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Injection Mold Trial Knowledge

Injection Mold

Mold Inspection And Acceptance


In order to ensure that the mold can produce qualified products, it can be put into production normally, ensure the production service life of the mold, and meet the production and use requirements of product design.

The standard recognizes the standards of molds in terms of product quality, mold structure, injection molding process requirements, etc., and evaluates mold quality accordingly. Through training, we understand the mold trial process and precautions of plastic molds.


  1. Familiarize yourself with the mold trial process and key precautions during the mold trial process by understanding the following materials.
  2. Understand the actual mold trial process by visiting the mold trial site for practice.
  3. Inspect the mold appearance, mold material, pouring system, mold support, reset, core extraction, extraction, exhaust, water transportation system, injection molding process molding system, product appearance, size and function coordination for acceptance

As the mold acceptance party, there are things that should be clarified before and during mold trial.

Before mold trial:

(1) In the mold design stage

During technical communication with the mold manufacturer, it is necessary to confirm the applicable machine for the mold, production capacity requirements, whether to use automatic production, mold life requirements, shrinkage rate settings of product materials, mold structure ( Judgment based on the glue feeding method of the mold), the design of the PL line.

For important appearance parts, mold manufacturers are also required to conduct mold flow analysis in order to better foresee and evaluate possible defects in the mold during production.

(2) After mold manufacturing is completed, before the first mold trial is carried out

Confirm whether the mold has enhanced protection devices (such as whether there is a forced retreat mechanism or an ejector plate limit switch mechanism. These mechanisms ensure that the mold will not be damaged under abnormal conditions)

Confirm whether the ejection and retraction mechanism of the mold has been installed.

The common ejection and retraction mechanisms include the pull rod mechanism (you need to confirm whether the pull rod is balanced and whether the number of pull rods is sufficient) and the oil cylinder mechanism.

Sometimes there is a gas-assisted ejection assist, depending on whether the nozzle needle is made into a Z shape to pull. Stay in the cold material position (it is found that the nozzle is often stuck to the mold in workshop six production).

The end surface of the return rod is flat and there is no spot welding. There is no gasket at the bottom of the embryo head, it is spot welded.

Any mold that makes a slider should have an oil groove at the moving part of the slider.

After the mold is installed on the injection molding machine, do not rush to adjust the injection mold immediately. Instead, ask the technician to set the injection molding machine to manual operation and require the technician to manually perform each action of the mold.


  1. Eject the ejector pin (determine whether the ejection is smooth and balanced, whether the position is sufficient for the product to fall off, and whether there is any abnormal friction sound)
  2. ​​Reset the ejector pin (whether the ejector pin can be returned to its original position? If not, it will cause damage to the front mold membrane cavity. You should check it in time. Then proceed to the next step)
  3. ​Whether the ejector pin has a limit device and whether the slider can slide into place.
  4. Whether the mold can be closed and opened normally.

Office Chair Backrest Mould

Mold Adjustment

In addition, in addition to the size, appearance and other defects of the sample itself, it must also be combined with an overall assembly confirmation. Therefore, every time you try out the mold, you must try to bring all the assembly parts with you.

The overall assembly confirmation can provide a more direct understanding of the assembly problems existing in the trial mold product. In addition, it can more conveniently analyze the modification plan for the existing assembly problems. It can avoid complexity and save time.

Acceptance of molds, introduction of new molds before mold trial and mold trial process

  1. Make it clear that all the problem points have been solved, and there are no problems after normal production of a certain quantity (for example, 5,000 beers) on the designated machine.
  2. Identify the wearing parts of the mold and require the mold workshop to provide spare parts for wearing parts to prevent production from being affected by damage to wearing parts during production.
  3. It is required to apply anti-rust paint on the exposed parts of the mold and make the name of the mold. ​
  4. Defects are not allowed on the product surface: lack of material, burnt, white top, material flowers, burrs, blistering, whitening (cracks, breaks), shrinkage, snake marks.

