How to Scientifically Inspect the Plastic Mold

To ensure that molds can produce qualified products, be put into normal production, guarantee the service life of molds, and meet the production and usage requirements of product design, standards for acknowledging molds are established from aspects such as product quality, mold structure, and injection molding process requirements, based on which the quality of molds is evaluated.

I. Appearance, Size, and Fit of Molded Products

1. Defects are not allowed on the product surface: shortage of material, burn, white mark, white lines, flash, bubbling, whitening (or cracking, fracturing), embossing, wrinkles.
2. Welding marks: the length of general circular welding marks should not exceed 5mm, and the length of irregular welding marks should be less than 15mm, and the welding marks should have sufficient strength to pass functional safety tests.
3. Shrinkage: obvious shrinkage is not allowed on the appearance surface, slight shrinkage (no dents felt by hand) is allowed on non-obvious areas.
4. Deformation: the flatness deviation of general small products should be less than 0.3mm, and the assembly requirements should be guaranteed for products with assembly requirements.
5. Obvious air lines and flow lines are not allowed on the apparent surface, and generally, there should be no bubbles in the product.
6. The geometric shapes and dimensional accuracy of the product should meet the requirements of the formal and valid mold drawings (or 3D files). The product tolerance should be based on the tolerance principle, with negative tolerance for axial dimensions and positive tolerance for hole dimensions, according to customer requirements.
7. Product wall thickness: the product wall thickness generally requires an average thickness, and non-average thickness should meet the requirements of the drawings. Tolerances should be -0.1mm according to the characteristics of the mold.
8. Product fit: the fit between the surface shell and the base shell: the surface misalignment should be less than 0.1mm, and there should be no scraping phenomenon. For holes, shafts, and surfaces with fit requirements, the fit clearance and usage requirements should be guaranteed.

II. Mold Appearance

1. The mold nameplate should be complete, with clear characters arranged neatly.
2. The nameplate should be fixed near the mold foot close to the template and reference angle. The nameplate fixing should be reliable and not easy to peel off.
3. Plastic block plug-in water nozzles should be selected for cooling water nozzles, and customer requirements should be followed if specified.
4. Cooling water nozzles should not protrude from the mold frame surface.
5. Cooling water nozzles should be machined with counterbores, with diameters of 25mm, 30mm, and 35mm, and the hole openings should be chamfered uniformly.
6. Inlet and outlet marks should be provided for cooling water nozzles.
7. English characters and numbers on the markings should be greater than 5/6, positioned 10mm below the water nozzle, with clear, beautiful, neat, and uniform spacing.
8. Mold accessories should not affect the lifting and storage of the mold. During installation, if there are exposed oil cylinders, water nozzles, pre-positioning mechanisms, etc., support legs should be provided for protection.
9. Support legs should be installed by screws through the support legs fixed on the mold frame, and excessively long support legs can be secured on the mold frame using externally threaded pillars processed by a lathe.
10. The size of the mold ejector hole should meet the specified requirements of the injection molding machine. Except for small molds, a single central ejector should not be used.
11. The positioning ring should be firmly fixed, with diameters of 100mm and 250mm, protruding 10-20mm above the base plate. Except for customer requirements.
12. The external dimensions of the mold should meet the specified requirements of the designated injection molding machine.
13. For molds with directional requirements, arrows should be used to indicate the installation direction on the front or back templates, with the word "UP" next to the arrow in yellow, and the arrows and text should be 50mm in height.
14. The mold frame surface should be free of pits, rust, excess lifting rings, water vapor, oil holes, and other defects affecting the appearance.
15. The mold should be easy to lift and transport, and mold components should not be disassembled during lifting. The lifting rings should not interfere with water nozzles, oil cylinders, pre-positioning rods, etc.

III. Mold Material and Hardness

1. The mold frame should be made of standard frames that meet the standard requirements.
2. Molded parts and gating systems (core, cavity insert, moving insert, runner cone, push rod, sprue bushing) should be made of materials with performance higher than 40Cr.
3. When molding plastics that are prone to corrosion, corrosion-resistant materials should be used for molded parts, or anti-corrosion measures should be taken on the molding surface.
4. The hardness of mold molded parts should not be lower than 50HRC, or the surface hardening treatment hardness should be higher than 600HV.

