Metal Processes And Finishes

Question 1

What is Press Forming

Answer 1

Press forming is used to shape sheet metal into 3D forms, like metal seat, car bodies, and containers. Metals such as medium carbon steel and aluminium are typically used in press forming due to their malleability and ductility.

Question 2

What Type of Production is Press Forming?

Answer 2

Press forming is usually used in mass production or large-scale batch production (due to the cost and complexity of the process)

Question 3

Process of Press Forming

Answer 3

1. Sheet metal is clamped over a die of the product that will determine the final shape of the pressing
2. A hydraulic press pushed the die into the sheet metal cutting blades may be included to punch holes into the sheet and trim the excess from the edges.
3. The hydraulic die is lowered and the pressed sheet component is removed
4. The sheet may be placed into further press forming machines for additional pressing, where the shape is complex.

Question 4

What is Spinning

Answer 4

It is an alternative process to press forming, where circular sheet metal components that are symmetrical can be produced by forcing a metal blank onto a rotating former.

Question 5

What type of Production is Spinning

Answer 5

It is typically used in mass production, and can be set up by computer controlled machines, so thousands of identical shapes can be made

Question 6

Process of Spinning

Answer 6

1. 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.
2. The roller tool is moved into the blank and is rotated with the mandrel. This starts to stretch the metal over the mandrel
3. The roller tool is moved along the mandrel as pressure is maintained against the rotating blank.
4. The roller tool is moved to the end of the mandrel, while still maintains contact with the blank. Thais finishes the shape of the product.
5. The finished product is removed from the mandrel
6. Excess material is trimmed off following the process.

Question 7

What is Cupping and Deep Drawing

Answer 7

The cupping and deep drawing processes are used to form tube-like shapes like fire extinguishers and high pressure aerosol cans.

The process is similar to piercing and blanking metal with a punch except that in deep drawing, the corners of the punch are rounded. This caused the metal to stretch rather than being sheared

Question 8

What is the Difference between Cupping and Deep Drawing

Answer 8

It is considered ‘deep drawing’ when the depth of the pressing exceeds the diameter. Conversely, it is cupping when the depth of the pressing is less than the diameter.

Question 9

What type of Production is Cupping and Deep Drawing

Answer 9

The big setup costs of the hydraulic presses and dies used in cupping and deep drawing mean that this process is only suitable for mass or continuous production

Question 10

Process of Cupping and Deep Drawing

Answer 10

1. The pressing blank is clamped over a deep drawing die using a pressure pad or clamping ring known as a retainer.
2. 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.
3. The ‘cup’ is then pressed further down through the deep drawing due to make the desired tube shape.

Question 11

What is Drop Forging

Answer 11

Drop forging is used to shape hot metal into finished products. This process is used when the finished product needs to be impact resistant and hard. Typically products such as spanners, pliers, and screwdriver shafts are made using this.

Question 12

What type of Production is Drop Forging

Answer 12

Drop forging is used in mass production of identical items, due to the fact that the dies are dedicated to making on specific item.

Question 13

Process of Drop Forging

Answer 13

1. A die is made from fast tool steel and this is secured to the top of an anvil.
2. A ram is also equipped with a die that resembled a mould.
3. The metal ‘billet’ to be forged is heated to above recrystallisation temperature. This stops the product from work hardening as it cools, which would make it brittle.
4. Using tinge, the heated billet is placed by an operator into the anvil die, and the hydraulic ram is brought down with force. This makes the hot billet spread around the shape of the die.
5. The ram is lifted and the completed product remove for cooling and finishing.

Question 14

What is Bending

Answer 14

Bending sheet or plate metal in industry is done using a machine called a press brake. The desired bends are achieved by clamping the stock metal between a matching punch and die. A hydraulic, pneumatic, or mechanical brake holes the metal sheet or plate, and lowers the punch to bend the material to shape.

Unlike press forming, bending doesn’t usually combine any punching or trimming.

Question 15

What type of Process is Bending?

Answer 15

Bending is a process that can be done as a one-off production method. However, in industry where press brakes are used, it is more typically used in large-scale batch production.

Question 16

What is Rolling

Answer 16

Rolling is a metal forming process in which the stock metal material is passed through sets of rollers to reduce the thickness of the material. This process is usually carried out that hot metal that has been heated to above its recrystallisation temperature (known as hot rolling), but can be rolled below its recrystallisation temperature (cold rolling).

Question 17

What is Rolling used to make

Answer 17

Rolling is typically used to make structural steel members such as I beams for the construction industry, and metal stock forms such as angle, bar, plate, and channel. Other examples might include rails for railway tracks.

Question 18

What is Sand Casting

Answer 18

Sand casting is used to form high melting point metals into components and products. Sand casting does not give a very high quality surface finish because the molten metal will pick up the grainy texture of the sand.

