From a 1 mm Punch Movement to the Required Holding Force

In plastic injection molding, hydraulic cylinders are often used to move slides, cores, punches and other mold components. In many applications, however, moving the component is only part of the problem.

The hydraulic cylinder must also keep the component firmly in position while injection pressure is acting on the mold.

This becomes particularly important when a punch or core is located on the injection side of the mold. During injection, the molten plastic can generate a substantial force against the punch. If the hydraulic system does not provide sufficient holding capability, even a very small displacement can affect the molded component.

A real application analyzed by the Vega Technical Team illustrates this problem clearly.

The customer reported that two punches operated by hydraulic cylinders were moving approximately 1 mm backwards during the injection phase. The cylinders were installed on the injection side of the mold, and the material being processed was PA6.6 with 30% glass fiber.

The problem therefore was not simply one of movement.

The cylinders could move the punches, but they were not providing the required stability against the force generated during injection.

The technical analysis started from the geometry of the punch and from the estimated injection pressure, and led to the selection of a V260CF hydraulic cylinder with a 36 mm bore, together with a mechanical holding solution and check valves.

This article examines the engineering reasoning behind that solution.

1. The Real Problem: The Punch Was Moving During Injection

The customer’s original request was very specific.

Two punches, operated by hydraulic cylinders installed on the injection side of the mold, were retracting by approximately 1 mm during injection.

A displacement of 1 mm may appear insignificant.

In an injection mold, however, the position of a punch can be critical to:

cavity geometry;
wall thickness;
dimensional accuracy;
sealing areas;
flash formation;
surface quality;
repeatability between molding cycles.

The fact that the movement occurred during injection is particularly important.

The problem was not necessarily that the cylinder was incapable of generating movement.

The problem was that the hydraulic cylinder and its holding system were being subjected to a force generated by the injection pressure that could cause the punch to move backwards.

This changes the engineering question completely.

Instead of asking:

How much force is required to move the punch?

the designer must ask:

How much force is required to keep the punch in position while the plastic is being injected?

2. Moving a Punch and Holding a Punch Are Different Problems

A hydraulic cylinder can be perfectly capable of moving a mold component and still be unsuitable for maintaining that component in position under injection pressure.

These are two different operating conditions.

Movement

The cylinder must generate enough force to move the component against:

friction;
guide resistance;
mechanical loads;
the mass of the moving components.

Holding

The cylinder must resist the force generated by the molding process.

The second condition can be considerably more demanding.

In the application analyzed by Vega, the customer specifically reported backward movement during the injection phase.

This meant that the holding condition had to be calculated rather than relying simply on the force required for movement.

3. Starting From the Punch Geometry

The Vega Technical Team began the analysis by determining the effective area of each punch exposed to the injection pressure.

The reported frontal surface of each individual punch was approximately 12.5 cm².

This is the critical area for evaluating the force generated by the pressure acting on the front surface.

The customer estimated an injection pressure in the cavity of 500 bar.

These two values provide the fundamental parameters for determining the force that the locking system must withstand.

4. Injection Pressure Becomes Mechanical Force

Pressure by itself does not tell us how much force acts on a component.

The force depends on the area exposed to that pressure.

The relationship is:

Force = Pressure × Area

For the application:

frontal area ≈ 12.5 cm²
estimated cavity pressure = 500 bar

The resulting useful holding force calculated by Vega was:

6,250 kgf

The figure is explicitly reported in the technical correspondence.

This is the first major lesson from the application:

A relatively small punch can be subjected to a very large force when exposed to high injection pressure.

5. Why the Number Is So Large

It can initially seem surprising that a punch with a frontal area of only approximately 12.5 cm² can generate a force of more than six tonnes-force.

The reason is the very high pressure involved.

An injection pressure of 500 bar is equivalent to approximately 500 kgf acting on every square centimetre of exposed area.

When this pressure acts over 12.5 cm², the resulting force becomes substantial.

This is why the design of hydraulic cylinders for injection molds must always start from the actual projected area exposed to injection pressure, rather than simply from the physical dimensions of the cylinder.

