Page 236 - CITS - Welder - Trade Theory

WELDER - CITS

Lathe: A machine spins the stock while a hardened cutting blade removes excess material into the desired shape.
Milling: The stock is mounted on a movable table that maneuvers around a fixed cutting blade.
Laser-Cutting
Key criteria for comparing these two methods include:
Thickness of Materials. Lasers perform better on materials three-eighths of an inch thick or less. While it’s possible
to cut thinner materials with a water jet by cutting multiple layers at once (i.e., stacking them), doing so reduces
precision. Laser-cutting speed for these thinner materials is faster than that of a water jet. However, depending on
the materials, once you get above acertain thickness lasers are no longer an option, while water jets are. Lasers
can’t cut through inch-thick steel, for example, but water jets can (although very slowly) Precision. The minimum
size of the laser-cutting slit is 0.006 inches versus the water-jet-cutting slit of .02 inches - so lasers can cut finer
details. The tolerance of laser cutting is also better, typically +/- 0.005”, while a water jet is typically +/- 0.010”.
And, as just noted, when materials are stacked, a water jet’s precision diminishes further.
Time. Laser jets cut thinner materials faster and more precisely than water jets can. Also, water-jet jobs generally
take longer to prepare, meaning you have to allow more time in your production schedule for material cutting, and
alert your vendor if you plan to use an outside vendor for cutting.
Surface Abrasion and Staining. Water jets with abrasive particles may stain your materials or delaminate (abrade)
the surface, while lasers won’t. Cost. It generally costs less to cut thinner materials with a laser and costs less to
cut thicker materials with a water jet.
Resistance welding processes, principal, application,

advantage, Elements, control parameter, various types,

viz spot welding, seam welding, Projection welding, Flash

butt welding

Objectives : At the end of this lesson you shall be able to
• describe the principal of resistance welding.
• explain the spot welding
• explain the seam welding.

Principle of resistance welding: Resistance welding is a welding process wherein coalescence is provided by
the heat obtained from the resistance offered by the work to the flow of electric current in a circuit and the joint is
effected by the application of pressure.
The fundamental principle on which all resistance welding is based is as follows. The heat is generated due to the
resistance offered by the parts to the passage of heavy electric current for a fraction of a second.
Heat produced at the junction is calculated by the formula H = I Rt
2
where H for Heat, I stands for the amount of current in amps. R for resistance offered in ohms t - time taken for
duration of current flow in seconds. This heat at the junction of the two parts changes the metal to a plastic state,
Fig 1

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CITS : C G & M - Welder - Lesson 77 - 82 CITS : C G & M - Welder - Lesson 77 - 82