Plastic Injection Molding

• Plastic injection molding is the most common manufacturing process for producing plastic parts of all sizes
• Plastic injection molding incorporates an injection molding machine, raw plastic, and a mold
• The plastic is melted, injected into the mold, cooled, and solidified into the final part
• Plastic parts are nearly ubiquitous and found in various sectors such as automotive, medical, plumbing and agriculture
• Plastic injection molding has evolved over the last 20 years
• Position, peak pressure, and process repeatability are now key elements
• Scientific molding and related experts were pioneers in developing decoupled and data-driven injection molding practices
• Injection molding machines consist of a material hopper, barrel, injection ram/rotating screw, heating device, moveable pattern, ejectors, and mold
• Machines usually operate horizontally
• Two clamping methods exist: toggle and straight-hydraulic

Injection Mold

• Molds are made of high-strength metal components machined to operate in two pieces to allow the injection molder to open and close

Plastic Injection Molding Process

• This is a short process usually lasting from six second to 2mins
• The process consists of:
• Clamping: Two halves of the mold are secured using a clamping unit
• Injection: Raw plastic is fed into the machine, heated, and conveyed toward the mold
• Cooling: Molten plastic cools inside the mold
• Ejection: Once cooled, the part is ejected via the ejection system

Plastic Injection Molding Post-Processing

• Post-processing applications are sometimes required and may include processes for decorative or functional purposes
• Common injection molding post-processing applications:
• Gate Trimming
• Painting
• Laser Marking
• Pad Printing
• Heat Staking
• Ultrasonic Welding

Plastic Injection Molding Machine Classifications

• Injection molding machines are classified by tonnage, or clamping pressure/force
• Press sizes range from less than 5 tons to over 4000 tons
• The higher the press ton rating, the larger the machine

Advantages of Plastic Injection Molding

• Aesthetic and functional versatility make plastic injection molding and excellent cost effective manufacturing choice
• Injection molding is a very simple process that can be highly automated, so it is also rapid

Benefits of Plastic

• Plastic is lightweight, yet strong and is considered for replacing metal or steel
• Injection molded parts have very good dimensional consistency compared to other plastics manufacturing processes
• Injection molding easily integrates with computer-aided design (CAD), computer-aided manufacturing (CAM), and SolidWorks
• Over 15,000 variations of plastics are available to achieve desired functional results
• Resins that comply with FDA, NSF, REACH, and RoHS requirements are available when needed
• It produces minimal waste because it is so accurate and efficient, and any excess material can be recycled

Types of Plastic Injection Molding

• Plastic injection molding techniques can be used to achieve different types of end results.
• Standard molding: uses a single color and material to produce the part
• Two-shot (dual-shot) molding: Create a part or product using multiple colors and plastic types simultaneously, without using multi-stage assembly
• Insert molding: An application in which a prefabricated part is used as the substrate
• Overmolding: A two-step process used to produce items that require two different types of plastic

Thermoplastic

• Polymer resins become molten when headed so they can be hardened.
• Thermoplastics can be highly resistant to temperature extremes, corrosive materials, or environments.
• Common Thermoplastics: acrylic (PMMA), acrylonitrile butadiene styrene (ABS), polyamide (PA), polylactic acid (PLA), polycarbonate (PC), polyether ether ketone (PEEK), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), high impact polystyrene (HIPS)

Industries Utilizing Plastic Injection Molding

Automotive

• Plastic parts in automobiles need to function correctly and require a range of intricate design features.
• Typical injected molded components used in automobiles include bumpers, dashboards, and smaller parts, such as cup holders, mirror housings
• The characteristics of plastic parts for the automotive industry:
• Weather and wear-resistant
• High-heat plastic parts that maintain integrity in high-temp scenarios
• Polymers stable from the degradation of chemical exposure
• Effective alternative for discontinued parts
• Noise and vibration reduction
• Reduced cost and weight

Medical

• Plastics have been widely used for medical device manufacturing
• Offering superior quality, precision, and exceptional mechanical properties, custom plastic parts are used in a variety of medical components
• The characteristics of plastic parts for the medical industry:
• Various colors, shapes, and sizes
• A high level of design and application flexibility
• High tensile strength
• Resistance to high temperatures
• Reduced cost and weight

Construction

• Manufacturers use injection molded parts to produce cost-effective construction parts and products, including tools, fasteners, and accessories
• Excellent stability and durability when exposed to environmental elements
• Cost-effective compared to metal or wood
• Energy efficient
• Lightweight
• Many finish options

Plumbing

• Plastic plumbing components offer qualities that metal plumbing does not
• Corrosion resistance
• Low heat conductivity
• Non-reactive to chemicals
• Reduced cost and weight

Appliance

• Appliance manufacturing favors the high-volume, highly repeatable process of creating plastic components for product production
• Resistance to heat, chemicals, and corrosion
• Added durability and longevity
• Decreased weight
• Design flexibility
• Ability to incorporate complex processes, such as overmolding

Electronics

• Plastics have a superior ability to improve safety and provide insulation.
• High voltages and high temperatures can be withstood without degradation
• Good design flexibility
• Superior insulating properties, dielectric strength, and thermal performance
• Reduced cost and weight

Automation

• Automation helps ensure each manufactured component will be identical to the validated design
• Lights-out manufacturing: Automation that allows companies to keep facilities running 24/7, with a scaled-back workforce or virtual oversight

Lights-out manufacturing has transformed injection molding in 5 ways:

• It has helped domestic manufacturers gain a globally competitive advantage
• Large orders can be completed quickly without the higher costs of additional shifts
• Cost containment, delivery, and quality control can be more easily optimized
• A highly specialized, dedicated workforce must be put-in-place to manage and maintain automated equipment and processes.
• Further intellectual property safeguards are in place

Steps of Developing a Plastic Part

Design for Manufacturing

• Necessary steps should be taken to avoid delays and reduce the risk of costly design changes
• DFM involves optimizing manufacturing efficiencies for equipment to realize the lowest possible unit costs
• Design decisions can determine 70% of manufacturing costs
• Design for Manufacturing
• Design for Functionality
• Design for Assembly
• Design for Sustainability

Determine the Molding Process

• Custom injection molding is a popular technique to produce high-volume plastic parts
• The process one chooses depends on initial design, needed quantity, and overall use
• One should work with an injection molder as they may offer post-molding capabilities such hot stamping, heat staking or inserting

Prototyping

• Working with a plastic prototype molding partner to create custom injection mold tools and components will support the overall efficiency
• Prototype molds are: -Typically low-cost -Different from production molds -Meant only for short-term use -Useful for reviewing specifications, functionality and performance

Considerations When Selecting an Injection Molder

• Important criteria should be evaluated when selecting a molder that fits ones requirements.
• If parts need to pass inspections or meet regulations, it is imperative that you partner with an ISO certified partner
• Choose a partner with exceptional customer service and communication.
• Available resin partners can help design and produce successful materials
• Price and value come into play when considering price for part production