Historical Overview Of Press Development

Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Historical Overview of Press Development In simple configurations, presses have been used since antiquity to extract or Press oil and other substances from vegetable matter. A simple primitive form of lever press is illustrated in Figure 1. A pole or timber is placed under a rock ledge, which serves as a fixed pivot. The material to be pressed is placed on a suitable hollowed out stone, which also acts to gather the liquid pressed from the material. The liquid is collected in a simple container. Pressure is supplied by stones placed on the end of the timber. This type of press is still used by primitive cultures. 1

Simple Wooden Lever Press

Figure 1. A simple lever press used to extract or press substances from vegetable matter.

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R. Ellen, A Vertical Wedge Press from the Banda Islands, Technology and Culture, January 1992, Volume 33, Number 1, © The University of Chicago Press. In this article a photograph of a level beam press together with a drawing of the wedge press principle are shown. The evolution of the design of the wedge press shown in figure 2 is considered to have originated in ancient China, and the design used elsewhere.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Another simple press, illustrated in Figure 2, makes use of the wedge and ramp principle. A rectangular timber framework contains the wooden pressing platens. Pressure is applied by driving two or more wedges together to apply pressure to the pressing blocks. Such presses are considered to have their origin in ancient China. A similar design was found being used for lacquer production in 19th century Japan.

Wooden wedge and Ramp Press

Figure 2. Another simple press for vegetable matter makes use of the wedge and ramp principle. Its historical development is described in reference 1.

SCREW PRESSES Early printing and coinage presses are the most familiar examples of screw press applications. This type of press was well developed by the 16th century. Screw presses of metal construction, and fitted with a heavy large diameter screw actuating hand wheel, develop large forces upon contact with the work. The amount of energy stored, and hence the work performed is controlled by how fast the hand-wheel is rotating before contacting the work. The control over the amount of available energy is a very useful feature of a screw press.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Manually Operated Toolroom Screw Presses Manually operated screw presses still find limited use in small die construction and tryout work. A toolroom screw press is illustrated in Figure 3. Typical applications include die-tryout, as well as die assembly and disassembly involving pressing operations. Limited use is still made of such presses for forming mold cavities of very ductile steel with a hardened steel male master called a hub. The latter process is known as hubbing. After the hubbing steel receives the impression of the hub to the correct depth, the mold cavity so formed is hardened for wear resistance, usually by carburizing.

Figure 3. A toolroom screw press employs the centuries-old design principle of early printing and coinage presses. Smith & Associates Hand-operated screw presses also remain useful for shear fitting irregularly shaped punches into tool-steel die blocks and strippers. Hand presswork operations such as hubbing mold cavities and shear fitting of dies have been largely replaced with either conventional, or wire-burn electrical discharge machining (EDM).

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Modern Screw Press Applications Nearly all-current production of screw-presses is limited to power-actuated types. In its modern power-driven form, they are very useful for precision forging and coining operations. Power driven screw presses have a distinct advantage for closed die forging operations when compared to crankshaft-actuated machines. The flywheel rotational speed of the screw press is set for energy needed to perform the operation. At the completion of the operation, the flywheel stalls and is reversed to open the press. Another feature of some screw presses is a torque limiting slop clutch between the flywheel and the screw.

TRIP AND DROP HAMMERS In order to increase the productivity of forging operations, a hammerhead of substantial weight was attached to the end of a lever. Early trip hammers were operated by foot power, thus leaving both hands free to position the work. Foot actuated kick presses are still used by manufacturing jewelers for precious metal forming and shearing operations. Water powered designs evolved for large work. A widespread application in the eighteenth and nineteenth centuries was forge refining of gray iron into wrought iron. Gray iron typically contains 2% to 3% carbon and contains impurities such as silicon, sulfur and phosphorus. Gray iron is too brittle to use for engineering applications such as steam boilers, structural members subject to tensile loading, and highly stressed machine parts. By working the gray iron while in a plastic state in a hot forge with a trip hammer, the excess carbon is oxidized. The other impurities are converted to a slag, most of which is forced out of the heated mass. The slag remaining in the finished iron results in a fibrous structure, which had superior fatigue and brittle fracture resistance than both the early Bessemer and open-hearth steels of the early twentieth century. Wrought iron also has excellent corrosion resistance compared to carbon steel. The shock and fatigue resistance of wrought iron is due to its fibrous nature. When strained, it can be compared a strong wooden branch or steel cable rather than a homogeneous steel rod. Even with the advent of low-cost process for steel making, the A. M. Byers Company of Pittsburgh instituted the Aston Process in 1927 for producing wrought iron by mixing a ferrous silicate slag with molten Bessemer steel.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Board and Roller Actuated Drop Hammer

