Exame Final versão A
Complementos de Tecnologia Mecânica
Mestrado em engenharia Mecânica
1º Semestre do ano lectivo 2014/2015
Duração: 1h30
5 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
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
1
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
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
2
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
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
3
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
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)
4
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
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
5
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
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
d) Originates bad distribution of heat and stresses
6
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
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
7
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
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
8
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
c) Cracks
d) Lack of fusion
9
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: 15mm
High quality level
The welds (with full penetration) are realized with basic covered electrodes (dried at
250ºC )
Base material - Steel Ck45:
C(%)
0.45
Nb(%)
-
Mn (%)
0.30
Si(%)
≤0.04
S (%)
≤0.01
Cr (%)
-
Mo (%)
-
Answer the following questions:
a) (2val) Discuss the susceptibility of occurrence of the metalurgical problems
you know, in the practical case under study
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.
10
Valores Críticos de Dureza e Escala de Ceq
SER com eléctrodos secos a 350ºC
SAS e SFF
MIG/MAG com fio sujo
SER com eléctrodos secos a 450ºC
SAS
MIG/MAG com fio limpo
TIG
A
350
C
B
B
B
400
375*
375
375
Preparação de junta
maquinada
220*
300*
A
B
C
A
A
250*
350*
375
400
350
350
*
B
C
D
B
B
300*
375*
400
450*
375*
375
*
C
C
500*
400*
400
*
A
A
350
350
D
C
C
C
450
400*
400
400
D
D
D
A
C
D
500
450*
450
450
350*
400*
450*
Casos especiais
A
350
Preparação de junta
normal
Desalinhado
A
350*
Constrangimento
elevado
350
Normal
Superfície irregualr
A
Canto
Penetração total
Soldadura por eléctrodo revestido
SER
Soldadura por arco submerso (SAS)
(fluxo básico)
Soldadura com fios fluxados (SFF)
(fluxo básico)
SER com eléctrodos secos a 250ºC
SAS
SFF
Superfície contínua
Processos e Consumíveis
Topo
Penetração parcial
Muito Baixo
Baixo
Médio
Elevado
Nível de Hidrogénio
Depósito sobre
chapa
300*
300
*
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 (E c) :
Onde : ti – corresponde à espessura da estrutura de índice i, adjacente ao cordão de soldadura.
Ec  t1  t2  t3
Nota 1: Nas juntas topo-a-topo, t1 é a espessura média num comprimento de 75mm (a partir do centro do
cordão)
T3=0
Nota 2: A espessura combinada (Ec) para cordões de canto iguais e directamente oposto em juntas em T é
dada por :
Ec 
1
t1  t2  t3 
2
11
Espessura combinada (mm)
(a) Temperatura mínima de pré-aquecimento local (ºC)
C equ  %C  %
Mn  %Cu  %Ni   %Cr  %V  %Mo 



6
15
5

 

12