Working in the plastics industry is not an easy task if you are a processor. It takes many years to learn the ins and outs of the industry. I have been working in plastics for 19 years and I am still learning. From start to finish, it takes a lot of knowledge to be able to make a part. From the design stage, to the mold build, all the way through the finished product it can take up to a year or more sometimes. As I keep learning and polishing my skill set, I am preparing for a new stage in my career. Hopefully with the steps I have taken and knowledge I have and continue to learn I will be in a position to help myself, others and most importantly my family. 

Hopefully after viewing my blog and reading the posts I have entertained you and given you some insight into the plastics world. Though you still may not understand what you read, there are millions of google searches that can be done to answer any questions you may have.

Feel free to comment on any post and I will answer any questions. Until next time my friends always seek the knowledge you deserve. 

After molding plastic parts some need a little more attention. There are parts that can be ultrasonic welded together. Parts also can be assembled together to make a function assembly. Depending on the application the parts will be used for depends on how many steps it takes to complete the part. The more steps used to complete the part the more the part will cost. Parts that take more than one step to complete are called value added. This means the cost of producing the final parts will cost more money.


 If it is a simple shoot and ship part (no secondary applications) then the part could cost as little as .02 cents to make. Think of a model car kit. When you open the box and take out the pieces they are all attached as one. You have to break these pieces off separately, this is due to no other assembly being done at the molder. A simple product molded and packed in a box then shipped out the door.

  


If the part involves assembly and ultrasonic welding with other added parts, then they could cost as much as $20 to make.



Welding basics.....

Just as important as getting a good consistent part, it is also important to not get molding defects. These will happen from time to time. Good preventive measures can help prevent most molding defects. Defects will arise and have to be dealt with. There are a number of types of defects, but the most common are:


Quick overview of molding defects



Contamination is in my mind the number one molding defect. It can be caused by mixed materials, degraded material or grease from the mold itself.

 

Flash is a defect that appears when parting lines get damaged or the plastic pressure is too much for the clamping pressure to with stand and material leaks into the parting lines. Though correctable, flash is difficult to content with.











Short shots or underloads as they are sometimes called are places on the part that do not fill in completely. These can be caused by gases from the plastic being trapped in the cavity or the full shot of material didn't get injected into the mold creating a nozzle leak. The process may not be developed correctly causing an unbalanced fill between cavities.

Producing and maintaining plastic parts to a tolerance is quit difficult. To ensure parts are consistently good the parts are measured periodically. Measuring plastic parts are done with various tools. Smaller parts can be measured by hand using calipers. Calipers are used to measure from one point to another and can measure to within .0001" These are used by hand so accuracy can sometimes be off.






Another measuring device is the CMM or Coordinate Measuring Machine is used to measure a tight tolerance on the part. It can also give surface readings and the dimensions inside of parts. The CMM is programmed by a trained CMM programmer to set points that need be inspected. CMM machines use these precise data points to give critical read outs of the part dimensions. These can find fractional molding errors and the potential to stop the release of bad product.










CMM in action......

Along with the molding machine and robotics, a very key piece to making a plastic part is the mold itself. Now the mold or die (as it is sometimes called) consists of the mirror image of the part. There are a front or cavity side and the rear or core side. These are cut and formed on a CNC milling machine that can be so precise it can cut steel to within .001". After the part design has been finalized the mold is made to match the part. During the mold making process there are a number of components that make up the mold. I'm will not go into great detail, but I will point out a few key components.

Guide pins of the mold eliminate the mold halves from becoming out of position with each other. Just as the name states guide pins help guide the back half to the front half or the front half to the back half. This will ensure the cavity and core fit back together without any damage each cycle.

We have channels (which make a circuit in and out) cut into the steel plates that will run either water or oil through the mold to help cool the part. These channels can be just a couple all the way to 20 or more different circuits.

Vents are cut running from the mold features outward. Vents exist so air can escape the mold as the plastic is being injected into the mold.

Ejector pins are made to run from the back of the mold to the front of the core side. These assist in the removal of the molded part. Ejector pins can also be vented to help air escape the mold as the plastic is being injected.






Molding basics.....

With advancements in technology, not only of plastic, but also in robotics. These, sometimes complex machines can do much more than the average human. Robots are used in many ways throughout the industry. They can be use for a simple task of removing a molded part from a mold, all the way to assembling and painting. Like plastic there are many types of robots. There are simple pick and place robots called 3 axis. These travel on X axis (left to right), Z axis (up and down) and Y axis (forward and backward). These are the most common used in most plastic factories.

Pick and place robot in action.............

How is plastic made into different shapes? This is done in a couple of ways. Injection molding is a widely known process around the world. The process uses an injection molding machine which uses heat and pressure to melt and inject the plastic into a mold. The mold has precise features that are cut with a CNC machine to mirror what the part looks like. After the melted plastic is injected into the mold it takes a few seconds to cool the plastic to hold its shape.












Kinda lengthy, but worth the look..........