Untitled Flashcards Set

Lecture 5: Injection Molding (Part 2) – Detailed Study Notes

1. Injection Molding Process Review

• Injection molding is a high-volume manufacturing process for creating plastic parts.

• The process involves:

  1. Material Melting – Plastic pellets are heated in the barrel until they become molten.

  2. Injection – The molten plastic is injected into a mold cavity under high pressure.

  3. Cooling – The plastic solidifies as it cools inside the mold.

  4. Ejection – The part is ejected from the mold.

🔹 Why it's important?
Injection molding is widely used due to its ability to create complex shapes with high precision and repeatability.

🔹 Study Tip:
Watch this video for a visual understanding:
📌 Plastic Injection Molding Process

2. Surface Finish & Texture in Injection Molding

• Surface finish is an integral part of mold design because it affects the aesthetics and function of the final product.

• Types of Surface Finishes:

  1. Etched Textures – Fine patterns added to the mold surface to create matte or textured finishes.

  2. EDM (Electrical Discharge Machining) – Used for high-precision texturing and rough surfaces.

  3. Machined Finishes – CNC or manually machined textures that create specific patterns.

Two Categories of Surface Finishes:

✅ Integral Finishes

• Created directly in the mold.

• Example: A polished mold gives a glossy part finish.

✅ Added Finishes

• Applied after molding.

• Includes coatings, painting, or surface treatments.

🔹 Why it's important?
The surface finish affects appearance, grip, and functionality (e.g., textured finishes reduce glare or improve handling).

3. Overmolding & Multi-Shot Molding

What is Overmolding?

• A two-step injection molding process where one material (e.g., rigid plastic) is molded first, then a second softer material (e.g., rubber) is molded over it.

• Common in ergonomic grips, such as toothbrushes and power tools.

Overmolding Process:

1. Mold Part A (usually rigid plastic).

2. Place Part A into another mold.

3. Second material (elastomer) is injected over specific areas.

✅ Benefits of Overmolding:

• Creates multi-material components without assembly.

• Enhances grip, aesthetics, and durability.

🔹 Study Tip:
Watch this Toothbrush Overmolding video:
📌 Two-Color Toothbrush Molding

4. Insert Molding & Outsert Molding

What is Insert Molding?

• A method where a metal or non-plastic component is placed inside the mold before plastic injection.

• The plastic flows around the insert, securing it inside.

✅ Examples of Insert Molding:

• Metal screw threads in plastic casings.

• Electrical connectors with embedded metal parts.

What is Outsert Molding?

• The opposite of insert molding.

• Instead of embedding an insert, plastic is molded around an existing component.

✅ Benefits of Insert & Outsert Molding:

• Reduces assembly costs.

• Improves strength and durability.

🔹 Study Tip:
📌 Insert Molding Process Video

5. Co-Injection Molding (Sandwich Molding)

• Process where two different plastics are injected into a mold in layers.

• The core material is typically recycled plastic, while the outer layer is a high-quality material.

✅ Advantages:

• Cost savings by using recycled material.

• Improved structural integrity without extra weight.

🔹 Study Tip:
Understand how different plastics interact in the co-injection process.

6. Structural Foam Molding

What is Structural Foam Molding?

• Uses a chemical blowing agent to create a foamed structure inside the plastic.

• Produces lightweight yet rigid parts.

✅ Key Benefits:

• Stronger & more impact-resistant than standard plastic.

• Reduces material usage while keeping strength.

✅ Common Uses:

• Pelican cases

• Large enclosures for electronics.

🔹 Study Tip:
📌 Structural Foam Molding Animation

7. Gas-Assisted Injection Molding

What is Gas Assist?

• Pressurized gas is injected after plastic to create hollow sections.

• Used in thick parts to prevent sink marks.

✅ Benefits of Gas-Assisted Molding:

• Reduces material costs.

• Creates lightweight, strong parts.

• Improves surface quality.

🔹 Study Tip:
Understand the difference between gas-assist and structural foam molding.

8. Reaction Injection Molding (RIM)

How it Works:

1. Two liquid thermoset materials are mixed.

2. Injected into the mold where they chemically react and solidify.

3. Used for large, lightweight parts.

✅ Examples:

• Automotive panels

• Medical enclosures

🔹 Study Tip:
Remember, RIM uses thermosets, not thermoplastics.

9. Structural Web Molding

• Variation of gas-assist molding where hollow sections add strength.

• Reduces weight while maintaining rigidity.

✅ Common Uses:

• Automotive parts.

• Large enclosures.

Lecture 4: Injection Molding (Part 1) – Detailed Study Notes

1. Introduction to Injection Molding

• Injection molding is a manufacturing process used to produce plastic parts in high volumes.

