Patent Publication Number: US-6655268-B2

Title: Compact hot press

Description:
FIELD OF THE INVENTION 
     This invention relates generally to hot presses and, more particularly to, single unit portable hot presses. 
     BACKGROUND OF THE INVENTION 
     Many processes are known in the art for forming metallic parts. These processes include, among others, milling, stamping and pressing. The use of a hot press to form metallic parts is often preferred over other forming processes. However, current hot press designs and their resulting forming processes are relatively inefficient. Additionally, current hot press technology poses safety hazards to press operators and press equipment. 
     Typical hot presses are large, multi-unit machines. Each machine includes a press unit, a control unit, and a hydraulic unit. Each unit is typically a stand-alone unit with minimal interconnection between the units. Consequently, each machine occupies a significant volume of shop space. Moreover, the volume of space typically occupied by each machine exceeds by orders of magnitude the size of part being produced. Additionally, to move the machine, each unit must be disconnected from the other units, moved separately, and subsequently re-connected. Thus, not only do current hot presses inefficiently utilize space, but they also require excessive time and effort to relocate. 
     Thermal inefficiencies are another drawback of current hot presses. The thermal inefficiencies are derived from several sources. Heated platens employed by the press typically are not adequately insulated and only heat a single surface of the die. Also, the lack of insulation surrounding the platens results in excessive heat loss, which requires additional energy to achieve and maintain die temperature. The single heating point design requires additional time to achieve a desired thermal equilibrium throughout the die. Additionally, current hot presses include large access doors that must be opened to insert or remove the parts to be formed. The large doors allow a massive amount of heat loss every time they are opened. This problem is compounded because these same presses lack structure to align the die within the press during die loading, the doors must remain open for an excessive length of time during the part and die loading process. Consequently, considerable time is spent, and thus heat energy lost, while manually positioning the part and die in the press. 
     Current hot press designs create a number of safety hazards. The lack of adequate insulation surrounding the heating platens results in a considerable amount of convective heat being radiated. Consequently, an operator is required to wear a great deal of thermally-resistive safety clothing and equipment. This safety equipment is generally uncomfortable and cumbersome to wear. Further, the cumbersome nature of the equipment potentially creates additional hazards by inhibiting the operator&#39;s movement. 
     Standard hot presses employ a downward directed press motion that creates another safety hazard. The downward directed press movement requires elements of the hydraulic unit to be above the heated platens. Thus, any leaking of hydraulic fluid from the hydraulic unit can contact the heated platens creating a fire hazard. 
     Thus, there is an inert need in the art for a hot press that efficiently uses space, is thorough, efficient, and overcomes safety hazards posed by current hot presses known in the art. 
     SUMMARY OF THE INVENTION 
     The present invention is a hot press that efficiently uses space, is thermally efficient, and overcomes safety hazards associated with known hot presses. 
     The present invention is a portable, compact hot press. The hot press includes a frame that has a press unit attached thereto. The press unit has a crown plate, a bolster plate, and a base plate. An upper press unit is attached to the crown plate and a lower press unit is attached to the bolster plate. The lower press unit is configured to contact the upper press unit when the press is in a closed position. The press further includes a control unit attached to the frame. The control unit is configured to manually or automatically control press operation. Additionally, the press includes a hydraulic unit that is attached to the frame and is configured to facilitate motion of the press operation. 
     Another aspect of the present invention is a method of operating a compact hot press. A part is loaded into the press. The part is preheated to a predetermined temperature. After the press is preheated, the press is closed and the part is placed under load. The load is maintained for a predetermined time. At the expiration of the predetermined time, the press is opened and the part is removed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings. 
