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Ten steps of plastic mold design

Release time:2021-10-08

1、 Accept the assignment

The specification of molded plastic parts is usually proposed by the part designer, and its contents are as follows:

1. Approved drawings of regular parts are reviewed and signed, and the brand made of transparent plastic is marked.

2. Instructions or technical requirements of plastic parts.

3. Production output.

4. Samples of plastic parts.

Usually, the mold design assignment is proposed by the plastic part technologist according to the plastic part forming assignment, and the mold designer designs the mold according to the plastic part forming assignment and the mold design assignment.

2、 Collect, analyze and digest original data

Collect and sort out relevant part design, forming process, forming equipment, machining and special processing data for mold design.

1. Digest the drawings of plastic parts, understand the use of parts, and analyze the technical requirements of plastic parts, such as processibility, dimensional accuracy, etc.

For example, what are the requirements for appearance modeling, color transparency and use performance, whether the geometric structure, inclination, inserts, etc. are reasonable for plastic parts, the allowable degree of welding marks, shrinkage holes and other molding defects, and whether there are post-processing such as coating, electroplating, gluing, drilling, etc.

Select the size of plastic parts with high dimensional accuracy, analyze whether the estimated forming tolerance is lower than that of plastic parts, and whether the plastic parts can be formed to meet the requirements. In addition, we should also know the plasticization and molding process parameters of plastics.

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

The molding material shall meet the strength requirements of plastic parts and have good fluidity, uniformity, isotropy and thermal stability. According to the application of plastic parts, the molding materials should meet the requirements of dyeing, metal plating conditions, decorative performance, necessary elasticity and plasticity, transparency or reverse reflection performance, adhesive or weldability, etc.

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

4. Select molding equipment

According to the type of molding equipment, you need to be familiar with the performance, specifications and characteristics of various molding equipment. For example, for an injection molding machine, the following contents should be known from the specification: injection capacity, mold locking pressure, injection pressure, mold installation size, ejector and size, nozzle hole diameter and nozzle spherical radius, gate sleeve cage size, mold large thickness and small thickness, template stroke, etc.

It is necessary to make a preliminary estimate of the overall dimensions of the mold to determine whether the mold can be installed on the selected injection machine.

5. Specific structural scheme

(1) Determine mold type

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

(2) Determine the main structure of the mold type

Choosing the ideal mold structure is to determine the necessary molding equipment and the ideal number of cavities, so that the mold itself can work under reliable conditions to meet the technological and economic requirements of plastic parts. The technological requirements of plastic parts are to ensure the geometric shape, surface finish and dimensional accuracy of plastic parts. The economic requirement of production is to make plastic parts with low cost, high production efficiency, continuous work of molds, long service life and labor saving.

3、 Factors affecting mold structure and single mold system:

1. Cavity layout. The number and arrangement of cavities are determined according to the geometric characteristics of plastic parts, dimensional accuracy requirements, batch size, mold manufacturing difficulty, mold cost, etc.

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

3. Determine the gating system (main sprue, sub sprue and gate size, shape and position) and exhaust system (exhaust mode, exhaust slot size and position).

4. Select the ejection method (ejector rod, pipe jacking, push plate, combined ejection), and determine the side concave treatment method and core pulling method.

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

6. According to the mold material, strength calculation or empirical data, determine the thickness, external dimension, external structure and the position of all connections, positioning and guiding parts of the mold parts.

7. Determine the structural form of main formed parts and structural parts.

8. Considering the strength of each part of the mold, calculate the working size of the formed parts.

When these problems are solved, the structural form of the mold is naturally solved. At this time, we should start to draw a sketch of the mold structure to prepare for the formal drawing.

4、 Draw mold drawing

It is required to draw according to the national drawing standard, but it is also required to combine the factory standard with the factory customized drawing method not specified by the state.

Before drawing the mold assembly drawing, the process drawing should be drawn first, and the requirements of part drawing and process data should be met. The dimension guaranteed by the next process shall be marked with "process dimension" on the drawing. If there is no other processing except burr repair after forming, the process drawing is exactly the same as the part drawing.

It is best to mark the part number, name, material, material shrinkage, drawing proportion, etc. under the process drawing. Generally, the process drawing is drawn on the mold assembly drawing.

Draw the general assembly structure drawing

The drawing of the general assembly drawing should adopt the scale of 1:1. Firstly, draw the cavity, and draw the main view and other views at the same time.

5、 The general assembly drawing of the mold shall include the following contents:

1. Structure of moulded parts.

2. Structural form of pouring system and exhaust system.

3. Parting surface and parting part taking method.

4. Outline structure and position of all connectors, positioning and guiding parts.

5. Mark the height dimension of the cavity (not required, as required) and the overall dimension of the mold.

6. Auxiliary tools (tools for taking out and demoulding parts, calibration tools, etc.).

7. Make the serial numbers of all parts in sequence and fill in the detailed list.

8. Mark the technical requirements and instructions.

6、 Contents of technical requirements for mold assembly drawing

1. Performance requirements of some mold systems. For example, the assembly requirements for ejection system and sliding block core pulling structure.

2. Requirements for mold assembly process. For example, after the mold is assembled, the joint clearance of the parting surface joint surface should not be greater than 0.05mm, which requires the parallelism requirements of the upper and lower parts of the mold, and points out the size determined by the assembly and the requirements for this size.

