Finding Real Savings in Screen Production
Today many window and door fabricators manufacture their own screens, while others prefer to buy them from an outside source. Larger, more vertically integrated companies typically make their own screens, with many taking advantage of new automated screen manufacturing equipment.
Recent advances in these low cost, flexible screen machines are also attracting the attention of those manufacturers that buy from screen specialists. Medium and even some smaller companies are tackling these tasks themselves, finding not only substantial savings within the screen department but also better control of inventories, lead-times and product quality.
IN-HOUSE VS. OUTSOURCING
Often, the screen is the last component attached to the window prior to packaging. Some companies pack or ship their screens separately—an approach that has its own challenges. Many window manufacturers currently offer multiple screen options for each window they sell. Different types of screen cloth, hardware, frames and color can make the screen assembly area a complicated part of the manufacturing process.
Choosing to buy from a screen specialist eliminates many of the scheduling, staffing and inventory problems that arise from making screens in-house. Some screen supply companies will manufacture and ship screens to a company in the same order their windows are being manufactured, streamlining the process of marrying each screen to the appropriate window. “We not only build custom screens for many large window manufacturers in North America, we also carry a large stock of screen components and accessories that our customers may need at a moments notice,” says Jennifer Small, president of Screenco Manufacturing Ltd. She describes her company as “a one-stop shop for her customers’ screening needs.” This type of comprehensive, personal service is another reason why successful screen supply companies continue to do well.
Whether made in-house or outsourced, most screen frames are made of extruded or roll formed aluminum, with corner keys connecting all four sides. With most extruded products, a metal corner key is used, usually crimped into place. Roll-formed components use plastic corner keys most often, which are inserted but don’t require crimping. There are in fact many types of corner fasteners, but the corner key seems to be most widely used. In addition, suppliers continue to develop new screen components. Bob Green from Magnolia Metal & Plastic Products reports that his company’s corner keys have a pull-tab molded into them, eliminating a step in the production process. “This innovative solution reduces production time and the number of parts a fabricator needs to inventory,” he notes.
Both types of screens frames—roll-formed and extruded—are assembled and screened using very similar methods, most of which are compatible with the high-speed production equipment available today. The typical screen department has many workstations. At the beginning, the frame pieces are cut to size from full stock lengths. The second station is where the holes or slots for the hardware are punched, drilled or routed. Hardware such as springs, lock pins or pull-tabs are typically installed next, and the four mating frame parts are assembled. Finally, the screen mesh is attached to the frame.
The task of placing the mesh into the finished screen frame varies widely among window makers. Using one common manual approach, the assembled screen frame is placed on a table. The operator then manually pulls the screen cloth over the frame and holds the screen cloth tight with one hand, attempting to avoid wrinkles or hourglassing (the result of the cloth being pulled too tightly, causing the center of the screen frame to bow inwards towards the opposite side). With the other hand, the operator uses a spline roller to insert the spline into a groove in the frame. As you can imagine this is very cumbersome and takes a great deal of training and practice before an operator becomes efficient.
Many of these jobs are tedious, and some can even cause repetitive-motion injuries to employees. The process requires an assembly team at the end of each production line, or else several teams are located in a designated screen assembly area of the plant. With this type of manual assembly, expected screen output is approximately 1 screen per minute, or about 250 to 300 screens per shift, utilizing three to four assemblers.
Manual operations like this not only produce a low number of finished units and create the potential for injury, but the repetitive nature of this process can result in mistakes ultimately generating scrap. When hourglassing occurs, for example, the screen will not fit uniformly into the screen opening in the finished window. The screen cloth must be removed and the process repeated. Sometimes, after the groove in the screen frame has been used once, it will not hold the spline a second time. When this happens, the entire frame must be remade resulting in lost time and material. Additionally, cloth tensioning and size are often overlooked in order to get the screens out the door resulting in expensive callbacks later.
These common challenges are reasons why window manufacturers outsource screen production. They are also the reasons why many window manufacturers are investing in a variety of automated manufacturing equipment specifically designed to eliminate these problems.
