1.Title of the invention
Controlled Solidification of Aluminium Alloy Investment Casting

2. Field of Invention

The present invention relates to improving mechanical properties through controlling the solidification rate and direction based on the product during solidification of molten aluminum metal in the ceramic shell during investment casting process.

3. Background of invention

Investment castings are typically used to produce parts having complex shapes that are cost prohibitive to produce by other casting methods or which cannot be made by other methods such as sand or permanent mold casting. AI-7%Si-0.3%Mg and AI-7%Si-

0.6%Mg alloy are high strength aluminium alloys widely used for aeronautical and automotive structural parts using investment casting route. During the investment casting process, molten metal is poured into a pre-heated ceramic shell mold. A known characteristic of the ceramic shell mold used in investment casting has slow solidification. Slow solidification produces a coarse and heterogeneous casting microstructure. This leads to low mechanical properties, i.e., yield strength, tensile strength and elongation.

Hence,' there is a need to improve mechanical properties of these alloys as these cannot be replaced with other alloys in view of considerable weight savings obtained by these alloys. Therefore,.a process needs to be designed/ developed, so as to improve the solidification rate and direction during pouring of the molten metal into the ceramic shell, which could result in finer Dendritic Arm Spacing (DAS), thereby improving the mechanical properties.

Based on the literature and market survey, it was found that there are two proprietary and one patented technologies as listed below are available which can improve the mechanical properties of aluminum alloy investment castings.

1. Hero Process

2. SOFIA Process

3. Patent: Rapid Solidification Investment Casting by Hamilton Sundstrand Corporation, Rockford, IL (US), US 6,622,774 B2, 23.9.2003.

However, these technologies involve huge capital and highly proprietary in nature. Hence, there was a need to establish a low cost and indigenous development of this technology within India. This led to the below mentioned invention. /[)

4.
Summary of the present invention
‘Solidification Chamber’ was designed and fabricated with a provision for filling up of quenching medium (to be pumped through pumps-1 & 2 from ‘reservoir’) from the bottom of the chamber filling upwards. Once the pouring of molten metal is completed in the ceramic shell, which is placed inside the solidification chamber through a 'sliding ceramic mold holder’. 'Pump -1 (high) and -2’ (low) are of different capacity so as to cover faster as well as medium solidification rates respectively. Post solidification/ cooling of casting inside the ceramic shell, quenching medium to be pumped back into the reservoir through a return pump (‘pump-3’).

An electronic ‘control panel’ placed in front of the reservoir (and next to solidification chamber) is used for controlling the ‘quenching medium’ level, speed at which quenching medium rises inside the chamber during solidification.

The solidification Chamber consists of four ‘sensors’, three of which senses the level of quenching medium during the operation of system. The fourth sensor records the temperature of the quenching medium inside the solidification chamber. The three level sensors are placed at ‘Top', ‘Middle’ and ‘Bottom’ of the solidification chamber. The purpose of these three sensors are explained as follows:

a) Top Sensor: Used to stop the quenching medium pumping from reservoir to solidification chamber. It is a fixed position sensor, usually placed just below the rim of the solidification chamber to avoid overflow of quenching medium.

b) Middle Sensor: This is a height adjustable sensor. It is used for setting the initial level of quenching medium before the pouring of molten metal into the shell. The sensor is usually placed at a level, just below the bottom of the ceramic shell. The location of the middle sensor needs to be adjusted based on the height of the ceramic shell during the casting process. The level of quenching medium in the solidification chamber can be visually observed through a glass indicator with fixed scale, which is placed between solidification chamber and control panel. The middle sensor level can be adjusted manually (through a sensor level with a fixed scale) based on the level in the glass indicator with fixed scale.

c) Bottom Sensor: It is used to stop the draining of the quenching medium to the reservoir post solidification/ cooling of casting in the ceramic shell. This is usually placed at the bottom of the solidification chamber.

The purposes of three Pumps (identified as 1,2 & 3) are as indicated below.

