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Exame Final versão A Complementos de Tecnologia MecânicaMestrado em engenharia Mecânica 1º Semestre do ano lectivo 2014/2015Duração: 1h305 de Janeiro, 8h

Grupo I – Perguntas múltipla escolha (15Valores)

IMPORTANT: In the following questions, select from among the 4 answers given, which correct. Please note that the number of correct answers can vary between 0 and 4. Evaluation Criteria: +0.075 correct values for each point and each point -0.075 incorrect

1. Indicate four factorsthat diferenciate brasing from mechanical bonding

a)

b)

c)

d)

2. Indicate the physical state of the materials involved in the following Welding processes

Base Material Filler Material

Fusion Welding

Brasing

3. The types of energy sources used in welding are

a) Electric Arc, Flame

b) Electric, Mecanichal and Chemical

c) Resistance, electric arc, flame and radiation

d) Oxigás, explosion, friccion

4. Indicate the true and false sentences (CA-Alternative current;CC-continuos current)

a) The electric arc is less stable when CA is used instead of CC

b) The is a hogher risk of magnetic blow when CA is used comparatively to CC

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c) The metal transfer mode is more unstable when CA is used comparatively to CC.

d) Heat input is higher when CA is used comparatively to CC

5. What is arc Welding?

a) It is the group of Welding processes that achieves the joining of metails by cooling with na electric arc, with or without pressure or filler material

b) It is the group of Welding processes that achieves the joining of metails by heating with an electric arc, with or without pressure or filler material

c) It iswelding in a butt joint with na arc shape

d) It is the joining of materials obtained by melting

6. Indicate the type of protection used with the following Welding processes

a) TIG (GTAW) ________________________________________________

b) Elétrodo revestido (MMAW) ____________________________________

c) Fios Fluxados (FCAW) ________________________________________

d) Arco Submerso (SAS) ________________________________________

7. Indicate the type of consumable used with the following Welding processes

TIG (GTAW) ________________________________________________

Elétrodo revestido (MMAW) ____________________________________

Fios Fluxados (FCAW) ________________________________________

Arco Submerso (SAS) ________________________________________

8. Which of the following safety measuras help avoiding the effect of radiation from the electric arc

To use a welding mask

To use gloves

To use a fume extractor

To use non inflamable clothes

9. Indicate which of the sentences are true and false quais as afirmações verdadeiras e quais as afirmações falsas

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a) In MMAW the arc is initiated by short circuiting

b) In GMAW (MIG/MAG) the arc is initiated by using a high frequency current

c) In Plasma Arc Welding the arc can be initiated either by short circuiting or high frequency

d) In GTAW (TIG) the arc is initiated by short circuiting

10. Which of the following sequences represents Welding processes organised by decreasing order of energy density?

a) Spot Welding, laser welding, electron beam welding, oxigas welding

b) Electron beam welding, laser welding, Spot Welding , oxigas welding

c) arc welding; laser Welding ; Spot Welding; oxigas welding

d) laserwelding ; arc welding

11. Which of the following alternatives are true?

a) One of the roles of the electrode cover is to increase the level of hidrogen in the weld.

b) One of the physical functions of the electrode is to supply gases for the shielding atmosphere.

c) One of the electrical functions of the cover of the electrode is electrical isolation.

d) In manual metal arc Welding the electrode supplies the filler metal.

12. Fill in the table bellow indicating true(T) and False (F) on the options for the shielding gas used in GMAW for the materials indicated.

Gás

Material Argon Argon + CO2 CO2 Argon + O2

Stainless steel

Alumínium

Low alloy and micro alloy

steel

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13. Which is the type of static characteristic (V/I) of the welding equipment that promotes the self-regulating effect

a) Dropping

b) Horizontal

c) Vertical

d) Oblíquos

14. What is deposition rate?

a) It is the tax paid to the deposited metal per unit of time

b) It is the tax of removed material from a weld

c) It is the weight of the deposited material per unit of time.

d) It is the weight of material per time interval

15. In GTAW the electrode should be connected to

a) positive pole

b) negative pole

c) the plate

d) the filler wire

16. Submerged arc welding (SAW) is used in:

a) Thick plate, downhand position

b) Thin plate

c) Thick plate, vertical position

d) Overlap joints

17. The welding parameters that must be selected when starting Welding with submerged arc Welding area

a) Stick out

b) Welding speed

c) wire/flux binary

d) wire diameter

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18. Indicate the best Welding process to be used, considering cost and quality, for full penetration circular welds en carbon steel with 450mm diametrr and 10mm thick, for prodution og high number of parts.

a) Submerged arc welding

b) Manual Metal arc welding

c) GTAW(TIG)

d) GMAW (MIG/MAG)

