Introduction
Injection molding machine failure generally refers to an event or phenomenon in which the machine or system loses or degrades its specified functionality during use. Injection molding machines are equipped to meet the production process requirements of injection molded products. The function of an injection molding machine reflects its value in the production of injection molded products and the degree to which it guarantees injection molding production.
In modern injection molding machine production, due to the complex structure, high degree of automation, and close connection between hydraulics, electronic control, and mechanics, any failure of the injection molding machine, even a partial failure, will cause the entire injection molding machine to stop production. Injection molding machine failure directly affects the quantity and quality of injection molded products.
Classification of injection molding machine failures
Injection molding machine failures are diverse and can be classified from different perspectives.
1, According to the state of the fault, it can be divided into:
(1) Gradual fault.
This is caused by the gradual deterioration of the initial performance of the injection molding machine. Most of the failures of injection molding machines belong to this type of failure. This type of failure is closely related to the wear, corrosion, fatigue and creep of electronic control and hydraulic mechanical components.
(2) Sudden failure.
These failures are caused by a combination of adverse factors and accidental external influences that exceed the limits of the injection molding machine.
For example, a screw may break due to overload caused by iron entering the barrel, or the injection molding machine’s electronic board may be damaged by high voltage.
These failures often occur suddenly, without any prior warning. Sudden failures often occur during the use of the injection molding machine and are often caused by defects in design, manufacturing, assembly, materials, or operating errors or violations of regulations.
2, According to the nature of the fault, it can be divided into:
(1) Intermittent fault. The injection molding machine loses some of its functions for a short period of time, which can be restored with a little repair and debugging, without the need to replace parts.
(2) Permanent failure. Some parts of the injection molding machine are damaged and need to be replaced or repaired before they can be put back into use.
3, According to the degree of impact of the failure, it can be divided into:
(1) Complete failure. The injection molding machine loses all functions.
(2) Local failure. The injection molding machine loses some functions.
4, According to the cause of the failure, it can be divided into:
(1) Wear failure. Failure caused by normal wear of the 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 weaknesses in the injection molding machine during normal use.
5, According to the danger level of the fault, it can be divided into:
(1) Dangerous faults. For example, the safety protection system loses its protective function due to a fault when it is required to act, causing personal injury and injection molding machine failure; faults caused by failure of the hydraulic and electronic control system, etc.
(2) Safety failures. For example, the safety protection system is activated when it is not required; the injection molding machine is started when it cannot start.
6, According to the occurrence and development patterns of injection molding machine failures, they can be divided into:
(1) Random failures. The time of failure is random.
(2) Regular failures. The occurrence of failures has a certain pattern.
Each failure has its key characteristics, known as a failure mode or condition.
While the failure modes of various injection molding machines are quite complex, they can be categorized as follows: abnormal vibration, mechanical wear, input signals that cannot be received by the computer, no solenoid valve output signal, mechanical hydraulic component rupture, proportional linearity loss, hydraulic pressure drop, hydraulic leakage, oil pump failure, hydraulic noise, circuit aging, abnormal sound, oil deterioration, power supply voltage drop, no amplifier output, temperature runaway, and others.
The proportion of these various failure modes varies across different types of injection molding machines.
Fault Analysis and Troubleshooting Procedures
In order to ensure that fault analysis and troubleshooting are quick and effective, a certain procedure must be followed, which is roughly as follows.
Step1: Analyze symptoms while maintaining the scene
1, Ask the operator
(1) What failure occurred? Under what circumstances? When did it occur?ใใ
(2) How long has the injection molding machine been running?ใ
(3) Were there any abnormal phenomena before the fault occurred? Any sound or sound and light alarm signals? Was there any smoke or odor? Was there any incorrect operation (pay attention to the way of asking)?
(4) Is the control system operating normally? Are there any changes to the operating procedures? Are there any special difficulties or abnormalities during operation?
2, Observe the condition of the entire machine and various operating parameters.