• Default Material: Thermoplastics (plastics that soften when heated and harden when cooled).

🔹 Why it’s important?

• Can produce complex shapes with high precision.

• Efficient for mass production of plastic parts.

2. Advantages & Disadvantages of Injection Molding

✅ Advantages:

• Creates complex parts with high accuracy.

• Lightweight, detailed, and finished parts.

• High production efficiency – Can produce hundreds to millions of identical parts.

• Low part cost when produced in large volumes.

• Widely used – Many suppliers and manufacturers support injection molding.

❌ Disadvantages:

• Tooling is expensive – Creating molds is costly, especially for complex parts.

• Injection molding machines are expensive.

• Long lead times for mold production – Typically 8–20 weeks.

• Solution: Some companies offer quick-turn prototyping services (e.g., Protolabs).

🔹 Study Tip:
Understand the trade-offs – Injection molding is efficient but requires high initial investment.

3. Injection Molding Process Overview

Basic Steps of Injection Molding:

1. Clamping – The mold is closed tightly using a clamping unit.

2. Injection – Molten plastic is injected under high pressure.

3. Cooling – The part solidifies inside the mold.

4. Ejection – The cooled part is ejected from the mold.

🔹 Study Tip:
📌 Watch this overview video: Injection Molding Process

4. Injection Molding Machine Components

Key Parts of an Injection Molding Machine:

• Injection Unit: Melts and injects plastic into the mold.

• Clamping Unit: Holds the mold shut during injection.

• Mold Tooling: The cavity where the plastic takes shape.

• Cooling System: Controls the temperature for part solidification.

• Ejection System: Pushes the finished part out of the mold.

🔹 Why it's important?
Understanding these components helps in troubleshooting defects (e.g., improper cooling can cause warping).

5. Line of Draw (LOD)

• Line of Draw (LOD) is the direction in which the mold separates to release the part.

• Why it matters?

  • Parts must be designed to follow the LOD to avoid undercuts, which can make ejection difficult.

6. Cycle Time & Production Efficiency

• Cycle time is the total time required to complete one injection molding cycle (clamping → injection → cooling → ejection).

• Factors Affecting Cycle Time:

  • Material cooling rate (some plastics cool faster than others).

  • Mold design (well-designed molds reduce cycle time).

  • Part complexity (more complex parts may require longer cooling).

🔹 Example:

• High-speed production: A 96-cavity mold for bottle caps can have a cycle time of 4 seconds.

📌 Watch this bottle cap production video:
96-Cavity Mold Cycle

7. Injection Molding Machines – Tonnage & Clamping Force

• Tonnage rating measures the force required to keep the mold shut during injection.

• Larger parts require higher tonnage to keep the mold sealed under high pressure.

🔹 Study Tip:
Remember: Higher tonnage = Stronger clamping force needed for larger parts.

8. Mold Types in Injection Molding

Two-Plate Mold (Basic)

• Most common mold type.

• Contains two halves: A stationary side and a moving side.

• Runner system delivers molten plastic to the cavity.

Three-Plate Mold

• Has an extra plate to separate parts from runners.

• Advantage: Reduces waste by allowing automatic runner ejection.

Runnerless (Hot-Runner) Molds

• Uses heated channels instead of runners.

• Reduces material waste.

Stack Molds

• Multiple layers of cavities to double production efficiency.

🔹 Study Tip:
Know the differences between 2-plate, 3-plate, and stack molds.

9. Plastic Flow & Gating Systems

• Runner System: Channels that direct molten plastic into the mold.

• Gate Types:

  • Edge gate – Used for simple shapes.

  • Submarine gate – Allows automatic part separation.

  • Hot tip gate – Used in runnerless molds.

🔹 Why it matters?
The gate location affects surface finish and part strength.

10. Design Considerations for Injection Molding

1. Draft Angles

• Draft angles allow for easy part ejection from the mold.

• Standard rule: 1°–3° draft for most parts.

📌 Watch this draft angle explanation video:
Injection Molding 101: Draft Angles

2. Wall Thickness & Uniformity

• Thin walls cool faster but may be weak.

• Thick walls take longer to cool and may cause sink marks.

• Ideal thickness: 1–4 mm for most injection-molded parts.

3. Ejection Systems

• Ejector pins: Push the part out after molding.

• Stripper plates: Help remove fragile parts.

• Automated removal: Uses pneumatics & suction cups.

📌 Watch this ejector pin video:
Injection Molding 101: Ejector Pins

4. Undercuts & Parting Lines

• Undercuts prevent easy removal and require side-action cores or collapsible cores.

• Parting lines are seams where the mold separates.

🔹 Why it matters?

