FORM 2
THE PATENT ACT 1970 (39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION
{See Section 10, and rule 13)
1. TITLE OF INVENTION
CNC VERTICAL MACHINING CENTER-MODEL PVM65
2. APPLICANT(S)
a) Name : PREMIER LIMITED
b) Nationality : INDIAN Company
c) Address : 58, NARIMAN BHAVAN,
NARIMAN POINT, MUMBAI-400 021, MAHARASHTRA, INDIA
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed : -

FIELD OF INVENTION
The present invention relates generally to Vertical Machining Centers and more specifically to a new and unique CNC Vertical Machining Center which is adapted for high-speed production of parts with greater stability and less vibration and chatter.
BACKGROUND AND PRIOR ART
To meet the need of heavy engineering and automobile industry, high speed FMS oriented, compact Vertical Machining Center are capable of offering high precision machining and cost effective machining solutions.
Vertical Machining Centers are generally adapted to produce a wide variety of parts. They are capable of operating at a wide variety of speeds and holding a large number of different cutting tools, which can be interchanged during the machining process to produce the desired part. While conventional machining centers are well adapted to perform a wide variety of machining operations, there are several drawbacks with the existing machining centers. Primarily, the drawbacks are low production rate and accuracy.
The Vertical Machining Center according to the present invention having milling spindle nose BT-50 Taper is designed to accommodate very high load on the table for machining of work-pieces weighing up to 1200kg. It overcomes the drawbacks of the prior art mentioned above.
OBJECTS OF THE INVENTION
The primary object of the invention is to overcome the drawbacks of the prior art. Another object of the invention is to provide a VMC having a machine base which

has an ultra-wide base structure adapted to separate chips and coolant from the base structure.
A further object of the invention is to provide a machine which overcomes vibration and chatter because the base and column have adequate mass and structural rigidity to provide significant damping.
Yet another object of the invention is to provide a VMC having an automatic tool changer unit which greatly reduces tool change time to only 2.5 seconds.
A further object of the invention is to provide a high speed vibration free and compact VMC suitable for machining both steel and aluminium.
Yet another object of the invention is to provide a VMC with precision X, Y and Z axis drives through large diameter precision-ground ball screws driven by servomotors with inbuilt encoders.
A further object of the invention is to provide a VMC with rapid traverse rates of 32 m/min for X, Y and Z axis and feed rates of up to 10000 rnm/min.
A still further object of the invention is to provide a VMC with a high precision spindle which can rotate between 1-6000 RPM.
SUMMARY OF THE INVENTION
A CNC controlled VMC comprises of a machine base, a cross slide, a table and a spindle assembly mounted on a column. Also provided are an electrical control cabinet, an ATC, a machine guard, a chip conveyor and coolant tank. The column and the cross slide are mounted on the machine base which has an ultra-wide base structure for separating chip and coolant from the base structure. A high precision spindle of nitride steel mounted on high precision ball bearings can rotate between