IV. Ejection, Resetting, Core Pulling, and Part Removal

1. Ejection should be smooth, without jamming or abnormal noises.
2. The inclined ejection surface should be polished, and the ejection surface should be lower than the core surface.
3. Sliding parts should have oil grooves, and the surface should be nitrided. After treatment, the surface hardness should be above HV700.
4. All ejector rods should have anti-rotation positioning, and each ejector rod should be numbered.
5. Ejection distance should be limited by limit blocks.
6. Reset springs should be standard parts, and the ends of the springs should not be polished or cut.
7. Sliders and cores should have stroke limits. Small sliders should be limited by springs, and if springs cannot be installed conveniently, ball screws can be used. Oil cylinder core pulling must have stroke switches.
8. Sliders for core pulling generally use inclined guide posts, and the angle of the inclined guide post should be 2°~3° smaller than the angle of the slider locking surface. If the slider stroke is too long, oil cylinder extraction should be used.
9. When the molded part of the oil cylinder core pulling is covered, the oil cylinder should be equipped with a self-locking mechanism.
10. Large sliders with a width exceeding 150mm should have wear-resistant plates underneath. The material of the wear-resistant plate should be T8A, and after heat treatment, the hardness should be HRC50~55. The wear-resistant plate should be 0.05~0.1mm higher than the large surface and should have oil grooves.
11. Ejector rods should not move up and down.
12. Hooks should be added on the ejector rods, and the direction of the hooks should be consistent for easy removal from the product.
13. The fit clearance between the ejector rod hole and the ejector rod, the length of the sealing stage, and the surface roughness of the ejector rod hole should meet the requirements of relevant enterprise standards.
14. The product should be easy for operators to remove.
15. When ejecting the product, it should follow the inclined ejection, and grooves or patterns should be added to the ejector rod.
16. The ejector block fixed on the ejector rod should be firm and reliable, with a slope of 3°~5° on all sides that are not molded parts, and the lower edge should be chamfered.
17. There should be no iron filings or debris in the oil passage holes on the mold frame.
18. The end face of the return rod should be flat, without spot welding. There should be no gaskets at the bottom of the rough head, no spot welding.
19. The guiding sliding of the three-plate mold gate plate should be smooth, and the gate plate should be easy to open.
20. The limit pull rods of the three-plate mold should be arranged on both sides of the mold installation direction, or additional pull plates should be added outside the mold frame to prevent interference with operators.
21. The oil passage and air passage should be smooth, and hydraulic ejection and resetting should be in place.
22. There should be exhaust ports at the bottom of the guide bush.
23. The installation of locating pins should have no gaps.

V. Cooling and Heating Systems

1. The cooling or heating system should be fully unobstructed.
2. The sealing should be reliable, and there should be no leakage under 0.5MPa pressure, which is easy to maintain.
3. The size and shape of the sealing groove opened on the mold frame should meet the relevant standard requirements.
4. When placing the sealing ring, apply grease and make it slightly higher than the mold frame surface after installation.
5. Water and oil flow channel baffles should be made of materials that are not easily corroded.
6. Concentrated water supply and method should be used for the front and rear molds.

VI. Casting System

1. The gate setting should not affect the appearance of the product and meet the requirements for product assembly.
2. The section and length of the runner should be reasonably designed to minimize the process while ensuring molding quality, reduce the cross-sectional area to shorten filling and cooling time, and minimize the loss of plastic in the casting system.
3. The sectional area of the split runner on the back of the front mold should be trapezoidal or semi-circular.
4. The three-plate mold has a broken material handle on the gate plate, and the diameter of the gate entrance should be less than 3mm, and there should be a step recessed into the gate plate 3mm deep at the ball head.
5. The ball head pull rod should be reliably fixed, pressed under the positioning ring, and fixed with a headless screw or pressed with a plate.
6. The gates and runners should be machined according to the dimensions on the drawings and should not be hand-ground.
7. The gate should meet the specifications at the gate location as required.
8. The front end of the split runner should have an extended part as a cold slug well.
9. The Z-shaped turning of the pull rod should have a smooth transition.
10. The split runner on the parting surface should be circular, and the front and rear molds should not be misaligned.
11. Submarine gates on ejector rods should have no surface shrinkage.
12. The diameter and depth of the transparent product's cold slug well should meet the design standards.
13. The gates should be easy to remove, with no gate marks on the appearance of the product and no residual gates at the assembly of the product.
14. For bent hook submarine gates, both parts of the insert block should be nitrided, and the surface hardness should reach HV700.

VII. Hot Runner System

1. The layout of the hot runner wiring should be reasonable and easy to maintain, and the wiring number should correspond one-to-one.
2. The hot runner should undergo safety testing, and the insulation resistance to ground should be greater than 2MW.
3. Standard components should be used for temperature control cabinets, hot nozzles, and hot runners.
4. The main nozzle sleeve is connected to the hot runner with threads, and the bottom surface has a flat contact seal.
5. The hot runner should have good contact with the heating plate or heating rod, and the heating plate should be fixed with screws or bolts, with good surface fit.
6. J-type thermocouples should be used and matched with temperature controllers.
7. Each group of heating elements should be controlled by a thermocouple, and the arrangement of thermocouples should be reasonable.
8. The nozzle should meet the design requirements.
9. The hot runner should have reliable positioning, with at least two positioning pins or fixed with screws.
10. There should be a heat-insulating pad between the hot runner and the mold.
11. The temperature set by the temperature controller should have an error of less than ±5°C from the actual displayed temperature, and the temperature control should be sensitive.
12. The mounting holes for the cavity and nozzle on the mold should be through.
13. The hot runner wiring should be bundled and covered with a pressure plate.
14. Two sockets of the same specification should be clearly marked.
15. The control lines should be sheathed and undamaged.
16. The structure of the temperature control cabinet should be reliable, and the screws should not be loose.
17. The sockets should be installed on insulating boards and should not exceed the maximum size of the mold.
18. The wires should not be exposed outside the mold.
19. Rounded transitions should be provided at all points where the hot runner or mold contacts the wire.
20. Before assembling the mold, all circuits should be free of open or short circuits.
21. All connections should be correctly made, and the insulation performance should be good.
22. After clamping on the mold, all circuits should be checked again with a multimeter.

