China's mold production technology has been greatly improved, and the production level of some molds has approached or reached the international level. So what should we pay attention to in mold design? Let me tell you about this work.

First, accept the task book.

The task book of molded plastic parts is usually put forward by the part designer, and its contents are as follows:

1. Approved drawings of official parts? And indicate the brand and transparency of the plastic used.

2. Description or technical requirements of plastic parts.

3. Output.

4. Samples of plastic parts.

Usually, the mold design task book is put forward by the plastic part technician according to the molding part task book, and mold designer designs the mold according to the molding part task book and the mold design task book.

Second, collect, analyze and digest raw data.

Collect and sort out information about parts design, molding technology, molding equipment, mechanical processing and special processing for use in mold design.

1. Digest the drawings of plastic parts, understand the purpose of plastic parts, and analyze the technical requirements such as the manufacturability and dimensional accuracy of plastic parts. For example, what are the requirements for plastic parts in terms of appearance, color transparency and performance? Are the geometric structure, inclination and inserts of plastic parts reasonable? Allowable degree of forming defects such as weld marks and shrinkage cavities, and post-treatment such as painting, electroplating, gluing and drilling. The dimension with the highest dimensional accuracy of plastic parts is selected for analysis to see whether the estimated molding tolerance is lower than that of plastic parts and whether the required plastic parts can be molded. In addition, we should also know the plasticizing and molding process parameters of plastics.

2. Digest the process data, and analyze whether the requirements such as molding method, equipment model, material specification and mold structure type proposed in the process specification are appropriate. Can it be implemented? Molding materials should meet the strength requirements of plastic parts and have good fluidity, uniformity, isotropy and thermal stability. According to the use of plastic parts, molding materials should meet the requirements of dyeing and metallization conditions, decorative performance, necessary elasticity and plasticity, transparency or opposite reflection performance, adhesion or weldability.

3. Determine the molding method

Adopt direct tabletting method, casting pressure method or injection method.

4. Select molding equipment

According to the type of molding equipment, so we must be familiar with the performance, specifications and characteristics of various molding equipment. For example, for an injection machine, the following contents should be understood from the specification, such as injection quantity, clamping pressure, injection pressure, mold installation size, ejection device and size, nozzle diameter and nozzle spherical radius, gate sleeve positioning ring size, mold maximum and minimum thickness, template stroke, etc. See related parameters for details. It is necessary to estimate the overall size of the mold and judge whether the mold can be installed and used on the selected injection molding machine.

5. Specific structural scheme

① Determine the mold type.

Such as compression mold, open mold, semi-closed mold, closed mold, casting mold, injection mold, etc.

② Determine the main structure of the mold type.

Choosing the ideal mold structure lies in determining the necessary molding equipment, and the ideal number of cavities can make the mold itself work to meet the requirements of the manufacturability and production economy of plastic parts under absolute conditions. The technological requirements of plastic parts are to ensure the geometric shape, surface smoothness and dimensional accuracy of plastic parts. The requirement of production economy is to make the cost of plastic parts low, the production efficiency high, the mold can work continuously, the service life is long and the labor force is saved.

3. There are many complicated factors that affect the mold structure and a single system.

1. Cavity layout. According to the geometric structure characteristics of plastic parts, dimensional accuracy requirements, batch size, mold manufacturing difficulty, mold cost, etc. The number and arrangement of cavities are determined. Injection mold, plastic parts accuracy level 3 3a, weight 5g. The hardened pouring system is adopted, and the number of cavities is 4-6, while the plastic parts are 4-5. The molding material is local crystalline material, the number of cavities is 16-20, and the weight of plastic parts is 12- 16g.

For amorphous plastic parts, the recommended number of cavities is 24-48, 16-32, 6- 10. When the weight of plastic parts is increasing, multi-cavity molds are rarely used. Compared with plastic parts with 4-5 precision, the maximum number of cavities of plastic parts with 7-9 precision is increased to 50%.

