Working With Metals Flashcards
(113 cards)
1
Q
Press Forming
A
Used to shape sheet metal into 3D forms.
2
Q
What metals are used for press forming?
A
Medium carbon steel, aluminium and other malleable and ductile metals.
3
Q
Cons of press forming
A
Making dies is high skilled, so it is costly. Only used when manufacturing in high volumes to recoup costs.
4
Q
Process of press forming
A
- Sheet metal is clamped over a die of the product that will determine the final shape of the pressing.
- A hydraulic press pushes the die into the sheet metal. Cutting blades may be included to punch holes into the sheet and trim the excess form the edges.
- The hydraulic die is lowered and the pressed sheet component is removed.
- The sheet may be placed into further forming machines for additional pressing, where the shape is complex.
5
Q
Spinning
A
Used to shape sheet metal into 3D forms with radial symmetry.
6
Q
Spinning process
A
- A former called a mandrel is put into the chuck. The sheet metal blank is held in place between the mandrel and the tail stock.
- The roller tool is moved into the blank and is rotated with the mandrel. This starts to stretch the metal over the mandrel.
- The roller tool is moved along the mandrel as pressure is maintained against the rotating blank.
- The roller tool is moved to the end of the mandrel, whilst maintaining contact with the blank. This finishes the shape of the product.
- The finished product is removed from the mandrel.
- Excess material is trimmed off following the spinning process.
7
Q
Spinning scales of production
A
Used in mass production or bath production, where the quantity required does not justify the cost of press forming.
8
Q
Deep drawing vs cupping
A
Deep drawing: when the depth of the pressing exceeds the diameter.
Cupping: when the diameter exceeds the depth of the pressing.
9
Q
Cupping and deep drawing process
A
- The pressing blank is clamped over the deep drawing die using a pressure pad or clamping ring known as a retainer.
- A hydraulic press moves the deep drawing punch to be in contact with the blank. It then pushes the blank into the die cavity to make a cup shape.
- The cup is then pressed further down through the deep drawing die to make the desired shape.
10
Q
Cupping and deep drawing
A
Used to form tube like shapes.
11
Q
Cons with cupping and deep drawing
A
The high setup costs of the hydraulic press and dies mean that the process is only suitable for mass or continuous production for identical items.
12
Q
Drop forging
A
Is used to shape hot metal into finished products.
13
Q
When is drop forging used?
A
When the finished product needs to be tough (impact resistant) and hard.
14
Q
Drop forging in mass and batch production
A
Used in mass production or bath due to the fact that the dies are dedicated to making one product, but dies can be easily be changed for batch production.
15
Q
Drop forging process
A
- A die is made from cast tool steel and this is secured to the top of an anvil.
- A ram is also equipped with a die that resembles a mould.
- The metal billet to be formed is heated to above its recrystallisation temperature. This shops the product work hardening as it cools, which would make it brittle.
- Using tongs, the heated billet is placed by an operator into the anvil die, and the ram is brought down with force. This makes the hot billet spread around the shape of the die.
- The ram is lifted and the completed product is removed for cooling and finishing.
16
Q
Wrought Iron
A
A form of iron that is suitable for forging, rolling and bending rather than casting. Less than 0.08% carbon so is malleable and suitable for hammering into shape.
17
Q
A
18
Q
Tools used in wrought iron forging
A
Tongs for holding the metal. Hammers, anvil, scroll formers and twisting bars.
19
Q
What type of production is wrought iron forging used for?
A
One-off production to limited batch production.
20
Q
Bending
A
Is done by a machine called a press brake. The desired bends are achieved by clamping the stock material between the metal punch and die. A hydraulic, pneumatic or mechanical brake holds the sheet metal or plate and lowers the punch to bend the material into shape.
21
Q
Back gauge
A
Modern press brake machines have a back gauge that accurately positions the metal, so the break bends in the correct place.
22
Q
Bending scales of production
A
Can be used in one off production, but in industry, it is more typically used in large scale batch production.
23
Q
Rolling
A
The stock metal is passed through the rollers to reduce the thickness of the material. This process can e carried out with heated rollers above the recrystallisation temperature (hot rolling), but can be rolled bellow its recrystallisation temperature (cold rolling).
24
Q
Hot rolling
A
Results in a material with mechanical properties that are uniform through the sample. Rolling the material while hot means that it will not have any deformation or stresses. The disadvantage of hot rolling is that the surface is usually coated with carbon deposits, which need to be removed by acid pickling. Hot rolled materials have more generous tolerances because of the carbon deposits on the surface.
