Injection molding machines have large fixed asset investments, large production scales, high raw material consumption, high labor productivity, and high output value. They are a form of production organization with high labor efficiency.
Injection molding machines are organically combined with mechanical, hydraulic, electrical, and special accessories according to needs of injection molding process technology. They have a high degree of automation and are closely related to each other. Injection molding machines can operate continuously for 24 hours in 3 shifts. If a component of injection molding machine fails, it will cause downtime.
Although injection molding machine is simple to operate and has few workers, management and maintenance of injection molding machine has high technical content and a large workload. Therefore, to ensure that injection molding machine is always in good condition, it is necessary to strengthen management of injection molding machine and strictly control occurrence of injection molding machine failures. In order to achieve purpose of reducing failure rate, reducing maintenance costs, and extending service life.
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 of injection molding products and degree of guarantee for injection molding production.
In production of modern injection molding machines, due to complex structure of injection molding machine, high degree of automation, close connection between hydraulics, electronic control and machinery, failure of injection molding machine, even a partial failure, will cause the entire injection molding machine to stop production. Failure of injection molding machine directly affects quantity and quality of injection molded products.

 

There are many types of injection molding machine failures, which can be classified from different angles.
1. According to state of failure, it can be divided into:
(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, hydraulic and mechanical components.
(2) Sudden failure.
It is caused by combined effect of various adverse factors and accidental external influences, which exceeds limit 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 penetrated due to high voltage. Such faults often occur suddenly without any prior signs.
Sudden faults often occur during use of injection molding machine, often due to defects in design, manufacturing, assembly and materials, or operating errors and illegal operations.
2. According to nature of fault, it can be divided into:
(1) Intermittent fault.
Injection molding machine loses some of its functions in a short period of time, which can be restored with a little repair and debugging, without need to replace parts.
(2) Permanent fault.
Some parts of injection molding machine are damaged and need to be replaced or repaired before they can be restored to use.
3. According to degree of impact of fault, it can be divided into:
(1) Complete fault. Injection molding machine completely loses its function.
(2) Local fault. Injection molding machine loses some functions.
4. According to cause of fault, it can be divided into:
(1) Wear fault. Failures caused by normal wear and tear of injection molding machine.
(2) Misuse failures. Failures caused by operating errors and improper maintenance.
(3) Inherent weakness failures. Failures caused by weak links in injection molding machine due to design problems during normal use.
5. According to danger of failure, it can be divided into:
(1) Dangerous failures.
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; failures caused by failure of hydraulic electronic control system, etc.
(2) Safety failures.
For example, safety protection system acts when it does not need to act; injection molding machine starts when it cannot start.
6. According to occurrence and development rules of injection molding machine failures, it can be divided into:
(1) Random failures. Time of failure is random.
(2) Regular failures. Occurrence of failures has a certain pattern.
Each type of failure has its main characteristics, namely the so-called failure mode, or failure state. Fault conditions 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 fault 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. This procedure is roughly as follows.

1. Ask operator
(1) What fault occurred? Under what circumstances? When did it happen?
(2) How long has injection molding machine been running?
(3) Was there any abnormal phenomenon before fault occurred? Is there any sound or sound and light alarm signal? Is there any smoke or odor? Is there any wrong operation (pay attention to way of asking)?
(4) Is control system operating normally? Has operating procedure changed? Are there any special difficulties or abnormalities during operation?
2. Observe condition of the whole machine and various operating parameters
(1) Are there any obvious abnormal phenomena? Are 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 device
(1) Check whether all readings are normal, including pressure gauge and other instrument readings, and oil level.
(2) Check whether filter, alarm and interlock device, action output or display are normal.
4. Injection molding machine inspection (under permitted conditions)
Check intermittent condition, persistent condition, fast forward or slow forward condition to see whether these conditions affect output and whether they may cause damage or other dangers.

1. Use sensory inspection (continue to observe in depth)
First look: whether there are any abnormalities in plug and socket, whether motor or pump is running normally, whether control adjustment position is correct, whether there are traces of arcing or burning, whether fuse is good or bad, whether liquid is leaking, whether lubricating oil circuit is unobstructed, etc.
Second touch: vibration of injection molding machine, temperature of components (groups), temperature of oil pipe, and state of mechanical movement.
Third listen: whether there are any abnormal sounds.
Fourth smell: whether there is any burning smell, leakage smell, or other odors.
Fifth check: changes in shape and position of workpiece, changes in performance parameters of injection molding machine, and circuit abnormality inspection.
2. Evaluate inspection results
Evaluate whether fault judgment is correct, whether fault clues are found, and whether inspection results are consistent.

1. Identify system structure and determine test method
Check manual of injection molding machine to identify structure of injection molding machine, what method to use for testing, what test means are needed, what test parameters or performance parameters may be obtained, under what operating conditions to test, what safety measures must be followed, and whether an operating license is required.
2. System detection
Use the most suitable technical detection for system structure. At appropriate test point, compare results obtained based on input and feedback with normal value or performance standard to find out suspicious location.

1. Repair
Find cause of fault, repair injection molding machine fault and take preventive measures; check related parts to prevent spread of fault.
2. Replacement
Correctly assemble and debug the replacement parts, and pay attention to related components. Replaced parts are repaired or scrapped.

1. Start injection molding machine
Start injection molding machine after parts are assembled and debugged, first manually (or inching), then perform no-load and load measurements.
2. Adjust load change speed from low to high, load from small to large, maximum system pressure cannot exceed 140kg/cm2, and measure performance according to specified standards.
3. Expand scope of performance test
According to needs, gradually expand scope of performance test from local to system. Pay attention to operation status of system in non-fault area. If performance meets requirements, it will be delivered for use. If it does not meet requirements, fault location will be re-determined.

