Everyone wants to save money on manufactured parts. It sounds simple, but one of the easiest ways to reduce price-per-piece cost in injection molding is by increasing part quantity. That is because the initial upfront cost to design and machine the mold amortizes over more parts. At Protolabs, for example, up to 25,000 parts or more can be molded from the same tool.
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However, maybe your molding project calls for only a handful of parts. No worries. Protolabs builds cost-effective molds for production quantities as low as 25 pieces, often within a few days of ordering.
While injection molding may seem costly compared to processes like CNC machining and 3D printing, the ability to scale and manufacture thousands of parts makes it a cost-effective solution for mass production. Determining the cost of injection molding is a combination of several factors. The main determinant of molding cost is the amount of time it takes to produce the tooling. This means, the more complex the part's geometry, the higher your manufacturing costs will be. Simple parts, without undercuts or more advanced surface finishes, will be the most affordable.
In addition to per-unit costs, consider the material. Many plastics overlap in strength and functionality, but some are inherently easier to mold, driving down part costs. You can experiment with different materials in the interactive quote you receive when you upload your design to Protolabs.
Here are 11 injection molding design considerations to stretch your manufacturing dollar:
1. Eliminate undercuts
2. Get rid of unnecessary features
3. Use a core cavity approach
4. Reduce cosmetic finishes and appearances
5. Design self-mating parts
6. Modify and reuse molds
7. Pay attention to DFM analysis
8. Use a multi-cavity or family mold
9. Choose on-demand production option
10. Consider part size
11. Use overmolding
Undercut features complicate and, in some cases, prevent part ejection. Get rid of them if you can, but maybe that’s not possible, if, for example, you need a side action, sliding shutoff or pick out. One alternative may be using sliding shutoffs and pass-through cores, or by changing the parting line and draft angles to provide an easier mold build. These reduce tooling costs as you avoid additional pieces to the mold that add to manufacturing costs. In addition to the rise in manufacturing costs of using hand-loaded inserts, this also may have an impact on your piece part price because of longer cycle times and manual mold operation.
Textured surfaces, molded part numbers, and company logos look cool, but be prepared to pay a bit extra for these and other non-mission critical features. That said, permanent part numbers are a requirement for many aerospace and military applications. Use a mill-friendly font such as Century Gothic Bold, Arial, or Verdana (san-serif fonts), keep it above 20 pt., and don’t go much deeper than 0.010 to 0.015 inch. Also, be prepared to increase draft if part ejection is a concern.
If you need an electronics housing or similar box-shaped part, you can either sink the wall cavities deep into the mold base, requiring long thin tools to machine ribs into the mold, or machine the aluminum material down around the core and mold the part around it. The latter approach is known as a core cavity, and is a far more cost-effective method of molding tall walls and ribbed surfaces. Better yet, this makes it easier to provide smooth surface finishes, adequate venting, improved ejection, and can eliminate the need for super-steep draft angles.
Pretty parts are nice, but they often require bead blasting, EDM, or high mold polish to achieve an elevated level of cosmetic appearance. This drives up tooling costs. Anything greater than a PM-F0 (as machined) finish requires some level of hand work, up to an SPI-A2 mirror finish using Grade #2 diamond buff. Avoid fine finishes such as these unless they’re required for the job. One thing to consider regarding cosmetics is to let Protolabs know if you need the entire half of the mold polished or maybe just one small area. You could save costs by only polishing the area needed versus the entire side of a mold. When requesting a custom finish, just send Protolabs a color-coded image of the critical areas and desired finish level for each area.
Maybe you’re designing a snap-together case for some medical components, or two interlocking halves of a portable radio. Why build two mating parts when you can make one? Redesign the snaps so that the halves can be fit together from either direction, thus building a so-called “universal” part. Only one mold is needed, saving production expenses up front. And you can now mold twice as many of one part, instead of half the quantities of two.
It is relatively easy to remove metal from an existing metal mold. Adding metal, on the other hand, can be difficult or, for all practical purposes, impossible with rapid injection molding. To look at this from the part perspective, you can add plastic, but you can’t take it away. Designing with this in mind is called “metal safe.”
Some injection-molded parts go through multiple iterations until a final, workable design emerges. Instead of purchasing a new mold for every revision, a little clever planning will allow the same mold to be used multiple times. Starting with the smallest, most basic part design, mold as many pieces as needed, then re-machine the mold to include additional part features, or a larger, taller version of the same part, and mold again. This is not an exact science, but given the right part, this re-use approach can save dollars on tooling development.