A MORE AUTOMATED APPROACH
As window and door manufacturers continue to look at all aspects of their operations to reduce costs, many are finding savings in the screen department. Recent improvements in screen manufacturing equipment are providing real cost reductions. Depending upon a manufacturer’s needs, a variety of operator-assisted and automated machines can provide cost effective solutions, such as attaching the screen mesh to the assembled frame.
With an operator-assisted machine, the operator loads the frame onto the table, pulls the cloth over the frame, holds it in place, and moves an articulated arm around the screen frame to insert the spline. This approach makes sense for the fabricator with limited capital for machine purchases. Such machines—which apply the pressure necessary to insert the spline—help address the issue of injuries due to repetitive motions, and also increase production.
The fully automated machines are nearly hands free. The operator’s only requirement is to load the assembled frame, pull the screen mesh over it and press a start button. The machine cycle starts and inserts the spline. Built-in clamping devices are designed to hold the mesh taught during this process and are automatically controlled. While the spline is being inserted, the more advanced machines can be programmed to move along an arch, controlling the hourglass effect commonly seen on larger units, like patio doors. After the spline is inserted, the machine cuts it to length while at the same time cutting the trailing end of the screen mesh. At this point, the operator removes the finished screen and replaces it with an empty frame. This entire cycle requires less than 40 seconds.
After starting the machine cycle for the following frame, the operator is kept busy trimming the excess mesh from around the previously completed frame. Working as a team in this cellular configuration, the machine and operator together are capable of producing over 400 screens per shift. With an operated-assisted machine, it would typically take two operators—one trimming and one screening—to keep up with the fully automated approach.
A typical fully automated screening machine can handle screen sizes from 14 by 10 inches to as large a 4 by 8 feet for patio doors. These new machines alleviate the repetitive motion injuries caused by hand rolling and improve overall quality of the finished product. In addition, they will increase output by as much as 50 percent, while manufacturing a more consistent product.
Rather than buying full-length sections of pre-made screen frames, many fabricators are continuing to vertically integrate by roll forming their own screen frames. These manufacturers usually produce multiple screen frame shapes in a variety of colors, or sometimes manufacture just one custom shape to differentiate themselves from others. Typical users of this equipment produce at least 500 units per shift, although some manufacturers with lower volumes look at these machines for doing custom screen frame shapes or gaining better inventory control. Other lower volume companies have justified purchasing their own roll formers by producing both screen frame and muntin bars using the same machine.
Roll forming is a very simple technology that has been around for many years. Flat material, typically pre-painted aluminum coil stock for screens, is fed through a series of rollers, with each set performing one bend. Fig. 1 illustrates how the flat material takes on the form of the final shape, one bend at a time.
The roll-forming equipment available today includes machines that form and cut parts to length automatically, reducing scrap by as much as 30 percent when compared with cutting screen frames to length from full lineal lengths. Some machinery manufacturers offer options for automated fabrication processes that take place before or sometimes after forming the part. Automating these processes in the roll-former eliminates the need for supplementary off-line fabrication equipment and additional material handling and labor. In addition, the lengths and fabrication steps can be downloaded from a central office computer in common batch file formats, further streamlining the production flow. Labor requirements are minimal, as one operator can control a typical automated roll forming line. During the screen frame production process, the operator’s main task is simply to bin or assemble the frame parts as they exit the roll former.
Some of today’s more advanced machines don’t stop and restart when they cut the parts to length. They can roll form batches of screen frames, fabricate them and cut them to the finished sizes while running at speeds approaching 150 feet per minute. These same machines possess the flexibility to produce more than one screen frame shape without a roll change (saving valuable downtime for shape changes). This innovative feature also reduces the need to purchase multiple machines in order to manufacture a variety of screen shapes, further enhancing the return on investment. With just one roll former and operator, it is reasonable to assume that a minimum reduction of two to three assemblers and related workstations is possible when compared to the more manual approach.
Window and door manufacturers have embraced automation in the processing of frame and sash components, as well as IG production. Increasingly, they are looking to other operations like screen production, to keep pace with their other lines, to maintain quality and cut costs. Combine this with the reduction of scrap and injuries, and it all adds up to real savings for the fabricator. Over the past decade, we’ve seen a steady increase in the number of companies investing in automating their screen operations. Given their return on investment, that number will grow further in the next several years.