REVIEW QUESTIONS

Question 1

22. Explain the different working principles (work-, force-and path-bound) of press machines.

Answer 1

Energy driven - Most simple because the only energy in the process is defined by the machine. The more energy you put in the machine to move the ram the higher forming force you get.

Force driven - Most contemporary because it uses
hydraulic presses. You control the force by controlling the hydraulic pressure. Slow though.

Path driven - Still commonly used, the other principles developed from this one. Crank mechanism driven by transmission and electrical motor. Forming force depends on the path where the ram is positioned. When in upper position we have different availability of the force needed to deform the material.

Question 2

21. Define static stiffness of a press and describe its experimental determination by measurements.

How is static stiffness related to static compliance?

Answer 2

Stiffness = the capacity of a “mechanical system” to sustain loads without deformation.

A force between the table and the ram (guided slide) is applied and measured in the displacements/offset with a force transducer. A linear graph shows the displacements and force, area where the displacement is proportional to the load/force, the ratio between the force and the measured displacement is called static stiffness.

Compliance is the ratio of deformation to force causing this deformation. The compliance is inversely proportional to the stiffness, stiffness gives a minimal compliance.

Question 3

23. Describe the basic ideas of a closed die and an open die process to produce fiber-reinforced polymer.

Answer 3

Closed die – Two parts of a die, put sheet/bulk molding compound in between and press while applying heat. The same can be done with liquid composite molding, resin is pumped into the die, also where the fibers are put. Better for low volume, which is the case in aerospace, and better than hand-layup or compression molding.

Open die – Only one side of a mold. Vacuum or air pressure can be used to press the compound against the walls in the die. If need for very high pressure or if the component is very large, an autoclave can be used. Both hand lay-up and spray lay-up is used for applying resin and reinforcement. This is done manually and it is slow and costly.

Question 4

24. What are the fundamental principles behind the reduction in the cutting forces and cutting temperature in orbital drilling?

Answer 4

The cutting tool can move in axial direction to drill or machine a hole and navigate horizontally (like a milling tool) to machine an opening or cavity larger than the diameter of the tool. With vortices created, the heat is extracted and a gap between the tool and the hole to get rid of the chips. In orbital drilling only one or two cutting edges are used, in opposed to conventional drilling where typically more cutting edges are engaged in the workpiece. From an energy point of view, this will result in fewer forces – less energy use – less thermal energy

Question 5

1. How did the 1st industrial revolution change manufacturing?

Answer 5

Transition from manual production to machine production, often using steam power.

It was the start of the factory system and gave way for new manufacturing processes that allowed for more standardized and precise products that could be manufactured a lot faster, which gave competitive advantages.

Question 6

2. What are the major aspects of Industry 4.0?

Answer 6

Digitalization of manufacturing and smart machines/factories that are connected by IoT. Connectivity between assets which enables them to communicate and make decision without the help or supervision of humans. Platforms where information and services can be shared.

Question 7

3. Define manufacturing in terms of technology and economics.

Answer 7

Manufacturing in technological terms is using physical processes to change the shape, look or other properties of a material. Or workpiece to obtain a specific part or product. In economics terms it means to process materials or assembly pieces so that the product values are increased.

Question 8

25. What are the fundamental principles behind the reduction in the cutting forces and cutting temperature in vibration-assisted drilling?

Answer 8

Cyclic engagement and disengagement between the tool and workpiece. As for orbital drilling up and down movements creates vortices, which lets the tool cool down between the cutting. Progressive material removal, also chip breaking so no long pieces of chips are formed. Easier chip removal.

Question 9

31. Identify the two forces that can be measured in orthogonal cutting.

Answer 9

Cutting force: Fc

Thrust force: Ft

Question 10

20. What are the main elements of machines for metal forming?

Answer 10

1. Drive
2. Guide
3. Controls
4. Frame

Question 11

19. How is productivity of a certain machining operation associated with machine tools? Consider putting the discussed case study into a perspective.

