Stanley R. Rosen
The end of World War II released the ambition within many of the discharged veterans to seek new careers in the relatively new plastics industry. The U.S. Government’s G.I. Bill of Rights paid for the veterans education in technical, academic, or business fields and this provided a foundation for many energetic plastics entrepreneurs.
In 1946 the First National Plastics Exposition was held in New York City and it was besieged by attendees. Critics complained that most of the visitors were ‘not from the trade’ and they were classified as ‘interested spectators’. These amateurs were anxious to see at firsthand how plastics was processed into products. They needed to develop personal contacts with the plastics resin suppliers, mold makers and machine manufacturers. Unfortunately there was not any commercial vacuum forming equipment on exhibit and it took another six years for these machines to be developed and displayed.
At the 1952 SPI National Plastics Exhibition in Philadelphia, PA, the first commercial vacuum forming machine was operating on site and it became the star of the show. What made this process so appealing was the equipment, and molds were quite inexpensive compared to injection molding or extrusion equipment. This meant that a whole universe of plastics parts could be produced in small quantities to develop many new markets.
The former chief of the Army Map Services, E. Bowman (Bow) Stratton, Jr., helped introduce “vacuum forming” to the plastics world. The Army Map Service labored for twenty years to find a way to produce topographic maps in three dimensions, testing various materials and settling on thermoplastics. At the end of WWII, Bow Stratton and some of the former Army Map Service employees worked for a number of years to develop a commercial vacuum former. Bow traveled throughout the U.S. and Canada to speak at plastics and packaging forums about the virtues of vacuum forming. He was the sales manager of the Industrial Radiant Heat Corp. of New Jersey which demonstrated the first vacuum former at the 1952 plastics show
A mix of vacuum forming startups concentrating in various fields – packaging (blister packs), advertising and displays (3-D beer signs), paper box inserts (cosmetics, toys), and heavy gauge products – quickly set up shop. New ventures were evenly split between in-plant departments and commercial vacuum forming shops. All of these earlier machines were manually operated, using timers to control the vacuum forming cycles. Pressure forming equipment was developed later and the word thermoforming (either pressure or vacuum forming) was not in common usage until 1962.
Vacuum formed multi-cavity plastics shots required that each cavity be perimeter trimmed for use by the customer. The paper industry cut out individual pieces from a sheet, using inexpensive steel rule dies mounted in large area powerful short stroke presses. These die cutting presses did not provide the long stroke and clearance necessary for high-profile formed plastics parts. Shoe leather components are manually cut from a hide on a small area clicker press using similar knife edge dies. The clicker machine daylight opening can be adjusted and adapted easily for manually die cutting formed plastics shots. All kinds of punch and hydraulic presses were then mobilized and converted into service for steel rule die cutting. Very accurate cut parts were trimmed in metal working punch presses using a punch and die. Thick gauge sheet thermoformed components were manually band-sawed or router-trimmed with their rough edges hand-finished. Large area heat-assisted presses were introduced which were specifically designed for steel rule die cutting thermoformed sheets.
A mold is an essential tool used to form thermoformed parts. For short runs, molds should be inexpensive enough to be amortized over an initial small run to be competitive to injection molding. Mold cavities were often fabricated on site using a pattern maker’s wooden master and reproducing multi-mold cavities in plaster, or aluminum-filled epoxy. These cavities were mounted on a wooden vacuum box base with the finished shot cooled by fans. Early vacuum forming machines could only run at 1-3 cycles per minute on thin sheet, so the poor thermal efficiency of these non- metallic molds was sufficient for the small orders of the times.
Advertising and display firms were able to distortion copy artwork images on to plastics sheets. After vacuum forming, the distorted sheet returned to the features seen in the original artwork. Simple loose reusable letters were used as molds for what were called 3-D advertising signs which were vacuum formed at very low cost. Theatrical and movie companies formed backdrop scenery for their productions. Ubiquitous Santa Claus and Elves were thermoformed for the Christmas Holidays. Protective cases for instruments, home movie protectors, industrial tote boxes and machinery safety enclosures were vacuum formed from thicker gauge sheet.
Some independent vacuum forming firms were slow to upgrade or increase their capacity until forced to by growing product demand. Manual vacuum forming machines were being replaced by new professionally-designed machines which obsoleted the individual sheet-fed machines with roll-fed continuous equipment. The new roll-fed thermoformers required the efficient heat transfer from the mold to reduce the cooling cycle time. The use of water cooled aluminum cavities increased the tooling cost but raised the output significantly. The increased production of formed shots caused a backup of parts waiting to be manually steel rule die cut and this problem took some time to be resolved.
Thermoforming firms realized that integrated forming and trimming was a necessity for progress in processing the finished trimmed parts. Machinery builders needed firm orders to proceed with the design and development of this next step in the evolution of thermoforming. The go-ahead came from a large paper cup manufacturer who visualized plastic cups and lids as a viable profitable product. A collaboration between Dow Chemical and Gaylord Brown (Brown Machine) and Maryland Paper Cup in the early1950s developed the first commercial inline forming and trimming systems. This roll-fed vacuum forming machine consisted of a tunnel oven, a vacuum forming station with an indexing system to transport the web through the machine. The moving thermoformed web was introduced into a self-indexing punch and die trim press and both machines were synchronized. The cups were punched through the die and packaged and the scrap was cut into small pieces and recycled. This system was practical for large volume components but the tooling was too costly for use for low and medium production.
A further thermoforming development was for an inline pressure former incorporated with a steel rule die cutting press. The equipment evolved after Jack Pregont (Prent Corp) convinced Gaylord Brown to build a simple inexpensive version of his inline thermoformer and trim press. This type of machine became the workhorse for custom thermoformers to this day for its moderate cost of tooling and high productivity.
All of the thermoforming machines previously described were heated using various forms of radiant heat emitters (tubular, quartz, ceramic, etc.) Contact heating of plastics requires that the plastic be in intimate contact with a heated metal surface. Contact heat thermoforming combines the forming and trimming in a single tool and it is mainly used for the forming of oriented polystyrene (OPS). Robert Butzko was the engineer-partner of Bow Stratton at AutoVac Corporation (an early thermoforming machine building company). Bob Butzko left AutoVac in the 1950s to establish Thermtrol Corporation to design and build roll-fed contact heat thermoformers. The machine and tooling was comparatively inexpensive and the machine was extremely easy to operate.
Prior to the 1950s thermoforming machines of some sophistication and merit were designed and built for the use of private firms. However the market during that period for thermoformed products was weak and demand for equipment was light.
Many of the early pioneering thermoforming family-owned companies are gone, sold or merged, except for some notable exceptions. Large financial corporations have heavily invested in this industry that was once crudely described as “the poor man’s injection molding”.