There are two types of threads on plastic parts: external threads and internal threads. External threads with low accuracy generally use lateral core-pulling mechanism. The internal thread has two structures: forced ejection and automatic ejection.

Mass production of threaded cover requires automatic unscrew thread injection molds. This article introduces the automatic unscrew thread structural design of the screw cap. Let’s dive in together.

The size of this thread cover is larger. The product has a diameter of 149.11mm and a height of 43.09mm. Because the product size is large, the mold only has one cavity. The product picture is shown below.

Three-point inlet into the fine nozzle. Because of the large size of the product, this design is needed. Because the material flow is more uniform, the product denaturation is relatively small. Round products usually use this gate design.

The overall size of this mold is: 550mmX750X816mm. The three-plate mold structure is a medium-sized mold. As shown below.

The thread part adopts the automatic unscrew thread structure, which is realized by the rotation of the gear driven by the oil cylinder. As shown below.

The structural accessories of the thread are shown below. The thread-removing mechanism adopts the “rack + gear” mechanism. The oil cylinder drives the rack, the rack drives the main gear G1, and the main gear G1 drives the large gear G2. The large gear G2 drives the main shaft gear G3 to rotate. To achieve automatic thread ejection of the product.

Design details of threaded structural parts

The product is right-handed double-ended thread. Tooth pitch = lead / head number. Number of retracted teeth required: total stroke/pitch +0.5.

Screw pitch

The retraction pitch of the tooth axis should be the same as that of the product, and the angle can be different.

Locating pin and stopper

The positioning pin is used to fix the dental shaft and the gear. The positioning pin can ensure the synchronous rotation of the dental shaft and the gear, but it cannot prevent the gear from falling down, so a block must be designed.

The transmission ratio of the main shaft gear G1 and the large gear G2 is preferably above 1:2.5, so that the smaller the driving force of the oil cylinder is, the smaller the transmission ratio.

1. Support the dental shaft and withstand the injection pressure.

2. The product thread retreats back against the inner belt of the dental burr. If it does not, it will only rotate in place.

3. Adjust the height of the dental shaft, and adjust the height and tightness through the three U-shaped grooves behind the tooth. After adjusting it, fix it with a constant-height screw. It is not easy to loosen the screw with a washer.

Cooling system

The products on the rear mold side are cooled by double rotating water transport.

Ejection system

The thimble ejects the product, and the arrangement of thimble is shown.

Most automatic unscrew thread injection molds are multi-cavity molds. Excluding larger-sized threaded plastic parts. Multi-cavity threaded injection mold means more mechanisms. This threaded lid mold is relatively simple. The complex thread mechanism can be expanded by referring to this article.

Among auto molds, auto injection molds are the most common molds. In auto injection molds, there are two main distinctions. One is the exterior and interior parts of the car, and the other is the structural parts.

On the complexity of auto mold structure. The car exterior structure is headed by a bumper. Car interiors are led by instruments. Automotive structural parts should be led by automotive air conditioners and intake manifolds.

The example studied in this article is the air outlet of an automobile brand air conditioner. Let’s dive in together.

The plastic parts are automobile air conditioning vents. There are many ribs and undercuts inside. The plastic material is crystalline engineering plastic PBT + PCGF10, with an average wall thickness of 2.0mm.

There are many external ribs and undercuts on the plastic parts, and the wall thickness is uneven. This is prone to injection defects such as short shots and unsatisfactory filling. Therefore, the position of the parting surface of the plastic part, the slider mechanism and the depth are the design difficulties.

In order to improve production efficiency, this car mold adopts a 2-cavity structure. Simultaneously mold 2 plastic parts of air outlet.

The fixed part is shown in the figure below. The staubli water collector is installed in the fixed mold. This is to adapt the customer’s injection molding machine. The angle pin is used to drive the slider. The positioning block is that there is no deviation when the mold is opened and closed. Because the mold size is relatively large.

Movable mold of auto mold

The moving mold part of the car mold is shown in the figure below. The cooling system is in the movable mold. Pay attention to the cooling water connection of the slider. Sink the B board first, and then connect from the B board. The design of the cooling water channel should try to ensure that the mold cools evenly and quickly. To shorten the molding cycle. The temperature difference between the water inlet and outlet of the mold should be <2°C.

