Investment Casting Process-II

Introduction and Special Features of Investment Casting Process

In this section, the lecturer introduces the topic of investment casting process and reviews the special features of this process.

Special Features of Investment Casting Process

• Investment casting process has several special features:

• It can produce very thin and complex features.

• It offers excellent surface finish, often requiring little to no machining.

• It provides excellent dimensional accuracy.

• It can be used to cast a wide range of metals and alloys.

Alloys Covered in Investment Casting Process

This section discusses the alloys that can be cast using different manufacturing processes and specifically focuses on the alloys covered in investment casting process.

Alloys Covered in Investment Casting Process

• The investment casting process can cover all types of metals and alloys, including:

• Ductile iron

• Tool steels

• Steels

• Stainless steel

• Aluminum

• Magnesium alloys

• Copper

• Bronze

• Brass

• Titanium alloys

• Super alloys

Alloys Covered in Other Manufacturing Processes

This section compares the alloys that can be cast using different manufacturing processes other than investment casting.

Alloys Covered in Other Manufacturing Processes

• Die casting process:

• Can cast aluminum, magnesium alloys, copper, bronze, brass.

• Cannot cast ductile iron, tool steels, steel, titanium alloys, super alloys.

• Forging:

• Can use tool steels, steels, stainless steel, aluminum, magnesium alloys,

copper, bronze brass,titanium alloys,superalloys.

• Cannot use ductile iron for forging.

• Powder metallurgy process:

• Can manufacture tool steels, steels, stainless steel, titanium alloys.

• Cannot manufacture ductile iron, copper, bronze, brass, super alloys.

• Sand casting process:

• Can manufacture ductile iron, tool steels, steels, stainless steel,

aluminum,magnesium alloys,copper,bronze brass,superalloys.

• Cannot manufacture titanium alloys using sand casting process.

• Weldments:

• Can weld steels,stainless steel ,aluminum,magnesium alloys,copper,

bronze brass,titanium alloys,superalloys.

• Cannot weld ductile iron and tool steels.

Alloys Covered in Investment Casting Process

This section focuses on the alloys that can be manufactured using investment casting process.

Alloys Covered in Investment Casting Process

• The investment casting process can cover all types of metals and alloys including:

• Ductile iron

• Tool steels

• Steels

• Stainless steel

• Aluminum

• Magnesium alloys

• Copper

• Bronze

• Brass

• Titanium alloys

• Super alloys

Developments of Investment Casting Process

This section discusses the developments in the investment casting process during the twentieth century.

Developments of Investment Casting Process

• Initially used solid mold or block mold with wax as the pattern material.

• Later replaced ceramic material with plaster mold for better surface finish.

• Mercast process was developed using mercury as the pattern material but is no longer in use due to associated problems.

• Ceramic shell investment casting process has gained importance worldwide. It involves creating a shell around a wax pattern by dipping it multiple times into a ceramic slurry and applying stucco coating.

Major Steps in Ceramic Shell Investment Casting Process

This section outlines the major steps involved in the ceramic shell investment casting process.

Major Steps in Ceramic Shell Investment Casting Process

• Wax injection: Injecting wax into the pattern die and removing it.

• Pattern assembly: Assembling several wax patterns together.

• Dipping in ceramic slurry: Dipping the wax assembly into a ceramic slurry, followed by drying and repeating the process multiple times to create a shell around the pattern.

• Shell creation: After multiple cycles of dipping and drying, a shell is created around the wax pattern.

• Dewaxing: Removing the wax from the shell.

• Casting: Pouring molten metal into the shell.

• Knockout: Breaking or removing the shell to reveal the cast metal part.

• Cut off: Removing any excess material from the cast part.

• Finishing and secondary operations: Performing additional processes such as machining or surface treatment on the cast part.

Conclusion

The lecturer concludes by highlighting that virtually all alloys can be manufactured using investment casting process, making it a unique and versatile manufacturing method.

Wax Injection and Tree Assembly

This section explains the process of wax injection and tree assembly in investment casting.

Wax Injection Process

• Wax patterns are produced using a wax injector.

• Hundreds or thousands of wax patterns can be produced in a single session.

• The wax patterns are assembled onto a tree, where multiple patterns are joined together.

