Key points of maintenance and management of the ho

2022-08-26
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Key points of maintenance and management of plastic molds

necessity and key points of mold maintenance and management

even if the size of formed products is changed and the forming conditions are adjusted, the situation of "burrs and short shots constantly appear" can often be found on the site, and this is the main factor affecting the quality of formed products (forming pressure, heat, mold loss, etc.). If it is the forming conditions that can be changed temporarily, it cannot be improved

The original text of

maintenance is "maintain", which means to maintain in the initial set state

therefore, preventive maintenance must be taken into account in the design. Although the mold is this kind of design, if the key maintenance is not carried out, the original effect will naturally not be achieved

The main maintenance positions and items are:

PL surface of the mold

folding part of the mold

mold cavity, core surface

relaxation of bolts

cooling water hole

disconnection of anti electric heater, etc.

the maintenance frequency and treatment method will change with the type of resin, cycle cycle cycle, mold structure, mold material, mold temperature, product accuracy, etc

for example, for materials that are prone to generate gas like POM (polyacetal), if the PL surface gas drainage ditch and mold cavity core are not cleaned, the gas emission will be poor, and the formed products will produce burrs, short shots, melting marks, and paste spots, and our Jinan new era gold Testing Instrument Co., Ltd. will produce dimensional changes after assembly and testing

however, PC (polycarbonate) hard and brittle materials are prone to gate cutting waste, which will adhere to the mold cavity surface or PL surface and become surface defects

if there is no oil film in the folding part (such as guide tip and guide bushing), burning (Burr) will occur, so lubricant must be applied, but too much lubricant will fly away, which will adversely affect the quality of products, so special attention should be paid

the grade containing refractory materials is prone to produce corrosive gases (halogen, chlorine). Regardless of the corrosion of the mold cavity core, dimensional defects and surface defects will be formed

therefore, the degree of mold maintenance usually directly affects the quality of formed products. Because the focus of each product is different, it is very important to establish three-dimensional customization and management according to each similar product

continuous products should be maintained regularly, and intermittent products must be maintained after a batch production, so that they can be used in the initial state at the beginning of the next production

mold maintenance and management concept at the manufacturing site

the company's molds are almost 7-40 tons of resin and quenched molds. Because of frequent quenching, the runner sometimes holds the product, but the PL surface and die core are not easy to be damaged, and the loss of the undercut part is less

the maintenance is carried out on a daily and regular basis according to the "mold maintenance operation sequence table", and after confirmation and operation with the "mold inspection table", each product item is recorded on the record sheet

this record is the record of the mold, which is very helpful in the future inspection. The key point of maintenance is to carefully implement it at a fixed necessary frequency and time

1 · examples of stable forming due to maintenance

gears with vibration accuracy of ± 0.0o5mm suffer from vibration, damage, burr and other defects, and only one or two dies formed in one die with four holes are formed continuously. At first, it was handled by changing the forming conditions on site. The problem still existed, and the goods were still not delivered. The customer asked to solve the problem as soon as possible. At the beginning, skilled people could adjust the mold and shape the products smoothly, but after continuous production, various problems occurred repeatedly

therefore, after disassembling and cleaning the mold and improving the position structure, the daily spot inspection items in the maintenance project are determined as follows:

cleaning the parting surface and runner surface → twice a day

guide the tip, bushing and position to determine the oil supply of the tip → once a day

spot check of temperature regulator, dryer and product extractor → once a day

a checklist is placed on the forming machine for maintenance and management. As a result, the four formed two sets of molds are all good products, and all the last goods will be handed over in a month, and there is sufficient inventory

maintenance focuses on the prevention concept of "not repairing immediately after an accident, but preventing the occurrence of an accident". But the situation of the mold is a little different. There are many things that will be known after they are done. Therefore, in the design stage, more attention should be paid to the design, size, material, machining knife method, heat treatment and surface treatment of the above-mentioned main items. And make corrections and standardization according to the on-site feedback data

2. An example of extending the service life by using design and heat treatment changes

in the forming of POM cam parts with a diameter of 6, when about 10000 parts were formed, the small (core) was damaged, and after several times of rework, there were still many goods that could not be delivered. The damaged part is where the thickness of the heart-shaped undercut is about 1mm, and there is no effect of attaching r within the tolerance range. Daily maintenance work such as disassembly and cleaning has no effect

because it is presumed that the cause of the damage is the impact during the biting and cutting of the pressing limb in the resin, the improvement of

position determination structure

improvement of die plate structure

improvement of heat treatment method

the decomposition and cleaning and other maintenance items are determined, and the results of regular maintenance have achieved more than 300000 stable forming with no damage

the same design changes have been made to similar cam dies, which has become the design basis for receiving orders in the future. Accidents usually happen repeatedly with the same problems. Because the delivery period is very short, and accidents occur during the period, there is no way to make much improvement and there are many cases of remaking. However, in this case, it is also very important to re-examine the basic design, in addition to improving the structure, and to indicate the key points of maintenance for the mold

when accidents occur, quite a lot of situations are related to strength and the movement of the folding part. Because the situation of mold design is the same as that of a product, the design usually must rely on personal experience and technology. At the same time, the theory of mechanical design has not been successfully developed, so it is very difficult to formulate design benchmarks