25
Cold rolling
Results in a metal that has a higher tolerance because carbon deposits are not formed during the rolling process. This means the surface finish is much better than hot rolling.
26
Sand casting
Used to form high melting point metals into components and products. The moulds are single use, meaning it is suitable for one-off and small batch production runs.
27
Problems with sand casting
Does not give a very high quality surface finish because the molten metal will pick up the grainy texture of the sand.
28
Cold rolling
Results in a metal with tighter tolerances because carbon deposits are not formed during the rolling process. The surface finish of cold rolled metal is therefore much better.
29
Sand casting
Used to form high melting point metals into products and components. Used in one-off and limited run batch productions.
30
Problems with sand casting
1. The process is slow and labour intensive.
2. The moulds are not reusable.
3. Does not give a high quality finish because the molten metal takes the grainy texture of the sand.
31
Sand casting mould making process
1. A pattern is made usually with wood. This is a replica of the item (divided into two halves) that will be cast and is placed in a steel box called a drag. The drag is then filled with sand, which is packed around the pattern and levelled.
2. The drag is turned over and a second box called the cope is clamped into position on top of the drag. The top half of the pattern is placed into this to mate with the bottom half of the pattern. Wooden stakes are positioned into the cope. These will form the sprue or runner and riser later in the process.
3. Sand is packed into the cope around the runner, riser and pattern. A small depression is made on the surface around the sprue to make a pouring basin.
4. The cope and drag are separated and the stakes and patterns are removed. Connecting channels are cut to join the sprue to the pattern cavity and then the riser. The cop and drag are then reassembled and the mould is ready.
32
Sand casting pouring process
1. Small metal spikes may be inserted and removed to make vent holes. These will allow gases from the casting process to escape.
2. The molten metal is poured into the poring basin. It flows down the runner into the cavity. When the cavity is full, the molten metal flows up the riser, indicating to the worker that the cavity is full. Once cool, the sand is removed to reveal the casting. The runner, channels and riser are cut off with a hacksaw and the casting is ready for machining.
33
Die casting
Used to mould lower melting point metals such as aluminium, alloys of aluminium and zinc based alloys.
34
Pros and cons of die casting
Pros: the process uses steel moulds that are reusable, produces a high quality finish.
Cons: the complexity and cost making of the dies means that it is used in high volume batch production and mass production.
35
Gravity die casting process
This process relies on gravity to help the metal flow through the mould. There is a runner and riser. The runner is used to poor the metal into the mould and the riser indicated when the mould is full. Once the metal is cooled, the mould is opened and the casting can be removed.
36
What is gravity die casting used for?
Used to make parts that have a thicker or heavier section than pressure die casting.
37
Pressure die casting
Used to produce cast items quickly and in high volumes.
38
Hot chamber pressure die casting process
The molten metal is stored in a chamber which is part of the high pressure die casting machine. A pneumatic or hydraulic plunger forces a shot of molten metal through the goose neck into the die. Because this process uses high pressure, all the mould is filled and it allows fine detail to be moulded. The process is also very fast because the molten metal is not stored separately and transported to the casting machine. Aluminium is not cast in this process as it picks up iron from the steel chamber.
39
Cold chamber high pressure casting
The molten metal is kept separately in a melting crucible. The molten metal is then labelled into the shot chamber, and a hydraulic ram forces the molten metal into the mould cavity. When the metal has hardened, the mould opens and the ejector pins push the finished casting out.
40
Investment casting
Is a process used to cast items that are intricate or awkward shapes that would be near impossible to mould using any other casting processes. Stainless steel, brass, aluminium and carbon steels are used in investment casting.
41
42
Investment casting process
1. An exact replica or pattern of the product to be cast is made using wax. This may be made using a master mould machined in steel or aluminium if the product is to be batch produced. Where several items are to be cast, further wax patterns may be joined together in a tree, including a replica of the runner that will be used to pour the molten metal in.
2. The wax patterns may be is dip coated with refractory clay. It is then fired in a kiln to bake the clay hard. The wax is burned away and leaves a hollow clay mould.
3. Molten metal is poured into the clay mould. Once the metal has filled the mould, it is left to cool.
4. The clay mould is then broken away, revealing the casting.
5. The runner and any other connecting channels are machined off.
43
Low temperature pewter casting process
1. A mould is made from MDF, plywood or high density modelling foam. If made from MDF or plywood, the mould might be laser cut or cut with a fret saw. The mould will include a sprue or runner which will be used to pour pewter into.
2. The mould is sandwiched between two pieces of MDF and clamped together. The top of the mould will be level with the top side pieces.
