Mr. Kevin Kang
Tel:86-574-87394139 
FAX:86-574-56702909
E-mail: info@ka-castings.com
on line:    

Address: No. 32 Shunke Road, Yangming Industrial Zoom, Yu Yao, Ningbo, China

 

Technical Support

The Choice of Process - Sand Casting, Gravity & High Pressure Die Casting

In order to select the most appropriate alloy in which to cast a component, designers should first select the most appropriate casting method.  This decision is usually based on the anticipated production volumes of the component.  It can also be influenced by considerations of the required dimensional accuracy and surface finish. 
Once the most appropriate process has been selected, designers should decide upon the alloy which has the mechanical and physical properties most appropriate to the particular application, whilst also considering whether the casting characteristics are appropriate to the chosen process.
The table below will assist you to choose the process most appropriate to your requirements, however it is often necessary to obtain quotations for more than one process in order to decide which will be the most economic.

 

 

 Sand Casting

 Gravity Die Casting

 High Pressure Die Casting

 Tolerances on Critical
 Dimensions

 Up to 25mm
 Each Additional cm Across
 Parting Line Ad.

 ± 1mm
 ± 0.39mm
 ± 1mm

 ± 0.4mm
 ± 0.02mm
 ± 0.25mm

 ± 0.1mm
 ± 0.016mm
 ± 0.12mm

 Minimum Taper

 On Inside Walls
 On Outside Walls

 2°
 2°

 1°
 1°

 1°
0.5°

 Minimum Wall Thickness

 On Small Castings
 On Large Castings

 3mm
 5mm

 3mm
 4mm

 1mm
 2mm

 Minimum Size of Cored Hole

 15mm

 3mm

 2mm

 Ability to use Sand Cores

 Yes

 Yes

 No

 Surface Finish

 Poor
 6.5-12.5 m

 Fair
 4-10 m

 Good
 1.5 m

 Typical Production Quantities per annum

 1-500

 250-50000

 2000-500000

 Typical Tool Life

 5,000

 100,000

 500,000
 
  SAND CASTING
Sand casting offers the simplest medium for production of non-ferrous castings, by pouring molten metal into a sand mould.  This process is chosen for the production of small numbers of castings, for complex shape castings requiring intricate cores, or for large castings.  Advantages include low tooling costs, largest casting sizes achievable, very low gas porosity is possible, and general versatility of the process is good.  Limitations include low casting rate, 3-5mm minimum wall thickness, poor linear tolerance (e.g. 4mm/m), rough surface finish (6.5-12.5mm), and a coarser grain size than gravity die castings. Further information on Sand Casting
  GRAVITY DIE CASTING (ALSO KNOWN AS PERMANENT MOULD OR CHILL CASTING)
Gravity die casting is produced by pouring molten metal into permanent cast-iron moulds.  This process produces chill castings.  The process has a higher casting rate than sand casting, but the metal moulds are higher cost than sand patterns.  Advantages include the possibility of low gas porosity, and fine grain sizes can be obtained.  Less finishing and polishing will be required than for sand castings.  Gravity die casting tends to produce the highest quality castings, however the accuracy achievable is limited.  Minimum wall thickness possible is c. 3-5mm.
  LOW PRESSURE DIE CASTING
Low pressure casting is a development of the permanent mould process, in which the metal is introduced into the chill mould from below.  Gas pressure holds the metal in the die until it solidifies.  As with high pressure diecasting the process requires complex machinery.  It is repetitive, and may be automated.  Production rates are fair, but not as good as high pressure.  Minimum wall thickness' are as little as 2-3mm.  It has high yields of over 90%, as runners and risers are excluded, also reducing fettling and trimming costs.  Pore-free castings are obtainable.  Machine size will limit the size of castings.  Surface finishing and minimum wall thickness' are both better than gravity die casting, but poorer than high pressure die casting.
  HIGH PRESSURE DIE CASTING
High pressure die casting, often shortened to Pressure Die Casting, is a repetitive process where identical parts are cast at high production rates by injecting molten metal under pressure into a metal die.  Again, this process requires complex machinery.  High pressure die casting is ideally suited to high production rates, and wall thickness' can be as little as 1-2.5mm.  It provides the best surface finish (1.5m), and a very fine grain surface can be obtained.  Pressure die casting has high strength.  Castings may be quenched from the die.  Machine size will limit casting size.  Sound thick sections are difficult to cast, and core configurations must be complex to enable disassembly.  High pressure die castings may suffer from porosity, although evacuated chamber and other techniques may reduce this.  High start up costs are only reduced by long casting runs, thus enabling low unit cost with a high volume production.  Pressure die castings cannot be fully heat treated.
  INVESTMENT CASTING (ALSO KNOWN AS LOST WAX CASTING)
This casting method involves producing a "wax pattern" by injecting wax or plastic into a pattern die.  The pattern is attatched to gating and runner systems and this assembly is dipped in a hard setting refractory slurry which is then cured.  The pattern is melted out of the mould to leave an exact cavity.  The mould is heated to cure the refractory and to volatilize the remaining pattern material. The moulds are baked and molten metal is poured into the mould cavity.  On solidification of the casting, the mould material is broken away from the casting