plastic product manufacturing PROCESS EXPLAINED

In the world of plastic product manufacturing, there is a multitude of different processes which makes it confusing on which process is the best process for your produce you unique product. On this page, we will explain some of the most used processes, the material used in each, and the strengths and limitations of each. This will allow you to select the process that meets your unique MOQ, Engineering/Design, manufacturing, and COST requirements. The plastic manufacturing processes we will discuss are:

Table of Contents

plastic product manufacturingMachined ABS Plastic Tray
Machined ABS Plastic Tray

Plastic Machining Plastic Product Manufacturing

When machining plastic in Plastic Product Manufacturing are relatively endless machining process possibilities to machine plastics as long as the plastic is rigid. Most in the thermoplastics plastic with a few thermosetting plastics have the ability to be machined.

Process

Any standard machining process can be used. This is one of the most underutilized processes since 3D printing became readily available. This is because it is a common thought that if you want a prototype utilizing 3D printing is the lowest cost. For smaller parts, one, two our five parts this might be true, however larger more complex parts with runs from 3-25 machining can be the more economical and quicker

Strengths

Can be economical for quantities of 1-25 in 1-3 weeks

Limitations

Parts will have machining marks and better suited for machine shops who specialize in the machining of plastics with the availability of powder coating to give the part a more cosmetically pleasing look.

Materials of Machined Plastics

They are relatively endless as long as they are rigid mostly in the thermoplastics plastic with a few thermosetting plastics with the ability to be machined.

Thermoplastic Plastic Injection molding

Plastic injection molding uses “thermoplastics”, plastics that melt with heat, and inject the melted plastic into a mold cavity to create a cavity image, the finished plastic part. A typical plastic injection unit can be broken out an explained in three specific areas

A. The Thermoplastic Injection Unit

B. The Mold

C. The Clamp

The Thermoplastic Injection Unit:

The Plastic Injection Unit is comprised of 5 major parts:

    1. Plastic Pellet Hopper
    2. Injector Barrel
    3. Hydraulic Ram
    4. Heating Bands
    5. Reciprocating Screw

      In the plastic injection molding process, the plastic pellets are first put into the hopper which feeds the pellets into the plastic injection unit’s barrel. As the reciprocating screw turns the pellets are pushed forward and are mixed by the flutes/flights on the screw.  The screw diameter increases closer to the mold and with the combination of the friction of the screw action and heat distributed by the heating bands the plastic melts and is fed into the chamber in front of the screw. Then the hydraulic ram pushed the screw forward injecting the mold sprue with the melted plastic in a matter of seconds. Most times in less than seconds the plastic component is ejected out of the mold and the process repeats itself. For larger plastic components and plastic housings, the timing will be longer.

      Mold:

      The Plastic Injection Mold is comprised of

        1. Clamping Plates: Two on each side to hold the mold, the “Mold Cavity Half” and the “Mold Core Half”, to the injection unit.
        2. Cooling Water inlets and Water Channels in the mold: this speeds up the process of thermoplastic solidification
        3. Guide Pins: Help guide the mold during operation.
        4. Ejector Back Plate:
        5. Ejector Plate: The Ejector Back Plate and Ejector plate hold the “ejector pins”.
        6. Ejector pins (or Pin Outs): Used to eject the plastic part of the mold.

      The Thermoplastic Mold Process in Plastic Product Manufacturing: The molding process starts when the Injection Unit injects the melted thermoplastic into the sprue, the inlet that feeds the thermoplastic into the mold cavity in a closed plastic mold. Cooling water is circulated in the mold through water channels to help speed up the Thermoplastic solidification. Once solidified the mold will only slightly open a 1/64″-1/32 to break the vacuum for a couple of seconds the open all the way. The ejector plate and backplate move forward pushing the ejector pins which in turn pushed the finished plastic part, ejects it, from the mold cavity. Them the ejector assembly moves back, and the mold is closed, and the operation repeats itself.

      Mold Design

      Mold Design: When designing a part and having a plastic injection mold designed and manufactured to produce your part you need to have a more detailed understanding of design and mold components considerations to:

      1. Make sure your part can be manufactured or economically manufactured
      2. Meet the part designers’ cosmetic expectations, they are not overlooked by the mold designer.

