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Our technology

CPP Poland - the Investment Casting Foundry - has many years of experience in casting critical elements of the hot aero engine parts, specializing in low- and high-pressure turbines. 

 

The technology of precise casting of hot parts of aero engines by the method of melted models,  currently used in CPP, includes the following processes:

 

  • execution of a wax casting model and a gating system using the method of injection into metal molds,

  • construction of a wax model set and a multi-layered ceramic mold, drying of the mold, removal of wax, sintering the wax residue after the smelting process,

  • annealing the mold before liquid metal casting,

  • installation of ceramic foam filters in the gatting system,

  • melting the alloy in a vacuum furnace in a ceramic crucible and casting a ceramic mold,

  • post-casting processing 

  • heat treatment in a vacuum furnace,

  • quality control 

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Historical overview

Investment  casting is one of the oldest production methods. In ancient times, in Central Asia (3000 BC) and Greece (500 BC), this method was used in the production of articles of everyday use. Initially, the material used in the production of foundry molds was clay, which was then replaced by ceramic materials.

 

In the Middle Ages, casting was already widely used in the production of artistic and jewelry products in almost all parts of the world (Europe, South America, Africa, Asia).

Waxes

Waxes

The wax-based modeling compound is injected at a defined temperature and pressure into the matrix. The model substance can be injected in liquid, semi-solid or solid (paste) forms. Liquid waxes are injected at higher temperatures and at lower pressures, while pastes are injected at higher pressures and at lower temperatures. Wax models have a decisive impact...
The wax-based modeling compound is injected at a defined temperature and pressure into the matrix. The model substance can be injected in liquid, semi-solid or solid (paste) forms. Liquid waxes are injected at higher temperatures and at lower pressures, while pastes are injected at higher pressures and at lower temperatures. Wax models have a decisive impact on the quality of the product in the form of a casting - they influence, among others, the surface quality of castings and their dimensional accuracy.

In the production of large castings, models are made and later processed individually, while for small and medium castings, e.g. jet engine turbine blades, models are combined into model sets consisting of an gating system and models that are mounted on the so-called beams. One model set can consist of several to several dozen parts.

Ceramic cores are also used in the production of casting models. They are used to shape internal cooling channels of turbine blades and segments of steering apparatus. The purpose of using empty spaces inside is to ensure proper cooling during operation of the turbine engine, which allows the temperature of operating gases to increase, as well as to reduce the mass of the cored elements.
Ceramic molds & Wax smelting & Mold sintering

Ceramic molds & Wax smelting & Mold sintering

In the investment casting, multi-layered ceramic casting molds are made by dipping a model set in a ceramic mixture, which is prepared by adding powdered refractory materials and anti-foaming agents and wetting agents to the binder, which are mixed in special mixers.

Then, the model set is manipulated (e.g., by rotating it) in a way that allows full cov...
In the investment casting, multi-layered ceramic casting molds are made by dipping a model set in a ceramic mixture, which is prepared by adding powdered refractory materials and anti-foaming agents and wetting agents to the binder, which are mixed in special mixers.

Then, the model set is manipulated (e.g., by rotating it) in a way that allows full coverage of the surface of the models, after which the model set is immersed in a fluidized bed with backfill or it is sprinkled from above.
As a result of the use of appropriate binder materials and ceramic matrix, and subjecting the mold to a controlled process of drying and heat treatment (smelting, sintering and annealing) molds with the required mechanical strength, resistance to high temperature, high gas permeability and low roughness of the model layer can be obtained. The above properties of the ceramic mold allow for casting complicated details in it, such as, for example, turbine blades of aero engines.

The multi-layered ceramic molds used in the precise casting of nickel superalloys are most often made of metal oxides .

Smelting due to the thermal expansion of the wax and the change in its volume due to this process is a very difficult and complicated technological process. The wax, which increases its volume under the influence of temperature, can cause cracking and destruction of the mold or a change in its dimensions. Therefore, zonal, very fast heating of the mold from the outside to the inside is applied, which causes quick melting of the external parts of wax models and the outflow of wax through special channels. There is a void space that allows further increase in wax volume without fear for the mold damage.