VIII. Forming Parts, Parting Surfaces, and Vent Slots

1. The front and rear mold surfaces should be free of irregularities, pits, rust, or other defects that affect the appearance.
2. There should be a gap of less than 1mm between the insert block and the mold frame, and there should be a small radius at the corners.
3. The parting surface should be kept clean, tidy, without sanding or voids, and the sealing part should not be depressed.
4. The depth of the vent slot should be less than the overflow value of the plastic.
5. The fitting of inserts should be in place, easy to place, and reliably positioned.
6. The insert blocks, core inserts, etc., should be reliably positioned and fixed, circular parts should have anti-rotation, and no copper or iron sheets should be placed under the insert block.
7. The end face of the ejector rod should match the core.
8. There should be no defects such as undercuts or chamfers in the molded parts of the front and rear molds.
9. The ribs should be smoothly ejected.
10. For multi-cavity molds, the left and right parts should be symmetrical, and should be marked with L or R where required by the customer, generally in places that do not affect the appearance or assembly, with a font size of 1/8.
11. The mating surface of the mold frame should be in place, with 75% or more of the area in contact.
12. Ejector rods should be arranged close to the sidewalls and ribs or bosses, and larger ejector rods should be used.
13. The same parts should be numbered 1, 2, 3, etc.
14. All collision and penetration surfaces and parting surfaces should be accurately mated.
15. The sealing part of the parting surface should meet the design standards. For molds below medium size, 10~20 mm should be machined for voids, and the rest should be machined to avoid voids.
16. The grain pattern and sandblasting should be uniformly up to customer requirements.
17. For products with appearance requirements, screws on the product should have anti-loosening measures.
18. Screws with a depth of more than 20mm should use a core pin.
19. The wall thickness of the product should be uniform, with a deviation controlled within ±0.15 mm.
20. The width of the ribs should be less than sixty percent of the wall thickness on the visible surface.
21. The core inserts on inclined ejection and sliders should have reliable fixing methods.
22. When the front mold is inserted into the rear mold or the rear mold is inserted into the front mold, there should be a bevel lock around it, and it should be machined to avoid voids.

IX. Injection Production Process

1. The mold should have stability in injection production within the normal injection molding process conditions and repeatability in adjusting process parameters.
2. The injection pressure during mold injection production should generally be less than 85% of the rated maximum injection pressure of the injection molding machine.
3. The injection speed during mold injection production, at three-quarters of the stroke, should not be less than 10% of the rated maximum injection speed or more than 90% of the rated maximum injection speed.
4. The holding pressure during mold injection production should generally be less than 85% of the actual maximum injection pressure.
5. The clamping force during mold injection production should be less than 90% of the rated clamping force of the applicable machine model.
6. During injection production, it should be easy and safe to remove products and sprue materials (usually within 2 seconds each).
7. The installation of inserts in molds with inserts should be convenient during production, and the inserts should be securely fixed.

X. Packaging and Transportation

1. The mold cavity should be cleaned and sprayed with anti-rust oil.
2. Lubricating oil should be applied to sliding parts.
3. Lubricating grease should be used to seal the gate sleeve inlet.
4. The mold should be equipped with locking plates, the specifications of which should meet the design requirements.
5. Spare parts and vulnerable parts should be complete, with a detailed list and supplier names attached.
6. Sealing measures should be taken for the water, liquid, gas, and electric inlets and outlets of the mold to prevent foreign objects from entering.
7. The outer surface of the mold should be painted, according to customer requirements.
8. The mold should be packaged to prevent moisture, water, and damage, according to customer requirements.
9. The mold product drawings, structural drawings, cooling and heating system drawings, hot runner drawings, parts and mold material supplier details, user manuals, trial reports, factory inspection certificates, and electronic documents should be complete.

Acceptance Judgment

1. The mold should be checked against this standard item by item, and acceptance records should be made.
2. Acceptance judgment is divided into qualified items, acceptable items, and unacceptable items. If all items are qualified or acceptable, the mold is qualified.
3. If the number of unacceptable items is: one for product; one for mold material; four for mold appearance; two for ejector, reset, and core pulling; one for cooling system; two for casting system; three for hot runner system; three for forming parts; one for production process; three for packaging and transportation; then the mold needs to be rectified.
4. If the number of unacceptable items is: more than one for product; more than one for mold material; more than four for mold appearance; more than two for ejector, reset, and core pulling; more than one for cooling system; more than two for casting system; more than three for hot runner system; more than three for forming parts; more than one for production process; more than three for packaging and transportation; then the mold is judged as unqualified.