LASER BEAM MACHINING

Laser-beam machining (LBM) is accomplished by precisely manipulating a beam of coherent light to vaporize unwanted material. LBM is particularly suited to making accurately placed holes. It can be used to perform precision micromachining on all microelectronic substrates such as ceramic, silicon, diamond, and graphite. Examples of microelectronic micromachining include cutting, scribing and drilling all substrates, trimming any hybrid resistors, patterning displays of glass or plastic and trace cutting on semiconductor wafers and chips.

In laser beam machining (LBM), an intense beam of collimated, single wave-length, in-phase light is focused by an optical lens onto the workpiece point to be machined. The light absorbed by the workpiece is converted to heat, which melts and vaporizes the workpiece material. Molten material is evacuated from the cut by the adjacent vaporization turbulence which typically occurs in drilling operations, or by the use of an "assist gas" in cutting operations. Laser beam machining uses a directional, coherent, monochromatic beam of light to achieve precision in cutting and drilling. The intensity of this light produces a tremendous amount of heat at the point of application to the workpiece, and laser beam machining can take place at relatively high speeds.

A number of different types of lasers are used in laser beam machining, each with certain advantages for different operations or applications. The most commonly used lasers for machining are Nd:YAG lasers, which have certain advantages for hole drilling due to their higher pulse energy, and CCh gas lasers, which have certain advantages in cutting since they are capable of delivering much higher average power. Lasers may be operated in either pulsed or continuous-wave (CW) modes. The most powerful CCb lasers, however, are operable only in CW mode. CCb lasers can have output power generally ranging from 100 to 2000 W when pulsed and from 250 to 50(K) W in CW mode. Some lasers are capable of an output power of 25,000 W.

A 1250-W CO2 laser can cut mild steel at speeds ranging between 40 and 140 crrr/min, depending on material thickness. At a thickness of 12 mm, the cut can be 40 enrr/min. At a thickness of 2 mm, a 1250-W CO2 laser can cut at a rate of 140 enrr/min. Aluminum is generally cut at about one-half the speed of carbon steel with a CO2 laser because of the high thermal conductivity of the aluminum. In cutting applications, the laser beam may be "transmitted" and "switched" by using mirrors to manipulate the beam, or with Nd.YAG lasers by the use of a combination of fiber optic cables and switches. Below is the typical average power range and maximum pulse energy for the two types of lasers most commonly used in laser beam machining.

In the application of laser beam machining, it is possible to perform the operations of drilling and cutting with speed and precision. For instance, percussion (i.e. repeated pulse) drilling of Inconel 718 with a 250-W Nd:YAG laser can produce accurate holes 12 mm deep in under 10 sec and holes 25 mm deep in 40 sec. Length-to-diameter ratios are limited to about 30 or 40 to 1 with conventional Nd: YAG lasers. However, other laser technologies allow the length-to-diameter ratio to be higher. Frequently, gas is used to assist laser beam machining. A coaxial columnar flow of gas (oxygen, air, or inert gas) at pressures ranging from 1 to 6 bar expels molten metal from the cut. Oxygen assists in cutting steel and other materials at an increased rate because of the oxidation reaction with the metals.

Laser beam machining uses thermal energy to drill and cut with speed arid precision that traditional machining methods often cannot duplicate. Its applications are becoming more varied as new techniques are developed.

 

Exercise 5. Answer the questions to the text, using the active vocabulary of the lesson.

1) How does laser beam machining work?

2) When using LBM, what is the difference between cutting operation and drilling operation process?

3) Why can laser beam machining take place at relatively high speeds?

4) What are the most commonly used lasers for machining? What are the advantages of them?

5) What operating modes for lasers do you know?

6) Why is it necessary to transmit or switch a laser beam?

7) Describe the working process of the gas assisted laser beam machining.

8) Why does LBM work with such a speed and precision?

