James L. Throne, Sherwood Technologies, Inc., Dunedin Florida 34698
Peter J. Mooney, Plastics Custom Research Services, Advance North Carolina 27006

Abstract

Thermoforming is the process of heating and shaping plastic sheet into rigid containers, components of final assemblies, and stand-alone end-use parts. The value of all thermoformed parts produced in North America in 2003 exceeded US$10 billion. Traditionally, about ¾ of all thermoformed products are produced from sheet of 1.5 mm or less in thickness and are primarily rigid disposable packaging products. Most of the rest is produced from sheet of 3 mm or more in thickness and are primarily durable structural goods.

Thermoforming has benefited by its ability to fabricate thin-walled parts having large areas, using relatively inexpensive, single-sided aluminum tooling. Its deficiencies – variable wall thickness, the added cost of sheet and trim regrind, and extensive trimming and additional cost to reprocess the trim – are offset by the ability to economically produce low-volume, thick-walled parts or high-volume thin-walled parts.

The advances in thermoforming technology in the past decade have allowed the industry to grow at a rate that exceeded the growth rate of the plastics industry in general. However, this pattern has changed in the past few years. Newer advances in plastic materials, tooling, forming machinery, and auxiliary equipment are needed to regain earlier growth rate momentum.

This paper considers several emerging technologies such as forming composite sheet materials, surface decoration, and new material development. It also considers the effect of globalization on both thin-gauge and heavy-gauge domestic thermoformers.

Introduction

The thermoforming process begins with an extruded sheet of plastic. It is heated between infrared heaters to its forming temperature. Then it is stretched over or into a temperature-controlled metal mold. It is held against the mold surface until it is cooled. The formed sheet is then removed from the mold and the formed part is trimmed from the sheet. The trim is then reground and returned to the extruder to be mixed with virgin plastic for extrusion into sheet.

There are two general thermoforming process categories. Sheet 1.5 mm (0.060 inches) or less in thickness is usually delivered to the thermoforming press in rolls. Thin-gauge, roll-fed thermoforming applications are dominated by rigid or semi-rigid disposable packaging products. Sheet 3 mm (0.120 inches) or more in thickness is usually delivered to the forming press cut close to final dimensions and stacked on pallets. Heavy- or thick-gauge, cut sheet thermoforming applications are primarily permanent structural components. There is a small but growing medium-gauge market that forms sheet 1.5 mm to 3 mm in thickness. Thermoformed parts are as small as thimbles with wall thicknesses less than 0.015 mm (0.0006 inches) or as large as swimming pools with wall thicknesses greater than 25 mm (1 inch).

The North American thermoforming market has traditionally been split into ¾ thin-gauge products and ¼ heavy-gauge products. There are about 150 thin-gauge thermoformers in North America. Sixty percent form proprietary products, 30% are custom formers, and 10% are OEMs with in-house forming capability. There are about a dozen thin-gauge formers having annual sales of US$100 million or more. The largest, Pactiv Corporation of Lake Forest, IL, has annual sales in excess of US$1,000 million.

There are about 250 heavy-gauge formers in North America. Nearly all are custom formers. Only a handful of heavy-gauge formers have annual sales of more than US$100 million. In 2003, the largest, Wilbert Plastic Services of St. Paul, MN, had annual sales of about US$140 million.

Historically, thermoforming is one of the oldest plastics processes (1). Baby rattles and teething rings were formed of camphorated cellulose nitrate or pyroxylinTM in the 1890s (2). The industry did not grow substantially until the 1930s when the development of cellulose acetate and acrylic provided the industry with formable sheet. The earliest roll-fed thermoforming machines were developed in the late 1930s in Europe (3). Throughout WWII, heavy-gauge forming depended on convection oven heating of the sheet and hand draping of the sheet over male or positive molds (4,5). Shuttle presses were developed in the late 1940s, and rotary machines followed in the late 1950s and early 1960s.

Growth Dynamic for the Industry

For many years, the growth rate of the industry exceeded the growth rate of the plastics industry, in general. The forming industry grew at about 8.5% to 9% annually through the 1970s. From 1984 to 2000, the heavy-gauge growth rate was in excess of 5% annually, but by the second half of the 1990s, the thin-gauge packaging business had slowed to about 3.4% annually (6). From 2000 to 2003, the overall industry growth rate dropped to zero. The forecast for the coming years for both thin-gauge and heavy-gauge forming is a growth rate below that of the plastics industry, in general (7). A maturing industry and the effects of globalization are the primary forces behind this decrease in its growth rate.

Maturation of the Industry

It is our observation that the thermoforming industry is moving into its mature stage. In the last half-century, the industry has evolved from toaster-wire heaters, using sag as a measure of formability, wooden molds, and hand trimming, to energy-efficient heaters, sheet temperature monitoring, temperature-controlled molds, and advanced trimming machines. Because of this evolution, one wag has said, “We’ve formed all the easy, pretty parts.”

Market penetration requires ratcheting up the technical level. But it also increases piece-part costs and invites competition. Injection molders, for example, for some time have been molding plastics with superior mechanical strength to compete with structural thermoformed parts, and they are now bidding for low-volume parts to just cover their variable costs. They are once again investing in large-platen, high-tonnage presses to challenge heavy-gauge formers. Rotational and blow molders are strongly resisting inroads by twin-sheet thermoformers into hollow part production (8). Yet, as we note below, new thermoforming techniques may help counter these infringements.

Globalization

Over the last half-century, the three North American economies have been truly transformed by globalization. In the United States, the share of foreign trade in our gross national product has risen from roughly 5% a half-century ago to over 10% today. The opportunities for expanding production through exports have increased. At the same time, consumer choice has been enhanced through imports (9).

