Power Press | Different Operations on Power Press

ABSTRACT

Power Press is a functional sheet metal machine that is utilized for bending, cutting, pressing and forming work-piece into different sizes and shapes. It is primarily used in metal manufacturing firms and shops. This multi-tasking equipment that involves a press mechanism applies pressure to compress and shape the required material. The machinery has an ability to clamp the sheet of metal between the machinery tools. Its force or tonnage, as well as working length, defines its elementary frameworks. Power Press Machines are easily available in the market as per its standard and custom specifications.

INTRODUCTION

In the Mid19th century, manual and rotary-cam hammers began to be replaced in industry by the steam hammer, which was first described in 1784 by James Watt, a Scottish inventor and Mechanical Engineer who also contributed to the earliest steam engines and condensers, but not built until 1840 by British Inventor James Nasmyth. By the late 19th century, steam hammers had increased greatly in size; in 1891 the Bethlehem Iron Company made an enhancement allowing a steam hammer to deliver a 125-ton blow.

Most modern machine presses typically use a combination of electric motors and hydraulics to achieve the necessary pressure. Along with the evolution of presses came the evolution of the dies used within them.

A power press is a very useful machine used in mass production mainly from cold working of ductile materials such as mild steel. Normally a power press has a rotating flywheel which acts like a storehouse of energy and is used to operate the ram which provides the necessary impact to the work-piece. The various operations of the power press are performed using the components such as the bed, bolster plate and ram. There is also a mechanism which is known as knock out and its main function is to help eject the finished workpiece from the press tool. Since a huge impact is made on the work-piece it is necessary to ensure that proper cushioning is provided beneath the bolster. The adjacent image shows a typical power press which is used commonly is the manufacturing industry.

The operations carried out include a wide variety of processes such as bending, deep drawing, curling, piercing and so forth. Although power presses are quite fast, still they could be made even faster by automating them and this is what we are going to discuss in this article.

Automation in Power Presses

Time is money and this is equally true for a production line in industry. Hence engineers are always on the lookout for making better machines and improvising on those machines to make them work even faster. The same thing applies to a power press wherein the production can be increased by over four times if automation is applied.

Before one could think about automating a mass production machine such as a power press, the main points to be considered are the least wastage of the raw material used in production, having proper security procedures in place and so on. Various other technical parameters are considered prior to automation design including current speed of the press, width of the stock etc.

Since it is important to have a continuous feed of the stock when performing automated operations using a power press, the stock is not fed in a straight fashion but from a circular loop which normally comes either in cradle wound format or reel format. The choice depends on the thickness of the sheet and reel type format is used for thinner sheets while cradle is used for thicker sheets.

The rolled sheet passes through a mechanism which straightens it out by removing any residual effect of the coiled arrangement. This is done by using various methods such as passing the sheet through a set of rollers and could be using a powered system for the same. The sheet is then fed intermittently into the feeder where the necessary operations are performed at each increment.

The above process may seem quite simple yet a lot of things have to be considered so that the feed is done is a proper manner. All alignments should be nearly perfect otherwise there could be defect in the pieces that are manufactured which could result in wastage and loss of production.

It is important to mention at this stage that the process of automation does not only relate to making the stock getting fed automatically to the system but also should contain the provision to automatically eject the finished parts apart from a system from scrap removal. Last but not least there should be safety provisions in place so that the power press achieves automatic shutdown in case any dangerous situation develops.

Evolution of Press Machine over the years

               

FIG TECHNOLOGICAL EVOLUTION OF PRESS MACHINES

TYPES OF PRESS

There are following types of Press Machines:

·        Manually Operated (Fly) Press:

The press is operated by human hands. It is a bench mounted press commonly used for the production of small components. It is a simple and low cost press, suitable for light operations, like piercing, blanking, bending, etc. As the Fig. 1.5. shows, the arm is rotated manually, the ram moves, up and down to perform the necessary operation. The ram is fitted with punch and the job is resting on the bed

FIG A MANUALLY OPERATED (FLY) PRESS

·         Electric Motor Operated Press:

The press is operated by an electric motor. The motor drives the crank shaft which converts the rotary motion into reciprocating motion of the ram. The ram fitted with the punch, to operate upon the job held on the die block and bolster. The electric motor supplies energy to the fly wheel and this energy are transferred to the ram via a clutch and crankshaft.

e.g. Power Press etc.

TYPES OF POWER PRESS

·         Pillar Type: 

It is used for producing reliability, high work proficiency, and safety.

·         Hydraulic Power Press: 

Working on the principles of Pascal, this machinery uses a hydraulic cylinder to create a Compression strength.

