Abstract:
A friction welding method and apparatus for holding and joining thermo-plastic resin elements together by rotational torque friction. The method includes precise orientation of the joined surfaces together, applying pressure to the elements and precisely controlling a pre-determined rotation of the rotatable element against the fixed element within a fraction of a second achieving welding of the thermo-plastic part. Precise starting and stopping of the rotatable element achieves a rapid superior weld joint between the elements. Control parameter inputs are defined by selective feedback of positioning and rotation motors to achieve repeatable control in the welding sequence.

Description:
This is a CIP patent application of Ser. No. 08/876,325, filed Jun. 16, 1997, now abandoned, which is a CIP of Ser. No. 08/719,428, now issued U.S. Pat. No. 5,772,103 filed Sep. 25, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This device relates to friction welding apparatus that rely on friction between two mechanical components. One of the components develops friction at the interface of the two parts to be joined in order to generate the required temperature for welding. The other component produces pressure after the required temperature is achieved completing the weld. Currently, there are two general methods for friction welding as disclosed by the American Welding Society “Inertia and Continuous drive”. Both methods employ high velocity and pressure to achieve the friction required to weld. “Inertia” method stores total energy in a fly wheel that becomes free wheeling at one point in the weld using stored energy to complete the weld. “Continuous Drive” method provides a motor and clutch brake wherein an element is brought up to speed and the clutch is engaged with moderate interface pressure generating heat. A brake is applied once the forging range of material is reached. 
     2. Description of Prior Art 
     Prior art devices of this type have relied on a number of different friction welding techniques utilizing the “Continuous drive” and “Inertia” methods and varieties on same, see for example U.S. Pat. Nos. 3,542,274, 3,542,275, 3,562,073 and 3,750,927. 
     In U.S. Pat. No. 3,542,274 a speed program friction weld control is disclosed wherein an electronic loop employing circuits to continuously compare critical speed of the drive with the program speed throughout the weld cycle and adjusting same. 
     U.S. Pat. No. 3,542,275 discloses a reciprocating friction welder that provides means to position and align weld pieces in a reciprocating friction welder. 
     U.S. Pat. No. 3,562,073 is directed towards friction welding a pair of plastic members in an angular relationship in a spin welding device to weld an elbow fitting to a pump housing. 
     In U.S. Pat. No. 3,750,927 a device for angular alignment of inertia/friction weld parts wherein weld parts are aligned by turning one part with respect to the other through the hot plasticized interference after the parts have been welded. 
     U.S. Pat. No. 4,552,609 is directed to a method and application for friction welding having a controlled system that terminates the applied rotational force after determined rotations have been achieved allowing the rotating element to coast, and a final forging pressure is applied. 
     Applicant&#39;s method of the invention uses a pressure alignment of parts to be welded before rotation i.e. welding takes place. Accordingly, it is the applied torque between the parts that achieves welding thereof within a fraction of a second by rapidly accelerating to full speed and de-accelerating to a predetermined stop position before the weld sets, all within several arc seconds. 
     SUMMARY OF THE INVENTION 
     A friction welding method and apparatus that achieves a complete weld between a fixed and rotating thermo-plastic parts by applying pressure and instantaneous rotation and rotational stop within milliseconds. The method is directed to precisely holding and aligning thermoplastic parts under pressure, rotating the weld part against the fixed part, achieving a superior weld between the parts by holding said welded parts for a predetermined cool time after rotation has stopped and then releasing the completed assembly. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustrative front elevational view representing a typical welding apparatus of the invention; 
     FIG. 2 is an illustrative side elevational view of the welding apparatus of the invention; 
     FIG. 3 is an enlarged graphic illustration of a typical mounting and receiving fixture which illustrates parts to be welded within; 
     FIG. 4 is a rotational weld orientation graph illustrating rotational distance required to achieve a weld under the method of the invention compared to prior art rotation needed; 
     FIG. 5 is a time line graph illustrating welding cycle of the method of the invention; 
     FIG. 6 is an illustrative side elevational view of an alternate welding apparatus of the invention; and 
     FIG. 7 is a flow chart illustrating control path for the alternate welding apparatus illustrated in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS.  1 - 3  of the drawings, a welding assembly  10  can be seen having a mounting base  11  and a back plate  12 , shown in broken lines. A support carriage  13  is movably positioned on the block plate by multiple linear bearing assemblies  14  on respective bearing races  15 . The welding assembly has a power welder  16  secured within the support carriage  13 . The power welder  16  has a servo motor  17 , connected to a gear reducer  18  by a motor adapter  19 . The gear reducer  18  has a spindle assembly  20  with an attached driver  21 , best seen in FIGS. 1 and 2 of the drawings which will be discussed in greater detail hereinafter. 
     The carriage  13  is movable in a vertical plane by a piston and cylinder assembly  22  secured to the back plate  12 . A piston rod  23  extends from the piston and cylinder assembly  22  and is secured to the movable carriage assembly as will be well understood by those skilled in the art. 
     The servo motor  17  is of a three phase electrical servo positioning motor, the type manufactured by Emerson under Model No. DXM6200 having the ability to accelerate from a forced stop position to maximum R.P.M. in a fraction of a second and to de-accelerate to the force stop position just as rapidly. Such servo motors  17  are characterized by their ability to constantly start and spin and stop within six arc seconds of a predetermined position which is critical to the method of the invention and weld characteristics of the thermoplastic parts disclosed herein. The output of the servo motor  17  is connected to the gear reducer  18  by the adapter  19  that mechanically interconnects therebetween. The gear reducer  18  is commercially available at Model ATO14-003 which is a 3 to 1 gear reduction manufactured by Micron Instrument Corporation using multiple planet gears revolving around a single true “sun” gear well known to those skilled in the art. 
