Investment Casting Process
Ningbo Investment Casting Co., Ltd carries out strict quality control process, has established strict standards for material inspection, process control, finished goods inspection, evaluation and selection of audited suppliers. We pay closer attention to each production links, and formulate the optimized technology by process design and analysis.
For our investment casting, most metals are available. We can cast the materials of carbon steel, alloy steel, high chromium iron, high manganese steel, heat-resistance stainless steel and general stainless steel etc. We can customize investment casting parts as per our customers’ material specifications, and do chemical analysis as per customer’s sample by spectrometer is feasible for production.
We’ll do strict quality control in each investment casting process to ensure the quality. Below is our investment casting foundry’s whole process:
1. Investment Casting Tooling Production
To make a casting tooling is the first step to start investment casting process. We’ll make a 3D model as per customer’s drawing, with our tooling director’s approval to proceed with tooling or pattern production by CNC mold maker. Usually, the tooling cost will be prepaid with order and we could provide 3-5 samples for customers’ approval prior to placing mass production order. It’s just one-off paid, we’ll not ask for the tooling fee for our future orders, and we’ll repair the tooling or pattern by ourselves if there are any problems of the investment casting tooling. Before the tooling or pattern service in the investment casting process, it will be fully inspected by our QA person. Please see below photos:
Process & Tooling Design
2. Wax Injection
The second step in investment casting is to produce a wax replica of the desired part. This is typically accomplished by injecting wax into an aluminum die cavity. The process utilizes a sacrificial pattern with the same details as the finished part, except that there is an allowance for thermal contraction (shrink). We will repeat the wax injection job for more wax patterns. The wax patterns will be more than order quantity in case of any rejects during investment casting process.
After wax injection, the wax replica is removed from the injection tool. The wax patterns are cleaned the excess rough edges, inspected for tolerance and then cleaned for assembly.
Wax Pattern Inspection
Wax Pattern Repair
3. Wax Pattern Assembly
Wax replicas also called wax patterns are “wax welded” to a central sprue or cluster to facilitate pouring, looks like a “wax tree”. To form the gate and runner metal delivery system. Finally hang these pattern assemblies in the room temperature for drying. Many replicas are attached to sprues for increased efficiency, and the reasonable quantity attach in the sprue could ensure the castings quality and save cost. Depending on the size and configuration of the desired finish component, multiple wax patterns may be processed using a single tree.
4. Shell Building
The assembled sprue is then dipped or “invested” in into ceramic slurry. After draining, the sprue is then coated or “stuccoed” with fine ceramic sand also called refractory material. This process is repeated several times using progressively coarser grades of ceramic material until reaching or to “build” sufficient “shell” thickness and strength, which is sufficiently strong to retain the molten metal during casting. Thus, the ceramic shell is built and then dried in an atmospherically-controlled environment.
Automic Shell Building
5. Wax Removal
The entire shell built sprue is placed in a steam autoclave to melt away most of the wax through the gate and pouring up under high temperature.
After autoclaving, the ceramic shell molds must be fired in furnace to burn out the remaining amount of wax that soaked into the ceramic shell. At this point, all of the residual wax pattern and gating material has been removed, and the ceramic mold remains with a cavity in the shape of the desired cast part.
This high temperature operation also increases the ceramic material strength and stability. In addition, it helps to minimize reaction of the shell and metal during pouring. The temperature range is 1600-2000 degrees Fahrenheit. That’s why the Investment Casting is also called Lost Wax Casting.
6. Melt and Pouring
Cast pouring is the key step in the whole investment casting process. After de-waxing, the mold is preheated to a specific temperature in preparation for casting. The other reason for this process is to remove the rest moisture in the shell for a better surface after casting. We will melt the steels into liquid status, and pour the liquid metal into the sprue, then cool it under room temperature. Nearly most of carbon steel, alloy steel, high chromium iron, high manganese steel, heat-resistance stainless steel and general stainless steel can be produced by using this process. Either air melting or vacuum melting may be employed as dictated by the alloy chemistry.
Before the molten metal is poured into the shell, we’ll do chemical composition analysis to ensure the correct range of the metal.
Melting and Pouring
7. Knock Out and Sand Cleaning
When the casting has cooled sufficiently nearly to room temperature, the ceramic shell will be knocked out and broken way from the casting. The gates and runners will be cut, and the individual investment casting parts will be got from the sprue. Finally remove the excess metal from casting body by grinding.
8. Heat Treatment
To improve the mechanical properties of casting blank parts, heat treatment is usually done. However, we’ll do heat treatment only when customers have such requirements in the drawings or production specifications, and the extra cost will be charged by customer when quoting. Main heat treatment processes are: Normalizing, Tempering, Annealing, Quenching and tempering, carburizing and etc.
9. Shot Peening
To remove the rest surface sands, scales, oxide skins and achieve a better surface finish, investment casting parts will be shot blasted by tiny steel balls or sand blasted. To service our several sets of casting lines, our foundry is equipped with 6 shot blasting machines.
In order to provide finished parts to our customers as per their drawings, our foundries was equipped with machining capacity, to help our customers save time and cost.
11. Inspection and Quality Control
Inspection is also a necessary and important step to ensure the high quality of the investment casting parts. Our QC engineers will implement destructive and non-destructive tests, including dimensional inspection, 100% visual inspection, chemical analysis, mechanical properties test, metallographic observe, hardness test, MPI, LPI, UT test and etc. All the parts are qualified and all reports are verified prior to shipping. Sometimes, the specified testing requirements are determined by our customers’ quality level, so we do the inspection jobs according to the service condition of the investment casting parts. We are also co-working with international third-party testing labs to make sure all our customers’ requirements are satisfied.
Most of our investment castings are exported to overseas, so normally we will pack the casting parts into big bags to protect products from rusting on the sea, and then put them into a suitable plywood case or steel case, and others which is determined by customer. With our rich experience from the year of 1983, all of the packages must be carried out on the basis of free from damage during shipping. We can also supply customize package according to customers’ special requirements.