Exam Style Questions: Metal Processes Flashcards
Give three reasons why sand casting is suitable process to manufacture the
G-cramp (3 marks)
- The clamp will be made from medium to high carbon steel or cast iron. All of which have high melting points and low malleability, therefore a hot forming process would be most suitable to form the metal without it cracking or breaking in use
- A high-quality surface finish is not required for the clamp to function as intended therefore the additional expense of a high-quality surface finish is not necessary
- Material is not wasted during manufacture as the runner and riser can be recast
- During hot forming the recrystallisation of the metal’s atomic structure means that the final product should not have any weakness or cracks which could happen if cold formed
- A rougher surface finish such as the one given by and casting could improve the ergonomics of the clamp as it would increase grip when clamping objects
Describe the process of wrought iron forging (6 marks)
- Wrought iron is heated in forge to red-hot heat
- It is then shaped using specialist tools whilst hot
- Tools and techniques used include tongs, hammering over an anvil or using scroll formers or twisting bars
- It can also be shaped using hydraulic and mechanically powered rams
- Templates and jigs can be used to aid batch production
- When the metal cools during forming it is reheated as required until the desired design is achieved
Explain why sand casting is only suitable for one-off or batch production (2 marks)
Award 1 mark per relevant point up to a maximum of 2 marks.
Process is slow / labour intensive / moulds are single use / skilled - semi-skilled workforce needed
Give three reasons why drop forging is used to make spanners (3 marks)
Award 1 mark per relevant point up to a maximum of 3 marks.
Spanners need to be tough (1) and hard (1) as drop forging uses hot metal to shape into forms, the original grain structure of the metal is retained (1) this
means there a no stress fractures or cracks in the spanner (1) causing it to
have even strength (1)
Give two additional methods of hot forming metal and two applications (4 marks)
Award 1 mark for each method and 1 mark for each application up to a
maximum of 4 marks
Sand casting – railway carriage wheels, woodworking clamps, drain covers, post-boxes
Investment casting – engine components, gas turbine blades
Rolling – Angle, I beam, bar and channel section for construction
Die casting – alloy wheels, engine components, toy cars, door knobs
Pewter casting – school projects, jewellery, key fobs, decorative components
Evaluate the advantages and disadvantages of the spinning process to produce metal products. Comment on both CNC equipment and hand held tools in your answer (6 marks)
Advantages:
- A suitable process for mass production using CNC machinery, increases
repeatability, accuracy and reduces time spent manufacturing
- Use of mandrel to form the metal ensure repeatability of form even when
using hand held tools
- Spinning metal blank around an axis ensures radial symmetry
- Unlike deep drawing and cupping the spinning process ensures even wall
thickness of the product all the way round
- Little material is wasted in the process
- Short set-up times and changeover times mean multiple different items can
be spun using the same machine making it suitable for batch production as
well as mass production
- Product retains its structural integrity
- Relatively low set-up costs for tooling in comparison to other processes
Disadvantages:
- There are a variety of size and shape limitations due to the maximum
practical diameter of the spinning blank at the start of the process
- Little room for errors especially in hand held tooling and manufacture
- A small or minor error will lead to immediate scrapping of the piece
- If operated by hand, a highly skilled worker is required to run the machine in
addition to a good physical capacity
- Repetitive nature of manufacture using worker could result in injuries and
increase downtime and costs of production
- Longer time to produce finished component than other methods of cold
forming such as deep drawing and press forming
- Only viable for radially symmetrical shapes
Evaluate the use of nuts and bolts in construction when compared to rivets (6 marks)
- Rivets will not loosen when subjected to vibration, so would withstand a variety of weather conditions, or being close to transportation highways, such as railways and motorways.
- Rivets fill the hole they are installed in, to create a tight/interference fit.
- The process of cutting and tapping threads is not required with the installation of rivets.
- Rivets are a semi-permanent method of joining metals together and whilst this gives them good vibration resistance, it makes disassembly incredibly difficult.
- Rivets can be time consuming to install increasing construction time and labour costs.
- Rivets require highly skilled labourers to install them correctly.
- Some types of rivets require specialist equipment which can be difficult to use in some locations, such as heating equipment and pneumatic rivet gun to set the rivet.
- Pop rivets do not require access to both sides of a joint, unlike nuts and bolts.
- Nuts and bolts can suffer from loosening after assembly and through vibrations.
- Nuts and bolts have a higher shear strength than rivets so can withstand greater forces using less material.
- Assembling nuts and bolts can still take time even with power tools, however the use of power tools enables less skilled labourers to complete the construction, saving costs on training workers.
