Complete PET bottle preform mold design process

Complete PET bottle preform mold design process

The first step: the analysis and digestion of the 2D and 3D images of the product, which includes the following aspects:

1. The geometry of the product.

2. Dimensions, tolerances and design benchmarks of products.

3. The technical requirements of the product (ie technical conditions).

4. The name, shrinkage and color of the plastic used in the product.

5. Surface requirements of products.

Step 2: Determination of the injection type

The determination of injection specifications is mainly based on the size and production batch of plastic products. When the designer chooses the injection machine, the main consideration is its plasticization rate, injection volume, clamping force, effective area of ​​the installed mold (spacing between the tie rods of the injection machine), volume modulus, ejection form and fixed length. If the customer has provided the model or specification of the injection used, the designer must check its parameters, and if it cannot meet the requirements, it must be discussed with the customer for replacement.

Step 3: Determination of the number of cavities and arrangement of the cavities

The determination of the number of mold cavities is mainly based on the projected area of ​​the product, geometric shape (with or without side core pulling), product accuracy, batch size and economic benefits.

The number of cavities is mainly determined according to the following factors:

1. The production batch of the product (monthly batch or annual batch).

2. Whether the product has side core pulling and its treatment method.

3. The dimensions of the mold and the effective area of ​​the injection mold (or the distance between the tie rods of the injection machine).

4. The weight of the product and the injection volume of the injection machine.

5. The projected area and clamping force of the product.

6. Product accuracy.

7. Product color.

8. Economic benefits (production value of each set of molds).

These factors are sometimes mutually restrictive, so when determining the design scheme, it must be coordinated to ensure that its main conditions are met. After the number of strong properties is determined, the arrangement of the cavities and the layout of the positions of the cavities are carried out. The arrangement of the cavity involves the size of the mold, the design of the gating system, the balance of the gating system, the design of the core pulling (slider) mechanism, the design of the insert core and the design of the hot runner system. The above problems are related to the selection of the parting surface and the gate position, so in the specific design process, necessary adjustments should be made to achieve the most perfect design.

Step 4: Determination of the parting surface

The parting surface has been specified in some foreign product drawings, but in many mold designs, it must be determined by the mold personnel. Generally speaking, the parting surface on the plane is easier to handle, and sometimes it encounters a three-dimensional form. The parting surface should be paid special attention. The selection of its parting surface should follow the following principles:

1. It does not affect the appearance of the product, especially for products with clear requirements for appearance, more attention should be paid to the impact of typing on the appearance.

2. It is beneficial to ensure the accuracy of the product.

3. It is beneficial to mold processing, especially the processing of cavity. Reinstatement agency.

4. It is beneficial to the design of pouring system, exhaust system and cooling system.

5. It is beneficial to the demoulding of the product, and it is ensured that the product is left on the side of the movable mold when the mold is opened.

6. It is convenient for metal inserts.

When designing the lateral parting mechanism, it should be ensured that it is safe and reliable, and try to avoid interference with the setting mechanism, otherwise a first-return mechanism should be set on the mold.

The sixth step: the determination of the mold base and the selection of standard parts

After all the above contents are determined, the mold base will be designed according to the predetermined contents. When designing the mold base, choose the standard mold base as much as possible, and determine the form, specification and thickness of the A and B plates of the standard mold base. Standard parts include general standard parts and mold-specific standard parts. Common standard parts such as fasteners, etc. Mold-specific standard parts such as positioning ring, sprue sleeve, push rod, push tube, guide post, guide sleeve, mold-specific spring, cooling and heating elements, secondary parting mechanism and standard components for precision positioning, etc. It should be emphasized that when designing the mold, the standard mold base and standard parts should be selected as much as possible, because a large part of the standard parts have been commercialized and can be purchased in the market at any time, which is extremely important for shortening the manufacturing cycle and reducing the manufacturing cost. advantageous. After the buyer's size is determined, it is necessary to perform the necessary strength and rigidity calculations for the mold-related parts to check whether the selected mold base is appropriate, especially for large molds, which is particularly important.

Step 7: Design of the gating system

The design of the gating system includes the selection of the main runner, the determination of the cross-sectional shape and size of the runner. If a point gate is used, in order to ensure the shedding of the runner, attention should also be paid to the design of the gate removal device. When designing the gating system, the first step is to select the location of the gate. Whether the selection of gate location is appropriate or not will directly affect the molding quality of the product and whether the injection process can proceed smoothly. The selection of gate location should follow the following principles:

1. The gate location should be selected as far as possible on the parting surface, so as to facilitate mold processing and gate cleaning.

2. The distance between the gate position and the various parts of the cavity should be as consistent as possible, and the process should be the shortest (generally, it is difficult to achieve a large gate).

3. The gate position should ensure that when the plastic is injected into the cavity, it faces the wide and thick-walled part of the cavity to facilitate the inflow of plastic.

4. Prevent the plastic from rushing to the cavity wall, core or insert when it flows into the cavity, so that the plastic can flow into each part of the cavity as soon as possible, and avoid deformation of the core or insert.

5. Try to avoid welding marks on the product. If it does, make the melting marks in the unimportant place of the product.

6. The location of the gate and the injection direction of the plastic should be such that the plastic can flow evenly in the parallel direction of the cavity when it is injected into the cavity, and is conducive to the discharge of the gas in the cavity.

7. The gate should be designed at the most easily removed part of the product, and at the same time, it should not affect the appearance of the product as much as possible.

