Abstract:
Parts (10) with terminals (17) wrapped with insulation coated wire (20) are loaded into quick clamp and release fixtures (24) and then advanced by a conveyor (26) through a flux applying station (42) and then through an insulation removing and solder depositing station (46). Solder is pumped through a well (47) and divided into two oppositely flowing sets of streams capped by open top housings (66, 67 and 68). The hot solder flowing counter to the direction of movement of the terminals acts to melt and wash away the insulation whereafter the solder flowing in the direction of movement of the terminals acts to deposit solder on the wire wrapped terminals.

Description:
FIELD OF INVENTION 
     This invention relates to methods and systems for soldering one or more parts coated with a thermo-plastic insulation, and more particularly, to a conveyorized facility for releasably holding parts that are advanced along a solder filled channel, wherein a portion of the solder flows in a direction opposite to the direction of advance of the parts to remove the insulation, and the remaining portion of solder flows in the direction of advance of the parts to deposit solder on the parts. 
     BACKGROUND OF THE INVENTION 
     In the course of manufacture of certain electrical devices, it is often necessary to apply solder to parts of the device that are coated with a thermo-plastic insulation. These parts may be soldered by a manually controlled dip solder method, wherein a device, or a group of devices, is loaded in a fixture which is moved to dip the parts in a pot of molten solder. The part is held in the solder pot for a time sufficient to melt the insulation, whereafter solder is deposited on the now insulation free immersed portions of the part. Insulation removal and solder deposit at acceptable manufacturing rates is attained by heating the solder well above the solder melting point, e.g., 700° F., and then holding the parts in the solder pot for a period of time, e.g., three seconds. However, this method is still slow and the temperature encountered often results in heat damage to other portions of the electrical device. 
     More specifically, the use of high temperature soldering methods may induce thermo-stress or shock. For example, where the parts to be soldered are terminal posts extending from a coil frame with the ends of the insulation coated coil wires wrapped around the square terminal posts, the heat encountered in the dip process may expand the wires which are subsequently contracted during cooling to strain the wire at the junction of the wire wrappings and the square edges of the terminal posts. Such stressing at the junction may lead to breakage of the wires. In addition, the high heat may result in the melting of the insulation on the coil wires resulting in shorting out certain of the coils thus ruining the device. Further, with the use of the solder dip method, the melted insulation abets the formation and build-up of dross and other impurities on the surface of the solder pot, thus requiring frequent dross skimming operations. 
     What is needed is a continuous process wherein the parts may be rapidly loaded into fixtures which are transported to move the parts through a wave solder machine to remove the insulation and solder the parts, whereafter the soldered parts may be rapidly ejected from the fixtures. Numerous wave solder machines are available for applying solder to non-coated metal parts. As an example, U.S. Pat. No. 3,482,755 to J. A. Raciti, issued Dec. 9, 1969, shows a machine for producing a solder wave which crests and falls away in opposite directions. A first portion of the solder wave falls back into a solder reservoir, while the second portion is flowed along a path that is in the direction of movement of terminals projecting from the underside of a conveyor moved circuit board. The solder path along which the terminals are advanced is configured to impart turbulence to the solder stream that acts to inhibit the formation of solder icicles projecting from the terminals and solder bridges extending between adjacent terminals. 
     SUMMARY OF THE INVENTION 
     The present invention contemplates, among other things, a solder wave machine and method for flowing solder from a common well into two contiguous channel sections running in opposite directions so that insulation coated parts immersed in and advanced along the oppositely flowing solder streams cause the insulation to be melted and removed, whereafter further advancement along the stream causes the solder to be deposited on the parts. 
     More particularly, solder is pumped through a solder well into central portions of a set of horizontally extending channels causing a quantity of the solder to flow in first sections of the set of channels in a first direction, while the remainder of the solder flows in the other or second sections of channels in a second or opposite direction. Parts having portions coated with insulation are loaded into automatic clamp and quick release fixtures for transport by a conveyor which functions to move the insulation coated portions of the parts through the first channel sections where the counter flowing solder melts and removes the insulation from the immersed portions of the parts. Subsequent movement of the now insulation free portions of the parts through the solder flowing in the direction of movement of the parts in second sections of the channels results in the deposit of solder. The lengths of the channels are selected to be long enough to ensure that the insulation is removed and the solder is deposited at relatively low temperatures so that heat damage to other portions of the parts is avoided. The insulation that is melted is immediately washed away. Further, the flow rate of the solder stream through the solder applying sections of the channels is controlled so as to be at the same rate as the advance of the parts to thereby minimize the formation of bridging solder icicles. 
