Investment Casting | Process, Material, Pros, and Cons

Table of Contents
Overview of Investment Casting
Process of Investment Casting
Pattern Creation
Assembling Wax Patterns and Tree Formation
Mold Shell Formation
Wax Removal
Melting and Casting
Final Operations
Overview of Materials Used in Investment Casting
Stainless Steel
Low Alloy Steel
Cast Aluminum
Carbon Steel
Super Alloy
Cast Iron
Copper Alloy
Special Alloys
Surface Treatments in Investment Castings
Various 
Plating
Polishing
Surface Hardening
Powder Coating
Tolerances in Investment Casting
Advantages of the Investment Casting Process
Considerations When Using Investment Casting
Conclusion

Overview of Investment Casting

Investment casting, also called lost-wax casting, is a manufacturing technique with a rich investment casting history spanning thousands of years. It's renowned for its capacity to produce parts with superior surface finish, high dimensional accuracy, and intricate details. This process is utilized across many industries, such as aerospace, automotive, and medical, to create parts that may be challenging to manufacture using other casting methods. The investment casting process is a testament to the versatility and precision of Investment & precision casting Ltd.

investment-casting-parts

Process of Investment Casting

The investment casting process encompasses several crucial steps. Following is the investment casting process step-by-step:

Pattern Creation

The journey begins with creating a wax pattern that mirrors the final product. This pattern is typically crafted using injection molding, where molten wax is injected into a metal mold (die) and left to solidify.

investment-casting-wax-pattern-creating

Assembling Wax Patterns and Tree Formation

After the wax patterns are crafted, they are assembled onto a sprue to form a structure resembling a tree. This assembly permits multiple parts to be cast simultaneously, enhancing the efficiency of the investment casting process.

Mold Shell Formation

The wax tree is subsequently dipped into a ceramic slurry to form a shell around the wax patterns. This shell is developed through multiple dips, with drying time between each dip.

lost-wax-casting-ceramic-shell-creating

Wax Removal

Once the ceramic shell is dry, the wax is melted in a furnace, resulting in a hollow mold. This step gives the lost wax process its name.

Melting and Casting

The mold is then preheated and filled with molten metal. The metal solidifies within the ceramic mold, forming the final part of the investment casting process.

Final Operations

After the metal has cooled and solidified, the ceramic shell is broken away, and the individual parts are cut from the sprue. To achieve the final dimensions and surface finish, the parts undergo finishing processes, such as grinding, sanding, or machining.

Overview of Materials Used in Investment Casting

The versatility of investment casting is evident in the various investment casting materials that can be utilized. The selection of Investment casting materials hinges on several factors, including application, cost, mechanical properties, and casting characteristics. The most frequently used materials encompass various types of steel, aluminum, and special alloys, demonstrating the broad scope of the investment casting process.

Diverse Materials in Investment Casting

Investment casting accommodates a broad spectrum of materials, each offering unique properties:

lost-wax-casting-materials

Stainless Steel

Renowned for its corrosion resistance and excellent mechanical properties, stainless steel is frequently employed in food processing, medical, and marine applications.

Material Classification

Material Grade

Applicable Process

Datasheet

Austenitic Stainless Steel

304 (CF8)

Investment Casting

304 Datasheet

Austenitic Stainless Steel

316 (CF8M)

Investment Casting

316 Datasheet

Martensitic Stainless Steel

410 (CA15)

Investment Casting

410 Datasheet

Martensitic Stainless Steel

17-4 PH (CB7Cu-1)

Investment Casting

17-4 PH Datasheet

Ferritic Stainless Steel

430 (CF3)

Investment Casting

430 Datasheet

Duplex Stainless Steel

2205 (CD3MN)

Investment Casting

2205 Datasheet

Low Alloy Steel

This material offers improved mechanical properties compared to carbon steel. It's often used in applications that require high strength and toughness.

Material Classification

Material Grade

Applicable Process

Datasheet

Low Alloy Steel

4130 (L80)

Investment Casting

4130 Datasheet

Low Alloy Steel

4140 (L80)

Investment Casting

4140 Datasheet

Low Alloy Steel

4340 (L80)

Investment Casting

4340 Datasheet

Low Alloy Steel

8620 (L80)

Investment Casting

8620 Datasheet

Low Alloy Steel

8630 (L80)

Investment Casting

8630 Datasheet

Low Alloy Steel

9310 (L80)

Investment Casting

9310 Datasheet

Cast Aluminum

Lightweight and corrosion-resistant, cast aluminum is used in various industries, including automotive and aerospace.

Material Classification

Material Grade

Applicable Process

Datasheet

Aluminum Alloy

A356

Investment Casting

A356 Datasheet

Aluminum Alloy

A357

Investment Casting

A357 Datasheet

Aluminum Alloy

6061

Investment Casting

6061 Datasheet

Aluminum Alloy

7075

Investment Casting

7075 Datasheet

Aluminum Alloy

356-T6

Investment Casting

356-T6 Datasheet

Aluminum Alloy

380

Investment Casting

380 Datasheet

Carbon Steel

Carbon steel is a cost-effective material that offers a good balance of strength and flexibility in investment casting.