3. The pewter is melted in a ladle and then labelled into a sprue.
4. Once the casting is cooled, it is removed from the mould.
5. The sprue or riser is removed with a hacksaw.
6. The casting is then filed and cleaned up using abrasive wet and dry paper.
7. The casting would then be polished.
44
MIG welding
A fabrication process used to weld thin gauge metal (medium carbon steels) or aluminium (where aluminium electrode wire is used). This is because the heat generated by the electric arc is localised to a small area. If done correctly, it will not burn through the metal or distort it. It is the preferred way to weld tubular steel.
45
MIG welding process (Metal Inert Gas)
uses and electric arc to create heat that melts the joint area. A wire electrode (the same metal that is being joined) also melts in the arc and fills the gap between the two pieces being joined. The operator swirls the welding gun as they move it over the joint, to form a continuous bead of weld. The electrode is stored on a reel and advances through the weld gun as the trigger is pressed. Inert gas such as carbon dioxide or argon is used to form a flux shield over the area that is being joined. This gas shield replaces oxygen at the joint area, which helps prevent oxidation that would prevent the weld from forming properly.
46
TIG welding (Tungsten Inert Gas)
Is a process sued to weld metals such as stainless steel as well as non ferrous metals such as aluminium, copper or magnesium alloys.
47
TIG welding pros and cons
Pros: allows for greater control by the operator and more accurate and stronger welds.
Cons: the process requires a high level of skill and is quite slow.
48
TIG welding process
The electrode is made from tungsten and does not weld. Instead, a separate filler rod is used to melt and fill the gaps between the two joined metals. A gas shield or argon or helium is used to protect the weld area from oxidation.
49
Oxy acetylene welding
Is used to weld low carbon steel sheet, tube or plate where arc welding processes are not available. Is useful in remote locations as electricity is not needed. Uses high pressure oxygen and acetylene to form an intense flame that can burn at temperatures of 3,500°C. The two gases are stored in different tanks but are mixed in the blow torch. The intensity of the flame can be adjusted by changing gas and oxygen mixture through valves on the bottles and torch to allow for either flame cutting, welding or blazing.
50
Oxy acetylene welding process
1. The metal is prepared by grinding an angle on the edges of the two metals to be joined to form a V shape. This is done to ensure that the weld runs through the entire thickness of the material.
2. The joint area is heated to form a melt pool and at the same time, a steel rod is introduced to the joint area. The melt pool is extended to form a continuous bead along the length of the joint . The molten metal will flow to the hottest part of the metal, therefore by moving the torch along the joint line, a continuous seam is formed.
51
Brazing (hard soldering)
The process uses a lower temperature than welding, so is suitable for thinner gauge low carbon steel tube or bar. This resulting joint is not as strong as welding but is ideal for general fabrication. Brazing filler rod is made from brass and melts at 850°C . Ideal for use in school or college projects for fabricating prototypes.
52
Brazing process
1. The material to be joined is cleaned and degreased.
2. The two pieces are clamped together.
3. A flux is applied (this helps to prevent the joint from oxidising).
4. The joint is heated use in an oxy acetylene or gas/air torch to a temperature of approximately 850°C.
5. The brazing rod is applied to the joint area. The brazing spelter will flow along the joint by capillary action to the hottest part, so it can be made to follow the joint line by manipulating the torch.
53
Soldering process
1. Metal is cleaned and degreased.
2. The joint area is wired up or clamped.
3. The metal is heated up to the melting point of the solder.
4. The solder is added to the metal. The solder will flow along the joint using capillary action.
5. The metal is cleaned to remove any flux residue.
54
Riveting
Is a semi-permanent joining method usually used to join sheet metal or plate. Rivets are metal fasteners with a head at one end and a shaft or tail at the other.
55
56
Cold riveting
The two pieces to be joined are overlapped and drilled. The rivet shaft is inserted into the hole. The head of the rivet is dome shaped and a set tool is placed over this (also known as a snap). The end of the shaft is then hammered over to squeeze the two pieces together.
57
Pop riveting process
The rivet used in pop riveting has a rivet and a pin. The rivet head is pushed through the hole drilled through both pieces. Riveting pliers grip and pull the pin, as this happens, the head of the rivet squashes squashes and pulls the two pieces of metal together. The pin breaks off and is disposed of.
58
Pop riveting use
Used where the underside of the joint is inaccessible. A form of pop riveting is also used in aircraft production to join sheet aluminium to structural parts.
59
Why is the nylon insert used in nuts?
Helps stop the nut coming undone through vibrations.
