How many holes can be opened in a mold: the decision on the number of holes is more important than imagined

The number of mold holes - how many parts can be formed in one mold at a time - is one of the most cost-effective decisions in small part mass production. Insufficient production capacity and high allocation of individual molds due to insufficient opening; Having too many molds is expensive, difficult to debug, and results in poor consistency between cavities. The more holes there are, the better. It is a comprehensive account.

How does the number of holes affect the cost

The mold cost increases with the number of holes, but not linearly. From 2 to 8 holes, the mold cost may only increase by half - the processing cost of the cavity itself is only an increment, and the fixed parts such as the mold frame, heating system, and ejection system do not change with the number of holes. Within the span of 8 to 32 holes, this pattern begins to fail, the cavity layout becomes more complex, temperature control requirements increase, and cost increases accelerate again.

The allocation of molds in the cost of a single item=mold cost/number of holes x single item. Roughly speaking, it is clear that the difference between opening 4 holes in a 30000 yuan mold and opening 16 holes in a 50000 yuan mold is several times when the output is large.

But the cost account is only one of the three variables.

The second variable: inter cavity consistency

The normal state of multi cavity molds is that the flow distance and temperature control position of each cavity are not exactly the same. The filling conditions of the corner cavity and the center cavity in the 8-hole mold are different, resulting in slight variations in the size and weight of the produced parts. The more holes there are, the harder it is to suppress this dispersion.

For ordinary parts, it is sufficient to control the inter cavity dispersion within the tolerance. For parts that need to be precisely matched with metal parts, or for parts that are traced cavity by cavity during customer acceptance, the number of holes should be conservative - it is better to use two sets of 8-hole molds than to use one set of 16 hole molds. If there are problems, it is easy to troubleshoot and modify the mold.

The third variable: flexibility of production exchange

The number of holes and order structure should match. Fixed large orders, single products, expanding the number of holes, and taking advantage of production capacity and allocation. There are many varieties of small items, and multiple orders are often cut back and forth. As the number of holes increases, changing production and scheduling becomes more difficult: a set of 32 hole molds can produce 32 pieces at a time, even if only 500 pieces are needed, they have to run more than ten cycles on the machine platform, and the number of debugging pieces is several hundred pieces.

So the common practice is to mix high and low: for main products, use multi hole mass production molds, and for long tail small orders, use sample molds or low hole number molds. A set of hole counting production methods that dominate the world, there must be people waiting for machines in multi variety scenarios.

Several practical decision-making references

If the expected total lifespan exceeds 100000 pieces and the structure is stable without further modifications, the number of holes should be increased; The lifespan usage is in the tens of thousands of pieces, and there may be some modifications, with 8 to 16 holes being relatively stable; For thousands of pieces, it is uncertain whether there will be a redesign. First, use a low hole number mold or even a soft mold for transition, and then proceed to mass production mold once it is finalized.

Another easily overlooked point is that the number of holes cannot be changed after being determined. The number of cavities is fixed by the mold design, and later we wanted to change from 8 holes to 16 holes, which is equivalent to reopening a pair. So the decision on the number of holes needs to be discussed clearly before opening the mold, including the quantity, probability of modification, and delivery time. This discussion is worth spending time on - regretting after opening the mold comes at the cost of the entire mold.

When you see "mold fee" on the quotation, remember to ask one more question: How many holes? How many holes is the unit price calculated based on? The bargaining space for adding quantity later is completely different for the same single item price but different hole numbers.