In 2005 Rehrig International, the largest manufacturer of shopping carts in the world, had joined forces with GE Plastics and tech start-up MediaCart to create an innovative, industry-first design. They looked to develop the first entirely plastic shopping cart, which would be more quiet, lighter weight, and crucially, rust-free. Having worked with SPARK previously for tool-ready component designs, Rehrig again turned to SPARK for mechanical design, engineering, and plastics expertise on this tremendous undertaking.
In 2007, Rehrig International asked SPARK to help them create the world’s first all-plastic shopping cart. The result was an exploration of advanced plastics design and CAD software’s then budding capabilities.
A MASSIVE INVESTMENT
Injection mold tools are expensive. Large injection mold tools are very expensive. And large injection mold tools that form parts like a shopping cart basket require expanding (or exploding) cavity molds, which are enormously complex and expensive.
Consequently, the 3D CAD work produced by SPARK needed to be 100% tool-ready to ensure accurate tool pricing, so Rehrig could determine product feasibility. Smaller components, such as the seat assembly and lower tray assembly, were relatively simple in comparison; however, the main basket and frame, in particular, were anything but easy to design.
Large injection mold tools that form parts like a shopping card basket require expanding (or exploding) cavity molds, which are enormously complex and expensive.
SPARK prides itself on our understanding of how to design parts for injection molding. For the shopping cart frame, an exceptional understanding of surface modeling techniques needed to be combined with absolute control of parting lines where the mold components meet.
The frame required a complex tool with both an expanding cavity and collapsing core. It also was to be molded using high-end engineering resin and low pressure structural foam. SPARK worked closely with both the tool builders and the part molders to ensure that their trade-specific knowledge was fully incorporated in the 3-D design.
PUSHING THE LIMITS
Rehrig required the parts to be built in Solidworks, which at the time did not have the capabilities of Pro/Engineer software. SPARK pushed Solidworks (and the personal computers running the program) to the limit to design the cart. In fact, SPARK’s CAD work on the shopping cart was so inventive that some of the techniques we developed were included in Matt Lombard’s 2007 SolidWorks Bible, as well as his 2009 SolidWorks Surfacing and Complex Shape Modeling Bible.
BEFORE ITS TIME
Sadly, this incredible, and beautiful, design was never built, as Rehrig’s partner company could not raise the necessary capital (well over $1 million) for the molds. At the time Rehrig’s customers, including Target, were not willing to commit to purchasing the advanced, but more expensive design.
Years later, Target joined forces with an advanced injection molder and produced their now infamous all-plastic cart. While SPARK’s work merely paved the way for future innovation, the Rehrig cart remains a powerful example of engineering and plastics capabilities.