The best way to figure out how much you can save with injection molding services over other manufacturing methods is to compute the cost per part. Although there are certain factors that can drive the cost of injection molding up or down, if you begin with the right formula to calculate the cost per part, you may be able to make adjustments that will lower that figure.
The recommended way to determine the cost of each part for injection molding:
- Take the cost of material plus the cost of tooling.
- Next, divide the answer by the number of parts plus hourly costs.
- Finally, divide that answer by the production time.
The tooling cost matters
The cost of tooling is what will be your highest expense for injection molding manufacturing. The easiest way to control the cost in this area is to order as many parts as you need as opposed to the least amount required. When you do that, each part will cost less to make.
The cost of the material makes a difference
Pellets for injection molding are purchased in bulk, so the cost of material is comparatively small when considering other costs associated with injection molding. Be sure to add in the cost of the runner system when you assess the weight of the material as well. Note that since the cost is already on the low side, there may be little room to make reductions in the cost of the material.
Hourly costs for machine usage and labor
The part’s size and the location of the facility where the parts are manufactured are included in the hourly costs. If a part is large, injection molding pressures have to be higher than they are for a smaller part. The higher the pressure needed, the more expensive the machine.
Here’s an example of how to do the computation
Say your part has these measurements:
- Part Size = 200 mm x 200 mm x 4 mm
- Weight = 50 grams
Now, the part is very large; therefore, the mold will be on the higher-priced side. Pellet cost differentiation is by the grade, meaning you’ll pay more for High-density polyethylene (HDPE) or Acrylonitrile butadiene styrene (ABS) pellets. For this example, we’ll say since the device is a common household product, you’ll be using standard materials.
- Cost of Mold = $30,000
- Pellet Cost = $10 per kg
- Cycle time = 80 seconds
- Injection Molded Parts Manufactured = 45 per hour
- Machine Usage and Labor = $30 per hour
Volumes affect production cost
You can reduce your cost per part for injection molding when you consider your volume. For example, for volumes with units of more than 20,000, the cost is around $2. However, the cost would be $30 if the volume was only 1,000 units.
You remain in control. To reduce the cost, simplify the part in its elaborateness and make it smaller.
If you’re making a prototype and require just 50 – 100 parts at a time, you could consider 3D printing low-run injection molds. The molds won’t last indefinitely though, so keep this in mind.
Injection molding advantages
- Cost-efficient for manufacturing plastic parts that are the same
- Variety of plastic materials available
- Customized design of parts to meet your requirements
- Fast production cycles are common at less than a minute per cycle
Injection molding considerations
- The start-up cost is high for small scale productions
- Modifications of mold are costly if changes are requested much later after the designing steps have already started
- Turn-around times vary from 4 weeks and could extend to months if the part is large and complex (This is longer than 3D printing using sheet metal and some other manufacturing options.)
Taking time to estimate the cost of injection molding is an important step to make before you proceed. Realize that smaller, non-complex parts cost less to make than more elaborate parts. This is because the mold is what raises the cost of injection molding production.
Lastly, always review your designs thoroughly before moving to the production stage. You’ll want to do this whether you’re running a sheet metal fabrication project, ordering CNC machining, planning 3D printing, or opting for injection molding production. Get started today!