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5. Continue the following sentences:

  1. Plasma welding allows avoidance of …

  2. The usage of this welding method leads to…

  3. Modern electronics allows…

  4. Plasma surfacing gains wide acceptance in …

6. Fill in the gaps using the following words and word-combinations:

Constriction, straight polarity, reverse polarity, straight polarity, single pass, dilution, penetration, single pass.

  1. The … … plasma arc can weld copper up to 50 mm. thick in a … … .

  2. The important property of microplasma welding is a high degree of … of the arc.

  3. Plasma surfacing can be performed at a direct current of … or … polarity.

  4. Owing to minimum … of the base metal and its minimum … with the deposited metal the plasma surfacing provides the preset properties in the first of the deposited layers.

  5. Plasma arc can weld copper up to 50 mm. thick in a … … without groove preparation.

7. Find in the text the sentences with Passive Voice.

8. Make 10 questions to the text.

9. Choose the correct verb form in the following sentences:

      1. Plasma welding (provides, has provided) the highest effect when used for joining metals.

      2. Plasma welding (allows, allowed) avoidance of preheating.

      3. The important property of plasma welding (is, are) a high degree of constriction of the arc.

      4. Plasma surfacing (can be performed, can perform) at a direct current or reverse or straight polarity.

      5. Plasma surfacing (gains, has been gained) wide acceptance.

10. Retell the text. Text c laser welding

Today there are numerous welding techniques other than gas welding and arc welding for every special field, because different materials call for different techniques. There are numerous techniques just for welding metals. Laser welding is the future for welding metal.

Other conventional welding techniques like, for example, TIG(tungsten inert gas welding), MAG(metal active gas welding), or plasma welding do not reach the energy densities needed for a deep welding effect.

The principle of laser welding is to create laser radiation and with it the energy, that is necessary for the welding process. This energy is lead by a deflection mirror and a focusing device, e.g. focusing mirror, to where it should have it’s effect, to the joint of the work pieces.

The work pieces themselves are positioned and fixed in such a way in the work piece seat, that the focused laser beam can be diverted exactly on the additional seam. The laser welding head moves along the joint over the work piece. The enormous energy density of the laser beam in focus makes the material melt and vaporize

The pressure of dissipating metal vapor can become so high, that a vapor channel forms in the material – the so-called “ keyhole”. This “keyhole” penetrates a few millimeters deep into the material.

When the laser welding head moves over the work piece, the keyhole moves with it under the laser welding head. The two casts flow into one another behind it. The joined and mixed material cools off and the cast solidifies to a narrow welding seam.

The welding seam is usually protected from reaction with the air by a shield gas during the machining. Other gases, the work gases, can aid and control welding process. When welding with a laser, two different welding techniques are used: heat conduction welding and deep welding. When using heat conduction welding, the material is melted only on the surface. In this way, welding seams a few tenths of a millimeter deep are formed. This welding technique is useful with pulsed laser, which is used for welding components for the electronic industry or for medical small parts. When producing, for example, gear parts, profiles or thick walled tubes, very deep and narrow welding seams are required. In these cases, deep welding is done with the CO2 laser.

In industrial practice laser welding is used mainly for joining coated materials, sheet stacks and components of different sizes where distortion at risk.

With steels, the weldability of the workpiece depends in the first place on the amount of carbon in it. Chrome nickel steels are generally easy to weld and permit high welding speeds because of their low heat conductivity. Non – ferrous metals are generally poorer to weld as steel. The reason for this is that these alloys have a lower degree of absorption for the laser radiation than in the case with steels.

Titanium and titanium alloys are easy to weld with the laser. A feature, though, make the welding process difficult – they react heavily to principle components in the air: oxygen and nitrogen. Here both by welding and by cooling down, the welding seam must be selectively work on with shield gas or even in a shield gas atmosphere.

If you compare laser welding with tungsten inert gas welding, metal active gas welding or plasma welding, the great advantage of laser welding can be seen in the possibility of deep welding. With other techniques, it is not possible to achieve the required energy density for a deep welding effect.

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