Tenta Flashcards
1
Q
What are the two different types of waterjet cutting?
A
- Pure Waterjets
2. Abrasive Waterjets
2
Q
In simple terms how do a waterjet cutting work?
A
High-pressured water, 3000-4000 and low water flow rate bar which is focused through an orifice creating a high-speed jet.
3
Q
What is different with abrasive water jets?
A
in abrasive waterjets, abrasive particles are added and the jet is re-focused in a second nozzle.
4
Q
Draw the system for a waterjet and pump.
A
See lecture ‘Waterjet’ for figure
5
Q
What are typical materials that pure WJ cuts?
A
- Interior vehicle parts
- Plastic
- Rubber
- Food
- Fibre wool
6
Q
What is the typical orifice diameter for pure WJ?
A
0,1-0,3 mm
7
Q
How does the pure WJ cut material?
A
High-pressure water from the nozzle shoots on to the part where pressure is distributed and sheer stress in the material occur. Material is sheared away.
8
Q
What types of errors can occur when cutting with a puer WJ?
A
For a ductile/sofe material shearing/deformation can occur.
For a brittle material crack propagation can occur.
9
Q
What is typical water orifice diameter for an AWJ?
A
0,23-0,35 mm
10
Q
What is the ratio between water orifice diameter and abrasive nozzle diameter for an AWJ?
A
Ratio 1:3
11
Q
What types of materials are AWJ used for?
A
- Metals
- Alloys
- Stones
- Ceramics
- Glass
- Composites
12
Q
What is the most used abrasive for AWJ?
A
Garnet
13
Q
What is the most important application for AWJ?
A
Cutting of plate material
14
Q
What plate thickness can AWJ cut?
A
10-100 mm plate thickness
15
Q
What are the advantages of AWJ?
A
- Small diameter, flexibility with respect to geometry
- Can cut thick dimensions as well as thin
- Not sensitive to classically difficult-to-machine alloys
- No heat affected zone
- Relatively easy to learn
16
Q
What are the disadvantages of AWJ?
A
- Relatively low cutting speeds
- Relatively expensive
- The jet continues after the cute
- The water makes oxidization a risk
17
Q
Explain variation in a process and how it can affect the outcome/customer
A
A process or operation produce something to a customer who has requirements on what is delivered, performance target.
Since everything vary the customer usually accept deliveries within some specification limits, ULS och LSL.
A stable predictable process varies between control limits.
If the control limits is not in the specifications limits there is waste and rework. Control factors can used to get the variation/control limits in the appropriate scope for the specification limits.
18
Q
Explain statistical control
A
A process that only contains common causes of variation is said to be in statistical control.
A process in statistical control is stable and predictable.
19
Q
When is a process in control?
A
When based on past experiences we can predict within limits how it will vary in the future.
20
Q
What is the goal with statistical process control?
A
- Control the process so it remains stable (so that no new special cause variation are introduced)
- To avoid over control of processes
- Find and eliminate special causes of variation
21
Q
Explain Western Electric Rules 1 and 4
A
Test special causes
Rule 1: Any single data point falls outside the 3-sigma limit from the center line
Trend shift
Rule 4: Nine consecutive point fall on the same side of the center line
22
Q
What is VOP?
A
The Voice of the Process is the natural process variation.
23
Q
What is VOC?
A
The Voice of the Customer is the customer expectation and its upper and lower tolerance limit.
24
Q
How do you want VOP and VOC to relate?
A
You want the customer needs to be broader than the process variation with some margin. You also want the process variation to be centered in between the customers tolerance limits.
25
What are two improvement strategies for process capability?
1. Decrease variation (standard variation)
| 2. Process towards center (mean)
26
What is the difference between Cp and Cpk?
- Cp will only consider process variation.
| - Cpk consider process both variations and center.
27
How do stability affect process capability?
Stability is required for process estimations without there will be no capability.
28
What are two mistakes of data analysis for statistics?
1. Interpreting the routine variation of noise as if it amounted to a signal of change in the underlying process, thereby sounding a false alarm.
2. Thinking that a signal of change in the underlying process is merely the noise of routine variation, thereby missing a signal.
The trick is to strike a balance between the two by filtering out the noise of routine variation in the data.
29
What are the two types of data for statistics?
- Observational studies
| - Experimental studies
30
Describe what the 3-sigma limit is?
3-sigma limits will filter out virtually all of the routing variation regardless of the shape of histogram
Points outside the three-sigma limits is a potential signal
31
Why is it important to look at the variation?
It's a risk to lose info when condensing into just a number.
Several graphs can have the same mean and standard deviation but show vastly different things.
32
Describe measurements precision
The measurement noise have to be small enough to let you see the difference that you want to see.
