10/1/2003 | 4 MINUTE READ

Plastic Processes Can Protect Business

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 Many consumer products are produced in China nowadays.


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Many consumer products are produced in China nowadays. So far, at least with regard to the U.S. auto market, the number of components being made by Chinese companies is comparatively low. Still, there has been some public discussion by OEMs with regard to their pricing expectations. And the word “China” has been used in that discussion. Which leads one to think that if suppliers, in particular, are going to be interested in protecting and maintaining their business, then perhaps they could learn a thing or two from the consumer products companies that continue to produce products in the U.S.

According to Barr Klaus, vice president-Technology, Milacron Plastics Technology Group (Batavia, OH), there are several trends that are going on in the world of consumer goods manufacturing that have direct applicability to automotive—and, yes, some companies are already embracing them in their efforts to increase productivity and reduce costs.

Done In Two. One of these is to use equipment that permits two-component molding. It’s sometimes referred to as “over molding.” Essentially, there is a single machine that has a tool set that contains two molds. In the first mold, there is a given material injected. That part is then indexed into the second mold. There is a second injection made of another material over that first step. So when the mold is opened again, a finished part is ejected. (Of course, after the first cycle, this is a case wherein each time the clamp opens, a finished part is ejected.) Did you ever pay attention to the manual toothbrushes with the elaborate handles? Chances are, they were produced with this over molding process. Not only does this two-component molding process facilitate color changes, but it is also possible to mold in different components. In addition, there is the possibility of achieving significant material cost savings by using a less expensive material for the core of a part, then over molding a more expensive material. According to Klaus, they have supplied equipment to an agricultural equipment manufacturer that is using over molding for a steering wheel. In this instance, the outer material—the user interface—is different from the core. First the skin is injected, then the core follows.

According to Klaus, there are several advantages to this process. For one thing, there is the issue of floor space: This equipment is comparable in size to machines that perform a single injection process. Yet the productivity is measurably greater. There is savings in handling. Instead of having to move a part from one machine to another, this is simply a case of transferring parts within the machine. There are also benefits with regard to inventory: This simplifies things greatly because there is what’s known in the lean manufacturing world as “one-piece flow.”

An area where there has been significant attention of late with regard to this process is in moving the part from cavity 1 to cavity 2. Apparently, the early versions made use of a rotary turntable but the configuration was such that in order to rotate the tools, there was a large swing requirement, one that meant, for example, that a component that could be made with a 500-ton machine had to be made on a 1,000-ton machine because it had a platen with a sufficient size. This disadvantage has been overcome in a variety of ways, such as mounting the tools in a stack configuration so that when the clamp is open, the rotation is perpendicular to the centerline of the machine. In this setup, there are four faces to the rotary cube, which means that on the two faces that aren’t used for the injection process other operations (e.g., adding labels, cooling) can be performed, thereby reducing cycle time. Another approach is using a robot that removes the part from one mold and places it in another.

Stacking Up. Another process that is getting more attention is a process that’s been used for some 30 years in the production of things like coffee can lids. This involves multiple parting lines, stacking molds within a machine. According to Klaus, back when this coffee lid application was initiated, it was determined that it was possible to make 16 lids (two molds) with about the same amount of clamp force required for eight lids (one mold). (The difference was on the order of about 10 to 15%.) But it is important to note a characteristic of the parts in question: Comparatively flat.

Klaus suggests that while parts including door panels (assuming that there isn’t a great deal of curvature involved) could be handled, parts with greater curvature, such as instrument panels, would be more difficult, because of both the stack height and the weight of the tools (it would probably require a special machine).

While it is common to think of automotive being a place where the volumes are comparatively high, Klaus points out that when you take into account variations between companies as well as variations within a company’s models, compared to the production of some items—like DVD packages—the volumes aren’t as high, so while the expense for special tooling can be readily cost-justified by some consumer products companies, that may not be the case for auto component suppliers.


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