PREAMBLE: The invention resulted in development process, used for machining of critical and highly accurate Main Gear Box Housing-OTS (MGB) for Mk-IV version of ALH helicopters. The sophisticated machining process included Liner Assembly and Machining also.
FIELD OF INVENTION: This invention relates to design & development of a manufacturing process, which is used for machining of MGB Housing-OTS on modern ALH Mk-IV helicopters. The machining process so developed is proved to manufacture most accurate parts, having highest level of consistency with minimum effort.
USE OF INVENTION: This manufacturing process developed, has been helpful is record time development of process/Special Tooling's of highest accuracy.
This concept adopted for various applications having similar requirements of accuracy of other helicopter configuration such as Indian light Utility Helicopter (LUH).
PRIOR ART: This parts is newly developed to meet Defense Forces requirement for High altitude operations in Utility configuration. ALH Mk-III has higher Empty Weight, and load carrying capacity was constrained due to this. Usage of higher power engine would adversely affect life of Transmission components, rigidity of MGB housing and vibration level of helicopter. Thus, Transmission System was modified to OTS (Optimized Transmission System) with more powerful SHAKTI engine fitted with helicopter to enhance helicopter performance. MGB Housing was modified to OTS MGB Housing. Net Weight was reduced by 10 Kg with this configuration, which was a major achievement for any aerospace product..

ALH MAIN GEAR BOX HOUSING-OTS
ABOUT MAIN GEAR BOX ASSEMBLY
The Advanced Light Helicopter (ALH), called Dhruv is designed for
multirole operations in all terrains viz high altitude, low altitude, very high
and low temperatures including desert areas. The power for the rotation of
the blades is supplied from the twin engines through Integrated Dynamic
System (IDS) which consists of Upper Control System (UCS) housed inside
Main Gear Box (MGB). ,

MAIN GEAR BOX [MGB]
MGB Housing assembly is very important and essential component of the power transmission assembly in an ALH it is a casing which houses input gear, Collector Gear Input Pinion and Collector pinion. ALH have 2 input gears driven by two engines. The MGB receives power from the engine and transmits it into both the main rotor blades through Collector Gear to Integrated Rotor Mast and Stub shaft and through TPTO to Tube Segment, IGB, and TGB to Tail Rotor Blades. So MGB is the mother of power transmission in ALH. Original Housing had been updated to meet high altitude requirements by transferring more power/torque and reduction in weight. Main functionalities of MGB Housing Assembly are
1. POWER TRANSMISSION
Power is transmitted from engine to the input gear through flexible drive shaft, free wheel and input pinion. Then input gear transmits the power to tbencollector gear through collector pinion. The collector gear transmits

power to the main rotor blades through upper control system (UCS). The power to the tail rotor blades is transmitted through auxiliary gear box, Input gear box and Tail gear box.
2. SPEED REDUCTION
The speed of typical ALH engine is 36000 RPM, which is reduced to 6000 RPM at the Input pinion, which is then reduced to 2050 RPM at the Input gear as the gear ratio of Input pinion/Input gear is 27/79.
Salient Features of OTS (Optimized Transmission System)
• OTS (Optimized Transmission System) is different from regular system in terms of its capacity to transmit more power at higher altitude.
• It has Spiral Bevel Gears, Spur Gears, Helical Gears, Freewheel Assembly, Control Rods, Integrated Rotor Mast, Bearings etc. as assembly component.
Accuracies required and it's Importance
MGB Housing acts like Heart for Helicopter Transmission. It is the link between Engine to Main Rotor Blades, Engine to Tail Rotor Blade and supplies power to other Accessories and Hydraulic Systems of the Helicopter. It contains parts manufacture with Highest Accuracy requiring precise degree of Assembly requirement and highly controlled vibration characteristics. It houses Oil Jets with Coolants and has "Cast Oil Holes" inside housing. Any misalignment beyond drawing limits would be hazardous and Flight Safety Critical for Helicopter functioning.
OBJECT OF INVENTION:
MGB Housing is made of proprietary Magnesium-Zirconium Alloy, molded usingsSand Casting processes. Casting is loaded for machining to maintain

