A Customer Case on Cylinder Sizing, Thrust and Pulling Force, and the Choice Between Two Hydraulic Solutions
Selecting a hydraulic cylinder for an injection mold is not simply a matter of checking the available hydraulic pressure and choosing a cylinder with a suitable bore.
The cylinder must be matched to the actual forces generated by the mold mechanism, while also considering the available pressure, installation space, stroke, speed and overall cost.
A real Customer application reviewed by the Vega Team provides a useful example.
The Customer was concerned that the hydraulic cylinder selected for the application might be incorrect and asked the Vega Team to check the drawing again. The specified hydraulic working pressure was 100 bar.
After reviewing the drawing, the Vega Team confirmed that its calculations were correct and identified two possible hydraulic solutions:
- CF071, with the final code to be defined;
- CR080036, also with the final code to be defined, with a minimum working pressure of 80 bar.
After considering the required thrust and pulling forces and the different cylinder prices, the Vega Team suggested considering the CR080036 solution.
This case demonstrates an important engineering principle:
The correct hydraulic cylinder is not necessarily the largest cylinder or the one with the highest pressure rating. It is the cylinder that provides the required force under the actual operating conditions of the application.
1. The Customer’s Concern
The Customer asked the Vega Team to review the drawing because there was concern about making a mistake when selecting the hydraulic cylinder.
The working pressure was specified as:
100 bar.
This type of request is common in injection-mold engineering.
A wrong cylinder selection can lead to:
- insufficient force;
- excessive hydraulic pressure;
- inadequate movement speed;
- unnecessary installation space;
- increased hydraulic consumption;
- higher costs;
- modifications to the mold after manufacturing.
For this reason, checking the cylinder selection before finalizing the mold can prevent much more expensive problems later.
2. The Drawing Must Be the Starting Point
The Vega Team did not simply confirm the previously suggested cylinder.
It reviewed the drawing again and concluded that the original calculations were correct.
This is an important aspect of engineering design.
When there is uncertainty about cylinder sizing, the correct approach is to return to the application itself:
What force does the mold actually require?
Only after answering that question should the engineer select the hydraulic cylinder.
3. The Role of the Hydraulic-Cylinder Manufacturer
The Vega Team also clarified an important distinction regarding engineering responsibility.
Vega explained that it is not the mold designer, but designs and manufactures hydraulic cylinders.
This distinction is important because the cylinder manufacturer and mold designer have different areas of expertise.
The mold designer knows:
- slide geometry;
- guide systems;
- mechanical loads;
- mold structure;
- cycle sequence;
- friction conditions.
The cylinder manufacturer knows:
- cylinder geometry;
- hydraulic force;
- bore and rod dimensions;
- pressure limits;
- sealing systems;
- cylinder configurations.
The best result comes from combining these two areas of expertise.
4. The 100 bar Working Pressure
The main hydraulic parameter provided by the Customer was:
100 bar working pressure.
The basic hydraulic-cylinder force relationship is:
F = P × A
where:
- F = hydraulic force;
- P = hydraulic pressure;
- A = effective piston area.
For a circular piston:
A = π × D² / 4
where D is the piston bore.
Therefore, for a given pressure, increasing the bore increases the available hydraulic force.
5. Why 100 bar Alone Does Not Determine the Cylinder Size
Knowing that the hydraulic system operates at 100 bar is not enough to select the correct cylinder.
The critical question is:
How much force does the application actually require?
For example, two different cylinders may generate the required force:
- a smaller cylinder at higher pressure;
- a larger cylinder at lower pressure.
Both can be technically valid.
The final selection depends on the complete application.
Vega’s current technical material similarly emphasizes that hydraulic-cylinder selection should begin with the forces generated by the mold mechanism rather than simply choosing a cylinder from a catalog.
6. Thrust Force and Pulling Force
A hydraulic cylinder must normally be evaluated in both directions.
