Due to the use of plastic products,the appearance of high demand, the impact toughness is better,and the injection molding process is a complex process involving many factors in the production process,will appeared in the process of product defects,this paper analyses the production of plastic parts causes of common defects, and from the molding technological conditions (temperature,pressure,time the injection speed,etc.),the rationality of structure adjustment of mould modification,raw material use before treatment and other aspects of proposed measures to solve the problem and countermeasure.
plastic injection molding
Plastic injection molding is an effective manufacturing process for making plastic products. A high pressure injector squeezes molten thermoset or thermoplastic resin into a pre-cast steel die, where the resin is allowed to set and form into a proper state. It is an efficient mode of production that can produce short and long runs to tight tolerances. Depending on the type of plastic or foam used, the material can range from very durable to soft and malleable.
However, as with any manufacturing process, problems can arise due to machine, material and human error. Troubleshooting common errors can alleviate the frequency of these situations, however, and being prepared can foster a smoother manufacturing run.
Common Defects:
Blister
A blister is a raised area on the plastic surface, very similar to the medical condition of the same name. It is generally the product of too much heat on the tool or by inadequate cooling or venting. Depending on the type of tool, you can also find areas where full coverage is not working. For instance, if the injector has a flow pattern issue, it might not inject all the resin at once, allowing air bubbles to enter the molten resin. A hot runner tool might also suck air into the die because of area constriction, slowing the passage of the resin.
Burn Marks
Burn marks are generally caused by problems similar to blistering. They manifest as literal burn marks on the plastic, black discolorations that resemble scorches. The general cause of burn marks is improper ventilation for the resin. When this happens, the burns are usually located in the position farthest away from the ventilation gate. Another cause might be that the resin is getting trapped in the injector and heating too long. Cleaning the tool often solves this problem.
Burrs
A common problem in many types of machining, burrs appear on injected plastic products when extra pieces or scraps are attached to the finished piece. A common, everyday occurrence of burrs can be found on green plastic Army men, who often have little extra pieces on their heads or thin sheets of plastic connecting their arms to their bodies. Burrs are usually a result of dull or inaccurately cut dies or molds. Sharpening or cleaning the dies are typically the most effective ways to remedy the situation.
Embedded contaminates
Then there is detritus in the finished product, it means that contaminates have somehow worked their way into the resin. A full cleaning of the machine may be necessary to find the source.
Flow marks
Flow marks are look like discolored lines or patterns on the finished product. When they occur, your injector might be functioning at too low a temperature. The gate might also not be properly ventilating the mold.
Lamination
This occurs when contaminates are introduced into the injection mold or resin but manifest as shiny flake layers in the wall of the part. These are a sign that purging compound was accidentally left in the mold.
Sink marks
Sink marks are small holes or depressions, similar to tiny potholes, in the surface of the piece. There are a number of reasons they might appear. First, the material might simply be insufficient for the job. A cause that is easier to remedy is temperature variation, such as too short cooling time or too high melt and mold temperatures. The mold design can contribute to these causes, so it might be necessary to start from scratch.
Short shot mold
A “short short mold” refers to a mold that is not completely filled, leading to deformation or “shortened,” parts. This occurs when the resin cannot fill the mold due to blockage, bottlenecking or injection that is either too fast or too slow.
Simulation Moldflow software provides tools for injection mold design, plastic part design, and the injection molding process. View videos to see how Simulation Moldflow, part of the Prototyping solution, helps you avoid potential manufacturing defects and get innovative products to market faster.
