Plastic injection molding solutions to problems

In the injection molding process, mainly due to product defects is

1) molding plastic parts design is not

(2) mold design, manufacturing unreasonable;

Nature (3) of the plastic itself;

4) the inappropriate choice of molding process conditions;

(5) injection molding machine model matching unreasonable. Therefore, to solve the problem of plastic injection molding bad, we can start from the injection machine, molding conditions and mold (including product design), plastics and so on. However, the reasons for seeking to defect from the plastic is very difficult, because the defect molded parts are often made in front of several reasons why the mutual coupling formed by the action (see Table 1), it causes the defect depends on the vast project experience and judgment of the technical staff

Countermeasure

1, the rational design of plastic parts

Design of plastic parts to uniform thickness, it is because the molding cycle cooling time is never a given thickness of plastic parts, if a part of the thick, partially affected by the thickness of the cooling time and extended cycle times, reduce the efficiency of the molded ; Also, if uneven wall thickness, is caused by uneven shrinkage, resulting in reduced pit or internal stress, as well as deformation or cracking. Plastic stripping designed to have a certain slope to ensure the smooth stripping of plastic parts. Because the internal stress tends to be concentrated at the intersection of the surface and the surface, i.e., focused on the corner, in order to reduce distortion in the root fillet can design stress dispersion, while also improving the fluidity of the plastic, but also conducive to the release. Sometimes in order to enhance the plastic parts or to increase the fluidity of plastics, set the ribs, pay attention to the stripping direction to be provided with a reverse slope.

2. Improved mold design

Gate design is an important and complex issue, in the form of a direct gate, side gate, submarine gate, gate and other points. How to choose the actual manufacturing arrangement runner, gate type and position, mostly by the shape of plastic parts, dimensional accuracy and appearance requirements and decisions, while its runner-type system is varied. In order to make the plastic filling process ends at the same time, the gate and the runner must be balanced. In the injection molding process, the injection into the mold cavity of the molten plastic temperature is about 200300 ℃, but when removed from the mold cavity after the plastic parts which cure temperature 60 0C or less, the mold temperature is lowered due to the cooling water through the heat away, so a reasonable cooling system directly affects the dimensional accuracy of plastic parts and mechanical properties. In the actual injection mold exhaust problem must also be considered, if the injection mold cavity gas can not be discharged smoothly, will make products bubble, loose, filling dissatisfaction, welding is not strong, the workpiece surface fat bird, or at the time of the injection due produced by high-temperature gas is compressed so that the bottom parts of the charred charring. Common exhaust many ways, for example using an exhaust vent grooves, with the gap such as exhaust. Set the top of the system should be considered in order to avoid distortion, bleaching, catching phenomenon.

3, adjusting the injection molding process

For the different types and grades of plastics, which drying and molding the melt temperature are clearly defined, and therefore in the development of the molding process, according to the specific requirements of products used in plastics, to determine its drying and heating barrel temperature. Pressure is also forming important process parameters, the pressure into the injection pressure and holding pressure in two stages. Injection pressure is pushing the screw will melt into the mold cavity pressure used, packing pressure is nearing completion filling in, inject the melt is cooled and solidified to complement the products due to volume shrinkage caused by replenishment process of pressure used, in molding process, the right choice injection pressure and holding pressure and injection speed, is the key to the success of the molding process. Currently, most computer-controlled injection molding machines, injection to the decentralized approach.

4, the choice of efficient equipment

Selection of the injection molding machine should consider matching the mold clamping force is necessary to meet the requirements can not be too large, each injection is not less than the plastic parts plus runner condensate material weight. Pay attention to regular maintenance of equipment to ensure the normal operation of the production. IV Conclusion

Since the injection molding is a complex process, a lot of factors affecting the molding products, often a result of improved product defects caused by forming factors, may cause another previously insignificant factors stand out, make the product the emergence of new defects. Thus, in the development and adjustment molding process, not only to build pressure, speed, the right combination of temperature and the right choice for screw speed, injection pressure screw each position, holding pressure. Back pressure and cooling time and other issues should be fully valued. Advanced tooling, efficient equipment and reasonable modern injection molding process is the production of three elements. Therefore, in addition to research as a mold designer and mold structure and processing technology, but also a certain amount of injection molding technology, especially for products in the molding process common defects and solutions should have a 

full understanding.

