XHW – A global manufacturer & supplier of rubber seals & gaskets
+86 13925295320
joyzhong@xhwrubber.cn
XHW – A global manufacturer & supplier of rubber seals & gaskets
+86 13925295320
joyzhong@xhwrubber.cn
When we receive a new plastic part for mold development, we should not rush into mold splitting or mold structure design. The first and most important step is to carefully analyze the product structure and determine whether the part is suitable for injection molding.
A proper product analysis should include draft angles, wall thickness, undercuts, parting direction, gate location, material, shrinkage, appearance requirements, and other molding-related considerations. These factors directly influence the mold structure, manufacturing cost, mold life, and final product quality.
For engineers who are new to injection mold design, this process may initially seem difficult. However, product analysis is a skill that develops through continuous practice and experience. Once the draft angles, wall thickness, and undercuts in the mold-opening direction have been analyzed, the general direction of the parting line and the possible gate location can usually be determined.
However, these decisions should always be confirmed with the customer before finalizing the mold design.
Before starting the actual mold design, several important items must be confirmed. Failing to clarify these requirements in advance can result in major design changes later.
The key information includes:
A good mold designer should understand not only the part itself but also how the part will be manufactured, assembled, and used.
The customer’s injection molding machine specifications must be confirmed before designing the mold.
Important parameters include:
These parameters determine whether the completed mold can actually be installed and operated on the customer’s machine.
For example, a designer might create a sophisticated mold using a hydraulic core-pulling system, only to discover that the customer’s production machine does not support the required hydraulic system. This kind of mistake can result in major redesign work after the mold has already been completed.
Therefore, machine compatibility should always be confirmed before mold structure design begins.
The mold clamping method is another important requirement that must be confirmed in advance.
Common methods include:
The selected clamping method determines whether the mold requires:
Ignoring the customer’s clamping method can make an otherwise correct mold difficult or impossible to install.
The plastic material and its actual grade must be confirmed before mold design.
Do not simply assume that a material has a fixed shrinkage rate. For example, different PP grades can have significantly different shrinkage characteristics depending on the formulation, additives, reinforcement, processing conditions, and supplier.
The designer should confirm:
The correct shrinkage value is essential for determining the mold dimensions and achieving the required final part dimensions.
If possible, the mold designer should understand how the product is assembled and what the product is used for.
This information can help determine:
Understanding the actual function of the product often allows a complicated structure to be simplified.
A good mold designer should not simply accept every feature in a product design. If a product contains an unnecessarily complicated undercut, the mold designer should communicate with the product engineer and determine whether the structure can be modified.
The fundamental purpose of mold design is to turn complex problems into simple, reliable, and manufacturable solutions.
Before designing the mold, the customer’s external connection requirements should be confirmed.
These normally include:
Understanding these requirements in advance allows the designer to plan the internal layout properly.
Otherwise, a mold may be almost completely designed before discovering that additional hydraulic connections or internal oil circuits are required. At that point, the cooling channels, ejector pins, screws, and other components may already occupy the available space, making redesign extremely difficult.
For molds with hydraulic core-pulling or hydraulic ejection systems, the hydraulic circuit should normally receive early consideration.
The hydraulic circuit should be arranged as evenly as possible. An unbalanced hydraulic circuit can cause cylinders to move at different speeds, resulting in uneven mold actions.
A flow divider can be used when necessary, but this adds complexity to the system.
Cooling should then be considered carefully because cooling-channel distribution directly affects:
Electrical and pneumatic connections can generally be arranged after the main hydraulic and cooling requirements have been established.
The exact layout should always follow the customer’s mold-standard requirements.
Once the basic product requirements have been confirmed, the next step is product analysis.
The designer should carefully examine:
Draft is especially important because surfaces parallel to the mold-opening direction generally require sufficient draft for reliable part release.
After completing this analysis, the designer can begin determining the parting line.
The basic principle of parting-line design is:
Keep it as simple as possible.
Whenever a surface can be created through a simple extrusion or extension, avoid unnecessary complex surface construction.
The parting surface should also follow the natural geometry and trend of the product whenever possible.
A well-designed parting line can help reduce:
Parting-line location also affects draft direction, ejection, gate location, mold complexity, and product appearance, so it should be considered during the early DFM stage rather than after the mold structure has already been finalized.
When creating a parting surface, avoid unnecessary complexity.
For example:
A mold may look impressive in CAD because it contains many complicated surfaces, but complexity itself is not a sign of good mold design.
A better question is:
Can the mold shop manufacture, assemble, polish, and maintain this structure efficiently?
The best design is usually the simplest design that reliably meets the product requirements.
Slides and lifters must be considered while developing the parting surface because their movement may require changes to the parting geometry.
Typical slide mechanisms include:
Most of these mechanisms are based on geometric relationships and mechanical motion used to release undercuts.
The designer must verify not only the theoretical movement but also the actual mold-opening sequence.
The slide mechanism should be designed according to the required stroke and available space.
The angle of the angled guide pin should generally be kept moderate. In many conventional designs, keeping the angle below approximately 30 degrees is a practical guideline, although the actual limit depends on the mold structure, load, stroke, friction, and manufacturer standards.
The angled guide pin should also have sufficient diameter and strength because it carries the load generated by the slide mechanism.
The principle is simple:
Do not make the guide pin unnecessarily small just to save material.
Strength, wear resistance, and service life are more important than minimal component size.
Lifters are widely used to release internal undercuts.
