Fillet Brazed, This is where the joining tubes are precisely mitered and joined with a brass-bronze filler rod material that melts at a lower temperature than the base metal. The brazed filler joint is not very nice to look at and Schwinn spent labor time hand finishing the brazed joints. The early production models had beautiful joints, but by the early 1980's the joints on bikes like the chromoly BMX Competition Scramblers looked pretty crude with unfinished brazed joints. The brazing produced a very strong joint, but required longer production time mitering the tubes, hand assembling the frame into a jig, then hand brazing, and hand finishing the joint after it was cooled. My 1971 Paramount Tandem was built with this WW1 welding technology. Millions of Schwinn frames on many different models were built this way. It was an expensive production method.
Lugged, I believe this style of Schwinn frame construction began about 1938. Oscar, and Emil Wastyn had a big part in getting the Schwinn Paramount model produced. At the beginning, lugs were stamped out, and the two halves welded together. The frame tubes had to be closely mitered, the frame was jigged up and all the parts were silver brazed (soldered) at a low temperature. This method allowed Schwinn to use a very thin wall tubing for lightweight, and the lug added extra material at the high stress joints. By the 1980's the former pressed lugs were made by a then new investment casting technique. The main advantage in using the more expensive casting method was the labor time saved in assembling the frame because the cast lugs were more accurate and required less clean up time. This is the way most steel framed Paramount's were made right up until Waterford Cycles closed. Note, they did make some TIG welded frames, and some Filet Brazed frames on "one off" custom bikes that had weird geometries, like my Paramount Pursuit frame.
Electro Forged, This is the style of frame fabrication that Schwinn is "for better, or worse" best known for building. Let's start off with the marketing name. Nothing is FORGED in a "so called" Electro Forged Frame! It's all press formed. This name had to have come from one of the marketing guys that was bored playing right field on a Tuesday night soft ball game. Schwinn needed a way to build a quality frame, at a low cost, in large production quantities. The highest stress point in a bicycle frame is directly next to the welded joint. By making a head tube with fingers moving the welded joint back about one inch from the head tube the butt-welded tube joint strength was increased. It also gave the smooth transition appearance of Schwinn's long term Fillet Brazed frames, but without all of the costly hand finishing. If they could pull it off, it was a win/win. They pressed a right side and a left side head tube half. The metal was formed on a press brake, it was not forged like a handlebar stem or a crank that were forged "off site" from Schwinn's Chicago factory. The right and left half's were joined with electric welding. Think of it like a linear spot weld. Take a look at common electrical conduit tubing and you will see the same linear electric weld inside the tubing. Schwinn made their own tubing on a tube mill and electronically welded the tubing made from flat coiled flat metal. The downside of this high production technology was they needed to use thicker walled tubing to make a strong butt-welded frame tube joint. The result was excess weight. One of the active projects in the late 1970's/early 1980's was Marc Mueller one of Schwinn's engineers (best known for Paramount's and Waterford Cycles) was working on a High Strength, Low Weight steel that had been developed for the automobile industry to reduce car weights in an effort to improve the CAFE (corporate average fuel economy) numbers for Detroit. He was also working an aluminum kickstand sprags for the Schwinn built-in kickstands. They were working on very high pressure tires to make the Electro Forged bikes ride easier, and weigh less on a scale.
Uni-Lug, This is a project Schwinn developed to bring lugged frame production down into the high volume lower price point models. The Schwinn Greenville, MS. factory was built around the idea of high-volume Uni-Lug bicycle frame construction. The frame's head tube, the top head lug, and the bottom head lug were all cast in one piece. The casting lug was made from a low melting temperature plastic (wax). Then the plastic lug was spray coated with a very light weight white ceramic material (it looked like asbestos, LOL). The coated parts were put into an oven and they melted the plastic out and poured liquid metal into the molds. They made these on trees with about 6-8 all connected. They broke off the ceramic coating, broke the parts apart, and they were ready for the frame building. Jewelry is made by this Investment Casting technology. The frame tubing did not require any precision mitering, just an exact length to fit the shoulder cast inside the lug. The tubes received a small square dimple pressed into the tube. Into this dimple they placed a small (less than 3/16") brass pellet, then the tube with the pellet was inserted into the Uni-Lug. The frame was jigged into a fixture, automated brazing torches from both sides heated the Uni-Lug and the tubes red hot and melted the pellet. The frame was removed from the jig and required almost no clean up. This gave the appearance of any other normal "Lug Framed" bicycle, but at a much lower production cost to manufacture. This technology worked well; it was just too little, too late to have a positive impact on the bottom line.
Blow mold Carbon Fiber, This was a technology purchased by Schwinn from CCI (Cycle Composite's Incorporated) located in Watsonville, CA. This technology was years ahead of Trek and Specialized that were still selling carbon wrapped tubes glued into aluminum lugs. This small production carbon fiber company-run by former Trek managers, built bicycles under the Kestrel brand name. It was a very high-tech blow mold, one piece type frame. Schwinn became their marketing arm. The four Schwinn Sales Companies sold more Kestrels in the first year of Schwinn's distribution than they had ever sold in the company's history.
Aluminum Welded, Schwinn's dealers asked for aluminum framed models. When Schwinn built the Greenville, MS. factory they also built an aluminum frame line in the factory. Schwinn chose to use 7000 series aluminum tubing because they wanted to heat treat, (stress relieve) the tubing after it had been TIG welded together. The frame technology was good in that very few ever broke, but you will still see many today with frame tubes that "took on a bow" during the stress relieving process. IMO, Schwinn ran out of time before they fully developed this new welding and Alcoa 7000 series tube technology.
I'm sure I forgot something but that's a start.
John
