Lost Wax Investment Casting Foundry | Stainless Steel Foundry

Investment casting, also known as lost wax casting or precision casting, is a process that has been practiced for thousands of years, with the lost wax process being one of the oldest known metal forming techniques. Investment casting is a manufacturing process that can be traced back over 5,000 years ago. From then, when beeswax formed the pattern, to today's high technology waxes, refractory materials and special alloys, the lost wax castings ensure high quality components are produced with the advantages of accuracy, repeatability, and integrity.

Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused.

Lost Wax Investment Casting Foundry

Lost Wax Investment Casting Foundry

Investment Casting Capacities and Cast Metals at RMC Casting Foundry

The metals which can be used for investment casting include low carbon steel, medium carbon steel, alloy steel, stainless steel, duplex stainless, brass, bronze and other metal or their alloys. RMC's investment casting foundry is capable of meeting a wide variety of alloys material specifications according to ASTM, SAE, AISI, ACI, DIN, EN, ISO, GOST and GB. We have more than 100 different ferrous and non-ferrous alloys with which we cast parts using complex design structure. Due to the complex structure in dimension and geometric, the investment castings are produced to net shape or near net shape, minimizing the need for secondary processes such as lathing, turning or other machining process.

Lost wax investment casting can reach dimensional tolerance grade CT 5-7 according to ISO 8062. Our fully organized equipment and automation process controls allow for consistent and repeatable tolerances as close as ±0.1 mm. The lost wax casting parts can also be produced in a wide size range, they may be as small as 10 mm long x 10 mm wide x 10 mm high and weigh as little as 0.01 kg, or as big as 1000 mm in length and weigh as much as 100 kg.

Lost wax casting processed can produce steel casting partswith good surface quality, less surface defects, high accuracy in dimensions, small but complex structure with thin wall thickness. However, the cost per unit piece of investment casting would be comparatively higher than sand casting, lost foam casting and vacuum casting processes. Generally speaking, the lost wax investment casting with water glass as shell bond is about 1.2-1.7 times of sand casting, and the lost wax casting with silica sol as shell bond is about 1.5-2.5 times of water glass castings, by weight per kilograms, depending on the structure and size of the desired casting parts.

Lost Wax Investment Casting Metals
  • Carbon Steel:  from Low Carbon Steel to High Carbon Steel, AISI 1020  - AISI 1060,
  • Alloy Steel: ZG20SiMn, ZG30SiMn, ZG30CrMo, ZG35CrMo, ZG35SiMn, ZG35CrMnSi, ZG40Mn, ZG40Cr, ZG42Cr, ZG42CrMo...etc on request.
  • Stainless Steel: AISI 304, AISI 304L, AISI 316, AISI 316L, CF8M, CF8, 1.4408...etc. Precipitation Hardening Stainless Steel and other stainless steel grade.
  • Duplex Stainless Steel: 1.4460, 1.4462, 1.4468, 1.4469, 1.4517, 1.4770, 2205, 2507.
  • Nickel Base Alloys: Hastelloy-C, Inconel 625 etc.
  • Cobalt Base Alloys. 
  • Brass, Bronze & Copper based alloys.
  • Gray Cast Iron, Ductile Cast Iron, Aluminium alloy and other ferrous and non ferrous metals on request

Capabilities of Lost Wax Investment Casting  
  • Max Size per Casting: 1,000 mm × 800 mm × 500 mm
  • Weight Range: 0.01 kg - 100 kg
  • Annual Capacity: 2,000 tons
  • Binder Materials: Silica Solution (Silica Sol), Water Glass (Sodium Silicate) or their mixtures
  • Casting Tolerances: CT4~CT8 or on request according to ISO 8062.

RMC is a leading precision casting foundry in China of top-quality investment castings committed to delivering excellent quality, superior value and exceptional customer experience. RMC has the experience, technical expertise and quality assurance processes to consistently and reliably deliver an extensive range of precision castings with further processing.

shell making for investment casting

Shell Making

Wax Patterns

Wax Patterns

Shell Drying

Shell Drying

Shell Drying

Shell Drying for Investment Casting

Steps of Lost Wax Investment Casting Process

Investment casting is a multi-step process that produces near-net shape precision casting parts. The process begins with wax being injected into a die to create a replica pattern of the finished product. The patterns are then affixed to wax runner bars to create the cluster. A special machine dips the cluster repeatedly into a slurry to develop a ceramic shell, and then the wax is removed in a steam autoclave. Once the wax is removed, the ceramic shell is preheated and then filled with molten metal to create the desired castings.

