The Complete Step-by-Step Injection Molding Process

From Design to Production: The Complete Step-by-Step Injection Molding Process

Injection molding is a complex, multi-stage manufacturing process that converts plastic pellets into functional finished products. Each phase builds on the last, transforming initial concepts into high-quality plastic parts through careful planning, precision tooling, scientific molding, and quality assurance. This guide will walk through the complete injection molding workflow – from initial design steps to production and completion. Understanding the full sequence of events provides crucial context for both molders and customers to set realistic expectations and production schedules.

Product Design and Engineering

The injection molding process begins on paper or CAD software. Initial product design steps include:

  • Conceptualizing the form, function and aesthetic
  • Drafting 2D technical drawings or 3D models
  • Material selection based on performance needs
  • DFM analysis to optimize moldability and manufacturability
  • Simulations to predict outcomes and prevent defects
  • Prototyping early samples to test the design

Thoughtful design engineering ensures parts can be molded accurately, repeatably and efficiently right from the start.

Mold Design and Tool Fabrication

With an engineered design in place, mold makers create precision cavities, cores, and components that will form each product part. Key mold design steps include:

  • Evaluating part drawings and models
  • Blueprinting mold components and the cooling layout
  • CAD mold design with specialized software
  • CNC machining mold components from steel or aluminum
  • Polishing and finishing mold surfaces
  • Assembling the finished mold tool

The quality of finished parts depends directly on mold tool craftsmanship and accuracy.

Mold Testing and First Article Inspection

Before full production, initial samples are molded to test mold performance. Engineers will:

  • Run mold tryouts and make any adjustments
  • Measure critical dimensions and compare to specs
  • Check cosmetics, function, material fill
  • Tweak process settings as needed
  • Document settings for production parameters

First article inspection ensures the tool produces perfect parts meeting design specifications.

Material Preparation

With molds ready for production, raw plastic must be prepared. Steps include:

  • Selecting and sourcing resins pellets or powders
  • Inspecting materials upon receipt
  • Drying or conditioning material per specs
  • Blending, adding colorants, reinforcements as needed
  • Testing and certifying materials properties

Proper material prep maximizes performance properties and cosmetics.

Mold Setup and Preparation

Prior to production, molds are installed into injection molding machines. Setup steps involve:

  • Clamping the mold tool into the press
  • Connecting water, pneumatic, hydraulic lines
  • Testing mold open/close mechanisms
  • Verifying machine controls and robotics settings
  • Preheating mold surfaces and hot runner systems
  • Setting process parameters per first article data

Correct mold setup is imperative for production consistency.

The Injection Molding Production Sequence

With preparations complete, the cyclical molding process begins:

  1. Clamping – The mold halves close and clamp together
  2. Injection – Molten plastic enters the mold cavity
  3. Packing – Pressure packs material in to fill details
  4. Cooling – Coolant lines solidify the plastic
  5. Ejection – Pins eject the finished part
  6. Reset – The mold opens and resets for the next cycle

Automating this sequence enables fast, efficient production of parts.

Post-Molding Operations and Finishing

After molding, additional secondary operations may refine part geometry, appearance or function:

  • Trim excess plastic from parts (degating)
  • Join sub-components together via welding, fastening, adhesive
  • Decorate parts with pad printing, laser marking, plating
  • Add protective or functional coating
  • Assemble smaller parts into finished products

Value-added finishing gives products market-ready appeal and performance.

Post-Production Inspection and Testing

Prior to shipment, products undergo final checks:

  • Dimensional inspection of critical features
  • Functional performance testing as needed
  • Visual examination for cosmetic defects
  • Documentation of results for full traceability
  • Application of any protective packaging

End-of-line quality control ensures shipment of defect-free products.

Packaging and Shipment

The last step is preparing parts for distribution:

  • Group products according to customer orders
  • Apply protective interior packaging materials
  • Organize cartons on pallets for easy transport
  • Secure pallets with strapping, wrap
  • Label cartons and pallets with identifiers
  • Load packaged goods for outbound shipping

Proper packaging prevents damage and keeps orders organized during transit.


The complete injection molding process is far more complex than simply melting plastic and forming parts. Each phase builds on the last in a interconnected sequence. From technical design to mold fabrication to secondary finishing, every step must be executed skillfully to turn raw materials into exceptional products. By understanding this full progression – the responsibilities each stage entails and how one impacts the next – both manufacturers and customers can better plan, collaborate and execute injection molding programs efficiently. Acknowledging the efforts behind each phase leads to realistic timelines, quality-driven outcomes and successful mass production.