electrical energy is converted to heat and light) to the energy conversion during welding. In welding, electrical energy is also converted into heat, which is used to melt and fuse metal, and this process can be calculated similarly using voltage and current.

What is the formula used to calculate the energy in a lamp?

The formula used to calculate the energy in a lamp is the product of the current (in amperes) and voltage (in volts). For example, if the current is 1.5A and the voltage is 100V, the energy is 150 watts (1.5A * 100V = 150W).

How is energy input calculated in welding?

In welding, the energy input can be calculated by multiplying the current (in amperes) and voltage (in volts) of the welding machine. For example, with 300A and 25V, the energy input is 7,500 watts (300A * 25V = 7,500W).

What does the efficiency of heat input mean in welding?

Efficiency of heat input refers to the proportion of the total energy converted into heat and transferred to the workpiece during welding. This efficiency varies by welding process, and understanding it helps in accurately calculating the energy input.

What are typical heat input efficiencies for different welding processes?

Different welding processes have varying heat input efficiencies: for SAW (Submerged Arc Welding), it ranges from 90-99%, for SMAW (Shielded Metal Arc Welding) it is 50-80%, for GTAW (Gas Tungsten Arc Welding) it ranges from 20-50%, and for FCAW (Flux-Cored Arc Welding) it is 65-85%.

Why is the speed of welding important for energy input calculations?

The speed of welding is important because it determines how much energy is applied per unit length of the weld. A slower welding speed results in higher energy input per unit length, affecting the final weld size and heat distribution.

What is the relationship between energy input and weld size?

As energy input increases, the weld size (especially the width of the heat-affected zone, or HAZ) generally increases. This is because more heat is applied to the metal, leading to greater melting and fusion in the weld area.

How does heat input affect the cooling rate in welding?

A larger heat input typically results in a slower cooling rate, as more heat is applied to the metal, causing it to remain in a molten state longer. This can lead to a wider heat-affected zone and potentially alter the mechanical properties of the weld.

How can the cooling rate be adjusted during welding?

The cooling rate can be influenced by adjusting the energy input, welding speed, and other parameters such as the use of cooling systems or the material's thermal conductivity. Lower energy input generally results in a faster cooling rate.