All About PET Preform Moulds and Chair Moulds for Injection Molding


PET preform moulds and chair moulds are essential tools in the injection molding process of manufacturing PET preforms and plastic chairs. As an experienced injection molding industry content writer, I’ll provide a comprehensive overview of these important mould types – from their design and manufacturing to their use in mass production. Whether you’re just learning about injection moulding or are a seasoned professional, read on for an in-depth look at PET preform and chair moulds.

An Introduction to Injection Moulds

Before diving specifically into PET preform and chair moulds, let’s start with a quick primer on what injection moulds are and how they work.

Injection moulding utilizes moulds to form plastic resin into finished products. During the process, pelletized plastic is melted down and injected under high pressure into the mould cavity. The mould is precision-engineered with a specific cavity shape to create the desired plastic product.

Once the molten plastic fills the mould, it cools and solidifies into the final shape. The mould opens and the finished part is ejected. This enables high volume production of plastic parts in a continuous cycle.

Injection moulds are commonly made of steel or aluminum. The two main components are the:

  • Cavity – the negative space that forms the shape of the part
  • Core – the male portion that locks into the cavity

Precision CNC machining is used to mill the cavity and core pieces to exact specifications. The mould base houses these components and provides structure.

High quality moulds are essential for fast cycle times, dimensional accuracy, and overall productivity. Next we’ll look specifically at PET preform and chair moulds.

PET Preform Moulds

PET preform moulds are used to produce PET preforms through injection molding. PET stands for polyethylene terephthalate, a commonly used thermoplastic polymer resin.

PET preform moulds require extreme precision to meet tight dimensional tolerances, especially around the neck area. The preform neck gets blow molded into the bottle neck and threads, which must mate perfectly with bottle caps. For more information on quality PET preform mould manufacturing, check out this PET preform mould company.

Here are some key facts about PET preform moulds:

  • Made of pre-hardened steel, such as P20 or NAK80, for durability
  • Designed with a neck finish cavity, tube cavity, and bottom base cavity
  • Clamping force required is generally 120-200 tons
  • High precision required for neck finish dimensions
  • 16-128 cavity moulds common for mass production
  • Automated post-mold handling is standard

The injection molding process starts by plasticizing and injecting PET resin into the mould cavities. After cooling and solidifying, the mould opens and the preforms are ejected.

Preforms are then reheated and blown into bottles in a separate blow molding process. This two-step method allows preforms to be injection molded in high volumes, stored, and blown into bottles on demand.

PET preform moulds require extreme precision to meet tight dimensional tolerances, especially around the neck area. The preform neck gets blow molded into the bottle neck and threads, which must mate perfectly with bottle caps.

Preform moulds are engineered with multiple cavities, generally 16 to 128 cavities, to maximize production volumes. An expert mould maker can ensure optimal fluid flow, cooling, and overall efficiency.

Chair Moulds

Chair moulds are used to produce plastic chair parts through injection molding. From patio chairs to office chairs, injection molded plastic chairs are ubiquitous.Chair moulds require extensive machining and polishing to form the various chair components. For specialized plastic chair mould production, I recommend connecting with this chair mould manufacturing company.

Some key facts about plastic chair moulds:

  • Made from P20, NAK80, or beryllium copper alloy
  • Complex multi-cavity moulds common
  • Lifter mechanisms and slides often incorporated
  • High cooling efficiency needed
  • Automated demolding required
  • Polished surfaces for aesthetic parts

Chair moulds require extensive machining and polishing to form the various chair components. The two main plastic resins used are:

  • Polypropylene (PP) – For flexible, durable chair designs
  • ABS – For strong yet lightweight chairs

A single chair often requires several moulds – one for the seat, another for the backrest, others for legs and connecting pieces. Multi-cavity moulds allow multiple parts to be produced in each cycle.

Ejector pins, lifters, and slides are commonly built into the mould to aid in demolding undercut areas and flexible parts like chair backs. Quality cooling channels are essential to reduce cycle times.

For chair seats and backs that show, mirror-polished mould surfaces are needed to impart a glossy, aesthetic finish. Automated demolding is a must to enable efficient, hands-free part ejection.

Chair Mould Manufacturing

The manufacture of high quality chair moulds is an exacting process. It starts with the mould design according to the customer’s chair product specifications.

The mould maker then machines individual steel blocks into the core and cavity components. CNC milling technology allows precise machining tolerances within 0.005 inches.

