LOW COST AUTOMATION IN A POWER PRESS

Abstract

            The aim of this project is to design a hydro-pneumatic power press using low cost automation.

            This project mainly emphasizes on reduction of working time and labor cost. The working time should be reduced in order to increase the productivity of any industry. Labor cost reduction is also very important nowadays, so that even small scale industries can afford to go for automation.

            The press that we have designed has proved to provide large tonnage capacity in small size. It also decreases the fatigue of the operator by reducing the consumption of human work. This device

also ensures safety of the operator’s hand as Two Hand Safety system is included in the circuit.

            Pneumatic power is used in this press for all movements as air is a cheap power source and also it is readily available. Pneumatics also ensures safer operation and ease of fabrication of components. For Punching operation alone hydraulic power is used in order to obtain very high pressure and to avoid fluctuation.

            The cost calculation for various raw materials and for all the machining operations are performed, also an analysis has been performed to calculate the deflection and stress distribution on the supporting members and the results are enclosed in this paper.       

           

Low Cost Automation

With the advent of liberalization and globalization, it is necessary that industries explore the methods of enhancing automation and productivity to acquire greater competitiveness. In this regard, low cost automation [LCA] is a technology that promises to be very useful for any kind of manufacturing organization.

Concepts of  Low Cost Automation

Low cost automation is defined as a technology that creates some degree of automation around the existing equipment, tools and methods, using mostly the standard equipment available in the market.

Technologies Used For LCA

Pneumatics circuits are extremely popular for applications due to their low cost, ease of fabrication and safe operation.  However, in most of the practical applications, hybrid systems are used since they use the advantages of different devices, while simultaneously minimizing individual disadvantages.  In this more than one system is used and they are interfaced appropriately with the others.  Depending on the systems that are coupled, they are called hydro-pneumatic, electro-pneumatic, electro-hydraulic, etc,

 Hydro Pneumatic Press

            Many Industries are using manual presses like toggle presses, fly presses, arbor presses for blanking, piercing, riveting, bending, embossing, etc., It is also used for forming two or more components in Manufacturing Industry.

            Manual operation of these presses gives fatigue to the operator, since he has to exert physical energy. Due to this the efficiency also gets lowered down.Considering these facts, the Hydro pneumatic press has been designed, which will reduce the wastage of human energy and increase the production rate.

           We know that hydraulic system is applied to attain precise movement. But in Pneumatics, due to the compressibility characteristic of the air, the air cylinder tends to slow down on meeting an increase in load and to accelerate or jump forward when working against a load which suddenly decreases. So, pneumatic actuators are not suitable for the finer movement of the machine tool movement

         These problems can be solved by combining the two fluids – air and oil. By the use of these two media, the quick action of air and the smooth high pressure action of oil blend ideally to provide a concept for the design of new Hydro-Pneumatic press. It should be made clear that although the two fluids are used in the circuit they are not to be mixed. In fact every precaution is taken to keep them separated.

The basic laws of Hydraulic and Pneumatics are Pascal’s law, Boyle’s law, Charles’ law, and Gay lussac’s law. These laws are obeyed by our Hydro-Pneumatic press.

Advantages of Fluid Power Systems

·      The fluid power drives are more compact than a mechanical drive because it      eliminates the need for links like cams and gears.

·         Multiplication of small forces to achieve greater forces for performing work.

·         It easily provides infinite and step-less variable speed control which is difficult to obtain from other drives.

·         Accuracy in controlling small or large forces with instant reversal is possible with hydraulic systems.

·         Constant force is possible in fluid power system regardless of special motion requirements, whether the work output moves a few millimeters or several meters per minute.

·         As the medium of power transmission is a fluid, it is not subjected to any breakage of parts as in a mechanical transmission.

·         The parts of hydraulic system are lubricated with the hydraulic liquid itself.

Comparison of Pneumatic and Hydraulic system

• For automation, most of the trade-offs favour pneumatic actuators since pneumatic system have low weight and leakage co-efficient.

• The most significant difference between hydraulic and pneumatic system is compressibility, which usually signifies disadvantage. 
• Further, the stiffness or impedance of the pneumatic system can be controlled more easily than with hydraulic counterpart. 
• Moreover, a pneumatic system allows easy energy storage.  The mechanical energy for automation can be stored as compressed air at a high pressure.  A regulator can expand the stored air to the proper working pressure. 

Construction Of Hydro-Pneumatic Press

            Basically the hydro-pneumatic press consists of the following parts,

• Hydro-pneumatic cylinder
• Cylinder mounting plate
• Supporting pillars
• Base plate
• Pneumatic control systems
• Electrical control panel
• Pneumatic pipelines

1. Hydro-Pneumatic Cylinder

            The main pressing operation of the press is given by this cylinder and hence it is also known as actuating cylinder.  This hydro-pneumatic cylinder is the active component in the press and it consists of the below parts,

·         Cap nut

·         Top end plate

·         Top barrel

·         Primary stroke piston

·         Top partition block

·         Middle barrel

·         Secondary stroke piston

·         By pass rod

·   Bottom partition block

·   Bottom barrel

·   Power stroke piston

·   Bottom end plate

·   O-rings

2. Cylinder Mounting Plate

            It is a mild steel block which is capable to withstand a high pressure caused by the hydro-pneumatic cylinder.  It consisting of drilled hole of diameter 32mm at extreme ends for accommodating the supporting pillars. It also consists of drilled hole at the centre of the plate for the reciprocation of the power stroke piston and for fixing the cylinder to the base structure. This plate is of 38mm thickness. 