• Avoid undercuts if possible to simplify tooling and reduce costs.

• Parting lines should be placed strategically to minimize visible defects.

5. Sink Marks & Ribs

• Sink marks occur when thick sections shrink during cooling.

• Solution: Use ribs instead of thick walls to maintain strength without excessive thickness.

6. Holes & Openings

• Holes should be designed in-line with the mold’s line of draw.

• Oblique holes require additional tooling.

11. Flash, Weld Lines, & Defects

• Flash: Extra plastic at the mold seam due to improper clamping.

• Weld lines: Weak areas where two plastic flows meet.

• Solutions:

  • Improve clamping force.

  • Optimize gate placement.

Week 3: Extrusion Blow Molding Process – Detailed Study Notes

1. Introduction to Blow Molding

• Blow Molding is a plastic manufacturing process used to create hollow objects by inflating a heated plastic tube (parison) inside a mold.

• Commonly used for bottles, tanks, and large hollow structures.

• Works with thermoplastics (can be reheated and reformed).

🔹 Why it’s important?

• Ideal for lightweight, strong, and hollow plastic parts.

• Used in packaging, automotive, and toy industries.

📌 Example:

• Little Tikes toys are made using blow molding.

2. Applications of Blow Molding

Blow molding is used in industries such as:

• Automotive: Fuel tanks, air ducts.

• Packaging: Bottles, containers.

• Toys: Large hollow plastic toys.

• Medical: Plastic enclosures for medical devices.

🔹 Why it’s important?

• Blow molding is widely used due to its cost-effectiveness for hollow plastic parts.

3. Extrusion Blow Molding (EBM) – Process Overview

Steps of Extrusion Blow Molding:

1. Plastic pellets are melted and extruded into a hollow tube called a parison.

2. The parison is clamped inside a mold.

3. Compressed air is blown into the parison, expanding it to fit the mold shape.

4. The part cools and solidifies.

5. Mold opens, and the finished part is ejected.

6. Trimming removes excess material.

📌 Watch this Extrusion Blow Molding Video:
Extrusion Blow Molding Process

4. Advantages & Disadvantages of Blow Molding

✅ Advantages:

• Can produce large hollow parts.

• Allows foam filling for lightweight yet rigid structures.

• Produces good surface finishes with integral color.

• Wall thickness can be adjusted during processing.

• Low internal stress, reducing material defects.

• Lower tooling costs compared to injection molding.

• Best stiffness-to-weight ratio among plastic molding processes.

❌ Disadvantages:

• Limited mold-in details – Features like threads may require secondary operations.

• Blow ratio limits design complexity.

• Surface finish on non-textured parts is lower than in injection molding.

• 360° trimming and deburring are required.

• Secondary operations (e.g., routing, deburring) add cost.

🔹 Why it’s important?

• Blow molding is more cost-effective than injection molding for hollow parts but has design limitations.

5. Blow Molding Equipment & Extruder Head

Key Equipment in Blow Molding:

• Extruder: Melts plastic and forms the parison.

• Mold: Shapes the expanding plastic.

• Blow pin: Injects air into the parison.

• Cooling system: Cools the part quickly.

• Trimming system: Removes excess material.

🔹 Study Tip:
Know the role of each component to understand how defects occur (e.g., improper cooling can cause warping).

6. Parison Control & Wall Thickness

• The parison is the extruded plastic tube that expands inside the mold.

• Challenges with Parison:

  • As it gets longer, gravity causes it to thin out at the top.

• Solution:

  • The die and mandrel system controls wall thickness.

  • Some machines allow wall thickness variation to compensate for gravity.

🔹 Why it matters?

• Ensuring even wall thickness prevents weak spots in the final product.

7. Design Considerations in Blow Molding

1. Blow Ratio (BR)

• Blow Ratio (BR) = Final Part Diameter / Parison Diameter.

• Higher BR = More material stretching → Risk of thinning.

🔹 Why it matters?

• If the BR is too high, parts can become weak or uneven.

2. Wall Thickness

• Uniform wall thickness is critical for strength and performance.

• Solutions for uneven walls:

  • Controlled parison programming.

  • Mold design adjustments.

3. Markings & Radii

• Markings: Can be embossed or engraved on the mold.

• Radii (rounded edges): Prevent stress points and improve strength.

🔹 Why it matters?

• Sharp corners can cause weak points and should be avoided.

4. Draft Angles & Parting Lines

• Draft angles help in easy part ejection from the mold.

• Parting lines are where the two halves of the mold meet.

🔹 Why it matters?

• Poor parting line placement affects appearance and requires extra trimming.

5. Rigidity & Large Flat Panels

• Blow-molded parts can be reinforced for strength using:

  • Ribs.

