Mold technology

Sixteen-step process of mold design

A mold is an industrial product that is shaped into a material in a certain structure in a certain way. It is also a production tool that can mass produce industrial product parts with certain shape and size requirements. From airplanes and automobiles to tea cups and nails, almost all industrial products must be formed by molds. The high precision, high consistency, and high productivity of using molds to produce parts are unmatched by any other processing method. To a large extent, the mold determines the product's quality, efficiency and new product development capabilities. Therefore, the mold has the honorary title of "Mother of Industry".

Mold design refers to the personnel who are engaged in the digital design of corporate molds, including cavity molds and cold stamping dies, based on traditional mold design, fully applying digital design tools, improving mold design quality, and shortening mold design cycles. Mold designers can find employment in the fields of mold CNC programming, mold 3D design, and product development 3D design.

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

1. The geometric shape of the product.

2. Product dimensions, tolerances and design benchmarks.

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: Determine the injection type

The determination of injection specifications is mainly based on the size and production batch of plastic products. When selecting the injection machine, the designer mainly considers its plasticization rate, injection volume, clamping force, effective area of ​​the mold installed (distance between the tie rods of the injection machine), modulus, ejector form and set length. If the customer has provided the model or specification of the injection used, the designer must check its parameters. If the requirements are not met, they must discuss the replacement with the customer.

The third part: the determination of the number of cavities and the arrangement of the cavities

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

1. Production batch of products (monthly batch or annual batch).

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

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

4. Product weight and injection volume of 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 restricted, so when determining the design plan, coordination must be carried out to ensure that its main conditions are met.

After the number of strong sex 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 parting surface and gate location, so in the specific design process, necessary adjustments must be made to achieve the most perfect design.

Step 4: Determine the parting surface

The parting surface has been specifically stipulated 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. Special attention should be paid to the parting surface. The selection of the parting surface should follow the following principles:

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

2. Conducive to ensuring the accuracy of the product.

3. Conducive to mold processing, especially cavity processing. First recovery agency.

4. Facilitate the design of pouring system, exhaust system and cooling system.

5. Facilitate the demoulding of the product and ensure that the product is left on the side of the movable mold when the mold is opened.

6. 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 set-out 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 is designed according to the determined 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 plate of the standard mold base. Standard parts include general standard parts and mold-specific standard parts. Common standard parts such as fasteners. Standard mold-specific parts such as positioning ring, sprue bushing, 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 needs to be emphasized that when designing molds, use standard mold bases and standard parts as much as possible, because a large part of standard parts has been commercialized and can be bought on the market at any time. This is extremely important for shortening the manufacturing cycle and reducing manufacturing costs. advantageous.

After the buyer's size is determined, the necessary strength and rigidity calculations should be performed on the relevant parts of the mold to check whether the selected mold base is appropriate, especially for large molds. This is particularly important.

Step 7: Design of the gating system

The design of the gating system includes the selection of the main runner and the determination of the cross-sectional shape and size of the runner.

If a point gate is used, in order to ensure that the runners fall off, attention should be paid to the design of the de-gate device.

When designing the gating system, the first step is to select the location of the gate. The proper selection of the gate location will directly affect the molding quality of the product and whether the injection process can proceed smoothly. The selection of the gate location should follow the following principles:

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

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 nozzle).

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

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

5. Try to avoid the production of weld marks on the product. If you want to produce it, make the melting marks appear in the unimportant part of the product.

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

7. The gate should be designed at the easiest part of the product to be removed, and the appearance of the product should not be affected as much as possible.

Step 8: Design of ejector system

The ejection forms of products can be summarized into three categories: mechanical ejection, hydraulic ejection, and pneumatic ejection.

Mechanical ejection is the last link in the injection molding process. The quality of ejection will ultimately determine the quality of the product. Therefore, product ejection cannot be ignored. The following principles should be observed when designing the ejector system:

1. In order to prevent the product from deforming due to ejection, the thrust point should be as close as possible to the core or the part that is difficult to demold, such as the elongated hollow cylinder on the product, which is mostly ejected by the push tube. The arrangement of thrust points should be as balanced as possible.