6. The Difference Between Holding Force and Pulling Force

The technical analysis did not stop with the force acting on the frontal surface.

The Vega Technical Team also evaluated the traction force associated with the lateral surface of the punch.

The reported lateral surface of each punch was approximately 14.9 cm², while the coefficient of adhesion of the material was given as 25 kg/cm².

The resulting useful traction force was calculated as:

370 kgf.

This is dramatically lower than the approximately 6,250 kgf required in the holding condition.

That difference is extremely important for understanding the application.

7. Two Different Forces Must Be Considered

The analysis therefore identified two different mechanical requirements.

Force in holding

Approximately:

6,250 kgf

Force in traction

Approximately:

370 kgf

These values describe different aspects of the application and should not be confused.

The very high holding force comes from the injection pressure acting on the frontal surface of the punch.

The lower traction force is associated with the resistance calculated from the lateral surface and the specified material adhesion coefficient.

This distinction is particularly useful when designing a hydraulic system for injection molds.

8. Why a Standard Hydraulic Cylinder May Not Be Enough

A conventional hydraulic cylinder generates force as a function of its piston area and hydraulic pressure.

For example, increasing the bore increases the theoretical hydraulic force available at a given pressure.

But in this application, the problem was not simply obtaining enough hydraulic force.

The punch needed to remain mechanically stable during injection.

If the injection force acts against the punch and the hydraulic cylinder is required to continuously resist that force through hydraulic pressure alone, several factors become important:

pressure stability;
hydraulic compressibility;
valve leakage;
hose and connection behavior;
system pressure;
cylinder geometry;
mechanical rigidity.

The source material does not document a detailed analysis of each of these factors for this particular application, so they should not be presented as diagnosed causes of the 1 mm movement.

The documented fact is simpler:

the punch was retracting during injection, and Vega therefore evaluated a hydraulic cylinder and locking configuration capable of providing the required holding force.

9. The Need for Mechanical Locking

The application belongs to a category where hydraulic power can be combined with a mechanical locking function.

The purpose is to prevent the mold component from moving when the injection force acts against it.

Vega’s current technical documentation describes this general principle for its self-locking hydraulic-cylinder technology: the mechanical locking system transfers the external force through the locking elements and reinforced cylinder body rather than relying exclusively on hydraulic pressure.

This principle is particularly relevant to mold components that must remain fixed while injection pressure is present.

The current Vega product family identifies mechanical locking as a dedicated application category for hydraulic cylinders used in plastic injection molds.

10. The Technical Objective Was Not Simply “More Hydraulic Pressure”

This distinction is essential.

If a punch moves under injection pressure, one possible reaction is to increase the hydraulic pressure.

But a more appropriate engineering question is:

How should the injection force be transferred through the cylinder and locking system?

The objective is not necessarily to make the hydraulic circuit work at ever-higher pressure.

Instead, the system should be designed so that the force generated during injection is safely resisted by the appropriate mechanical components.

Vega’s current self-locking-cylinder documentation describes this principle: once the locking system is engaged, external forces acting on the rod are transferred through the locking elements and reinforced cylinder body.

11. The V260CF Selected for the Application

After calculating the required forces, the Vega Technical Team recommended a V260CF hydraulic cylinder with a 36 mm bore.

The proposed quantity was:

2 × CF036NB020

with an alternative:

2 × CF036MB020.

The original technical correspondence therefore provides a direct connection between:

calculated injection force

→

required holding capability

→

cylinder selection

This is an important characteristic of the application.

The cylinder was not selected simply because its physical dimensions fitted the mold.

The selection followed a force calculation.

12. Why the Bore Matters

The bore of a hydraulic cylinder determines the effective piston area.

A larger piston area allows the cylinder to generate greater force at the same hydraulic pressure.

For this application, Vega recommended a 36 mm bore.

However, the actual selection cannot be reduced to the bore alone.

The cylinder must also be compatible with:

required stroke;
available mold space;
mounting configuration;
locking arrangement;
hydraulic connections;
required holding force.

