Injection molding machine failure generally refers to an event or phenomenon in which injection molding machine or system loses or reduces its specified function during use. Injection molding machine is equipped by enterprise to meet production process requirements of injection molding products. Function of injection molding machine reflects its value in production activities of injection molding products and degree of guarantee for injection molding production.
In modern injection molding machine production, due to complex structure of injection molding machine, high degree of automation, and close connection between hydraulics, electronic control and mechanics, if injection molding machine fails, even if it is a local failure, it will cause the entire injection molding machine to stop production. Injection molding machine failure directly affects quantity and quality of injection molded products.

Injection molding machine failures are diverse and can be classified from different angles.

(1) Gradual failure.
It is caused by gradual deterioration of initial performance of injection molding machine. Most injection molding machine failures belong to this type of failure. This type of failure is closely related to wear, corrosion, fatigue and creep of electronic control and hydraulic mechanical components.

(2) Sudden failure.

It is caused by combined effects of various adverse factors and accidental external influences, which exceed limits that injection molding machine can withstand. For example: screw breaks due to overload caused by iron entering barrel; electronic board of injection molding machine is broken due to high voltage intrusion. This type of failure often occurs suddenly without any signs in advance. Sudden failures often occur during use of injection molding machine, and are often caused by defects in design, manufacturing, assembly and materials, or operational errors and illegal operations.

(1) Intermittent failure. Injection molding machine loses some of its functions in a short period of time, can be restored with a little repair and debugging, without need to replace parts.

(2) Permanent failure. Some parts of injection molding machine are damaged and need to be replaced or repaired before they can be restored to use.

(1) Complete failure. Causes injection molding machine to completely lose its function.
(2) Local failure. Causes injection molding machine to lose some functions.

(1) Wear failure. Failure caused by normal wear of injection molding machine.
(2) Misuse failure. Failure caused by operating errors or improper maintenance.
(3) Inherent weakness failure. Failure caused by design problems that cause weak links in injection molding machine during normal use.

(1) Dangerous failure. For example, safety protection system loses its protective function due to a failure when it needs to act, causing personal injury and injection molding machine failure; failure caused by failure of hydraulic and electronic control system, etc.
(2) Safety failure. For example, safety protection system acts when it does not need to act; injection molding machine starts when it cannot start.

(1) Random failure. Time of failure is random.
(2) Regular failure. There are certain rules for occurrence of failures.
Each failure has its main characteristics, namely so-called failure mode or failure state. Failure states of various injection molding machines are quite complicated, but they can be summarized into following types: abnormal vibration, mechanical wear, input signal cannot be accepted by computer, solenoid valve has no output signal, mechanical hydraulic component rupture, proportional linear imbalance, hydraulic pressure drop, hydraulic leakage, oil pump failure, hydraulic noise, circuit aging, abnormal sound, oil quality deterioration, power supply voltage drop, amplifier board no output, temperature out of control and others. Proportion of various failure modes of different types of injection molding machines is different.

 

In order to ensure that fault analysis and troubleshooting are fast and effective, a certain procedure must be followed, which is roughly as follows.

1. Ask operator

(1) What failure occurred? Under what circumstances? When did it happen?

(2) How long has injection molding machine been running?

(3) Are there any abnormal phenomena before failure occurred? Are there any audible or visual alarm signals? Is there any smoke or odor? Is there any incorrect operation (pay attention to inquiry method)?
(4) Is control system operating normally? Are there any changes in operating procedures? Are there any special difficulties or abnormalities during operation?
2. Observe condition of the entire machine and various operating parameters
(1) Are there any obvious abnormal phenomena? Are there any parts stuck or damaged? Is hydraulic system loose or leaking? Are wires broken, scratched or burned?
(2) Are there any changes in operating parameters of injection molding machine? Are there any obvious interference signals? Are there any obvious damage signals?
3. Check monitoring and indicating devices
(1) Check whether all readings are normal, including pressure gauge and other instrument readings, and oil level.
(2) Check whether filter, alarm and interlocking device, action output or display are normal.
4. Inspect Injection Molding Machine (if permitted)
Inspect for intermittent operation, sustained operation, fast or slow feed conditions to determine whether these conditions affect output and could cause damage or other hazards.

1. Sensory Inspection (Continued Observation)
1. Observe: Check for abnormalities in plug and socket, whether motor or pump is operating properly, whether control adjustment position is correct, whether there are arcing or burning marks, whether fuse is in good condition, whether there are fluid leaks, whether lubrication lines are unobstructed, etc.
2. Touch: Check for vibration of injection molding machine, heat of components, temperature of oil pipes, and mechanical movement.
3. Listen: Check for abnormal sounds.
4. Smell: Check for burning, leaking, or other odors.
5. Check: Check for changes in shape and position of workpiece, changes in performance parameters of injection molding machine, and circuit abnormalities.
2. Evaluate Inspection Results
Evaluate whether fault diagnosis is correct, whether fault clues have been found, and whether inspection results are consistent.

1. Identify System Structure and Determine Test Method
Consult injection molding machine manual to identify machine's structure, testing method to be used, required testing tools, possible test parameters or performance parameters, operating conditions under which testing should be performed, necessary safety measures, and whether an operating permit is required.
2. System Testing
Use testing technology most appropriate for system structure. At appropriate test points, compare input and feedback results with normal values or performance standards to identify any suspected faults.

1. Repair
Identify cause of fault, repair injection molding machine, and implement preventive measures. Inspect related parts to prevent fault from spreading.
2. Replacement
Properly assemble and debug replacement parts, paying attention to related components. Repair or discard any replaced parts.