Question 19

What type of Production is Sand Casting

Answer 19

Because the process is quite slow and labour intensive, and the moulds are single use, this process is typically used for one-off and batch production.

Question 20

What is the Process of Sand Casting

Answer 20

1. A ‘pattern’ is made (usually from wood) which is a replica of the item that will be cast and is placed into the bottom of a steel box called a ‘drag’. The drag is filled with sand which is packed in tightly around the pattern and levelled.
2. The drag is turned over and a second box called the ‘cope’ is clamped into position over the 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. They will form the sprue or runner, and rinsed later in the process.
3. Sand is packed into the cope around the runner, riser, and pattern. A small indent 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 and pattern cavity, and from this to the riser. The cope and drag are then re-assembled and the mould is ready for pouring to begin.
5. Small metal spikes may be inserted and removed to make vent holes, which will allow gases from the casing process to escape.
6. The molten metal is poured into the pouring basin. It flows down the runner, into the cavity. When the cavity is full, the molten metal flows up the riser, indicating that the cavity is fill. Once set, the sand is removed and the runner. Channels, and riser are cut off and the casting is ready for machining.

Question 21

What Two Types of Die Casting are There?

Answer 21

The two main types of Die Casting are:
• Gravity Die Casting
• Pressure Die Casting

Question 22

What type of Production is Die Casting?

Answer 22

Die casting is only used in very large batch or mass production, as it costly and complex to construct the dies, and the steel moulds are re-usable.

Question 23

What is Gravity Die Casting

Answer 23

This is the simplest form of die casting, as it involves melting the metal and the pouring it into the mould. This process relies on gravity to help the metal flow through the mould. The runner is used to pour the molten metal into the mould, while the riser will indicate when the mould is full.

(This method of die casting is generally used to make parts that have a thicker or heavier section that pressure die casting).

Question 24

What are the Two forms of Pressure Die Casting

Answer 24

There are two forms of pressure die casting:
• Hot Chamber Pressure Casting
• Cold Chamber Pressure Casting

Question 25

What is Hot Chamber Pressure Die Casting

Answer 25

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 of the mould is filled and it allows fine detail to be moulded. The process is also very fast, as the molten metal is not stored separately.

(Aluminium is not cast using this process, as it picks up iron from the steel chamber. Instead, cold chamber pressure die casting is used).

Question 26

What is Cold Chamber Pressure Die Casting

Answer 26

With cold chamber high pressure die casting, the molten metal is kept separately in a melting crucible. The metal is then ladled into the shot charger, and a hydraulic ram forces the molten metal into the mould cavity. When the metal has hardened, the mould opens and ejector pons push the finished casting out.

Question 27

What is Investment Casting (Lost Wax Casting)

Answer 27

Investment casting is a process used to cast one,s that are intricate or awkward shapes which would be difficult or impossible to mould using any other casting process. Examples include cast jewellery or collectible figures.

Question 28

What type of Production is Investment Casting

Answer 28

Batch production would be used for this process, as it allows for repeatability because the wax patterns are cast from a master mould.

Question 29

Process of Investment Casting (Lost Wax Casting)

Answer 29

1. An exact replica or pattern of the product to be cast is made using wax. Where several items are to be cast, further wax patterns might be joined together in a ‘tree’, including a replica or the runner that will be used to pour the molten metal in.
2. The wax pattern is dip coated with a refractory clay. It is then fired in a kiln to bake the clay hard. The wax is burned away, leaving a hollow clay mould.
3. Molten metal is poured into the clay mould.
4. Once the metal has filled the mould, it is allowed to cool.
5. The clay mould is then broken away, revealing the casting.
6. The runner and any connecting channels are machined off.

Question 30

What is Low Temperature Pewter Casting

Answer 30

Pewter is an alloy with a low melting point, and is ideal for making small-scale items like jewellery for example.

Question 31

What type of Production is Low Temperature Pewter Casting

Answer 31

Due to the fact that it is easy to make the moulds for pewter casting from a range of materials, it is very suitable for one off production. However, for something like batch production, moulds would be machine from aluminium or steel.

Question 32

Process of Low Temperature Pewter Casting

Answer 32

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 the pewter into.
2. The mould is sandwiched between two piece of MDF and clamped together. The top of the mould will be level with the top of the side pieces.
3. The pewter is melted in a ladle and then ladled into the sprue.
4. Once the casting is cooled, it is removed from the mould.
5. The sprue or riser is removed with a junior hacksaw
6. The casting is the filed, and cleaned up using abrasive wet and dry paper
7. The casting is then polished.

Question 33

How Does MIG Welding Work

Answer 33

MIG (Metal Inert Gas) welding uses an electric arc to create heat which melts the joint area. A wire electrode (made from the same metal as the material 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 wire is stored on a reel and advances through the welding ‘gun’ as the trigger is pressed. MIG welding uses an inert gas such as CO2 or argon to form a ‘flux’ shield over the area that is being joined. The gas shield replaces the oxygen at the joint area, which helps to prevent oxidisation that would prevent the weld from forming properly.

