A pattern is an object that resembles the shape of a cast object and is used to create a mold cavity, which later hardens and forms a cast object according to the shape of the pattern when molten metal is poured.
Metal casting patterns can be made from various materials that meet pattern-making standards, including metal, wood, plastic, synthetic, and styrofoam.
Casting Pattern Types
Lost Pattern
Lost patterns, also known as disposable patterns, are typically made of styrofoam.
Reusable Pattern
Plate patterns, single patterns, and core boxes are examples of reusable patterns that can be used repeatedly.
Temporary Patterns
Temporary patterns are prone to shrinkage, deformation due to humidity, or wear and tear, such as wood patterns.
Permanent Pattern
Permanent patterns are typically made of aluminum alloy, cast iron, nodular cast iron, or steel, and are more robust, more resistant to friction, and more stable to changes in humidity.
Criteria for determining pattern type
Several criteria are used to determine the type of pattern to be used, including:
- Casting quantity
- Mold and core manufacturing methods
- Casting design
- Desired dimensional tolerances
- Type and size of molding frame and molding machine
Important Factors to Consider When Designing Metal Casting Patterns
The first step in creating a pattern is to read the casting technical drawing, then convert it to a pattern design drawing. Which will later be a pattern design drawing used as a reference when creating the pattern.
Several factors must be considered in the casting pattern design drawing, including pattern splits, additional work, pattern slope, and shrinkage. Here’s how it works:
Parting Line
Pattern making is generally divided into two or more parts, especially for complex shapes, with the exception of objects that are simple in shape and can be made without parting lines, which are referred to as single patterns. The pattern with the upper part is called Kup, and the pattern with the bottom part is called Drag.
In general, whether or not to use splits to determine the pattern is up to the designer; however, it should be remembered that the requirements should not complicate the next process.
Additional Work
This is the addition of size or thickness to parts that will be machined further. Additional work is usually done on products that require precise measurements and smooth surfaces.
Tilt
The slope of the pattern refers to the entire surface of the casting wall that is perpendicular to the cleavage line. The purpose of creating a slope is to make it easier to remove the pattern from the mold and to prevent damage to the pattern or the sand mold.
Positive, negative, and neutral slopes are the three types of pattern slopes. The pattern’s slope is determined by the engineer.
Shrinkage
To achieve the desired size of the casting, the pattern size must be multiplied by the shrinkage percentage of the metal material to be cast.
The table below shows shrinkage dimensions based on material:
| Casting Material | Depreciation % |
| Gray Cast Iron | 1 |
| Nodular Cast Iron | 1 |
| Malleable Cast Iron (White) | 1,6 |
| Cast Steel | 2 |
| Aluminum Alloy | 1,2 |
| Magnesium Alloy | 1,2 |
| Copper (Cu) | 1,9 |
| Bronze (Bronze) | 1,5 |
| Brass | 1,5 |
| Brass Alloy (Mn-Fe-Al) | 2 |
| Aluminum – Bronze (Al – Cu) | 1,8 |
| Zinc (Zn) | 1,3 |
| Black Lead (Pb) | 1 |