Plastic materials products cracking and deformation causes and solutions

cracking plastic materials, including filamentous workpiece surface cracks, crazing, top white, cracking and because parts stick mold, stick-runner or trauma caused by the crisis, according to a release time diversity cracking cracking cracking and Applications . Plastic materials injection products deformation, bending, twisting phenomenon occurs mainly due to the plastic molding shrinkage flow direction than in the vertical direction is large, so that the various parts to the shrinkage and warpage of plastic materials injection products Crack Cause

Cracking plastic materials, including filamentous workpiece surface cracks, crazing, top white, sticky parts due to cracking and mold, stick-runner or trauma caused by the crisis, according to a release time diversity cracking cracking cracking and applications. The main causes of the following aspects:

1. Plastic materials processing:

(1) The working pressure is too large, too fast, the more filling material, injection, dwell time is too long, too much stress can cause cracking.

(2) adjusting the speed and pressure of the mold to prevent the rapid releasing strong drawn products cause cracking.

(3) due to increase mold temperature, make parts easy to stripping, appropriate to reduce the material temperature to prevent decomposition.

(4) prophylaxis of welding marks, plastic degradation caused by low mechanical strength and cracking.

(5) appropriate use of mold release agents, pay attention to the mold surface adhesion often eliminate aerosol and other substances.

(6) The article residual stress, can be carried out immediately after forming annealing to eliminate stress and reduce the formation of cracks.

2. Plastic materials molds:

(1) To the top of the balance, such as the number of mandrel, the cross-sectional area should be sufficient, stripping slope should be enough, the cavity surface must be smooth enough to prevent the external force so that it leads to the top of the residual stress concentration and cracking.

(2) parts structure can not be too thin, the transition part arc transition should be adopted to avoid sharp corners, chamfers cause stress concentration.

(3) minimize the use of metal inserts to prevent different inserts and parts increased stress caused by shrinkage.

 (4) deep bottom parts of the release should set the appropriate air intake tract, preventing the formation of vacuum.

(5) the sprue gate large enough to feed when not enough time to solidify the release, so easy to mold.

(6) the sprue bushing and nozzle engagement should be prevented from leaving chilled drag material stuck to the fixed mold parts.

 3. Plastic raw material areas:

(1) renewable materials content is too high, resulting in low strength parts.

(2) the humidity is too large, resulting in the emergence of the top of the steam cracking of some plastics and chemical reactions, reducing the strength.

(3) the material itself is not suitable for processing environment or poor quality, contamination can cause cracking. 4. Plastic materials products using the machine: the injection molding machine plasticizing capacity should be appropriate, too small insufficient failed completely mixed plastics become brittle, degrades too large.

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Parts (ABS plus copper insert) cracking existential analysis, improvement

Plastic parts Name: raw materials: Terluran & reg; GP-22 type ABS + high concentration of black masterbatch problem: plastic parts intact when out of the mold in the air for 2 to 3 days, have vertical section surrounding parts of the copper insert crack, some have even been completely split. Reason analysis and improvement program: plastic parts do not have any problem during the molding process, the problem does not lie in molding equipment and technology, according to our understanding of the analysis, the problem is caused by environmental stress cracking. Cause environmental stress cracking might have the following areas:

First, the raw materials

(1) raw materials mixed with other impurities or doped with inappropriate or excessive solvents or other additives. Environmental stress cracking is a unique phenomenon polyolefin plastic, which refers to the product when there is stress, and some active media exposure, there will be a brittle crack, crack growth resulting in product damage. Such active substances may be detergents, soaps, water, oil, acids, alkalis, salts and no significant swelling effect of organic solvent materials. A necessary condition for environmental stress cracking is a pattern or part of memory in stress and stress concentration factors such as the existence of a gap, surface scratches and so on. The ABS contains a polyolefin component, and impurities contained in the starting material or solvent indirectly provides these active substances, when the ABS plastics during storage due to the emergence of a variety of causal factors surface chipped or scratched, so there will be cracks .

(2) Some plastics such as ABS, etc., in the damp heat condition can occur with moisture catalytic cracking reaction, the occurrence of large parts of the strain thus cracking.

(3) plastic barrel heating time is too long will cause brittle parts.

Second, product design

Such as polystyrene and plastic containing this ingredient as little as possible because the metal insert, because these plastic brittle cold specific volume. If the order to assemble and strength requirements must be added inserts, as inserts made of metal copper, while copper insert cooling dimensional change with heat-shrinkable plastic ABS values ​​vary greatly, resulting in a greater around the insert within stress, thus resulting in cracking products. Specific improvements are as follows:

(1) Replace the insert of the materials used to make the insert and the ABS product line expansion coefficient should be as close as possible;

(2) increase the insert sharp parts of each fillet, fillet products may cause stress concentration is too small, resulting in product cracking;

(3) increase the thickness of the insert around the plastic layer.