1. Start Injection Molding Machine
After assembling and debugging parts, start injection molding machine. Start manually (or inching), then perform no-load and load measurements.
2. Adjust load change rate from low to high and load from small to large. Maximum system pressure must not exceed 140 kg/cm². Measure performance according to specified standards.
3. Expand Performance Test Scope
Gradually expand performance test scope from local to systemic as needed. Pay attention to operating status of system in non-faulty areas. If performance meets requirements, release machine for use. If not, re-identify fault location.

1. Collect valuable information and data
Such information as time of injection molding machine failure, fault symptoms, downtime, repair hours, parts replaced, repair results, outstanding issues, and settlement costs should be archived according to specified requirements.
2. Statistical Analysis
Regularly analyze injection molding machine usage records, analyze downtime losses, revise memorandum, identify key measures to reduce maintenance work, study fault mechanism, and propose improvement measures.
3. Report any faults to relevant authorities according to procedures and provide feedback to injection molding machine manufacturer.

To effectively manage injection molding machine faults, it is necessary to understand causes of faults, accumulate data and information on common and typical faults, conduct fault analysis, prioritize research on fault patterns and mechanisms, and strengthen routine maintenance, inspections, and preventive repairs. Fault management implementation procedure includes following eight aspects:
1. Conduct effective publicity and education to encourage operators and maintenance personnel to conscientiously record, compile statistics, analyze injection molding machine faults, and provide rational solutions.
2. Based on actual injection molding production practices and characteristics of injection molding machines, categorize in-use injection molding machines into three categories: A, B, and C to determine focus of fault management.
3. Use monitoring instruments to systematically monitor key areas of key injection molding machines to promptly detect signs of faults and deterioration.
General injection molding machines should also undergo daily inspections, patrol inspections, periodic inspections (including precision checks), condition checks using both human senses and standard testing tools. This focus should be on understanding technical status and abnormalities of fault-prone areas, mechanisms, and components. At the same time, inspection standards should be established to define boundaries between normal, abnormal, and faulty injection molding machines.
4. Conduct fault analysis and train injection molding machine maintenance personnel in fault analysis methods.
5. Fault records are fundamental data for injection molding machine fault management and primary basis for fault analysis and resolution. Records must be complete and accurate. After on-site inspections and fault repairs, injection molding machine maintenance personnel should carefully complete "Injection Molding Machine Fault Repair Form." Workshop mechanics should compile and analyze these records monthly, submit them to injection molding machine management supervisor.
6. In addition to daily monitoring of fault conditions, workshop injection molding machine maintenance personnel should compile these "Fault Repair Forms" and maintenance records monthly. By compiling, organizing, and analyzing fault data, failure frequency and average time between failures for each type of injection molding machine can be calculated. Failure dynamics and key causes of individual injection molding machines can be analyzed to identify patterns in fault occurrence, enabling targeted countermeasures. This compiled and analyzed fault information should be fed back to planning department to facilitate development of preventive repair or improvement measures. This data can also serve as a basis for revising intervals, content, and standards for regular inspections.
Based on the statistically compiled data, statistical analysis charts can be drawn. For example, a dynamic statistical analysis chart of individual injection molding machine failures is an effective method for maintenance teams to visually manage failures and other issues. This not only allows management and maintenance workers to promptly understand status of various types of injection molding machine failures, but also provides clear objectives when determining maintenance countermeasures.
7. Through routine inspections and injection molding machine status checks by maintenance workers, status information and fault symptoms are obtained, along with relevant records and analysis data. Workshop's injection molding machine maintenance personnel or repair team leader will promptly schedule routine maintenance for each type of injection molding machine, making full use of production breaks and holidays to ensure proactive prevention and reduce occurrence of failures. For certain fault symptoms and hidden dangers that cannot be addressed through daily maintenance, feedback will be provided to planning department for scheduled repairs.
8. Develop a fault information management flow chart.

Studying failure patterns is extremely beneficial for developing maintenance countermeasures and establishing a scientific maintenance system. During use of injection molding machines, their performance or condition gradually declines over time. Many failures have early warning signs, known as latent failures. Identifiable physical parameters indicate an impending functional failure, which means injection molding machine has lost its specified performance standards.
Pattern of failure rates over time for injection molding machines is often referred to as bathtub curve. Failure rate of injection molding machines can be roughly divided into three stages: early failure period, occasional failure period, and wear-out failure period.
1. Early Failure Period
When an injection molding machine is in the early failure period, failure rate is initially high, but decreases rapidly over time. For mechanical products, early failure period is also known as running-in period. Length of this period varies depending on design and manufacturing quality of product or system. Failures that occur during this period are primarily caused by design and manufacturing defects or improper operating environment.
2. Occasional Failure Period
When an injection molding machine enters occasional failure period, failure rate remains relatively stable and approaches a constant value. During this period, failures occur randomly. During occasional failure period, failure rate of injection molding machine is lowest and most stable. Therefore, it can be said that this is injection molding machine's optimal operating period, or normal operating period. This period is called its useful life.
Failures during the occasional failure period are often caused by improper design, improper use, and inadequate maintenance. Therefore, by improving design quality, improving operational management, strengthening monitoring, diagnosis, maintenance, failure rate can be minimized.
3. Wear and tear failure period
During later stages of an injection molding machine's life, failure rate begins to rise. This is due to wear, fatigue, aging, and corrosion of its components. Performing a major overhaul at inflection point, or beginning of wear and tear failure period, can economically and effectively reduce failure rate.
Three stages of injection molding machine failure rate curve accurately reflect pattern of failure rate changes from run-in, commissioning, normal operation, to overhaul or scrapping. Strengthening daily management and maintenance of injection molding machine can extend occasional failure period. Accurately identifying inflection point can avoid excessive repairs or over-the-counter repairs, thereby achieving the best return on investment.