Dunnage: Often Ignored, Always Important
Packaging for shipping and processing parts pays dividends on the shop floor when the right materials, design and applications are used
By Nicky Borcea
Ann Arbor, MI
Dunnage used to ship and process automotive parts on the shop floor is a key component in the overall manufacturing process, yet it is often overlooked when companies are working to make lines lean and green. Today, it is important that manufacturers know that most dunnage used to transport parts from start to finish can be reused for the lifetime of production.
While virtually all automotive dunnage is custom, after a vehicle design is retired its associated packaging material can be recycled for future use. This is a win-win for the manufacturer and the environment. Before delving into case studies of companies that have taken advantage of this to streamline their processes, it will help to learn more about dunnage.
How Modern Dunnage is Manufactured
Injection molding and thermoforming are the two main methods for creating plastic packaging. Injection molding utilizes split dies and a flow of melted plastic into these dies. Thermoforming creates similar plastic parts by preheating a flat sheet of plastic and then pressing it into a mold. The main benefit of injection molding is that once the dies are created and molds set up, it can create multiple parts very rapidly. The drawbacks are the extremely high cost of the dies, very long lead times and the cost of maintaining and cleaning the injection molding equipment.
Thermoforming has been taking over the process of creating most critical dunnage because it takes much less time, with much lower cost for initial setup, and because it can be done using vacuum pressure and/or direct mechanical force. This process provides the close tolerances, tight specifications, and sharp detail that are needed for durable, reusable dunnage. It can take advantage of the newest rugged materials that not only conform to exact specifications, but will also resist wear and breakdown that could come from continued reuse in the harsh automotive manufacturing environment. Today, advanced finishing techniques result in thermoformed products equal or better than those formed by injection molding.
Thermoforming takes much less time, with much lower cost for initial setup and because it can be done using vacuum pressure and/or direct mechanical force.
Vacuum thermoforming, press molding, fabrication, drape molding and many more technologies are also used. Machined aluminum molds are typically built for shallow parts with small draw ratios. These molds are then mounted on a temperature control base to control the mold temperature during the forming process. Male or female molds and vacuum-form or pressure-form molds can be machined from aluminum. Cast aluminum molds are also used. These are cast at a foundry from a pattern machined by the dunnage designer. Cast aluminum molds typically are built for parts with large draw ratios and may be male or female and vacuum-form or pressure-formed.
Tolerances of ±0.005" (0.127 mm) from part to part may be necessary for the automation to work properly for robotic loading and unloading. This is not a problem for thermoforming, but is extremely difficult and expensive to try to replicate with injection molding.
Working with Auto Parts Manufacturers
Phil Krasny has been involved in the automotive industry for decades, first at General Motors and then with his own company, Returnable Packaging Solutions (RPS; Dexter, MI).
Krasny interfaces with all areas of auto parts manufacturing, but notes that there is a focus on finely tooled gears, clutches, transmission parts and other assemblies that often have very sharp and detailed edges. This is across the board for all his customers, including GM, Chrysler, Ford and Toyota.
Many components are quite large and often come in pairs, which need to be loaded in custom-designed individual tray cavities, shipped and unloaded at the assembly line. Typically this type of large gear dunnage is designed to be a part of the manufacturing process in which a robot takes the components out of the tray and feeds them directly into the assembly machine. The empty trays are then returned to the side of the machine that receives the final assembly. The final assembly is then placed robotically back into the same cavity that contained the original components. These trays are collected into skids and then shipped to the customer.
“The whole point of this is to reduce steps and streamline the process from part manufacture to building the final assembly,” Krasny says. “Developing a single design that works for the component supplier, the manufacturing line, and the final customer saves a substantial amount of time and cost and reduces potential errors by eliminating unnecessary operator handling. After using the parts in their assembly process, the automotive customer sends the trays back to the initial parts supplier repeating the cycle.”
Automotive Production Coordinator
Ghafari Associates (Dearborn, MI) is a 29-year-old full-service architecture and engineering organization. One division provides program management and consulting for industrial and process engineering. “My specific group,” says Greg Brenny, senior project engineer, “primarily focuses on packaging and material flow, line display for industrial and automotive plants. It’s a lot of material handling.”
Chrysler is a Ghafari customer that has different programs for different vehicles. Ghafari will coordinate between all suppliers and all the different groups at Chrysler to come up with a package that will get the parts from point A to point B using returnable containers. Parts ship to the factories in returnable containers and these containers go back to the parts supplier to be refilled and reshipped. Ghafari does not do any manufacturing or assembly of parts themselves. They do, however, handle the implementation of the dunnage design process.
“We manage the design and purchase of all of the containers, the dunnage; the specifications and how many are required from the beginning of the program to the official launch to make sure everybody has what they need,” Brenny explains. “We work with fabricators such as Sohner Plastics [Ann Arbor, MI], but Chrysler buys the actual products from the fabricator. We manage the process and work with the fabricator to make sure they meet the Chrysler specs. Containers are shipped to the supplier making the components.”