33
What is the definition of MSA?
Measurement System Analysis, MSA, is a set of statistical techniques for determining the error of a measurement system, commonly called R&R studies.
34
What are the three fundamental issues needs to be addressed in when evaluating a measurement system?
1. Does the measurement system have adequate discrimination?
2. Is the measurement system statistically stable over time?
3. Are the statistical properties consistent over the expected range and acceptable for process control - process decisions?
35
What are the impact of a poor quality measurement system?
- Actual process variation will never be known
- Good products may be falsely rejected
- Bad products may be falsely accepted
- Process capability will seem worse that it is
- Decision making will be more difficult
- Money will be lost
36
When can the measurement system be used for decision?
Measurement imprecision can be maximum 20% of spec width
37
What is measurement system discrimination?
Discrimination is adequate if its apparent resolution is small relative to the process variation
For adequate discrimination it recommended that:
- The apparent resolution to be at most on-tenth of the total process six sigma standard deviation
- Or that the apparent resolution to one-tenth of the tolerance spread.
38
What are the five categories of measurement system error?
1. Bias
2. Repeatability
3. Reproducibility
4. Stability
5. Linearity
39
For MSA what is bias?
Bias is the difference between the observed average of measurements and the reference value.
40
For MSA what is repeatability?
The variation in measurements obtained with one measurement instrument when used several times by one appraiser while measuring the identical characteristic on the same part.
41
For MSA what is reproducibility?
The variation in the average of the measurements made by different appraisers using the same measuring instrument when measuring the identical characteristic on the same part.
42
For MSA what is stability?
The total variation in the measurements obtained with a measurements system on the same master or parts when measuring a single characteristic over an extended time period.
43
For MSA what is linearity?
The difference in the bias values through the expected operating range of the gage.
44
Explain the material removal processes for AWJ
In the upper part of the cut:
- Grains hit at a shallow angle
- Chip (small) formation
- So called cutting wear
In the lower part of the cut:
- Grain hit at a not so shallow angle
- Erosion due to cyclic load of multiple grain
- Deformation wear
45
What can affect the cut using AWJ?
- Tapering
- Edge rounding
- Burr
As a result of the lag of the jet while changing directions at a constant cutting speed. Diminish speed in corners to reduce effect.
46
What are some design issues for AWJ?
- Avoid small inner outer radii. These will lower cutting speed.
- Unnecessary thick material will require low cutting speed.
- Define which surfaces should be of good quality.
47
How do fluid elements influence machine tools?
Short term
- Thermal influence
- Oscillation
- Leakage
- Foaming and gas entrainment
Long-term effects
- Corrosion
- Wear
Constant maintenance of fluids to avoid machine failures
48
Explain thermal aspects in regards to fluids
Power is transformed to heat.
From metal cutting it generates heat in the work piece, chip and tool. Where most heat is the chip and the least in the work piece.
The heat can be extracted via fluids.
49
Describe sustainability in regards of cutting fluids
- Sustainability and the total life cycle of the chemicals are of great concern.
- Metalworking fluid, as a lubricant and coolant in machining processes contributes to 72.500 tons of fluid industrial waste in Sweden.
- In the future, a fluid should fulfill not only the technical properties and performance but also sustainability.
- The chemicals should preferably be based on renewable resources, be recyclable and not cause much adverse effect to the surroundings .e. during processing and waste disposal, as well as to the workers health.
50
What is REACH?
Is an EU chemical ordinance which addresses the production and use of chemical substances.
51
What is the task for dry machining?
Substitute the functions of the metalworking fluids.
52
What are the effect of dry machining?
There is high temperatures of tool, chip and the work piece. This require:
- High hot hardness and hot wear resistance of the cutting material
- Tools with optimized geometry
- Adapted cutting parameters
53
What is MQL?
Minimum quantity lubrication which is a targeted and low-dose application of highly effective lubricants.
The effect is that you get better cutting that dry machining but without the extensive use of lubrication as in a normal system.
54
What are the cooling lubrication methods in the industry?
1. Dry machining
2. Minimum quantity lubrication
- Minimal lubrication
- Minimal cooling
3. Flood cooling
- Emulsions
- Oils
- Conventional supply
- High-pressure cooling
4. Cryogenic cooling
- Cold air
- CO2
- LN2
55
Explain high-pressure cooling
A targeted supply of the metalworking fluid to the cutting area under increased pressure.
56
What are the potential impact of the high-pressure cooling?
1. Effective cooling and lubrication of the tool and cutting area
2. Increase of productivity:
- Higher cutting values by reducing the thermal tool load and tool wear
3. Increase of process safety:
- Short chip formation and breaking
- Safer chip removal
- Longer tool life
57
Describe cryogenic machining
Cooling of cutting processes at very low temperatures
58
What is the general potentials of cryogenic cooling?