The original quotation therefore included not only the cylinders but also specific flanges and check valves.

13. Pre-Loading Flange Option

One of the proposed configurations included a flange with a preload adjustment system:

RF036211E.

The alternative was:

RF036271C, described as a neutral flange.

The inclusion of a preload-adjustable flange is particularly relevant to applications in which the position of the mold component must be maintained precisely under process pressure.

Vega’s current technical documentation explains that preloading can be used with mechanical locking to remove small clearances between the rod and the components connected to it, helping the mold component resist injection pressure and reducing the risk of imperfections caused by movement.

14. Why Preload Can Be Important in Injection Molding

During injection, the molten polymer exerts force on the mold components.

Even very small movements can affect the final molded part.

There may also be small accumulated tolerances between:

the cylinder;
rod;
punch;
mold components;
guides;
fixing elements.

A preload system can be used to reduce this free movement before the injection pressure reaches its maximum effect.

Vega’s current explanation of its self-locking technology specifically describes the use of a special preload flange to compress the rod and connected components during setup.

This provides a useful engineering connection between the real application and the broader operating principle of mechanically locking hydraulic cylinders.

15. The Role of the Check Valve

The proposed configuration also included:

2 × ZR35AH301/4-1/4 check valves.

The inclusion of the check valve is significant because the application involves maintaining the cylinder in a defined position.

However, it is important to distinguish the functions.

A check valve can help maintain hydraulic pressure in the cylinder circuit by restricting flow in the opposite direction.

It does not, by itself, create the same mechanical locking function as a mechanically self-locking cylinder.

The source document confirms that Vega included the check valves in the proposed configuration, but it does not provide a detailed explanation of their exact role in the circuit. Therefore, the specific circuit function should not be inferred beyond what the documentation supports.

16. Hydraulic Holding Versus Mechanical Locking

This distinction is central to the entire subject.

Hydraulic holding

The cylinder maintains position because hydraulic pressure remains in the chamber.

Mechanical locking

A mechanical system physically prevents the rod from moving under external load.

The current Vega documentation describes self-locking hydraulic cylinders as solutions for applications where mold components must remain mechanically locked while resisting injection pressure.

The historical application documented here involved the selection of a V260CF together with the specified flange and check-valve configuration.

Therefore, the article should distinguish the specific 2015 solution from Vega’s current product portfolio rather than automatically equating the V260CF with the current V270CG range.

17. The Material Also Matters

The customer specified the material as:

PA6.6 30% glass fiber.

This information is important because the behavior of the material during injection affects the loads acting on the mold.

However, the available document does not provide a detailed rheological analysis of the PA6.6 compound or a calculation linking its glass-fiber content directly to the 6,250 kgf holding force.

The documented calculation instead uses:

frontal punch area;
estimated cavity pressure;
lateral punch area;
specified material adhesion coefficient.

Therefore, the material specification should be presented as part of the real application context rather than as the direct mathematical source of the holding force.

18. The 1 mm Movement Was the Warning Sign

The most useful practical lesson from the application may be the 1 mm displacement itself.

The customer did not report a catastrophic failure.

The cylinders were not described as broken.

Instead, the process revealed a small but unacceptable movement:

approximately 1 mm during injection.

In mold engineering, this kind of small displacement can be an early indication that the holding architecture needs to be reconsidered.

The correct response is not necessarily to increase cylinder size blindly.

The designer should first determine:

what force is acting on the component;
what force the cylinder can generate;
whether the cylinder is intended to hold hydraulically or mechanically;
where the external force is transferred;
whether the locking and preload system are appropriate.

19. From the Symptom to the Engineering Calculation

The real application followed a logical sequence:

Observed problem

The punches moved backwards approximately 1 mm during injection.

Geometry

The frontal area of each punch was approximately 12.5 cm².

Process condition

The estimated cavity injection pressure was 500 bar.

Calculated holding force

Approximately 6,250 kgf.

Additional traction calculation

Approximately 370 kgf.

Recommended cylinder

V260CF, 36 mm bore.

Additional components

Preload-adjustable or neutral flanges and check valves.