The molds are sintered to completely remove moisture and wax residue from them, and to heat the mold before casting liquid metal to it, to avoid thermal shock.
Melting and casting

Melting and casting

CPP uses vacuum induction furnaces for melting. Vacuum technologies not only provide excellent casting quality, they enable casting of alloys containing reactive elements (superalloys of cobalt, nickel and alloys of titanium and high-melting metals). The process begins with inserting the batch into the melting chamber, closing the lock and creating a vacuum....
CPP uses vacuum induction furnaces for melting. Vacuum technologies not only provide excellent casting quality, they enable casting of alloys containing reactive elements (superalloys of cobalt, nickel and alloys of titanium and high-melting metals). The process begins with inserting the batch into the melting chamber, closing the lock and creating a vacuum. Then the melting process is conducted. After melting the metal, the crucible is tilted by a dedicated mechanism and mold casting occurs, which lasts from 2 to a few seconds.

Crucibles used in the casting processes are usually made of zirconium or aluminum oxide, produced in thixotropic casting processes, forming from bulk masses and isostatic pressing.

Along with the development of nickel superalloys, works were also conducted on the technology of mono and directionally solidified castings. Directional solidification of castings is widely used in the manufacture of hot parts of aero engines and industrial gas turbines, especially high-pressure turbine blades.

In CPP, the Bridgman - HRS (High Rate Solidification) method is used to produce DS./SX castings. In the directional solidification process, the ceramic mold filled with liquid metal is pulled out at a predetermined speed from the heating zone to the cooling zone of the device. A positive temperature of the gradient is obtained and the continuous solidification front moves along the cast height. A positive temperature gradient in the casting can be produced by various methods based on the control of the heat flow in the casting. Directional heat flow is caused by the use of intensive mold cooling below the heating zone of the furnace.
Post-casting processing

Post-casting processing

The first stage of the after-casting treatment is the so-called knocking out, it consists in breaking the mold and separating the ceramics from the casting, without damaging it. The mold residues adhered to the casting are removed in a high-pressure water jet. Removal of the cores occurs by pickling in solutions of NaOH lye or KOH.

The next stage of afte...
The first stage of the after-casting treatment is the so-called knocking out, it consists in breaking the mold and separating the ceramics from the casting, without damaging it. The mold residues adhered to the casting are removed in a high-pressure water jet. Removal of the cores occurs by pickling in solutions of NaOH lye or KOH.

The next stage of after-casting treatment is proper surface preparation by cutting, grinding, deburring, casting polishing and other locksmith operations.
Quality Control

Quality Control

The first quality control operation in the manufacturing of aerospace investment castings is always visual inspection. It is aimed at preventing cases in which the poor quality component is subjected to further expensive machining and then next stages of quality control. Subsequently, the chemical composition of alloy and the grain size (macro etching) are t...
The first quality control operation in the manufacturing of aerospace investment castings is always visual inspection. It is aimed at preventing cases in which the poor quality component is subjected to further expensive machining and then next stages of quality control. Subsequently, the chemical composition of alloy and the grain size (macro etching) are tested.

In the next stage, the quality of the surface is carried out by fluorescent penetrant inspection. The fluorescent dye is applied to the surface of an impermeable material to clearly identify surface defects under ultraviolet light. The X-ray methods, including X-ray computed tomography, are used to detect internal defects. The material density and thickness differences of the casting will attenuate the penetrating radiation through interaction processes involving scattering and/or absorption. The differences in absorption allow detecting the slag, porosity or other casting discontinuities. These methods are also used to determine the etching effectiveness of ceramic cores, consequently the "purity" of cooling channels.

Different techniques are used to measure the geometry and external dimensions by coordinate measuring machines or 3D scanners. For instance, the measurement of blade wall thickness is carried out using ultrasound or computed tomography.

Quality control

The quality control of castings is executed in the metallographic laboratory and on production site using destructive and non-destructive methods.
Visual inspection
Visual inspection
Metallurgical laboratory
Metallurgical laboratory
Grain size inspection
Grain size inspection
Dimentional inspection
Dimentional inspection
FPI inspection
FPI inspection
X - Ray inspection
X - Ray inspection
Final inspection
Final inspection