Figure 4. A board type drop hammer. The weighted hammer is lifted by the friction of the pulley driven rollers at the top of the machine against a wooden board attached to the weight. Either the wrought iron was forged into finished products, rolled into rod, bar, or sheet. Throughout most of the nineteenth and well into the twentieth century, wrought iron was widely employed for steam boiler construction, pipe, and a variety of structural uses. 2 2

W. T. Frier, Elementary Metallurgy, McGraw-Hill, New York, © 1952. Chapter 3, Cast and Wrought Iron, has an excellent description of the commercial uses of gray, malleable, and special cast irons as well as wrought iron at the mid twentieth century.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Small trip hammers deliver blows either continuously or as single hits by actuating foot treadle or hand-operated lever. Trip hammers found widespread application for forging items such as rifle barrels and wrought iron articles.

Simple Drop Hammer Early drop hammer presses for pressworking sheet metal consisted of wooden framework or housing in which a fixed lower die and movable upper die were placed. For forming simple metal parts such as embossed decorative metal panels, the lower die was made of zinc while the upper die was of lead cast directly onto the zinc lower die, which served as part of the mold. The lead upper die was raised in several ways depending on production requirements and the prime mover available. One simple lifting arrangement made use of a rotating horizontal drum at the top of the machine driven by water or steam power. To lift the upper die, a rope attached to the die having several turns around the drum was pulled taunt by the operator. Tightening the rope greatly increased the function of the rope on the drum, thus raising the upper die. Releasing the rope permitted the heavy upper die to fall onto the lower die with the work piece in place. Several blows might be required to completely form the work. The lead upper die would become dull more rapidly than the harder zinc lower die. The upper die was sharpened by simply dropping it onto the lower die several times without a workpiece in place. The zinc lower die was either manually redressed or recast when dull. Similar methods are still used to a limited extent for forming low-volume stampings such as aircraft sheet-metal parts. Factors that may cause this forming method to be replaced with other methods such as hydroforming are concerns over the toxicity of lead.

Drop Hammer Development Both open and closed die hot forging was a natural application for the drop hammer. Powerful blows were obtained by providing a heavy ram guided by the machine housing. The upper die was attached to the ram by a dovetail slot and/or bolts. Several other methods devised for raising the weight of the ram and upper die include lifting a long flat board attached to the ram by power-driven frictional rollers. A board type drop hammer is shown in Figure 4. The board type drop hammer is still in use in some shops. Other means to raise the weight of the ram include steam and pneumatic cylinders. The steam lifting arrangement was further improved upon by employing a double acting cylinder lifts the ram and drives it downward. In this form, the drop hammer evolved into the more powerful and productive steam hammer illustrated in Figure 5.

Steam Hammer 6

Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Figure 5. An example of a steam hammer employing a double acting cylinder to both raise and provide added downward force to the heavy weight of the hammer.

Today, the steam hammer is becoming obsolete. Drop hammers are often powered with compressed air to avoid the cost of maintaining a high-pressure steam boiler. Drop hammers are still in use. Applications include routine production work as well as application in versatile job shops. Small drop hammers capable of delivering sharp blows for coining work are used by manufacturing jewelers. Much of the current forging work is done with powerful and precisely controllable hydraulic presses having force capacities of 50,000 short tons (444,800 kN).

C-FRAME PRESSES

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

The 19th century fabrication of wrought iron into structural components and steam boilers required the punching of many rivet holes. Wrought iron contains abrasive impurities. Drilling the holes was slow and the tool, made of plain high-carbon steel, required frequent resharpening. The C-frame press evolved from the rivet punch, an example of which is illustrated in Figure 6. The screw and attached punch were actuated by manually turning a wrought iron bar inserted through the cross-drilled holes in the screw head. Historically, punching holes was much faster than drilling. Today, the punching process remains the most economical method of producing holes in materials ranging from thin foils to thick high alloy steel plates.

Example of Early Punching Capacity Early ironclad warships were covered with one or more thicknesses of wrought-iron plate. The Confederate warship CSS Virginia, better known as the Merrimack, was covered with two layers of two-inch (50.8 mm) thick rolled wrought iron plate. Punching holes in one-inch plate (25.4 mm) plate was possible in the early 1860s, but the two layers of two-inch (50.8 mm) plate used to armor the vessel required slow drilling. 3

Power Press Development These C-frame punches were used extensively in boiler and bridge construction as well as general steel fabrication employing rivets. The next step in the evolution of the boilermakers' rivet punch was to replace the screw mechanism with a hand-operated hydraulic pressure system. The mechanism employed is essentially the same as that of the familiar hydraulic bottle jack. Examples of this improvement were in use from at least 1895 and perhaps earlier. Portable hand-actuated C-frame structural steel punches are still produced with the essential design features unchanged for approximately a century. An important power press development was the replacement of the actuating screw in both the screw press and C-frame boilermaker's punch with a horizontal crankshaft fitted with a flywheel.

