Metal casting tools and Molding Services

The casting tooling for each metal casting process is different but is nonetheless indispensable to the quality of the final metal casting product. It is important to always get the tooling right before production starts or the inaccuracy of or defects in the metal casting tools and molds may lead to serious quality issues and losses further down the project path. You may find more Tooling details of each Metal Casting Methods:

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Tooling for Sand Casting

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The main tooling for sand casting is the pattern that is used to create the mold cavity. The pattern is a full-size model of the part that makes an impression in the sand mold. However, some internal surfaces may not be included in the pattern, as they will be created by separate cores. 

The pattern is actually made to be slightly larger than the part because the casting will shrink inside the mold cavity. Also, several identical patterns may be used to create multiple impressions in the sand mold, thus creating multiple cavities which will produce as many parts in one casting operation.

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 abrasion of 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 metal casting molds of the same part. Therefore, a pattern that lasts longer will reduce tooling costs. Patterns can be made many different ways, which are classified into the following four types:

  • 1. Solid Pattern
  • 2. Split pattern
  • 3. Split Pattern
  • 4. Cope and Drag Pattern

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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.

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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, the parting line being already determined. Split patterns are typically used for parts that are geometrically complex and are produced in moderate quantities.

 

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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.

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Cope and Drag Pattern

Cope and drag patterns are similar to match plate patterns, 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. 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, again, often used when the process is automated.

Sand Casting Tooling Cost

Tooling cost has two main components – the pattern and the core-boxes. The pattern cost is primarily determined by the size of the part (both the envelope and the projected area) as well as the part’s complexity. The cost of the core-boxes first depends on their size, a result of the quantity and size of the cores that are used to cast the part. Much like the pattern, the complexity of the cores will affect the time to manufacture this part of the tooling (in addition to the core size), and hence its cost.

The cost of the core-boxes first depends on their size, a result of the quantity and size of the cores that are used to cast the part. Much like the pattern, the complexity of the cores will affect the time to manufacture this part of the tooling (in addition to the core size), and hence its cost.

The quantity of parts to be cast will also impact the tooling cost. A larger production quantity will require the use of a tooling material, for both the pattern and core-boxes, that will not wear under the required number of cycles. The use of stronger, more durable tooling materials will significantly increase the cost.

Tooling for Die Casting

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The dies into which the molten metal is injected are the custom tooling used in this process. The dies are typically composed of two halves – the cover die, which is mounted onto a stationary platen, and the ejector die, which is mounted onto a movable platen. This design allows the die to open and close along its parting line.

Once closed, the two die halves form an internal part cavity which is filled with the molten metal to form the casting. This cavity is formed by two inserts, the cavity insert and the core insert, which are inserted into the cover die and ejector die, respectively.

The cover die allows the molten metal to flow from the injection system, through an opening, and into the part cavity. The ejector die includes a support plate and the ejector box, which is mounted onto the platen and contains the ejection system. 

When the clamping unit separates the die halves, the clamping bar pushes the ejector plate forward inside the ejector box which pushes the ejector pins into the molded part, ejecting it from the core insert. Multiple-cavity dies are sometimes used, in which the two die halves form several identical part cavities.

Die Design

There are many design issues that must be considered in the design of the dies. Firstly, the die must allow the molten metal to flow easily into all of the cavities. Equally important is the removal of the solidified casting from the die, a draft angle must be applied to the walls of the part cavity. The design of the die must also accommodate any complex features on the part, such as undercuts, which will require additional die pieces. 

Most of these devices slide into the part cavity through the side of the die and are therefore known as slides, or side-actions. The most common type of side-action is a side-core which enables an external undercut to be molded. Another important aspect of die design is material selection. Dies can be fabricated out of many different types of metals.

High-grade tool steel is the most common and is typically used for 100-150,000 cycles. However, steels with low carbon content are more resistant to cracking and can be used for 1,000,000 cycles. Other common materials for dies include chromium, molybdenum, nickel alloys, tungsten, and vanadium. Side-cores that are used in the dies can also be made out of these materials.