• The heads of the golf clubs are joined to the tree via gates.

Tree Assembly

• Multiple wax patterns are assembled onto a single tree.

• Each tree can hold several patterns, typically around seven.

• The assembled pattern represents the final shape of the desired product.

Ceramic Slurry and Shell Building

This section discusses the ceramic slurry used in investment casting and the process of shell building.

Ingredients of Ceramic Slurry

• Ceramic slurry is made up of three main ingredients:

• Refractory powder (60-80%): commonly zirconium silicate, fused silica, or fused aluminum oxide.

• Liquid binder (15-30%): options include ethyl silicate or colloidal silica.

• Solid binder (5-10%).

Shell Building Process

1. Dip Slurry:

• Fine texture slurry used for detailed grooves and engravings on the pattern.

• Typically, two to three different ceramic slurries are used during shell building.

2. Coarser Slurries:

• Second slurry coating is coarser than the first dips, building a thicker ceramic shell around the pattern.

3. Drying Between Dippings:

• Slurry must dry between successive dippings.

• Temperature and humidity are carefully controlled during this stage.

Dewaxing and Autoclave Oven

This section explains the dewaxing process and the use of an autoclave oven in investment casting.

Dewaxing Process

• Dewaxing is the removal of wax from the ceramic shell before pouring molten metal.

• An autoclave oven is commonly used for dewaxing.

• High steam pressure (around 8 kg per square centimeter) is injected into the sealed oven to melt and remove the wax from the ceramic shell.

Autoclave Oven Construction

• The autoclave oven consists of a steam boiler, accumulator, control valves, and an autoclave chamber.

• Steam at high pressure is injected into the autoclave chamber to melt and remove wax from the ceramic shell.

• Wax and condensate recovery systems are used to collect and refine melted wax for reuse in pattern making.

Casting Process

This section focuses on pouring molten metal into the ceramic shell during the casting process.

Heating Ceramic Molds

• Ceramic molds must be heated before pouring molten steel into them.

• Heating ensures proper flowability of molten metal within the mold.

Pouring Molten Metal

• Molten steel is poured from a crucible into the iron head mold.

• The liquid steel fills up the ceramic shell, forming a cast product.

• The filled shell is set aside to cool down and solidify.

Knockout Process

This section describes the knockout process, which involves breaking open the ceramic shell to remove the casting.

Cooling Ceramic Shells

• Freshly poured ceramic shells generate ambient heat as they cool down.

• Cooling time varies depending on factors such as shell thickness and size.

Knockout Process

• Knockout refers to breaking the ceramic shell and removing the casting.

• The ceramic shell is broken open, revealing the solidified metal casting inside.

New Section

This section discusses the process of removing traces of ceramic shell from castings using a sand blasting system.

Sand Blasting Chamber

• A sand blasting chamber is used to remove traces of ceramic shell from castings.

• The castings are placed inside the chamber and sand is blasted onto them.

• This process effectively removes any remaining ceramic shell.

New Section

This section covers the cut-off process, finishing, and secondary operations in investment casting.

Cut Off

• The cut-off process involves cutting the castings at the gates to remove excess material.

• After assembly, wax patterns are separated into individual castings using a grinding wheel.

Finishing and Secondary Operations

• Castings undergo heat treatment to normalize the metal.

• Heat treatment ovens can vary in size.

• Appropriate surface finishes, such as mirror or satin finishes, are polished on the parts.

• Cleaning of heads for final cosmetic preparations is done to ensure a pleasant appearance.

• Cosmetic paint may also be added as part of secondary operations.

New Section

This section highlights that investment casting can be used for casting a wide range of alloys.

Alloys Covered in Investment Casting Process

• Virtually all alloys can be cast using investment casting.

• The range of alloys includes nonferrous alloys, steels, nickel and cobalt base alloys, ductile or spheroidal graphite irons, titanium alloys, and special purpose materials.

New Section

This section provides examples of common investment cast alloys and their applications.

Common Investment Cast Alloys

1. Ductile Iron: Used for defense components, automotive components, pump and valve components, and general engineering components.

