In-Depth Analysis of Injection Molding and Blow Molding Processes — Equipment and Molds Edition

There’s a story in every cup, warmth in every life. Hello everyone, and welcome to "Dong Dong's Cup Talk" In our recent posts, some friends have privately messaged us asking about the differences between injection molding and blow molding. In fact, comparisons and analyses of these two processes are widely available online, including on a certain well-known search engine — just type in “differences between injection and blow molding,” and you’ll find extensive comparison articles. https://www.umbottle.com/ProductsDetail-IR-10109.htmlWe don’t need to show off amateur skills in front of experts, but as we’ve mentioned before, whenever friends have questions, we’ll do our best to answer them. Especially after reading many online comparison articles, we thought it would be helpful to explain the differences between these two processes in our own way, making it easier for everyone to understand.

In our sharing, we’ll focus on daily necessities, electronic products, and the cup and bottle industry — our area of expertise. We’ll explain the process principles, equipment selection, material compatibility, and some case studies in an easy-to-understand manner. We hope you find it helpful. If our content proves useful, please don’t forget to give us a like. https://www.umbottle.com/ProductsDetail-IR-10109.htmlAnd if you want to stay updated with our future posts, be sure to follow us.

Every bit of your support is the driving force behind our tireless efforts. Oh, and by the way, our factory not only produces stainless steel cups but also plastic cups. https://www.umbottle.com/ProductsDetail-IR-10109.htmlWe also handle the production of various plastic molds and process food-grade plastic products. Hahaha, this isn’t an ad — really, it’s not!

II. Core Differences in Equipment and Mold Design

1. Injection Molding Equipment and Molds

Equipment Selection:

Clamping force must be selected based on the projected area of the product (formula: clamping force ≥ projected area × material pressure coefficient). https://www.umbottle.com/ProductsDetail-IR-10109.htmlFor example, the pressure coefficient for PP material is 0.3-0.4 tons/cm².

Mold Design:

Considerations include gate location (pin gates are suitable for appearance parts) and cooling channels (conformal cooling channels can reduce cooling time by 20%).

Classic Case: Development of Two-Tone Plastic Cup Lids

- Requirement: A 100mm diameter cup lid with an outer layer of PP and an inner layer of TPE soft sealing ring.

- Solution:

- Use a two-color rotary injection molding machine https://www.umbottle.com/ProductsDetail-IR-10109.html(e.g., Haitian MA1600Ⅱ, with a rotary accuracy of ±0.01mm).

- Employ a rotary mold structure: first inject the outer layer, then rotate and inject the inner layer.

- Cost Difference:

- The conventional single-color machine + secondary processing approach yields only 85% efficiency, https://www.umbottle.com/ProductsDetail-IR-10109.htmlwhile two-color integrated molding achieves 98% efficiency.

- Mold cost increases by ¥200,000, but the per-unit cost decreases by ¥0.2.

2. Blow Molding Equipment and Process Selection

- One-Step Method (Parison formation and blow molding completed continuously): Suitable for high-transparency PET bottles.

- Two-Step Method (Preformed parison is reheated and blow-molded): https://www.umbottle.com/ProductsDetail-IR-10109.htmlSuitable for HDPE milk bottles.

- Injection-Stretch-Blow Method: Axial stretching enhances strength, making it suitable for PCspace cups.

Classic Case: Development of Panda-Shaped Plastic Cups

- Challenge: Complex curved surfaces such as ears and facial depressions easily lead to uneven wall thickness.

- Solution:

- Use a one-step injection-stretch-blow molding device (e.g., SIPA SBO 20, https://www.umbottle.com/ProductsDetail-IR-10109.htmlwith a stretch ratio control accuracy of ±2%).

- Add a localized cooling system to the mold and control the parison temperature gradient between 85-95°C.

- Cost Comparison:

- The traditional two-step method achieves only 75% efficiency, https://www.umbottle.com/ProductsDetail-IR-10109.htmlwhile the one-step method improves efficiency to 92%.

- However, equipment investment increases by 50%.