  • Curved surfaces instead of flat panels.

• Large, flat panels are difficult to mold without distortion.

🔹 Why it matters?

• Adding ribs or curves prevents warping.

6. Assemblies & Fasteners

• Blow-molded parts often need assembly features, like:

  • Snap fits.

  • Threaded inserts.

  • Ultrasonic welding.

🔹 Why it matters?

• These features must be designed into the mold to avoid extra assembly steps.

7. Neck Finishes

• Used for threaded caps and closures (e.g., bottles).

• Requires precise molding to ensure proper sealing.

🔹 Why it matters?

• Neck finishes affect cap fit and sealing quality.

8. Quality Control & Common Defects

Defects in Blow Molding:

1. Uneven Wall Thickness → Caused by poor parison control.

2. Flash (extra plastic at seams) → Due to improper mold clamping.

3. Warping or Distortion → Happens if cooling is uneven.

4. Weak Joints → Insufficient melt strength or poor design.

🔹 Why it matters?

• Understanding defects helps in troubleshooting manufacturing issues.

9. Extrusion Blow Molding vs. Stretch Blow Molding

Extrusion Blow Molding

• Used for large hollow parts (toys, tanks, industrial containers).

• More cost-effective for high-volume production.

Stretch Blow Molding

• Used for high-clarity, thin-walled bottles (e.g., PET water bottles).

• Involves stretching the plastic before blowing for better strength.

🔹 Study Tip:
Know when to use extrusion vs. stretch blow molding based on product needs.

Week 3: Rotational Molding – Detailed Study Notes

1. Introduction to Rotational Molding

• Rotational Molding (Rotomolding) is a plastic manufacturing process used to create hollow and seamless plastic parts.

• The process uses low pressure and high heat to melt and evenly coat the inside of a rotating mold.

• Commonly used for large, durable, and stress-free plastic products.

📌 Example Products:

• Kayaks

• Large storage tanks

• Playground equipment

• Automotive components

🔹 Why it’s important?

• Rotomolding is ideal for making strong, durable, and lightweight hollow parts without seams.

📌 Watch this Rotational Molding Video:
Rotational Molding Process

2. Principles of Rotational Molding

How It Works:

1. Loading the Mold

   • Plastic powder (usually polyethylene) is placed inside a hollow metal mold.

2. Heating & Rotation

   • The mold is heated while rotating on two perpendicular axes.

   • The plastic melts and coats the inner surface of the mold.

3. Cooling

   • The mold is cooled with air or water mist until the plastic solidifies.

4. Part Removal

   • The finished part is removed, and the process repeats.

🔹 Why it’s important?

• Rotomolding ensures uniform wall thickness and high durability without the need for seams or welds.

📌 Watch this Process Video:
Rotational Molding Principle

3. Applications of Rotational Molding

Rotomolding is used in various industries:

• Automotive: Fuel tanks, dashboards.

• Industrial Storage: Large chemical tanks.

• Toys & Recreation: Kayaks, playground slides.

• Medical: Hospital equipment enclosures.

🔹 Why it’s important?

• Rotomolding can produce small to extra-large parts while maintaining strength and durability.

4. Advantages & Disadvantages of Rotational Molding

✅ Advantages:

• Can create very large and small parts.

• Stress-free parts – No internal stress due to low-pressure molding.

• Complex shapes with undercuts & inserts are possible.

• Uniform wall thickness can be controlled.

• Good surface detail & texture can be achieved.

• Cost-effective molds compared to injection molding.

• Fast prototyping & short lead times.

❌ Disadvantages:

• Long cycle time – Takes more time than injection or blow molding.

• Internal ribs are not possible – Hollow parts cannot have structural ribs inside.

• Limited material choices – Usually uses polyethylene (PE).

• Metal molds have complexity limits – Cannot be as intricate as injection molds.

• Large machines require high energy and space.

🔹 Why it’s important?

• Rotomolding is ideal for simple, strong, and large hollow parts but has longer cycle times.

5. Rotational Molding Equipment

Types of Machines Used:

1. Carousel Machines – Continuous production with multiple molds.

2. Rock & Roll Machines – Used for long & narrow parts (e.g., kayaks).

3. Shuttle Machines – Two arms that move molds between stations.

4. Clamshell Machines – Compact design for small production runs.

🔹 Why it’s important?

• Machine choice depends on part size, volume, and complexity.

📌 Watch this Rotomolding Equipment Video:
Rotational Molding Machines

6. Materials Used in Rotational Molding

Material Requirements:

• Must be in powdered form (35-mesh grind size).

• Good flow properties – Must flow evenly to coat the mold.

• Thermal stability – Must withstand long heating cycles.

