Resin shell moulded castinG
Shell moulding, also known as shell-mould casting, is an expendable mold casting process
that uses a resin covered sand to form the mold. As compared to sand casting,
this process has better dimensional accuracy, a higher productivity rate, and lower labor requirements. It is used for small to medium parts that require high precision. Shell mold casting is a metal casting process similar to sand casting, in that molten metal is poured into an expendable mold. However, in shell mold casting, the mold is a thin-walled shell created from applying a sand-resin mixture around a pattern. The pattern, a metal piece in the shape of the desired part, is reused to form multiple shell molds. A reusable pattern allows for higher production rates, while the disposable molds enable complex geometries to be cast. Shell mold casting requires the use of a metal pattern, oven, sand-resin mixture, dump box, and molten metal.
Shell mold casting allows the use of both ferrous and non-ferrous metals,
most commonly using cast iron, carbon steel, alloy steel, stainless steel,
aluminum alloys, and copper alloys. Typical parts are small-to-medium in size and require high accuracy,
such as gear housings, cylinder heads, connecting rods, and lever arms.
The shell mold casting process consists of the following steps:
Pattern creation - A two-piece metal pattern is created in the shape of the desired part,
typically from iron or steel. Other materials are sometimes used,
such as aluminum for low volume production or graphite for casting reactive materials.
Mold creation - First, each pattern half is heated to 175-370 ｰC (350-700 ｰF)
and coated with a lubricant to facilitate removal. Next, the heated pattern is clamped to a dump box,
which contains a mixture of sand and a resin binder. The dump box is inverted,
allowing this sand-resin mixture to coat the pattern. The heated pattern partially cures the mixture,
which now forms a shell around the pattern. Each pattern half and surrounding
shell is cured to completion in an oven and then the shell is ejected from the pattern.
Mold assembly - The two shell halves are joined together and securely clamped to form the complete shell mold.
If any cores are required, they are inserted prior to closing the mold.
The shell mold is then placed into a flask and supported by a backing material.
Pouring - The mold is securely clamped together while the molten metal is poured from a ladle into the gating system and fills the mold cavity.
Cooling - After the mold has been filled, the molten metal is allowed to
cool and solidify into the shape of the final casting.
Casting removal - After the molten metal has cooled, the mold can be broken and the casting removed.
Trimming and cleaning processes are required to remove
any excess metal from the feed system and any sand from the mold.
||Advantages and Disadvantages
One of the greatest advantages of this process is that it can be completely automated for mass production.
 The high productivity, low labor costs, good surface finishes, and precision of the process
can more than pay for itself if it reduces machining costs.
There are also few problems due to gases, because of the absence of moisture in the shell,
and the little gas that is still present easily escapes through the thin shell.
When the metal is poured some of the resin binder burns out on the surface of the shell,
which makes shaking out easy.Automobile Industry
Defence Armament & Fire
Diesel & Gas Turbine Engines
Material Handling Equipment
Machine tools industry
Nuclear fuel industry
Food products machinery
Pneumatic tools industry
One disadvantage is that the gating system must be part of the pattern because
the entire mold is formed from the pattern, which can be expensive.
Another is the resin for the sand is expensive, however not much is required because only a shell is being formed
Advantages: Can form complex shapes and fine details, Very good surface finish,
High production rate, Low labor cost (if automated), Low tooling cost,
Little scrap generated. Can produce very large parts, Can form complex shapes,
Many material options, Low tooling and equipment cost, Scrap can be recycled, Short lead time possible.
Disadvantages: High equipment cost, Poor material strength, High porosity possible,
Secondary machining often required, High labor cost (if done manually).
Applications: Cylinder heads, connecting rods Engine blocks and manifolds, machine bases, gears, pulleys
Squeeze aluminium Die casting (Squeeze aluminium casting.) (Ferrous investment casting )
An engine block with aluminium and magnesium die castings.
squeeze aluminium Die casting is a metal casting process that is characterized by
forcing molten metal under high pressure into a mold cavity.
The mold cavity is created using two hardened tool steel dies
which have been machined into shape and work similarly to an injection mold during the process.
Most squeeze aluminium Die casting are made from non-ferrous metals, specifically zinc, copper,
aluminium, magnesium, lead, pewter and tin-based alloys
. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this tends
to limit the process to high-volume production. Manufacture of parts using die casting
is relatively simple, involving only four main steps, which keeps the incremental cost per item low.
It is especially suited for a large quantity of small- to medium-sized castings,
which is why die casting produces more castings than any other casting process.
Die castings are characterized by a very good surface finish (by casting standards) and
Applications of investment castings: