Plastic Injection Mold Manufacturing Since 2005

Introduction: The introduction of ejector injection molding in the manufacturing process has allowed for automated operations, faster production speeds, and a more efficient product. It has also improved the consistency of product design.

Even though injection molding has improved the manufacturing process, there are still many design flaws that need to be optimized. This is to make sure we have a better and more efficient product.So, in this article, we’re going to talk about ejector pins injection molding and how you can make it better.

What is an Injection Molding Ejector?

Ejectors are a must-have for making parts. They are a key part of the mold’s ejection system and determine what happens to the product when you’re making it with injection molding.Ejector injection molding is the process of removing the finished part from the mold. The mold is made of two parts: the A side and the B side.

When the plastic cools in the mold, the two parts of the mold are separated so the solid plastic can be taken out. The way the mold is built is that when it opens, half of the A side lifts up, leaving the molded part and the B side.

Ejector pins are located on the B-side half of the mold and they push the molded part out of the mold. The pin marks from the ejector mold are usually imprinted on the finished product as a dimple.

What are the Types of Ejector Pins?

There are many types of ejector pins used in product manufacturing. Here are the most common types you will find best suited for the process.

Through Hardened Ejector Pins

These ejector pins are heat treated to make sure they have the same hardness all the way around. Through Hardened pins can take temperatures up to 200°C and are best used in plastic ejection systems inside the mold.

Case Hardened Ejector Pins

Also known as Nitride H13 pins, they are harder than through hardened pins and are used in die casting ejection systems within the mold. Case Hardened pins are nitrided to 65 – 70 HRC and can withstand temperatures above 200°C.

Black Ejector Pins

These ejector pins were developed because Nitride H13 pins could not be used at operating temperatures above 600°C.

Black ejector pins are treated with a black surface to be self-lubricating and can withstand temperatures up to 1000°C. It is an expensive ejector pin suitable for metal ejection systems in automotive molds.

Ordinary Ejector Pin

The most commonly used and basic ejector pin among ejectors is the ordinary ejector pin. It is mainly made of alloy materials and is suitable for general semiconductor packaging.

Ordinary ejector pins are not only widely used in the electronics industry, but also have many applications in the fields of automobiles, medical treatment, and home appliances.

Metal Ejector Pin

Metal ejector pins are made of alloy materials, but they have a gold plating process added to them, which makes them look better and last longer than regular ejector pins. Metal ejector pins are used a lot in high-end electronic products and optical instruments.

Ceramic Ejector Pins

Ceramic ejector pins are mainly used in high-frequency and high-temperature environments because ceramic materials have excellent heat resistance, corrosion resistance, and wear resistance. They are suitable for complex packaging structures and high-precision packaging fields.

Needle Plate Ejector Pin

The needle plate ejector pin is an advanced ejector pin, mainly suitable for the packaging of MEMS chips. Compared with ordinary ejector pins, it has more uniform and delicate needles and uniform elastic properties. Moreover, the needle plate ejector pin has improved its adaptability to corrosive environments through anti-corrosion treatment and surface treatment.

Special Color Ejector Pins

Special color ejector pins are ejector pins made of special materials and special colors for the purpose of differentiation and management during the production process. Different colored ejectors can represent different production processes and different charging standards. Special color ejectors are suitable for high-end semiconductor packaging, precision testing, and other fields.

What are the Principles for Selecting Ejection Pin?

Use ejector pins with larger diameters. That is, when you have enough ejector positions, select ejector pins with larger diameters and preferred sizes.The ejector pins should be as few as possible. When selecting ejector pins, adjust the size of the ejector pins to minimize the size specifications, and select the preferred size series as much as possible.

The ejector pins you choose should be strong enough to handle the ejection. When you eject, you put a lot of pressure on the ejector pins. If you’re using small ejector pins, less than 2.5mm in diameter, you need to use a support ejector pin to keep them from bending or getting messed up.

What are the Precautions for Selecting Ejector Pins?

To prevent plastic parts from getting deformed or damaged, you need to correctly analyze the size and location of the adhesion between the plastic parts and the mold cavity, and choose the right demolding devices accordingly.

You want the ejection force to be applied to the part with the highest rigidity and strength, which is as close to the wall as possible, below the rib and pillar positions. You also want the effective area to be as large as possible (that is, use the largest diameter ejector possible) to prevent the plastic parts from getting deformed or damaged.

The structure should be reasonable and reliable, and the ejection mechanism should work reliably, move flexibly, be easy to manufacture, easy to replace, and have sufficient strength and rigidity.

