Unit 6. Tool wear and sharpening

Task 1. What do you know about the history of industrialization? Name the most important scientists in the field of engineering and describe their inventions.

Task 2. Look at these pictures. Try to compare them and discus the problem of industrial modernization and automation.

Task 3. Read the text and translate all underlined words into Ukrainian.

Tool wear

Metal cutting tools wear constantly when they are being used. A normal amount of wear should not be a cause for concern until the size of the worn region has reached the point where the tool should be replaced. Normal wear cannot be avoided and should be differentiated from abnormal tool breakage or excessively fast wear. Tool breakage and an excessive rate of wear indicate that the tool is not operating correctly and steps should be taken to correct this situation.

There are several basic mechanisms that cause tool wear. It is generally understood that tools wear as a result of abrasion which is caused by hard particles of work material plowing over the surface of the tool. Wear is also caused by diffusion or alloying between the work material and the tool material. In regions where the conditions of contact are favorable, the work material reacts with the tool material causing an attrition of the tool material.

The rate of this attrition is dependent upon the temperature in the region of contact and the reactivity of the tool and the work materials with each other. Diffusion or alloying also occurs where particles of the work material are welded to the surface of the tool. These welded deposits are often quite visible in the form of a built-up edge, as particles or a layer of work material inside a crater or as small mounds attached to the face of the tool.

Among the other mechanisms that can cause tool wear are severe thermal gradients and thermal shocks, which cause cracks to form near the cutting edge, ultimately leading to tool failure. This condition can be caused by improper tool grinding procedures, heavy interrupted cuts, or by the improper application of cutting fluids when machining at high cutting speeds. Chemical reactions between the active constituents in some cutting fluids sometimes accelerate the rate of tool wear.

The wear mechanisms described bring about visible manifestations of wear on the tool which should be understood so that the proper corrective measures can be taken, when required.

Flank Wear: Tool wear occurring on the flank of the tool below the cutting edge is called flank wear. Flank wear always takes place and cannot be avoided. It should not give rise to concern unless the rate of flank wear is too fast or the flank wear land becomes too large in size. The size of the flank wear can be measured as the distance between the top of the cutting edge and the bottom of the flank wear land.

Cratering: A deep crater will sometimes form on the face of the tool which is easily recognizable. The crater forms at a short distance behind the side cutting edge leaving a small shelf between the cutting edge and the edge of the crater. This shelf is sometimes covered with the built-up edge and at other times it is uncovered. Sometimes cratering cannot be avoided and a slow increase in the size of the crater is considered normal.

Cutting Edge Chipping: Small chips are sometimes broken from the cutting edge which accelerates tool wear but does not necessarily cause immediate tool failure. Chipping can be recognized by the appearance of the cutting edge and the flank wear land. A sharp depression in the lower edge of the wear land is a sign of chipping and if this edge of the wear land has a jagged appearance it indicates that a large amount of chipping has taken place.

Deformation: Deformation occurs on carbide cutting tools when taking a very heavy cut using a slow cutting speed and a high feed rate. A large section of the cutting edge then becomes very hot and the heavy cutting pressure compresses the nose of the cutting edge, thereby lowering the face of the tool in the area of the nose. This reduces the relief under the nose, increases the width of the wear land in this region, and shortens the tool life.

Surface Finish: The finish on the machined surface does not necessarily indicate poor cutting tool performance unless there is a rapid deterioration. The principal cause of a poor surface finish is the built-up edge which forms along the edge of the cutting tool. The most effective way to eliminate the built-up edge is to increase the cutting speed. When the cutting speed is increased beyond a certain critical cutting speed, there will be a rather sudden and large improvement in the surface finish.

Cutting tool materials that do not alloy readily with the work material are also effective in obtaining an improved surface finish. Straight titanium carbide and diamond are the two principal tool materials that fall into this category.

Task 4. Answer the following questions:

1. What is tool wear?

2. What does an excessive rate of wear indicate?

3. How can temperature influence tool wear?

4. What basic mechanisms that cause tool wear can you name?

5. From time to time cratering cannot be avoided and a slow increase in the size of the crater is considered normal, isn`t it?