In the process of injection molding, there are still many problems. For example

www.cnmoulding.com https://storify.com/cnmoulding/lackof-material-reasons#publicize

Injection product problems and solutions (b)

Overflow edge

  For the overflow edge processing should be mainly focused on improving aspects of mold. And in the molding conditions, we can begin to reduce liquidity. Specifically, the following methods may be used:

1) reduce the injection pressure.

2) reducing the temperature of the resin.

4) The use of high viscosity grades of material.

5) lowering the mold temperature.

6) mold surface grinding overflow edge occurred.

7) The harder the steel mold.

8) increase the clamping force.

9) Adjust the exact molds and other parts of the joint surface.

10) increase in die support columns, in order to increase the rigidity.

11) is determined depending on the material of the exhaust ducts of different sizes.

   

Burn

  According to Burns by different reasons machinery, molds or molding conditions caused by the solution adopted is different.

1) mechanical reasons, e.g., due to an abnormal condition caused by overheating of the barrel, the resin pyrolysis, injected into the product after burn

, Or simply because the material in the nozzle and the screw thread, check valve and other parts of the stagnation caused by the resin, after decomposition of color into the products, with dark brown burn scar in the article. At this time, we should clean up the nozzle, screw and barrel.

2) Cause molds, primarily because due to bad exhaust. Such burns generally occurs in a fixed place, easy to distinguish the first case. Then add exhaust ducts should pay attention to take measures such as anti-blow-down bar.

3) in the molding conditions, when the back pressure above 300MPa, the barrel portion would overheat, causing burns. Screw speed

When too high, it will produce heat, generally in the 40 ~ 90r / min range as well. Did not set in exhaust ducts or exhaust ducts is small, the injection speed too high will cause superheated gas burns.

Warping, deformation

  Injection products, warp, deformation is very difficult problem. Mainly from mold design to address, and to adjust the effect molding conditions is very limited. Warp, causes and solutions of this variation may refer to the following items:

1) residual stresses caused by the molding conditions cause deformation, by reducing injection pressure, improve mold and mold temperature uniformity and increase the resin temperature or the use of annealing method to eliminate stress.

2) the release of stress and deformation caused by bad, it can be solved by increasing the number or area of ​​the push rod, a release gradient methods.

3) As the cooling method is inappropriate, uneven cooling or insufficient cooling time, cooling method and the extension of the adjustable cooling time. For example, you can set up close to the deformation of the cooling circuit in place as possible.

4) For the deformation caused by mold shrinkage, it is necessary to revise the design of the mold. One of the most important to pay attention to the wall thickness is consistent. Sometimes, in the last resort, it had by measuring the deformation of the article, in the opposite direction trimming die, to be corrected. Larger shrinkage resin, a crystalline resin is generally ~ (e.g. polyoxymethylene, nylon, polypropylene, polyethylene and PET resin) than the non-crystalline resin (such as PMMA resin, polyvinyl chloride, polystyrene, ABS resin and AS resin) of deformation. Further, since the glass fiber-reinforced resin having fibers

Bubble

According causes bubbles, solving strategies in the following areas:

1) is larger in wall thickness, the outer surface of the cooling rate faster than the central portion, and therefore, as cooling proceeds, the resin shrinkage side edge of the central portion of the surface of the expansion, the central unit generates less filling. This condition is known vacuum bubbles. Solutions include:

a) according to the thickness, to determine a reasonable gates, runner dimensions. General gate height should be 50% to 60% of the wall thickness.

b) to the gate sealing up, leave some supplementary material injection.

C) injection time should be slightly longer than the gate seal.

d) reducing the injection speed, injection pressure increase,

e) the high melt viscosity grade material.

2) due to the generation of volatile gas bubble caused, the solution are:

a) full pre-drying.

b) reducing the temperature of the resin, to avoid decomposition gas.

3) bubble caused by poor liquidity, can be resolved by increasing the temperature of the mold resin and improve injection speed.