Investment casting requires a metal die (usually in aluminum), wax, ceramic slurry, furnace, molten metal, and other machines needed for wax injection, sand blasting, vibratory tumbling, cutting, and grinding. The lost wax investment precision casting process mainly involves the following steps:

1- Metal Die Making 
Based on the drawings and requirements of the desired casting parts, the metal die or mold, usually in aluminum, will be designed and produced. The cavity will form the same size and structure of desired castings, under the premise of considering the machining allowance.

2- Wax Injection
Also as known as pattern formation, lost wax casting patterns are created by injecting molten wax into the metal die produced in last process. The special wax injextion machines should be used for this process

3- Slurry Assembly
After fixing (if needed), the wax patterns are then attached to a gating system, which usually is a set of channels through which a molten metal flows to the mold cavity. After that, a structure like a tree is formed, which is suitable for mass casting at the foundry.

4- Shell Building
The investment castings outer shell casing is built up through dipping into a ceramic bath and then immediately coated with sand for several times. The process is usually repeated for many times and last for days in order to make sure the shell strong enough to withstand the molten metal later on.

5- De-waxing
The inner cavity of precision investment casting is then dewaxed, which leaves a hollow outer ceramic shell layer. The hollows are just the same space as the desired castings. During this process, the wax could be collected for re-usage.

6- Pouring & Solidification
Before pouring, the ceramic shell with cavity should be pre-heated. This prevents shock and the ceramic shell from cracking once the liquid metal at a high temperature is poured into the cavity. The chemical composition of the molten metals should also be tested before casting.

7- Sawing or Cutting
Once the molten metal has been cooled and solidified, the cast part(s) is then removed from the gating system tree cluster via shaking, cutting or friction sawing off the individual raw casting.

8- Shot Blasting and Secondary Processing
The casting part is then fully customized through grinding or additional heat treatments. Secondary machining or surface treatment might also be required depending on the requirements of the part.

9- Packing and Delivery
Then the lost wax casting parts will be fully tested for the dimensions, surface, mechanical properties and other required tests before packing and delivery.

Wax Patterns for precision casting

Wax Patterns

Shell Building for lost wax casting

Shell Building

Casting Mold pre-heating

Mold Pre-Heating

Lost wax casting parts

Stainless Steel Precision Castings

Casting Molds Warehouse

Casting Molds Warehouse

Wax Patterns Injection

Wax Patterns Injection

Wax Patterns Injection Machine

Wax Patterns Injection

Wax Injection Machine

Wax Injection Machine

Wax Patterns

Wax Patterns

Wax Replica for Investment Casting

Wax Replicas

Lost Wax Casting Wax Patterns

Wax Patterns

Shell Making

Shell Making

Shell Drying

Shell Drying

Shell for Pouring

Shell for Metal Pouring

Cooling and Solidification

Cooling and Solidification

Raw investment castings of stainless steel

Raw Casting before Cleaning and Shot Blasting

Applications of Precision Investment Castings

Components made by investment casting are utilized to cast a wide variety of items, including high quality, high performance industrial parts of complex structures.

The application of the precision investment casting (lost wax casting process) components covers a wide range of industries, in our foundry they are typically used in the following areas (including but not limited to):

Value-added Services of Lost Wax Casting

There are several reasons to choose RMC's foundry as your source for investment castings, including:

  • Engineering team whose members are focusing on metal casting field.
  • Extensive experience with investment castings of complex geometries
  • A broad range of materials, including ferrous and non-ferrous alloys
  • In-house CNC machining capabilities
  • One-stop solutions for investment castings and secondary process
  • Consistent quality guaranteed and continuous improvement.
  • Teamwork including toolmakers, engineers, foundryman, machinist and production technicians.

RMC's foundry has more than 20 years of experience in precision investment casting. Request a quote today on lost wax castings for your precision parts, or contact us for more information.