Pump-1: Motor of higher rating for achieving higher solidification rate during casting. Usually used for pumping quenching medium from middle level to top level just after the pouring of molten metal into the ceramic shell.

Pump-2: This motor is usually used for pumping quenching medium from bottom level to middle level before the placement of hot ceramic shell, which is to be transferred from shell heating furnace to the solidification chamber.

Note: Motor of lower rating may also be used for achieving moderate solidification rate during casting. In such case, the connections to the Pump-1/2 to the solidification chamber to be manually interchanged. In such instance of interchange, purpose of Pump-1 and 2 will also alter/reverse as explained above.

Pump-3: It is used for draining out of quenching medium from solidification chamber to reservoir.

Note: The entire set-up of reservoir/ pumps/ solidification chamber with level indicator/ control panel are placed on a platform. Further, the entire set-up to be kept at a location as close as possible to the shell heating furnace and melting furnace to avoid any time delays in withdrawing the ceramic shell from shell heating furnace solidification chamber and transferring molten metal from melting furnace to solidification chamber.

5. Brief description of drawings

Fig.1 schematically illustrates the views depicting all the components explicitly.
Reference Numerals Description
1 Reservoir
2 Solidification Chamber
3 Pipelines, fittings, valves
4 Platform
5 Control panel
6 Level indicator for solidification chamber
7 Pump-1

6. Detailed description of invention

Controlled Solidification of Aluminium Alloy Investment Casting (CSA1C) system is designed for controlled solidification rate and direction for Al-Si-Mg alloy for investment casting products.

CSAIC system is a movable setup fixed on a platform. The main function of this system is to control the solidification rate through controlling the rate of rise of quenching medium. Quenching medium is stored in the reservoir and pumped through pumps to the solidification chamber. Control panel is used to feed the required rate of quenching and the temperature of quenching medium in solidification chamber is displayed. CSAIC system is composed of the parts as mentioned in the Fig. 1.

a. Construction

Platform (4) with the provision for lifting for forklift holds all the items rigidly of the CSAIC system. Reservoir tank (1) is connected to Solidification chamber (2) through pipelines, fitting and valves (3). Pump-1 (7), pump-2 (8) are used for pumping the quench medium from reservoir (1) to solidification chamber (2) and pump-3 (9) is used to drain the oil from solidification chamber (2) to reservoir (1). Control panel (5) comprises of PLC, level controllers, HMI screen and emergency stop button (15). Solidification chamber (2) has the provision for holding the ceramic shell through sliding ceramic mold holder (12) and has temperature sensor and level sensors (10).

b. Function

Preheated ceramic shell is held inside the solidification chamber (2) using sliding ceramic mold holder (14). The quench medium level is preset according to the ceramic mold height with the adjustable middle level sensor. Predetermined quench rate (rpm) is fed through the control panel (5). Molten metal from the furnace is poured into the ceramic moJd. As soon as the mold is filled, the quench medium is allowed to raise
8
Pump-2
9
10
11
12
13
Pump-3
Quench medium level sensors
Scale for level sensor setting
Sliding Ceramic mold holder Emergency stop button