Albino

Whitening phenomenon occurs in the launch of the most important parts of ABS resin article. Stripping ineffective is the main reason. Injection pressure can be reduced, increased stripping slope, increase the number of push rod or area, reducing the surface roughness of the mold and other ways to improve, of course, spray release agent is also a method, but should be careful not to follow the process , such as stamping, painting and other adverse effects

In the process of injection molding, there are still many problems. For example

www.injectionmoldchina.com 

http://www.newswire.com/press-release/problem-cause-incomplete-filling-of-plastic-products-and

Plastic Injection product problems and solutions (a)

1. crack

  Cracks are more common form of plastic defects, the main reason is due to the stress caused by the deformation. There are stress and deformation residual stress, external stress and the external environment arising.

(-) Cracks caused by residual stress

    Residual stress is mainly due to the following three conditions, namely filling excess, stripping launch and metal inserts cause. As in the case of a crack filled with surplus produce, and its solution is mainly in the following aspects:

    (1) Since the minimum sprue pressure loss, so if a crack is generated in the vicinity of the main sprue, you can consider using the multi-point distribution point gate, side gate and handle-shaped gate way.

    (2) ensure that the resin does not decompose, it does not deteriorate the premise, an appropriate increase in the temperature of the resin melt viscosity can be reduced to improve flowability, but also can reduce the injection pressure, to reduce the stress.

    (3) Under normal circumstances, prone to stress when the mold temperature is low, the temperature should be raised. But when the high injection speed, mold temperature even lower, but also can reduce the stress.

(4) injection and dwell for too long can also cause stress, which is appropriate to shorten or Th hold pressure switching times better.

(5) a non-crystalline resin, such as AS resin, ABS resin, PMMA resin and other more crystalline resin such as polyethylene, POM prone to residual stresses, it should be noted.

  

Stripping launch, due to the small stripping slope, the mold plastic and punch roughness, so the introduction of excessive force, stress, and sometimes even the introduction of the rod around produce whitening or cracking phenomenon. As long as careful observation of crack-generating position, you can determine the cause.

  In injection molding, while embedded metal parts, most prone to stress, and prone to cracking after a period of time before, great harm. This is mainly due to thermal expansion coefficient differences between metal and resin stress, and over time, the stress exceeds the strength of the gradual deterioration of the resin material and cracks. To prevent cracks resulting, as experience, the wall thickness of 7 & quot; and metal parts embedded in an outer diameter substantially unsuitable for general-purpose polystyrene inserts should be added with minimal impact on the nylon insert. Since the thermal expansion coefficient of glass fiber reinforced resin material is smaller, more suitable for the insert.

  In addition, before forming the metal inserts were preheated, also has a good effect.

Crack (ii) external stress

External stress here is mainly due to the stress concentration caused by unreasonable design, especially in sharp corners should pay more attention. Figure 2-2 shows that the desirability R / 7 & quot; a 0.5 to 0.7.

Crack (iii) the external environment caused

Chemicals, moisture absorption due to water degradation, and excessive use of recycled materials will make the physical deterioration, cracks.

Second, less filling

  Filling the main reason for lack of the following aspects:. I insufficient capacity of the resin. ii. lack of cavity pressure. iii. resin illiquid. iv. not exhaust effect.

  As improvements, mainly from the following aspects:

1) extended injection time, to prevent the molding cycle is too short, causing the gate before the curing resin filled cavity upstream difficult. 2) increase the injection rate. 3) increasing the mold temperature.

4) increase the resin temperature. 5) increase the injection pressure.

6) expand gate size. Height generally equal to the gate of the wall thickness of 1/2 ~ l / 3. 7) Set the gate in the wall thickness is maximum.

8) Set exhaust ducts (average depth of 0.03mm, width 3 ~ smm) or exhaust strokes. More important for small workpieces. 9) between the screw and the injection nozzle to leave some (about smm) buffer distance. 10) selection of a low viscosity grade material. 11) the addition of lubricants.

In the process of injection molding, there are still many problems. For example

www.plastic-injectionmoulding.com 

http://cnmoulding.over-blog.com/2015/06/plastic-product-deformation-analysis-method.html

injection molded parts design features during the injection process

During the injection molding process, due to the plastic uneven cooling in the mold cavity and uneven shrinkage and molded parts design unreasonable, likely caused by a variety of defective products:

  

Microprinting, weld mark, porosity, deformation, galling, top injury, flash.

  

To obtain high-quality plastic products, we must fully consider the structure of the product design process, the following main structural features combined analysis of injection molded plastic products avoid injection defects.

