The Investment Casting Process

A perfect mix of automation and human control, provides you with a manufacturing process that cuts out time consuming tooling and delivers castings with a high dimensional accuracy.

Our plants in India and the USA use our process and the unrivalled casting technology at our foundry to manufacture both large and small parts at high volume.

Step One – Pattern Tooling Creation or Wax Prototyping


Wax Prototyping

    • First Article Inspections (FAI) must be performed on parts injected in production tooling to validate the tooling dimensions and release the tooling for production orders.

Invest Casting Wax Process

    • Any designs validated with prototyping would still need to be validated with an FAI once tooling was created. If wax prototyping is used, wax injection is not needed and the process skips straight to wax assembly.

Investment Casting Wax Process Aluminium

Pattern Tooling Creation

  • Tooling can have multiple cavities, automatic side cores, and ejection pins to allow for faster processing. Some undercuts and internal features can be created with automatic side cores built into the tool.
  • If geometries cannot be made with side cores from the tool and will have trouble shelling later do to size, shape, and location – ceramic cores can be placed in the tool.
  • Wax will fill around the cores and keep the complex space from affecting the desired pattern geometry. These cores can be dissolved later on in the process. Once the tooling has been cut and assembled it is ready to begin the process at injection.

Step Two – Wax Injection


    • The wax injection tooling created in the first step serves as a cavity that will be filled with liquid wax, allow the wax to solidify, and produce a positive of the final component in wax.
    • Tooling is located and clamped to a stationary table with a moving platen clamping the top half of the die.
    • The injection sprue is simply a path that the wax will follow as it is injected though the tool and into the cavity which will create a positive of the pattern.
    • Wax pellets are melted into a large holding tank located on the wax injection press.
    • The tank holds the wax at a liquid and is constantly agitated to ensure a homogeneous mixture of the wax constituents.
    • A hydraulic cylinder moves the wax into an injection cylinder to prepare for injection. Once the tool is closed, another hydraulic cylinder will push the wax through a heated hose and into the tool via the injection sprue, filling the cavity and allowing the wax to solidify inside.
    • Once solidified, the two halves of the die will open and the wax pattern will be removed from the tool. The wax injection operator will close the tool and start the next injection.
    • A gate is left on the patterns which will serve as a connection point to the wax runner in the next step in the process.  At this point the wax patterns are now ready to move to wax assembly.

Wax Pouring

Step Three – Wax Assembly


    • Once the wax pattern is complete, it must be assembled onto a wax runner. The wax runner will have multiple wax patterns attached to it and will later serve as a metal feeding system to supply all of the individual parts with metal during casting.
    • The runners are injected in wax with a process identical to the injection of wax patterns. The only difference is that a metal component is located at the end which has the wax injected around it; after injection this metal component has a pin fastened to it that extrudes from the end and can be connected to a hanger plate during shelling in the next process.
    • A ceramic cup is also attached to the end of the wax assembly. This ceramic cup will be locked to the ceramic mold during shelling and will act as a funnel for the metal when it is poured in during casting.
    • Once the runner is completed, the wax patterns are attached by their gates to the runner. This is done by melting the gate of the pattern on the surface that will interface with the runner and dipping it in a hot melt adhesive wax before pressing it to the runner.
    • The waxes will fuse together locking the patterns to the runner. The area around the gate/runner interface will then be welded with a small torch to make a smooth connection all the way around.
    • Once all of the patterns are attached to the completed runner the completed product is called an assembly. The completed assemblies are then ready to move the shelling as the next process.
    • Once the wax pattern is complete, it must be assembled onto a wax runner. The wax runner will have multiple wax patterns attached to it and will later serve as a metal feeding system to supply all of the individual parts with metal during casting.
    • Once the runner is completed, the wax patterns are attached by their gates to the runner. This is done by melting the gate of the pattern on the surface that will interface with the runner and dipping it in a hot melt adhesive wax before pressing it to the runner.
    • The waxes will fuse together locking the patterns to the runner. The area around the gate/runner interface will then be welded with a small torch to make a smooth connection all the way around.
    • Once all of the patterns are attached to the completed runner the completed product is called an assembly. The completed assemblies are then ready to move the shelling as the next process.

Investment Casting Assembly

Step Four – Shelling


      • Shelling is done by dipping the wax assemblies in a series of ceramic slurries and coating them in refractory sands.

    Investment Casting Shell Process

    • Multiple assemblies are hung from a hanger plate and pinned in place by the metal components protruding from the top of the assemblies.
    • A robot then interfaces with the robot plate, picking up the hanger, dipping the hanger in ceramic slurry, and removing from the slurry tank and draining while moving in certain positions to ensure uniform coverage and thickness of the slurry before entering a sander.

Wax Dipping Process

    • A sander drops refractory sand over the freshly dipped assemblies while the hanger is rotated and tilted to ensure complete and even sand coverage.

Sanding Process

    • Once the assemblies have been covered in sand, the robot will place the hanger on the drying conveyor and go to pick the next hanger for dipping.