Common Plastics Used:

1. Polyethylene (PE) – Most widely used.

   • LDPE (Low-Density PE) – Flexible, soft.

   • HDPE (High-Density PE) – Rigid, impact-resistant.

   • Cross-linked PE – High strength & chemical resistance.

2. PVC (Polyvinyl Chloride) – Flexible & durable.

3. Nylon (PA) – High strength & wear resistance.

4. Polycarbonate (PC) – High heat resistance.

🔹 Why it’s important?

• PE is the most common due to its flexibility, strength, and low cost.

7. Design Opportunities in Rotational Molding

1. Wall Thickness

• Cannot be varied within a single part.

• Tolerances are typically ±10%.

• Thinner walls = lower weight, but less strength.

• Thicker walls = higher strength, but heavier and costlier.

🔹 Why it’s important?

• Wall thickness consistency is critical for strength and durability.

2. Draft Angles

• Minimal draft is needed on the outer surface.

• Inside surfaces require more draft to allow easy part removal.

• Draft angles depend on material shrinkage.

🔹 Why it’s important?

• Proper draft angles prevent sticking and allow smooth demolding.

3. Surface Flatness

• Flat surfaces are never perfectly flat due to material shrinkage.

• Solution: Use slight crowning (curving) to reduce deformation.

🔹 Why it’s important?

• Flat areas should be slightly curved to prevent warping.

4. Corner Design

• Outside corners become thicker.

• Inside corners are thinner.

• Solution: Use large radii to ensure uniform thickness.

🔹 Why it’s important?

• Smooth transitions reduce stress points.

5. Double-Walled Parts

• Many rotomolded products are double-walled.

• Space between walls must be wide enough for plastic to flow (min. 5x wall thickness).

🔹 Why it’s important?

• Proper spacing ensures the inner wall forms correctly.

6. Stiffening the Part

• Internal ribs are NOT possible in rotomolding.

• Alternative ways to stiffen parts:

  • Increase material thickness.

  • Add kiss-offs (areas where inner and outer walls touch).

  • Use curved designs for strength.

🔹 Why it’s important?

• Stiffening must be designed into the shape itself.

7. Holes & Fastening

• Types of holes:

  • Surface holes – Simple open holes.

  • Blind holes – Holes that don’t go through.

  • Large holes – Used for caps, lids, or inserts.

• Fasteners must be added later using inserts or post-processing.

🔹 Why it’s important?

• Rotomolding does not naturally form precise holes.

8. Process Variations

1. Adding Foam

• Foam filling increases insulation and strength.

• Used for coolers, kayaks, and fuel tanks.

2. Metal & Foam Stiffening

• Metal rods or foam layers can be inserted before molding to reinforce parts.

3. Polymer Inserts

• Allows multi-layered parts with different colors or properties.

🔹 Why it’s important?

• Different materials can be combined to enhance performance.

Week 2: Plastic Extrusion – Detailed Study Notes

1. Introduction to Plastic Extrusion

• Plastic Extrusion is a continuous manufacturing process where molten plastic is forced through a die to create products with a fixed cross-section.

• Commonly used to produce pipes, sheets, films, and custom profiles.

📌 Example Products:

• Window frames

• Plastic tubing

• Packaging films

• Wire insulation

🔹 Why it’s important?

• Cost-effective for mass production of long, continuous parts with consistent profiles.

2. Advantages of Plastic Extrusion

✅ Key Benefits:

• High production speed – Ideal for continuous manufacturing.

• Low waste – Excess material can be recycled.

• Consistent quality – Produces uniform thickness and dimensions.

• Flexible material options – Can extrude various thermoplastics.

🔹 Why it’s important?

• Extrusion is more efficient for long plastic components than injection molding.

3. Plastic Extrusion Process – Overview

Basic Steps of the Extrusion Process:

1. Raw plastic pellets are fed into a heated barrel.

2. A rotating screw pushes the plastic forward, melting it as it moves.

3. Molten plastic is forced through a shaped die.

4. The extruded plastic is cooled (using air or water).

5. The finished product is cut to length or wound onto a roll.

📌 Watch this Extrusion Process Video:
Plastic Extrusion Process

4. Types of Plastic Extrusion

1. Sheet Extrusion

• Used to create flat plastic sheets that can be cut, shaped, or thermoformed.

• Common applications: Packaging trays, plastic panels, and signs.

📌 Watch this Sheet Extrusion Video:
Plastic Behavior in the Sheet Extrusion Line

2. Flat Film Extrusion

• Used to produce thin plastic films for food wrapping, medical packaging, and shopping bags.

• The cooling and stretching process determines the film thickness.

3. Tubular (Blown Film) Extrusion

• Produces plastic bags and flexible packaging.