Thrust force
The piston uses its complete effective area:
Fpush = P × πD² / 4
Pulling force
The rod occupies part of the piston area:
Fpull = P × π(D² − d²) / 4
where:
- D = piston bore;
- d = rod diameter;
- P = hydraulic pressure.
Therefore, for the same pressure:
pulling force is lower than pushing force.
This distinction becomes particularly important in injection molds where the cylinder may move a slide in one direction and extract a core or insert in the opposite direction.
7. The First Proposed Solution: CF071
After reviewing the drawing, the Vega Team identified:
CF071
as one possible solution, with the final product code to be defined.
This cylinder was therefore considered suitable based on the forces calculated for the application and the specified hydraulic conditions.
The important point is that the CF071 was not selected simply because the Customer’s hydraulic system operated at 100 bar.
The selection was based on the relationship between:
required force + hydraulic pressure + cylinder characteristics.
8. The Alternative Solution: CR080036
The Vega Team also proposed:
CR080036
with a minimum working pressure of:
80 bar.
Since the Customer’s specified hydraulic working pressure was 100 bar, the proposed operating condition was compatible with the minimum working-pressure value stated in the technical communication.
This created a second possible design approach.
Instead of selecting a smaller cylinder operating at a higher pressure, the Customer could consider a larger cylinder operating at a lower pressure.
9. Why a Larger Cylinder Can Operate at Lower Pressure
The principle is straightforward.
Hydraulic force depends on piston area.
A larger piston has a larger effective area and therefore produces more force for the same hydraulic pressure.
Consequently:
smaller bore + higher pressure
can produce a similar result to:
larger bore + lower pressure.
This is a fundamental principle of hydraulic design.
The Vega Team’s proposal of both CF071 and CR080036 illustrates this principle in a real mold application.
10. Why the CR080036 Was Worth Considering
The Vega Team did not only consider the technical force requirements.
It also considered the different prices of the cylinder solutions.
The communication specifically states that, based on the thrust and pulling forces and the different cylinder prices, the Vega Team suggested considering the CR080036.
This is an important engineering principle.
Once several solutions are technically valid, the design can be optimized according to:
- cost;
- available pressure;
- installation space;
- hydraulic-system capacity;
- expected operating conditions.
11. Oversizing Is Not Always Better
A common approach in hydraulic design is:
“If in doubt, use a larger cylinder.”
This may provide additional force, but it can create other problems.
An unnecessarily large cylinder can require:
- more installation space;
- greater oil volume;
- higher flow rates for the same speed;
- larger hydraulic connections;
- higher component cost.
Therefore, oversizing should not automatically be considered a safety measure.
The objective is to select an appropriate cylinder with a suitable engineering margin.
12. Pressure and Force Are Different Parameters
Another important distinction is between:
hydraulic pressure
and
hydraulic force.
Pressure is expressed in bar.
Force is expressed in N or kgf.
A pressure of 100 bar does not represent a fixed cylinder force.
The resulting force depends on the piston area.
For example, doubling the piston area doubles the theoretical hydraulic force at the same pressure.
Therefore:
100 bar × small area
and
100 bar × large area
produce very different forces.
13. The Importance of the Cylinder Bore
The bore is one of the most important parameters in cylinder selection.
Because:
A = πD² / 4
the piston area increases with the square of the bore diameter.
This means that relatively small increases in diameter can produce significant increases in available force.
This is why cylinder bore, pressure and installation dimensions must always be considered together.
14. The Hydraulic Circuit Must Also Be Considered
The pressure indicated for the machine or hydraulic system does not necessarily mean that the cylinder always receives exactly that pressure.
Pressure losses can occur through:
- valves;
- hoses;
- fittings;
- flow-control devices;
- manifolds;
- other hydraulic components.
The effective pressure at the cylinder should therefore be verified when the application is critical.
This is particularly important when the required force is close to the cylinder’s theoretical capacity.
15. Speed Is Also Part of Cylinder Selection
Force is only one side of the calculation.
The cylinder must also move the mold component at the required speed.
