Is Investment Casting Right for Me? Part 1

Welcome to our “Is Investment Casting Right for Me?” series. In this two part series we will be covering the pros and cons of investment casting, discussing the areas that investment casting is best suited for, and comparing investment casting with other types of manufacture. If you are unfamiliar with investment casting, we also urge to check our “What is Investment Casting?” series where we explain the process from beginning to end. If you are already familiar with the process, this series will help serve as a guide to show when it is most beneficial to use investment casting over other manufacturing processes – as well as cover process specific design for manufacture tips.

This first post in this series will give an overview of general design and economic considerations to take into account when considering investment casting for manufacture of a component.

General Design Considerations

Investment casting is most often used to satisfy the following component characteristics: complex geometry, tight tolerances, and use of high strength alloys. Investment casting allows for contoured surfaces, undercuts, and other features that make machining less than ideal or even impossible. Table 1, shown below, explains how investment casting stacks up against other manufacturing methods from a top level view. In general, for moderate production quantities of complex parts with tight tolerances, investment casting is often the clear choice.

Manufacturing Process Comparison
Alloy Type Investment Casting Machining Sand Casting Die Casting Powder Metallurgy Forging
Tooling Cost 3 5 5 1 2 1
Production Cost 3 1 4 5 5 4
Range of Materials 5 4 4 2 2 3
Surface Finish 4 5 2 3 1 2
Tolerances 4 5 2 3 2 2
Production Volume 4 2 2 5 5 5
Component Complexity 5 4 3 3 2 1
Average 4 3.7 3.1 3.1 2.7 2.4

Table 1: Strengths and weaknesses of common methods of manufacture
5 highest rating – 1 lowest rating

It is best for investment casting to be considered when a component is first in the conceptualization stage so that proper design for manufacture considerations can be incorporated into the design. Existing parts can always be converted to the investment casting process but there are certain considerations that must take place. Working directly with a knowledgeable investment casting supplier can often be the best route in ensuring the design is optimized for the investment casting process; this allows for the least expensive design and shortest lead times.

Suitable alloys for the process include carbon steels, low alloy steels, alloy steels, austenitic stainless steels, ferritic stainless steels, precipitation hardening stainless steels, nickel alloys, cobalt alloys, and tool steels. Materials which are not easily machinable are often excellent choices for investment casting since the process can limit the need for machining or eliminate the need altogether. Table 2 below shows some commonly used alloy types which are often used in investment casting. Although the list in Table 2 is not exhaustive, it provides a great reference for the most common types of alloys used in the investment casting process. If you are unsure if your alloy is right for the investment casting process, ask us! We are happy to help.

CobaltCobalt AlloysCobalt AlloysCo-3Co-4Co-6Co-12Co-31Co-93NickelNickel AlloysNickel-Copper AlloysM35-1Monel AMonel BMonel DMonel SMonel E

Alloy Capabilities
Base Category Sub-Group Examples of commonly used Alloy types
Ferrous Carbon Steels Low Carbon Steels 1010 1020 1025
Medium Carbon Steels WCB 1030 1035 1045 1050
High Carbon Steels 1060 1090 1095
Low Alloy Steels Chromium Steels 52100
Chromium-Molybdenum Steels 4130 4140 4150
Nickel-Molybdenum Steels 4620
Chromium-Vanadium Steels 6150
Nickel-Chromium-Molybdenum Steels 4330 4340 8620 8630 8640 8650
High Alloy Steels
(Stainless Steels)
Austentic Chromium-Nickel Steels 302 303 304/304L 309 310 316
Ferritic Chromium Steels 409 431 436 439
Martensitic Chromium Steels 410 416 420 431 436 440A
Duplex Steels CD-4MCu CD3MN $50 $50 $50 $50
Precipitation Hardening Steels 15-5 17-4
Tool Steels Air Hardening Steels A-2 A-6 H-11 H-13 H-43 T-1
Oil Hardening Steels D-2 D-3 0-1 0-2 M-2 M-42
Water Hardening Steels S-1 S-4 S-5 S-7
Cobalt-Chromium Alloys F-75 FSX 414 N-155
Nickel-Chromium Alloys Alloy B Alloy C Alloy X CW-2M Alloy 625

Table 2: List of commonly used alloy types for investment casting
*Examples listed are commonly used types and not an exhaustive list of all of TPC’s capabilities.

Economic Considerations

Investment casting is best suited for low to medium production quantities but can also be a great candidate for high volume components whose features would otherwise be limited by other manufacturing processes. Very small quantity production runs are also made possible with the application of rapid prototyping services. Though expensive for high quantities, 3D printed rapid prototypes can be a powerful tool for small, sample piece orders. Once the rapid prototypes have been generated they will follow the exact same process as a typical wax injected pattern.

Tooling costs for investment casting can be quite low when compared to other high production methods. Due to the properties of the wax which is used to create the patterns during injection, aluminum can be used as the base material for tooling. The ability to use aluminum for the tooling greatly reduces the machining cost during tooling manufacture. Although aluminum tooling is used, the life of investment casting tooling can be quite long and can often be repaired rather than replaced when it does become worn out. Investment casting dimensions will not change as the tool ages – allowing buyers a peace of mind once First Article Inspections or Production Part Approval Processes have been approved.

Due to high labour and consumable material costs, investment casting piece prices can be quite high when compared to other high production methods such as powder metallurgy and die casting; however, the flexibility of investment casting often allows buyers to better reach their bottom line. Buyers are able to simplify their design and reduce the number of components required to achieve their desired function or performance by utilizing investment casting’s ability to produce high strength alloys and complex geometries that other processes simply cannot recreate. The ability for investment casting to create net shape or near-net shape components can also remove secondary operations such as machining and welding, saving buyers in both lead time and cost.

The above sections give an overall summary for general design and economic considerations for investment casting. Please be sure to check back for our next post in the “Is Investment Casting Right for Me?” series where we will cover the design considerations in greater detail. Thanks for reading; we hope you have learnt something.