Casting Methods

Investment Casting

Investment Casting is the term applied to precision moulding using a metal die and ceramic coating in which the chosen metal is injected.

The mould material is usually:

HARD WAX	ideal for small parts high degree of precision lower tolerances higher cost than lost wax and lost foam casting excellent surface finish
LOST WAX	most common good degree of precision more cost effective than hard wax very good surface finish
LOST FOAM	not very common suited to part shapes that are difficult to make and handle in wax average surface finish

Sand Casting

Sand Casting is considered the traditional method of casting. The various common methods of sand casting revolve around the types of binders used to maintain mould strength (resist the molten metal). These methods are:

CLAY BONDED / GREEN SAND Inexpensive method due to 93-95 % recovery of the binder (for re-use) Suited to high automisation Best suited to high volume parts
HARD BONDED / RESIN Chemically bonded sand Ideal for large parts (up to 3000 kgs) with large sections Suited to lower volume requirements More expensive than green sand casting
THERMO SETTING RESIN SAND / SHELL Excellent surface finish High level accuracy Well suited to casting parts that have internal cavities that can be difficult to clear after the casting process. The binder reduces to small grain sand and can be simply poured from a small duct in the internal cavity. With other methods of casting the binder and resins can be difficult to remove.

 

The main points we look at when deciding between sand and investment casting are;

1. The size of the part
   Investment casting is best suited for small parts up to a maximum of 80 kgs and 1.2 metres in length.  Larger parts create too much pressure and distortion of the walls of the mould. Larger castings are best made as a sand cast.
2. Tolerances
   Lower tolerances and a better surface finish can be achieved  using the investment method.
3. Cost
   As a general rule we can produce investment castings at a better price than sand castings.  We only source castings from those who make them better than everyone else.  This means that our sand castings come from countries where the costs of production tend to be higher than countries that produce high quality investment castings, thus they are more expensive.

Casting Alloys

At ATC GROUP we produce castings in a wide range of ferrous and non ferrous alloys.

We don’t try to over complicate the alloys we use.   Unless a job specifically requires alloy manipulation – we use standard Australian and International materials.

We currently produce castings in the following materials:

STEEL
LOW ALLOY	Ni-Cr-Mo- 4130  4140 5140 8630
STAINLESS	17-4PH, AISI-316, AISI-310, AISI-309 DUPLEX STAINLESS HEAT RESISTANT STAINLESS HK,HF
MANGANESE	AS 2027 WORK HARDENING
WHITEIRON	AS 2027/Ni Cr1 550 (Ni hard) AS 2027/Ni Cr27 (27% Chrome)
ALLUMINUM ALLOYS	LM6