How to Determine Mold Cavity Number According to Product Output

The selection of mold cavity number is determined by total product output, delivery cycle, equipment condition and production cost. This article introduces calculation methods, selection rules and practical principles to guide reasonable cavity number design for plastic molds.

1. Confirm Basic Calculation Parameters

Collect basic data before cavity number design. First, clarify total order quantity, annual estimated output and batch size, and distinguish trial production orders and long-term mass production orders. Second, confirm delivery cycle and required daily output to restrict production capacity. Third, measure the standard injection cycle of single product, including filling, holding, cooling, mold opening, ejection and mold closing.

Fourth, calculate effective working hours according to production shifts. Single shift is 8 hours, double shift 16 hours and three-shift 24 hours. Deduct time for equipment maintenance, mold change and unplanned shutdown. Fifth, confirm injection machine tonnage, tie bar spacing and maximum mold size, which define the theoretical upper limit of cavity number.

2. Basic Production Capacity Calculation Formula

Convert daily effective working hours into total seconds: Daily effective seconds = Daily effective hours × 3600.

Daily output of single cavity = Daily effective seconds ÷ Single product cycle time.

Daily output of N-cavity mold = Daily output of single cavity × Cavity number N.

Calculate the minimum required cavity number in reverse according to delivery requirements: Target daily output = Total product quantity ÷ Total delivery days.

Minimum cavity number = Target daily output ÷ Daily output of single cavity. Round up the result to get the basic cavity number meeting delivery requirements.

3. Cavity Number Selection Standard by Output Volume

For small-batch production with total output less than 50,000 pieces, single-cavity mold is the preferred choice. It features low mold cost, short manufacturing cycle and flexible mold change, suitable for new product verification and products with complex structure or high appearance requirements.

For medium and small batches with total output from 50,000 to 200,000 pieces, select 2-cavity or 4-cavity molds. This type balances production capacity and mold cost. Mold size matches most standard injection machines, and product consistency is easy to control. It is widely used for stable small-batch mass production.

For medium and large batches with total output between 200,000 and 1,000,000 pieces, 4-cavity and 8-cavity molds are commonly adopted. Single-piece processing cost is reduced with improved production capacity. Mold structure is mature and applicable to most conventional orders.

For mass production with total output over 1,000,000 pieces and long-term repeated orders, select 8-cavity, 16-cavity, 24-cavity or multi-cavity combined molds. High cavity number greatly improves single-machine output and cuts production cost. This solution applies to standard parts, daily necessities and small electronic parts with simple structure, yet it puts forward higher requirements on runner balance, exhaust and cooling systems.

4. Restriction Conditions for Cavity Number Selection

Match mold size, clamping force and mold thickness with existing injection machines. If machine parameters cannot support high-cavity molds, reduce cavity number or arrange multiple sets of molds for parallel production.

Products with complex structure, uneven wall thickness and strict appearance requirements are not suitable for multi-cavity molds. Unbalanced runners will cause deviation on size and appearance among different cavities, so low cavity number is recommended for high-precision products.

Higher cavity number increases design difficulty and manufacturing cost of runners. Hot runner molds are adopted for ultra-large batches, while cold runners are used for medium and small batches to control cost.

Reserve 5% to 10% allowance for defective products, trial molding and shutdown loss during calculation, instead of only calculating theoretical full-load output. More cavities mean more mold components and higher difficulty of daily maintenance. Reduce cavity number for orders with low reorder frequency.

5. Optimization Schemes for Special Scenarios

When delivery is urgent and single high-cavity mold cannot meet capacity demand, arrange multiple sets of molds with the same cavity number for parallel production, rather than blindly increasing cavity number.

For orders with obvious seasonal fluctuation, select medium cavity number such as 2-cavity and 4-cavity molds. Adjust production shifts to cope with capacity changes. For serial products with multiple models, adopt combined cavity molds to improve equipment utilization.

6. Standard Operation Process

Firstly, collect total output, delivery cycle, molding cycle and effective working hours to calculate theoretical minimum cavity number. Secondly, select alternative cavity numbers according to output classification standards. Thirdly, verify injection machine parameters, product structure and mold cost to eliminate infeasible schemes. Finally, add loss allowance to confirm the optimal cavity number, or decide to use multiple sets of molds for production.