Mold Appearance

  1. The mold name must be complete, with clear characters and neat arrangement.
  2. The cooling water nozzle should not protrude from the surface of the mold base. ​
  3. The cooling water nozzle should have entrance and exit marks. ​
  4. The marked English characters and numbers should be larger than 5/6, and the position should be about 10mm from the faucet. The writing should be clear, beautiful, neat, and evenly spaced.
  5. Mold accessories should not affect the lifting and storage of the mold. During installation, if there are exposed oil cylinders, water nozzles, pre-reset mechanisms, etc. below, they should be protected by supporting legs. ​
  6. When installing the support legs, screws should be passed through the support legs to fix them on the formwork. If the support legs are too long, they should be processed with externally threaded columns and fastened to the formwork. ​
  7. The size of the mold ejection hole should meet the requirements of the specified injection molding machine. Except for small molds, only one center cannot be used for ejection. ​
  8. The positioning ring should be fixed and reliable. The diameter of the ring is 100mm and 250mm. The positioning ring should be 10~20mm higher than the bottom plate. Unless otherwise requested. ​
  9. The external dimensions of the mold should comply with the requirements of the designated injection molding machine. ​
  10. When installing molds with directional requirements, the installation direction should be marked with an arrow on the front or rear template.
  11. There should be no pits, rust, excess lifting rings, water vapor in and out, oil holes, etc. on the surface of the mold base, as well as defects that affect the appearance. ​
  12. The mold should be easy to hoist and transport. Mold parts must not be disassembled during hoisting. The lifting rings must not interfere with faucets, oil cylinders, pre-reset rods, etc. ​

Eject, reset, pull out the insert core, and remove parts

  1. When ejecting, it should be smooth, without stagnation or abnormal sound. ​
  2. The surface of the sloping top should be polished, and the sloping top surface should be lower than the core surface. ​
  3. The sliding parts should have oil grooves and the surface should be nitrided.
  4. All ejector pins should be positioned to prevent rotation, and each ejector pin should be numbered. ​
  5. The ejection distance should be limited by the limit block. ​
  6. The return spring should be made of standard parts, and both ends of the spring should not be polished or cut. ​
  7. The slider and core-pulling should have travel limits, and the small slider should be limited by a spring. When the spring is inconvenient to install, you can use wave screws. The core pulling of the oil cylinder must have a travel switch.
  8. The core-pulling of the slider generally uses an inclined guide post, 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, an oil cylinder should be used to extract it. ​
  9. If the slider width exceeds 150 mm, there should be a wear-resistant plate under the large slider. The wear-resistant plate should be 0.05~0.1 mm higher than the large surface, and an oil groove should be opened. ​
  10. The push rod should not move up and down. ​
  11. If barbs are added to the ejector pin, the direction of the barbs should be consistent and the barbs should be easy to remove from the product. ​
  12. The matching clearance between the ejector hole and the ejector pin, the length of the sealing section, and the surface roughness of the ejector pin hole should be in accordance with the standard requirements. ​
  13. When the product is ejected, it is easy to follow the inclined top, and grooves or etched patterns should be added to the ejection rod. ​
  14. The end face of the return rod is flat and has no spot welding. The bottom of the embryo head has no gasket and is spot welded. ​
  15. The gate plate of the three-plate mold guides and slides smoothly, and the gate plate is easy to pull apart. ​
  16. The limit tie rods of the three-plate mold should be arranged on both sides of the mold installation direction, or pull plates outside the mold frame to prevent the limit tie rods from interfering with the operator.
  17. The oil and air passages should be smooth, and the hydraulic ejection reset should be in place. 18. There should be an exhaust port at the bottom of the guide sleeve.

Cooling and heating system

  1. The cooling or heating system should be fully unblocked. ​
  2. The sealing should be reliable, the system should not leak under 0.5MPa pressure, and should be easy to repair. ​
  3. The size and shape of the sealing groove opened on the mold base should comply with relevant standards.
  4. The sealing ring should be smeared with butter when placed, and should be higher than the surface of the mold frame after placement. ​
  5. The water and oil flow channel spacers should be made of materials that are not susceptible to corrosion. ​
  6. The front and rear molds should use centralized water supply.

