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Plastic Mold Design Ten Steps
May 21, 2018

 First, accept the mission book


The task book for forming plastic parts is usually proposed by the designer of the part, and its content is as follows:


1. After reviewing the drawings of the formal parts, and indicating the grade and transparency of the plastic.


2. Instructions or technical requirements for plastic parts.


3. Production output.


4. Samples of plastic parts.


       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 designer designs the mold based on the molding plastic parts task book and the mold design task book.


       Collect and sort out relevant parts design, molding process, molding equipment, mechanical processing and special processing data to prepare for use when designing molds.


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


       For example, what are the requirements for the appearance, color transparency, and performance of plastic parts, whether the geometry, slope, inserts, etc. of plastic parts are reasonable, and the allowable degree of molding defects such as weld marks, shrinkage holes, etc. Equipment, electroplating, glue, drilling and other post-processing. Select the size of the highest dimensional accuracy of the plastic parts for analysis, and see if the estimated molding tolerances are lower than the tolerances of the plastic parts and whether the desired plastic parts can be molded. In addition, we must also understand the plastic plastics and molding process parameters.


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


      Molding materials should meet the strength requirements of plastic parts, have good fluidity, uniformity and isotropic, thermal stability. According to the use of plastic parts, molding materials should meet the requirements of dyeing, metallizing conditions, decorative properties, necessary elasticity and plasticity, transparency or the opposite reflective properties, bonding or welding.


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


      4, choose molding equipment


      Molds are made according to the type of molding equipment. Therefore, the performance, specifications, and characteristics of various molding equipments must be well known. For example, for the injection machine, the specification should be understood as follows: injection capacity, clamping pressure, injection pressure, mold installation size, ejection device and size, nozzle hole diameter and nozzle spherical radius, the size of the gate sleeve positioning ring, The maximum thickness and minimum thickness of the mold, the template stroke, etc., see the relevant parameters.


To initially estimate the dimensions of the mold, determine whether the mold can be installed and used on the selected injection machine.


      5. Specific structure plan


(1) Determine the mold type


      Such as pressing mold (open, semi-closed, closed type), casting mold, injection mold and so on.


(2) Determine the main structure of the mold type


      The choice of the ideal mold structure lies in the determination of the necessary molding equipment, the ideal number of cavity, under the conditions of absolute reliability, the work of the mold itself can meet the process technology and production economic requirements 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 requirements for production are to make the cost of plastic parts low, production efficiency high, the mold can work continuously, long service life, save labor.


Third, there are many factors that affect the mold structure and the individual mold system. It is very complicated:


      1. Cavity layout. According to the geometric characteristics of plastic parts, dimensional accuracy requirements, batch size, ease of mold making, mold cost, etc. to determine the number of cavity and its arrangement.


      2. Determine the parting surface. The location of the parting surface should be conducive to mold processing, venting, stripping and forming operations, and the surface quality of plastic parts.


      3. Determine the gating system (shape, position, size of the main runner, branch runner, and gate) and the exhaust system (exhaust method, exhaust slot location, size).


      4. Select the ejection method (jack, top tube, push plate, combined ejector) to determine the undercut method and core withdrawal method.


      5. Determine the cooling, heating method, shape and position of the heating and cooling groove, and the mounting position of the heating element.


      6. According to the mold material, strength calculation or empirical data, determine the mold parts thickness and dimensions, shape structure and all connections, positioning, guide position.


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


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


      If these problems are solved, the structure of the mold will naturally be solved. At this point, you should start sketching the mold structure to prepare for the formal drawing.


Fourth, draw a mold diagram


      It is required to be drawn in accordance with national drafting standards, but it is also required to combine the factory's standards with the factory's customary painting methods not specified by the state.


      Before drawing the mold assembly drawing, the process drawing shall be drawn and shall meet the requirements of the parts drawing and the process data. The dimensions guaranteed by the next process shall be marked on the drawing with the words "process size". If, after the molding, the burr is not repaired, no other machining is performed, and the process drawing is exactly the same as the drawing of the product.


      Below the process chart, it is better to mark the part number, name, material, material shrinkage, drawing ratio, etc. Usually the process drawings on the mold assembly drawing.


      Drawing assembly structure drawing


      Draw the assembly drawing as much as possible with a 1:1 ratio. The drawing starts with the cavity and the main view is drawn at the same time as the other views.


Fifth, the mold assembly drawing should include the following:


Mold structure

2. Structure of pouring system and exhaust system.

3. Parting surface and parting mode.

4. The shape and position of all connectors, positioning, and guides.

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

6. Auxiliary tools (removal mold release tools, calibration tools, etc.).

7. Edit all part numbers in sequence and fill in the schedule.

8. Label technical requirements and instructions for use.


Sixth, the technical requirements of the mold assembly drawing


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


      2. Requirements for the mold assembly process. For example, the fitting gap of the bonding surface of the parting surface after mold assembly should be no more than 0.05mm, and the parallelism requirements of the upper and lower sides of the mold, and the size determined by the assembly and the requirements for the size.


      3. Mold use, assembly and disassembly methods.


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


      5. Requirements for trial moulding and inspection.


Seven, draw all parts


      The order of dismantling the parts drawing from the mold assembly drawing shall be: first inside and outside, firstly complex and then simple, first forming the parts, and the latter parts.


