FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Provisional Specification
(See section 10 and rule 13)
A Method For Manufacturing Of Hollow Shafts
Bharat Forge Limited
Mundhwa, Pune Cantonment, Pune - 411036, Maharashtra, India, Indian company registered under the Indian Companies Act, 1956.
The following specification describes the invention:

A Method For Manufacturing Hollow Shafts Field of Invention
The present invention relates to hollow shafts, and more particularly to a method for designing and manufacturing of hollow shafts from solid blooms or ingots such that it results in more effective utilisation of raw material and enhancement of mechanical properties and performance of the shafts thus produced.
Background of Invention
Many industries including the wind energy industry use hollow shafts. Especially, hollow shafts which are used in gear boxes of required in these industries are typically subjected to high static and dynamic loads.
For many decades these components have been manufactured using conventional manufacturing process (i.e., forged bars made from continuously cast (concast) bloom or cast ingot, followed by proof machining, heat treatment and Final machining. Existing method of manufacturing such parts is therefore:
- Using cast polygonal/round ingot or bloom with no or minimal hot working as input.
- Machining (OD turning, finishing, facing; deep hole drilling; boring & counter boring)

- Heat treating
- Finish machining
In a nutshell, the existing manufacturing method is a combination of forming a forged bar from a concast bloom or an as-cast ingot followed by machining. It has been found that the existing process results in about 50% utilization of material (thereby leading to about 50% wastage of material from the time of forming a bloom/ingot to making of the proof machined part).
With conventional manufacturing method, which results into large machining time and poor yield, substantial raw material is thus wasted during mass production of such components.
Moreover, existing methods, which involve either no reduction or minimal reduction by hot working, do not result in superior material properties required for deployment in high power applications.
Another important limitation of the existing methods arises from the fact that the hollow shafts under consideration have steps in the bore involving multiple diameters. It is known that such multiple-stepped bores can be produced by machining only and therefore cannot provide continuous grain flow along the

contour of bore. This is one of the main reasons why the hollow shafts produced using the current methods lack superior grain flow characteristics and mechanical properties.
There is therefore a need to provide alternative methods of designing and manufacturing hollow shafts, involving near-net shape forging, which would result in superior grain flow characteristics and mechanical properties and result in more effective utilisation of raw material.
Objects of the Invention
Accordingly an object of the present invention is to provide a method of designing and manufacturing hollow shafts to be used in gearbox components deployed in wind energy applications.
Another object of the invention is to provide a method to optimize concast bloom or an as-cast round ingot to make it suitable for use in a near-net forging process.
One other object of the invention is to provide a near-net shape forging process for manufacturing hollow shafts so as to enhance utilisation of material from the forging to proof machining stages of manufacturing.

Yet another object of the invention is to provide forging die design for the near-net-shape forging process of the invention.
Yet another object of the invention is to provide hollow shafts of improved dense grain flow, and strength through forging followed by steps of normalising, hardening and double tempering prior to proof machining followed by stress relieving
Brief description of Figures:
Figure 1 shows a flow diagram for a typical conventional process of hollow shaft
manufacture
Figure 2a shows the flow diagram for the process of the present invention used for
rectangular shaped concast blooms
Figure 2b shows the flow diagram for the process of the present invention used for
as-cast round ingots
Figure 3 shows the hollow die and the pierce punch
Figure 4 shows the simulated, forged, and proof-machined stages of the hollow
shaft manufactured using the process of the present invention

Summary of the invention:
The present invention describes a method of manufacturing a near-net shaped hollow shaft useful for high power applications such as gearboxes for wind energy industry. The method involves providing a concast bloom (of a round or rectangular or of any polygonal cross section) or an as-cast round ingot from which a hollowed preform is prepared using hollow die punching, followed by the steps of heat treating, proof-machining and stress relieving.
Detailed Description of the Invention:
The present invention is applicable to any hollow shaft component manufacturing that are used in variety of industries, particularly those required in wind energy industry and any other industry where high power transmission gear boxes are use. The present description is provided on the basis of the hollow shafts used in the wind energy industry.
It is evident from the flow chart shown in Figure 1 that the existing processes of hollow shaft manufacturing typically involve the following steps:
Providing a cast ingot or concast bloom, typically - round in shape

