Molding and Casting
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Objective of this Week
- Review the safety data sheets for each of our molding and casting materials
- Make and compare test casts with each of them
- Compare printing vs milling molds
💡 Moulding makes the mould, and casting uses the mould to make parts
Moulding
Moulding is a fundamental process in manufacturing, that involves shaping a material into a desired form using a rigid frame called a mould. This technique has been widely used across industries such as automotive, construction, packaging, and household appliances.
Types
| Type of Moulding | Description |
|---|---|
| Injection Moulding | Molten plastic is injected into a mould to form complex plastic parts. |
| Blow Moulding | Used for making hollow plastic parts like bottles using air pressure. |
| Compression Moulding | Preheated material is placed into a heated mould and compressed into shape. |
| Rotational Moulding | Mould is rotated in multiple axes to coat and form hollow plastic products. |
| Extrusion Moulding | Material is forced through a die to form long shapes like pipes and tubes. |
| Sand Moulding | Uses sand to create moulds for metal casting (common in foundries). |
| Die Casting | Molten metal is injected into a metal mould under high pressure. |
| Vacuum Forming | Heated plastic sheet is shaped over a mould using vacuum pressure. |
| Transfer Moulding | Material is heated, then transferred into a mould cavity (used for electronics). |
Image source
Casting
Casting is a manufacturing process where a liquid material is poured into a mold and allowed to solidify. The solidified part, known as a casting, is then removed from the mold. It is used to create complex shapes that are difficult to achieve by other methods.
Types
| Casting Type | Description |
|---|---|
| Sand Casting | Uses sand as the mould material; low cost, suitable for large components. |
| Die Casting | Uses metal moulds; molten metal is forced under pressure; high precision. |
| Investment Casting | Uses wax pattern and ceramic shell; high accuracy and fine surface finish. |
| Centrifugal Casting | Molten metal is poured into a rotating mould; used for cylindrical parts. |
| Shell Moulding | Uses a resin-coated sand shell; better accuracy than sand casting. |
| Permanent Mould Casting | Reusable metal moulds; better strength and surface finish than sand casting. |
| Continuous Casting | Used for metals like steel; molten metal solidifies as it flows continuously. |
Image source: https://www.plasticmoulds.net/types-of-plastic-molding-process/
Materials
Moulding Types
| Moulding Material | Description |
|---|---|
| Green Sand | Mixture of silica sand, clay, and water; commonly used in sand moulding. |
| Dry Sand | Similar to green sand but baked before use for better strength. |
| Plaster | Used for precise, thin-walled castings; not suitable for high temperatures. |
| Ceramic | Used in investment casting; can withstand very high temperatures. |
| Metal (Die) | Used in die casting; reusable and durable; typically steel or cast iron. |
| Resin-Bonded Sand | Sand mixed with synthetic resins for improved surface finish and strength. |
| Wax | Used as a pattern in investment casting; melts away during mould preparation. |
Casting Types
| Casting Material | Description |
|---|---|
| Cast Iron | Excellent fluidity and wear resistance; used in engine blocks, pipes. |
| Aluminium | Lightweight, corrosion-resistant; used in automotive and aerospace parts. |
| Steel | Strong and tough; used in heavy-duty machinery and structural components. |
| Copper Alloys (Bronze, Brass) | Good conductivity and corrosion resistance; used in plumbing and decorative items. |
| Magnesium | Lightest structural metal; used in aerospace and electronics. |
| Zinc | Good for die casting; low melting point and high precision. |
| Titanium | High strength-to-weight ratio and corrosion resistance; used in medical and aerospace. |
Moulding Types
| Moulding Material | Description |
|---|---|
| Green Sand | Mixture of silica sand, clay, and water; commonly used in sand moulding. |
| Dry Sand | Similar to green sand but baked before use for better strength. |
| Plaster | Used for precise, thin-walled castings; not suitable for high temperatures. |
| Ceramic | Used in investment casting; can withstand very high temperatures. |
| Metal (Die) | Used in die casting; reusable and durable; typically steel or cast iron. |
| Resin-Bonded Sand | Sand mixed with synthetic resins for improved surface finish and strength. |
| Wax | Used as a pattern in investment casting; melts away during mould preparation. |
Casting Types
| Casting Material | Description |
|---|---|
| Cast Iron | Excellent fluidity and wear resistance; used in engine blocks, pipes. |
| Aluminium | Lightweight, corrosion-resistant; used in automotive and aerospace parts. |
| Steel | Strong and tough; used in heavy-duty machinery and structural components. |
| Copper Alloys (Bronze, Brass) | Good conductivity and corrosion resistance; used in plumbing and decorative items. |
| Magnesium | Lightest structural metal; used in aerospace and electronics. |
| Zinc | Good for die casting; low melting point and high precision. |
| Titanium | High strength-to-weight ratio and corrosion resistance; used in medical and aerospace. |
💡 Safety Precautions
- Wear protective gear such as heat-resistant gloves, face shields, safety goggles, and flame-resistant aprons to protect against burns and splashes.