    
    
     BRIEF DESCRIPTION OF DRAWING 
     Other advantages and features of the invention will be apparent upon consideration of the following detailed description in conjunction with the drawing wherein: 
     FIG. 1 is a perspective view of one type of insulation coated part that may be soldered by the method and system of the present invention; 
     FIG. 2 is a general schematic view of the conveyor system for advancing quick load and release fixtures through a solder applying apparatus embodying the principles of the present invention; 
     FIG. 3 is a side view of a number of workholding fixtures mounted on a conveyor chain with the view partially cut away to illustrate a quick load and release mechanism; 
     FIG. 4 is a top view of the fixture shown in FIG. 3; 
     FIG. 5 is a sectional view taken along line 5--5 of FIG. 3 showing a part clamped in the workholding fixture; 
     FIG. 6 is a side view of the solder applying apparatus with a side plate removed to illustrate the formation of two solder streams that flow along contiguous channels extending in opposite directions; 
     FIG. 7 is a rear view of the apparatus partially cut away to show solder channel configurations and an adjustable dam feature for controlling the solder flow rate; and 
     FIG. 8 is an enlarged sectional view taken along line 8--8 of FIG. 6 showing an insulation coated part immersed in the solder flowing through the channel. 
    
    
     DETAILED DESCRIPTION 
     The method and system constituting the present invention may be utilized to apply solder to many diverse insulated coated parts, such as terminals wrapped with thermo-plastic coated wires and extending from a circuit board or a connector. However, the description will be directed to the soldering of wrapped terminals extending from a bobbin on which is wound convolutions of thermo-plastic coated wires. One such device is known as a ferrod sensor which finds extensive use in telephone switching systems. 
     Referring to FIG. 1, there is shown a part 10 to be soldered. The part, e.g., a ferrod sensor coil, consists of a core body 11 with wraps of thermo-plastic insulated wire 12. The core is provided with three flanges 13, 14 and 15 from which extend three sets of square cross-sectional terminals 17, 18 and 19. Each of the terminals is wrapped with several turns of insulated wire 20. It is an applied object of the present invention to provide a solder machine, for melting the insulation on the terminal wire wraps and solder bond the wire wraps to the terminals. 
     More particularly, referring to FIGS. 2, 3, 4 and 5, the parts 10 are manually loaded at a load station 21 into pairs of nests 22 and 23 formed in one of a group of fixtures or carriers 24 mounted on pins 25 extending from a conveyor chain 26. Each carrier includes a plate 27 which is formed with a slot 28 in which is pivotally mounted a pair of part gripping levers 29 and 30 on an axle pin 31. First ends 32 and 33 of the levers are biased apart by an interposed spring 34 seated within opposed blind holes 35 and 36 formed in the respective levers. In use, an attending operator pushes a pair of parts down into the nests to pivot the levers 29 and 30 against the action of the interposed spring 34 which reacts to urge the levers to engage and hold the parts in the nests. The entries to the nests and the lever ends are beveled or rounded to facilitate the entry of the parts into the nests. 
     As disclosed in FIG. 2, the conveyor chain 26 is advanced by a sprocket 37 driven by a controlled speed motor 38. The conveyor chain passes over idler sprockets 39 and 40 and over the drive sprocket 37 to turn the carriers upside down whereupon the now downwardly extending terminals 17, 18 and 19 are moved through a flux applying station 42 where a rotating brush 43 applies flux from a pool 44 to the wire wraps on the terminals. 
     Next, the conveyor chain 26 advances the parts from the fluxing station to a solder applying apparatus 45 of the type shown in FIGS. 6, 7 and 8 where the insulation on the wire wraps is melted and removed and then solder is deposited on the wire wraps. Finally the soldered devices are conveyed to an unload station 46 whereat the devices are automatically dropped from the fixtures 24. 
