What you need to know about the injection molding part design?

Mold opening direction and parting line  

When designing each injection molded part ssproduct, we must first determine the mold opening direction and parting line to ensure that the core pulling slider mechanism is reduced as much as possible and to eliminate the influence of parting line on the appearance.

1.After the mold opening direction is determined, the reinforcement, clips, bumps and other structures of the product should be designed to be consistent with the mold opening direction as much as possible to avoid core extraction and reduce the parting line to prolong the mold life. 

2.After the mold opening direction is determined, the appropriate parting line can be chosen to avoid the existence of inverted buckle in the mold opening direction to improve the appearance and performance.  

Demold slope  

1.Appropriate release slope can avoid product pulling (pulling flower).

Smooth surface of the mold slope should be ≥ 0.5 degrees, fine grain (sand surface) surface is greater than 1 degree, coarse grain surface is greater than 1.5 degrees. 

2.The appropriate slope of the mold release can avoid product top injury, such as top white, top deformation, top broken. 

3.Deep cavity structure product design, the slope of the outer surface as far as possible requires greater than the slope of the inner surface.

In order to ensure that the mold core does not deviate when plastic injection molding, to get a uniform product wall thickness, and to ensure the material strength of the product opening parts. 

Products need uniform wall thickness

1.All kinds of plastics have a certain wall thickness range, generally 0.5 ~ 4mm, when the wall thickness exceeds 4mm, will cause too long cooling process, shrinkage and other problems, should consider changing the product structure.  

2.Uneven wall thickness will cause surface shrinkage.  

3.Uneven wall thickness will cause air holes and produces sink marks on molten plastic.  

The reinforcement  

1.The reasonable application of reinforcement, can increase product rigidity, reduce deformation.  

2.The thickness of the reinforcement must be ≤ (0.5 ~ 0.7) T product wall thickness, or cause surface shrinkage.  

3.The one-sided slope of the reinforcement should be greater than 1.5 °, to avoid top injury.  

Rounded corners  

1.Rounded corners are too small may cause stress concentration in the product, resulting in product cracking. 

2.Rounded corners are too small may cause the mold cavity stress concentration, leading to cavity cracking.  

3.Set a reasonable rounded corner, but also can improve the processing of the mold, such as the cavity can be directly milled with R cutter, and to avoid inefficient electrical processing.  

4.Different rounding angles may cause the movement of the parting line, should be combined with the actual situation to choose a different rounding or clear angle.  

The hole  

1.The shape of the hole should be as simple as possible, generally take the round.  

2.The axial direction of the hole and mold opening direction in line with the core can be avoided.  

3.When the hole length-diameter ratio is greater than 2, should be set to release the slope of the mold. At this time, the diameter of the hole should be calculated according to the small diameter size (maximum solid size).  

4.The blind hole length-diameter ratio generally does not exceed 4, anti-hole pin punching bend.

5.The distance between the hole and the edge of the product is generally larger than the size of the hole diameter.  

The injection mold core, slider mechanism and avoid  

1.When the plastic part according to the mold opening direction can not be smoothly off the mold,the injection molding machine should be designed to draw the core slider mechanism.

Core pulling mechanism slider can shape complex product structure, but it is easy to cause defects such as product stitching line and shrinkage, and increase mold cost to shorten mold life.  

2.During designing injection molding process, need to pay attention to the mold cycle,such as no special requirements, try to avoid the core pulling structure.

Such as hole axial and tendon direction to open the direction of the mold, the use of cavity core touch through and other methods. 

One-piece hinge  

1.Using the toughness of PP material, the hinge can be designed to be integrated with the product.  

2.The size of the film used as hinge should be less than 0.5mm, and it should be even.  

3.When injection molding one piece hinge, the gate can only be designed on one side of the hinge.  

Inserts 

1.During the manufacturing process,inserts in the injection molding products can increase local strength, hardness, dimensional accuracy and set small threaded holes (shafts) to meet various special needs. At the same time will increase the cost of the product.  

2.Inserts are generally copper, but can also be other metals or plastic parts.  

3.The part of the insert embedded in the plastic should be designed to stop the rotation and anti-pull-out structure. Such as: knurling, holes, bending, flattening, shoulders, etc.  

4.The plastic around the insert should be properly thickened to prevent stress cracking of the plastic parts.  

5.When designing the insert, should fully consider its positioning in the mold (hole, pin, magnetic)  

Marking  

Product marking is generally set at the flatter inner surface of the product, and in the form of raised, choose the normal direction and open the mold direction ruler may be consistent with the face of the marking, can avoid strains.  

Precision of injection molded parts

Due to the unevenness and uncertainty of the shrinkage rate during injection molding, the accuracy of injection molded parts is significantly lower than that of metal parts, can not simply apply the dimensional tolerances of mechanical parts should be selected according to the standard appropriate tolerance requirements.

China also released in 1993 GB/T14486-93 “engineering plastics molded plastic parts size tolerance”, the designer can be based on the plastic raw material used and the requirements of the injection mold tool, according to the provisions of the standard to determine the size tolerance of the parts.  

The deformation of injection molded parts  

Note the injection molding cycle time,improve the rigidity of the structure of injection molding products to reduce deformation. Try to avoid flat structure, set reasonable flanges, concave and convex structure. Set up reasonable reinforcement bars.  To better illustrate the point, consider that resins typically have large thermal expansion coefficients. As a result, parts may have to be measured at a consistent temperature to accurately determine expansion and contraction. These two characteristics largely dictate a part’s ability to maintain injection molding tolerances. 

Buckle position 

1.The buckle bit device is designed to share multiple buckle bits at the same time, so that the overall device will not be unable to operate because of damage to individual buckle bits, thereby increasing its service life, and then more ko filter plus rounded corners to increase the strength. 

2.Is the tolerance requirements of the relevant dimensions of the buckle is very strict, too many buckle position is easy to form a buckle damage.

On the contrary, too few buckle position is difficult to control the assembly position or the combination of part of the phenomenon of too loose.

The solution is to set aside to change the mold easy to add glue to achieve the way.  

Welding (hot plate welding, ultrasonic welding, vibration welding)  

1.The use of welding, can improve the strength of the joint.  

2.The use of welding, can simplify product design.