     FIG. 1 is a front view of a hot press according to the invention; 
     FIG. 2 is a side view of the hot press of FIG. 1; 
     FIG. 3 is a sectional view of a press unit; 
     FIG. 4 is an isometric view of a lift truck; 
     FIG. 5 is a flow chart of a power-on sequence; 
     FIG. 6 is a flow chart of automatic press operation; and, 
     FIG. 7 is a flow chart of manual press operation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a system and method for hot forming metallic parts. By way of overview and with reference to FIG. 1, one presently preferred embodiment of the present invention includes a hot press  20  including a press unit  28 , control unit  60  and a hydraulic unit  26  (see FIG.  2 ). The press unit  28 , control unit  60 , and hydraulic unit  26  are supported by a single frame  22 . The frame  22  includes a pair of lift sections  38  providing portability of the entire press  20  as a single unit via a forklift or similar machine. Specific details of the press  20  are described with more particularity below. 
     The press unit  28  is set in a four-post Danly die set with three plates  30 ,  32  and  34  and four columns  58 . The press unit  28  generally includes a base plate  30  attached to a lower portion of the frame  22  and a crown plate  34  attached to an upper portion of the frame  22 . Disposed between and mechanically connected to the base plate  30  and the crown plate  34  is a movable bolster plate  32 . A hydraulic cylinder  24  of the hydraulic unit  26  (see FIG.  2 ), is up-acting and attached to the middle of the bolster plate  32 , thereby vertically displacing the bolster plate  32  upwardly and downwardly during press  20  operation. 
     Attached to the crown plate  34  and the bolster plate  32  are upper and lower press units  36  and  37 , respectively. The lower press unit  37 , and the substantially similar upper press unit  36  each include non-load bearing insulation  40  that substantially surrounds a load bearing ceramic block  42 . In one presently preferred embodiment, at least six inches of insulation surround the ceramic block  42  in each press unit,  36  and  37 . However, it will be appreciated that any other insulation thickness is considered within the scope of this invention and may be used for a particular application. The arrangement of the insulation  40  and the ceramic blocks  42  is such that when an upper platen  46  is inserted into the upper press unit  36  or a lower platen  48  is inserted into the lower press unit  37 , each platen  46  and  48  contacts the corresponding block  42  while simultaneously being substantially surrounded by the insulation  40 . In this manner, the block  42  carries any loading resulting from operation of the press  20  while the insulation  40  prevents the platens  46  and  48  from experiencing excessive heat loss throughout the operating range of the press  20 . Additionally, it should be noted that the block  42  is suitably constructed from a ceramic material and is therefore an insulating element. 
     The upper platen  46  and lower platen  48  are substantially similarly shaped elements designed to entirely surround a die  52  when the press  20  is in a closed position. Each platen  46  and  48  includes a plurality of heater bores  50  extending into the platen. Each heater bore  50  is designed to receive a heater  104  (see FIG.  2 ), discussed in more detail below. 
     Referring now to FIGS. 1 and 2, a part (not shown) being formed in the press  20  is located between an upper portion  55  and a lower portion  57  of the die  52 . Thus, to remove or insert a part, the two portions  55  and  57  of the die  52  must be separated. To maintain production efficiency, the die  52  must be separated while the die  52  is at operational temperature. A die holding key  54  locks the upper portion  55  of the die  52  to the upper platen  46  thereby lifting the upper portion  55  when the press  20  is opened. The key  54  includes an elongated member extending through the upper press unit  36 . The key  54  is I-shaped and somewhat resembles a “dog bone.” The key  54  is easily inserted and removed by an operator by sliding the key  54  into and out of tube  59  and the upper press unit  36 . Thus, optimal thermal efficiency is maintained as the die  52  is at temperature during a part change and each portion  55  and  57  of the die  52  is in constant contact with its respective heating platen  46  and  48 . Consequently, cycle time for part formation is greatly reduced. 
     According to the present invention, the press  20  includes unique, passive die loading system. In a presently preferred embodiment, four pins  44  are mounted to the base plate  30 . FIG. 1 depicts the press  20  in the die load and unload position. When the press  20  is in this position, or fully down, the pins protrude through the bolster plate  32 , lower press unit  37 , and lower platen  48  to contact the die  52 . The pins  44  maintain the die  52  at an elevation above the lower press unit  37  thereby allowing a lift truck, discussed below, to remove the die  52 . In this manner, a full die  52  change is shortened from a time that exceeds twenty minutes for currently known presses to a time that is less than five minutes. 
