FIELD OF THE INVENTION
The present invention relates to a fixture for machining two jobs simultaneously in single loading on a CNC machine. More particularly, the present invention relates to a fixture for enhancing capability of a CNC manufacturing machine capable of performing, on metals or other hard surfaces, vital machining operations such as facing, step milling & centre drilling through having in it the capability of rigidly holding plurality of jobs.
BACKGROUND OF THE INVENTION
Machine tools and production or manufacturing capability can be simply defined as value addition processes by which raw materials of low utility and value are converted into high utility and valued products with definite dimensions, into high utility and valued products with definite dimensions, forms and finish imparting some functional ability.
Most of the engineering components such as gears, bearings, clutches, tools, screws and nuts etc. need dimensional and form accuracy and good surface finish for serving their purposes. Casting, forging etc. generally cannot provide the desired accuracy and finish. For that such preformed parts, called blanks, need semi-finishing and finishing and it is done by machining and grinding. Machining to high accuracy and finish essentially enables a product to fulfill its functional requirements, improve its performance, and prolong its service.

It is largely possible to manufacture a product of given material and desired configuration by several basic manufacturing processes such as facing, boring, drilling, turning etc. as well as other advance manufacturing processes.
With the increased versatility and precision (e.g., through CNC machines) and the advent of dedicated high productive special purpose machines, the need of using attachments is gradually decreasing rapidly. However, some special and customized-for-specific-use attachments, i.e., copying templates, taper turning attachment etc., are still being used purposefully on different machines for increasing the capability of a machine in terms of ergonomics for better user experience, lower power consumption, better quality output and above all, efficiency to constantly provide fit-for-use products.
In a thermal power plant a steam turbine is rotated with help of high pressure and high temperature steam and this rotation is transferred to a generator to produce electricity.
The steam flow path of a steam turbine is formed by a stationary cylinder and a rotor. A large number of stationary blades are attached to the cylinder in a circumferential array and similarly, a large number of rotating blades are attached to the rotor in a
circumferential array. The blade airfoils extract energy from the steam, thereby developing the power necessary to drive the rotor and the load attached to it.

Therefore, the turbine blades, manufactured from raw material i.e., Prismatic Alloy Steel Bars (hereinafter referred as blank(s)), are an extremely important factor in the thermodynamic performance of the turbine.
These blanks are first cut into pre-determined length by band saw machines and then preparatory machining operations such as face milling (as both ends of the blank for making the end surfaces plane), centre drilling (at both the ends of the blank for holding and alignment) and milling step (at one end of the blank for clamping the step with aforesaid work piece jaws) are first performed on these blanks on a 4-axis HMC before loading, as pre-machined blanks in work piece adaptor jaws of a single spindle 5-axis milling machines. The aforesaid adaptor requires a step and centre for clamping the blank through rectangular clamping jaws in the headstock side as well as a centre on a face-milled surface on the other end of the blank for tailstock holding.
Bar type steam turbine blades are manufactured at single axis 5-axis machines from blanks of different cross-sections & length. In single spindle CNC 5-axis milling machines, work piece holding is realized by holding the blank horizontally in machine’s A-axis which can rotate continuously. One end of the blank is clamped by two numbers of rectangular jaws in work pieced adaptor in head stock of the machine. The other end is held by a centre pin in the tailstock (ref. figure 1b, 1c).

Thus it is evident that the rate at which the blades are manufactured, a process that decides the total time in manufacturing a steam turbine, depends on the machining of blanks on 4-axis HMC. What is desired, therefore, is a device that have the capability to simultaneously hold the blank during machining of plurality of blanks/jobs in single loading on CNC of 4-axis HMC.
OBJECTS OF THE INVENTION
It is, therefore, a principal object of the invention is to develop a device for simultaneous machining of two jobs in single loading on CNC 4 axis horizontal milling centre that rigidly hold plurality of jobs in single loading so as to facilitate simultaneously machining that ensure in increasing overall capability of the machine.
Another object of the invention is to develop a device for simultaneous machining of two jobs in single loading on CNC 4-axis horizontal milling centre which reduces cycle time and increase productivity and efficiency in the aforesaid operations.
A further object of the invention is to develop a device for simultaneous machine of two jobs in single loading on CNC 4-axis horizontal milling centre that completely eliminate the need of acquiring multi-spindle CNC machine which is a costly alternative.

