The Misconceptions of Injection Mold Making: Seemingly Saving Money, Actually Costing More

In plastic product manufacturing, mold cost accounts for a large proportion of overall expenses. A set of injection molds often costs tens of thousands or even over a hundred thousand yuan. Therefore, manufacturers always try to cut costs wherever possible in mold development. However, some cost-saving practices in actual mold making end up costing far more in the long run. Today, we break down the three most common misconceptions in injection mold development to help you avoid cost traps.

Three Major Misconceptions in Injection Mold Making

Misconception 1: Blindly Choosing Low-Cost Mold Materials

Material quotation is always the top concern for most buyers. Many people take it for granted that as long as the mold can be made, the cheaper the material, the better.

For example, they use ordinary 45# steel to replace dedicated mold steel P20, or even recycled scrap steel, thinking this can directly cut material costs by 30%-50%.

In fact, mold material quality is the core determinant of mold lifespan, product precision and production stability. Saving on material costs in the early stage will lead to far higher expenses in the mass production phase.

1. Mold lifespan impact
   High-quality mold steel such as S136 and 718H features uniform texture, high hardness and strong wear resistance, supporting stable production of hundreds of thousands or even over one million shots.
   Low-cost steel contains many impurities with insufficient hardness. It may suffer cavity wear, dimensional deviation after only tens of thousands of shots, and even rusting, cracking and edge chipping, resulting in permanent mold scrapping in severe cases.
2. Product quality impact
   Low-cost steel has impure internal composition and uneven texture, failing to meet requirements for high polishing and high precision. Finished products are prone to defects, especially transparent parts, appearance parts and precision assembly parts, which can hardly pass quality inspection.
3. Higher processing cost
   Low-grade materials have poor machinability, prone to deformation and edge chipping during mold processing. This not only increases working hours but also causes repeated mold rework, further driving up manufacturing costs.
4. High later maintenance cost
   Molds made of cheap materials are prone to wear and failure, requiring frequent machine shutdowns for mold repair. This delays production schedules and order delivery, while labor and spare parts costs for repairs keep accumulating.

It is not absolutely impossible to adopt low-cost materials; the key is reasonable matching rather than blind pursuit of low prices.
Low-cost steel is only applicable for small-batch production, products with low appearance & precision requirements, simple structure and no long-term service demand.
For mass production, high-precision & high-appearance-demand products, or products using glass fiber reinforced raw materials, forcing the use of cheap materials is simply penny wise and pound foolish.

Misconception 2: Making Different-Shaped Products in One Combined Mold

Besides material selection, mold quantity planning is another common pitfall. Many manufacturers assume that putting several products of different shapes into one mold can reduce the number of molds and save initial mold costs.

While this seems to lower upfront investment, it hides multiple cost traps in design, production and maintenance. In most cases, the total cost is even higher than making separate individual molds.

1. Higher design & manufacturing cost for irregular multi-cavity molds
   Products with different shapes usually differ in wall thickness, demolding direction and shrinkage rate. Integrating them into one mold requires balanced melt distribution for all cavities, matched cavity temperature and interference-free ejection to avoid sink marks, weld lines and deformation.
   Such complex design raises difficulty and working hours greatly, requiring multiple mold flow analysis and optimization, which sharply increases design costs.
2. Poor production flexibility & high hidden costs
   An irregular multi-cavity mold produces all product models in every injection cycle. If product demand and production pace vary, hot-selling items will be in short supply while niche products pile up as inventory, raising inventory costs and capital occupancy.

Worse still, once one product needs redesigning, upgrading or is discontinued due to market changes, the entire mold has to be shut down and overhauled, halting production of all items. The shutdown loss far exceeds the maintenance cost of a single mold.

3. Difficult quality control & higher defect rate
   Products of different shapes have completely different requirements for injection molding process parameters. It is hard to find optimal parameters suitable for all cavities, easily causing partial products to have short shot, shrinkage, deformation and excessive flash.
   Especially for precision parts, the yield rate of combined mold production is 10%-20% lower than separate mold production. The loss from bulk scrapping is a substantial extra expense.

Combined multi-cavity molds are not entirely unusable, but their application scenarios are extremely strict.
They are only cost-effective when all products share the same material, similar process parameters, consistent demand & production pace, with stable mass production for more than 2 years.

Misconception 3: Choosing Mold Manufacturers with Unreasonably Low Quotations

Most buyers inquire with multiple mold factories and tend to select the lowest bidder, believing all mold making services are the same and a lower quote means cost savings.

In reality, mold quotation corresponds to the manufacturer’s technical capability, processing precision, material quality and after-sales service. Factories with excessively low quotes usually cut costs by skimping on materials, simplifying processes and abandoning after-sales support, leaving customers to bear all losses in the later stage.

Unscrupulous low-cost manufacturers mainly adopt three cost-cutting tactics:

1. Material substitution: They promise high-quality mold steel in writing but actually use low-grade steel or recycled scrap, leading to short mold lifespan, poor product quality and frequent repairs.
2. Simplified processing procedures: They skip key steps such as mold flow analysis, precision polishing and heat treatment, resulting in insufficient mold precision and unreasonable structure. The mold suffers frequent short shot, deformation and demolding difficulty in trial runs, requiring repeated rework that delays production and incurs extra costs.
3. Inadequate after-sales service: Molds inevitably have minor adaptation problems after completion. Formal manufacturers provide free after-sales debugging and maintenance, while low-cost factories either refuse after-sales support or charge exorbitant repair fees.

Investing in injection molds never means chasing the lowest price, but pursuing cost performance.

Often, the hundreds or thousands of yuan saved in the early stage will come back as doubled expenses on repairs, rework, mold scrapping and production shutdowns.

In contrast, spending a little more upfront on premium materials, reasonable mold design and reliable manufacturers can reduce failures, improve production efficiency and lower overall loss — achieving real total cost savings in the long run.