2. Carbon Steels: Used for locks, door handles, mining applications, military and firearms, and transportation parts.

3. Tool Steels: Used for making cutting tools such as lathe tools, milling cutters, and planning cutters.

4. Stainless Steels: Widely used in various industries for their corrosion resistance properties.

5. Aluminum Alloys: Commonly used in aerospace and automotive industries due to their lightweight nature.

6. Magnesium Alloys: Known for their high strength-to-weight ratio and used in aerospace and automotive applications.

New Section

This section focuses on the investment casting of ductile iron.

Investment Casting of Ductile Iron

• Ductile iron is manufactured by converting graphite flakes of gray iron into spheroidal or spherical nodules through an alloying process.

• Investment casting allows the production of complex parts with high dimensional accuracy using ductile cast iron.

• Applications include defense components, automotive components, pump and valve components, and general engineering components.

New Section

This section discusses the investment casting of carbon steels.

Investment Casting of Carbon Steels

• Carbon steel investment castings find applications in locks, internal lock mechanisms, door handles, closer units, mining applications, military and firearms, and transportation parts.

• These components require excellent surface finish, dimensional accuracy, and possess complex features.

New Section

This section covers the investment casting of tool steels.

Investment Casting of Tool Steels

• Tool steels are alloy steels used for making various tools such as cutting tools (lathe tools, milling cutters) and planning cutters.

New Section

This section discusses the use of investment casting for producing castings with a mirror finish and high corrosion resistance, particularly in austenitic stainless steel grades commonly used in investment casting applications.

Investment Casting of Stainless Steel Castings

• Austenitic stainless steel grades are commonly used for investment casting applications.

• Investment casting can produce castings with a mirror finish and excellent corrosion resistance.

• Examples include pelton wheel blades made from austenitic stainless steel.

New Section

This section explores the investment casting process for producing castings using different types of alloys, such as martensitic stainless steel, duplex stainless steel, aluminum, magnesium, copper, bronze, brass, titanium alloys, and super alloys.

Investment Casting of Different Alloys

• Investment casting is used to produce castings from various alloys.

• Examples include revolver frames made from martensitic stainless steel and corrosion-resistant valves made from duplex stainless steel.

• Aerospace components made from aluminum and magnesium alloys can also be produced using investment casting.

• Copper castings with thin blades and locomotive accessories are other examples of investment castings.

• Titanium alloy components like jet engine diffusers and Formula One race car suspensions can be manufactured through investment casting.

• Turbine impellers made from super alloys demonstrate complex features and thin blades that can be achieved through investment casting.

New Section

This section focuses on specific examples of investment castings that require excellent surface finish and have thin fins or complex features. It includes an aluminum automotive component as an example.

Investment Casting of Components with Thin Fins and Complex Features

• Some components produced by investment casting require very good surface finish due to their application requirements.

• Examples include components with thin fins or complex features.

• An aluminum automotive component is showcased as an example of investment casting.

New Section

This section highlights investment casting applications for copper, bronze, and brass alloys. It includes examples such as copper castings with thin blades and a locomotive accessory.

Investment Casting of Copper, Bronze, and Brass Alloys

• Investment casting can be used to produce castings from copper, bronze, and brass alloys.

• Examples include copper castings with thin blades and a locomotive accessory.

New Section

This section focuses on investment casting of titanium alloys. It showcases examples such as a jet engine diffuser and a Formula One race car suspension part that require complex features, thin sections, and excellent surface finish.

Investment Casting of Titanium Alloys

• Investment casting is utilized for producing components made from titanium alloys.

• Examples include a jet engine diffuser with complex features and thin sections.

• A Formula One race car suspension part also demonstrates the capabilities of investment casting in manufacturing titanium alloy components.

New Section

This section discusses the use of investment casting for super alloys. It presents an example of a turbine impeller with complex features and very thin blades manufactured through investment casting.

Investment Casting of Super Alloys

• Super alloys can be produced using the investment casting process.

• The example shown is a turbine impeller with complex features and extremely thin blades.

New Section

This section introduces rapid prototyping in the investment casting process. It explains how rapid prototyping has emerged as a means to produce patterns required for investment casting.

Rapid Prototyping in Investment Casting

• Rapid prototyping has become important in the investment casting process for producing patterns.

