Mold product drawing design standards

Time:2020-03-23 08:39:21 / Popularity: / Source:

mold drawings 

1 Topic content and scope

This standard specifies content and expression specifications that should be expressed in product drawings, which is conducive to improving quality of mold drawings and better guiding production.

2 Content

2.1 2D drawings

2.1.1 Two-dimensional drawings must conform to national standards for mechanical drawing.
2.1.2 Use PRO / E software to produce a two-dimensional diagram. File configuration content should be uniform.
2.1.3 Line width, font size and lines of drawings should be uniform. Thickness of thick solid line and thick dotted line is 0.5mm. Thin solid line, wavy line, double polyline, thin dotted line, double-dash line has a width of 1/3 of thick solid line, dashed line width has a width of 1/3 of thick solid line, segment length is 4mm, and segment interval is 1mm. Fonts (numbers, text) are 3.5mm high and 0.35 mm wide.
2.1.4 Scale of drawings is in accordance with national standards, and actual scale of printed drawings should be consistent with proportion noted in title bar. No scaling is allowed. According to size and complexity of product structure, custom drawing scale should be selected reasonably. View is not allowed to be too small and structure expression is unclear. Dimension lines are not allowed to be too dense and difficult to identify.         
2.1.5 Drawing dimensions: Product benchmarks shall be noted in drawings, and dimensions shall be marked on a uniform basis. Drawings shall be complete in size, correct, clear and reasonable, without missing dimensions, and distribution of dimension lines shall be reasonable. Dimensioning should be conducive to processing of mold. Important assembly dimensions, important parts, positioning dimensions and required inspection dimensions shall be marked with tolerances. Other dimensions are not marked with tolerance class. Required dimensions are key dimensions of product assembly and appearance. A serial number should be added after required size. Serial number is in the form of a number plus a circle. Serial numbers should be arranged in order, from left to right and top to bottom, for easy reference. Three-dimensional surfaces that are not easily labeled are marked with the largest external dimensions.
2.1.6 Stiffeners must be marked with size of big and small ends. When oblique parts are dimensioned, it must be clearly stated whether dimension is big-endian or little-endian.
2.1.7 Graphic representation is clear, eliminating unnecessary arc tangent lines.
2.1.8 Technical requirements should include: wall thickness, fillet, mold release slope, appearance requirements (such as mirror surface, transparent parts, spray paint, erosion, etc.), assembly relationship and clearance, required inspection dimensions and other special requirements.
2.1.9 Area or range should be marked with dotted lines on the appearance.
2.1.10 Appearance parts are marked with thick double-dotted lines in figure to indicate position of appearance surface.
2.1.11 Position of parting surface should be marked with thin solid lines in two-dimensional figure and explained with text.
2.1.12 Positions where gates are not allowed and ejection marks are not allowed are indicated in figure.
2.1.13 If ejection direction is not consistent with product assembly direction, generally draw product according to product ejection direction. Arrows should be used to indicate product assembly direction and datum on the drawing, and text should be explained.
2.1.14 Status of drawings shall be indicated, and replacement drawings shall be specially marked.
2.1.15 Two-dimensional drawing shall be consistent with three-dimensional drawing. If 3D graph is changed, 2D graph should be updated simultaneously.
2.1.16 In order to facilitate identification of images, add 3D axial side views at appropriate positions on 2D drawings.
mold assembly drawing 

3.1 3D stereogram

3.1.1 All structures of 3D stereograms should be expressed in solid form, missing structures or inconsistencies with 2D diagrams are not allowed.
3.1.2 Inner and outer surfaces of product that are perpendicular to direction of demoulding, movement of slider and core on three-dimensional drawing should be provided with a draft slope. Slope should be 0.5° ~ 1º. Before adding slope, position of each parting surface of product, assembly and appearance requirements of product should be clear to determine direction and size of slope. Position to be inserted should be inclined by 1º to 3º. Where possible, the larger slope, the better. Ribs should be as strong as possible. Generally, molding design task book is proposed by structural designer and mold designers according to task book of molding plastic product parts. Mold designers designs mold based on molding and molding design task book.