- Increased productivity via boosted cutting parameters
- Reduce cutting temperature and tool wear
- Dry and clean work pieces, chips and machine interior, no cleaning required
- The cost of cooling lubricant preparation, care and disposal is eliminated
- Less occupational safety issues
- Reduced environmental impact
59
Why are metalworking fluids applied in a manufacturing process?
Metalworking fluids re applied to improve workpiece quality, to reduce tool wear and to increase process productivity
60
What are the main tasks of metalworking fluids?
The main task are cooling and lubrication of the cutting zone and the removal of the chips.
61
What are sustainable alternatives to conventional flood cooling?
- Dry machining
- MQL
- Cryogenic machining
62
What is special with emulsion?
In the view of the life cycle and OHS and environmental impacts, emulsions require especially careful care.
63
What does LASER stand for?
Light amplification by emission stimulated radiation
64
What is the working principle of lasers?
Energy is conveyed to the laser media:
- For example using electrical discharged
- Electrons are excited
Electron absorbs energy and jumps to next level.
- Electrons strive to the lower energy-level: de-excitation
- Photons are emitted
- These photons leads to excitation in other atoms.
- By enclosing the media an amplification is accomplished.
Electrons releases energy and comes back to its energy level.
65
What are the basic components (functions) in a laser and draw accompanying figure?
1. Fully reflecting mirror
2. Loss energy (heat)
3. Active medium
4. Semi-reflecting mirror
5. Laser beam
6. Excitation energy or "pumping"
66
What are the important properties of the LASER-light?
1. Monochromatic
(same wave-length)
2. Coherent
(in phase)
3. Directed
(close to parallel)
67
What are the most common type of laser for cutting?
CO2-laser
68
Draw the beam delivery system
Most often used for CO2-laser: Rectangular system with mirrors
69
What are the components of an Nd-YAG-laser?
- Resonator mirror
- Elliptic reflector
- Flash lamps (deliveries excitation energy)
- Resonator mirror (semi reflecting)
- ND-YAG rod
See lecture slide Laser and EDM for figure.
70
Explain Nd-YAG-laser
Possibility to convey the laser through an optical fiber.
Other characteristics of Nd-YAG:
1. More difficult to cool.
- Lower power
- Somewhat reduced beam quality
2. Better for some materials
- Aluminum
71
What are the components and how the most common design of CO2 laser look?
1. Electrode
2. Unloading space
3. Resonator mirror
4. Gas cooler
5. Blower
72
Explain fibre laser
In fire laser, light from solid-state diodes is confined in the outer core of a thin stands of glass even when the strain is coiled. As the light bounces through the strands inner core, where the glass is doped with heavy metals it is converted intro an intense laser beam.
See lecture Laser and EDM for figure.
73
What are the advantages of fibre lasers?
1. Simple design (reliability, cost)
2. Lower losses
3. Easier to cool (high surface, volume)
3. Good beam quality
4. Short wave length
74
Draw the cutting head of a laser
See lecture Laser and EDM for figure.
75
Explain gas assistance for the cutting head.
- Blows away molten material
- Shiels the cutting head
- Air is one alternative
- Can be inert
- Oxygen provides additional energy in Fe-cutting
76
Why is cooling used for the cutting head?
To avoid so called "thermal lensing" with the aim to diminish the altering of shape and material properties of the lens.
77
What is the laser process parameters?
- Emitted power
- Continuous or pulsed emission
- Gas: nature and quality
- Focal length of lens
- Position of focal point
- Nozzle: pressure, flow-rate of gas
- Nozzle-workpiece distance
78
Draw the cutting process and name the different parts.
See lecture Laser and EDM for figure.
79
What plate thickness do laser cut?
From really small to around 30 mm.
80
What is the difference of continuous or pulsed laser cutting?
Using pulsed laser can give a better edges on the cut.
81
What are the advantages of laser cutting?
- Relatively small heat affected zone
- Narrow kerf
- Perpendicular kerf and no/lite burr
- No mechanical force
- Very fast for thin sheet = a very typical application
- Also useful for tube cutting
82
What are the disadvantages of laser cutting?
- Difficult to cut reflective materials
- Can produce hazardous gases
- Low energy efficiency
- Still some HAZ
- Investment level
83
How do EDM work?
A movable electrode (-) in the shape desired spark the work piece and slowly melt the workpiece (+) small fractions at a time. The workpiece is in a tank with dielectric fluid.
See lecture Laser and EDM for figure.
84
What are some important applications for EDM?
- Plastic molds, dies for stamping
- Small holes
- Complex geometries, especially with small inner corner
85
What will happen will the electrode?