Common variations include:
Although their structures may look very different, their basic purpose is the same: use controlled mechanical movement to release the undercut during mold opening and ejection.
A conventional lifter should generally avoid excessive inclination.
As a practical design guideline, keeping the lifter angle around 15 degrees or less is often preferred when the structure allows it. Larger angles may increase friction, reduce smoothness, increase wear, and make long-term reliability more difficult.
However, the final design must be evaluated based on:
The designer should always simulate the complete ejection movement before releasing the mold design.
Many special mold mechanisms are based on relatively simple mechanical relationships.
Understanding basic trigonometry and mechanics allows engineers to design:
The important point is not simply knowing how to use CAD software.
The real skill is knowing how to apply CAD tools to solve engineering problems.
A designer should understand the principle behind every CAD command rather than simply memorizing the command sequence.
After the parting line, slides, and lifters have been determined, the overall mold structure can be established.
Depending on the product and production requirements, possible mold structures include:
The purpose of choosing a mold structure is not to make the mold more sophisticated.
The purpose is to select the most appropriate structure for stable, efficient, and economical mass production.
When selecting the mold base, all previously confirmed customer requirements must be considered.
The mold base must be compatible with:
The mold base should provide sufficient space for all necessary components without creating unnecessary oversizing.
The basic principles of mold insert design are:
If a section of the mold contains a particularly thin or fragile area, it is often better to design it as a separate insert.
Replaceable inserts can simplify future maintenance and reduce the cost of repairing damaged areas.
The designer must also consider:
After the major mold structure has been established, standard components can be added.
Ejector layout should normally be considered early because it interacts closely with the cooling system and product structure.
Ejector pins should preferably be placed in areas where the product has sufficient structural strength, such as:
Avoid placing ejectors on weak or cosmetic surfaces whenever possible.
Poor ejector positioning can cause:
The ejection system should always be designed according to the actual product structure rather than using a purely symmetrical layout.
Cooling-channel design should be coordinated with the ejector system and mold structure.
Areas with high part retention force often require stronger ejection, but these areas may also correspond to hot spots that require effective cooling.
Therefore, ejector layout and cooling-channel layout must be optimized together.
The designer should balance:
Ejection requirements + Cooling requirements + Structural strength + Machining feasibility
Cooling design directly affects cycle time, dimensional stability, warpage, and product quality. Modern mold design reviews therefore commonly check cooling layout together with inserts, ejectors, slides, and other mold components.
The correct ejection method depends on the product geometry.
Possible solutions include:
For example, if the product tends to stick to the cavity side, the designer may need to reconsider the mold-opening relationship, add a suitable undercut on the core side, or introduce an appropriate ejection structure.
The correct solution becomes much easier to identify when the designer understands what happens to the product during filling, cooling, mold opening, and ejection.
Many mold design mistakes come from looking only at the CAD geometry and not considering the actual molding process.
The designer should ask:
A good mold design is based on the behavior of the part during the complete molding cycle, not simply on its static CAD geometry.
A completed mold design must undergo a systematic review before manufacturing begins.
At minimum, the following checks should be performed.
Check all mold inserts and forming surfaces for insufficient draft and unintended undercuts.
Perform a complete interference check between:
Interference checking is one of the most important steps in final mold design verification.
Simulate:
Even simple molds should be simulated if there is any uncertainty about the movement sequence.
Every component should be checked to determine whether it can actually be manufactured using the available machining processes.
The designer must verify that all components can be assembled in the correct sequence.
A theoretically correct mechanism is not necessarily a manufacturable mechanism. A design can satisfy all calculations and still fail because a component cannot physically be installed or removed.
There is no single “perfect” mold structure.
Mold design is always a balance between:
A more sophisticated mold may provide better functionality but also increase manufacturing cost and maintenance requirements.
A simpler mold may reduce cost but could require product modifications or compromise mold strength and service life.
Therefore, the goal is not to create the most complicated mold.
The goal is to find the best balance between product requirements, mold complexity, manufacturing cost, reliability, and service life.
Before releasing the final mold design, confirm the following:
A structured mold design review before steel cutting can prevent expensive downstream changes and reduce the risk of tooling problems during sampling and mass production.
Injection mold design is not simply the process of converting a 3D product model into a mold assembly. It is a systematic engineering process that starts with understanding the product and ends with verifying manufacturing, assembly, operation, and maintenance.
The most important principle is to think before designing.
Analyze the product first, confirm the customer’s production requirements, determine the correct parting line, simplify the mold structure, carefully design slides and lifters, coordinate ejection with cooling, and finally verify the complete mold through interference checks, motion simulation, machinability analysis, and assembly review.
A good mold designer does not try to create the most complicated structure. Instead, a good designer finds the simplest structure that can reliably manufacture the required product.
In injection mold design, the tool is important, but engineering thinking is even more important.
#cooling channel design #design for manufacturability #draft angle #ejector pin design #Injection Mold Design #injection mold DFM #injection mold ejection #injection mold optimization #injection mold structure #injection mold troubleshooting #injection molding #injection molding defects #injection molding machine compatibility #mold base selection #mold cooling system #mold design process #Mold Engineering #mold inserts #mold interference check #mold lifters #Mold Manufacturing #mold motion simulation #mold parting line #mold slides #parting surface design #Plastic Injection Mold #plastic part design #tooling design #undercut design #wall thickness
CONTACT US
Wechat: +86 13925295320
China Marketing Center: