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Look around you. That plastic phone case, your car's dashboard, even the keyboard you're typing on—they all started as tiny pellets of raw material. Molding transforms these materials into virtually every plastic and metal part we use daily, from medical devices to aerospace components. Yet most people have no idea how this $400 billion industry actually works.
Whether you're designing your first product or optimizing production costs, understanding molding processes can save you thousands in manufacturing mistakes. Here's what we'll cover:
● Injection molding basics and when to use it
● Seven core molding processes (blow, compression, LSR, extrusion, insert, overmolding)
● Plastic materials that actually work for different applications
● Molding vs. casting—which wins for your project
● Design principles that prevent costly rework
● Real process steps from pellet to finished part
At TEAM MFG, we've produced over 30 million molded parts across 1,220+ projects. We handle everything from rapid prototypes to full production runs, so you can test designs before committing to expensive tooling.
Molding is a manufacturing process that shapes raw materials—typically plastics, metals, or composites—into specific forms using heat, pressure, and specialized tooling. Think of it like a sophisticated waffle maker: you pour in material, apply heat and pressure, and out comes a perfectly formed part.
The process starts with raw material (pellets, powder, or liquid), which gets heated until pliable. This material then flows or gets pressed into a mold cavity—a hollow metal tool machined to your part's exact specifications. Once cooled and solidified, you've got your finished product.
Here's what makes molding so powerful:
● Repeatability: Once you have a mold, you can produce identical parts thousands of times
● Complex geometries: Create intricate shapes impossible with other methods
● Material efficiency: Minimal waste compared to subtractive manufacturing
● Speed: Parts produced in seconds to minutes, not hours
The real magic? You can mold everything from tiny medical components (0.5mm thick) to massive automotive bumpers. Different molding techniques handle different challenges, which is why understanding each process matters for your project's success.
Most of the China molding manufacturers, including TEAM MFG, combine multiple molding processes to optimize cost and quality across production volumes.
Every molding technique solves different manufacturing challenges. Pick the wrong one, and you'll burn through budget faster than plastic melts. Here's how each process works and when to use it.
Process | Best Volume | Tooling Cost | Cycle Time | Ideal Applications |
Injection Molding | 1,000-1M+ units | $3K-$100K+ | 15-120 seconds | Complex parts, electronics housings, consumer products |
Blow Molding | 5,000+ units | $10K-$50K | 5-30 seconds | Bottles, containers, hollow parts |
Compression Molding | 100-10,000 units | $5K-$20K | 2-10 minutes | Large flat parts, electrical components |
LSR Molding | 1,000+ units | $20K-$80K | 30-180 seconds | Medical devices, seals, baby products |
Extrusion | Continuous | $3K-$15K | Continuous | Pipes, profiles, weather stripping |
Insert Molding | 500+ units | $15K-$60K | 30-90 seconds | Threaded inserts, electronics encapsulation |
Overmolding | 1,000+ units | $20K-$70K | 45-120 seconds | Soft grips, multi-material parts |
The workhorse of manufacturing. Melted plastic gets injected into a closed mold under high pressure (10,000-20,000 PSI). The material fills every corner, cools, and ejects as a finished part.
● Best for: High-volume production (1,000+ units), complex parts with tight tolerances (±0.002"), thin walls
● Materials: ABS, PC, PP, nylon, TPE
● Cycle time: 15-120 seconds
Pro tip: Initial tooling costs run $3,000-$100,000+, but per-part costs drop dramatically at scale. TEAM MFG's injection molding services start with aluminum tools for testing before steel production molds.
Picture blowing up a balloon inside a bottle-shaped cavity. That's blow molding. A heated plastic tube (parison) gets inflated with compressed air until it takes the mold's shape.
● Best for: Hollow parts—bottles, containers, fuel tanks
● Wall thickness: 0.5-5mm typically
● Production speed: 1,000-10,000 parts/hour
The catch? You're limited to hollow shapes with relatively uniform wall thickness.
Old school but effective. Place pre-heated material into an open mold, close it, and apply massive pressure (1,000-2,000 PSI) while heating. The material flows and cures into shape.
● Best for: Large, flat parts with simple geometries
● Materials: Thermosets, rubber, composites
● Advantages: Low tooling costs, handles high-strength materials
Companies use this for electrical housings, automotive panels, and aerospace components where strength beats aesthetics.
Inject two-part liquid silicone that cures inside the mold. Unlike traditional rubber molding, LSR flows like water before curing, filling intricate details.
● Temperature resistance: -60°C to 250°C
● Applications: Medical devices, baby products, seals, gaskets
● Key benefit: Biocompatible and FDA-approved options
Push heated plastic through a die opening—like squeezing toothpaste. Creates continuous profiles with fixed cross-sections.