The electrode will wear because of that rough and finishing electrodes are often applied.
86
Give some examples of electrode materials
Graphite
- Large electrodes, complex shapes
- Easily machined
- High wear resistance due to high melting temp
- Fragile
Cu (Copper)
- Quite easily machined
- Ductile: good for thin sections and good for hole electrodes
Cu-W (Copper-tungsten)
- Wear resistant
- Expensive
87
What is wire EDM?
Using the same principle as the other EDM but with a wire that is on a spool over and under the workpiece that forms the workpiece.
The wire is in copper or brass and is continuously feed from the spool so the process has fresh electrodes.
It is used for thick dimensions, small inner radii and high tolerance demands.
88
What are three functions of dielectric fluid?
1. Insulates
- Prevent spark to occur before correct distance and voltage
2. Cools workpiece and tool
3. Flushes material away
- Help in the material removal
89
What are some economical of EDM?
- Low material rates
- Long lead times for EDM since tools need to be produced
- High tooling costs
- Moving tool can diminish costs and lead time
- High degree of automation
90
What are the characteristics of EDM?
- All electrically conductive materials
- Small deep holes, 0,05 mm
- No forces
- Very complex geometries can be produced
- Some HAZ
91
What are the different types of
| metal cutting machines?
Material removal with defined cutting edges:
- Lathes
- Milling and boring machines
- Drilling machines
With undefined cutting edges:
- Grinding machines
- Fine-finishing machines
92
Explain the steps in the value chain of machine processes?
1. Semi-finished
- Hot forming
2. Intermediate
- Soft machining
3. Finishing
- Grinding
4. Fine finishing
- Polishing
93
What are some specifications about grinding machines?
1. High cutting machine ranges
2. Grinding machines need massive protections against wheel failure
3. CNC driven dressing devices to generate the tool geometry
3. Large heat generated
- cooling dominated energy consumption
4. Grinding machines with as coolant require fire protection
5. High costs
94
What are some market-driven requirements for grinding?
- Productivity
- Accuracy
- TCO
- Resource and energy efficiency
- Foot print
- Safety and ergonomic impact
- Maintenance requirements
- Industry 4.0
95
Explain Total cost of ownership (TCO)
The total cost of ownership of machine-tool acquisition and depreciation, services and support, operating expenses, the cost of machine downtime och productivity losses.
96
Describe some of the principles of accuracy for grinding
- Error budgeting in design phase
- Use of materials with low coefficient of thermal expansion
- Use of feed-back system with high accuracy and linearity
97
What is chatter for grinding?
Chatter is self excited vibrations.
Grinding chatter is one of the most critical errors in grinding operations and one that has a strong impact on the ultimate geometrical workpiece accuracy.
98
Explain coolant supply for grinding
- Significant amount of coolant to counteract the grinding burn
- The circumferential wheel speed is very high
- Due to wear and dressing the grinding wheel changes geometry
- Dedicated systems, adaptive systems, closed loop controls
99
Explain finishing
Finishing is the final step in the manufacture of components which require the highest quality in term of form, accuracy and surface integrity.
100
Why is abrasive fine finishing important?
It can be used on all types of materials. Some can produce extremely fine surface finishes and can hold dimension extremely close to tolerance.
101
What is honing?
Honing is an abrasive process common in the finishing the bores (inside diameter) of internal combustion engines and gears.
The process used fixed abrasive tool as the cutting medium.
102
What surface finish gives honing?
Creates a characteristic cross-hatched surface that retains lubrication. Surface finishes of 0.1-0.2 micrometer or better.
103
What influence the mechanical performance of a honed surface?
- The honing angle
- Groove distribution
- Cracks
- The ratio of open graphite channels
104
Explain the particularities of honing?
- Material removal by a chip formation to that of grinding with low cutting speed.
- Cutting speed in grinding (30-120 m/s) are 10-100 times as great as typical speed in honing (1-3 m/s).
105
Explain the surface integrity and process design related to honing
In the industry, the honing process is usually carried out in three steps:
1. pre-honing
2. base-honing
3. plateau-honing
The plateau-honing
106
What is super-finishing?
- Super-finishing is a fine finishing process which uses abrasive grits bonded in a stone for cutting
- Widely used as a subsequent operation after grinding to enhance finish of the outside diameter and remove any chatter markers.
- Super-finishing correct size and shape variations and improve roundness.
- The mechanics are similar to those of grinding and honing.
107
What is lapping?
Lapping is an abrasive machining process in which abrasive grains are dispersed either in a paste or a fluid are applied to the moving surface of an opposing formed tool so that the individual grains follow a complex path.
Its is suitable for processing almost every material.
Lapping is increasingly used to process parts with a sealing function, high geometrical precision as well as workpieces which show characteristic crates surface.
