Guidelines on Insert Molding

What is Insert Molding?

Insert molding is a process of fabricating a finished part by applying a metal part into  moltenres in a mold. As compared to installing inserts into a plastic molded part in a post-molding process, the use of molded-in inserts eliminates the need for secondary installation of the inserts and thereby reduces costs. The mold temperature of INSERT MOLDING process is 65 -120 cels degree, and the material temperature is 260-320 cels degrees. Of course, different raw material ratios have different temperature ranges requirment and the resin producer will provide upper and lower limit temperature with the datasheet.   The upper limit temperature indicates the temperature at which the material begins to carbonize and decompose, while the lower limit temperature indicates the temperature at which the material begins to flow.On one hand, if the molten temperature is lower than the lower limit, the liquidity of the material is insufficient, and the insufficient plasticity of the molding screw can easily break the molding machine screw and plastic molded product can not be filled fully. On the other hand, if the material temperature is higher than the upper limit,viscosity will be decreased, which causes easy cartonization of plastic ,corrosion on injection mould and damage to molding machine screw. The temperature of the insert mold needs to be settled wihtin the temperature range of the material according to the structure of the product and the structure of the mould.

Tips to trouble shoot insert molding process

  1.Excessive plastic. The defect often occurs in the insert molded part where the R angle of the insert is used to seal the plastic. Most of the time the precision of R angle of themetal insert can not reach the theoretical size of the drawing after bending, thus the plastic overflow will show up around the gap between the insert and the mould. The thicker and the harder the metal part is, the greater the elastic deformation after stamping, the more obvious the overflow defect is. Therefore, avoid sealing off plastic with R angle as much as possible, or advise customers to enlarge R angle as  possible to reduce the risk of plastic overflow. If the accuracy of R angle can not be further improved, the mold maker needs to fit the mold according to the actual R angle on site.  

2. Poor bonding of insert molding. Since insert molding products are built-in structure by combing the metal parts and plastic injection molded partstogether, the defect of insufficient adhesion may occur. Lack of adhesion will cause mechanical problem and affec the use of products.To sovle thie issue, increase the binding area or improve combination method of plastic parts and metal inserts. In some case, the inser structure might need to changed as well.

 

3. The most difficult problem of the insert molding product is part During insert molding injection process, the metal inserts won’t contract whereas the plastic part will get cold when meeting the molded in inserts, so the hold pressure could not be used as normal and the plastic parts get deformed after cooling down.The defect could be solved from below aspects:
4. Check if thethe shrinkage deformation is caused by the insufficient binding force of the plastic part and the meal insert is considered
5. Check if the waterlines of plastic mold could be improved to eliminate the possiblity of shrinkage deformation caused by the uneven cooling.
6. Replace a resin to verify the deform of thesamples or  change the position and the number of injection

In a short, the development of insert mold is an chanllenging task.  Different issues may come up with different material, mold structure and molding process. Welcome to contact hsmolds for any technical discussion!!