Back to Basics: Thermobending with a Strip Heater

Copyright © 2012 by Davis Multimedia, Int'l. All Rights Reserved.
As Printed in September 2012, Volume 38, No. 3 of The Engravers Journal
Figure 1: Using a strip heater, you can thermobend plastic engraving stock to create freestanding signs.

   Contrary to what many engravers believe, “creative” doesn’t have to mean difficult, expensive and time-consuming. The process of thermobending is a prime example of how you can be creative without a lot of time, expense or unnecessary headaches.
   Thermobending is the process of bending a material under the application of heat. In the recognition and identification industry, this technique is commonly used with plastic materials, e.g. plastic engraving stock and acrylic.
   Being able to thermobend in-house provides you with a multitude of creative design possibilities, ranging from badges to picture frames, which will ultimately intrigue your customers and help you make more sales.
   Thermobending is not at all difficult. This article will provide some helpful tips for getting started and for getting the best results. Thermobending is not expensive. Indeed, the required material, equipment and accessories can cost under $300. And the process is not time-consuming. With a few helpful hints, you can quickly and easily create highly customized products in-house.
Applications
   Thermobending involves using a strip heater to bend thermo-formable materials, e.g. plastic. One of the most common applications for this process is freestanding desk and counter signs (Fig. 1). To create this type of sign, sheet material is heated and then bent into a slanted “L” shape with a small base and a larger front area.
   What many buyers find attractive about a freestanding sign is its one-piece construction. The sign is compact so it easily fits on a desktop or countertop (where oftentimes there are other items occupying space) and it doesn’t require a separate holder, such as a frame or a base. Because of this, freestanding signs are generally a less expensive option than other types of signs, yet they still offer distinction that many buyers find appealing. You’ve no doubt seen these signs as they are popularly used in many types of businesses, including fast-food restaurants, banks and hospitals.
   Another common application for thermobending is creating “tent” signs (Fig. 1). These are characterized by an “A” shaped construction and, again, are usually made of plastic. “Tents” are popular as two-sided signs and are frequently used in restaurants and by just about any business or organization with a reception desk or countertop, such as hotels, stores, banks, etc.


Figure 2: Slip-on pocket badges are another popular application for thermobending. Photo courtesy of Johnson Plastics, Minneapolis, MN.

   Badges are big business and one of the most common types available are “slip-on” pocket badges. This type of badge contains a “folded over” section that allows the wearer to slip the badge over his or her pocket, eliminating the need for a pin or other type of finding (Fig. 2). Slip-on pocket badges are easily created with the process of thermobending and are particularly popular among badge customers who don’t want to put holes in their clothing with pins or other types of findings.
   Thermobending opens up a variety of other potential product applications. Picture frames, for instance, are a popular product among many customers. You can create a freestanding frame with an L-shaped construction that allows the frame to stand, and a “fold over” section (like a slip-on badge) to hold a photo in place. Using clear acrylic, you can create attractive sign holders and badges, e.g. where the customer can insert a business card or other form of message. Other common applications include brochure holders, business card holders and a variety of desk accessories.
   The product possibilities of this inexpensive and easy process are virtually unlimited. One engraver thermobent a piece of acrylic to create a flashlight holder that he mounted next to his laser engraving machine. Another example is to heat bend an acrylic “hanger” which can be mounted on the back of a sign so the sign can be hung over a cubicle wall (Fig. 3). Using your imagination and a little creativity, you are sure to come up with your own unique applications.
Equipment
   Producing the highly salable products just described requires a strip heater. Generally there are two types available. The least expensive variety basically consists of a long, flexible heating element, similar to a long piece of cord-like tape, with a plug at one end. For a little more money, you can purchase an actual strip heating machine, which is generally more accurate and easier to use. This type of strip heater consists of a platform, or work table, with a long, straight heating element mounted on it (Fig. 4).
When selecting a strip heater, consider the length of the heating element. This determines the size of the area you can heat and, therefore, bend. Johnson Plastics, Minneapolis, MN, sells a 21" strip heater for $126 and a 33" strip heater for $165.