     Referring back to FIG. 1, in a presently preferred embodiment, the control unit  60  includes three main control sections: a process control  62 , a heater control  64 , and a ram control  66 . The process control  62  includes a cycle timer  70  that keeps track of various cycle times. For example, pre-heat time and loading time, are discussed in more detail below. An emergency stop switch  72  is a safety feature of the press  20 . The press  20  will not operate, or will stop operating, if the stop switch  72  is tripped. Also included in the process control  62  unit are an automatic cycle start switch  74  and a cycle stop  76  switch. The switches  74  and  76  provide a one-button cycle start/stop for the automated press  20 . Finally, a tool temperature chart recorder  68  and recorder actuator  78  are coupled together to track and record temperature of the tool or part during operation of the press  20 . The temperature chart recorder  68  is connected to thermcouples attached to the press units  36  and  37  and provides a written chart to record tool temperature throughout part forming operations. 
     The heater control  64  activates the heaters  104  used to heat the platens  46  and  48 . The heater control  64  includes a heater power switch  88 , which provides power to the heaters  104 . Additionally, the heater control includes upper platen heater control  80  and a lower platen heater control  84 , both of which are used to vary temperature in each respective platen  46  and  48 . Finally, the heater control  64  includes separate alarm indicators for both the upper platen  46  and the lower platen  48 . An upper platen alarm  82  and a lower platen alarm  86  notify the operator if either or both of the platens  46  and  48  are experiencing heating problems. 
     The ram control  66  includes manual controls for the press  20 . A manual press open switch  94 , a press close switch  96 , and a die unload switches  98  are provided. The switches allow the operator to manually open and close the press  20 , either fully or partially. Also, a load indicator  90  and a load adjust control  92  are provided to monitor and adjust the loading applied to the die  52 . 
     An additional safety feature of the press  20  is a light curtain  106  covering the front and back of the press  20 . The light curtain  106  projects a light beam, or curtain across a chosen portion of the press, such as the front or back of the press  20 . If the beam is broken or interrupted, for example, by a hand or any other part of an operator&#39;s body, the press operation stops. In this fashion, the operator is protected from accidental injury from the press. Likewise, the press  20  is protected from damage by foreign bodies entering the range of motion of the press  20 . Additionally, the sides of the press  20  are preferably covered with a suitable material, such as a wire mesh (not shown), to provide similar protection to the sides of the press  20 . 
     FIG. 2 depicts a side view of a presently preferred embodiment of the hot press  20 . The press  20  is viewed in a closed position. In this position, the die  52  is heated and is under load. The upper and lower platens  46  and  48  completely surround the die  52 , thereby heating the die  52  from all sides. Bulb seals  102  mate to prevent heat loss between the upper and lower press units  36  and  37 . 
     A plurality of quick-change heaters  104  are adjacent the rear portion of the press  20 . Each heater  104  is a separate, electrically controlled unit designed to pass through small openings (not shown) in the back of the press units and into the heater bores  50  of the platen  46  and  48 . In addition to providing heater access into the press  20 , the openings also provide the operator instant visual verification whether each heater  104  is operating. More specifically, in one embodiment of the invention, when a heater  104  is operating at temperature, an orange glow can be seen surrounding the hot portion of the heater  104 . To verify whether a heater is functioning properly the operator simply views axially down the opening and looks for the glow. This aspect of this invention provides practically instantaneous feedback regarding integrity of the heater  104 . If one or more of the heaters  104  is not functioning properly, attaining a desired thermal equilibrium within the press  20  becomes more difficult to attain, thereby increasing process time and/or adversely affecting part integrity. 
     The position of each heater  104  is maintained within the press  20  by a simple bracket (not shown) attached to an outer portion of the press  20 . Thus, to remove or insert each heater  104 , the operator simply releases the heater  104  from the bracket and slides the heater  104  out of or into the press  20 . The removal or insertion of the heater  104  does not require opening the press  20  or moving any insulation material. Thus, thermal integrity of the hot press  20  is not breached during change or inspection of a heater  104 . Heaters  104  can be changed while the press is hot. 
