3. 1 proccesses, techniques and specialist tools Flashcards

Question

sand casting products advantages disadvantages 3.1f

Answer 1

Products: Engine block Garden furniture ``` Advantages:  Inexpensive  Complex shapes can be produced  Large components can be made ``` ``` Disadvantages:  Sand moulds can only be used once  Surface finish not always good  Labour intensive  Slow production rates ```

Answer 2

Products: Mechanical parts Fan blades ``` Advantages:  Excellent surface finish  High dimensional accuracy  Extremely intricate parts are castable  Almost any metal can be cast  No flash or parting lines ``` ``` Disadvantages:  Overall cost, especially for short-run productions.  Specialized equipment  Many operations to make a mould  It can be difficult to cast objects requiring cores.  Usually limited to small casting  Requires longer production cycles compared to other casting processes. ```

Answer 3

Products: Traditional toy cars Engine parts ``` Advantages:  High dimensional accuracy is achievable  Fast Production  Thinner walls are achievable when compared to investment casting (0.6mm -0.8mm)  Wide range of possible shapes  Good finish ``` ``` Disadvantages:  Castings must be smaller than 600mm and the thickest wall section should be kept below 13mm  High initial cost (Cost of moulds and machine set up)  A large production volume is required to make the process cost effective ```

Answer 4

Products: Industrial prototypes Dentistry Model making ``` Advantages:  Cheaper moulds than injection moulding  Resin casting enables the casting of intricate designs  Can be casted or painted in any desired colour ``` ``` Disadvantages:  Drying time  Not good for batch/mass production ```

Answer 5

``` Products: Lock components Gears Valves Fittings Tooling Ornaments ``` ``` Advantages:  Excellent surface finish  Good dimensional accuracy  Produces minimal scrap material ``` ``` Disadvantages:  can only be used with non-ferrous materials  The used plaster cannot be reused.  Metal cools more slowly than in a sand mould ```

Answer 6

 Make a two part wooden pattern (replica of the product to be made) – the pattern must have sloping sides so it can be removed from the sand. It should have rounded edges and no undercuts. This is then often finished with gloss paint.  Prepare the sand – it needs sieving to remove any lumps.  The mould in sand casting is produced in two open boxes called the ‘cope’ and the ‘drag’.  The drag (bottom half) – turn this mould upside down and place half the pattern face down in the centre.  Sand is then packed around the pattern.  Ram the sand down and levelled off.  Turn the drag over and place on the cope.  Place the second part of the pattern onto the first half.  Place the sprue pins into the sand – this is where the molten metal is poured in.  Fill the cope with sand.  Remove the sprue pins.  Carefully separate the cope and drag.  Remove the pattern.  Re-assemble the cope and drag.  Pour molten metal into the sprue pin holes.  The metal is allowed to cool and solidifies.  Cope and drag is separated, the sand is broken up and the product is removed.  The product now requires ‘fettling’ to remove excess metal from the process.

Answer 7

 The first step in investment casting is to manufacture the wax pattern for the process – Since the pattern is destroyed in the process, one will be needed for each casting to be made.  When producing parts in any quantity, a mould from which to manufacture patterns will be desired. The mould to create wax patterns may be cast or machined from aluminium.  Since the mould does not need to be opened, castings of very complex geometry can be manufactured.  Several wax patterns may be combined for a single casting. Or as often the case, many wax patterns may be connected and poured together producing many castings in a single process. This is done by attaching the wax patterns to a wax bar, the bar serves as a central sprue.  A ceramic pouring cup is attached to the end of the bar. This arrangement is called a tree, denoting the similarity of casting patterns on the central runner beam to branches on a tree.  The pattern is then dipped in a ceramic slurry. A ceramic layer is obtained over the surface of the pattern. The pattern is then repeatedly dipped into the slurry to increase the thickness of the ceramic coat.  Once the refractory coat over the pattern is thick enough, it is allowed to dry in air in order to harden.  The hardened ceramic mould is turned upside down and heated to a temperature of around 90°C-175°C. This causes the wax to flow out of the mould, leaving the cavity for the metal casting.  The ceramic mould is then heated to around 550°C-1100°C. This will further strengthen the mould.  Molten metal is then poured while the mould is still hot.  The casting is allowed to set as the solidification process takes place.  Break the ceramic mould from the investment casting and cutting the parts from the tree.

Answer 8

 Clamping - The first step is the preparation and clamping of the two halves of the die. Each die half is first cleaned from the previous injection and then lubricated to facilitate the ejection of the next part. After lubrication, the two die halves, which are attached inside the die casting machine, are closed and securely clamped together. Sufficient force must be applied to the die to keep it securely closed while the metal is injected.  Injection - The molten metal, which is maintained at a set temperature in the furnace, is next transferred into a chamber where it can be injected into the die. The method of transferring the molten metal is dependent upon the type of die casting machine, whether a hot chamber or cold chamber machine is being used. Once transferred, the molten metal is injected at high pressures into the die. Typical injection pressure ranges from 1,000 to 20,000 psi. This pressure holds the molten metal in the dies during solidification. The amount of metal that is injected into the die is referred to as the shot. The injection time is the time required for the molten metal to fill all of the channels and cavities in the die. This time is very short, typically less than 0.1 seconds, in order to prevent early solidification of any one part of the metal.  Cooling - The molten metal that is injected into the die will begin to cool and solidify once it enters the die cavity. When the entire cavity is filled and the molten metal solidifies, the final shape of the casting is formed. The die cannot be opened until the cooling time has elapsed and the casting is solidified.  Ejection - After the predetermined cooling time has passed, the die halves can be opened and an ejection mechanism can push the casting out of the die cavity. The ejection mechanism must apply some force to eject the part because during cooling the part shrinks and adheres to the die. Once the casting is ejected, the die can be clamped shut for the next injection.  Trimming - During cooling, the material in the channels of the die will solidify attached to the casting. This excess material, along with any flash that has occurred, must be trimmed from the casting either manually via cutting or sawing, or using a trimming press. The scrap material that results from this trimming is either discarded or can be reused in the die casting process.

Answer 9

 Produce a pattern of the object you would like to produce a resin casting of.  Spray the pattern with the separating agent. This will help to later remove the model from the mould. Allow to dry.  Suspend the pattern in a container with sealed sides  Pour silicon into the container half the way up the pattern  Allow to set  Apply a layer of silicon separation cream  Pour the rest of the silicon over the top half of the pattern  Allow to set  Remove the silicon and separate the two halves  Remove the pattern  In the example shown here the model maker pours resin into the two halves separately. Letting the first half fully set before pouring the second and placing the first set mould over the top of the wet second half.  You can place a sprue inside with the pattern to allow the resin to be poured into the mould in one go.  You can see the sprue holes on the right hand side of this mould.  After removing the resin cast, you will need to clean the model to remove any excess resin from the process.

Answer 10

 Similar to sand casting except the moulding material is plaster of Paris instead of sand  Make a pattern in the shape of the product you require. The pattern is usually made from metal.  Spray a thin film of parting compound to prevent the plaster from sticking to the pattern.  Mix the plaster. The plaster is not pure plaster of Paris, but rather has additives to improve green strength, dry strength, permeability, and castability.  The plaster is then poured over the pattern and the unit shaken so that the plaster fills any small features.  The plaster sets, usually in about 15 minutes, and the pattern is removed.  The mould is then baked, between 120 °C and 260 °C, to remove any excess water.  The dried mould is then assembled, preheated, and the metal poured.  The metal solidifies.  The plaster is broken from the cast part.

Answer 11

milling/ routing drilling turning stamping/ pressing

Answer 12

Milling is the process of cutting away metal, by feeding a piece of work past a rotating cutter. A vertical milling machine is used to shape metals such as mild steel and aluminium.

Answer 13

Drilling is the process of making holes by using a rotating cutting tool that is either secured in either a hand operated drill or drilling machine.

Answer 14

Flat bits – deep holes in wood Forstner bits – flat bottom holes in wood Auger bits – deep holes using a brace Countersink bits – angled sides for screws Hole saw – large diamtre holes Tank cutters – circular cutters for metal

Answer 15

The work on a lathe turns. On a metalworking lathe the cutting tools are securely fixed, whilst on woodworking lathe, the cutting tools are held in the hand and are rested on a tool rest. On a metalwork lathe, work is held in a chuck and on a woodworking lathe the material is usually secured to a faceplate or turned between centres.

Answer 16

Centre drilling is when the lathe I used to drill a hole in the end of a rod or bar. It is the work which rotates in the chuck with the drill help securely in the tailstock.

Answer 17

Screw threads can be cut using a centre lathe. They are cut from a from a bar to produce the correct thread profile.

Answer 18

``` Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is cut or rolled into the material ```

Answer 19

Parting is the operation of cutting a piece off by slicing a groove all the way through it with a special parting tool.

Answer 20

Stamping (also known as pressing) is the process of placing flat sheet metal in either blank or coil form into a stamping press where a tool and die surface forms the metal into a net shape.

Answer 21

Lamination is where a material has been produced by gluing together thin sheets, or veneers, to make up that material. Lamination can also be used for shaping material. This is where strips of veneer are glued together and clamped in a former. When the glue has dried the work is removed and it retains the shape of the former.

Answer 22

lamin board (5-7 mm strips) block coard (upto 25mm strips) plywood

Answer 23

injection moulding blow moulding (pre-form) blow moulding (parison) vacuum forming extrusion rotational moulding

Answer 24

``` Casings for electrical products Packaging Toys ``` ``` pros  Good for mass production  Low unit costs for high volume  Precision moulding  Surface texture can be added to the mould ``` ``` cons  High set up costs  Expensive moulds to design and make ```

Answer 25

plastic bottles ``` pros  Intricate shapes  Hollow shapes  Thin walls to reduce weight and cost  Good for mass production ``` ``` cons  High set up costs  Expensive moulds to design and make ```

Answer 26

``` Products: Yoghurt pots Blister packs Chocolate box inserts Packaging ``` ``` pros  Good for batch production  Inexpensive  Relatively easy to make the moulds ``` ``` cons  Accurate mould design needed to prevent webbing  Large amounts of waste material produced ```

Answer 27

drain pipes tubes ``` pros  Continuous  High production volumes  Low cost per unit  Limited complexity of parts ``` cons  Uniform cross- sectional shape only

Answer 28

Buckets Footballs Oil drums Traffic comes ``` pros  The investment in equipment and tooling is less than vacuum forming and blow moulding.  No seams  Uniform wall thickness  Metal inserts can be added to the mould ``` cons  Lower volume production  Labour intensive

Answer 29

plastic bottles ``` pros  Intricate shapes  Hollow shapes  Thin walls to reduce weight and cost  Good for mass production ``` ``` cons  High set up costs  Expensive moulds to design and make ```