- Ensure proper ventilation to avoid inhaling harmful fumes, especially when working with materials like aluminium, zinc, and copper alloys.
- Handle molten metals carefully using appropriate tools like crucibles and tongs; never pour water on molten metal.
- Keep the workspace clean and dry to prevent accidents caused by moisture contact with hot materials.
- Be trained in emergency procedures such as handling metal spills, burns, and fire safety protocols.
💡 Safety Equipments
- Safety Goggles
- Rubber Gloves
- Face Mask
- Measuring Cylinder
- Measuring Cup
- Tongs
Polyurethane Casting Resin
Datasheet — Product details
| Brand | RapidCast / Example Brand |
|---|---|
| Product Name | Polyurethane Casting Resin Kit (Rigid) |
| System | Two-Part Polyurethane |
| Components | Part A (Resin) + Part B (Isocyanate Hardener) |
| Color | Amber / Translucent |
| Hardness | Approx. 75–85D (after full cure depending on formulation) |
| Curing Time | Initial set: 1–6 hours · Full cure: 24–72 hours (temperature dependent) |
| Mix Ratio | 2:1 by weight (Resin : Hardener) — check specific product label |
| Packaging | Varies — common: 1kg (667g Part A + 333g Part B) |
| Form | Liquid |
| Applications | Rapid prototyping, hard tooling, durable cast parts, industrial parts, small batch production |
| Purity | ~99% |
| Grade Standard | Industrial / Engineering Grade |
Key Features
- Fast cure and good dimensional stability
- High impact resistance and mechanical strength
- Good detail reproduction (when cast in well-prepared molds)
- Available in rigid and semi-flexible formulations
- Compatible with silicone molds and many release agents
- Low shrinkage compared to some polyester resins
User Instructions
Safety Precautions
- Work in a well-ventilated area or use local extraction.
- Wear nitrile gloves, eye protection, and an apron. Avoid inhaling vapors.
- If skin contact occurs, wash immediately with soap & water. Seek medical help for persistent irritation.
- Isocyanate-containing hardeners can sensitize — avoid prolonged exposure.
Preparation
- Ensure mold and workspace are clean, dry and free of contaminants.
- Use a mold release (commercial release or wax) suitable for polyurethane.
- Condition components to room temperature (20–25°C) before mixing for best flow.
Mixing
- Measure parts accurately by weight (use a calibrated scale) at the specified mix ratio (commonly 2:1 by weight).
- Pour the hardener into the resin (or follow manufacturer guidance) and stir slowly but thoroughly for 1–2 minutes, scraping sides and bottom.
- Avoid vigorous stirring to limit air entrapment. Some formulations benefit from a short vacuum degas if available.
Pouring
- Pour slowly into the mold from one side to allow air to escape.
- For deep casts, pour in stages or use controlled exotherm formulations to reduce overheating.