·         C Type Power Press: 

Fabricated with modern techniques, it is used for changing the shape of the work-piece into desired size or form by pressuring the application.

APPLICATIONS OF POWER PRESS

·         Power Press is used in the heavy manufacturing applications like allied industrial establishments, factories, and engineering plants.

·         It is used as a pressing machinery in the manufacturing industry.

·         Due to its simplified metal bending tasks, it is utilized as a workshop machine.

·         The enormous salient features are used for assembling, drawing, and straightening tasks.

·         They wield in industries like automobile, agriculture, bicycle, engineering, and electrical.

·         Hydraulic cylinders are plied to generate compressive force and for the formation of hydro.

etc

BENEFITS OF POWER PRESS

·         The designing and versatility of the machinery give users an advantage of moving its freely around the workplace.

·         It trims, presses, straightens, assembles, and disassembles into various shapes.

·         It is categorized as sturdy, durable and energy efficient machine.

·         Has low initial cost and is a user-friendly machine.

·         This Highly reliable machinery with amazing pressing, punching and clasping techniques doesn't require lofty maintenance.

·         The compact size of the machinery makes it stay steady for a longer term.

etc

PRESS WORKING TERMINOLOGY

A simple cutting die used for punching and blanking operation as shown:

                          I.            Bed:

The bed is the lower part of the press frame that serves as a table to which a

Bolster plate is mounted.

                       II.            Bolster Plate:

This is a thick plate secured to the press bed , which is used for locating and

supporting the die assembly. It is usually 5 to 12.5 cm thick.

                     III.            Die Set:

It is unit assembly which incorporates a lower and upper shoe, two or more guide parts and guide part bushings.

           IV.            Die Block:

It is a block or a plate which contains a die cavity.

                        V.            Lower Shoe:

The lower shoe of the a die set is generally mounted on the bolster plate of a press. The die block is mounted on the lower shoe, also the guide post are mounted on it.

          VI.            Punch :

This is male component of  a die assembly, which is directly or indirectly moved by and fastened to the press ram or slide.

         VII.            Upper Shoe:

This is the upper part of the die set which contains guide post bushings.

        VIII.            Punch Plate :

The punch plate or punch retainer fits closely over the body of the punch and holds it in proper relative position.

          IX.            Back up Plate:

Back up plate or pressure plate is placed so that intensity of pressure does

not become excessive on punch holder. The plate distributes the pressure

over a wide area and the intensity of pressure on the punch holder is reduced

to avoid crushing.

                       X.            Stripper:

It is a plate which is used to strip the metal strip from cutting a non-cutting

Punch or die. It may also guide the sheet.

FIG 1.6, PRESS WORKING TERMINOLOGY

PRESS OPERATIONS

a)    Sheet Metal Cutting

Sheet metal cutting is a major classification for many different press-working operations. Cutting operations involve the separation of the metal of the sheet in certain areas. This separation is caused by shearing forces acting on the metal through the edges of the punch and die. Press-working, a term referencing sheet metal operations in general, involves the working of a sheet between two die. In press-working, the upper die is called a punch. Sheet and plate generally refers to rolled metal with a high surface area to volume ratio. The difference is that sheet metal is under 1/4 inch (6mm) in thickness, while plate metal is thicker. Most of the sheet metal cutting processes discussed can be performed on both sheet and plate metal, although for many sheet metal operations difficulties will arise with increasing plate thickness. Usually "sheet" and "sheet metal" is also referencing plate.

FIG 1.7 CUTTING OF SHEET METAL

One of the simplest types of press working operations is a sheet metal cutting process called a straight cutoff. A punch separates a length of stock along a straight line. Industrial sheet metal cutting operations such as this will usually incline the punch so as to reduce the maximum force needed by distributing the required force over the cutting stroke. The angle that the punch may be inclined varies from 4 to 15 degrees, however the higher the angle, the greater the magnitude of the horizontal force component acting to displace the work. For that reason angles are usually under 9 degrees. The metal sheet is fed through after each cutoff and the process can be repeated very quickly.  

FIG 1.8 , STRAIGHT CUT OFF

b)    Cutoff And Parting Of Sheet Metal

Cuttoffs and partings are important basic sheet metal cutting processes performed in manufacturing industry. Cutoffs need not be straight, rather they may be over several lines and/or curves. Partings are similar, in that a discrete part is cut from a sheet or strip of metal along a desired geometric path. The difference between a cutoff and a parting is that a cutoff can be nestled perfectly on the sheet metal, due to its geometry. With cutoffs, the cutting of sheet metal can be done over one path at a time and there is practically no waste of material. With partings, the shape can not be nestled precisely. Partings involve cutting the sheet metal along two paths simultaneously. Partings waste a certain amount of material, that can be significant.

