Injection molding is by its nature a high cost process to establish and targeted at high volume applications. The tooling cost, even for the simplest/smallest part, is rarely below US$5k and rises quickly with size and complexity.
On the assumption that the required parts are needed in enough volume to justify the tooling cost, then amortizing the tool over large production runs erases the initial cost challenge – assuming a deal to build the tools can be funded.
The part cost issue then becomes one of material price and machine/operator time. These are two important factors that can be driven down by a variety of means. Chief among these means is reducing the machine/operator time by tooling the part(s) smartly.
I. What is Multi Cavity Injection Molding?
Where larger volumes of a single part are needed, it is common to cut multiple cavities into a single tool. These cavities are often identical copies of each other, connected by feeder galleries so that a single injection point can fill them all in a single action.
A tool that is 2x the size and contains (for example) 10 cavities that are all injected at one time will perhaps cost 2x the price of the single cavity tool, but the *tool cost per cavity* will be
2(more tool size) / 10(more cavities)
or 0.4x the single cavity cost.
In addition, the machine time to fill the tool and eject the parts might increase by a factor of 2, but the production rate will improve by a factor of
10(more cavities) / 2(slower operation)
or 5 x faster molding productivity for the same per-hour machine/operator cost, dramatically affecting part cost.
II. What is a Family Tool Injection Mold?
It is very common for an injection molded part to be one of several in an assembly. When these parts are all used to make the product and not excessively divergent in size, multiple cavities for multiple parts can be cut into a single tool.
These multiple cavities are analogous to multi cavity molding, the difference being that the various cavities are not necessarily identical – and often not very close in size.
This requires careful tool design to ensure that the cavities are balanced for flow and pressure – to prevent partial fill of one or other cavities, and to avoid cycle time/pressure difficulties.
In the simple example of a box and lid, the two parts can easily be close enough in size and flow characteristics that the cavities will be easy to balance. If the cycle time to fill the tool goes up by 1.5x, but the number of tools to be injected goes down by 2x, then machine/operator time drops by 0.75x.
While this can be viewed as a cost saving, it has a bigger effect on production scheduling and logistics, reducing operational cycles and the need for balancing production.
The value calculation should also account for reduced tool count/cost and reduced machine setup operations.
- Fewer tools for the same number of cavities has a pronounced effect on the up-front costs to establish injection molding production capacity.
- Fewer tooling setups and operational cycles is perhaps more important in the long term, as these are ongoing costs and cannot be amortized as they apply to every production run for the entire tool life.
III. Multi Cavity Injection Molds and Family Injection Molds: Which Method is Best for Your Application
There is a complex balance to be struck when selecting tooling formats and layouts.
Solutions vary considerably, and the higher the volume expectations the greater the opportunities for process acceleration, tool consolidation and reduced costs:
- A single, small to medium size component at high volume lends itself to multi cavity solutions, offering increased speed, greater machine utilization efficiency, lower material usage, all at the expense of greater complexity, driven by volume and price expectations.
These can be as simple as putting two cavities into a standard tool design and almost doubling productivity, for virtually no effect on cycle time per shot.
They can also be 20-30 cavity tools with hot runners and self trimming injection gates, to reduce material wastage to zero and make post injection trimming unnecessary and lower the part price to little more than that of the raw materials.
- A product with multiple unique components, or sets of duplicate or mirror parts, or any combination of these, potentially lends itself to being tooled in a family group, with diverse components molded in a single tool.
Family tools integrate all the parts of a plastic assembly into a single tool, to minimize the number of molding operations and to reduce the cost of otherwise tooling parts individually.
This offers the obvious advantage of reduced initial costs and reduced operational costs in manufacture. An added benefit is a significant improvement in manufacturing logistics, as all the plastic parts for a single product are molded in one operation.
- Finally it is possible, when scale demands it, to build multi cavity AND family tooling, to gain the advantages of both.
Multi Cavity Injection Molds : Benefits and Applications
Benefits of Multi-Cavity Injection Molds:
- Higher production output multi-cavity injection molds can produce several identical parts in a single cycle, which leads to a higher production output and lower manufacturing costs.