Curing
- Allow part to sit undisturbed at recommended temperature. Typical touch time: 1–6 hours, handleable after initial set.
- Full mechanical properties develop over 24–72 hours depending on ambient temperature and part thickness.
Removing
- Demold carefully using soft tools to avoid scratching or deforming the part.
- Post-cure (elevated temperature) may be recommended by the manufacturer to maximise properties—only if specified.
- Store unused components sealed, in a cool dry place away from moisture and direct sunlight.
Note: Mix ratio and safety precautions vary by manufacturer — always follow the product label and safety data sheet (SDS).
Unsaturated Polyester Resin (UPR)
Datasheet — Product details
| Brand | ClearCast |
|---|---|
| Product Name | Orthophthalic Unsaturated Polyester Resin |
| System | Two-Part (Resin + Peroxide Catalyst) |
| Components | Part A (Polyester Resin) + Part B (MEKP Peroxide Catalyst) |
| Color | Clear to Pale Yellow |
| Hardness | Approx. 70–80D after cure (varies with filler/fibreglass reinforcement) |
| Curing Time | Gel time: 5–30 minutes (depends on catalyst dose & temperature). Full cure: 24–48 hours. |
| Mix Ratio | Resin : Catalyst = typically 1–2% by weight of MEKP (manufacturer specified) |
| Packaging | Available in 1L, 5L, 20L drums |
| Form | Liquid (viscous) |
| Applications | Gel coat, laminating with fiberglass, mold making for concrete, casting small decorative objects (not ideal for deep casts) |
| Purity | ~99% |
| Grade Standard | Industrial / Marine Grade variants available |
Key Features
- Good mechanical strength when reinforced with fiberglass
- Fast cure options available for rapid lamination
- Cost-effective for larger molds and composite structures
- Good adhesion to many substrates when prepared correctly
- Not inherently UV-stable — requires UV-stabilised gel coat or additives for outdoor use
User Instructions
Safety Precautions
- Use gloves, goggles and ensure strong ventilation — styrene fumes can be irritating and harmful at high concentrations.
- MEKP is a strong oxidizer and can cause burns — handle in small measured doses and keep away from heat sources.
- Have a spill plan and refer to the SDS for first-aid procedures.
Preparation
- Clean substrate thoroughly; remove dust, oils and moisture.
- Use appropriate mold release for polyester systems (wax or PVA depending on finish needed).
- Maintain ambient temperature per datasheet (often 18–30°C) to control gel time.
Mixing
- Measure resin and then add catalyst at the recommended percentage (commonly 1–2% MEKP by weight). Do NOT exceed recommended catalyst amount.
- Stir thoroughly but avoid whipping air into the mixture. Work quickly — polyester gel times can be short.
Pouring/Laminating
- For casting thin items or laminating, wet-out the mold evenly. For fiberglass work use rollers to remove air pockets.
- For castings thicker than recommended, use incremental pours or a slow-curing variant to avoid excessive exotherm and shrinkage.
Curing
- Allow to cure at room temperature; full cure typically in 24–48 hours, depending on part thickness and ambient temp.
- Elevated post-cure (if compatible) will improve final mechanical properties and reduce residual styrene odor.
Removing
- Demold after the part is sufficiently firm — avoid demolding too early to prevent deformation.
- Trim excess flash with cutting tools. Sand and finish surfaces as required. Apply protective topcoat for UV exposure.
- Store components sealed and cool; peroxide catalysts should be kept cool and used fresh.
Note: Polyester resins emit styrene — use appropriate PPE and ventilation. Not ideal for high-detail thin castings without additives or specialized formulations.
CONCLUSION
For this group assignment we explored various materials used in the molding and casting process. To understand their individual properties, mixing ratios, and applications in mold-making. We studied two materials for this assignement Epoxy Resin and Moldsil 15 PLUS. By using the Material Datasheet, we learned how to calculate the required level of materials based on the design of our mold's size and how to properly mix those two-part systems (Part A and Part B) properly to get the better outcome.