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  • Ten steps of plastic mold design

Ten steps of plastic mold design

A, accept the task book

Formed plastic parts task letter is usually proposed by the part designer, its content is as follows.

1. the regular part drawing that has been reviewed and signed, and indicate the grade of plastic used, transparency, etc.

2. plastic part specification or technical requirements. 3.

3. production volume.

4. plastic parts samples.

Usually, the mold design task book is proposed by the plastic parts technician according to the task book of molding plastic parts, and the mold designer takes the task book of molding plastic parts and mold design task book as the basis to design the mold.

Second, collect, analyze and digest the original information

Collect and organize information about part design, molding process, molding equipment, mechanical processing, and special processing for use in designing molds.

1. digest the plastic parts drawing, understand the use of the parts, analyze the technology of plastic parts, dimensional accuracy, and other technical requirements.

For example, what are the requirements of the plastic parts in terms of appearance, color transparency, and performance, whether the geometry, slope, and inserts of the plastic parts are reasonable, the allowable degree of molding defects such as fusion marks and shrinkage, and whether there is post-processing such as painting, plating, gluing and drilling?

Select the highest dimensional accuracy of the plastic parts for analysis to see if the estimated molding tolerance is lower than the tolerance of the plastic parts and whether the plastic parts can be molded to meet the requirements. In addition, to understand the plasticization of plastic and molding process parameters.

2. Digest the process information and analyze whether the requirements of the molding method, equipment type, material specification, mold structure type, etc. proposed in the process task sheet are appropriate and can be implemented.

The molding material should meet the strength requirements of plastic parts, have good fluidity, uniformity and isotropy, and thermal stability. According to the use of plastic parts, the molding material should meet the requirements of dyeing, plating metal conditions, decorative properties, necessary elasticity and plasticity, transparency or opposite reflective properties, gluing or welding, etc.

3. Determine the molding method - using the direct pressing method, casting method, or injection method.

4. Select the molding equipment

According to the type of molding equipment to mold, so you must be familiar with the performance, specifications, and characteristics of various molding equipment. For example, for injection machines, the following should be known in terms of specifications: injection capacity, clamping pressure, injection pressure, mold installation size, ejector device and size, nozzle hole diameter and nozzle spherical radius, gate sleeve positioning ring size, maximum and minimum mold thickness, and template stroke, etc. See the relevant parameters.

It is necessary to make a preliminary estimation of the mold dimensions and to judge whether the mold can be installed and used on the selected injection machine.

5. Specific structural solutions

(1) Determine the mold type

such as pressing mold (open, semi-closed, closed), casting and pressing mold, injection mold, etc.

(2) Determining the main structure of the mold type

Choosing the ideal mold structure is to determine the necessary molding equipment, the ideal number of cavities, under the absolute reliable conditions can make the mold itself meet the work of the plastic parts of the process technology and production economy requirements. The technical requirements of the plastic parts are to ensure the geometry, surface finish, and dimensional accuracy of the plastic parts. The production economy requirement is to make the plastic parts low cost, high production efficiency, the mold can work continuously, long service life, save labor.

Third, the factors affecting the mold structure and mold individual system.

1. cavity arrangement. According to the geometric structure characteristics of plastic parts, dimensional accuracy requirements, batch size, mold manufacturing difficulties, mold costs, etc. to determine the number of cavities and their arrangement. 2.

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

3. determine the pouring system (main sprue, sub sprue, and gate shape, location, size) and exhaust system (exhaust method, exhaust slot location, size).

4. choose the ejecting method (ejecting rod, ejecting tube, ejecting plate, combined ejecting), decide the side concave treatment method and core extraction method.

5. Decide the cooling and heating method and the shape and position of the heating and cooling groove, and the installation part of the heating element.

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

7. Determine the structure form of main molding parts and structural parts.

8. Consider the strength of each part of the mold and calculate the working dimensions of the molded parts.

If these above problems are solved, the structure form of the mold is naturally solved. At this time, you should start to draw the mold structure sketch, ready for the formal drawing.

