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DIE CAST, INVESTMENT Cast & SAND CASTing PROCESS EXPLAINED

When considering parts to be manufactured using a casting process, you must understand each process’s strengths and limitations to select the process that fits your unique requirements Engineering/Design, Manufacturing, and COST. This selection of a casting process is especially important in the casting industry because casting factories typically only offer one type of process. Selection of the process that does not fit your unique needs could cost you an exorbitant amount of $s. The three processes discussed on this webpage are Sand Casting, Dies Casting, and Investment Casting. We will discuss how the casting process works and then give you the strengths and limitations to give you a perspective on where to start.

Table of Contents

Sand Casting List of Componentss
Sand Casting List of Components
Final Cast Part with Sprue, Gates, Runners and Riser
Final Cast Part with Sprue, Gates, Runners and Riser

Sand Casting

Components

Pattern, Cope, and Drag

In sand casting, you form a cavity from a “pattern” when you pack the pattern between 2 box halves called flask split horizontally in the middle, the “parting line” with the top being the “cope” with the bottom being the “drag.” Patterns are the replica of the part you want to be manufactured, typically made from wood, plastic, and metal. Wood is the lowest cost because it can be quickly and easily made. However, wood can deform and wear out more quickly. Metal patterns are more expensive but are more accurate and last longer.

Sands

There are numerous kinds of sand we tat we will not cover here because they are more product application-focused but make sure to ask your supplier about the bents and drawbacks; they supply

Cores

For more complex patterns, you might need a “core,” which is an internal cavity.  These casting cores are normally made from a resin base air or heat dried sand utilizing a steel mold to make. These are put in the pattern then, after casting, cleaned out of the cavities.

Additional Components

Also included in the mold is a “Sprue,” “Gates,” “Runners,” and “Risers.”  The sprue is where the molten metal is poured into the mold. First, the runner is the channel that allows flowing molten metal to the gate, where the molten metal enters the pattern cavity. Second, the riser is where the excess molten metal goes after it leaves the cavity. The riser is important to remove the impurities, have uniform heated material in the pattern cavity, and supply possible additional metal to the mold cavity during shrinkage.

The process is rather simple:

First, in the sand casting process, the flask will be put on a flat surface like a heavy flat board. Then ½ of the pattern is placed flat on a board, and the flask is filled with sand and packed and skimmed flat. This process forms the drag, and then it is flipped over.

Second, the top flask is put on top of the bottom, aligned with pins. The other half of the pattern is placed on top of the first half in the drag, usually aligned with pins or bolts. This is the ” Cope,” and these halves are now filled with sand and packed, forming the cope for the sand casting.

Third, the two halves are separated, so the pattern can be pulled out to form the casting pattern.

Forth, at this time, the “Sprue,” “Gates,” “Runners,” and “Risers” put in, and cores are placed in to form the cavities. Then the halves are put back together, ready for the molten metal to be poured into the sprue.

Fifth, the molten metal is then poured into the sprue from a ladle until first comes out the riser and is allowed to cool, forming the sand casting.

Last, the assembly is then “Shakeout,” removing the sand, and the cast part is removed with the “Sprue,” “Gates,” “Runners,” and “Risers” to be later removed from the sand casting.

Strengths

  1. A wide variety of materials can be cast like carbon steel, high alloy steel, stainless steel, aluminum and aluminum alloys, copper alloys, magnesium alloys, ASTM A106, ASTM A216WCB, and others can be used in sand casting.
  2. Small to huge casting sizes can be achieved.
  3. From a casting perspective, the porosity is controllable.
  4. Able to be used in pressure containment such as valves, fittings, pump housing, engine components by utilizing multiple ANSI/API/ASTM/ISO codes specifically to control the design and manufacturing processes, including material compliance, wall thickness, machinability, and NDE.
  5. Low tooling cost and startup
  6. Many materials are weldable for sand castings.  Note welding of other casting processes is limited or just not possible.
  7. Affordable to produce in low quantities, 1-1000 pieces.

Limitations

  1. Low “as cast” tolerances, ±1/32″/1mm, anything higher than that must be machined.
  2. Any features like threads, sealing faces on mating surfaces must be machined.
  3. Slow production rate.
  4. Time consuming for 1000+++ production runs.
  5. Hard to control flatness.
  6. The “as caste surface is rough.
 

Die Casting

Die casting uses a reusable COMPLEX steel mold, called a die, similar to plastic injection mold. First, the die is split into two main halves and is mounted on an injection machine. Second, the base die is a ridged mount, and the other side is mounted on an opposing hydraulic ram. When the ram closes the two dies, the molten metal is fed into an injector by a ladle and then is injected into the die, called a shot, at high pressures to prevent rather a quick solidification. 

Once the metal is solidified, then the die is separated, and the finished part is ejected using numerous pins or “pinouts” to eject the finished die-cast with the gates intact.  The complete cycle can take 10 seconds to a minute, depending on the size, and then is repeated. A robotic arm can be used to automate this process and even be programmed to reject if there is a problem with the part, as shown in the attached video.