Gate System

The injection mold adopts hot runner valve gate system. As shown below.

Auto mold molding part

According to the characteristics of the product, there are ribs and undercuts on all four sides. And plastic parts are not straight channels. Therefore, 4-sided slider is seted. Three of the sliders are controlled by inclined guide posts. One is controlled by the cylinder.

The touch surface between the slider and the fixed mold is inclined at 5 °. The larger the angle, the better. In order to better cooperate with each other and reduce wear. As shown below.
The inner slide of the product increases positioning interlock. Prevent the slider from being misaligned. as the picture shows.

Slider Mechanism

Inserts are embedded on the outside of the slider. As shown below. The benefits of this are:

1. During the EDM process, the entire slider does not need to stand up. The inserts are processed separately to reduce the processing cost.

2. The insert has a shut off surface, which is convenient for later replacement.

In addition, the area shown in the figure below is marked in red. Remind CNC and EMD to leave a margin during processing. These margins are used for assembly mold debugging.

There is snaps at the side of the product. The slider is provided with a delayed ejection mechanism for inserting needles. This is to prevent the snaps of the product from being damaged by stress when the slider is detached. As shown below.

The slider base adopts a splicing structure. This can save steel and process faster. And the mating surface can be disassembled and assembled separately, which is convenient for mold matching. As shown below.

Ejector System

The ejection system of this set of automobile molds adopts the mechanism combination of lifter and ejector.

3 small lifter structures. The lifter guide design adopts the lifter base as the guide, which is simple and practical.

There are many similar auto molds. The complex injection mold lies in the clever use of the mechanism. The grasp of its details is also very important.

If you have any questions about injection molds, please feel free to contact us for technical support.

Large injection molds mean high manufacturing costs. Compared with general injection molds, it has larger size and weight. Difficulties in the manufacturing, transportation, and installation of molds. So when designing, we have to combine many factors.

This article is a case study of injection molds for refrigerator transparent cabinets. This is a very classic case. 

This plastic part belongs to the thin shell box structure. Its surface requirements are very high. Its maximum size is 405mm × 368mm × 195mm, its wall thickness is 2.50mm, and its weight is about 1.1kg. Another characteristic of this plastic part is the complex core-pulling structure. It has a total of 4 undercuts. The undercut -3 and the undercut-4 form an angle of 46 ° with the mold opening direction. This is a difficult point in mold design. The plastic material is transparent PS with shrinkage rate of 0.5%.

The mold base adopts non-standard mold base. The dimensions are 900mm × 800mm × 895mm. This is already the category of large molds. The detailed structure is shown below.

The mold base adopts non-standard mold base. The dimensions are 900mm × 800mm × 895mm. This is already the category of large molds. The detailed structure is shown below.

The forming parts of this mold are composed of inserts 3, 9 and sliders 10, 30, 46 and cam 39. The inserts on both sides of the movable mold adopt the structure of wedge blocks -8,-33. The wedge tightening angle of the wedge block is 3 °. This is to ensure the accuracy of the mold and facilitate the installation and disassemble of large inserts.

The side core-pulling mechanism of the mold mainly includes four parts: three on the outer side and one on the inner side. Two of the outer cores adopt the conventional structure of “angle pin + slider”. It mainly includes angle pin -12, a slider -10, a locking -7, a stop pin 14, and a positioning ball 15. The other outer core is a “hydraulic cylinder + slider” structure. The parts include a hydraulic oil cylinder 42, a stopper 45, and angle pin 46. Although the cost is increased, the extraction and reset of the oblique slider is stable and reliable.

The oblique inner core pulling is the most difficult part of this mold. Since Pulling downward direction 46 °. Conventional cam structures cannot complete this process. Otherwise it will cause severe deformation of the plastic parts. To be able to solve this problem. When designing, the guide groove of the cam base is inclined by 46 °. This structure is simple and reliable. In addition, the inclined top adopts a split structure. It saves material, and is convenient for loading and unloading and maintenance. This part of the structure includes a cam 39, a link bar 47, a small slider 48 and a cam base 49.