1-6000 RPM. An Automatic Tool Changer (ATC) has a disc type magazine plate which accommodates 20 tools. It has a tool change time of only 2,5 seconds. The axes movements of the VMC are made through precision-ground ball screws. They are driven by AC servomotors with inbuilt encoders.
It is a low-vibration machine which has high-accuracy and has high production rate. It has a compact configuration, machining zone of 1065x620x620mm and is suitable for machining both steel and aluminium machine components.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The accompanying drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention, wherein
Figure 1(a) illustrates the front view of the vertical machining center according to the present invention;
Figure 1(b) illustrates the side view of the machining center.
Figure 1(c) illustrates the plan view.
Figures 2(a, b and c) illustrate the x-axis drive assembly, y-axis drive assembly and z-axis drive assembly respectively.
Figures 3 (a, b and c) schematically illustrate the x-axis kinematics, y-axis kinematics and z-axis kinematics respectively.
Figure 4 schematically illustrates the milling head (spindle assembly) of the Vertical Machining Center according to the present invention, and
Figure 5 schematically illustrates the ATC drive of the vertical machining center according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION
Having described the main features of the invention above, a more detailed and non-limiting description of a preferred embodiment will be given in the following paragraphs, with reference to the accompanying drawings.
The preferred embodiment of the present invention is shown in figures 1(a), 1(b) and 1(c).
The vertical machining center (VMC) according to the invention comprises of a machine base (1), cross slide (3), table (4) and the milling head (spindle assembly) (5) which is mounted on column (2). Column (2) and the cross slide (3) are mounted on the machine base (1). The thermo-symmetric column (2) is a cast iron structure. It is mounted at the rear side and at the top of the machine base (1).
The machine base (1) has an ultra-wide base structure with high quality cast iron. It has hardened and ground linear motion guide ways to ensure the best machining performance by eliminating structural distortion and deformation under heavy machining conditions. The revolutionary base design separates chip and coolant from the base structure. Thus, it minimizes thermal distortion of the machine base (1) caused by high temperature of chips and coolant. A slat type chip conveyor (14) is installed at the front side of the machine.
The cutting assembly is suitably mounted on column (2).
Table (4) is mounted on the cross slide (3). Said table (4) assembly holds and moves a piece of stock material relative to the milling spindle (5.10), best shown in figure 4, for machining. The motor and spindle (5.1) drive assembly, also shown in figure 4, is used for rotating the spindle at a desired speed. The milling head (spindle assembly) (5) is counterbalanced by a hydraulic counterbalance cylinder (8).

Cutting tools are used for machining the stock material. The ATC or automatic tool changer (6), shown in figure 5, holds a variety of cutting tools and allows for a number of cutting tools to be interchanged during machining a part. The VMC also comprises of a CNC (Computer Numerical Control) system which controls the positioning of a cutting tool with respect to said table (4) and the work-piece to produce the desired shape.
The vertical machining center (VMC) is adapted to manufacture a number of different machined parts at a very high rate of production. To meet this requirement, the VMC contains a minimal number of moving parts and assemblies with minimal vibration and chatter. Accordingly said machine base (1) and column (2) have adequate mass and structural rigidity to provide significant damping to the machine to reduce harmonics and vibrations (i.e., chatter) generated by cutting action of the machine and the motion of the slides. The base is of FG260 cast iron construction with heavy ribbing. Hardened and ground linear motion guide ways, pre-tensioned Class C5 accuracy Φ 40mm ball screws are provided. The servomotors are directly coupled by a flexible coupling to the ball screw for zero backlashes and improved positioning accuracy.
The VMC has a side mounted swing arm type ATC (6) which is driven by an electrical motor (5.1) for accurate and very short tool change time. High pressure coolant spray efficiently takes out chips and prevents heat build-up during deep hole machining, enhancing tool life and machining performance as well as delivering consistent part accuracy.
Additionally, the invented vertical machining center is highly versatile. It often requires the spindle speed to be adjusted depending upon the stock material. The automatic tool changer (6) houses a plurality of cutting tools, judicious use of which improves the flexibility and versatility of the machine.

As shown in figures 2(a), 2(b) and 2(c), AC servomotors (9.1, 10.1, 11.1) and flexible couplings (93,10.3 and 11.3) are used to drive the X-Axis, Y-Axis and Z-Axis slides. Column (2) carries the Z-Axis LM guides (11.4). The milling head (5) traverses up and down on column (2) guide ways. The milling head (spindle assembly) (5) is balanced by means of a hydraulic counterbalancing cylinder (8).
Automatic lubrication unit (7) provides lubrication in pressurized state to all moving elements of the machine like ball screws and LM guide ways.
Chip conveyor (14) is designed for maximum chip carrying capacity.
Coolant tank (13) is integral with the chip conveyor (14). This tank is equipped with two coolant pumps for cutting and bed flushing. Ring coolant pump (13.1) is mounted on the coolant Tank (13) is activated through M codes. When the machine is switched ON, bed wash coolant pump (13.2) runs continuously to clean the machine bed of chip particles until the machine is switched off.
Fig 2 (a, b and c) illustrate the X-Axis Drive Assembly, Y-Axis Drive Assembly and the Z-Axis Drive Assembly respectively incorporated in the VMC according to the present invention. The X, Y and Z axes drives have high precision and large size ball screws (9.2, 10.2 and 11.2) which provide good repeatability and fast traverse. All sliding surfaces of the assembly are hardened and ground for accurate sliding and long service. Ball screws are supported on both ends. Ball screws are directly driven by servo motors (9.1, 10.1 and 11.1) with inbuilt encoders and connected by flexible couplings (9.3, 10.3 and 11.3) which give accurate drive without backlash. Automatic oil lubrication unit (7) is provided for LM guide ways (9.4, 10.4 and 11.4) and ball screws (9.2,10.2 and 11.2) of X, Y and Z axis respectively. For holding the feed axis at a standstill without backlash during operation, a holding torque is generated by the servo motors (9.1,10.1 and 11.1).