Answer 11

Capacity increases if two spindles instead of one. But cost appr. 5 times more. Would then 2xone spindle machines be better? More maintenance. OEE, 80 % is the goal.

Question 12

18. Linear motors for machine drives and tables. Describe the two major types of motors and their key performance characteristics.

Answer 12

• Synchronous: Most common of linear motors. One side with permanent magnets. Electricity in the coils control the magnetic field and movement. Cooling is needed, water is usually used. Most common, cheap.
• Linear induction (asynchronous): Instead of magnets you have short circuit rods that create an opposing magnetic field that generates the movement. They are bigger and cheaper but don’t have the same performance as the linear synchronous motors.

Question 13

17. A ball screw is a linear drive that translates rotational motion to linear motion. Sketch the design of such a typical ball screw.

Answer 13

bild

Question 14

16. What is the roll of structural loop of a machine? Are there any negative effects of inadequate stiffness and damping on machining performance?

Answer 14

The structural loop of a machine tool needs to hold the components and to withstand the forces which are produced by thee process and from the machine motions. Structural loop is an assembly of mechanical components which maintain a relative position between specified components. The forces in the machine to remove material is static forces that will deform all elements, you want to avoid this with stiffness and damping in the system to reduce the vibration level to maintain high precision.

Question 15

26. Propose an approach to define the optimum cutting conditions while satisfying some of conflicting design requirements for quality attributes.

Answer 15

Use of model to predict forces and part damage. And how optimization of the design of different tool geometries (test different parameters) that can improve the cutting condition and at the same time met the design requirements for quality attributes.

Question 16

27. What are the main elements for off-line on-line adaptive control system for drilling a stack of materials?

Answer 16

When off-line, no tool wear can occur.
With off-line, forces can be used to calculate the correct cutting conditions. When tool wear occurs, we must go on-line to look at the power (force?) from the spindle for drilling for example.

Question 17

28. Name and briefly describe the three types of chips that occur in metal cutting

Answer 17

Segmented
Continuous
Cont. with BUE

Question 18

29. What is an orthogonal cutting operation? Why is the orthogonal cutting model useful in the analysis of metal cutting?

Answer 18

The cutting edge is perpendicular to the cutting speed. It is useful in the analysis of metal machining because it simplifies complex 3D machining situations to 2D.

Question 19

30. Identify the four forces that act on the chip in orthogonal cutting but cannot be measured directly in an operation.

Answer 19

Friction force: F
(And normal force to friction)
Shear force: Fs
(And normal force to shear)

Question 20

32. Elaborate on the thermal aspects of metal cutting (heat sources, heat partition, temperatures, etc.

Answer 20

During machining heat is generated at the cutting point from three sources. It is sheared by the chip, cutting tool and the blank. The distribution of heat depends on size and thermal conductivity of the tool – work material and the cutting condition. The majority (ca. 80%) of the energy is carried away with the flowing chip. 10-20 % goes into the tool and some heat is absorbed in the blank.

Primary shear zone - Where a major part of the energy is converted into heat.

Secondary deformation zone - At the chip – tool interface where further heat is generated due to rubbing and/or shear.

Worn out flanks – Due to rubbing between the tool and the finished surface.

Question 21

68. Grinding creates high temperatures. How is temperature harmful in grinding?

Answer 21

The most important aspects of surface integrity are associated with thermal damage caused by excessive grinding temperatures. It affects the quality of the workpiece.

Question 22

69. Which are the most common grinding operations? Illustrate them.

Answer 22

External cylindrical
Internal cylindrical
Surface

Question 23

72. Using the theory of Aggressiveness, if I increase the wheel RPM, will I do more cutting or more rubbing? Will surface finish get smoother or rougher?

Answer 23

If we increase the wheel speed to max chip thickness will decrease.
If we slow down the wheel will increase the maximum chip thickness.
Smaller chips give better smoother surface. But it will also generate more heat.
Many grits do not form a chip, but merely plow or rub. These three interactions produce forces and heat generation.

