Patterns are used in foundry casting to create the mold into which molten metal is poured to create a casting. Casting is a widely used process in the field of mechanical engineering that involves pouring molten material into a mold, which then solidifies and takes on the shape of the mold. One of the most important aspects of casting is the creation of a pattern, which serves as a model for the final product.
Different types of patterns are used depending on the complexity of the shape of the casting and the casting process being used. There are various types of patterns used in foundry casting, including single-piece patterns, two-piece patterns, gated patterns, multi-piece patterns, match plate patterns, skeleton patterns, sweep patterns, loose-piece patterns, follow board patterns, cope and drag patterns, segmental patterns, and shell patterns.
Each type of pattern has its own unique characteristics and is used in specific casting processes. The selection of the pattern type is important to ensure that the final casting is of the desired shape and quality. Well, in this article, I’ll be explaining the various types of patterns used in the casting process.
What is a pattern?
Patterns are replicas of the objects that are used to form a cavity into which molten materials are poured during the casting process to form the object. Materials used to form sand-casting patterns are wood, metal, plastic, etc. Depending on the quality of the pattern being constructed, patterns are built to precise requirements to give consistently acceptable casting and to last for a reasonable amount of time.
Many kinds of designs are typically made using materials like wood, metal, or plastic. Sometimes, wax patterns are required for specific applications. Wax patterns are used in the investment casting process.
Functions of a pattern
The following are some of the functions of patterns used in casting process:
- The right design pattern reduces casting defects and has a smooth surface.
- A portion of the pattern’s gates, risers, and runners are utilized to feed molten metal into the cavity.
- If casting calls for a core consisting of hollow components, the pattern includes a projection known as a core print.
- The design creates the chamber of the casting mold.
Read more: Understanding evaporative pattern casting
Types of casting patterns
The following are the types of patterns used in casting process:
- Single-piece pattern
- Split-piece pattern
- Loose piece pattern
- Gated pattern
- Match pattern
- Sweep pattern
- Cope and drag pattern
- Shell pattern
- Follow board pattern
These types of patterns are less complex in design and can be placed either in cope or drag. Single-piece pattern types are used in large castings, e.g., stuffing boxes for steam engines. This pattern is exactly like the desired object. A single-piece pattern is also known as a solid pattern.
This pattern is economical because it simply requires straightforward shapes and flat surfaces. It is perfect for straightforward operations and small-scale manufacturing. This is why industries where large objects are made make use of it.
Split or two-piece pattern:
These types of patterns are used for intricate casting. It is also known as the split-piece pattern. It has cope and drag as its major components. The cope component utilizes dowel pins and is aligned with the drag.
It contains two dowel pins and two dowel holes that are used to align and attach the two sections. The shape of the casting determines the position of the separation planes (irregular or flat). The use of split patterns can be found in the production of steam valves and weapons.
Loose piece pattern:
These types of patterns are obtained when a solid piece has a backdraft or projections that may lie above and below the parting plane. One disadvantage of loose patterns is that the adjustment of the projected pattern can be done during ramming. This may slow down the casting process.
Gate patterns contain one or more loose patterns attached to gates and runners. Gated patterns are used in producing small castings in mass-production systems. Just as earlier mentioned, casings are produced in bulk using multi-cavity molds.
The molds are made by joining a few patterns and gates and giving a single runner for the melting metal. These patterns are composed of metal, and gates and runners are created by attaching metal pieces to the pattern.
Match plate pattern:
These types of patterns are similar to split patterns. The cope and drag portions are mounted on opposite sides of a plate (usually metal), which adhere to the contour of the parting surface. Gates and runners are also mounted on the match plate. The match plate pattern is used for a large number of castings, resulting in higher productivity.
The other sides of a match plate are made of wood or metal. The plates also support the runners and gates. This kind of pattern is utilized in machine molding. It is widely used in industry for casting a variety of items, it is expensive, precise, and high-yield. Casting of metals like aluminum frequently employs this style of pattern.
Read more: What are the types of casting processes?
In a sweep pattern, the cavity is created by rotating a wooden board along one of its edges. These types of patterns are used when a large size of casting is required in a short time. Its components include a spindle, a base, and a sweep or wooden board. It is known for producing a casting in a short period.
Cope and drag pattern:
These types of patterns are similar to split patterns. They contain a cope and drag portion, each mounted separately on a match plate. They are used in the production of large casting. The process cannot be done by a single worker due to the weight of the molds. The cope and drag portions of the mold are made separately. This is because the entire mold is too heavy for one operator to lift.
Circular castings like wheel rims, gear blanks, and other similar items frequently use this kind of pattern. These patterns consist of pieces that are moved to create each piece of the mold to create the full mold.
This pattern is just like a sweep pattern made of wooden frames that carry the shape of the part to be cast. A skeleton pattern is for large casting having simple geometrical shapes. It is also used in pit and floor wooden processes.
Skeleton patterns are a suitable option for castings with simple sizes and shapes because of their large size. The type of casting pattern is expensive and immobile. Although it is not the most economical choice, it is quite good at getting rid of additional sand.
These types of casting patterns are produced in a mold that outlines the shape of the part to be coated. A shell pattern type is a great option for building structures with hollow interiors. It divides in half, then dowels the two pieces together.
Follow Board Pattern:
These types of patterns are used as a device. It is used for various purposes in foundry work. It is made of wooden board. As split or solid patterns become challenging, a follow board with a contour matching the precise geometry of one-half of the pattern is created.
That is all for this article, where the types of patterns used in the casting process are explained. I hope it was helpful, if so, kindly share it with others. Thanks for reading, see you around!