A brief meeting between all those involved with your molded part can save you time and money.
Over-the-wall engineering – All in their own cubicles: lack of communication
Benefits of concurrent engineering in injection molding
A few months ago, a customer of mine called me to go look at an issue he was having with a part being molded in a brand-new mold. It was a two-shot part, with TPE overmolded on to a PP substrate. The issue was that the PP substrate had voids in it, reducing the strength of the part. Injecting the TPE would result in filling the voids, bottoming out the screw, and potentially lead to short shots.
I was told it was a 30% glass filled PP. I looked at the gate, and thought it was too small for a glass-filled plastic. Then as I glanced at the hopper and looked at the sight glass, I noticed that there were no pellets in there, as the material was LFT (long fiber thermoplastic). The machine screw had a GP screw with a high compression ratio, which would destroy the glass fibers and sometimes segregate the melt from the glass.
At this point I knew that this was not only going to be a time-consuming challenge, but that it was also going to be an expensive deal to get to the final molded part with the required quality.
A few things had to change. Modifications would have to be made to the mold. The machine would need a different screw and barrel assembly. This would require not only time, but also money. Further, there would be a learning curve to figure out how to process such a material since there was no prior knowledge base in the company.
This was a situation where cross-functional meetings and prior discussions could have saved the company time and money. Prior knowledge could have produced the parts on time, with the required quality, and within the allotted budget.
Another customer of mine was told by someone that it is possible in an overmolding operation to make the same overmolded plastic in the same shot stick to one area of the substrate and not the other. Imagine a 10 by 10-inch plate with TPE overmolded all over, but the TPE did not have to bond to ten small squares on the surface. This was a very critical part for an assembly and they had almost completed the design. They were going to send it to a moldmaker to make the expensive two-shot mold. At this point, no molder had been contacted—just the moldmaker in Asia who was going to build the mold. It would have been an unfortunate and expensive failure.
Simply put, concurrent engineering is involving representatives from every department in the project at the earliest stage. This should be followed with subsequent meetings where the project details and any changes should be reviewed by the team to understand the impact it may have on their own individual departments. This way, when the product designer mentions that the material is a LFT, the process engineer knows he will need a different screw and nozzle tip or the scheduler knows that he will need to schedule time on the only machine in the shop with the special screw. Raising a red flag at this stage saves time and money and delivers the product on time. A conventional over-the-wall approach is commonplace in most companies, but disengaging each department is a common cause of failures, inefficiencies, and delayed launch of the product.
To understand this further, let us look at the matrix in Table 1. The first column is a list of departments typically involved in the design and manufacture of a product. The top row describes the activities involved. A ‘Y’ at the intersection of a row and a column means that the particular activity has an impact on that department. For example, for the process engineer, the mold design is very important, whereas for the quality department, the mold design is of no value. Please note that this is a universal matrix and there will be exceptions.
Each member of this development chain has specific involvement with the process and, just as important, involvement with the other links in the chain.
The product designer
This is where the process starts and is usually the first step.
Conventional involvement: Product design is where the concept first takes shape as a CAD model or a prototype. At this time, they have a general idea of what the requirements of the plastic material are and therefore may or may not have selected it. The machine, the mold design, the molding process, or any of the other factors are of no concern to them. They are looking for a functional concept.
Required involvement: A product designer should understand the manufacturing process, especially the processing end of it. Design for manufacturability principles must be implemented. Common examples include: a thick section in a part must be cored out to reduce sink, or sufficient draft must be provided on the part to release the part from the mold. An explanation of the function of the part to the molder and his team would be beneficial to the molder. This way, the process engineer knows the particular material he needs to process or can raise a flag saying the tolerances are impractical.
The tooling engineer
Once the product designer has an acceptable design, the tooling engineer gets involved in the design and the economics of building the mold. Of all the job functions, the tooling engineer is probably the one who has been most involved in the project since direct involvement is required at many of the various stages.
Conventional involvement: The tooling engineer is usually the liaison between the moldmaker and the molder, whose job has been to deliver the mold to the molder and fix the issues that the molder sees during the processing. Any design changes to the parts, features, or dimensions need to get reflected in the mold, and the tooling engineer is responsible for this function.
Concurrent requirement: A tooling engineer must understand the concepts of developing a robust process. The techniques and the benefits of scientific processing should be familiar to him. The tools must be qualified using these techniques, and changes to the mold must be made to support a robust process. For example, having a process window is extremely important for understanding that reducing mold temperatures below the recommended mold temperatures for a crystalline material is risking product failure. The tooling engineer must closely work with the process engineer, the quality engineer, and the moldmaker.
The mold designer and moldmaker
Most moldmakers have their own mold designers. They are given the part model and they design the mold accordingly. Note: One of the biggest disconnects I have seen is between the moldmaker/designer and the material supplier.
Conventional involvement: The mold designer acquires the design from the part designer and designs the mold for the number of cavities, and the moldmaker fabricates the mold. The designer knows the type of material that will be used for molding the part, but sometimes does not have the details.
Concurrent involvement: The mold designer and the moldmaker must get in touch with the material supplier to get information for designing the runners, gates, and vents. For instance there is a huge difference between using a 30% glass-filled material and a 30% long-fiber glass-filled material. Apart from this, the mold design must be reviewed between the part designer, the mold designer, the moldmaker, and the process engineer. At first shots, the moldmaker must be present to see how the mold functions. The moldmaker must also understand the concepts of scientific processing and why a process window is important.
The material supplier
In most cases the material supplier sells the resin and if the customer does not call with any questions, the supplier usually will not call the customer to see if they were able to make acceptable parts. However, material suppliers are the greatest source of information for mold design, part design, and processing, and therefore must be used to the full potential.
