Technical specs.

What the MM casting process can deliver:

• Thin walls as fine as 0.2 mm (0.008"), typically 1-3 mm (0.04" - 0.12").
• Light weight components, weighing as little as 1g (0.04 oz.) can be produced using techniques to minimise material usage whilst retaining component integrity.
• Maximum size of 190 mm x 160 mm x 160 mm (8" x 6" x 6"). A length of 250 mm (10") is possible providing no other dimension exceeds 100mm (4").
• Complex detail on internal and external features.
• Superfine surfaces with 0.8 micrometres (32 micro inches) being the "as cast" finish.
• Zero draft angles

Wall sections

Thin walls and uniform wall thickness always produce superior castings with minimum porosity, distortion and tolerance spreading. Constant section thin walls are preferred but large changes of section can be accommodated through critical analysis of the component design and special tooling design features. Wall thickness and flatness over large surfaces are better controlled if through-holes and ribs are incorporated in the design.

Wall section tolerances

Section	Tolerance
<0,5	±0,10
0,5 - 1,0	±0,15
1,0 - 2,0	±0,20
2,0 - 4,0	±0,25
4,0 - 8,0	±0,30

Casting Tolerances

Tolerances depend on the geometry of each part, but the following tolerances are suggested as a guide to designers.

Lengths including hole diameters, held to :

Flatness
Generally held to ±0.13mm (0.005") per 25 mm (1.00") square. Total Indicator Reading (T.I.R.) will, however, depend on configuration.

Straighness
Generally held to ±0.1 mm (0.004") max per linear 25 mm (1.00"). Total Indicator Reading (T.I.R.) will, however, depend on configuration.

Squareness and Angularity
±0.5 degree Note: Angular tolerances are affected by irregular geometries.

When tolerancing, use of a central feature as a datum may allow detail to be cast that would otherwise carry too large a tolerance. Where a mechanical interface feature is required on a surface, it helps to use the centre of the feature as a datum.

Improved tolerances can generally be achieved by machining. This however introduces additional cost and lead time. The more machining operations that can be avoided, especially milling operations, the more cost effective the MM casting process becomes.

Drawings should indicate the essential tolerances and should relax those which are unimportant.

Cast Holes
The mould material used by the MM casting process is applied as a slurry and is easily removed by water jets. This enables fine through holes to be cast. Length to diameter ratios can vary upwards from 4:1 dependent on diameter. Blind holes can be cast provided the depth to diameter ratios do not exceed 3:1. Holes of under 0.5 mm (0.020") diameter are often cast. Elongated holes can easily be cast allowing the take up of tolerances within an assembly. Threads are best not cast but provision of a hexagonal cavity around a bolt hole allows the use of a captive nut or bolt, removing the need to tap a hole. Also holes can be cast which are suitable for self tapping screws.

Draft Angles

The MM casting process does not normally require draft angles as the wax has relatively low injection pressure, is self lubricating and has minimal shrinkage. However, if investment casting is being employed to develop a component, which may eventually be produced in very large quantities as a pressure die casting, then draft angles can be incorporated to simulate those which will eventually be needed.

Special features

Soluble cores

Complex internal features such as swept bends can be formed by the use of soluble cores. Tolerances however may require relaxing.

Wax assembly

Tooling for a complex component can sometimes be simplified by joining two or more patterns together at the wax stage.

Cast gears and teeth

Components requiring teeth for gripping or gear applications may be impossible to produce by machining. The definition achieved by the MM process is ideal for these applications. Integrally cast rivets can be peened over to give an economic, strong and permanent joint.

Radii
Radii Square corners are a feature of the MM casting process. Internal radii can be easily introduced to increase strength. An external 1 mm (0.04") radius is often useful on larger parts as it reduces any tendency of the mould material to crack on firing, however, square corners can be accommodated if required.

Surface finishes
"As cast"- parts removed directly from the mould have a surface finish equal to or better than 0.8 micrometres (32 micro inches); this finish may show variable colour.

Chip rumbling - removes any sharp edges left after linishing, leaving a surface suitable for most subsequent "finishing" processes.

Automatic grit blasting - gives a uniform matt finish, suitable for most subsequent finishing operations.

Bead blasting - using stainless steel shot, is generally suitable for brass components and gives a slightly polished surface.

Glass bead blasting - produces a more highly polished surface finish and is most suitable for aluminium parts.

Special surface effects - such as textures and knurling can be incorporated in the MM casting process. Surfaces which need to be blemish free should be highlighted on a drawing.

Integrated Labelling
It is possible to include many types of permanent product identification which can eliminate further need for labelling. Logos and text may be produced with minimum cost if the design ensures that detail is in the line of draw of the wax from its die. Ideally, cast labels should use raised lettering on the casting face (engraved into the wax tool). Where such information must be below a functional surface, it can be sited on a pad sunk into the cast face. Preferred depth of engraving: 0.25 mm - 0.50 mm (0.010" - 0.020") Types of labels (click label in bold for a pop-up example)

Applied surface treatments
The following treatments can be applied:

Alocrom1200 / Iridite / Chromate Conversion - are processes which provide corrosion resistance to aluminium parts whilst providing an electrically conductive surface.

Anodising - for protective purposes can be carried out on aluminium alloy castings but cast alloys do not readily accept decorative anodised finishes.

Plating - can be applied to most alloys, this requirement needs to be identified at the enquiry/design stage.

Hipping (Hot Isostatic Pressing) - is used to improve the mechanical properties of aluminium castings by sealing internal voids. This technique can be used as a non-destructive test on critical aluminium parts.

Impregnation - can be carried out on "as cast" or machined parts where pressure tightness is essential. Paint - for protection or visual purposes.