Question 24

4. Briefly define quality and quantity in terms of manufacturing.

Answer 24

Quality is how well a product is made and meets the requirements/demands of the customers. Quantity is the amount produced and the resources necessary to manufacture it.

Question 25

5. What is accuracy and precision in manufacturing?

Answer 25

Accuracy describes how closely a manufacturing machine’s output conforms to the measurement from the system. Describes “close-to-true value”.
Precision for a machine or process is the ability to repeat an action the same way every time with no introduced or random error. Describes “repeatability”.

Question 26

6. Name some of the reasons why surfaces are important?

Answer 26

Aesthetic reasons, safety, friction, and wear, affects mechanical and physical properties as well as assembly.

Question 27

8. What is the purpose with: VOP ≠ VOC

Answer 27

VOP is the voice of the process that is normally captured with control limits. VOC is the voice of the customer, which is expressed with specification limits (tolerances). There is no physical connection between the two.

Question 28

9. What is the purpose with: Common vs. special causes of variation

Answer 28

Common cause of variation is caused by unknown factors, resulting in a steady but random distribution of the output.

Special cause of variation is unexpected variation in the process. There is no specific cause that can be assigned to the variation. Requires actions to address these variations.

Question 29

33. Name and illustrate the basic kinematics of the three most common machining processes.

Answer 29

Turning
Drilling
Milling

Question 30

34. Schematically illustrate (peripheral) milling process and explain the difference between down-and up-milling operation.

Answer 30

In peripheral milling the side of the cutter grinds away at the top of the workpiece. In contrast to face milling where the tip of the cutter presses against the workpiece.

In up milling the cutter and the feed moves in opposite directions. The rotary moves against the feed. The chips increases from minimum to maximum. Massive friction between the cutter and workpiece which results in generating quite large amount of heat. Requires more force compared to down milling and the finish is poorer. Mostly used for rough cutting operations. You get more tool wear and reduced tool life.

In down milling the cutter rotates in the same direction as the feed. Less friction, results in minimum heat. The thickness of the chip varies from maximum to minimum during the process. Requires less amount of force and give a good finish.

Question 31

35. Explain and illustrate the most common machining processes used in the manufacture of gears.

Answer 31

Hobbing

Broaching

Skiving

Question 32

36. In below picture of an AWJ cut part, about 10 mm thick – which of the sections I, II and III is the (most) correct one? Assuming you are cutting quite fast. The hole is about 10 mm in diameter.

Answer 32

The first one (I) – The hole will be larger at the bottom since the jet lag will point outward away from the center of the hole as jet lag is reduced slightly further away from the cutting head.

Question 33

37. Describe in detail how an AWJ-cut surface is formed, what mechanisms are involved etc. Also point out how different surface qualities are related to different mechanisms of removal.

Answer 33

The jet contains water droplets, abrasive particles, and air. A pure water jet (pressure converted to high speed) is let out in a small mixing chamber. There, the jet creates a vacuum and draws in abrasives that are fed into a tube. The abrasives are accelerated through a nozzle and let out as abrasive waterjet.

Defects occur as a result while changing directions at a constant cutting speed. The material removal mechanisms are:

In the upper part of the cut:
• Grains hit a shallow angle
• Chip small formation
• So called cutting wear

In the lower part of the cut:
•	Grains hit at a not so shallow angle
•	Erosion due to cyclic load of multiple grains 
•	Deformation wear
•	Larger pieces of material are removed

Question 34

38. From the perspective of a designer (of mechanical parts) –what optimization/adaption should you make to your design so that it is cut (more) quickly? Point out at least four things and explain how and why they affect manufacturing time.

Answer 34

Geometry – Avoid sharp corners (small inner and outer radii) these require deceleration and acceleration to avoid geometrical defects in corners due to lag of the jet (bottom part behind). Will lower the cutting speed.

Thickness – Thicker material means slower cutting speed. But if selecting a thinner material, it might need to be stronger.

Material – A typically difficult-to-machine material can be chosen but consider the need of final machining.

Quality of cut – Define which surfaces are to be of good quality and whether only “separation cuts” are OK on other surfaces.

