The injection molding tool is the most important part of any molding process. The injection molding tool often requires weeks to months of careful design and planning, manufacturing, polishing, and assembly, but when it’s done, a good injection molding tool will produce hundreds of thousands of identical plastic components quickly and efficiently. But in order to get the full performance out of an injection molding tool, it’s important for injection molders to maintain their tooling and repair.
Common Defects that can be caused by a Faulty Injection Molding Tool
These are a few of the common injection molding problems that can occur directly as a result of a tooling mold that has been improperly designed, maintained, or simply needs repaired. There are many other defects that can occur as a result of improper temperature and pressure control, and machine malfunctions, but the focus here is on the tooling itself.
Short Shots
When the plastic resin doesn’t entirely fill the mold cavity, it’s referred to as a ‘short shot’, and results in incomplete and unusable parts. There are several different things that can cause short shots, such as areas of restricted flow in the mold. If the gates used in the tool are too narrow, the resin won’t be able to flow properly through them. Air could get trapped in the cavity due to insufficient ventilation. Areas with restricted flow can become blocked with gasses and volatiles over time without good maintenance. A defect in the machine could cause insufficient injection pressure and speed–any of these could cause a short short.
Flash
Flash or flashing is a problem when excess material attaches to the molded product and must be removed. This defect is typically caused by resin leakage in the mold as a result of low clamp force, damage to the parting line or insert in the tool, poor venting, or improper machine and mold set-up. Foreign contamination on the parting line surface can also result in flashing, as it will keep the tool from closing completely.
Burn Marks
Burn marks are usually the result of excessive initial melting temperatures or high screw rotation speeds, but they can also occur when the melted resin flows through a restricted path like a nozzle, runner, gate, or other section of the mold. The shear rate of the flow increases the amount of heat affecting the material, resulting in a burn mark. Improper venting or clogged vents also contribute to burn marks, as the gas cannot escape fast enough and will ignite after it is compressed, leaving a small char mark on the part surface.
Practical Ways to Maintain Injection Molding Tools
One of the things that sets World Class Plastics, Inc. apart is our in-house team and facility dedicated to tooling maintenance and repair. Repairs can be expensive, and having to outsource either maintenance or repair of a mold can extend downtime and increase those costs. Repairs are always going to be necessary from time to time, but to reduce the frequency of these repairs, here are a few practical ways to maintain injection molds.
Inspection
Regular inspection of the tool is a must, as it allows the inspector to identify potential issues early on and prevent them from escalating. Every injection molding tool is set up with two different levels of cleaning and inspections at predetermined intervals. These routine inspections check for signs of wear and tear, loose components, residue build-up on the surface as well as in restricted flow areas, leaks, and other problems that could affect the tool’s performance.
Lubrication
Proper lubrication–and being very careful not to over or under-lubricate equipment is essential for smooth, long-lasting operation. It also can prevent friction related damage from moving components.
Cleaning
Regular tool cleaning is essential to remove any residue, contamination, or other debris that could reduce performance or even cause damage to the parts or the mold itself, especially when it comes to areas that are prone to build-up, like cooling channels, ejector pins, and vents. We use an ultrasonic dip tank to thoroughly clean the tool and tooling components.
Temperature
Careful temperature control is essential throughout the actual molding process, from melting the resin, to holding it within the mold, to cooling. Any temperature controls, heating elements, and cooling systems should also be regularly inspected to ensure that everything is cleaned and functioning properly.
About World Class Plastics, Inc.
World Class Plastics, Inc. is an injection molding company well known for our excellent customer service and our industry expertise. If you’re interested in working with us, head over to our website to request a quote on your next project!