PRESS SELECTION AND MAINTENANCE
Success in any activity requires that a number of tasks be done correctly. In metal stamping, everything from poor quality parts to accelerated die wear and damage often is caused by poor press selection,diesetting and machine maintenance. No responsible machine shop manager would neglect machine tool lubrication, alignment and repair. The same principle must be applied to press selection and maintenance. A power press is a machine used to supply force to a die that is used to blank, form, or shape metal or nonmetallic material. Thus, a press is a component of a manufacturing system that combines thepress, a die, material and feeding method to produce a part. The designer of the manufacturing system must also provide proper point of operation guards to safeguard pressroom personnel. Each of the components of this manufacturing system is important and will be discussed in turn later in this work. A foundation for understanding the system is acquiring a working knowledge of the press. Examplesof good practices and warnings against bad practices are to be found throughout this training. It is very important that the good practices that are appropriate for your shop are the ones that you adopt as your standard diesetting, production and die maintenance procedures.
Types of Presses
There are over 300,000 presses in use in the United States and many more worldwide. Mechanical andhydraulic presses fall into two predominant types: gap frame and straight side presses. The frame types used in mechanical presses are similar to those used in many hydraulic presses. Most power presses are actuated by electrical motor driven mechanical or hydraulic energy. However, gravity drop hammer and foot powered kick presses are also used. The drive systems, clutches, brakes, counterbalancesystems, die cushions, electrical, hydraulic and pneumatic features are similar in both the gap frame and straight side types. The type and size of press selected is mainly determined by the work to be done.
Gap Frame Presses
Gap-frame or C-frame presses derive their name from the C-shaped throat opening. In addition to the familiar open back design, this style of machine has a long history of usefor portable hole punching. The press-brake is also a type of gap-frame press.
Features of Gap-Frame Presses
Gap or C-frame presses have many useful features. These include excellent accessibility from the front and sides for die setting and operation. The machines also cost substantially less than straight-side presses. The open back is available for feeding stock as well as ejection ofparts and scrap.
Press Selection and Maintenance - D02.doc & PDF © 1993 - 2001 Rev- August 22, 2005 Smith & Associates, 530 Hollywood Drive, Monroe, Michigan 48162-2943
A further advantage of a gap frame press is that the machine is easier to set-up than a straightside press. The diesetter has much greater freedom of access to locate and bolt the die in place. The open back is alsoaccessible for discharging finished parts and scrap as well as feeding stock. Gap-frame presses generally have less height than a straightside press of comparable tonnage. This is a valuable consideration when overhead clearance is limited.
Figure 1. An older style unguarded open back inclinable (OBI) gap frame press (A) with tie-rods added to reduce angular deflection. A modern gapframe OBI press (B). A modern OBS guided plunger press (C). Illustrations (B) and (C) Courtesy of Minster Corporation Presses with force capacities up to 250 tons (2,224 kn.) and larger, gap frame presses are less costly than a straightside press having the same force capacity. In the 35 to 60-ton (311 to 534 KN) force range, they cost approximately half that of straightside presses. The main...