Servomotor (11.1) for the vertical Z-Axis is equipped with a holding brake to prevent the milling head (spindle assembly) (5) from dropping down when power fails. The permanent magnet holding brake operates according to the principle of closed circuit current. When the permanent magnet is used, it exerts a fractional force on the armature brake disc by means of its magnetic field. When de-energized, the brake is closed and the motor shaft is held.
Figures 3 (a, b and c) illustrate the kinematics of the X-Axis Drive Assembly, Y-Axis Drive Assembly and the Z-Axis Drive Assembly respectively for the present invention. The axes movements of the VMC are through large diameter precision-ground ball screws (9.2,10.2 and 11.2) driven by AC servomotors (9.1,10.1 and 11.1) with inbuilt encoders. The ball screws are laid out symmetrically with respect to the slide ways for achieving better accuracy. The ball screws are equipped with linear motion guide ways (9.4, 10.4 and 11.4) for all axes ensuring excellent positional accuracy and repeatability. Rapid traverse rates of 32 m/min for X, Y and Z Axis and feed rates up to 10000 mm/min with absolute encoder are suitable for both steel and aluminum machining.
Fig. 4 shows the milling head (spindle assembly) (5). Spindle (5.10) is driven by AC spindle motor (5.1) with external encoder (5.6) through timer belt drive (5.3). The spindle (5.10) is stopped dynamically to bring it to a standstill at a pre-determined position for tool change. Bearings of the spindle are grease lubricated for long life. To secure better machining parameters, the machine is equipped with a timer belt (5.3) driven by timing pulleys (5.2, 5.4). External encoder (5.6) is equipped with spindle motor (5.1) for providing rigid tapping facility. Another timer belt (5.9) driven by timing pulleys (5.7, 5.8) is used for receiving signals from external encoder (5.6). Clamping of tools is controlled by hydro-pneumatic clamp/unclamp cylinder (5.5) through M codes. A tool holder-gripper (5.11) is mounted on the storage device enabling a tool holder to be transferred between a tool holder station and the spindle. The spindle is rotated at a rate between 1-6000 RPM (revolutions per minute).

Figure 5 illustrates the ATC Drive for the present invention. There are two ATC motors (6.5, 6.6 as shown in figure 1(c)) used in ATC Drive arrangement, one for the disc type magazine plate (6.1) rotation and another for ATC arm (6.2) rotation. Adjusting blocks are used for X and Y Axis adjustment (6.3 and 6.4) of ATC tool in line with spindle. (5.10).
A controller, which may be a conventional controller, is used for controlling the functioning of the machine.
Electrical control cabinet (12) is mounted on rear side of machine and provided with AC for cooling (18). An ergonomically designed swiveling operator control pendant box with AC for cooling is mounted on machine front.
Accurate control of the motors, which can be accomplished through known control systems, permits the cutting tool to be guided precisely along the desired path relative to the work-piece for creating the desired shape with very low tolerances through machining.
The following operations can be performed on the VMC.
1. Face Milling
2. Drilling
3. Boring
4. Tapping
5. Reaming
The vertical machining center has a compact design configuration. Its integral mechanical-electrical construction minimizes floor space requirement and enhances productivity per unit of floor space. It has a machining zone of 1065x620x620mm.