Question 34

What is TIG Welding

Answer 34

TIG (tungsten inert gas) welding is a process used to weld metals such as stainless steel as well as non-ferrous metals such as aluminium and copper or magnesium alloys.

Question 35

How Does TIG Welding Work

Answer 35

It is an electric arc welding process that is similar to MIG welding, except that the electrode made from tungsten does not melt in the process. Instead, a separate filler rod is used. A gas shield of argon or helium is used to protect the sled area from oxidisation.

The TIG process allows for greater control by the operator and more accurate, stronger welds can be created. However, the process requires higher levels of skill and is write a slow method.

Question 36

Where may TIG welding be used

Answer 36

TIG welding might be used in fabricating stainless steel ladders for boats or swimming pools, and welding stainless steel car exhaust.

Question 37

What is Oxy-acetylene Welding (How Does It Work)?

Answer 37

Oxy-acetylene welding uses a mixture of two high pressure gases - oxygen and acetylene - to form an intense flame that can burn at temperatures of around 3,500°C. The two gases are stored in separate bottles and mixed in a blow torch. The intensity and temperature of the flame can be adjusted by changing the gas and oxygen mixture through valves on the bottles and torch, to allow for either flame cutting, welding, or brazing.

Question 38

Process of Oxy-acetylene Welding

Answer 38

1. The metal is prepared by grinding an angle on the edges of the two pieces to be joined to form a ‘v’ shape. This is done to ensure that weld runs through the entire thickness of the metal
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 poop 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, Ethelred by moving the torch along the joint line, a continuous seam is formed.

Question 39

What is Brazing

Answer 39

Brazing (also known as hard soldering) can be carried out using either oxy-acetylene or a gas and compressed air brazing hearth. The process uses a lower temperature than welding, and the resulting joint is not as string as welding, but is ideal for fabrication.

Question 40

Process of Brazing

Answer 40

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 using an oxy-acetylene or gas/air torch to a temperature of approximately 850°C
5. The grading 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.

Question 41

What is Soldering

Answer 41

Soldering is a similar process to brazing, but is only used for lightweight application and the gauge metals. Soldering requires the metal to be very clean and it is important that there are no gaps between the areas that are being joined. It is also used to non components to printed circuit boards.

Question 42

Process of Soldering

Answer 42

1. The metal is cleaned and degreased
2. The joint area is wired up or clamped
3. The metal is heated up to the melting joint of the solder.
4. The solder is added on to the metal. The solder will flow along the joint using capillary action.
5. The metal is cleaned to remove any flux residue.

Question 43

What is Riveting?

Answer 43

Riveting is a permanent joining method, usually used to join sheet metal or plate. Rivets are metal fasteners that have a ‘head’ at one end, and a shaft or tail at the other end.

Question 44

What Happens in Traditional Riveting

Answer 44

In traditional 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 hammered over to squeeze the two pieces together.

Question 45

What Happens in Pop Riveting

Answer 45

Pop riveting (the more modern form of riveting) is used for join thin sheets of metal. The rivet I used in pop riveting has a rivet and a pin. The rivet head is pushed through a hole drilled through the two pieces of metal being joined.

Riveting pliers drip and pull the pin and, as this happens, the head of the rivet squashes and pulls the two pieces of metal together. The pin breaks off and disposed of.

(Pop riveting is ideal for use where the underside of the join is inaccessible for example in aircraft production to join sheet aluminium to structural parts)

Question 46

What are Self Tapping Screws and How are they used

Answer 46

Self-tapping screws are used for joining thin sheet metal. A pilot hole is drilled through the metal parts to be joked. The screw has a coarse thread which is made from hardened steel. When it is screwed into the pilot hole, it cuts its own thread, which holds the screw in place.

Question 47

What are Machine Screws and how are they used

Answer 47

Machine screws (usually with a metric head) are a type of bolt that is used to Jon thicker pieces of metal together - typically machine parts, or parts that need to be removed for maintenance. They have a thread the entire length of the shaft. Where there are two pieces to be joined, the top pipe e will have a clearance hole larger than the thread on the bolt. The bolt goes through this, and is then screwed into a threaded hole in the second piece.

(Machine screws are often tightened with a spanner or allen key).

Question 48

What are Nuts and Bolts and How are they used

Answer 48

Bolts are similar to machine screws, but instead of being inserted into a threaded hole, they are put all the way through both pieces of metal, and then a nut is tightened on to the end of the bolt to keep the pieces together. Spacers known as ‘washers’ may be put under the head of the bolt and under the nut in order to spread the tightening force over the surface of the material and to stop the bolt head and nut from digging into the surface.

