Plastic Injection Mold Design Standard

As you know plastic injection mold is Base of industry, a great mold design will define the industry success or not, more and more people are involve in mold area currently. Different mold design engineer will design mold differently, but to avoid make a big mistake during mold design stage, and avoid bring difficult or problem to mold making or mold manufacturing stage. we need a mold design standard or injection mold basics to follow. So that the mold design engineer can follow it during the mold design stage.

Today let’s dig into the mold design standard, which is our company design guide from decade years design and mold building experience. Follow this mold design guideline will guarantee you mold life and mold working smoothly.

How to chose injection mold material

Part NameSteel StyleHeat treatmentRequirmentsRemarks
Mold Cavity and Core material Value2344QuenchingHRC48-52
Mold Cavity and Core material Value8407QuenchingHRC48-52
Mold Cavity and Core material ValueS136QuenchingHRC48-54
Mold Cavity and Core material ValueS starQuenchingHRC48-52
Mold Cavity and Core material ValueNAK80
Mold Cavity and Core material Value718H
Insert of SliderSame as the Cavity and core MaterialSame as the Cavity and core MaterialNo shut-off
Insert of Slider8407Quenching HRC48-52Have shut-off
Angle Lifter738HNitriding300k times or less
Angle Lifter2344Quenching HRC48-52Avoid using S136 and 2083 hard in any case
Slider BaseH13QuenchingHRC48-52Hardness according to customer requirement
Jaw2510QuenchingHRC52-54Hardness according to customer requirement
Ware Plate2510QuenchingHRC52-54
Jib2510QuenchingHRC52-54
Sprue BushingH13QuenchingHRC48-52
Ejector plate,KNOCKOUT Pillar,Gear,BearingP20All Injection mold

Injection Mold Insert design guide

A.The Function of the Plastic mold insert:

  1. good ventilation effect
  2. easy to process and easy to replace
  3. good polishing effect
  4. Logo and code are easy to process
  5. Help heat dissipation (Beryllium Copperinsert)

B.Design key-points:

1. The Bracket of Mold inserts should be in a straight and flat (as shown below).

ear mold insert

2.The bracket should be made on the long side of the insert. The insert should not be angled as much as possible. It should have a rounded corner of about 0.30mm.

mold cavity and core insert

3.The support position should be shorter than the straight position, and the two sides should have a flat position of 0.50~.2.00mm. Width of the bracket W to fit the insert size, and the ratio of H to W is 3:2. It is now required that the height of the bracket should be at least 5mm and the width should be at least 1.5mm.

insert mold making

4.When it is not convenient to make the bracket, the insert is made to have a draft angle of 1°~2°, if the draft angle around the insert is to be finished with the finished product. When the angle is output, the minimum angle is 1/4° or the tolerance range is beveled. Note that the projection length of the upper and lower heights generally exceeds 0.15 mm, otherwise the fit mold is difficult. (as shown below)

insert for mold

5.In general, there are three ways to design inserts:

Figure A: This design insert can be directly processed, and the processing is simple and convenient. However, the position of the glue position during polishing cannot be determined. If it needs to be polished, it must be assembled. (Used when the beer is easy to take the materials of the front)

Figure B: This design can ensure that the insert line is not visible on the product. When designing, the straight position must be extended into the glue position by 0.5mm to prevent the product from being glued. (Used when special requirements are required)

Figure C: This design ensures that the product can be polished well, and there is no problem that the R angle may occur due to the product requiring a right angle and the line is cut. (in general, this method is used)

insert mold process

6. The edge of the insert can not be sharp, and the minimum is 0.5 mm Radius.

7. Straight Ejector plate is made as square as possible, loaded from the mold surface, and fixed on the needle plate with screws. The profiled Ejector plate top and the lower hanging table are not easy to fit.

Plastic mold Steel order guide

Square inner mold and square large bulk material

Hardening material with precision machining:

dimension of material<400mm, add 0.3mm balance on single side.

dimension of material≥400mm, add 0.5mm balance on single side.

Hardening material with roughness machining:

dimension of material<400mm, add 1.5mm balance on single side.

dimension of material≥400mm, add 2.0mm balance on single side.

Steel material without Hardeness: Add 3mm in each direction.

Inner mold small insert material: When the length of the three sides is less than 50mm, the material need to be ordered together; the material layout of insert is considered to minimize the cross-sectional area when wire cutting process, so as to save the cost and time of wire cutting. The layout requirements are as follows

  • Inserts with high precision, 3mm interval
  • JAW equally spaced 0.5mm
  • Shaped parts have draft angle,add 5mm on height direction

The circular inner mold needs to be heat treated and then finished with a precision grinding machine. The length direction is plus 15mm.

Beryllium copper and bronze have no precision material, leaving a margin of 1mm in the length and width direction and a 0.5mm margin in the thickness direction.

Order the insulation board with a thickness of 6 or 8mm. The outer dimensions are 3mm smaller than the single side of the mold clamp plate.