Third, preheat aspects inserts

With inserts in plastic products, around the insert easily crack or cause product strength decline, which is made of metal and plastic inserts for thermal and shrinkage caused by large differences. Therefore, in designing parts, should increase the wall thickness around the insert, in order to overcome this difficulty, preheated before molding is an effective measure to carry out metal inserts. Because the temperature difference between the warm-up can reduce the melt and insert in molding can melt cooling inserts around slowly, more uniform shrinkage occurs some hot material feeding action to prevent exerted around the insert large internal stress. Fourth, since the annealing processing plasticized plastic in the cylinder uneven or different cooling rate in the mold cavity, so often produce uneven crystal orientation and contraction, resulting in product there internal stress, which produces thick-walled or tape more pronounced when metal inserts products. There are parts of internal stress occurs in the storage and use of the Central Standing Committee mechanical performance, optical performance deterioration, surface crazing, cracking or deformation. Production of solving these problems is the power of a law article annealing. The method of the article is annealed in the constant temperature liquid heating medium (e.g. hot water, hot mineral oil, glycerin, ethylene glycol, and liquid paraffin, etc.) or a hot-air circulating oven was allowed to stand for some time. For ABS plastic parts plus insert, refer to the following: annealing treatment medium: water annealing temperature: 10 ~ 20 ℃ low i.e. 60 ~ 70 ℃ annealed heat distortion temperature than ABS time (85 ~ 100 ℃): 2 hours

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Plastics Cracking Analysis and Countermeasures

Summary

Abstract: The cracking plastic products often fatal flaw; cracking, including filamentous workpiece surface cracks, crazing, top white, sticky parts due to cracking and mold, stick-runner or trauma caused by the crisis, by cracking time points cracking cracking and stripping applications. Causes cracking aspect relates to a mold, molding process, plastic material or the like. This paper discusses the cracking of the plastic material selection angle.

Keyword

Keywords: plastic material selection plastic cracking hot ductility balance

1: Summary of plastics defect

Plastics can be divided into external manifestation of defects defects (such as appearance, size, etc.) and internal defects (such as cracks, brittleness, etc.). The nature of the causes of defects of plastic products can be summarized as P (power), V (fill volume), T (temperature). The ultimate cause of plastic cracking is due to P (power) caused.

2: plastic cracking

Stripping cracking: plastic product from the mold stripping out or cracking in the machining process; the causes and consequences of this cracking to produce relatively easy to estimate. Applications cracking: cracking plastic products appear in the post-period of time or use. This cracking is often more difficult to predict, the consequences can be fatal. As some time before the emergence of 3G iPhone Mobile white version cover cracking phenomenon for Apple to bring in big trouble. (Battery heating up the plastic cover cause thermal expansion and contraction caused by uneven)

3: Cracking products analysis

   Whatever plastics, eventually cracking because of the nature of the force (internal stress, external force, etc.) caused. Thus we must better understand the source of power. Currently some customers some errors in the plastic of choice, resulting in a large number of plastic cracking. Now some typical case analysis

4: plastic plastic cracking prevent cracking prevention

Ways to improve the plastic cracking foreign counterparts summed up a lot of valuable experience, now from plastic material selection point of view to explore how to effectively solve the plastic cracking. In terms of product selection, we should take full account of the way the plastic molding material, component structure, heat transfer and other operational issues the actual process; for some hollow structure, should take full account of the thickness, size and so hollow. Such as thin-walled, large hollow core member should try to use good ductility (elongation at break), good thermal conductivity of plastic, and use plastic rods processed into plastic pipe will have to fully take into account the heat balance, as far as possible choose ductile plastic rods, for some ductility bad plastic pipe, as far as possible avoid using bar processed into pipe (pipe general factory has been heat-treated residual stress). For some ductility bad plastic, plastic pipes and plastic rod effect is not the same. Cracking satisfy the conditions: μl / hßΨ≥ ξ μ- empirical process factor, h- wall thickness, l- hollow perimeter, ß- plastic shrinkage, Ψ- plastic thermal conductivity, ξ- breaking elongation 5. Conclusion prevent cracking of the most difficult point of plastic products is how to prevent the plastic products in different parts of the apparent thermal equilibrium, and the use of carbon fiber or metal filled plastic, because the strong heat conduction capability, so a relatively small chance of cracking. From the viewpoint of a plastic material, products related to cracking the wall thickness, volume hollow products, plastic ductility.