- Nuts and bolts are temporary joining methods, therefore it is relatively easily to disassemble and reassemble parts of the construction when required, without compromising attached componentry.
- Nuts and bolts require less equipment.
- Nuts and bolts are quicker to install.
Explain the difference between welding and soldering metals (2 marks)
Welding uses a filler rod of the same metal as the two metals being joined (1), whereas soldering uses a filler metal with a lower melting point than the two parent metals (1).
Describe the basic steps of MIG welding (3 marks)
Award 1 mark per relevant point up to a maximum of 3 marks.
- Clean the metals to be joined.
- Secure them firmly on the bench using a jig or clamps.
- Clamp the ground clamp (cathode) to the piece of metal being welded,
or onto a metal welding table.
Accept: Ensure health and safety procedures are followed.
Practice a weld, check/change the power and then weld.
List three safety factors to consider when MIG welding (3 marks)
Award 1 mark per relevant point up to a maximum of 3 marks
- Use a welding mask/googles to prevent welding arc eye
- Wear protective leather gauntlets and apron
- Keep all skin covered to prevent UV burns
- Wear sturdy shoes to prevent hot metal falling on feet
- Weld in a well-ventilated area to prevent inhaling hazardous fumes
- Use a protective screen to prevent onlookers seeing the arc
Explain the purpose of the shielding gas in a MIG welding gun (2 marks)
To prevent the metal from oxidising (1) as it is heated, and therefore
to prevent causing porosity in the weld (1).
Give two advantages of oxy-acetylene welding over electric arc welding (2 marks)
Award 1 mark per relevant point up to a maximum of 2 marks.
Oxy-acetylene welding does not require electricity (1) and can therefore be used in
remote areas without access to a power source (1). The temperature of the flame
can be adjusted (1) so it can also cut through metal (1) or be used for brazing two
dissimilar metals together (1).
Evaluate the use of TIG welding against MIG welding in car body construction (6 marks)
- MIG welding can weld thicker metals faster than TIG welding, resulting in more car bodies being produced saving time and keeping costs low.
- MIG welding requires less skill and accuracy than TIG welding making it easier and less time consuming to train labourers, or programme robotic arms, keeping set-up costs lower than TIG welding.
- MIG welding can produce spatter where the wire electrode does not fuse with the weld pool, which can result in a weaker weld.
- MIG welding is a less precise process than TIG welding and therefore more material could be wasted, and weight added to the vehicle reducing fuel efficiency.
- TIG welding produces a more accurate and smaller weld seam, therefore if aesthetics is important to the manufacturer TIG welding could be seen as the preferable option.
- TIG welding is often the preferred option to use on thin gauge metals as there is a smaller weld pool, consequently it could be used to keep weight of the car body to a minimum increasing fuel efficiency.
- Whilst TIG welding is very precise it is also slower than MIG welding and could increase time and production costs.
- In manual TIG welding both hands and a foot are required to operate the machinery requiring high levels of skill and concentration. This could result in labourers needing to take more frequent breaks, or inaccuracies in the welding process reducing the quality of manufacture.
- TIG welding gives the operator greater control, therefore less material would be wasted in the process than TIG welding, reducing the waste of material resources and saving costs in the long term.
Explain why complex metal components such as engine blocks are often CNC milled (6 marks)
- The accuracy required on an engine block is extremely high, and milling can create this from one block of metal, creating a dimensionally stable engine block that withstand vibrations, high pressure and shocks.
- The complex geometry of an engine block is able to be achieved through the use of a 4th and 5th axis.
- Using CNC milling means that computer code (G code) can be generated from a - CAD model and the machine will recreate the CAD model to a high degree of accuracy in far less time than manually milling would be able to achieve.
- Milling is suitable to create the parts of an engine block that would near impossible to achieve with any other process including investment casting.
- The engine block is relatively large so would require a very large machine if it were to be produced using any additive processes.
- The milling machine can be easily reprogrammed for a different engine block or allow for refinements and changes to the production run quickly and easily.
- The CNC milling machine can run repeatedly as part of either a mass or batch production line.
Explain the differences between flame cutting and plasma cutting (4 marks)
- Flame cutting does not require electricity, whereas plasma cutting does.
- Flame cutting focuses oxy-acetylene into a cutting flame at 3,500°C, whereas plasma cutting sends an electric arc through a blast of plasma at around 28,000°C.
- Plasma cutting generates a faster cleaner cut than flame cutting.
- Flame cutting is used to cut low carbon and alloy steel plate, whereas plasma cutting can cut through steel, stainless steel, aluminium, brass and copper.
- Flame cutting is less expensive than plasma cutting.
- Plasma cutting is suitable for use with aluminium and stainless steel whereas flame cutting is not.
