Casting is a very common manufacturing process to produce metal parts. It creates molds also called casting patterns where the manufacturers pour the molten metal next, and metal parts are finished after the cooling of shaped metal materials.
During the casting process, the casting pattern is very crucial because of its effect on final products. Casting manufacturers should consider the casting pattern design completely according to the final products. There will have an expensive changing cost after casting.
What Is Pattern in Casting?
In casting, a pattern is a replica of the object to be cast, used to prepare the cavity into which molten material will be poured during the casting process.
Patterns used in sand casting may be made of wood, metal, plastics, or other materials. Patterns are made to exacting standards of construction, so that they can last for a reasonable length of time, according to the quality grade of the pattern being built, and so that they will repeatably provide a dimensionally acceptable casting.
The making of patterns, called patternmaking, is a skilled trade that is related to the trades of tool and dies making and mold making but also often incorporates elements of fine woodworking.
Patternmakers learn their skills through apprenticeships and trade schools over many years of experience. Although an engineer may help to design the pattern, it is usually a patternmaker who executes the design
Materials of Casting Pattern
Your casting pattern materials should have these properties:
- Lower cost and less weight: with the lower cost and less weight you are easier to find the balanced point of costs and returns.
- Resistance of water: choosing the material with resistance of water protects your casting pattern from rusting. Casting patterns with this kind of material will have a long lifetime and produce high quality patterns.
- Durable: durable material provides a long lifetime of your casting pattern, so you should consider the durable property of the material before you choose casting pattern materials.
- Versatile: various industries need casting patterns to create the casting process, so the versatile property of casting pattern material is very important. It ensures the pattern can be used in many kinds of industries, and repaired easier.
Casting Pattern Allowances
Other factors like the type of casting pattern and the properties of casting metal should also consider. Therefore, there have some casting pattern allowances you should pay attention to when you make a casting pattern.
- Draft allowances: draft allowances create a taper for removing casting patter without any distortion. And the accurate angle of taper depends on the type of mold and surface, and the complexity of the casting pattern.
- Shrinkage allowance: usually the casting pattern has a bigger size of the mold, because most metal material contracts when it cools. The shrinkage allowance compensates for the cooling shrink of metal, and the precise parameter of the allowance depends on the metal material.
- Distortion allowance: casting patterns have a special design for avoiding the expected cooling distortion. We call it a distortion allowance.
- Machining allowance: excess material in the finishing stage for compensating some loss materials.
Casting VS. Pattern
The main difference between pattern and casting is that a pattern is a tool while casting is a kind of process.
- Casting: It is a kind of process that manufacturers pour the molten metal into a mold, where the material cools and solidifies. The final shape of products was decided by the mold cavity, while the shape of the mold should be considered, and that is where the pattern appears.
- Pattern: Before you make a mold, you should design a pattern firstly. The pattern is the primary shape of the mold and finally, the product shapes according to the pattern.
Types of Patterns in Casting
As we discussed, casting objects are highly dependent on the pattern. According to the shape and size of casting and method of making cavity, the pattern can be classified as follow:
- Single piece pattern,
- Split pattern,
- Gated pattern,
- Multi piece pattern,
- Match plate pattern,
- Skeleton pattern,
- Sweep pattern,
- Lose piece pattern,
- Cope and drag pattern,
- Shell pattern.
There have more details about each of the casting patterns.
#1. Single Piece Pattern.
Solid pattern is another name for the single-piece pattern. It is the least expensive casting pattern available. Casting producers prefer these types of patterns as the rectangular blocks used are appropriate for simple operations and small-scale manufacturing.
It is used to create stuffing boxes for steam engines.
#2. Split pattern.
Casting patterns for complicated casting are carried out frequently using the two-piece pattern. It is also known as the split-piece pattern. It has two components: Drag and cope. 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.
#3. Multi Piece Pattern.
A multi-piece pattern is a go-to choice for designs that are more complicated and difficult to construct. These types of patterns consist of three or more patterns, each of which contributes to the process of mould production.
Take, for instance, the pattern consisting of three separate pieces. The top, the bottom, and the middle are all components that make up the design. The component at the top is called the cope, the part at the bottom is called the drag, and the part in the middle is called the checkbox.
They are commonly used in the production of joints like mitre and dowel.
#4. Match Plate Pattern.
The match plate pattern utilises a metallic plate to separate the cope and drag sections on the reverse side of the plate. In addition, the gates and runners are held by the plate. These types of patterns require less effort yet manage to produce high-volume results.
The manufacturing industry makes extensive use of it, and as a result, it often has a high cost. We should consider the fact it requires precision to produce a high yield. These types of patterns are frequently utilised in the production of metals like aluminium, piston rings, and rotor hubs.
#5. Gate Pattern.
