up to 80 miles per gallon equivalent (MPGe) in city driving,” Timothy Kuniskis, head of passenger car brands, FCA-North America, said in a press release. Chrysler touts the magnesium liftgate


as one of its innovative “fi rsts” for a minivan, along with 37 other innova- tions tallied with the 2017 Pacifi ca. For Meridian Lightweight Technologies, this fi rst was a natural progression from what the magnesium casting company had been doing over the last several years. “We have been casting parts like this in magnesium at lower produc- tions, so a lot of the things we learned then we could apply to the higher volume required for the Pacifi ca,” said Tom Faupel, engineering manager, Magnesium Products of America, Eaton Rapids, Michigan. Magnesium was a lightweight ma-


terial choice for the liftgate because of its mechanical properties, particularly its ductility, which helps in meet- ing the crash testing requirements. Originally a weldment of seven steel stampings, the redesigned liftgate was combined into a single magnesium part. T e joining technologies required, such as spot welds and rivets, were reduced from 84 to 10. “When we search for potential


applications, we look at what magne- sium does well,” Faupel said. “It doesn’t handle high temperature, so that rules out engine applications, but its me- chanical properties make it a very good structural material.” T e magnesium liftgate surpassed


all its crash requirements—the same ones required by the original steel version. Two of the main challenges of the liftgate were the casting size and volumes required. “You want to have large, thin-


walled parts like this cool as evenly as possible to maintain dimensional stability,” Faupel said. “Magnesium wants to cool rapidly, and fi lling the mold is made more challenging with large, thin-walled parts.” Meridian relied on multiple


advanced thermal management tech- nologies it had developed over the years to help the metal stay molten as it fills the mold. This thermal management allowed Meridian to


incorporate extra features into the casting that otherwise would have been added as extra parts or second- ary processes, such as pockets for the tail lamps and rear speakers. It also incorporates an aluminum stamping wiper bracket reinforcement in part to provide for the gating area to feed the extremities of the casting. Because of the high volume


required, Meridian runs two die casting machines, with a third die in rotation at its Eaton Rapids, Michigan, location. As the two dies are used in production, the third will undergo preventive maintenance to address any wear on the die and assure dimensional stability and repeatability. The two casting lines merge into a single process flow for secondary finishing, which includes surface preparation, dimensional measurements, piercing and machin- ing operations, and powder coating. T e fi nished castings are shipped to


the Tier 1 supplier for assembly with the rest of the liftgate substructure before it is delivered to Fiat Chrysler’s plant in Windsor, Ontario, Canada, to be placed on the Pacifi cas. According to Jon Weiler, metal-


lurgist at Meridian’s Global Tech- nology Centre, cutting weight in one area of the vehicle, like the liftgate, provides secondary benefits to the automotive design. “Because of the liftgate being lighter to start with, the designers can use smaller motors, struts, hinges, etc. All of that allows them to save additional weight, and it’s significant.” Beyond the weight reduction, the magnesium diecast liftgate allowed for an improved rearward visibility by close to an inch, achieved bet- ter noise, harshness and vibration performance by more than 16 Hz in bending, and prevents cavita- tion from idle boom and road boom through local ribbing, integrated gussets and added thickness in select areas of the component. T e Pacifi ca’s liftgate structure opens up the possibility for other mass market automobiles to incorporate magnesium in its rear hatches or side doors. T e 2017 Pacifi ca was unveiled in


January and will be available in fi ve models in dealerships this spring. Two hybrid models will be available later this year. T e magnesium liftgate frame will be in all of them. 


Casting of the Year


Cast Component: Magnesium liftgate inner casting. Casting Supplier: Meridian Lightweight Technologies, Strathroy, Ontario, Canada.


Material: AM60B magnesium. Process: High pressure diecasting. Weight: 15.1 lbs. Dimensions: 57.1 x 47.6 x 12.4 in. Application: Liftgate closure casting for the 2017 Chrysler Pacifi ca.


Converted From: Assembly of steel stampings and plastic.


• T e magnesium casting reduced the part count from seven steel stamp- ings to one casting and reduces joining technologies required, such as spot welds and rivets, from 84 to 10.


• It incorporates an aluminum stamping wiper bracket reinforcement in part to provide for the gating area to feed the extremities of the casting.


• Designing the liftgate casting for diecasting allowed for an improved rearward visibility by close to an inch and achieved better noise, harsh- ness and vibration performance.


May/Jun 2016 | METAL CASTING DESIGN & PURCHASING | 23


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