Mold is a kind of industrial product which can be shaped by a certain way with a specific structure. It is also a kind of production tool which can mass produce industrial product parts with certain shape and size requirements. From airplanes and automobiles to teacups and nails, almost all industrial products must be molded by molds. The high precision, high consistency and high productivity of the parts produced by mould are incomparable to any other processing method. Mould determines the quality, benefit and new product development ability of products to a great extent. So the mold has the honorary title of "mother of industry".
Mold design refers to those who are engaged in the digital design of enterprise mold, including cavity mold and cold stamping mold. On the basis of traditional mold design, they make full use of digital design tools to improve the quality of mold design and shorten the cycle of mold design. Mold designers can be employed in mold NC programming, mold 3D design, product development 3D design and other fields.
1： The analysis and digestion of 2D and 3D drawings of products include the following aspects:
1. The geometry of the product.
2. Dimension, tolerance and design basis of products.
3. Technical requirements (i.e. technical conditions) of products.
4. Name, shrinkage and color of plastics used in products.
5. Surface requirements of products.
2： Determination of injection type
The specification of injection is mainly determined according to the size and production batch of plastic products. When selecting the injection machine, designers mainly consider its plasticization rate, injection volume, clamping force, effective area of the mold (inner distance of the pull rod of the injection machine), capacitance modulus, ejection form and fixed length. If the customer has provided the injection model or specification, the designer must check its parameters. If it can not meet the requirements, the designer must discuss with the customer for replacement.
3： Determination of cavity number and cavity arrangement
The number of mold cavity is mainly determined according to the projection area, geometric shape (with or without side core pulling), product precision, batch size and economic benefit of the product.
The number of cavities is mainly determined by the following factors:
1. Production batch number of products (monthly batch number or annual batch number).
2. Whether the product has side core pulling and its treatment method.
3. The overall dimension of the injection mold and the effective area of the injection mold (or the inner distance of the injection machine rod).
4. The weight of the product and the injection volume of the injection machine.
5. The projection area and clamping force of the product.
6. Precision of products.
7. Product color.
8. Economic benefit (production value of each set of mould).
These factors sometimes restrict each other. Therefore, in determining the design scheme, coordination must be carried out to ensure that the main conditions are met.
After determining the number of strong, we will arrange the cavity, and the layout of the cavity position. The arrangement of the cavity involves the mold size, the design of the gating system, the balance of the gating system, the design of the core pulling (sliding) 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 should be made to achieve the perfect design.
4： Determination of parting surface
Parting surface has been specified in some foreign product drawings, but in many mold design, it should be determined by mold personnel. Generally speaking, the parting surface on the plane is relatively easy to handle, and sometimes special attention should be paid to the three-dimensional parting surface. The selection of parting surface should follow the following principles:
1. It does not affect the appearance of products, especially for products with clear requirements for appearance, more attention should be paid to the influence of parting surface on appearance.
2. To ensure the accuracy of the products.
3. It is good for mold processing, especially for cavity processing. First reply mechanism.
4. It is beneficial to the design of gating system, exhaust system and cooling system.
5. It is conducive to demoulding of products, and ensures that the products are left on the side of the moving mold when opening the mold.
6. Convenient for metal inserts.
When designing the lateral parting mechanism, we should ensure its safety and reliability, and try to avoid the interference with the setting mechanism, otherwise, we should set up the repeat mechanism on the die.
6： Determination of mold base and selection of standard parts
After all the above contents are determined, the mold base will be designed according to the determined contents. In the design of the mold base, the convenient and accurate mold base should be selected as far as possible, and the form, specification and thickness of a and B plates of the standard mold base should be determined. Standard parts include general standard parts and mold special standard parts. Common standard parts such as fasteners, etc. Special standard parts for mould, such as positioning ring, gate sleeve, push rod, push pipe, guide post, guide sleeve, special spring for mould, cooling and heating elements, secondary parting mechanism and standard components for precise 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 bought in the market at any time, which is extremely beneficial to shorten the manufacturing cycle and reduce the manufacturing cost.