Mechanical Bulldozer The term bulldozer was applied to a specialized type of horizontal mechanical power press years before the familiar earth moving traction machine was invented. A 19th century mechanical bulldozer press is shown in figure 7. Machines of this type are still built in hydraulically powered versions. While the term bulldozer is now equated with a type of earth moving machine, it is still correctly applied to this type of press.

Screw Actuated Rivet Punch 3

Edward R. Crews, The Industrial Bulwark of the Confederacy, American Heritage of Invention and Technology, Winter 1992, © American Heritage, New York.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Figure 6. An early example of a screw-actuated rivet hole punch, which evolved into the C-frame press. Smith & Associates Bulldozers are very versatile for a variety of plate and structural steel forming operations. In the 19th century, they were widely used for applications ranging from forming parts of wrought iron boiler shells to punching rivet holes and forming irregular curves in wrought iron structural members. The machine is open on three sides. Heavy work is easily positioned with a crane in the opening. The tooling for bending and punching operations is simple and easily fashioned by a clever blacksmith.

Double Back Geared Mechanical Bulldozer

Figure 7. A line drawing of a 19th century mechanical bulldozer. These machines were extensively used for a variety of heavy plate and structural metalworking operations. Note the lack of guarding of the reduction gearing. The Bulldozer is essentially a C-frame press laid on its back. This type of machine remains useful for a variety of heavy structural metalforming applications today.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Power C-frame Presses The C-frame press has great versatility. It is open on three sides for setting dies and inserting large workpieces. A problem common to all C-frame presses is machine deflection, which results in angular misalignment under load. The angular deflection may be reduced by installing two tierods on the front of the press. The tie rods will reduce, but not eliminate angular deflection. A 19th century C-frame press of the open back inclinable (OBI) style is illustrated in Figure 8. This machine was built by the E. W. Bliss Company. The company first entered the press building business during 1857 in Brooklyn, New York.

An Early Style of Open Back Inclinable C-frame Press

Figure 8. An early C-frame open back inclinable (OBI) press built by the E. W. Bliss Company. Note the foot pedal, which actuated a full revolution clutch. E. W. Bliss Company

Some C-frame presses currently being built incorporate the open back inclinable (OBI) feature. The inclinable feature was originally developed in order to facilitate gravity discharge of parts and scrap through the rear of the machine. Today, air blow-off and conveying devices are mainly used to serve this purpose. Cframe press angular deflection is held to acceptable limits by heavy frame construction.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

The press frame structure rests directly on the foundation or shop floor. This type of press is known as an open back stationary (OBS) machine.

An Early Straightside Style Press In 1855, Augustus Alfred, a New England farmer, machinist and clock-maker, built the small straight-side press shown in Figure 9. The press, like many screw-presses of the period, was equipped with a hand-actuated flywheel and slide guiding system. The combination of flywheel momentum and the mechanical advantage of the crankshaft provided sufficient force to punch out clock parts by hand. The machine shows wear on the flywheel indicating that it was also power driven with a flat leather belt. Today, this machine is located at the Smithsonian Institution in Washington D.C.

Figure 9. The 1855 straight-side clockmaker's press built by Augustus Alfred. Smithsonian Institution. 4

E. W. Bliss Brooklyn Foundry

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Brooke Hindle and Steven Lubar, Engines of Change, The American Industrial Revolution, 1790-1860, Smithsonian Institution Press, Washington, D.C., © 1986. The 1855 Alfred press is at the Smithsonian Institution. The authors of Engines of Change note that the periphery of the large handwheel has wear indicating that the machine was belt driven at some time. Judging from the extreme amount of crown in the wheel, power operation probably was not the inventor’s original intention.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Figure 10. The E. W. Bliss Company Foundry department in Brooklyn, New York. E. W. Bliss Company In the United States, the E. W. Bliss Company was a leading manufacturer of power presses. To date, the company has built over 400,000 presses, many of which are still in use. Many early and mid 19th century power presses had no provision to permit single stroking. From both the standpoint of operator safety and productivity, an important improvement was the addition of a mechanical clutch. When this style of clutch was engaged by momentarily pressing a foot pedal, the press completed a full revolution and stopped at the top of the press stroke. The press shown in Figure 8 incorporates this feature. Few full revolution clutch presses are built today. The application is mainly limited to small low cost C-frame bench presses. OSHA safeguarding requirements severely restrict the application of full revolution clutch presses.

