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All aspects of defects in injection molding
- Oct 26, 2018 -

1. The defect of the so-called injection part is that the injection part can not meet the original design, use and other quality requirements of the injection part in the injection molding process. Description of defects may include a possible cause.

For example, insufficient injection, i.e. incomplete injection, may be described as insufficient filling pressure of the mold or insufficient plastics of the filling mold. It is very useful to try to describe the simplest words without any possible reasons. In this way, we will not have any preconceptions when we look for the causes of shortcomings.

Finding the cause of the defect may be a long process, because he needs to consider the plastic, injection molding machine, mold processing. The following is the recommended Guide:

A, plastics: check level or type, check the impurities and confirm the manufacturer's specifications. If this defect is evident on several batches of plastics from the same manufacturer or on the same plastics from another supplier, it means plastics are not a problem. We should pay special attention to the different processing characteristics of the new material.

B. Injection Molding Machine: Check all the functions of the injection molding machine and consider any factors that may affect the pressure, temperature, ratio and time. If the drawbacks are intermittent, this usually implies that the injection molding machine operates incorrectly, such as a temperature fluctuation caused by a poor thermocouple. If the defect occurs in the same position as a single cavity mold, this implies that the cause of the problem lies in the device of the injection cylinder (such as the return valve) or in the control adjustment of the injection molding machine.

C. Mould: Make sure the mold is properly installed and at the right temperature, and all parts are running smoothly. If defects always occur in the same or several cavities of a multi-cavity mold, they usually exit in the feed system (i.e., the runners or gates of these cavities).

D, processing: check pressure, temperature and time according to the recommendation of plastic suppliers. If the defect disappears when the mold is used in another injection molding machine, the defect may be due to the consistency of the processing conditions used with the production on the original machine. If another person fails to operate the injection molding machine, the defect may be human error. Inspection speed, injection operation management and residence time of safety door opening and closing should be checked.

3. Solving the shortcomings of the injection parts The appearance of the shortcomings of the injection parts undoubtedly brings the quality hidden danger to the injection production.

A. Determine the impact of shortcomings: If the shortcomings make injection parts can not be used or sold, this shortcoming must be eliminated. If it is only a weak influence, it may not necessarily be completely eliminated.

B. Determine where the responsibility lies: This may be an academic interest, but if the shortcomings recur, the operators, plastics, injection molding machines, molds and processing processes need to be reviewed.

C. Take action to avoid shortcomings: Failure to take appropriate action can result in poor injection molding and consequently have a devastating impact on the profitability of the project.

D, take steps to prevent defects from appearing again: record all the conditions for the elimination of defects. Indicate the repair or change of mold or injection molding machine, as well as the type of plastic and the change of grade work quality. If recycled materials are used, the quality of the proportions used must be specified.

These steps to deal with shortcomings may seem redundant, but none of them is perfect unless all of them are taken into account. Although defective products can be recycled, making defective products is not economical.

4. Injection defects and remedies A logical, systematic approach to dealing with defects that people desire, and many actual injectors have their operational strategies. Compiling these strategies is most important to ensure that all the terms are clear and understood by all concerned. To clearly describe the defects of injection molded parts, all possible causes should be checked. The impact should also be taken into account, and when the cause is determined, necessary steps should be taken to reduce and prevent its recurrence. There are six strategies.

1, naming defects. Because the defects have different names, they should not change after deciding to use that name.

2, describe shortcomings. Description of defects may include a possible cause. For example, "insufficient injection", i.e. incomplete injection, may be described as "insufficient filling pressure in the mold" or "insufficient plastics in the mold" trying to describe it in the simplest terms without any possible cause. This is a useful way to use this method, and we will look for the cause of the defect in the next step. There will be no preconceptions.

3. Looking for the cause of the defect, this may be a long process, because he needs to consider the plastic, injection molding machine, mold processing process. The following is the recommended guide.

A: plastic: check level or type, check the impurities, and confirm whether it meets the manufacturer's specifications. If this defect is similar to several batches of plastics from the same manufacturer or to the same plastics from another supplier, it means plastics are not a problem.

C. Mould: Determine whether the mold is properly installed and at the right temperature, and all parts are running smoothly. If the defect disappears and always appears in the same or several cavities of the multi-cavity, the defect usually occurs in the feed system (i.e. the runner or gate serving the cavities).

D, processing: check pressure, temperature and time according to the recommendation of plastic suppliers. If the defect disappears when the mold is used in another injection molding machine, the defect may be due to the consistency of the processing conditions used with the production on the original machine. If another person fails to operate the injection molding machine, the defect may be human error. Speed should be checked, management of injection action and residence time of safety door opening and closing.

4. Determine the impact of the shortcomings, if the shortcomings make injection parts can not be used or sold, this shortcomings must be eliminated.

5. Determining where the responsibility lies may be an academic interest, but if the shortcomings recur, the operator will also have to review the raw materials, injection molding machines, molds and machining processes.

6, take actions to avoid shortcomings. Failure to take appropriate action will produce inferior injection molded parts and consequently affect the profitability of the project.


In each case of injection defects, the defects of the injection parts are usually caused by the following factors: the operation of the injection molding machine, the function of the mold or the performance of the plastic processing, etc., and the problems or shortcomings are usually caused by more than one cause. Each of the following shortcomings provides recommended remedies under the headings of injection molding machines, moulds and plastics.