Bending ABS Plastic: A Comparison of Thermoforming, Hot Bending, and Cold Bending

Acrylonitrile butadiene styrene (ABS) plastic is commonly used across many industries due to its durability, flexibility, and ability to be bent into a variety of shapes. From automotive trim pieces to plastic enclosures to pipes and tubes, properly bending ABS plastic sheets is crucial for creating high-quality finished parts.

However, bending ABS plastic can also crack or craze the material if the right techniques are not used. In this guide, we’ll compare the most common methods for bending ABS plastic sheets and parts - thermoforming, hot bending, and cold bending. We’ll highlight the advantages and disadvantages of each process so you can determine the ideal approach based on your specific application and production requirements.

An Introduction to Bending ABS Plastic

ABS is an incredibly versatile thermoplastic polymer with properties that make it suitable for bending into custom parts and products. Some key traits of ABS plastic include:

• Durability - ABS offers good impact resistance and tensile strength, making it more durable than materials like PVC or polystyrene for bent applications.
• Flexibility - At standard thicknesses and temperatures, ABS can be flexed and bent repeatedly without fracturing or cracking. This flexibility makes it suitable for bending intricate shapes.
• Customizable - ABS plastic maintains its stability when bent into unique forms, enabling the creation of custom enclosures, housings, and components.
• Workability - Compared to metals and other plastics, ABS is relatively easy to machine and work into various designs.
• UV/chemical resistance - ABS provides resistance to ultraviolet light exposure and many common chemicals, retaining its strength and appearance over time.

With the right techniques and processing methods, ABS can be repeatedly bent to angles exceeding 90 degrees without showing signs of damage. Proper ABS plastic bending techniques are crucial to prevent cracking, crazing, rippling, or other defects.

Thermoforming, hot bending, and cold bending are three of the most common industrial techniques used for contouring ABS plastic sheets into the desired shapes. Each approach has its own set of pros, cons, ideal applications, and equipment requirements.

We’ll do a detailed comparison of all three options so you can determine the right ABS plastic bending process for your specific needs.

Thermoforming ABS Plastic

Thermoforming uses heat and pressure to mold thermoplastic sheets into new shapes with custom curves and bends. It is one of the most popular plastic fabrication methods across many industries including automotive, appliance, packaging, and construction.

The thermoforming process consists of clamping the ABS plastic sheet into a temperature-controlled frame. The sheet is then heated until it becomes flexible and stretchable. Next, it is transferred to a mold and conformed precisely over the contours of the male or female mold shape. Pressure and/or vacuum is applied to force the warmed plastic tightly around the mold. The formed piece is held against the mold while cooling and sets into the desired shape.

Thermoforming allows ABS plastic to be bent into forms that would otherwise crack or fracture the material. Key benefits of thermoforming include:

• Produces uniform, consistent bends in the ABS plastic.
• Heat is evenly distributed so the entire sheet reaches optimal forming temperature.
• No leftover stresses in the material after cooling that could cause cracking.
• Smooth surface finish and accurate reproduction of the mold shape.
• Ideal for prototyping and short production runs. Lower tooling costs than injection molding.
• Allows very tight inside radii and complex bends in the plastic.
• Dimensional stability. The bend radius and angles maintain their form once cooled.
• Can form many parts quickly through gang forming or rapid tooling changeovers.

Thermoforming does come with some downsides to consider as well:

• Requires a high initial investment in thermoforming machinery and the forming molds.
• Limited to relatively thin-gauge ABS sheets, usually under .120” thickness.
• Only suitable for short-moderate production runs, not extremely long runs.
• Additional secondary finishing work may be needed after forming.
• Relatively slow process compared to other methods. Cycle times range from 30 seconds to 30 minutes.

Thermoforming has some key advantages in working with ABS plastic since it can heat and form the material into complex or tight bends without damage. It is the ideal choice when consistent, wrinkle-free high-quality bends are needed for prototypes or short-run production.