This is a very good example of how an apparently simple mold problem can be converted into a structured engineering calculation.

20. The Broader Design Principle

A hydraulic cylinder installed in an injection mold should not be selected solely by asking:

Can this cylinder move the component?

A better question is:

Can the complete cylinder and locking system maintain the component in its required position under the actual process forces?

That means considering:

injection pressure;
projected area;
holding force;
traction force;
cylinder bore;
hydraulic pressure;
locking mechanism;
preload;
valves;
mold geometry.

The real application documented by Vega demonstrates exactly this approach.

21. Conclusion of Part 1

The reported problem was simple to describe but technically significant: two hydraulic-cylinder-driven punches on the injection side of a mold were moving backwards by approximately 1 mm during injection. The mold processed PA6.6 with 30% glass fiber.

The Vega Technical Team did not approach the problem simply by selecting a larger cylinder.

The first step was to calculate the forces acting on the punch.

With a frontal area of approximately 12.5 cm² and an estimated cavity pressure of 500 bar, the calculated useful holding force was 6,250 kgf. The corresponding traction calculation, based on a lateral surface of approximately 14.9 cm² and a specified adhesion coefficient of 25 kg/cm², resulted in 370 kgf.

Based on these calculations, Vega recommended a V260CF with a 36 mm bore, with two cylinder configurations proposed, together with either a preload-adjustable or neutral flange and two check valves.

The important lesson is that the force required to hold a punch during injection can be dramatically greater than the force required simply to move it.

In the second part, the technical analysis can go deeper into the self-locking principle, preload, the function of the locking system, the relationship between injection pressure and punch stability, and the design criteria that should be considered when selecting a mechanically locking hydraulic cylinder for an injection mold.

Mechanical Locking, Preload, Check Valves and the Correct Load-Holding Strategy

In the first part of this article, we examined a real injection-molding application in which two punches operated by hydraulic cylinders moved backwards by approximately 1 mm during injection.

The mold processed PA6.6 with 30% glass fiber, and the estimated cavity pressure was 500 bar. For each punch, Vega calculated a frontal area of approximately 12.5 cm², resulting in a useful holding force of approximately 6,250 kgf. The calculated traction force was approximately 370 kgf.

Based on these calculations, the Vega Technical Team recommended a V260CF hydraulic cylinder with a 36 mm bore, together with specific flange and check-valve configurations.

The second part of the analysis concerns a broader engineering question:

How should a hydraulic cylinder hold a mold punch securely when the injection process generates a force that tends to push it backwards?

The answer requires distinguishing between hydraulic force, mechanical locking, preload and hydraulic load holding.

1. Moving the Punch Is Not the Same as Locking the Punch

The first and most important distinction is between actuation and position retention.

A hydraulic cylinder can be perfectly capable of moving a punch into position.

However, once the punch reaches its working position, the injection process may generate a force that attempts to move it in the opposite direction.

The system therefore has two separate requirements:

Actuation

The cylinder must move the punch.

Holding

The cylinder system must prevent the punch from moving when the injection pressure acts on it.

In the real application, the customer had already identified the second problem: the punches were moving backwards approximately 1 mm during injection.

This means that cylinder selection must be based on the complete operating cycle rather than simply on the movement required.

2. Why Injection Pressure Can Move a Punch

During injection, molten plastic enters the cavity under high pressure.

That pressure acts on the surfaces exposed to the cavity.

If a punch has a frontal projected area of approximately 12.5 cm² and the cavity pressure reaches approximately 500 bar, the resulting force can become extremely large.

The Vega calculation for the application produced approximately 6,250 kgf of useful holding force.

The punch therefore does not need to be particularly large to experience a substantial load.

This is why the correct starting point for the design is always the projected area exposed to the process pressure.

3. The Load Must Be Understood Before Selecting the Cylinder

A common mistake in hydraulic-cylinder selection is to begin with the cylinder.

For example:

“We normally use this cylinder for this type of mold.”

That approach can be dangerous when the process conditions change.