2. The thrust point should act on the part where the product can withstand the greatest force, and the part with good rigidity, such as ribs, flanges, and wall edges of shell-type products.

3. Try to avoid the thrust point acting on the thinner surface of the product, to prevent the product from topping white, top height, etc., such as shell-shaped products and cylindrical products are mostly ejected by push plates.

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

5. In order to make the product evenly stressed during ejection and 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, and push tube composite Ejector, or use air intake push rod, push block and other setting devices, if necessary, an air intake valve should also be provided.

Step 9: Design of the cooling system

The design of the cooling system is a relatively tedious task, and the cooling effect, the uniformity of cooling and the influence of the cooling system on the overall structure of the mold must be considered. 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. Determination of the specific location and size of the cooling system.

3. Cooling of key parts such as moving model cores or inserts.

4. Cooling of side sliding block and side sliding core.

5. The design of cooling elements and the selection of standard cooling elements.

6. Design of sealing structure.

The tenth step:

The guiding device on the plastic injection mold has been determined when the standard mold base is used. In general, the designer only needs to choose according to the specifications of the mold base. However, when precision guiding devices are required to be set according to product requirements, the designer must carry out a specific design based on the mold structure.

The general guide is divided into: the guide between the movable and the fixed mold; the guide between the push plate and the fixed plate of the push rod; the guide between the push plate rod and the movable template; the guide between the fixed mold base and the pirated version. Generally, due to the limitation of machining accuracy or the use of a period of time, the matching accuracy of the general guide device will be reduced, which will directly affect the accuracy of the product. Therefore, for products with higher accuracy requirements, precision positioning components must be designed separately, and some have been standardized, such as cones. 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.

Part 11: Selection of mold steel

The selection of materials for mold forming parts (cavity, core) is mainly determined according to the batch size of the product 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 with glass fiber reinforcement, Cr12MoV and other types of hardened steel with high wear resistance should be used.

When the material of the product is PVC, POM or contains flame retardant, corrosion-resistant stainless steel must be selected.

Twelve Steps: Draw an assembly drawing

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

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

When drawing a cavity or core diagram, it is necessary to consider whether the given molding dimensions, tolerances and demolding inclination are compatible, and whether the design basis is compatible with the design basis of the product. At the same time, the manufacturability of the cavity and core during processing and the mechanical properties and reliability during use must also be considered.

When drawing the structural part drawing, when the standard formwork is used, the structural parts other than the standard formwork are drawn, and most of the structural parts drawing may not be drawn.

Step 14: Proofreading of design drawings

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

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

Step 15: Countersignature 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 big opinion that needs to make major changes, it must be redesigned and then handed over to the customer for approval until the customer is satisfied.

The sixteenth step:

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

1. Use the exhaust slot. The exhaust groove is generally located at the last part of the cavity to be filled. The depth of the vent groove varies with different plastics, and is basically determined by the maximum clearance allowed when the plastic does not produce flash.

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

3. Sometimes, in order to prevent the vacuum deformation of the work-in-process, it is necessary to design the exhaust insert.

in conclusion

Based on the above mold design procedures, some of them can be combined and considered, and some of them have to be considered repeatedly. Because the factors are often contradictory to each other, they must be continuously demonstrated and coordinated in the design process to get a better deal. Especially the content involving the mold structure must be taken seriously, and several plans are often considered at the same time. This structure lists the advantages and disadvantages of each aspect as much as possible, and analyzes and optimizes them one by one. Structural reasons will directly affect the manufacture and use of the mold, and the serious consequences may even cause the entire mold to be scrapped. Therefore, mold design is a critical step to ensure mold quality, and its design process is a systematic engineering.

Key points in mold design:

1. The overall layout of the mold is reasonable,

2. Selection of parting surface

3. Arrangement of runners and selection of glue inlet

4. Ejection device

5. Water transportation arrangement

6, the choice of exhaust

7. Pay attention to the draft angle when parting the mold, the extraction of inserts, the treatment of the rubbing angle, and the selection of material shrinkage

8. The processing drawing should be detailed, but simple