Question 35

39. Define and explain at least three macro-geometrical defects one might find on an abrasive waterjet cut part. For two of the defects, you should also explain its cause. (Explanation of type of defects in question: form errors or geometrical errors which are NOT part of the surface topography).

Answer 35

Tapering – The cut is wider at the top.
The reason is that the jet has a lag, and it is
therefore, narrower in the bottom.

Top edge rounding – Due to spraying of
abrasive particles, non-perfectly focused jet.

Corner defects – Due to lag of the jet, the
bottom part of the jet is geometrically in behind the top
programmed path. Even though deceleration in corners it’s
still there and more visible in low quantities.

Question 36

41. Laser cutting:
    a) Why are pulsed lasers of interest in cutting? How can the quality of a part be improved by using a pulsed laser?
    b) Why can the cutting speed for laser cutting typically be much higher in ordinary mild steel than it is for cutting in stainless steels? Explain!

Answer 36

It is a simple way to continuously control the power. Continuous laser can result in excessive heating in corners and lower traverse speed, avoided by using
pulsed laser, receiving higher quality.

Because of exothermal reactions. Stainless steel does not react in the same way as mild steel.

Question 37

42. Describe a cutting head for laser cutting (make a sketch). There are typically three separate “functions” or parts in a cutting head. What are these and what are the purpose of each? Details on the interactions with the workpiece are not necessary.

Answer 37

Gas assistance:
•	Blows away molten material
•	Protects the cutting head
•	Can prevent oxidation
•	Oxygen provides additional energy in Fe-cutting

Cooling:
• To avoid so called “thermal lensing”
• Reduce the change in lens shape and material properties

Lens for focusing on point at workpiece:
• The lens needs to retain the shape accurately, since it gets heated by the laser it needs to be cooled down.

Question 38

43. Laser light must be transmitted from the laser source to the cutting head. There are at least two main different laser types, commonly used for cutting, which use two different methods for transmission of the laser light.

• Which are the laser types (laser media)?
• What two different methods (technologies) of transmission of the light do these laser types normally use, and how does this influence the possibility of automation?
• What basic property of the laser light is the cause of this difference?

Answer 38

CO2 (most common), Nd-YAG laser and fiber.

In CO2, light is produced when electricity runs through a gas-filled tube with mirror at both ends.

Fiber laser. Light is created by banks of diodes. Easier to use in industrial robots.

Question 39

44. Lasers
    a) Laser lights have some particular properties (compared to say an ordinary flashlight). Which are these? (Describe them shortly.)
    b) What main functions or components are there in the laser source?

Answer 39

• Monochromatic (same wavelength)
• Coherent (in phase)
• Directed (close to parallel)

Components: 
o	Mirrors (fully reflected and semi)
o	Active medium
o	Excitation energy 
o	Laser beam
o	Loss of heat/cooling device.

Question 40

45. The dielectric fluid in EDM has several functions. Shortly explain 2 functions. Answer mainly for sink (ram) EDM.

Answer 40

Insulates – Prevents sparking to occur before correct distance and voltage

Cools workpiece and tool – EDM is a thermal and slow method creating heat

Flushes material away - Helps in the material removal

Question 41

46. Why is EDM used in industry? Why hasn’t for example milling replaced EDM? Discuss some important features/advantages of the method –mainly for Ram/sink EDM. But also –point out some important disadvantage of EDM.

Answer 41

Complex geometries can be produced
No forces required
High degree of automation
Not sensitive to conventional hard to machine materials as long as they are conductive

Question 42

47. Forming Limit Diagrams (FLD) are useful in sheet metal forming operations:

• What is an FLD and how do you use it?
• What information is necessary for being able to use it? - Give some examples of some state of deformation that indicates something valuable from the diagram and explain shortly.

Note: You should not try to explain how the diagram itself is constructed (what tests are made etc. to construct it). This is typically made by the sheet-metal supplier.

Answer 42

FLD are useful tool for evaluating strains in metal sheets. It represents the forming limits and shows where the major/minor stresses and local necking failures occurs.

