Accurate machining of ejector pins is very critical for injection molding. If properly machined, these pins eject molded parts smoothly, reduce downtime and increase mold life.
In this blog post we will learn important machining methods for ejector pins and how to select appropriate materials. We will also cover practical tips for producing high quality ejector pins.
What are Ejector Pins and Why Precision Is Important?
Basically ejector pins are thin rods made of hardened steel. These pins are used in injection molds to eject plastic parts from the mold cavity after they have cooled and hardened.
It is very important that the ejector pins are machined and positioned correctly. If their machining is not precise, the molded parts can stick, warp or break during ejection. Such problems lead to defects and material waste.
Even a slight deviation of 0.01 mm can cause dimensional inaccuracies or noticeable marks on molded parts – particularly in mass production. Therefore precision machining is essential for achieving consistent quality, efficient automation and longer mold life in your injection mold components.
Ejector Pin Machining Process Overview
Now we will see the ejector pin manufacturing process in detail.
1. Material Selection
The first step in machining workflow is the selection of appropriate material. Generally H13 tool steel is selected for ejector pins due to its high hardness (48–52 HRC) and ability to withstand temperatures up to 600°C.
At RICHCONN our material specialists work with you to select the most cost effective alloy based on your production cycle and thermal requirements. This approach provides balanced performance for your molding application.
2. Cutting to Length
The raw steel bars are then cut to the required length. In order to ensure accuracy and reduce material waste, CNC machines or lathes are usually used for this task.
3. Turning
After cutting, the pin undergoes shaping on a lathe. The diameter of pin and other necessary features are adjusted according to the mold specifications through a turning operation.
4. Milling
Next milling machines add special features like slots or flats depending on the pin design requirements.
5. Grinding
Surface grinding is then performed. This step finalizes the pin dimensions and provides a smooth surface finish.
6. Heat Treatment
The pins receive heat treatment afterward. Due to this treatment characteristics like hardness and wear resistance increases.
7. Coating
Additional coatings like black oxide or nitriding are also applied to some pins. The purpose of these coatings is to improve lubrication and wear resistance.
8. Quality Control Measures
Each pin is thoroughly checked at the end. Inspectors confirm hardness, dimensional accuracy and surface finish. This detailed examination guarantees that each pin meets strict standards needed for use in precision molds.
Main 5 Techniques for Ejector Pins Machining
CNC Milling
If your ejector pins need custom head, flats or slots then CNC milling is the best option. Through this technique you can make complicated shapes with precision. It is particularly useful for customizing pin ends to meet the requirements of specific molds.
Also See: A Complete Guide to CNC Milling
CNC Turning
Manufacturers depend a lot on CNC turning for the production of ejector pins. Through this technique, features like shoulders and heads are created. CNC turning guarantees tight tolerances and concentricity with accuracies up to ±0.001 inches
At Richconn our experts use live tooling and Swiss type CNC lathes to obtain even greater runout tolerances( around 0.002 mm). This capability proves particularly useful for the machining of complex shaped ejector pins.
Wire EDM (Electrical Discharge Machining)
For complicated shapes or extremely hard materials, Wire EDM machining is most suitable. In this method the desired shapes are cut using a thin wire or electric sparks. Since it is free from mechanical stress, it works best for ejector pins which have tight internal corners or unusual profiles.
Surface Grinding
The final diameter and mirror like finish of ejector pins are created using surface grinding
This process consistently produces surface roughness values under Ra 0.2 µm. As a result pins slide easily inside the mold which reduces wear and friction. This step is particularly important when ejector pins must fit tight mold tolerances.
See Also: What is Precision Grinding
Centerless Grinding
For the production of high volume ejector pins, centerless grinding is the best choice This fast, accurate process guarantees uniform diameters throughout the length of pin. To ensure better roundness and tighter dimensional tolerances, centerless grinding is often performed after heat treatment.
Appropriate Materials for Ejector Pins
H13 Tool Steel
The industry standard material for ejector pins is H13 tool steel. It provides excellent heat resistance and toughness with maximum hardness ratings of 54 HRC. Due to these properties, H13 is useful for high temperature molding processes.
SKD61 (Equivalent to H13)
In Asia SKD61 is used as an alternative to H13 due to similar specifications. Generally its hardness is around HRC 40. However nitriding treatments can increase the surface hardness to approximately 900 HB which significantly improves wear resistance for difficult applications.
SKH51 (High Speed Steel)
In cases of prolonged mold operation, SKH 51 is an excellent choice. It provides outstanding wear resistance and hardness of 55 to 60 HRC. It is particularly effective for molds which are subjected to repeated cycles.
M2 High Speed Steel
M2 high speed steel provides even better wear resistance with a hardness of up to 64 HRC. It maintains sharp edges with effective sharpening. Therefore it is best suited for high volume or abrasive molding operations.
Material Selection Considerations
You must consider factors such as plastic type, mold temperature and expected cycle time when selecting ejector pin materials. The availability and cost of materials in your area also influence your decision. By selecting right material you can reduce downtime, minimize pin replacements and ensure consistently superior molded components.
Important Tips for Machining Ejector Pins
Maintain Tight Tolerances
It is extremely important to keep tolerances tight. Even a deviation as small as 0.01 mm can result in mold damage, sticking parts or noticeable defects. By using an accurate gauge, regularly measure the tolerances. Make sure that each ejector pin meets the mold’s specific requirements.
For example, recently at RICHCONN an automotive client of ours transitioned to our ISO 2768-f compliant pins. This change resulted in a 68% reduction in ejection failures.
Implement Proper Heat Treatment
By doing proper heat treatment, you can significantly improve hardness and wear resistance of pins.For example ejector pins after nitriding generally achieve surface hardness levels of 65–74 HRC
Moreover it is very important to comply with the recommended heat treatment process for your material. This guarantees maximum durability of your tools.
Achieve Optimal Surface Finish
High quality surface finish is essential to reduce friction and wear. Make sure surface roughness remains within 0.2 to 0.4 microns for most mold applications. Pins with smoother finishes slide more easily. This prevents galling and increases service life.
Use Appropriate Coatings
Wear resistance and friction reduction can be further improved by using appropriate coatings. Coatings such as PVD (TiN, TiCN) also provide protection against rusting and galling. This protection is particularly useful for high volume production environments.
See Also: What is PVD Coating
Regular Inspection & Maintenance
After each production run, carefully check the ejector pins for signs of deformation, cracks or wear. Immediately replace damaged or weakened pins. By regular inspections, consistent mold performance is maintained.
To Sum Up
In short, accurate machining of ejector pins is very important for high quality injection molding results. It directly affects production efficiency and quality of molded parts. By following correct production practices, using quality materials and doing regular maintenance, you can significantly increase the mold life and minimize defects.
If you need machining services for any kind of custom ejector pins then Richconn is your best option. You can contact us anytime.
Related Questions
What are the common causes of ejector pin breakage during operation?
Major causes leading to ejector pin breakage are improper pin alignment, excessive ejection force and inadequate lubrication or maintenance.
How can ejector pin marks on molded parts be minimized or eliminated?
To minimize ejector pin marks, increase draft angles, optimize pin position and lower injection pressure & dwell time. Additionally make sure cavity surfaces are smooth and ejection is balanced.
What is the surface and core hardness of the ejector pin?
The nitrided surface hardness of ejector pins is generally between 65 to 74 HRC and core hardness is around 42 to 55 HRC.
Is it possible to machine ejector pins on a lathe machine?
Yes ejector pins can be machined on a lathe; however for high precision requirements the final finishing process is conducted using a surface grinder.
