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Tips to reduce injection molding costs
Generally speaking, there are four main categories of plastic injection molding costs:
Part design
Plastic materials
Tools
Production and secondary processing
1. Part design
Is your part manufacturable as currently designed? This is the first question DFM aims to ask and answer. However, expert DFM is more than just this basic test. To minimize costs, designers need to know if parts are easy to manufacture. Parts that are difficult but can be injection molded are more expensive, and parts that are difficult to mold increase the risk of defects and the need for rework.
When injection molded parts are still in the design phase, small modifications don't take as long or take as much to complete, and it's best to change part tolerances early. Once the mold is created, any design changes may require changes to the injection mold, which increases costs and lengthens the project timeline. If your product launch is delayed, there is also an opportunity cost. Designers need to keep in mind that with injection molding, complexity increases cost. These recessed features provide fastening points or positioning edges, but undercuts also make injection-molded parts harder to eject, increasing costs.
2. Plastic materials
Are you using too much plastic in your part design? You can reduce material use by replacing thicker walls with thinner walls that use ribs for support or bosses for fasteners. Walls that are too thick (or too thin) also have longer cycle times and are therefore more expensive to produce. However, walls need to be thick enough to meet functional requirements, so cost isn't the only consideration.
When it comes to materials, you can also make other cost-saving decisions. For example, depending on your application requirements, do you need commodity plastics or specialty plastics? Does the material require additional drying costs, or are there additional costs associated with additives? Can you replace virgin plastic with recycled material?
Commodity plastics are less expensive and there are hundreds of different resins to choose from, each with specific end-use characteristics. There are also different grades of the same plastic material, including resin types with fillers, such as glass or fiberglass. Note that commodity plastics are not the right choice for demanding applications, and inexpensive polymers may not be able to support the tolerances you need. In addition to polymer price, you should also consider processing requirements, as longer cycle times come with higher costs.
Specialty plastics cost more than commodity plastics, but have material and performance properties that are suitable for more demanding requirements. Typically, these engineering plastics and resins are used in medical, automotive, and electronics applications. Sometimes, particularly demanding requirements require the use of polymer blends.
3. Mold
Usually, injection molds are made of aluminum or steel. Aluminum has a shorter processing time, but aluminum molds wear out faster and are not suitable for plastics that require high forming temperatures. Steel comes in different grades, including those that are cost-effective for prototyping and low-volume production. Semi-hardened steels cost more than mild steels, but they also extend tool life.
Hardened steel molds are the most expensive, but they are ideal for high volumes because they can withstand more injection cycles. If you're designing a part that will be produced for a long time, steel tools have a higher upfront cost but a higher return on investment (ROI). Mold maintenance is also a key consideration, as molds for higher volumes or tighter part tolerances may require more frequent refurbishments.
Since tighter part tolerances require more expensive molds, you may want to reconsider whether you really need tight tolerances. In addition, cost-saving tooling strategies include simplified part ejection and setting the parting lines of the mold on sharp edges instead of rounded surfaces. Molds with cooling channels of the right size and location can also reduce injection molding costs.
Cooling channels or cooling lines support uniform cooling of the mold and the production of defect-free plastic parts. Since cooling typically accounts for 75% of cycle time, it is critical that mold makers optimize cooling channel design and injection molders use optimal cooling equipment. These variables may seem beyond the designer's control, but a comprehensive DFM still takes them into account.
4. Production and secondary processing
During the plastic injection molding process, molders need to use the proper clamping pressure – that is, the force required to keep the mold closed. If this pressure is not high enough, the mold may open prematurely. This can result in a flash on the surface of the part, an unwanted surface defect that may require secondary treatment to remove.
Expert DFM also considers methods to minimize secondary processing, such as custom insertions and painting. By changing the part design or choosing a different material, you can achieve your design goals while avoiding additional setup costs. In addition, mechanisms such as movable hinges created during the injection molding process can eliminate the need for assembly and other secondary operations.
