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What Kind of Mold Do I Need and How Much Will It Cost?

November 6, 2017

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What Kind of Mold Do I Need and How Much Will It Cost?

November 6, 2017

 

Why Molds Are So Important

 

The injection mold is one of the most critical and expensive components of a plastic injection molding project.


It's a complex, precision piece of equipment. It must operate flawlessly at high temperatures and high hydraulic pressure - and over thousands or millions of cycles.

 

Effective molds integrate parts design, mold design, and the resin used to make the part with the customers’ market penetration plans and volume requirements.

 

Plastics industry expert Clare Goldsberry has an excellent overview of molds in her book So, You Think You Have a Great Idea! – The Inventor’s Guide to the Process of Plastic Parts Design, Development and Manufacturing (available from https://www.amazon.com.)

 

The book’s a non-technical, concise guide to the entire injection molding process from idea inception to reaching the market and well worth reading.

 

She defines a mold as “a metal form with one or more cavities in the inverse shape of the part or parts to be molded.” It forms the parts when molten plastic is put into it.

 

The most common questions we get about about molds, particularly in the early stages of projects, are:

  1. What kind of mold do I need?

  2. How much will it cost?

The answer, of course, is that “it all depends.”

 

If you’re wondering on what it depends on, keep reading. Here’s an introduction to plastic injection molds. and the fundamental choices that drive their selection and cost.

 

How Molds Are Classified

 

Molds are typically made from high grade hardened steel for high and medium production volumes and may be made from milder steels or aluminum for lower volumes or prototype development.

 

They’re classified by the Society of the Plastics Industry on the scope of the work to be done, the mold’s material, and the plastic resins that will be used to mold the parts.

 

Here are the classifications for commonly used molds up to 400 tons:

 

CLASS 101 MOLD


Cycles: One million or more*

 

Description: Built for extremely high production. This is the highest-priced mold and is made with only the highest quality materials.

  • Detailed mold design required.

  • Mold base to be a minimum of 280 BHN (Brinell Hardness Number**).

  • Molding surfaces (cavities and cores) must be hardened to a minimum of 48 R/C range. All other functional details should be heat treated.

  • Temperature control provisions to be directly in the cavities, cores, and slides wherever possible.

  • Parting line locks are recommended for all models.

  • The following items may be required depending on the ultimate production quantities anticipated. They should be made a firm requirement for quoting purposes:

    • Guided ejection

    • Slide wear plates

    • Corrosive resistant temperature control channels

    • Plated cavities

 

CLASS 102 MOLD

 

Cycles: Not exceeding one million*

 

Description: Medium to high production mold, good for abrasive materials and/or parts requiring close tolerances. This is a high quality, fairly high-priced mold.

  • Detailed mold design required.

  • Mold base to be a minimum of 280 BHN (Brinell Hardness Number).

  • Molding surfaces (cavities and cores) must be hardened to a minimum of 48 R/C range. All other details, such as slides, heel blocks, gibs, wedge blocks, etc. should also be of hardened tool steels.

  • Ejection should be guided.

  • Slides have wear plates.

  • Temperature control provisions to be in cavities, cores, and slides wherever possible.

 

CLASS 103 MOLD
 

Cycles: Under 500,000*

 

Description: Medium production mold. This is a popular mold for low to medium production needs. Most common price range.

  • Detailed mold design required.

  • Mold base to be a minimum of 165 BHN.

  • Cavities and cores must be 280 BHN or higher.

  • All other components are optional.

CLASS 104 MOLD
 

Cycles: Under 100,000*

 

Description: Low production mold. Used only for limited production preferably with non- abrasive materials. Low to moderate price range.

  • Mold design recommended.

  • Mold base can be of mild steel or aluminum.

  • Cavities can be aluminum, mild steel or any other agree upon metal.

  • All other components are optional.

CLASS 105 MOLD


Cycles: Not exceeding 500*
 

Description: Prototype only. This mold will be constructed in the least expensive manner possible to produce a limited quantity of prototype parts.