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The plastic aberration to control

Products color is common defects in injection molding, because the accessories and aberration caused by injection molding machine, does not see small batch scrap. Aberration affected by many factors, involving raw materials for resin, pigment, pigment mixed with raw materials, such as injection molding process, injection molding machine, mold, and because of the impact is widespread, so the aberration control technology is also one of recognized difficult to master the technology of injection molding. The actual production process we generally from the following six aspects: to control the aberration.

1, to eliminate the influence of the injection molding machine and mold factors to choose with considerable injection molding machine, injection molding products for capacity if material corner problems in injection molding machine, best replacement equipment. For mould gating system, such as exhaust slot cause off color, through the corresponding part of the mould maintenance mode to solve. Must first solve the problem of good injection molding machine and mold to organize production, to reduce complexity of the problem.

2, eliminate the influence of raw material resin, color master control of raw materials is the key to thoroughly solve the aberration. Therefore, especially the production of light color products, not ignore the thermal stability of resin raw material the obvious effects of different colour and lustre of products fluctuations. Given that most of the injection molding manufacturers itself does not produce plastic masterbatch or masterbatch, such, can be the focus of attention on the production management and raw material inspection. Namely to strengthen raw material incoming inspection; As much as possible in the production of the same products using the same manufacturer, same brand masterbatch, masterbatch production. For pigment, we will try to check the color before mass production, as well as with the last time to proofread, and in the comparison, if the aberration is not big, qualified, can be thought of as has slight aberration, color master batch can be used after mixing pigment back again, in order to reduce uneven mixing pigment itself the brightness of the photo. With, we still need to focus on inspection raw material resin, pigment, the thermal stability of the poor thermal stability, we suggest that the manufacturer and exchange.

3, eliminate the influence of uneven pigment mixed with masterbatch plastic masterbatch mixed with pigment is bad also can make the product color changes. After mother and masterbatch mechanical mixing, through the absorption into the hopper, due to electrostatic interactions, masterbatch masterbatch with separation, easy adsorption in the hopper walls, and this is bound to cause injection cycle at the mother volume changes, resulting in a aberration. This kind of circumstance can take again after raw material suction hopper to artificial mixing solution. Now there are a lot of companies feed machine is used to add pigment, thereby saving a lot of manpower, and for the aberration control provides a lot of help, but many companies because of improper use, the results are often difficult to satisfactory. Join masterbatch feeding machine under fixed speed depends on plasticizing time, and plasticizing time itself is volatile, sometimes even more volatile, so to ensure the constant feed rate, the feeder must be fixed feeding time, and set a time less than the minimum plasticizing time. In the use of feeding machine need to notice, due to the feeder exports is small, use after a period of time, may be because the accumulated material used in the feeding machine screw powder caused blanking, even cause feeding machine stops, so need to regular cleaning.

4, reduce the influence of cylinder temperature on aberration in a heating coil damage failure of production often encounter or control of heating control part long fire ChengLiao tube rapid changes in temperature to produce off color. This kind of reason of aberration is easy to determine, general damage of heating coil Produce off color, but at the same time will be accompanied by plasticizing uneven phenomenon, and the heating control part is out of control long burning gas spot is often associated with products, severe discoloration even coking phenomenon. So the need to check the heating part of the production, found that the heat damage or change in time maintenance when out of control, in order to reduce this kind of aberration.

5, and reduce the influence of the injection molding process adjustment when the chromatism reason need adjust injection molding process parameters, as far as possible, don't change the molding temperature, the amount of back pressure, the injection molding cycle and masterbatch, adjust at the same time also need to observe the effects of process parameters change on colour and lustre, for example, when found aberration should be and adjustment. As far as possible avoid the use of high speed and high back pressure injection cause strong shearing action of the injection molding process, prevent due to factors such as local overheating or thermal decomposition of the brightness of the photo. Strict control of cylinder each heating section temperature, especially the nozzle and close to the heating part of the nozzle.

6, master cylinder temperature, the influence of the change of product color masterbatch quantity before color adjustments must also know the product color change with temperature, pigment volume trends. Different mother color change with the temperature of the production or the amount of pigment, the product color change law is different. Color can be through the test process to determine its change law. Unless you have know this kind of pigment color change rule, otherwise cannot be quickly adjusted the aberration, especially in the new color masterbatch production.

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The judgement of plastic product aberration

When molding plastic products, its product colors and materials has a direct touch its mainly manifested in the following aspects:

1. The color relations with incoming plastic granule. Due to the product raw material plastic material batch change frequently, and each batch of raw material Material, were inconsistent aberration phenomenon, such as some incoming slant blue color, has the processing slant red color, and so on, so we in the acceptance of incoming (sample) must sample product contrast aberration with customer's original sample and luster. Only in color and luster completely in line with and without other problems when the material can be thought of as good.