Several rounds of trial fitting and adjustments are done to ensure the core and cavity mate accurately. The components are then hand polished and assembled into the final mould base.

Fully automated 5-axis CNC machining produces the most advanced chair moulds. For multi-cavity moulds, flow simulations optimize the runner and cooling layout.

Manufacturing technology has progressed rapidly, allowing more complex chair moulds to be made faster than ever. But skilled mould makers still play a vital role in ensuring mould perfection.

The Role of PET Preform and Chair Moulds

PET preform and chair moulds serve an invaluable function – they enable mass production injection molding of these ubiquitous plastic products. Without these moulds, we simply would not have the volumes of PET bottles or injection molded chairs needed globally.

Some key roles these moulds play:

  • Produce plastic parts within tight dimensional tolerances
  • Allow millions of parts to be molded consistently
  • Enable high production volumes and low unit costs
  • Impart fine surface finishes on end products
  • Produce technically challenging shapes that cannot be made otherwise
  • Represent significant upfront investments that are recouped over production runs

Brand owners rely on the quality and output of PET and chair moulds to meet consumer demand. Moulds also minimize secondary processing since parts eject molded to near-finished shape.

In the hands of a skilled mould manufacturer, even the most complex PET and chair moulds can be crafted to support the customer’s exact needs. The precision and repeatability provided by these moulds is critically important.

Factors That Influence PET Preform and Chair Mould Costs

PET preform and chair moulds require huge initial investments. But this is recouped over the lifetime production volumes of the molds. What are the key factors that influence the costs of these mould types?

Mould Size & Weight

Larger moulds require more raw material. A 16-cavity PET preform mould may weigh 2 tons, while a 128-cavity one over 10 tons. More steel equals higher cost.

Machining Complexity

Intricate mould shapes require extensive CNC programming and machining time, increasing costs. Deep undercuts and core/cavity layouts also add cost.

Tight Tolerances

Holding tighter tolerances demands precision machining and polishing, adding machining time and expense.

Mould Base Features

More advanced mould bases with hot runner systems, cam tracks, and precise temperature controls cost more.


Turnkey automated work cells require integration of robots, conveyors, and secondary equipment.

Cycle Requirements

Faster cycling moulds need optimal cooling designs and machining.


Higher cavity moulds boost initial cost but reduce per-part costs. They require balanced runners and cooling.

Surface Finishes

Mirror polishing and specialized coatings add cost for shiny chair moulds.

As you can see, many variables influence mould costs. An experienced mould maker can optimize these factors based on the product needs and budget.

Real World Examples of PET Preform and Chair Moulds

To make this all more concrete, here are two real world examples of PET preform and chair moulds.

72-Cavity PET Preform Mould

A PET preform mould maker was tasked with creating a 4-drop, 72-cavity system for making 28mm diameter preforms.

The mould components and base were CNC machined from P20 steel. The cavity and core halves were precision milled and polished to tightly hold +/- 0.005″ dimensional tolerances.

Special attention was given to ensuring consistent wall thickness and neck finish dimensions. The hot runner system was engineered for balanced fill across all cavities.

The mould was assembled, tested, and fine tuned to achieve a tight process capability index (Cpk) of 1.33. It was validated in production at 3 second cycle times and 8,640 preforms/hour.

16-Cavity Chair Mould

A chair manufacturer needed moulds for a new lightweight outdoor patio chair line. A mould maker engineered a two-piece family mould system.

The seat mould was 4 drops of 4 cavities each = 16 cavities. The backrest mould was also 16 cavities. Slides, lifters, and side cores were incorporated to allow flexibility and optimal cooling.

Both moulds were machined from NAK80 steel for strength and machining stability. Extensive hand polishing ensured glossy, aesthetic chair surfaces.

In production trials, the moulds consistently produced parts within 0.3mm of specifications. Cycle times averaged 45 seconds owing to the optimized cooling designs.


PET preform and chair moulds are prime examples of the invaluable role injection moulds play in enabling volume plastics manufacturing. Without these precisely engineered “parent” tools, we would simply not have access to the many PET and plastic products we rely on daily.

In the right hands, even the most challenging mould projects can be brought to fruition successfully. Mould makers must balance numerous technical and commercial factors to craft moulds that meet the customer’s needs.

I hope this article served as a helpful introduction to PET preform and chair moulds for injection molding. Please reach out if I can assist with any mould projects or provide more information from my 20 years in the industry.