Trimming
Thermoformed parts are trimmed in several ways: with matched shearing dies, steel rule cutting dies, saws, routers, hand knives, and 3 or 5-axis NC routers. The trim method selected is usually determined by the quantity, geometry, and customer specifications of the parts to be trimmed.
Additional key factors to consider when determining trim approach are repeatability, cycle time, labor requirement, and safety.
Holes are added to parts in a variety of ways. Pins can be placed in the mold to provide hole locations for hand or drill press drilling. Drill fixtures with guide bushings can be created, allowing the part to be clamped in place while a single hole, or multiple holes of the same or various sizes are drilled. In computer controlled trim applications, the same fixture and program that trims the part can also add the required holes.
Hand Trim
Appropriate in sample parts or very short runs, hand trimming has the advantage of not requiring sophisticated dies or fixturing. The disadvantages are cycle time, operator safety, and inconsistency part-to-part.
Saw Trim
Bandsaws are commonly used for rough trim operations (removing flashing from a freshly formed part or separating parts formed on multiple cavity tools) and occasionally for final trim where parts are large and tolerances are not critical. The advantages of bandsaw trim are the ability to handle very large parts, the minimal fixturing required, and the relative speed that can be achieved by skilled operators. Disadvantages are the quality of the trim cut (usually requires considerable secondary clean-up), potential for part-to-part inconsistency, significant labor requirement, and operator safety.
Steel Rule Die Trim
Reserved for parts that are reasonably thin (0.030" wall thickness is common, but in certain applications steel rule trim can work with parts up to 0.100" thick), steel rule die trim provides speed and consistency. High volume packaging and in-line forming applications frequently employ steel rule die trim. Dies are generally low in cost and easily repairable. Die wear is a factor to consider, as well as finished part clean-up (an issue as material gets thicker with higher impact strength).
Match Shearing Die Trim
Most commonly used in high volume roll fed applications, these dies are usually designed with a hardened steel punch that will pass through a slightly softer steel die that can be peened when it becomes dull. Parts are punched through the die successively and exit from the trim station in nested fashion. Matched shearing dies can be quite sophisticated, providing slots, special holes, and other features. Advantages are rapid cycle time and excellent repeatability. Disadvantages are high initial die cost and the cost of die maintenance.
Table and Pin Router Trim
Excellent for thicker, high production parts where trim is basic and part cycle is short. By using the right combination of clamping fixture, collet, bit and/or blade this is a low cost approach to achieving quality trim of basic parts. Operator skill is required and safety concerns are an issue.
3-Axis Computer Controlled Router Trim
For jobs with a high level of complexity and close tolerances, computer controlled trim offers many advantages. Parts are generally held to a computer controlled "X/Y" table with vacuum fixtures, and bit/blade height is also controlled by computer. These three variables in combination provide precise, repeatable, safe trim and hole application on a wide variety of part configurations. Particularly useful in pressureforming applications, 3-axis computer controlled trim coupled with innovative tool design can produce finished parts that look and perform just like injection molded units, but at a fraction of the up front costs. Advantages are repeatability, precision, reduced labor (operator loads the machine then performs other task while program is running), and safety. Disadvantages are increased fixturing and programming costs.
5-Axis Computer Controlled Router Trim
Combining all the advantages of 3-axis trim, but with the ability to handle very large parts (5' X 10'), the flexibility to trim complex angles and radii, and add holes in any orientation, 5-axis trim is ideal for big, thick complex parts where tolerances are close and volume is moderate to high. Advantages are incredible flexibility, repeatability, safety, and precision. Disadvantages are fixturing costs and programming time and expense.