Injection mold Slider design

Mold Slider design keypoints

  • The height of the JAW must have 2/3 of the height of the slider, exceeding the center of gravity of the slider (because the slider is usually horizontally placed)
  • The angle of the slider angle surface is generally specified within 10 to 25 degrees
  • The angle of angle pin is 2 degrees larger than the angle of slider
  • The slider travel distance is more than 3mm longer than the maximum undercut length
  • The slider width is more than 160mm, and the guide block should be added in the middle of the bottom of the slider.
  • The width of the slider  is more than 100mm, 2 angle pin need to be added.
  • When the slider height is too high, lower the starting point of the angle pin hole so that the slider slides smoothly (see the figure below)
plastic mold slider with heel block

Increase angle pin hole into a ring shape, and the mold Slider will have a delay function when the injection mold is opened (see the figure below).

Slider mold manufacturers

The length of the Angle pin into the hole is more than 175mm, and the slider should be Moved by hydraulic cylinder.

Mold Heel Block Design Guide

When the height of injection mold slider is more than 2/3 of mold cavity’s height, it is best to make the mold slider directly on the mold cavity, no need to make the slider separately.(see the figure below)

mold slider

When the slider depth is mainly in the mold core side, the Heel Block is made into inserts, and when the molding parts with big surface , caused the slider is big, The Heel Block Should be made into an anti-lock styles (see the figure below)

Mold slider calculation

When the slider is small, the Heel block can be made into the following figure, and its height H is greater than or equal to 2/3 times of the slider height.

(see the figure below)

Mold slider design

Mold slider Positioning Method

Spring
Plunger Ball
DME slider retainer
Hydraulic cylinder

The situation need to use Springs to fixing the Slider

  • The mold slider movement up or diagonally
  • There are protruding small inserts or Pins in the slider
  •  There is ejector pin at the bottom of the slider

The situation need to use Plunger ball to fixing the Slider

  • The mold slider is side or downward movement, and it is generally reliable to use a diameter of 6 mm or more.

Method of hiding mold springs

  • The spring is placed in the slider
  • When the springs installing over 50mm, consider external spring
  • Spring hidden under the slider with dowel pin as Push bar
Injection mold slider and lifter

Gib and wear plate

Material: 2510 HRC52-54 (HRC54-56)

Export Mold GIB & Wear plate design method

mold slider angle with GIB

Domestic Mold GIB & Wear plate design method

plastic mold slider

Lifter design for injection mold Guide

Function: The Molded part have undercut need to use lifter to eject the part out from mold.

Design requirements:

The angle of lifter is generally within 3~10 degrees range, Normally taking 5 degrees.

In order to prevent the shovel from appearing during the lifter movement, the top plastic position of the lifter is usually add material by 0.03~0.05mm. (See the figure below)

According to the shape of the product, considering the thickness of the lifter head (requires at least 5mm), the design method is as follows: A.B two design methods: (must have a straight body)

The thickness for the guide block of lifter below the B plate is 12mm, and the M5 cup head screw,material is made of bronze.

Mold Spring design

First, the scope of use:

The mold spring is mainly made up of a rectangular flat-line coil spring. If the diameter is less than 10mm, the round wire can be used.

All springs must be worn through the shaft to prevent the spring from being suspended when moving, and the amount of compression of the spring in the mold, It is related to the life of the mold, as follows:

  • When the mold life is below 300,000 times, the compression ratio does not exceed 45%
  • When the mold life is less than 500,000 times, the compression ratio does not exceed 40%
  • When the mold life is more than 1 million times, the compression ratio is not more than 35%.
  • When designing the spring, the preloading length must be taken into account, generally 5~15mm. (often take 10mm).

Calculation method of spring length:

Example 1: The Guide pin with spring requires a stroke of 30 mm to calculate the length of the spring. (Mold life is 1 million times)

  •          Length L=(30+10)/35%=40/35%=114mm   Therefore, the length of the spring can be taken as 120mm.
  •          The depth of the spring hole is L1=120-30 (stroke)-10 (preload)=80mm

O ring mold design

function:

Prevent water leaking out of the mold.

Classification of O-ring:

  1. Ordinary o-ring: suitable for mold temperature of -30~80 degrees
  2. High temperature o-ring: suitable for mold temperatures between -15 and 150 degrees

O-ring selection:

  1.  Ordinary O-ringcan be used for molds that generally use water.
  2. If the material of Injection(such as PC, PA, etc.) needs to use hot water or hot oil, it must use high temperature rubber ring.

O-ring size writing (if the O-ring wire diameter is 2.5mm): O.D A x 2.5d (A indicates the outer diameter of the O-ring )

O-ring size calculation method: O-ring outer diameter A = Cooling channel hole diameter + 8mm

The Vonosat molds for export are all required to process O-ring slot in full accordance with the HASCO standard.

