Pressure, speed control and mechanical locking in an injection mold
In an injection mold, a hydraulic cylinder used for locking a slide or insert performs a very different function from a conventional actuator.
The cylinder must first move the component into position and then ensure that it remains securely locked while injection pressure acts on the mold. If the system is not correctly designed or controlled, excessive pressure, uncontrolled speed or impact at the end of the stroke can lead to premature wear or even cylinder damage.
A real application analysed by the Vega Team provides an interesting example of how these problems can be addressed.
The Customer was developing a new mold and needed to verify the hydraulic-cylinder selection, the required operating pressure and the best way to protect the locking system from excessive loads.
The case also raised an important question:
Does increasing hydraulic pressure always increase the locking force?
According to the technical assessment provided by the Vega Team, the answer is no. Above 120 bar, increasing the pressure does not increase the locking force; it only increases the cylinder’s traction force.
1. The Customer’s Application
The Customer was working on a new mold and had identified several issues that needed to be addressed before production:
- hydraulic pressure;
- locking force;
- cylinder speed;
- end-of-stroke impacts;
- cylinder wear;
- possible overload;
- pressure regulation;
- flow regulation;
- rod pre-loading.
The Customer was particularly concerned because some cylinders had reportedly been wearing too quickly or even breaking. The objective was therefore not simply to select a cylinder, but to understand how the complete hydraulic system should be operated safely.
This is an important distinction.
A hydraulic cylinder can be correctly sized and still experience premature damage if the pressure and flow are not properly controlled.
2. Calculating the Injection Force
The Customer had performed a preliminary calculation based on Moldflow simulation data.
The maximum pressure acting on the slide face was:
23 MPa
or approximately:
3336 psi
The surface area considered was:
2.5 in².
The Customer calculated:
2.5 × 3336 = 8340 lb/f
which corresponds to approximately:
3782 kgf.
The Customer then compared this load with a stated locking capacity of approximately:
8000 kgf
and therefore considered that the application had a safety factor of approximately 2:1.
This calculation was the starting point for the technical discussion.
3. The Cylinder Used in the Application
The application involved a V260CF cylinder with:
- 36 mm bore;
- 10 mm stroke;
- cylinder code CF036M010.
At the time of the technical discussion, the cylinder had completed approximately:
150,000 cycles.
The Customer wanted to understand the possible root cause of the problems and whether the cylinder selection was appropriate.
4. The Vega Team Could Not Independently Recalculate Everything
An important point in this case is that the Vega Team did not have the complete 3D models of the mold and molded component.
For this reason, the Vega Team could not independently verify all of the Customer’s calculations.
The technical response therefore made an important qualification:
if the Customer’s calculations were correct, the CF036 cylinders were considered suitable for the application.
This distinction is important when documenting an engineering case study.
The calculated injection load came from the Customer’s analysis, while the Vega Team’s contribution was the assessment of the cylinder application, pressure requirements and operating conditions.
5. The Critical Point: 120 Bar Is Not a Target Pressure
The Customer initially questioned whether the cylinder should operate at a higher pressure because the cylinder itself had a considerably higher pressure rating.
The Vega Team clarified that using the cylinder above 120 bar would not provide additional locking force.
Instead, it would only increase the cylinder’s traction force.
This is one of the most important lessons from the case.
A maximum pressure rating should not automatically be interpreted as the recommended operating pressure.
In a self-locking system, the mechanical locking mechanism takes over the load once the rod reaches the locking position.
Therefore:
higher hydraulic pressure ≠ automatically higher mechanical locking force
6. Minimum Pressure and Maximum Performance
For the specific application analysed, the Vega Team indicated that the minimum hydraulic oil pressure required to guarantee proper locking was approximately:
90–100 bar
while:
120 bar
was the pressure indicated for maximum performance.
These values belong specifically to the application documented in the case.
They should not be interpreted as universal operating pressures for every Vega cylinder or every mold.
The correct pressure must always be determined according to the specific application, load and cylinder configuration.
7. Why Mechanical Locking Changes the Situation
A conventional hydraulic cylinder generally relies on hydraulic pressure to maintain a load.
A self-locking cylinder works differently.
The current Vega V270CG technology uses a mechanical locking system between the cylinder rod and body. Vega describes it as a self-locking hydraulic cylinder specifically intended for moving and locking mold components such as slides, pins and plugs.
Once the rod reaches the locking position, the mechanical system transfers the external load through the locking components and reinforced cylinder body.
The hydraulic pressure therefore does not have to remain continuously high simply to hold the mold component in position.
Vega’s technical documentation explains that the mechanical locking system can maintain the position with minimum pressure inside the hydraulic chamber.
8. Pressure and Flow Perform Different Functions
Another important lesson from the case is the difference between pressure control and flow control.
In simplified terms:
Pressure → force
Flow → speed
Increasing pressure increases the hydraulic force available from the cylinder.
Increasing flow generally increases the cylinder’s movement speed.
This means that if the problem is excessive movement speed, simply reducing pressure is not necessarily the correct solution.