After the buyer's size is determined, it is necessary to calculate the strength and rigidity of the relevant parts of the mold to check whether the selected mold base is appropriate, especially for large molds.
7： Design of gating system
The design of the gating system includes the selection of the main runner, the determination of the cross-section shape and size of the splitter.
If the point gate is used, in order to ensure the shedding of the runner, the design of the gate device should also be paid attention to.
In the design of gating system, the first step is to select the gate position. The selection of gate position is directly related to the molding quality and the injection process. The selection of gate position should follow the following principles:
1. The gate position should be selected on the parting surface as far as possible, so as to facilitate the mold processing and the use of gate cleaning.
2. The distance between the gate position and each part of the cavity should be consistent as far as possible, and the process should be short (it is difficult to do with large gate).
3. The gate position should ensure that when the plastic is injected into the cavity, it faces the spacious and thick wall part in the cavity, so as to facilitate the plastic to flow in.
4. To avoid the plastic directly rushing to the cavity wall, core or insert when flowing into the cavity, the plastic can flow into all parts of the cavity as soon as possible and avoid the deformation of the core or insert.
5. Try to avoid the product to produce weld marks, if you want to produce, so that the dissolution mark produced in the product is not important.
6. The gate position and plastic injection direction should be that the plastic can flow evenly along the parallel direction of the mold cavity when it is injected into the mold cavity, and it is conducive to the discharge of gas in the mold cavity.
7. The gate should be designed to be easily removed from the product, and the appearance of the product should not be affected as much as possible.
8： Design of ejection system
The ejection forms of products can be divided into mechanical ejection, hydraulic ejection and pneumatic ejection.
Mechanical ejection is a link in the process of injection molding. The quality of ejection will determine the quality of products. Therefore, the ejection of products can not be ignored. The following principles should be observed in the design of ejection system:
1. In order to avoid the deformation of the product due to ejection, the thrust point should be as close as possible to the core or the parts difficult to demould. For example, the slender hollow cylinder on the product is usually ejected by pushing pipe. The arrangement of thrust points should be balanced as far as possible.
2. The thrust point should act on the parts with high bearing force and good rigidity, such as rib, flange, wall edge of shell products, etc.
3. Try to avoid the thrust point acting on the thin plane of the product to prevent the white and high top of the product. For example, shell shaped products and cylindrical products are usually pushed out by push plate.
4. Try to avoid the impact of ejection marks on the appearance of products, and the ejection device should be set on the concealed surface or non decorative surface of products. In transparent products, we should pay special attention to the selection of location and ejection form.
5. In order to make the products bear uniform force during ejection and avoid the deformation of products due to vacuum adsorption, composite ejection or special ejection systems are often used, such as push rod, push plate or push rod, push pipe composite ejection, or fixed ejection devices such as air inlet push rod and push block are used, and air inlet valve shall be set when necessary.
9： Design of cooling system
The design of the cooling system is a complicated work. The cooling effect, cooling uniformity and the influence of the cooling system on the overall structure of the die should be considered. The design of cooling system includes the following contents:
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. Cooling of key parts such as moving core or insert.
4. Cooling of side slide block and side slide core.
5. Design of cooling elements and selection of cooling standard elements.
6. Design of sealing structure.
The guide device on the plastic injection mold has been determined when the standard mold base is used. In general, designers only need to select according to the mold base specifications. However, according to the requirements of the product, the precise guide device must be designed by the designer according to the mold structure.
The general guide is divided into: the guide between the moving die and the fixed die; the guide between the push plate and the push rod fixed plate; the guide between the push plate rod and the moving die; the guide between the fixed die seat and the push plate. Generally, due to the limitation of machining accuracy or the decrease of matching accuracy after a period of use, the precision of products will be directly affected. Therefore, the products with higher precision requirements must be designed with precision positioning elements. Some of them have been standardized, such as conical positioning pin, positioning block, etc., but some precision positioning devices must be designed according to the specific structure of the module It's specially designed.
