What Is Compression Blow Forming? Process, Benefits & Applications

High-density polyethylene (HDPE) is a staple in pharmaceutical packaging, and for good reason. Where medicines were once stored in glass bottles, nowadays HDPE bottles provide a cost-effective, versatile, and more durable alternative.

Typically, these bottles are manufactured using a technology called Injection Blow Molding (IBM), which has been the standard for decades. However, companies and their [product teams] now have more choice than ever, thanks to a new method called Compression Blow Forming. While both methods deliver high-quality results in HDPE packaging, compression blow forming is quickly becoming the go-to for certain applications. 

What Is Compression Blow Forming?
Compression blow forming is a breakthrough process technology that combines compression molding and blow molding to better meet the rigorous demands of pharmaceutical manufacturers. 

Unlike injection molding or blow molding, where thermoplastic is melted into a liquid before being injected into a mold, compression blow forming is a continuous rotary process. Where these other methods require starting and stopping production at each stage, compression blow forming eliminates station-to-station indexing time. In simple terms, this means idle time is virtually eliminated from the manufacturing process. 

Along with shortening cycle times, compression blow forming also produces high-quality products while reducing cost and material waste. 

How Does Compression Blow Forming Work?
The compression blow forming process starts by introducing resin into a continuously operating extruder. The extruder keeps a constant supply of resin flowing, which is then cut into pellets. After pellets are cut, they’re sent into an open compression mold. Here, a neck ring brings the plastic preform through the continuous rotary motion with the compression and blow mold assembly. 

Each assembly is synchronized together by servo motors, motors with an encoder that allows it to control its position and speed, with a plastic shot transfer arm assembly. At this point, the machine enables process sequencing, plastic shot insertion, compression, and pre-blow of the preform, and a final blow to finish the container before the end result is ejected.

All of this is achieved in the same mold station, without parison transfer. Not only does this significantly reduce production cycle times, but it also results in an overall better quality product.

How Is Compression Blow Forming Different?
Compared to other plastic molding techniques, CBF is unique in its precision and strength. These factors allow compression blow forming to succeed where similar processes like extrusion blow molding and thermoforming can sometimes fall short. 

Compression Forming vs. Blow Molding
While extrusion blow molding allows a variety of shapes to be formed by forcing liquid plastic into a die, it often requires post-production finishing. For example, HDPE bottles need to be cut to the right length after they’re formed, adding to production time.

In compression blow forming, a precise shape and cut are achieved directly in the compression mold, reducing or eliminating post-production work.

Compression Forming vs. Thermoforming
In thermoforming, large sheets of plastic are heated over a single-sided mold until they’re flexible enough to be compressed into the mold. It’s a simple process, but not a versatile one. What’s more, this technique can create uneven thickness across completed parts, causing weak points.

Because compression blow forming uses a pre-blow process, parts come out stronger, thanks to a more consistent weight distribution. 

Compression Blow Forming Applications
Compression blow forming is specifically designed to enhance the production of rigid plastic containers. As such, it’s an ideal method for manufacturing commercial HDPE pharmaceutical bottles between a range of 45 and 500 cc. 

Advantages of Compression Blow Forming
As the global health industry grows, production must be able to keep up with rising demand. Over the past few years, the pharma blow-molded bottle market has experienced exponential growth, making new innovations like compression blow forming essential. And for companies using compression blow forming HDPE bottles, the benefits are plentiful.

Advantages of compression blow forming include:

Higher quality: Because compression blow forming doesn’t use a manifold hot runner system, there are no temperature differences when parts are distributed to their respective mold cavities. This means the plastic resin can cool down before being compressed into the preform, lowering the risk of resin burning or degradation. Ultimately, this results in stronger, higher-quality products.

Additionally, the rotary motion and speed of the pre-blow process allow a higher level of precision in separating plastic from the compression core. This leaves parts with a more uniform wall thickness distribution, while also reducing the chance of excess of material that leaks from the intended boundaries of a mold.

Improved productivity: Lower temperatures during the compression blow forming process mean there’s less heat to remove after blowing. There’s also a secondary cooling process after products are removed from the conveyor. This novel approach to heating, along with the continuous rotary motion of the machine, reduces cycle times.

Enhanced sustainability: Lower temperatures during production also translate into meaningful reductions in energy usage, bringing both cost savings and sustainability benefits.

Lightweighting options: Compression blow forming also allows for lightweighting, a process that refines product designs to remove excess materials. This results in products that are lighter, stronger, and use less material, all without compromising on quality. By using less material and energy, lightweighting can also deliver cost savings. 

Innovation That Meets the Moment
Every detail counts in pharmaceutical manufacturing. That’s why we partner with the world’s leading machine, tooling, and automation manufacturers to keep innovation moving forward. Some of our newest technologies include compression blow forming for pharmaceutical bottles, along with Direct Co-Inject^® processing for child-resistant closures.

Your products deserve to be made with best-in-class technology and expertise. At Alltrista, we combine both to help you unlock every possibility. Reach out today to learn more about manufacturing with high-impact compression blow forming.