The appropriate solution may instead be to control the hydraulic flow.
9. Controlling Cylinder Speed
The Vega Team indicated a maximum speed of:
0.1 m/s
for this type of cylinder and recommended flow regulators as a way to maintain a controlled speed and reduce shocks at the end of the stroke.
This recommendation is particularly relevant to short-stroke cylinders.
The cylinder involved in the Customer application had only:
10 mm of stroke.
With such a short movement, uncontrolled hydraulic flow can cause the cylinder to reach the end of the stroke very quickly.
The problem is therefore not simply whether the cylinder can move fast enough.
The important question is:
How quickly does the cylinder reach the end of the stroke, and what happens when it gets there?
10. End-of-Stroke Shock
A cylinder reaching the end of its stroke at excessive speed can generate a significant mechanical impact.
This can result in:
- high local loads;
- stress on the locking elements;
- premature wear;
- deformation;
- damage to mechanical components;
- possible cylinder failure.
For this reason, the Vega Team suggested using flow regulators to achieve a controlled and substantially constant speed and to reduce the risk of shocks at the end of the stroke.
This is an important preventative measure.
The goal is not simply to stay below the maximum speed.
The objective is to control the entire movement profile.
11. Why Short Strokes Require Careful Speed Control
The Customer’s cylinder had a stroke of only:
10 mm.
Consider the difference between a cylinder moving 10 mm slowly and the same cylinder covering 10 mm almost instantaneously.
The total distance is the same, but the dynamic loads can be very different.
This is why flow regulation becomes particularly useful in short-stroke mold applications.
A controlled movement allows the locking mechanism to reach its final position without generating unnecessary impact.
12. Pre-Loading the Rod
The technical discussion also addressed another important feature: rod pre-loading.
The Vega Team referred to a dedicated fixing flange, identified in the documentation as RF…211E, for regulating the pre-load.
Pre-loading can be useful in injection molds because even very small movements of a slide or plug can affect the quality of the molded component.
During injection, pressure acts on the moving component.
If small clearances exist between the different mold elements, the component can move slightly.
This movement may allow plastic material to enter the gap and produce a flash or burr.
13. How Pre-Loading Can Improve Mold Quality
Vega’s current technical documentation explains that the self-locking mechanism can also be used for pre-loading the rod.
The dedicated pre-loading flange allows the operator to apply a controlled mechanical preload during setup, compressing the rod and the components connected to it. This helps keep the mold component firmly in position during injection.
The principle can be summarized as:
pre-load → reduced clearance → improved component stability → reduced risk of flash
This means that the self-locking system can provide more than simple mechanical locking.
It can also contribute to improved mold precision.
14. The Current Vega V270CG Solution
The technical principles described in the Customer case are directly relevant to the current V270CG Self-Locking Hydraulic Cylinder.
Vega describes the V270CG as a self-locking hydraulic cylinder with a special locking system between the rod and cylinder body. The standard range includes bores from 30 to 84 mm and strokes from 30 to 150 mm.
The main application is moving and locking mold components such as:
- slides;
- pins;
- plugs;
- other components that can create undercuts.
The system is also intended to help prevent plastic flash between moving mold components.
15. The Mechanical Locking Principle
The V270CG does not rely exclusively on hydraulic pressure to maintain the mold component in position.
According to Vega’s technical explanation, the rod-piston assembly incorporates a floating piston and high-resistance locking sectors.
As the rod reaches the locking position, the conical piston expands the sectors into the dedicated groove inside the cylinder body.
The sectors then transfer the external force through the reinforced cylinder structure.
The result is a mechanically locked position that can be maintained with minimum hydraulic pressure.
This is particularly useful when the mold component must resist significant injection forces.
16. Why Mechanical Locking Can Protect the Hydraulic System
If a conventional cylinder must continuously maintain a large load using hydraulic pressure, the hydraulic system remains under pressure for the entire holding period.
With a mechanical locking system, the load can instead be transferred through the mechanical locking elements.
This can reduce the need for continuous high hydraulic pressure.
The advantage is therefore not simply higher locking capacity.
It is also the possibility of separating:
movement
from:
mechanical load holding.
This distinction can be very valuable in injection molding.
17. Pressure Regulation Must Be Performed at the Hydraulic Source
The Customer also asked where the hydraulic pressure should be controlled.
The Vega Team explained that oil pressure should be regulated either:
- through the press control panel, or
- directly through the control valve of the machine’s hydraulic power unit.
This means that pressure management should be considered as part of the hydraulic circuit rather than as something that needs to be solved by modifying the cylinder itself.
The cylinder receives the hydraulic conditions defined by the machine’s hydraulic system.
18. A Cylinder Should Not Be Operated at Maximum Pressure by Default
One of the most common misconceptions in hydraulic systems is:
“If the cylinder can withstand a higher pressure, using the higher pressure must be better.”
The Customer case demonstrates why this is not necessarily true.
For the specific application, the Vega Team indicated:
90–100 bar → minimum pressure for proper locking
120 bar → maximum performance indicated
and clarified that increasing pressure above 120 bar would not increase the locking force.
