Roger has been involved exclusively with the plastics industry since 1981, when he worked at a shop in Tempe, AZ. Prior to that he managed a toolroom in Minnesota that produced everything from small injection molds to steel stamping dies to custom designed assembly fixtures to early NC programmable machining centers. Product design started as a service to his customer base where they knew how they wanted their new products to service their customers and the general public, but were held back by a lack of knowledge applying the principles of injection molding to their production.
Designing a plastic part in a way that is most suitable for consistent manufacturing is based on simple characteristics. First, uniformity. The thickness of every part of your part should be as uniform in thickness as you can possibly make it. This is because as the part is injected with molten plastic, any pressures and perimeters that the machine operator sets up to make one area of your part look good, all the other areas of your part will come out the same (based on straight-forward hydraulic principle). Necessary strength factors that have to be incorporated into your part can be accomplished with ribs and gussets in such a way as to not effect the uniformity of your consistent thicknesses. Secondly, design your parts to get them out of the mold. Imagine a Jello mold that also has an inside to the two-piece mold form. The bottom and the top are lined up and held together. the space in between the two halves is where the Jello will be formed. When the Jello has set up and is firm, you would pull one side of the two-piece mold off of the assembly and the Jello would be inside the other half still unaffected by the removal of the first half. Baking a bunny cake works the same way. This is the most cost effective way to design parts when it comes to tooling costs (where the word tooling refers to the mold that is custom made to make your new part). Undercuts can be incorporated into the tooling, but they add cost to your project. Thirdly, choose a poly material that best suits your part and customer needs for appearance, performance, longevity expectations.
Come to the table with realistic expectations about how poly materials will serve the needs of your part function and your customer needs. Injection molding production parts are a truly cost-effective way to manufacture many useful items in today's modern world, but their are natural limits to the process reality. Quantity is the first reality. There are 2 major components of the plastics manufacturing process. First, there is the tooling expense and second, there is the material and molding expense. The tooling expense is (most often) a 'one-time' up-front cost...say $5,000. The molding expensive is an ongoing expensive for every part that is produced...say $.50 per part. The true part cost to you must take into account the amortization of the tooling expense over the life and quantity of the parts that you eventually make with the mold. Say you only expect to sell a 1,000 pieces of the part you want to mold. Amortizing the mold cost over a 1,000 pieces gives you a cost of $5.00 per part plus the $.50 to mold it. This makes your cost to manufacture $5.50 per part. Now if you are going to make 100,000 parts over the life of the product and mold, your total part cost would be only $.55 because you are spreading out the cost of the tooling over many more molded parts.
Help can be found for your project in the businesses that support the plastics industry all across the country and across the world. A company that specializes in injection molding is usually called a 'custom molding house' in the industry. Most major cities (and even some of the smaller towns in America) have at least one and most likely more than one. The word custom in the slang vernacular, refers to the fact that they mold on a custom-need basis for random customers as opposed to have a set of molding machines that are molding their own products in-house, which would in turn be called a proprietary molding house. Custom molding houses will also usually have available designers and other design help to insure proper tooling and part designs are attempted to best serve all involved in a project. Keep in mind that if a poorly designed mold and part get into a custom molder's press, it will probably be wasting his time as well as your money and in the end produce nothing notable worth selling for any constructive purpose.
Stand-alone design firm, like NITEC in Southwestern Idaho, also exist to help companies and individuals make the most out their manufacturing investments in order to produce viable products for the marketplace and the betterment of consumers.
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