     In one presently preferred embodiment, the heating system suitably includes six heaters  104  in each of the upper platen  46  and the lower platen  48  for a total of twelve heaters  104 . The heaters  104  suitably operate on 120 volts AC electrical power. The heaters  104  suitably provide an output of 1.67 kW. Each heater  10  suitably measures 0.935-inch in diameter with a heated length of 21.5 inches. Thus, each heater produces 26.4 watts per square inch. However, it will be appreciated that any number of heaters  104  is considered within the scope of this invention. Likewise, the power requirements and geometric configuration of the heaters  104  are variable based upon press application  20  and are considered within the scope of this invention. 
     The location of the hydraulic unit  26  in a presently preferred embodiment of the instant invention is also depicted in FIG.  2 . The hydraulic unit  26  is located in the bottom rear portion of the press  20 . The location of the hydraulic unit  26  keeps all hydraulic fluids below all heated elements of the press, thereby preventing a fire. This location of the hydraulic unit  26  also prevents any unwanted fluid quenching of the formed part or die  54 . 
     In a presently preferred embodiment, the hydraulic unit  26  is suitably capable of providing in excess of ten tons of load for proper part formation. A unique air/oil system using a one hundred psi air pump (not shown) over a hydraulic system is employed. Two air pumps (not shown) pump hydraulic fluid to a thirty-ton hydraulic cylinder  24 . A five hundred psi low pressure pump (not shown) moves the bolster plate  32  up and down when the press  20  is not under load. A thirty-four hundred psi high pressure pump (not shown) provides the forming load. The hydraulic cylinder is preferably rated at thirty tons. It will be appreciated that air over oil pumps are well known in the art. As a result, a detailed explanation of construction and operation of the air over oil pumps discussed herein is not necessary for an understanding of the invention. Suitable air over oil pumps include SP5455 available from Sprague. It will be appreciated that other air pumps, air over oil hydraulic pumps, and hydraulic cylinders may be used as desired for a particular application. 
     FIG. 3 depicts a more detailed view of lower press unit  37 , including the insulation  40  and platen  48  arrangement. It is to be understood that the upper press unit  36  is substantially similar in design to the lower press unit  36 . The insulation  40  surrounds the platen  48  to minimize heat transfer from the platen  48  to the surrounding environment. Additionally, surrounding the platens  46  and  48  with insulation improves safety by reducing the temperature around the press  20 . For example, in one presently preferred embodiment, the platens  46  and  48  heat the die  52  (FIG. 1) to about 1300 degrees Fahrenheit. However, the insulation  40  surrounding the platen  46  keeps the outside of the press units  36  and  37  at approximately 140 degrees Fahrenheit. Consequently, the operators do not need to wear bulky heat resistant safety equipment. 
     Another advantage of the invention depicted in FIG. 3 is the geometry of the platens  46  and  48 . The heater platens  46  and  48  form a cavity  49  in which the die  52  sits. When the platens  46  and  48  are brought together, the die  52  is completely surrounded. Thus, during the heating process, the die  52  is heated from all sides. This greatly reduces heating time and heat loss during operation. Additionally, the die cavity  49  automatically aligns the die  52  within the press thereby reducing cycle time to the die  52 . 
     An insulated door  53  is also depicted in FIG.  3 . In a presently preferred embodiment, the lower press unit  37  includes a pair of the insulated doors  53  located adjacent a top center surface of the lower press unit  37 . However, other arrangements are considered within the scope of this invention. For example, a single door  53  or a no-door arrangement is considered within the scope of this invention. The doors  53 , when closed, insulate the heated platens  46  and  48 . When open, the doors  53  provide an access point to insert and remove the die  52 . 
     FIG. 4 depicts a lift truck  107  having a unique single lift fork  112  specifically designed to pick up and locate the dies  52  within the press  20 . The truck  107  also includes truck guides  114  that couple with frame guides  56  (see FIG. 1) attached to the frame  22  (FIG.  1 ). When the frame guides  56  and truck guides  114  act in concert, the truck  107  is placed in the proper position left-to-right and fore-to-aft. 
