Injection mold parts design

- May 30, 2018-

                                Injection mold parts design?

(1) design cavity structure of injection mold parts

   The integral structure is suitable for the simple shape and easy processing of the cavity.

   The integral impeller type can save the mould material and reduce the cost.

   The partial mosaicing type is used when the local machining is difficult.Superior four - wall combination type, used for large size, easy to heat - treat deformation of mold.

(2) core structure

    The core is integrated with the template.

    Bamboo compound.

   Press small core is processed separately and then embedded in the template.

   The non-circular small core makes the installation part round and easy to process, while the formed part is shaped in a different shape and connected with the shaft shield.Transaction complex core combination.

(3) calculation of working dimensions of molded parts

The working dimension refers to the dimension directly used to shape the plastic parts on the molded parts: the radial dimension of the core and the cavity;Height dimensions of the core;Depth dimensions of the cavity;Center distance dimension.

   The factors that affect the dimensions of the parts

A - manufacturing tolerance for molded parts.

B. Wear and tear during use.

C shrinkage fluctuation.

Calculation of specific dimensions of substances

A. Feed according to the formula of average shrinkage.

B. For products with accuracy requirements of level 6 or above, the calculation result of mold size shall be two decimal places, and only one decimal place shall be reserved for products with accuracy below level 6.

(4) rigidity and strength check of molding parts

When the cavity is fully filled, the internal pressure reaches a maximum value.

Insufficient rigidity is the main problem in the large-size shaped chamber, which is dominated by rigidity check.

    The problem of insufficient strength is the main contradiction in the small size cavity.

   The formula for checking the strength of the concave die.

(5) other auxiliary components

   Refers to the parts that are used for installation, guidance, assembly, cooling, heating and mechanism action.

   Function of guide parts: positioning, guiding and bearing side pressure.Type: guide column guide, dimension guide, incline guide, etc.

A. Guide pillar: it is composed of guide sleeve or guide hole structure of guide column;The guide column is required to be 6-8cm higher than the convex mould.The end of the guide column is tapered or semi-spherical;The surface of guide column has good abrasion resistance, the core is tough and not easy to break.Transitional coordination with template assembly;How the guide column is connected to the template.

   Guide sleeve: guide sleeve front side square;Guide sleeve hardness is lower than guide column;The roughness of guide sleeve and template mating surface;The way in which the guide sleeve is fixed to the template.

   Guide hole: suitable for small batch production of mold, the required precision is not high.

B. cone, cant guide For large, deep cavity, accuracy is not high, especially for thin wall plastic parts, containers, partial core, because of the large pressure causes the partial core core cavity, guide pillar unbearable, cone positioning can be used.

   Parliamentary assembly fixed parts

A. The fixed plate is used to fix core, cavity, guide column, guide sleeve, drawing rod, etc.    It requires certain strength and thickness.

   There are three ways to connect the core with the fixed plate: step hole fixation method, which is suitable for the installation and fixation of small and medium-sized punch.The method of steam hole fixation is suitable for installation and fixation of medium punch.Planar fixation method for large punch.

B. Function of washplate: prevent core, guide column, drawing rod, etc. From disengaging from the fixed plate, and bear pressure.Requirements: high parallelism and hardness.

C. Action of supporting parts (such as die pins) : the movement space of the ejector mechanism is formed, the total thickness of the mould is adjusted, and the installation is fixed.

The temperature of the mould for cooling and heating parts directly affects the forming quality and productivity of the parts.

   Cooling device: the cooling water hole is generally not less than 10mm away from the cavity

Heating device: electric heating, steam heating, hot water heating.

(6) demoulding mechanism

The mechanism by which plastic parts are removed from the mould is called demoulding mechanism or ejecting mechanism.

It is required that the plastic parts do not deform, do not damage, and the top parts are not obvious.

It's the same thing as the pressure

A. (demoulding) when the plastic parts are cooled and shaped in the mould, the packing force is generated due to the shrinkage of the volume.

B. Without the through-hole shell plastic parts, the air pressure should be overcome when the molds are removed.

C. frictional resistance to the movement of the mechanism itself.

D. Adhesion force between plastic parts and molds, initial demoulding force, and resistance to be overcome at the moment of demoulding.The demoulding force is related to the thickness of the plastic part wall, the length of the core, and the projection area of the plastic part perpendicular to the demoulding direction.The larger the shrinkage and elastic modulus of the plastic parts, the greater the demoulding force: the greater the friction between the plastic parts and the core, the greater the demoulding resistance.

The form of string release mechanism

A. The ejection mechanism of the top rod is generally used for cavity parts with small demoulding force.The guide part of the top bar is short.Due to the strong local demodulation force, the reinforcement should be added.Top bar material is 45 steel, T8 or T10 steel.The fit with the hole of the top bar is the clearance fit.The fixed form of the top bar;The structure of the top bar.

B. The top plate demoulding mechanism can be adopted for thin-walled container, shell shaped plastic parts and plastic parts that are not allowed to leave the mark of ejection bar on the surface of the parts.Characteristics of top plate demoulding mechanism: uniform top output force, smooth movement, large top output force, fixed connection type, non-fixed connection type.

C. The double parting mechanism (two parting surfaces) USES spring to realize the first demoulding, which is applicable to plastic parts with little adhesion force and long distance from moulding.The demoulding of the die is realized by the action of lever.

D. Secondary demoulding mechanism (double jacking action)

(7) core pulling mechanism

    When the parts have a side hole or side concave side holes or side concave molding parts must be movable cores, demoulding, activity core must go out and complete profile activity core drawn agency called core-pulling mechanism.

The calculation of the determined extraction force and extraction distance is the same as the calculation of the demoulding force. The extraction distance = the depth of the side hole or side concave + 2 ~ 3mm(safety value).

   The form of parliamentary vacuum core extractor

   Inclined guide pillar: bevel is commonly below 25 °, cooperate with the transition between the fixed plate;Inclined guide pillar only have the effect of driving the slider, the movement of the sliding block stability by guide chute between the slider and cooperate to ensure precision, slider final location by locking wedge that of oblique guide pillar and slide block hole with relatively loose;The bevel Angle of oblique guide column is greater than that of oblique guide column.Inclined block: integral and combined.Guide chute.Slider positioning device.The sealing wedge (compression block) : the xizhou Angle of the sealing wedge should be greater than that of the oblique guide column.

   The structure of the oblique guide column in fixed mode and sliding block in moving mode in the form of the inclined guide column core pulling mechanism;The structure of an oblique guide column in a moving die.

(8) reset mechanism

   After the mold-removing mechanism is finished, the top rod extends out of the cavity, and the next injection cycle can only be carried out after the resetting rod is reset.Top bar reduction;Spring reset;Automatic reset.


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