Multi-Cavity, Single Cavity, Mold Insert, MUD Insert, Mold Base

I often get asked “Why is there such a wide spread in mold costs?” If the age old proverb says “You get what you pay for”, then the next question is “What am I paying for?” In as few words as possible, I am going to try to explain this, but if I answered this question without writing about molded piece costs, I wouldn’t be doing it justice. You probably already know, if you are buying a mold, it’s because you want molded parts at the least total cost at your desired quality that meets your scheduling requirements. Therefore, I think it would be best if we talked about this in those terms.


If you want more than tens of thousands of parts per month, then a Multi-Cavity Mold is for you. I actually recommend more than a single cavity mold when the capacity is going to be greater than 40,000 pieces a month. That capacity limitation is what would generally force you to buy a multi-cavity tool. I also recommend going to a multiple cavity mold when the customer is trying to meet a certain price point. But if you do go with multiple cavities, know that your larger investment in molds gets rewarded with lower piece prices. It is this reward that sometimes drives customers to purchase multi-cavity molds even when capacity isn’t reached. A multi-cavity mold could be 2, or 64 cavities or anywhere in between. You’ll quickly find out that what you are really buying is machine time. So the less machine time it takes to mold your parts, the less your parts will cost. Unfortunately, a multi-cavity mold can grow to quite an investment as cavities are added. But the sooner you make that investment, the sooner you can reap its rewards.

Family Mold

Now let’s say you need four molded parts in your new project. You added up the costs of making a four multi-cavity molds, one for each part, because you want lower per piece costs and you quickly realize that four molds are not in your budget. But your project won’t work unless you get the piece price down. Well there’s an answer for you. You need a Family Mold. A family mold consists of more than one unique part in the same mold. In my example, this family mold would be designated 1+1+1+1 on the quotation and it would make four different parts. Since the machine time is split among the four parts, you get the advantages of multi-cavity tooling at a lower initial cost. Let’s say your project requires two pieces of the first part, and only one each of the three other parts. Then the family mold would be designated 2+1+1+1. The general guideline is that the parts should be molded out of the same plastic and that they should be ordered in the same ratios as they are molded.

Inserts vs. Bases

Let’s say you only need a few hundred or a few thousand of only one part. You still have options to reduce your per piece costs, but here’s where we remember that old proverb, “You get what you pay for”. Well basically, you can have up to three choices. They are Mold Insert, MUD Insert, or Mold Base. They sound the same, don’t they? But they’re not.

If you get a quote on a Mold Insert, and the price looks much lower than the two other bids you got that don’t use the word “insert”, you might want to jump at it. It’ true that buying a mold insert is a lower initial investment, but there is a reason. Mold Inserts are typically proprietary to that molder. You won’t be able to take that insert to another molder, because no one else will have the mold base that insert fits in. That molder probably has hundreds of inserts that all run on his one proprietary mold base. To run your job, he has to wait for the other jobs running in that mold base to finish, remove the last insert, put your insert in the mold base, then run it. So there is an additional lead time to wait and also set up time that you are paying for every time your insert runs. I am not saying don’t buy a mold insert, just be aware that you probably won’t be able to change vendors without buying another insert, and that your piece price will reflect additional setup time. We can provide you with a Mold Insert option but don’t be surprised if we explain the pros and cons of this option several times to make sure you understand what you are buying.

MUD Bases are similar to Mold Inserts, but they are at least standardized. A MUD insert is a type of mold Insert that fits in a standardized mold base, or “frame”. Most custom molders have a several sizes of MUD frames so if you do buy a MUD Insert, you will have the option to move to another molder. If a molder is running MUD frames exclusively, the setup time can actually be reduced. However, very few custom molders run MUD frames exclusively, so there will be that additional setup every time your MUD insert runs, albeit that setup cost would be much smaller than the non-standard Mold Insert mentioned in the previous paragraph. MUD inserts are also slightly less costly than a standardized mold base but I believe that the slightly higher per piece cost could quickly eliminate any savings.

By far, the majority of molds we make are in their own mold base. We believe this option serves the customer best. Standard mold bases can be set up quickly, they do not require assembly every run, they do not pose the same capacity bottle necks as inserts do, and they give the customer the freedom to transfer the mold should the need arise. You know that saying, “If you love something, set it free”, well, we love our customers and there actually have been occasions where our molds had to visit other molders. When they got there, our customers did not have to spend a dime on mold changes. Unfortunately, I cannot say the same about customers that brought us mold inserts.

As always, we are here to provide solutions to your plastic manufacturing requirements whether they be one hundred parts or one hundred million parts. Consider us as your partner helping you through these decisions. And when you are buying molds, don’t make the mistake of only looking at the mold price. Make sure your decision is based on what your parts are costing you.