108
Draw the lapping set-up.
See lecture Honing, Lapping, polishing for figure.
109
What are the removal mechanics of lapping?
There are difference between processing ductile, metallic materials and brittle hard materials such as glass och ceramics.
Ductile
- micro, plastic deformations of surfaces, hardening, embrittlement as well as breakaways of particles
Brittle
micro crack are induced and crack systems occur, which lead to breakaways of particles
110
Explain polishing
Polishing is an abrasive process in which loose abrasives, dispersed in a fluid or paste, are rubbed against the work piece without changing its dimensions or shape.
Laps for industrial polishing consist of a soft pad adhered to a rigid pate onto which the normal loads is applied.
The surfaces are smoothed to a "mirror" level with roughness Ra of 20-200nm.
111
Explain the mechanisms of polishing
1. Wear: Formation of fine cracks and eventually chips
- The wear hypothesis states that polishing is simply a smaller scale of grinding therefore the smoothing result from the cutting action.
2. Surface flow: Material resettlement by plastic deformation.
- The surface flow hypotheses admits that due to friction the highest asperities on the surface may reach high temperature. The heat causes a local softening of the material or even melting.
3. Chemical: Material removal confined to a chemically modified layer.
- Chemically modifier layers are formed during the polishing.
112
Explain gear manufacturing
The manufacturing methods include:
- machining
- forging
- casting
- stamping
- additive manufacturing
Of these, is machining the most common method used.
- Employing cutting and a number of grinding/abrasive finishing technologies
113
Process selection and sustainability
Look at lab 2
114
What is the relation between the material cutting and the material being cut for grinding?
For material A to cut material B, material A need to be at least 20% harder.
As long as there are no weird chemical reactions.
115
What are the conventional- and super abrasives for grinding?
Conventional abrasives
- Aluminum oxide
- Silicon carbide
Superabrasives
- Cubic Boron Nitrite
- Diamond
116
What chip-formation processes are there?
- Turning
- Milling
- Drilling
- Grinding
117
What impact has the wheel speed during grinding on the chip?
- Slowing down the wheel increases the maximum chip thickness
- Speeding up the wheel decreases the maximum chip thickness
118
What is humankind’s oldest profession? How did early humans use grinding?
Sa du sten?
119
Explain the aggressiveness equation and its impact
See lecture Grinding for the equation.
High workpiece speed and depth of cut give a higher aggressiveness number.
Lower specific material removal rate gives a finer surface finish.
Lower aggressiveness gives finer surface finish, less wheel but more heat.
120
What is definition of machinability?
Three different definitions:
1. The machinability of an alloy is similar to the palatability of wine, easily appreciated but not readily measured in quantitative terms.
2. Machinability describes the ability with which a workpiece material can be machined under given process conditions and might be assessed by one or more of the criteria:
- Tool life
- Material removal rate
- Cutting force
- Surface finish
- Chip shape
- Environmental impacts
3. Machinability is the ease with which a workpiece material can be machined under given process conditions
121
Describe tool life capability
Tool life capability is the ability of a tool and workpiece to endure a machining process. The tool life capability is affected by the edge-holding property of the cutting tool, the machinability of the workpiece material and the cutting conditions.
122
Describe what cutting conditions are
Cutting conditions are all available conditions at the machining operation
123
What is cutting edge durability?
Cutting edge durability is the capability of a tool to retain its cutting efficiency during chip formation process
124
What is cutting ability?
Cutting ability is the suitability of a tool to perform work under given conditions.
125
Explain a bit about cutting force
A larger cutting force gives high power consumption during the cut.
Hardened steel have a high cutting force while aluminum alloys have a low cutting force.
126
Describe tool life behavior
Tool life behavior is the ability of a working pair (tool and workpiece) to withstand a certain cutting process. This is influenced by the cutting edge durability of the tool, by the machinability of the workpiece and by tool life conditions.
127
What are the affects of tool wear?
- Surface integrity (residual stress roughness)
- Dimensional accuracy of machined part
- Process stability
- Increased force and temperature
128
Describe tool wear
Tool wear is used as a grading scale to determine the machinability of a material. In machining of hard to cut materials higher thermal and mechanical loads are present.
129
Explain chip control
Scenario 1: Long unbroken snarls winding around the tool or workpieces.
- Increase the feed and depth of cut
- Select an insert geometry with better chip breaking capabilities.
Use a tool with high precision coolant
- Select a smaller nose radius
Scenario 2: Very short chips, often sticking together, caused by too hard chip breaking. Hard chip breaking often causes reduced tool life or even insert breakages due to too high chip load on the cutting edge.
- Choose a geometry designed for higher feed or reduce the feed
- Select a larger nose radius
130
What make a diffcult-to-cut materials?
