Injection Moulding

We are located in Shenzhen China, supplying professional mould making & injection moulding services for international companies for more than 10 years, capable of designing the mould & products based on your companies' requirements and making cost-effective injection moulding for your plastic parts. Hundreds of existing customers from America & Europe are happy with our services and willing to recommend their friend companies to make mould in our factory, also doing reference per our request for new customers.
The most common cause of black streak is the material residue in the injection moulding machine barrel.Residue remains in the plunger injection moulding machine.For valve gated injection moulding machine, the valve-regulated part also tends to remain residue.The air is compressed to a high temperature in the cylinder, with the high temperature gas in the gate, so it will be easy to be black streak.
Black Streaks
Using only one sprue (gate), without confluence the material from two directions, in this way the molded parts generally do not have weld line. If you want to avoid weld lines, you can only change the position of the sprue in the injection mould so that the welding mark will not occur in obvious places.
Change the location of the sprue in injection mould
Fracture looks like crack, but the essence is different, that the fracture is not like a void defects, coupled with stress in the polymer due to the parallel arrangement direction of itself. If heat the product, it can return to the state without fracture. In this way, we can distinguish the reticular fracture and crack.
Polystyrene has high impact resistance. The rubber particles dispersed in the polystyrene stress concentration point, majority cause tiny fracture. This is because the absorption of deformation energy. ABS is very subtle, so the fracture is very tiny, and has superior impact resistance.
Injection moulding defects generally decide by mould shape and material liquidity. When defect is due to the setting of moulding material, injection moulding condition setting should be set towards the right direction, namely to improve the mould and barrel temperature, injection pressure and speed.
Spiral flow mould
If the cavity exhaust edge is not well designed, the air in the mould will be difficult to be discharged. In addition to cause moulding defect, it will also cause burn mark and fusion mark.
It is very easy to find an injection mould maker, the most simple and effective way is to participate in relevant exhibitions. You will be able to walk around and get a stack of business cards and collect leaflets. Combined my experiences, the key point should be 'appropriate' in choosing a plastic mould maker in China.
Mould Maker
Mechanical processing plants are varying quality. When purchasing higher-cost custom plastic moulds, how to identify reliable injection mould maker for your company?
There are many different ways to calculate the an injection mould price, but, they have one thing in common, that is taking efforts to make technical and economic indicators organically combine in order to produce mutual benefits. It will make the injection mould to have competitive prices from the valuation to offer, to contract and to the settlement price.

Empirical Calculation Method
Mould price=material cost + design + process and profit + VAT + tryout cost + packing and shipping cost. Usually in the ratio:
  • Material cost: materials and standard parts accounted for 15%-30% of the total cost of the injection mould;
  • Process and profit: 30%-50%;
  • Design fees: 10%-15% of the total cost;
  • Tryout cost: medium-sized mould can be controlled within 3% while small precision moulds controlled within 5%;
  • Packing and shipping cost: according to the actual or calculated at 3% of the total;
  • VAT: 17%.
In the production process, sink mark is the highest frequency of occurrence of undesirable phenomena in plastic injection mould. The early cooling part surface will be hard first, at the same time, the internal will produce bubbles. The sink mark is the concave surface in the direction of contraction of the bubble of the slow cooling part.
Avoid sink marks
Materials with large shrinkage are also easy to produce sink mark. When you want to change the moulding conditions to eliminate sink mark, you should set conditions to a low contraction direction. That is to reduce plastic mould and cylinder temperature, increase injection pressure. It should be noted that this may cause internal residual stress.
When you are moulding a part, the mould temperature and melt temperature may be same irrespective of climate. So the environment at injection moulding is uniform (assuming that the material is predried if it has moisture). If moisture is present, the weld strength would be low and at the same time you will notice surface defects. The molecular chain would break and the material strength would be low; as good as low molecular weight material. The stresses developed due to climate change can cause problems. Thus, you have to analyze the problem whether it is in individual part or in an assembly.

I used to assist periodically in a moulding shop in Nigeria, with >90% RH at >40°C (104°F) and had not been made aware of this problem. That is not to say, of course, that it wasn't there.
In the next decade, the development trends of Chinese mould industry are: mould products develop toward large-scale, sophisticated, complex, economy, rapid direction; continuously improve the technological content of the mould, mould manufacturing cycles continue to shorten; mould production towards information technology, not drawing, fine quality, automated direction; mould manufacturing companies toward technology integration, well-equipped, product branding, management, information technology, international business direction. Chinese mould industry market
Injection Mould ClampFor big PP parts with undercuts, how do you evaluate the additional clamping force needed to keep the wedges (slides) closed and avoid flash? I want to develop a method to predict Injection Mould Clamping force for big PP parts with a lot of undercuts (8 big wedges in the mould). At the moment, I am using moldflow to predict tonnage but I am always missing 25% in comparison to the real life! I know that this is due to the side pressure on the wedges which makes them moving backward and the part is flashing. Do you have any idea of how to predict the right clamping force? Or what mould design change (bolster plates thickness, wear plate angle,...) could reduce the clamping force?
In comparison to the shear stresses in the flowing polymer melt, the gravity force is very small. (You can do a simple order of magnitude comparison to confirm this). However, I have seen cases in Gas Injection Moulding where the melt sagged around the gas core during the gas pressure holding phase. This is reasonable. If all melt in the cavity is pressurized to approximately the same pressure, then the shear stress are zero (or near zero) and so the gravity force is the only significant directional force acting on the melt. (To put it another way, the buoyancy of the gas core causes it to rise up through the polymer melt. Of course it won't displace the frozen skin layer).

I once had a Chinese injection moulder argue with me about this on a project where the weld lines where located in a bad location for the part's mechanical performance. He added gates (From one to four) and rotated the tool in the press. When the weld lines moved on the part he naturally said "See! Gravity does make a difference!"

Online tour of our plastic injection mould making factory in Shenzhen China.
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