# Injection Mold Cavitation Optimizer: How Many Cavities Minimize Cost per Part > Source: https://netray.co/tools/injection-mold-cavitation-optimizer-total-cost-calculator > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Sweeps the number of cavities from 1 to 32 and shows machine cost plus tooling cost per part, so you can see where adding cavities stops paying for itself. ## Category engineering-plm ## Industry Plastics and Injection Molding ## Audience - Mold designer - Tooling engineer - Estimator - Program manager ## Tool **Kind:** calculator **Currency:** $ **Inputs:** #### Annual volume **Key:** volume **Type:** number **Default:** 600000 **Min:** 1000 **Step:** 10000 **Unit:** parts/yr #### Program life **Key:** years **Type:** number **Default:** 5 **Min:** 1 **Max:** 15 **Step:** 1 **Unit:** years #### Cavities to evaluate **Key:** cavities **Type:** number **Default:** 8 **Min:** 1 **Max:** 64 **Step:** 1 **Unit:** cavities **Help:** The chart sweeps this input from 1 to 32. #### Cycle time, 1 cavity **Key:** base_cycle **Type:** number **Default:** 28 **Min:** 3 **Step:** 0.5 **Unit:** s **Help:** Total cycle of the single-cavity case, dominated by cooling time. #### Cycle penalty per added cavity **Key:** cycle_pen **Type:** slider **Default:** 1.5 **Min:** 0 **Max:** 5 **Step:** 0.25 **Unit:** % **Help:** Longer fill, pack and plastication as the shot grows. 1 to 3 percent is typical. #### Mold cost, 1 cavity **Key:** mold_1 **Type:** number **Default:** 22000 **Min:** 0 **Step:** 500 **Unit:** $ **Help:** Quoted or estimated price for a single-cavity version of the same tool. #### Mold cost scaling exponent **Key:** mold_exp **Type:** slider **Default:** 0.7 **Min:** 0.4 **Max:** 1 **Step:** 0.05 **Help:** Mold cost grows roughly as cavities to the power 0.6 to 0.8 for a family of similar parts. #### Press hourly rate, smallest press **Key:** rate **Type:** number **Default:** 65 **Min:** 0 **Step:** 1 **Unit:** $/hr **Help:** Fully burdened machine rate for the press sized to a single cavity. #### Press rate increase per added cavity **Key:** rate_step **Type:** slider **Default:** 3 **Min:** 0 **Max:** 10 **Step:** 0.5 **Unit:** % **Help:** Larger tonnage presses cost more per hour. #### Press efficiency **Key:** oee **Type:** slider **Default:** 85 **Min:** 40 **Max:** 98 **Step:** 1 **Unit:** % **Outputs:** #### Cycle time **Key:** cycle **Expr:** base_cycle * (1 + cycle_pen / 100 * (cavities - 1)) **Format:** decimal **Description:** Seconds per shot at this cavity count. #### Good output rate **Key:** parts_hr **Expr:** cavities * 3600 / cycle * oee / 100 **Format:** integer **Description:** Parts per press hour after efficiency losses. #### Mold cost **Key:** mold_cost **Expr:** mold_1 * pow(cavities, mold_exp) **Format:** currency #### Press hours per year **Key:** press_hours **Expr:** volume / parts_hr **Format:** hours **Description:** Check this against the hours your press can actually run. #### Machine cost per part ($) **Key:** machine_part **Expr:** rate * (1 + rate_step / 100 * (cavities - 1)) / parts_hr **Format:** decimal #### Tooling cost per part ($) **Key:** tool_part **Expr:** mold_cost / (volume * years) **Format:** decimal #### Total cost per part ($) **Key:** total_part **Expr:** machine_part + tool_part **Format:** decimal **Primary:** true **Description:** Machine plus tooling cost only. Resin, labor and packaging are the same for every cavity count. #### Lifetime machine plus tooling cost **Key:** life_cost **Expr:** total_part * volume * years **Format:** currency **Primary:** true **Chart:** #### Cost per part vs number of cavities **Type:** line **X:** cavities **From:** 1 **To:** 32 **Steps:** 32 **Series:** - total_part - machine_part - tool_part **Disclaimer:** Planning model. Mold cost scaling, cycle penalty and press rates vary by part, steel and shop. Replace the defaults with quotes, and add cost of capital if tool payback matters. Check shot size and clamp tonnage before choosing a cavity count. ## Content **Intro:** Every added cavity cuts