• Process:

  1. Melted plastic is extruded through a circular die.

  2. Air is blown inside to create a bubble.

  3. The bubble expands, cools, and flattens into a continuous sheet.

  4. The sheet is cut into bags or packaging film.

📌 Watch this Tubular Film Video:
Blown Tube of Film

🔹 Why it’s important?

• Blown film creates uniform, flexible, and stretchable plastic films.

4. Profile Extrusion

• Creates custom-shaped plastic profiles (e.g., window frames, door seals, and pipes).

• Process:

  • Plastic is forced through a custom die to achieve the desired shape.

📌 Watch this Profile Extrusion Video:
Profile Extrusion Process

🔹 Why it’s important?

• Used for structural plastic components with complex shapes.

5. Plastic Extrusion Design Opportunities

1. Wall Thickness

• Keep wall thickness uniform to prevent shrinkage or warping.

• Thin walls cool faster but may be weaker.

• Thicker walls are stronger but take longer to cool.

🔹 Why it’s important?

• Consistent wall thickness ensures structural integrity and uniform cooling.

2. Secondary Operations

After extrusion, additional processing can be done:

• Cutting: Parts can be cut into fixed lengths.

• Punching: Holes can be added.

• Drilling: Used for inserting screws or fasteners.

• Embossing: Adds surface textures or patterns.

🔹 Why it’s important?

• Secondary operations improve functionality but add costs.

3. Composite Profiles (Co-Extrusion)

• Co-extrusion allows multiple materials to be extruded together.

• Used to combine hard and soft plastics into one profile.

📌 Example Uses:

• Window frames with a rigid core and a soft sealing edge.

• Multi-layer pipes with different material properties.

4. Foamed Extrusion

• A blowing agent is used to create a lightweight, foamed plastic core.

• Reduces material use while maintaining strength and insulation.

📌 Example Uses:

• Foamed plastic decking

• Insulated panels

🔹 Why it’s important?

• Foamed extrusion creates lightweight, strong, and cost-effective parts.

5. Metal Embedment in Extrusion

• Metal wires, rods, or mesh can be embedded inside extruded plastic.

• Commonly used for:

  • Reinforced tubing

  • Electrical wire coverings

  • Structural plastic parts

📌 Watch this Metal Embedment Video:
Co-Extrusion & Metal Embedment

🔹 Why it’s important?

• Combining plastic with metal improves strength, durability, and conductivity.

6. Cost Factors in Plastic Extrusion

Several factors influence extrusion costs:

1. Material choice – Some plastics are more expensive.

2. Complexity of the die – More intricate shapes require higher tooling costs.

3. Production speed – Faster cycles reduce per-unit costs.

4. Post-processing requirements – Cutting, embossing, or drilling adds cost.

🔹 Why it’s important?

• Optimizing design and materials reduces manufacturing costs.

Week 1 (Part 2): Thermoplastics – Heat Forming, Fabrication & Vacuum Forming – Detailed Study Notes

1. Overview of Thermoforming

• Thermoforming is the process of heating plastic to just below its melting point and shaping it using a jig, vacuum, or mechanical pressure.

• After forming, the material cools and retains its new shape.

📌 Two Major Types of Thermoforming:

1. Heat Forming – Uses heat and jigs to shape the plastic.

2. Vacuum Forming – Uses heat and vacuum pressure to form the plastic onto a mold.

🔹 Why it’s important?

• Thermoforming is cost-effective for small-to-large parts with low internal stress and good surface detail.

2. Stock Plastics & Fabrication

Stock plastics are available in different forms:

• Sheet

• Profiles

• Film

• Tubes

• Rods

🔹 Why it’s important?

• Different stock forms affect the forming method used.

3. Heat Forming – Definition & Process

• Heat Forming involves heating plastic just below its melting point and forcing it to bend using a jig or fixture.

• Cooling is essential to retain the new shape.

📌 Key Tools Used in Heat Forming:

• Jigs and fixtures – Used to hold the material in place.

• Brake Press – Can cold-form Polycarbonate (PC).

📌 Watch this Heat Forming Video:
Heat Bend Acrylic

🔹 Why it’s important?

• Heat forming allows simple bends without the need for complex molds.

4. Common Fabrication & Cutting Methods

1. Score & Break (For Plastic Sheets)

• Plastic sheets can be cut by scoring and then snapping over a hard edge.

• Used for Acrylic and Polycarbonate.

📌 Watch this Cutting Video:
TAP Plastics - Score and Break

2. Bandsaw & CNC Cutting

• Bandsaws allow for curved and intricate cuts.

• CNC machines offer high precision for trimming.

🔹 Why it’s important?

• CNC cutting is commonly used in mass production.