Fourth, draw the mold drawing

It is required to draw according to the national drawing standard, but it is also required to combine the factory standard and the factory customary drawing method which is not stipulated by the country.

Before drawing the general assembly diagram of the mold, the process diagram should be drawn and should be in line with the requirements of the part drawing and process information. The dimensions guaranteed by the next process should be marked on the drawing with the word "process dimensions". If there is no mechanical processing after molding except for burr repair, the process diagram is identical to the part drawing.

The part number, name, material, material shrinkage rate, and drawing ratio should be indicated below the process drawing. Usually, the process drawing is drawn on the general assembly drawing of the mold.

Draw the general assembly structure diagram: Draw the general assembly diagram as far as possible using the ratio of 1:1, starting from the cavity, the main view, and other views at the same time to draw.

V. The general assembly drawing of the mold should include the following contents.

1. mold forming part structure

2. structure form of pouring system and exhaust system. 3.

3. the parting surface and the way of taking parts from the mold

4. shape structure and the position of all connecting parts, positioning, and guiding parts. 5.

5. the height of the marked cavity size (not forced, as needed) and the overall dimensions of the mold.

6. Auxiliary tools (picking and unloading tools, alignment tools, etc.).

7. Serialize all parts in order and fill in the detailed table.

8. mark the technical requirements and instructions for use.

Six, the technical requirements of the mold assembly drawing content

1. for the performance requirements of certain systems of the mold. For example, the assembly requirements for the ejector system, slider core structure. 2.

2. the requirements of the mold assembly process. For example, the fitting gap of the fitting surface of the parting surface after mold assembly should be no more than 0.05mm, the parallelism requirement of the top and bottom of the mold, and point out the size is decided by the assembly and the requirement of the size.

3. mold use, assembly, and disassembly method.

4. anti-oxidation treatment, mold numbering, lettering, marking, oil seal, storage, and other requirements.

5. the requirements for mold testing and inspection.

Seven, drawing all parts diagram

The order of drawing parts from the mold assembly diagram should be: first inside and then outside, first complex and then simple, first forming parts, then structural parts. 1.

1. graphic requirements: must be drawn to scale, allowing enlargement or reduction. The view selection is reasonable, the projection is correct, and the arrangement is appropriate. In order to make the processing patent number easy to read, easy to assemble, graphics as far as possible with the general assembly drawings, graphics should be clear.

2. Marking dimensions require uniformity, concentration, order, and completeness. The order of marking dimensions: first mark the size of the main part and out of the mold slope, and then marked with the size, and then marked all dimensions. The non-major parts of the diagram are first marked with the size and then marked all the dimensions.

3. surface roughness. The most applied a roughness marked in the upper right corner of the drawing, such as marked "the rest of 3.2." Other roughness symbols are marked on each surface of the part.

4. other content, such as the name of the part, mold drawing number, material grade, heat treatment, and hardness requirements, surface treatment, graphic scale, free size machining accuracy, technical instructions, etc. should be filled out correctly.

Eight, proofreading, review, tracing, send to the sun

(a), self-proofreading content is.

1. the relationship between the mold and its parts and the drawing of the plastic parts

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

2. plastic parts

Whether the flow of plastic material flow, shrinkage, fusion marks, cracks, the slope of mold release, etc. affect the performance, dimensional accuracy, the surface quality of plastic parts. Is there any deficiency in the design of the pattern, is the processing simple and is the shrinkage rate of the molding material selected correctly.

3. Molding equipment

Is the injection volume, injection pressure, clamping force sufficient, the installation of the mold, the core of the plastic part, the mold release problem, the nozzle of the injection machine, and the querulous sleeve are correctly contacted.

4. Mold structure

1). Whether the position of parting surface and finishing accuracy meet the needs, whether overflow will occur, and whether the plastic parts can be guaranteed to stay on the side of the mold with the ejector device after opening the mold.

