Lost Wax Investment Casting 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 foam 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.

Investment Casting Capacities and Cast Metals at Densen Group 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 parts with 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, 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: Hastelly-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

• Tolerances: CT4~CT8 or on request according to ISO 8062.

Densen Group 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.

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.