Investment casting, also known as lost-wax casting, is a metal forming process that allows the manufacturing of intricate, high-quality metal parts. The process involves creating a wax pattern, coating it with a ceramic slurry material to create a mold, melting out the wax, and then pouring metal into the mold to make the final part. The equipment used in investment casting plays a key role in ensuring high quality results. This article provides a comprehensive guide to understanding the various types of investment casting equipment and their functions.
The key equipment used can be broadly divided into wax pattern production equipment, ceramic shell building equipment, wax removal equipment, and metal pouring and post-casting equipment. Wax pattern equipment includes injection wax machines, wax 3D printers, CNC waxlathes, etc. Ceramic shell building utilizes manual and automated dipping machines, stucco applicators, and drying ovens. For wax removal, flash fire dewaxing ovens, autoclaves, and thermal catalytic dewaxers are common. Finally, metal pouring relies on vacuum assisted and air melt furnaces, while shot blasting and cut-off saws are needed for finishing. Proper selection, use and maintenance of these equipment is crucial for defect-free, high precision investment cast parts.
With the right investment casting equipment, foundries can reap maximum benefits from this versatile process and expand their capabilities and markets served.
Wax pattern production equipment creates the sacrificial pattern
The first step in investment casting involves creating a disposable wax pattern that replicates the shape of the desired final metal part. Pattern equipment is highly specialized for this purpose.
Injection wax machines inject wax into metal dies to mass produce identical wax patterns. They allow rapid prototyping and high volume production. The wax properties like viscosity and melting point must be optimized based on part geometry.
Wax 3D printers create patterns directly from CAD models through additive manufacturing. This enables rapid design iterations and parts with complex geometries. The patterns have good surface finish but limited dimensional accuracy.
CNC wax lathes and CNC milling machines are used for machining custom wax patterns for prototyping or low volume production. The versatile subtractive process can handle a wide variety of part shapes. Multiple patterns can also be combined on a single wax tree to optimize mold yields.
Other specialty equipment like spin casters and vacuum wax pattern assemblies may also be used as needed. The wide range of wax pattern equipment provides flexibility to investment casting foundries.
Ceramic shell building equipment surrounds the pattern with refractory mold
Once wax patterns are ready, the next key investment casting equipment is utilized for surrounding them with a protective ceramic shell mold. This refractory mold supports the metal during pouring and prevents defects.
Manual and automated dipping machines are most commonly used for repeated dipping of patterns into ceramic slurries. Dipping creates uniform, high integrity molds. Control of process parameters like dwell time and drip time is key.
Between dips, stucco applicators aid in coating patterns with coarse ceramic granules. This strengthens the shell by providing mechanical interlocking sites. Shell thickness and permeability can be controlled through the stucco size and layers.
Proper drying of each layer is achieved in atmosphere ovens before the next dip. Convection ovens, infrared ovens and fluidized bed dryers are among equipment choices here. Faster drying increases mold output.
Other shell building methods like pouring slurry over patterns, roll coating, vacuum impregnation and electrophoretic deposition may also be suitable based on specific needs.
Wax removal equipment clears wax from ceramic shell
Before metal pouring, the wax pattern must be completely removed from the ceramic shell mold while keeping the mold intact. Investment casting equipment for this critical dewaxing step includes:
Flash fire dewax ovens use direct gas fired burners to rapidly melt out the wax in seconds. They yield quick turnaround but can thermally shock the shell. Modulating the flame is important.
Autoclaves provide pressurized steam heating to gently melt the wax over longer periods. This reduces mold damage risks and may improve surface finishes.
Thermal catalytic dewaxers pass heated air through catalysts to oxidize the wax pattern into gaseous byproducts that exit the shell. No liquid wax residues remain.
Infrared dewaxers employ IR radiation lamps for fast, uniform heating. Hybrid systems pairing IR and convection may improve control over shell temperatures.
The choice of method depends on required dewax times, shell strength, pattern complexity, metal reactivity and other parameters specific to each foundry’s process.
Metal melting and pouring equipment fills ceramic mold with alloy
Once dewaxing is complete, the empty ceramic shell must be filled with the desired alloy to form the cast part. Investment casting equipment for this critical stage includes:
Air melt furnaces rely on combustion heating and an air atmosphere. They allow melting most alloys like steels and nickel-based superalloys for aerospace applications.
Vacuum induction melting furnaces use electromagnetic induction and vacuum conditions. This enables reactive alloys like titanium and aluminum to be melted without reactions or contamination.
Pouring under vacuum is also often used to fill molds. This increases mold yields by enabling porous shells, improves surface finish by reducing turbulence, and prevents reactions. Tilting mechanisms simplify casting of large or complex parts.
For quick solidification and fine microstructures, counter-gravity pouring processes may be used. Pressure chambers allow gas-pressurized filling. Centrifugal casting can also be integrated.
Post-casting equipment removes shell and finishes parts
Once solidified, the shell must be removed from the cast metal parts without causing damage. Additional finishing operations are also performed. Key investment casting equipment here includes:
Vibratory grinders use abrasive media to shake off shells via impact stresses. It is fast but can distort parts and leave shell fragments.
Shot blasting equipment propels a stream of metal/ceramic shot media to more gently abrade the shell. It leaves components cleaner but has dust generation issues.
Cut-off saws trim parts from sprues and runners using abrasive saw blades. This also removes surface defects from contact areas. Further milling/grinding may then be done.
Final finishing steps like heat treatment, machining, welding, testing and inspection ready the parts for end-use. The equipment must match the allowable tolerances.
In summary, investment casting relies extensively on specialized wax pattern production, ceramic shell building, wax removal, metal melting/pouring and finishing equipment. Each step in the process chain depends on proper equipment selection and usage to create defect-free castings. With the right investment casting equipment set up, foundries can reap maximum quality and productivity benefits from this technology.