The major components i.e. machine base (1), column (2), cross slide (3), table (4), milling head (spindle assembly) (5) are made with special grade cast iron in sturdy box type construction duly ribbed to ensure stable and heavy duty machining.
The milling head (spindle assembly) (5) is equipped with high precision spindle (5.10) of nitride steel mounted on special class high precision preloaded angular contact ball bearings. The shape of the spindle nose is designed for easy access into the work-piece/fixture. For quicker and accurate tool change, this assembly is equipped with external encoder system for quick orientation.
A twin arm auto tool changer unit (ATC) (6) has a disc type magazine plate (6.1) accommodating 20 tools. It has a one-motion tool replacement feature whereby a new tool is accepted on the spindle and the earlier tool is returned back to the tilted pocket of the tool magazine of the ATC in a single movement. This greatly reduces tool change time to only 2.5 seconds. Meticulous design consideration is provided so that the tool is easily removed from and put back into the ATC magazine during a tool changing cycle. The ATC software utilizes the latest bi-directional random selection mode whereby the earlier tool occupies the pocket emptied by the new tool. After each such tool change operation, the computer updates the data relating to the tool number and pocket number.
State of art operator-friendly CNC technology is equipped with a powerful programmable logic controller for sequencing the various machine functions and interfacing with the CNC system. It also provides ample input/output diagnostic facility for quick location of faults on the machine. All commonly used user functions are available with an array of optional features to enhance machining capability and programming ease. It is also designed in line with total productivity maintenance (TPM) concept.

Chip conveyor (14) system for efficient swarf disposal is positioned in the front of the machine guard (16). It collects the chips directly from machining zone and carries them to chip bin (17).
The ergonomically superior design of the VMC ensures minimum operator fatigue by way of centralized pendant type electrical control cabinet (12), easy chip disposal, easy accessibility etc.
It is amply clear from the above that the present invention represents an advancement over similar machines of the prior art by providing a mechanically stronger machine exhibiting improved dynamic characteristics and yet one which is economical to produce. The invented machine is more reliable than the similar machines of the prior art.
The present invention has been described with reference to some drawings and a preferred embodiment purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described herein before and claimed in the appended claims.

WE CLAIM:
1. A CNC vertical machining center (VMC) comprises of machine base (1), cross
slide (3), table (4), milling head (spindle assembly) (5) mounted on column (2),
electrical control cabinet (12), ATC (6), machine guard (16), chip conveyor (14),
and coolant tank (13),
wherein said machine base (1) has an ultra-wide base structure adapted to separate chip and coolant from the base structure, said column (2) is a thermo-symmetric cast iron structure mounted at the rear side top of said machine base (1) and said column (2) and said cross slide (3) are mounted on said machine base (1).
2. The VMC as claimed in claim 1, wherein hardened and ground linear motion
guide ways (9.4,10.4,11.4) are provided to eliminate structural distortion and deformation.
3. The VMC as claimed in claim 1, wherein said table (4) is mounted on the cross
slide (3).
4. The VMC as claimed in claim 1, wherein said spindle assembly (5) contains a
spindle (5.10) which is driven by AC spindle motor (5.1) with external encoder (5.6) through timer belt drive (5.3).
5. The VMC as claimed in claims 1 and 4, wherein said spindle (5.10) is rotated at a rate between 1-6000 RPM (revolutions per minute).
6. The VMC as claimed in claim 1, wherein said spindle (5.10) is a high precision
spindle of nitride steel mounted on special class high precision preloaded angular contact ball bearings.

7. The VMC as claimed in claim 1, wherein said machine base (1), column (2),
cross slide (3), table (4) and spindle assembly (5) are made with special grade FG260 cast iron in sturdy box type construction duly ribbed to ensure vibration and chatter free, stable and heavy duty machining.
8. The VMC as claimed in claim 1, wherein said ATC (6) is a twin arm auto tool changer unit which has a disc type magazine plate (6.1) accommodating 20 tools and greatly reduces tool change time to only 2.5 seconds.
9. The VMC as claimed in claim 1, wherein said ATC (6) has two motors, one for
driving disc type magazine plate (6.1) rotation and the other for driving ATC arm (6.2) rotation.
10. The VMC as claimed in claim 1, wherein said chip conveyor (14), and coolant
tank (13), are positioned in front of said machine guard (16) and the conveyor
(14) is a slat type chip conveyor which is adapted to carry curly chips.