60
Flame cutting
A wasting process that uses oxy-acetylene gas and a special flame cutting torch to deliver a very intense and focused flame above 3,500°C. It is used to cut low carbon and alloy steel plate.
61
Flame cutting process.
1. The metal is heated and a melt pool begins to form.
2. An additional jet of oxygen is introduced. This intensifies the flame and pierces the metal, forcing a jet of metal and carbon (slag) with it.
3. The flame is then moved along the cutting path to continue the cut.
62
Flame cutting pros and cons
Pros: economical process as the set up equipment is readily available, does not require electricity, can be set up with CNC when repeated cutting is needed.
Cons: difficult to maintain a parallel line with high tolerances, may be structural changes, deformation and tempering on the cut edge.
63
Plasma cutting
Used super heated ionised gas to transfer energy from the power supply to the conductive metal, resulting in a cut that is faster and cleaner than using oxy acetylene.
64
Plasma cutting process
The plasma arc is directed out of a torch where a gas (oxygen, compressed air, argon, nitrogen) is forced through a tiny nozzle. An electric arc is generated from a transformer and, combined with the gas, forms a jet of plasma. The heat generated can be as high as 28,000°C, which quickly burns through the material and blows it away.
65
What type of production is plasma cutting used for?
One-off production
66
Typical setup of a plasma cutter:
- a power supply which converts AC mains to DC - this is usually varied between 200VDC to 400VDC depending upon the material thickness being cut.
- an arc starting console; this provides a spark inside the torch to start the plasma arc.
- a plasma torch; this contains an electrode and nozzle which are consumable parts. The torch can be used manually or controlled by CNC systems for accuracy and repeatability.
67
68
Laser cutting process
The laser beam is emitted from a laser tube, where it is reflected through a series of mirrors in a similar way to a periscope into a laser head. The head contains the lens, which focuses the laser into a fine beam for cutting and engraving. Laser beams usually have a very fine tolerance and the amount of material removed in the cutting process can be less than 1mm.
69
Punching/stamping
Is a wastage process that that uses CNC to stamp out section of a sheet metal using hardened punches. The CNC program moves the table in the x and y direction under the punch.
70
Modern CNC punching machines
Can be programmed using a GUI so specialist programming skills are not needed. Information is taken from 2D CAD drawings to select the correct tooling to make the desired part. Software is also used to establish the most efficient layout of parts from a given sheet, known as nesting.
71
Punching/Stamping process
Uses the shearing action on a sheet metal placed between an upper tool (punch) and a lower tool (die). The punch pushes through the sheet material, producing a punching slug that drops through a hole in the die. The pieces are collected via a chute for further work of recycling if the punched steel is the desired part.
72
How is the metal prepared for cellulose and acrylic paints?
The surface of the metal must be cleaned and degreased prior to paint application. A suitable primer is used to provide a surface for the paint to adhere to. Then ann undercoat, similar to the colour of the top coat, is added.
73
Electroplating
Involves coating a cheaper metal base in a more expensive metal to provide a protective layer and enhance the metal’s aesthetics.
74
Electroplating process
The product and donor metal is placed in a container with an electrolyte solution. As the DC is applied, the product attracts the donor metal ions and the product is electroplated.
75
Polymer dip coating process
The metal is heated to approximately 230°C. The hot part is then dipped into a tank of fine polymer powder, which has air blowing through it (fluidisation bath). The fluidisation of the plastic powder is an aid to provide even coating of the product. The retained heat from the product allows the polymer powder to melt over the product, which is then simply air-cooled to allow the coating to set evenly.
76
Metal dip coating
Metals can be coated with other metals by dipping the product into a tank of molten plating metal. Metal drippings and plating is often used for inexpensive materials. Prior to the dipping process, the metals must be cleaned and degreased.
77
Tin plating
Pass sheets of steel through a tank of molten tin at approximately 320°C. This process is often used to provide a non corrosive coating to food cans.
78
Zinc plating (galvanising)
Involves dipping the steel into molten zinc at approximately 460°C. Used for many industrial an agricultural applications such as beams, gates and animal pens.
79
Powder coating process
1. The product is initially statically charged negative.
2. The positively charged thermoset polymer resin powder is then sprayed through the air gun. The use of the charge results in a strong attraction between the powder and the product.
3. The product is then baked in an oven; the heat melts the powder over the product to give an even coating that is more hardwearing than painting.
80
Varnishing
Is a way to provide a clear finish on the metal to protect the metal and allow the colour of the base metal to show through. It is primarily use on more expensive metals such as aluminium, brass and copper, which all have good aesthetic qualities.