various drawing dimensions. One of the most critical dimension is "Axis Position of 3 bore shall intersect component center line within 10 Micron accuracy and intersection point shall be within 10 microns from defined plane". Intersection point is an imaginary point (as per Fig. 3), it make the machining highly complicate and required special tooling and fixtures to maintain accuracy and ensure repeatability is achieved.
In the earlier process for Regular Housing machining, machining was done on rotary table with Jobbing Method, which would introduce additional

errors in machining arising out of indexing errors of rotary table. Further, it required very high level of expertise and skill to machine the part. This casting is very costly due to process and proprietary material, any rejection has catastrophic effect on production schedule and cost effectiveness of the product.
The invention was necessitated in order to overcome the technical difficulties / short comings that existed in the prior manual method, in order to ensure quality & consistency. It was also necessitated to reduce the cycle time of operation.
The invention is a unique, high precision, special purpose machine/fixture for machining of MGB Housing-OTS of ALH Helicopter.
DETAILED DESCRIPTION OF THE INVENTION:
1. Process Planning: identifying sequence of operation, machines,Toolings, Jigs and Fixtures
2. Design of Special Tools/Fixtures and Fabrications
3. Process Prove-out
Process Planning:
Considering that parts requires ultra precision machining, and repeatibilty, it was planned to use HMT 4-axis Machining Center for Rough Machining and SIP 5000-7 5-Axis Jig Boring Machine for final Machining of MGB Housing. Input material is Casting, which will hav ehigh degree of variance between part to part, thus Reference Machining is introduced in intial stage of Machining. Same will be used for carrying out Rough machining of various features of MGB Housing. Further, Post-stres releiving operations will be carried out using this Reference. As component is unque in size ansd complexity, standard tools avialble in market did not suit all the requirements of machining. Hence, special Boring Tools and Drills are designed and procured. MGB Housing Machining involves machimng of

Magnisium- Zirconium alloys which is has special machining characterstics due to its ductillity, and configuration.
Sequence of operations defined for machining is as per following sketch

Design of Special Tools/Fixtures and Fabrications
Special Fixutres are designed to machines MGB Housing as per sketch provided below. Fixtures were fabricted with highest accuracy (i.e. 5 microns flatness over 15,38,600 sqaure mm area) with manual scrapping operation. These fixtures are made of CAST IRON and are highly rigid and stable in nature.

Fixture as per Drawing 5(a), 5(b) & 5(c) are designed for carrying out Reference Machining and Final machining of MGB Housing.
Operations Sketch for machining using Fixture is shown as per Figure 6(a), 6(b), 6(c) & 6(d).

Fixture as per Drawing 7(a) & 7(b)) are designed for carrying out Rough Machining of MGB Housing.
Operations Sketch for machining using Fixture is shown as per Figure 8(a), 8(b), 8(c) & 8(d).

Additionally, special Boring bars, Drills, Back-face Milling cutters are designed by keeping in mind the complexity of the part.
PROCESS PROVEOUT:
Process was established by in-depth study of MGB material behavior, its accuracy, ease of manufacturing, rigidity of Tooling, vibrations characteristics, special requirement of material machining. This material has low Flash point, thus it is highly inflammable and on the other side, material reacts to Chlorinated coolants very quickly. Thus coolants are not used in this technology and special machining parameters are established to ensure fast productivity.

CLAIMS: We claim that
1. This is one of its kind Technology, developed for machining of MGB Housing-OTS for ALH Mk-IV Helicopters.
2. This manufacturing technology ensures safe, easy production and repeatable in nature while maintaining highest level of accuracy for the part.
3. This technology reduces the risk of damage to the component.
4. The process is easy to set up & operates using especially designed tooling and does not require highly skilled technicians.