      1. Graphic Requirements: Be sure to draw a scale, allowing you to zoom in or out. The view is reasonable, the projection is correct and the layout is proper. In order to make the processing patent number easy to understand and easy to assemble, the graphics should be consistent with the assembly drawings as far as possible, and the graphics should be clear.


      2. The dimensioning requirements are uniform, centralized, orderly, and complete. The dimensioning order is: the primary part size and draft angle are marked first, then the matching dimensions are marked, and then all dimensions are marked. Label the fit dimensions on the non-primary part drawing, then label all dimensions.


      3. Surface roughness. The most applied roughness is marked in the upper right corner of the drawing, as indicated in the rest of the drawing. Other roughness symbols are marked on each surface of the part.


      4. Other content, such as part name, mold drawing number, material number, heat treatment and hardness requirements, surface treatment, graphic scale, free-size machining accuracy, technical description, etc. must be filled in correctly.


VIII. Proofreading, reviewing drawings, tracing and sending in the sun


(a) The content of self-proofing is:


      1. The relationship between molds and their parts and plastic parts drawings


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


      2. Plastic parts


      Whether plastic flow flow, shrinkage holes, weld marks, cracks, draft angles, etc., affect the requirements of the use of plastic parts, dimensional accuracy, surface quality, etc. Whether the pattern design is insufficient or not, whether the processing is simple, and whether the shrinkage rate of the molding material is selected correctly.


      3. Forming equipment


      The injection volume, injection pressure, and clamping force are not enough. Whether the mold is installed, the core of the plastic part, or the mold release is in question, and whether the injection nozzle and the nozzle cover are in correct contact.


      4. Mold structure


      1). Whether the position of the parting surface and the precision of finishing meet the requirements will not happen flash. Can the plastic parts remain on the mold side of the ejector after the mold is opened?


      2). Whether the demoulding method is correct or not, and whether the size, position, and quantity of the promotion rod and the push tube are appropriate, the push plate will not be jammed by the core, and it will not cause scratches on the molded parts.


      3). Mold temperature adjustment. Heater power, quantity; whether the cooling medium flow line position, size, quantity is appropriate.


      4). How to deal with undercuts made of plastic parts, whether the mechanism for removing the undercuts is appropriate, such as whether the sliders and push rods in the slanted guide core-pulling mechanism interfere with each other.


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


      5. Design drawings


      1). Whether the position of each mold part on the assembly drawing is appropriate or not is indicated clearly or not.


      2). Part number, name, manufacturing quantity, part internal or external purchased parts are standard parts or non-standard parts, parts processing precision, high-precision dimensions of the molded plastic parts at the correction processing and margin , mold parts of the material, heat treatment, surface treatment, surface finish is marked, clearly described.


      3). The main parts of the parts, the working dimensions and the matching dimensions of the molded parts. The size figures should be correct and should not be converted by the producer.


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


      6. Check processing performance


(Whether the geometry of all the parts, view drawing, dimensions, etc. are favorable for machining)


      7. Main working dimensions of the recalculation aid


      (B). Professional proofreading is carried out in accordance with the designer's self-proofing project; however, it should focus on structural principles, process performance and operational safety.


      When drawing, you must first digest the graphic, draw it according to the requirements of the national standard, and fill in all the dimensions and technical requirements. Self-education after signing and signing.


      (3). Submit the drawn base map to the designer for proofreading and signing. The customary practice is to review by the relevant technical personnel of the tool manufacturing unit, sign the contract, check the manufacturing process, and then send it to the sun.


      (d). Preparation of manufacturing process cards


      The manufacturing process card is prepared by the tool manufacturer's technicians and is ready for processing.


      In the manufacturing process of mold parts, inspections should be strengthened and the focus of inspection should be on the dimensional accuracy. After the mold assembly is completed, the inspector conducts the inspection according to the mold inspection table. The main point is to check whether the performance of the mold parts is in good condition. Only in this way can the manufacturing quality of the proverb molds be achieved.


Nine, test mode and repair mode


      Although the mold design is performed under the expected process conditions when the molding material and molding equipment are selected, people's understanding is often imperfect. Therefore, after the mold processing is completed, the mold test is performed and the molded parts are observed. How is the quality? Always find out afterwards that the wrong correction is done.


      There are many kinds of plastic products that have bad appearances, and the reasons are also very complex. There are reasons for molds, and there are also reasons for the process conditions. The two are often handed over together. Before repairing the mold, careful analysis and study should be conducted according to the actual conditions of the plastic parts, and the remedial measures should be proposed after finding out the cause of the defects of the plastic parts. Because the molding conditions are easy to change, the general practice is to first change the molding conditions. When changing the molding conditions does not solve the problem, it is considered to repair the mold.


      Repairing molds should be more prudent and not fully grasped. The reason for this is that once the conditions of the mold have been changed, it will not be possible to make major changes and restitution.


Ten, organize data for archiving


      After the mold has been tested, if it is not used temporarily, it should be completely wiped off the mold slag, dust, oil, etc., coated with butter or other anti-rust oil or rust inhibitor, closed to the storage place.


      Start design molds until the molds are successfully machined and passed inspections. Technical data generated during this period, such as job books, parts drawings, technical specifications, mold assembly drawings, mold parts drawings, base drawings, mold design specifications, and inspection records Table, trial die repair records, etc., according to the provisions of the system collation, binding, numbering for archiving. This may seem like a hassle, but it is useful for repairing molds and designing new molds.