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Difference Between Injection Molding and Blow Molding

Difference-Between- Injection-Molding-and-Blow-MoldingMost people in the plastics manufacturing industry are familiar with both blow injection molding and blow molding these days. However there is still some confusion by product designers and engineers new to the industry about the difference between injection molding and blow molding . The blow molding process has become a standard for specific applications and understanding the differences between these two plastic molding processes can save design, prototyping and production time. This of course results in money savings and increases the speed of completion and delivery of your plastic part.

There are several significant differences between injection molding and blow molding:

  • manufacturing process itself
  • tolerances and margins of error
  • design considerations
  • role of the process for intended result

Main difference between injection molding and blow molding:

  • Injection molding – produces a part that is solid such as a reusable coffee cup lid
  • Blow molding – produces hollow parts such as water bottles

The blow molding process can produce plastic parts with very complex shapes. However to achieve this the wall thickness may vary from place to place depending on how much the material has to stretch when it is being blown. The thickness of a plastic part created through injection molding is determined by the relationship of the mold and the core.

You will be farther ahead if you are able to determine the best molding process for your plastic product in the product development stage. 

Be prepared to answer a lot of questions from plastic mold engineers:

  • How is your plastic part going to function?
  • Is it a stand alone item?
  • Is it a part that connects to other parts or works in tandem with other parts to achieve a result?
  • Does it need to pivot, move, expand, condense?
  • Is the weight critical to the function?
  • Will the part need to withstand extreme levels of cold or heat?
  • Does the item need to adjust to specific pressure levels or PSI?
  • Will the part hold fluids?
  • Does it need to be food safe?
  • Does it need to be flexible or does it need to be solid and rigid?
  • What length does the part need to be, width, depth?

Answering these questions when designing and manufacturing any item is good a idea. With items requiring plastic molding the large variety of plastics to choose from, the importance of accuracy, and the difference between injection molding and blow molding it’s best to determine these answers as soon as possible. When one millimeter size difference can make the item usable or unusable for its intended purpose, accuracy and creative solutions are required. That’s why we have engineers, right?

Custom Plastic Molding Solutions

Because of the many variable in producing molded plastic parts, nearly every part we produce requires a custom solution. Engineers review all variables based on the end use of the product.

Variables to consider in Molded Part Production:

  • type of plastic used
  • flexibility or strength
  • psi pressure rate required
  • withstand temperatures levels – hot or cold
  • wall thickness
  • product dimensions

Once these variables are considered the whole process will go much smoother and quicker. The use of 3D printers in the prototype stage helps to reduce time too. Designing molds and fine tuning them to perfection can take a few tries but once complete production can begin.

When injection molding is determined to be the best process for your plastic part once you have an approved mold you’re practically golden. The injection molding process begins, the product is produced and there is very little concern of production issues with the injection process.

Therein lies another difference between injection molding and blow molding. In the blow molding process getting the mold perfect is only part of the battle. During the blow molding production process there are many variables manufacturers must pay attention to. The iterative nature of the blow molding process lends itself to production variables.

Periodically checking the production line is important for quality control. If the plastic is stretched too much small pin holes or cracks in seals can result. Checking for wall thickness uniformity to ensure they are within the tolerances needed for the part to behave as it is intended is also critical. As an example, a plastic bellows is made to collapse when pressure is applied and then expand back to it’s original form once pressure is released. Consistent wall thickness helps the bellows to function correctly. If the plastic bellows collapses on one end faster than the other because the wall is thinner your plastic part may wear out quicker and may not function smoothly. Having sold process control systems in place will produce consistent parts with high quality function.

Blow Molding Production Concerns:

  • pinhole leaks
  • leaking seals
  • flexibility or strength
  • velocity or pressure of blown air
  • speed of the mold closing
  • process temperature
  • wall thickness
  • poor function
  • consistent product dimensions

You can learn more about the various plastic molding processes that are applicable to your product or new invention at Plastic news.

Do you have a new plastic product invention and you aren’t sure about which plastic mold process is the best solution for your item? Give SPI a call today, our engineers love a challenge! We will help guide you in the most appropriate and cost efficient plastic molding solution for your unique requirements.

3d printer plastic prototype a type of prototype for your plastic part

Benefits of 3D Printers for Plastic Prototypes

3d printer plastic prototype for plastic manufacturingDo you have a product invention that you think is ready to go to market? Whether you are an established company or a start-up entrepreneur manufacturing plastic prototypes can be costly and time consuming. Historically many new product design concepts never hit the market because of the time and expense involved in creating the prototype to prove the value to investors or stockholders.

Most of the product inventors on Shark Tank would never be able to step foot on stage if they had to rely on traditional plastic manufacturing methods to make their first product prototype! Fortunately the techies have come to rescue to reduce plastic prototype manufacturing costs. Whether your product prototype will be used in the furniture, agricultural, lawn and garden or even appliance or automotive industry a 3-D printer can be a game changer. Inventors and companies with new product lines can now have detailed prototypes without the expense and time commitment of a full production.

Benefits of a 3D Printer for Plastic Prototypes:

  • considerably less cost
  • considerably less time to produce
  • no need to secure factory space
  • no production line set up
  • no jigs or fixtures or expensive dies required
  • low cost for supplies / prototype material
  • reduce or eliminate shipping and procurement cost
  • plastic prototypes can be created in less than a day

The 3D printer specifications for SPI Blow Molding and SPI Injection molding can be found here. A 3D printer can be the solution for many inventions or newly revised plastic parts. Whether the finished part or finished product will require blow molding or injection molding, SPI can provide a quick and inexpensive prototype in your hands within days. All that’s needed are the specifications for the plastic part or plastic product you want to manufacture. SPI will create a design based on your specifications and develop it for the 3D printer and you will have a prototype.

Once a 3D plastic prototype part is tested fine tuning can be done to the design until a final prototype is approved for manufacturing. Production of plastic parts and products can be handled through the SPI Injection Molding plant or SPI Blow Molding plant depending on the product design.

Inventors and designers rejoice – you don’t have to break the bank to get your new product to market when a 3D printer and plastic prototypes allow you to create mock ups inexpensively and quickly until you achieve the perfect product you envisioned.

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