Although some domestic industries have benefited from globalization, the overall domestic plastics industry has suffered. Injection molders, in particular, have endured a continuing decrease in their markets as many domestic OEMs have either relocated their manufacturing operations to Asia and other regions of the world or have outsourced the production of parts – in some cases, entire assemblies – to foreign countries with comparative advantages in the form of low-cost labor. Injection molders are particularly susceptible to this trend because their mode of production has become standardized and automated, and their output is typically small in physical size and economical to transport in container ships.

Thin-gauge part formers have already been impacted by this trend to globalization as parts produced offshore are usually also packaged offshore. Heavy-gauge formers are just now beginning to feel the globalization effects. The major barrier that Asian heavy-gauge part formers faced in the past was poor quality sheet. This is now beginning to change. To meet the inevitable growing challenge of foreign competition, the domestic heavy-gauge part formers must be relentless in reviewing their entire operation to increase overall efficiency. And they need to explore export opportunities, which have traditionally been a small fraction of their customer base.

A Caveat on Newer Advances in Thermoforming

In Table 1, we list several recent advances of importance to formed sheet fabrication. However, we must keep in mind that thermoformers tend to be very pragmatic regarding new concepts. In many cases, formers are aware of these technologies, but they will only adopt them when the customer is willing to pay for the time and effort needed to learn how to use them. Technologies such as twin-sheet forming, multi-axis trimming of heavy-gauge parts, formable PP, and syntactic foam for pre-stretching thin-gauge parts were tested and available for years before thermoformers chose to employ them. Interestingly, once thermoformers learn the value of these technologies, they quickly embrace them.

Technologies Available by 1980 But Adopted Much Later by Thermoformers

Table 1

Tungsten-wire halogen heater (late 1800s)
Nichrome wire in quartz glass heater (1930s)
Low-pressure natural gas or propane heater (1800s)
Electric platen drive (1960s, injection molding)
Enclosed oven heating (1970s, Japan)
Twin-sheet forming (late 1800s)
Pressure forming (late 1800s)
Computer models for predicting heating rates (1970s)
Polypropylene for thin-gauge forming (1970s)
Oil-less bearing surfaces (1960s)
Localized matched-tool forming or “coining” (1970s, injection molding)
Syntactic foam (1970s)
In-mold labeling (1970s)
Infrared temperature measurement (1970s)
Scrapless thermoforming (Dow STP, 1970s)
Multi-axis trimming (3-axis,1930s metalworking; 5-axis,1950s woodworking)
Computer-driven machining (1960s, metalworking)
Machining and bending for assembly (1940s, hobbyists)
Computer-aided distortion printing (1970s, Hollywood morphing)
Mathematical wall thickness prediction (1970s, Fukase, blow molding)

Is Thermoforming Evolving?

Nearly a decade ago, one of us (PJM) conducted the first extended survey of North American industrial thermoforming (10). At that time, he noted that most of the companies interviewed had little or no interest in the latest thermoforming technologies. In the forward to this report, the other of us (JLT) noted that many of these same companies had recently invested heavily in pressure forming, CNC trimmers, syntactic foam plugs, epoxy foam prototype tools, extensive sheet drying equipment, ceramic, quartz, and/or natural gas heaters, and in-house vacuum and pressure systems. Many of these techniques were experimental or not fully developed only a decade earlier. So, despite thermoformers’ claims that they have no interest in the latest innovations, they do ultimately adopt them. This year he (PJM) conducted a follow-up survey of these processors (7) and once again, he concluded that this attitude toward new technological advances still prevails.

So, what new developments should formers be adopting in the days and years ahead? Table 2 lists many technologies that have been around for a while but have not yet become part of the thermoformers’ lexicon. Some of these will become economically important in the next few years.

Technologies Known Since 1980 But in Limited Use Now

Table 2

Small-particle fillers (including nanofillers)
Biodegradable and compostable polymers
In-mold decorating
Secondary reinforcement of formed part
Water jet cutting
Short, long, and continuous glass fiber-reinforced sheet
Coordinate measurement uses (other than QC)
Porous metal and porous ceramic mold materials
Formable high-performance sheet applications
Antistatic and static-dissipative sheet applications
Surface venting – poppet valve
Thin-gauge, in-mold, trim-in-place forming
High-density foam sheet
Thin-gauge wheel forming
Linear motor multi-axis trimming devices

References

  1. Throne, J.L., “Thermoforming: From Baby Rattles to Bed Springs and Beyond,” 60th SPE ANTEC, San Francisco, SPE Tech. Papers, 47, 4089-4095, (2002).
  2. DuBois, J.H., Plastics History U.S.A., Cahners Books, Boston, 44-45 (1972).
  3. DuBois, J.H., Plastics History U.S.A., Cahners Books, Boston, 248-249 (1972).
  4. Anon., 1941 Modern Plastics Catalog, Breskin Publishing Corp., New York, 52 and 180 (1940).
  5. Anon., 1943 Modern Plastics Catalog, Plastics Catalogue Corp., Chicago, 130, 395, 508-516, and 524-528 (1942).
  6. Mooney, P.J., “Understanding the Thermoformed Packaging Business,” Plastics Custom Research Services, Advance NC (May 2002).
  7. Mooney, P.J., “The Industrial Thermoforming Business: Review and Outlook,” Plastics Custom Research Services, Advance NC (Nov. 2004).
  8. Beall, G.L., and J.L. Throne, Hollow Plastic Parts: Design and Manufacture, Hanser Publishers, Munich (2004).
  9. Mooney, P.J., “It’s the Economy, Stupid!” Plastics News, 6, 23 (15 Nov 2004).
  10. Mooney, P.J., “An Analysis of the North American Industrial Thermoforming Business,” Plastics Custom Research Services, Advance NC (Sep. 1995).

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