Investment casting (lost-wax casting) is a manufacturing method used for producing very complex shapes of metallic parts and provides excellent dimensional tolerances/surface finish. Over the last 20 years, India has emerged as a worldwide investment casting hub for OEMs within the automotive, aerospace, oil & gas, pumps & valves, medical devices, defense, railways, and general engineering sectors.
This article will highlight why Indian foundries are competitive, what capabilities, quality and certification standards to expect, and a practical checklist when procuring suppliers.
Why India for Investment Casting?
Cost-effectiveness without compromising quality
Investment casting foundries India can offer low prices because of cheap labour, large production volume, and established supply chains for wax patterns, ceramic shells, or alloys. Plenty of foundries work as an integrated plant—in that they have tooling for pattern, casting, heat treatment, machining and finishing in-house—which limits hand-off and logistics losses.
Skilled engineering talent
Advanced process control/perpetual improvements, a deep pool of metallurgists, production engineers, toolmakers and CNC machinists. Many foundries keep a toolroom in-house to facilitate quickest pattern creation and quick design changes.
What the Process Looks Like
The investment casting process comprises a number of precisely and methodically controlled steps to produce components that are as accurate and reliable as intended. Each investment casting process begins with tooling and wax pattern, where aluminum or steel dies and even 3D printing can make exact representations of the required parts from wax patterns. Wax patterns can then be assembled into a tree, and the investment casting process then proceeds to shell building, where the wax patterns undergo a series of dips in a ceramic slurry to build up a strong and refractory ceramic shell. Once the wax is melted out, the shell is dewaxed. It is then fired to achieve a level of strength before it is ready to receive the molten alloy during the pouring phase, using gravitational, or vacuum assisted depending on the alloy requirements. After the alloy has solidified, it proceeds through knockout, cut-off and finishing, where the ceramic shell is removed and then gates and risers separated and dressed. In some cases, components may be heat treated or hot isostatically pressed (HIP’d) to attain the required mechanical properties; more critical aerospace or energy related components may be subjected to this. After finishing, the parts will be precision machined using CNC technologies in order to produce tight tolerances and to reach final specifications. It is at this point that the components will be examined, and validated. Each part is examined using CMM, various non-destructive testing methods, spectrochemical analysis where relevant, mechanical testing, and surface quality assessments. This would be part of the pay-off to guarantee part performance and compliance.
Typical Capabilities and Tolerances
Investment-casting foundries in India possess a broad range of capabilities based on the different requirements mandated by industry. Components can be anything from small micro parts with a mass of 5 grams to castings over 50 kilograms, depending on the experience of the supplier. Finishing and mastering investment-casting technologies consistently provide outstanding surface finishes (Ra 3.2–6.3 μm) with the possibility of finer results from alloy selection and optimization of the investment-casting process. Dimensional accuracy allows tolerances of ±0.1–0.3 mm and GD&T tolerances can be verified depending on process control and machining. Parts can be complex geometries with no pattern having relatively thin wall sections that are theoretical possibilities of 1.5–2.5 mm. This makes it an ideal process, and with a lightweight, high-strength potential. Foundries can facilitate everything from a prototype run to full volume production, allowing customer scalability. More importantly, many suppliers offer value-added services such as heat-treatment, passivation, surface finishing, plating, coating, assembly, and some testing with options to allow turn-key solutions for global industries.
Industries and Applications
The investment casting foundries of India not only furnish a multitude of industries, but also fulfill the need for precision engineered parts across important applications. Castings for automotive and commercial parts can include turbocharger wheels, various transmission parts, steering knuckles, brackets and critical safety items like seat belt and airbag hardware. Various components for the pumps and valves sector are also produced by foundries, such as impellers, casings and discs made from corrosion-resistant alloys to survive demanding environments for service performance. A variety of flow-control components, downhole tools, fittings, and safety-critical hardware are produced for oil & gas, and petrochemical industry investment castings. With the necessary certifications and regulations, Indian suppliers will also meet similar needs for aerospace and defense parts manufacturing – specifically structural brackets, actuators and turbine components. Certain certified foundries will also source conforming materials or manufacturing standards required for medical applications – such as orthopedic implants and surgical instruments made from either stainless steels or Co-Cr alloys. For both food and pharmaceutical components, hygiene standards are met and followed with products such as hygienic fittings and clamped fitted from 316L stainless steel with polished finishes.