● Products: Pipes, tubes, weather stripping, window frames
● Output: 50-500 kg/hour depending on size
● Length: Technically unlimited (cut to size)
Mold plastic around pre-placed components (metal inserts, electronics, other plastics). The insert becomes permanently encapsulated.
● Common applications: Threaded fasteners in plastic, sealed electronics, multi-material assemblies
● Benefit: Eliminates assembly steps, creates stronger bonds than gluing
Similar to insert molding, but you're molding plastic over another molded part. Think soft-grip handles on tools or multi-color parts.
● Materials: Often rigid plastic base with TPE overmold
● Uses: Ergonomic grips, waterproof seals, aesthetic enhancements
At TEAM MFG, we regularly combine these processes—starting with rapid prototyping to test designs, then scaling to appropriate production methods based on volume and requirements.
Not all plastics play nice with every molding process. Choose wrong, and you'll get warped parts, weak bonds, or materials that literally burn during production. Here's what actually works.
● ABS (Acrylonitrile Butadiene Styrene): The Swiss Army knife of plastics. Strong, cheap, and easy to mold. Your keyboard, LEGO bricks, and car interior trim? All ABS.
○ Melting point: 200-250°C
○ Cost: $1.50-2.50/kg
○ Why use it: Balanced properties, takes paint well, machines easily
● Polypropylene (PP): The most-produced plastic globally. Flexible, chemical-resistant, and survives repeated bending without breaking.
○ Applications: Living hinges, food containers, automotive bumpers
○ Special power: Fatigue resistance (survives 1M+ flex cycles)
○ Processing tip: Shrinks 1.5-3%—account for this in mold design
● Polycarbonate (PC): Bulletproof glass is polycarbonate. Need we say more? Crystal clear, impact-resistant, handles heat up to 135°C
○ Where it shines: Safety glasses, phone screens, medical devices
○ Watch out: Costs 3x more than ABS, requires drying before molding
● Nylon (Polyamide): Engineering-grade toughness. Self-lubricating, wear-resistant, and stronger than most metals by weight.
○ Grades: PA6, PA66, glass-filled variants (30-50% stronger)
○ Moisture problem: Absorbs water—must dry 4-8 hours before molding
● TPE/TPU (Thermoplastic Elastomers): Rubber-like flexibility with plastic's processability. Soft-touch grips, seals, and medical tubing all use TPE.
○ Hardness range: 20-95 Shore A
○ Bonds to: ABS, PC, PP (perfect for overmolding)
Need | Best Material | Why | Typical Cost/Part |
High strength | Glass-filled nylon | 30% stronger than unfilled | $0.50-$5 |
Transparency | Polycarbonate, acrylic | Optical clarity 88-92% | $1-$10 |
Chemical resistance | PP, HDPE | Survives acids, bases | $0.20-$2 |
Heat resistance | PEEK, PEI | Handles 250°C+ | $10-$100 |
Food contact | PP, HDPE, some TPEs | FDA approved grades | $0.30-$3 |
Outdoor use | ASA, PC, stabilized ABS | UV resistant | $0.80-$8 |
You've got two roads to plastic parts: molding (high pressure, closed molds) or casting (gravity-fed, open molds). The winner depends on three factors: volume, complexity, and timeline.
● Production volume above 500 units: Molding's higher tooling costs ($5K-$100K) spread across more parts. At 1,000 units, molded parts cost 70% less than cast ones.
● Tight tolerances required: Injection molding holds ±0.002" consistently. Casting? You're lucky to get ±0.010". For parts that must fit together precisely, molding wins every time.
● Complex internal features: Side actions, undercuts, threaded inserts—molding handles complexity that would require multiple casting operations.
● Fast cycle times needed: Molding: 30-second cycles Casting: 20-minute minimum cure times Do the math on 10,000 parts. That's 83 hours vs. 3,333 hours.
● Prototypes and low volumes (<100 units): Silicone molds for urethane casting cost $500-$2,000. Perfect for market testing before committing to injection mold tooling.
● Large, thick parts: Casting handles 2-inch thick sections without sink marks or voids. Injection molding struggles above 0.25 inches.
● Clear, bubble-free parts: Vacuum casting produces crystal-clear parts without injection molding's potential flow lines or weld marks.
Smart manufacturers don't choose—they sequence. Start with cast prototypes for testing, then transition to molding for production. TEAM MFG's rapid prototyping services often combine both: cast parts for initial validation, then aluminum tooling for pilot runs, finally steel molds for mass production.
Real numbers from a recent project:
● 10 prototypes via casting: $200/part, 5-day turnaround
● 500 units via aluminum tooling: $40/part, 15-day lead time
● 10,000 units via steel tooling: $3/part, 25-day initial run
The takeaway? Casting proves the concept, molding pays the bills.