The correct engineering approach is therefore to determine the pressure actually required by the application.
19. The Root Cause May Be the Hydraulic System, Not the Cylinder
The Customer’s concern about premature cylinder wear or breakage naturally led to the question:
Is the cylinder defective?
But a complete engineering analysis has to consider the entire system.
Potential causes include:
- excessive pressure;
- excessive flow;
- uncontrolled speed;
- end-of-stroke impact;
- incorrect preload;
- excessive external load;
- incorrect installation;
- mechanical misalignment.
The available documentation does not establish one definitive root cause for the reported failures.
The Vega Team specifically noted that it could not perform a complete verification without the necessary 3D models.
Therefore, the correct conclusion is not that one specific factor caused the failures, but that pressure and speed control are important measures for reducing the risk of damage.
20. A Systematic Approach to Cylinder Protection
The Customer case suggests a practical engineering procedure.
Step 1 — Determine the external mold force
Use the mold design and, where appropriate, Moldflow simulation.
Step 2 — Calculate the required locking capacity
Compare the external load with the mechanical locking capacity.
Step 3 — Determine the minimum hydraulic pressure
Select the pressure required to reliably activate the locking system.
Step 4 — Avoid unnecessary overpressure
Do not use the maximum available machine pressure simply because the cylinder can tolerate it.
Step 5 — Control the flow
Use flow regulators to control cylinder speed.
Step 6 — Avoid end-of-stroke shocks
Ensure that the cylinder reaches the final position at a controlled speed.
Step 7 — Verify preload
Where appropriate, adjust the rod preload during mold setup.
Step 8 — Monitor the complete system
Pressure, flow, mechanical alignment and mold loads should be considered together.
21. What the Customer Case Teaches Mold Designers
Several important lessons emerge from this application.
1. Maximum pressure is not necessarily operating pressure
The cylinder should be operated at the pressure required by the application.
2. Mechanical locking changes the load path
Once mechanically locked, the external load can be transferred through the locking mechanism rather than being supported only by hydraulic pressure.
3. Pressure and flow must be controlled separately
Pressure determines force; flow controls movement speed.
4. Short strokes require careful speed management
The Customer’s cylinder had a 10 mm stroke, making controlled movement particularly relevant.
5. End-of-stroke impacts can be dangerous
Flow regulators can help reduce shocks and protect the locking system.
6. Pre-loading can improve mold stability
A correctly adjusted preload can help minimize movement and reduce the risk of flash.
Conclusion
This Customer case demonstrates that the correct use of a hydraulic locking cylinder involves much more than simply selecting a cylinder with sufficient bore and pressure rating.
The Customer calculated a maximum force of approximately 3782 kgf from a Moldflow pressure of 23 MPa acting on a 2.5 in² slide surface.
The Vega Team could not independently reproduce the complete calculation because the required 3D models of the mold and plastic component were not available. However, based on the Customer’s calculations, the CF036 cylinders were considered suitable for the application.
For this application, the Vega Team indicated 90–100 bar as the minimum hydraulic pressure required to guarantee proper locking and 120 bar for maximum performance.
Most importantly, the Vega Team clarified that increasing pressure above 120 bar would not increase the locking force, but would only increase the cylinder’s traction force.
The analysis also highlighted the importance of controlling cylinder speed. The maximum speed indicated for the cylinder was 0.1 m/s, and flow regulators were recommended to maintain controlled movement and reduce end-of-stroke shocks.
The broader lesson is clear:
A self-locking hydraulic cylinder should not simply be operated at the highest available pressure. The pressure must be appropriate for the application, the movement speed must be controlled, and the mechanical locking and preload systems must be correctly adjusted.
This approach can reduce unnecessary mechanical stress, improve reliability and help protect both the hydraulic cylinder and the mold.
Vega’s current V270CG technology incorporates these principles into a dedicated self-locking hydraulic cylinder designed for moving and mechanically locking mold components.
Useful and Verified URLs
1. V270CG – Self-Locking Hydraulic Cylinder
Official Vega product page for the V270CG. It provides the current product configuration, available bore and stroke options, integrated sensors and self-locking characteristics.
V270CG – Self-Locking Hydraulic Cylinder
2. Self-Locking Hydraulic Cylinders
Official Vega technical page explaining how the mechanical self-locking system works, including the locking sectors, load transfer and pre-loading flange. This is the most relevant technical reference for this Customer case.
Self-Locking Hydraulic Cylinders
3. Mechanical-Locking Hydraulic Cylinders
Official Vega category page dedicated to mechanical-locking cylinders. It identifies the V270CG as the current Vega solution for moving and locking mold components.
Mechanical-Locking Hydraulic Cylinders
4. Hydraulic Cylinders for Molds
Official Vega overview of hydraulic cylinders for plastic injection molds and die-casting molds, organized by application, including the Mechanical-Locking category.
5. Hydraulic Cylinders Catalogue
Official Vega catalogue page covering the different cylinder families and application categories, including Mechanical-Locking.