Relationship. 2. The color and material tube temperature used material aberration with the feed tube temperature relationship which were as follows; Feed tube at the higher temperature, a partial value red color, b value big yellow, L value little darker. But there are also in the process of forming phase for special case, so in molding should also to match the die temperature in debugging off color problem. Mould temperature, the higher the L value into negative dimmed, a, b.

3 colors and material drying temperature care generally speaking, the color and material drying temperature also has relatively direct contact: such as PC/PA transparent material, drying temperature too high and the time is too long, the color will be become yellow or black, forming the product transparency. Such as ABS material, drying temperature too high or too long, will lead to poor products change yellow and sex. We in front of the molding products must be in 3 to 4 hours before starting the preliminary drying to dry materials will be not too long time and too high temperature baking, so as to avoid product color run, as a result of product aberration And bad. But when molding material tube temperature is too high there will be some phase should be quality problem,, such as product performance, product package (poor exhaust) wind and so on. So I have aberration when molding products mainly come from raw materials incoming problem, method of control can only play an auxiliary role.

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Problem Cause incomplete filling of plastic products and solutions

A meaning: after the melt into the mold cavity does not fill completely, causing plastic parts shortage of material.

Second, Causes and Remedy:

①, improper selection of equipment: When sorting equipment, melt glue machine must be greater than the amount of molten plastic products, plastic parts by weight of the machine can only account for 85% of the total amount of melt.

②, feed shortage: the charging port if there is "bridging" phenomenon, may be appropriate to increase the screw injection stroke, increasing the feed rate.

③, raw illiquid: improved die casting system stagnation defect, a reasonable set of pouring glue position, expanding gates, runners and injection spout sizes and use larger nozzle, an appropriate increase in raw material temperature.

④, gating system design is unreasonable: gating system design, pay attention to the gate balance, the weight of the plastic parts of each cavity is proportional to the gate, the cavities are filled simultaneously, gate locations to be selected in the original wall parts, sub-runner balance design layout can also be used.

⑤, mold exhaust bad: check cold material cavity, or location is correct, for deep cavity mold, should be added to the exhaust vent in the trenches and less injection site, the clamping surfaces can be opened Deep 0.02 -0.04mm, 5-11mm in width exhaust ducts, vents should be provided in the final filling of the mold cavity. Also in the process of operation, by increasing the die temperature, reducing the injection speed, gating system to reduce resistance, and to reduce the clamping force.

⑥, mold temperature is too low: the mold must be preheated to the required temperature before starting the process, if the mold temperature does not rise up, check the mold design is not only reasonable waterway.

⑦, the injection pressure is insufficient: the length of the injection pressure is close to a positive relationship with the die, injection pressure is too small, short filling length, filling the cavity dissatisfaction, which can slow down the plunger forward speed through proper injection ting long time to improve injection pressure.

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Analysis of the solution injection flow lines

Flow marks (Flow Lines) definition:

Linear traces of the molded article surface, this trace shows the direction of flow of melt glue. Injection molding machine

1. Injection pressure and dwell inadequate

Injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Increase injection pressure and holding pressure, condensate layer can be pressed against the mold surface until the product setting, free from the generated flow marks.

2. The residence time (Residence Time) improper

Plastic tube inside the residence time is too short, melt glue temperature is low, even if we manage to fill the mold cavity, when packing or plastic can not be compacted, leaving in the direction of flow of melt glue sink marks. Plunger tube material for the ratio (Shot-to-Barrel Ratio), should be 1 / 1.5 and 1/4 between.

3. Cycle time (Cycle Time) improper

When the cycle time is too short, plastic tube inside the heating less, melt glue temperature is low, even if we manage to fill the mold cavity, holding pressure still can not leave the plastic melt adhesive pressure to stay in the flow direction of sink marks, cycle time fully extended to plastic melting temperature high enough to melt glue so that the flow direction generated by the appropriate without sink marks.

4. Tube temperature is too low

When the tube temperature is too low, melt glue temperature is low, injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Improve the material temperature, injection pressure and holding pressure condensate layer is pressed against the mold surface until the products stereotypes, not by the generated flow marks. Material temperature setting can refer to the material manufacturer's recommendations. After the feeding tube, middle and front nozzle (Rear, Center, Front and Nozzle) in four districts, later setting forth the material temperature should gradually improve, every forward one area, increased 6C. If necessary, sometimes the material temperature of the nozzle area and / or the front region of the set and in the same area.

