PCB Assembly Graphic

How Much Does Plastic Parts Manufacturing Cost?

Plastic injection molding manufacturing

Plastics are a very good fit for manufacturing and their use becomes, even more, cost-effective as volume increases. 

Plastics are used to fabricate products in every major industry such as medical, automotive, electronics, housewares, etc due to their cost advantages. 

Besides cost, plastics are often used in high-volume manufacturing due to the consistency of parts and the wide range of mechanical properties available through plastic material selection. 

The purpose of this article is to inform you about how plastic part pricing is determined in manufacturing and how the number of cavities is driven by sales forecasts

The Basic Economics of Plastic Parts Manufacturing

Plastic Manufacturing Setup

It’s helpful to have a basic understanding of how plastics manufacturing operates and how manufacturers charge their customers. 

  • A mold first needs to be installed into the molding machine, typically using an overhead crane system. The mold is installed into the molding machine by bolting the mold to the molding machine platens. 
  • Meanwhile, the molding machine is heating up to temperature, new plastic is loaded into the molding machine, and after reaching temperature the old plastic material in the molding machine barrel is purged and primed with new plastic. 

This process of installing the mold and purging material is called “setup”. This is a separate fee that the manufacturer charges either at a fixed price or at an hourly rate.

Multiple factors contribute to mold setup costs:

  • First, setup requires molding technician labor.
  • Meanwhile the molding machine is offline and not producing parts during setup.
  • Also, several pounds of plastic are consumed to purge the old material in the molding machine barrel.

The setup fee charged typically doesn’t provide profit to the manufacturer. The manufacturer is only seeking to cover their expenses, understanding that customers tend to be averse to a large setup charge. The manufacturer does everything possible to minimize the number of setups because they are expensive and disruptive to normal manufacturing.

Machines Manufacturing Plastic Parts
Manufactured Blue Plastic Parts

Hourly Prototype Plastic Injection Molding Machine Rate

The manufacturer will typically have an hourly rate that they charge per molding machine. However, the molding machine hourly rate doesn’t have any meaning to customers, so it is converted to cost per part. After all, that’s the key information that the customer needs to know, how much will each part cost? We’ll get into how to make that conversion later.

The hourly molding machine rate needs to cover these items:

  • Electricity to run the machine,
  • Staff to supervise the machine running, facilities, and other overhead.
  • Sometimes the hourly molding machine rate includes the cost of plastic, but some manufacturers charge the customer for plastic separately.

The Effectiveness of Mold Cavitation

Here’s an example to illustrate the machine rates. Let’s assume an hourly molding machine rate of $130/hr.

To convert this to the “cost per part” that is quoted to the customer we need to know two things: 

  • The cycle time of the molding process, and
  • The number of cavities in the mold.

Cycle time means how long each cycle (in seconds) is required to complete all stages of the injection molding process one time. 

From the cycle start, injection molding includes these steps: 

  • Mold closing,
  • Plastic injection into the mold,
  • Cooling/dosing (completed in parallel, dosing is when the next plastic shot is loaded in the barrel), mold opening, and
  • Part ejection from the mold.
Clear Plastic Injection Molded Parts being manufactured in facility
White Plastic Injection Molded Parts in Container

As the number of mold cavities increases, injection molding cost per part decreases. Continuing the example from above let’s assume that we are using an 8-cavity mold. This means that every time the mold opens and parts are ejected, 8 parts fall out of the mold. Let’s assume a cycle time of 30 seconds. Every 30 seconds yields 8 parts.

Step 1 – Calculate how many cycles are completed per hour by dividing 3600 seconds per hour by the cycle time.

\((\frac{3600 sph} {30 pph}) = 120 cph\)

Step 2 – Calculate the number of parts per hour by multiplying the cycles per hour from step 1 by the number of mold cavities (parts per cycle)

\(120 cph * 8 ppc = 960 pph\)

Step 3 – Calculate the cost per part by dividing the machine rate per hour by the number of parts per hour from step 2.

$ \((\frac{130 ph}{960 pph}) = 13.5   \) cents per part for an 8-cavity mold

Keep in mind this calculation is a simplification. The actual calculation is more complex including an assumed reject rate, less than 100% efficiency, and other factors but for the purposes of this article, the simplified calculation is sufficient to see the beneficial effect of increasing cavitation to cost.

Let’s repeat steps 2 and 3 but let’s assume a 32-cavity mold.

