Mold making process

1. Accept the letter of assignment

The task sheet for molded plastic parts is usually proposed by the part designer and its contents are as follows:

1. Approved positive regulation drawings, and indicate the use of plastic grade, transparency, etc.

2. Plastic parts specification or technical requirements.

3. Production volume.

4. Production sample.

Usually, the mold design task book is proposed by the plastic parts technician according to the molding plastic parts task book, and the mold designer designs the mold based on the molding plastic parts task book and the mold design task book.

2. Collect, analyze and digest the original data

Collect and sort out relevant parts design, forming process, forming equipment, machining and special processing information for use in mold design.

1. Digest the plastic parts drawing, understand the use of the parts, analyze the technical requirements of the plastic parts, such as the process and dimensional accuracy. For example, what are the requirements of plastic parts in terms of appearance shape, color transparency, performance, whether the geometric structure, slope, insert and other conditions of plastic parts are reasonable, the degree of welding marks, shrinkage holes and other forming defects, whether there is painting, electroplating, bonding, drilling and other post-processing. Select the size of the plastic parts with the highest dimensional accuracy for analysis to see whether the estimated molding tolerance is lower than the tolerance of the plastic parts, and whether the plastic parts can be formed in line with the requirements. In addition, it is also necessary to understand the plasticization and molding process parameters of plastics.

2. Digest the process data, analyze whether the molding method, equipment model, material specification, mold structure type and other requirements proposed in the process task book are appropriate and can be implemented.

Forming materials should meet the strength requirements of plastic parts, with good fluidity, uniformity and isotropy, thermal stability. According to the use of plastic parts, forming materials should meet the dyeing, gold-plated conditions, decorative properties, necessary elasticity and plasticity, transparency or opposite reflection properties, bonding or weldability requirements.

3. Determine the molding method

Direct pressing, casting or injection method.

4, choose molding equipment

According to the type of molding equipment to mold, it is necessary to know the performance, specifications, characteristics of various molding equipment. For example, for the injection machine, the following contents should be understood 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, mold maximum and minimum thickness, template stroke, etc., see the relevant parameters for details.

It is necessary to estimate the outline size of the mold and determine whether the mold can be installed and used in the selected injection machine.

5. Specific structural plan

(A) Determine the mold type

Such as pressing die (open, semi-closed, closed), casting die, injection die, etc.

(2) Determine the main structure of the mold type

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

Third, there are many factors affecting the mold structure and the individual system of the mold, which are very complicated:

1. Cavity layout. According to the geometric structure characteristics of plastic parts, dimensional accuracy requirements, batch size, mold manufacturing difficulty, mold cost and so on to determine the number of cavity and its arrangement.

For the injection mold, the precision of the plastic parts is 3 and 3a, the weight is 5 grams, the hardening gating system is used, and the number of cavities is 4-6; The plastic parts are of general accuracy (4-5 grade), the molding material is local crystalline material, and the number of cavities can be 16-20; The weight of the plastic parts is 12-16 grams, and the number of cavities is 8-12; The weight of 50-100 grams of plastic parts, the number of cavities to take 4-8. The recommended number of cavities for amorphous plastic parts is 24-48, 16-32 and 6-10. When the weight of plastic parts continues to increase, multi-cavity molds are rarely used. For plastic parts of grade 7-9 accuracy, the maximum number of cavities is increased to 50% compared with the plastics of grade 4-5 accuracy indicated.

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

3. Determine the pouring system (shape, position and size of main runner, sub-runner and gate) and exhaust system (exhaust method, exhaust groove location and size).

4. Select the ejecting method (ejecting rod, ejecting tube, pushing plate, combined ejecting), decide the side concave treatment method and core pulling method.

5. Determine the cooling and heating methods, the shape and position of the heating and cooling groove, and the installation position of the heating element.

6. According to the mold material, strength calculation or experience data, determine the thickness and outline size of the mold parts, outline structure and the location of all connections, positioning and guiding parts.

7. Determine the structure of the main forming parts and structural parts.

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

If the above problems are solved, the structural form of the mold will naturally be solved. At this time, you should start to draw a sketch of the mold structure to prepare for the formal drawing.