The gate pattern, also known as the gated pattern, is utilised to manufacture several pieces within a single mould. A gated pattern is simply a pattern composed of many patterns. These are unstructured patterns with attached gates and runners.
Moulds with several cavities are utilised in the mass manufacture of casings. The illustration shows that such moulds are made by linking various types of patterns and gates, providing a common runner for the molten metal.
These types of designs are fabricated from metal and are used in the production of small castings like corner brackets.
#6. Skeleton Pattern.
The skeleton pattern is large and is an excellent choice for castings with a simple shape and size. They consist of strips and frames made of wood. The mould is properly filled, and the excess sand is removed.
The pattern is made of two sections and assembled with screws or glues to produce round shapes. Pit and floor welders rely heavily on the skeletal pattern for their welding process. These types of patterns are not adaptable to changes and are costly.
#7. Sweep Pattern.
The cavity for casting is created by rotating a wooden board along one of its edges while working with the sweep pattern. It includes three components: a spindle, a base, and a sweep or wooden board. It is known for producing a casting in a remarkably short period.
The vertically directed spindle is attached to the base sand. Then, the spindle is rotated by an axis called the sweep axis, turning the plane by 360°. To create large, consistent moulds with a circular cross-section, the sweep pattern is employed.
#8. Loose Piece Pattern.
The removal of a single solid pattern piece above or below the separating plane of the mould can be facilitated by a loose piece pattern, as shown in the diagrammatic representation below.
These types of patterns require additional expert effort, resulting in an expensive casting pattern. They are used in the production of axle pins.
#9. Cope and Drag Pattern.
As the name indicates, Cope and drag patterns comprise two distinct plates with two components that can be independently moulded on the pattern moulding box. The cope and drag portions of the mould are made independently when the entire mould is too heavy for one operator to lift.
The pattern is split into two halves, each put on a separate plate. The cavity created using these types of patterns is similar to that of two-piece patterns, but the former is used for large-scale casting. These types of patterns are used in flange pipe manufacturing.
#10. Shell Pattern.
The shell pattern is mostly made of metal. The design is divided down the middle part of the pattern, and the two parts are put together as shown in the figure below.
Here, the outer shapes serve as the mould, while the inside shapes serve as the core. The shell pattern is a good choice for designing hollow and straight structures such as pipes.
Applications of Patterns in Casting
Patterns play a crucial role in the casting process and find extensive applications across various industries. Some notable applications of patterns in casting include:
- Foundry Industry: Patterns are widely used in foundries for producing metal castings of various shapes and sizes. They are essential in creating the mold cavity, which is filled with molten metal to obtain the desired final product. Patterns enable the replication of intricate details and complex geometries, making them valuable in the production of components for automotive, aerospace, and industrial applications.
- Jewelry and Artistic Casting: Patterns are utilized in the production of intricate jewelry and artistic castings. They allow for the creation of unique and visually appealing designs, ranging from delicate jewelry pieces to ornate sculptures. Patterns enable the precise replication of artistic concepts, ensuring accurate reproduction in the final metal castings.
- Manufacturing and Prototyping: Patterns are used in the manufacturing industry for producing prototypes, allowing designers and engineers to test and evaluate product designs before mass production. By creating patterns that represent the intended parts, manufacturers can assess functionality, fit, and aesthetics, facilitating design improvements and cost-effective production.
Limitations of Patterns in Casting
While patterns are essential in the casting process, they also come with certain limitations that need to be considered. Here are some notable limitations of patterns in casting:
- Cost and Time: Developing patterns can be time-consuming and expensive, especially for complex or large-scale castings. Designing, fabricating, and maintaining patterns require skilled labor, specialized equipment, and materials. The cost of pattern production can significantly impact the overall cost of casting operations.
- Pattern Wear and Durability: Patterns are subjected to repeated use and contact with molding materials, which can lead to wear and degradation over time. The pattern materials must withstand the stresses, abrasion, and chemical reactions involved in the casting process. Regular maintenance and pattern repair may be required to ensure their longevity and accuracy.
- Limited Pattern Size: The size of patterns can pose limitations in casting. Large-scale or oversized patterns may be difficult to handle, transport, or fabricate. They may require additional structural support, specialized equipment, and more significant resources, adding complexity and cost to the casting process.
- Pattern Shrinkage and Dimensional Accuracy: During the casting process, the molten metal undergoes shrinkage as it cools and solidifies. This shrinkage needs to be accounted for in the pattern design to ensure accurate dimensions in the final casting. Pattern makers must consider the appropriate allowances for shrinkage and dimensional changes to achieve the desired casting specifications.
Conclusion
During the casting process, casting patterns are very important which decide the casting molds and the quality of castings. Before choosing the casting pattern, you should consider some factors, such as the size, shape of your casting products, and choose the best pattern for your casting business.