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September  2004

Well-Needed Advancements
Breakthroughs in PVC Welding and Cleaning Systems

by Paul Barbero

Over the past few years the demand for vinyl windows has continued to remain high and as a result the competition between the large (500 or more units per shift) PVC window manufacturers has intensified. Significant pricing pressures have been placed on each manufacturer by the major distributors they supply. As a result, manufacturers have been looking for ways to decrease their production costs simply to maintain their ever-decreasing profit margins.

Decreasing Costs With Welding and Cleaning Systems

One production area of keen interest during the past two or three years has been the production rates for welding and cleaning of the PVC window frames and sash.

Due to the intrinsic nature of the welding process, a specific time (30 to 40 seconds) is required to weld a frame or sash. Since the process time is fixed, the only way to increase production rates is to have multiples of the welding machines (requiring large capital expenditures, manpower and floor space) or to develop ways to weld multiple frames or sashes simultaneously in one machine.

The efforts to weld multiple frames during one weld cycle started many years ago. However, it is only in the past year or so that we have been able to weld as many as four main frames in one cycle successfully or six sash in one cycle while holding the required size tolerances of  +/-1/32 inches.

In order to succeed, technical challenges involving fixturing designs, heater plate configurations and welder structural design had to be overcome. As a result of having met these technical challenges and having now increased welding production rates by factors of two and three, the production bottleneck became the next step in the manufacturing process, which is the corner cleaning task.

In order to keep up with the welder output it first became necessary to develop twin-head cleaners which would clean two corners at a time. (The original corner cleaning machines worked on only one corner at a time and it could take well over a minute to complete just one frame or sash.) As the welder volumes have increased even further in the past year, it has become necessary to evaluate and develop four-head cleaners.  These four-head cleaners (all four corners cleaned simultaneously) have proven to be most successful in sash applications where both corner cleaning and secondary sash processing (e.g. tilt latch routing, weep slots, pivot bar holes, etc.) are required after welding.

At the same time that individual welding and cleaning machine capacities were increasing, we were developing more automated welding and cleaning systems. These would decrease manpower requirements, eliminate handling and increase the quality of the product while taking advantage of the increased volumes made possible in the advanced welding and cleaning machine designs.

One of the unique welding and cleaning systems presently in operation is the Sigma 7000 System developed specifically for multi-level (up to three) main frame welding/cleaning. This system includes a horizontal four-point welder with automatic ejection of the welded frames on to a transfer system that automatically loads the frames into a matching four-head NC corner cleaner. The cleaner then ejects the completed frame that would be passed on to the next manufacturing or assembly phase.

The Sigma 7000 has the ability to produce one frame every 30 to 45 seconds and requires just one operator. 

What’s Next

The latest development (presently in the design phase) is the Ultra 6000 welding and cleaning system which is designed specifically for sash. It will eliminate the welder ejection system and the intermediate buffer stations required on the Sigma 7000 and replace them with an overhead “pick and place” system. This will decrease significantly the time required to remove the completed sash from the welder and decrease floor space by about 50 percent.

The “pick and place” system will grab all four sash (or as many as have been welded) simultaneously and remove them from the welder in one motion. The sash will then be transferred over to the cleaner where the “picker” will act as a magazine loader and place one sash at a time into this four-head cleaner. The cleaner will eject the completed sash so it can be glazed. Once all four sash have been “dropped” by the “picker,” it will return to the welder to gather four more sash.

The Ultra 6000 is expected to produce one sash every 20 to 30 seconds (including secondary processing operations), and it will require one operator.

While much effort has been spent on multi-level welding and multi-corner cleaning, very little time has been spent evaluating the time it takes for the operator to load parts into the welder.

  The actual welding process cycle time is the same regardless of the number of frames welded in one cycle. However, the time required to load all of the parts into the welder increases linearly with the number of frames to be welded simultaneously.

Consequently, the loading time (for as many as 24 parts when welding six sash per cycle) becomes the largest single time factor in the overall process (i.e. load, weld, unload).

At present, the challenge is to develop a reliable system for magazine loading multiple parts in less time than is required with manual loading … stay tuned for further developments.

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