Stack and Tandem Moulds
- Our Experience
- Why Choose Kore
- What is Stack Mould?
- Benefits of Stack Mould
- What is Tandem Mould?
- Benefits of Tandem Mould
- Difference between Stack and Tandem Moulds
- Why Stack and Tandem Moulds?
- When do we start to consider Stack moulds and Tandem moulds as possible plastic injection moulds options?
Why Choose Kore?
- We are definitely the pioneers in Asia to manufacture and test successful tandem moulds. To date, we have built multiple tandem moulds and are in production in America and Europe.
- Tandem moulds are often difficult to test or run production on-site in China, however, we are equipped with the appropriate injection moulding machine and auxillary equipment to run the moulds.
What is a Stack Mould?
Stack moulds are, as the name literally refers to, two or more moulding surfaces ‘stacked’ together. This multilayer plastic injection mould doubles the moulding capacity as compared to a normal plastic injection mold. Stack moulding increases the output of the moulding machine by providing multi layers for moulding output at the same time.
Contrary to the common perception, stack mould does not require additional clamping force in spite of having double the moulding surface. It is even possible to set different number of cavities in each mould parting surface. Stack moulding can also be used for multi-material injection that means, different types of materials can be injected in the cavities using stack moulding using a secondary plastic injection unit.
Advantages of stack moulding
- Requires less number of machines
- Reduces the overall cost by increasing the number of parts without increase in press size or clamp force.
What is a Tandem Mould?
Tandem moulding is very similar to stack moulding. Like stack moulding, tandem moulding also has two parting lines. However, the difference lies in the material injection process. Unlike stack moulding where injection takes place concurrently on the multiple moulding surfaces. The melt in the tandem mold is, however, injected in the cavities one moulding surface at a time, in an alternating sequence.
For example, the material will be injected in the first moulding surface and then after a hold, the material is injected in the second face while the first face cools. Tandem moulding optimizes processing costs by utilizing cooling time of one moulding surface to execute the filling and pack/hold sequence of the other moulding surface.
Benefits of Tandem Moulding
- Utilizes the cooling time of one moulding surface to execute filling/pack/hold of the other moulding surface
- Number of parts manufactured per machine increases in the case of Tandem moulding.
- Each side is processed separately resulting in more optimized process window
- Compatible with many injection moulding machines
Difference between Stack and Tandem Mould
The first major difference between a Stack and a Tandem injection moulds is the control of the opening and closing of the multiple parting line surfaces. A Stack moulds technology is purely mechanical racks/pinions and Tandem moulds is electronically controlled with magnetic locks.
The second major difference is a Stack moulds opens its dual parting lines and ejects all its moulded parts in one single cycle and the Tandem moulds opens one parting line at a single cycle and ejects only moulded parts in that parting line.
Why Stack and Tandem Moulds?
If the demand for a certain plastic injection moulded article doubles that the current output of a 16 cavity plastic injection mould producing this part is no longer adequate. And let’s assume that this mold runs on a 200 ton injection moulding machine. It therefore figures that the particular injection moulding press capacity is limited to one 16 cavity injection moulds, two 200 ton injection moulding press of same specifications only has capacity for two 16 cavity injection mouldss, so on…
Instead of requiring two 200 ton injection moulding machines with two 16 cavity plastic injection mould to meet the doubled demand, we can utilize the stack or tandem moulds technology that would only require one stack/tandem plastic injection mould and One 200 ton injection moulding machine to potentially meet the doubled demand!
What the Stack or Tandem moulds technology does is to incorporate two injection moulds into one. The key difference between a 2 cavity plastic injection mould and a 2 cavity Stack/Tandem injection mould is that a 2 cavity injection moulds is structurally one plastic injection mould and the 2 cavity Stack/Tandem injection moulds is technically two plastic injection mould in terms of construction.
To be sure, the decision making process whether or not to apply Stack or Tandem injection moulding technology starts with maximizing the number of cavities in a conventional single parting line plastic injection mould. Assuming the part geometry and the size of the injection moulder limits the injection moulds to 8 cavities, and any width or length increase of the injection mould would make the injection mould too big to fit the injection moulding press.
The key here is the width and length limitations of the injection moulding press.