Material Classification

Material Grade

Applicable Process

Datasheet

Carbon Steel

1010

Investment Casting

1010 Datasheet

Carbon Steel

1020

Investment Casting

1020 Datasheet

Carbon Steel

1030

Investment Casting

1030 Datasheet

Carbon Steel

1045

Investment Casting

1045 Datasheet

Carbon Steel

1080

Investment Casting

1080 Datasheet

Carbon Steel

4140

Investment Casting

4140 Datasheet

Super Alloy

Superalloys are used for their ability to withstand high temperatures and corrosive environments. They are commonly used in jet engines and industrial gas turbines.

Material Classification

Material Grade

Applicable Process

Datasheet

Nickel-based Superalloy

IN718

Investment Casting

IN718 Datasheet

Nickel-based Superalloy

IN625

Investment Casting

IN625 Datasheet

Nickel-based Superalloy

IN713C

Investment Casting

IN713C Datasheet

Nickel-based Superalloy

IN738

Investment Casting

IN738 Datasheet

Cobalt-based Superalloy

Mar-M-247

Investment Casting

Mar-M-247 Datasheet

Cobalt-based Superalloy

Haynes 25

Investment Casting

Haynes 25 Datasheet

Cast Iron

Known for its excellent castability and machinability, cast iron is often used in automotive and industrial applications.

Material Classification

Material Grade

Applicable Process

Datasheet

Gray Iron

Class 20

Investment Casting

Class 20 Datasheet

Gray Iron

Class 30

Investment Casting

Class 30 Datasheet

Gray Iron

Class 40

Investment Casting

Class 40 Datasheet

Ductile Iron

65-45-12

Investment Casting

65-45-12 Datasheet

Ductile Iron

80-55-06

Investment Casting

80-55-06 Datasheet

Ductile Iron

100-70-03

Investment Casting

100-70-03 Datasheet

Copper Alloy

Copper alloys, including brass and bronze, are known for their excellent conductivity and corrosion resistance.

Material Classification

Material Grade

Applicable Process

Datasheet

Copper Alloy

C83600

Investment Casting

C83600 Datasheet

Copper Alloy

C92200

Investment Casting

C92200 Datasheet

Copper Alloy

C95400

Investment Casting

C95400 Datasheet

Copper Alloy

C95800

Investment Casting

C95800 Datasheet

Copper Alloy

C17200

Investment Casting

C17200 Datasheet

Copper Alloy

C17510

Investment Casting

C17510 Datasheet

Special Alloys

Special alloys are used for specific applications that require unique properties. These can include high strength at high temperatures, magnetic properties, or resistance to wear. Such Titanium alloys, Cobalt Alloys, and Nickel Alloys

Material Classification

Material Grade

Applicable Process

Datasheet

Titanium Alloy

Ti-6Al-4V

Investment Casting

Ti-6Al-4V Datasheet

Titanium Alloy

Ti-6Al-2Sn-4Zr-2Mo

Investment Casting

Ti-6Al-2Sn-4Zr-2Mo Datasheet

Cobalt-based Superalloy

CoCrMo

Investment Casting

CoCrMo Datasheet

Cobalt-based Superalloy

MP35N

Investment Casting

MP35N Datasheet

Nickel-based Superalloy

Rene 41

Investment Casting

Rene 41 Datasheet

Nickel-based Superalloy

Hastelloy X

Investment Casting

Hastelloy X Datasheet

Surface Treatments in Investment Castings

Surface treatments are applied to investment castings to enhance their aesthetic appeal, improve corrosion resistance, modify material properties, and shield the surface from external influences. The requirements of the final product determine the type of Investment casting surface treatment used.

Various Surface Treatments in Investment Casting 

Investment casting employs several surface treatment methods:

lost-wax-casting-parts-surface-finishes

Plating

Electroplating

Electroplating is a process that uses electrical current to reduce dissolved metal cations in a solution and coat a conductive object with a thin layer of the metal. The part to be plated is immersed in a solution containing metal salts and acts as the cathode (negative electrode). The anode (positive electrode) is also immersed in the solution and is made of the metal that will form the plating. When an electric current is applied, metal ions in the solution are attracted to the part's surface, depositing a thin metallic coating. Electroplating coats objects with a metal layer to enhance corrosion and wear resistance, change surface friction, improve aesthetics, and more. Typical metals used in electroplating include chromium, nickel, copper, zinc, tin, gold, and silver. Electroplating is widely used in industry and manufacturing for coating parts, auto bodies, jewelry, tools, and more. Its key benefits are its ability to plate objects with uniform coatings quickly and economically.

PVD plating

PVD (Physical Vapor Deposition) is a coating process that applies skinny, high-performance coatings onto parts and products. It works by heating the coating material until it vaporizes and deposits as a thin film onto the coated surface. PVD allows for precise control and can deposit metals, ceramics, and other materials to improve hardness, corrosion resistance, wear resistance, and other properties. It is used across many industries, including tools, automotive, aerospace, medical, and more. Its key benefits include depositing thin, uniform coatings with excellent adhesion while providing attractive finishes. Overall, PVD enables versatile, high-quality coatings for various demanding applications.

