How far has the development of casting techniques come with respect to making thinner sections, say 2-2,5 mm, in complicated castings?

Shareholder, Tommy Haraldsson

For engine block castings, most iron foundries are currently quoting nominal minimum wall thickness of 3.5 mm. The typical tolerance is -0.5 mm and +1.0 mm, which means that a nominally 3.5 mm wall can vary from 3.0 mm to 4.5 mm. The risk with thin-wall castings is that the sand core can shift inside the mould resulting in a nominally 3.5mm wall being, for example, 5.5 mm thick on one side of the core and the opposite wall being only 1.5 mm thick.

Wall thickness is a very "open" question and I would like to make three specific comments to further clarify the subject:

  1. The minimum wall thickness also depends on the ’type’ of wall. Foundries will be more willing to specify thin (<3.5 mm nominal) walls in small (ie, 2 cm x 2 cm) wall sections or small features such as reinforcing ribs and webs. Larger sections, in which it is more difficult to support and align the sand cores, will have thicker minimums. The curvature of the wall must also be considered in determining the minimum.
  2. One of the biggest changes in foundry moulding over the past 5-10 years is that almost all new cylinder blocks are produced in a so-called core package. This means that the entire block is produced in sand that is chemically bonded (glued) as opposed to traditional green sand (pressed together). The use of core packages reduces the risk of core shift and has thus reduced the nominal minimum wall thickness from about 4.5 mm to 3.5 mm over the past ten years. Core package technology should continue to improve, thus allowing for thinner walls in the future.
  3. Minimum wall thickness is not really a foundry issue. All foundries buy their core making and moulding machines on the open market. Foundries that purchase the same machines will have the same capabilities.

Finally, it is important to realise that reducing the minimum wall thickness from 4 mm to 2 mm is not the key to weight reduction. A typical passenger car engine block will only have about 10% of its weight in thin (<4 mm) walls, and reducing this to 3 mm will only achieve a 2.5% weight saving. The real key to weight reduction is to make the thick (10-25 mm) load-bearing walls thinner, by using stronger materials such as CGI. Changing a 25 mm main bearing section to 15 mm has a huge impact on weight reduction, and has almost no impact on the foundry’s ability for thin-wall moulding. The thin-wall/weight reduction debate is more relevant for products such as exhaust manifolds, which are almost entirely comprised of thin walls. Thinner and thinner is certainly important for blocks and heads, but it is not the main issue.