Plastic Molds are a Process Control Key

Tooling is a key component on the approach to any plastics process. Even subtle changes in a mold can lead to huge process variations. There are many different categories in which molds as a controlling factor are found at the top of the list. This article will touch on several of tooling's primary influences on a plastic process:

-Watering: Early in the initial stages of the crossover from convential molding to scientific method, a debate was often seen on the production floor whether directional water flow had any influence on a molding process. I can tell you first hand, it is a PRIMARY consideration. I have run into numerous situations where a process was found to be outside normal operating conditions due to changes in directional flow. Many companies are reducing the impact of this factor by simply hard plumming their tools to assure consistent watering. I highly recommend this practice...As I've said in several of the previous articles: the key to repeating process consistency is repeatability of your set up procedure!

-Vents: Vents are not just a pretty channel installed for the purpose of impressing your customers. Materials produce gas..both in the barrel through shear, as well as they are moving in the flowfront. Vents should be inspected and cleaned on every tool once per shift...NO EXCEPTIONS. Whenever you run into a molding issue that could directly relate to a flowfront or gas trap issue, you should first inspect and clean your mold before any process change is made. When running a tool new to the floor, you may experience unfill or burn conditions in the end of fill area...and on occasion, just a repeating area with no relationship to end of fill. There are numerous approaches to fixing these sort of problems. It is important to remember in any molding issue...take the simple approach first! A method of testing to see if a vent should be installed would be to take pieces of aluminum tape and tape these in two pieces with the are between the taping resembling a vent channel. If your process seems to respond well to this "pseudo-vent", then it may be a good approach to place a vent in the area. I will write an article that gets more detailed in the different venting issues later...

Top of Mold: Ever run into a situation where it seems like no matter what approach you take, you can't seem to get rid of a contamination issue? Let me ask you this...how often do you clean the top of your mold, and when was the last time you did so? Cleaning the top of your tool can be as important as cleaning the cavitational areas themself.

Grease: Grease is such a touchy area... because you have to ride the middle line when applying it. A moldmaker is right when he says, "you can't have too much grease". True...this is good for tooling that repetitively pulls apart, and compresses under tonnage. But grease can be a processor's worst nightmare...for instance when it bleeds off of ejectors, or splatters off of pins into the part cavity. A good point to make here is that if you are spraying down the moveable half of your tool while cleaning, you could be setting yourself up for failure. Mold cleaner breaks down grease, and can lead to an oily mess that is out of control. When cleaning the moveable half, spray mold cleaner on your rag...then wipe the tool down.

Noise: Learn to listen to your mold... a mold should make certain noises when in good running condition. Squeals, cracking and thumps are warning signs. Learn to recognize them and take steps to inspect your tool and make corrections to your clamping setpoints as a precaution to causing tool damage.

Mold Safe and Low pressure close: If these terms mean nothing to you, stop what you are doing IMMEDIATELY and find someone who knows what they do and how to set them! This will save you alot of downtime and frantic tool repairs to make shipment.

Water: Can't stress water enough...when you are running a good process, you should document the to/ from pressure of each circuit, as well as get mold temperature data from several different points in your tool at a running state temperature. This will save you tons of headaches when an issue arrises and you need to verify whether these factors have changed.

More tooling articles to follow. This is a very huge subject, and I will have to write numerous pieces to cover it all. Point to be made is, that tooling can define you...or defeat you instead. It is all determined by your ability to recognize potential causes of part defects, and analyze the data associated with it.