Large molds use large sliders. Compared with ordinary sliders, the movement principle is the same. The inclined angle of the angle pin is 15 ° ~ 25 °. The locking angle is 2-3 degrees larger than that of the angle pin.

1. The angle pin is pulled out differently. See Figure L2 B-B.

2. The shape is different. The center is dug and the sliding surface is processed to lubricate the oil storage tank.

3. It is best to design craft screws on the top of the slider. Easy to process and install.

4. Add a central guide block. See picture L3.

5. The larger the safety distance, the better, if there is space. The core drawing distance is generally 8-10mm greater than the depth of the plastic part. ,

6. Be sure to add water to cool. As shown L3.

7. Both sides of the slider must be widened and guided by the quenched pressure block. As shown L3.

8. Be sure to add wear-resistant blocks on all friction surfaces, including the bottom of the slider. As shown L3.

The design of the cooling system directly affects the molding cycle of the mold and the accuracy of the plastic part. This is especially important for large mold cooling systems. The molds use straight-through cooling water channels. Its large number and reasonable location make it a classic.

All cooling water channels in the moving and fixed mold inserts are uniformly arranged along the cavity surface. This can be a rapid cooling of the mold. The temperature of each part of the cavity is balanced. Conducive to improving the accuracy and production efficiency of plastic parts.

The size of the cam of the mold is large, and the contact area with the melt is large. A large amount of heat is absorbed during molding, and this part of the heat must be discharged in time. Otherwise it will affect the molding cycle. In severe cases, the cam may become stuck. The cam of the mold is sufficiently cooled, as shown in the figure L4.

Same as the case of cam. The slider of this mold also needs to be cooled. The layout of the watercourse is shown in the figure L1,L2,L3.

For large transparent thin-walled plastic parts, the ejection system is a difficult point. The ejection system of this mold is composed of stripper bar 13, 28, 34 and high-pressure gas valves 37, 38. The high-pressure gas valve on the fixed mold side is mainly used to blow gas into the cavity when the mold is opened. Prevent the plastic parts from sticking to the surface of the cavity on the fixed mold side. It should be particularly noted that pushing the bottom surface with a ejector pin will leave obvious marks. The push-out effect is very poor, and the plastic parts are easily whitened, deformed, and even worn. The best choice is to use stripper bar and air push.

During the working process of the injection mold, the parts will move and rub against each other. The design of the guidance system can ensure the relative position accuracy of the mold and the safety and reliability of the parts. The guide parts of the mold include a movable template guide post 25, a guide sleeve 27, a push rod fixing plate guide post 21, a guide sleeve 23, and a small slider 48, a base 49 and a clamp and a guide block . The positioning parts include a positioning block 35, a stopper pin 14 and a positioning ball 15 of the slider, a stopper 45, and a cone-shaped positioning groove on the cam.

When designing large molds, you must have a complete set of thinking methods and skills. From the perspective of the force components of the mold, rigidity should be considered. For injection molding, the melt should fill the cavity quickly and orderly. In terms of plastic part quality and production efficiency, the mold should be kept at a constant temperature to speed up the entire heat exchange process.

In order to smoothly ejection the plastic part from the cavity and the core during mold opening. The inner and outer surfaces of the plastic part must be bounded by the parting line of the mold, and a reasonable draft angle should be set. The draft angle of  plastic part prevents the plastic parts from sticking to the mold, which causes the plastic part to deform. The draft angle is generally 3°-5°.As shown below.

The inner side and the outer side of the plastic part are ejection in the same direction. Draft angle of the female mold should be larger than the draft angle of the male mold. The purpose of this is to leave the plastic part in the male mold and facilitate the ejection of the plastic part. As shown below.

1.The higher the height of the plastic part, the deeper the hole, and the plastic part with more forming holes takes a larger draft angle.

2.A plastic part with a large wall thickness can take a larger value.

3.For products with higher precision requirements, avoid excessive draft angle.