Part design
Plastic materials
Tools
Production and secondary processing
1. Part design
Is your part manufacturable as currently designed? This is the first question DFM aims to ask and answer. However, expert DFM is more than just this basic test. To minimize costs, designers need to know if parts are easy to manufacture. Parts that are difficult but can be injection molded are more expensive, and parts that are difficult to mold increase the risk of defects and the need for rework.
When injection molded parts are still in the design phase, small modifications don't take as long or take as much to complete, and it's best to change part tolerances early. Once the mold is created, any design changes may require changes to the injection mold, which increases costs and lengthens the project timeline. If your product launch is delayed, there is also an opportunity cost. Designers need to keep in mind that with injection molding, complexity increases cost. These recessed features provide fastening points or positioning edges, but undercuts also make injection-molded parts harder to eject, increasing costs.
2. Plastic materials
Are you using too much plastic in your part design? You can reduce material use by replacing thicker walls with thinner walls that use ribs for support or bosses for fasteners. Walls that are too thick (or too thin) also have longer cycle times and are therefore more expensive to produce. However, walls need to be thick enough to meet functional requirements, so cost isn't the only consideration.
When it comes to materials, you can also make other cost-saving decisions. For example, depending on your application requirements, do you need commodity plastics or specialty plastics? Does the material require additional drying costs, or are there additional costs associated with additives? Can you replace virgin plastic with recycled material?
Commodity plastics are less expensive and there are hundreds of different resins to choose from, each with specific end-use characteristics. There are also different grades of the same plastic material, including resin types with fillers, such as glass or fiberglass. Note that commodity plastics are not the right choice for demanding applications, and inexpensive polymers may not be able to support the tolerances you need. In addition to polymer price, you should also consider processing requirements, as longer cycle times come with higher costs.
Specialty plastics cost more than commodity plastics, but have material and performance properties that are suitable for more demanding requirements. Typically, these engineering plastics and resins are used in medical, automotive, and electronics applications. Sometimes, particularly demanding requirements require the use of polymer blends.
3. Mold
Usually, injection molds are made of aluminum or steel. Aluminum has a shorter processing time, but aluminum molds wear out faster and are not suitable for plastics that require high forming temperatures. Steel comes in different grades, including those that are cost-effective for prototyping and low-volume production. Semi-hardened steels cost more than mild steels, but they also extend tool life.
Hardened steel molds are the most expensive, but they are ideal for high volumes because they can withstand more injection cycles. If you're designing a part that will be produced for a long time, steel tools have a higher upfront cost but a higher return on investment (ROI). Mold maintenance is also a key consideration, as molds for higher volumes or tighter part tolerances may require more frequent refurbishments.
Since tighter part tolerances require more expensive molds, you may want to reconsider whether you really need tight tolerances. In addition, cost-saving tooling strategies include simplified part ejection and setting the parting lines of the mold on sharp edges instead of rounded surfaces. Molds with cooling channels of the right size and location can also reduce injection molding costs.
Cooling channels or cooling lines support uniform cooling of the mold and the production of defect-free plastic parts. Since cooling typically accounts for 75% of cycle time, it is critical that mold makers optimize cooling channel design and injection molders use optimal cooling equipment. These variables may seem beyond the designer's control, but a comprehensive DFM still takes them into account.
4. Production and secondary processing
During the plastic injection molding process, molders need to use the proper clamping pressure – that is, the force required to keep the mold closed. If this pressure is not high enough, the mold may open prematurely. This can result in a flash on the surface of the part, an unwanted surface defect that may require secondary treatment to remove.
Expert DFM also considers methods to minimize secondary processing, such as custom insertions and painting. By changing the part design or choosing a different material, you can achieve your design goals while avoiding additional setup costs. In addition, mechanisms such as movable hinges created during the injection molding process can eliminate the need for assembly and other secondary operations.