- Carrying out OD turning, finishing, and facing
- Carrying out deep hole drilling
- Boring and counter boring Providing heat treatment
- Carrying out final machining
As discussed in the background section, it has been noted that the current hottow shaft manufacturing processes do not deploy near-net-shape forging techniques in the manufacturing process, which consequently means that these processes do not result in recognizable grain structure in the components. Though these components typically meet the strength and other mechanical requirements, the additional factors of safety required in high stake applications are often difficult to achieve with any consistency.
Figures 2- and 2-b show flow diagrams of the process of the present invention to make hollow shafts. The process of the present invention begins with providing a concast bloom or an as-cast round ingot with specified reduction ratios. The reduction ratios should be greater than three for round ingots and greater than five for concast blooms. This is in order to comply with the requirements of microscopic and macroscopic cleanliness, fineness of the grain size, mechanical properties. With the present invention the inventor has found that a much higher reduction ratio of 8:1 is achieved through small size of input raw material. This is

much higher than the typical industry requirement for reduction ratio of >3:1 for round ingots and >5:1 for concast blooms.
The process of the present invention comprises the following steps:
- Providing an concast bloom (input object) of rectangular cross section
- Heating in a furnace
- Upsetting to an inteimediate height
- Drawing to an intermediate dianieter
- Providing booster heating
- Upsetting in a hollow die to the final height of the preform
- Punching in a hollow die
- Providing heat treatment to carry out normalising, hardening and double tempering
- Proof-machining (OD turning, finishing, and facing; boring and counter boring)
Stress-relieving
In the case where the concast bloom or ingot is round in cross section, the process of the present invention comprises the fallowing steps:
- Providing a concast bloom or an as-cast ingot (input object) of round
cross section
Heating in a furnace

- Drawing to an intermediate diameter
- Upsetting to an intermediate height
- Providing booster heating
- Drawing to the diameter achieved after the previous drawing step
- Providing booster heating if required
- Upsetting in a hollow die to the final height of the preform
- Punching in a hollow die
- Providing heat treatment to carry out the steps of normalising, hardening and tempering
- Proof-machining (OD turning, finishing, and facing; boring and counter boring)
- Stress-relieving
The following advantages of the process of the present invention over the existing methods are observed;
1. The weight of the input object right at the start of the process is reduced significantly compared to that used in a conventional process. For example, a 30% reduction is achieved as illustrated in examples 1 and 2. In other words, the yield of the process (ratio of output to input weight expressed as percentage) improves by approximately 25-30%.
2. The time of machining is reduced (in comparison with an existing process) by approximately 40-45%.

3. The grain flow of the final product resulting from the process of the invention is much improved compared to the existing manufacturing processes. This results in better micro-structure and mechanical properties.
4. The factors of safety provided by the products are much higher and consistent across the products than those for existing processes, which are required in high stake applications, and which are often difficult to achieve with any consistency in the case of existing processes.
Figure 3 shows the typical 3-D CAD near-net shape design models of dies designed as a part of the present invention and used for upsetting, drawing, and hollow punching. With an iterative simulation approach, numerous manufacturing concepts for near-net shape forging were evaluated to optimize the near-net shape geometry, and manufacturing process using Virtual manufacturing techniques. Forging process was also optimized using 3D metal flow simulation and machining process was optimized using CAM simulation. Based on the results of the simulation, an optimal manufacturing methodology was developed for manufacturing components such as hollow shafts used in applications, for example, such as gear boxes for wind energy.
It is important to understand the significance of the optimisation of the near-net shape. Many near net shapes are possible as a starting point for producing a given component. However, the final shape of the component and the tool type and size may make many of the near-net shapes virtually impossible to use. Therefore the