Every quote for an injection-molded part at Protolabs is accompanied by a free design for manufacturability (DFM) analysis. This identifies potential problem areas, or opportunities for design improvement. Insufficient draft angles, “un-machinable” features, impossible geometries—these are just a few examples in which part designs can and should be improved before clicking the “accept” button. Be sure to review these suggestions thoroughly, and contact an applications engineer at Protolabs with any design-related questions.
Maybe you are after a higher volume of parts? You can still achieve high volumes using aluminum tooling with two-, four-, or eight-cavity molds depending on size and part geometry that can reduce your piece part price, although this would impact your tooling costs.
Got a family of parts that all fit together? How about multiple molding projects at one time? There’s no reason to build a mold for each individual part, provided A) everything is made of the same plastic, B) each part is roughly the same size (e.g., have similar processing times), and C) can all be squeezed into the same cavity, while still allowing for proper mold functioning.
In addition, maybe you can join some of those parts with a living hinge? This method is a great way, for example, to mold two halves of a clamshell-style container. These parts would otherwise need a pin-type assembly to open and close. The only caveat here is that a flexible and tough material must be used, such as polypropylene (PP).
Still another way to reduce molding costs, depending on your part volumes, is to consider on-demand manufacturing. At Protolabs, two injection molding service options are available (see table below). One is best suited for those who need smaller part quantities, usually associated with prototyping. The other option, Protolabs calls it on-demand manufacturing, is a good fit for those who require slightly larger part quantities, typically up to 10,000-plus parts from aluminum molds. On-demand production can be a great option to manage demand volatility of your parts, reduce total cost of ownership, and leverage cost-efficient bridge tooling.
Generally, the injection molding process has no fixed cost for every application. Custom injection molding cost has a varying value that ranges from thousands to hundreds of thousands. Below are common factors that impact the cost of injection molding.
It is expensive to machine the mold and mold base for the products, even though the molding equipment is a one-time investment. Besides, the process used to create the molds determines the cost. The standard techniques used in making molds include CNC machining, electric discharge machining, and 3D printing.
The CNC machining process is well-suited for making metal molds from aluminum or steel materials. For instance, CNC machines use cutting tools to remove materials from an aluminum block to machine an aluminum mold. Besides, this machining method produces aluminum molds with high accuracy.
Electrical Discharge Machining (EDM) is an assisted technique for making molds with complex and precise features. It involves using electrical discharge to melt and form the metal workpiece into the desired size and shape. Although EDM offers excellent accuracy, it is compatible with only metal molds.
3D printing is one of the fastest procedures for making molds for plastic injection molding projects. This method uses a 3D printer and doesn’t necessarily require a skilled operator. Hence, it saves labor and mold costs. However, 3D printed components are often limited in dimensions due to the size of the 3D printer’s build platform. Similarly, printed molds are more likely to experience shrinkage.
The injection molding process requires unique equipment. However, the machine’s size and level of sophistication determine the cost and range from small to large machine. Therefore, it would help to consider the following injection molding machine types and how they influence injection molding costs.
Electric molding machines utilize an electro-servo motor to direct the machine during injection molding. They utilize less energy, incur low operating and maintenance costs, and are accurate and easy to use. Nevertheless, their initial investment cost is high and requires routine maintenance.
These hydraulic injection machines perform injection molding operations with a hydraulic pump. They are usually durable, offer highly consistent ejection and injection, and have economical initial purchase costs. However, they can be imprecise and consume excessive energy.
Hybrid injection molding machines combine the characteristics of electric and hydraulic injection molding machines. It uses a servo motor and hydraulic pump to distribute the oil used in producing hydraulic pressure that creates the component in the machine.
These machines provide high precision, repeatability, and energy efficiency. Furthermore, they have high initial investment costs and require heavy maintenance since they use electric motors and hydraulic pumps.
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However, it may be ideal to outsource to injection molding service providers instead of buying a machine to avoid the high cost of an injection molding machine.
Plastic injection molding is compatible with an extensive range of plastic resins with varying availability, price, applications, and properties. Typical examples of plastic injection materials include PC, ABS, PU, PP, and PE.
The cost of plastic pellets material used in plastic injection molding technique ranges from 1 dollar per kg to 5 dollars per kg. However, the injected material’s final cost depends on the used amount and the required design.
Molded parts’ variables, such as design, size, and volume of injection molding components, often decide injection mold cost. You can optimize the cost of your project significantly when you understand how these variables impact the project’s plastic injection molding cost.
