The thermoforming process consists of the following steps:
1. Heating the sheet to the forming temperature
2. Pre-forming the heated sheet by preheating and stretching
3. Vacuuming the product to form the product
4. Cooling the product
5. Demolding the product
Mold forming is divided into male and female molds
I. Differences between Female and Male Molds
1. Structure
Female mold (concave mold): The mold surface is concave inward. During the vacuum forming process, the material covers the outside of the mold, forming the product.
Male mold (convex mold): The mold surface is convex outward. During the vacuum forming process, the material covers the inside of the mold, forming the product.
2. Product Appearance
Female mold: The outer surface of the product is smooth (the side exposed to air), and the inner surface may be rough (the side that contacts the mold).
Male mold: The inner surface of the product is smooth (the side that contacts the mold), and the outer surface may be rough (the side that contacts the mold).
3. Demolding Ease
Female mold: Demolding is easier because the plastic naturally escapes from the cavity as it cools and shrinks. Male molds: Demolding is more difficult, especially for deep-cavity products. Draft angles, air holes, or ejector mechanisms may be required.
4. Applicable Material Thickness
Female molds: Suitable for thinner materials (e.g., 0.2-1.0 mm) because they exhibit less stretching.
Male molds: Suitable for thicker materials (e.g., over 1.0 mm) because they require greater stretching.
5. Typical Applications
Female molds: Products requiring high appearance, such as food trays, cosmetic packaging, and electronic linings.
Male molds: Products requiring deep cavities or high interior wall precision, such as bathtubs, automotive interiors, and large industrial parts.
II. How to Choose a Female or Male Mold?
1. Choosing Based on Product Appearance
External surface requirements (e.g., printing, smoothness) → Female molds are preferred.
Internal surface requirements (e.g., dimensional accuracy, assembly structure) → Male molds are preferred.
2. Choosing Based on Product Shape
Shallow, flat products (e.g., trays, lids) → Female molds are more suitable, offering easier molding and faster demolding. Deep-cavity products (such as barrels and boxes) → A male mold is more suitable, but demolding issues need to be considered.
3. Selection Based on Production Efficiency
Large-batch production → A female mold is more optimal, offering faster cooling and easier demolding.
Small-batch or complex structures → A male mold with auxiliary demolding features (such as air blowing or ejector pins).
4. Selection Based on Cost
A female mold: Simple structure, low processing cost, suitable for projects with limited budgets.
Positive mold: Complex structures may require higher mold costs, but can ensure inner wall precision.
III. Practical Application Examples
1.Packing tray (such as fast food boxes) → A female mold: Ensures a smooth outer surface and good printing results.
2.Automobile dashboard covers → A male mold: Ensures precise inner wall dimensions and fits the part.
3.Medical trays (with card slots) → A female mold with a partial male mold structure: Balances appearance and functionality.
A female mold: Suitable for projects with high aesthetic requirements, shallow structures, and large-scale production. Male molds: Suitable for products with high inner wall precision, deep cavity structures, and special functional requirements.
Complex products: A male and female mold (compound mold) can be combined, but this is more expensive.
Choosing the right mold requires a comprehensive consideration of product design, material properties, production efficiency, and cost. Hopefully, this guide will help you make a more informed decision!
Comparison between positive and negative mold products
| Feature | Male mold products | Female mold products |
| Molding accuracy of products | On the inside | On the outside |
| Dimensioning (when drawing) | On the inside | On the outside |
| posterior margin area | Stretching causes thinning of the edges | The edges are not actually stretched and the wall thickness remains the same as the initial thickness |
| Thickest part | At the bottom | On the edge |
| Thinnest part | At the edge (transition to the sidewall) | At the bottom (transition to the sidewall) |
| Danger of quilt wrinkles | At the corner formed by the edge | No pleats formed |
Cooling marks on male forming parts. On relatively flat male molded parts, cooling marks most often appear at the top edge of the mold. During large stretching processes, cooling marks are pulled toward the sidewalls during the molding process. Cooling marks on female molded parts. Unlike cooling marks on male molded parts, during the molding process, the sheet material does not continue to slide down the sidewalls after contact with the mold at a certain point, resulting in cooling marks