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The Role of Consultants…

I am often asked questions similar to the one I just received…

Ben
We are going to need some technical help… how do I determine whether I should hire another engineer or get a consultant?
My Response
We deal with technical issues within the plastics industry all the time. Although we openly advertise our expertise in creating employee development systems… we routinely visit companies around the globe to provide technical consultation for plastics, processing, and training.
In general, this question can be handled using four common approaches…
1) If you have a unique issue such as troubleshooting, equipment evaluation, or beginning a new program… a consultant is often the best way to resolve the situation. Many companies hire an engineer to help handle a specific situation… and then under use their talents performing routine tasks once the situation is resolved.
2) If you want to create a long term change in behavior such as 5S or process documentation… a consultant can often help you determine the best approach to determining the best behavior, educating your employees, and maintaining the behavior. Once this is established, it will be very easy to determine whether your current employees can implement the strategy… or if additional staff is necessary to ensure the success of the initiative.
3) If there are only one or two routine tasks which take place monthly or quarterly such as a tool design review or a molding trial… having a consultant on retainer may save you money in the long term.
4) If you have an established routine or series of complex tasks which need to be performed, hiring an engineer or technician is most likely the best course of action.
Additional Thoughts
Always try to hire employees and consultants with the intention of exploiting their talents… for example, hiring a consultant to measure and weight a large number of parts may not be cost effective… but hiring a consultant arrange outside testing, or to evaluate the results and help draw conclusions may be very helpful. Adversely, when our consultants help a company develop a strategy for training their employees, their engineers, managers, and supervisors are often the best people to implement and carry out this training with their employees.
-Andy

Profiling Injection Due to Moldflow Results…

I saw this unique question in my e-mail yesterday…

MJ
What is your opinion about profiling the injection based on the results of a Moldflow analysis?
My Response
Mold filling analysis programs such as moldflow can provide a variety of options for filling. For example, you can use the software to profile in order to minimize variations in fiber orientation, shear rate, shrinkage, etc. Many seasoned injection molders will agree that the simulation information is very helpful, but the final process will depend more factors than can be programmed into the computer… The biggest factor being Quality.
Overall, I find these simulations extremely helpful in establishing the mold design, and to determine the general approach to processing the final tool. If such a program suggests an injection profile, then I would use that information to better understand potential complications with the process. For example, if the software recommended a lower speed through a thin section and a faster speed through a thicker section… I would personally evaluate whether to first try one speed through both, or profile my speeds during the initial setup.
One thing to keep in mind when processing… each injection speed is a variable… the more variables you introduce into the process, the more variation you potentially introduce.
My Response
All data such as blueprints, analysis, and customer requirements are helpful to the person establishing the process. Additionally, the more complex the part and tool, the more useful this data can become.
-Andy

Adjusting for Differences from Machine to Machine

This is a topic which often occurs when you are processing with various machines.
M.

How do I compensate for the differences in how my machines handle the transfer from fill to pack?

My Response
Although we often talk in generalities… each brand and generation of machine has it’s quirks.
For example, when using an older ____ controller… I often have use profiling to incrementally drop the injection speed at the end of fill to slow down the large ram so it does not overshoot during pack.
Also, I recently used a ____ all-electric molding machine which would stop the ram when I turned off second stage pack, but would allow the ram to overshoot once pack was turned on. In that case, I had to turn on pack… but reduce the pressure to the minimum setting to get a realistic performance.
Additional Thoughts
Think of it like a car, an older truck may need 3rd gear to climb a hill at 40 MPH… while a newer sports car could easily climb it in 2nd, 3rd, or 4th gear. Some choices are preference… while some are from necessity.
The key is to establish a way to document the process in a manner which can be duplicated and transferred to your different molding machines.
-Andy

Providing a Buffer To Accommodate for Variation

I recently received this follow-up question regarding an earlier blog entry…
Firdaus
To establish a molding parameter, what is the normal percentage tolerence to be used for the injection pressure and other parameters? Currently my process does not have any tolerence and sometimes this may cause difficulty in troubleshooting which will result short mold and etc.
My Response
In general, a well-established process encounters approximately 10% variation. For this reason, it is critical to ensure you have enough room to adjust your process inputs for this. 
For example, if first stage injection becomes pressure-limited, the machine can no longer maintain the desired injection rate, resulting in an inconsistent fill rate and injection time. This generally leads to unwanted short shots, sinks, and flash on the final part.
To avoid a pressure-limited process, you should always have more pressure available to fill the mold than is actually necessary. This will allow the machine to maintain the ‘injection speed set point’, ensuring the highest possible repeatability.
The problem you may encounter is the fact that many machines actually need an additional buffer to perform properly. For instance, a process may reach a peak pressure of 10,000 psi during first stage fill… yet, if the machine has a maximum setting below 10,500 psi, the process could become pressure limited.
The best way to approach this is to do the following…
1) Establish a good process with significantly more pressure than is necessary.
2) Reduce the maximum injection pressure until it affects the injection time by increasing the 1st stage fill time.
3) Increase this maximum by 10-15% to accomodate for material variablity.
I also recommend you review a few of our related posts… including
dditional Thoughts
If you are running a lot of regrind, or off-spec material, you may want to increase this buffer to as much as 20%. In such a case, it is imperative that you use a short-shot during 1st stage fill.
-Andy

How Many Clamps To Use?

In response to a recent blog entry, I got this series of questions…

Mauricio
How many clamps are needed to hold a specific tool? Which is the correct distance between clamps? Is there an order or sequencing to tightening the bolts?

My Response
When asked ‘How many clamps should I use?‘ one plant manager I know likes to respond with ‘As many as you can‘. In reality, each clamping system, mold base, and platen is different. When discussing standard adjustable height mold clamps, I prefer to use six clamps per half on smaller molds, and as many as a dozen for larger molds. In general, the spacing of the clamps are usually dictated by the platen hole location and rail size.
When tightening the bolts, I recommend using an alternating pattern which alternates back and forth as well as up and down. For example, when using a four clamp setup, starting with the top right hand corner, you would tighten in this order:
└ Top Right

┐ Bottom Left (diagonally across)

┌ Bottom Right (across)

┘ Top Left (diagonally across)
The intent is to balance the force being applied to the mold base to prevent any uneven stress on the mold base or platen.
Additional Thoughts
Ultimately, the more clamps that you use, the less stress that is applied to any specific clamp point. This will increase the life of the clamps, and help prevent damage to the platen holes. 
-Andy 

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