3. Examples of damage accidents corresponding to design changes

mold with insufficient delivery date has also suffered from heart-shaped damage during trial production. In the case of urgent delivery, the completion of the mold is the first priority, so the impact is also great

it is presumed that the deformation may be caused by the internal pressure of the resin. There is a saying in the code of design experience that "in case of damage, the strength should be doubled". However, the strength is increased by 2 times. Although the thickness is increased by 1.25 times, the die plate must be redone, so it corresponds to the change of material and the attachment of R at the turning ridge

as a result of retry, although the service life was extended by a number of times, the heart-shaped fracture still occurred from the same part. So I made up my mind to fundamentally review the design, increase the thickness of the heart shape to 1.25 times, and redo the die plate. At the same time, routine maintenance was assigned to the unstable parts such as folding. As a result, the small size was no longer damaged

4. Examples of improving the burr of the folding part

the forming die with special structure produces burr at the folding part after half a day of forming, which leads to the problem that it cannot be formed normally. Because the mold structure is special, it is difficult to deal with past examples. After disassembling the mold and observing the folding part, improve the lubrication of the

folding part

guided improvements

the design of oil groove in the folding part originally has no effect, so the sliding bearing with solid lubricant is used, but the effect is very good. Because the strength of the guide tip of the guide part is insufficient, the diameter is increased, and at the same time, the sliding bearing is changed into a rotating bearing

as a result, the movement of the die becomes very smooth, and stable forming can be carried out under regular maintenance

skilled personnel for maintenance and management must understand the mold structure and be able to disassemble and assemble

have skills such as grinding combination

it can control grinding, lathes, milling machines and other manual machines

load measurement can be judged by observing the mold: the balance wing instrument tensile testing machine adopts fs0.02% imported high stability, high-precision load sensor. There is a problem with the broken part

in terms of decomposition and cleaning, a cleaning machine using alkaline solution is sold in the market, which can be cleaned without disassembling the mold, but many parts of other knife surfaces still depend on the skills of the person in charge. Especially in the diagnosis of mold, it is impossible to make an appropriate diagnosis without understanding the forming technology and mold technology (from structure to work)

the company allocates operators with on-site forming experience to the final project of the mold to cultivate maintenance skilled personnel

purchasing skills of universal experimental machine that is easy to maintain? The above content is a detailed introduction to this problem. The mold design

mentioned at the beginning that it completely depends on the maintenance design, which is not a good design. In the design, it should be considered that

pay attention to the maintenance free and safety device structure

it is easy to assemble and disassemble

it is easy to process

the unstable parts such as strength and wear adopt the sub structure

the accuracy is required when machining is possible, It is very important to choose materials, heat treatment, piping of cooling pipes and other containers in accordance with the requirements and specifications of products, and clearly mark the good design that can reflect the operability of on-site opinions

due to the layout, it is impossible to discuss matters related to the design basis, so only the strength surface and guidance are specially discussed

the strength of the mold is usually set according to the feeling and experience of the designer. It can be calculated when it is damaged. It adapts to a relatively large tension, which is a little too slow, so it is best to calculate

basically, the formula of material mechanics is applicable to strength calculation. For example, as shown in Figure 1, the heart shape of single month structure can be calculated by the following formula

δ= P. A4/8e. I

P: internal pressure kg/cm2

e: yield rate

I: section twice torque

according to the above formula, the deflection is at least 0 Below o2mm. If it exceeds, it is necessary to increase the thickness of the heart or two pieces of structure

the second is guidance, which usually differs from designer to designer. The guidance methods include wideguide (with a larger guidance range) and narrowguide (with a smaller guidance range). For example, suppose that the driving force P, the folding resistance Q, the pressure r generated by the torque borne by the guide surface, and the friction coefficient of the sliding heart (Figure 2) μ,

R=XQ/L

P=(1+2 μ X/l) q

from this formula, the amplitude of guidance has nothing to do with distortion. However, the longer the guide length is, the better, and the smaller the friction coefficient of the guide surface is, the better

in fact, because the wider the range of guidance is, the more vulnerable it is to the influence of temperature difference, especially in the case of high-temperature forming such as PPS, it is best to use narrow guidance

secondly, when looking at the sliding heart shape from the side (Fig. 3), because there is a driving force on the outside of the guide, the conditions without distortion are shown in the following formula

μ (b+2d)/b <1

at this time, the longer the guide length is, the better, and the friction coefficient of the guide surface is

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