Basic of sand casting pattern making process :
The pattern part of casting process, it is replica of the object to cast, and used to prepare the mold cavity into molten material poured during the casting process. The sand casting pattern making is duplicate component of molding. The design patterns material such as wood, metal or plastic and more.The main pattern types such as solid pattern,split pattern,cope and drag,sweep pattern sand casting in process.
The sand casting pattern making with same shape of part, not exactly in same size. Because of shrinkage provide when it convert from liquid form into solid state. So the cavity made in little large than the exact actual part required. There should be some of allowances with in machining and finishing process.
It required to modification are addition of pattern allowances. if the hollow casting provided, the core are used to create the cavity in finished part. The quality of casting depends on the design patterns material and construction.sweep pattern sand casting is mainly for circular part make.
Function of pattern:
- The proper design pattern to made with smooth surface and reduce casting defects.
- Gates, risers and runners are used in feeding of molten metal in cavity form a part of pattern.
- The pattern contains projection known as core print, if casting requires a core made of hollow part.
- The pattern form mold cavity for making a casting.
Some Important design patterns material:
The sand casting pattern making material such as woods, metal and alloys like aluminum, white metal, brass, cast iron, wax, resins, plaster of Paris and plastic.
The above design patterns material, most common material as wood used in casting process. Because of readily available in all places and most important of low weight. And also wood material produce the pattern should be easily shaped and cheaper. The one disadvantages of wood, ability of absorption in moisture for pattern making, which can cause dimensional changes.
The good design patterns material should be follow properties:
The design patterns material is having following properties.,
- Easy manufactured, shaped and joined.
- Low weight.
- Hard, strong and durable.
- Resistant to wear and corrosion.
- Low cost.
- Resistant to water absorption.
The important pattern types in casting:
The pattern types in casting process depends on the part to be manufactured. The sand casting pattern making will be easy remove from the mold without any damage in the mold product.It is based on design patterns material and more. The different types of pattern as follows,
- Solid or single piece pattern
- Split pattern or two piece pattern
- Multi-piece pattern
- Cope and drag pattern
- Match plate pattern
- Gated pattern
- Skeleton pattern
- sweep pattern sand casting
- Loose piece pattern
- Segmental pattern
- Follow board pattern
- Shell Pattern
Solid pattern in casting process:
The solid pattern types is a most and simple method for simple shape casting. It pattern can make without any sub-part or joint in the mold part. In this type of pattern only produce simple shape and withdrawn for very easily from the mold. The solid pattern placed in the drag position. That is used for make a flat surface like as gear blanks, square blocks and more.it solid pattern made depend on design patterns material, shape and more.
split pattern (or) two piece pattern:
When contour of casting manufacture. The sand casting pattern making withdraw from the mold is difficult or when the part depth too high in the casting. The pattern is split into two half part. For one half is contained in the drag and another one in cope. For intricate shape part manufactured using the two or more pattern pieces. The dowel pins used to piece are aligning together. This pattern types is known as split pattern. The split pattern is common method for intricate casting part to produce. The two halves of pattern to align properly by using dowel pin. It placed on the top half of pattern.The split pattern is above figure.
Multi piece pattern:
It is one type of pattern types. When complicated part molded together, to require a sand casting pattern making in more than two parts in order to casting process with easily withdrawal and mold. This pattern contain may be three, or more number of pattern based on the design. For following example of multi piece pattern.
It is having three piece patterns. The top part is cope, bottom is drag and middle part of molding box is called check. They are three pattern will be connected by using dowel pins and molding box clamped by using clamp.
Cope and drag type of pattern:
In this pattern types used to provide complicate product. The more complicated part to be made, the complete sand casting pattern making become too heavy to be handled by a single operator. In this Cope and drag type of pattern made in two parts, which separately molded in different molding box. After molding process completed to form of complete mold cavity. When the one part is drag and another one is cope. It is Called cope and drag. It is different from the split pattern because of drag and cope pattern both are molded separately in the assembled position. The cope and drag type of pattern as above diagram.
Match plate type pattern:
The match plate pattern types is having two parts, one for one side and another one for another side of pattern. It is called match plate pattern. The sand casting pattern making in two pieces. It also having gates and runner attached with pattern. The molding process completed after that match plate removed together, the gating is obtained for joining the cope and drag. It pattern is mainly used for casting of metal, usually aluminum are machined in this method with light weight and machinability. It should be possible for mass production of small casting with high dimensional accuracy. They are also used for machine molding. The cost will be high of molding but it is easily compensated by high rate of production and more accuracy.
To make multiple parts with in single mold and single pattern for all the part cavity of mold. The multi cavity mold is prepared a single sand mold carries a multiple number of cavities. The gates are used to connect the pattern each other. The suitable gates or channels are provided for feeding the molten metal into cavity. All the cavity are feed by using single runner. It mainly consider for low molding time and uniformly feeding of molten metal. It used for mass production of small casting.
The casting size is very large but easy to shape and only possible for little number of parts to be made, also not economical with low quantity of large solid pattern of size. In this stage a pattern consists of wooden frame and strips is made. It is called skeleton pattern. The mold is filled properly. The surplus sand is removed together by means of stickler.
sweep pattern sand casting Method:
The plane is rotated about an axis with 360⁰ called symmetry or sweep. In this sweep pattern sand casting prepare the sand mold by using this method. It is called sweep pattern. It could be economical to save money and make with full pattern because of symmetry. In this pattern used for prepare the mold of large symmetrical casting by mean of circular cross section.
The sweep pattern sand casting consists of base are placed on the sand mass, vertical spindle and wooden template is called sweep. The outer ends of the sweep having corresponding to the shape of require casting. The cavity formed together, from sweep is rotated about the axis. The sweep and spindle is removed from the cavity for leaving the base in the sand. The removal of spindle, in this cause to provide hole and it is patched up by filling the sand.It sweep pattern sand casting Method mainly for Circular solid Part make.
The segmental pattern is used to prepare the mold of larger circular casting to avoid the use of solid pattern of exact size. It is similar to sweep pattern, but the difference from Sweep pattern, the sweep pattern is give a continuous revolve motion to generate the part, the segmental pattern itself and mold is prepared. In this segmental pattern construction should be save the material for pattern make and easy carried.
The segmental pattern is mounted on the central pivot and mold in one position for after prepare of mold the segment is moved for next position. That is repeat together the complete mold is done.
Loose piece pattern:
A single piece are made to have loose piece in easy to allow withdrawal from the mold the molding process are completed, after the main pattern is withdrawn leaving from that piece in the sand. After the withdrawal of piece from mold, it cavity separately formed by the pattern. It loose piece pattern is highly skilled job and expensive.
Follow board type pattern:
In casting process some portions are structurally weak. It is not supported properly and may be break under the force of ramming. In this stage the special pattern to allow the mold may be such as wooden material.
It shell pattern is used to molding of hollow shape product with curved or straight. It means of pipe work done it process. It pattern usually made of metal. That pattern parted along with the center line and both halves are doweled.