Polishing

Polishing is a process that creates a smooth, lustrous surface finish using abrasives. In polishing, an excellent abrasive compound is repeatedly applied to the surface and rubbed in a circular motion. This gradually removes delicate layers of material, smoothing the surface and enhancing reflectivity. A polished surface has minimal roughness and a mirror-like brightness. Polishing is commonly used on metals, glass, and plastics in applications ranging from finishing manufactured parts to restoring clarity to headlights. It provides aesthetic benefits like shine and light reflection while smoothing the surface to prevent contamination buildup and ease cleaning. Polishing is a versatile finishing method that enhances visual appearance and functional performance through controlled abrasion, creating a smooth, glossy surface texture.

Surface Hardening

Surface hardening is a process where only the surface layer of a metal part is selectively hardened while the core remains tough and ductile. Various methods include infusing the surface with carbon or nitrogen, rapidly heating, quenching the surface, and laser melting. This creates a tough, wear-resistant outer layer able to withstand friction, abrasion, and erosion, while the softer core provides strength and shock resistance. Surface hardening is widely used in automotive, aerospace, and manufacturing to selectively reinforce wear-prone areas on metal components like gears, shafts, and bearings. It provides an extended part of life in demanding environments. Overall, surface hardening lets manufacturers optimize strength, hardness, and wear properties in one part.

Powder Coating

Powder coating is an industrial finishing process where a dry powder material is applied to a surface and then cured under heat to form a hard, uniform coating. The powder particles are given an electrostatic charge to stick to the grounded target surface during application. The coated parts are heated to melt and fuse the particles into a smooth, durable film. Powder coating can apply much thicker coatings than conventional painting, providing excellent corrosion resistance, chip resistance, hardness, and durability. It is commonly used to coat metals and is valued for its efficiency and high-quality finish. Powder coating is a versatile industrial method that produces tough, uniform, protective, and attractive coatings.

Tolerances in Investment Casting

Investment casting is capable of delivering excellent, repeatable as-cast tolerances. With as-cast capabilities of +/- three standard deviations when a single point is repeatedly measured—typically +/- .003 to +/- .004 per inch. Part configuration primarily influences tolerance capability and can vary depending on your part design.

Tolerance Capability in the Investment Casting Process

Several factors influence the tolerance capability of the investment casting process. 

- Factors Influencing Tolerance Capability

Part configuration significantly influences tolerance capability. Symmetrical shapes with uniform wall sections solidify with significantly less variation than non-uniform and non-symmetrical wall sections.

- As-Cast Capabilities

The investment casting process can achieve excellent as-cast tolerances, typically +/- .003 to +/- .004 per inch.

Linear Tolerances

Linear tolerances for regular dimensions reflect three sources of variation:

- Prediction of Part and Casting Shrinkage Factors

This accounts for about 20% of the variation in tolerance.

- Diemaker and Tooling Tolerance

This accounts for about 10% of the variation in tolerance.

- Process Variation

This accounts for about 70% of the linear tolerance. The variation in tolerance is a combination of part configuration effects that result in non-uniform shrinkage and all other process variations in producing a wax pattern, ceramic mold, and casting.

Strategies for Achieving Premium Linear Tolerances

All three sources of variation can be reduced by:

- Part Redesign

Including the addition of tie bars, ribs, and gussets.

- Tuning of Wax Injection Tooling

After the first sample meets nominal dimensions.

- Straightening/Coining

- Additional Inspection/Gaging

- Machining

Superior tolerance capability can be achieved but must be considered on a part-by-part, dimension-by-dimension basis. Signicast can hold +/- .002" in some features, although +/- .004" per inch is a more typical premium cast tolerance.

Advantages of the Investment Casting Process

Investment casting offers several advantages:

lost-wax-casting-process-advantages

-Investment castings size range: Investment casting can produce parts of virtually any size, from small to large.

- Versatile and Intricate Shapes: The process allows for producing parts with complex geometries that would be difficult to achieve with other manufacturing methods.

- Accurate and Smooth Surfaces: Investment casting can achieve excellent surface finishes and high dimensional accuracy without additional machining.

- Dimensional Accuracy: The process offers excellent, repeatable as-cast tolerances.

- Quality and Integrity: Investment cast parts have excellent mechanical properties and structural integrity.

Considerations When Using Investment Casting

While investment casting offers many advantages, there are also some investment casting considerations to keep in mind:

- Tooling Cost: The initial cost can be high, especially for complex parts.

- Size Limitations: While investment casting can produce parts of virtually any size, limitations may be based on the foundry's capabilities.

- Very Small Structures: Tiny and intricate structures may be complex to cast accurately.

- Timing: The investment casting process can be time-consuming, especially for complex parts or large production runs.

Conclusion

Investment casting is a versatile manufacturing process that offers many advantages, including producing complex parts with excellent surface finish and high dimensional accuracy. However, it's essential to consider the specific requirements of your project, including the desired material, surface treatment, and tolerances, when deciding whether investment casting is the right choice for you.

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