     The truck  107  also includes fork height indicators  116 . The indicators  116  visually communicate the height of the fork  112  relative to an acceptable die load and unload height range. The operator lifts the fork  112  until the top of a back plate  118  is within the proper height range for the operation being preformed, either loading or unloading the die. Once the proper height is attained, the truck  107  can be aligned with the frame  22  via the guides  56  and  114 . The combination of guides  56  and  114 , and height indicators  116  insure the proper placement and removal of the die  52  in the shortest time possible. 
     FIG. 5 depicts a flow diagram  120  of a presently preferred power-on sequence and press operational safety features. Initially, the press  20  is turned to a power-on state as indicated by block  122 . At this state the press control unit  60  has electrical power but the press  20  will not operate until two safety conditions are met. More specifically, block  124  assesses whether an emergency stop switch  72  is in the run or stop position. If the switch  72  is in the stop position the press  20  will not run, as indicated by block  110 . Conversely, if the switch  72  is in the run position then a second safety condition is prompted. Block  126  indicates that the light curtain  106  is checked for interference, as discussed above. If the optical screen of the light curtain  106  is broken at any time during press  20  operation the press  20  will not operate as indicated by block  129 . However, if the light curtain  106  is clear, as indicated by block  128 , then the press  20  is ready to begin operation, either in automatic or manual mode. 
     FIG. 6 depicts a one-button start up and run cycle  112 . After the power-on cycle  100  discussed above is complete, the press  20  will now operate. Initially the press  20  is open as indicated by block  130 . At block  134 , the operator loads a part into the press via methods discussed above. At this point the one-button automatic cycle begins. 
     At a block  136 , the automatic cycle  130  is initiated by activating the cycle start switch  74  (FIG.  3 ). At a block  138 , the press  20  checks limit switches (not shown) attached to the press  20  for indication of any obstructions, such as an open door  53 , to press operation. Subsequently, at a block  140 , the press  20  partially closes to a pre-heat location. Once the press reaches the pre-heat location, at a block  142  a timer  70  begins and the part is heated for a predetermined amount of time. In a presently preferred embodiment, the pre-heat time is about four minutes and a heat temperature is about 1300 degree Fahrenheit. However, it will be appreciated that any length of time or any heating temperature is considered within the scope of this invention. After the pre-heat stage is complete at a block  144  the press  20  closes and loading begins. 
     Loading involves applying a predetermined load to the part being formed for a predetermined amount of time at a block  146 . In a presently preferred embodiment, a load of about ten tons is applied to the heated part for a period of about nine minutes at a block  148 . However, it will be appreciated that any load value applied for any length of time is considered within the scope of this invention. After the predetermined amount of time has expired, at a block  150  an indicator, for example a horn or light, notifies the operator. Subsequently, the operator stops the cycle at a block  152  by pressing the stop cycle switch  76 . The operator actuates the press open switch  96  at a block  154 . The press  20  then opens to the part load position at a block  156 . The operator removes the formed part at a block  158 , thereby completing the cycle. 
     FIG. 7 depicts a flow diagram of a presently preferred manual control of the press  20 . Although the advantages of operating the press  20  in the automatic cycle mode  130  discussed above are many, there are times when manual press operation is desirable. Thus, three manual control modes  160  are included in this invention. The manual control modes  160  include an open mode  162 , close mode  164 , and a die unload mode  166 . As discussed above, before any movement of the press  20  can occur, the power-on sequence  120  must meet the clear-to-run condition. Once the clear to run condition is met, the various manual modes  160  may be employed. 
     Manual operation is very simple. To manually open the press  20 , the operator activates the press open switch  96  at a block  168 . Upon actuation of the open switch  96 , the press  20  will open to the part load position at a block  172 . In a similar fashion, to manually close the press, the operator actuates the press close switch  94  at a block  174 , and the press will close at a block  176 . An operator can change dies  52  manually by activating the die unload switch  98  at a block  178 . Upon activation of the die unload switch  98 , the press  20  checks various limit switches (not shown) for indication of a clear unload travel path at a block  180 . When the travel path is clear, the press  20  opens to a die unload position at a block  182 , wherein the die is fully supported on the pins  44 . 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.