Pattern manufacture and mould assembly

Published - 24th Sep 2020

Pattern manufacture plays a critical role in the intricate sand casting process to ensure the highest quality and finish of the final product.

The pattern is created by specialist pattern makers using either paper designs, 3D models or software drawings supplied by our customer.

Design considerations

First of all, our team at Haworth Castings will interrogate the customer design to identify any manufacturing issues or limitations. Various factors have to be considered, such as the metal thicknesses in the pattern, the flow of metal into the mould and the potential for shrinkage or porosity.

We advise the pattern maker on the position of the runners and risers and various other elements. If any cavities are required in the final casting, the pattern maker manufactures patterns for any cores needed to create them.

The next step is to produce the pattern, which is manufactured from a high-quality resin. The hardness of this resin is determined by the expected life of the pattern.

The pattern is not an exact replica of the metal casting; it is made slightly larger than the finished product to allow for metal contraction during the solidification process.

Once the resin pattern has been machined, pattern assembly can begin. The resin pattern is accurately secured into a wooden moulding box, which has a top (the cope) and a bottom (the drag).

A previous blog on Sand Core making in casting is available for you to read.

Mould assembly

The box is filled with sand, which is mixed with a hardening agent before it forms a solid mould around the pattern. The sand moulds are then removed from their wooden boxes before being joined together to form a closed casting cavity.Any cores are inserted before the two halves are closed and dypurs and sleeves are added to create a running system. This ensures a steady flow of the molton metal through the mould. Finally, the mould is ready for the metal pour.

The mould cavity must:

• retain its shape until the metal has solidified
• be strong enough to sustain the weight of the molten metal
• allow any gases formed within the mould to escape into the air
• be malleable enough to permit the metal to contract
• resist the erosive action of molton metal
• be easily removable from the finished casting[1]

So, these preparatory phases are critical in ensuring the highest quality castings. You can see a short film about the sand casting process on our website at: www.haworthcastings.co.uk

[1] Bullets extracted from the 2006 Casting Service Directory, Engineering Casting Solutions

If you would like to find out more about our sand casting capabilities, please email us today at: sales@haworthcastings.co.uk or call +44 (0)1794 512685.