3. Supporting Pillars

            The supporting pillars are made up of mild steel of diameter 32mm, the whole weight of the cylinder and the cylinder mounting plate will act on these shafts.  Usually the raw material is of greater diameter and then it is turned to the required diameter.

4. Base Plate

            This is the plate where the job will be placed and the operation is performed.  For facilitating the clamping operation a T-slot has been provided.  This block is of thickness 40mm and cross-section 350mm x 240mm.  It consists of holes for accommodating the supporting pillars.

5. Pneumatic Control Systems

            This system includes various DCV’s, FRL unit, Mufflers, etc. They are used to regulate and direct the flow of air in the respective pipelines.

Solenoid Operated Direction Control Valves (DCV)

            A very common way to actuate a spool valve is by using a solenoid.  When the electric coil (solenoid)      is energized it creates a magnetic force that pulls the armature into the coil.  This causes the armature to push on the push rod to move the spool.  There are no seals around the armature to wear or restrict its movement; this allows all the power developed by the solenoid to be transmitted to the valve spool without having to overcome seal friction.  Impact loads which frequently cause premature solenoid failure are eliminated with this construction. 

Working

            The Working of the Hydro-Pneumatic press comprises of four stages.

v  Start Position

v  Low Force High Speed  approach

v  High force short travel power stroke

v  Low force Rapid retraction

Start Position

            In this stage all the pistons are in their respective TDC positions. The air is sent into the port 3 of the press and the air from both 1 and 2 ports are exhausted. The oil is filled into top barrel through the bore in the primary stroke piston rod. Simultaneously oil gets filled in the bottom barrel through the bypass rod. In this position, the oil remains static and no pressure is exerted to it. The punch head remains in the maximum distance from the base plate.

Low Force High Speed Approach

When the DCV A is actuated, the compressed air flows through the port 1. This results in the extension of the Primary stroke piston. So the primary stroke piston makes the oil to exert pressure on the Power stroke piston. Thus, the rapid extension of the punch head takes place.

High Force Short Travel Power Stroke

When the DCV B is also actuated along with the DCV A, the compressed air is made to enter into the port 2. This extends the secondary stroke piston. The rod of this secondary stroke piston enters into the bore in the Power stroke piston. The same force is exerted in the very small area which results in a very high pressure. This very high pressure is capable of doing the punching operation.

Low Force Rapid Retraction

            When both the solenoids are de-energized, both the DCV’s come to their offset mode, thus exhausting the ports 1 and 2, and sending air into the port 3. This results in the retraction of all the three pistons to their initial positions.

Two Hand Safety Operation

Push Buttons are provided to energize the solenoids. When the first button is pressed, rapid extension takes place. By keeping the first button down, if the second button is also pressed, punching operation takes place. If both the buttons are released, then the retraction takes place. If only button 2 is pressed, the ram goes to its initial position. Thus, to make the press working, the worker has to use both of his hands. So, safety is ensured for the worker.

            

Specifications

Size                             :350mm x 250mm x 1000mm

Material                       :All steel body

Input air                      :6.2 kg/cm²

Electric power            :For timer 12V DC   or   24V DC

                                   :For solenoid    48V AC   or   220V AC

Bed to Ram Height    :150mm

Bed Size                     :350mm x 240mm

Bed Plate  Thickness :40mm

Stroke Length            :72mm

Circuit explanation

            The DCV A is two position five port solenoid operated spring offset valve.  The port 1 and 3 of the cylinder are connected in the offset position of the valve A.  The DCV B is two position three port solenoid operated spring offset valve, which connects the opening 2 of the cylinder in the offset port condition initially.  Input source to both the valves are given in a single line.  An emergency unit is set up which consist of a solenoid actuated two position two port DCV.  The input unit includes compressor, FRL unit, and pressure regulator.  The exhaust port of each DCV is connected with muffler.

Circuit Performance

            When DCV A is energized,  it shifts to position of the valve.  Thus the

pressurized air supply is given to opening1of the cylinder and the air exhaust from the opening 3 of the cylinder.  When DCV B is energized and hence supply is given to opening 2 of the cylinder.  When both the DCV’s are in de-energized condition, the supply is given only to opening 3 and hence it helps in retraction of the piston.When the emergency valve is energized the supply to the entire unit is stopped immediately.

Ladder Diagram

            The electrical diagram is called the ladder diagram.  PB1 (NO) is a push button when pressed, SOL A gets actuated and hence extension takes place.  When PB2 (NO) is pressed, SOL B gets actuated and hence power stroke takes place, when stop button is in NC condition. When it is pushed, the 1-CR gets de-energized, this breaks 1-CR and de-energizes it, and hence SOL C is de-activated.

Salient Features

·         Fast action

·         Compact, light weight and vibration free pneumatic valves

·         Force and speed infinitely adjustable

·         Energy efficient: 50% to 70% raising over equivalent hydraulic and pneumatic systems

·         Low cost: upto 60% cheaper than an equivalent hydraulic press

·         Safety: true, non tie down, interlocked two hand safety operation

Conclusion

            All the basic expectations of today’s industry such as automation, increased production, low cost, and appreciable quality are met by this Hydro-Pneumatic press. Low cost is proved by using Pneumatic source and getting the same tonnage capacity as that of a Hydraulic press.

            A single compressor is enough to run two or more Hydro-Pneumatic presses. The safety of the worker is also ensured by employing the Two Hand Safety system in the fluid circuit.

             This press is also portable and reliable as it has very small machine structures and can give the large tonnage. So, this press is expected to meet today’s Industrial Manufacturing scenario.                                                                                                                                 

Bibliography

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