The correct sequence is:

Mold geometry

↓

Projected area

↓

Process pressure

↓

External force

↓

Required holding capability

↓

Cylinder and locking system

This was essentially the approach followed by the Vega Technical Team in the real application.

4. Hydraulic Holding Versus Mechanical Locking

There are two fundamentally different ways of keeping a hydraulic cylinder in position.

Hydraulic holding

The cylinder remains stationary because pressure is maintained in the hydraulic chamber.

Mechanical locking

A mechanical mechanism physically prevents the rod from retracting or extending.

The advantage of mechanical locking is that the external load can be transferred through the mechanical locking components rather than being continuously resisted only by hydraulic pressure.

Vega’s current documentation describes its self-locking system precisely for applications in which mold components must remain mechanically locked against the force generated by the molded material.

This distinction is particularly important in injection molding.

5. How Vega’s Self-Locking Principle Works

According to Vega’s current technical documentation, the self-locking system uses a floating piston and high-resistance floating sectors.

When the rod reaches the locking position, the piston causes the sectors to expand into a groove machined inside the cylinder body.

The sectors then fill the space between piston and body, mechanically locking the rod in the extended position.

The external force generated by the molded material is consequently transferred through the locking sectors and the reinforced cylinder body.

Only a minimum hydraulic pressure is required to maintain the locked condition.

This is fundamentally different from relying exclusively on hydraulic pressure to maintain the position.

6. Why Mechanical Locking Is Valuable in Injection Molds

Injection molds frequently operate with very high process forces.

If the mold component must remain absolutely stable during injection, a mechanical locking system can provide an additional level of security.

The current Vega documentation explains that self-locking cylinders are specifically intended for applications in which a component on the fixed part of the mold must remain mechanically locked so that the molded part maintains the desired shape and does not develop burrs.

This is directly relevant to applications where even a small displacement can affect the final component.

7. The Importance of the Locking Position

A mechanical locking cylinder does not simply lock at an arbitrary point.

The rod must reach the correct position for the locking mechanism to engage.

This is an important design consideration when integrating a self-locking cylinder into an injection mold.

The mold designer must therefore verify:

complete rod extension;
correct locking position;
available installation space;
mechanical clearance;
interaction with the punch or slide;
end-of-stroke position.

A cylinder can be correctly sized in terms of force and still be incorrectly integrated if its locking position cannot be reached.

This is why dimensional verification of the mold is just as important as force calculation.

8. Preload: A Second Level of Mechanical Stability

Mechanical locking can also be combined with preload.

Vega’s documentation explains that injection pressure can cause the plug or moving component to give up a very small amount of space because of the compressibility of hydraulic oil and accumulated mechanical tolerances.

Even a small displacement can allow plastic to enter between mating surfaces.

The result can be:

burrs;
flash;
dimensional imperfections;
manual finishing operations;
reduced component quality.

For this reason, preload can be extremely useful in precision injection-molding applications.

9. How the Preloading Flange Works

Vega’s self-locking system can be combined with a preloading flange.

During setup, the external ring of the flange can be tightened, compressing the rod and the components connected to it.

This removes small clearances and creates a preloaded mechanical condition before injection begins.

The concept can be represented as:

Cylinder reaches working position

↓

Mechanical lock engages

↓

Preloading flange is adjusted

↓

Clearances are reduced

↓

Punch is mechanically preloaded

↓

Injection pressure acts on the system

The result is greater resistance to unwanted movement.

10. Why Preload Is Particularly Important for Small Movements

The real application involved a displacement of only approximately 1 mm.

That is precisely the type of situation in which small mechanical clearances can become significant.

The purpose of preload is not necessarily to increase the cylinder’s hydraulic force.

Instead, it can eliminate or reduce the free movement available before the structural components begin carrying the external load.

This distinction is extremely important.

A system can have a very high theoretical holding force and still permit a small displacement if there is mechanical clearance within the assembly.

11. The Role of the Flange in the Real Application

The original Vega proposal included two possible flange configurations.

The first was:

RF036211E – flange with preload adjustment system

The alternative was:

RF036271C – neutral flange.