     The soldering apparatus, as shown in FIGS. 6, 7 and 8, includes a well 47 into which solder is flowed by a pump (not shown). The opposed side walls 48 and 49 of the well 47 extends upwardly and angularly along sections 51 and 52 and then upwardly along crenulated support sections 53 and 54. Secured in the troughs between crenated sections 53 and 54 are a pair of spaced rails 56 and 57 interposed between inwardly extending sections 58 and 59 of the front and back walls 61 and 62 of the well 47. Three solder channel defining housings 66, 67 and 68 are mounted in the troughs of the crenulated support sections 53 and 54 and are provided with laterally extending flanges that extend beneath the rails 56 and 57 and the sections 58 and 59. The housings project through the spaces between the rails 56 and 57 and the inwardly projecting wall sections 58 and 59 to provide three discrete solder flow channels. The housings have projecting triangular-shaped top sections 71, 72 and 73 which are terminated to provide elongated slot openings 76, 77, 78 through which the wire wrapped terminals 17, 18 and 19 are advanced. 
     The pressure on the solder is set so that a sufficient quantity of solder flows into and fills the housings 66, 67 and 68 with solder streams having exposed surfaces that project slightly through the openings 76, 77 and 78. The channel housings are made of a non-solder wettable material, such as titanium, hence the edges of the solder streams will be repelled which, in conjunction with the normal meniscus effect, allows the top surfaces 79 (see FIG. 8) of the solder channel streams to rise above the level of the openings in the housings. It should be noted that the solder streams do not flow over the sides of the housings 66, 67 and 68. 
     The solder flows as channel streams in opposite directions inside the individual channel housings and exits at opposite ends over dams 86 and 87 adjustably secured by screws 88 and 89 to the side surfaces of the upwardly extending parts of the crenulated sections 53 and 54 of the well housing. The rate of solder flow may also be controlled by adjusting the effective heights of the dams 86 and 87. More specifically, the screws extend through adjustment slots 90 formed in the dams so that the dams may be set up or down to control the volume of solder exiting over the respective sets of the dams from the associated channels. 
     A pair of secondary housings 90 and 91 surround the well housing to provide return paths 92 and 93 for the exiting solder. The flow of solder over the dams is such that the exiting streams are propelled in an arcuate path to strike flared sections 94 and 96 of the secondary housings at obtuse angles. The respective solder streams are bounced off the flared sections at obtuse angles and strike reverse bend sections 97 and 98 of the flared sections 94 and 96, whereafter the solder stream is diverted downwardly along the flared sections through return passages 101 and 102 returning to the solder pump well. The structure of the well 47 and the secondary housings 90 and 91 are mounted on an apertured frame plate 103 which may be secured by bolt structures 104 and 105 to the commercial pump and return reservoir facilities (not shown). Any of a number of commercial solder pumping facilities may be used, e.g., a pumping system known as Wave Dipper Mini-Pot, #WDC-6-HT, furnished by Electrovert, Ltd. of Montreal, Canada, was used in one installation of the system. 
     In summary of the operation of the system, pairs of parts 10 are loaded in the fixtures 24 with the insulated wire wrapped terminals 17, 18 and 19 extending upwardly. The conveyor advances the parts to move the terminals through the fluxing station 42 and then into the respective channelled solder streams wherein the parts are maintained in the stream for sufficient time to melt the plastic insulation of the wire wraps and deposit solder on the exposed wires and the underlying sections of the terminals. Inasmuch as the streams are of considerable length, the parts may be rapidly moved along the stream, and yet the parts will be in the stream long enough to melt the plastic insulation on the wires and deposit the necessary solder to effectuate a good solder bond between the wire wraps and the terminals. 
     The speed of the conveyor is set to equal the speed of the solder stream exiting over the dams 87 at the exit end of the channels. This allows the solder stream to fall away from the moving terminal in a substantially vertical direction, hence solder icicles, if any, are formed to extend vertically downward from the terminal. If the speeds are not the same, there would be a tendency for the icicles to form at angle so as to bridge the gaps between the terminals. Moreover, the streams, particularly the solder depositing sections of the streams, flow at a rapid rate, and hence, the parts may be advanced by the conveyor at the same rapid rate. Ultimately, the soldered parts are returned to the unload station 46 where a pair of strikers 106 and 107 are moved to hit the extremities 32 and 33 of the levers to flex the levers in a scissor-like fashion to release the parts 10 which drop into a receptacle 108.