Aluminium is lightweight, resistant to high temperatures and other adverse environmental factors. Therefore, there is no doubt it can successfully replace old steel structures or machine parts made of other metals.
Castings made from aluminium alloys show high electrical and thermal conductivity as well as corrosion resistance. They are easy to machine, have few defects, and can be recycled multiple times. Replacing old components with aluminium castings will certainly bring added value to your products.
Our designers make 3D casting designs based on drawings, photographs, sketches or 3D models sent by customers. The designs serve as the basis for further talks with clients and for making specific arrangements.
Pattern Design—Basic Rules
Selection of Casting Method
Before we start making a pattern, we perform a preliminary analysis. The pattern designer considers the desired shape of the casting, the type of aluminium used, and the lot size.
Patterns are usually made of plastic. Its advantages include: high density, strength and chemical resistance, as well as low abrasion. Epoxy and polyester resins, PVC, ABS, PLA, PET are all used.
For small lots, wood is also utilised. It has many advantages as well as disadvantages, e.g. uneven structure, which changes due to moisture, cracking, etc.
By contrast, metal patterns for mass production are made from aluminium or copper alloys.
Fundamentals of Pattern Design
The pattern, regardless of the material it is made of, must allow for the moulding sand to be properly compacted and for the mould to be stripped. Additionally, it must guarantee correct pouring parameters.
Solid Patterns, Split Patterns and Loose-Piece Patterns
Based on their complexity, patterns are designed as solid, split or loose-piece. Solid and split patterns are made for castings with simple shapes.
More advanced castings require split or loose-piece patterns. The loose pieces are usually quite small and they are not positioned on the split line.
Importance of Draft
Draft is used to make stripping of the mould easier. During the process, it creates a clearance between the pattern and the mould cavity, which prevents the sand from dropping down.
Surface Finish of Patterns
The surface finish of a pattern—roughness—is key when removing the casting from the mould. It is important for the surface to be as smooth as possible. When the surface is rough, the casting gets damaged during the removal.
What is Casting Shrinkage
Casting shrinkage is the percentage reduction in the dimensions of the casting compared to the dimensions of the pattern. Shrinkage occurs when the liquid aluminium in the mould cools and continues cooling after solidification.
Casting shrinkage is a source of stresses and cracking. The pattern should be bigger than the casting in order for the latter to have good dimensions.
Machining allowance is additional stock on the surface of a casting. It is removed at the machining stage so that the casting has the desired dimensions and parameters of the final product. The size of the machining allowance required can be found in standards.
Thoni Alutec Sp. z o.o.
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