  

1 mold parting line direction

Each injection product design at the beginning of the first to determine the direction and the mold parting lines, in order to ensure as much as possible to reduce the pulling mechanism and eliminate the effect of the parting line of appearance.

 1.1 mold after determining the direction, product ribs, snap, projections and other structures designed to be consistent with possible mold direction, in order to avoid reducing core pulling patchwork line, extend die life.

1.2 Example: bumper mold direction is generally the vehicle coordinate χ direction, if a model designed to χ axis direction is inconsistent, it must indicate their angle in the product drawing.

  

1.3 mold direction is determined, choose the appropriate parting lines to improve the appearance and performance. 2 stripping slope

A proper draft is to avoid product nap. Smooth surface stripping slope greater than 0.5 degrees, one degree higher than the surface of fine sticks, sticks rough surface is greater than 1.5 degrees.

2 proper draft is to avoid products top injury.

  

3 Deep cavity design requires less than the slope of the outer surface of the inner surface of the slope, to ensure that when the injection mold core without deviation, to obtain a uniform product thickness, and the opening portion of the product to ensure the strength of the material density.

  

3 Product thickness

  3.1 All kinds of plastic have a certain thickness range, generally 0.5 ~ 4mm, when the thickness of more than 4mm, will cause the cooling time is too long, resulting in microprinting and other issues, should consider changing the product mix.

  

3.2 microprinting surface can cause uneven thickness. 3.3 will cause uneven thickness and weld porosity marks.

4 ribs

4.1 to strengthen the rational use of ribs, increase product rigidity and reduce distortion.

 4.2 stiffener product wall thickness must be less than 1/3, otherwise the surface microprinting.

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Injection molding design issues should be noted

1. Injection should be consistent with the outer surface smooth Requirements: High visibility area, A level surface, the local tangent continuous. Less visible areas, grade B surface, tangent continuous. Invisible area, grade C surface, continuous position.

2. Injection to smooth the edges, and other pieces of gap should be uniform.

3. Surface do striae member draft angle greater than 5 °. Structural strength, reliable, secure and stable installation.

Surface quality interior trim pieces demanding surface defects are not allowed. Most of the current use of injection molding, compression molding process for forming the inner trim, interior trim to consider outside surface should be in the direction of releasing no "negative" to ensure that in the mold design, mold parting lines are not assigned On the surface of the door trim panel, so as to ensure the surface quality of the outer surface of the door trim board. Determine the draft direction injection molded parts should also consider whether there are avoidable negative angle to reduce costs. After the interior molding surface does not allow flawed, sink marks, so the design should guarantee for the wall thickness, ribs strengthen the rational distribution, rib thickness should be less than 1/2 of the maximum can not be greater than 1 / 1.6.

4. Injection skeleton material thickness is generally 2.5-3 mm,

5. In general, small parts with snap, catches connection, large parts or parts to increase the force and increase the need to strengthen the screw connection

Structure. Snap snap connection should consider the amount of axial rebound 0.5 mm, the amount of compression side pressed into 0.75 mm, snap common vias φ8 (φ6.5) card withhold the end of the large diameter φ9.5 (φ8). Brackets size recommended modifications compensation snaps. Where zero is designed components and peripheral parts in contact with the touch should be zero, and should leave enough local non-contact sufficient space; the supporting surface should be considered when designing plastic parts require a larger plane as the bearing surface, if the Omo as a whole by the bearing surface, in the manufacturing process is not easy to meet the requirements.

6. Aperture shape and position size should be rounded, aperture in line with standardized, serialized.

7. Check the manufacturing process: the appearance of molded parts to be uniform thickness; interior trim is a large thin-walled injection molded parts, requiring the materials

Have better liquidity, along with high precision parts and resistance to UV stability, the general use of modified polypropylene. In the structural design of plastic parts, to avoid excessive use acute and right angles, since stress concentration at sharp corners, easy to crack, the impact strength of the workpiece; in order to avoid stress concentration should be used arc transition, which for mold manufacturing, life is very advantageous. General plastic parts each connection should be 0.5-1mm rounded, and large rounded corners imposed transition, to reduce stress, and to ensure consistent wall thickness. Hole vias should generally be designed to avoid ф5 less blind holes. The bottom of the blind hole should be designed hemispherical or conical surface, in order to facilitate the flow of materials, pore size and depth ratio is generally 1: 2-1: 3. The length of the larger parts should minimize the length direction on both sides of the mold slide stroke. Pulling the slider injection should be considered within the smallest space. Plastics welding process should also consider whether it is reasonable. Rib design is reasonable. Plastics welding process is reasonable