Figure 3: The hanger on the back of this sign was created by thermobending a piece of acrylic. Photo courtesy of Rowmark, LLC, Findlay, OH.

Figure 4: This strip heating machine is available from Johnson Plastics.

Figure 5: This bending fixture from Gravograph, Duluth, GA, is no longer available, but with a little time and effort,
you could make one yourself.

   The width of the heating element is another important consideration. Narrower heating elements heat the material along a narrow line, producing a tight, sharp angle on the bend which is commonly desired on products such as freestanding signs. Heating elements with larger widths produce bends with more of a “rounded” shape. This type of bend is recommended for items like slip-on badges and picture frames where something is intended to slide into the bend.
   Most strip heaters are standard with a relatively narrow heating element in addition to a heating element adaptor. The adaptor is usually a wider metal bar that can be placed over the fixed heating element to increase the size (width) of the heating area for different applications.
   Another important feature to consider is an adjustable temperature control. Most strip heaters are adjustable from 0? F to 450? F. Being able to adjust the temperature is useful for bending different materials in various thicknesses. In addition, some users find that it helps to have an actual thermostat control, i.e. where you can preset the temperature, rather than a dial with arbitrary settings.
   An adjustable material-positioning stop is a feature that you might find handy. By presetting the stop before bending, you can abut the material against the stop so the bend is in the correct place and the heating is even. This is also useful for repeatability, e.g. when you are bending several identical items.
   A bending fixture is a helpful accessory for thermobending signs and other products. At one time, Gravograph, Duluth, GA, sold a bending fixture for creating L-shaped bends as well as bends for items like slip-on badges (Fig. 5); however, the company no longer sells strip heating equipment or bending fixtures. Another option is to design your own bending fixture which is fairly easy to do.
   The last component required in order to thermobend is bendable materials. In general, any material that can soften to a bendable state under approximately 300? F-450? F will work. This includes all types of flexible plastic engraving stock and acrylics. Note that very thin and thick plastic materials are not recommended. Some plastics with a microsurface foil cap do not bend well as they tend to crack rather than stretch. We suggest that you do some testing before quoting jobs with these materials. Metals and phenolic, of course, are not thermo-formable.

 

 

Figure 6: Angles of 50, 60 and 70 degrees are commonly used for freestanding signs. Figure 7: The base size for a popular range of sign sizes and included angles.

   As indicated earlier, there are two general types of bends. The sharp bend is used for creating items like freestanding signs while the fold-over bend is better suited for products such as slip-on badges and picture frames.
Thermobending a Freestanding Sign
   The procedures for creating a freestanding sign with a sharp bend are straightforward. One consideration is whether to engrave the sign before or after bending. Although the decision is up to individual preference, most people prefer to engrave the sign first due to the fact that holding a bent sign in an engraving machine is sometimes difficult.
   Next, determine the angle of the bend. The most common angles include 50?, 60? and 70? (Fig. 6), although you can deviate from this if desired. When selecting the angle of the bend, keep in mind the intended use of the sign. Small signs that will be read from a short distance and placed low, e.g. inside a display case, generally are most readable at a 50? angle. Larger signs and desk signs that are read from a greater distance and placed on a counter or desk are often best proportioned at a 60 ?-70? angle.
   When preparing to make a freestanding sign, keep in mind that stability is an important factor. The sign should have a large enough base so it doesn’t easily tip over, e.g. when a breeze flows through the room or if someone slams a door. When you determine the size of the base, you need to consider the height of the sign and the included angle. In general, the center of gravity should be approximately centered from front to back over the base. Figure 7 provides the base size for a popular range of sign sizes and included angles.
   Before attempting any bends, consider the thickness of the material. Most strip heaters are capable of bending up to 1/4” thick material. With thicker materials, however, there is the potential problem of a rounded, poorly defined edge along the face of the bend because the material has not been thoroughly heated. One suggested solution is to rotary engrave a V-shaped slot on the reverse side of the material along the bend line. Use a fine tip cutter with an included angle of around 90? and cut up to halfway through the material. Then proceed with the heating and bending as normal.