More Information You Want to Know About Investment Casting

Investment casting, which is also known lost wax casting or precision casting, refers to the formation of ceramic around the wax patterns to create a multi or single part mold to receive molten metal. This process utilizes an expendable injection molded wax pattern process to achieve complex forms with exceptional surface qualities. To create a mold, a wax pattern, or cluster of patterns, is dipped into ceramic material several times to build a thick shell. De-wax process is then followed by the shell dry process. The wax-less ceramic shell is then produced. Molten metal is then poured into the ceramic shell cavities or cluster, and once solid and cooled, the ceramic shell is broken off to reveal the final cast metal object. Precision investment castings can achieve exceptional accuracy for both small and large casting parts in a wide range of materials.

✔ Excellent and smooth surface finish

✔ Tight dimensional tolerances.

✔ Complex and intricate shapes with design flexibility

✔ Capability to cast thin walls therefore a lighter casting component

✔ Wide selection of cast metals and alloys (ferrous and non-ferrous)

✔ Draft is not required in the molds design.

✔ Reduce the need for secondary machining.

✔ Low material waste.

During the investment casting process, a wax pattern is coated with a ceramic material, which, when hardened, adopts the internal geometry of the desired casting. In most cases, multiple parts are cast together for high efficiency by attaching individual wax patterns to a central wax stick called a sprue. The wax is melted out of the pattern – which is why it is also known as the lost wax process – and molten metal is poured into the cavity. When the metal solidifies, the ceramic mold is shaken off, leaving the near net shape of the desired casting, followed by finishing, testing and packaging.

Investment castings are widely used in pumps and valves, automobile, trucks, hydraulics, forklift trucks and many other industries. Because of their exceptional casting tolerance and exellent finish, the lost wax castings are used more and more. Especially, the stainless steel investment castings play a vital important role in the shipbuilding and boats because they have strong anti-rust performance.

According to the different binder materials used for making the shell, the investment casting could be divided into silica sol casting and water glass casting. The silica sol investment casting process have better Dimensional Casting Tolerances (DCT) and Geometrical Casting Tolerances (GCT) than water glass process. However, even by same casting process, the Tolerance Grade will be different from each cast alloy due to their various castability. Our foundry would like to talk with you if you have special request on the required tolerances. Here in the following are the general tolerances grade we could reach both by silica sol casting and water glass casting processes separately:

✔ DCT Grade by Silica Sol Lost Wax Casting: DCTG4 ~ DCTG6

✔ DCT Grade by Water Glass Lost Wax Casting: DCTG5 ~ DCTG9

✔ GCT Grade by Silica Sol Lost Wax Casting: GCTG3 ~ GCTG5

✔ GCT Grade by Water Glass Lost Wax Casting: GCTG3 ~ GCTG5.

Almost most of the ferrous and nonferrous metal and alloys could be cast by investment casting process. But, at our lost wax casting foundry, we mainly cast the carbon steel, alloy steel, stainless steel, super duplex stainless steel, gray cast iron, ductile cast iron, aluminium alloys and brass. Additionally, certain applications require the use of specialized other alloys used primarily in harsh environments. These alloys, such as Titanium and Vanadium, meet the additional demands that might not be achieved with standard Aluminum alloys. For example, Titanium alloys often are used to produce turbine blades and vanes for aerospace engines. Cobalt-base and Nickel-base alloys (with a variety of secondary elements added to achieve specific strength-strength, corrosion-strength and temperature-resistant properties), are additional types of cast metals.

Yes, we could provide the 3.1 material certificate if you request.

The investment casting is also called precision casting because it have much better surface and higher accuracy than any other casting process. Especially for the silica sol casting process, the finished castings could reach the CT3 ~ CT5 in geometrical casting tolerance and CT4 ~ CT6 in dimensional casting tolerance. For the casings produced by investment, there will be less or even no need to make the machining processes. To some extent, the investment casting could replace the rough machining process.

The investment casting gets its name because the patterns (wax replicas) is invested with the surrounded refractory materials during casting process. The "invested" here means being surrounded. The wax replicas should be invested (surrounded) by the refractory mateials to withstand the high temperature of the flowing molten metals during casting.