optimisation of the near net shape seeks to arrive at that near-net shape which will provide least wastage of material and also achieve quickest machining while arriving at the final component. The present process incorporates the step of such optimisation of the near net shape through forging.
Another key aspect of the present invention is that the near-net shape forging process is designed using a combination of upsetting and drawing using flat dies, and further upsetting and punching using hollow dies to provide a near-net shaped input to proof machining. Figure 4 shows the simulated, forged, and proof-machined stages of the hollow shaft manufactured using the process of the present invention.
It is to be noted that, in the process of the present invention, the near-net shape forging is being performed by any suitable forging equipment, for example, a 4000 ton hydraulic press. The resultant component is heat treated to achieve the required micro-structure and mechanical properties.
The heat treated component is proof-machined using suitable machining equipment and followed by stress relieving Stress relieving process helps to eliminate the stresses induced during proof machining.
The key advantages of the present invention will now be illustrated with the help of the following examples.

Examples: The invention is now illustrated through examples.
Example 1 (see Figure 2a):
A concast bloom of a rectangular cross-section was cut to 320mm x 400mm x 950mm (L) size. It was heated to a temperature of 1250 °C and upset by keeping hot bloom on machine bed (of a 4000t hydraulic press), locate centrally (final upset height 500 mm). Next, the upset bloom was rotated through 90° to make it horizontal, and drawn to required stock size (Dia. 400 mm). Booster heat was provided to the bloom to raise its temperature to 1250 °C. The hot drawn perform thus obtained was once again upset to 648 mm. This was done by keeping it on the machine bed, located centrally and bumped in a hollow die to descale (upset approximately to 100 mm below die face). Following this, the part was lifted with its scales removed, kept centrally on the machine bed and upset in a hollow die. The upset perform was punched to required height of 634 mm. The resultant component had a near-net shape suitable for further processing.
The heat treated component was machined using the steps of OD turning, finishing and facing. The machined component was next bored and counter bored to the final shape as shown in Figure 4.
Example 2 (see Figure 2b):
A round ingot of 615mm diameter was cut to a length of 401mm. It was heated to
a temperature of 1250 °C and drawn to 400 mm diameter. The drawn ingot was

upset by keeping it on the machine bed (of a 4000t hydraulic press), and located centrally (final upset height 500 mm). Next, booster heat was provided to the ingot to raise its temperature to 1250 °C. The hot ingot was once again drawn to a diameter of 400 mm. Booster heat was provided once again to raise the temperature of the ingot to 1250 °C. Following this the part was lifted, with its scales removed, kept centrally on the machine bed and upset in a hollow die to 648 mm height. The upset perform was punched to a height of 634 mm. The resultant component had a near-net shape suitable for further processing.
The heat treated component was machined using the steps of OD turning, finishing and facing. The machined component was next bored and counter bored to the final shape as shown in Figure 4.
A number of operational benefits arising out of the process of the invention have been observed. These are easily evident from the data obtained from the above examples (see Tables 1 and 2).
Table 1: Reduction In Input Material
PARAMETERS OLD PROCESS INVENTED PROCESS SAVINGS
Proof /Finish machining weight 658 kg 658 kg -
Input bloom size Diameter 535x750L (mm) =1322 kg Con-cast bloom 320 x 400 x 950L(mm) OR Diameter 615 x 401L (mm) = 935 kg 387 kg. (30%)
Yield % (proof machining weight/ cut weight) 49.8% 70.4% 20.6%
Forging weight NA 889 kg -

Table 2: Reduction In Machining Time
PARAMETERS OLD PROCESS INVENTED PROCESS SAVINGS
Proof/Finish 658 kg 658 kg -
machining
weight
Input bloom size Diameter Con-cast bloom 387 kg.
535 x 750L (mm) 320 x 400 x 950L(mm) (30%)
= 1322 kg OR
Diameter
615x401L(mm) = 935 kg
Yield % (proof 49.8% 70.4% 20.6%
machining
weight/ cut
weight)
Forging weight NA 889 kg -
The following observations are made based on the above tables:
1. Input weight was reduced by 30%
2. Yield was improved to 70.4% from 49.8%) (20.6% increase based on the forging input weight)
3. Productivity of manufacturing was improved substantially
4. Machining time was reduced by 41%.