 

Exercise 6. Match the words and expressions on the left with those on the right:

1) optical lens a) мягкая сталь

2) molten material b) импульсная энергия

3) drilling operation c) оптическая линза

4) cutting operation d) процесс сверления

5) laser beam e) лазерный луч

6) pulse energy f) расплавленный материал

7) output power g) резание

8) mild steel h) выходная мощность

9) carbon steel i) реакция окисления

10) oxidation reaction j) углеродистая сталь

 

Exercise 7. Complete the sentences with given words and translate them into Russian:

Beam of light, modes, mirrors, drilling, heat, machining, lasers, speeds, thermal energy, output power, thickness.

 

1) A number of different types of … are used in laser beam machining.

2) Laser beam machining uses a … to achieve precision in cutting and ….

3) Some lasers are capable of an … of 25,000 W.

4) In cutting applications, the laser beam may be "transmitted" and "switched" by using … to manipulate the beam

5) Laser beam machining uses … to drill and cut with speed arid precision.

6) A 1250-W CO2 laser can cut mild steel at … ranging between 40 and 140 crrr/min.

7) At a … of 12 mm, the cut can be 40 enrr/min.

8) The most commonly used lasers for … are Nd:YAG lasers.

9) The intensity of light produces a tremendous amount of … at the point of application to the workpiece.

10) Lasers may be operated in either pulsed or continuous-wave (CW) ….

Exercise 8. A. Find the synonyms to the following words and translate them:

Beam, workpiece, to machine, energy, speed, amount, precision, flow, to duplicate, to operate, percussion, technology, varied.

 

B. Find the antonyms to the following words:

To heat, to melt, advantages, capable, single, high power, maximum pulse energy, to increase, traditional, frequently, mild steel.

 

Exercise 9. Compose several sentences, using the following words:

Types of lasers, laser beam machining, to cut steel and other materials, with speed and precision, laser technologies, thermal energy, to drill and cut, to manipulate the beam, power output, new techniques.

 

Exercise 10. A. Remember the cases, where the infinitive is used without particle “to”:

· After modal verbs;

· After verbs “to let” and “to make”;

· In Complex Object after the verbs of perception (to feel, to hear, to see, etc.);

· After expressions “I would rather…”, “You had better…”.

 

B. Now translate the following sentences, using infinitive with or without particle “to”:

1) Мы хотели бы купить несколько лазерных станков этой фирмы.

2) Я впервые увидел, как луч лазера убирает ненужный материал.

3) Ты выглядишь уставшим. Лучше бы ты закончил гравирование завтра.

4) Разреши помочь тебе, и я с удовольствием расскажу о сферах применения лазера.

5) Думаю, я легко смогу научиться сверлить отверстия при помощи лазера.

6) Что заставляет тебя полагать, будто лазерный луч можно применять к керамике, кремнию и графиту?

7) Тебе необходимо запомнить, что лазер модели 1250-W CO2 может резать мягкую сталь.

8) Я слышал, как представитель рассказывал, что даже липкие материалы не являются проблемой для лазерного луча.

9) Я сделаю все возможное, чтобы починить этот станок, и уже завтра вы сможете выполнять резку и сверление материала с прежней точностью.

10) Лазерным лучом можно «управлять» при помощи зеркала, либо волоконно-оптических кабелей и переключателей.

Exercise 11. Speak on the advantages of laser cutting and drilling. Use the information given below and the active vocabulary of the lesson.

A. Laser Drilling Advantages:

· Using laser system software, the operator instantly can control hole shape and size to produce round, oval or rectangular holes, or any shape imaginable. This eliminates downtime due to tool changes.

· Very small holes can be laser drilled in production. A focused spot can be as small as 0.1mm (0.004") in diameter.

· Since the tool is a beam of light, the tool never needs to be replaced eliminating downtime because of punch breakage.

B. Laser Cutting Advantages:

· There is almost no limit to the cutting path; the point can move in any direction unlike other processes that use knives or saws.

· The laser beam is always sharp and can cut very hard or abrasive materials.

· Cutting with lasers is a very cost effective process with low operating and maintenance costs and maximum flexibility.