5. Nozzle temperature is too low

 Plastic absorption heating zone (Heating Bands) in the feed tube heat release caused by rotation of the screw and the plastic molecules frictional heat generated by the relative motion, the temperature is gradually increased. Feed tube in a heating zone of the last nozzle, this should melt adhesive material to achieve the desired temperature, subject to moderate heating, in order to maintain the best condition. If the nozzle temperature is set high enough, because the nozzle and mold exposure, taking too much heat, melt temperature will drop, injection pressure and holding pressure is insufficient condensed die face pressed against the skin, leaving the melt glue in the flow direction of sink marks. Increase the nozzle temperature. Usually the nozzle zone temperature set lower than the front region of high temperature 6C °

Mold

1. Mold temperature is too low

Mold temperature is too low will cause the material temperature drops too fast, injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Increase mold temperature, maintain a high melt temperature, injection pressure and holding pressure condensate layer is pressed against the mold surface until the products stereotypes, not by the generated flow marks. Mold temperature can be set from the proposed value starting material manufacturers. Every incremental adjustments may be 6C, plastic injection 10 times, after forming in stable condition, according to the results and decide whether further adjustments.

2. Gate (Sprue), runner (Runner), or / and gate (Gate) small gate (Sprue), runner (Runner), or / and gate (Gate) is too small, the flow resistance to improve , if the injection pressure is insufficient, advance melt glue wavefront will become increasingly slow, plastics will become increasingly cold, injection pressure and holding pressure is insufficient condensed die face pressed against the skin, leaving the melt glue in the flow direction The sink marks. In CAE (such as C-MOLD) on your computer to different melt adhesive delivery system (including the sprue, runners and gates) filling simulation analysis to identify the ideal sprue, runner and gate size ( including the length and cross section of dimensions such as diameter, etc.), it is feasible way.

2. Venting inadequate

inadequate venting will make melt glue filling blocked, before melt glue wave can not be condensed in the mold is pressed against the skin surface, leaving in the direction of flow of melt glue sink marks. Each section of the flow channel at the end began to exhaust, so you can exclude a large number of air before pouring into the mold cavity. Cavity exhaust but can not be overlooked. Parting surface opposite the gate, consider adding vents, corresponding to the product at the end of the blind hole, consider adding exhaust ejector pin. CAE (such as C-MOLD) simulation melt glue filling, can help us quickly find all possible at the end of the filling (Last Filled Area), which is required to increase the vent areas. Figure claims vary, foolproof. Installation of a vacuum system, was evacuated before filling and when filling, it is an effective method of exhaust. For some bite flower decoration products face words, this may be the only exhaust recipe.

Plastic

1. Illiquid

Flow length of the wall thickness ratio (Flow Length to Thickness Ratio) large cavity, shall be easily flowing plastic filling. If the plastic flow is not good enough, moving further and further slow melt glue, the more slowly the more cold, injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Materials manufacturers depending on the particular design, can provide professional advice: In principle no burrs, selection of the most free-flowing plastic. 2. Using forming lubricant (Molding Lubricant) improper lubricant content is generally less than 1%. When the flow length to thickness ratio, the lubricant content must be appropriate to improve to ensure that the condensate is pressed against the mold surface until the products stereotypes, not by the generated flow marks. Increase the content of the lubricant, and shall be agreed upon after the material manufacturer.

Operator

1. Bad habits

Operators too early or too late switch forming machine door, will make molded inconsistent results. When the feeding tube heater due to heat loss irregular attempt to replenish calories, plastics uniform temperature easily, and have cold spots (Cold Spot) produced, injection pressure and holding pressure is not easy to cold near the surface of the skin is pressed against the mold on the left in the direction of flow of melt glue sink marks. Usually it should continue to educate the operator, so that we understand the trouble forming cycle inconsistency may bring, and understand the importance of maintaining good habit forming operation. Proper rest shifts, the operator can be prevented due to not following the physical, mental concentration, and cause errors. Using robots (Robots) and other automated molding cycle is to keep a consistent road.

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Plastic Injection Molding Manufacturer CNMOULDING Benefits Clients by Cutting Sales Costs

By taking advantage of Internet, CNMOULDING gets the edge in supplying the most cost-effective plastic injection molding products to customers from all over the world. Now CNMOULDING is providing an array of first-class products and services in automotive, home appliances and electronics

 Plastic injection molding products has been widely used in many industries and CNMOULDING promises customers direct benefits through its easy and definitive consumer approach module. The company's objective to become the "one stop shop" is facilitated through its 2000 sq meters workshop in China.  Powered by world-class infrastructure, a large and adroit workforce and a solid management team, the company has become a trusted supplier of plastic molds for many European and North American based companies. Furthermore, CNMOULDING claims to be the only China plastic molding injection company that offers complete cost analysis and full transparency to prospective buyers.