  • May be constructed from cast material, epoxy, or any other material strong enough to the required quantity of prototype parts.

 

Notes:

 

*Cycles are approximate and for comparison only.

** Learn about Brinell Hardness Numbers at https://www.youtube.com/watch?v=RJXJpeH78iU.

 

These classifications are for mold specifications only and in no way guarantee workmanship. It’s important that buyers deal with vendors whose workmanship standards and reliability are proven.

 

How Big Can Molds Be?

 

Molds can have single or multiple cavities and cores. Multi-cavity molds have 2, 4, 8, 16, 24, 36, etc. cavities. There’s also a “family” mold that has cavities that mold different parts at the same time.

 

See how molds are made at https://www.youtube.com/watch?v=seZqq1qxW30.
 

Things to Consider When Buying Your Mold

 

1. Injection molded parts are only as good as the mold that produced them.

Buy the right mold for your job. Find the mold class that provides the optimal combination of price, cycle time, uptime, and parts quality.

 

2. Consider the mold’s total cost of ownership, not just its price.

 

Maintenance and defect rates are two often overlooked ownership cost drivers. Excessive amounts of either can have a major impact on the average unit costs of the usable parts produced, particularly those made at high volumes using expensive engineered resins.

 

Molds are depreciable assets. This means there’s a potential for tax savings! under the IRS’s Modified Accelerated Cost Recovery System (MACRS), injection molds are Asset Class 30.21 and have a three-year recovery period. A $50,000 plastic injection mold’s first year depreciation is $16,667 using the half year convention, for example.
 

Check out IRS Publication 946 How To Depreciate Property @ https://www.irs.gov/pub/irs-pdf/p946.pdf) and check with your accounting team or financial advisors for details on the depreciation effect on your P&L.

 

3. The cheapest mold may not produce the lowest price parts.

 

All molds are not created equal. Designing injection molds is both a science and an art. It’s unlikely that two (or more) mold designers will design identical molds. Caveat emptor. You get what you pay for so know who you’re dealing with.

 

Remember, the goal is lowest total cost of ownership – not lowest mold price.

 

And don’t forget Murphy’s Law. It’s alive and well. Top mold makers get things right the first time. And they’re great at quickly adjusting to and overcoming unforeseen glitches that come out of nowhere and threaten to destroy the economics of your injection molding project.

 

4. Should I buy a mold in the US or overseas?

 

If you have a small budget, a simple part, or lots of time, then overseas might be a reasonable choice. As a rule of thumb, overseas molds can cost up to 30 percent less than domestically designed and manufactured molds. The downside is that lead times are often 4 to 5 weeks longer than domestically designed and manufactured molds. Make sure to calculate the opportunity cost of the longer lead time.

 

On the other hand, if speed to market is important, or you have complex parts, or need high volume output, overseas may not be your best choice. Mold price is a cost driver that can be easily eclipsed by poor mold performance that yields excessive downtime or poor parts quality.

 

The fact is that US mold makers have greater expertise in making high cavity, high tolerance, and high performance than their overseas competitors.

 

So, consider the trade-offs carefully.

 

And don’t forget the legal ramifications of your purchase. In the US, we’re governed by a common set of laws called the Uniform Commercial Code (UCC). If your US mold maker violates these provisions, you have recourse – enforceable recourse. If you have a problem with your overseas mold maker, good luck – you’re a stranger in a strange land and the deck is stacked against you.

 

Clare Goldsberry, in So You Think You Have a Great Idea!, documents some of the horror stories US mold buyers encountered with offshore mold makers. Short version:  they don’t play by the same rules as we do and it’s tough to overcome their home court advantage if things don 't go the way you think they should.

 

Once again, Caveat Emptor!

 

Be sure you go into an overseas transaction with your eyes wide open.
 

At the End of the Day

 

We have solid working relationships with both domestic and overseas mold designers and makers and are familiar with the pros and cons of each. We can help with your project regardless of its size and scope.

 

Feel free to call us at 480-834-4200 or shoot an email to info@pcmmolding.com to learn more about how to choose a mold or to discuss your injection molding project.

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