DIE CAST, INVESTMENT CAST & SAND CAST PROCESS EXPLAINED

When considering part 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. This selection is especially important in the casting industry because casting factories typically only offer one type of process. The three processes that are 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.

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

Sand Casting

In sand casting, you for 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 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,” this is an internal cavity.  These casting cores are normally made from a resin base air, or heat dries sand utilizing a steel mold to make. These are put in the pattern then after casting cleaned out of the cavities.

 
Comonents

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 so that you remove the impurities, have uniform heated material in the pattern cavity, and during shrinkage, supply possible additional metal to the mold cavity.

The process is rather simple:

First, 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 this halve is now filled with sand and packed, forming the cope.

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.

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.

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, and others.
  2. Small to very large 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. Affordable to produce in low quantities, 1-1000 pieces.
Limitations
  1. Low tolerances, ±1/32″/1mm, anything higher than that must be machined
  2. Any features like threads must be machined.
  3. Slow production rate.
  4. Time consuming for 1000+++ production runs.
  5. Hard to control flatness.
  6. The “as casted” surface is rough.
 
 

Die Casting

Die casting uses a reusable complex steel mold, called a die, similar to plastic injection. First, the die is split into two main halves and are mounted on an injection machine. Second, the base die is a ridged mount, and the other side are 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 quick solidification. Once the metal is solidified, then the die is separated, and the finished part is ejected using numerous pins or “pin outs” 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.

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 +++ are normal.
  5. Very smooth surfaces are achievable
Limitations:
  1. Mold cost is high.
  2. Small number of standard materials limited to Aluminum, Zink and Magnesium. Others are available ant increased cost.
  3. Routine size, from very small 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 must limit the amount of machining not to expose pores cutting too deep.

.

Die-Cast Machine Components
Mold showing the inlet, pin-outs and gates
Play Video
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 process first 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, 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 to first 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, and the runners are removed.

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.
  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. Good surface finish.
  6. Due to the high achievable tolerances, parts can be used as is.
Weaknesses
  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 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 a 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 perhaps at the beginning of marketing your product, 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 from sand cast or investment cast or even economically machine the part from a solid metal block. Your NRE investment would be low but part price might be higher but absorb-able. When your volume gets high enough to justify die cast I

 

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