Cost of Injection Molds
The cost structure of injection molds is complex, involving multiple steps, including design, materials, processing, and assembly. Material costs account for approximately 30%-40% of the total cost, making them the fundamental factor influencing total costs. The choice of mold steel directly determines material costs. Ordinary carbon structural steel (such as S50C) costs approximately 8 yuan per kilogram and is suitable for low-volume production (less than 10,000 mold runs). High-quality alloy mold steel (such as 718H) costs up to 30 yuan per kilogram and can withstand production runs exceeding 500,000 mold runs. Using 718H steel for a particular automotive parts mold increased material costs by 50,000 yuan, but the mold life was extended fivefold, resulting in a lower overall cost. The cavity and core, as core components, account for 60% of the total material cost. For example, the cavity of a mobile phone casing mold uses mirror-polished NAK80 steel (priced at 45 yuan per kilogram). The cavity material cost alone reached 8,000 yuan, far exceeding the 2,000 yuan for ordinary structural steel. In addition, the cost of standard parts (guide pins, ejector pins, etc.) accounts for about 10%. Imported brands (such as HASCO) are 50% more expensive than domestic parts, but have better precision and lifespan.
Processing costs account for the largest portion of the total cost of an injection mold (40%-50%), primarily including CNC machining, EDM, and wire cutting. The higher the precision required, the greater the cost difference. CNC milling costs for standard molds are approximately 80 yuan/hour, while precision molds (accuracy ±0.005mm) require a high-speed machining center, costing up to 150 yuan/hour. The cavity machining of a particular optical lens mold took 120 hours, with CNC machining costs alone reaching 18,000 yuan. Electro-discharge machining (EDM), used for complex cavity forming, costs approximately 100 yuan/hour. For a household appliance mold with a deep cavity structure, EDM took 80 hours and cost 8,000 yuan. Wire cutting is charged by area (approximately 0.5 yuan/mm²). The wire cutting of a special-shaped insert with an area of 20,000 mm² cost 10,000 yuan. Surface treatment costs (such as nitriding and chrome plating) account for about 5%-10% of the processing cost. After nitriding treatment, the surface hardness of a mold requiring high wear resistance reaches HV900. The treatment cost increases by 5,000 yuan, but the wear rate is reduced by 70%.
Although design costs account for a small proportion (5%-10%), they are crucial to overall cost control. Excellent design can reduce subsequent processing and trial mold costs. Mold design fees are usually charged according to complexity. Simple molds (such as bottle caps) cost about 5,000 yuan, and complex molds (such as car bumpers) require 50,000-100,000 yuan. A multi-cavity mold with side core pulling and hot runners has a design fee of 80,000 yuan. Through CAE simulation and structural optimization, the processing cycle was shortened by 20%, indirectly saving 100,000 yuan in costs. The rework cost caused by design errors often far exceeds the design fee. Because a mold did not consider the layout of the cooling water channel, uneven cooling was found after the trial mold. The water channel needed to be reprocessed, resulting in an additional cost of 30,000 yuan and a two-week delay in delivery. Modular design can reduce design costs. By reusing 30% of standard modules, a company shortened the design cycle from 30 days to 20 days, reducing costs by 25%.
Mold trial and revision costs are necessary pre-delivery expenses, accounting for approximately 10%-15% of the total cost. These expenses include trial materials, injection molding machine time, and revision processing fees. Initial trial costs vary depending on mold size, ranging from approximately 2,000 yuan per trial for small molds to 10,000 yuan per trial for large molds (such as car dashboards). One complex mold required five trials before passing, resulting in a total trial cost of 30,000 yuan. Revision costs after trial vary significantly. A mold requiring cavity grinding due to dimensional deviations cost 5,000 yuan, while a mold requiring core remanufacturing due to structural errors cost 50,000 yuan, representing 20% of the original mold cost. Using virtual trial technologies (such as Moldflow) can reduce the number of trial runs. One company, through simulation analysis, identified weld mark issues early, increasing their first-trial pass rate from 60% to 90%, reducing trial costs by 50%.
The batch size and complexity of a mold significantly impact unit cost. The cost per cavity of a multi-cavity mold is lower than that of a single-cavity mold. For example, a 16-cavity connector mold cost 200,000 yuan in total, with a per-cavity cost of 12,500 yuan, a 37.5% reduction from the 20,000 yuan per cavity cost of a four-cavity mold. Complex molds (including side core pulls, threaded demolding mechanisms, and other features) cost over 50% more than simple molds. A mold with three sets of side core pulls costs 150,000 yuan, while a similar mold without side core pulls costs only 80,000 yuan. The mold’s lifespan also impacts cost. Long-life molds (1 million cycles) cost 30%-50% more than short-life molds (100,000 cycles), but the cost per cycle is lower. The per-cycle cost of a long-life mold is 0.5 yuan, just 41.7% of the 1.2 yuan cost of a short-life mold. In addition, regional differences lead to different costs. The mold cost in the Yangtze River Delta region is 10%-20% higher than that in the inland area, but the processing cycle is shortened by 30%, which is more advantageous for urgent orders.