This is significant because the flange was not simply a mounting accessory.

The available configuration included a specific mechanism for adjusting preload.

For an application in which the customer was experiencing punch movement during injection, this capability was directly relevant to the mechanical stability of the system.

12. Why a Neutral Flange May Also Be Used

The technical correspondence also included a neutral flange as an alternative.

This demonstrates that the correct flange configuration depends on the mechanical requirements of the mold.

Not every application necessarily requires preload adjustment.

The choice depends on:

required positioning accuracy;
mechanical tolerances;
external forces;
mold geometry;
required locking behavior.

The important point is that the flange must be considered part of the complete cylinder assembly.

13. The Function of the Check Valve

The original configuration also included two ZR35AH301/4-1/4 check valves.

A check valve can prevent hydraulic flow in one direction and therefore help maintain hydraulic pressure in the cylinder circuit.

This can be important when a cylinder must remain in a defined position.

However, it is important to distinguish:

hydraulic load holding

from

mechanical locking.

A check valve does not perform the same function as the mechanical locking sectors of a self-locking cylinder.

The historical correspondence confirms that Vega included the check valves in the proposed configuration, but does not provide enough circuit information to establish their exact hydraulic role beyond this.

14. Why a Check Valve Alone Is Not the Same as Mechanical Locking

Suppose a cylinder is holding a load using hydraulic pressure.

If the hydraulic circuit is perfectly sealed, the cylinder can theoretically remain stationary.

But real hydraulic systems contain:

seals;
valves;
hoses;
fittings;
oil;
pressure variations;
thermal effects.

A mechanically locked cylinder uses a physical mechanical path to resist the external load.

This is why Vega’s current self-locking technology is specifically designed to transfer external forces through the mechanical locking system and reinforced cylinder body.

15. The Correct Load Path

For a mechanically locked cylinder, the desired load path is fundamentally different from a purely hydraulic holding system.

A simplified hydraulic holding path is:

Injection force

↓

Punch

↓

Rod

↓

Piston

↓

Hydraulic oil

↓

Valve / circuit

A mechanically locked system instead creates a mechanical path:

Injection force

↓

Punch

↓

Rod

↓

Locking mechanism

↓

Cylinder body

↓

Mold structure

The second path removes much of the burden from the hydraulic circuit.

16. Why This Matters at 500 bar Injection Pressure

The application was based on an estimated cavity pressure of 500 bar.

At such pressures, the external force acting on even relatively small projected areas can become very large.

This makes the load path extremely important.

The question is not simply:

“Can the cylinder generate enough force?”

It is also:

“Can the complete mechanical structure safely transmit and resist the force generated during injection?”

This is a fundamental difference between cylinder sizing and system engineering.

17. Why the Cylinder Bore Still Matters

Mechanical locking does not eliminate the need for correct cylinder sizing.

The cylinder still needs to:

move the punch;
reach the locking position;
release the locking mechanism;
overcome friction;
overcome the mechanical resistance of the mold.

The original technical analysis therefore still selected a specific hydraulic cylinder:

V260CF, 36 mm bore.

The cylinder must be capable of performing its complete cycle even though the mechanical locking system carries the external holding load once engaged.

18. The Difference Between Locking Force and Breakaway Force

A further engineering distinction is useful.

A locking mechanism can withstand a very large external force while the hydraulic cylinder itself may only need to generate a smaller force to move or unlock the system.

These are different quantities.

Holding capability

How much external force the locked mechanism can resist.

Actuation force

How much force the cylinder can generate to move the mechanism.

Breakaway force

How much force is required to release the mechanism and initiate movement.

These values should not automatically be assumed to be identical.

This distinction is particularly important when evaluating self-locking mechanisms.

19. The Release Phase Can Be More Demanding Than Expected

A mechanically locked system can provide enormous resistance against external loads.

But when the cylinder has to unlock, the hydraulic actuator must overcome the resistance of the locking mechanism and any external mechanical loads.

This means that a cylinder must be evaluated for both:

the locked condition;
the unlocking condition.

