Reel-to-reel insert molding can prove a more efficient process for design engineers when it comes to lowering assembly costs. The process is best suited for products that require dimensional stability and need to function in harsh environments, such as drug-delivery device parts and components.
How It Works
Reel-to-reel insert overmolding combines two technologies: stamping and molding.
In the reel-to-reel process, stamped components or frames arrive from the stamper in continuous form on a disposable cardboard, Masonite, plastic, or other type of reel. The base material of the stamped frame can be any material — copper or nickel-based alloys are the most common.
The perforated, continuous strip resembles a movie film. Perforations, known as pilot holes, advance the coiled sheet and locate the metal strip in the progressive die. The accuracy of the relationship between the mold's cavity and the pilot hole guarantee that the plastic detail always remains in the right place. The pilot hole also helps ensure the correct alignment of components in any subsequent manufacturing operation, such as forming, bending, soldering, welding, or assembly.
Technicians mount the stamped, reeled-up frame onto a pay-out reel (uncoiled), which feeds into the molding machine. Like the feeding motion in the die, the frame advances through the mold after each molding cycle. Here, the feeding unit on the punch press is usually mounted on the beginning of the progressive die and pushes the strips through the die.
This arrangement is opposite in the molding process, where the feeding unit mounts at the end of the mold, and the strip is pulled through the mold. Molding can take place in a horizontal or vertical molding machine. Following the molding process, the frame rolls back onto a reel, and the part is ready for any secondary operation or shipment to the customer.
The reel-to-reel system saves money by eliminating waste and reducing processing hours, as well as minimizing the need for additional equipment and manpower. It also enables improved designs and lower up-front costs. Because the device developer receives a continually molded and oriented product, less sophisticated assembly tooling is required.
It decreases up-front tooling costs compared with shuttle or rotary molding. Reel-to-reel requires only one “A” and one “B” side mold, whereas rotary or shuttle molding can require multiple “B” sides. Further, the process employs vertical molding, which is lower in cost for hourly machine rates and part costs because the press is less expensive and has a smaller footprint.
Reel-to-reel also offers savings in terms of reducing operating needs and material waste. No operators are required to place stamped inserts into the mold cavity or assemble them into load bars. And the single continuous frame eliminates the need (and cost) of a robot or other delivery system. The continuous, unattended operation ensures consistent, repeatable cycle times, with a high-quality product result.
Flash and mold damage is practically eliminated because components are placed accurately, automatically. Medical device parts can be expensive and can be made from expensive alloys, such as gold, for plating. The process doesn't waste gold in the stamped contact area of electronic components.
Finished parts fit onto a single reel, ensuring an economical, safe way to package and transport components.
Higher output gives the engineer greater latitude in designing a product, especially when two strips are fed into a mold. The tolerances achievable in reel-to-reel are the same as for any other type of insert molding and are limited only by the resin selected (as far as plastic part dimensions are concerned) and what the blank tolerances of the strip can be maintained. Typically, the thinner the metal used, the greater the accuracy between plastic and metal. For some liquid crystal polymer resins, the accuracy can be in the 0.01 mm range.
While reel-to-reel offers significant savings and flexibility, it is important to consider a few design and operation matters. Keep in mind that the part needs to fit the application; otherwise, the process will require more metal to make the same part. The geometry of the part should also fit the process — the carrier strip may not allow movements for undercut features.
Be sure to monitor the strip position during the cycle. The tool can get damaged if the strip position goes over a shutoff. Likewise, have a process in place to monitor part quality coming out of the tool, particularly if a secondary process is in line and the parts are high value. A technician must be able to stop and fix an issue before making a ton of scrap. With these simple requirements, reel-to-reel can offer a variety of advantages for medical devices.
This article was written by Armand Pagano, Mold Design Manager/CNC Lead at Weiss-Aug Co., East Hanover, NJ. For more information, visit here.