BACKGROUND AND PRIOR ART
Background of Invention (origin of invention or the problem to which the invention is a solution for) 1. Foundry and Forge Division, HAL is in the business of manufacturing investment castings for various military aircrafts and helicopters. Recently, HAL was getting enquiry for new products with same alloys requiring better mechanical properties which is in normal process is difficult to achieve due to inherit nature of investment casting process itself. 2. Al- Si-Mg alloys are used for structural aircraft parts, due to good strength to weight ratio, mechanical properties and machinability. Castings manufactured through investment casting have larger grains due to slow solidification rate resulting in coarse grain and low mechanical properties. Rate of controlling of solidification has direct co-relation with the grain structure of castings, indirectly controlling the mechanical properties. 3. On research, we found few technologies are available in the industry which were proprietary and cost intensive which has led to the present innovation.
Existina Inventions in the same field (literature available) 1. Hero Process 2. SOFIA Process 3. Patent: Rapid Solidification Investment Casting by Hamilton Sundstrand Corporation, Rockford, IL (US), US 6,622,774 B2, 23.9.2003
Drawback of the existing inventions 1. Huge cost 2. Proprietary in nature
Advantaaes of the Dresent invention over existing inventions Lower cost (less than 7 lakh) 2. Portable 3. Various speed range for different solidification rate 4. Up to 400 mm diameter part can be cast 5. Different quench medium can be used.
IPR APPLICATION REQUIREMENTS
Testina (Has the invention been tested) Invention is well Tested and in regular production from 2020 onwards.
Is the invention available as a manufactured Droduct (If yes, provide details) Yes Invention is well Tested and available in Investment Casting Shop in Foundry and Forge Division, HAL, Bangalore.
Does the Drocess/oroduct have industrial applicability Yes Invention is well Tested and available in Investment Casting Shop in Foundry and Forge Division, HAL, Bangalore. ?
ADDITIONAL PARAMETERS FOR OBTANING IP PROTECTION
Is the invention alreadv in use on anv Dlatform of HAL (If so, then since when) It is applicable for only Foundry and Forge Division and available in F&F Division, HAL Bangalore.
Has it been oublished or demonstrated anvwhere else/is it Dlanned to be Dublished or Dresented anvwhere in the near future (details to be provided) NO
CSAIC system is designed for controlled solidification rate and direction for Al-Si-Mg alloy for investment casting products.

Description of Invention
CSAIC system is a movable setup fixed or a : platform. The main function of this system is to control the solidification rate through controlling the rate of rise of quenching medium. Quenching medium is stored in the reservoir and pumped through pumps to the solidification chamber. Control, panel is used to feed the required rate of quenching and the temperature of quenching medium in solidification chamber is displayed. CSAICsystem is composed of the parts as mentioned in the Fig.1.
Reference

Numerals
Description
1

2

Z

4
Reservoir

Solidification Chamber Pipelines, fittings, valves
Platform

5 Control panel
6 Level indicator for solidification chamber
7 Pump-1
8 Pump-2
9 Pump-3
10 Quench medium level sensors
11 Scale for level sensor setting
12 Sliding Ceramic mold holder
13 Emergency stop button

i

i

a. Construction

Platform (4) with the provision for lifting for forklift holds all the items rigidly of the CSAICsystem. Reservoir tank (1) is connected to Solidification chamber (2) through pipelines, fitting and valves (3). Pump-1 (7), pump-2 (8) are used for pumping the quench medium from reservoir (1) to solidification chamber (2) and pump-3 (9) is used to drain the oil from solidification chamber (2) to reservoir (1). Control panel (5) comprises of PLC, level controllers, HMI screen and emergency stop button (15). Solidification chamber (2) has the provision for holding the ceramic shell through sliding ceramic mold holder (12) and has temperature sensor and level sensors (10).

b. Function

Preheated ceramic shell is held inside the solidification chamber (2) using sliding ceramic mold holder (14). The quench medium level is preset according to the ceramic mold height with the adjustable middle level sensor. Predetermined quench rate (rpm) is fed through the control panel (5). Molten metal from the furnace is poured into the ceramic mold. As soon as the mold is filled, the quench medium is allowed to raise controlling the solidification rate and direction of the casting. After complete solidification, the mold is taken out for further processing.
Methodoloav for construction of invention (if aoolving for a product patent) Not applicable
CRITERIA FOR OBTAINING IP PROTECTION
Noveltv (features that make the invention novei) 1. Solidification rate and direction control using quench medium. 2. SAE 20 to 60 quenching oil is used as a quench medium. {Flash point >180°C)
Inventive steD (are the novel features inventive enouah to not be obvious to a person skilled in the art) This is completely new practise in India.