The basic relationship is:
Q = A × v
where:
- Q = hydraulic flow rate;
- A = effective piston area;
- v = cylinder velocity.
A larger cylinder requires more oil to achieve the same linear speed.
Therefore, choosing a larger bore may solve a force problem but create a flow-rate problem.
This is another reason why cylinder sizing must be optimized rather than simply maximized.
16. Thrust, Pulling and Mechanical Load
The hydraulic force calculated from pressure and piston area is not necessarily the same as the actual mechanical force required by the mold.
The mold may include:
- wedges;
- inclined slides;
- mechanical locks;
- guides;
- levers;
- friction surfaces.
These mechanisms can transform the force.
Vega’s technical material specifically emphasizes that slide geometry can significantly change the force transmitted to the hydraulic cylinder.
Therefore, the cylinder should be selected only after understanding the complete mechanical force path.
17. The Importance of Mold Geometry
Consider a hydraulic cylinder connected to an inclined slide.
The cavity pressure may generate a very large force on the slide.
However, the geometry of the slide can transform that force before it reaches the cylinder.
This means that:
cavity pressure ≠ cylinder force
unless the mechanical geometry is direct.
This principle is particularly important for side-action mechanisms.
The mold designer should therefore provide the cylinder manufacturer with the relevant drawing or 3D model whenever the force path is complex.
18. Mechanical Locking Can Change the Calculation
Some injection molds use mechanical locking systems.
When the mold is mechanically locked, the mechanical structure can absorb the injection load directly.
In such applications, the hydraulic cylinder may not need to resist the complete cavity pressure during injection.
Instead, the cylinder may primarily be responsible for:
- moving the slide;
- unlocking the mechanism;
- extracting the insert;
- positioning the component.
Vega’s current technical documentation describes this principle in relation to self-locking hydraulic cylinders.
This can dramatically change the required cylinder size.
19. The Difference Between Hydraulic Holding and Mechanical Locking
There are two fundamentally different approaches.
Hydraulic holding
The cylinder remains pressurized to maintain the component in position.
Mechanical locking
A mechanical system carries the load once the component reaches its locked position.
The second approach can reduce the continuous hydraulic force required during the injection phase.
For applications requiring mechanical locking, Vega currently offers the V270CG self-locking hydraulic-cylinder family.
20. Why the Customer’s Drawing Is So Important
The Vega Team’s response emphasizes that the calculation depends on the drawing supplied by the Customer.
This is an important lesson for mold designers.
When requesting cylinder sizing, the most useful information includes:
- mold drawing;
- 3D model;
- cylinder mounting position;
- stroke;
- required movement;
- hydraulic pressure;
- slide mass;
- cavity pressure;
- draft angle;
- friction conditions;
- required cycle time.
The more complete the information, the more reliable the cylinder selection.
21. A Practical Cylinder-Selection Procedure
For a similar application, the design process can be organized into the following steps.
Step 1 — Analyze the mold mechanism
Determine exactly what the cylinder has to move.
Step 2 — Calculate the required mechanical force
Consider the actual load, not just hydraulic pressure.
Step 3 — Determine the available hydraulic pressure
Use the pressure actually available at the cylinder.
Step 4 — Calculate the required piston area
Use:
A = F / P
Step 5 — Select a suitable bore
Choose a standard cylinder with sufficient effective area.
Step 6 — Verify pulling force
Do not evaluate thrust only.
Step 7 — Verify stroke and speed
Ensure the cylinder can complete the movement within the required cycle time.
Step 8 — Consider the mechanical design
Check wedges, guides, friction and locking systems.
Step 9 — Compare alternative cylinders
If several technically valid solutions exist, compare their dimensions, pressure and cost.
Step 10 — Validate the complete application
The final cylinder selection should be checked against the real mold and hydraulic circuit.
22. Two Valid Engineering Solutions Can Exist
One of the most useful lessons from this Customer case is that there does not necessarily have to be a single “correct” cylinder.