Common O ring parameter table

Cooling Channel DiameterO Ring Groove outer diameterO ring Section DiameterO ring outer diameterO ring Groove section WidthO ring Groove section Height
4mm13mm2.5mm12mm3.35mm2.0mm
6mm15mm2.5mm14mm3.35mm2.0mm
8mm17mm2.5mm16mm3.35mm2.0mm
10mm19mm2.5mm18mm3.35mm2.0mm

Injection mold Cooling design

Function: maintain the temperature of the mold at the injection molding and cool the finished product

Cooling Channel Design Guide

  • The mold cooling Channel and the mould parting surface and other parts should be kept at a certain distance, as follows:
  • The distance between the mold cooling Channel and the mould parting surface shall not be less than 1 times the diameter of the mold cooling Channel.
  • The distance between the mold cooling Channel and the Ejector pin or screw should be more than 6mm, and at least not less than 3mm.
  • A minimum distance of 10 mm or a thickness of the water line plug plus 2 mm should be maintained between the mold cooling channel and the inner mold side.

The distance between the water cooling channel should be 3 to 5 times the diameter of the mold cooling channel.

Each mold cooling Channel should not be turned more than 15 times. (The number of turns using the water baffle is 4 times, and the diameter of the baffle hole is larger than the diameter of the cooling channel hole)

Each Mold cooling channel should be of the same diameter.

The position of the water plug should be designed in the same direction or as little as possible.

Labeling of the pattern letters and water characters: English or numbers are placed in front of IN or OUT.

Types and descriptions of common water plugs:

BSP Inch standard straight pipe thread (example: 1/8 “BSP”).

PT Inch standard 55 degree taper pipe thread (Example: R1/8 “This has a sealing effect, if it is G1/8″ there is no sealing effect). The BSP is the same as the PT, and the water connection can be used universally, such as: Z81/9/R1/8.

NPT American standard 60 degree taper pipe thread (example: 1/8″ NPT).

DME commonly used water plug model size and description:

Standard short Jiffy connector: JP X5Y (X indicates the size of the joint, 2 indicates the standard, 3 indicates the big head; Y indicates the size of the tooth, 1 indicates 1/8), 2 indicates 2/8″, and 3 indicates 3/8″)

Standard extension Jiffy connector: JPB X5YZ (B indicates lengthening type, X, Y is the same as above, Z is the length, 1 means 1″, 2 means 2”, and so on)

Dimensions of the water Jiffy connection:

Injection mold cooling channel

There are 2 ways to design a circular cooling insert

Figure A:This design method is best, except that the material size is slightly larger and the cost is relatively high. (this is preferred)

Figure B: This design method is worse than Figure A, but the material cost is lower than Figure A. (secondary election)

Note: All edges of the water tank and the o-Ring groove need to be added radius to prevent the o-ring from damage.

Mold making cooling channel design

The Cooling connector of the 1/8″ tooth is required to be screwed into the mold 10mm

The Cooling connector  of the 1/4″ tooth is required to be screwed into the mold 13mm;

The Cooling connector of the 3/8″ tooth is required to be screwed into the mold 15mm;

The Cooling connector of the 1/2″ tooth is required to be screwed into the mold 20mm. The drawing method in the injection mold drawing and the ordering jiffy connector when ordering the water connector must be strictly in accordance with this standard. The jiffy plug is not limited.

Plastic Injection mold cold Runner design

Circular Runner is generally used, followed by a trapezoidal Runner with a round bottom.

For multi-cavity molds, the Mold Runner balance should be designed as much as possible. Generally, a circular mold runner is selected. If the mold runner balance is demanding very high, the mold runner is designed to be trapezoidal. When designing, half one is in the Cavity side, and the other half is in the core side. In this way, the upper and lower staggered can make the inner and outer temperature of the molten Plastic break the direction when turning, basically ensuring that the temperature difference between inner of plastic and the outer of plastic is not large, thus ensuring the balance of the plastic injection.

If a runner channel is branched into two runner channels, the diameter of the branch runner channel is 20% smaller than the diameter of the upper runner channel, if a runner path has no branches, only the direction changes, the size of the runner must be keep same.

The diameter of the runner should be at least 1.0mm thicker than diameter of the gate, which avoids the material of runner is colded first than the material of part. If like that, even we increase hold pressure the material will not keep flow into part. Due to the runner already cold and blocked the material.

Slag wells and Air vent should be added at the end of the runner.

Types of injection mold gate

Side gate:

Gate size calculation method: h=nt w=2h

w = gate width h = gate depth t = Plastic thickness n = plastic constant L= takes 0.75 ~ 1 mm

Side Gate

Point Gate

Advantages: The gate is automatically separated from the finished product during demoulding without post-processing.

Disadvantages: Due to its shape, it is not possible to independently control the sealing time and Material inflow rate.

Point gate, many type of mold suitable for it , such as three-plate mold,  hot runner mold and so on.

Point Gate

Sub Gate

Advantage: The gate cools quickly and the production cycle is short
Easy to process, economical

Disadvantage:  When the diameter of the gate is large, the finished product may be dragged.
Be careful and precise when processing

Submarine gate

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