Four, draw mold drawing

It is required to draw in accordance with the national drawing standards, but it is also required to combine the factory standards and the factory custom drawing methods not stipulated by the state.

Before drawing the final assembly drawing of the mold, the process drawing should be drawn, and it should meet the requirements of the parts drawing and process data. The dimensions guaranteed by the next process shall be marked with the words "process size" on the drawing. If after forming, in addition to repairing burrs, no other mechanical processing is carried out, then the process drawing is exactly the same as the parts drawing.

Under the process drawing, it is best to mark the part number, name, material, material shrinkage, drawing scale, etc. Usually the process is drawn on the mold assembly drawing.

1. Drawing the final assembly structure drawing should adopt a 1:1 ratio as far as possible, starting from the cavity, and drawing the main view and other views at the same time.

5. The mold assembly drawing shall include the following:

1. Mold forming part structure

2. Structure of pouring system and exhaust system.

3. Parting surface and parting take-up method.

4. Shape structure and all connectors, positioning and guiding parts.

5. Mark the cavity height size (not required, according to need) and the overall size of the mold.

6. Auxiliary tools (taking and removing tools, correcting tools, etc.).

7. List all parts in order and fill in the list.

8. Mark technical requirements and instructions for use.

Six, the technical requirements of the mold assembly drawing:

1. Performance requirements for some systems of molds. For example, the assembly requirements of ejector system and slider core-pulling structure.

2. Requirements for mold assembly process. For example, after the mold assembly, the fitting gap of the fitting surface of the parting surface should not be greater than the parallelism requirements on and below the 0.05mm mold, and the size determined by the assembly and the requirements for the size are pointed out.

3. Mold use, assembly and disassembly methods.

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

5. Requirements for mold testing and inspection.

Seven, draw all parts drawings

The sequence of the parts drawing from the mold assembly drawing should be: first inside and then outside, first complex and then simple, first formed parts, and then structural parts.

1. Graphic requirements: be sure to draw to scale, allowing amplification or reduction. View selection is reasonable, projection is correct, layout is appropriate. In order to make the processing patent number easy to read and easy to assemble, the graphics should be consistent with the final assembly drawing as much as possible, and the graphics should be clear.

2. The dimensioning requirements are unified, centralized, orderly and complete. The order of dimensioning is: first mark the size of the main parts and the inclination of the die, then mark the matching size, and then mark the full size. On the non-main parts drawing, first mark the matching size, and then mark the full size.

3. Surface roughness. Mark the most used roughness in the upper right corner of the drawing, such as "Other 3.2." Other roughness symbols are marked separately 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, processing accuracy of free size, technical description, etc., should be filled in correctly.

8. Proofreading, reviewing, tracing and sending

A. The content of self-proofreading is:

1. The relationship between the mold and its parts and the plastic parts drawings

Whether the material, hardness, dimensional accuracy and structure 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 hole, weld mark, crack, release slope, etc. affect the requirements of the performance, dimensional accuracy and surface quality of plastic parts. Whether the pattern design is insufficient, whether the processing is simple, and whether the shrinkage rate of the forming material is selected correctly.

3. Molding equipment

Whether the injection amount, injection pressure and clamping force are enough, whether the installation of the mold, the south core of the plastic parts and the demoulding are wrong, whether the nozzle of the injection machine and the shed cover are in correct contact.

4. Mold structure

1) Whether the parting surface position and finishing accuracy meet the needs, whether there will be overflow, and whether the plastic parts can be ensured to stay in the mold side with the ejecting device after opening the mold.

2). Whether the demoulding method is correct, whether the size, position and quantity of the extension rod and push tube are appropriate, whether the push plate will be stuck by the core, and whether it will cause scratches to the formed parts.

3) Mold temperature regulation. The power and quantity of heater; Whether the position, size and quantity of the flow line of the cooling medium are appropriate.

4) The method of dealing with the side concave of plastic parts, whether the mechanism of removing the side concave is appropriate, such as whether the slider and the push rod in the inclined guide rod core-pulling 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 placement of each mold part on the assembly drawing is appropriate, whether it is clearly expressed, and whether there is any omission

2) The part number, name, production quantity, internal or external parts, standard or non-standard parts, the processing accuracy of parts, the correction processing and allowance of high precision dimensions of molded plastic parts, the material, heat treatment, surface treatment and surface finishing degree of die parts are marked and described clearly.