To make complex parts, you must create a mold with even complexity using manufacturing methods such as 3D printing, CNC machining, or EDM machining. Besides, you need more material to fill the mold to produce complex parts. Consequently, this increases the injection molding material cost. At the same time, complex parts may require extended production time since they may require additional steps in the production process.
Creating large molded parts will require more injection molding material, hiking the costs of injection molded components. Similarly, it would be best to use the proper injection molding machine and manufacture the right mold size when handling large parts.
Generally, the undercut injection molding features complicate and in some instances prevent parts injection. Eliminate them if possible. If you find it hard to get rid of them, try sliding shutoffs, pass-through cores, or change the parting line and draft angles to simplify the mold build.
Unnecessary features that do not add significant value to your final products will increase plastic injection molding costs. Textured surfaces, for instance, may simply not be needed. This holds true for cosmetic add-ons like bead blasting or high mold polish too. Remember that excess features might also require more mold cavities that further drive costs north.
Most procedures associated with injection molding are automated and controlled by software systems. However, typical labor costs involved in injection molding include:
Different production volumes are also an essential factor in the cost of injection molding. Moreover, the production volume influences the amount of raw material used in injection molding, required machine sophistication, and injection mold properties such as durability, strength, and other properties. Here are the typical types of production volume injection molding:
Low-volume plastic molding includes any production of parts between a hundred to a couple of thousand. Manufacturers often make the molds in-house and perform the molding themselves without necessarily using sophisticated machines. Hence, manufacturers produce molds of 3D-printed polymer resin or fast rapid tooling since it is affordable and doesn’t require a long production cycle.
The complete production run for low-volume molding usually takes precisely three days to create the finished parts. For instance, let’s assume the following parameters for a 100 – 200 part run:
Mid-volume quantities in injection molding often range between five thousand to tens of thousands of molded parts. This production type requires mold made from pre-hardened steel or aluminum. You can outsource the mold production and molding procedures for this production scale.
However, let’s assume the following injection molding cost calculation for a 5,000 – 10,000 unit volume. These are the same parts made using thermoplastic materials such as polypropylene.
High-volume injection mold production involves a few hundreds of thousands of molded parts. This procedure often requires steel molds due to their long life expectancy. Likewise, large-volume projects require a sophisticated machine, which adds to the injection molding cost. However, high-volume production offers higher cost distribution per part, ensuring lower cost per part.
For instance, let’s assume we are molding 100,000 to 300,000 parts of the same type using ABS.
However, it is evident that the injection molding price per part reduces considerably for high-volume production. Hence, high-volume projects offer the best cost advantage for injection molding costs.
As we mentioned above, the simplest trick to reduce the price per piece is by increasing the parts quantity since the upfront costs while machining and designing the mold can be used over more parts. In addition to that, you can also try the following several ways to reduce injection molding costs and help you get the best results for your project.
DFM (Design for Manufacturing) in injection molding involves creating a part within a client’s stipulated budget and fulfilling the intended purpose. Analysts often consider different factors for DfM based on technology, art, and science to determine the most efficient design. Hence, it significantly reduces the costs of injection molding.
It may be compulsory to use complex molds and additional steps during plastic injection molding due to the complex features of your products. Therefore, removing unnecessary features would be best to lower the injection molding price. At the same time, you can save more money by removing any features that only add cosmetic finishes.
If you do not require a custom mold, consider using the universal mold. These molds are often less expensive than custom molds and can still produce high-quality parts.
Also, If you need a custom mold, always consider having a CAD model in place prior to commencing the manufacturing process. It will help optimize designs and identify potential problems such as steep draft angles, unnecessary wall thicknesses, complex shapes, etc.
The cost of the preferred material for your parts often influences the overall injection molding cost. Where possible, use lower-cost materials such as ABS or polypropylene. It helps to keep a minimal production cost.
Insert injection molding and overmolding are effective technologies that save costs in the long run. For instance, insert molding prevents the need to make threads on the plastic to fasten it to metal parts, thereby making the process economical.
The more cavities there are in a mold, the higher the cost will be. Therefore, it is important to minimize the number of cavities in your mold whenever possible.
One way to reduce the number of cavities is to use a moldflow analysis to optimize the design of your part. Moldflow analysis can help you to identify areas where cavities can be eliminated without compromising the function or aesthetics of the part.
Making self-mating parts is one of the most reliable ways of saving injection molding costs and simplifying design. These parts are those that attach to themselves when turned 180 degrees. These parts are ideal because you can use a single half mold to make the whole part. It reduces mold cost, and the injection mold size is half.
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