(1) Are there any obvious abnormalities? Are any parts stuck or damaged? Is the hydraulic system loose or leaking? Are any wires cracked, scratched, or burned?ใ
(2) Are there any changes in the operating parameters of the injection molding machine? Are there any obvious interference signals? Are there any obvious damage signals?
3, Check the monitoring and indicating devices
(1) Check whether all readings are normal, including the pressure gauge and other instrument readings, oil level.
(2) Check whether the filter, alarm and interlock device, action output or display are normal.
4, Inching injection molding machine inspection (under permitted conditions)
Check for intermittent conditions, persistent conditions, and conditions during fast or slow forwarding to see if these conditions affect the output and could cause damage or other hazards.
Step 2: Check the injection molding machine (including parts, components and circuits)
1, Use sensory inspection (the process of continuing in-depth observation)
- 1, Check: whether there are any abnormalities in the plug and socket, whether the motor or pump is operating normally, whether the control adjustment position is correct, whether there are any signs of arcing or burning, whether the fuse is good or bad, whether there is any liquid leakage, whether the lubrication oil line is unobstructed, etc.
- 2, Touch: vibration of injection molding machine, heat of components (assemblies), temperature of oil pipes, and state of mechanical movement.
- 3, Listen: Check for any abnormal sounds.
- 4, Smell: Check for burnt smell, leakage smell, or other strange smell.
- 5, Check: changes in the shape and position of the workpiece, changes in the performance parameters of the injection molding machine, and circuit abnormality inspection.
2,Assessment and inspection results
Evaluate whether the fault judgment is correct, whether the fault clues are found, and whether the results of various inspections are consistent.
Step 3: Determine the fault location
1, Identify the system structure and determine the test method.
Consult the manual of the injection molding machine to identify the structure of the 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 testing uses the most appropriate technology for the system structure.
At appropriate test points, the input and feedback results are compared with normal values โโor performance standards to identify suspicious locations.
Step 4: Repair or Replace
1, Repair and find the cause of the fault, repair the injection molding machine fault and take preventive measures; check related parts to prevent the fault from spreading.
2, Replace the parts correctly, assemble and debug them, and pay attention to the relevant parts. The replaced parts should be repaired or scrapped.
Step 5: Conduct performance measurement
1, Start the injection molding machine. After assembling and debugging the parts, start the injection molding machine manually (or inching), and then perform no-load and load measurements.
2, Adjust the load change speed from low to high and the load from small to large. The maximum system pressure cannot exceed 140kg/cm2. Measure the performance according to the specified standards.
3, Expand the scope of performance testing: As needed, gradually expand the scope of performance testing from local to system-wide. Pay attention to the system’s operating status in non-faulty areas. If performance meets requirements, release the system for use. If not, redefine the fault location.
Step 6: Record and provide feedback
1, Collect valuable information and data
For example, the time when the injection molding machine failure occurred, the failure phenomenon, downtime, repair hours, repair parts, repair results, problems to be solved, settlement costs, etc. should be stored in the archives according to the prescribed requirements.
2, Statistical analysis Regularly analyze the use records of injection molding machines, analyze downtime losses, revise the memorandum catalog, find key measures to reduce maintenance work, study the failure mechanism, and propose improvement measures.
3, Report the relevant faults to the competent department according to the procedures and feedback to the injection molding machine manufacturer.
Fault Management Deployment Procedure
To do a good job in injection molding machine fault management, it is necessary to understand the causes of failures, accumulate information and data on common and typical failures, conduct fault analysis, pay attention to the study of failure patterns and failure mechanisms, and strengthen daily maintenance, inspection and preventive repairs. The following 8 aspects are involved in the development of fault management.
1, Carry out publicity and education work to make operators and maintenance workers consciously record, count and analyze the failures of injection molding machines and put forward reasonable suggestions.
2, Closely combine the actual injection molding production and the characteristics of the injection molding machine status, and divide the injection molding machines in use into three categories: A, B, and C to determine the focus of fault management.
3,Use monitoring instruments to conduct planned monitoring of key parts of key injection molding machines to promptly detect signs of failure and deterioration information.