     Referring now to FIG. 3 of the drawings, the driver  21  can be seen having a parts engagement fixture  24  secured thereto. The fixture  24  is simplified for illustration purposes and would be of a custom design for each part configuration to be joined as is typical in the art. 
     A fixed base part fixture  25  is illustrated with pre-positioned thermoplastic parts  26  and  27  therein to be joined together. The parts  26  and  27  have abutting joining surfaces. 
     In use, the power welder assembly  10  defines a unique welding method that first positions and holds the thermoplastic parts  26  and  27  together, then applies sufficient pressure to build up substantial energy in the process before the spindle  20  and associated driver  21  and fixture  24  actually turns. 
     The position of the movable carriages  13  is physically controlled by the piston and cylinder assembly  22  in combination with carriage positioning sensors  28  and input control activation commands from a pre-programmed C.P.U. (Central Processing Unit) interconnected to the power welder assembly  16 . Torque is applied to the thermoplastic parts by the output of the servo motor  17  responding to the input control activation commands from the C.P.U. in accordance with its pre-programmed instructions in combination with input from the positioning sensor  29  within the driver  21 . 
     Referring now to FIG. 5 of the drawings, a time line activation graph  30  is illustrated that indicates a typical activation time for the servo motor  17  to effect a power weld between the thermoplastic parts  26  and  27  as hereinbefore described. 
     The graph  30  has time lines  31  and  32  in micro-seconds and second respectively with acceleration (A) indicated at  33 , and de-acceleration (DA) illustrated at  34  (in milliseconds) and hold time (H) illustrated at  35  (in seconds) before joined parts are released. The critical element of thermoplastic welding is to achieve a weld temperature between the parts as rapidly as possible, illustrated by the acceleration bar  33  and the de-accelerate before the formed weld joint begins to set up (cools) that occurs as the parts de-accelerate illustrated by the de-acceleration bar  34 . 
     The precise controlling of the acceleration and de-acceleration of the motor  17  is achieved by the hereinbefore described ability of the servo motor  17  that is controlled by the pre-programmed C.P.U. with feedback from positioning sensor  29  achieving “stop” position of the driver  21  and fixture  24  in a consistent and repeatable fashion. 
     The resulting weld between the joined parts is characterized by high consistence with little or no flashing thereabout. 
     Referring to FIG. 6 of the drawings, an alternate welding assembly  40  can be seen having a mounting base  41  and a back support frame  42 . A support carriage  43  is movably positioned on the support frame  42  by a plurality of linear bearing assemblies  44  on reciprocal bearing races  45  attached to the support frame  42 . 
     The support carriage  43  of the alternate welding assembly is movable in a selective vertical plane by a servo-motor and ball screw assembly  46  secured to the back support frame  42 . A servo motor  47  of the servo motor and ball screw assembly  46  has a gear reducer  48  which has an output shaft  49  registerable with a bearing assembly  50  attached to the support frame  42 . A zero backlash coupling  51  interconnects the output shaft  49  with a ball screw  52  having a second bearing support assembly  53 . 
     A screw engagement nut  54  on the ball screw  52  is secured to the support carriage  43  allowing precise incremental linear vertical movement thereto based on the control rotation of the ball screw  52  by the servo motor  47 . 
     A power welder  55  is secured within the support carriage  43  and has a power servo motor  56  interconnected to a gear reducer  57  by a motor adapter  58 . 
     The gear reducer  57  has a spindle assembly  59  extending therefrom with an attached driver  60  which provides for engagement with a thermo-plastic part to be welded. 
     A fixed base part fixture  61  is aligned directly below the driver  60  on the mounting base  41  in a similar manner as that of the hereinbefore described power welder  16  illustrated in FIGS.  1 - 4  of the drawings. 
     The servo motor  47  is controlled by the pre-programmed CPU that responds to operator input and feedback information as illustrated in FIG. 7 of the drawings with inputs from the motor  47  and corresponding rotation of the ball screw  52  as indicated by current load on the motor, activation time and other linear input characteristics of the servo motor as will be understood by those skilled in the art. 
     It is therefore now possible to selectively adjust all of the critical control and position criteria for different thermo-plastic parts, determining exact preferred weld characteristics as hereinbefore described by adjustments of functional input such as pressure, torque, time and distance associated by activation of the motor as noted. 
     Inter-reactive fine tuning of the welding parameters is now possible by combining the feedback input of the carriage positioning servo motor  47  and the welding servo motor  56  for each thermo-plastic weld part situation and thus creating a repeatable set of parameters for multiple accurate reproduction of welding of thermo-plastic parts in a production type setting. 
     The CPU provides specific control over servo motors  47  and  56  by being interconnected to motor controllers  61  that regulate the incremental power input to the respective servo motors defining by power input, direction and current load, the hereinbefore referred to feedback parameters of the welding apparatus and power welder within. 
     Referring now to FIG. 4 of the drawings, a comparison graph of effective rotational duration of prior art spin welding to the method of the invention is illustrated. Graphic arrows  36  illustrate the typical (minimum) rotational revolution required by prior art spin welding that is currently possible at three-quarter of a revolution to achieve welding. The graph arrow  37  illustrates the method of the invention where an efficient superior welding can be achieved in as little as one-third of a rotation. The rotational difference (rotational time RT) of less than half illustrated is demonstrative of other time rotational differences achieved in more than a full rotation in which the method of the invention will always achieve a reduced rotational difference and correspondingly reduced weld time (T) to achieve a superior quality weld, thus duration of weld cycle is reduced and production is increased. 
     It will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.