Hot Bending ABS Plastic

Hot bending is the process of using heat to soften ABS plastic sheets to make them pliable enough to bend without fracturing, then cooling to set the shape. Localized heat is applied immediately before the bend using tools like heat guns, strip heaters, ovens, or heat bends.

The key advantage of hot bending ABS is that the heat softens and “plasticizes” the material so it can flex without damage. Key benefits include:

• Allows bending the ABS sheet to tighter radii than is possible with cold bending.
• Lower risk of material stress and cracking during and after the bend.
• Bends have a smooth, rounded contour rather than a sharp V-shape.
• Ideal for relatively short, straight bends rather than complex curving shapes.
• Faster process than thermoforming and lower equipment costs.
• Enables bending thicker sheets up to .25” thickness.
• Small lot sizes and prototypes can be bent using simple heat guns.

Hot bending does require some precautions and disadvantages to consider:

• More labor-intensive process since heat must be continually applied during bending.
• Risk of overheating or burning the ABS material if temperature isn’t controlled.
• Cooling and setup of the bent shape takes time.
• Requires appropriate heating equipment based on volume - from heat guns to ovens.
• Precise process control needed to avoid under/over heating.
• Some trial and error may be needed to find ideal heat settings.
• Works best for short, gentle bends rather than multiple or complex shapes.

Overall hot bending is ideal for gently contouring ABS sheets up to .25” thick when you need tighter bend radii and less cracking risk than cold bending. It offers the versatility to bend small custom or short-run components using a heat gun or batch bend higher volumes in an oven or thermal box.

Cold Bending ABS Plastic

Unlike thermoforming and hot bending, cold bending does not apply heat during the bending process. The ABS plastic sheet is bent at room temperature using tools like presses, brakes, or mandrels.

Cold bending is common for ABS applications like:

• Simple brackets
• Short production runs
• Retaining clips
• Small plastic parts

Benefits of cold bending include:

• Very fast process and short lead times, no heating or cooling.
• Lower equipment investment. Manual or CNC presses suffice.
• Eliminates risks of fire hazards or fumes from heating.
• Consistent results once tools are setup and calibrated.
• Does not alter the molecular structure like heating.

However, cold bending also comes with some downsides:

• Higher risk of cracking, crazing, or rippling, especially with thicker sheets.
• Only capable of relatively wide bend radii, minimum 2-3x sheet thickness.
• Increased internal stress in the bent area after forming.
• More likely to get a sharp bend with increased fragility at bend apex.
• Not ideal for extremely tight radii or complex compound bends.
• Requires rigid clamping and bend fixtures to prevent sheet slippage.

In summary, cold bending works well for simple ABs plastic components that do not require tight radii. It is the fastest processing method but also carries the most risk of damage or cracking. Thinner gauges under .100” thickness cold bend the best.

Comparing the Tradeoffs of Each Bending Method

To summarize the key pros and cons:

Thermoforming works well when even heating, tight bend radii, and dimensional precision are critical, such as for moderate production runs above 1,000 parts.

Hot bending is ideal for short-run bending of sheets up to .25” thickness when you need tighter radii than cold bending allows.

Cold bending provides the fastest lead times but should be limited to room temperature bending of thin ABS sheets into relatively wide radii.

Finding the Right Bending Technique for Your ABS Application

As this comparison shows, thermoforming, hot bending, and cold bending all have their own advantages and limitations when working with ABS plastic sheets. The right method for your application depends on factors such as:

• Production quantity (prototypes, small lots, longer runs)
• Sheet thickness and bend radii needed
• Equipment available
• Level of precision and process control required
• Secondary finishing time

Most importantly, consult with your chosen ABS sheet manufacturer and plastic specialist when selecting a bending technique. An experienced ABS forming company can recommend the ideal process based on your product goals, provide technical advice, and help you avoid common pitfalls.

At Bee Plastic, our team has specialized in custom ABS plastic thermoforming, bending, and fabrication for over 20 years. Contact us today to request a quote or discuss your unique ABS plastic bending needs.