The historical documentation does not provide a breakaway-force calculation for the V260CF application, so no specific breakaway value should be attributed to this case.

The general engineering principle, however, is important when designing any self-locking system.

20. Mechanical Geometry Is as Important as Hydraulic Pressure

The efficiency of a self-locking mechanism depends on its mechanical geometry.

The locking components must:

engage correctly;
transfer the external load;
disengage reliably;
remain within their intended operating geometry.

This is why the mold design must be checked together with the cylinder.

A cylinder cannot compensate for an incorrectly designed locking interface.

21. The Importance of the Mold’s Structural Rigidity

Even a perfectly selected hydraulic cylinder cannot compensate for an excessively flexible mold structure.

If the punch, cylinder support or surrounding mold components deform under injection pressure, the punch may move even though the cylinder itself is correctly sized.

The correct engineering approach therefore considers:

cylinder force;
locking system;
preload;
mounting;
punch geometry;
mold stiffness.

The 1 mm movement reported in the real application is precisely why the complete mechanical system had to be considered rather than the cylinder alone.

22. Why 1 mm Can Be a Major Problem

In general mechanical engineering, 1 mm may appear insignificant.

In injection molding, it can be enough to create:

flash;
dimensional deviations;
incorrect wall thickness;
unwanted deformation;
visible defects.

The exact consequence depends on the geometry and tolerances of the molded component.

The source material does not specify the final molding defect produced by the 1 mm displacement, so it would be incorrect to attribute a particular defect to the case.

What is documented is that the customer considered the approximately 1 mm backward movement during injection a problem requiring a technical solution.

23. Designing the Complete System

A robust design process should therefore consider the following sequence:

Step 1 – Determine the projected area

Calculate the area exposed to injection pressure.

Step 2 – Determine the process pressure

Use the expected cavity pressure for the specific molding process.

Step 3 – Calculate the external force

Multiply pressure by projected area.

Step 4 – Determine the required holding capability

Establish whether the cylinder must hydraulically resist the force or whether a mechanical locking system will carry it.

Step 5 – Calculate the movement force

Consider friction, adhesion and all other forces that the cylinder must overcome.

Step 6 – Select the cylinder

Choose the bore, stroke and configuration.

Step 7 – Select the locking system

Determine whether mechanical locking, hydraulic locking or another solution is appropriate.

Step 8 – Verify preload

Determine whether accumulated clearances need to be removed.

Step 9 – Verify the hydraulic circuit

Check valves, pressure, flow and release conditions.

Step 10 – Validate the complete mold

Verify the complete mechanical and hydraulic assembly.

24. Why This Approach Is Better Than Choosing a Cylinder From Experience

Experienced mold designers often have preferred cylinder sizes.

This can be useful as a starting point.

But the real application demonstrates why experience should not replace calculation.

The customer had a specific problem:

approximately 1 mm of backward movement during injection.

The Technical Team then calculated:

6,250 kgf holding force

and

370 kgf traction force.

Only after these calculations was the V260CF Ø36 mm recommended.

This is a much more reliable engineering process than simply selecting the cylinder used on a previous mold.

25. The Relationship Between the Punch and the Cylinder

The punch should be considered part of the hydraulic system’s mechanical load path.

Its:

projected area;
lateral contact area;
guide system;
geometry;
connection to the rod;

all influence the force required from the cylinder.

This is why the Vega calculation considered both the frontal surface and the lateral surface of each punch.

The cylinder cannot be sized independently of the component it moves.

26. The Role of the Material

The customer specified PA6.6 with 30% glass fiber.

The material influences the molding process and the interaction between the polymer and the mold surfaces.

In the specific calculation documented by Vega, the traction-force calculation used a coefficient of adhesion of 25 kg/cm².

The calculated useful traction force was therefore 370 kgf.

This shows why the material and its interaction with the mold surfaces should be included in the engineering analysis.

27. Holding Force and Extraction Force Must Not Be Confused

The application is a useful reminder that different stages of the molding cycle can generate completely different loads.

During injection:

The punch must resist the injection force.

During movement or extraction:

The cylinder must overcome the forces resisting movement.

