What information need for mold design

It is frustrating and wastes valuable time to find during your work that information is missing, or when significant changes are made after starting that can affect the concept of the mold.

Are the Tolerances Shown?

Are the dimensional tolerances specified on the drawing the same as when the mold cost was first estimated and the mold price quoted? This can have serious implications, especially if no tolerances were shown when the job was quoted; for example, if a molder requests an approximate mold cost so that he can estimate the final cost of the product for his customer. Unfortunately, sometimes there is not even a drawing, just a sample or model of the product used for the estimate.

While it is desirable that the mold designer is involved in the product design, to ensure that the product can be easily molded and will be satisfactory for the purpose intended, mold designers should not agree to make a product drawing, and if they do, they must insist that it be signed by the customer as acceptable. This will eliminate any possible unpleasantness later on, if the product does not look or function as expected.

Are the Tolerances Reasonable?

Are the requested product tolerances feasible, in view of the size of the product and the plastic specified? This is sometimes overlooked when quoting. As we have seen in Section 4.10,while it is nearly always possible to make the mold parts accurately, to very close tolerances, this does not mean that the molded part will satisfy often unreasonable and unnecessary requests for close tolerances. If very close product tolerances are wanted, an experimental setup may be required to determine steel sizes, a process that can be very costly and time-consuming. This must be made clear before work is started. Note that in the case of very stringent tolerances, production (the actual molding) can become very expensive, requiring close inspection of the molded products and possibly causing many rejects.

What are the Cycle Times?

The designer should never guarantee cycle times and must make sure that the customer understands this. If the customer insists on any guarantee, it could require experimental work (test molds, remaking of mold parts, etc.), which could become very expensive. Any such anticipated costs should be brought to the attention of the customer, and added to the mold price. However, the designer should have some idea of the expected cycle, from past experience with similar products, or should try to get this information from someone with molding experience with such products.

What is the Expected Production?

The designer must be aware of the total production expected from the mold, and the expected life of it. There is a significant difference if the mold should be built for 1000,100,000,1,000,000,or 10,000,000 or more parts. This consideration will affect all aspects of a mold, from mold materials selection to many mold features selected by the designer.

It cannot be repeated often enough that the mold is the most important, but only one link in a chain of requirements to produce a molded product. The molder, or the final user, should not really be interested in the mold cost, but only in the cost of the molded product. It is the duty of the designer to advise the customer accordingly and build the most economical mold for the intended job.

The following is also a frequent scenario: A new widget is to be marketed. After a few hundred test samples, the customer estimates that during the next year he could sell 10,000 pieces. He does not yet know if the widget will be accepted at large. What size mold will be required? How will the mold cost, divided by this quantity, affect the cost of the widget? Obviously, because of the small quantity, the mold cost will be significant in this calculation. Also, because of the relatively small quantity, there may be only one cavity or at most 2 or 4 cavities required. This means low productivity, resulting in a higher molding cost. A simple cold runner system could be suitable and quite inexpensive. But what if the widget turns out to be a success and the required quantities increase to an estimated 1,000,000 over the next 3 years? The first mold probably will not be able to produce these quantities in time. This will then require a new, much different mold, with more cavities, a hot runner system, and so on—in short, a more complicated mold, which will cost much more but, despite the higher mold cost, will result in a much lower cost of the molded piece. Which is the better mold? They are both good, and each one is suitable for the specified requirement.