The Relationship of the Power Press to the Machine Tool Industry Figure 3 illustrates the E. W. Bliss Brooklyn press erection floor. The construction of 19th century power presses required an efficient foundry to cast iron press structural parts and bronze bearings illustrated in Figure 10. Large machine tool such as lathes, plainers and boring machinery was also required to fit the parts.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

In the early press construction shops, considerable hand fitting was also required by filing and hand scraping sliding surfaces such as the ram-guiding surface known as the gibs. Bearings for shafts also required hand fitting by scraping. Today, precision presses still are fitted together by hand scraping. However, improved machine tool accuracy has greatly lessened the amount of hand fitting required to build a modern press. Much of the hand fitting takes place on the press erection floor illustrated in Figure 11. Modern press builders specializing in large machines assemble the presses in pits that may be two or more stories deep. This permits the erection of safe scaffolding around the machine as it is assembled. Another advantage of the assembly pit method of erection is that overhead crane height requirements are not as high as would be required without the availability of erection pits.

E W. Bliss Press Erection Floor

Figure 11. An early press erection floor at E. W. Bliss Company. This is where the final fitting of the machine takes place. E. W. Bliss Company

An Example of an Early Pressroom The presses in Figure 12 utilized an overhead line shaft to drive the flywheel of the machine. Early machines had no clutch and ran continuously. Feeding the work into the continuously running press was very difficult.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

The press in the foreground has a dial feed mechanism and point of operation safeguarding. The dial feed is powered by the press and indexes in synchronism with the ram motion. This permits safe loading of blanks or parts requiring multiple operations. Dial feeds could be designed with tooling to accomplish several operations in the same press.

A Row of Presses Driven by an Overhead Lineshaft

Figure 12. A line of presses driven by an overhead lineshaft. The lineshaft could be driven by waterpower, a steam engine, or a large electrical motor. A typical application for equipment of this type was for the production of ammunition cartridges. E. W. Bliss Company

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

A Double Action Press for Deep Drawing Work

Figure 13. A double action press with a separate blankholder and plunger for deep drawing and multiple redrawing work. E. W. Bliss Company

Development of the Partial Revolution Clutch Late in the 1880’s, a mechanical friction clutch was introduced. This clutch used a number of wooden blocks for a friction lining. This device was the forerunner of the air friction clutches used today. As metal part shapes became more complex, special machines to produce these shapes were developed. Figure 13 illustrates a double action press with a separate blankholder and plunger for deep drawing and multiple redrawing requirements. The double action press was used for producing items ranging from baking tins to wheelbarrows and locomotive headlight reflectors from metal sheet stock. The growth of automobile mass production in the early 20th century created a market for larger power presses.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

A new type twin end drive double action toggle press illustrated in figure 14 was introduced in April of 1910 to meet the need for larger drawing press capacity. This machine was used by Chalmers Motor Company to manufacture drawn fenders. As automotive production grew, production rates were increased to supply the assembly lines. This created a demand for improved material handling and automatic feeding devices.

1910 Double Action Toggle Press

Figure 14. A twin end drive double action toggle press used by Chalmers Motor Company to manufacture drawn fenders. E. W. Bliss Company

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

HYDRAULIC PRESSES Like the mechanical press, the hydraulic press has an interesting evolutionary history. Augustus Q. Tucker founded one pioneering firm in the field, The Hydraulic Press Manufacturing Company or HPM of Mount Gilead, Ohio. He was both a distinguished student of mechanical engineering and owned extensive apple orchards. In 1867, he started research and experimentation that ten years later resulted in the first practical hydraulic cider press. Figure 15 shows the principle operating features of this machine.

Augustus Q. Tucker’s Hydraulic Cider Press

Figure 15. A model of the first practical hydraulic cider press redrawn by the author from an old photograph. Note the dual moving carts and the pumping mechanism. 5 The Hydraulic Press Mfg. Company / Smith & Associates Many of the parts comprising the framework, and even the up acting vertical ram, were made of wood. The original working fluid was water.

