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Plaster Mold Castings

Aluminum Plaster Mold Castings, Zinc Plaster Mold Castings
Plaster Mold Cast Part











How, When and Why To Use Plaster Mold Casting

  • To produce precision and premium quality aluminum and zinc castings
  • For aesthetic applications where appearance is critical
  • Prototyping to assist engineering in debugging design before committing to hard tooling
  • For low volume applications where quantities do not justify die cast tooling
  • For high volume applications of complex or unusual shapes
  • For castings with thin walls or where weight is critical
  • To simulate die castings for prototype and pilot production
  • Tooling is low cost and allows ease of modification
  • To reduce "time to market" on new programs and evaluate market potential
  • To reduce time for machining and secondary operations
  • To fill the gap if dies are lost, damaged, or delayed
  • To assist and reduce time for U.L. approval

Size

No limitation but best range within 2" cube to 36" cube.

Finish

Can hold 63 micro-inch but normally 90 micro-inch.

Shape

Considerable design freedom for unusual and complex shapes.

Wall Thickness

  • Thin Wall:  .030" - .060"
  • Average:  .080" - .120"

General Tolerances

  • 0" - 2" ± .010
  • 2" - 3" ± .012
  • 3" - 6" ± .015
  • 6" - 12" ± .020
  • 12" - 18" ± .030
  • 18" - 30" ± .040
  • Tighter tolerances can be negotiated

Limitations

The process is limited to non-ferrous metals with pouring temperatures below 2,000° Fahrenheit. This includes all aluminum, zinc casting alloys and some copper based alloys.

Holes

Not economical to cast small holes ¼" or less unless odd shapes or inaccessible areas for machining.

Alloys

All aluminum and zinc casting alloys to the commercial and military specifications. See separate technical sheet.

Draft

Typically ½" to 2". Zero draft is possible in specified areas. Corner radii and fillets as required,
type: 1/16" R.

Mechanical Properties

Tensile-Yield-Elongation - as per the appropriate com-metrical and "military specifications".

Tooling-Pattern Equipment

  • Loose Pattern:  to expedite for up to 20 pieces
  • Epoxy Resin: usually up to 500 pieces
  • Metal: Aluminum or Brass - used to obtain best tolerances and quality
  • Rubber: for quantities up to 1,000 pieces. Tooling can be duplicated easily from master tooling to expedite delivery or for higher volumes

Cost

Rule of thumb for complex shapes in 15" cube Range: Tooling - 10% of die cast tools Place Piece Price - 10 times die casting price.

Delivery

1-2 weeks for simple parts 6-8 weeks for complex parts.

Typical Applications

Castings for telecommunications, business machines, medical equipment, computers, automotive, aerospace, electronics, robotics. Molds for plastics industry-rotational molds, vacuum form, expanded polystyrene molds, kirksite injection molds.

Plaster and Sand Molding Combination

For castings requiring high metallurgical integrity verified by radiographic and fluorescent penetrate inspection. When used in combination with no bake sand molds, the properties of plaster mold castings can be enhanced considerably taking advantage of the faster cooling rates inherent in sand molds in combination with the insulating aspect of plaster molds.

The Plaster Mold Process

Briefly stated, this is a method of producing aluminum or zinc castings by pouring liquid metal into plaster (gypsum) molds.

Step 1: Model or Master PatternPlaster Mold Casting - Negatives and Model
  1. This is made from customer drawing or CAD file.
  2. Stereolithography, traditional hand crafted or machined.
  3. Model is engineered to include:
      - Metal shrinkage
      - Mold taper-if required
      - Machine stock-if required
  4. We can "clone" or adapt customer supplied model if requested.
Step 2:  Foundry Pattern EquipmentPlaster Mold Casting - Foundry Pattern Equipment
  1.  Negative molds are made from model
  2.  Core plugs are made from negative molds
  3. A positive resin cope and drag pattern is now made from the negative molds.
  4. Core boxes are made from the core plugs.
  5. Gating, runner system and flasks are added as necessary.
  6. Duplicate sets of tooling can be made from the master negative.
Step 3: Plaster MoldPlaster Mold Casting - Pouring Plaster
  1. A liquid plaster slurry is poured around the cope and drag pattern and into the core boxes.
  2. The plaster mold is next removed from the cope and drag patterns.
  3. The plaster mold and cores are then baked to remove moisture.


Step 4:  Pour CastingPlaster Mold Casting - Pouring Metal Casting
  1. Molten metal is prepared by degassing and a spectrographic sample is taken to check the chemical analysis.
  2. The molten metal is then poured into the assembled plaster mold.
  3. The plaster is removed by mechanical knock-out and high pressure waterjet.
  4. When the casting has cooled the gates and risers are removed.
Step 5: Secondary Operations
  1. The raw castings are inspected and serialized.
  2. Flash and excess metal is removed (snagged).
  3. Castings may then require (per customer specification):Plaster Mold Casting - Finished Casting
      -Heat Treatment
      -X-Ray
      -Penetrant Inspection
After finish inspection casting is ready for:
  • Machining
  • Chemical film, chromate conversion, paint of special finishes
  • Assembly

 

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