The Vega Team identified:
CF071
and:
CR080036.
Both were considered technically suitable.
The final choice could therefore be influenced by practical factors such as:
- installation space;
- hydraulic pressure;
- component cost;
- available hydraulic equipment;
- preferred cylinder configuration.
This is normal engineering optimization.
23. The Best Cylinder Is the Best Compromise
In industrial engineering, the best solution is rarely the component with the highest specification.
The objective is to find the best balance between:
performance
reliability
installation
hydraulic requirements
cost
A cylinder that is technically capable but unnecessarily large may not be the optimal engineering solution.
Conversely, a low-cost cylinder that does not provide an adequate force margin is also not acceptable.
The correct solution is the one that satisfies the application requirements with an appropriate engineering margin.
24. What This Customer Case Teaches
The case provides several practical lessons.
1. Always verify the drawing
The Vega Team rechecked the drawing before confirming its calculation.
2. Do not select the cylinder from pressure alone
The 100 bar working pressure was only one parameter in the selection process.
3. Calculate both thrust and pulling force
The Vega Team specifically referred to both forces when comparing the alternatives.
4. Consider the mechanical system
The cylinder is part of the mold mechanism, not an isolated component.
5. Compare technically valid alternatives
The case produced two possible cylinder solutions.
6. Consider total cost
The Vega Team explicitly included the different cylinder prices in its recommendation.
Conclusion
Selecting the correct hydraulic cylinder for an injection mold requires a structured engineering approach.
In this Customer application, the hydraulic working pressure was specified as 100 bar, and the Customer requested that the Vega Team verify the cylinder selection because of concerns about making an error.
The Vega Team reviewed the drawing and confirmed that its calculations were correct.
Two possible solutions were identified:
- CF071;
- CR080036, with a minimum working pressure of 80 bar.
After considering the required thrust and pulling forces together with the different cylinder prices, the Vega Team suggested considering the CR080036 solution.
The main engineering lesson is therefore:
Cylinder selection should begin with the forces generated by the mold and end with the comparison of technically suitable cylinder configurations.
Pressure alone is not enough.
The designer must consider:
force → pressure → bore → pulling force → stroke → speed → mold geometry → installation → cost.
This approach avoids unnecessary oversizing while ensuring that the selected hydraulic cylinder has sufficient capacity for the real application.
It also highlights the value of cooperation between the mold designer and the hydraulic-cylinder manufacturer.
The mold designer understands the mechanical system.
The cylinder manufacturer understands the hydraulic actuator.
When both perspectives are combined, the result is a more reliable and cost-effective mold design.
Useful and Verified URLs
1. Hydraulic Cylinders for Injection Molds
Official Vega page presenting the current range of hydraulic cylinders specifically designed for plastic injection molding and die-casting applications.
Hydraulic Cylinders for Injection Molds – Vega Cylinders
2. How to Calculate the Correct Hydraulic Cylinder Size for Injection Molds
Official Vega technical article explaining cylinder sizing through core-pull force, plastic adhesion, hydraulic pressure and safety factors.
How to Calculate the Correct Hydraulic Cylinder Size for Injection Molds
3. How to Calculate the Pulling Force of Hydraulic Cylinders in Injection Molds with Mechanical Locks
Official Vega technical article explaining pulling-force calculations and the difference between mechanical locking and hydraulic force requirements.
How to Calculate the Pulling Force of Hydraulic Cylinders in Injection Molds with Mechanical Locks
4. The Angle That Changes Everything: Understanding Force Transformation in Injection Mold Slides
Official Vega article explaining how slide geometry transforms cavity pressure into the force actually transmitted to the hydraulic cylinder.
The Angle That Changes Everything – Vega Cylinders
5. Hydraulic Cylinder Manufacturer and Supplier
Official Vega company page describing its experience in hydraulic cylinders for plastic injection and aluminum die-casting molds, as well as its design, production and technical-support activities.
Hydraulic Cylinder Manufacturer and Supplier – Vega Cylinders