Drying Process

  • As water is removed and the silica particles move closer together, they are eventually stuck together by Van der Waals forces which will not be broken even if moisture is reintroduced to the mold. Because of this humidity and air speed must be controlled in the drying room.
  • Temperature must also be controlled tightly from injection to dewax to prevent the wax from distorting dimensions or cracking the mold once shelling has commenced.
  • A series of ceramic dips will take place with specified dry times in between to ensure that there is sufficient drying of the previous coat.
  • The first dip must be able to withstand the molten alloy during casting by not reacting with the metal and also controls surface finish.
    The consecutive dips add thickness and strength to the shell so that it may hold the liquid metal without cracking or leaking.
  • Once the dip sequence and drying times are complete the completed shells are unloaded for the robot and ready for the dewax process.

Step 5 – Dewax


    • Before casting this wax must be removed. The wax must be melted quickly so that it does not have time to expand before becoming liquid and rapidly dropping in viscosity. It also must not be burnt out.
    • Due to the amount of wax present in the shell during dewax, burning out with combustion will lead to amorphous carbon which will not readily burn out and leave deposits in the shell which will later displace metal during casting.
    • The parts are quickly loaded into the vessel, a pressure door is sealed, and the boiler valve opens allowing steam to enter the vessel and cause rapid pressurization. This rapid pressurization causes the temperature to quickly rise due to the Ideal Gas Law.
    • This rapidly melts the wax without the use of combustion. Once the wax has melted out, the pressure of the vessel is exhausted and the door can be opened.

Dewax Process

    • The wax that comes out of the shell can be reclaimed and reused after removing water and other impurities from the wax.
    • The small amount of wax that remains in the shell can then be burnt out in the next process without the worry for amorphous carbon being created.
    • The boiler still remains pressurized and this process can be repeated for the next batch of shells.

Dewax Investment Casting Finished

Step Six – Casting


    • Once the shells have been dewaxed, they must be allowed to dry to prevent the rapid expansion of water during heating in the next process.
      Heating the shells also gives the liquid metal more time to move through the shells without freezing off before filling shell cavity completely.
      While the shells are reaching steady-state temperature in the burnout oven, alloy is being melted in induction furnaces so that it can be poured into the shells.

Investment Casting Oven

    • When alloy is placed in the furnace, a liquid cooled copper coil with high power moving through it creates an electro-magnetic field (EMF). The EMF induces a current in the metal alloy and the natural resistivity of the alloy creates heat which can quickly melt the metal.
    • The copper coil is protected from the molten alloy with a refractory crucible which can withstand the harsh conditions that come with being in contact with molten metal for extended periods of time.
    • Once the alloy has been melted to the desired temperature a few extra operations may be done before melting.
    • First, all heats (each new batch of molten alloy) have a sample collected from the bath for compositional analysis. Optical Emission Spectroscopy vaporizes a portion of the metal sample and analyzes the intensity of light at different wavelengths to determine the amount of each element present in the alloy. This ensures that all heats are at the correct composition for the specified standard.
    • Degassing agents may also be added to the melt to remove any soluble gases that may be left in the casting as it solidifies after pour.
      Finally slag is removed from the melt so as not to pour slag inclusions into the shell which would displace metal from the desired negative space created by the shell.
    • Slag is the formation of oxides, nitrides, and other compounds which may form inside the bath as the metallic elements reacted with gases in the air. Once these operations are complete, the heated shell is removed from the oven and the molten metal is poured into the shell.
    • The metal is left to solidify in the shell to form the desired metal components.

Investment Casting Pouring

Step Seven – Shell Removal


    • Once the shell has cooled and the metal is solidified, much of the shell will begin to flake off on its own. This is due to phase changes that occur in the ceramic as it cools.
    • The remaining ceramic is removed by imparting vibrations to the metal assemblies or blasting the ceramic off with high pressure water. Either way the process is automated.
    • The parts are fixture and either hit on the runner with a pneumatic hammer or fixture so that multi-axis water jets can blast the ceramic off of the castings.

Shell Removal
Finished Metal Casting

Step Eight – Cutoff


    • After the shell has been removed, the running system that parts where attached to has now served its purpose.
    • The next step in the process is to remove the parts from the runner. This is done by an automated process in which the metal assembly is fixture in a robotic cutoff machine.
    • Using robotics and servos, the assembly is manipulated so that a saw can be used to cut the parts from the tree.

Cut Off

Step Nine – Grind


    • After cutoff a portion of the gate will remain which is not desired on the final part. To remove this, manual or robotic grinding can be utilized to remove material and leave only the desired component geometry.
    • The material removal is done with the use of belt grinder equipped with coarse grains for maximum material removal.
    • This can either be done by manually manipulating the part or placing multiple parts in a grind fixture so that it can be manipulated and ground by robotics.
    • In this case an operator simply loads the parts onto a fixture, runs the cycle, and removes the parts when complete. The operator repeats this cycle on consecutive parts.

Gate Grind

Step Ten – Finishing


  • Once grind is complete, the casting is now left in the desired shape of the final casting.
  • There are a few finishing operations necessary to make the part to acceptable quality for the customer. If any defects on any of the castings are present, these defects can be cleaned up with the use of hand finishing tools.
  • If any positives are present on the part they can be ground off. Negatives can we welded if allowed by the customer’s casting specification.
  • If the parts need straightened to meet certain GD&T callouts, hydraulic straightening presses can be used to put these features in tolerance.
  • After all other finishing operations are complete a final blasting operation takes place to bring the parts to their desired surface requirements.

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