① The concept of insert molding
Insert injection molding (Insert Molding) is a kind of insert pre-fixed in the injection mold in the appropriate position, and then injected into the plastic molding, mold opening inserts are cooled and cured plastic wrapped tightly buried in the plastic to get with such as threads, electrodes, and other inserts with inserts in the process of products.
Plastic inlaid with metal, glass, wood, fiber, paper, rubber or molded plastic parts called inserts, the most common inserts for the metal.
Inserts injection molding inserts in the mold is placed in two ways:
(1) manual placement; this will significantly increase the injection molding cycle, applicable to small batch production or complex structure of the product;
2) Automated placement; this is a better choice for mass production, which helps to reduce manual errors, improve efficiency, shorten injection molding cycle time and improve product reliability.
② The advantages and disadvantages of insert injection molding
2.1 Advantages of insert injection molding
(1) plastic easy to mold, elasticity and metal rigidity, strength and heat resistance of the mutual combination of complementary can be made of complex and sophisticated metal-plastic integration products; reduce the size and weight of the product;
(2) the use of plastic insulation and metal conductivity of the combination of molded products can meet the basic functions of electrical products; can also meet certain special requirements, such as magnetic conductivity, wear resistance and fastening;
(3) The addition of metal inserts in plastic can improve the strength of plastic parts;
(4) Insert injection molding increases the flexibility of product design and provides new possibilities for the combination of plastic and metal and other parts;
5) Avoiding secondary processes such as heat fusion, welding and riveting, there is an opportunity to shorten assembly time and cost;
6) Inserts are not limited to metal, but also cloth, paper, wire, plastic, glass, wood, coil type, electrical parts and plastic parts and many other;
(7) For rigid molding products, rubber sealing gasket plate on the bending elastic molding products, through the base on the injection molding made of integrated products, can save the arrangement of the complex operation of the sealing area, making the automation of the combination of post-processes easier;
(8) Since molten plastic is combined with metal inserts, the gap between the metal inserts can be designed narrower than in the press molding method, resulting in higher product reliability and easier passage of vibration and other tests;
(9) Selection of appropriate plastics and molding conditions, i.e., for products that are prone to deformation and breakage (e.g., glass, coils, electrical parts, etc.), they can be sealed and fixed with plastics;
(10) Select the appropriate mold structure, inserts can also be completely sealed into the plastic.
(11) Vertical injection molding machine and robot, inserted pieces of products such as the combination of the whole series of devices, insert molding project can be achieved mostly automated production.
2.2 Disadvantages of insert molding
(1) inserts are often placed so that the mold structure is complicated, injection molding cycle is extended, the manufacturing cost increases, increasing the difficulty of automated production;
(2) inserts and plastic thermal expansion coefficient is not consistent, easy to make the final product to produce internal stress, resulting in product rupture; this is particularly evident in the injection molding of nut inserts;
(3) Or because of the inserts and plastic thermal expansion coefficient is not consistent, resulting in product deformation;
(4) Inserts (especially nut inserts) often need preheating or drying treatment, etc., in order to reduce the internal stress;
(5) Inserts must be well fixed in the mold, otherwise it is easy to shift or deform under the impact of the solute;
(6) insert injection molding once the defective products such as bad injection, insert leakage, bad position, etc., will cause the whole product scrap, the cost is huge;
(7) Insert injection molding is not conducive to product recovery and scrap.
③. The application of insert injection molding
Insert injection molding is widely used in automotive, medical, electronic products and connectors and other industries.
④. Insert injection molding design guidelines
When designing insert injection molding, the process characteristics of insert injection molding must be fully considered for the design of DFM;
The design guidelines for insert injection molding include:
(1) the choice of insert materials. Copper, aluminum, steel, hard dissimilar plastic parts, ceramics, glass and plastics can be used as insert materials, of which, brass is not rust, corrosion resistance, easy to process and affordable, is a common material for inserts.
(2) insert shape. As far as possible, the use of round or axisymmetric shape, does not allow the existence of sharp corners or sharp corners, in order to facilitate the uniform contraction and prevent the generation of local stress, or even stress concentration phenomenon;
(3) The insert itself needs to consider its own DFM. metal inserts are machined by cutting or stamping, so the shape of the insert must have good machining processability.
4) In order to facilitate the placement and positioning in the mold, the outreach of the insert (i.e., the part that rests in the mold) should be designed as a cylindrical shape, because it is easiest for the mold to process round holes;
(5) Inserts should have structures such as sealing tabs to prevent overflow during injection molding;
(6) in order to avoid the appearance and strength of the plastic bottom is too thin ripple-shaped shrinkage marks and affect the appearance and strength, should be taken to the bottom of the insert from the plastic wall of the minimum distance T> D / 6;
(7) The distance between the insert and the side wall of the product should not be too small to ensure that the mold has a certain strength;
(8) the setup of inserts in the cam, in order to ensure the stability of the combination of inserts and the strength of the plastic substrate, inserts should be extended to the bottom of the cam (need to ensure that the minimum thickness of the bottom), the head of the inserts made into rounded corners;
(9) small cylindrical inserts can be used in the middle of the slot or surface rhombus knurling structure planted in the plastic substrate, knurling groove depth of 1 ~ 2mm;
(10) plate, sheet inserts can be fixed with hole window fixing method, but thin inserts (thickness less than 0.5mm) should be fixed with incision or bending method;
(11) rod-shaped inserts can be used to flatten the head, punch shortage, bending, splitting and other forms of fixed, can also be used to flatten the middle part of the round rod method of fixing;
(12) tube-shaped stamping inserts, can be processed in the stamping convex part of the expansion, to enhance the fastening force;
(13) in the connector, the terminal inserts in the plastic fixed firmness is the priority of each product design engineers to consider the problem, commonly used methods are the following kinds of methods, can greatly enhance the firmness of the terminal in the plastic;
Terminal perforation in plastic;
Shaping of terminals in plastic;
Bending of terminals in plastic;
Increasing the roughness of the terminals in plastic, bumping points;
Increasing the plastic wall thickness.
⑤. Automatic insert molding system design selection considerations.
1, Metal insert molding is easy to produce molding shrinkage % uneven, beforehand should do the important parts of the shape, dimensional accuracy of the limit test.
2,The injection process of metal inserts "easy deformation and displacement, should give full consideration to the mold composition and easy to maintain the metal insert mold shape design. For the insert shape can not change the product, prior testing is indispensable.
3,If the metal inserts are arranged separately and a conveyor is used, the contact between the metal inserts and between the inserts and the vibration ball may cause minor damage to the surface of the inserts and affect the quality of the product. The permissible limit of quality should be checked in advance.
4, Should be measured in advance because of the metal inserts stamping processing% caused by the jagged, warped amount of material thickness difference, diameter difference, the thickness difference caused by the processing of gold, etc., on the basis of automation equipment supporting the choice of design and mold structure design.
5,Mold gate location, molding cycle and other constraints on the mold structure of the predictable matters, as far as possible to solve in advance or have the corresponding improvement measures.
6, Should confirm whether the metal inserts need to be preheated or dry explosion treatment. The purpose is to ensure product quality and molding stability.
7,The mold set up a variety of detection devices, in order to mold by heat, force, vibration and other environmental conditions, to ensure that the molding action is stable and used, should confirm whether to use.
MAKES YOUR INSERT MOLDING BEING PERFECT
