Applying Lean Manufacturing to In-Mold Decoration
by Bob Travis, Vibrant Graphics
As companies implement initiatives such as lean manufacturing to stay competitive in a global marketplace, they often adopt new solutions like in-mold decoration to achieve their goals. Unfortunately, these initiatives frequently stop short of exploring how lean principles applied to new technologies can create even greater benefits. This article will explore how in-mold decoration can be used to achieve the goals of lean manufacturing initiatives and venture into new areas where lean principles can be applied specifically to the in-mold decorating process to extract even greater benefits.
The Seven Wastes of Lean Analysis
Modeled after the Toyota Production System, lean manufacturing methods help to identify and eliminate the seven wastes of manufacturing. Every process is broken into activities that can be categorized as value-add and non-value- add. The non-value-add activities are considered waste and can be sub-categorized in seven distinct areas: defects, overproduction, transportation, waiting, inventory, motion, and over-processing. The goal is to improve the value-add steps and eliminate or minimize the non-value-add steps.
The seven wastes and the strategies to manage them have been a focus for injection molding companies for years. Unfortunately, as molders have become more adept at making their processes lean, market demands have forced them to introduce new capabilities and product offerings to stay competitive. Often these added capabilities introduce a new set of wastes, or add even greater waste to existing processes.
Plastics decorating is a capability that molders often add as a competitive necessity or table stake to satisfy their customers. The growth of this area may even be the result of the customers lean initiatives that shift decorating to the molder to eliminate non-value-add activities within the customers facility. But simply shifting waste from the customer is not enough. When evaluating and implementing plastics decorating methods, it is important that the molder continue to pursue lean principles to minimize areas of potential waste.
The Emergence of In-Mold Decoration
In-mold decorating for injection molding is a technology that is gaining acceptance in North America as a viable plastics decorating option. In addition to minimizing waste, in-mold decorating has gained momentum because it can deliver additional printing benefits such as variable imaging, high-resolution graphics, and a broader color gamut that direct imaging technologies cannot achieve. To understand the impact of in-mold decoration, it is important to start with a clear understanding of the process. p>Flat film in-mold decoration involves the placement of a preprinted graphic on the surface of an injection molding tool. The graphic is designed to be an insulator, so when a static charge is placed on the label the charge is captured on the label, causing it to stick to a grounded surface. For in-mold decoration, the ground reference is the injection mold. In addition to being an insulator, the in-mold graphic also is designed to fuse with the molten resin that is injected into the cavity. This fusion can occur with tie coats, laminates, or compatible film technologies.
|Exhibit 1 – Flat Film IML/IMD Methods|
Beyond flat film applications, in-mold decoration also can be achieved with the use of pre-formed graphic inserts. Pre-formed inserts are a very specialized method of in-mold decoration that achieves a three-dimensional result that cannot be achieved with other decorating methods. Because it is dissimilar from other decorating methods and is not considered a substitute for pad printing, thermal transfer, PSA labeling, or hot stamping, it is not part of this analysis and is mentioned only to establish a distinction from flat film solutions.
In-Mold Reduction of the Seven Wastes
Although any process can create waste, the very nature of in-mold decoration eliminates many of the more common wastes identified with other direct imaging technologies. The following is an explanation of how in-mold decoration can reduce the seven wastes:
- Defects: In-mold decorating graphics are printed by the printer in a printing plant. The very nature of printing requires a clear environment to eliminate the impacts of dirt, grease, and dust. When printed defects do occur, the scrap is an un-molded graphic, not an entire plastic part, therefore minimizing the cost of defects.
- Overproduction: Overproduction still occurs with in-mold decoration, but the cost of the overproduction comes from the printed graphic instead of the molded part. In-mold decoration allows the molder to shut off his molding machine when enough good products are produced, instead of producing extra molded parts to cover potential printing defects to make an order.
- Transportation: Transportation of parts to a secondary decorating station is eliminated with in-mold decorating, because when the part comes out of the mold it is complete.
- Waiting: In-mold parts have no cure time for cooling, since the decoration occurs in the mold. However, there is some waiting, or mold open penalty, that does occur with in-mold decoration in order for the label to be placed in-mold. This waste may or may not be favorable over other decorating waiting waste.
- Inventory: In-mold decorating will increase the cost of the graphic inventory in a process. The inventory usually is less costly than the work in progress of molded parts waiting to be decorated.
- Motion: In-mold decoration occurs with automation in the injection molding machine. The takt time of in-mold decoration motion usually occurs within the takt time of the molding press.