11： Selection of die steel
The material selection of mold forming parts (cavity, core) is mainly determined according to the batch of products and plastic category. For high gloss or transparent products, mainly choose 4Cr13 and other types of martensitic corrosion-resistant stainless steel or age hardening steel.
For plastic products reinforced with glass fiber, Cr12MoV and other quenched steel with high wear resistance should be selected.
When the material of products is PVC, POM or containing flame retardant, corrosion-resistant stainless steel must be selected.
12： Drawing assembly drawing
The assembly drawing can be drawn after the positioning die base and related contents are determined. In the process of drawing assembly drawing, the gating system, cooling system, core pulling system and ejection system have been further coordinated and improved to achieve a more perfect design from the structure.
13： Drawing of main parts of mould
When drawing the cavity or core drawing, it is necessary to check whether the given molding dimension, tolerance and demoulding angle are consistent, and whether the design basis is consistent with the product design basis. At the same time, the processability of cavity and core in processing, the mechanical properties and reliability in use should also be considered.
When the standard mold base is used, most of the structural parts outside the standard mold base can not be drawn.
14： Proofreading of design drawings
After the mold drawing design is completed, the mold designer will submit the design drawing and relevant original data to the supervisor for proofreading.
The proofreading personnel shall systematically proofread the overall structure, working principle and operation feasibility of the mould according to the relevant design basis and requirements provided by customers.
15： Countersignature of design drawings
Die design drawings must be submitted to customers for approval immediately after completion. Only after the customer agrees, the mold can be prepared and put into production. When the customer has a big opinion and needs to make a major modification, it must be redesigned and then submitted to the customer for approval until the customer is satisfied.
The exhaust system plays an important role in ensuring the molding quality of products
1. Use the vent. The exhaust groove is generally located at the part where the cavity is filled. The depth of the exhaust groove varies with different plastics, which is basically determined by the large clearance allowed when the plastic does not produce flash.
2. Use the fit clearance of core, insert and push rod or special exhaust plug to exhaust.
3. Sometimes, in order to prevent the work in process from causing vacuum deformation, it is necessary to design the exhaust pin.
Based on the above mold design procedures, some of them can be considered in combination, while others need to be considered repeatedly. Because the factors are often contradictory, we must constantly demonstrate and coordinate in the design process in order to get a better treatment, especially the content related to the mold structure, we must take it seriously, often need to do several programs at the same time, list the advantages and disadvantages of each structure as far as possible, and analyze and optimize one by one. Structural reasons will directly affect the manufacture and use of the mold, and even cause the whole set of mold scrapping. Therefore, mold design is a key step to ensure the quality of mold, and its design process is a system engineering.
Key points in mold design:
1. The overall layout of the die is reasonable,
2. Selection of parting surface
3. The layout of flow channel and the selection of rubber inlet
4. Ejection device
5. Water transport layout
6. Exhaust selection
7. During parting, attention should be paid to draft angle, extraction of insert, treatment of rubbing angle and selection of material shrinkage
8. The processing drawing should be detailed but simple.
Can demould! Easy to process! The top is easy!
H13, also known as 2344 in Europe and SKD61 in Japan, is a kind of soft material with good hardenability and wear resistance. Generally, it can be used in molds with more than 300000 beer. After heat treatment, it can reach 56hrc, and the commonly used hardness is 48 ~ 56hrc.
For the general inclined top material, the surface hardness is required to be high, and the internal toughness is required to be certain. Therefore, if the die core is H13, when it is hardened to 52hrc, the inclined top can be pre hardened with NAK80, etc In the general large companies, it is required that the mold core material should not be the same as the inclined top material. If the customer clearly specifies the same material, the mold core material must be positive or negative 5HRC after heat treatment, so as to prevent burning or biting in the molding process, and improve its wear resistance.
