Pattern making

[مع الله]

·Contents:

1.Pattern Making.

2.Types of Patterns.

3.Patterns Allowance.

4.Pattern Design.

Reference.5.


1.Pattern Definition.

In [عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا], a pattern is a replicat of the object to be cast, used to prepare the cavity into which molten material will be poured during the casting process.
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.

Several different materials can be used to fabricate a pattern, including wood, plastic, and metal. Wood is very common because it is easy to shape and is inexpensive, however it can warp and deform easily. Wood also will wear quicker from the sand. Metal, on the other hand, is more expensive, but will last longer and has higher tolerances. The pattern can be reused to create the cavity for many molds of the same part. Therefore, a pattern that lasts longer will reduce tooling costs. A pattern for a part can be made many different ways

2.Pattern Making.

The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part), which are typically made out of wood, sometimes metal. The cavity is contained in an aggregate housed in a box called the flask

3.Types of Patterns.

Solid pattern - A solid pattern is a model of the part as a single piece. It is the easiest to fabricate, but can cause some difficulties in making the mold. The parting line and runner system must be determined separately. Solid patterns are typically used for geometrically simple parts that are produced in low quantities.

[عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا]

Solid pattern

·Split pattern - A split pattern models the part as two separate pieces that meet along the parting line of the mold. Using two separate pieces allows the mold cavities in the cope and drag to be made separately and the parting line is already determined. Split patterns are typically used for parts that are geometrically complex and are produced in moderate quantities.

[عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا]

Split pattern

·Match-plate pattern - A match-plate pattern is similar to a split pattern, except that each half of the pattern is attached to opposite sides of a single plate. The plate is usually made from wood or metal. This pattern design ensures proper alignment of the mold cavities in the cope and drag and the runner system can be included on the match plate. Match-plate patterns are used for larger production quantities and are often used when the process is automated.

[عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا]

Match-plate pattern

·Cope and drag pattern - A cope and drag pattern is similar to a match plate pattern, except that each half of the pattern is attached to a separate plate and the mold halves are made independently. Just as with a match plate pattern, the plates ensure proper alignment of the mold cavities in the cope and drag and the runner system can be included on the plates. Cope and drag patterns are often desirable for larger castings, where a match-plate pattern would be too heavy and cumbersome. They are also used for larger production quantities and are often used when the process is automated.

[عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا]

Cope and drag pattern

sweeping patterns -In several cases it could be economical to save the money and efforts of making the full pattern because of symmetry. The cavity in such a case could be made by sweeping the pattern (which is a part of the full shape) around a central axis, hence these are known as sweeping patterns

4.Pattern Design.

Contraction allowances

The pattern needs to incorporate suitable [عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا] for shrinkage; these are called contraction allowances, and their exact values depend on the alloy being cast and the exact sand casting method being used. Some alloys will have overall linear shrinkage of up to 2.5%, whereas other alloys may actually experience no shrinkage or a slight "positive" shrinkage or increase in size in the casting process (notably [عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا] and certain cast irons). The shrinkage amount is also dependent on the sand casting process employed, for example clay-bonded sand, chemical bonded sands, or other bonding materials used within the sand.
Draft allowances

The pattern needs to incorporate suitable allowances for draft, which means that its sides are tapered so that when it is pulled from the sand, it will tend not to drag sand out of place along with it. This is also known as taper which is normally between 1 and 3 degrees.
Sprues, gates, risers, cores, and chills

[IMG]file:///C:/DOCUME%7E1/Omar/LOCALS%7E1/Temp/msohtml1/01/clip_image008.gif[/IMG]The patternmaker or foundry engineer decides where the sprues, gating systems, and risersare placed with respect to the pattern. Where a hole is desired in a casting, a [عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا] may be used which defines a volume or location in a casting where metal will not flow into. Sometimes chillsmay be located on a pattern surface, which are then formed into the sand mould. Chills are heat sinks which enable localized rapid cooling. The rapid cooling may be desired to refine the grain structure or

determine the freezing sequence of the molten metal which is poured into the mould.


Reference



[عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا]

[عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا]

http://www.custompartnet.com/wu/SandCasting

[عزيزي الزائر يتوجب عليك التسجيل لمشاهدة الرابط للتسجيل اضغط هنا]