6. How can chipping be recognized?

7. When does deformation occur?

8. How to eliminate the built-up edge of a tool?

Task 5. Decide whether the following statements are true or false:

1. An excessive rate of wear indicates that the tool is not operating correctly and it should be corrected.

2. Wear is caused only by alloying between the work material and the tool material.

3. Where the conditions of contact are favorable, the work material reacts with the tool material causing an acceleration of the tool material.

4. The rate of attrition is dependent upon the temperature in the region of contact and the reactivity of the tool and the work materials with each other.

5. Chemical reactions between the active constituents in cutting fluids accelerate the rate of tool wear at all.

6. Flank wear is a tool wear occurring on the flank of the tool below the cutting edge.

7. Often cratering cannot be avoided and a slow increase in the size of the crater is considered quite normal.

8. Chipping can be increased by the appearance of the cutting edge.

9. The principal cause of a poor surface finish is the built-up edge which forms along the edge of the cutting tool.

10. The most effective way to eliminate the built-up edge is to decrease the cutting speed.

Statement	1	2	3	4	5	6	7	8	9	10
T
F

Task 6. Put these words into the right word order to make a sentence.

1. entire length / the width of the / ideal conditions / surprisingly / along its / quite frequently / occur / flank wear land / Under /will be very uniform / which .

2. are encountered / the heated metal / also contributes to / Oxidation of / tool wear, / and high cutting temperatures / particularly when / near the cutting edge / fast cutting speeds.

3. and diamond are / Straight titanium carbide /the two principal tool materials/ this category /that fall into.

4. The most / the built-up edge is/ to increase /effective way to eliminate/the cutting speed.

5. occurs on carbide/ Deformation/ and a high feed rate / cutting tools /when taking a very heavy/ cut using a slow cutting speed.

Task 7. Match the beginnings (1-10) of the sentences with their endings (a-j).

	beginning		ending
1	Breakage of the cutting edge caused by overloading, heavy shock loads, or improper tool design...	a	... at cutting speeds where a good surface finish will result.
2	However, if the rate of crater growth is rapid, ...	b	... is enlarged at the nose of the tool.
3	Cemented carbide tools can operate successfully at higher cutting speeds, where the built-up edge ...	c	... increase the cutting speed.
4	Whenever possible, cemented carbide tools should be operated ...	d	... of the wear land may become somewhat slanted.
5	The best measure of tool wear ...	e	... quite large in relation to the subsequent total amount.
6	When the depth of cut is uneven the bottom edge ...	f	... is flank wear.
7	When a sharp tool is first used, the initial amount of flank wear is ...	g	... leading to a short tool life, corrective measures must be taken.
8	Under normal operating conditions, the width of the flank wear land will increase at a uniform rate ...	h	... is not normal wear and should be corrected.
9	The most effective way to eliminate the built-up edge is to ...	i	... until it reaches a critical size after which the cutting edge breaks down completely.
10	Often the size of the wear land ...	j	... does not occur and where a good surface finish is obtained.

Task 8. Fill in the gaps using the words from the box. Use each word only once.

material, disadvantage, lubricated, reduces, expensive, water, provided, creating, diamond, stones, exposed, polishes, softer, easier, than, sharpening

Sharpening is the process of 1)_____ or refining a sharp edge of appropriate shape on a tool or implement designed for cutting. The substance on the 2)_____ surface must be harder 3)_____ the material being sharpened; 4)_____ is extremely hard, making diamond dust very effective for sharpening, though 5)_____; less costly, but less hard, abrasives are available, such as synthetic and natural Japanese waterstones.

T he Japanese traditionally used sharpening 6)_____ lubricated with water (using oil on a waterstone 7)_____ its effectiveness). They have been doing this for many hundreds of years, and the first stones were naturally occurring. The geology of Japan 8)_____ a type of stone which consists of fine silicate particles in a clay matrix. This is somewhat softer than Novaculite.