If the diameter of the ejector is less than φ2.5 and the position is enough, make a shouldered ejector; if the wall thickness of the ejector is less than 1mm or the wall thickness ratio of the ejector is ≤0.1, make a shouldered ejector, and make the fixed part as large as possible.

The effective matching length of the ejector = (2.5~3)D, the minimum shall not be less than 8mm, and we generally take 20-25mm during the production process.

Don’t put the ejector at the insert joint. For the long arc glue position with a height of more than 10mm, it is recommended to use a flat ejector to eject. The shorter the flat part, the better the strength and the easier the processing. The length of the cylindrical part should be indicated in the design specifications; for the pipe column position above 10mm, it is recommended to use a push tube to eject.

For applications with inclined ejectors, to prevent the product from sliding with the inclined ejector, the ejector surface near the inclined ejector should be ground with a “+” groove. Make sure the moving speed and force of the ejector are moderate to avoid excessive load or damage to the injection molded parts.

To make sure the ejector works right and lasts long, keep it clean and greased. Check it often to see if it’s worn out, bent, or loose. If there’s a problem, fix it or get a new one. Follow the rules and be safe.

What are the Precautions for Ejector Design?

The ejector pin edge should be at least 3/32” away from other pins. The ejector pin on the ejector plate should have a 1/64” virtual position. The ejector pin on the template should have a 1/32” free space. All ejector pins should use standard sizes, and the ejector pin should not be ground low.

When you make nylon and flower materials, you need to measure the diameter of each ejector pin. If the virtual position between the pin and the hole is greater than 0.02mm, there is a chance of slipping. All ejector pin holes must be vertical and smooth (Ra~0.25μm).

When the rubber material is PE/PP/Nylon, the hole diameter = needle diameter + 0.01 mm; when the rubber material is HIPS/PC/ABS, the hole diameter = needle size + 0.02 mm. The ejector pins must strictly pass through the bottom plate, ejector plate and mold. After all ejectors are installed, the ejector plate must be able to slide down by itself.

All ejector and ejector plate meson head hiding positions should have corresponding fonts and the same direction to avoid wrong installation. All forming ejectors should have tube positions to prevent wrong direction installation.

Once you’ve installed the ejector pins, you need to check for any mistakes or leaks before you put the back plate on. After you’ve installed the ejector pin, use a flashlight to check the bone position and hole position one by one from the direction of the mold core, and check that there are no mistakes in the ejector sleeve before you put the back plate on.

When you’re designing the ejector pin position, you need to make sure that the ejection force is enough, and you also need to make sure that the finished product can be ejected in parallel. There are two main types of ejectors, full hard and faded, and you need to pay attention to the surface hardness and the hardness of the steel core.

What are the Design Considerations for Injection Molding?

The injection mold design has to run as planned. If you make mistakes in the design, the part will crack or shrink, and it will be too expensive or too much of a pain in the ass to fix.So, it’s really important to do a well-structured design, and there are some things you need to think about.

Create a Draft Angle

The draft angle is a slanted shape added to both sides of the injection mold. This slight change in the shape of the mold makes it easy for the plastic to come out of the mold.When you take the part out of the mold, you need draft to keep it from sticking. More draft will make it easier to get the part out of the mold . No draft angle will result in big ejector marks on the part when you take it apart and scratches on the mold wall.

Uniform Wall Thickness

When you pour molten material into a mold with uniform wall thickness, it flows freely and unrestricted, filling the cavities of the wall and taking on its prescribed shape.If the mold walls aren’t even, the thinner parts of the molten stuff will cool down faster. So, as the thicker parts cool down, they’ll shrink, and that’ll cause stress to build up.

Eventually, when you take it out, it’ll crack.But if your design doesn’t allow for uniform wall thickness, you can fix it by coring and adding gussets.(Coring is the process of removing molten plastic from a large area to ensure uniformity along the wall. Gussets are support structures added to the wall as reinforcement to reduce the thickness of the wall) .

Ensure Rounded Edges

There are a few good reasons to have rounded corners on the inside and outside of a part. It reduces stress concentrations and prevents part cracking.Sharp corners restrict the flow of molten plastic in the mold. As the plastic cools, it pulls toward the sharp corners and becomes difficult to remove.Rounded edges are easier to make, cheaper, and let you make and take out products better.

Reduce Undercuts

Undercuts are a big problem in mold design because they make it hard to get the part out of the mold. You have to have undercuts in mold design because they keep the part from just falling out of the mold.But undercuts can be fixed by making interlocks or latches that let you take it apart or put it together easily. The design team should try to keep the number of undercuts as low as possible and the ejector system in the mold to a minimum.