2). Whether the mode of mold release is correct, whether the size, position, and number of promotion rods and push tube are suitable, whether the push plate will be stuck by the core, and whether it will cause scratches to the molded parts.

3). Mold temperature adjustment. The power and quantity of the heater; whether the location, size, and quantity of the flow line of the cooling medium are suitable.

4). The method of dealing with the side concave of plastic parts, whether the mechanism of removing the side concave is appropriate, for example, whether the slider and push rod in the inclined column core extraction mechanism interfere with each other.

5). Whether the location and size of the pouring and exhaust system are appropriate.

5. Design drawings

1). Whether the parts of the mold are properly placed on the assembly drawing, whether they are clearly indicated and whether there are any omissions.

2). Parts number, name, production quantity, parts made or purchased, standard parts or non-standard parts, parts with processing accuracy, molding plastic parts with high-precision size correction processing and allowance, mold parts of the material, heat treatment, surface treatment, surface finishing degree is marked, clear description.

3). Parts of the main parts, molding parts working dimensions, and fit dimensions. Size figures should be correct, do not make the producer convert.

4). Check the view position of all parts and assembly diagram, the projection is correct, whether the drawing method is in line with the national standards of cartography, there are no missing dimensions.

6. check the processing performance

(All parts geometry, view drawing, size scale', etc. is conducive to processing)

7. recalculate the main working dimensions of auxiliary tools

(II). Professional proofreading in principle according to the designer's self-checking items; but focus on structural principles, process performance, and operational safety.

When tracing the drawing, you should first digest the figure, depict it according to the national standard requirements, and fill in all the dimensions and technical requirements. Self-calibrate and sign after tracing.

(iii). The tracing of the base map to the designer to proofread and sign, the customary practice is to be reviewed by the relevant technical staff of the tool manufacturing unit, countersign, check the manufacturing process, and only then can be sent to the sun.

(iv). Preparation of manufacturing process card

By the tool manufacturing unit technical personnel to prepare manufacturing process card, and for processing and manufacturing ready.

In the manufacturing process of mold parts to strengthen the inspection, the focus of the inspection is on dimensional accuracy. After the mold is assembled, the inspector will carry out an inspection according to the mold inspection table, the main thing is to check whether the performance of the mold parts is good, only then can the manufacturing quality of slang mold.

Nine, mold test and mold repair

Although it is in the selection of molding materials, molding equipment, mold design in the expected process conditions, but people's understanding is often imperfect, so must be completed in the mold processing, mold trial test, to see how the quality of molded parts. After finding always, carry out the mold repair to exclude the error nature.

There are many kinds of defective plastic parts, and the reasons are very complicated, there are reasons for the mold, there are also reasons for the process conditions, the two are often crossed together. Before repairing the mold, we should analyze and study the defect in detail according to the actual situation of the molded part, and find out the cause of the defect and propose remedial methods. Because the molding conditions are easy to change, so the general practice is to change the molding conditions first, when changing the molding conditions can not solve the problem, then consider repairing the mold.

Repair the mold should be more cautious, not very sure not to take rash action. The reason is that once the mold conditions are changed, it is not possible to make a big transformation and restore the original state.

Ten, organize information for archiving

After the test, if the mold is not used, it should be completely wiped off the mold dross, dust, oil, etc., coated with butter or other anti-rust oil or anti-rust agent, off to the storage place for safekeeping.

From the beginning of the design of the mold to the successful processing of the mold, inspection, and passing, the technical data generated during this period, such as the mission statement, parts drawings, technical specifications, mold assembly drawings, mold parts drawings, base drawings, mold design instructions, inspection record sheets, test mold repair records, etc., according to the provisions of the system to organize, binding, numbering for archiving. This seems to be very troublesome, but it is useful for repairing molds and designing new molds in the future.
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