       

      These considerations are (see the Mold Diagram):

      1. Draft angles: A draft angle allows the Plastic part to be pulled from the mold with a reasonable force and without damaging the final product. if you made a part with no draft angles it would take a tremendous amount of force to remove the product from the mold and also could damage the part. Typical draft angles are from 1°-3°. The application and placement of these angles should be carefully discussed with the mold designer.
      2. Ejector Pins (Pin Outs): As discus previously in the Thermoplastic Mold Process, ejector pins push the plastic injection process part of the core half of the mold. These pins are located in this core half and can be adjusted however there will be round “witness marks” were these ejector pins are located. The location should be discussed thoroughly with the mold designer, so they are not located in a cosmetic surface.
      3. Shrinkage Cavities: These are caused by basically having to thick of section in the design. This could because just from being thick or from a conjunction of a thick and thin part. This is easy to correct by proper re-design making multiple sections or gussets to reduce the initial thickness.
      4. Parting Line: This is where the two mold haves come together. The two molds have are never “perfectly aligned and could have a very slight radius. Many times, this is at the bottom of the plastic part so it will not be cosmetically noticeable. If it is required on the side, not the parting line will be visible.
      5. Vents: These are machines into the landing face and are 10-50 µm to allow trapped air to vent out at the parting line however since the thermoplastic in the plastic injection process is viscous, the plastic will not flow through.
      6. Cosmetic Surface: Keep on mind the plastic is a perfect replica of the mold. So any surface imperfections or blemishes on the mold will be produced on the surface of the plastic parts. To remedy these cosmetic surfaces are textured. The Plastic injection process has many different types and roughness textures that can be used. Keep in mind that plastic textures cost money to produce and vary widely in cost. Discuss this carefully with the mold designer.
      7. Mold Cost: Mold cost can range from $2500 to $500,000+. Keep in mind mold designers typically design a mold to be able to do 500K-1M shots. Know your life cycle, if your life cycle is much lower than this discuss this with your mold designer. This could save you 10-30% if the mold cost. Also, not molds are made from tool steel, for some part aluminum can be used to significantly lower the mold cost but be aware aluminum mold like are only typically 10,000 to 50,000 shots. This is a good option if your design might change.
      8. Multi-cavity Molds: There are 2 considerations for multi-cavity molds. First is to increase production, a single part is made in the same mold as 2, 4, 6, and so on quantities.  This reduces cost and decreases production time. Second is you have an assembly say with 2-4 parts that are similar in size, but a lower production is needed. These multiple parts can be fitted in the same mold reducing the mold/NRE cost. There are other considerations when using a multi-cavity mold:
      • Runners: These are channels that allow the flow of thermoplastic to each part cavity. Note that in a multi-cavity mold with runners, the sprue is contacted to the runners, not the part.
      • Gates: these are reduction of the runner to the part cavity that regulates the flow to the cavity plus reduces the amount of area of plastic that needs to be cut from the part. This will leave a small noticeable mark at the parting line and should not be in an area that has high cosmetic requirements.

      Clamp:

      In the thermoplastic injection unit, the clamp houses the mold. Before the injection process, the two halves of the mold must be mounted to the “clamp”. On either side of the clamp, there is a large stationary plate called the platen. Each side of the mold must be mounted to the corresponding platen. The front half of the mold, the mold cavity, is mounted to the front plate aligning with the injection unit nozzle. The rear plate, the core half of the mold, is mounted to the rear platen that operates, moves the mold utilizing a large hydraulic ram.

      Strengths of the plastic injection Molding process:

      1. Very economical for single part runs of 1000-100,000+ however smaller runs of 250-500 can be produced with smaller parts.
      2. Very simple to very complex shapes can be produced.
      3. Overholds was a sheet metal part that is molded into a plastic part that can be produced.
      4. A multitude of colors, transparencies, and materials are available
      5. Can use regrinds, re-grinded scrap plastic from the molded process, and recycled material from the outside.
      6. Low labor cost.
      7. Short production lead time.

      Limitations of the plastic injection Molding process

      1. High Mold cost, $2500 to $500,000+ depending on the size and complexity of the plastic part.
      2. Mold designs are hard if not impossible to change. If there is a change possible, there will be a noticeable blemish in the mold thus a noticeable blemish in the plastic injection prices part.
      3. Lead time on the mold is 4-10 weeks depending on the complexity of the part.

      Materials of Thermoplastic Injection Unit Process

      Thermoplastics come in pellets that can be mixed to get the desired color or transparency:

      • POM/Acetal
      • PMMA/Acrylic
      • ABS/Acrylonitrile Butadiene Styrene
      • CA/Cellulose Acetate
      • PA/Polyamide (Nylon)
      • PBT, PET/Polyester – Thermoplastic
      • PES/Polyether Sulphone
      • PEEKEEK/Polyetheretherketone
      • PEI/Polyetherimide
      • LDPE/Polyethylene – Low Density
      • HDPE/Polyethylene – High Density
      • PPO/Polyphenylene Oxide
      • PPS/Polyphenylene Sulphide
      • PETG/Polyethylene Terephthalate Glycol
      • PP/Polypropylene
      • GPPS/Polystyrene – General purpose
      • HIPS/Polystyrene – High impact
      • PVC/Polyvinyl Chloride – Plasticised
      • UPVC/Polyvinyl Chloride – Rigid
      • SAN/Styrene Acrylonitrile
      • TPE/R/Thermoplastic Elastomer/Rubber
      plastic-product-manufacturing Plastic injection molding machine
      Plastic Injection Molding Machine
      plastic injection molding Plastic Pellets
      Plastic Injection Molding Plastic Pellets
      Plastic Injection Mold Diagram Exploded
      Plastic Injection Mold Diagram
      Thermoplastic Mold Design Key Features
      Plastic Injection Mold Example Without Daft Angles
      Plastic Injection Mold Example Without Daft Angles
      Plastic Injection Mold Example With Draft Angles
      Plastic Injection Mold Example With Draft Angles
      Part showing the Sprue, Runners, Gates and Parting Line
      Multi-Cavity Plastic Part
      LSR Liquid Silicon Spout
      LSR Liquid Silicon Spout
      Liquid Silicone Rubber Mold
      Liquid Silicone Rubber Mold