- Reduced cycle time, as molds can produce several parts in a single (somewhat longer) cycle, they significantly reduce the time needed for the manufacturing process.
- Reduced material waste by using less runners (feeders) etc per part, which contributes to cost savings.
Applications of Multi-Cavity Injection Molds:
- Automotive industry: in the production of various automotive parts such as car bumpers, dashboards, and interior trims, in some of the largest mold tools of any sector.
- Agriculture: in production of consumables such as stem clips and suspension devices for glasshouses and seedling pots
- Consumer products: devices such as clothes pegs, tableware, cups, higher volumes audio and peripheral devices etc
- FMCG packaging: widely used in the production of consumer packaging such as bottles, containers etc.
- Medical industry: in the production of medical consumables such as syringes, catheters, and drug delivery systems.
- Electronics industry: in the production of various electronic components such as switches, connectors, and housings.
Family Injection Molds: Benefits and Applications
Benefits of family injection molds:
- They are cost-effective, as they allow the production of multiple parts in a single mold, which reduces the cost of tooling and setup.
- They increase production efficiency, as multiple parts are molded simultaneously, which increases production efficiency and reduces cycle time.
- They improve part consistency, eliminating quality variations that often occur when using various mold machines and settings.
- They reduce tool volume and handing, as multiple cavities are integrated into a single mold, reducing the need for additional equipment/tools.
Applications of Family Injection Molds:
- Automotive industry: in the production of automotive parts such as interior trim components, dashboard components, handles and door panels.
- Medical industry: where these tools are used in the production of medical devices such as syringes, catheters, and drug delivery systems.
- Consumer goods: when applied in the production of consumer electronics products, hand tools, toys etc.
- Electronics industry: widely used in the production of electronic components such as switches, connectors, and housings.
IV. Differences Between Multi Cavity Injection Molds and Family Injection Molds
There are a variety of areas in which family tools and multi cavity tools differ, though their principles of operation are essentially identical:
Type of Mold
Multi-cavity molds are designed to produce multiple identical parts in each cycle of the injection molding process. The tool consists of multiple cavities, or impressions, that are formed into the mold, allowing for the simultaneous production of several parts.
Multi-cavity molds are often used when large quantities of identical parts are required, as they can significantly increase production speed and efficiency.
Family molds are designed to produce multiple parts that are related or similar to each other, but not identical. Family molds consist of multiple cavities, each of which can be used to produce a different part within the same injection molding cycle.
This allows for the efficient production of multiple parts that share similar design features, such as size or shape. Family molds are often used when a range of parts with similar features are required, as they can reduce the need for multiple separate molds and increase manufacturing efficiency.
Quantity Per Cycle
Multi-cavity molds are typically more productive than family molds, as they can produce multiple identical parts in each cycle, leading to higher output rates and reduced cycle times. Since each cycle produces multiple parts, the overall production capacity is higher compared to family molds.
Family molds, on the other hand, may have lower productivity rates since each cycle produces multiple parts with different shapes, sizes, and features, requiring more complex molding processes. The production process may also involve different molding conditions for different parts, which can lead to longer cycle times and reduced output rates.
However, family molds can be more efficient in certain situations where a range of related parts is required. Using a family mold can reduce the need for multiple molds, and simplify the production process by producing related parts in a single mold. This can reduce manufacturing costs and improve overall production efficiency.
Multi-cavity molds tend towards shorter build schedule than family molds, as the tool design is often simpler and the production process more repetitive.
The mold is designed with multiple identical cavities, each of which molds a part in each cycle, which can reduce the number of specialist EDM tools required. Hence the build schedule for a multi-cavity tool can be shorter compared to a family tool.
Family molds can have a longer build schedule due to the complexity of the mold design and intricacy of the manufacture. Since each cavity produces a different part, the mold may require more complex molding processes and additional components such as slides or lifters.
Additionally, family molds often require more rigorous testing and adjustments during the build process, to ensure each cavity molds well.
However, the build schedule for both multi-cavity molds and family molds is likely to be more heavily influenced by the size of the mold, the manufacturing process used, and the complexity of the tool design. In general, larger and more complex molds require more time to build regardless of whether they are multi-cavity or family molds.