- Over-processing: In-mold decorating leaves the printing to the printer, eliminating the involvement of engineers to achieve competency. Additionally, in-mold decoration uses automation that eliminates most molding operator involvement in the decorating process. While there is potential for automation systems to be over-designed for this process, proper system design should prevent over-processing waste.
When in-mold decorating is compared to other decorating technologies with the seven wastes of lean manufacturing, it is apparent that in-mold decoration has many advantages.
Identifying Decorating Waste beyond the Molding Operation
Despite the apparent win that in-mold decoration can have at eliminating typical decorating waste, the continuous improvement process of lean manufacturing should not stop with the value- and non-value-add activities of the molder. In fact if another facet of lean analysis known as the waste of unevenness is applied to the entire process of in-mold decoration, then in-mold decorating costs can be reduced and in-mold decorating can be even more robust.
When the entire in-mold decorating process is value-stream mapped from printer to molder and the wastes are identified, it is very clear that there is unevenness waste that impacts the printer and molder differently. Yet if the waste can be put into balance, then the in-mold decorating process at the molder would become more robust and the cost of the graphic from printer to molder would become less.
The Challenge of the Stack
The unevenness waste is the stack of in-mold labels. When the entire value stream is evaluated, there are very strong correlations of scrap generation surrounding the label stack for both the printer and the molder. In the printers case, the scrap occurs when the labels are put into the stack. At very high speeds the thin, unsupported label films can jam in the cutting equipment and create non-value-add activity straightening the labels and re-stacking. For the molder, the problem is in the un-stacking of the label. Inherent static causes labels to stick together when being removed from the nest. This un-stacking can cause a phenomenon known as doubles or can create orientation problems of the labels in the stack. In either case, over-processing waste often occurs as engineers and managers try to overcome the challenges of the label stack.
Surprisingly, molders or printers seldom return to their lean principles to overcome the challenge of the label stack. Yet the solution is clear when tatk time is considered for the entire process and not merely the tatk time of just the printer or the molder. A printer could solve its issue of cutting if it did not need to cut labels as fast as its printing takt time. And molders dont require labels as fast as a printer can cut them. If they could pick a single label when needed, they would eliminate the waste of the stack.
Therefore, the solution is to remove the stack and move the cutting operation to the molder where the takt time is dictated by the injection molding machine. Systems are currently running in North America where the printer ships printed rolls of parts to the molder, and the molder cuts the label next to the injection molding machine precisely when needed. This process immediately eliminates the scrap and problems surrounding the label stack, because the labels are never stacked; they are cut and picked from the material web and placed in-mold.
The first reaction of many molders is that the printers are merely giving the cutting problem to the molder, but this is not the case. A printer could solve its cut and stack problems by running its equipment at slower speeds. But equipment is expensive and not intended to run at slow speeds. For the molder, cost-effective equipment can be designed to run at a slow speed that is well within the molding takt time. This equipment would supplant the label magazine and handling automation and simplify the process of presenting a single label to the automation.
More Work to be Done
Currently, the systems that are running use a slit and chop method of cutting because the labels are rectangular. Contour shapes add complexity to the cutting equipment, but there are numerous systems on the drawing board. In the coming year, press-side cutting solutions with diecut shapes will become available. These solutions will be implemented not because they constitute a different approach to in-mold decoration but because they are a part of the lean approach to in-mold decoration.
In-mold decoration is a decorating technique that has some very clear advantages when evaluated from a lean manufacturing perspective. But like all decorating technologies, the process needs continual improvement to yield the best results for the molder and its customer. Based on the industrys current experience with in-mold decoration, the label stack is still a source of waste and innovation must continue to occur to make in-mold decoration a robust solution. Lean manufacturing analysis would suggest the best solution to the problem of the stack is a paradigm shift as to where an in-mold label should be cut. Mold-side cutting eliminates the stack and the problem. More work must be done. To compete in a global marketplace, molders must consider innovation and tools like lean manufacturing analysis to survive.
Bob Travis has over 22 years of sales, marketing, and product development experience in the printing industry, with an emphasis over the past 10 years on printed products for in-mold decorating and labeling. He has a wealth of experience with static charging techniques, different IML materials, IML troubleshooting, and IML automation. Currently, he is the general manager of Vibrant Graphics (specializing in developing digitally printed product solutions for OEM and IML markets), Milwaukee, Wis., and is acting president of the In-Mold Decorating Association (IMDA). He can be contacted at email@example.com.