1. Strength is maintained at high temperatures during machining
- Due to their high temperature properties
2. Work hardening occurs rapidly during machining
3. High abrasive wear owning to the presence of hard abrasive carbides
4. Poor thermal diffusivity of nickel-based alloys
- Often generates high temperature at the tool tip as well as high thermal gradient in the cutting tool
131
Give examples of two difficult-to-machine materials
1. Ni-Alloys
| 2. Titanium
132
What is done to titanium to be able to machine it?
Place the alloy in a soft, relatively machinable condition.
133
What are the three methods to heating the alloy Ti to increase its machinability?
1. Mill annealing
2. Duplex annealing
3. Solution treating and aging.
134
Explain mill annealing for Ti
To do this the alloy is heated to about 730 C for 4 hours than furnace cooled to 25 C.
Gives a yield strength of 945 MPa and tensile strength of 1069 Mpa. Elongation at fracture 10 %.
135
Explain duplex annealing
Heat it to 955 C for 10 minutes than air cooled. It then is heated to 675 C for 4 hours and air cooled to 25 C.
Gives a yield strength of 917 MPa and tensile strength of 965 Mpa. Elongation at fracture 18 %.
136
Explain solution treating and aging.
Heat to 955 C for 10 minutes, water quenched, then aged for 4 hours at a temperature between 540 and 675 C, followed by air cooling to 25 C.
Gives a yield strength of 1103 MPa and tensile strength of 1151 Mpa. Elongation at fracture 13 %.
137
What are the tool requirements to machine Ti?
1. Coating to reduce thermal tool load
- Should have low adhesion to titanium
2. Small edge rounding
- To stabilize the cutting edge
3. Positive rake angle
- To reduce cutting force and increase the cutting ability
4. Substrate with good thermal conductivity, high hot hardness, high resistance to abrasion wear and low adhesive tendency
5. Large clearance angle
- due to high elastic deformability
- due to the low elastic modulus
138
Why is Ni-based superalloys hard to machine?
1. A high mechanical and thermal load on the tool cutting edge
2. A strong tendency of the material for adhesion to the cutting material and possibility of BUE.
3. High abrasive wear due to carbides and intermetallic phases.
4. Unfavorable chip formation (ribbon and snarled chips)
139
What is BUE?
Built-up-Edge is an accumulation of material against the rake face, that seizes to the tool tip, separating it from the chip.
Good for tool life bad for quality of piece.
140
Explain what happen with the blank during conventional drawing
In the upper part:
Material is compressed in the plane when moving inwards under blankholder which give some thickness increase.
In the middle:
Materials is somewhat stretched
Lower area:
Thinnest section because this material has not been compressed in the flange
See lecture 'Sheet metal forming 1' for figure
141
What is the function of a blankholder?
Blankholder to prevent compression to become a wrinkling.
This creates friction, a counter-acting force occurs. This force increases with blankholder area/drawing ratio.
If blankholder force too high:
- risk of too much stretching
- fracture
142
What are the components of deep drawing?
- Blank
- Blankholder
- Punch
- Die
- Knockout
143
What happens with the wall thickness of a drawn cup?
See lecture 'Sheet metal forming 1' for figure
144
What is drawing ratio?
Blank diameter/punch diameter, D/d.
145
Explain limiting drawing ratio
Limiting drawing ratio, LDR, is the highest drawing ratio that can be drawn without failure.
146
What is formability?
Mostly refers to the possibility to form plastically without fracture.
Also formability refers to the possibility to form without geometrical errors:
- springback
- wrinkling
147
Why do we have anisotropy?
1. Single grains and oxides are elongated in the rolling direction. Thus resulting in a "mechanical fibre-texture".
2. The crystallographic direction is rotated within each single grain int he rolling direction resulting in a "crystal-texture".
148
What is anisotropy?
The deformation resistance in the plate material varies depending on direction of deformation.
Normal to the plane and in the plane.
149
What is plastic strain ratio?
Plastic strain ratio, r is the ration between elongation in the plane and normal to the plane.
A higher ratio gives better formability, increased LDR.
150
What is work hardening (strain hardening)?
In the neck (local thinning) work hardening/strain hardening is larger than in the surrounding material.
Surrounding material is less strain hardened and will therefore deform more easily.
151
What is drawing beads and what is it used for?
- In drawing to be able to control degree of stretching or material flow.
- To control the material flow during a press operation.
152
What are some important factors within bending?
- Springback
- Crack initiation at the outer edges
- Minimum bend radius
- Workpiece length
- Bending near holes
153
What is bottoming?
Pressing the bend to the bottom of the little V thing. Full plastic deformation in bottom.
It's used for minimizing springback.