Question 49

What is Milling

Answer 49

Milling is the machining process of using rotary cutters to remove material. The process of using a machine with a rotary cutter to cut and shape material.

Machines have cutters that can be moved on 3 axes and works in a similar way to routing.

Question 50

What is Turning

Answer 50

Metal turning is done on a centre lathe also called a metal lathe. This is a machine that is used to turn material, so that it can be shaped to a cylindrical shape or bowl.

Question 51

How can Turning be done?

Answer 51

Turning can be done manually or using CNC (computer numerically controlled) lathes. The material is machined by cutting tools held in a tool post which can be moved in and out, and along the bar. Most lathes have a rotating tool past which can ho,d a variety of different tools for different machining operations.

Question 52

What is Flame Cutting

Answer 52

Flame cutting is 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.

Question 53

How does Flame Cutting Work

Answer 53

The flame cutting process resembles welding - the metal is heated and a melt pool begins to form. At this point, an additional jet of oxygen is introduced. This intensifies the flame and pierces the metal, forcing a jet of melted metal and carbon (known as slag) with it. The flame is then moved along the cutting path to continue the cut.

Question 54

What are the Advantages to Manual Flame Cutting

Answer 54

Manual flame cutting in an economical process to set up because the equipment is readily available. It can be carried out in almost any location because electricity is not required. Flame cutting can be set up with a CNC system where 5here is a need for repetitive cutting. The disadvantage of flame cutting is that it is difficult to maintain a parallel line with high levels of tolerance. There may also be deformation, structural changes and tempering on the cut edge.

Question 55

What is Plasma Cutting

Answer 55

Plasma is super-heated ionised gas that is electrically conductive. A plasma cutter will use this conductive gas to transfer the energy from the power supply to a conductive material such as steel plate. The resulting cut is faster and cleaner than using oxy-acetylene.

Question 56

How does Plasma Cutting Work

Answer 56

The plasma arc is directed out of a torch where a gas such as oxygen, nitrogen, argon or compressed air is forced through a tiny nozzle. An electric arc is generated from a transformer and, combined with the gas, forms a jet of plasma. This burns through the material and blows it away.

Question 57

What type of Production is Plasma Cutting

Answer 57

Plasma cutting can be used for one-off production, for example, cutting silhouette shapes from heavy steel plate to make a sculptural sign.

Question 58

What does a Plasma Cutting System Include

Answer 58

The typical setup of a plasma cutter system includes:

• A power supply which converts AC mains to DC
• An arc starting console (this provides the spark inside the torch to start the plasma arc)
• A plasma torch (contains an electrode and nozzle which are consumable parts). The torch can be used manually or controlled by a CNC for accuracy and repeatability.

Question 59

What is Laser Cutting

Answer 59

A laser cutter can use a computer aided design (CAD) to cut or engrave complex shapes out of materials.

Question 60

What type of Production can Laser Cutting use?

Answer 60

Laser cutting can be used for one-off production as well as larger scale batches too.

Question 61

What are some Advantages of Laser Cutting compared to other Methods?

Answer 61

Laser cutting produced a fine cut with with high-quality surface finish. With laser cutting, there is less warping or distortion because the heat zone is much smaller than in other processes such as plasma cutting.

Question 62

What is Punching/Stamping

Answer 62

Punching is a wastage process that uses computer controlled machines which stamp out sections of sheet material using hardened lunches following a CNC program.
The program moves the table of the machine in the x and g direction (x moves left and right, y moves forwards and backwards) under the punch.

Question 63

How Does Punching/Stamping

Answer 63

The process uses the shearing action on a sheet of metal placed between an upper tool (punch) and a lower tool (due). 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 or recycling if the punched sheet is the desired part.

Question 64

What is Cellulose Paint and what is it used for

Answer 64

This is especially useful where a shorter drying time is required due to it being a “air drying” paint. As soon as it’s applied the thinners will begin to evaporate leaving a film of paint on the surface. Cellulose paint will require 4-5 layers to achieve a full and proper finish.

Common cellulose uses include: Car panels (including bumpers), Doors, Building panels, Picture frames

Question 65

What are Sealants and what are they used for

Answer 65

Sealant is a substance used to block the passage of fluids through surfaces, joints or openings in materials. A thin, plastic coating often painted on the surface. The most widely used, the most versatile sealant to use for metals is silicone. Silicone has many uses for sealing many types of metal structures.

The various metals it can be applied to are iron,
copper, aluminum, steel, stainless steel and galvanized steel.

Question 66

What are Preservatives and what are they used for

Answer 66

Non-Rust lubricating liquids and preservatives are used for various metal applications to preserve ferrous and/or other metal parts such as all types of engines, and other systems such as hydraulic systems, compressors, transmissions, and gear boxes.