Save Costs by Prototyping Injection Molds with a 3D Printer

Article by Rod Mackay created/updated December 30, 2015

Injection molding (IM) — the process of injecting plastic material into a mold cavity where it cools and hardens to the configuration of the cavity — is best used to mass-produce highly accurate, and often complex, three dimensional (3D) end-use parts and products. However, the development of molds for this process is often painstaking, highly expensive and time intensive.

Read this article to learn how prototyping injection molds with a 3D printer is now being used to reduce the time, effort and costs of creating a mold:

3D Printed Mold

Plastic part from a 3D Printed Injection Mold

The High Cost of creating Molds

Hard-tooling molds are usually made from tool steel with a CNC milling machine or via electrical discharge machining (EDM). When used in mass production, they can last for millions of cycles but cost hundreds of thousands of dollars. What’s more, lead times to produce these molds are often measured in months rather than weeks or days. When tens of thousands of injection molded parts are needed, soft-tooling is an option. Made in aluminum, these molds are less expensive (typically $2,500 – $25,000) and faster to produce (2 – 6 weeks).

Unfortunately, the cost and time of tooling molds is often compounded by factors like:

  • Design mistakes that require the mold be remade correctly or,
  • The need to create multiple iterations before the final part design and quality are achieved.

It is with these issues in mind that manufacturers have begun to embrace the use of 3D printed molds to create functional IM prototypes.

3D Print a Prototype Mold: The Modern Alternative

PolyJet technology is an exclusive method of 3D printing offered with an Objet™ Production Series 3D Printer from Stratasys® that gives companies the ability to build injection mold prototypes in-house, quickly and easily. PolyJet printing creates 3D objects by positioning successive layers of liquid photopolymer into desired configurations. The plastic is then cured (solidified) with UV light. Once fully cured, molds can immediately be placed into IM equipment and used to create prototypes from the same material that is specified for use in the final product. These precision prototypes give manufacturers the ability to create realistic, finished-product examples that can then be used to gather true-to-life, performance data.

3D Printed Mold Test

3D printed mold inserts on a molding machine. Left is the core and right is the cavity.

Prototype injection molds created with a 3D printer are not intended to be replacements for soft or hard tools used in mid and high volume production. Rather, they are intended to fill the gap between soft tool molds and 3D printed prototypes. The following chart (Figure 1) illustrates the niche PolyJet technology fills in the prototype development process.

Figure 1: The characteristics of 3D printing versus traditional prototype production methods
Prototype
Method
Optimal Quantity
of Parts
Material Used to
Produce Prototype
Average
Mold Cost
Average
Cost/Part
3D Printed Part*1-10FDM or PolyJet PlasticN/AHigh
Machine Milling1 – 100ThermoplasticN/AHigh
Silicone Molding5 – 100ThermosetLowMedium
Injection molding
3D Printed Mold
10 – 100ThermoplasticLowMedium
Injection molding
using Soft Tools
100 – 20,000+ThermoplasticHighLow

 

* Although Fused Deposition Modeling (FDM) and laser-sintered processes use thermoplastics to create prototypes, the mechanical properties will not match those of an actual injection molded part because a) the processes used to create the prototypes will be different, and b) the materials used to create FDM and laser-sintered prototypes are not generally the same as those materials used to injection mold final parts.

Key points related to 3D printing a prototype mold:

  • The initial cost of creating a PolyJet mold is relatively low. However, PolyJet molds are best suited for prototyping or for short production runs ranging up to 100 parts depending on the type of thermoplastic used and mold complexity. As a result, the cost per part is medium.
  • Building a PolyJet mold is relatively quick; a mold can be built within a few hours as compared to days or weeks to create traditional molds.
  • In cases where design changes are required, a new iteration of the mold can be created in-house at minimal cost. This, combined with the speed of PolyJet 3D printing, allows designers and engineers greater design freedom and faster prototype production.
  • Molds created in Digital ABS material can be precisely built in 30 micron layers, with accuracy as high as 0.1 mm. These production features create a smooth surface finish so post processing is not needed in most cases.
  • Complex geometries, thin walls, and fine details can easily be programmed into the mold design. What’s more, these molds cost no more to make than simpler molds.
  • No pre-programming is needed to create PolyJet molds. Also, once the CAD design files are loaded, the 3D printing process can run without manual intervention.
  • The manufacturing time to injection mold a part using a PolyJet mold is relatively low, although not as low as conventional molding.

Take functional testing to a new level

The use of PolyJet 3D printed molds allows manufacturers the ability to take functional testing to a new level, by creating product prototypes from the same IM process and materials that will be used to create the final product. With this technology, companies can generate superior performance data and validate certification confidence.

3D Printed Injection Mold

3D Printed Injection Mold

PolyJet molds are unique in that they perform in the same way as metal molds but are much cheaper, easier and faster to make. With PolyJet technology, mold manufacturers can produce prototypes at speeds and costs far below traditional methods. As a result, 3D printing allows manufacturers to easily evaluate the performance, fit and quality of potential products before mass production starts.

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Rod Mackay

Rod has been using 3D CAD software for over 25 years and has trained thousands of designers to use their CAD systems more effectively. Rod is the Javelin Webmaster and is based in Ottawa, ON., Canada.

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