Plastic molds are tools used in the plastics processing industry to match plastic molding machines, giving plastic products a complete configuration and precise dimensions. Due to the variety of plastics and processing methods, the structure of plastic molding machines and plastic products is complicated, so the types and structures of plastic molds are also diverse.
First, accept the task book
The task book for molded plastic parts is usually proposed by the part designer, and its contents are as follows:
1. The formal drawings of the finished parts that have been examined, and indicate the grades and transparency of the plastics used.
2. Plastic parts specifications or technical requirements.
3. Production output.
4. Plastic parts samples.
Usually, the mold design task book is proposed by the plastic parts craftsman according to the task book of the molded plastic parts. The mold design personnel design the mold based on the molded plastic parts task book and the mold design task book.
Second, collect and organize related parts design, molding process, molding equipment, machining and special processing materials, in order to use when designing molds.
1. Digest the plastic parts drawing, understand the use of the parts, analyze the technical requirements of the plastic parts, dimensional accuracy and other technical requirements.
For example, what are the requirements for the appearance, color transparency, and performance of plastic parts, whether the geometrical structure, slope, inserts, etc. of the plastic parts are reasonable, the allowable degree of molding defects such as weld lines and shrinkage holes, and whether or not they are coated Post-processing such as loading, plating, gluing, drilling, etc. Select the size of the plastic part with the highest dimensional accuracy for analysis to see if the estimated molding tolerance is lower than the tolerance of the plastic part, and whether the desired plastic part can be formed. In addition, it is necessary to understand the plasticization and molding process parameters of plastics.
2. Digest the process data, analyze whether the requirements of the molding method, equipment model, material specification, mold structure type, etc. proposed in the process task book are appropriate and can be implemented.
The molding material should meet the strength requirements of plastic parts, with good fluidity, uniformity, isotropy and thermal stability. Depending on the use of the plastic part, the molding material should meet the requirements for dyeing, metallization, decorative properties, necessary elasticity and plasticity, transparency or reverse reflection properties, adhesive properties or weldability.
3. Determine the molding method - using direct pressure method, casting pressure method or injection molding method.
4. choose molding equipment
The mold is carried out according to the type of molding equipment, so it is necessary to be familiar with the performance, specifications, and characteristics of various molding equipment. For example, for the injection machine, the following should be understood in terms of specifications: injection capacity, mold clamping pressure, injection pressure, mold mounting size, ejection device and size, nozzle hole diameter and nozzle spherical radius, gate sleeve positioning ring size, The maximum thickness and minimum thickness of the mold, the stroke of the template, etc., see the relevant parameters.
To initially estimate the mold dimensions, determine if the mold can be installed and used on the selected injection machine.
5. Specific structural plan
(1) Determine the mold type
Such as pressing die (open, semi-closed, closed), casting die, injection mold, and the like.
(2) Determine the main structure of the mold type
Choosing the ideal mold structure is to determine the necessary molding equipment, the ideal number of cavities, and under the absolutely reliable conditions, the work of the mold itself can meet the requirements of the process technology and production economy of the plastic parts. The technical requirements for plastic parts are to ensure the geometry, surface finish and dimensional accuracy of the plastic parts. The economic requirement of production is to make the cost of plastic parts low, the production efficiency is high, the mold can work continuously, the service life is long, and labor is saved.
Third, the factors affecting the mold structure and the individual system of the mold are many and complex:
1. Cavity arrangement. The number of cavities and their arrangement are determined according to the geometrical characteristics of the plastic parts, the dimensional accuracy requirements, the batch size, the difficulty in mold manufacturing, and the cost of the mold.
2. Determine the parting surface. The location of the parting surface is conducive to mold processing, exhaust, demoulding and forming operations, surface quality of plastic parts, etc.
3. Determine the gating system (the shape, position, and size of the main runner, split runner, and gate) and the exhaust system (the method of exhaust, the location and size of the vent).
4. Select the ejector mode (top rod, top tube, push plate, combined ejector) to determine the undercut treatment method and core pulling method.
5. Determine the shape and position of the cooling, heating method and heating and cooling grooves, and the mounting location of the heating element.
6. According to the mold material, strength calculation or empirical data, determine the thickness and shape of the mold parts, the shape structure and the position of all connections, positioning and guides.
7. Determine the structural form of the main molded part and structural part.
8. Consider the strength of each part of the mold and calculate the working size of the molded part.
If these problems are solved, the structural form of the mold will naturally be solved. At this point, you should start sketching the mold structure and prepare for the formal drawing.
Fourth, draw the mold map
It is required to draw according to the national drawing standards, but it is also required to combine the factory standards and the factory customary methods not specified by the state.
Before drawing the master assembly drawing, the process drawing should be drawn and conformed to the requirements of the parts drawing and process data. The size guaranteed by the next process shall be marked with the words "process size" on the drawing. If, after the molding, no other machining is performed except for the repair of the burrs, the process diagram is exactly the same as the workpiece drawing.
It is best to mark the part number, name, material, material shrinkage rate, drawing ratio, etc. under the process diagram. Usually the process picture is on the mold assembly drawing.
Drawing the assembly structure
Draw the final assembly drawing as much as possible with a 1:1 ratio. Start with the cavity and draw the main view at the same time as the other views.
Fifth The final assembly drawing of the mold shall include the following contents:
1. Mold forming part structure
2. The structure of the gating system and exhaust system.
3. Parting surface and parting mode.
4. Outline structure and position of all connecting parts, positioning and guiding parts.
5. Mark the cavity height dimension (not required, as needed) and the overall size of the mold.
6. Auxiliary tools (removal tool, tool, calibration tool, etc.).
7. Program all the part numbers in order and fill out the schedule.
8. Mark technical requirements and instructions for use.
The steps to make plastic molds are complicated, and the length of the article is too long. Therefore, it is divided into two parts of the context. Interested friends should follow up.
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