Step 8: Design of ejector system

The ejection form of the product can be summed up into three categories: mechanical ejection, hydraulic ejection and pneumatic ejection. Mechanical ejection is the last link in the injection molding process, and the quality of the ejection will ultimately determine the quality of the product. Therefore, the ejection of the product cannot be ignored. The following principles should be observed when designing an ejector system:

1. In order to prevent the product from being deformed due to ejection, the thrust point should be as close as possible to the core or the part that is difficult to demould. The arrangement of thrust points should be as balanced as possible.

2. The thrust point should be applied to the part where the product can withstand the greatest force, and the part with good rigidity, such as the rib, flange, wall edge of shell-type products, etc.

3. Try to avoid the thrust point acting on the thin surface of the product, to prevent the product from being white and high, such as shell-shaped products and cylindrical products, most of which are ejected by push plates.

4. Try to avoid the ejection marks from affecting the appearance of the product, and the ejection device should be located on the hidden surface or non-decorative surface of the product. For transparent products, special attention should be paid to the choice of position and ejection form.

5. In order to make the product evenly stressed during ejection, and to avoid the deformation of the product due to vacuum adsorption, composite ejection or special forms of ejection systems are often used, such as push rod, push plate or push rod, push tube composite Ejection, or use the air intake push rod, push block and other fixed devices, and if necessary, an intake valve should be installed.

Step 9: Design of the cooling system

The design of the cooling system is a tedious task, and it is necessary to consider the cooling effect, the uniformity of the cooling and the influence of the cooling system on the overall structure of the mold. The design of the cooling system includes the following:

1. The arrangement of the cooling system and the specific form of the cooling system.

2. Determine the specific location and size of the cooling system.

3. Key parts such as the cooling of the moving model core or inserts.

4. Cooling of side sliders and side sliders.

5. Design of cooling components and selection of cooling standard components.

6. Design of sealing structure.

Step 10:

The guide device on the plastic injection mold has been determined when the standard mold base is used. Under normal circumstances, designers only need to select according to the specifications of the mold base. However, when a precise guide device is required according to the product requirements, the designer must carry out a specific design according to the mold structure. The general guide is divided into: the guide between the moving and fixed molds; the guide between the push plate and the push rod fixed plate; the guide between the push plate rod and the moving template; the guide between the fixed mold seat and the push pirate. Due to the limitation of machining accuracy or the reduction of the matching accuracy of the general guide device after a period of use, it will directly affect the accuracy of the product. Therefore, for products with higher accuracy requirements, precision positioning elements must be designed separately, some of which have been standardized, such as conical Positioning pins, positioning blocks, etc. are available for selection, but some precision guiding and positioning devices must be specially designed according to the specific structure of the module.

The eleventh step: the selection of mold steel

The selection of materials for mold forming parts (cavity, core) is mainly determined according to the batch of products and the type of plastic. For high-gloss or transparent products, 4Cr13 and other types of martensitic corrosion-resistant stainless steel or age-hardening steel are mainly used. For plastic products reinforced with glass fiber, quenched steel with high wear resistance such as Cr12MoV should be used. When the material of the product is PVC, POM or contains flame retardant, corrosion-resistant stainless steel must be selected.

Step 12: Draw the assembly drawing

After the alignment mold base and related contents are determined, the assembly drawing can be drawn. In the process of drawing assembly drawings, the selected casting system, cooling system, core pulling system, ejection system, etc. have been further coordinated and perfected to achieve a relatively perfect design from the structure.

The thirteenth step: the drawing of the main parts of the mold

When drawing the cavity or core diagram, it is necessary to check whether the given molding size, tolerance and demolding slope are coordinated, and whether the design basis is coordinated with the design basis of the product. At the same time, the manufacturability of the cavity and the core during processing and the mechanical properties and reliability during use should also be considered. For the drawing of the structural parts diagram, when the standard mold base is used, most of the structural parts other than the standard mold base can be drawn without drawing the structural part diagram.

Step 14: Proofreading design drawings

After the mold drawing design is completed, the mold designer will send the design drawing and related original data to the supervisor for proofreading.

The proofreader should systematically proofread the overall structure, working principle and feasibility of operation of the mold according to the relevant design basis provided by the customer and the requirements of the customer.

Step 15: Countersigning of design drawings

After the mold design drawing is completed, it must be immediately submitted to the customer for approval. Only after the customer agrees, the mold can be prepared and put into production. When the customer has a major opinion and needs to make major revisions, it must be redesigned and then handed over to the customer for approval until the customer is satisfied.

Step 16:

The exhaust system plays a vital role in ensuring the molding quality of the product. The exhaust methods are as follows:

1. Use the exhaust slot. The exhaust groove is generally located in the last part of the cavity to be filled. The depth of the exhaust slot varies with the plastic, and is basically determined by the maximum clearance allowed by the plastic without flash.

2. Use the matching clearance of the core, inserts, push rods, etc. or special exhaust plugs to exhaust.

3. Sometimes in order to prevent the vacuum deformation caused by the work in process, it is necessary to design the exhaust needle.

Conclusion: Combining the above mold design procedures, some of them can be considered together, and some of them need to be considered repeatedly. Because the factors are often contradictory, they must be continuously demonstrated and coordinated in the design process to get a better deal, especially the content related to the mold structure, which must be taken seriously, and often several plans should be considered at the same time. This structure lists the advantages and disadvantages of various aspects as much as possible, analyzes them one by one, and optimizes them. Structural reasons will directly affect the manufacture and use of the mold, and even the entire set of molds will be scrapped if the consequences are serious. Therefore, mold design is a key step to ensure mold quality, and its design process is a systematic project.