The build cost for multi-cavity molds and family molds can differ based on several factors, such as the complexity of the mold design, the number of cavities, and the size of the mold. These factors will commonly, but not always, overwhelm the cost implications of a multi cavity/family differential.
Multi-cavity molds can often have a lower build cost compared to family molds, as the mold design is simpler and requires fewer components.
Since the mold is designed with identical cavities that can produce multiple parts in each cycle, this potentially reduces the complexity of wedges/lifters and ejection pins, as all cavities are identically treated. This can sometimes result in lower design, material and labor costs.
Family molds can have a higher build cost due to the complexity of the mold design, in which each cavity requires unique treatments and may have singular features. Since each cavity produces a different part, the mold complexity may be affected by wedges/lifters for unique component features.
These molds generally require more testing and adjustments to ensure that each cavity produces a quality part.
However, the build cost for both multi-cavity molds and family molds can also be influenced by other factors such as the manufacturing process used, the size of the mold bolster, and the complexity of the overall tool design.
In general, larger molds and more complex part designs may require more time and resources to build regardless of whether they are multi-cavity molds or family molds, which can impact the overall build cost.
Price Per Part
The largest influence on the part price for any tool is the quantity of material consumed to make the part.
Typical multi cavity tools AND family tools generally reduce the net material usage per component, by integrating multiple parts into either type of tool, reducing the sprue volume used for each component, though this can be a small benefit.
Where the galleries in a family tol are complex and balancing of cavity flows is not straightforward, further material wastage may be required in family tools than in a typical multi cavity tool.
The biggest influence on material usage is the integration of hot runners into the tool. These keep all the main feeder galleries liquid between injection cycles, reducing the amount of waste plastic that must be ejected with the part.
Hot runners are mainly applicable to extensive multi cavity tools and very high volume production, but they do find application in family tools at times.
The second biggest influence on part cost is the machine/operator time required per cycle. A two cavity (multi cavity) tool halves the machine time per part approximately. A 20 cavity tool reduces it more than tenfold (accounting for increased cycle times).
This reduces machine costs per part, although it is more complex as the larger tool also requires a larger molding machine that has higher running costs.
Overall, the influence on part price between multi cavity and family tools is not simple to analyze.
V. Multi Cavity Injection Molds vs. Family Injection Molds: An Overview of Each Welding Process
Welding, in the context of injection molded polymers, is the process whereby internal features in a cavity cause the influx of molten polymer to part and flow around the cavity on complex flow fronts and then rejoin at the extremity, when the two or more areas of propagation meet.
Not all parts end up with a weld, it is highly dependent on part geometry and good gate (polymer inflow point) design.
For a good quality part to result, where there IS a weld, it must occur between two propagating flow masses that remain hot enough to merge fully and leave an invisible or near invisible seam or weld line. This is open to being influenced by mold machine parameters.
There are no hard and fast rules in the welding process for parts made in multi cavity OR family mold tools. Welding prediction and optimization is a skilled area of flow modeling and tooling design and it relies on long experience to get great results.
However, as a general principle, multi cavity tools fill geometry and flow process should be close to identical between the cavities as they fill in parallel off simple galleries, making the weld solution for all cavities, in a well designed tool.
For family tools, the fill process is likely to be considerably more complex, requiring the balancing of cavities or varied size and geometry, and sometimes the feeding of cavities from other cavities rather than direct from a gallery.
This can lead to increased complexity of flow and, in a poorly planned tool, it can exacerbate the issues related to good quality weld formation, resulting in ugly joint lines marring the part cosmetics.
It is common for difficulties to occur in selecting molding parameters that give perfect results in all cavities, so some compromise is required at times. Often this compromise is to optimize the high cosmetic parts weld line finish, at the expense of allowing visible weld lines on non cosmetic parts or faces.
Multi Cavity Injection Molds : Principle of Process
Multi cavity tools are generally designed for simplicity and repeatability between cavities.
There are two modes in which cavities are filled, however they are arrayed on the face of the tool:
- As with any mold tool, it is placed in a molding machine and set up according to ideal parameters.