These 9)_____ Japanese stones have a few advantages over harder stones. First, because they are softer they do not become glazed or loaded with the 10)_____ they are sharpening. New particles are constantly 11)_____ as you work with them and thus they continue to cut consistently. Second, they can be 12)_____ effectively with water (rather than oil, which can ruin the stone) so nothing but 13)_____ is required. Finally, because they are soft, the worn material and the water form slurry that in conjunction with the stone sharpens and 14)_____ the blade.

A 15)_____ is that they become uneven faster than other types of sharpening stone, although at the same time this makes them 16)_____ to flatten.

Task 9. Make 5 questions of different types to the previous text on sharpening and ask your partner to answer them.

Task 10. Watch the video manual on sharpening a cutting tool. Do you know any other ways of sharpening metal cutting tools? Discuss with your partner all dangers and safety precautions working with sharpening tools.

Task 11. a) Why is it important for an engineer to know the properties of engineering materials? List the properties you know. Compare your list with that of your partner.

b) Discuss new ways and techniques in tool sharpening with your partner. Make a dialogue and present it to a group. The following words will help you. That’s how we attract somebody’s attention and express gratitude in English. Study this table.

HOW TO ATTRACT ATTENTION: Well… Listen … I say... Look … Look here … You know …

HOW TO EXPRESS GRATITUDE: Thank you. Not at all. Thanks. You are welcome. Many thanks. That’s all right. Thank you so much. Don’t mention it. Thanks a lot.

Task 12. Translate the following sentences into English:

1. Процес різання супроводжується утворенням теплоти.

2. Частіше за все при обробці різанням застосовують мастильно-охолоджуючі рідини.

3. Абразивне зношування – це механічне зношування матеріалу в результаті різання твердих тіл чи твердих частинок.

4. Інструменти зі швидкорізальної сталі володіють відносно невисокою теплостійкістю, середньою твердістю, невеликими міцністю при вигині і ударною в'язкістю.

5. Зношення різального інструменту залежить від шляху різання.

6. Основними елементами режиму різання є глибина різання, швидкість різання і подача.

7. Значний вплив на зношування здійснює температура нагріву різального леза.

8. При великих швидкостях різання, коли в зоні його розвивається дуже висока температура, твердосплавний інструмент інтенсивно зношується під дією дифузії.

	ARGUMENTATIVE ESSAY An argumentative composition is a piece of formal writing. There are various types of argumentative compositions such as: outlining the advantages and disadvantages of a certain question, giving your opinion on a subject, provid­ing solutions to problems and discursive essays. You should start a new paragraph for each new point you make. Each paragraph should start with a key sen­tence (a key sentence is a sentence which summarises the paragraph). You should provide examples and reasons to justify your points of view. Using quotations, whether writing the exact words spoken or paraphrasing, is a way of making your argumentative composition more interesting. e.g. "There is enough in the world for everyone's need, but not enough for everyone's greed." Frank Buchman” Before writing your composition, you should first make a plan. Plans for argumentative essays are given below.
		Introduction	Main Body		Conclusion
Advantages/ Disadvantages		Paragraph 1 state topic	Paragraph 2 advantages/ arguments for	Paragraph 3 disadvantages/ arguments against	Final Paragraph І Give a balanced consideration or your opinion without using personal words or expressions
Exoressing opinions		Paragraph 1 state opinion	Paragraph 2 argument 1 & reason	Paragraph 2 argument 2 & reason	Final Paragraph Restate opinion using different words
* When writing an argumentative essay expressing opinion, you may include the opposite point of view (other people`s opinion) in a sperate paragraph before the conclusion.
Providing solutions		Paragraph 1 state the problem	Paragraph 2 suggestion 1& reason	Paragraph 3 suggestion 2 & reason	Final Paragraph summarise opinion or give best suggestion and reason
Discursive essays		Paragraph 1 state topic	Paragraph 2 one point of view (e.g. political)	Paragraph 3 another point of view (e.g. economic)	Final Paragraph give your own opinion based on the points already mentioned

T ask 13. Look at the picture and write an argumentative essay (not over 100-120 words) about tool sharpening evolution. Special attention should be given to the problem of tool wear and advantages/disadvantages of modern types of sharpening.