What is spot welding?

Describe the process of heating in spot welding.

Tell about methods of spot welding.

Exercise 15. Translate the following sentences from English into Russian

1. In resistance welding heat is obtained from the resistance of metal to the flow of an electric current.

2. Resistance causes heat which melts the metals and creates the weld.

3. The subsequent cooling and combination of the materials forms a “nugget” alloy of the two materials with larger grain growth.

4. There is little melting and minimum grain growth, but a definite bond and grain interface.

5. The resultant bond has definite interfaces with minimum grain growth.

6. Typically the process requires a longer (2 to 100 ms) heating time at low weld energy.

Exercise 16. Watch the resistance welding video www.youtube.com/watch?v=PLg1OUwAO40 and discuss the following questions:

1. What is resistant welding?

2. How can one achieve the permanent bond? Give the algorithm.

3. What photography method was used the show this welding process?

4. What spot welding is usually used for?

5. How can the electrode tips affect the spot welding quality?

6. What are the main factors to be controlled for resistance welding?

7. How time is measured in projection welding?

8. How the total time is divided for projection welding?

Exercise 17. Study the following words:

Exercise 18 . Fill in the Work sheet 4

A. GIVE THE MAIN FACTORS ABOUT RESISTANT WELDING:

·  

·  

·  

WHEN THESE FACTORS ARE IN PROPER BALANCE AN _______________________ ____________________________ WILL FOLLOW.

B. SPOT WELDING. In spot welding the diameter of the electrode tips are extremely important, as they control the size of the weld area:

Smaller tip diameter on _____________________ parts.

larger tip diameter on _______________________ parts

C. pROJECTION WELDING:

PRESS TYPE WELDER ________________ HAS A ___________________________ OR A __________________________ CYLINDER.

D. DRAW A SCHEME FOR PROPER HEAT, time and pressure BALANCE FOR pROJECTION WELDING (USE THE DEFINITION ON THE LEFT)

PROPER HEAT BALANCE - IT IS WHEN THE FASTENER AND THE COMPONENT PART ARE BROUGHT TO THE ___________________ TEMPERATURE ___________________________________.
How total time is expressed:
total time is devided into ____________ main categories:	· squeeze _________________   · ________________ time   · ________________ ___________
Pressure balance
Excessive pressure may cause: · Resistance ________________   · weak, incomplete or ______________________________	Insufficient pressure may cause:   · Flashing   · _____________   · _____________

Individual Work:

Text 5.Seam welding

Resistance seam welding is a process that produces a weld at the faying surfaces of two similar metals. The seam may be a butt joint or an overlap joint and is usually an automated process. It differs from butt welding in that butt welding typically welds the entire joint at once and seam welding forms the weld progressively, starting at one end. Like spot welding, seam welding relies on two electrodes, usually made from copper, to apply pressure and current. The electrodes are disc shaped and rotate as the material passes between them. This allows the electrodes to stay in constant contact with the material to make long continuous welds. The electrodes may also move or assist the movement of the material.

A transformer supplies energy to the weld joint in the form of low voltage, high current AC power. The joint of the work piece has high electrical resistance relative to the rest of the circuit and is heated to its melting point by the current. The semi-molten surfaces are pressed together by the welding pressure that creates a fusion bond, resulting in a uniformly welded structure. Most seam welders use water cooling through the electrode, transformer and controller assemblies due to the heat generated. Seam welding produces an extremely durable weld because the joint is forged due to the heat and pressure applied. A properly welded joint formed by resistance welding is typically stronger than the material from which it is formed.

A common use of seam welding is during the manufacture of round or rectangular steel tubing. Seam welding has been used to manufacture steel beverage cans but is no longer used for this as modern beverage cans are seamless aluminum.

Vocabulary :

Faying surfaces - плотно соединенные поверхности

Voltage -  напряжение

round - круглый

rectangular - прямоугольный

modern  - современный