3) Parts main parts, molding parts working size and matching size. Size figures should be correct and do not allow producers to convert.

4). Check the view position of all parts drawings and final assembly drawings, whether the projection is correct, whether the drawing is in line with the national standard of the drawing, and whether there is any missing size.

6. Check the processing performance

(Whether the geometric structure, view drawing, size marking, etc. of all parts are conducive to processing)

7. The main working size of the double counting aid tool

B. Professional proofreading should be carried out according to the designer's self-proofreading project in principle; However, we should focus on the structural principle, process performance and operation safety.

When drawing, it is necessary to digest the graphics first, describe according to the national standard requirements, and fill in all dimensions and technical requirements. Draw and proofread and sign.

C. The sketched base drawing to the designer proofread and sign, the customary practice is required by the relevant technical personnel of the tool manufacturing unit.

2. Plastic parts

Whether the flow of plastic material flow, shrinkage hole, weld mark, crack, release slope, etc. affect the requirements of the performance, dimensional accuracy and surface quality of plastic parts. Whether the pattern design is insufficient, whether the processing is simple, and whether the shrinkage rate of the forming material is selected correctly.

3. Molding equipment

Whether the injection amount, injection pressure and clamping force are enough, whether the installation of the mold, the south core of the plastic parts and the demoulding are wrong, whether the nozzle of the injection machine and the shed cover are in correct contact.

4. Mold structure

1) Whether the parting surface position and finishing accuracy meet the needs, whether there will be overflow, and whether the plastic parts can be ensured to stay in the mold side with the ejecting device after opening the mold.

2). Whether the demoulding method is correct, whether the size, position and quantity of the extension rod and push tube are appropriate, whether the push plate will be stuck by the core, and whether it will cause scratches to the formed parts.

3) Mold temperature regulation. The power and quantity of heater; Whether the position, size and quantity of the flow line of the cooling medium are appropriate.

4) The method of dealing with the side concave of plastic parts, whether the mechanism of removing the side concave is appropriate, such as whether the slider and the push rod in the inclined guide rod core-pulling 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 placement of each mold part on the assembly drawing is appropriate, whether it is clearly expressed, and whether there is any omission

2) The part number, name, production quantity, internal or external parts, standard or non-standard parts, the processing accuracy of parts, the correction processing and allowance of high precision dimensions of molded plastic parts, the material, heat treatment, surface treatment and surface finishing degree of die parts are marked and described clearly.

3) Parts main parts, molding parts working size and matching size. Size figures should be correct and do not allow producers to convert.

4). Check the view position of all parts drawings and final assembly drawings, whether the projection is correct, whether the drawing is in line with the national standard of the drawing, and whether there is any missing size.

6. Check the processing performance

(Whether the geometric structure, view drawing, size marking, etc. of all parts are conducive to processing)

7. The main working size of the double counting aid tool

B. Professional proofreading should be carried out according to the designer's self-proofreading project in principle; However, we should focus on the structural principle, process performance and operation safety.

When drawing, it is necessary to digest the graphics first, describe according to the national standard requirements, and fill in all dimensions and technical requirements. Draw and proofread and sign.

C. The sketched base to the designer proofread signature, the customary practice is to be reviewed by the relevant technical personnel of the tool manufacturing unit, countersign, check the manufacturing process, and then can be sent to the sun.

D.. Write manufacturing process cards

The manufacturing process card is written by the technical staff of the tool manufacturing unit and is prepared for the processing and manufacturing.

In the manufacturing process of die parts, inspection should be strengthened, and the emphasis of inspection should be placed on dimensional accuracy. After the mold assembly is completed, the inspector will inspect according to the mold inspection table. The main thing is to check whether the performance of the mold parts is good. Only in this way can the manufacturing quality of the mold be described.

Test and repair mold

Although it is in the selection of molding materials, molding equipment, mold design under the expected process conditions, but people's understanding is often imperfect, so it is necessary to test the mold after the completion of the mold processing, to see the quality of the molded parts. After finding that it is always possible to eliminate errors, repair the mold.

There are many types of undesirable phenomena in plastic parts, and the reasons are also very complex.