Menguasai Desain Pola Cetak Pasir untuk Bagian Berkualitas Unggul

Customer almost never sees most important part of sand casting, because that’s pattern. Pattern is what forms cavity in sand that’s subsequently filled with molten metal. Get pattern design right dan sand casting process produces quality parts that need minimum machining. Get it wrong dan you’ll be forever wrestling with casting defects, poor yields dan customer complaints.

Making a Hole in the Sand

Unlike die casting, which needs precision molds machined from massive pieces of steel, sand casting needs nothing more than sand, two boxes dan wooden pattern. That makes it economical process untuk small dan medium volume orders.

Pattern is nominally same size dan shape as finished part, with adjustments to accommodate sand casting process dan properties of metal being poured. In addition, sprues, runners, gates dan risers must all be included. These are passages via which metal flows into cavity formed in sand by pattern.

Sand for sand casting is packed into two boxes. After pattern is removed these are stacked one on top of other. Lower box, drag, always has void formed by pattern. It will also have channels for metal to flow in.

Upper box, cope, may not have any shape formed into it, in which case it’s called “flat back.” Most complex castings do however need part of shape forming in cope, which creates split dan parting line in casting.

Pattern Considerations

There are several points to consider when designing dan making pattern.

• Pattern releases without damaging sand – achieved by giving sides of pattern draft angle rather than being vertical.
• Cavity fills smoothly – gates, usually positioned so cavity fills from bottom, are openings that limit how quickly metal flows in. Optimal speed fills with no turbulence atau bubbles dan without metal freezing before it reaches all internal corners dan surfaces.
• Shrinkage dan distortion allowances – metal contracts as it cools so to produce part size needed, pattern must create slightly larger cavity. Plus, metal won’t cool at same rate everywhere.
• Riser size – riser is open region in cope that is last part to fill. This provides visual indication that cavity is full. It also forms reservoir of molten metal that flows back into cavity as metal there cools dan shrinks.

Planning How to Cast a Part

First consideration is to ensure pattern leaves no pockets where air can be trapped as cavity fills. One aid to achieving that is to put riser at highest point. One feature of sand casting though is that, unlike die casting, trapped air can permeate through sand to small extent.

When cast part comes out of sand it has gates dan risers attached. These must be cut off before part can be machined.

A split casting will have parting line running around periphery. Tolerances in how cope dan drag fit together, dan in pattern placement, mean there may be small offset between top dan bottom halves of casting.

Casting team will work with part designer before pattern is made to minimize how these features affect machining dan final part.

It’s all About the Pattern

A sand cast part can only be as good as pattern allows. It takes great deal of experience to get best out of process. At Impro we are internationally recognized for sand casting expertise. If you’d like to know how we’d approach casting your parts, please contact us.