FIG 1.9 CUTOFF VS PARTING

c)     Blanking Of Sheet Metal

Blanking is the cutting of a sheet metal part along a closed contour in one step. The piece cut out is called a blank and may be further processed. Many blanks are often continuously cut out of a sheet or strip. Blanking will waste a certain amount of material. When designing a sheet metal blanking process, the geometry of the blanks should be nestled as efficiently as possible to minimize material waste. A distinction should be made between the two sheet metal cutting processes of blanking and punching, since essentially they are the same process. In punching, the piece cut out is waste. In blanking, the piece cut out is the work and is kept.

FIG 2.0 BLANKING

d)    Sheet Metal Slitting

Slitting is a shearing process in which the sheet metal is cut by two opposing circular blades, like a can opener. Slitting can be performed in a straight line or on a curved path. The circular sheet metal cutters can be driven, or the work may be pulled through idle cutters. Slitting usually produces a burr that must be removed.

FIG 2.1 SLITTING OF SHEET METAL

Slitting is often an important sheet metal cutting process, performed early in the processing of manufactured parts. Press-working machines and die may require a strip of a certain width. Sheet metal usually arrives to the factory in coil, (see metal rolling ). These sheets are usually much wider than needed and are cut into strips of desired width by slitting. Sheet metal coil can be cut into many strips at once, by several simultaneous slitting operations. These strips provide sheet metal stock for further press-working processes.

FIG 2.2 CUTTING OF METAL STRIPS

e)     Perforating Of Sheet Metal

Sometimes it is desirable to punch many holes in a piece of sheet metal, often in a certain pattern. These holes may be round or some other shape. Perforating sheet metal will allow for the passage of light or fluid material through the sheet. It can often serve in ventilation and filtration of fluid substances. Perforated sheet metal is also used in structure and machine construction, to reduce weight and for cosmetic appearance. Special equipment is employed that punches many holes at once, at a high rate. In industrial manufacturing practice, the size of these holes is usually from .04 inches to 3 inches, (1-75mm). The upper rate at which some special perforating machines can punch holes is 100,000 to 300,000 per minute.

FIG 2.3 PERFORATING

f)      Punching And Slotting

Punching is also a basic sheet metal cutting process, that has many different forms and applications in pressworking manufacture. Punching involves cutting out a piece of material from a metal sheet. The material removed may be round or some other shape. This excess metal, once punched out, is called a slug and is usually discarded as scrap. Slotting is a type of punching operation. Slotting refers specifically to the punching of rectangular or elongated holes.

Mechanics of Cutting Sheet Metal

Mechanics of cutting sheet metal should be understood when designing a pressworking manufacturing process. The work piece in a sheet metal cutting operation is secured to the lower die, while the motion of the upper die, (called a punch), enacts the cutting. Edges of the punch and die do not line up precisely, due to a clearance or space between them. The punch is designed to enter the matching hole in the lower die and is always at least a little smaller. Clearance size, in sheet metal cutting, will vary with different process factors and its selection will affect the quality of the manufactured part.

FIG 2.4 SHEET METAL CUTTING SETUP

Cutting Considerations

Lubrication is an important factor in maintaining sheet metal cutting molds. Sheet cutting operations are powered mainly by mechanical presses, the crank press is often used, (see presses). The lower die are straight near the top of the hole, then an angular clearance is provided to allow for the expansion of the blank or slug after it is forced out of the hole. Another consideration concerning the blank or slug is its tendency to warp, due to the forces involved during the cutting process.

Power press machine and the cutting die

  

   

FIG 2.6 CUTTING DIE OF POWER PRESS

FIG 2.7 POWER PRESS

A mechanical power press (MPP) is a machine that uses dies and pressure to shear, punch, form, and assemble metal or other material. They can develop up to several thousand tons of pressure, and the area where they perform work - the "point of operation" - poses a serious pinch point hazard.(THE CAPACITY OF THIS MACHINE IS =40TONS)

                       

FIG 2.8 , LABELED IMAGE OF POWER PRESS

FIG 2.9 CUTTING DIE

FIG 3.0  WORKING ON POWER PRESS

CONCLUSION

The mechanical press transforms the rotational force of a motor into a translational force vector that performs the pressing action.

Power press is mostly used for industrial purposes where a large pressure is required for compressing metals into thin sheets. An industrial press uses the material to be worked upon along with the help of the press plates to crush or punch the material into a thin sheet.

Power Press Machine is one of the most beneficial and convenient workshop machinery which wields for pressing, cutting, bending and forming the sheet metal into various sizes and shapes along with multitasking tools.