Plastic moulds Maintenance points
The necessity and importance of mold maintenance management:
Even if the size of the molded product is changed, and the molding conditions are adjusted, it is often found that "bursts and short shots are constantly appearing" on the spot, which is a factor that affects the quality of the molded product (forming pressure, heat, loss of the mold, etc.) If it is a molding condition that can be changed temporarily, it cannot be improved.
Therefore, it is necessary to consider the design of preventive maintenance, and although the mold is such a design, if the maintenance is focused on the end, it is naturally impossible to obtain the original effect.
The main maintenance locations and projects are:
Mold PL surface
Molding part of the mold
Cooling water hole
Anti-electric heater disconnection, etc.
The frequency of maintenance and the treatment method will vary depending on the type of resin, cycle time, mold structure, mold material, mold temperature, and product accuracy.
For example, POM (polyacetal) is a material that is easy to generate gas. If the PL surface gas is not drained or the cavity core is cleaned, the gas is discharged poorly, and the molded product is burred and short shot. , melt marks, spots and changes in size.
However, a PC (Polycarbonate) hard and brittle material is prone to cutting waste of the gate, and the waste adheres to the cavity surface or the PL surface, and becomes a surface defect.
If there is no oil film in the folding part (such as the guiding tip and the guiding bushing), it will burn (burr), so it is necessary to apply the lubricant, but the lubricant will fly too much, which will adversely affect the quality of the product. pay attention.
Corrosive gases (halogen gas, chlorine gas) are prone to corrosive materials, and dimensional defects and surface defects are formed regardless of the corrosion of the cavity core.
Therefore, the maintenance degree of the mold usually directly affects the quality of the molded product, and because the focus of each product is different, it is very important to establish institutionalization and management according to each similar product.
Continuously produced products should be maintained on a regular basis, and intermittently produced products must be maintained after a batch production to make them ready for use at the beginning of the next production.
Mold maintenance management concept at the manufacturing site
The company's molds are almost 7 to 40 tons of resin and quenching molds. Because quenching is often performed, the flow path sometimes catches the product, but the PL surface and the cavity core are not easily damaged, and the loss of the bite portion is less.
Maintenance is carried out on a daily basis and on a regular basis, and is carried out in accordance with the "Mold Maintenance Operation Order Form", and after confirming and operating the "Mold Inspection Form", each product item is recorded on the record sheet.
This record is a record of the mold and will be of great help in future inspections. The main point of maintenance is to perform it carefully at a fixed frequency and time.
1. Examples of stable formation due to maintenance
Gears with a vibration accuracy of ±0.05 mm have vibrations, damage, burrs, etc., and the molds formed in one die are formed by only one or two. At first, it was handled by changing the forming conditions on the spot. The problem still exists, the goods are still not delivered, and the customer requests to solve the problem as soon as possible. At the beginning, the mold was adjusted by the skilled person, and the product was formed smoothly. However, after continuous production, various problems were repeated.
Therefore, after disassembling and cleaning the mold and improving the positional structure, the daily inspection items in the maintenance project are determined as follows:
Parting surface, runner surface cleaning → twice daily.
Guide the tip, bushing, position to determine the tip of the oil → once a day.
Checking the temperature control machine, dryer, and product removal machine → once a day.
A checklist is placed on the molding machine to maintain maintenance. As a result, the four formed two sets of molds are all good products, and all the goods that have been handed over will be fully paid in one month, and there is sufficient stock.
The focus of maintenance is on the concept of prevention, which is not to repair immediately after an accident, but to prevent accidents. But the situation of the mold is a bit different, and there are many things that will be known later. Therefore, in the design stage, attention should be paid to the design, size, material, machining method, heat treatment and surface treatment of the above-mentioned main items. Corrected and normalized according to the information on site.
2. Examples of extending life by design and heat treatment changes
In the formation of a POM cam (cam) part of diameter 6, when about 10,000 pieces are formed, the core is broken, and after several times of redo, many items cannot be delivered. The damaged part is where the thickness of the heart-shaped bite is about 1 mm, and it is not effective to attach R within the tolerance range. Maintenance work such as disassembly and cleaning every day has no effect.
Because the reason for the presumed damage is the impact when the inside of the resin is bitten, it is carried out.
Improvement of position determination structure
Improvement of mold plate structure
Improvement of heat treatment method
We decided to dismantle and maintain maintenance items such as cleaning, and as a result of regular maintenance, we achieved more than 300,000 stable breaks.
The same design changes have been made to similar cam molds, which is already the design basis for subsequent orders. Accidents are usually the same problem that repeats. Because the delivery time is very short, and there is an accident during the period, there is no way to make too much improvement and re-manufacture. However, in this case, it is also important to re-examine the fundamental design, in addition to improving the structure, indicating the maintenance focus of the mold.
In the event of an accident, quite a number of situations are related to the strength and movement of the distraction. Because the design of the mold is the same, the design usually depends on the individual's experience and technology, and the theory of mechanical design has not been smoothly developed, so it is very difficult to formulate the design basis.
3. Examples of damages due to design changes
A mold with a short delivery time has also experienced an accident of heart-shaped damage in the trial stage. In the case of a very tight delivery time, the completion of the mold is the first priority, so the impact is also great.
The reason for the presumption may be deformation due to internal pressure of the resin. In the design code of practice, there is a saying that "when damage is broken, the strength should be increased by 2 times." However, the strength is increased by a factor of two. Although the thickness is increased by 1.25 times, the die plate must be redone. Therefore, the material is changed and the R is attached to the turn.
As a result of the retry, although a certain life span was extended, cardiac fracture occurred from the same site. Therefore, we made up our mind to re-examine the design from the root, and increased the thickness of the heart shape to 1.25 times. The mold plate was also redone. At the same time, the unsettled part of the folding was designated for routine maintenance. As a result, the small size was not damaged.
4. Examples of improving the burrs of the folding part
When the molding die having a special structure is formed for half a day, the crease portion is burred, and the problem of failure to form normally occurs. Because the mold construction is special, it is very difficult to deal with the past examples. After the mold is disassembled and the hinged portion is observed,
The lubrication of the hinge is improved.
The Plastic moulds design of the oil groove in the folding part originally had no effect, so the use of a sliding bearing with a solid lubricant was very effective. However, because the strength of the guiding portion of the guiding portion is insufficient, the diameter is increased, and the sliding bearing is also changed to the rotating bearing.
As a result, the movement of the mold becomes very smooth, and stable molding can be performed under regular maintenance.
Skilled personnel for maintenance management must be
Understand the mold construction and be able to disassemble and assemble.
Has skills such as grinding combinations.
It can control manual machines such as grinding, lathe, and milling machines.
Observing the mold can determine which part of the problem.
In the case of disintegration cleaning, a washing machine using a liquid in the market can be sold in the market without disassembling the mold, but many other parts of the knife face still depend on the skill of the responsible person. Especially in the diagnosis of molds, it is impossible to make an appropriate diagnosis without understanding the forming technology and the mold technology (from construction to work).
The company arranges the operator with the experience of the forming site in the final project of the mold to cultivate the maintenance technicians.
Easy to maintain mold design
As mentioned at the forefront, it is entirely a matter of maintaining the design. It is not a good design. In design, it should be considered.
Pay attention to maintenance-free and safety device construction
Easy to assemble and decompose
Easy to process
Intensity, wear and other unstable parts adopt the substructure
Require precision when machining is possible, and dispose of parts
Select materials and heat treatment according to the specifications of the product requirements
The piping of the cooling pipe, etc.
Good design that reflects the operational nature of the site is very important.
These are plastic moulds Maintenance points