Die Casting Tooling cost

The tooling cost has two main components – the die set and the machining of the cavities. The cost of the die set is primarily controlled by the size of the part’s envelope. A larger part requires a larger, more expensive, die set. The cost of machining the cavities is affected by nearly every aspect of the part’s geometry.

The primary cost driver is the size of the cavity that must be machined, measured by the projected area of the cavity (equal to the projected area of the part and projected holes) and its depth. Any other elements that require additional machining time will add to the cost, including the feature count, parting surface, side-cores, tolerance, and surface roughness.

The number of parts and materials used will affect the tooling life and therefore impact the cost. Materials with high casting temperatures, such as copper, will cause a short tooling life. Zinc, which can be cast at lower temperatures, allows for a much longer tooling life. This effect becomes more cost-prohibitive with higher production quantities.

One final consideration is the number of side-action directions, which can indirectly affect the cost. The additional cost for side-cores is determined by how many are used. However, the number of directions can restrict the number of cavities that can be included in the die. For example, the die for a part that requires 3 side-core directions can only contain 2 cavities. There is no direct cost added, but it is possible that the use of more cavities could provide further savings.

Tooling for Gravity Die Casting

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Molds for the gravity die casting process consist of two halves. Molds are usually formed from grey cast iron because it has about the best thermal fatigue resistance, but other materials include steel, bronze, and graphite. These metals are chosen because of their resistance to erosion and thermal fatigue. They are usually not very complex because the mold offers no collapsibility to compensate for shrinkage. Instead, the mold is opened as soon as the casting has solidified, which prevents hot tears. Cores can be used and are usually made from sand or metal.

The mold is heated prior to the first casting cycle and then used continuously in order to maintain as uniform a temperature as possible during casting cycles. This approach decreases thermal fatigue, facilitates metal flow, and helps control the cooling rate of the casting metal.

Venting usually occurs through the slight crack between the two mold halves, if this is not sufficient then very small vent holes are used. These are small enough to let air escape but not the molten metal. A riser must be included to compensate for shrinkage. This usually limits the yield to less than 60%.

Mechanical ejectors in the form of pins are used when coatings are not enough to remove casts from the molds. These pins are placed throughout the mold and usually leave small round impressions on the casting.

Tooling for Investment Casting

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Wax-injection dies used for investment casting are often made out of aluminum. Aluminum’s properties make it an ideal material for investment casting. First, its high thermal conductivity allows heat to quickly dissipate, helping to reduce cycle times during wax injection.

Aluminum is also less dense than other alloys, and so aluminum dies to weigh less and are easier to handle and transport. Furthermore, aluminum is highly machineable, so machining costs to produce aluminum dies are relatively low. Aluminum is also easily accessible; toolmakers and machine shops can acquire aluminum stock with minimal cost and effort.

Since investment wax is non-abrasive, aluminum die cavities do not wear as a result of the wax injection process. Moving parts, or components that experience friction during the molding process, are often made from steel, brass or anodized aluminum to increase longevity.

Investment casting tooling can be much lower than tooling for other casting processes. Tool pricing can range from $2,000 up to and beyond $20,000.

One of the main factors affecting the cost of investment casting tools is casting complexity. Overly complex parts may require more moving parts within the tool, which increases the amount of time and the number of processes required to construct it. Another factor is size.

Larger parts require larger tools, which require more material for constructing tooling and more time to machine the mold cavity in the tool. In specific cases, soluble cores may be required. While soluble cores are a great asset in the production of complex inner cavities, they require their own tool which increases the up-front tooling costs.

As in any industrial manufacturing process, designing and producing tooling is an integral aspect of investment casting. By understanding the production, costs and variables associated with wax-injection dies, investment casting customers can better predict the overall costs and timelines for bringing a new product to market.