Company insiders indicate that the biggest plus of working with CNMOULDING is in the direct method of approach that the company adopts. As a top plastic injection molding manufacturer, CNMOULDING has earned its fame though innovation, quality control and cost-down.  According to their reports, CNMOULDING picks up direct consumer leads from the Internet and then tries to establish direct contact. Company officials have also, on several occasions, shown why the conventional way of marketing through trade shows is becoming obsolete. The company plans further expansion and the owners indicated that they are bringing more innovation in the manufacturing process to accelerate production and reduce downtime.

CNMOULDING has also made an elaborate effort to keep their price structure transparent for their international clients. While most similar companies would make every effort to conceal the numbers, CNMOULDING promises to give their clients a sneak peek into the pricing and profit structure.

The CEO of CNMOULDING recently addressed the local press. He laid great emphasis on the sales team of the company: "Most companies tend to carry out their sales through salespersons who exhibit an acute lack of product knowledge. At CNMOULDING, our sales manager deals with all the sales and effectively communicates the messages in and out of the company. We also make it a point to adhere to transparent pricing."

About the company

CNMOULDING is a leading direct plastic injection company based out of China. The company caters to both the Chinese and international markets.

More information about the company is available at www.cnmoulding.com

How Additive Manufacturing Is Making Injection Molding Cooler

Plastic part manufacturers are always looking for ways to reduce cycle time and get more productivity out of their injection molding machinery. One of the longstanding constraints in injection molding production has been cooling time. Removing parts from the mold before they have cooled induces warping or shrinking. But wait time works against productivity.

Another constraint has been cooling channels drilled straight through the metal blocks of injection molds using CNC machining. While coolant is passed through the channels to cool the mold and draw heat away from the part after it has been injected, the efficiency of that cooling process is limited by the conventional straight-line drilling that's used for the channels.

But if those cooling channels could more closely conform to the shape of the part, the cooling process could become more efficient and faster. According to Tober Sun, manager for the technical research division at software provider Moldex3D, a typical production cycle for a plastic part is 30 seconds to a minute, but cooling takes more than half of that cycle time.

Thus, he says conformal cooling has emerged as a practice, which is being aided by advances in additive manufacturing. With a conformal cooling channel design, the toolmaker can use an additive process to lay down the mold one layer at a time, fashioning the cooling channels along the way and curving them to any desired shape.

According to plastics consultant Robert A. Beard, “a typical cycle-time reduction range for a properly engineered, conformally cooled mold is 20% to 40%.” Such savings can lead to much greater productivity, especially in high-volume plants producing millions of parts.

Many industry observers associate conformal cooling with laser sintering, in which a solid object is printed by melting metallic powder using lasers. Sun told Design News that he prefers the broader term “additive manufacturing,” because of the widespread perception that sintered molds are not as strong as machined molds.

“It's not really sintering anymore. I prefer to call it remelting,” as it produces a solid metal object, he said. Sun stresses that additive manufacturing technologies are now handling very strong and durable materials, such as stainless steel and titanium, which compete well with machined molds. “Strength is no longer an issue,” he contended.

Sun recognizes that the added design effort and the use of additive technologies will increase the cost of mold development. But injection molds are expensive to start with, as they usually cost anywhere from $30,000 up to $1 million. The true economic concern shouldn't be the comparative cost of conformal molds versus traditional molds, Sun insists, but the trade-off between the added cost of the conformal mold versus the savings in cooling time on the production line. “The mold is quite unique and expensive, but you are using that single mold to make millions of parts. So it's important to increase the efficiency of that mold.”

Gate type-film gate-mould design

Film gate as shown in figure 6-19, also known as flash gate, thin film gate like circular runner, but used in flat edges of plastic parts, it has a flat gate, the gate width can jumper the whole or part of the cavity cavity edge. Film gate is suitable for pressing LiSu pieces, and often used in large, flat plastic parts

Film gate F as shown in figure 6-19, also known as flash gate (flash gate), thin film gate like circular runner, but used in flat edges of plastic parts, it has a flat gate, the gate width can jumper the whole or part of the cavity cavity edge. Film gate is suitable for pressing LiSu pieces, and often used in large, flat plastic parts, in order to keep the minimum of the warp. Film gate size is small, the thickness is about 0.25 ~ 0.63 mm, width is about 0.63 mm

                                     6-19

Automatic removal of gate Automatic removal of gate and mold actions, during ejection plastic parts cut gate. They are applied to: y avoid removing gate secondary processing. Y to maintain uniformity of cycle time

Y minimize gate marks. Automatic removal of gate includes the following types: needle gate, the latent type gate and hot runner gate, and the valve gate.