8. Structural strength analysis: the force components higher strength material should be used, the part in the force area should consider reinforcing structure,

CAE strength analysis carried out if necessary. In large part locally 160 × 160 range without additional support should be considered when the support structure, or foam support blocks. The rim flange parts generally should be designed, firstly, to increase strength, the second is to avoid the flash. Flanging should be added to the appropriate stripping slope.

9. Motion check: moving parts must be checked for motion to prevent interference and determined movement parting gap.

10. Analysis of the final assembly process must carry out parts assembly process analysis, analysis of parts are smooth installation and removal, mainly to have a removal tool installation space and parts activities smooth place. Parts should normally positioning guide structure.

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Plastic products Warpage

Molds:

Improper (1) or an insufficient number of gate location.

(2) the top of the improper position or article discontinuity.

Technological aspects:

(1) die, cylinder temperature is too high.

(2) injection or the injection pressure is too high too fast.

(3) the holding time is too long or too short cooling time.

Raw materials: phthalocyanine pigments can affect the degree of crystallinity of polyethylene deformation caused by products.

Product design:

(1) uniform wall thickness, wall thickness changes suddenly or too small.

(2) improper product structure modeling.

Dimensionally unstable

Equipment:

(1) feeding system is not normal.

(2) back pressure instability or temperature instability.

(3) failure of the hydraulic system.

Molds:

(1) gate and runner size uneven.

(2) the cavity dimensions are not allowed.

Technological aspects:

(1) The mold temperature cooling circuit caused uneven or improper mold temperature control unreasonable.

(2) injection pressure is low.

(3) injection dwell time is not enough or there are fluctuations.

(4) high cylinder temperature or the injection cycle is unstable.

Raw materials:

(1) change the batch, the resin properties have changed.

(2) Material particle size erratically.

(3) a large amount of moisture.

(4) Replace the aid of influential law contraction.

White steam cracking

Mold: the top of the organization is poor.

Technological aspects: (1) lower cylinder temperature or mold temperature is low. (2) a high injection pressure. (3) long dwell time.

Raw materials: (1) lubricants, release agents, or the amount is too inappropriate. (2) grades, grades do not apply.

Product design: product design is unreasonable, leading to local stress concentration.

Delamination

Technological aspects: (1) barrel, nozzle temperature is low. (2) back down. (3) for PVC plastics, the injection speed is too low or the mold temperature may also cause delamination.

Raw materials: (1) raw material contamination or foreign matter. (2) Different plastic mix.

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Plastic parts Gloss bad

Plastic parts Gloss bad because:

Equipment:

(1) feed shortage.

(2) the timing of refueling tube is not clean.

Molds:

(1) gate is too small or too thin runner.

(2) the difference between the surface roughness of the cavity.

(3) Exhaust bad or mold temperature is too low.

(4) No cold well.

Technological aspects:

(1) uneven heating barrel, barrel temperature is too high or too low.

(2) pre-plastic backpressure nozzle is too small or too low.

(3) the injection speed is too large or too small.

(4) plasticized uneven.

Raw materials:

(1) Not dried material.

(2) containing a volatile substance.

(3) The excessive amount of aid or release agent.

Stripping difficulties (gate or plastic parts tightening in the mold)

Equipment: ejection force is not enough.

Molds:

(1) releasing structure is unreasonable or improper location.

(2) stripping slope is not enough.

(3) The mold temperature is too high or bad ventilation.

(4) runner cavity wall or surface roughness.

(5) the inlet nozzle and the mold match against posts or nozzle diameter greater than the diameter of the inlet.

Technological aspects:

(1) cylinder temperature is too high or too injection volume.

(2) injection pressure is too high or long dwell and cooling time.

Raw materials: lack of lubricant.

In the process of injection molding, there are still many problems.For example

www.injectionmoldchina.com  https://storify.com/cnmoulding/burrs-flash#publicize