These are not necessarily the same.

In the documented application:

useful holding force ≈ 6,250 kgf;
useful traction force ≈ 370 kgf.

The ratio between these two values illustrates how dramatically the required force can change depending on the operating phase.

28. The Engineering Value of Preload

Preload is particularly interesting because it addresses a different problem from cylinder force.

A larger cylinder increases the available hydraulic force.

Preload instead reduces the amount of free movement available within the mechanical assembly.

In other words:

larger cylinder → more force

preload → less mechanical clearance

These are different engineering tools.

Vega’s current self-locking documentation specifically identifies preload as a method for preventing small movements caused by oil compressibility and accumulated tolerances.

29. The V260CF Configuration Proposed by Vega

The original technical response proposed:

Hydraulic cylinders

2 × CF036NB020

Alternative cylinders

2 × CF036MB020

Flange

2 × RF036211E

Alternative flange

2 × RF036271C

Check valves

2 × ZR35AH301/4-1/4.

This level of detail is useful because it shows that the solution was not simply “use a V260CF.”

The complete proposed assembly included the cylinder, mounting/interface components and hydraulic circuit components.

30. From a Cylinder to a Complete Locking System

The most important conclusion from the real application is that the cylinder should not be considered independently.

The actual solution was:

V260CF

flange

possible preload adjustment

check valve

punch

mold structure

hydraulic circuit

The performance of the system depends on how these components interact.

31. A Practical Design Checklist

Before approving a hydraulic locking system for an injection mold, the following questions should be answered.

Process

What is the maximum cavity pressure?
What material is being molded?
What is the projected area?

Force

What is the injection force?
What is the extraction or traction force?
What safety margin is required?

Cylinder

What bore is required?
What stroke is required?
Can the cylinder reach the complete locking position?

Locking

Is mechanical locking required?
What external force must the lock withstand?
Can the cylinder reliably unlock it?

Preload

Are there accumulated clearances?
Is a preload-adjustable flange required?

Hydraulic circuit

Is a check valve required?
How is pressure maintained?
How is the cylinder released?

Mold structure

Is the support sufficiently rigid?
Can the punch move under load?
Are the guides correctly designed?

32. The Main Engineering Lesson

The real lesson from this application is not simply that a V260CF Ø36 mm was selected.

The more important lesson is the methodology used to reach the selection.

The customer reported a real process problem:

the punches moved approximately 1 mm during injection.

Vega then translated the mold geometry and process conditions into mechanical forces:

12.5 cm² × 500 bar → approximately 6,250 kgf holding force.

A second calculation based on the lateral surface and material adhesion produced approximately 370 kgf traction force.

Only after defining these loads was the cylinder and its associated hardware selected.

This is the correct engineering sequence.

33. Conclusion

A hydraulic cylinder installed on an injection mold is not simply an actuator.

In applications where injection pressure acts directly on a punch, slide or core, the system must be designed to move the component and keep it stable under process load.

The real application examined by the Vega Technical Team involved two punches that moved approximately 1 mm backwards during injection. The material was PA6.6 with 30% glass fiber, and the estimated cavity pressure was 500 bar.

The calculated frontal area of each punch was approximately 12.5 cm², producing a useful holding force of approximately 6,250 kgf. The corresponding traction calculation produced approximately 370 kgf.

Vega therefore recommended a V260CF with 36 mm bore, together with either a preload-adjustable or neutral flange and two check valves.

The broader engineering principle is clear:

The correct hydraulic-cylinder solution is determined not only by the force required to move a mold component, but also by the force acting on it during injection and by the way that force is mechanically resisted.

Mechanical locking and preload can be particularly valuable when the mold component must remain stable under high injection pressure. Vega’s current self-locking technology is designed precisely to transfer external loads through a mechanical locking system and reinforced cylinder structure rather than relying exclusively on hydraulic pressure.

For mold designers, the most important lesson is therefore to evaluate the complete load path before selecting the cylinder.

A one-millimetre movement may be small in dimensional terms, but it can reveal a much larger engineering problem.