Bad design kills good products. We've seen $50,000 molds scrapped because someone ignored basic design rules. Follow these principles, or prepare to explain to your boss why the parts won't eject from the mold.
Keep walls uniform and thin. Varying thickness causes warping, sink marks, and longer cycle times that destroy profitability.
Target thickness by material:
● ABS: 1.5-3.5mm
● PC: 2.0-3.8mm
● PP: 0.8-3.0mm
● Nylon: 0.8-3.0mm
Thick sections? Core them out. That 10mm boss doesn't need to be solid—honeycomb or rib structures provide strength without the bulk.
No draft = stuck parts = broken molds. Add 1-2° minimum draft on all vertical surfaces. Textured surfaces need more (3-5°).
Quick math: 1° draft on a 25mm tall wall creates 0.44mm offset at the top. Plan for this in assemblies.
Ribs for strength:
● Maximum thickness: 60% of wall thickness
● Height: <3x thickness
● Add 0.5° draft minimum
Bosses for fasteners:
● OD = 2x insert diameter
● ID = core pin diameter + 0.1mm
● Connect to walls with ribs, not solid sections
Undercuts—avoid or pay dearly: Side actions add $5,000-$15,000 to tooling. Sometimes you need them. Usually, you don't. Consider pass-through cores or design changes first.
Design Error | Result | Fix | Cost Impact |
Sharp corners | Stress concentration, cracks | 0.5mm minimum radius | Part failure, warranty claims |
No draft | Parts stick, mold damage | 1-2° on all verticals | $10K+ mold repair |
Thick walls | Sink marks, warping | Core out or add ribs | 50% longer cycles = higher cost |
Long cantilevers | Breakage during ejection | Support with ribs | Production delays |
Text/logos wrong depth | Illegible marking | 0.5mm depth/height minimum | Mold rework $2-5K |
Pro tip from TEAM MFG's engineering team: Send us your CAD files before cutting steel. Our design for manufacturing (DFM) analysis catches 90% of issues that cause mold modifications. Free service that saves thousands.
Here's what actually happens from raw material to finished part—the stuff manufacturers don't always explain clearly.
Drying is mandatory for most plastics. Skip this, and moisture turns to steam, creating bubbles and weak parts.
● Nylon: 80°C for 4-8 hours
● PC: 120°C for 4 hours
● ABS: 80°C for 2-4 hours
● PP: Usually runs without drying
Materials get loaded into hopper dryers that continuously circulate hot, dry air. One bad batch of wet material can ruin an entire production run.
Mold closes (2-5 seconds):
Hydraulic or electric clamps apply 50-2,000 tons of force. Less force than material pressure = flash everywhere.
Injection (1-10 seconds):
Screw pushes molten plastic at 10,000-20,000 PSI. Material fills the cavity at 100-300mm/second. Too fast causes burn marks; too slow creates flow lines.
Packing/Holding (5-25 seconds):
Maintains pressure while the outer skin solidifies. This compensates for shrinkage—typically 0.5-2% volume reduction.
Cooling (10-60 seconds):
Makes up 80% of cycle time. Cooling channels circulate 15°C water through the mold. Part must cool below ejection temperature (usually 30°C below melting point).
Mold opens and ejection (3-5 seconds):
Pins push the part out. Too much force = deformation. Too little = stuck parts.
● Gate removal: Every part has a gate mark where plastic entered. Manual cutting, automated trimming, or hot-tip gates that separate cleanly.
● Quality inspection:
○ First article inspection (FAI) on initial parts
○ Dimensional checks every 30-60 minutes
○ Visual inspection for defects
● Secondary operations (if needed):
○ Machining for tight tolerances
○ Pad printing or laser etching for marking
○ Assembly of multiple components
○ Packaging to prevent shipping damage
Understanding each step helps you spot optimization opportunities. Shaving 5 seconds off cooling or reducing wall thickness by 0.5mm might seem minor, but across 100,000 parts, you're talking serious money.
Molding isn't rocket science—it's about matching the right process to your project. Whether you need 100 prototypes or 100,000 production parts, success comes from understanding materials, design rules, and process capabilities.
Key takeaways:
● Choose injection molding for high volumes and complex parts
● Keep walls uniform (1.5-3mm) and add 1-2° draft everywhere
● Material selection drives 40% of part cost—pick wisely
● Start with prototypes, scale to aluminum tools, then commit to steel
● Every 5-second cycle reduction saves thousands at scale
TEAM MFG handles all seven molding processes under one roof, from your first prototype to mass production. We've helped 1,220+ projects avoid costly mistakes through free DFM analysis and smart tooling strategies. Upload your CAD files, and we'll show you exactly which process gets you the best parts at the lowest cost.