19. Dilution changes, among others, with the Welding process. Indicate the true sentences.

a) In brasing the dilution is 0%

b) In autogeneous welding dilution is 100%

c) In solid state welding dilution is 0%

d) Dilution is the relation between the quantity of the melted base material and the total melted material

20. Indicate four factors that influence the susceptibility of cold cracking in steels:

a)

b)

c)

d)

21. In stainless steels which weldability problems may occur?

a) Cold cracking

b) Hot cracking

c) Occurence of phase

d) Precipitation of cromium carbides

22. Lamelar tearing that can occur in welded joints is characterized by:

a) Occuring essencial in high ductility steed in the direction of the thickness of the plates

b) Occuring in the HAZ of thin laminated plates, subjected to tensions perpendicular to the laminating direction

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c) Occuring in the fusion zone of laminated thick plates which have low ductility in the direction of the thickness and subjected to tensions perpendicular to the laminating direction.

d) Occuring in all types of stells in T joints

23. Indicate four actions you would take for minimising the risk of hot cracking in a low alloy steel

a)

b)

c)

24. In laser welding, when comparing concuction and key hole welding, which ofthe sentences are correct:

a) The power used\is\the same but the speed is different

b) The quality of the weld is different

c) The temperature reached during welding is the same.

d) The coupling of the baem is higher in key hole than in conduction mode.

25. Comparing electron beam welding with laser welding using the power, the same interaction time and the same beam diameter for welding 4mm thick aluminium, which of the options\are correct

a) Penetration is the same.

b) The welding speed is higher in electron beam welding

c) Reflectivity ofthe beam only occurs in laser welding

d) The weld beads obtained are equal

26.For Hybrid weding which of the following sentences are correct

a) Laser is the main responsible for penetration, while the arc adds the filler metal

b) Laser and arc don’t need to share the same weld bead

c) It doesnt’t have any adavantage since the arc slows the processs

d) It is only used in thin plates

27. Which of the following do not apply to friction stir welding

a) Heat generation is related with friction mechanisms

b) The tool used is consumable

c) Heat generation is influenced by rotational speed

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d) The tools developed promote a descendente flow of material to consolidate the weld.

28. Which of the following processes are solid state welding processes

a) Explosion welding

b) Resistance welding

c) Difusion weding

d) Friction welding

29. The diferent solid state welding processes have the following common characteristics

a) Use of non consumable tools

b) Existance of three diferent metalurgical zones

c) Difusion joining

d) External heat sources

30. Brasing is characterised by:

a) Utilising fillers with fusion temperature higher than the pieces to join

b) Joining is affected by diffusion and metallurgical reactions on the surfaces of the parts to join.

c) The filler metal needs to wet the surface.

d) Joining of the parts is permanent.

31. The basics of weak brasing are:

a) The filler materials have a fusion temperature bellow 450C

b) The mechanical configuration of the joint can improve the joint resistance.

c) Joining is due to the adhesion force in the interfaces of the parts

d) The joining process occurs at a temperature higher that the fusion temperature of the parts to join.

32. Brasing is:

a) Advantageous for complex jints

b) Not good for joining metals to nonmetals

c) The joints require low or no finishing

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d) Originates bad distribution of heat and stresses

33. In oxigas welding:

a) No filler metal is used.

b) The surfaces of the metal to join are melted by a flame.

c) No pressure is needed

d) The process uses two gases, oxigene and acetylene.

34. Oxi acetylene welding is characterised by

a) Being able to use three types of flames

b) The reductive flame is characterised for using an excess of oxygen.

c) The reductive flame is usually used to weld steels

d) The flame can reach 3300C

35. In oxigas welding

a) The fluxes are used to prevent oxidation of the base material

b) The protection equipment includes goggles

c) Flame ignition must be done by first using oxygen and the combustible gas afterwards.

d) When switching off the equipment the combustible gas must be closed first

36. Indicate four resistance welding processes

a)

b)

c)

d)

37. Indicate the main parameters in resistance welding

a) Time

b) Force

c) Current intensity

d) Material to join

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38. Indicate the true and false sentences regarding resistance welding

a) Fusion occurs in the interface with higher resistance

b) Cooling under pressure doesn’t bring any benefit

c) For the same material, the thckness of the parts to weld doesn’t influence the process parameters

d) In Projection welding, the picks present less resistance than the remaining material

39. Indicate four advntages and four disavantages regarding adhesive bonding in comparision with welding

Advantages

a)

b)

c)

d)

Disadvantages

a)

b)

c)

d)

40. In destructive molding the quality, complexity and cost increase as follows:

a) Investment casting; “Shell molding” and green sand

b) Green sand; shell molding” and investment casting

c) “shell molding”; green sand and investment casting

d) All present the same quality level

41. Investment casting presents the following disavantages:

a) It is a hard working and costly process

b) It is a process usually used for large series of parts

c) There is the need to control tightly all the phases of manufacturing, as any dimensional error is transfered in all the subsequente phases.