\(120 cph * 32 ppc = 3840 pph\)

$ \((\frac{130 ph}{3840 pph}) = 3.4 \) cents per part for an 32-cavity mold

Protoshop and Mold Fabrication

Your first reaction after reviewing the calculations might be “sign me up for a 32-cavity mold or larger. I like the lower price much better”. However, selecting the number of mold cavities is not that simple. Production mold fabrication cost and lead time increase substantially with the number of cavities. It’s critical to have an accurate estimate of the sales forecast over the next 3-5 years. The number of cavities to build is determined by developing a mold fabrication strategy that will meet sales projections.

Sales forecast example:

Year 1

Year 2

Year 3

Year 4

Year 5

500,000 ea

1,000,000 ea

2,000,000 ea

3,000,000 ea

4,000,000 ea

 The 8-cavity mold will provide approximately 5 million parts per year and the 32-cavity mold will provide approximately 20 million parts per year. Although the part price is attractive for the 32-cavity mold it wouldn’t make sense financially or by the capacity to invest in such a large mold. The 8-cavity mold would cover all forecasted molding needs for the first five years. Again, this is a simplification. There are scenarios where fabricating 2 ea 4-cavity molds would make sense as well. 

I hope this insight into how plastic part costs are determined in manufacturing and the power of cavitation to reduce those costs has been helpful. Feel free to contact Dylann Ceriani at Protoshop (888) 316-3334 x2 or send an email to dceriani@protoshopinc.com if you have any further questions.

Based on 7 reviews
Dana Taylor
Dana Taylor
If you're in need of a molding prototype shop, Dylann and Jimmy at Protoshop are sure to not only meet but exceed your expectations. Their team demonstrates remarkable responsiveness and proactiveness, contributing to an exceptionally efficient overall process. The speed at which they deliver top-notch work is truly impressive. Protoshop's commitment to customer satisfaction is apparent in their flexibility and willingness to closely collaborate with clients to address specific needs. An exemplary instance of this was their accommodation of our request to have our customer onsite for part evaluation and mold changes while we were present. What sets Protoshop apart is not solely their technical proficiency but also their dedication to providing valuable insights and design advice. Their expertise extends beyond standard projects, showcasing proficiency in handling complex components for diverse applications, be it over-molded sealing parts or flexible components. In conclusion, if you're on the lookout for a reliable and efficient partner for your manufacturing and molding requirements, I wholeheartedly recommend Protoshop. Their combination of expertise, responsiveness, and commitment to customer satisfaction makes them an exceptional choice for a variety of projects.
Brittany Mason
Brittany Mason
I have worked with Photoshop on several mold designs over the past year. From the moment I reached out to them with an inquiry, they were prompt in their communication and eager to assist me. I have greatly appreciated and benefited from their extensive expertise and prompt feedback. They consistently offering valuable suggestions and insights that ultimately saved us money in the overall design. As for the quality of work they provided, Dylann and her team have always come through. If any issues do arise, they have been quick to offer solutions and kept us up to date throughout the whole process. If you're looking for a reliable partner for your plastics molding needs, I would check them out.
Stacie Depner
Stacie Depner
Having worked with Dylann and Jimmy prior to Protoshop, I knew the immense level of expertise they have for this business and it proved to carry through. They are honest straight shooters that will help guide you and find the best solution for your molds. We needed a mild that could be versatile and allow us to easily change out one side of the design. Dylann helped us come up with an approach that will allow us to continuously iteration the design without having to make a whole new mold every time.
Chad Follmar
Chad Follmar
Dylann and team are wonderful to work with. On multiple programs, they have delivered quality product in a matter of days. The design for moldability support is unparalled to ensure your part is ready to order.
Garrett Garner
Garrett Garner
We work regularly with Protoshop on a variety of complex components for various projects. They are an excellent company to work with providing a vast history of experience to help their clients optimize designs. We have worked with them on microfluidic chips with small feature sizes, over molded sealing parts and flexible parts. They have experience working with many materials including Topas (COC), polycarbonate, TPE, PE, and PP. I would highly recommend reaching out on your next project. The team is very responsive to design changes as well as delivering to tight timelines. They also offer design advice and best practices which have helped expedite design iterations.
Steven Soeder
Steven Soeder
Great experience with Protoshop. Dylann is extremely responsive and great to work with. Very fast turn-around. Worked with us on our order to get what we needed. I was able to drop ship 3d printed parts from another vendor to Protoshop to have them match-fit and incorporated into our tooling. I will be back again.
Wendell Woidyla
Wendell Woidyla
Dylann at Protoshop is excellent to work with: highly responsive and proactive. This is possibly the fastest, high-quality work I have ever witnessed. 1 week...from payment (start) to delivery (after CTQ measurements at Protoshop), we had 100 test samples of a component we intend to use in high volume manufacturing. Thank you for the tremendous work! I would highly recommend Protoshop, and will plan to use Protoshop services in the future.