Material Considerations

The three mainly used materials that need to be considered are:

  1. Zinc Die Casting, this material is primary used for smaller parts for its ease of use in smaller cavities and lower cost.
  2. Aluminum Die Cast is the go-to from small parts to the very largest die castings possible due to its ease to work with and economy of scale with very available Aluminum Die cast of ADC 12 and ASTM A380 Aluminum including A360.0, 383.0, 384.0, and A4130.
  3. Magnesium Die Cast is primarily used because it is lightweight. However, it is the most expensive due it is more hazardous to pour and machine.

Strengths:

  1. With a fast production rate, the per-part cost is low.
  2. Complex shapes can be easily formed.
  3. High tolerances as cast, ±0.10″/0.25mm.
  4. Small runs can be as low as 100 to Large productions runs; 10,000 +++ is normal.
  5. Very smooth surfaces are achievable.
  6. Lowest per part cost.

Limitations:

  1. The highest Mold/NRE cost is high.
  2. A small number of standard materials are limited to Aluminum, Zinc, and Magnesium. Others are available at an increased cost.
  3. Routine size, from tiny the size of a penny to about 30″ x 30″ x 8″. Larger sizes are available but only at a limited number of manufacturers.
  4. The design is sometimes used as is; however, the designer must limit the amount of machining not to expose pores cutting too deep.
Die-Cast Machine Components
Die-Cast Machine Components
What is die casting Mold showing the inlet, pin-outs and gates
Die Cast Mold
Investment Cast Wax Pattern
Investment Cast Wax Pattern
Wax Tree
Investment Cast Wax Tree
Ceramic covered tree
Ceramic Covered Wax Tree
Bolted Cover Steel
Finished Steel Cover

Investment Casting:

Investment casting, or what is more commonly known as lost wax, is the oldest and simplest process that produces the highest tightest tolerances of the casting processes

The General Process Steps Are:

First, the investment casting process starts with a metal injection mold for wax. This mold is the exact replica of the part required. The mold is then injected with wax and separated with the wax replica removed.

Second, this replica is then attached to a wax gating system with a “sprue” at the top, sometimes called a tree for the way it looks.

Third, In the investment casting process, this complete assembly is then dipped into a ceramic solution. Then additional ceramic particles are dropped or blow on top of this ceramic base forming a thick layer. Depending on the part design, this process could be repeated.

Fourth, the “tree” is then put in a furnace at 1000°F-2000°F first to melt out all the wax, and secondary strengthen the ceramic tree mold.

Fifth, the ceramic tree mold is then removed from the furnace, and the molten metal is poured in the sprue and allowed to cool.

Last, the solidified tree is then sent to an agitator or water jet to remove the ceramic coating depending on the material and design requirements. Then runners are removed from the investment casting.

If any secondary processes are required, they are performed now; however, many investment castings are designed to be used as-is.

Strengths:

  1. Numerous materials such as aluminum, carbon steel, alloy steel stainless steel, nickel, copper, and more can be used in investment casting.
  2. High tolerances up to ±0.003″/.08mm, including external threads depending on the foundry.
  3. Normal cost-efficient quantities if 100-5000.
  4. Short production times.
  5. The good surface finish on the investment cast.
  6. Due to the high achievable tolerances, parts can be used as-is.

Limitations:

  1. Size, most foundries can only handle a maximum of 1 FT³/0.028CM volume of a part.
  2. Slower production time as compared to die cast.
  3. Higher per part cost than Die Cast.

Conclusion, Processes

First, for selecting the correct casting process, about 70% comes down is what is the industry standard for your part. You should investigate what others are doing for similar products and if there are no codes and stands that regulates the manufacturing of that part. If you find nothing within your industry, then you need to evaluate your quantity, size, and finish requirements and try to fit it in the above strengths and weaknesses of each of the above unless your part is large, then you can only use the sand casting process. 

Second, the last two items you must consider are a “Cradle to Grave” and a FULL-SERVICE COMPONENT CONTRACT MANUFACTURER. 

FULL-SERVICE means the contract manufacturer can provide you with a finished cast part including machining, PEM/Fastener installation, Powder Coating, & silk screening/engraving, a “one-stop-shop“ eliminating having to resend out your part for a secondary process to separate multiple vendors. This makes controlling processes errors from multiple sources difficult.

“Cradle to Grave” means as your product matures, we will continually give you suggestions (process changes, material changes, sub-assemblies) to reduce your cost giving you an improved sales advantage. An example would be per at the beginning of marketing your product, PROTOTYPING, your volumes are low, and you do not want to make the investment in die cast mold and manufacturing quantity. 

Ionthis could make your finished part or parts from machining from a solid block or fabrication or from sand cast or investment cast or even economically machine the part from a solid metal block. Your NRE investment would be low, but the part price might be higher but absorb-able. When your volume gets high enough to justify die cast, then Ionthis can move you into a Die Cast. This is “Cradle to Grave.”

For a DFM/Analysis and recommendations of your Die Cast, Investment Cast, and Sand Cast component or assembly, feel free to contact Ionthis at engr@ionthis.com. 

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