154
What is u-bending?
Bending it in a (square) U instead of a V shape.
Overbending is not possible.
155
What cause springback?
Elastic deformation.
156
What is the problem with bending near holes?
Hole is deformed if it's a insufficient distance from bend.
157
What can be done to minimize crack initiation?
- Avoid bending lines in rolling direction
| - Avoid to have burr side on the tensile side.
158
What is stretch forming?
In stretch forming the materiel is plasticized all the way through the material. No part is still just elastically deformed. Thereby springback is much reduced.
159
What are two ordinary sheet metal forming operations?
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1. Press line
Combination of different operations:
- One or several forming stages
- Bending
- Punching
- Shearing
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2. Progressive dies
Sheet metal is indexed forward in between consecutive strokes.
160
What is hydroforming?
Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press room temperature working material into a die.
161
What are the steps of hydroformed parts?
The process chain for hydroformed parts typically comprise:
1. Pre-forming
- normally radial or/and axial bending
2. Hydroforming
2. 1 Crush-forming, can be made in pre-forming
2. 2 Pressurizing, free forming
2. 3 Calibration, final forming against die-wall
2. 4 Final part
3. Post-processing
- for example additional hole-making
162
What are the economic advantages of hydroforming?
- Elimination of welding operations
- Diminished number of parts
- Lower tooling costs
163
What are the advantages of hydroforming from an design aspect?
- Relatively high flexibility/freedom of design
- Good for narrow spaces, "packing of complex part"
- More uniform wall thinning
- Strain is more uniform, more uniform work-hardening
164
What are other advantages of hydroforming besides economical and design?
Quality:
- Geometrical tolerance, tight fit to die
Weight reduction:
- No weld-flanges
- Optimized design
165
What are the disadvantages of hydroforming?
- Further joining of hydroformed parts may be more difficult
- Uses dry lubricants which are costly
- Dry lubricants can be difficult to remove
- Relatively long cycle tome for hydroforming
- Handling time relatively long
- Still, there are restriction in size and shape
166
What are a application of hydroforming?
Common in car industry for example structural tubular components and rear axis.
167
What failures can occur with hydroforming?
- Buckling
- Wrinkling
- Folding back
- Bursting
- Necking
It depends on the relationship between axial force and internal pressure.
168
What is roll forming?
Consecutive bending in between rolls:
Multiple steps, number depending on:
- Thickness and strength
- Complexity of shape
- Tolerance
169
Give example of some applications of roll forming
- Building, roofing
- Furniture parts
- Automotive
170
What further processing can be done during or after roll forming?
In line processing possible:
- Punching (if constant distance)
- welding
Post processing:
- Bending
- Punching
- Laser cutting
171
What are some geometrical issues with roll forming?
1. Spring-back will occur
- Typically "over-bending" is used to compensate
2. End flare: Difference in between ends and center part of beam
Several bend + high-strength material + sensitive application = extra care must be taken
172
What are the advantages of roll forming?
- Low load on tools
- Simple tooling and can still make relatively complex shape
- Robust relatively simple process, few variations
- Productive especially if integration of in-line processes
- Well adapted to high strength steel
- Well adapted to high-strength steels
- High utilization of material
173
What are the disadvantages of roll forming?
- Limitations to 2D
| - Some issues regarding skewed parts and flare.
174
What are the increasing demands on vehicle bodies?
- Crash safety
- Fuel consumption
- Emission
175
What are the components of press hardening/hot stamping?
1. Coiler
2. Punch
3. Blank
4. Furnace
5. Press, stamping and cooling
176
What are the difference between direct hot stamping and indirect hot stamping?
For indirect hot stamping the blank is cold pre-formed before the steps of:
- Austenitization
- Transfer
- Calibration and quenching, (forming and quenching for direct hot stamping)
- Part
177
What influence on the formation of production system does press hardening have?
1. Fast transportation is of high importance
2. Ovens need to be dimensioned to meet cycle time
3. Punching after quenching/hardening might be difficult
- More frequent use of laser cutting
4. Weldability worse for press-hardened parts
178
What are the application of press hardening?
Cars:
- An alternative to direct use of advanced high-strength steel
- More complex shapes possible
- In never Volvo's it used 40% f the total BIW weight
179
What are the disadvantages of press hardening?
- Higher cost
| - More complex process
180
Explain cold forming of advanced high-strength steels (AHSS)
Formability limitations:
- Knowing there is a limitation
- Knowing that the limitations is not as sever as ordinary materials properties indicate
Being closer to the limit
- through testing, simulation, optimization needed
Tool material and wear
There are several term
181
What are the key application for AHSS?
- Bumpers
- Seats
- Side impact beams
182
What are the forming limitations ans issues of AHSS?
