1) Title of the invention

Design and Development of Manufacturing process of Defect free Equiaxed Alpha Plus Beta Titanium .Alloy High Pressure Compressor Blade through Multi- Stage Precision Forging.

2) Field of invention

The present invention is a design and development of manufacturing process for high pressure
compressor rotor blades through precision forging. The invented state of art manufacturing process as flow chart has been shown in Figure-1, ' '

3) Use of invention

The developed methodology is used for manufacturing of complex shaped high precision compressor blades through hot precision forging route. The forging of such blades is a multi-stage forging process. The forging technique and tool design has been modified to yield defect free components along with desired mechanical and metallurgical properties.

4) Prior art

The compressor blades were being manufactured in multi stage precision forging as shown in the Figure-2. The horizontal upsetter machine was used for 2 stage pre-forming operation as shown in the Figure-2, The two split dies are used for horizontal upsetter to produce preform. Split dies lead to fin formation during preforming-1 and complete dressing is required before forging preform-2. Preform-2 is a kind of heading operation which resembles the rough shape of the head of the compressor blade. Preform-2 contains folds and cold crack generated due to heat check and needs dressing before finish forging.

5) Draw backs of prior art

The folds and cold cracks used to occur during preforming stage-1 to preforming stage-2. The defect removal is a time consuming, non value added activity and also contributes to rejection and poor quality of the component. The Aerofoil sections had more variation from leading edge to trailing edge while forging from preforming stage-2 to Finisher forging. The surface of the finished blades was also poor due to drastic change in the aerofoil section during finisher forging.

6) Comparison between prior art and present invention

The invented process involves modified perform design where performing is carried out in screw press without side flash. No defects are observed between performing stage-1 to performing stage-2. The perform stage-2 has extended rough aerofoil shape with 2.0 mm material envelope which reduces extent of deformation required during finish forging, which in turn improves surface quality and good aerofoil dimensional control. All these factors not only reduce rejection but also reduce the cycle time for production of compressor blades.

7) Aim of the invention

Aim of the invention is to develop a new precision forging process which would produce a defect free high compressor rotor blades in shorter cycle time.

8) Summary of the present invention

The present invention is development of manufacturing process for high pressure compressor rotor blade. The tool design and process has been modified to yield defect free compressor blades.
9) Brief description of drawings
 
The tool drawing for preform-1 forging as per invented method is shown in the Figure-4. The tool drawing for preform-2 is shown in the Figure - 6.
 

10) Statement of The compressor blades are manufactured through multi-stage precision forging in the invention. The preforming-1 and peforming-2 forgings are as per tool designs shown in Figure -4 and Figure -6 respectively. The process sequence as per Figure -1 will yield a defect free equiaxed alpha plus beta ■titanium alloy high pressure compressor rotor blades.

11) Detailed description of invention

The high pressure compressor rotor blades are manufactured by precision forging. The forging of such complex shaped blades carried out through multi stage forging process. The round bars are the raw material for producing these blades. The hot forging of alpha plus beta titanium alloys carried out at 30-40 °C below beta transus temperature. Since titanium alloys are prone to pick up hydrogen during the heating for forging, a suitable environmental protective coating (silica glass based) is applied before each stage of forging (150-200 microns). This coating also acts as lubricant at forging temperature and also reduces the heat check during transfer from furnace to dies for forging.

For easy removal and to reduce friction between part and tools water based thin coating of graphite (100-150 microns) is also applied during forging of each part. The dies are heated 150-250 °C during forging to reduce flow stresses and heat check during the contact of hot part to dies. The resistance heating type of furnace is used to avoid any foreign contamination during heating for forging.

Performing-1 is carried out from suitable size of bar stock. Performing-1 is carried out to gather material at one end, as the compressor blades have thin aerofoil sections and bulky head (large difference in the volume of raw material required to form head and aerofoil). The performing-1 is carried out by using tool as shown in the' Figure-4, which is a single die and hence no fin formation during this operation. Modified Performing-1 design (Figure -3. sketch-6) reduces fin grinding time and needs less material to form performing-2. The preforming-2 die consists two halves namely top and bottom halves of the preform.. Preform-2 is modified and has broader rough aerofoil shape, which reduces the drastic change in shape while forging from preform-2 (Figure -3, SKETCH-7 and Figure-5) to finisher. The shape and volume has also been modified to fill sufficiently the head portion of finisher. In other words the modified preform-2 assimilates the similar design features as the finisher has except twisted aerofoil shape and orientation of aerofoil with respect to platform of head. This design makes preform-2 to suit ideally to finisher, wherein less deformation required to form finisher, which not only reduces the surface imperfection caused by friction between part and die, but also maintains uniform dimensional control over the aerofoil sections of the compressor blade. The finisher forging carried out from preform-2 yields a defect free compressor blades. The aerofoil section of the blades may have twist due to hot forging and a coining operation is carried out in the coining dies. The finished blades are aged at 570-590 °C for 8-10 hours which yields a perfect equiaxed alpha, plus beta phase distributed throughout the matrix (Figure -7). After heat treatment these blades are subjected to dimensioning and platform machining for fitment in the engine.

TITLE: Design and Development of Manufacturing process of Defect free Equiaxed Alpha Plus Beta Titanium Alloy High Pressure Compressor Blade through Multi-Stage Precision Forging.
Claims
"We claim"
1. The preform-1 design used for producing the high pressure compressor rotor blade.

2. The preform-2 design used for producing the high pressure compressor rotor blade.

3. The hot forging of alpha plus beta titanium.alloys carried out at 30-40 °C below beta transus temperature to avoid phase transformation during forging operation.

4. Titanium alloys are prone to pick up hydrogen during the heating for forging, a suitable environmental protective coating (silica glass based) is applied before each stage of forging (150-200 microns)

5. The dies are heated 150-250 °C during forging to reduce flow stresses and heat check during the contact of hot part to dies
6. The application of a thin coating of water based graphite (100-150 microns) for easy removal
and to reduce friction between part and tools during forging of each part.

7. The coining operation is carried out at 30-40 °C below beta transus temperature by pressing the finish part for 20-30 seconds between the top and bottom parts of the finisher die; rather than making separate coining die.