METAL PROCESSES Flashcards
Explain press forming?
-Sheet metal is clamped over a die that determines the final shape of the product.
-A hydraulic press forces the die into the sheet metal. Cutting blades may also cut holes in the sheet or trim excess material.
-The hydraulic press is lowered and the pressed sheet is removed.
-The sheet may be pressed again for more complex shapes.
-Metals have to be malleable and ductile (Medium carbon steel and aluminum).
-Used for mass production due to the expensive, complex nature of the dies.
Explain spinning?
-A mandrel is put in a chuck, and the sheet metal is held in place between the mandrel and the tail stock.
-The roller tool is moved into the sheet metal as it is rotated with the mandrel. This starts to stretch the metal over the mandrel.
-The roller is moved along the metal on the mandrel, maintaining the pressure.
-The roller is moved to the end of the mandrel while maintaining contact with the metal in order to finish the shape of the product.
-The finished product is removed and any excess material trimmed off.
Explain cupping and deep drawing?
-The pressing blank is clamped over a deep drawing die.
-A hydraulic press is moves the deep drawing punch, pushing the blank into the die cavity to create a cup.
-It is then pressed further to make the desired tube shape.
-Only suitable for mass production due to high set up costs.
-Used for the production of aerosol cans and fire extinguishers.
Explain drop forging?
-A die is made and secured on the top of an anvil.
-A die is also attached to a ram.
-The metal billet to be forged is heated above its recrystallisation temperature, to prevent the product work hardening as it cools, which would make it brittle.
-The billet is placed onto the anvil die and the hydraulic ram is brought down with force.
-The ram is lifted and the product removed.
-Produces products with good toughness and hardness, such as spanners and pliers.
-Used for mass production due to the die being dedicated to making only one product.
Explain wrought iron forging?
-Wrought iron is malleable and is therefore suitable for hammering into shape.
-Wrought iron is heated and shaped by holding it with tongs and hammering it over an anvil.
-It is suitable for one-off or batch production because there is no need for any dies or formers.
Explain bending?
-The metal is clamped between a complementary punch and die.
-The punch is lowered to bend the metal, usually into a V shape.
Explain rolling?
Explain sandcasting?
-A replica is made of the item being cast, and the bottom half is placed in a steel box called a drag. The drag is then filled with sand, which is packed tight around the pattern.
-The drag is turned over and a second box called a cope is placed on top. The top half of the pattern is matched up with the bottom half and wooden stakes are positioned to form sprues.
-Sand is packed into the cope around the runner riser and pattern and a small depression is made around the sprue to make a pouring basin.
-The cope and drag are separated and the stakes and pattern are removed, connecting channels are cut to join the runner and riser to the pattern cavity. The cope and drag are then reassembled.
-Small metal spikes are inserted and removed to create vents holes that allow gases to escape.
-The molten metal is pored into the pouring basin, it flows down the runner into the cavity. Once it fills the metal flows up the rises to indicate the casting has finished.
-Once it cools, the sand is removed and the runner and riser channels are removed.
Explain die casting?
-Gravity die casting, the molten metal is poured into a mould. It relies on gravity to help the metal to flow into the mould. The runner is used to pour the molten metal into the mould and the riser indicates when the mould is full. Once the metal has cool the mould is opened and the casting is removed.
-High pressure die casting, a hydraulic ram forces molten metal into the die. Because it is done at high pressure the mould is filled and it allows fine detail to be moulded. When the metal has hardened the mould is opened and ejector pins push the finished casting out.