(1)  needle gate Pin gate (pin gate) as shown in figure 6-20, usually applied to three board mould, the runner system located in a component model online templates, cavity plastic parts meet the main parting line. The gate with a back taper Angle direction parallel to the template through the middle template. When open cavity of main parting line, the small diameter end of the needle gate from plastics tore off, then open the port can be parting line out port waste. This system can also open port parting line first, then using assistive devices off port waste. Needle gate used most often in a single plastic parts more into the water, in order to ensure symmetrical filling, or shorten the length of flow channel in order to ensure the parts of the holding operation. The typical needle gate 0.25 ~ 1.6 mm in diameter.

(2)   submarine gate the latent type gate Latent type gate (submarine gate) or is called the tunnel gate (tunnel gate), chisel gate (chisel gate), as shown in figure 6-21, used in the two plate mold, below the parting line, the end of the passage between the cavity and processing a tilt the cone of the tunnel. Ejection parts and runner, gate will be separated from the plastic parts. Typical latent type gate is 0.25 ~ 2.0 mm in diameter, runner from coarse to fine, until become globular endpoint. If parts of the functional area has the characteristics of large diameter of the needle, it can be connected to the latent type gate, to reduce processing costs. If the needle features occur in the hidden surface, also can not remove him. To multiple submerged in cylinder inside the gate design, can replace the disk gate, and have the function that automatically remove the gate, to the periphery of the molded parts roundness than disk gate parts of roundness is poor, but also can also accept it.

6-20 Pin gate                       6-21 Latent type gate

(3) hot runne the hot runner gate The hot runner gate (Hot - runner gate) or is called thermal probe gate (hot - the probe gate), as shown in figure6-22, usually from electrothermal vertical sprue and heat flow transmitted directly melt into the cavity, to produce plastic parts without a runner. Control the pressure maintaining cycle in plastic parts near the gate of solidification. When the template is opened, a fairly high temperature plastic tear from the cavity.

(4) Valve gate valve type gate valve type gate (Valve gate) as shown in figure 6-23

, in the hot runner gate increase a needle bar, in order to close the gate before gate solidification.

It can be applied in larger gate without gate trace. Because of the holding period is controlled by needle bar, valve type gate can get better the holding period and the stable quality of plastic parts.

(5)The side gate automatic gate design Side of the gate in the general design is not automatically take off a gate, if the product and the runner design into different time out, can realize automatic gate effect.

(6) take the bottom gate Take the bottom side gate of gate of improvement, products suitable for a particular shape. 1), in the case of side gate is not permitted.

2) and avoid the fluxion phenomenon; Backoff delay needle

3) in addition to the hard PVC, suitable for most of the products.

(7)The fan gate The fan gate is the improved side gate, its width increases with the decrease of depth. 1), suitable for large flat type shape products

2), the plastic into the cavity is flat, reduce the production flow and clamp water lines.

3), suitable for any except hard PVC plastic,

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Injection mold principle

Plastic injection mold is given to the shape and size of the molding member. Although the structure of the mold and performance of varieties of plastic, shape, and configuration and the type of plastics injection molding machine may be different and changing, but the basic structure is the same. Die mainly by gating system, molded parts and structural parts of three parts. Gating system and molded parts which are in direct contact with the plastic part, and with the plastics and products change, the mold is the most complex and the biggest change, the most demanding part of the process finish and accuracy.

Gating system refers to the plastic from the nozzle portion of the cavity before entering the flow path, including the main channel, cold-slug, diversion channel and the gate and so on. Forming part refers to the shape of the various parts constituting products, including dynamic simulation, the fixed mold and cavity, core, forming rod and exhaust ports and so on. A typical mold structure as shown.

Sprue

   

  It is mold injection machine nozzle connected to a shunt or cavity section channel. Sprue concave top to the nozzle convergence. Sprue inlet diameter should be slightly larger than the diameter of the nozzle (O.8mm) to avoid overflow and prevent the interception of convergence between the two are not allowed to occur due. Imported products according to the size of the diameter, usually 4-8mm. Expanding the diameter of the main channel at an angle of 3 ° to 5 ° should be within in order to release the flow channel thereof is superfluous.

Cold slug

    

It is located in the main channel at the end of a hole to trap shoot between the ends of two injections of mouth generated by cold material, thereby preventing the diversion channel or gate blocked. If cold material once mixed with the cavity, then the system is easy to produce products in the internal stress. Cold slug diameter of about eight a lOmm, depth of 6mm. In order to facilitate mold release, normally borne by the bottom of the release lever. Top release lever should be designed to zigzag trench subsidence hook or set up in order to successfully pull the sprue superfluous matter when stripping.