2. Determine the parting surface. The location of parting surface should be conducive to mold processing, exhaust, demoulding and molding operations? Surface quality of plastic parts.

3. Determine the gating system: the shape, position and size of the main runner, the auxiliary runner and the gate, the exhaust system, the exhaust mode, and the position and size of the exhaust slot. .

4. Select ejection mode: ejector pin, pipe jacking, push plate, combined ejection, determination of side concave treatment mode and core pulling mode.

5. Determine the cooling and heating mode, the shape and position of the heating and cooling tank, and the installation position of the heating element.

6. According to the mold material, strength calculation or empirical data? Determine the thickness, external dimensions, external structure and position of all connecting, positioning and guiding parts of die parts.

7. Determine the structural forms of main molded parts and structural parts.

8. Consider the strength of each part of the mold? Calculate the working dimensions of the molded parts. The above problems are solved, and the structure of the mold is naturally solved. Is it time to start sketching the mold structure? Prepare for the official draw.

Fourth, draw a mold diagram.

Require drawing according to national drawing standards? However, it is also required to combine the factory standards and factory customized painting methods that are not stipulated by the state. Before drawing the mold assembly drawing, the process drawing should be drawn, which should meet the requirements of part drawing and process data. The guaranteed dimensions of the next process shall be marked with the words "process dimensions" on the drawing. If there is no other machining except burr repair after molding, then the process drawing is exactly the same as the part drawing.

It is best to indicate the part number, name, material, material shrinkage, stretching ratio, etc. Under the flow chart. Usually, this process is drawn on the mold assembly drawing. When drawing the assembly drawing, the ratio of 1: 1 should be adopted as far as possible, starting from the cavity, and drawing the front view and other views at the same time.

Five, the mold assembly drawing should include the following contents

1. Mould forming part structure;

2. Structure of gating system and exhaust system;

3. Parting surface and method;

4. The external structure and position of all connectors, positioning and guiding parts;

5. Mark the cavity height size (not required) and the overall size of the mold as required;

6. Auxiliary tools, parts taking and demoulding tools, calibration tools, etc.

7. Make up the serial numbers of all parts in sequence and fill in the schedule;

8. Mark the technical requirements and instructions for use.

Technical requirements of die assembly drawing of intransitive verbs

1. Performance requirements of some mold systems. For example, the assembly requirements of the ejection system and the slider core-pulling structure.

2. Requirements of mold assembly process. For example, the joint clearance of the parting surface should not be greater than the parallelism requirement of the upper and lower surfaces of the 0.05mm mold after clamping, and the size determined by assembly and the requirements for this size are pointed out.

3. The use, assembly and disassembly methods of the mold.

4. Anti-oxidation treatment, mold number, lettering, marking, oil seal, storage and other requirements.

5. Requirements for mold testing and inspection.

Seven, draw all the parts.

The order of drawing parts in die assembly drawing should be from inside to outside, from complex to simple, from formed parts to structural parts.

1. Graphic requirements: it must be drawn in proportion, and enlargement or reduction is allowed. Reasonable scene selection, correct projection and proper layout. In order to make the processing patent number easy to understand and assemble? The graphics should be as consistent as possible with the general assembly drawing, and the graphics should be clear.

2. The dimensions shall be uniform, centralized, orderly and complete. The order of dimensioning is to dimension the main part size and draft angle first, then the matching size, and then all the dimensions. On the drawing of non-major parts, the matching dimensions are marked first, and then all dimensions are marked.

3. Surface roughness: mark the most widely used roughness in the upper right corner of the drawing, such as "Other 3.2" and other roughness symbols on each surface of the part.

4. Other contents: such as part name, mold drawing number, material grade, heat treatment and hardness requirements, surface treatment, graphic proportion, free dimension machining accuracy, technical description, etc. It should be filled in correctly.

Eight, proofreading, drawing review, tracing and drying.