- Once the system is up to operating temperature, plastic is injected from the barrel into the tool and fills the cavities.
- Often s run-up period s required to get the tool to a stable operational temperature, so the first shots are waste
- Galleries to distribute polymer are generally symmetrically arrayed, so the flow path length from the injection point to the gates are equivalent. This aids in regular and repeatable filling of cavities.
- These galleries can be at the split line of the tool and be ejected attached to the parts and then trimmed. Gallery material can then be reground and used again, or treated as waste/second grade material depending on quality requirements. In this case, gates will usually be tab variety and at the split line.
- The galleries can be cut as subterranean passages within the cavity side of the tool, feeding the cavities via subterranean gates. In thos case, heaters must be placed in the galleries (hot runners) to keep this plastic molten during the manufacturer process. This reduces wastage as the runners/galleries are not ejected with the part but left in the tool, liquid.
- All cavities being identical, ejector pins work on all parts at the same moment as the tool opens, pushing out the finished molding (attached to runners or not)
Family Injection Molds: Principle of Process
Family tools are generally designed to deliver a part count and fill all cavities cleanly and without overpacking/short-shot (underfilled cavities).
Cavities arrayed on the face of the tool primarily to meet flow/fill requirements:
- As with a multi cavity tool, it is placed in a molding machine and set up according to ideal parameters.
- Once the system is up to operating temperature, plastic is injected from the barrel into the tool and fills the cavities.
- Often a run-up period s required to get the tool to a stable operational temperature, so the first shots are waste
- Galleries generally lie at the split line of the tool and gallery fill is ejected attached to the parts and then trimmed. Gallery material can then be reground and used again, or treated as waste/second grade material depending on quality requirements. Gates will usually be tab variety and at the split line.
- Cavities varying, ejector pins may work differently on some parts, making pushing out the finished molding and runners more troublesome.
VI. Should you Choose Multi Cavity Injection Molds Or Family Injection Molds
The selection of whether to open multi cavity tooling is often not a clear one.
The decision as to whether to use individual or family tooling for a diverse set of parts for an assembly is generally a simple one:
- The choice between family or multi cavity tooling is generally an obvious one;
- when large numbers of a relatively simple part being required, a multi cavity solution is practical to reduce costs
- When more modest numbers of a group of parts to make an assembly are required, a family tool is a good option to reduce tooling costs and manufacturing logistics. Be aware of the quality hazards in family tooling and the relatively slow production rates that make this not suitable as a high volume option
- If early production volumes are lower, then investing in future production needs can be difficult, causing a push towards simple tooling and higher cost tolerance at the beginning
- It is often wise to make a single cavity tool for difficult components, to validate the design, material choice and manufacture before committing to the high cost of mass production tooling. Multi cavity tools with a large array of components and hot runners can be very costly – potentially 10x a small single cavity test tool (or more). Mistakes and design changes on multi cavity tools can be very challenging.
- If a family of parts is required and volumes do not justify individual or paired part tools, then a family tool is a way to consolidate and reduce tooling costs. Family tools CAN also be considered multi cavity tools when two or more family groups of cavities are included.
VII. Choose Kemal for Your Injection Molding Needs
Kemal is well placed and respected as a leader in our chosen fields. We have the knowledge and experienced to deliver full spectrum tooling and molding services to suit all of your needs.
- Molding Manufacturing
- Mold Design
- Mold Manufacturing
- CNC machining
- CNC machining service
- CNC milling
- CNC turning
- Injection molding
- Injection molding service
- Plastic injection molding
- Clean room injection molding
- Insert molding
- 3D printing
- Online 3D printing service
- Metal parts
- Die casting
- Metal stamping
- R&D and manufacturing solutions
- Rapid Prototyping
- Low-Volume Manufacturing
- Surfaces Finishing
Kemal has a great team, and leading facilities. We are the right partners for all your manufacturing needs and we adhere to the highest quality standards, to always provide the peak of services.
To know more about our services and how we can serve within your project, please contact us to demonstrate our team and capabilities. Let us show you how we can help to smooth your path to a great product and a flexible mass production.