Plastic Injection Molding Machine     Injection molding is an excellent way to bring out the best in plastics. It is universally used to make complex, finished parts, often in a single step, economically, precisely and with little waste. Designers face a huge number of options when they create injection-molded components. This article explores many of these options as they concern design approaches, resin selection and common features used to make optimum parts.

    Design Approaches
    Design generally involves three overriding factors. First, build parts around functional needs. Combine them to reduce weight, eliminate fabrication and assembly steps, improve structural integrity and lower cost.  Second, optimize cost and performance by keeping plastic use to a minimum while satisfying structural, functional, molding and economic demands. And the third, find the right resin. Manufacturers often select a familiar grade of plastic from a similar application or rely on recommendations from molders, toolmakers or suppliers. Resins chosen this way may be adequate, but are rarely optimal. Plastic selection is a complex task that involves many considerations, such as:
• Temperature - look at thermal stress during normal and extreme end-use conditions,
as well as during assembly, finishing and shipping.
• Chemical resistance - evaluate the effect on the part of every solid, liquid or gas that
can contact it.
• Other conditions - consider all other items relevant to fabrication, assembly and end use.
These include maximum loads, deflections and other mechanical stresses, relative motion between
parts, electrical stresses, color and tolerances (to define the precision of various steps).
• Agency approvals - factor in governmental and private standards for properties such as
heat resistance, flammability, and electrical and mechanical capabilities.
• Assembly - ensure the proposed plastic works with all assembly steps, such as solvent bonding, mechanical fasteners or ultrasonic welding.
• Finish - also ensure the plastic can provide the desired gloss, smoothness and other appearance values as it comes from the mold or that it can be finished economically.
• Cost - use total finished-part cost to guide design. In addition to resin pricing, factor in manufacturing, maintenance, assembly and disassembly to reduce labor, tooling, finishing and other costs.
• Availability - make sure the resin is available in the amount needed for production.

     Part Elements
     Injection-molded plastic parts tend to have similar elements. They all have walls of a certain thickness (the nominal wall) and usually have one or more of the following: ribs to add strength; bosses as points of attachment; radii where surfaces intersect; and open internal spaces. Walls should be as thin as possible without sacrificing mechanical integrity. Depending on the plastic used, wall thickness in injection- molded plastic parts usually is 0.03 to 0.19 in. For instance, typical thicknesses with acetal fall between 0.03 and 0.12 in., while with polyester they are 0.025 to 0.125 in. If walls are too thin, parts can
fail under load. If they are too thick, products can be unattractive, overweight or expensive, and take too long to mold.

     Wall thickness should not vary more than 10 to 25 percent. If greater variations are unavoidable, Transitions should be gradual and the polymer should flow toward the thin sections, so thick areas fill well and stress is minimized. Designers increase part strength and stiffness in several ways. One option is to switch to a different plastic or a glass-reinforced version of the same resin. Another possibility is to thicken the nominal wall, but this can add cost and molding time. A third way is to beef up the part with ribs, gussets (small triangular ribs), corrugations, crowning and other features.Ribs are most commonly used to add strength. They are varied in height and number according to load and available space. Multiple, evenly spaced ribs usually distribute loads better than one large rib. The thickness of a rib at its base is usually half that of the adjacent wall, but can equal that of the wall if structural integrity matters more than appearance or if the resin has little shrinkage. Rib height is typically 2.5 to three times wall thickness.For more information,please visit http://www.bossgoo.com