• Patterns are crucial for investment casting, and rapid prototyping offers a solution to produce them efficiently.

• Several rapid prototyping processes are available, including stereo lithography (SLA), selective lasering laser sintering (SLS), 3D printing, and fused deposition modeling (FDM).

• These processes enable the production of patterns required for investment casting.

New Section

This section provides a brief overview of important rapid prototyping processes used in investment casting. It mentions stereo lithography (SLA), selective lasering laser sintering (SLS), 3D printing, and fused deposition modeling (FDM).

Important Rapid Prototyping Processes

• Stereo lithography (SLA) is a rapid prototyping process that uses a liquid resin cured by a laser system to produce solid components layer by layer.

• Selective lasering laser sintering (SLS) is similar to stereo lithography but uses powder instead of liquid polymer.

• 3D printing and fused deposition modeling (FDM) are also utilized in rapid prototyping for investment casting.

• Bio plotter is another important rapid prototyping process used in investment casting.

New Section

This section explains the principles behind stereo lithography as one of the important rapid prototyping processes used in investment casting.

Principle of Stereo Lithography

• Stereo lithography involves using a liquid resin that can be cured by a laser system.

• A scanner directs the laser onto the liquid resin, curing it and creating solid components layer by layer.

• The photopolymer inside the vat becomes solid when exposed to the laser, forming the desired component.

• Support structures are used during the process to ensure stability.

New Section

This section introduces selective lasering laser sintering (SLS) as another rapid prototyping process used in investment casting.

Principle of Selective Lasering Laser Sintering

• Selective lasering laser sintering (SLS) is similar to stereo lithography but uses powder instead of liquid resin.

• The laser scanning system selectively sinters the powder, layer by layer, to create solid components.

• The primary difference from stereo lithography is the use of powder as the material for creating patterns.

The remaining sections will be continued in subsequent responses.

New Section

This section discusses the process of creating patterns using powder and a scanning system.

Powder Stage and Roller Movement

• The powder stage moves one step upwards.

• The roller moves to distribute the powder evenly.

• The scanning system cures the second layer.

• The Z stage comes down one step.

New Section

This section explains the process of three-dimensional printing using liquid adhesive instead of a laser system.

Selective Laser Sintering with Liquid Adhesive

• In this process, liquid adhesive replaces the laser system used in selective laser sintering.

• There are two stages: the powder stage and the roller stage.

• The powder stage moves up one step at a time, while the roller distributes the powder above the Z stage.

• Liquid adhesive is released and distributed over the model created in the computer.

• It hardens and comes down by one step, followed by another round of powder distribution and curing.

New Section

This section introduces fused deposition modeling as another 3D printing process.

Fused Deposition Modeling

• Fused deposition modeling uses support material and build material spools that move during the process.

• An extrusion nozzle spreads the build material, which is connected to a computer for control.

• The liquifier head moves in X and Y directions to create thin sheets of material.

• Each sheet is cured before moving on to create another sheet.

New Section

This section highlights ice patterns as an effective method in investment casting.

Ice Patterns in Investment Casting

• Ice patterns are found to be effective in investment casting.

• Advantages of ice patterns include better surface finish and elimination of cracks during pattern removal.

• Unlike wax patterns, ice patterns do not cause cracking in the ceramic shell when heated.

• Ice is a cost-effective raw material compared to wax.

New Section

This section concludes the discussion on investment casting processes and their advantages.

Summary of Investment Casting Processes

• The lecture covers various developments in investment casting processes, including solid mold, plaster molding, mercast, and ceramic shell.

• Ceramic shell investment casting involves steps such as wax injection, pattern assembly, shell building, dewaxing, casting, knockout, cut off, finishing, and secondary operations.

• Ceramic shell investment casting offers thin and complex features with excellent surface finish and dimensional accuracy.

• It can be used for casting all types of metals and alloys.

New Section

This section concludes the lecture series on investment casting processes.

Conclusion

• The lecture series covered the developments in investment casting processes throughout the twentieth century.

• Different methods such as solid mold, plaster molding, mercast with mercury patterns, and ceramic shell were discussed.

• Ceramic shell investment casting offers thin and complex features with excellent surface finish and dimensional accuracy for various metals and alloys.