1. Collect valuable information and data, such as time when injection molding machine failure occurred, failure phenomenon, downtime, repair hours, parts replacement, repair effects, problems to be solved, settlement costs, etc., and store them in archives according to specified requirements.
2. Statistical analysis
Regularly analyze use records of injection molding machines, analyze downtime losses, revise memo catalog, find key measures to reduce maintenance operations, study failure mechanism, and propose improvement measures.

3. Feedback relevant failures to competent department according to procedures, and feedback to injection molding machine manufacturing unit.

 

To do a good job in injection molding machine fault management, it is necessary to understand causes of faults, accumulate information and data on common and typical faults, conduct fault analysis, pay attention to study of fault laws and fault mechanisms, and strengthen daily maintenance, inspection and pre-repair.
There are 8 aspects to deployment procedures of fault management.
1. Do a good job in publicity and education, so that operators and maintenance workers consciously record, count and analyze injection molding machine faults and put forward reasonable suggestions.
2. Closely combine actual injection molding production and characteristics of injection molding machine status, and divide injection molding machines in use into three categories: A, B, and C to determine focus of fault management.
3. Use monitoring instruments to carry out planned monitoring of key parts of key injection molding machines to timely discover signs of faults and deterioration information. General injection molding machines should also be inspected daily, patrolled, regularly inspected (including precision inspections), in good condition through human senses and general detection tools, focusing on mastering technical status and abnormal phenomena of parts, mechanisms and parts prone to failure. At the same time, it is necessary to formulate inspection standards and determine boundaries of normal, abnormal and faulty injection molding machines.
4. Carry out fault analysis and train injection molding machine maintenance workers to master fault analysis methods.
5. Fault records are basic data for realizing injection molding machine fault management, are also original basis for fault analysis and processing. Records must be complete and correct. After injection molding machine maintenance workers conduct inspections and fault repairs on site, they should carefully fill in "Injection Molding Machine Fault Repair Form" according to content, workshop mechanics will conduct monthly statistics and analysis and report to injection molding machine management supervisor.
6. In addition to mastering fault situation on a daily basis, workshop injection molding machine maintenance personnel should collect "fault repair forms" and maintenance records on a monthly basis. Through statistics, collation and analysis of fault data, fault frequency and average fault interval of various injection molding machines are calculated, fault dynamics and key fault causes of a single injection molding machine are analyzed, occurrence law of faults is found out, so as to highlight key points and take countermeasures, fault information collation and analysis data are fed back to planning department to arrange preventive repairs or improvement measures. It can also be used as a basis for modifying regular inspection interval, inspection content and standards.
According to statistical data, statistical analysis charts can be drawn. For example, dynamic statistical analysis table of single injection molding machine failure is an effective method for maintenance team to visually manage failures and other problems. It is convenient for managers and maintenance workers to grasp failures of various types of injection molding machines in a timely manner, and to have clear goals when determining maintenance countermeasures.
7. Through daily inspections of maintenance workers and status inspections of injection molding machines, status information and fault signs, as well as relevant records and analysis data, workshop injection molding machine maintenance personnel or repair team leader will arrange daily maintenance in time for existing problems of various types of injection molding machines, make full use of production gap time or holidays, take prevention in advance to control and reduce occurrence of failures. For some fault signs and hidden dangers that cannot be borne by daily maintenance, feedback will be given to planning department to arrange planned repairs.
8. Develop a fault information management flow chart.

Researching failure rules is very beneficial to formulating maintenance countermeasures and even establishing a scientific maintenance system. During use of injection molding machines, their performance or status gradually declines with passage of time. Many failures will have some signs before they occur, which are called potential failures. Their identifiable physical parameters indicate that a functional failure is about to occur. Functional failures indicate that injection molding machine has lost specified performance standards. Law of change of failure rate of injection molding machine over time is often called bathtub curve.
Change of failure rate of injection molding machine over time can be roughly divided into three stages: early failure period, occasional failure period and wear and tear failure period.
1. Early failure period
Injection molding machine is in the early failure period. Failure rate is very high at the beginning, but failure rate drops rapidly over time. The early failure period is also called running-in period for mechanical products. Length of this period varies depending on design and manufacturing quality of product and system. Failures that occur during this period are mainly caused by defects in design and manufacturing, or improper use environment.
2. Occasional failure period
When injection molding machine enters occasional failure period, failure rate is roughly stable and tends to a constant value. During this period, failure occurs randomly. During occasional failure period, failure rate of injection molding machine is the lowest and stable. Therefore, it can be said that this is the best state period or normal working period of injection molding machine. This section is called effective life.
Failures during occasional failure period are mostly caused by improper design, use and poor maintenance. Therefore, by improving design quality, improving use management, strengthening monitoring diagnosis and maintenance, failure rate can be reduced to the lowest level.
3. Wear and tear failure period
In later period of use of injection molding machine, failure rate begins to rise. This is caused by wear, fatigue, aging, corrosion and other factors of injection molding machine parts. If an overhaul is carried out at inflection point, that is, beginning of wear and tear failure period, failure rate can be reduced economically and effectively.
Three stages of change in failure rate curve of injection molding machine truly reflect law of change in failure rate of injection molding machine from running-in, debugging, normal operation to overhaul or scrapping. Strengthening daily management and maintenance of injection molding machine can extend occasional failure period. Accurately finding inflection point can avoid excessive repairs or expansion of repair scope to obtain the best investment benefits.