Quality Systems You Should Expect
Top investment casting foundries in India employ tough quality assurance systems, that are compliant with recognised objectives. They are certified with ISO 9001, IATF 16949 for automotive application and as required with AS9100 for aerospace, providing customers with the industry-specific requirements compliance*. In terms of material control, heat-wise traceability, purchase order based spectrometer chemical analysis, and melters with certified processes means these companies operate with solid control over their raw material inputs. The suppliers’ process control is well-documented and spans a variety of controls influence by tamper-proof SOP’s such as statistical process control (SPC), monitored pouring parameters regarding shell integrity, etc. Each part is subjected to inspection and testing, including dimensional verification using CMM, non-destructive testing (NDT) techniques such as dye penetrant inspection (DPI), magnetic particle inspection (MPI) ultrasonic testing (UT) and radiographic testing (RT) metallographic property tests, and mechanical property tests. In addition, the documented assurance and reliability process includes a variety of documents via a production part approval process (PPAP), control plan, failure modes and effects analysis (FMEA), measurement system analysis (MSA) studies, and a full test certificate for every batch to ensure our customers can be confident in the reliability of the product s.
Cost Drivers and How to Optimize
There are several factors which affect the overall cost of investment casting, which can help manage both design and price, if understood. Tooling complexity is important; tooling costs can rise with complex tooling, multi-slide dies, and/or very intricate features and tight tolerances. In addition, tooling complexity and cost is important; consideration should be given to modular tooling when under tight budgets and DFM reviews should be used for purchasing efficiencies. The choice of alloy also affects cost; nickel- and cobalt-based alloys risk added cost, but often for ceramic shells and/or vacuum melting. Good yield is achieved through early consideration of yield and gating. Simulation has shown opportunities to reduce rework, and scrap, to drop overall cost. The workload required for machining also can be reduced through establishing near net shape features, as well as ensuring that stock allowances were consistent with machining allowance, thus reducing cycle times and increased productivity. Surface requirements also often risk additional steps and costs, such as mirror polishing; electropolishing and/or specialty coatings. Stainless steel is often poorly priced when given and requires extensive finish specifications. Therefore, when building specifications and design requirements, ensuring that finish requirements were based strictly on functional needs is best.
How to Select an Indian Investment Casting Partner
The process of identifying an investment casting foundry in India requires an evaluation process to ensure the company provides the type of performance and quality that is needed, so that a long-term partnership can be obtained. To help facilitate this evaluation process for a supplier, the buyer should match the certifications to the buyer’s sector. There are numerous certifications that a casting company can achieve, including IATF 16949 for automotive and AS9100 or NADCAP for aerospace and defense applications. Certification will reduce the risk of poor quality. Quality would incorporate all aspects of the supply chain in terms of design and inputs, compliance, track-and-trace, supplier history, sustainability, and hazards, etc. Then assess the end-to-end capabilities of the supplier, which could be in-house tooling, heat treatment, machining, non-destructive testing (NDT), etc. Multiple processes in-house facilitates faster lead-times and more accountability; therefore helps the partnership between the buyer and supplier.
In addition to identifying the supplier and certification, the buyer should review the same or similar case studies and a production part approval process (PPAP) sample report with a dimensional report(s), Cp/Cpk and stability reports, etc., to help assess the suppliers performance and consistency. An audit on the workflow of process controls should ensure that there is a standard process, and an understanding of the process controls in wax handling, shell building, pouring, and melting of materials. Buyers should ensure that metallurgy expertise is in place for selecting materials, heat treat designs, and failure analysis. The buyer should develop their own traceability and compliance system, which may include heat-to-part records, bar coding, and using digital QMS for compliance. Engaging in a design-for-manufacturing (DFM) review with suppliers early-on can help identify thin-wall risks which can save time and costs in unnecessary expenses. Before engaging in full production, the buyer can conduct a pilot run with appropriate NDT and functional testing to validate tooling and systems to mitigate potential downstream issues.
When Investment Casting is the Right Choice
When your part requires very complex geometry, very thin walls, very tight tolerances, very good surface finish, and material freedom, such as when machining from solid would be substantially wasted, or when you can consolidate many machined parts into one cast part, choose investment casting. Investment casting allows you to discover high-temperature, corrosion-resistant, or wear-resistant alloys and shapes that would be too difficult or uneconomical to make by other methods.