d) It is applied to parts of large dimensions

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42. Casting in permanent metal moulding is not advised for casting the following materials

a) Steels

b) Aluminium and magnesium alloys

c) Copper, zinc and its alloys

d) All metals

43. All plastic materials present the following characteristics

a) Are good termal and electrical isolators

b) Present low processing temperatures

c) Present higher corrosion resistance by oxidation than metals

d) Are light

44. The extursion process is able to produce

a) Plastic parts of high geometrical complexity

b) Parts with constant or variable transversal section

b) Plates and profiles in plastic

d) “Lego” parts

45. Caso necessite de realizar uma avaliação por ensaios não destrutivos de uma soldadura de alumínio de 3 mm de espessura, que técnicas poderia utilizar:

In case you need to anlyse by non destructive testing a 3mm aluminium weld, which techniques would you use

a) Ultrasonic

b) Visual inspection

c) Magnetic particles

d) Radiografy

46. Industrial radiography allows to detect with higher clarity than conventional ultrasonic testing, the following type of defects:

a) Porosity

b) Slag Inclusions

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c) Cracks

d) Lack of fusion

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Grupo II – Análise Quantitativa (5.0 valores)

A company wants to build heat exchangers for which there is a need to manufacture pipes and to weld them as represented in thee figure below:

Notas:Piping thickness: 15mmHigh quality level The welds (with full penetration) are realized with basic covered electrodes (dried at 250ºC )

Base material - Steel Ck45:

C(%) Nb(%) Mn (%) Si(%) S (%) Cr (%) Mo (%)

0.45 - 0.30 ≤0.04 ≤0.01 - -

Answer the following questions:

a) (2val) Discuss the susceptibility of occurrence of the metalurgical problems y o u k n o w , i n t h e p r a c t i c a l c a s e u n d e r s t u d y

b) (2val) Analyse the need of pre heating by calculating the pre heating temperature and justifying your answer.

Consider that the weld was done with the following parameters: I = 180 A; V= 15 V; v =1.5 mm/s; η=65%. Justifique

b) (1val) Consider that the samecompany has also to weld the same type of parts but the pipes ahve now 5mm of thickness. The welding proces chosen is TIG and the same parametrs will be used. In this case would pre heating be needed? Justify your answer.

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Valores Críticos de Dureza e Escala de CeqDepósito sobre

chapaTopo Canto

Nív

el d

e H

idro

géni

o

Processos e Consumíveis

Supe

rfíc

ie c

ontín

ua

Supe

rfíc

ie ir

regu

alr

Nor

mal

Des

alin

hado

Pene

traçã

o pa

rcia

l

Pene

traçã

o to

tal

Prep

araç

ão d

e ju

nta

norm

al

Prep

araç

ão d

e ju

nta

maq

uina

da

Con

stra

ngim

ento

el

evad

o

Cas

os e

spec

iais

Elev

ado

Soldadura por eléctrodo revestido SERSoldadura por arco submerso (SAS) (fluxo básico)Soldadura com fios fluxados (SFF) (fluxo básico)

A350

A350*

A350

A350 220* 300*

A350

A350 300* 300

*

Méd

io

SER com eléctrodos secos a 250ºCSAS SFF C

400B

375*B375

B375 250*

A350*

B375

C400

A350

A350*

Bai

xo

SER com eléctrodos secos a 350ºCSAS e SFFMIG/MAG com fio sujo D

450C

400*C400

C400 300*

B375*

C400

D450*

B375*

B375*

Mui

to B

aixo SER com eléctrodos secos a 450ºC

SASMIG/MAG com fio limpoTIG 500

D450*

D450

D450

A350*

C400*

D450* 500*

C400*

C400*

Notas: Os valores de dureza marcados com (*) são estimativos. As letras (as mais claras representam valores estimativos) referem-se às quatro escalas de Carbono

Equivalente (Ceq) nas figuras seguintes e permitem a selecção da escala correcta.

Procedimento de cálculo da Espessura Combinada (Ec) :Onde : ti – corresponde à espessura da estrutura de índice i, adjacente ao cordão de soldadura.

Nota 1: Nas juntas topo-a-topo, t1 é a espessura média num comprimento de 75mm (a partir do centro do cordão)

Nota 2: A espessura combinada (Ec) para cordões de canto iguais e directamente oposto em juntas em T é dada por :

T3=0

Ec=t 1+t 2+t 3

Ec=12 (t1+t2+t3)

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Espessura combinada (mm)

(a) Temperatura mínima de pré-aquecimento local (ºC)

5156Mo%V%Cr%Ni%Cu%Mn%C%Cequ