In mold design, use of strong release mechanism for product undercut is also a style of plastic mold release mechanism. Not all similar undercut can be used in this mechanism, and several factors affecting reverse buckle are considered.
One: Is there any space for undercut deformation?
Two: Is material property suitable for strong release?
Three: How big is product reverse deduction? Will it break buckle?
Four: Is position of undercut reasonable? Have you considered maximum ejector force position and ejector balance?
Five: Is there any R angle added to fragile position?
Some years ago, Gud Mould Industry Limited made several sets of molds with strong plastic mold release as shown in figure. All the first mold trial failed. The first three points of attention were taken into consideration, only last two points, selection of ejection position was wrong. Product's fragile position is not chamfered, resulting in several broken tops. I will share this case with you, I hope that I will encounter such similar problems in the future and analyze five points mentioned above.

 

Undercut molding deformation space is an essential element for forced demoulding. Product will not become less and more after injection molding. You have to find a way to create deformation space for undercut molding position. For example, the first case shown in picture takes this problem into consideration. Middle of undercut molding is evacuated, and emptying position is made into a needle out of front mold. After mold is opened, product is empty in the middle of buckle. When top is out, buckle is deformed to middle and mold is released smoothly. In second case, after front and rear molds are divided, outer glue position of undercut molding is outside cavity, which also creates a deformation space for undercut, and can also be sequentially reversed.

 

Properties of material compound will affect inverted material. Some material compounds are softer, toughness is better, elasticity is more suitable for strong plastic mold release, for example, PP material. Some material compounds are harder, brittle and easy to break, such as PA PA66 POM PC. Etc. This kind of material does not mean that it must not be strong plastic mold release. It should be considered in combination with amount of undercut molding. Generally, amount of reverse buckle can be strong release below 0.5mm, which is based on position of undercut molding in the product and similar mold used by customer.

Product back-off amount is less than 0.2mm, and it can achieve strong plastic mold release. It does not need to consider deformation space problem. Generally, amount of reverse buckle is 0.3mm to 0.5mm. It is necessary to consider whether there is any deformation space, and whether it can be strong released with product material. For example, mold that our company made before, product material is PA, buckle amount is 0.37mm, strong mold release is completely no problem.

 

Position of strong pull-off buckle should be selected at the position closest to undercut, force of top pullout should be the largest. Top force should be considered for balance of force. It is best to push out under sides of undercut molding, as shown in the first mold trial. Reason for failure of undercut of molded product is related to selected ejection position, which is a little far from undercut, not maximum force point for undercut molding. Shape of undercut molding on the other side is different, and ejection is not stable. Top end of product is inclined to the side where force is large, causing buckle to break. After second mold trial changes ejection position, problem of reverse buckle is solved, and the other problem is ignored. Buckle is trapped (can be seen in picture), because buckle is end of glue, problem exists in metropolis, and exhaust needle is also increased. A set of mold has been tested three times to complete, great experience and lessons, which wastes manpower and material resources, hopes to attract everyone's attention.

 

Reverse position of undercut molding add R angle can enhance product toughness and avoid cracks in product. This must be recommended by customer. Even if customer does not agree, we can also add R0.2. It is difficult to see after product finished. Just in case, try to save costs for your boss.