What Is It Like To Be A Plastic Injection Mold Maker?

Ok, raise your hand if you personally know a plastic injection mold maker, hmmm… I don’t see any hands up! Well, who knows what a mold maker does?  This doesn’t look good, so I will try to give you a little insight into this unknown world.

 I have one of those “invisible jobs” that is seldom recognized, but universally valued. You see, almost everyone likes using their cell phone, computer, driving their car, playing CD’s, and generally enjoying the fruit of all our hard work.

 Yet, almost nobody ever thinks about where all this stuff comes from. In fact, I’ve been asked some very strange questions over the years about what I do, such as when my own mother asked me how many molds I made a day! I told her it takes anywhere from 4-12 weeks to make a typical mold and she just sort of cocked her head and replied, ‘Oh.”

 Let’s just take your computer mouse for example. It is entirely made of plastic, and it took a mold maker to make the mold to make the mouse components. I am guessing that there are 10 pieces altogether in the mouse, so that means 10 different molds had to be made.

Here is a little view into a typical day of an American plastic injection mold maker. It doesn’t really vary too much around the world either, just in the details and amount of overtime and specialization.

He, (I’ve never seen a she, though I heard about one once) starts work at either 6 or 7 a.m. I also have never known a mold maker who started later on a regular basis. He typically works a 9 or 10 hour day and often 5 hours on Saturday. Before Asia became a mold making force to be reckoned with, there was basically unlimited overtime for everyone.

He is likely a master mold maker with 25 years experience, two years of technical school, and 4 years of apprenticeship behind him. That is a lot of training and experience, which is quite necessary because there is so much to know and master.

Here is the process in a nutshell, a small nutshell

Once somebody comes up with the idea to make the computer mouse, he gets a preliminary product design made, then a mold making company is contracted to build the mold, a mold designer comes up with a “blueprint” (nobody uses blueprints anymore, it is called CAD because it is done on a computer), and finally the mouse gets molded into the plastic part.

 So, the mold maker gets the plan from the mold designer and together they come up with a “how to” procedure. The entire mold is gone over in every minute detail because, in the end, a mold a really a million little details that fit together.

So, for the next month or two, the mold maker works together with machinists, apprentices, and other mold maker to fabricate all the shapes and pieces that comprise a finished mold. They need to cut steel with special cutters on very sophisticated machinery that can easily cost $150,000.00 each.

Then there is the very mysterious machine called an electrical discharge machine that is truly strange to the initiated.  This machine, which goes by the name of EDM, is the main way that all these shapes are produced in the plastic parts you use, such as the curvy mouse.

The EDM is a bit like sinking your fist into a ball of dough and leaving the imprint of you fist in the dough. Only the dough is hardened steel and your fist would be some graphite, (like pencil lead) made in the shape of the mouse. The EDM produces whatever shape you can make in the graphite into the steel.

So, the mold maker gets the steel with the shapes, and puts them in a holder (mold base), and makes everything fit perfectly so the plastic part comes out nice and clean. If he does a poor job, you will see the little ugly lines on the part, or little fins of plastic sticking out, like you might see on a cheap Chinese toy.

Did I bore you yet?

One thing people don’t seem to understand is that all these pieces have to fit together like a puzzle, only the gaps cannot be more than about one-eighth of a hair (.0005 in.). This isn’t so difficult, until the shapes are on angles or have weird radii that are very complicated to produce and measure.

In a typical day he might run a surface grinding machine, a CNC milling machine, an EDM machine, polish by hand, fit the pieces together, analyze everything on his computer and try to keep track of the various projects he is responsible for. Often one mold maker runs several jobs simultaneously and has highly skilled specialists working a bit like sub-contractors in the same shop.

When the mold is finished, it goes to the injection molder, who will put it in an injection molding machine for sampling. This is always a nerve-wracking experience because you are never really 100% certain that everything is correct.

Hopefully, the part runs well, is the right shape and size, has the right finish and is free from defects. Sometimes it is a complete disaster. Maybe he overlooked something important, maybe the design was flawed, maybe he just made a mistake in interpreting the plan, things can and do happen! This is where Murphy’s Law is most applicable!

If the part is good, he might get an “attaboy”, often nothing is said. If it’s bad, he will certainly hear about it! Generally though, most companies treat mold makers with at least a little respect. The worst is when the boss is from an accounting background or has an MBA. They have no clue as to what it takes to actually make a mold, to them it is about numbers and more numbers. When the boss is from a manufacturing background he has been there and felt the dread of a scrapped $10,000 piece of steel.

Hopefully, our mold maker get 3 weeks vacation, earns almost enough to raise a family, and keeps his stress level at a tolerable point by enjoying other activities outside of work.

Years ago alcoholism was a big problem, but that seems to have mostly disappeared. Most mold makers like hunting, fishing, cars, trucks, boats, snow mobiles, and building things. I have also known some excellent musicians as well. Literature, travel, language, the arts and culture don’t seem to be very popular.