3.2 Collect, analyze and digest raw data

Collect and sort out relevant design information, molding technology, molding equipment, machining and special processing data for use in designing molds.
⑴Digest drawings of plastic parts, understand use of parts, analyze technical requirements of plastic parts, such as processability and dimensional accuracy. For example, what are requirements for appearance, color transparency, and performance of plastic parts, whether geometry, slope, and inserts of plastic parts are reasonable, allowable degree of molding defects such as welding marks, shrinkage holes, whether there are post-processing such as painting, plating, bonding, drilling, etc. Select size with the highest dimensional accuracy of plastic parts for analysis, see if estimated forming tolerance is lower than tolerance of plastic product part, and whether it can form a satisfactory plastic product part. In addition, you need to understand plasticization and molding process parameters of plastics.
⑵Digest process data and analyze whether molding methods, equipment models, material specifications, mold structure types, other requirements proposed in process task book are appropriate and can be implemented. Molding material should meet strength requirements of plastic parts, have good fluidity, uniformity, isotropy, and thermal stability. According to use of plastic parts, molding material should meet requirements of dyeing, metal plating conditions, decorative properties, necessary elasticity and plasticity, transparency or opposite reflection properties, adhesiveness or weldability.

3 Choose molding equipment

Molds are made according to type of molding equipment, so you must be familiar with performance, specifications, and characteristics of various molding equipment. For example, for an injection machine, following should be understood in terms of specifications: injection capacity, clamping pressure, injection pressure, mold installation size, ejector and size, nozzle hole diameter and nozzle spherical radius, gate sleeve positioning ring size, mold maximum and minimum thickness, stroke of mold plate, etc., see specific parameters. It is necessary to initially estimate mold dimensions, determine whether mold can be installed and used on selected injection machine.

4 Specific structure plan:

⑴ Determine type of mold.
⑵ Determine main structure of mold type. Ideal mold structure is to determine necessary molding equipment and ideal number of cavities. Under absolutely feasible conditions, work of mold can meet technological and production economic requirements of plastic part. Technical requirements for plastic parts are to ensure geometry, surface finish and dimensional accuracy of plastic parts. Production economic requirement is to make cost of plastic parts low, production efficiency high, mold can work continuously, service life is long, and labor is saved.

There are many factors that affect structure and individual system of mold, which are very complicated:

① Cavity layout. According to geometrical characteristics of plastic parts, dimensional accuracy requirements, batch size, mold manufacturing ease, mold cost, etc., determine number of cavities and their arrangement. For injection molds, precision of plastic parts is grades 3 and 3a, weight is 5 grams, hardened casting system is used, number of cavities is 4-6; plastic parts are of general precision (grade 4-5),molding material is local crystalline material, number of cavities can be 16-20; plastic parts weight 12-16 grams, number of cavities is 8-12; while plastic parts weighing 50-100 grams, number of cavities is 4-8. Recommended number of cavities for amorphous plastic parts is 24-48, 16-32 and 6-10. When weight of plastic parts continues to increase, multi-cavity molds are rarely used. For plastic parts with 7-9 grade accuracy, maximum number of cavities is increased to 50% compared to 4-5 grade plastics indicated.
② Determine parting surface. Location of parting surface should be conducive to mold processing, exhaust, demolding and molding operations, surface quality of plastic parts.
③ Determine pouring system (shape, position and size of main runner, sub-runner and gate) and exhaust system (exhaust method, location and size of exhaust trough).
④ Select ejection method (ejector, ejector, push plate, combined ejection), determine undercut processing method and core pulling method.
⑤ Decide cooling and heating method, shape, position of heating and cooling grooves, installation location of heating element.
⑥ Determine thickness and overall dimensions of mold parts, overall structure, and positions of all connections, positioning, and guides based on mold material, strength calculation, or empirical data.
⑦Determine structural form of main mold parts and structural parts.
⑧Considering strength of each part of mold, calculate working size of molded part. If these problems are solved, structural form of mold will be solved naturally. At this time, you should start to sketch mold structure to prepare for formal drawing.
⑨Drawing of mold requires drawing according to national drafting standards, but it also requires combination of our factory standards and factory's customary methods not prescribed by state. Before draw mold assembly drawing, process drawing should be drawn, it must meet requirements of drawing and process data. For dimensions guaranteed by next process, words "process dimensions" should be marked on drawing. If no mechanical processing is performed except for repairing burrs after molding, process drawing is exactly same as product drawing. It is best to mark part number, name, material, material shrinkage, drawing scale, etc. below process chart. Process drawings are usually on mold assembly drawing.

