Specifying a material must be a shared process, with the ultimate responsibility falling to the OEM.
Increasing material costs make it difficult for molders to give their customers the annual cost reductions they have come to expect. The circumstances leading up to this situation were reviewed in Part 1 of this article (April 2005 IMM).
A January 2005 survey cited raw material pricing as processors’ primary concern for the future. The cost of plastic materials is dictated by the material manufacturers and to a lesser extent by their distributors. These costs are established based on a lot of interrelated factors. In the final analysis, the price is what the market will bear.
Plastic Material Selection
Traditionally, the OEM selected and specified which plastic material would be used for a given application. This method of working was based on the sound logic that the OEM knew the most about the functional and regulatory requirements of its products. It frequently conferred with material manufacturers and molders, but in the final analysis it was the OEM that specified the material to be used. This is as it should be, as it is the OEM that introduces the product into the stream of commerce and has the most to gain or lose in marketing it.
Back in the days when OEMs specified materials, many buyers were not plastics specialists. They conveniently convinced themselves that all nylon 6/6 or polypropylenes were the same. They might or might not have considered melt index, but in general they chose a material based on its low cost. The resulting molding problems and functional failures actually increase the molder’s and eventually the OEM’s costs.
Selecting the optimum material for an application is obviously an important design and manufacturing decision. The ideal material for an application always was, and still is, the lowest-cost material that performs as required. Finding that lowest-cost material has become a relentless pursuit. These downward costing pressures are now changing the old tried and proven procedure for selecting a material.
A growing number of OEMs are now holding their suppliers responsible for selecting a suitable material. The primary reason behind this change is to minimize cost. Another factor is that downsizing by OEMs has eliminated many of the engineers who used to select the materials of construction. Today there are only a few very large OEMs that still have materials specialists on staff. The remaining nontechnical staff is totally befuddled by the smorgasbord of available materials.
The IDES Prospector plastics search engine (www.ides.com) lists more than 57,000 plastic materials for sale. It is virtually impossible for the human brain to develop a familiarity with this many materials. The computer does an excellent job of reducing a large number of materials to a more manageable number of prime candidates. It does, however, require a knowledgeable person to conduct the search.
OEMs also believe that they are in the furniture, automotive, plumbing, housewares, or electronics business and are not a part of the plastics industry. They reason that their suppliers, who work with plastics all day, every day, are materials specialists. This is true, but only up to a point.
Supplier’s Expertise
Resin manufacturers are materials experts; however, their expertise is often limited to the materials they sell. In recent years, downsizing by resin manufacturers and their distributors has reduced the number of technically competent people available to help OEMs.
Resin producers have always advised OEMs on material selection. Their recommendations were, however, viewed with some skepticism. There was a suspicion that the supplier would not suggest the ideal material unless it was available from his company. This certainly happened, but most resin manufacturers would give their customer an honest recommendation. A molder’s expertise is in knowing enough about product design, materials, tooling, and molding to bring these four elements together to produce an acceptable part. Plastic materials are just one of the four elements molders have to know about.
Molders possess extensive knowledge of the plastics that they routinely mold. A custom molder has no incentive to become familiar with all of the other materials that his company doesn’t mold. It would be only the largest custom, or captive, molders who could afford to have full-time materials specialists on staff.
Some argue that they are not interested in the whole spectrum of available plastics as they work only with polystyrene, nylon, and propylene. Today there are 1218 polystyrenes, 4280 nylons 6/6, and 4311 individual polypropylenes offered for sale. Many of those compounds are duplicates from competing manufacturers, but no two are identical. There are subtle differences that can mean success or failure in processing or performance. Among the members of a family of materials, such as polypropylene, costs vary by a few cents. The OEM is expecting his molder to sort through 4311 propylenes to find the one lowest-cost grade that will perform as required. Finding that lowest-cost material takes time and effort. This activity also requires constant attention, as plastic material costs frequently change. Anyone can determine the cost of a plastic material. However, it takes a technically competent person with detailed knowledge of the application to analyze the material’s published properties and determine that it will perform as required. That person also has to verify that the material meets the regulatory requirements such as FDA or UL. If the product is to be exported, what are the requirements in the target countries? Last, but not least, can this lowest-cost material be efficiently processed in the existing molding machines and molds?
A molder is certainly better than his customer at determining the processibility of a material. The OEM, on the other hand, has or should have a better understanding of the regulations and functionality requirements of the product in its end-use environment. In other words, the molder doesn’t know as much about an application as his customer. It is, therefore, impractical to make a molder solely responsible for selecting a material for a given application.
It must also be remembered that in lieu of any other written agreements, whoever specifies a material is in effect guaranteeing that it will be suitable for its intended purpose. The greater technical knowledge possessed by resin manufacturers and molders is such that it is highly desirable for them to recommend plastic materials for their customers’ consideration. The final selection of a plastic material for a given application must, however, be made by the OEM.