press time per part but raises mold price and needs a bigger press. Somewhere the savings stop. This optimizer sweeps the cavity count and plots machine cost, tooling cost and their sum so you can see the minimum and how flat it is. **Sections:** #### How to use it **Body:** Start with your annual volume and program length, then enter the cycle time and mold quote for a single cavity. Set the scaling exponent and cycle penalty from your tool shop's quotes at two cavity counts, or leave the defaults. Read the chart: the total curve usually drops steeply, flattens, then rises slightly as mold cost and press rate catch up. Pick the lowest point, then move left if volume is uncertain, because fewer cavities hedge the risk of a program that ends early. #### The model **Body:** Output rate is cavities times 3600 divided by cycle seconds, times efficiency. Cycle grows by a small percentage with every added cavity. Mold cost is the single-cavity price times cavities to the power of the exponent, a common rule of thumb for similar part families. Machine cost per part is the hourly rate, scaled for larger presses, divided by good parts per hour. Tooling cost per part is mold cost spread over lifetime volume. The cavity count with the lowest sum is the cost optimum. **Bullets:** - Parts per hour = cavities x 3600 / cycle x efficiency - Mold cost = single-cavity cost x cavities^exponent - Tooling per part = mold cost / (annual volume x years) #### Reading the result **Body:** At 600,000 parts a year over 5 years the default case lands in the low double digits, with the curve nearly flat across 8 to 16 cavities. That flatness is the useful finding: when two cavity counts are within a few percent, choose the one with lower tool risk, a smaller press and shorter lead time. Raise volume and the optimum moves right. Cut program life or add cost of capital and it moves left. #### Limits and checks **Body:** The cost model ignores physical limits. A high cavity count may not fit the platen, may exceed shot capacity, may not balance the runner, or may force a hot runner you did not budget. Part quality also drops when cavity-to-cavity variation grows. Confirm clamp and shot with a tonnage check and get a real quote for the final choice. **Bullets:** - Compare press hours per year with available hours - Confirm shot size is 20 to 80 percent of barrel capacity - Ask for quotes at two cavity counts to calibrate the exponent **Cta:** If your cycle times, press rates and mold costs sit in an ERP and MES, Netray can build an agent that evaluates cavitation scenarios for new quotes from your own history. **Faq:** #### Is a mold with twice the cavities twice the price? **Answer:** No. Shared base, runner system and mold setup mean cost typically rises with cavities to a power between 0.6 and 0.8, so doubling cavities adds roughly 50 to 75 percent. Your tool shop's quotes at two cavity counts give the real exponent for your part. #### Why does the cycle time increase with more cavities? **Answer:** Cooling time depends on wall thickness and does not change, but a larger shot takes longer to plasticize, fill and pack, and bigger molds open and close more slowly. The penalty is small, usually 1 to 3 percent per added cavity. #### Does the optimizer include resin cost? **Answer:** No. Resin per part is the same at every cavity count except for runner size, so it does not change the optimum for a given design. Use the resin impact and part cost tools for a full cost view. #### What if volume is uncertain? **Answer:** Run the optimizer at low, expected and high volume. If the best cavity counts differ, choose the lower one, or consider a family or modular mold that can add cavities later if volume proves out. ## Search terms how many cavities should a mold have, mold cavitation optimization, cavity count calculator, multi cavity mold cost per part, injection mold cavity break even, optimal number of cavities injection mold, mold cost vs cavities, tooling cost per part cavities --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json