What tooling problems can be avoided at the time of manufacture?

1. Guide column damage

The guide pillar mainly plays a guiding role in the mold to ensure that the molding surfaces of the core and cavity do not touch each other under any circumstances.

In the following two cases, the dynamic and fixed mold will produce a huge lateral offset force during the injection.

When the wall thickness of the plastic part requires unevenness, the rate of material flowing through the thick wall is large and a large pressure is generated here.

Asymmetry of the side of the plastic part, such as the stepped parting surface of the mold, the counter pressure on both sides of the opposite side is not equal.
 

2. Difficulty of gate release

In the process of injection, the sprue sticks in the sprue sleeve and is not easy to be taken off. When the mold is opened, the product is cracked and damaged. In addition, the operator must use the tip of the copper rod to knock out from the nozzle to make it loose before demoulding, which seriously affects the production efficiency.

The main reason for this failure is the poor finish of the conical hole of the gate and the knife marks in the circumferential direction of the inner hole. Secondly, the material is too soft, and the small end of the cone hole is deformed or damaged after using for some time, and the arc of the nozzle sphere is too small, resulting in the riveting head of the sprue material here. The tapered hole of the sprue is difficult to process, so standard parts should be used as much as possible, if you need to process it by yourself, you should also make your own or buy a special reamer. The tapered hole should be ground to Ra0.4 or less.

In addition, the sprue puller or sprue ejector must be set.

3. Mold deflection

In large molds, due to the different charging rates in each direction and the influence of the mold's self-weight during the mold loading, the moving and fixed mold deflections are generated.

In these cases, the lateral offset force will be added to the guide column during injection, and the surface of the guide column will be stretched and damaged when the mold is opened, and in serious cases, the guide column will be bent or cut off, and even the mold cannot be opened.

To solve the above problems, a high-strength positioning key is added on each side of the mold parting surface, and the easiest and most effective is to use a cylindrical key. The perpendicularity of the guide pillar hole and the parting surface is crucial.

In the processing is the use of dynamic, fixed die alignment after clamping, in the boring machine once boring, to ensure the concentricity of the dynamic, fixed die hole, and make the verticality error minimum. In addition, the heat treatment hardness of the guide pillar and guide bush must meet the design requirements.
 

4. Bending of moving mold plate

Mold in the injection, the mold cavity molten plastic generated huge backpressure, generally in 600 ~ 1000 kg / cm2. mold makers sometimes do not pay attention to this problem, often change the original design size, or the dynamic template with low-strength steel plate instead, in the top bar top material in the mold, due to the large span between the two sides of the seat, resulting in injection when the template down bending.

Therefore, the moving template must use high-quality steel, to have enough thickness, do not use A3 and other low-strength steel plates, when necessary, should be set up below the moving template support column or support block, reduce the thickness of the template, to improve the bearing capacity.
 

5. Top bar bending, fracture or leakage

The quality of the homemade top bar is better, that is, the processing cost is too high, now usually choose standard parts, general quality. If the gap between the top bar and the hole is too large, there will be material leakage, but if the gap is too small, the top bar will be stuck due to mold temperature increase during injection, and the top bar will expand. What's more dangerous is that sometimes the top bar is not able to be ejected for a general distance and breaks, as a result, the exposed top bar can't be reset during the next mold closing and crashes the concave mold.

To solve this problem, the top bar is resharpened by keeping a 10~15mm mating section at the front end of the top bar and grinding the middle part smaller by 0.2mm. All the top bars in the assembly must be strictly checked from the fit clearance, generally within 0.05 ~ 0.08 mm, to ensure that the entire ejector mechanism can enter and exit freely.
 

6. Bad cooling or water leakage

The cooling effect of the mold directly affects the quality of products and production efficiency, such as poor cooling, products shrink large, or uneven shrinkage and warp surface deformation, and other defects. On the other hand, the mold as a whole or local overheating, so that the mold can not be formed properly and stop production, and in serious cases, so that the top bar and other moving parts of thermal expansion jammed and damaged.

The design of the cooling system, processing to product shape, do not because the mold structure is complex or processing difficulties and omit this system, especially large and medium-sized mold must be fully considered cooling problems.
 

7. The length of the guide slot is too small

Some molds are limited by the template area, the length of the guide slot is too small, the slider in the core action is completed to reveal the outside of the guide slot, so that in the core after the stage and the initial stage of the mold reset are easy to cause the slider tilt, especially in the mold, the slider reset is not smooth, so that the slider damage, and even bending damage.

According to experience, the length of the slider should not be less than 2/3 of the full length of the guide slot after the completion of the core extraction action.
 

8. Fixed distance tensioning mechanism failure

Pendulum hook, buckle, and other fixed distance tensioning mechanism is generally used in the fixed mold core or some secondary demoulding mold, because such institutions in the mold on both sides of the face of the pair set, its action must be synchronized, that is, close the mold at the same time buckle, open the mold to a certain position at the same time off the hook.

Once lost synchronization, will inevitably cause the template of the pulled mold skewed and damaged, the parts of these institutions to have high rigidity and wear resistance, adjustment is also very difficult, the institutional life is short, try to avoid using, can be replaced with other institutions. In the case of relatively small extraction force can be used to spring out of the fixed die method, in the case of relatively large core extraction force can be used to move the die back when the core sliding, first complete the core extraction action and then the structure of the mold, in large molds can be used hydraulic cylinder core extraction.
 

9. Tilt pin slider type core extraction mechanism damage

Most of the more common faults of this mechanism are not in place on the processing and are too small with the material, mainly the following two problems.

Slant pin tilt angle A large.

The advantage is that it can produce a large core extraction distance within a short mold opening stroke.

However, if the inclination angle A is too large when the extraction force F is a certain value, the bending force P=F/COSA on the slanted pin in the process of core extraction is also larger, and the slanted pin is prone to deformation and wear of the slant hole.

At the same time, the slanted pin on the slider's upward thrust force N = FTGA is also greater, this force makes the slider on the guide groove guide surface pressure increase, thus increasing the friction resistance of the slider when sliding. Easy to cause sliding is not smooth, guide groove wear. According to experience, the inclination angle A should not be greater than 25 °.