Blow molding is the ideal process for a variety of products and parts used across many markets. You may find that blow molding is the “process of choice” when you have criteria for appearance, structural strength, resistance to corrosion, manufacturability as a single piece, integral color and other attributes. As with any process, for custom blow molded products, the design of the product should be considered along with the manufacturing process at the outset. Our designers and engineers will work with you to ensure optimum results. Here are a few of the major design considerations for custom blow molded products.
– General rule for proportion of the product: the blow molding process injects air into a tubular plastic extruded element known as a “parison” that is clamped between two halves of the mold. As the air pushes the material to fill out the cavity of the mold, the material is stretched. You will want to maintain width vs. depth proportions so that the depth of the cavity is no greater than half of the width. This is frequently known as the “blow ratio.”
– Corners: the blow ratio is also influenced by the shape of the part and its intended use. For example, a cylindrical part – think of a bottle – is an ideal shape because it doesn’t have corners in which the material will naturally be thinned. A product such as a stadium seat generally has a very shallow aspect ratio, so that “deep draw” situations that cause corner thinning are avoided. Bottom line, corners are not a problem with proper design. The inclusion of sufficient radii in the design will ensure that the product performs perfectly.
– Corner radii: avoid sharp corners. The inclusion of radii will increase the strength of corners and can be varied based on the depth of the product and the strength needed.
– Draft: the side surfaces of the product should be designed with a “draft angle” that will allow the finished piece to be easily removed from the mold. Since the molded part shrinks as it cools, it can be removed from the mold with minimal draft, but this will depend on the overall design of the product – depth of the part, relationship of opposing side walls, and so on. There are ways to “push the envelope” on this requirement, but will require the review of our designers and engineers.
– Weld points: for additional rigidity, the opposite sides of a product can be connected by weld points, in which the two sides of the part are connected and “welded” together by features in the mold that push the two sides of the parison together. When cooled, the two sides form a single piece.
– Product strength needed: the wall thickness of the final part can be controlled, and design elements can be included to increase the final product strength and rigidity.
– Post-processing: some products, such as custom ductwork for automotive applications require areas to be cut away after molding. This process must be considered in the design to allow efficient “routing” or cutting away of the material using best practices.
– External parts and components: a custom blow molded part may be a complete product by itself, may require the addition of secondary parts, or may be a component of some larger assembly. With this in mind, the design process should consider any attachment points that are required. Reinforced mounting flanges and surfaces can be provided, and some fasteners, such as threaded inserts, can be molded into the part. Western Case can also provide assembly services, so that we ship you a finished product, no further assembly required.
Here are a few of the products that we have manufactured:
– Automotive ducts
– Traffic safety – cones, delineators, barricades and drums
– tadium seating and chairs
– Containers, trays, reservoirs and tanks
– Fan housings
– Floats, stands, panels and doors
– Toys and sporting goods
– Watering cans and household products
Bottom line: with our years of experience in blow molding all types of products, Western Case the technical experience to guide you in the optimum design for your custom blow molded product. Contact us early in the process and we can work together to design a product that provides the function and appearance that you need and can be produced economically.