There is a lot of shroud and mystery around the process of tool and mold making. Creating molds for production is one of the more pricey investments a business can make, though it will save time and money down the road.
So, why is mold making so hard?
A lot of the mystery comes from the tradition of the craft. Mold making techniques and practices have long been passed down amongst tool makers and are often proprietary within specific mold shops.
Now that we are in the era of sharing, people want to know how to do these age-old, craftsman-developed techniques without committing themselves to years of being a journeyman or apprenticing.
Mold making is hard because like many things in the world of machining, a specific finish or end product can be achieved a number of different ways – arguably, some ways are better, more efficient, or longer-lasting than others.
CNC Mold Making
Most molds require a certain level of precision, so it’s best to turn to CNC machining for the initial process. Not only is the cavity for your molded part important to keep accurate, you also need to consider precision when it comes to venting (which allows air to escape as the mold fills), runner balance (where material flows into your mold), and flow (how the material will fill your mold).
CNC machines also have the ability to get close-to-final surface finishes. Depending on the industry that your mold is designed for, different surface finishes are needed on different areas of the mold. CNC can help with this process, though they will rarely be the final step.
Varying materials in varying industries can have different requirements for mold surface finishes. While CNC machines can often get close (they are precise afterall), dealing with a mold creates a whole different challenge. Microscopic or even atomic level finishes can have an effect on a mold – those are finishes that we can’t detect by touch.
This is where hand finishing and polishing takes over.
Depending on your CAM techniques and your CNC machine, you can get finishes that are down to what is known in the machining world as tenths (0.0001”). But if you’re part material is sticky or used for the medical industry (just as two easy examples), that just isn’t smooth enough. Those tiny steps in the 3D surface may look and feel great, but the material will know the difference.
Hand finishing is truly an art for this reason. It requires patience and meticulous understanding of what will be required of your final mold.
What to Consider
There are four big things to consider when you’re designing a mold. If you weigh these properly, making a mold won’t be quite as challenging.
- Consider you final part material and it’s properties. This will determine how stringent or lenient you can be about certain features of your mold.
- The curing and release process for your chosen material. Putting the material in the mold is just the first step, you need to consider how the mold will come apart and how the curing process will occur.
- Different materials move differently through a mold. Make sure to design your mold for the best flow for your given material.
- Surface finish required for your final part. This will be heavily influenced by the surface finish of your mold. You have to make a judgement call between efficiency/overall cost and what your final part will look/feel like.
There’s a lot more to consider when you’re making a mold, but that is why mold making isn’t easy. Experimentation and experience are keys to making the best possible molds.