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“It Started with an Apple”, 75th Anniversary Commemorative Publication of The Hydraulic Press Manufacturing Company, Mount Gilead, Ohio, 1952. This out-of-print publication is also the source for several half tone illustrations reproduced in this paper.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Note that the original design featured dual moving carts upon which the apples awaiting pressing are loaded in cage like containers (not shown). The two carts and bed arrangement permitted maximizing the pressing duty cycle. Pressed apple pulp is removed and new apples loaded during the pressing cycle. This ingenious dual cart cider press predated the invention of the dual moving bolster system for stamping presses by more than three quarters of a century. Engineer Vasil Georgeff of Danly Machine, a Chicago press builder, invented the latter in 1956. 6 7 Tucker's press worked so well enthusiastic stockholders provided that adequate capital in 1877. Under Tucker, and his successors, the firm prospered. Improved HPM fruit presses employed mainly metal parts. The later production models, most of which are still in service, functioned essentially in the same manner as the compression molding press for thermoplastics shown in Figure 15. HPM did not invent the hydraulic press. Earlier uses in Europe include the application of both screw and hydraulic presses for compressing black powder military rocket propellant. The hydraulic press proved superior in terms of uniformity and safety of rocket production, especially considering the former method was to use a drop hammer. However, HPM is an example of a company that was responsible for many developments that adapted the hydraulic press to high throughput pressworking applications.

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D. Smith, “Quick Die Change”, The Society of Manufacturing Engineers, Dearborn, Michigan, © 1991. The origin of the Quick Die Change (QDC) dual moving bolster for mechanical power presses is discussed in chapter one. The acronym QDC is a licensed trademark of the Danly Machine Company.

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D. Smith, “Quick Die Change Video Training Series”, The Society of Manufacturing Engineers, Dearborn, Michigan, © 1992. Tape one of the five-tape set has an interview with Tom Schafer, retired Engineering Liaison Manager and Attorney as well as Ron Votava, Engineering Manager of Chicago press builder Danly Machine Company. They clearly give credit to Engineer Vasil Georgeff (deceased) for patenting the device in 1956 on behalf of Danly. Cross Licensing of the design was required with another Chicago press builder USI-Clearing in order to employ a captive die cushion pin patent often required by this design. Some writers give credit to Japanese Industrial Engineer Shigeo Shingo for the concept of using a second bolster or carrier prestaged with a new die to effect die changes in less than ten minutes (the SMED or single minute die change concept) at Toyota in 1969. According to the Danly interviews, the complete transcripts of which are contained in the video series Facilitators Guide PP 405-414 dual moving bolster presses, and at least one complete six press tandem line so equipped was sold to Toyota as early as 1959, with the capability to change over from one product to another in under ten minutes. Tony Rante, Danly Mechanical Engineering Manager, is also quoted in the interview, but not included in the finished videotape because of time constraints. This historical data is in no way intended to discredit Shingo. If the system is not properly prestaged, changeover in less than ten minutes will not occur. Shingo's approach to doing as much external changeover work as possible before changeover starts is an accepted industrial engineering practice in setup reduction, provided it results is the lowest overall cost method. For example, it might not be good economy to spend 20 minutes making a product change by interchanging die details as external setup if the same change can be made in a minute or two with the die in the press.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Hydraulic Thermosetting Plastic Molding Press

Figure 16. A historic photograph of compression molding of thermoplastic material utilizing a hydraulic press operation. The Hydraulic Press Mfg. Company.

Hydraulic Presses for Metalworking Applications where prolonged clamping pressure is required such as die-casting and plastic molding operations almost exclusively make use of hydraulic presses. Increasingly, hydraulic presses are being used in metal stamping operations. A major advantage of hydraulic presses for deep drawing is the availability of full tonnage anywhere in the press stroke. Figure 16 is a historic HPM photograph of a deep drawing hydraulic press application from reference five. Increasingly, hydraulic presses are built with double actions or controllable hydraulic die cushions that permit precise drawing speed and blankholder force control. 8

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T. Altan and others “Improvement of Part Quality in Stamping by Controlling Blankholder Force and Pressure”, The Ohio State University Engineering Research Center for Net Shape Manufacturing, presented at FMA/SME Presstech Conference, Detroit, Michigan, © May 1992.

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Historical Overview of Press Development Rev., November 29, 2000 ©1993-2000 Smith & Associates 530 Hollywood Drive, Monroe, Michigan 48162-2943

Deep Drawing Work With a Hydraulic Press

Figure 17. A historic photograph of a deep drawing hydraulic press operation. The Hydraulic Press Mfg. Company Mechanical stamping presses are built with capacities up to 6.000 tons (53.376 MN) or more. Such machines are generally very large. Higher tonnages or construction that is more compact is practical in modern hydraulic presses. Hydraulic presses for cold forging are built up to 50,000 tons (445 MN) capacity. Some fluid cell presses have force capacities over 150,000 tons (1334 MN).

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