Injection molding machines generally require daily inspections, patrol inspections, periodic inspections (including precision inspections), and condition inspections using human senses and common testing tools. This focuses on understanding the technical status and abnormalities of parts, mechanisms, and components prone to failure. Inspection standards should also be established to determine the boundaries between normal, abnormal, and faulty conditions for injection molding machines.
4, Carry out fault analysis and train injection molding machine maintenance workers to master fault analysis methods.
5, Fault records are the basic data for injection molding machine fault management and the original basis for fault analysis and processing. Records must be complete and correct. After on-site inspection and fault repair, injection molding machine maintenance workers should carefully fill out the “Injection Molding Machine Fault Repair Form”. The workshop mechanics will perform monthly statistical analysis and report to the injection molding machine management supervisor.
6, In addition to daily monitoring of fault conditions, maintenance personnel for injection molding machines in the workshop should compile “fault repair orders” and maintenance records on a monthly basis. By collecting, sorting, and analyzing fault data, they can calculate the fault frequency and average fault interval of various injection molding machines, analyze the fault dynamics and key fault causes of individual injection molding machines, and identify the patterns of fault occurrence so that they can focus on key issues and take countermeasures.
The fault information and analysis data should be fed back to the planning department to arrange preventive repairs or improvement measures. It can also serve as a basis for modifying the regular inspection interval, inspection content, and standards.
Based on the statistically organized data, statistical analysis charts can be drawn. For example, the dynamic statistical analysis chart of a single injection molding machine failure is an effective way for the maintenance team to visually manage failures and other issues.
It not only makes it easier for management personnel and maintenance workers to grasp the failure situations of various types of injection molding machines in a timely manner, but also allows them to have clear goals when determining maintenance countermeasures.
7, Through routine inspections and injection molding machine status checks by maintenance workers, status information and fault signs are obtained, as well as relevant records and analysis data.
The workshop injection molding machine maintenance personnel or repair team leaders will arrange daily maintenance in a timely manner for each type of injection molding machine problem, making full use of production gaps or holidays to ensure prevention in order to control and reduce the occurrence of faults.
For certain fault signs and hidden dangers that cannot be covered by daily maintenance, feedback will be given to the planning department for scheduled repairs.
8, Develop a fault information management flow chart.
Failure rules of injection molding machines
Studying failure patterns is very beneficial for developing maintenance strategies and even establishing a scientific maintenance system. During the use of injection molding machines, their performance or status gradually declines over time. Many failures have some signs before they occur. These are called latent failures. Their identifiable physical parameters indicate that a functional failure is about to occur. Functional failures indicate that the injection molding machine has lost its specified performance standards.
The pattern of changes in the failure rate of injection molding machines over time is often called the bathtub curve. The changes in the failure rate of injection molding machines 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 machines are in the early failure period, with a high failure rate initially but rapidly decreasing over time. This period is also known as the running-in period for mechanical products.
The length of this period varies depending on the design and manufacturing quality of the product and 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 the occasional failure period, the failure rate remains roughly stable and approaches a constant value.
During this period, failures occur randomly. During the occasional failure period, the failure rate is lowest and most stable. Therefore, this is the optimal operating period for the injection molding machine, or the normal operating period. This period is called the effective lifespan.
Failures during the sporadic failure period are mostly caused by improper design, improper use, and poor maintenance. Therefore, by improving design quality, improving operation management, and strengthening monitoring, diagnosis, and maintenance, the failure rate can be reduced to the lowest level.
3, Wear and tear failure period: In the later stages of an injection molding machine’s life, the failure rate begins to rise. This is due to wear, fatigue, aging, corrosion, and other factors affecting the machine’s components.
Overhauling the machine at the inflection point, i.e., the beginning of the wear and tear failure period, can effectively and economically reduce the failure rate.
The three stages of the injection molding machine failure rate curve truly reflect the pattern of failure rate changes from running-in, commissioning, normal operation to overhaul or scrapping.
Strengthening the daily management and maintenance of injection molding machines can extend the period of occasional failures. Accurately identifying the inflection point can avoid excessive repairs or expansion of the repair scope, thereby obtaining the best investment returns.