3. Use, assembly and disassembly methods of molds.

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

5. Mold testing and inspection requirements.

7、 All parts of the part drawing

The order of drawing the part drawing from the mold assembly drawing should be: from the inside to the outside, from the complex to the simple, from the formed part to the structural part.

1. Graphic requirements: it must be drawn to scale, and it is allowed to zoom in or out. Reasonable selection of views, correct projection and reasonable arrangement. In order to make the processing patent number easy to understand and easy to assemble, the graphics should be as consistent and clear as possible with the general assembly drawing.

2. The dimensions shall be unified, centralized, orderly and complete. The order of dimensioning is: first mark the size of main parts and die inclination, then mark the matching size, and then mark all sizes. On the drawings of non main parts, mark the matching dimensions first, and then mark all dimensions.

3. Surface roughness. A lot of roughness shall be applied to the mark in the upper right corner of the drawing, such as "other 3.2". Other roughness symbols shall be marked 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, machining accuracy of free dimension, technical description, etc., should be filled in correctly.

8、 Proofreading, drawing review, drawing tracing, and sun transmission

(1) Self proofreading content:

1. Relationship between mold and its parts and plastic part drawing

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

2. Plastic parts

Whether the flow, shrinkage, welding cracks, cracks, demoulding slope of plastic materials will affect the requirements of plastic parts in terms of performance, dimensional accuracy, surface quality and so on. Whether the pattern design is deficient, whether the processing is simple, and whether the shrinkage of molding materials is selected correctly.

3. Molding equipment

Whether the injection volume, injection pressure and clamping force are enough, whether there are problems in mold installation, mold core and demoulding of plastic parts, and whether the nozzle of the injection machine is in correct contact with the throat sleeve.

4. Mold structure

1) Whether the position and finishing accuracy of the parting surface meet the needs, whether there will be overflow, and whether the plastic parts can be guaranteed to remain 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 promotion rod and push tube are appropriate, whether the push plate will be stuck by the core, and whether it will scratch the formed parts.

3) Mold temperature regulation. Power and quantity of heaters; Whether the flow line position, size and quantity of cooling medium 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 sliding block and push rod in the inclined guide pillar core pulling mechanism interfere with each other.

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

5. Design drawings

1) Whether the placement position of each mold part on the assembly drawing is appropriate, whether it is clearly marked, and whether there is any omission.

2) On the part drawing, whether the part number, name, manufacturing quantity, whether the part is manufactured in-house or purchased, whether it is a standard part or a non-standard part, whether the part is matched with the processing accuracy, the correction processing and allowance at the high-precision dimension of the molded plastic part, and whether the material, heat treatment, surface treatment and surface finish of the mold part are clearly marked and described.

3) Working size and matching size of main parts and formed parts. The size figures should be correct. Do not make the manufacturer convert.

4) Check the view position of all part drawings and general assembly drawings, whether the projection is correct, whether the drawing method conforms to the national standards of drawings, and whether there are missing dimensions.

6. Check processing performance

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

7. Recalculate the main working dimensions of auxiliary tools

(2) Professional proofreading shall be carried out according to the self calibration project of the designer in principle; However, we should focus on the structural principle, process performance and operation safety.

When tracing, we should first digest the graphics, draw according to the requirements of national standards, and fill in all dimensions and technical requirements. Self proofread and sign after tracing.

(3) The prepared base map shall be submitted to the designer for checking and signing. Usually, the relevant technicians of the tool manufacturing unit shall review, countersign and check the manufacturing process before it can be sent to the sun.

(4) Prepare manufacturing process card

The technicians of the tool manufacturing unit prepare the manufacturing process card and prepare for processing and manufacturing.

In the manufacturing process of mold parts, inspection should be strengthened, with the focus on dimensional accuracy. After the mold is assembled, the inspector will inspect according to the mold inspection table, mainly to check whether the performance of the mold parts is intact. Only in this way can we slang the manufacturing quality of the mold.

9、 Mold test and repair

Although the mold design is carried out under the expected process conditions when selecting forming materials and forming equipment, people's understanding is often imperfect, so it is necessary to carry out mold test after the mold processing to see how the quality of the formed parts is. Always repair the mold to eliminate errors after discovery.

There are many kinds of defects in plastic parts, and the causes are also very complex, including mold reasons and process conditions, which are often combined. Before mold repair, it is necessary to carefully analyze and study the actual situation of plastic parts' defects, find out the causes of plastic parts' defects, and then put forward remedial measures. Since the forming conditions are easy to change, the general practice is to change the forming conditions first. When changing the forming conditions cannot solve the problem, only consider repairing the mold.

Be more cautious in mold repair. Don't act rashly if you're not sure. The reason is that once the mold conditions change, it is impossible to carry out major transformation and restore to the original state.

10、 Sort out data for archiving

After the mold test, if it is not used temporarily, the demoulding residue, dust, oil stain, etc. should be completely wiped off, coated with butter or other antirust oil or antirust agent, and stored in the storage place.

From the beginning of mold design to the successful completion of mold processing inspection, the technical data generated during this period, such as task statement, part drawing, technical specification, mold general assembly drawing, mold part drawing, foundation drawing, mold design specification, inspection record sheet, mold test repair record, etc. It shall be systematically sorted, bound, numbered and archived according to the regulations. This seems troublesome, but it is very useful for later mold repair and new mold design.

Copyright: Shenzhen Zhongyuan Plastic Co., Ltd. | mold processing customized manufacturer. If you want to know the processing price of the factory, how much is it, and which is good, please contact us Yue ICP Bei No. 17060480