Conventional involvement: Material suppliers provide material specs to the designer, help in the material selection, and sell the resin.
Concurrent involvement: Invite the material supplier to the mold design review to determine if the vent sizes are right or if the gate design is acceptable for the part fill. Subgates are great for self-degating but should not be used for highly fiber-filled materials. When the material is going to be molded for the first time in a particular facility, the molder must invite the material supplier. The material supplier will make sure that the material is processed in the right manner for optimum properties and cycle time. It also helps to involve the material supplier at the mold design stage, especially if this is a new material.
The process engineer
Unfortunately, in many cases, the process engineer is the most neglected member of the whole team and ironically is the most important one. This is the person everyone is looking at to deliver the final product. The process engineer has to take the brunt of all the factors that were not taken into consideration and all the mistakes and miscommunications during the entire project.
Conventional involvement: This depends on the individual organization. I know of some organizations where the process engineer sees the mold or knows about the project on the day it is scheduled and in other cases is involved at the mold design stage.
Concurrent requirement: The process engineer must be involved at every stage of the project. Based on their molding experience, a number of suggestions can be given to improve the overall molding operation. They are better judges of features such as vents, gate locations, and so on. Mold designers tend to place gates in locations convenient for moldmaking, which are not always the best locations overall. Even non-technical requirements such as the orientation of the mold can be reviewed by the process engineer.
The choice of machine must be left to the process engineer. Again, based on calculations of tonnage, percentage of shot size used, and residence time, a process engineer can suggest the right machine. In a few instances, I have seen a mold being processed using about 5% of the total shot size, leading to issues of low cps and Cpks.
The quality engineer
Typically the quality engineer is only considered a ”measurement person” and again is often neglected. The quality engineer can have valuable insight from past experiences on similar parts or plastics, and usually has information about shrinkages and the tolerances one can hold during production.
Conventional involvement: The quality engineer is one of the invitees of the product release meetings and is usually assigned the task of obtaining drawings and working on methods for measuring the final molded parts.
Concurrent requirement: The drawings must be discussed with the product designer. If a SLA or a prototype model is available, it should be used to detail out the inspection plan. Sometimes fixtures are required, and these can be planned in advance. Initial gage R&R studies can even be performed on prototype parts. Any impractical tolerances can be mentioned to the designer in advance.
The molder's sales team
The sales team is usually responsible for introducing the product designer to the molder. They are looking to increase the sales of the molder and therefore try to acquire as much business as possible. However, they must understand the technical aspects in order to get the right set of customers. If the product and the molder are not the right match and the mold still comes into the facility, this could have a negative impact not only on the product, but also on the relations between the two parties. All future work can be jeopardized. I know a molder that tried to mold a part that was about 3% of the total shot of the machine. There was inconsistency, material degradation, and at the end, an upset customer who is probably never going to come back to this very capable molder.
Conventional involvement: The sales force brings in a job mainly based on machine tonnage. Then there are other factors that they consider, such as special requirements. These include cleanrooms, inmold decoration, or insert molding. A company I know would never want a part that was not insert molded unless it was part of an assembly of an insert-molded component.
Concurrent involvement: The sales team must understand the capabilities of the molder in depth. This also includes the strength and weaknesses of each department in the organization. If not, the sales team is setting up the company for failure. The rules of machine selection for a particular job must be clearly understood. Tonnage, shot sizes, percentage of shot size used, residence times, and so on must be known before accepting a job. For example, if the machine shot sizes are expressed in polystyrene, the melt density would be different for other materials, which is a technical aspect in which the sales team must be well versed.
Concurrent engineering – Communicating and voicing concerns
at an early stage
Must-have knowledge for all departments
The final molded part is the result of the efforts of all the departments involved. In traditional over–the-wall practices, every department performed its list of things to do and passed it on to the next department. However, the practice fails to address the issues the receiving departments could have as a result of an action from the previous department. Understanding the needs of each department makes the jobs easier, more efficient, and ensures on-time delivery of a part that meets specifications. Every department must understand --cross-functional duties and have a basic understanding of each other’s job function.
For example, everyone must know what scientific processing is and why it is important to have a good a process window. If the process engineer sends a mold back to the moldmaker or the tooling engineer because there is no process window, it is a very valid reason. Even if ten good parts can be made, it doesn’t mean that half a million good parts can be made, because the process is not capable. The knowledge of process capability must be commonplace in every department of the molding facility.
Implementing concurrent engineering
Concurrent engineering is probably the easiest concept to implement. All it takes is to make sure all the departments are involved in the complete process. Table 1 is a simple matrix of the typical job functions and activities involved. Be sure to set up a meeting between the representatives of each department for the various phases of the project. For example, the sales team must be involved in the machine selection process. Please note that the order of the activities is not necessarily the order in which the activities are performed. For example, to make sure the molder has the machine for the particular job, the machine must be selected at the quoting stage—not when the job has been accepted and a machine must be selected from those that the molder has. This list of activities and job functions is a general list and every company has its own organization structure, so a customized matrix must be generated.
The molding business is becoming extremely competitive in terms of cost and lead times. The timelines from art to part are shrinking, and the expectations are to produce acceptable parts on the first molding attempt. Only those companies that can achieve this are likely to survive in the growing but competitive market. Concurrent engineering provides the extra sets of eyes needed to look out of the box and raise potential concerns. These are meetings well spent, and regular reviews must be done, especially if there is a change in the design, material, timeline, etc., which must be communicated to everyone. The final product, good or bad, is a result of the involvement of the whole team.
Author Suhas Kulkarni ([email protected]) is president of consulting firm Fimmtech Inc. (Vista, CA).