Mold Making

The Sterling Advantage... OneSource from Concept to Consumer

Sterling tool design and mold making programs are set-up to aggressively price our molds to get your products to market.   

The rotational moldog process uses centrifugal force and gravity, not pressure, to fill the mold. This allows rotational molds to have a lower up front cost compared to other processes like injection molding and blow molding. Sterling will help customers choose the right type rotational mold for their application. Each type of mold lends itself to different types of products.

The following is an overview of molds available for the plastic rotational molding process.

• Cast Molds are the most common type of rotational molds to produce parts small to large. Cast molds produce parts that require considerable detail or elaborate shapes and they can be modified to integrate design changes. This is also a great way to 'pull' the texture and/or shape from existing objects.  Basically, parts with compound curves or unique geometrical features such as rain barrel or ornamental planter would be cast.

• Fabricated Molds are used mainly for large parts with simple shape Fabricated from steel, aluminum or stainless steel these molds are lightweight, have a consistently thin cavity wall and are the lowest cost approach when dealing with large molds. These molds are ideal for products with simple geometries such as generic fuel tanks or storage containers.

• CNC Molds are used when extreme precision or extended production runs are required. Because of a higher cost, they are used only in special cases.

• Epoxy Molds use a liquid thermosetting polyester and epoxy material that is formed and cured at room temperature. Similar to Cast Molds, these Epoxy Molds are perfect for short runs and concept designs that are likely to be tweaked before a final version and/or mold is produced.  Epoxy molds are fairly inexpensive but won't last many production rounds and generally have poor tolerances compared to other types of molds.

The most important thing to consider with all types of molding is the quality of the mold. There is no substitute for an excellent mold. A Production rotational molder can advise you on the type of mold best for your application, and the plastic material most suitable for your product.

Sterling Technologies can help you make the right decisions to make your product stand out from the rest. Click here, to learn more about the advantages of rotational molding process.

How a Cast Aluminum Mold is made

Sand castings are produced in a foundry using sand as the mold material and is a relatively inexpensive process to produce parts from almost any molten metal; typically iron, steel, bronze, brass, aluminium, magnesium alloys.

The model or pattern of the tool is made of a plastic such as expanded polystyrene.

The sand is mixed with a bonding agent to produce a strong aggregate suitable for molding and is poured into mold boxes or flask. The sand is compacted around model or pattern creating the mold cavity and gate system.

Molten aluminum is poured into the casting cavity through a runner system and feeders which maintain good flow. Gas and steam generated during casting exit through the permeable sand or out risers inserted into the flask. The mold box is then left to cool.

After the casting has cooled, the sand is removed revealing a rough casting. The aluminum from the sprue and risers is trimmed and the rough casting is then machined to create a strong seal at the seam. Further finishing operations include surface grinding and polishing, boring holes, and adding the fame and fasteners.