Generally, it is not recommended to use type 420 as inclined roof, because it is stainless steel and easy to burn.
The focus is on structure
When we receive a product, one of the problems is to find out the large parting surface, roughly determine the front and rear dies, and then analyze the front die structure and the rear die structure on the basis of this parting surface: insert, row position, inclined top and other auxiliary mechanisms, So as to determine the rationality of the structure: inlaid or not inlaid; should CNC or line cutting; should CNC or carving, etc. structure affects processing, processing costs and delivery time
So how can we possibly simplify the mold structure?
On the one hand, when reviewing the products with customers, it is necessary to focus on the mold problems caused by the products and whether to improve the products; on the other hand, whether to hold a meeting in the company before mold design to seek a variety of feasible structural suggestions and determine the plan from the perspective of processing and customer requirements
1. The feasibility analysis of the designed mold products, taking the computer chassis as an example, first of all, the product drawings of each component are analyzed by using the design software, that is, the set of drawings mentioned in the work, to ensure the correctness of the product drawings before the mold design, on the other hand, we can be familiar with the importance of each component in the whole chassis, so as to determine the key dimensions in the mold design It's very beneficial. I won't give a detailed introduction to the specific method of drawing.
2. The work to be carried out after the product analysis, which kind of mold structure should be used to analyze the product, and arrange the process of the product, determine the stamping content of each process, and use the design software to carry out the product development. When the product development is generally carried out from the follow-up project, for example, one product needs five processes, and when the stamping is completed, it is carried out from the product drawing Starting from the fourth project, the third project, the second project and the first project, and starting a graphic copy, and then starting the work of the previous project, that is, completing the product development work of the fifth project, and then carrying out the detailed work. Note that this step is very important, at the same time, it needs to be particularly careful. If this step is completed well, it will save a lot of time in drawing the mold drawing, and it is very important for each project After the stamping content is determined, including in the forming die, the inner and outer lines of the product material thickness are retained to determine the punch and die size. The method of product development is not explained here, but will be introduced in detail in the product development method.
3. Material preparation: prepare the material according to the product development drawing, and determine the template size in the drawing, including the fixed plate, discharge plate, punch and die, insert, etc. pay attention to prepare the material directly in the product development drawing, which is of great benefit to drawing the mold drawing. I have seen that many mold designers directly calculate the product development drawing to prepare the material, which is too inefficient, Directly draw the template size on the drawing, and express it in the form of assembly drawing. On the one hand, it can complete the material preparation, on the other hand, it saves a lot of work in the work of mold accessories, because in the work of drawing each component, it only needs to add positioning, pin, guide pillar and screw hole in the material preparation drawing.
4. After the completion of material preparation, you can fully enter the drawing of the mold drawing, and make another copy in the material preparation drawing for the drawing of various components, such as adding screw holes, guide post holes, positioning holes and other holes, and in the punching die, all kinds of holes need wire cutting, in the forming die, the forming gap between the upper and lower dies, must not be forgotten, so after these work is completed, the die of a product will be finished The drawing has almost completed 80%. In addition, in the process of drawing the mold drawing, we need to pay attention to: all processes, such as Fitter marking, wire cutting and other different processing processes, have a complete production layer, which has great benefits for wire cutting and drawing management, such as color distinction, dimension marking is also a very important work, but also a troublesome work Because it's a waste of time.
5. After the completion of the above drawings, in fact, the drawings can not be issued. It is also necessary to proofread the mold drawings, assemble all the accessories, make different layers for each different mold plate, and analyze the mold assembly with the same benchmark, such as the guide post hole, and insert the product development drawing of each process into the assembly drawing, so as to ensure the consistency of the hole position of each template and the upper and lower mold bending position Check whether the clearance fit is correct.