It’s interesting to know that roll forming is a highly applicable and important process for shaping metals, with over 40% of the steel used in various industries, including construction, automotive, and machinery manufacturing, produced through this technology. Given its significance, in this section of the Persian Sazeh blog, the largest building information database in the country, we delve into this topic to provide you with comprehensive details about this field. So, stay with us!
What is the Roll Forming Process?
It’s noteworthy that roll forming is a widely used yet relatively unknown process. In fact, describing and explaining the roll forming process is not straightforward; however, in general terms, it can be defined as the shaping of metal sheet strips along a straight, longitudinal path, parallel to bending lines, using several pairs of contour rollers without changing the thickness at room temperature.
Regarding the Roll Forming Process and Its Details
In general, roll forming is recognized as a highly applicable and important process, having developed over the last half-century as one of the most efficient technologies for shaping metals. Interestingly, approximately 35 to 45 percent of all steel produced by factories in the U.S. is generated through the roll forming process, a quantity greater than that used in the automotive industry. Due to this fact, hundreds of vehicles, buildings, agricultural machinery, tanks, and other products are produced daily through roll forming; however, most people outside this profession have little to no familiarity with the industry.
Throughout the century-long history of roll forming, thousands of tools, equipment, designers, and users have worked in this field, and many are still active today. Unfortunately, a significant portion of the experience gained by operators, installation engineers, and designers has never been documented or recorded. As a result, among all articles and research reports, only a limited number are interpretable and applicable in the roll forming industry. Analyzing the roll forming process is not an easy task. The international definition provided for the roll forming process reflects this complexity. Therefore, to understand this process, several important points must be considered, including:
- The products produced by roll forming typically have curvature.
- The angle of bending lines can be 90 degrees.
- Bending lines are not always straight and may sometimes be intentionally curved. Additionally, bending lines are not always parallel, which is often done at the customer’s request.
- It should be noted that the thickness of the sheet always decreases in the bent areas or bending lines.
- The rollers of the roll forming machine have specific passages that can reduce the thickness of the sheet wherever necessary. In curved products that are thin, the outer strands and bumps are thinner than the inner ones.
- While it is mentioned that the ambient temperature does not change during the operation:
- To prevent cracking of the coating at bending lines, metal sheets are heated before roll forming.
- The operating temperature for sheets that have been soldered, annealed, or brazed needs to be increased.
Introduction to Vacuum Forming Machines and Their Types
Vacuum forming is commonly used for shaping plastic sheets. This process involves direct or inductive heating. In this operation, after placing the sheet in the machine’s sheet holder, the heater applies direct heat to the sheet. At this point, the sheet becomes pliable, and the mold approaches the sheet, completing the forming process while evacuating the air between the sheet and the machine. It is important to note that this process is applicable to soft sheets. The various methods of vacuum forming include:
• Vacuum Forming
Vacuum forming, or vacuum molding, refers to the process of shaping heat-softened sheets using direct or inductive heat and the evacuation of air between the sheet and the mold, allowing the sheet to conform to the mold’s shape.
In general, during this process, a heat-sensitive plastic sheet (thermoplastic) is heated until it becomes soft and flexible. The softened sheet is then placed over the mold, and a vacuum is applied to pull the air out, stretching the sheet over the mold and allowing it to take its shape.
The thermoforming process occurs in two stages:
1. Heating Stage: The plastic sheets are positioned at a certain distance from the heating elements, where they become soft.
2. Shaping Stage: The flexible sheets are then placed over the cavity molds, where the vacuum within the mold pulls the plastic into the mold’s shape.
After forming and the plastic sheet hardens, the final piece is removed from the mold, and any excess parts are trimmed away.
• Air Pressure Forming
In this method, flexible plastic sheets are shaped by applying force through air pressure from above onto the sheet mold. In this case, the sheet is drawn into the mold cavity. It is important to note that to expel the air trapped between the sheet and the mold, vents must be incorporated into the mold to ensure that the air pressure forming process is carried out effectively.
• Mechanical Forming
In this method, a heat-sensitive plastic sheet is placed between the positive and negative parts of the mold. Ultimately, mechanical pressure is applied directly from the positive part of the mold to the plastic, pulling the sheet into the cavities of the negative mold. It is worth mentioning that one of the most prominent advantages of this method is better dimensional accuracy of the product and more precise geometric details on both sides of the piece compared to the other two methods. The only drawback of this method is the requirement for both positive and negative mold parts, which results in higher production costs.
Introduction to Types of Roll Forming Systems
As you may have read in other Persian Sazeh articles, the most important component of a roll forming line is the rolling machine. This is because the rolling machine provides the necessary force and support to the rollers, which shapes the metal. Interestingly, the design of rolling machines in this field is virtually limitless, but they can be classified into the following categories: suspended machines, duplex machines, combined duplex machines, standard machines, and flat machines. Additionally, machines that do not fit into any of these categories are considered special rolling machines.
