Plastics Information

What is Injection Molding?

Injection molding is by far the primary process for converting plastics into useful plastic widgets. Just about all of us touch an injection molded widget every hour of every day. All thermoplastics can be injection molded with a few exceptions like polyimides and PTFE to name a few. Injection molding takes pelletized materials and heats them up to the point where they can flow properly through the injection process. The hot, molten material is then injected into a closed mold to create the desired part or shape. Then, after the part cools, the part is removed from the mold.

Advantages of injection molding:

-Extremely high output rates.

– Inserts and fillers can be used with this process.

– Process can be completely automated and run with little downtime.

– Scrap from the process can be ground and reused into the process.

– Small, complex parts can be molded economically.

Disadvantages:

-No cost effective for short runs.

-Large capital investment in equipment and overhead required.

-Molds can be very expensive requiring large runs to justify ROI of tooling.

-Requires a high degree of design and process expertise and experience to produce good parts and have low scrap rates.

-Thick cross sections can not be easily or reliable produced.

Injection molding will always be the number one way that large volume plastic parts are produced. When a part volume is too small or need to be tested before a final investment is made in tooling, machiend plastic stock shapes are the go to method for producing reliable plastic parts.

Plastics Machining

What is Casting?

Casting involves introducing a liquefied plastic into a mold and allowing it to solidify. In contrast to molding and extrusion, casting relies on atmospheric pressure to fill the mold rather than using significant force to push the plastic into the mold cavity. Some polymers have a viscosity similar to bread dough even when they are at elevated temperature so they are not candidates for the casting process. Examples of this are polymers like POM, PC, PP and many others. Casting includes a number of processes that take a monomer, powder or solvent solution and pur them into a mold. They transition from liquid to solid by either evaporation, chemical action, cooling or external heat. The final product can be removed from the mold once it solidifies.

Casting has several advantages:

-Cost of equipment, tooling and molds are low.

-The process is not complex.

-Products have little or no internal stress.

Casting can have some disadvantages:

-The output rate is slow and has long cycle times.

-Dimensional tolerances are not very good.

-Moisture and air bubbles can be difficult to manage and may cause problems.

There is a vast array of materials than can be cast. Nylon Type 6 is one of the most popular and commonly used cast products. You can see some of our product offering by clicking on this link. Polyurethanes are another example of cast materials we offer. Either way, the casting process is often times the preferred method providing large size stock shapes for machining parts. Make the most of this process by optimizing your part blank with a near net cast shape, give us a call and we can explain how.

Plastics Information

What is Extrusion?

The word extrusion is taken from the Latin word extrudere meaning (ex) out and (trudere) to push. In the extrusion process, a pellet or dry powder plastic is heated and forced through a die. The majority of extrusion is done by screws although ram extrusion is still used for UHMW powder specifically. The screws will melt and mix the material and force it out of the opening in the die. An extruder can either be single barrel or twin screw/double barrel equipment. The material being extruded determines what which extrusion technology is required. Double barrel extruders are primarily use for compounding in line of basic plastics with different plasticizers, fillers, colorants and other ingredients. Extrusion lends itself to make tube, rod, profiles, film or sheet plastic products in a variety of widths and thicknesses.

Extrusion is one of the primary ways machine stock shape plastics are made. Extrusion has several advantages:

-The high output (compared to other processes) offers lower material costs.

-Depending on the volume, there can be a greater variety in width and length options to maximize yields.

-Relatively low tooling costs.

Extrusion can have some disadvantages:

-Thickness limits for some materials.

-From a machining standpoint, the material may have a higher level of stress in the sheet making secondary or post manufacturing annealing necessary to help relieve stress so the stock shape is more machinable.

– Close tolerance shapes are difficult to achieve.

-Limited to shapes of uniform cross sections (along the length).

Extrusion is one of the most common ways to produce plastic stock shapes. When done by a reputable extruder, using the highest quality materials the machining of these stock shapes can be a successful part of any job shops business. To find the widest selection of quality stock shapes for machining, just click here.