What Stack and Tandem technology do is that they make use of the width or the daylight of the machine platen opening to fit “another” 8 cavity injection mould into the injection moulding machine.
- The key advantage of Stack and Tandem injection moulds is that it potentially doubles the output of the available injection moulding equipment and labor.
For example, a conventional 4 cavity automotive bracket mould with 700grams shot weight would require 55 seconds cycle time on a 400 ton injection moulding machine that moulds about 260 parts per hour.
The same part with a Tandem moulds would be 4 cavity (parting line A) + 4 cavity (parting line B) moulds with 700 grams shot weight but only 30 seconds cycle time. This optimization is achieved through overlapping cooling and processing of parting lines A and B. To be sure, while parting line A is undergoing cooling (about 30 seconds), parting line B is undergoing filling/packing/holding/cooling and ejected and vice versa.
The output for the above mentioned Tandem mould is a staggering 480 parts per hour representing an 85% increase in output with the same injection moulding equipment and labor, if any.
The Stack mould, like the Tandem mould, would be 4 cavity (parting line A) and 4 cavity (parting line B). However, the key difference is that when the Stack mould opens both A and B parting lines open at the same time. That said, the same bracket part injection moulded using Stack mould technology on the same 400 ton injection moulding press would have a shot weight of 1,400 grams in 8 parts with a 70 second cycle time.
What this translates to is a 58% increase in output with the same injection moulding equipment and labor, if any that is.
Key Disadvantages of Stack and Tandem Injection Moulds
The first concept the moulder has to get his/her head around is the sheer size of the injection mould build and commensurate effort and infrastructure required to operate and maintain the Stack and Tandem injection mould. Since the Tandem locks in the Tandem moulds technology are controlled by electronics, servicing and maintenance might involve more costs vis-à-vis a conventional moulds or even a Stack moulds. So bear that in mind while planning for maintenance budgets.
In spite of the superior unit economics of Stack and Tandem moulds plastic injection technology, especially with the right or high volume programs. There are other things to consider before adopting Stack and Tandem moulds technology in injection plastics processing.
So let’s see what we should be looking at internally before the adoption of Stack moulding and/or Tandem moulding technology in your plastic injection process
- evaluate Stack moulds and/or Tandem moulds’s potential weight
- evaluate hoist and cranes’ maximum weight lading limits
- evaluate forklifts maximum weight limits
- evaluate if current injection moulding presses has the necessary daylight to fit a Stack moulds in moulds open position (including end-of-arm-tooling fixture if applicable)
- evaluate with injection moulding machine vendor to see if current injection moulding presses could be reconfigured to process the signaling of the Tandem locks on the Tandem moulds
- evaluate injection moulding machine’s core pull capabilities to ensure there’s sufficient core pulls to operate valve-gates, slide actions, etc.
- evaluate hot runner controller to see if there’s sufficient number of zones in the hot runner controller for the Stack/Tandem moulds hot manifold
- evaluate if shop floor is able to withstand the combined weight of the Stack/tandem moulds without additional concrete reinforcement
- evaluate man power resource available to operate and perform maintenance on the Stack moulds and/or Tandem moulds; a typical Stack moulds or Tandem moulds would require a 2-crew team to perform moulds hanging and preventive maintenance on
- come up with training program to evaluate man power’s skill sets and capability is adequate for handling Stack moulds and/or Tandem moulds
- evaluate internal or external moulds repair sources’ capabilities for handling Stack moulds and Tandem moulds
Most plastic injection moulding shop applying the technologies in the initial periods might be put off by the amount of work required just to hang the moulds or to do basic preventive maintenance.
However, if the economics of Stack or Tandem injection moulding technology justifies its adoption. The moulder need to perceive the Stack or Tandem injection mould as two injection moulds instead of just one mould and allocate resources and schedule lead time accordingly to avoid unnecessary frustrations.
When do we start to consider Stack moulds and Tandem moulds as possible plastic injection moulds options?
- when our plastic injection moulds are at the maximum number of cavities for the largest available injection moulding machines sizes
- when our largest injection moulding machines running your maxed-out-cavities moulds are running at full or near full loading
- when we have limited room in the shop floor for more large injection moulding machines
- when we are having a hard time finding operators for current injection moulding stations, let alone adding more stations