SUMMARY OF THE INVENTION
A device (1) for simultaneous machining of two jobs in single loading on CNC 4-axis horizontal milling centre and a method for the same, wherein the blanks (11), made of alloy steel rectangular bars, are loaded in the fixture (1), mounted and fastened on t-slots (13) of machine table (12), on resting blocks (3) for machining in such a way that side faces of the blanks (11) touch the side faces of the entre block (4); Blanks (11) are clamped from top by using tightening clamping arms (10); Tightening is done by tightening the nuts (14) mounted on upper hinge threads (6); Upper clamping grip (8) is fixed on the upper clamping arms (10) with pivot pins (9); Upper clamping grips (8) can rotate freely in ± 5 degree around the mentioned pivot pins (9) to ensure maximum area of clamping of blanks (11) from top; In case of smaller blank thickness, suitable packings can be placed between the top surfaces of blanks (11) and upper clamping grips (8) for rigid clamping. The present fixture has provisions of placing upper clamping grip (8) at 3 different positions to rigidly hold blanks (11) of wide range of width.
BRIEF DESCRIPTION OF ACCOMPANIED DRAWINGS
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout, and in which: Figure 1A – represents the developed device (1)

Figure 1B – is the holding arrangement of the blank in CNC 5-axis single spindle machine.
Figure 1C – shows blank after machining.
Figure 2 – is the line diagram of base block (2) used as base of the invented device.
Figure 3 – is the line diagram of resting block (3) used in invented device.
Figure 4 – is the line diagram of centre block (4) used in invented device.
Figure 5 – is the line diagram of lower hinge (5) used in invented device.
Figure 6 – is the line diagram of upper hinge (6) used in invented device.
Figure 7 – is the line diagram of pivot block (7) used in invented device.
Figure 8 – is the line diagram of upper clamping grip (8) used in invented device.
Figure 9 – is the line diagram of pivot pin (9) for upper clamping grip (8) used in invented
device.
Figure 10 – is the line diagram of clamping arm (10) used in invented device.
Figure 11 – represents the photographic representation of fixture and jobs loaded in the
machine.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION
A fixture is a work-holding or support device used in the manufacturing industry for holding and locating the job in a specific position or orientation as well as supporting the job which in the present case is a blank.

As per the proposed device, multiple blanks can be rigidly held during machining at 4-axis CNC HMC and therefore the critical man-hours, need of a costly multi-spindle CNC machine and other operational charges are substantially reduced.
A fixture/device has therefore been developed with primary purpose is to create a secure and rigid clamping of the blanks, allowing for support during balancing operation with accuracy, precision, reliability during the balancing operation. The present fixture has provisions of placing upper clamping grip (8) at 3 different positions to rigidly hold blanks (11) of wide range of width.
The assembly of the connecting part with the development fixture will be done as per below:
1. Steam turbine blades are manufactured from alloy steel rectangular bars on CNC
5 axis milling machines in one setup. The rectangular bars are called blanks (11). These are prepared by cutting rectangular bars of 4 to 5 metres of different cross sections and material grades in band saw machines according to required length (blade length plus technological / holding allowances along length).
2. For this two numbers of blanks (11) are loaded in the fixture on resting blocks (3).
The complete assembly of fixture (1) is mounted and fastened on t-slots (13) of
machine table (12) is as shown in figure 1a.