      LSR (Liquid Silicon Rubber) Injection Molding:

      1. LSR (Liquid Silicon Rubber) Injection Molding: this is a very similar process to the Thermoplastic Injection molding process with a few differences:
        1. Two-part material
        2. Two material holders
        3. Pump
        4. Mixer
        5. Hot Mold

      Although the processes vary slightly between the manufacturers of the LSR injection machines typically the LSR (Liquid Silicon Rubber) Injection Molding starts with 2 buckets are barrels of different silicone components.  These components are then pumped into a mixer. The mixed material is COLD. The LSR is then sent to a screw. Sometimes the screw will directly inject the LSR into the mold or send the mixed LSR to a separate plunger that then injects the mixed LSR into a HOT (275F-390F) mold that then rapidly solidifies the LSR part and then the part is removed.

      LSR Injection Molding Strengths Plastic Product Manufacturing:

      1. Very economical for 1000-100,000 part runs.
      2. Very simple to complex shapes can be produced.
      3. Short production lead time.
      4. FDA and Medical grade materials are readily available.
      5. Parts can be used in high operating temperatures.

      LSR Injection Molding Limitations:

      1. High Mold cost, $2500 to $500,000+ depending on the size and complexity of the LSR part.
      2. Mold designs are hard if not impossible to change. If there is a change possible, there will be a noticeable blemish in the mold thus a noticeable blemish in the plastic injection prices part.
      3. Lead time on the mold is 4-10 weeks depending on the complexity of the part.

      Rubber/Silicone Compression Molding

      Rubber/Silicone Compression Molding: This is one of the oldest a very simple molding process. Rubber/Silicone Compression Molding only has two major components:

      A. The Mold

      B.Compression Press

      The process is also relatively simple. A premeasured amount of un-vulcanized rubber or silicone material, slug, is placed in one half or both halves of the mold. The mold is closed and heated to a predetermined time, and the rubber or silicone is vulcanized.

      Strengths of the Rubber/Silicone Compression Molding

      1. Mold is a lower cost than injection molding, especially on larger parts.
      2. Overhead & machine costs are lower.
      3. Per part cost on larger products is lower.
      4. Turnaround on mold is much faster than injection molds, 1-4 weeks.
      5. A good option for prototyping.

      Limitations of the Rubber/Silicone Compression Molding

      1. The process is slower than injection molding, but this can be overcome by using multi-cavity molds.
      2. Part may have flashing that needs to be removed
      3. Not a good option for complicated parts.

      Materials for Rubber/Silicone Compression Molding:

      • Neoprene
      • Viton
      • Buna
      • EDMP
      • Natural Rubber
      • Silicone
      Silicone Gaskets
      Silicone Gaskets

      Conclusion, Processes

      First, for selecting the correct plastic component manufacturing process, it comes down is what material you require, NRE cost you can recuperate and the physical geometry of the part to be manufactured.

      Second, the last two items you must consider are a “Cradle to Grave” and a FULL-SERVICE COMPONENT CONTRACT MANUFACTURER. 

      FULL-SERVICE means the contract manufacturer can provide you with a finished cast part including machining, PEM/Fastener installation, silk screening/engraving and metal components if required, a “one stop shop“, eliminating having to resend out your part for a secondary process to a separate multiple vendors. This makes controlling processes errors from multiple sources difficult.

      “Cradle to Grave” means as your product matures, we will continually give you suggestions, (process changes, material changes, sub-assemblies) to reduce your cost giving you an improved sales advantage. An example would be per at the beginning of marketing your product, PROTOYPING, your volumes are low, and you do not want to make the investment in molds and manufacturing quantity, Ionthis could make your finished part or parts from machining from a solid block or unitize an aluminum mold. Your NRE investment would be low but part price might be higher but absorb-able. When your volume gets high enough to justify the NRE then Ionthis can move you into a high production molds. This is “Cradle to Grave”.

      For a DFM/Analysis and recommendations of your Die Cast, Investment Cast and Sand Cast component or assembly, feel free to contact Ionthis at engr@ionthis.com