Die cutting and converting involves making parts by “converting” thin materials such as films, foams, foils, and adhesives into products and components. Applications for the medical device and pharmaceutical industries include microfluidic devices, diagnostic test strips, ostomy bags, wound dressings, and drug-delivery systems.

Converting services or converters fit in the supply chain between raw material suppliers, and OEMs or contract manufacturers. Converters typically source materials from a variety of suppliers.

Materials

One of the biggest challenges when developing a die-cut product is sourcing materials. It is important to find material suppliers with appropriate traceability, cleanliness, and minimum order quantities. In addition to design requirements, product developers should outline the material supply requirements early in the development process to avoid increasing risks and costs later on.

Raw materials come as adhesives, films, foams, laminates, and non-wovens. They vary significantly in tolerances, tool costs, and cleanliness. The two most commonly used materials to fabricate components are plastic films and adhesives. Certain films are difficult to find in the necessary thickness or color. Some converters can extrude materials, as in cast or blown film. But for small runs, a custom extrusion adds to cost.

Pressure-sensitive adhesives often go into the fabrication of die-cut components. Adhesives come as single coated, double coated, and adhesive transfer tapes (unsupported adhesives). There are different formulations for the types in rubber, acrylic, and silicone. A qualified converter can help select proper adhesives.

How it's done

When a material is sourced, it is often only available in bulk format. This means it needs to be prepared prior to cutting. Preparation can involve laminating an adhesive or other material to the material or slitting it into rolls for a manageable width. Slitting is done by various methods depending on factors such as required tolerance, edge quality, and allowable tension.

Once materials are prepared, they can be die-cut or integrated into a converting process. Methods for die cutting materials into needed shapes are steel rule, match metal, rotary die, rotary match-metal, digital die, and laser. Steel-rule cutting, for example, feeds material between a flat anvil surface and a cutting die made from a flat wood or plastic base and a hardened steel blade. The blade pushes the material against the anvil and forces it out to the side. Also referred to as stamping or flat-bed cutting, this is the most common type of cutting. Tolerances for rigid plastics such as polyester are about ± 0.020 in. Users must ensure blade spacing accounts for manual sharpening and ongoing maintenance. Steel rule cutting is suitable for large parts, thin foams, and low to medium production volumes. Cutting speeds are typically under 1,000 strokes/minute.

Match metal cutting, also referred to as punching or zero-clearance die cutting, feeds material through mating metal dies made of machined, hardened steel. Costs and lead times for tooling are much greater than those for steel-rule cutting, but cuts are much cleaner and more precise. Here, tolerances for rigid plastics such as polyester are about ± 0.005 in. Match metal cutting suits small parts, rigid films, and low to medium production volumes.

Rotary die cutting feeds material through two rollers. One is a rotary die and the other is a smooth cylinder anvil. The blades are machined into the die. As with steel rule cutting, the blade pushes the material against the anvil's surface. The difference is the capability to feed and register material at high speeds, which lets the same piece of equipment perform a series of cuts and laminations. Material is more commonly cut in continuous roll form (also called a web).

Numerous webs can be processed and integrated with one pass through the machine. This allows for more complicated parts including island placement (placing an object within a web), adding peel tabs, and in-line packaging. Finished parts can be supplied in roll form so they will be simple to use in later manufacturing operations sorting or manual placement. Tolerances for rigid plastics such as polyester are about ± 0.015 in. Registration from one component to another is typically about ± 0.030 in. Rotary-die cutting is suitable for a variety of thin materials and medium to high-volume production. Process speeds are typically under 30 ft/min.

Rotary match-metal cutting combines the benefits of rotary cutting with those of match-metal cutting. Dies are specialized tooling intended to shear the material in a rotary fashion. Tooling costs are relatively high, but this method is high-speed and precise. Tolerances for rigid plastics such as polyester are about ± 0.005 in. Registration from one component to another is typically better than ± 0.030 in.

Digital die cutting uses a digitally controlled knife on an X-Y table to cut the material. This method is useful for low-part quantities (typically less than 1,000) because although it might take a few minutes to cut out a complex shape, it requires no custom tooling. This method also works well for prototyping. Limitations include slow speed, need for manual de-slugging, and a potentially low-quality cut edge. Higher-speed digital die cutting is available for use with moving webs.

Laser cutting is similar to digital die cutting in that the laser is digitally controlled and requires no tooling. The laser burns through the material on a flat surface. This method is increasingly used but has significant limitations. One is charring the material being cut. Another alters the chemistry of the cutting edge. And laser sputtering can generate unacceptable amounts of particulate. Furthermore, burning certain materials emits fumes that are unpleasant and potentially dangerous to operators and the environment. However, the method can work well for prototyping. Higher-speed laser cutting is available for use with moving webs.

Packaging

Typically, die cut parts are stacked, rolled, fan folded, or pouched. The converter should know the customer's design goals so it can optimize how parts are packaged. It is important to know how the die-cut product will work with downstream processes. Critical details include size and type of cores for roll form parts. Fiber cores are inexpensive but they can shed particles. Plastic cores don't shed, but they are more expensive. In-line pouching also minimizes particulate from handling.

DFM

There are few absolutes when it comes to applying design-for-manufacturing to die cut and converted parts. However, several things do facilitate high-volume production. These include understanding the product requirements and manufacturing process, and maintaining an open dialog with the converter. Other considerations include the process outline.

Converters should help customers outline and visualize each step needed because the success of each depends on the accuracy of the previous. Hence, process controls and tolerances should be clear. Some converters rely on simple tolerances, others use statistical methods.

The manufacturing method and tooling each affect cleanliness. Match metal cutting is cleaner than steel rule cutting. Generally, the lower the tooling cost, the shorter the tooling life. Cut quality decreases as the tool wears. Lasers are appealing as a way to avoid tooling costs, but they tend to generate a lot of particulate.

High-volume processing necessitates linear or web processing. The better the part aligns with equipment, the less expensive the method will be. Liners, adhesive layers, and components should be positioned for linear motion wherever possible.

A hole in a die cut part generates a slug that needs removal. This can be done with a vacuum or mechanical de-slugging. It is almost always preferred to avoid a hole. For example, a slot connecting the scrap to the matrix outside of the part ensures slug removal. Small slugs are a significant risk, and can be considered particulate.

Sharp corners increase the risk of particulate, incomplete cuts, and die wear. Corners require that cutting blades intersect. But sharpening the blades can be difficult, resulting in a burr in the part. From a manufacturability perspective, materials, tooling volumes, and methods always dictate the needed radius. However, within these constraints, the larger the radius, the better.

Lastly, when it comes to prototyping, the relatively low cost of steel rule and rotary dies might make them a good way to manufacture large prototype or clinical quantities. Tooling is typically around $1,000 to $5,000, significantly lower than injection-molding tooling. When dimensions are somewhat certain, it might be best to proceed to these tools, rather than try to imitate production with the digital or laser method.