81
Varnishing process
1. The metal should be polished to a shine and any surface grease removed.
2. The varnish is then applied by either a spray or with a fine tooth brush to coat the metal with the protective layer.
82
Sealants
Metal sealants are tough polymers-base d
83
Sealants
Are tough polymer based coatings that protects polished surfaces from decay and tarnishing.
84
Why type of sealant is used in the automotive industry?
Silicone based clear sealants are used in automotive bodywork to provide a barrier against the effects of weathering, road salts and insect attack.
85
Sealant process
The sealant is generally applied with cloth or machine pad to produce a film that is then allowed to cure for 15 mins. It is then buffed with a cloth to make it shine.
86
Metal preservatives
Can provide temporary or final post-processing, medium to long term protection of metal surfaces. Preservatives are often used on moulds and dies to prevent fingerprints showing on the surface, minor atmospheric corrosion or condensation build up. They can be applied by wiping on with a cloth, spray, immersion.
87
Silicone sealants as preservatives
They can be classed as preservatives and can be used on machine beds to provide smooth, snag free surface to allow the materials to be pushed across the bed more easily and safely.
88
Anodising
Is a finishing process used on aluminium products, which enhances the natural oxide layer on the surface of the metal. This results in a harder and tougher aluminium.
89
Anodising process
1. The electric current passes through the sulphuric acid electrolyte solution from the part to be created (anode) to the negative cathode.
2.As the charge flows, the aluminium oxide layer builds up on the treated part as oxygen ions are released.
3. Anodised products can then be finished using a clear lacquer or varnish to seal the finish and provide further protection against scratches.
90
Cathodic protection
Is a method used to control the rate of corrosion of the metal by making it a cathode in an electrochemical cell. The anode of the electrochemical cell is a sacrificial metal which is more reactive. The anode corrodes, while the base metal is protected.
91
Two methods of cathodic protection
Impressed current, sacrificial anodes
92
Impressed currents
The component to be protected is connected to an electrical power supply. The impressed DC flows for an inert electrode through any liquid to the component to be protected. The metal becomes the cathode and the electrode becomes the anode, which protects the metal.
93
Sacrificial anode
It uses sacrificial metal to protect a metal product of value. A more electrochemically active metal is wrapped around the or joined to the less active metal to provide corrosion resistance. On large structures, the sacrificial metal is monitored for signs of corrosion and replaced when the base metal is no longer protected.
94
95
How is an electrochemical cell formed when two metals are joined?
Each metal have their own voltage, so when they are joined, an electrical current is formed. If water is present at the join, this results in the formation of an electrochemical cell and one of the metals will corrode.
96
Cold working
Metal is worked by hammering, bending and rolling. Stresses are introduces into the metal, and it becomes work hardened. Heat treatments can be used to restore the original properties of the work hardened metal.
97
Annealing
Is the application of heat to relieve internal stresses, making the metal more malleable and easy to work. Ferrous metals are heated to a cherry red colour (725°C) and slowly allowed to cool. Aluminium is heated to 350-400 °C and air cooled. Copper and brass are heated to a dull red and allowed to air cooled or quenched.
98
Heat treatments
Annealing, hardening, tempering, case hardening
99
Hardening
Steel is hardened by heating it to a red heat and quenching it in water or oil. The degree of hardness depends on the carbon content of the steel (min 0.4%).
100
Tempering
Used to reduce the brittleness and increases the toughness after a metal has been hardened. Medium or high carbon steel is heated to a critical temperature depending on its intended application. The temperature is judged by the colour of the oxide layer. Once the desired toughness is reached, the piece is air cooled.
101
Blue 316 °C
Scrapers, plane blades, saws
102
Purple 293 °C
Screwdrivers, spring, gears
103
Burgundy 282 °C
Cold chisels, centre punches, needles
104
Deep orange 260 °C
Axe heads, wood chisels, larger taps and dies
105
Orange 249 °C
Drill bits, knurling tools
106
Red 271 °C
Taps and dies
107
Amber 238 °C
Punches
108
Lemon 227 °C
Lathe tools, milling tools
109
Yellow 232 °C
Drill bits
110
Light lemon 221 °C
Engraving tools and razor blades
111
Very light lemon 216 °C
Knives and hammers
112
Case hardening
Is used to harden the outer layer of steel while maintaining a soft core. This technique is used for steels with lower carbon content. A steel part is carburised, dipped in a carbon powder and heated.
113
Normalising
A form of annealing for ferrous metals which have a faster cooling time. It removes internal stresses and improves overall strength, hardness and structure avoiding too much softening. It involves heating to between 700-900 °C and holding (soaking) it at this temperature before it is air or gas cooled.