Gating system

  1. The gate setting should not affect the appearance of the product and satisfy the product assembly. ​
  2. The cross-section and length of the flow channel should be designed reasonably. The process should be shortened as much as possible while ensuring the forming quality. The cross-sectional area should be reduced to shorten the filling and cooling time. At the same time, the plastic loss in the pouring system should be minimal. ​
  3. The cross-section of the three-plate mold sub-runner on the back of the front formwork should be trapezoidal or semicircular. ​
  4. The three-plate mold has a feed head on the gate plate. The diameter of the sprue entrance should be less than 3 mm. There is a 3 mm deep step recessed into the gate plate at the ball head.
  5. Gates and runners should be machined according to the drawing size requirements, and grinding machines are not allowed. ​
  6. Point gate The gate should be in accordance with the specifications. ​
  7. There should be an extension at the front end of the runner as a cold material hole. ​
  8. The Z-shaped undercut of the pull rod should have a smooth transition. ​
  9. The runner on the parting surface should be circular, and the front and rear molds cannot be misaligned.
  10. The latent gate on the ejector rod should have no surface shrinkage. ​
  11. The diameter and depth of the cold material cavity for transparent products should comply with the design standards. ​
  12. The material head is easy to remove, there are no gate marks on the appearance of the product, and there is no residual material head at the product assembly area. ​
  13. For curved hook latent gate, the two parts of the insert should be nitrided.

Molding part, parting surface, exhaust groove

  1. The surface of the front and rear molds should not have unevenness, pits, rust and other defects that affect the appearance. ​
  2. The parting surface should be kept clean and tidy, and the sealing parts should be free of dents.
  3. The depth of the cut surface of the exhaust groove should be less than the overflow value of the plastic. The air groove can be deepened about 10mm away from the cut surface.
  4. The inserts fit in place, are placed smoothly, and are positioned reliably. ​
  5. Inserts, inlays, etc. should be reliably positioned and fixed, round parts have anti-rotation, and no copper or iron sheets should be placed under the inlays.
  6. The end surface of the ejector pin is consistent with the core. ​
  7. There are no defects such as undercuts and chamfers in the front and rear molding parts. ​
  8. For multi-cavity mold products, the left and right parts are symmetrical and should be marked with L or R. If there are requirements for position and size, they should meet the requirements. Generally, they should be added where they do not affect the appearance and assembly. ​
  9. The mold base locking surface fit (flying mold) should be in place, with more than 75% of the area touching. ​
  10. The ejector pin should be arranged closer to the side wall and next to the ribs and bosses, and a larger ejector pin should be used. ​
  11. For the same pieces, the numbers 1, 2, 3, etc. should be marked for easy identification. ​
  12. Each collision surface, insertion surface, and parting surface should be in place with the trial fit (flying mold). ​
  13. The sealing part of the parting surface should comply with the design standards. ​
  14. The skin texture and sandblasting should be uniform and meet the requirements. ​
  15. For products with required appearance, the screws on the products should have anti-shrinkage measures. ​
  16. When the front mold is inserted into the rear mold or the rear mold is inserted into the front mold, the surroundings should be locked with bevels and machined to avoid voids.

Injection molding production process

  1. The mold should have the stability of injection molding production and the repeatability of process parameter adjustment within the range of normal injection molding process conditions.
  2. The injection pressure during mold injection molding 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 molding production, the injection speed of the three-quarter stroke shall not be less than 10% of the rated maximum injection speed or exceed 90% of the rated maximum injection speed. ​
  4. The holding pressure during mold injection molding 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 model. ​
  6. During the injection molding production process, the removal of the product and nozzle material must be easy and safe (the time generally does not exceed 3 seconds each). ​
  7. For molds with insert products, the inserts should be installed easily during production and the fixing of the inserts should be reliable.

Contact Person: Alex Chu
WhatsApp/ WeChat: 0086 18968677763
Email: sc10@solidcomould.com
Website: www.solidcomould.com

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