3. Trimming & Finishing

• After forming, parts often require edge trimming.

• Methods include:

  • Polishing & Routing for smooth edges.

  • Deburring to remove rough edges.

📌 Watch this Finishing Video:
Polish and Rout Edges

5. Joining & Bonding Plastic Materials

• Common Joining Methods:

  • Adhesives & Solvent Bonding – Used for Acrylic and Polycarbonate.

  • Welding – Uses heat to bond plastic parts.

  • Mechanical Fasteners – Screws, nuts, and T-slot aluminum extrusions.

📌 Example:

• MiniTec T-Slotted Aluminum Frames are used for assembling plastic panels.

🔹 Why it’s important?

• Choosing the right bonding method depends on material type and application.

6. Vacuum Forming – Overview

• Vacuum forming is a type of thermoforming where heated plastic is pulled onto a mold using vacuum pressure.

📌 Process Steps:

1. Plastic sheet is heated until soft.

2. The soft plastic is placed over a mold.

3. A vacuum pulls the plastic tightly onto the mold.

4. The plastic cools and hardens.

5. Excess material is trimmed.

📌 Watch this Vacuum Forming Video:
Homemade Helmet Shell

🔹 Why it’s important?

• Vacuum forming is used for rapid prototyping and large-scale production of simple shapes.

7. Advantages & Disadvantages of Vacuum Forming

✅ Advantages:

• Low-cost tooling compared to injection molding.

• Can produce large parts with low internal stress.

• Shorter lead times (4-6 weeks for production).

• Pre-decorated parts possible (printed or textured sheets).

• Easy to modify molds for product changes.

❌ Disadvantages:

• Wall thickness varies, affecting part strength.

• Requires trimming, leaving raw edges.

• Plastic sheet cost is higher than pellet-based processes.

• Secondary operations (e.g., hole drilling) add costs.

🔹 Why it’s important?

• Vacuum forming is great for low-volume, large plastic parts but has material limitations.

8. Positive vs. Negative Molds in Vacuum Forming

Positive Mold (Male)

• The plastic is stretched over the mold.

• Requires more draft (5-7°) to release easily.

Negative Mold (Female)

• The plastic is pulled into the mold cavity.

• Requires less draft (2-3°).

📌 Why it matters?

• Positive molds create sharper outer details.

• Negative molds provide more control over inner details.

🔹 Test Tip:

• More draft is needed in positive molds to prevent sticking.

9. Draw Ratio in Vacuum Forming

• Draw Ratio = Surface Area of Product / Area of Sheet Available for Stretching.

📌 Typical Draw Ratios:

• Positive Molds: 1:1 (stretches more).

• Negative Molds: 0.6:1 (less stretching).

🔹 Why it’s important?

• Understanding draw ratios helps prevent tearing and thinning of plastic sheets.

10. Vacuum Forming Process Enhancements

• Plug Assist:

  • Pre-stretches the plastic before vacuuming.

  • Helps maintain uniform thickness.

📌 Example Uses:

• Deep-draw parts like food trays.

🔹 Why it’s important?

• Using plug assist prevents material thinning in deep molds.

11. Common Issues in Vacuum Forming

1. Webbing

• Excess material folds at corners.

• Fix: Adjust mold design or use plug assist.

2. Uneven Thickness

• Plastic thins in stretched areas.

• Fix: Optimize draw ratio.

3. Poor Surface Finish

• Caused by trapped air or dirty molds.

• Fix: Improve mold venting.

🔹 Why it’s important?

• Understanding defects helps in optimizing the vacuum forming process.

Week 1 (Part 2): Introduction to Polymers & Plastics – Detailed Study Notes

1. Introduction to Polymers & Plastics

• Polymers are large molecules composed of repeating structural units.

• Plastics are a subset of polymers that can be shaped and formed using heat.

• Used in industrial design, manufacturing, and product development.

📌 Two Main Classes of Polymers:

1. Thermoplastics – Soften when heated, harden when cooled (reversible).

2. Thermosets – Undergo a chemical reaction when heated, making the change permanent (non-reversible).

🔹 Why it’s important?

• Thermoplastics can be remolded and recycled, while thermosets are used for durable, heat-resistant applications.

2. Design for Manufacturing (DFM)

• DFM ensures that products are designed for ease of manufacturing while maintaining cost-efficiency, quality, and performance.

• Key considerations in design:

  • Function & Performance – Must meet product requirements.

  • Manufacturing & Assembly – Should be easy to produce.

  • Sustainability – Reduce waste and energy use.

  • Aesthetics & Usability – Must be marketable and user-friendly.

📌 Key Principle:
🔹 "Form follows function after manufacture."

• Products must be designed with manufacturing processes in mind.

