Advertisement

Responsive Advertisement

what is investment casting, it's process, advantages and disadvantages


INVESTMENT CASTING:

Principle      
Method also called as precision investment casting. The method involves the use of expendable Pattern with a shell of refractory material surrounded to form a casting mould. Since the pattern made up of wax is melted out and gets destroyed. That is why the name-"Lost wax method"

Size limits -As small as (1/10) inch but usually less than 10 lb.
Thickness limits -As thickness as 0.025 inch but less than 3 inch.
Typical tolerance -Approximately 0.005 inch.
Draft allowance -Not required.
Surface finish -50 to 125 micron

PROCEDURE:
1. Produce a master pattern
The pattern is a modified replica of the desired product made from metal, wood, plastic, or some other easily worked material.

2. From the master pattern, produce a master die
This can be made from low-melting-point metal, steel, or possibly even wood. If low-melting-point metal is used.

3. Produce wax patterns
Patterns are made by pouring molten wax into the master die, or injecting it under pressure, and allowing it to harden. Plastic and frozen mercury have also been used as pattern material.

4. Assemble the wax patterns onto common wax sprues
The individual wax patterns are attached to a central sprues and runner system by means of heated tools and melted wax. In some cases, several pattern pieces may first be united to form a complex.

5. Coat the cluster with a thin layer of investment material
This step is usually accomplished by dipping the cluster into a watery slurry of finely ground refractory material.

6. Produce the final investment around the coated cluster
After the initial layer is formed, the cluster can be re dipped, but this time the wet ceramic is coated with a layer of sand and allowed to dry. This process can be repeated until the investment coating is the desired thickness (typically 5 to 15 mm)

7. Allow the investment to fully harden






8. Melt or dissolve the wax pattern to remove it from the mould
This is generally accomplished by placing the moulds upside down in an oven, where the wax melts and runs out, and any residue subsequently vaporizes.

9. Preheat the mould in preparation for pouring
Heating to 550 to 1100°C (1000 to 2000°F) ensures complete removal of the mould wax, curves the mould to give added strength, and allows the molten metal to retain its heat and flow more readily into all of the thin sections.

10. Pour the molten metal
Various methods, beyond simple pouring, can be used to ensure complete filling of the mould, especially when complex, thin sections are involved.

11. Remove the casting from the mould
This is accomplished by breaking the mould away from the casting. Techniques include mechanical vibration and high-pressure water.

Advantages:
i) Smoother surfaces (1500 to 2250 µm rms).Close tolerance (of +0.003 mm/mm)
ii) High dimensional accuracy
iii) Intricate shape can be cast
iv) Castings do not contain any disfiguring parting line
v) Machining operations can be eliminated

Disadvantages:
i) Process is relatively slow
ii) Use of cores makes the process more difficult
iii) The process is relatively expensive than other process
iv) Size limitation of the component part to be cast. Majority of the castings produce weight less than 0.5 kg.

Post a Comment

0 Comments