What is Reaction Injection Molding?
The term RIM refers to Reaction Injection Molding. RIM is the ideal process for achieving a superior finish on high-quality, limited-run (200-2000 per year) custom enclosures and housings. Even when longer production runs are anticipated, many designers choose RIM because of the exceptional appearance of our parts - with the added benefit of lower initial tooling costs.
The RIM material can be molded with a wall thickness varying from .250" to .750" within the same part-without sink marks. It has a finished density of 35 to 45 pounds per cubic foot, and it meets industry standards for combustibility and impact resistance required on most consumer products (UL rating 94V-O, 94-5VA).
Design guidelines for designing plastic parts in RIM structural foam are quite similar to those that one would use in designing thermoplastic structural foam. One added benefit to using the RIM process is the absence of sink lines. Due to this fact, molding thick cross-sections next to thin ones is no longer an obstacle. In order to reduce your engineering time, we recommend that you contact us during the early phase of your design process so that we can assist you in answering any questions that you might encounter.
General Design Guidelines:
- Wall Thickness: A minimum of 0.125" or 0.250", depending which system is being used, must generally be applied in order to maintain the U.L. rating. (Up to 0.750" in some cases.) Small, isolated areas can be molded as thin as 0.100" and as thick as 1.00" (please consult with us first).
- Draft Angles: 1 to 3 degrees per side. (Some isolated areas can be as little as 1/2 degree.)
- Bosses: A typical boss with a 6-32 threaded insert should be about 0.500" at the top with a draft angle of 1 to 2 degrees per side. A free standing boss that is longer than 3" becomes very difficult to eject from the tool.
- Vents: A vent width of 0.250" with a 0.250" rib is generally recommended. Vent lengths over 3.00" will require a support on the backside. Blind, or double kiss-thru vents are not possible in our tooling due to the difficulty of cleaning the flash between the shut-offs.
- Undercuts: Most undercuts can be achieved through the use of removable aluminum core pieces or side cores. (The cost of tooling and parts will be affected by this.)
- Radii & Fillets: Due to the fact that RIM foam is very viscous in its liquid state, generous radii and fillets are always recommended in order to insure proper filling of the tool during the molding process. A general guideline of 0.060" radius and a 0.125" fillet can be used.
- Threaded Inserts: Threaded inserts are typically molded-in to ensure proper tolerances and pull-out strength for fasteners. Stock usually includes 2-56, 4-40, 6-32, 8-32, 10-32, 1/4-20 and 3/8-16 fasteners. (Usually in three different lengths of each size.) Metric inserts and specific insert lengthsare available on request.
Although we do not have test data on all inserts, pull-out results for standard length 6-32 molded inserts show that the average pull-out force is in excess of 390 pounds per insert.
- Tolerances: We recommend the following tolerances be used when designing in RIM polyurethane foam:
- .XX = 0.020" up to 5.00", over 5.00" add 0.002"/inch
- .XXX = 0.010" up to 5.000", over 5.00" add 0.001"/inch
- Coating & Painting: two-component polyurethane and water-based paints, color-matching services to match any chip, Pantone or Federal Standard color.
- EMI/RFI Shielding: Nickel and Silver Plated Copper systems, ideal for higher attenuation needs.
- Electronic CAD Files
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