Hinkle Manufacturing Inc. (Perrysburg, OH) offers full-service packaging. “We design, develop and manufacture the packaging that takes parts from wherever they are being manufactured to their end destination,” Taber H. (“Tab”) Hinkle, president & CEO says.
Hinkle designs and manufactures the dunnage product and delivers it to the parts vendor at the beginning of the automotive part product launch. After that, it goes out to the end users. Hinkle Manufacturing is not involved as a service provider between the parts vendor and the end user. Tab Hinkle says he is looking for the best material to use to create the initial packaging.
The type of dunnage the company designs and manufactures is typically used in assembly plants that are sequencing parts. Hinkle says that a good example is the sequencing rack made for auto headlamps. The sequence in the tray indicates which vehicle the part number goes on. The tray will be presented to a line using in-line sequencing to serve up parts to multiple vehicles simultaneously. This is typically handled manually, so it presents different issues than dunnage used for automated lines. It has to be rugged, but still operator friendly.
The material used to create such trays must fit the exact needs of the end use: does the part need special protection? Does the tray need to be extra resistant to damage due to the weight or design of the product that will go into it? While almost all standard dunnage for various industries and even some automotive dunnage are manufactured from standard forms of plastic, high-precision trays used for critical parts packaging, handling and delivery systems often use special materials. The most common are:
ABS (acrylonitrile butadiene styrene): This is the most common plastic for automation dunnage trays and packaging. The most important mechanical properties of ABS are impact resistance and toughness. Stability under load is excellent with limited loads. ABS can be prepared in different grades by changing its components. Two major categories would be ABS for extrusion and ABS for injection molding.
ABS/TPU: This material it is co-extruded with a rigid base layer of ABS and a cut resistant cover of TPU (thermoplastic polyurethanes) which is a class of polyurethane plastics with many useful properties, including elasticity, transparency, and resistance to oil, grease and abrasion. Extremely damage resistant, ABS/TPU can’t be cut by the sharp machined edges of the parts.
Conductive HDPE (high-density polyethylene): This material protects parts/components against electrostatic discharge. This may occur between the charged surfaces and the grounded objects in the immediate vicinity and can lead to undesired interference or damage of sensitive electronics in devices and sensors. HDPE materials are specifically formulated to prevent this. HDPE is commonly recycled, and has the number “2” as its recycling symbol.
HMWPE (high molecular weight polyethylene): This very light weight material offers good wear and abrasion resistance. It resists water and chemicals and provides high mechanical strength. It is also very good for electrical insulation with high dielectric properties.
TriPly: This is a new, three-layer polypropylene composite consisting of a central structural sheet sandwiched between two smooth exterior sheets. The key feature is the design of the geometry of the middle structural sheet, which provides exceptional rigidity in all directions. Constant wall thickness improves the quality of the welded bond between the structural middle and the outer sheets, improving rigidity. Polypropylene is recyclable. It can be manufactured in 2100-mm width and any required length. Advantages are its extremely lightweight, water and chemical resistance and high strength.
All of the above materials have a place in dunnage, however the requirements of each specific application will determine which is best for the design and application. This is where collaboration between the material supplier, dunnage manufacturer and packaging designer comes into play.
RPS uses a thermoformed ABS/TPU material for almost all of its applications. The cut resistance is extremely important when handling large assemblies and parts with sharp edges. The concern with any plastic dunnage is how long it will last. This is because little portions typically start getting shaved off over time and this becomes not only an issue of fit but also of contamination: If particles get into the final product, there could be warranty damage to the transmission.
“After using the parts in their assembly
process, the automotive customer
sends the trays back to the initial parts
supplier repeating the cycle.”
While at GM, Krasny performed tests on materials to find one that could stand up to the sharp edges of parts and gears for dunnage. He performed random vibration testing on three tray packs for cam phasers. The dimensions were 36 × 32" (914 × 813 mm) with a test weight of 850 lb (382.5 kg). The test items were subjected to ASTM D 4728, Standard Test Method for Random Vibration Testing of Shipping Containers. The power spectral density profile was based on ASTM D 4169 Truck Assurance Level II breakpoints, which were modified with the approval of Tom Su of GM NAO Containerization. The test item was subjected to the modified ASTM D4169 Truck Assurance Level II random vibration profile for 180 min.
“ABS/TPU is also very good with rejecting moisture or oil, which can also be a concern. One little stamp mark on the tray could cause a problem over time. The ID stamps are typically petroleum products and they can degrade other materials over the years. This material is completely resistant to that. After years of use, you just wash it and dry it and it looks like the day you bought it,” Krasny says. ME
This article first appeared in the October issue of Manufacturing Engineering magazine. A PDF of the article can be found here.