Question 43

48. Two “types” of anisotropy is of importance in forming. Which are these? Define them and discuss their role and importance. A mathematical definition is not needed (or intended).

Answer 43

The material will deform more/less easy in different directions.

Normal anisotropy – How much easier the material will deform in the
plane than in the thickness direction. This is good, gives better formability.

Planar anisotropy – Is when deformation happens more (or easier) in one or
several directions in the plane. This leads to earing e.g. (see pic.)

Question 44

49. Which material properties (or material features) affect formability? Explain how and why they affect!

Answer 44

Formability is the ability of a given metal workpiece to undergo plastic deformation without being damaged. Knowledge of the material formability is very important to the layout and design of any industrial forming process.

Tensile strength
Ductility
Anisotropy

Question 45

50. Explain where (approximately) in a Forming Limit Diagram one would find indication of wrinkling. (Draw an FLD)

Answer 45

Left down corner(negativ e_min)

Question 46

95. What are the main differences between micro-machining and conventional machining procedures?

Answer 46

• Uncut chip thickness – material removal rate is much lower
• Dimensions and accuracy of micro parts or features
• Cutting tool geometry (much sharper)
• Cutting environment must be more stable

Question 47

96. What is the size effect and how can affect the micro-milling process?

Answer 47

Chip thickness is smaller than the grain size of the material. Always negative rake angle. The size effect is defined as the ratio between the depth of cut and the angle radius of the tool. The tool radius is the most important aspect of the chip thickness.

Three size effects:

a. Chip thickness is lower than the radius. Not cutting only pushing the material, gives only plastic deformation, bad surface, and heat.
b. Chip thickness is equal than minimum chip thickness  may remove material.
c. Chip thickness is larger than minimum chip thickness. Surface is good, should be like this. Important to know the tool radius.

Question 48

97. Name 4 challenges in the micro-milling process and explain how they can be addressed and reduced in the micro-milling?

Answer 48

• Tool Run-out – Is characterized by misalignment and/or eccentricity between the axis the spindle and the axis of symmetry of the tool.
• Tool Wear and Life – More important than in conventional processes. Wear dependent on material alloy.
• Micro-Burr Formation – Burr reduces part accuracy and quality but also affects its assembly and functionality of the part. Removing this is expensive and time consuming when the parts are so small.
• Process Conditions Optimization – For industrial production, there is always a tradeoff between performance and productivity. Improving both together is a challenge. In micro milling, changing cutting parameters are not so easy.

Question 49

99. Name 5 important criteria in the case of micro-machines.

Answer 49

• Design requirements
• Active cooling
• Environment
• The Limits of positioning accuracy
• Precision in nano scale

Question 50

100. What is the critical chip thickness in micro-grinding (with a graph)?

Answer 50

Bild

Question 51

54. What main process parameters are there in hydroforming? Name and describe (shortly) at least three. In your answer include a short process description or figure where the process parameters are included.

Answer 51

Pressure – Provides forming and calibration in cavities
Axial force – Provides sealing and is correlated to the position
Horizontal path – Position of the axial cylinder

Question 52

55. In hydroforming, an advantage mentioned is that wall thickness is more uniform. Why would that be the case? (Why is the wall thickness more uniform within a part?) Compared to what?

Answer 52

Less localized wall thinning. Hydroforming flows the metal rather than stretching it. Therefore, the material thin out is minimal.

Question 53

56. Below parts are to be formed with hydroforming. Which one is more difficult (and even impossible). Short explanation required.

Answer 53

The 2 one is easier. The 1 one, infeed is needed for making the deformed middle part from a straight tube. Infeed through bends is difficult.

Question 54

57. Roll forming: It is mentioned that increased sheet material strength reduces the number of roll forming steps necessary. Why do we have this dependence?

Answer 54

Roll forming can lead to plastic deformation in between the roll pairs which is not wanted – you want the deformation to take place in the rolls. Otherwise not controlled and problems with straightness of beams. The higher strength material will stay more in the. Elastic stage and the risks diminished.