A. Draw assembly structure diagram

mold assembly drawing 
When drawinn final assembly drawing, use a 1: 1 ratio as much as possible. Start with cavity first, draw main view and other views at the same time. Mold assembly drawing should include following:
① Mold forming part structure
② Structural form of pouring system and exhaust system.
③ Parting surface and part picking method.
④ Outline structure and position of all connecting parts, positioning and guides.
⑤ Mark cavity height (not required, as required) and overall mold size.
⑥ Auxiliary tools (pick-up and demolding tools, calibration tools, etc.).
⑦ Number all parts in order and fill in detailed list.
⑧ Mark technical requirements and instructions for use.

B. Contents of technical requirements for mold assembly drawing:

① For performance requirements of some systems of mold. For example, assembly requirements for ejection system and slider core structure.
② Requirements for mold assembly process. For example, bonding gap of bonding surface of parting surface after mold is assembled should not be greater than 0.05mm mold parallelism requirements of upper and lower sides, dimensions determined by assembly and requirements for dimensions should be indicated.
③ Mold use, assembly and disassembly methods.
④ Anti-oxidation treatment, mold number, lettering, marking, oil seal, storage and other requirements.
⑤ Requirements related to mold test and inspection.

C. Draw all parts. Order of disassembling parts from mold assembly drawing should be: first inside, then outside, first complicated, then simple, first forming parts, then structural parts.

① Graphic requirements: Be sure to draw according to scale, allow zoom in or zoom out. View is selected properly, projection is correct, and layout is proper. In order to make processing patent number easy to understand and easy to assemble, graphics should be consistent with final assembly drawing as much as possible, and graphics should be clear.
② Dimensions must be uniform, centralized, orderly and complete. Order of dimensioning is as follows: firstly mark size of main part and draft angle, then mark mating size, and mark entire size. Mating dimensions are marked on non-main parts drawings first, and then all dimensions are marked.
③ Surface roughness. Mark most commonly used roughness in upper right corner of drawing, such as "Remaining 3.2" Other roughness symbols are marked on each surface of part.
④ Other contents, such as part name, mold drawing number, material grade, heat treatment and hardness requirements, surface treatment, graphic proportion, free dimension processing accuracy, and technical description must be filled in correctly.

D. Proofreading and self-proofing of plan review are:

① Relationship between mold, its parts and drawing of plastic part, whether material, hardness, dimensional accuracy, structure of mold and part of mold meet requirements of plastic part drawing.
② In the case of plastic parts, whether flow, shrinkage, weld marks, cracks, demolding angles of plastic material flow affect requirements of performance, dimensional accuracy, and surface quality of plastic parts. Is there any shortage of pattern design, whether processing is simple, and whether shrinkage of molding material is selected correctly?
③ In terms of molding equipment: injection volume, injection pressure, and clamping force are not enough; whether installation of mold, core of plastic product part, and demoulding of mold are all correct; whether nozzle of injection machine and mouthpiece are in proper contact.
④ In terms of mold structure:
a. Whether position of parting surface and precision of finishing meet requirements, whether there will be overflow, whether plastic parts can be left on the mold with ejection device after mold is opened.
b. Whether demolding method is correct, whether size, position quantity of promotion rod and push tube are appropriate, will push plate be caught by core, will molded parts be scratched.
c. Mold temperature adjustment. Whether power and quantity of heater, location, size and quantity of flow line of cooling medium are appropriate.
d. Method of dealing with undercuts of plastic parts, whether mechanism for removing undercuts is appropriate, such as whether slider and push rod in oblique guide column core pulling mechanism interfere with each other.
e. Whether location, size of pouring and exhaust system are appropriate.
f. Design drawings
g. Whether location of each mold part on assembly drawing is appropriate, whether it is clearly displayed, and whether there are any omissions.
h. Part number, name, production quantity, internal or external purchase of part drawing, whether it is a standard or non-standard part, processing accuracy of part, correction processing and margin of high-precision dimensions of molded plastic part. Whether material, heat treatment, surface treatment, and surface finish of mold parts are marked and described clearly.
⑤Working dimensions and fitting dimensions of main parts and forming parts. Dimensional figures should be correct, and should not be converted by producer.
⑥ Check view position of all parts and assembly drawings, whether projection is correct, whether drawing method conforms to national standard of drawing, and whether there are missing dimensions.
⑦ Check processing performance: (whether geometric structure, view drawing and dimension of all parts are favorable for processing)
⑧ Main working dimensions of recalculation auxiliary tools are to be checked by designer in principle according to designer's self-calibration project; however, it should focus on structural principles, process performance and operational safety. After review and sign, it will be reviewed by technicians with manufacturing experience, signed and checked for manufacturing process before being sent to mold shop.
mold structure 

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