3. Manufacturing Processes for Polymers

1. Thermoplastic Processing Methods

• Extrusion – Produces continuous plastic parts (pipes, films).

• Thermoforming – Heats plastic sheets to shape them over molds.

• Vacuum Forming – Uses suction to shape heated plastic over a mold.

• Extrusion Blow Molding – Used to make hollow plastic parts like bottles.

• Rotational Molding – Rotates a mold to form large, hollow objects.

• Injection Molding – Injects melted plastic into a mold cavity.

📌 Why it’s important?

• Understanding these processes helps in selecting the right method for different products.

2. Thermoset Processing Methods

• Compression Molding – Uses heat and pressure to form plastic parts.

• Reaction Injection Molding (RIM) – Uses chemical reactions to form solid parts.

• Composites Hand Layup – Used for fiberglass and carbon fiber products.

• Pultrusion – Continuous process for reinforcing fiberglass rods and beams.

🔹 Why it’s important?

• Thermosets are used for high-strength, durable applications where remolding is not needed.

4. Material Properties of Polymers

Key Material Properties:

1. Toughness – Ability to absorb energy without breaking.

2. Strength – Resistance to stress without failure.

3. Ductility – Ability to deform under tension (malleability).

4. Stiffness (Young’s Modulus) – Resistance to bending or deformation.

5. Electrical Resistivity – How well a material resists electrical flow.

📌 Study Tip:

• Know the difference between strength and toughness.

• Stronger materials resist force, but tougher materials absorb impact better.

5. Thermoplastics vs. Thermosets

Thermoplastics:

• Softens with heat, hardens when cooled (reversible process).

• Can be recycled and remolded multiple times.

• Used in packaging, automotive parts, and consumer goods.

📌 Examples:

• Polyethylene (PE) – Used for plastic bags and bottles.

• Polycarbonate (PC) – Strong and impact-resistant (used in helmets, eyewear).

• Nylon (PA) – Tough and flexible (used in gears, clothing).

• Polystyrene (PS) – Used in disposable cups and packaging.

Thermosets:

• Undergo a chemical reaction that permanently hardens the material.

• Cannot be remelted or remolded after curing.

• Used for high-temperature and high-strength applications.

📌 Examples:

• Epoxy – Used in adhesives and coatings.

• Polyester Resins – Used in fiberglass composites.

• Phenolics – Used for electrical insulation.

🔹 Why it’s important?

• Thermoplastics are recyclable, while thermosets provide high durability and heat resistance.

6. Amorphous vs. Crystalline Thermoplastics

• Amorphous Plastics:

  • Have a random molecular structure.

  • Clear and brittle (e.g., Acrylic, Polycarbonate).

  • Low shrinkage after molding.

• Crystalline Plastics:

  • Highly ordered molecular structure.

  • Opaque and tough (e.g., Nylon, Polypropylene).

  • Higher shrinkage after molding.

📌 Why it’s important?

• Amorphous plastics are used when transparency is needed.

• Crystalline plastics are stronger but shrink more after molding.

7. Shrinkage in Thermoplastics

• Polymers shrink as they cool after molding.

• Amorphous plastics shrink less than crystalline plastics.

📌 Implications for Design:

• Shrinkage must be accounted for in mold dimensions.

• Different plastics have different shrink rates.

🔹 Why it’s important?

• Ignoring shrinkage can cause dimensional inaccuracies in molded parts.

📌 Read more about Polymer Shrinkage:
Omnexus Shrinkage Guide

8. Measuring Hardness in Plastics

• **Plastics are measured on the Shore Hardness Scale.

  • Shore A: Soft, rubbery plastics.

  • Shore D: Hard, rigid plastics.

📌 Example Applications:

• Shore A (Soft plastics): Rubber gaskets, shoe soles.

• Shore D (Hard plastics): Hard hats, plastic casings.

🔹 Why it’s important?

• Shore hardness helps in selecting materials for different applications.

📌 Learn More:
Shore Hardness Guide

9. Stress & Strain in Polymers

• Stress: Force applied per unit area.

• Strain: Deformation caused by stress.

• Tensile Strength: Maximum stress before breaking.

📌 Types of Tensile Tests:

1. Yield Strength Test – Measures permanent deformation.

2. Ultimate Strength Test – Measures maximum force before breaking.

3. Elongation at Break Test – Measures how much a material stretches before failure.

🔹 Why it’s important?

• Understanding stress and strain helps in selecting durable materials.

📌 Learn More:
Xometry - Stress vs. Strain

10. Temperature & Melting Points

• Thermoplastics melt between 100°C and 300°C.

• Thermosets do not melt once cured.

📌 Why it matters?

• Different plastics require different molding temperatures.