Familiarization with Various Methods of Sheet Roll Forming
To achieve an efficient and practical product, various processes are observed to yield a desired output. Accordingly, there are several methods of sheet roll forming, which can be categorized as follows:
1. Cold Roll Forming Method
In a broader sense, sheets produced by hot rolling with minimum thickness typically undergo thickness reduction or shape alteration through cold rolling after acid washing. Cold rolling specifically aims at reducing the thickness of steel sheets with precise dimensional control. Furthermore, in the cold roll forming process, the sheets can be flattened during operation, where a roller system with two sets of small diameter rollers removes the curvature created in the previous process, resulting in a smooth exit from the rollers. The objective of cold roll forming is to reduce the sheet thickness under very high pressure, usually at room temperature or up to 200 degrees Celsius. The success of this cold process depends on factors such as the characteristics of the roll forming machine, the skill of the tool designer, the quality and performance of the designed tools, the operator’s skill, the setup of the tools, and the ductility of the sheet strip. This process has a wide range of applications in sheet metal industries, covering everything from low-precision parts to sensitive and precise components.
2. Hot Roll Forming Method
The hot roll forming method is applied to shape thicker sheets. Generally, in this method, the temperature of the metal sheets is raised significantly to facilitate the forming of thick sheets. Hot rolling is less popular than cold rolling, and the products produced by this method have limited practical uses. Products such as I-beams, angles, or thick formed sheets like plates are roll formed using hot rolling. Carrying out the roll forming of sheets using the hot rolling method requires great precision in temperature adjustment; any temperature change or heating variation could lead to product failure. This is why only a few factories use the hot rolling method.
How is the Forming Process for Galvanized Sheets?
As you know, galvanized sheets, which have a coating of zinc on their surface, are produced in various colors. The coloring of galvanized sheets is done using spray methods or by placing them in special ovens. Galvanized sheets with a thickness of 6 to 18 millimeters are formed using forming machines in various designs. One traditional method for shaping this product is the sinusoidal pattern, which resembles sea waves and is often used in the construction of roofs or false ceilings. Another method for shaping galvanized sheets is the trapezoidal pattern, which is generally more suitable for high-traffic areas with humid conditions. This method itself has three different types: Dampas, used for covering roofs or internal wall sections; facade designs for sloped surfaces; and facade designs for external surfaces or warehouses. Galvanized sheets with attractive colors and designs, as well as high resistance to environmental factors, are very popular among customers. This product not only enhances the aesthetic appearance of structures but also has a lightweight nature, increasing its resistance to earthquakes and making transportation and installation easier, while also reducing costs.
Familiarization with Types of Forming Machines
The machines used in the forming process vary in type depending on their application. In this section, we will introduce each of these machines:
1. Sinusoidal Forming Machine
The dimensions of the sinusoidal forming machine are a complete line width of 1.7 meters and a length of 8 meters, with a chain pitch of 100 millimeters, making it easily transportable by trailer. This type of system has 11 gates with a mold diameter of 180 millimeters and a motor speed of 50 RPM.
2. Trapezoidal Forming Machine
The trapezoidal forming machine has a length of 10 meters and a width of 1.7 meters, with a chain pitch of 100 millimeters, also easily transportable by trailer. This system features a main shaft with a 75-millimeter transmission and is equipped with two gear motors and a 75-millimeter shaft running at 50 RPM.
3. Shadowline Forming Machine
The shadowline forming machine consists of 11 gates along with a 75-millimeter main shaft and a motor speed of 50 RPM. This system comes with a 75-millimeter gearbox motor, featuring dual gears of 170-millimeter base depth and 30-millimeter depth, along with a 100-millimeter chain pitch, making it one of the optimized machines in this process.
4. Steel Deck Forming Machine
The steel deck forming machine has 26 gates, a 90-millimeter main shaft, and two gearbox motors with a 1200-millimeter chain pitch. The machine measures 15 meters in length and 1.7 meters in width. Moreover, this machine is approved by municipal inspection authorities and works with a roll sheet thickness of 80% and up to 1.25 millimeters.
5. Fine Sinusoidal Forming Machine
The fine sinusoidal forming machine has 22 longitudinal gates with a 65-millimeter shaft, approximately 950 molds, and measures 13 meters in length and 1.5 meters in width. It is worth noting that the motor power of this machine is 40 RPM. This forming machine is very sensitive, and if you wish to form a one-meter-wide roll sheet, it can be designed with 18 gates. However, the last two edges of the sheet will be bent down, and only a one-meter-wide roll can be fine-formed.
Familiarization with the Advantages of Using the Roll Forming Method
It can confidently be stated that the roll forming process is one of the efficient methods for bending and shaping various sheets. Given this, the advantages of such a method include:
- Any type of sheet and any material can be shaped using roll forming methods.
- The strength and integrity of the products produced through this process are reliable and efficient.
- This process allows for the production of a high volume of products at a low cost.
- Roll forming imposes no limitations on the sizes of sheets that can be shaped.
- Overall, production using the roll forming method is carried out at a higher speed and does not require direct operator involvement.