The draft angle should be selected according to the type and rigidity of the plastic. Hard plastics and plastics with large shrinkage have a large draft angle. For reinforced plastic products, a large draft angle should be used, and the draft angle is generally 1°-1°30′.

If the draft angle is not large enough, the plastic surface is prone to burrs and whitening. Below are the draft angles for different surface requirements.

1.The matte surface has a draft angle of 2 degrees or more.

2.Textured surface draft angle is 3°-5°.

3.The draft angle of the text and pattern is 8°-10°.

4.The draft angle of the symbol surface is greater than 10°

5.The draft angle of the symbol surface is greater than 10°

Textured depth and corresponding draft angle

The release angle in the table is determined based on ABS plastic. In actual use, it should be adjusted according to the molding conditions, molding materials, and wall thickness.

Plastic parts should be set to a reasonable draft angle. Refer to the shape, material, molding conditions, wall thickness, surface texture, etc. of the plastic part. If you still have questions, please contact us.

We may need metal casting molds in many field. Do you know the process of manufacturing metal casting molds?

To form the sprue — a passage through which you’ll pour the metal — measure the depth of the cope, and mark this distance with tape on the side of a section of thin-walled 3/4-inch pipe. Push the pipe straight down into the sand in the cope, in a spot where it will not hit the pattern. Twist the pipe back and forth to cut an opening through the sand, stopping when the tape mark meets the surface of the sand. Use a slick to carve a funnel shape in the sand around the pipe, beveling the edges of the sprue opening. Then slip the pipe out, with the sand core inside, leaving a passageway through which you’ll pour the molten metal.

On the other side of the pattern, form the riser opening — the passage into which excess metal will rise — by using a slightly larger diameter pipe to cut through the sand in the cope.

Use a 1/16-inch welding rod or a stiff wire (a bicycle spoke is ideal) to poke channels through the sand in the cope, so that hot gases can escape. Push the rod into the sand, stopping about 1/2 inch from the pattern. Make about a dozen vents over the pattern area.

Lift the cope from the drag and set it on edge, off to one side, where it will not be disturbed.

Before lifting the pattern from the drag, firm the pattern edge of a water-based sand mold by moistening it with a molder’s bulb or a small brush dipped in water. This will help to keep the sand from collapsing when the pattern is removed. Screw draw pins into the holes in the back of the pattern and lightly tap the pattern to loosen it from the sand. Then gently pull on the draw pins, lifting the pattern straight up and out of the casting cavity.

Using a piece of sheet metal bent into a 1/2-inch-wide U shape, cut a channel, or gate, running from the casting cavity to the riser position. Lift out a bit of sand at a time, forming a gate slightly smaller than the diameter of the riser and slightly shallower than the depth of the casting cavity. Scoop out a similar gate from the casting cavity to the sprue position. For large molds, cut several gates to the sprue and the riser from various parts of the casting cavity. Blow out or tamp down any loose bits of sand in the gates.

Rebuild crumbled sections of the casting cavity by adding bits of moist sand, smoothing it into place with molding tools. Tamp down or blow away all loose sand to prevent it from mixing with the molten metal when the metal is poured.

Replace the cope over the drag and set the flask, still on the bottom board, in the sandbox near the furnace. If you are not going to pour the casting immediately, cover the mold to keep dirt from falling into the sprue and riser.

With a helper, lift the crucible shank and hook its safety lock over the lip of the crucible by pushing the latch forward. Lift and tilt the crucible a few inches above the mold, pouring the molten metal quickly and steadily into the sprue, or molten metal passage, into the cast. Stop pouring when the metal nearly reaches the top of the riser. Immediately, while it is still molten, pour all the extra metal into the ingot mold. Leave the casting mold in place until the metal in the sprue and in the riser is hard. To test the newly cast metal for hardness, tap it with the tongs.

When the metal has hardened, carry the mold to the sand-storage area. Wearing gloves, separate the cope and the drag. Lift out the hot metal casting with tongs. Break apart the sand in the mold, and dump it back into the sand-storage container. Set the casting aside to cool, leaving in place the extrusions that the sprue, riser, and gates formed.

When the casting is completely cool, cut off the gates with a hacksaw and file down the rough areas. Finish the surface as desired.