3. Side faces of the blanks (11) touch the side faces of the centre block (4). Blanks (11) are then clamped from top by using tightening clamping arms (10). Tightening is done by tightening the nuts (14) mounted on upper hinge threads (5). Upper clamping grip (8) is fixed on the upper clamping arms (10) with pivot pins for upper clamping grip (9). These upper clamping grips (8) can rotate freely in ± 5 degree around the mentioned pivot pins for upper clamping grips (9) to ensure maximum area of clamping of blanks (11) from top. In case of smaller blank thickness, suitable packings can be placed between the top surface of blanks (11) and upper clamping grips (8) for rigid clamping. The present fixture has provisions of placing upper clamping grip (8) at 3 different positions to rigidly hold blanks (11) of wide range of width.
4. For machining, average thickness of blank is treated as blank thickness and width of the blanks are measured by Vernier and higher width value is fed in the NC program.
5. Face milling at both ends is done with face mill cutter. Rough step milling is done by same cutter followed by finishing with HSS end mill. Centre drilling is done by HSS/carbide centre drill.
6. The blanks (11) are loaded in aforesaid CNC 5 axis milling machines along a continuously rotating ‘a’ axis of machine (refer figure 1b) with the help of a clamping chuck/having two jaws & centre pin at the head stock side of the machine and with the help of a centre pin at tail stock. The clamping force applied is approximately 45 bar along ‘a’ axis of the machine.

7. As shown in figure 1b and figure 1c the blank (11) has two faces, namely face-A
and face-B. These two faces are pre-machined before loading in the 5 axis CNC milling machine. For this face milling is done on face-A and face-B; step milling on face-A of the blank as shown in figure 1c; centre drilling at both face-A and face-B.
It is now apparent that the embodiment of the invention, as described hereinabove, will provide an extremely critical device for simultaneous machining of two jobs in single loading on CNC 4-axis Horizontal Milling Centre.
The foregoing is considered as illustrative only of the principles of the invention. It is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted too, falling within the scope of the invention as claimed.

WE CLAIM

1. A device (1) for clamping two jobs for simultaneous machining in single loading on
CNC 4-axis horizontal milling centre comprising:
a pair of base blocks (2) mounted on the T-slot (13) of machine table (12); a set of one number of centre block (4) with two numbers of resting block (3) on either side placed over the base block (2) such that the top surface of centre block (4) protrudes over the top surface of resting blocks (3) when the inner side faces of the blank (11) abut with the side faces of centre block (4) wherein the job blank (11) are clamped and positioned by a locking mechanism comprising a clamping arm (10), clamping grip (8), lower hinge (5), upper hinge (6), pivot block (7) and pivot pin (9).
2. A method for simultaneous machining of two blanks in a single loading on CNC 4-
axis horizontal milling centre as claimed in claim 1, comprising:-
mounting the assembly fixture (1) through T-slot (13) provided in the machine
table (12) wherein the bottom surface of plurality of base blocks (2) abuts with the
table surface;
placing a set of one number of centre block (4) with two numbers of resting blocks (3) on either side of centre block (4) over base block (2) such that the top surface of centre block (4) protrude over the top surface of resting block and screwing them by the threaded holes provided on them;

mounting a pair of blanks (11) over the fixture such that the bottom surface of the blanks (11) rest on top surface of resting block (3) whereas the inner surface of each blank (11) abut with vertical side faces of the centre block (4) wherein the blanks (4) are clamped tightly by the clamping arm (10) after proper positioning by a combination of locking components pivot block lower hinge (5), upper hinge (6), upper clamping grip (8) and pivot pin (9);
pre-machining the surfaces (A, B) of the blank (11) (shown in fig 1B) by face milling with face mill cutter in a sequence of rough milling followed by finishing with HSS end mill;
performing centre drilling by carbide centre drill; and followed by
loading the blanks on faces A and B (fig B) in CNC 5 axis milling machine along a
continuously rotating axis ‘A’ for further performing the machining operation on the
job.