- Low ductility
- More springback
- Wear on tools
183
What are important tool material properties?
General:
- Compressive strength
- Wear resistance/hardness
- High ductility
- Good machinability
- Easy to polish
For press hardening tools also:
- Good properties at elevated temperature
- Good thermal conductivity
184
What are the cold processes of joining?
- Locked seams
- Rivets
- Adhesives
185
What are the hot processes of joining?
- Soldering
- Brazing
- Welding
186
What is soldering and brazing?
1. Joining of metallic parts through addition of a filler material, the solder ( or filler metal in brazing)
2. The solder is metaled and has a different composition than the base material.
3. The melting temp of the solder is lower than the base materials.
4. The base materials is not melted.
187
What are the specifics for soldering?
- Melting point below 450 C
- Can withstand some mechanical load
- Used mostly for electrical and thermal connects as well as plumbing
188
What are the specifics for brazing?
- Melting point of solder (filler material) over 450 C
- Typically for higher mechanical loads
- Common heat sources: torch, furnace
189
What is the general process of soldering and brazing?
1. Heating of the soldering position of the whole parts to above the melting point of the solder.
2. Fluxing.
3. Solder application
- Wetting of the solder
- Diffusion: solder, base material
- Cleaning
Typical:
- The quality of the diffusion zone determines the quality.
190
Where is solder applied?
- External application
- Pre-placed
- Solder pot, dipping
191
What is wetting?
See lecture '
| Joining 1' for picture
192
What is solder materials made of?
EU-directive that all electronics products in EU should be lead-free.
Important alternatives to Pb-Sn:
- Sn-Ag-Cu
- Sn-Cu
- Sn-Ag
193
What do flux do?
- Removes oxides
- Prevents oxidation
- Increases wetting
194
What are the applications of brazing?
- Gas and fluid transportation
- Catalytic converters
- Coolers
- Heat exchangers
195
How do adhesives work?
A mixture of physics, chemistry and mechanics.
1. Molecular adhesion
- Attraction between molecules when close enough
- Can der Wahl's forces
- The adhesive must be a liquid o come this close
- The adhesive must be able to "wet" the material
Mechanical adhesion
- Locking by filling pores and clinging to irregularities
196
Explain adhesives and wetting
Wetting is important for adhesives.
197
What types of adhesive are used?
1. Natural
2. Synthetic, most common.
- Thermoplastic
- Thermosets
198
What is thermosets?
Is typically the strongest adhesive.
Curing (hardening):
- Heating
- Radiation
- Evaporation of liquid
Work environment:
- Thermosets can cause allergy, asthma, eczema and irritation in eyes
- Hazardous in the its non-hardened state
- Gloves etc and fume hoods are required
199
What are the advantages of adhesives?
- Many materials and combinations of material can be joined
- Large area bonding
- Sealing and electric insulation
- Low temperature process
- There are adhesives that are flexible
- Quite simple joint design
200
What are the disadvantages of adhesives?
- Lower strength than other joining methods
- Adhesive must be chosen to be compatible with joined material
- Service temperature is limited
- Less available technologies for non-destructive test
- Work environments
201
Explain production system from an adhesive perspective
Supply:
- Transporting the adhesive to the station
Dosage:
Right quantity/flow-rate adhesive to the surface
Application:
How the adhesive is place on the surface.
- Manual or automated
- Pattern
202
What are the main obstacles and drawbacks?
- High investment cost
- More stringent requirements on parts’ and positioning tolerances
- Need for specific repair methods for after market repair shops
- Worse risk for corrosion damage compared to RSW
203
What are the laser types in welding?
- CO2, for higher metal thickness > 4mm
- Nd-YAG for lower metal thickness
- Disc laser
- Fiber laser
204
What are the advantages of laser welding?
- Narrow heat-affected zone (HAZ)
- Reduced deformation in the welded area
- Negligible influence on the materials
- Stable and tight parts tolerances
205
What are new laser technologies in the automotive industry?
- Remote laser welding
| - Laser brazing
206
What are the advantages and disadvantages of laser brazing?
Advantages:
- CuSi3 wire melted by a laser heat source
- Wire feeding similar to Gas Metal Arc Welding
- Thin diffusion zone (=good)
- Fast
- “Low” temperature process (high focused beam)
- Can be used in visible areas (valid for all brazing)
Disadvantage:
Lower strength
207
What types of mechanical joining techniques?
Mechanical Joining - Rivets:
- Clinch joining
- Self-piercing riveting
208
Describe the benefits of mechanical joining techniques
- Environmental friendly processes, free from emissions + low energy consumption
- Simple joining techniques, similar to spot welding
- Technical advantages, such as improved fatigue strength
- Tools with long service lives
- High precision due to no heat
