How to Reduce the Mold Cost of Injection Molded Parts: 10 Key Considerations

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How to Reduce the Mold Cost of Injection Molded Parts: 10 Key Considerations

Every business wants to save money on part manufacturing. How do you reduce the cost of a single part in injection molding? One might think that the easiest way is to increase the number of parts and spread the initial cost of designing and machining the mold over each part. At Speedmaster, using the same mold supports the manufacture of multiple parts, which helps you save on manufacturing costs.

How much does injection molding cost?

While the initial cost of injection molding may seem higher compared to processes such as CNC machining and 3D printing. It is only when the number of parts scales into the thousands that it becomes a cost-effective solution. The most significant factor in determining the cost of injection molding is the time it takes to produce the molds, which means that the more complex the geometry of the part, the more expensive it is to manufacture. After analyzing the 16 million + parts manufacturing experience of Speed Plus, it has been found that simple parts without no undercuts or without complex surface finishes are the most affordable.

In addition to unit cost, there are materials to consider. Many plastics overlap in strength and functionality, but some are inherently easier to mold, which reduces part cost. When you upload your drawings to Sega, our engineers will assist you in quickly prototyping your product by providing process optimization recommendations based on the product’s final realized use.

Here are 10 injection molding design considerations that can help you save on manufacturing costs:

1. Eliminate undercutting

2. Remove unnecessary features

3. Use core and cavity methods

4. Reduce surface finish and appearance

5. Design self-fitting parts

6. Modify and reuse molds

7. Pay attention to DFM analysis

8. Use multi-mold-cavity or family molds

9. Selecting Build-to-Order Options

10. Consider part size


Undercut features make part ejection difficult and may even prevent part ejection. It is better to have none if you can, but perhaps this is not possible, for example, if you need a side action, slide off or take out. An alternative might be to use a sliding shutoff valve and a straight-through core, or to simplify mold making by changing the parting line and extraction angle. This can reduce the cost of mold manufacturing by avoiding the need to add additional parts to the mold. In addition to the increased manufacturing costs of using manual inserts, longer cycle times and manual mold operations may also have an impact on the price of your parts.

Unnecessary Features

Textured surfaces, molded part numbers, and company logos may look cool, but there is an additional cost to complete these non-critical features. That said, permanent part numbers are a requirement for many aerospace and military applications. Use fonts appropriate for factory use, such as CenturyGothicBold, Microsoft Black, Microsoft YaHei or Verdana (san-serif fonts), keeping them above 20 pounds and no deeper than 0.25 mm to 0.38 mm. Also, be prepared to add extractors if part release is a concern.

Core Cavities

If you need an electronics enclosure or similar box-shaped part, you can either countersink the wall cavity to the bottom of the mold and use a long, thin tool to machine the ribs into the mold, or you can machine the aluminum material down around the core and form it around the part. The latter method, known as core cavities, is a more cost-effective method of molding. Better yet, this method is more likely to provide a smooth surface finish, adequate venting, improved pop-out, and eliminate the need for ultra-steep draft angles.

Surface Finishing

Parts that look good on the outside usually require sandblasting, EDM, or advanced mold polishing, which undoubtedly adds to the cost. Any injection molded part with a finish greater than PM-F0 (e.g. machined) will require a secondary process such as polishing to a SPI-A2 mirror finish using a class 2 diamond polishing wheel. Avoid such fine surface finishes unless the job requires it.

Adaptive Parts

Let’s say you’re designing a cassette for a medical part or a splice housing for a portable radio, why design two parts when you can solve it with one? Design the splice part as a snap so that the two halves can be assembled together from either side at ease, creating a so-called “universal” part that requires only one mold to be made.

Mold Modifications

Removing metal from an existing metal mold is relatively easy, but adding metal is more difficult or, in fact, impossible with rapid injection molding. From a part standpoint, you can add plastic, but you can’t remove it. Keep this in mind for “metal safe” designs.

Some injection molds go through many iterations until a workable design finally emerges, eliminating the need to make a new mold for each modification. It is possible to start with the smallest, most basic part design, mold as many parts as needed, and then rework the mold to include additional part features, or a larger, taller version of the same part, and then mold it again. This is not an exact science, but if the right parts are given, then this method of reuse can save money in tool development.

Moldability-DFM Analysis

XY-GLOBAL can provide you with a free Design for Manufacturing (DFM) analysis for your injection molded part quote, which can identify potential problem areas or opportunities for design improvement. Inadequate draft angles, “unmachinable” features, impossible geometries – these are just a few examples of how a part design can and should be improved before finalizing on the machine. Be sure to read these suggestions carefully and contact one of our process engineers for any design-related questions.

Multiple Cavities and Series Molds

Maybe you need more parts? You can still use aluminum molds with two, four, or eight cavity molds to achieve high throughput, depending on size and part geometry, and while this will affect your tooling costs, it can lower the price of the part.

Do you have a series of parts that can be combined together? How about multiple molding projects at once? There is no need to make a mold for each individual part, as long as everything is made of the same plastic, each part is roughly the same size, and can all be extruded into the same cavity while allowing the mold to function properly. Alternatively, parts can be joined together with movable hinges.

On-demand options

Depending on the number of parts you have, another way to reduce molding costs is to consider on-demand manufacturing. At Speedy Plus, two injection molding service options are available (see table below). One is best suited for those who need a smaller part count, usually associated with prototyping. The other option, which Quick Plus calls Manufacturing on Demand, is ideal for those who need slightly larger part quantities, often upwards of 10,000 aluminum molded parts. On-demand manufacturing is an excellent option for managing fluctuations in part demand, lowering total cost of ownership, and utilizing cost-effective bridge tools.

Another way to reduce injection molding costs is to consider on-demand manufacturing. XY-GLOBAL offers four injection molding service options including single color injection molding, two color injection molding, overmolding and insert molding. With the ability to offer on-demand manufacturing services at different quantity levels based on your project needs, XY-GLOBAL is an effective tool for managing fluctuations in part demand and lowering your total cost of ownership.

Part Size

Part size is also a factor to consider. Different sized parts require different tonnages of injection molding machines, which affects the cost of the mold and the cost of the part. Currently, the largest size injection molded part that XY-GLOBAL can support is 900*800*400mm.

Of course, if your molding project is still in the sampling stage and you only need a few parts, don’t worry, XY-GLOBA can provide you with very cost-effective molds with as fast as 2 hours delivery. Click on this link to upload 2D/3D drawings and get a quote for your order!