Shunt

It is a multi-slot die cavity connecting the main channel and each channel. In order to melt each cavity is filled with equal speed, diversion channel on the mold arrangement should be symmetrical and equidistant distribution. Runner-sectional shape and size of the plastic melt flow, and ease of mold release products has an impact. If the feeding amount in equal flow, it places the smallest cross-section of the flow path resistance. But because of the cylindrical flow channel surface area is small, the cooling of the shunt superfluous material adverse, and this shunt must be opened on the two halves of the mold, both labor-and easy alignment. Therefore, regular use of the trapezoidal or semi-circular cross-section of the runner, and the opening on one half of the mold with a release lever. Channel surface polished to reduce flow resistance must provide faster filling speeds. Depends on the size of the plastic flow channel variety, size and thickness of the article. For most thermoplastics, the shunt section width does not exceed 8m, up to 10 a large 12m, special small 2-3m. Under the premise of meeting the needs of the cross-sectional area should be minimized to avoid increasing the shunt Warts and extend the cooling time.

Gate

It is on the main road (or shunt) and the cavity of the channel. Sectional area of ​​the channel can be with the mainstream channel (or shunt) are equal, but are usually reduced. So it is the smallest part of the whole system, the cross-sectional area of ​​the flow path. The shape and size of the gate great impact on product quality. The role of the gate is: A, control the material flow velocity: B, due to the injection can be stored in this part of the condensate and prevent melt back earlier: C, so that the melt by strong shear by increasing the temperature , thereby reducing the apparent viscosity to increase flowability: D, easy separation of products, and the flow channel system. Gate design shape, size and position depend on the nature, size and structure of the article of plastics. The gate of the cross-sectional shape is generally rectangular or circular cross-sectional area should be small and the length should be short, not only based on the above effects, but also because larger than the small gate easy, and it is very difficult to reduce the large gate. Gate location should generally be selected in the products do not affect the appearance of the thick places. Gate size should be designed to take into account the nature of the plastic melt.

Cavity

It is the mold space molded plastic products. Component as constituting the cavity collectively referred to as molded parts. Various molded parts are often specific names. The molded article constituting the shape of the concave part called a die (also known as the female mold) to form the internal shape of the article (such as holes, slots, etc.) is referred to as core or convex mold (also known as the male mold). First, the overall structure of the cavity to be determined according to performance, the geometry of products, dimensional tolerances and use requirements designed plastic molded part time. Second, to select sub-surface, the gate and the vent mode position, and release according to the determined structure. Finally, press the control product dimensions of each part of the design and determine the combinations between the various components. Plastic melt with high pressure into the cavity, so the molded parts to be reasonable selection and check the strength and stiffness. To ensure the smooth plastic surface appearance and easy stripping, where contact with the plastic surface roughness Ra> 0.32um, but also resistant to corrosion. Molded parts are generally by heat treatment to improve the hardness and corrosion-resistant steel manufacturing.

Vent

A groove which is open in a mold outlet, and for discharging the original gas into the melt. When the molten material into the cavity, the original is stored in the cavity from the melt into the air and gas must be discharged through the exhaust port to die at the end of the stream outside, otherwise it will make products with holes, bad splices, filling dissatisfaction, even accumulated compressed air due to high temperature and the product burns. In general, both exhaust holes provided in the cavity of the melt flow at the end, may be provided on the mold parting surface. The latter was set up at the side of the die deep 0.03-0.2mm, wide shallow groove 1.5-6mm's. Injection, the vent does not have a lot of melt leakage, because the melt is cooled and solidified in where the channel blocked. Never open position toward the exhaust port operator, to prevent accidental discharge wounding melt. It will also use the top of the bar with the gap with the top of the hole, the top block and the stripper plate and with the gap cores like exhaust.

Structural parts

  

  It refers to the various parts constituting the mold structure, including: orientation, ejection, core pulling and genotyping of various parts. As the front and rear plates, after deduction templates, pressure plate, bearing columns, guide posts, stripper, stripping pole and the return pole and so on.

Heating or cooling means

   

  This is to make the melt solidified in the mold shape of the device for thermoplastic male and female mold is typically a cooling medium passage, and by circulating cooling medium to the cooling purposes. Pass into the cooling medium and the structure of an article with the type of plastic and the like, cold water, hot water, hot oil and steam. The key is uniform cooling high efficiency, uneven cooling products will directly affect the quality and size. Should be based on the thermal properties of the melt (including crystallization), the shape of the article and the mold structure, consider selecting the arrangement of the cooling passage and the cooling medium.

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