A. the content of self-study is

1. Relationship between mould and its parts and plastic parts drawing

Whether the materials, hardness, dimensional accuracy and structure of molds and mold parts meet the requirements of plastic parts drawings.

2. Plastic parts

Whether the flow, shrinkage cavity, weld mark, crack and demoulding inclination of plastic material flow affect the requirements of plastic parts in terms of performance, dimensional accuracy and surface quality. Whether the pattern design is insufficient, whether the processing is simple, and whether the shrinkage of the molding material is selected correctly.

3. Molding equipment

Is the injection quantity, injection pressure and clamping force enough? Mold installation, south core of plastic parts, whether there is any problem with demoulding, and whether the nozzle of injection machine is in correct contact with the sleeve.

4. Mold structure

1) Whether the parting surface position and finishing accuracy meet the requirements, whether there will be flash, and whether the plastic parts can stay on the side of the mold with ejector after mold opening.

2) Whether the demoulding method is correct, whether the size, position and quantity of the telescopic rod and the push tube are appropriate, whether the push plate will be stuck by the core and whether the plastic parts will be scratched.

3) mold temperature adjustment. Whether the power and quantity of heaters and the position, size and quantity of cooling medium flow paths are appropriate.

4) How to deal with the side concave of plastic parts and whether the mechanism for removing the side concave is appropriate, such as whether the slider and push rod in the core-pulling mechanism of inclined guide pillar interfere with each other.

5) Pay attention to whether the position and size of the exhaust system are appropriate.

5. Design drawings

1) Whether the placement parts of each mold part on the assembly drawing are appropriate and clearly expressed, and whether there are any omissions.

2) Part number and name on the part drawing? Production quantity, whether the parts are self-made or purchased, standard parts or non-standard parts, matching machining accuracy of parts, correction machining and allowance of high-precision dimensions of molded plastic parts, and whether the materials, heat treatment, surface treatment and surface finish of mold parts are clearly marked and described.

3) Working dimensions and matching dimensions of main parts and molded parts. Size figures should be correct, don't let the manufacturer convert them.

4) Check the view position of all parts drawings and assembly drawings, whether the projection is correct, whether the drawing method meets the national drawing standards and whether there are any size omissions.

6. Check the processing performance

Whether the geometric structure, view and size of all parts are favorable for machining. ?

7. Recalculate the main working dimensions of auxiliary tools.

B. Professional proofreading shall be conducted according to the designer's self-calibration project in principle, but the structural principle, technological performance and operational safety shall be emphasized. When drawing, you should first digest the drawing and fill in all the dimensions and technical requirements according to the national standard. Self-correcting signature after tracing.

C. Submit the drawn base map to the designer for proofreading and signing. Usually, the manufacturing process is reviewed, countersigned and checked by the relevant technicians of the tool manufacturing unit.

D preparation of manufacturing process cards: technicians of tool manufacturing units prepare manufacturing process cards to prepare for processing and manufacturing. In the manufacturing process of mold parts, it is necessary to strengthen inspection, and the focus of inspection is dimensional accuracy. After the mold assembly is completed, the inspector will carry out inspection according to the mold inspection list, mainly to check whether the performance of the mold parts is good, and only in this way can the manufacturing quality of the mold be slandered.

Nine, try to repair the mold

Although the mold design is carried out under the expected technological conditions when selecting molding materials and molding equipment, people's understanding is often imperfect, so it is necessary to carry out a mold trial test after the mold processing is completed to see how the quality of the molded parts is. It is always found that the mold repair to eliminate errors will be carried out later.

There are many kinds of bad phenomena of plastic parts, and the reasons are also very complicated, including mold reasons and process conditions, which are often only together. Before repairing the mold, we should make a detailed analysis and study according to the actual situation of the bad phenomenon of plastic parts, find out the causes of the defects of plastic parts, and then put forward the remedies. Because the molding conditions are easy to change, the general practice is to change the molding conditions first, and then consider mold repair when changing the molding conditions can't solve the problem.

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