Figure 8: Building your own bending “fixture” can be simple yet very effective. Figure 9: A slip-on badge being formed in a homemade bender.


   The first step in thermobending is to heat the material. Preheat the strip heater at the desired temperature based on the type and thickness of the material. Generally speaking, flexible plastic engraving stock can be heated at around 300? F; microsurface plastic engraving stock at 275? F; and acrylic at around 300? F. (Some strip heater suppliers provide suggested guidelines based on the material type and thickness.)
   Set the adjustable stops on the strip heater at the desired dimension for the bend. When the strip heater is up to temperature, place the material face up on the heating element (so the back of the bend is closest to the heating element) for the required amount of time. Again, the time depends on the type and thickness of the material but generally ranges from 30 seconds for 1/16" thick plastic engraving stock to 8 minutes for 1/4" thick acrylic. The material will begin to “sag” slightly when it is heated and ready to be bent.
   In many cases, it helps to use heated weights during the heating process to avoid the problem of uneven heating. Weights can be made of a steel bar with a screw or other item protruding from it (to facilitate removing the weights without burning your fingers). Preheat the weights by placing them directly on the strip heater’s heating element. When you’re ready to heat the material, place the weights on top of the material and the heating element. This ensures that the material is in tight, even contact with the heating element and prevents the material from curling at the edges.
   After heating the material at the recommended time and temperature, remove it from the heater, place it in your bending apparatus, bend and allow the sign to cool.
Step 1: Place the badge blank on the strip heater and heat.

Step 2: Use a 1/8" aluminum rod (or rotary cutter blank) as the bending apparatus.

Step 3: Fold the plastic around the rod.

 

Step 4: Press the plastic around the rod to finish the bend.

Step 5: Remove the rod after bending.

Step 6: Place the badge in cooling fixture to allow it to cool.
Figure 10: Thermobending a slip-on pocket badge. Photos courtesy of Johnson Plastics.

   As mentioned earlier, the process will be much easier and more consistent if you devise some sort of bending fixture to bend the piece with and allow it to cool. Figure 8 shows a simple bending apparatus for a freestanding sign that basically consists of two strips of acrylic clamped to a workbench. So, for example, if you were creating a tent sign and the distance between the “legs” of the sign are to be 2" apart, mount the acrylic pieces on the workbench parallel to each other and 2" apart. Not only does this simplify the bending process, it ensures repeatability when you are bending a quantity of the same size signs.
Thermobending a Slip-On Badge
   The process for creating a fold-over bend, e.g. for a slip-on badge, is equally simple. To create a slip-on badge, first calculate the length of the plastic blank. A simple way of doing this is to add the height of the badge surface to the height of the insert (back) plus 1/4" for the bend.
   Preheat the strip heater and metal weights (if you are using them), and adjust the stop on the strip heater and your bending fixture. Place the badge blank on the heating element (face up) and place the weight on top of the blank. After heating, place the blank in the bender (face down) and immediately bend the badge (Fig. 9).
   Instead of using a bending fixture for slip-on badges, another option is to use a metal rod to create the bend and then a separate fixture to allow the badge to cool. For example, a 1/8" diameter rotary cutter blank or piece of aluminum works well as a bending “fixture” as shown in Figure 10. If the badges will be worn on uniforms with thick pockets and require a larger bend, you may want to use a ¼” metal rod. After bending, place the badge in a cooling fixture and allow it to cool.


Figure 11: Common problems and causes when thermobending slip-on badges.

   Thermobending slip-on badges is not difficult, but you may encounter a few potential problems. Figure 11 provides a checklist of common problems and causes. Note that if the problem is not enough heat, the solution is to increase the temperature and/or time and vice versa. If uneven heating is the problem, try using heated weights.
Conclusion
   Products like easel signs, slip-on badges, picture frames, etc., all have a solid place in the market. With a small investment, you can be well on your way to creating these products quickly and easily in-house. And with a little extra time investment, you just may be able to develop some new, interesting and creative ideas. You never know—you may even have fun while you work!

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