Tooling for Lost Foam Casting

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Typically, tooling is composed of a split-cavity, machined aluminum die that is the negative mold from which the foam pattern is produced. The tooling is highly specialized and must be constructed by experienced tooling manufacturers familiar with the requirements of foam molders and foundries.

Most tooling for Lost Foam patterns will compare favorably with permanent and die cast tooling. As a result of the materials used and the process stresses, Lost Foam tools can be expected to have 3 to 4 times the cycle life of permanent mold or die casting tools.

The first step is producing a foam pattern and gating system by foam molding press. The process of pattern making can vary depending on the number of items that will be replicated. In most cases, the pattern is molded in polystyrene (2.5% polystyrene and 97.5% air) in a closed mold. The pattern can be molded with either the risers and gates already in place, or it can be assembled (usually glued) from various molded parts. 

In the pattern making process, very detailed attention is needed as it will determine the quality and reliability of the final product. Techniques for making patterns include closed die molding, assembly of the pattern from various parts and machining the pattern from a solid piece of polystyrene. 

The gating systems and pattern (either one molded piece or assembled from various parts) are glued together to make what is called the cluster. This cluster is then coated with a permeable refractory coating and left to dry under very controlled conditions.

Tooling for Shell Mold Casting

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Metal casting tools production is where shell mold casting differs from other sand-casting processes like air set and green sand. When resin-coated sand is applied to the pattern or core box, the casting tooling is heated to temperatures between 350- and 700-degrees F. That means plastic, wood and aluminum, common materials for tooling in other sand-casting methods, are not options for shell mold casting.

Various grades of iron can be used for standard tooling because of its high resistance to heat fatigue, good machinability and excellent durability. For larger volumes, steel can further increase tooling longevity.

While production processes are limited by the alloys needed for shell mold casting tooling, a number of techniques are commonly used. Many pattern plates are rolled or formed to rough dimensions, then machined to their final shape.

Ejector pins are also custom-formed and machined to achieve the final length and diameter. In some cases, tooling is cast to shape and then machined to the final size, which helps speed up the onboarding process for new products. When the pattern plate or core box is ready, gating is bolted on in the final step.

Casting tools are one of the key fixed costs for any manufacturing operation, and shell mold casting is no exception. While the manufacturing casting foundry is responsible for tooling designing, the customer often maintains ownership of the patterns, core boxes and other tooling elements. Shell mold casting tooling often costs between $1,500 and $5,000, and the price is affected by a number of factors.

One major factor that affects tooling costs is production volume. Especially large volume tooling will need to undergo periodic maintenance or even replacement. Typical iron pattern tooling will last approximately 300,000 impressions, while iron core boxes can reach approximately 250,000 shots. Steel patterns and core boxes can last nearly twice as long, often exceeding 500,000 impressions or shots. While it lasts longer, steel tooling is more expensive to produce.

As patterns and core boxes approach the end of their useful lifespans, the chance of producing off-dimension parts increases. Aging patterns and core boxes sometimes also sustain dings and scratches from repeated sand coatings, and the abrasion also gradually roughens the surface finishing. If gating components are worn but the pattern plate or core box is still fully functional, the gating can simply be replaced. The same applies to pattern inserts and ejector pins.

Other factors that affect the tooling cost include size, number of core boxes, number of plate cavities, number of gate contacts and the number of pattern inserts. All of these features of tooling determine the overall degree of complexity of the project. The higher the complexity, the higher the cost.

Metal Casting Tooling and Molding Servicese at Omnidex

The Omnidex Casting Team understands the challenges you may face in all kinds of metal casting projects. Through our Omnichannel Manufacturing Network, we are able to provide top-tier casting molding and tooling design and making to our customers. Our toolmakers are equipped with the latest CNC machines and EDM equipment and can offer all the casting tooling you required at very competitive prices and short lead times. 

The Omnidex Casting Team is experienced in every aspect of the casting tools and molding process, from die making to equipment preparation.

Talk to our tooling experts today to learn more.

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