Parts smaller than a pennyPrecise Mold & Engineering’s engineering and production team can produce relatively large parts, but they have the skill and expertise to make very small products as well.  Displayed to the right is a part only a fraction the size of a penny, yet the bore through the center, wall thickness, thread count and finish are even smaller yet.  Big or small we pay attention to the detail.  Where this is not one of our smallest parts, it has all the care and attention of the smallest part and it is just as important as the biggest part.  Complying with ISO-9001 standards ensures attention to the finest detail and the ability to repeat the performance consistently hundreds-of-thousands of times without error.

The theories for molding resins are classified by four distinct processes: Plasticizing, Injection, Chilling and Ejection.  These four processes are clearly separate segments of the entire process where appropriate control of each is critical to the entire process.  Knowing each process and its impact help engineers quickly understand where failures or weaknesses in a process may lie.  Certainly experience aids in the early and correct implementation of any production process from the simplest mold to undercuts and live hinges.

  • Plasticizing – is the term used when a polymer material is converted from a hard pellet/granular form at room temperature to a higher temperature where it liquefies to a consistency required for the injection process.  Different resins will melt and have different traits at different temperatures.
  • Injection – Is the function of the screw feed which forces the melted resin into the cavities of the mold through appropriately designed injectors and channels.  Relief points must be built into the mold to allow any trapped air to escape without loosing the melted resin.  Higher temperature resins may require additional heating elements to achieve the desired results.  Chrome plated and highly polished mold surfaces may also be required to ensure a scratch free surface for clear products.  Poorly designed channels and injectors can cause product failure.
  • Chilling – is the process of reducing the temperature of the molded part to a level that allows the resin to solidify.  Typically as a part cools it shrinks away from the mold.  This shrinkage must be compensated for by over sizing the mold just enough to compensate for shrinkage during cooling.
  • Ejection – is the mechanical release of the molded and hardened resin from the mold cavity, cores or inserts.  Additional work may be required to release mold components manually such as components used to impart threads.  Premature release of a part can cause it to sage or warp.

Injection molding regardless of the end product’s size and function requires a lof of attention to detail.  Satisfactory parts require an understanding of resin properties.  How they behave under stress, the types of edges they may hold, the ability to achieve thin or thick walls and how they will perform in a mold and press.

Melting and molding plastics is a complex process where expertise and experience go hand in hand with success.  Try this experiment at home. 

Melt some chocolate chips in a sauce pan to 115 degrees F to destroy all six types of crystals.  Now reduce the chocolate to 80 degrees F to restore crystals 4 and 5, but not 1, 2 and 3.  You now need to bring the temperature to 88 degrees F without going to 90 degrees (where crystal type 6 is formed) to destroy the crystal type 4.   You are left with only type 5, which creates a tempered chocolate similar to a candy bar or the chips from which you started.  It is simple enough to say, but rather tricky to accomplish.

Melting plastics has many more variables and is much more complex than what one finds in melting chocolate.  If you try the above experiment, you will find residual heat in the pan from the heating process driving the temperature up further.  In the cooling process the chocolate can cool too far.  You need to know far more that just the temperatures for tempering chocolate, you need to know the behavior of the equipment you are using.  Even the room temperature can be a variable.  Timing is everything in making resin based parts.  It requires an understanding not only of the parts but the machines, the mold and the environment to create successful parts.  Timing, temperature, pressure and the type of resin in use are just the starting point.  Especially when making parts almost too small to see.

Need to replace metal parts with non-ferrous materials

If you have small brass parts which contain lead and need replacement parts, share your concerns with us and we can show you how traditional brass parts may be well suited to plastic replacements.

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